Development of a dual phantom technique for measuring the fast neutron component of dose in boron neutron capture therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakurai, Yoshinori, E-mail: yosakura@rri.kyoto-u.ac.jp; Tanaka, Hiroki; Kondo, Natsuko

2015-11-15

Purpose: Research and development of various accelerator-based irradiation systems for boron neutron capture therapy (BNCT) is underway throughout the world. Many of these systems are nearing or have started clinical trials. Before the start of treatment with BNCT, the relative biological effectiveness (RBE) for the fast neutrons (over 10 keV) incident to the irradiation field must be estimated. Measurements of RBE are typically performed by biological experiments with a phantom. Although the dose deposition due to secondary gamma rays is dominant, the relative contributions of thermal neutrons (below 0.5 eV) and fast neutrons are virtually equivalent under typical irradiation conditionsmore » in a water and/or acrylic phantom. Uniform contributions to the dose deposited from thermal and fast neutrons are based in part on relatively inaccurate dose information for fast neutrons. This study sought to improve the accuracy in the dose estimation for fast neutrons by using two phantoms made of different materials in which the dose components can be separated according to differences in the interaction cross sections. The development of a “dual phantom technique” for measuring the fast neutron component of dose is reported. Methods: One phantom was filled with pure water. The other phantom was filled with a water solution of lithium hydroxide (LiOH) capitalizing on the absorbing characteristics of lithium-6 (Li-6) for thermal neutrons. Monte Carlo simulations were used to determine the ideal mixing ratio of Li-6 in LiOH solution. Changes in the depth dose distributions for each respective dose component along the central beam axis were used to assess the LiOH concentration at the 0, 0.001, 0.01, 0.1, 1, and 10 wt. % levels. Simulations were also performed with the phantom filled with 10 wt. % {sup 6}LiOH solution for 95%-enriched Li-6. A phantom was constructed containing 10 wt. % {sup 6}LiOH solution based on the simulation results. Experimental characterization of the depth dose distributions of the neutron and gamma-ray components along the central axis was performed at Heavy Water Neutron Irradiation Facility installed at Kyoto University Reactor using activation foils and thermoluminescent dosimeters, respectively. Results: Simulation results demonstrated that the absorbing effect for thermal neutrons occurred when the LiOH concentration was over 1%. The most effective Li-6 concentration was determined to be enriched {sup 6}LiOH with a solubility approaching its upper limit. Experiments confirmed that the thermal neutron flux and secondary gamma-ray dose rate decreased substantially; however, the fast neutron flux and primary gamma-ray dose rate were hardly affected in the 10%-{sup 6}LiOH phantom. It was confirmed that the dose contribution of fast neutrons is improved from approximately 10% in the pure water phantom to approximately 50% in the 10%-{sup 6}LiOH phantom. Conclusions: The dual phantom technique using the combination of a pure water phantom and a 10%-{sup 6}LiOH phantom developed in this work provides an effective method for dose estimation of the fast neutron component in BNCT. Improvement in the accuracy achieved with the proposed technique results in improved RBE estimation for biological experiments and clinical practice.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, D. A.; Chadwick, M. B.; Capote, R.

We describe the new ENDF/B-VIII.0 evaluated nuclear reaction data library. ENDF/B-VIII.0 fully incorporates the new IAEA standards, includes improved thermal neutron scattering data and uses new evaluated data from the CIELO project for neutron reactions on 1H, 16O, 56Fe, 235U, 238U and 239Pu described in companion papers in the present issue of Nuclear Data Sheets. The evaluations benefit from recent experimental data obtained in the U.S. and Europe, and improvements in theory and simulation. Notable advances include updated evaluated data for light nuclei, structural materials, actinides, fission energy release, prompt fission neutron and γ-ray spectra, thermal neutron scattering data, andmore » charged-particle reactions. Integral validation testing is shown for a wide range of criticality, reaction rate, and neutron transmission benchmarks. In general, integral validation performance of the library is improved relative to the previous ENDF/B-VII.1 library.« less

Modularized Parallel Neutron Instrument Simulation on the TeraGrid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Meili; Cobb, John W; Hagen, Mark E

2007-01-01

In order to build a bridge between the TeraGrid (TG), a national scale cyberinfrastructure resource, and neutron science, the Neutron Science TeraGrid Gateway (NSTG) is focused on introducing productive HPC usage to the neutron science community, primarily the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). Monte Carlo simulations are used as a powerful tool for instrument design and optimization at SNS. One of the successful efforts of a collaboration team composed of NSTG HPC experts and SNS instrument scientists is the development of a software facility named PSoNI, Parallelizing Simulations of Neutron Instruments. Parallelizing the traditional serialmore » instrument simulation on TeraGrid resources, PSoNI quickly computes full instrument simulation at sufficient statistical levels in instrument de-sign. Upon SNS successful commissioning, to the end of 2007, three out of five commissioned instruments in SNS target station will be available for initial users. Advanced instrument study, proposal feasibility evalua-tion, and experiment planning are on the immediate schedule of SNS, which pose further requirements such as flexibility and high runtime efficiency on fast instrument simulation. PSoNI has been redesigned to meet the new challenges and a preliminary version is developed on TeraGrid. This paper explores the motivation and goals of the new design, and the improved software structure. Further, it describes the realized new fea-tures seen from MPI parallelized McStas running high resolution design simulations of the SEQUOIA and BSS instruments at SNS. A discussion regarding future work, which is targeted to do fast simulation for automated experiment adjustment and comparing models to data in analysis, is also presented.« less

Neutron crosstalk between liquid scintillators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verbeke, J. M.; Prasad, M. K.; Snyderman, N. J.

2015-05-01

We propose a method to quantify the fractions of neutrons scattering between liquid scintillators. Using a spontaneous fission source, this method can be utilized to quickly characterize an array of liquid scintillators in terms of crosstalk. The point model theory due to Feynman is corrected to account for these multiple scatterings. Using spectral information measured by the liquid scintillators, fractions of multiple scattering can be estimated, and mass reconstruction of fissile materials under investigation can be improved. Monte Carlo simulations of mono-energetic neutron sources were performed to estimate neutron crosstalk. A californium source in an array of liquid scintillators wasmore » modeled to illustrate the improvement of the mass reconstruction.« less

Conceptual design of the early implementation of the NEutron Detector Array (NEDA) with AGATA

NASA Astrophysics Data System (ADS)

Hüyük, Tayfun; Di Nitto, Antonio; Jaworski, Grzegorz; Gadea, Andrés; Javier Valiente-Dobón, José; Nyberg, Johan; Palacz, Marcin; Söderström, Pär-Anders; Jose Aliaga-Varea, Ramon; de Angelis, Giacomo; Ataç, Ayşe; Collado, Javier; Domingo-Pardo, Cesar; Egea, Francisco Javier; Erduran, Nizamettin; Ertürk, Sefa; de France, Gilles; Gadea, Rafael; González, Vicente; Herrero-Bosch, Vicente; Kaşkaş, Ayşe; Modamio, Victor; Moszynski, Marek; Sanchis, Enrique; Triossi, Andrea; Wadsworth, Robert

2016-03-01

The NEutron Detector Array (NEDA) project aims at the construction of a new high-efficiency compact neutron detector array to be coupled with large γ-ray arrays such as AGATA. The application of NEDA ranges from its use as selective neutron multiplicity filter for fusion-evaporation reaction to a large solid angle neutron tagging device. In the present work, possible configurations for the NEDA coupled with the Neutron Wall for the early implementation with AGATA has been simulated, using Monte Carlo techniques, in order to evaluate their performance figures. The goal of this early NEDA implementation is to improve, with respect to previous instruments, efficiency and capability to select multiplicity for fusion-evaporation reaction channels in which 1, 2 or 3 neutrons are emitted. Each NEDA detector unit has the shape of a regular hexagonal prism with a volume of about 3.23l and it is filled with the EJ301 liquid scintillator, that presents good neutron- γ discrimination properties. The simulations have been performed using a fusion-evaporation event generator that has been validated with a set of experimental data obtained in the 58Ni + 56Fe reaction measured with the Neutron Wall detector array.

Neutron Transport Simulations for NIST Neutron Lifetime Experiment

NASA Astrophysics Data System (ADS)

Li, Fangchen; BL2 Collaboration Collaboration

2016-09-01

Neutrons in stable nuclei can exist forever; a free neutron lasts for about 15 minutes on average before it beta decays to a proton, an electron, and an antineutrino. Precision measurements of the neutron lifetime test the validity of weak interaction theory and provide input into the theory of the evolution of light elements in the early universe. There are two predominant ways of measuring the neutron lifetime: the bottle method and the beam method. The bottle method measures decays of ultracold neutrons that are stored in a bottle. The beam method measures decay protons in a beam of cold neutrons of known flux. An improved beam experiment is being prepared at the National Institute of Science and Technology (Gaithersburg, MD) with the goal of reducing statistical and systematic uncertainties to the level of 1 s. The purpose of my studies was to develop computer simulations of neutron transport to determine the beam collimation and study the neutron distribution's effect on systematic effects for the experiment, such as the solid angle of the neutron flux monitor. The motivation for the experiment and the results of this work will be presented. This work was supported, in part, by a Grant to Gettysburg College from the Howard Hughes Medical Institute through the Precollege and Undergraduate Science Education Program.

A qualitative analysis of the neutron population in fresh and spent fuel assemblies during simulated interrogation using the differential die-away technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tobin, Stephen J.; Lundkvist, Niklas; Goodsell, Alison V.

In this study, Monte Carlo simulations were performed for the differential die-away (DDA) technique to analyse the time-dependent behaviour of the neutron population in fresh and spent nuclear fuel assemblies as part of the Next Generation Safeguards Initiative Spent Fuel (NGSI-SF) Project. Simulations were performed to investigate both a possibly portable as well as a permanent DDA instrument. Taking advantage of a custom made modification to the MCNPX code, the variation in the neutron population, simultaneously in time and space, was examined. The motivation for this research was to improve the design of the DDA instrument, as it is bemore » ing considered for possible deployment at the Central Storage of Spent Nuclear Fuel and Encapsulation Plant in Sweden (Clab), as well as to assist in the interpretation of the both simulated and measured signals.« less

A qualitative analysis of the neutron population in fresh and spent fuel assemblies during simulated interrogation using the differential die-away technique

DOE PAGES

Tobin, Stephen J.; Lundkvist, Niklas; Goodsell, Alison V.; ...

2015-12-01

In this study, Monte Carlo simulations were performed for the differential die-away (DDA) technique to analyse the time-dependent behaviour of the neutron population in fresh and spent nuclear fuel assemblies as part of the Next Generation Safeguards Initiative Spent Fuel (NGSI-SF) Project. Simulations were performed to investigate both a possibly portable as well as a permanent DDA instrument. Taking advantage of a custom made modification to the MCNPX code, the variation in the neutron population, simultaneously in time and space, was examined. The motivation for this research was to improve the design of the DDA instrument, as it is bemore » ing considered for possible deployment at the Central Storage of Spent Nuclear Fuel and Encapsulation Plant in Sweden (Clab), as well as to assist in the interpretation of the both simulated and measured signals.« less

Neutron density profile in the lunar subsurface produced by galactic cosmic rays

NASA Astrophysics Data System (ADS)

Ota, Shuya; Sihver, Lembit; Kobayashi, Shingo; Hasebe, Nobuyuki

Neutron production by galactic cosmic rays (GCR) in the lunar subsurface is very important when performing lunar and planetary nuclear spectroscopy and space dosimetry. Further im-provements to estimate the production with increased accuracy is therefore required. GCR, which is a main contributor to the neutron production in the lunar subsurface, consists of not only protons but also of heavy components such as He, C, N, O, and Fe. Because of that, it is important to precisely estimate the neutron production from such components for the lunar spectroscopy and space dosimetry. Therefore, the neutron production from GCR particles in-cluding heavy components in the lunar subsurface was simulated with the Particle and Heavy ion Transport code System (PHITS), using several heavy ion interaction models. This work presents PHITS simulations of the neutron density as a function of depth (neutron density profile) in the lunar subsurface and the results are compared with experimental data obtained by Apollo 17 Lunar Neutron Probe Experiment (LNPE). From our previous study, it has been found that the accuracy of the proton-induced neutron production models is the most influen-tial factor when performing precise calculations of neutron production in the lunar subsurface. Therefore, a benchmarking of proton-induced neutron production models against experimental data was performed to estimate and improve the precision of the calculations. It was found that the calculated neutron production using the best model of Cugnon Old (E < 3 GeV) and JAM (E > 3 GeV) gave up to 30% higher values than experimental results. Therefore, a high energy nuclear data file (JENDL-HE) was used instead of the Cugnon Old model at the energies below 3 GeV. Then, the calculated neutron density profile successfully reproduced the experimental data from LNPE within experimental errors of 15% (measurement) + 30% (systematic). In this presentation, we summarize and discuss our calculated results of neutron production in the lunar subsurface.

Neutron Angular Scatter Effects in 3DHZETRN: Quasi-Elastic

NASA Technical Reports Server (NTRS)

Wilson, John W.; Werneth, Charles M.; Slaba, Tony C.; Badavi, Francis F.; Reddell, Brandon D.; Bahadori, Amir A.

2017-01-01

The current 3DHZETRN code has a detailed three dimensional (3D) treatment of neutron transport based on a forward/isotropic assumption and has been compared to Monte Carlo (MC) simulation codes in various geometries. In most cases, it has been found that 3DHZETRN agrees with the MC codes to the extent they agree with each other. However, a recent study of neutron leakage from finite geometries revealed that further improvements to the 3DHZETRN formalism are needed. In the present report, angular scattering corrections to the neutron fluence are provided in an attempt to improve fluence estimates from a uniform sphere. It is found that further developments in the nuclear production models are required to fully evaluate the impact of transport model updates. A model for the quasi-elastic neutron production spectra is therefore developed and implemented into 3DHZETRN.

Investigation of Workplace-like Calibration Fields via a Deuterium-Tritium (D-T) Neutron Generator.

PubMed

Mozhayev, Andrey V; Piper, Roman K; Rathbone, Bruce A; McDonald, Joseph C

2017-04-01

Radiation survey meters and personal dosimeters are typically calibrated in reference neutron fields based on conventional radionuclide sources, such as americium-beryllium (Am-Be) or californium-252 (Cf), either unmodified or heavy-water moderated. However, these calibration neutron fields differ significantly from the workplace fields in which most of these survey meters and dosimeters are being used. Although some detectors are designed to yield an approximately dose-equivalent response over a particular neutron energy range, the response of other detectors is highly dependent upon neutron energy. This, in turn, can result in significant over- or underestimation of the intensity of neutron radiation and/or personal dose equivalent determined in the work environment. The use of simulated workplace neutron calibration fields that more closely match those present at the workplace could improve the accuracy of worker, and workplace, neutron dose assessment. This work provides an overview of the neutron fields found around nuclear power reactors and interim spent fuel storage installations based on available data. The feasibility of producing workplace-like calibration fields in an existing calibration facility has been investigated via Monte Carlo simulations. Several moderating assembly configurations, paired with a neutron generator using the deuterium tritium (D-T) fusion reaction, were explored.

ENDF/B-VIII.0: The 8th Major Release of the Nuclear Reaction Data Library with CIELO-project Cross Sections, New Standards and Thermal Scattering Data

NASA Astrophysics Data System (ADS)

Brown, D. A.; Chadwick, M. B.; Capote, R.; Kahler, A. C.; Trkov, A.; Herman, M. W.; Sonzogni, A. A.; Danon, Y.; Carlson, A. D.; Dunn, M.; Smith, D. L.; Hale, G. M.; Arbanas, G.; Arcilla, R.; Bates, C. R.; Beck, B.; Becker, B.; Brown, F.; Casperson, R. J.; Conlin, J.; Cullen, D. E.; Descalle, M.-A.; Firestone, R.; Gaines, T.; Guber, K. H.; Hawari, A. I.; Holmes, J.; Johnson, T. D.; Kawano, T.; Kiedrowski, B. C.; Koning, A. J.; Kopecky, S.; Leal, L.; Lestone, J. P.; Lubitz, C.; Márquez Damián, J. I.; Mattoon, C. M.; McCutchan, E. A.; Mughabghab, S.; Navratil, P.; Neudecker, D.; Nobre, G. P. A.; Noguere, G.; Paris, M.; Pigni, M. T.; Plompen, A. J.; Pritychenko, B.; Pronyaev, V. G.; Roubtsov, D.; Rochman, D.; Romano, P.; Schillebeeckx, P.; Simakov, S.; Sin, M.; Sirakov, I.; Sleaford, B.; Sobes, V.; Soukhovitskii, E. S.; Stetcu, I.; Talou, P.; Thompson, I.; van der Marck, S.; Welser-Sherrill, L.; Wiarda, D.; White, M.; Wormald, J. L.; Wright, R. Q.; Zerkle, M.; Žerovnik, G.; Zhu, Y.

2018-02-01

We describe the new ENDF/B-VIII.0 evaluated nuclear reaction data library. ENDF/B-VIII.0 fully incorporates the new IAEA standards, includes improved thermal neutron scattering data and uses new evaluated data from the CIELO project for neutron reactions on 1H, 16O, 56Fe, 235U, 238U and 239Pu described in companion papers in the present issue of Nuclear Data Sheets. The evaluations benefit from recent experimental data obtained in the U.S. and Europe, and improvements in theory and simulation. Notable advances include updated evaluated data for light nuclei, structural materials, actinides, fission energy release, prompt fission neutron and γ-ray spectra, thermal neutron scattering data, and charged-particle reactions. Integral validation testing is shown for a wide range of criticality, reaction rate, and neutron transmission benchmarks. In general, integral validation performance of the library is improved relative to the previous ENDF/B-VII.1 library.

Dynamics of crystalline acetanilide: Analysis using neutron scattering and computer simulation

NASA Astrophysics Data System (ADS)

Hayward, R. L.; Middendorf, H. D.; Wanderlingh, U.; Smith, J. C.

1995-04-01

The unusual temperature dependence of several optical spectroscopic vibrational bands in crystalline acetanilide has been interpreted as providing evidence for dynamic localization. Here we examine the vibrational dynamics of crystalline acetanilide over a spectral range of ˜20-4000 cm-1 using incoherent neutron scattering experiments, phonon normal mode calculations and molecular dynamics simulations. A molecular mechanics energy function is parametrized and used to perform the normal mode analyses in the full configurational space of the crystal i.e., including the intramolecular and intermolecular degrees of freedom. One- and multiphonon incoherent inelastic neutron scattering intensities are calculated from harmonic analyses in the first Brillouin zone and compared with the experimental data presented here. Phonon dispersion relations and mean-square atomic displacements are derived from the harmonic model and compared with data derived from coherent inelastic neutron scattering and neutron and x-ray diffraction. To examine the temperature effects on the vibrations the full, anharmonic potential function is used in molecular dynamics simulations of the crystal at 80, 140, and 300 K. Several, but not all, of the spectral features calculated from the molecular dynamics simulations exhibit temperature-dependent behavior in agreement with experiment. The significance of the results for the interpretation of the optical spectroscopic results and possible improvements to the model are discussed.

FY17 Status Report on NEAMS Neutronics Activities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, C. H.; Jung, Y. S.; Smith, M. A.

2017-09-30

Under the U.S. DOE NEAMS program, the high-fidelity neutronics code system has been developed to support the multiphysics modeling and simulation capability named SHARP. The neutronics code system includes the high-fidelity neutronics code PROTEUS, the cross section library and preprocessing tools, the multigroup cross section generation code MC2-3, the in-house meshing generation tool, the perturbation and sensitivity analysis code PERSENT, and post-processing tools. The main objectives of the NEAMS neutronics activities in FY17 are to continue development of an advanced nodal solver in PROTEUS for use in nuclear reactor design and analysis projects, implement a simplified sub-channel based thermal-hydraulic (T/H)more » capability into PROTEUS to efficiently compute the thermal feedback, improve the performance of PROTEUS-MOCEX using numerical acceleration and code optimization, improve the cross section generation tools including MC2-3, and continue to perform verification and validation tests for PROTEUS.« less

Effect of particle size and percentages of Boron carbide on the thermal neutron radiation shielding properties of HDPE/B4C composite: Experimental and simulation studies

NASA Astrophysics Data System (ADS)

Soltani, Zahra; Beigzadeh, Amirmohammad; Ziaie, Farhood; Asadi, Eskandar

2016-10-01

In this paper the effects of particle size and weight percentage of the reinforcement phase on the absorption ability of thermal neutron by HDPE/B4C composites were investigated by means of Monte-Carlo simulation method using MCNP code and experimental studies. The composite samples were prepared using the HDPE filled with different weight percentages of Boron carbide powder in the form of micro and nano particles. Micro and nano composite were prepared under the similar mixing and moulding processes. The samples were subjected to thermal neutron radiation. Neutron shielding efficiency in terms of the neutron transmission fractions of the composite samples were investigated and compared with simulation results. According to the simulation results, the particle size of the radiation shielding material has an important role on the shielding efficiency. By decreasing the particle size of shielding material in each weight percentages of the reinforcement phase, better radiation shielding properties were obtained. It seems that, decreasing the particle size and homogeneous distribution of nano forms of B4C particles, cause to increase the collision probability between the incident thermal neutron and the shielding material which consequently improve the radiation shielding properties. So, this result, propose the feasibility of nano composite as shielding material to have a high performance shielding characteristic, low weight and low thick shielding along with economical benefit.

Search for deviations from the inverse square law of gravity at nm range using a pulsed neutron beam

NASA Astrophysics Data System (ADS)

Haddock, Christopher C.; Oi, Noriko; Hirota, Katsuya; Ino, Takashi; Kitaguchi, Masaaki; Matsumoto, Satoru; Mishima, Kenji; Shima, Tatsushi; Shimizu, Hirohiko M.; Snow, W. Michael; Yoshioka, Tamaki

2018-03-01

We describe an experimental search for deviations from the inverse-square law of gravity at the nanometer length scale using neutron scattering from noble gases on a pulsed slow neutron beam line. By measuring the neutron momentum transfer (q ) dependence of the differential cross section for xenon and helium and comparing to their well-known analytical forms, we place an upper bound on the strength of a new interaction as a function of interaction length λ which improves upon previous results in the region λ <0.1 nm , and remains competitive in the larger-λ region. A pseudoexperimental simulation is developed for this experiment and its role in the data analysis is described. We conclude with plans for improving sensitivity in the larger-λ region.

Unfolding the neutron spectrum of a NE213 scintillator using artificial neural networks.

PubMed

Sharghi Ido, A; Bonyadi, M R; Etaati, G R; Shahriari, M

2009-10-01

Artificial neural networks technology has been applied to unfold the neutron spectra from the pulse height distribution measured with NE213 liquid scintillator. Here, both the single and multi-layer perceptron neural network models have been implemented to unfold the neutron spectrum from an Am-Be neutron source. The activation function and the connectivity of the neurons have been investigated and the results have been analyzed in terms of the network's performance. The simulation results show that the neural network that utilizes the Satlins transfer function has the best performance. In addition, omitting the bias connection of the neurons improve the performance of the network. Also, the SCINFUL code is used for generating the response functions in the training phase of the process. Finally, the results of the neural network simulation have been compared with those of the FORIST unfolding code for both (241)Am-Be and (252)Cf neutron sources. The results of neural network are in good agreement with FORIST code.

Modeling the Martian neutron and gamma-ray leakage fluxes using Geant4

NASA Astrophysics Data System (ADS)

Pirard, Benoit; Desorgher, Laurent; Diez, Benedicte; Gasnault, Olivier

A new evaluation of the Martian neutron and gamma-ray (continuum and line) leakage fluxes has been performed using the Geant4 code. Even if numerous studies have recently been carried out with Monte Carlo methods to characterize planetary radiation environments, only a few however have been able to reproduce in detail the neutron and gamma-ray spectra observed in orbit. We report on the efforts performed to adapt and validate the Geant4-based PLAN- ETOCOSMICS code for use in planetary neutron and gamma-ray spectroscopy data analysis. Beside the advantage of high transparency and modularity common to Geant4 applications, the new code uses reviewed nuclear cross section data, realistic atmospheric profiles and soil layering, as well as specific effects such as gravity acceleration for low energy neutrons. Results from first simulations are presented for some Martian reference compositions and show a high consistency with corresponding neutron and gamma-ray spectra measured on board Mars Odyssey. Finally we discuss the advantages and perspectives of the improved code for precise simulation of planetary radiation environments.

LDRD Final Review: Radiation Transport Calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goorley, John Timothy; Morgan, George Lake; Lestone, John Paul

2017-06-22

Both high-fidelity & toy simulations are being used to understand measured signals and improve the Area 11 NDSE diagnostic. We continue to gain more and more confidence in the ability for MCNP to simulate neutron and photon transport from source to radiation detector.

Numerical study of neutron beam divergence in a beam-fusion scenario employing laser driven ions

NASA Astrophysics Data System (ADS)

Alejo, A.; Green, A.; Ahmed, H.; Robinson, A. P. L.; Cerchez, M.; Clarke, R.; Doria, D.; Dorkings, S.; Fernandez, J.; McKenna, P.; Mirfayzi, S. R.; Naughton, K.; Neely, D.; Norreys, P.; Peth, C.; Powell, H.; Ruiz, J. A.; Swain, J.; Willi, O.; Borghesi, M.; Kar, S.

2016-09-01

The most established route to create a laser-based neutron source is by employing laser accelerated, low atomic-number ions in fusion reactions. In addition to the high reaction cross-sections at moderate energies of the projectile ions, the anisotropy in neutron emission is another important feature of beam-fusion reactions. Using a simple numerical model based on neutron generation in a pitcher-catcher scenario, anisotropy in neutron emission was studied for the deuterium-deuterium fusion reaction. Simulation results are consistent with the narrow-divergence (∼ 70 ° full width at half maximum) neutron beam recently served in an experiment employing multi-MeV deuteron beams of narrow divergence (up to 30° FWHM, depending on the ion energy) accelerated by a sub-petawatt laser pulse from thin deuterated plastic foils via the Target Normal Sheath Acceleration mechanism. By varying the input ion beam parameters, simulations show that a further improvement in the neutron beam directionality (i.e. reduction in the beam divergence) can be obtained by increasing the projectile ion beam temperature and cut-off energy, as expected from interactions employing higher power lasers at upcoming facilities.

Improvement of the prompt-gamma neutron activation facility at Brookhaven National Laboratory.

PubMed

Dilmanian, F A; Lidofsky, L J; Stamatelatos, I; Kamen, Y; Yasumura, S; Vartsky, D; Pierson, R N; Weber, D A; Moore, R I; Ma, R

1998-02-01

The prompt-gamma neutron activation facility at Brookhaven National Laboratory was upgraded to improve both the precision and accuracy of its in vivo determinations of total body nitrogen. The upgrade, guided by Monte Carlo simulations, involved elongating and modifying the source collimator and its shielding, repositioning the system's two NaI(Tl) detectors, and improving the neutron and gamma shielding of these detectors. The new source collimator has a graphite reflector around the 238PuBe neutron source to enhance the low-energy region of the neutron spectrum incident on the patient. The gamma detectors have been relocated from positions close to the upward-emerging collimated neutron beam to positions close to and at the sides of the patient. These modifications substantially reduced spurious counts resulting from the capture of small-angle scattered neutrons in the NaI detectors. The pile-up background under the 10.8 MeV 14N(n, gamma)15N spectral peak has been reduced so that the nitrogen peak-to-background ratio has been increased by a factor of 2.8. The resulting reduction in the coefficient of variation of the total body nitrogen measurements from 3% to 2.2% has improved the statistical significance of the results possible for any given number of patient measurements. The new system also has a more uniform composite sensitivity.

Geant4 simulation of the CERN-EU high-energy reference field (CERF) facility.

PubMed

Prokopovich, D A; Reinhard, M I; Cornelius, I M; Rosenfeld, A B

2010-09-01

The CERN-EU high-energy reference field facility is used for testing and calibrating both active and passive radiation dosemeters for radiation protection applications in space and aviation. Through a combination of a primary particle beam, target and a suitable designed shielding configuration, the facility is able to reproduce the neutron component of the high altitude radiation field relevant to the jet aviation industry. Simulations of the facility using the GEANT4 (GEometry ANd Tracking) toolkit provide an improved understanding of the neutron particle fluence as well as the particle fluence of other radiation components present. The secondary particle fluence as a function of the primary particle fluence incident on the target and the associated dose equivalent rates were determined at the 20 designated irradiation positions available at the facility. Comparisons of the simulated results with previously published simulations obtained using the FLUKA Monte Carlo code, as well as with experimental results of the neutron fluence obtained with a Bonner sphere spectrometer, are made.

A multi-detector neutron spectrometer with nearly isotropic response for environmental and workplace monitoring

NASA Astrophysics Data System (ADS)

Gómez-Ros, J. M.; Bedogni, R.; Moraleda, M.; Delgado, A.; Romero, A.; Esposito, A.

2010-01-01

This communication describes an improved design for a neutron spectrometer consisting of 6Li thermoluminescent dosemeters located at selected positions within a single moderating polyethylene sphere. The spatial arrangement of the dosemeters has been designed using the MCNPX Monte Carlo code to calculate the response matrix for 56 log-equidistant energies from 10 -9 to 100 MeV, looking for a configuration that permits to obtain a nearly isotropic response for neutrons in the energy range from thermal to 20 MeV. The feasibility of the proposed spectrometer and the isotropy of its response have been evaluated by simulating exposures to different reference and workplace neutron fields. The FRUIT code has been used for unfolding purposes. The results of the simulations as well as the experimental tests confirm the suitability of the prototype for environmental and workplace monitoring applications.

Capacitive Deionization of High-Salinity Solutions

DOE PAGES

Sharma, Ketki; Gabitto, Jorge; Mayes, Richard T.; ...

2014-12-22

Desalination of high salinity solutions has been studied using a novel experimental technique and a theoretical model. Neutron imaging has been employed to visualize lithium ions in mesoporous carbon materials, which are used as electrodes in capacitive deionization for water desalination. Experiments were conducted with a flow-through capacitive deionization cell designed for neutron imaging and with lithium chloride ( 6LiCl) as the electrolyte. Sequences of neutron images have been obtained at a relatively high concentration of lithium chloride ( 6LiCl) solution to provide information on the transport of ions within the electrodes. A new model that computes the individual ionicmore » concentration profiles inside mesoporous carbon electrodes has been used to simulate the capacitive deionization process. Modifications have also been introduced into the simulation model to calculate results at high electrolyte concentrations. Experimental data and simulation results provide insight into why capacitive deionization is not effective for desalination of high ionic-strength solutions. The combination of experimental information, obtained through neutron imaging, with the theoretical model will help in the design of capacitive deionization devices, which can improve the process for high ionic-strength solutions.« less

ENDF/B-VIII.0: The 8 th Major Release of the Nuclear Reaction Data Library with CIELO-project Cross Sections, New Standards and Thermal Scattering Data

DOE PAGES

Brown, D. A.; Chadwick, M. B.; Capote, R.; ...

2018-02-01

We describe the new ENDF/B-VIII.0 evaluated nuclear reaction data library. ENDF/B-VIII.0 fully incorporates the new IAEA standards, includes improved thermal neutron scattering data and uses new evaluated data from the CIELO project for neutron reactions on 1H, 16O, 56Fe, 235U, 238U and 239Pu described in companion papers in the present issue of Nuclear Data Sheets. The evaluations benefit from recent experimental data obtained in the U.S. and Europe, and improvements in theory and simulation. Notable advances include updated evaluated data for light nuclei, structural materials, actinides, fission energy release, prompt fission neutron and γ-ray spectra, thermal neutron scattering data, andmore » charged-particle reactions. Integral validation testing is shown for a wide range of criticality, reaction rate, and neutron transmission benchmarks. In general, integral validation performance of the library is improved relative to the previous ENDF/B-VII.1 library.« less

ENDF/B-VIII.0: The 8 th Major Release of the Nuclear Reaction Data Library with CIELO-project Cross Sections, New Standards and Thermal Scattering Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, D. A.; Chadwick, M. B.; Capote, R.

We describe the new ENDF/B-VIII.0 evaluated nuclear reaction data library. ENDF/B-VIII.0 fully incorporates the new IAEA standards, includes improved thermal neutron scattering data and uses new evaluated data from the CIELO project for neutron reactions on 1H, 16O, 56Fe, 235U, 238U and 239Pu described in companion papers in the present issue of Nuclear Data Sheets. The evaluations benefit from recent experimental data obtained in the U.S. and Europe, and improvements in theory and simulation. Notable advances include updated evaluated data for light nuclei, structural materials, actinides, fission energy release, prompt fission neutron and γ-ray spectra, thermal neutron scattering data, andmore » charged-particle reactions. Integral validation testing is shown for a wide range of criticality, reaction rate, and neutron transmission benchmarks. In general, integral validation performance of the library is improved relative to the previous ENDF/B-VII.1 library.« less

Neutron Science TeraGrid Gateway

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lynch, Vickie E; Chen, Meili; Cobb, John W

The unique contributions of the Neutron Science TeraGrid Gateway (NSTG) are the connection of national user facility instrument data sources to the integrated cyberinfrastructure of the National Science FoundationTeraGrid and the development of a neutron science gateway that allows neutron scientists to use TeraGrid resources to analyze their data, including comparison of experiment with simulation. The NSTG is working in close collaboration with the Spallation Neutron Source (SNS) at Oak Ridge as their principal facility partner. The SNS is a next-generation neutron source. It has completed construction at a cost of $1.4 billion and is ramping up operations. The SNSmore » will provide an order of magnitude greater flux than any previous facility in the world and will be available to all of the nation's scientists, independent of funding source, on a peer-reviewed merit basis. With this new capability, the neutron science community is facing orders of magnitude larger data sets and is at a critical point for data analysis and simulation. There is a recognized need for new ways to manage and analyze data to optimize both beam time and scientific output. The TeraGrid is providing new capabilities in the gateway for simulations using McStas and a fitting service on distributed TeraGrid resources to improved turnaround. NSTG staff are also exploring replicating experimental data in archival storage. As part of the SNS partnership, the NSTG provides access to gateway support, cyberinfrastructure outreach, community development, and user support for the neutron science community. This community includes not only SNS staff and users but extends to all the major worldwide neutron scattering centers.« less

Towards radiation hard converter material for SiC-based fast neutron detectors

NASA Astrophysics Data System (ADS)

Tripathi, S.; Upadhyay, C.; Nagaraj, C. P.; Venkatesan, A.; Devan, K.

2018-05-01

In the present work, Geant4 Monte-Carlo simulations have been carried out to study the neutron detection efficiency of the various neutron to other charge particle (recoil proton) converter materials. The converter material is placed over Silicon Carbide (SiC) in Fast Neutron detectors (FNDs) to achieve higher neutron detection efficiency as compared to bare SiC FNDs. Hydrogenous converter material such as High-Density Polyethylene (HDPE) is preferred over other converter materials due to the virtue of its high elastic scattering reaction cross-section for fast neutron detection at room temperature. Upon interaction with fast neutrons, hydrogenous converter material generates recoil protons which liberate e-hole pairs in the active region of SiC detector to provide a detector signal. The neutron detection efficiency offered by HDPE converter is compared with several other hydrogenous materials viz., 1) Lithium Hydride (LiH), 2) Perylene, 3) PTCDA . It is found that, HDPE, though providing highest efficiency among various studied materials, cannot withstand high temperature and harsh radiation environment. On the other hand, perylene and PTCDA can sustain harsh environments, but yields low efficiency. The analysis carried out reveals that LiH is a better material for neutron to other charge particle conversion with competent efficiency and desired radiation hardness. Further, the thickness of LiH has also been optimized for various mono-energetic neutron beams and Am-Be neutron source generating a neutron fluence of 109 neutrons/cm2. The optimized thickness of LiH converter for fast neutron detection is found to be ~ 500 μm. However, the estimated efficiency for fast neutron detection is only 0.1%, which is deemed to be inadequate for reliable detection of neutrons. A sensitivity study has also been done investigating the gamma background effect on the neutron detection efficiency for various energy threshold of Low-Level Discriminator (LLD). The detection efficiency of a stacked structure concept has been explored by juxtaposing several converter-detector layers to improve the efficiency of LiH-SiC-based FNDs . It is observed that approximately tenfold efficiency improvement has been achieved—0.93% for ten layers stacked configuration vis-à-vis 0.1% of single converter-detector layer configuration. Finally, stacked detectors have also been simulated for different converter thicknesses to attain the efficiency as high as ~ 3.25% with the help of 50 stacked layers.

SU-E-T-21: A D-D Based Neutron Generator System for Boron Neutron Capture Therapy: A Feasibility Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsieh, M; Liu, Y; Nie, L

2015-06-15

Purpose: To investigate the feasibility of a deuterium-deuterium (DD) neutron generator for application in boron neutron capture therapy (BNCT) of brain cancer Methods: MCNP simulations were performed using a head phantom and a monoenergetic neutron source, which resembles the point source in a DD generator that emits 2.45-MeV neutrons. Source energies ranging from 5eV to 2.45MeV were simulated to determine the optimal treatment energy. The phantom consisted of soft tissue, brain tissue, skull, skin layer, and a brain tumor of 5 cm in diameter. Tumor depth was varied from 5–10 cm. Boron-10 concentrations of 10 ppm, 15 ppm, and 30more » ppm were used in the soft/brain tissues, skin, and tumor, respectively. The neutron flux required to deliver 60 Gy to the tumor as well as the normal tissue doses were determined. Results: Beam energies between 5eV and 10keV obtained doses with the highest dose ratios (3.3–25.9) between the tumor and the brain at various depths. The dose ratio with 2.45-MeV neutrons ranged from 0.8–6.6. To achieve the desired tumor dose in 40 minutes, the required neutron flux for a DD generator was between 8.8E10 and 5.2E11 n/s and the resulting brain dose was between 2.3 and 18 Gy, depending on the tumor depth. The skin and soft tissue doses were within acceptable tolerances. The boron-neutron interaction accounted for 54–58% of the total dose. Conclusion: This study shows that the DD neutron generator can be a feasible neutron source for BNCT. The required neutron flux for treatment is achievable with the current DD neutron technology. With a well-designed beam shaping assembly and treatment geometry, the neutron flux can be further improved and a 60-Gy prescription can be accurately delivered to the target while maintaining tolerable normal tissue doses. Further experimental studies will be developed and conducted to validate the simulation results.« less

Monte Carlo simulation of moderator and reflector in coal analyzer based on a D-T neutron generator.

PubMed

Shan, Qing; Chu, Shengnan; Jia, Wenbao

2015-11-01

Coal is one of the most popular fuels in the world. The use of coal not only produces carbon dioxide, but also contributes to the environmental pollution by heavy metals. In prompt gamma-ray neutron activation analysis (PGNAA)-based coal analyzer, the characteristic gamma rays of C and O are mainly induced by fast neutrons, whereas thermal neutrons can be used to induce the characteristic gamma rays of H, Si, and heavy metals. Therefore, appropriate thermal and fast neutrons are beneficial in improving the measurement accuracy of heavy metals, and ensure that the measurement accuracy of main elements meets the requirements of the industry. Once the required yield of the deuterium-tritium (d-T) neutron generator is determined, appropriate thermal and fast neutrons can be obtained by optimizing the neutron source term. In this article, the Monte Carlo N-Particle (MCNP) Transport Code and Evaluated Nuclear Data File (ENDF) database are used to optimize the neutron source term in PGNAA-based coal analyzer, including the material and shape of the moderator and neutron reflector. The optimized targets include two points: (1) the ratio of the thermal to fast neutron is 1:1 and (2) the total neutron flux from the optimized neutron source in the sample increases at least 100% when compared with the initial one. The simulation results show that, the total neutron flux in the sample increases 102%, 102%, 85%, 72%, and 62% with Pb, Bi, Nb, W, and Be reflectors, respectively. Maximum optimization of the targets is achieved when the moderator is a 3-cm-thick lead layer coupled with a 3-cm-thick high-density polyethylene (HDPE) layer, and the neutron reflector is a 27-cm-thick hemispherical lead layer. Copyright © 2015 Elsevier Ltd. All rights reserved.

Further Improvement of the RITS Code for Pulsed Neutron Bragg-edge Transmission Imaging

NASA Astrophysics Data System (ADS)

Sato, H.; Watanabe, K.; Kiyokawa, K.; Kiyanagi, R.; Hara, K. Y.; Kamiyama, T.; Furusaka, M.; Shinohara, T.; Kiyanagi, Y.

The RITS code is a unique and powerful tool for a whole Bragg-edge transmission spectrum fitting analysis. However, it has had two major problems. Therefore, we have proposed methods to overcome these problems. The first issue is the difference in the crystallite size values between the diffraction and the Bragg-edge analyses. We found the reason was a different definition of the crystal structure factor. It affects the crystallite size because the crystallite size is deduced from the primary extinction effect which depends on the crystal structure factor. As a result of algorithm change, crystallite sizes obtained by RITS drastically approached to crystallite sizes obtained by Rietveld analyses of diffraction data; from 155% to 110%. The second issue is correction of the effect of background neutrons scattered from a specimen. Through neutron transport simulation studies, we found that the background components consist of forward Bragg scattering, double backward Bragg scattering, and thermal diffuse scattering. RITS with the background correction function which was developed through the simulation studies could well reconstruct various simulated and experimental transmission spectra, but refined crystalline microstructural parameters were often distorted. Finally, it was recommended to reduce the background by improving experimental conditions.

Beam Characterization at the Neutron Radiography Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sarah Morgan; Jeffrey King

The quality of a neutron imaging beam directly impacts the quality of radiographic images produced using that beam. Fully characterizing a neutron beam, including determination of the beam’s effective length-to-diameter ratio, neutron flux profile, energy spectrum, image quality, and beam divergence, is vital for producing quality radiographic images. This project characterized the east neutron imaging beamline at the Idaho National Laboratory Neutron Radiography Reactor (NRAD). The experiments which measured the beam’s effective length-to-diameter ratio and image quality are based on American Society for Testing and Materials (ASTM) standards. An analysis of the image produced by a calibrated phantom measured themore » beam divergence. The energy spectrum measurements consist of a series of foil irradiations using a selection of activation foils, compared to the results produced by a Monte Carlo n-Particle (MCNP) model of the beamline. Improvement of the existing NRAD MCNP beamline model includes validation of the model’s energy spectrum and the development of enhanced image simulation methods. The image simulation methods predict the radiographic image of an object based on the foil reaction rate data obtained by placing a model of the object in front of the image plane in an MCNP beamline model.« less

Current and anticipated uses of thermalhydraulic and neutronic codes at PSI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aksan, S.N.; Zimmermann, M.A.; Yadigaroglu, G.

1997-07-01

The thermalhydraulic and/or neutronic codes in use at PSI mainly provide the capability to perform deterministic safety analysis for Swiss NPPs and also serve as analysis tools for experimental facilities for LWR and ALWR simulations. In relation to these applications, physical model development and improvements, and assessment of the codes are also essential components of the activities. In this paper, a brief overview is provided on the thermalhydraulic and/or neutronic codes used for safety analysis of LWRs, at PSI, and also of some experiences and applications with these codes. Based on these experiences, additional assessment needs are indicated, together withmore » some model improvement needs. The future needs that could be used to specify both the development of a new code and also improvement of available codes are summarized.« less

Spent nuclear fuel assembly inspection using neutron computed tomography

NASA Astrophysics Data System (ADS)

Pope, Chad Lee

The research presented here focuses on spent nuclear fuel assembly inspection using neutron computed tomography. Experimental measurements involving neutron beam transmission through a spent nuclear fuel assembly serve as benchmark measurements for an MCNP simulation model. Comparison of measured results to simulation results shows good agreement. Generation of tomography images from MCNP tally results was accomplished using adapted versions of built in MATLAB algorithms. Multiple fuel assembly models were examined to provide a broad set of conclusions. Tomography images revealing assembly geometric information including the fuel element lattice structure and missing elements can be obtained using high energy neutrons. A projection difference technique was developed which reveals the substitution of unirradiated fuel elements for irradiated fuel elements, using high energy neutrons. More subtle material differences such as altering the burnup of individual elements can be identified with lower energy neutrons provided the scattered neutron contribution to the image is limited. The research results show that neutron computed tomography can be used to inspect spent nuclear fuel assemblies for the purpose of identifying anomalies such as missing elements or substituted elements. The ability to identify anomalies in spent fuel assemblies can be used to deter diversion of material by increasing the risk of early detection as well as improve reprocessing facility operations by confirming the spent fuel configuration is as expected or allowing segregation if anomalies are detected.

Working Gas Selection of the Honeycomb Converter-Based Neutron Detector

NASA Astrophysics Data System (ADS)

Fang, Zhujun; Yang, Yigang; Li, Yulan; Wang, Xuewu

2017-07-01

To reduce the manufacturing difficulty and improve the robustness of traditional boron-lined detectors that may replace the 3He counter, the honeycomb neutron converter-based gaseous neutron detector has been proposed. A drift electric field is applied to drive electrons ionized by α or 7Li after the 10B(n, α)7Li reaction from their origination positions to the incident surface of the gas electron multiplier (GEM), which multiplies electrons and forms the neutron signal. As the working gas affects the energy deposition of α or 7Li, the transverse diffusion of electrons in the migration process, as well as the multiplication of electrons in the GEM detector, the working gas selection of the honeycomb converter-based detector would be very important. Fourteen different working gases are investigated in detail through simulation research. Four working gases, Ar:iC4H10:CF4 = 90:7:3, Ar:CO2 = 95:5, Ar:CH4 = 90:10, and Ar:DME = 95:5, are experimentally tested. Both the simulation and experimental results demonstrate that working gases of Ar:iC4H10:CF4 = 90:7:3, Ar:CO2 = 95:5, and Ar:DME = 95:5 show good performances benefitting from both the large stopping powers of α or 7Li and the small transverse diffusion coefficients of electrons. The simulation results indicate that the detection efficiency with one of the three gases is 1.33 to 1.48 times the Ar:CH4 = 90:10, while the experimental results demonstrate that there is 1.34-1.49 times of the detection efficiency. The research in this paper helps improve the performance of the honeycomb converter-based neutron detector.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lafleur, Adrienne M.; Ulrich, Timothy J. II; Menlove, Howard O.

Objective is to investigate the use of Passive Neutron Albedo Reactivity (PNAR) and Self-Interrogation Neutron Resonance Densitometry (SINRD) to quantify fissile content in FUGEN spent fuel assemblies (FAs). Methodology used is: (1) Detector was designed using fission chambers (FCs); (2) Optimized design via MCNPX simulations; and (3) Plan to build and field test instrument in FY13. Significance was to improve safeguards verification of spent fuel assemblies in water and increase sensitivity to partial defects. MCNPX simulations were performed to optimize the design of the SINRD+PNAR detector. PNAR ratio was less sensitive to FA positioning than SINRD and SINRD ratio wasmore » more sensitive to Pu fissile mass than PNAR. Significance was that the integration of these techniques can be used to improve verification of spent fuel assemblies in water.« less

Simulated and measured neutron/gamma light output distribution for poly-energetic neutron/gamma sources

NASA Astrophysics Data System (ADS)

Hosseini, S. A.; Zangian, M.; Aghabozorgi, S.

2018-03-01

In the present paper, the light output distribution due to poly-energetic neutron/gamma (neutron or gamma) source was calculated using the developed MCNPX-ESUT-PE (MCNPX-Energy engineering of Sharif University of Technology-Poly Energetic version) computational code. The simulation of light output distribution includes the modeling of the particle transport, the calculation of scintillation photons induced by charged particles, simulation of the scintillation photon transport and considering the light resolution obtained from the experiment. The developed computational code is able to simulate the light output distribution due to any neutron/gamma source. In the experimental step of the present study, the neutron-gamma discrimination based on the light output distribution was performed using the zero crossing method. As a case study, 241Am-9Be source was considered and the simulated and measured neutron/gamma light output distributions were compared. There is an acceptable agreement between the discriminated neutron/gamma light output distributions obtained from the simulation and experiment.

The MCUCN simulation code for ultracold neutron physics

NASA Astrophysics Data System (ADS)

Zsigmond, G.

2018-02-01

Ultracold neutrons (UCN) have very low kinetic energies 0-300 neV, thereby can be stored in specific material or magnetic confinements for many hundreds of seconds. This makes them a very useful tool in probing fundamental symmetries of nature (for instance charge-parity violation by neutron electric dipole moment experiments) and contributing important parameters for the Big Bang nucleosynthesis (neutron lifetime measurements). Improved precision experiments are in construction at new and planned UCN sources around the world. MC simulations play an important role in the optimization of such systems with a large number of parameters, but also in the estimation of systematic effects, in benchmarking of analysis codes, or as part of the analysis. The MCUCN code written at PSI has been extensively used for the optimization of the UCN source optics and in the optimization and analysis of (test) experiments within the nEDM project based at PSI. In this paper we present the main features of MCUCN and interesting benchmark and application examples.

Improvement effect on the depth-dose distribution by CSF drainage and air infusion of a tumour-removed cavity in boron neutron capture therapy for malignant brain tumours

NASA Astrophysics Data System (ADS)

Sakurai, Yoshinori; Ono, Koji; Miyatake, Shin-ichi; Maruhashi, Akira

2006-03-01

Boron neutron capture therapy (BNCT) without craniotomy for malignant brain tumours was started using an epi-thermal neutron beam at the Kyoto University Reactor in June 2002. We have tried some techniques to overcome the treatable-depth limit in BNCT. One of the effective techniques is void formation utilizing a tumour-removed cavity. The tumorous part is removed by craniotomy about 1 week before a BNCT treatment in our protocol. Just before the BNCT irradiation, the cerebro-spinal fluid (CSF) in the tumour-removed cavity is drained out, air is infused to the cavity and then the void is made. This void improves the neutron penetration, and the thermal neutron flux at depth increases. The phantom experiments and survey simulations modelling the CSF drainage and air infusion of the tumour-removed cavity were performed for the size and shape of the void. The advantage of the CSF drainage and air infusion is confirmed for the improvement in the depth-dose distribution. From the parametric surveys, it was confirmed that the cavity volume had good correlation with the improvement effect, and the larger effect was expected as the cavity volume was larger.

Improvement effect on the depth-dose distribution by CSF drainage and air infusion of a tumour-removed cavity in boron neutron capture therapy for malignant brain tumours.

PubMed

Sakurai, Yoshinori; Ono, Koji; Miyatake, Shin-Ichi; Maruhashi, Akira

2006-03-07

Boron neutron capture therapy (BNCT) without craniotomy for malignant brain tumours was started using an epi-thermal neutron beam at the Kyoto University Reactor in June 2002. We have tried some techniques to overcome the treatable-depth limit in BNCT. One of the effective techniques is void formation utilizing a tumour-removed cavity. The tumorous part is removed by craniotomy about 1 week before a BNCT treatment in our protocol. Just before the BNCT irradiation, the cerebro-spinal fluid (CSF) in the tumour-removed cavity is drained out, air is infused to the cavity and then the void is made. This void improves the neutron penetration, and the thermal neutron flux at depth increases. The phantom experiments and survey simulations modelling the CSF drainage and air infusion of the tumour-removed cavity were performed for the size and shape of the void. The advantage of the CSF drainage and air infusion is confirmed for the improvement in the depth-dose distribution. From the parametric surveys, it was confirmed that the cavity volume had good correlation with the improvement effect, and the larger effect was expected as the cavity volume was larger.

Improved Fission Neutron Data Base for Active Interrogation of Actinides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pozzi, Sara; Czirr, J. Bart; Haight, Robert

2013-11-06

This project will develop an innovative neutron detection system for active interrogation measurements. Many active interrogation methods to detect fissionable material are based on the detection of neutrons from fission induced by fast neutrons or high-energy gamma rays. The energy spectrum of the fission neutrons provides data to identify the fissionable isotopes and materials such as shielding between the fissionable material and the detector. The proposed path for the project is as follows. First, the team will develop new neutron detection systems and algorithms by Monte Carlo simulations and bench-top experiments. Next, They will characterize and calibrate detection systems bothmore » with monoenergetic and white neutron sources. Finally, high-fidelity measurements of neutron emission from fissions induced by fast neutrons will be performed. Several existing fission chambers containing U-235, Pu-239, U-238, or Th-232 will be used to measure the neutron-induced fission neutron emission spectra. The challenge for making confident measurements is the detection of neutrons in the energy ranges of 0.01 – 1 MeV and above 8 MeV, regions where the basic data on the neutron energy spectrum emitted from fission is least well known. In addition, improvements in the specificity of neutron detectors are required throughout the complete energy range: they must be able to clearly distinguish neutrons from other radiations, in particular gamma rays and cosmic rays. The team believes that all of these challenges can be addressed successfully with emerging technologies under development by this collaboration. In particular, the collaboration will address the area of fission neutron emission spectra for isotopes of interest in the advanced fuel cycle initiative (AFCI).« less

ENDF/B-VII.0: Next Generation Evaluated Nuclear Data Library for Nuclear Science and Technology

NASA Astrophysics Data System (ADS)

Chadwick, M. B.; Obložinský, P.; Herman, M.; Greene, N. M.; McKnight, R. D.; Smith, D. L.; Young, P. G.; MacFarlane, R. E.; Hale, G. M.; Frankle, S. C.; Kahler, A. C.; Kawano, T.; Little, R. C.; Madland, D. G.; Moller, P.; Mosteller, R. D.; Page, P. R.; Talou, P.; Trellue, H.; White, M. C.; Wilson, W. B.; Arcilla, R.; Dunford, C. L.; Mughabghab, S. F.; Pritychenko, B.; Rochman, D.; Sonzogni, A. A.; Lubitz, C. R.; Trumbull, T. H.; Weinman, J. P.; Brown, D. A.; Cullen, D. E.; Heinrichs, D. P.; McNabb, D. P.; Derrien, H.; Dunn, M. E.; Larson, N. M.; Leal, L. C.; Carlson, A. D.; Block, R. C.; Briggs, J. B.; Cheng, E. T.; Huria, H. C.; Zerkle, M. L.; Kozier, K. S.; Courcelle, A.; Pronyaev, V.; van der Marck, S. C.

2006-12-01

We describe the next generation general purpose Evaluated Nuclear Data File, ENDF/B-VII.0, of recommended nuclear data for advanced nuclear science and technology applications. The library, released by the U.S. Cross Section Evaluation Working Group (CSEWG) in December 2006, contains data primarily for reactions with incident neutrons, protons, and photons on almost 400 isotopes, based on experimental data and theory predictions. The principal advances over the previous ENDF/B-VI library are the following: (1) New cross sections for U, Pu, Th, Np and Am actinide isotopes, with improved performance in integral validation criticality and neutron transmission benchmark tests; (2) More precise standard cross sections for neutron reactions on H, 6Li, 10B, Au and for 235,238U fission, developed by a collaboration with the IAEA and the OECD/NEA Working Party on Evaluation Cooperation (WPEC); (3) Improved thermal neutron scattering; (4) An extensive set of neutron cross sections on fission products developed through a WPEC collaboration; (5) A large suite of photonuclear reactions; (6) Extension of many neutron- and proton-induced evaluations up to 150 MeV; (7) Many new light nucleus neutron and proton reactions; (8) Post-fission beta-delayed photon decay spectra; (9) New radioactive decay data; (10) New methods for uncertainties and covariances, together with covariance evaluations for some sample cases; and (11) New actinide fission energy deposition. The paper provides an overview of this library, consisting of 14 sublibraries in the same ENDF-6 format as the earlier ENDF/B-VI library. We describe each of the 14 sublibraries, focusing on neutron reactions. Extensive validation, using radiation transport codes to simulate measured critical assemblies, show major improvements: (a) The long-standing underprediction of low enriched uranium thermal assemblies is removed; (b) The 238U and 208Pb reflector biases in fast systems are largely removed; (c) ENDF/B-VI.8 good agreement for simulations of thermal high-enriched uranium assemblies is preserved; (d) The underprediction of fast criticality of 233,235U and 239Pu assemblies is removed; and (e) The intermediate spectrum critical assemblies are predicted more accurately. We anticipate that the new library will play an important role in nuclear technology applications, including transport simulations supporting national security, nonproliferation, advanced reactor and fuel cycle concepts, criticality safety, fusion, medicine, space applications, nuclear astrophysics, and nuclear physics facility design. The ENDF/B-VII.0 library is archived at the National Nuclear Data Center, BNL, and can be retrieved from www.nndc.bnl.gov.

Dosimetric characteristics of the University of Washington Clinical Neutron Therapy System

NASA Astrophysics Data System (ADS)

Moffitt, Gregory B.; Stewart, Robert D.; Sandison, George A.; Goorley, John T.; Argento, David C.; Jevremovic, Tatjana; Emery, Robert; Wootton, Landon S.; Parvathaneni, Upendra; Laramore, George E.

2018-05-01

The University of Washington (UW) Clinical Neutron Therapy System (CNTS), which generates high linear energy transfer fast neutrons through interactions of 50.5 MeV protons incident on a Be target, has depth-dose characteristics similar to 6 MV x-rays. In contrast to the fixed beam angles and primitive blocking used in early clinical trials of neutron therapy, the CNTS has a gantry with a full 360° of rotation, internal wedges, and a multi-leaf collimator (MLC). Since October of 1984, over 3178 patients have received conformal neutron therapy treatments using the UW CNTS. In this work, the physical and dosimetric characteristics of the CNTS are documented through comparisons of measurements and Monte Carlo simulations. A high resolution computed tomography scan of the model 17 ionization chamber (IC-17) has also been used to improve the accuracy of simulations of the absolute calibration geometry. The response of the IC-17 approximates well the kinetic energy released per unit mass (KERMA) in water for neutrons and photons for energies from a few tens of keV up to about 20 MeV. Above 20 MeV, the simulated model 17 ion chamber response is 20%–30% higher than the neutron KERMA in water. For CNTS neutrons, simulated on- and off-axis output factors in water match measured values within ~2%  ±  2% for rectangular and irregularly shaped field with equivalent square areas ranging in a side dimension from 2.8 cm to 30.7 cm. Wedge factors vary by less than 1.9% of the measured dose in water for clinically relevant field sizes. Simulated tissue maximum ratios in water match measured values within 3.3% at depths up to 20 cm. Although the absorbed dose for water and adipose tissue are within 2% at a depth of 1.7 cm, the absorbed dose in muscle and bone can be as much as 12 to 40% lower than the absorbed dose in water. The reported studies are significant from a historical perspective and as additional validation of a new tool for patient quality assurance and as an aid in ongoing efforts to clinically implement advanced treatment techniques, such as intensity modulated neutron therapy, at the UW.

RE-EVALUATION OF THE NEUTRON EMISSION FROM THE SOLAR FLARE OF 2005 SEPTEMBER 7, DETECTED BY THE SOLAR NEUTRON TELESCOPE AT SIERRA NEGRA

DOE Office of Scientific and Technical Information (OSTI.GOV)

González, L. X.; Valdés-Galicia, J. F.; Musalem, O.

2015-12-01

The X17.0 solar flare of 2005 September 7 released high-energy neutrons that were detected by the Solar Neutron Telescope (SNT) at Sierra Negra, Mexico. In three separate and independent studies of this solar neutron event, several of its unique characteristics were studied; in particular, a power-law energy spectra was estimated. In this paper, we present an alternative analysis, based on improved numerical simulations of the detector using GEANT4, and a different technique for processing the SNT data. The results indicate that the spectral index that best fits the neutron flux is around 3, in agreement with previous works. Based onmore » the numerically calculated neutron energy deposition on the SNT, we confirm that the detected neutrons might have reached an energy of 1 GeV, which implies that 10 GeV protons were probably produced; these could not be observed at Earth, as their parent flare was an east limb event.« less

CHARACTERIZATION OF A THIN SILICON SENSOR FOR ACTIVE NEUTRON PERSONAL DOSEMETERS.

PubMed

Takada, M; Nunomiya, T; Nakamura, T; Matsumoto, T; Masuda, A

2016-09-01

A thin silicon sensor has been developed for active neutron personal dosemeters for use by aircrews and first responders. This thin silicon sensor is not affected by the funneling effect, which causes detection of cosmic protons and over-response to cosmic neutrons. There are several advantages to the thin silicon sensor: a decrease in sensitivity to gamma rays, an improvement of the energy detection limit for neutrons down to 0.8 MeV and an increase in the sensitivity to fast neutrons. Neutron response functions were experimentally obtained using 2.5 and 5 MeV monoenergy neutron beams and a (252)Cf neutron source. Simulation results using the Monte Carlo N-Particle transport code agree quite well with the experimental ones when an energy deposition region shaped like a circular truncated cone is used in place of a cylindrical region. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Neutron Resonance Radiography for Explosives Detection: Technical Challenges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raas, W L; Blackburn, B; Boyd, E

2005-11-09

Fast Neutron Resonance Radiography (NRR) has recently become a focus of investigation as a supplement to conventional x-ray systems as a non-invasive, non-destructive means of detecting explosive material concealed in checked luggage or cargo containers at airports. Using fast (1-6 MeV) neutrons produced by the D(d,n){sup 3}He reaction, NRR provides both an imaging capability and the ability to determine the chemical composition of materials in baggage or cargo. Elemental discrimination is achieved by exploiting the resonance features of the neutron cross-section for oxygen, nitrogen, carbon, and hydrogen. Simulations have shown the effectiveness of multiple-element NRR through Monte Carlo transport methods;more » this work is focused on the development of a prototype system that will incorporate an accelerator-based neutron source and a neutron detection and imaging system to demonstrate the realistic capabilities of NRR in distinguishing the elemental components of concealed objects. Preliminary experiments have exposed significant technical difficulties unapparent in simulations, including the presence of image contamination from gamma ray production, the detection of low-fluence fast neutrons in a gamma field, and the mechanical difficulties inherent in the use of thin foil windows for gas cell confinement. To mitigate these concerns, a new gas target has been developed to simultaneously reduce gamma ray production and increase structural integrity in high flux gas targets. Development of a neutron imaging system and neutron counting based on characteristic neutron pulse shapes have been investigated as a means of improving signal to noise ratios, reducing irradiation times, and increasing the accuracy of elemental determination.« less

Neutron Capture Gamma-Ray Libraries for Nuclear Applications

NASA Astrophysics Data System (ADS)

Sleaford, B. W.; Firestone, R. B.; Summers, N.; Escher, J.; Hurst, A.; Krticka, M.; Basunia, S.; Molnar, G.; Belgya, T.; Revay, Z.; Choi, H. D.

2011-06-01

The neutron capture reaction is useful in identifying and analyzing the gamma-ray spectrum from an unknown assembly as it gives unambiguous information on its composition. This can be done passively or actively where an external neutron source is used to probe an unknown assembly. There are known capture gamma-ray data gaps in the ENDF libraries used by transport codes for various nuclear applications. The Evaluated Gamma-ray Activation file (EGAF) is a new thermal neutron capture database of discrete line spectra and cross sections for over 260 isotopes that was developed as part of an IAEA Coordinated Research Project. EGAF is being used to improve the capture gamma production in ENDF libraries. For medium to heavy nuclei the quasi continuum contribution to the gamma cascades is not experimentally resolved. The continuum contains up to 90% of all the decay energy and is modeled here with the statistical nuclear structure code DICEBOX. This code also provides a consistency check of the level scheme nuclear structure evaluation. The calculated continuum is of sufficient accuracy to include in the ENDF libraries. This analysis also determines new total thermal capture cross sections and provides an improved RIPL database. For higher energy neutron capture there is less experimental data available making benchmarking of the modeling codes more difficult. We are investigating the capture spectra from higher energy neutrons experimentally using surrogate reactions and modeling this with Hauser-Feshbach codes. This can then be used to benchmark CASINO, a version of DICEBOX modified for neutron capture at higher energy. This can be used to simulate spectra from neutron capture at incident neutron energies up to 20 MeV to improve the gamma-ray spectrum in neutron data libraries used for transport modeling of unknown assemblies.

Development of a New 47-Group Library for the CASL Neutronics Simulators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Kang Seog; Williams, Mark L; Wiarda, Dorothea

The CASL core simulator MPACT is under development for the neutronics and thermal-hydraulics coupled simulation for the pressurized light water reactors. The key characteristics of the MPACT code include a subgroup method for resonance self-shielding, and a whole core solver with a 1D/2D synthesis method. The ORNL AMPX/SCALE code packages have been significantly improved to support various intermediate resonance self-shielding approximations such as the subgroup and embedded self-shielding methods. New 47-group AMPX and MPACT libraries based on ENDF/B-VII.0 have been generated for the CASL core simulator MPACT of which group structure comes from the HELIOS library. The new 47-group MPACTmore » library includes all nuclear data required for static and transient core simulations. This study discusses a detailed procedure to generate the 47-group AMPX and MPACT libraries and benchmark results for the VERA progression problems.« less

Analysis of a Neutronic Experiment on a Simulated Mercury Spallation Neutron Target Assembly Bombarded by Giga-Electron-Volt Protons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maekawa, Fujio; Meigo, Shin-ichiro; Kasugai, Yoshimi

2005-05-15

A neutronic benchmark experiment on a simulated spallation neutron target assembly was conducted by using the Alternating Gradient Synchrotron at Brookhaven National Laboratory and was analyzed to investigate the prediction capability of Monte Carlo simulation codes used in neutronic designs of spallation neutron sources. The target assembly consisting of a mercury target, a light water moderator, and a lead reflector was bombarded by 1.94-, 12-, and 24-GeV protons, and the fast neutron flux distributions around the target and the spectra of thermal neutrons leaking from the moderator were measured in the experiment. In this study, the Monte Carlo particle transportmore » simulation codes NMTC/JAM, MCNPX, and MCNP-4A with associated cross-section data in JENDL and LA-150 were verified based on benchmark analysis of the experiment. As a result, all the calculations predicted the measured quantities adequately; calculated integral fluxes of fast and thermal neutrons agreed approximately within {+-}40% with the experiments although the overall energy range encompassed more than 12 orders of magnitude. Accordingly, it was concluded that these simulation codes and cross-section data were adequate for neutronics designs of spallation neutron sources.« less

Monte Carlo N-particle simulation of neutron-based sterilisation of anthrax contamination

PubMed Central

Liu, B; Xu, J; Liu, T; Ouyang, X

2012-01-01

Objective To simulate the neutron-based sterilisation of anthrax contamination by Monte Carlo N-particle (MCNP) 4C code. Methods Neutrons are elementary particles that have no charge. They are 20 times more effective than electrons or γ-rays in killing anthrax spores on surfaces and inside closed containers. Neutrons emitted from a 252Cf neutron source are in the 100 keV to 2 MeV energy range. A 2.5 MeV D–D neutron generator can create neutrons at up to 1013 n s−1 with current technology. All these enable an effective and low-cost method of killing anthrax spores. Results There is no effect on neutron energy deposition on the anthrax sample when using a reflector that is thicker than its saturation thickness. Among all three reflecting materials tested in the MCNP simulation, paraffin is the best because it has the thinnest saturation thickness and is easy to machine. The MCNP radiation dose and fluence simulation calculation also showed that the MCNP-simulated neutron fluence that is needed to kill the anthrax spores agrees with previous analytical estimations very well. Conclusion The MCNP simulation indicates that a 10 min neutron irradiation from a 0.5 g 252Cf neutron source or a 1 min neutron irradiation from a 2.5 MeV D–D neutron generator may kill all anthrax spores in a sample. This is a promising result because a 2.5 MeV D–D neutron generator output >1013 n s−1 should be attainable in the near future. This indicates that we could use a D–D neutron generator to sterilise anthrax contamination within several seconds. PMID:22573293

Monte Carlo N-particle simulation of neutron-based sterilisation of anthrax contamination.

PubMed

Liu, B; Xu, J; Liu, T; Ouyang, X

2012-10-01

To simulate the neutron-based sterilisation of anthrax contamination by Monte Carlo N-particle (MCNP) 4C code. Neutrons are elementary particles that have no charge. They are 20 times more effective than electrons or γ-rays in killing anthrax spores on surfaces and inside closed containers. Neutrons emitted from a (252)Cf neutron source are in the 100 keV to 2 MeV energy range. A 2.5 MeV D-D neutron generator can create neutrons at up to 10(13) n s(-1) with current technology. All these enable an effective and low-cost method of killing anthrax spores. There is no effect on neutron energy deposition on the anthrax sample when using a reflector that is thicker than its saturation thickness. Among all three reflecting materials tested in the MCNP simulation, paraffin is the best because it has the thinnest saturation thickness and is easy to machine. The MCNP radiation dose and fluence simulation calculation also showed that the MCNP-simulated neutron fluence that is needed to kill the anthrax spores agrees with previous analytical estimations very well. The MCNP simulation indicates that a 10 min neutron irradiation from a 0.5 g (252)Cf neutron source or a 1 min neutron irradiation from a 2.5 MeV D-D neutron generator may kill all anthrax spores in a sample. This is a promising result because a 2.5 MeV D-D neutron generator output >10(13) n s(-1) should be attainable in the near future. This indicates that we could use a D-D neutron generator to sterilise anthrax contamination within several seconds.

Image enhancement using MCNP5 code and MATLAB in neutron radiography.

PubMed

Tharwat, Montaser; Mohamed, Nader; Mongy, T

2014-07-01

This work presents a method that can be used to enhance the neutron radiography (NR) image for objects with high scattering materials like hydrogen, carbon and other light materials. This method used Monte Carlo code, MCNP5, to simulate the NR process and get the flux distribution for each pixel of the image and determines the scattered neutron distribution that caused image blur, and then uses MATLAB to subtract this scattered neutron distribution from the initial image to improve its quality. This work was performed before the commissioning of digital NR system in Jan. 2013. The MATLAB enhancement method is quite a good technique in the case of static based film neutron radiography, while in neutron imaging (NI) technique, image enhancement and quantitative measurement were efficient by using ImageJ software. The enhanced image quality and quantitative measurements were presented in this work. Copyright © 2014 Elsevier Ltd. All rights reserved.

Fast neutron detection with a segmented spectrometer

NASA Astrophysics Data System (ADS)

Langford, T. J.; Bass, C. D.; Beise, E. J.; Breuer, H.; Erwin, D. K.; Heimbach, C. R.; Nico, J. S.

2015-01-01

A fast neutron spectrometer consisting of segmented plastic scintillator and 3He proportional counters was constructed for the measurement of neutrons in the energy range 1-200 MeV. We discuss its design, principles of operation, and the method of analysis. The detector is capable of observing very low neutron fluxes in the presence of ambient gamma background and does not require scintillator pulse-shape discrimination. The spectrometer was characterized for its energy response in fast neutron fields of 2.5 MeV and 14 MeV, and the results are compared with Monte Carlo simulations. Measurements of the fast neutron flux and energy response at 120 m above sea-level (39.130°N, 77.218°W) and at a depth of 560 m in a limestone mine are presented. Finally, the design of a spectrometer with improved sensitivity and energy resolution is discussed.

Investigation of neutron interactions with Ge detectors

NASA Astrophysics Data System (ADS)

Baginova, Miloslava; Vojtyla, Pavol; Povinec, Pavel P.

2018-07-01

Interactions of neutrons with a high-purity germanium detector were studied experimentally and by simulations using the GEANT4 tool. Elastic and inelastic scattering of fast neutrons as well as neutron capture on Ge nuclei were observed. Peaks induced by inelastic scattering of neutrons on 70Ge, 72Ge, 73Ge, 74Ge and 76Ge were well visible in the γ-ray spectra. In addition, peaks due to inelastic scattering of neutrons on copper and lead nuclei, including the well-known peak of 208Pb at 2614.51 keV, were detected. The GEANT4 simulations showed that the simulated spectrum was in a good agreement with the experimental one. Differences between the simulated and the measured spectra were due to the high γ-ray intensity of the used neutron source, physics implemented in GEANT4 and contamination of the neutron source.

Neutron-Induced Charged Particle Studies at LANSCE

NASA Astrophysics Data System (ADS)

Lee, Hye Young; Haight, Robert C.

2014-09-01

Direct measurements on neutron-induced charged particle reactions are of interest for nuclear astrophysics and applied nuclear energy. LANSCE (Los Alamos Neutron Science Center) produces neutrons in energy of thermal to several hundreds MeV. There has been an effort at LANSCE to upgrade neutron-induced charged particle detection technique, which follows on (n,z) measurements made previously here and will have improved capabilities including larger solid angles, higher efficiency, and better signal to background ratios. For studying cross sections of low-energy neutron induced alpha reactions, Frisch-gridded ionization chamber is designed with segmented anodes for improving signal-to-noise ratio near reaction thresholds. Since double-differential cross sections on (n,p) and (n,a) reactions up to tens of MeV provide important information on deducing nuclear level density, the ionization chamber will be coupled with silicon strip detectors (DSSD) in order to stop energetic charged particles. In this paper, we will present the status of this development including the progress on detector design, calibrations and Monte Carlo simulations. This work is funded by the US Department of Energy - Los Alamos National Security, LLC under Contract DE-AC52-06NA25396.

An Update on Improvements to NiCE Support for PROTEUS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bennett, Andrew; McCaskey, Alexander J.; Billings, Jay Jay

2015-09-01

The Department of Energy Office of Nuclear Energy's Nuclear Energy Advanced Modeling and Simulation (NEAMS) program has supported the development of the NEAMS Integrated Computational Environment (NiCE), a modeling and simulation workflow environment that provides services and plugins to facilitate tasks such as code execution, model input construction, visualization, and data analysis. This report details the development of workflows for the reactor core neutronics application, PROTEUS. This advanced neutronics application (primarily developed at Argonne National Laboratory) aims to improve nuclear reactor design and analysis by providing an extensible and massively parallel, finite-element solver for current and advanced reactor fuel neutronicsmore » modeling. The integration of PROTEUS-specific tools into NiCE is intended to make the advanced capabilities that PROTEUS provides more accessible to the nuclear energy research and development community. This report will detail the work done to improve existing PROTEUS workflow support in NiCE. We will demonstrate and discuss these improvements, including the development of flexible IO services, an improved interface for input generation, and the addition of advanced Fortran development tools natively in the platform.« less

Evaluation of the 235U prompt fission neutron spectrum including a detailed analysis of experimental data and improved model information

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neudecker, Denise; Talou, Patrick; Kahler, Albert Comstock III

We present an evaluation of the 235U prompt fission neutron spectrum (PFNS) induced by thermal to 20-MeV neutrons. Experimental data and associated covariances were analyzed in detail. The incident energy dependence of the PFNS was modeled with an extended Los Alamos model combined with the Hauser-Feshbach and the exciton models. These models describe prompt fission, pre-fission compound nucleus and pre-equilibrium neutron emissions. The evaluated PFNS agree well with the experimental data included in this evaluation, preliminary data of the LANL and LLNL Chi-Nu measurement and recent evaluations by Capote et al. and Rising et al. However, they are softer thanmore » the ENDF/B-VII.1 (VII.1) and JENDL-4.0 PFNS for incident neutron energies up to 2 MeV. Simulated effective multiplication factors k eff of the Godiva and Flattop-25 critical assemblies are further from the measured k eff if the current data are used within VII.1 compared to using only VII.1 data. However, if this work is used with ENDF/B-VIII.0β2 data, simulated values of k eff agree well with the measured ones.« less

Evaluation of the 235U prompt fission neutron spectrum including a detailed analysis of experimental data and improved model information

DOE PAGES

Neudecker, Denise; Talou, Patrick; Kahler, Albert Comstock III; ...

2017-09-13

We present an evaluation of the 235U prompt fission neutron spectrum (PFNS) induced by thermal to 20-MeV neutrons. Experimental data and associated covariances were analyzed in detail. The incident energy dependence of the PFNS was modeled with an extended Los Alamos model combined with the Hauser-Feshbach and the exciton models. These models describe prompt fission, pre-fission compound nucleus and pre-equilibrium neutron emissions. The evaluated PFNS agree well with the experimental data included in this evaluation, preliminary data of the LANL and LLNL Chi-Nu measurement and recent evaluations by Capote et al. and Rising et al. However, they are softer thanmore » the ENDF/B-VII.1 (VII.1) and JENDL-4.0 PFNS for incident neutron energies up to 2 MeV. Simulated effective multiplication factors k eff of the Godiva and Flattop-25 critical assemblies are further from the measured k eff if the current data are used within VII.1 compared to using only VII.1 data. However, if this work is used with ENDF/B-VIII.0β2 data, simulated values of k eff agree well with the measured ones.« less

Evaluation of the 235U prompt fission neutron spectrum including a detailed analysis of experimental data and improved model information

NASA Astrophysics Data System (ADS)

Neudecker, Denise; Talou, Patrick; Kahler, Albert C.; White, Morgan C.; Kawano, Toshihiko

2017-09-01

We present an evaluation of the 235U prompt fission neutron spectrum (PFNS) induced by thermal to 20-MeV neutrons. Experimental data and associated covariances were analyzed in detail. The incident energy dependence of the PFNS was modeled with an extended Los Alamos model combined with the Hauser-Feshbach and the exciton models. These models describe prompt fission, pre-fission compound nucleus and pre-equilibrium neutron emissions. The evaluated PFNS agree well with the experimental data included in this evaluation, preliminary data of the LANL and LLNL Chi-Nu measurement and recent evaluations by Capote et al. and Rising et al. However, they are softer than the ENDF/B-VII.1 (VII.1) and JENDL-4.0 PFNS for incident neutron energies up to 2 MeV. Simulated effective multiplication factors keff of the Godiva and Flattop-25 critical assemblies are further from the measured keff if the current data are used within VII.1 compared to using only VII.1 data. However, if this work is used with ENDF/B-VIII.0β2 data, simulated values of keff agree well with the measured ones.

Optimization of a Light Collection System for use in the Neutron Lifetime Project

NASA Astrophysics Data System (ADS)

Taylor, C.; O'Shaughnessy, C.; Mumm, P.; Thompson, A.; Huffman, P.

2007-10-01

The Ultracold Neutron (UCN) Lifetime Project is an ongoing experiment with the objective of improving the average measurement of the neutron beta-decay lifetime. A more accurate measurement may increase our understanding of the electroweak interaction and improve astrophysical/cosmological theories on Big Bang nucleosynthesis. The current apparatus uses 0.89 nm cold neutrons to produce UCN through inelastic collisions with superfluid 4He in the superthermal process. The lifetime of the UCN is measured by detection of scintillation light from superfluid 4He created by electrons produced in neutron decay. Competing criteria of high detection efficiency outside of the apparatus and minimum heating of the experimental cell has led to the design of an acrylic light collection system. Initial designs were based on previous generations of the apparatus. ANSYS was used to optimize the cooling system for the light guide by checking simulated end conditions based on width of contact area, number of contact points, and location on the guide itself. SolidWorks and AutoCAD were used for design. The current system is in the production process.

Physical particularities of nuclear reactors using heavy moderators of neutrons

NASA Astrophysics Data System (ADS)

Kulikov, G. G.; Shmelev, A. N.

2016-12-01

In nuclear reactors, thermal neutron spectra are formed using moderators with small atomic weights. For fast reactors, inserting such moderators in the core may create problems since they efficiently decelerate the neutrons. In order to form an intermediate neutron spectrum, it is preferable to employ neutron moderators with sufficiently large atomic weights, using 233U as a fissile nuclide and 232Th and 231Pa as fertile ones. The aim of the work is to investigate the properties of heavy neutron moderators and to assess their advantages. The analysis employs the JENDL-4.0 nuclear data library and the SCALE program package for simulating the variation of fuel composition caused by irradiation in the reactor. The following main results are obtained. By using heavy moderators with small neutron moderation steps, one is able to (1) increase the rate of resonance capture, so that the amount of fertile material in the fuel may be reduced while maintaining the breeding factor of the core; (2) use the vacant space for improving the fuel-element properties by adding inert, strong, and thermally conductive materials and by implementing dispersive fuel elements in which the fissile material is self-replenished and neutron multiplication remains stable during the process of fuel burnup; and (3) employ mixtures of different fertile materials with resonance capture cross sections in order to increase the resonance-lattice density and the probability of resonance neutron capture leading to formation of fissile material. The general conclusion is that, by forming an intermediate neutron spectrum with heavy neutron moderators, one can use the fuel more efficiently and improve nuclear safety.

Three-Dimensional General Relativistic Monte Carlo Neutrino Transport in Neutron Star Mergers

NASA Astrophysics Data System (ADS)

Richers, Sherwood; Radice, David

2018-06-01

How neutrinos interact with the debris ejected from merging neutron stars determines how much matter escapes, how hot the matter is, and the relative amounts of neutrons and protons. This makes understanding neutrino irradiation of ejected matter a necessary part of interpreting recent and future observations of so-called "kilonovae" to determine whether neutron star mergers can be the origin of heavy elements in the universe. I will discuss a new Monte Carlo method for simulating neutrino transport in these highly relativistic, multi-dimensional environments. I will use this tool to estimate how well approximate transport methods capture the neutrino irradiation and propose improvements to approximate methods that will aid in accurate modeling and interpretation of kilonovae.

3D Space Radiation Transport in a Shielded ICRU Tissue Sphere

NASA Technical Reports Server (NTRS)

Wilson, John W.; Slaba, Tony C.; Badavi, Francis F.; Reddell, Brandon D.; Bahadori, Amir A.

2014-01-01

A computationally efficient 3DHZETRN code capable of simulating High Charge (Z) and Energy (HZE) and light ions (including neutrons) under space-like boundary conditions with enhanced neutron and light ion propagation was recently developed for a simple homogeneous shield object. Monte Carlo benchmarks were used to verify the methodology in slab and spherical geometry, and the 3D corrections were shown to provide significant improvement over the straight-ahead approximation in some cases. In the present report, the new algorithms with well-defined convergence criteria are extended to inhomogeneous media within a shielded tissue slab and a shielded tissue sphere and tested against Monte Carlo simulation to verify the solution methods. The 3D corrections are again found to more accurately describe the neutron and light ion fluence spectra as compared to the straight-ahead approximation. These computationally efficient methods provide a basis for software capable of space shield analysis and optimization.

Sensitivity Analysis of Cf-252 (sf) Neutron and Gamma Observables in CGMF

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carter, Austin Lewis; Talou, Patrick; Stetcu, Ionel

CGMF is a Monte Carlo code that simulates the decay of primary fission fragments by emission of neutrons and gamma rays, according to the Hauser-Feshbach equations. As the CGMF code was recently integrated into the MCNP6.2 transport code, great emphasis has been placed on providing optimal parameters to CGMF such that many different observables are accurately represented. Of these observables, the prompt neutron spectrum, prompt neutron multiplicity, prompt gamma spectrum, and prompt gamma multiplicity are crucial for accurate transport simulations of criticality and nonproliferation applications. This contribution to the ongoing efforts to improve CGMF presents a study of the sensitivitymore » of various neutron and gamma observables to several input parameters for Californium-252 spontaneous fission. Among the most influential parameters are those that affect the input yield distributions in fragment mass and total kinetic energy (TKE). A new scheme for representing Y(A,TKE) was implemented in CGMF using three fission modes, S1, S2 and SL. The sensitivity profiles were calculated for 17 total parameters, which show that the neutron multiplicity distribution is strongly affected by the TKE distribution of the fragments. The total excitation energy (TXE) of the fragments is shared according to a parameter RT, which is defined as the ratio of the light to heavy initial temperatures. The sensitivity profile of the neutron multiplicity shows a second order effect of RT on the mean neutron multiplicity. A final sensitivity profile was produced for the parameter alpha, which affects the spin of the fragments. Higher values of alpha lead to higher fragment spins, which inhibit the emission of neutrons. Understanding the sensitivity of the prompt neutron and gamma observables to the many CGMF input parameters provides a platform for the optimization of these parameters.« less

Optimising the neutron environment of Radiation Portal Monitors: A computational study

NASA Astrophysics Data System (ADS)

Gilbert, Mark R.; Ghani, Zamir; McMillan, John E.; Packer, Lee W.

2015-09-01

Efficient and reliable detection of radiological or nuclear threats is a crucial part of national and international efforts to prevent terrorist activities. Radiation Portal Monitors (RPMs), which are deployed worldwide, are intended to interdict smuggled fissile material by detecting emissions of neutrons and gamma rays. However, considering the range and variety of threat sources, vehicular and shielding scenarios, and that only a small signature is present, it is important that the design of the RPMs allows these signatures to be accurately differentiated from the environmental background. Using Monte-Carlo neutron-transport simulations of a model 3He detector system we have conducted a parameter study to identify the optimum combination of detector shielding, moderation, and collimation that maximises the sensitivity of neutron-sensitive RPMs. These structures, which could be simply and cost-effectively added to existing RPMs, can improve the detector response by more than a factor of two relative to an unmodified, bare design. Furthermore, optimisation of the air gap surrounding the helium tubes also improves detector efficiency.

Simulations of the Neutron Gas in the Inner Crust of Neutron Stars

NASA Astrophysics Data System (ADS)

Vandegriff, Elizabeth; Horowitz, Charles; Caplan, Matthew

2017-09-01

Inside neutron stars, the structures known as `nuclear pasta' are found in the crust. This pasta forms near nuclear density as nucleons arrange in spaghetti- or lasagna-like structures to minimize their energy. We run classical molecular dynamics simulations to visualize the geometry of this pasta and study the distribution of nucleons. In the simulations, we observe that the pasta is embedded in a gas of neutrons, which we call the `sauce'. In this work, we developed two methods for determining the density of neutrons in the gas, one which is accurate at low temperatures and a second which justifies an extrapolation at high temperatures. Running simulations with no Coulomb interactions, we find that the neutron density increases linearly with temperature for every proton fraction we simulated. NSF REU Grant PHY-1460882 at Indiana University.

Results of GEANT simulations and comparison with first experiments at DANCE.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reifarth, R.; Bredeweg, T. A.; Browne, J. C.

2003-07-29

This report describes intensive Monte Carlo simulations carried out to be compared with the results of the first run cycle with DANCE (Detector for Advanced Neutron Capture Experiments). The experimental results were gained during the commissioning phase 2002/2003 with only a part of the array. Based on the results of these simulations the most important items to be improved before the next experiments will be addressed.

Design and construction of shoulder recesses into the beam aperture shields for improved patient positioning at the FiR 1 BNCT facility.

PubMed

Auterinen, I; Kotiluoto, P; Hippeläinen, E; Kortesniemi, M; Seppälä, T; Serén, T; Mannila, V; Pöyry, P; Kankaanranta, L; Collan, J; Kouri, M; Joensuu, H; Savolainen, S

2004-11-01

Improvements have been made at the FiR 1 BNCT facility to ease the positioning of the patient with a tumor in the head and neck region into a lateral neutron beam. Shoulder recesses were constructed horizontally on both sides of the beam aperture. When shoulder recesses are not needed, they are filled with neutron attenuating filling blocks. MCNP simulations using an anthropomorphic human model BOMAB phantom showed that the main contribution to the increase in the effective dose to the patient's body due to the shoulder recesses was from the neutron dose of the arm. In a position when one arm is inside the shoulder recess, the maximal effective dose of the patient was estimated to be 0.7Sv/h. Dose measurements using the twin ionization chamber technique showed that the neutron dose increased on the sides as predicted by the MCNP model but there was no noticeable change in the gamma doses. When making the recesses into the lithium containing neutron shield material tritium contamination was confined using an underpressurized glove box and machine tools with local exhaust. The shoulder recesses give space for more flexible patient positioning and can be considered as a significant improvement of the Finnish BNCT facility.

New evaluation of thermal neutron scattering libraries for light and heavy water

NASA Astrophysics Data System (ADS)

Marquez Damian, Jose Ignacio; Granada, Jose Rolando; Cantargi, Florencia; Roubtsov, Danila

2017-09-01

In order to improve the design and safety of thermal nuclear reactors and for verification of criticality safety conditions on systems with significant amount of fissile materials and water, it is necessary to perform high-precision neutron transport calculations and estimate uncertainties of the results. These calculations are based on neutron interaction data distributed in evaluated nuclear data libraries. To improve the evaluations of thermal scattering sub-libraries, we developed a set of thermal neutron scattering cross sections (scattering kernels) for hydrogen bound in light water, and deuterium and oxygen bound in heavy water, in the ENDF-6 format from room temperature up to the critical temperatures of molecular liquids. The new evaluations were generated and processable with NJOY99 and also with NJOY-2012 with minor modifications (updates), and with the new version of NJOY-2016. The new TSL libraries are based on molecular dynamics simulations with GROMACS and recent experimental data, and result in an improvement of the calculation of single neutron scattering quantities. In this work, we discuss the importance of taking into account self-diffusion in liquids to accurately describe the neutron scattering at low neutron energies (quasi-elastic peak problem). To improve modeling of heavy water, it is important to take into account temperature-dependent static structure factors and apply Sköld approximation to the coherent inelastic components of the scattering matrix. The usage of the new set of scattering matrices and cross-sections improves the calculation of thermal critical systems moderated and/or reflected with light/heavy water obtained from the International Criticality Safety Benchmark Evaluation Project (ICSBEP) handbook. For example, the use of the new thermal scattering library for heavy water, combined with the ROSFOND-2010 evaluation of the cross sections for deuterium, results in an improvement of the C/E ratio in 48 out of 65 international benchmark cases calculated with the Monte Carlo code MCNP5, in comparison with the existing library based on the ENDF/B-VII.0 evaluation.

Neutron streaming studies along JET shielding penetrations

NASA Astrophysics Data System (ADS)

Stamatelatos, Ion E.; Vasilopoulou, Theodora; Batistoni, Paola; Obryk, Barbara; Popovichev, Sergey; Naish, Jonathan

2017-09-01

Neutronic benchmark experiments are carried out at JET aiming to assess the neutronic codes and data used in ITER analysis. Among other activities, experiments are performed in order to validate neutron streaming simulations along long penetrations in the JET shielding configuration. In this work, neutron streaming calculations along the JET personnel entrance maze are presented. Simulations were performed using the MCNP code for Deuterium-Deuterium and Deuterium- Tritium plasma sources. The results of the simulations were compared against experimental data obtained using thermoluminescence detectors and activation foils.

Measurements and Monte-Carlo simulations of the particle self-shielding effect of B4C grains in neutron shielding concrete

NASA Astrophysics Data System (ADS)

DiJulio, D. D.; Cooper-Jensen, C. P.; Llamas-Jansa, I.; Kazi, S.; Bentley, P. M.

2018-06-01

A combined measurement and Monte-Carlo simulation study was carried out in order to characterize the particle self-shielding effect of B4C grains in neutron shielding concrete. Several batches of a specialized neutron shielding concrete, with varying B4C grain sizes, were exposed to a 2 Å neutron beam at the R2D2 test beamline at the Institute for Energy Technology located in Kjeller, Norway. The direct and scattered neutrons were detected with a neutron detector placed behind the concrete blocks and the results were compared to Geant4 simulations. The particle self-shielding effect was included in the Geant4 simulations by calculating effective neutron cross-sections during the Monte-Carlo simulation process. It is shown that this method well reproduces the measured results. Our results show that shielding calculations for low-energy neutrons using such materials would lead to an underestimate of the shielding required for a certain design scenario if the particle self-shielding effect is not included in the calculations.

Simulated workplace neutron fields

NASA Astrophysics Data System (ADS)

Lacoste, V.; Taylor, G.; Röttger, S.

2011-12-01

The use of simulated workplace neutron fields, which aim at replicating radiation fields at practical workplaces, is an alternative solution for the calibration of neutron dosemeters. They offer more appropriate calibration coefficients when the mean fluence-to-dose equivalent conversion coefficients of the simulated and practical fields are comparable. Intensive Monte Carlo modelling work has become quite indispensable for the design and/or the characterization of the produced mixed neutron/photon fields, and the use of Bonner sphere systems and proton recoil spectrometers is also mandatory for a reliable experimental determination of the neutron fluence energy distribution over the whole energy range. The establishment of a calibration capability with a simulated workplace neutron field is not an easy task; to date only few facilities are available as standard calibration fields.

Application of the MCNPX-McStas interface for shielding calculations and guide design at ESS

NASA Astrophysics Data System (ADS)

Klinkby, E. B.; Knudsen, E. B.; Willendrup, P. K.; Lauritzen, B.; Nonbøl, E.; Bentley, P.; Filges, U.

2014-07-01

Recently, an interface between the Monte Carlo code MCNPX and the neutron ray-tracing code MCNPX was developed [1, 2]. Based on the expected neutronic performance and guide geometries relevant for the ESS, the combined MCNPX-McStas code is used to calculate dose rates along neutron beam guides. The generation and moderation of neutrons is simulated using a full scale MCNPX model of the ESS target monolith. Upon entering the neutron beam extraction region, the individual neutron states are handed to McStas via the MCNPX-McStas interface. McStas transports the neutrons through the beam guide, and by using newly developed event logging capability, the neutron state parameters corresponding to un-reflected neutrons are recorded at each scattering. This information is handed back to MCNPX where it serves as neutron source input for a second MCNPX simulation. This simulation enables calculation of dose rates in the vicinity of the guide. In addition the logging mechanism is employed to record the scatterings along the guides which is exploited to simulate the supermirror quality requirements (i.e. m-values) needed at different positions along the beam guide to transport neutrons in the same guide/source setup.

Innovative and Advanced Coupled Neutron Transport and Thermal Hydraulic Method (Tool) for the Design, Analysis and Optimization of VHTR/NGNP Prismatic Reactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rahnema, Farzad; Garimeela, Srinivas; Ougouag, Abderrafi

2013-11-29

This project will develop a 3D, advanced coarse mesh transport method (COMET-Hex) for steady- state and transient analyses in advanced very high-temperature reactors (VHTRs). The project will lead to a coupled neutronics and thermal hydraulic (T/H) core simulation tool with fuel depletion capability. The computational tool will be developed in hexagonal geometry, based solely on transport theory without (spatial) homogenization in complicated 3D geometries. In addition to the hexagonal geometry extension, collaborators will concurrently develop three additional capabilities to increase the code’s versatility as an advanced and robust core simulator for VHTRs. First, the project team will develop and implementmore » a depletion method within the core simulator. Second, the team will develop an elementary (proof-of-concept) 1D time-dependent transport method for efficient transient analyses. The third capability will be a thermal hydraulic method coupled to the neutronics transport module for VHTRs. Current advancements in reactor core design are pushing VHTRs toward greater core and fuel heterogeneity to pursue higher burn-ups, efficiently transmute used fuel, maximize energy production, and improve plant economics and safety. As a result, an accurate and efficient neutron transport, with capabilities to treat heterogeneous burnable poison effects, is highly desirable for predicting VHTR neutronics performance. This research project’s primary objective is to advance the state of the art for reactor analysis.« less

Beam shaping assembly of a D-T neutron source for BNCT and its dosimetry simulation in deeply-seated tumor

NASA Astrophysics Data System (ADS)

Faghihi, F.; Khalili, S.

2013-08-01

This article involves two aims for BNCT. First case includes a beam shaping assembly estimation for a D-T neutron source to find epi-thermal neutrons which are the goal in the BNCT. Second issue is the percent depth dose calculation in the adult Snyder head phantom. Monte-Carlo simulations and verification of a suggested beam shaping assembly (including internal neutron multiplier, moderator, filter, external neutron multiplier, collimator, and reflector dimensions) for thermalizing a D-T neutron source as well as increasing neutron flux are carried out and our results are given herein. Finally, we have simulated its corresponding doses for treatment planning of a deeply-seated tumor.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bearinger, J P

This month's issue has the following articles: (1) Leveraging the National Ignition Facility to Meet the Climate-Energy Challenge--Commentary by George H. Miller; (2) The Journey into a New Era of Scientific Discoveries--The world's largest laser is dedicated on May 29, 2009; (3) Safe and Sustainable Energy with LIFE--A revolutionary technology to generate electricity, modeled after the National Ignition Facility, could either be a pure fusion energy source or combine the best of fusion and fission energy; (4) A Simulated Rehearsal for Battle--Livermore's Joint Conflict and Tactical Simulation is the most widely used tactical model in the world; (5) Improving Catalysismore » with a 'Noble' Material--By infusing carbon aerogels with platinum, researchers have produced a more affordable and efficient catalytic material; and (6) A Time Machine for Fast Neutrons--A new, robust time-projection chamber that provides directional detection of fast neutrons could greatly improve search methods for nuclear materials.« less

Neutron production from beam-modifying devices in a modern double scattering proton therapy beam delivery system.

PubMed

Pérez-Andújar, Angélica; Newhauser, Wayne D; Deluca, Paul M

2009-02-21

In this work the neutron production in a passive beam delivery system was investigated. Secondary particles including neutrons are created as the proton beam interacts with beam shaping devices in the treatment head. Stray neutron exposure to the whole body may increase the risk that the patient develops a radiogenic cancer years or decades after radiotherapy. We simulated a passive proton beam delivery system with double scattering technology to determine the neutron production and energy distribution at 200 MeV proton energy. Specifically, we studied the neutron absorbed dose per therapeutic absorbed dose, the neutron absorbed dose per source particle and the neutron energy spectrum at various locations around the nozzle. We also investigated the neutron production along the nozzle's central axis. The absorbed doses and neutron spectra were simulated with the MCNPX Monte Carlo code. The simulations revealed that the range modulation wheel (RMW) is the most intense neutron source of any of the beam spreading devices within the nozzle. This finding suggests that it may be helpful to refine the design of the RMW assembly, e.g., by adding local shielding, to suppress neutron-induced damage to components in the nozzle and to reduce the shielding thickness of the treatment vault. The simulations also revealed that the neutron dose to the patient is predominated by neutrons produced in the field defining collimator assembly, located just upstream of the patient.

Benchmarking of Neutron Production of Heavy-Ion Transport Codes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Remec, Igor; Ronningen, Reginald M.; Heilbronn, Lawrence

Accurate prediction of radiation fields generated by heavy ion interactions is important in medical applications, space missions, and in design and operation of rare isotope research facilities. In recent years, several well-established computer codes in widespread use for particle and radiation transport calculations have been equipped with the capability to simulate heavy ion transport and interactions. To assess and validate these capabilities, we performed simulations of a series of benchmark-quality heavy ion experiments with the computer codes FLUKA, MARS15, MCNPX, and PHITS. We focus on the comparisons of secondary neutron production. Results are encouraging; however, further improvements in models andmore » codes and additional benchmarking are required.« less

Monte Carlo Simulations Comparing the Response of a Novel Hemispherical Tepc to Existing Spherical and Cylindrical Tepcs for Neutron Monitoring and Dosimetry.

PubMed

Broughton, David P; Waker, Anthony J

2017-05-01

Neutron dosimetry in reactor fields is currently mainly conducted with unwieldy flux monitors. Tissue Equivalent Proportional Counters (TEPCs) have been shown to have the potential to improve the accuracy of neutron dosimetry in these fields, and Multi-Element Tissue Equivalent Proportional Counters (METEPCs) could reduce the size of instrumentation required to do so. Complexity of current METEPC designs has inhibited their use beyond research. This work proposes a novel hemispherical counter with a wireless anode ball in place of the traditional anode wire as a possible solution for simplifying manufacturing. The hemispherical METEPC element was analyzed as a single TEPC to first demonstrate the potential of this new design by evaluating its performance relative to the reference spherical TEPC design and a single element from a cylindrical METEPC. Energy deposition simulations were conducted using the Monte Carlo code PHITS for both monoenergetic 2.5 MeV neutrons and the neutron energy spectrum of Cf-D2O moderated. In these neutron fields, the hemispherical counter appears to be a good alternative to the reference spherical geometry, performing slightly better than the cylindrical counter, which tends to underrespond to H*(10) for the lower neutron energies of the Cf-D2O moderated field. These computational results are promising, and if follow-up experimental work demonstrates the hemispherical counter works as anticipated, it will be ready to be incorporated into an METEPC design.

Structure of aqueous proline via parallel tempering molecular dynamics and neutron diffraction.

PubMed

Troitzsch, R Z; Martyna, G J; McLain, S E; Soper, A K; Crain, J

2007-07-19

The structure of aqueous L-proline amino acid has been the subject of much debate centering on the validity of various proposed models, differing widely in the extent to which local and long-range correlations are present. Here, aqueous proline is investigated by atomistic, replica exchange molecular dynamics simulations, and the results are compared to neutron diffraction and small angle neutron scattering (SANS) data, which have been reported recently (McLain, S.; Soper, A.; Terry, A.; Watts, A. J. Phys. Chem. B 2007, 111, 4568). Comparisons between neutron experiments and simulation are made via the static structure factor S(Q) which is measured and computed from several systems with different H/D isotopic compositions at a concentration of 1:20 molar ratio. Several different empirical water models (TIP3P, TIP4P, and SPC/E) in conjunction with the CHARMM22 force field are investigated. Agreement between experiment and simulation is reasonably good across the entire Q range although there are significant model-dependent variations in some cases. In general, agreement is improved slightly upon application of approximate quantum corrections obtained from gas-phase path integral simulations. Dimers and short oligomeric chains formed by hydrogen bonds (frequently bifurcated) coexist with apolar (hydrophobic) contacts. These emerge as the dominant local motifs in the mixture. Evidence for long-range association is more equivocal: No long-range structures form spontaneously in the MD simulations, and no obvious low-Q signature is seen in the SANS data. Moreover, associations introduced artificially to replicate a long-standing proposed mesoscale structure for proline correlations as an initial condition are annealed out by parallel tempering MD simulations. However, some small residual aggregates do remain, implying a greater degree of long-range order than is apparent in the SANS data.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Konobeevski, E. S., E-mail: konobeev@inr.ru; Burmistrov, Yu. M.; Zuyev, S. V.

The first results are obtained in a kinematically complete experiment devoted to measuring the n + d {sup {yields}}p + n + n reaction yield at energies in the range E{sub n} = 40-60 MeV and various angles of divergence of two neutrons ({Delta}{theta} = 4{sup o}, 6{sup o}, and 8{sup o}) in the geometry of neutron-neutron final-state interaction. The {sup 1}S{sub 0} neutron-neutron scattering length a{sub nn} is determined by comparing the experimental energy dependence of the reaction yield with the results of a simulation in the Watson-Migdal approximation, which depend on a{sub nn}. For E{sub n} = 40more » MeV and {Delta}{theta} = 6{sup o} (the best statistics in the experiment), the value a{sub nn} = -17.9 {+-} 1.0 fm was obtained. A further improvement of the experimental accuracy will make it possible to remove the existing disagreement of the results from different experiments.« less

Real-time detection of fast and thermal neutrons in radiotherapy with CMOS sensors.

PubMed

Arbor, Nicolas; Higueret, Stephane; Elazhar, Halima; Combe, Rodolphe; Meyer, Philippe; Dehaynin, Nicolas; Taupin, Florence; Husson, Daniel

2017-03-07

The peripheral dose distribution is a growing concern for the improvement of new external radiation modalities. Secondary particles, especially photo-neutrons produced by the accelerator, irradiate the patient more than tens of centimeters away from the tumor volume. However the out-of-field dose is still not estimated accurately by the treatment planning softwares. This study demonstrates the possibility of using a specially designed CMOS sensor for fast and thermal neutron monitoring in radiotherapy. The 14 microns-thick sensitive layer and the integrated electronic chain of the CMOS are particularly suitable for real-time measurements in γ/n mixed fields. An experimental field size dependency of the fast neutron production rate, supported by Monte Carlo simulations and CR-39 data, has been observed. This dependency points out the potential benefits of a real-time monitoring of fast and thermal neutron during beam intensity modulated radiation therapies.

Physical particularities of nuclear reactors using heavy moderators of neutrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kulikov, G. G., E-mail: ggkulikov@mephi.ru; Shmelev, A. N.

2016-12-15

In nuclear reactors, thermal neutron spectra are formed using moderators with small atomic weights. For fast reactors, inserting such moderators in the core may create problems since they efficiently decelerate the neutrons. In order to form an intermediate neutron spectrum, it is preferable to employ neutron moderators with sufficiently large atomic weights, using {sup 233}U as a fissile nuclide and {sup 232}Th and {sup 231}Pa as fertile ones. The aim of the work is to investigate the properties of heavy neutron moderators and to assess their advantages. The analysis employs the JENDL-4.0 nuclear data library and the SCALE program packagemore » for simulating the variation of fuel composition caused by irradiation in the reactor. The following main results are obtained. By using heavy moderators with small neutron moderation steps, one is able to (1) increase the rate of resonance capture, so that the amount of fertile material in the fuel may be reduced while maintaining the breeding factor of the core; (2) use the vacant space for improving the fuel-element properties by adding inert, strong, and thermally conductive materials and by implementing dispersive fuel elements in which the fissile material is self-replenished and neutron multiplication remains stable during the process of fuel burnup; and (3) employ mixtures of different fertile materials with resonance capture cross sections in order to increase the resonance-lattice density and the probability of resonance neutron capture leading to formation of fissile material. The general conclusion is that, by forming an intermediate neutron spectrum with heavy neutron moderators, one can use the fuel more efficiently and improve nuclear safety.« less

Large Survey of Neutron Spectrum Moments Due to ICF Drive Asymmetry

NASA Astrophysics Data System (ADS)

Field, J. E.; Munro, D.; Spears, B.; Peterson, J. L.; Brandon, S.; Gaffney, J. A.; Hammer, J.; Langer, S.; Nora, R. C.; Springer, P.; ICF Workflow Collaboration Collaboration

2016-10-01

We have recently completed the largest HYDRA simulation survey to date ( 60 , 000 runs) of drive asymmetry on the new Trinity computer at LANL. The 2D simulations covered a large space of credible perturbations to the drive of ICF implosions on the NIF. Cumulants of the produced birth energy spectrum for DD and DT reaction neutrons were tallied using new methods. Comparison of the experimental spectra with our map of predicted spectra from simulation should provide a wealth of information about the burning plasma region. We report on our results, highlighting areas of agreement (and disagreement) with experimental spectra. We also identify features in the predicted spectra that might be amenable to measurement with improved diagnostics. Prepared by LLNL under Contract DE-AC52-07NA27344. IM release #: LLNL-PROC-697321.

Thermal Neutron Capture onto the Stable Tungsten Isotopes

NASA Astrophysics Data System (ADS)

Hurst, A. M.; Firestone, R. B.; Sleaford, B. W.; Summers, N. C.; Revay, Zs.; Szentmiklósi, L.; Belgya, T.; Basunia, M. S.; Capote, R.; Choi, H.; Dashdorj, D.; Escher, J.; Krticka, M.; Nichols, A.

2012-02-01

Thermal neutron-capture measurements of the stable tungsten isotopes have been carried out using the guided thermal-neutron beam at the Budapest Reactor. Prompt singles spectra were collected and analyzed using the HYPERMET γ-ray analysis software package for the compound tungsten systems 183W, 184W, and 187W, prepared from isotopically-enriched samples of 182W, 183W, and 186W, respectively. These new data provide both confirmation and new insights into the decay schemes and structure of the tungsten isotopes reported in the Evaluated Gamma-ray Activation File based upon previous elemental analysis. The experimental data have also been compared to Monte Carlo simulations of γ-ray emission following the thermal neutron-capture process using the statistical-decay code DICEBOX. Together, the experimental cross sections and modeledfeeding contribution from the quasi continuum, have been used to determine the total radiative thermal neutron-capture cross sections for the tungsten isotopes and provide improved decay-scheme information for the structural- and neutron-data libraries.

Measurement of the Neutron Beta Decay Lifetime using Magnetically Trapped Ultracold Neutrons

NASA Astrophysics Data System (ADS)

Adamek, Evan Robert

The neutron lifetime is an important parameter in the Standard Model of particle physics, with influences on the electroweak interaction and on Big Bang nucleosynthesis. Measurements of this quantity in cold beam experiments and in experiments using ultracold neutrons (UCN) disagree; this discrepancy may indicate that these measurements possess unaccounted-for systematic errors. The UCNtau experiment at Los Alamos Neutron Science Center (LANSCe) utilizes an asymmetrical magneto-gravitational storage volume with an in-situ vanadium detector. This setup is designed to either avoid or control many of the weaknesses that reduce systematic precision in other UCN lifetime experiments. Controlling for the many measurable errors requires detailed calculation and simulation, aided, for example, by the Geant4 Monte Carlo particle transport toolkit, which has been used to create a high fidelity model of the UCNtau experiment for modeling UCN transport, storage, and detection. Through the course of running the experiment, improvements in knowledge of particle measurement have led to improvements to the transport and to the detectors used in various parts of the experiment. With the experimental setup optimized to account for the subtleties of the measurement, the 2014-2015 beam period at LANSCe generated 85 measurement runs from which we could calculate the storage lifetime. Careful analysis of the effects of background on the vanadium detector assembly allowed for elimination of undesired signal and allowed for the extraction of a preliminary value for the neutron lifetime and the determination of areas to improve for the following run cycle.

Advances in associated-particle neutron probe diagnostics for substance detection

NASA Astrophysics Data System (ADS)

Rhodes, Edgar A.; Dickerman, Charles E.; Frey, Manfred

1995-09-01

The development and investigation of a small associated-particle sealed-tube neutron generator (APSTNG) shows potential to allow the associated-particle diagnostic method to be moved out of the laboratory into field applications. The APSTNG interrogates the inspected object with 14-MeV neutrons generated from the deuterium-tritium reaction and detects the alpha-particle associated with each neutron inside a cone encompassing the region of interest. Gamma-ray spectra of resulting neutron reactions identify many nuclides. Flight-times determined from detection times of the gamma-rays and alpha-particles can yield a separate course tomographic image of each identified nuclide, from a single orientation. Chemical substances are identified by comparing relative spectral line intensities with ratios of elements in reference compounds. The high-energy neutrons and gamma-rays penetrate large objects and dense materials. Generally, no collimators or radiation shielding are needed. Proof-of-concept laboratory experiments have been successfully performed for simulated nuclear, chemical warfare, and conventional munitions. Most recently, inspection applications have been investigated for radioactive waste characterization, presence of cocaine in propane tanks, and uranium and plutonium smuggling. Based on lessons learned with the present APSTNG system, an advanced APSTNG tube (along with improved high voltage supply and control units) is being designed and fabricated that will be transportable and rugged, yield a substantial neutron output increase, and provide sufficiently improved lifetime to allow operation at more than an order of magnitude increase in neutron flux.

Improved adaptive genetic algorithm with sparsity constraint applied to thermal neutron CT reconstruction of two-phase flow

NASA Astrophysics Data System (ADS)

Yan, Mingfei; Hu, Huasi; Otake, Yoshie; Taketani, Atsushi; Wakabayashi, Yasuo; Yanagimachi, Shinzo; Wang, Sheng; Pan, Ziheng; Hu, Guang

2018-05-01

Thermal neutron computer tomography (CT) is a useful tool for visualizing two-phase flow due to its high imaging contrast and strong penetrability of neutrons for tube walls constructed with metallic material. A novel approach for two-phase flow CT reconstruction based on an improved adaptive genetic algorithm with sparsity constraint (IAGA-SC) is proposed in this paper. In the algorithm, the neighborhood mutation operator is used to ensure the continuity of the reconstructed object. The adaptive crossover probability P c and mutation probability P m are improved to help the adaptive genetic algorithm (AGA) achieve the global optimum. The reconstructed results for projection data, obtained from Monte Carlo simulation, indicate that the comprehensive performance of the IAGA-SC algorithm exceeds the adaptive steepest descent-projection onto convex sets (ASD-POCS) algorithm in restoring typical and complex flow regimes. It especially shows great advantages in restoring the simply connected flow regimes and the shape of object. In addition, the CT experiment for two-phase flow phantoms was conducted on the accelerator-driven neutron source to verify the performance of the developed IAGA-SC algorithm.

Development of MCNPX-ESUT computer code for simulation of neutron/gamma pulse height distribution

NASA Astrophysics Data System (ADS)

Abolfazl Hosseini, Seyed; Vosoughi, Naser; Zangian, Mehdi

2015-05-01

In this paper, the development of the MCNPX-ESUT (MCNPX-Energy Engineering of Sharif University of Technology) computer code for simulation of neutron/gamma pulse height distribution is reported. Since liquid organic scintillators like NE-213 are well suited and routinely used for spectrometry in mixed neutron/gamma fields, this type of detectors is selected for simulation in the present study. The proposed algorithm for simulation includes four main steps. The first step is the modeling of the neutron/gamma particle transport and their interactions with the materials in the environment and detector volume. In the second step, the number of scintillation photons due to charged particles such as electrons, alphas, protons and carbon nuclei in the scintillator material is calculated. In the third step, the transport of scintillation photons in the scintillator and lightguide is simulated. Finally, the resolution corresponding to the experiment is considered in the last step of the simulation. Unlike the similar computer codes like SCINFUL, NRESP7 and PHRESP, the developed computer code is applicable to both neutron and gamma sources. Hence, the discrimination of neutron and gamma in the mixed fields may be performed using the MCNPX-ESUT computer code. The main feature of MCNPX-ESUT computer code is that the neutron/gamma pulse height simulation may be performed without needing any sort of post processing. In the present study, the pulse height distributions due to a monoenergetic neutron/gamma source in NE-213 detector using MCNPX-ESUT computer code is simulated. The simulated neutron pulse height distributions are validated through comparing with experimental data (Gohil et al. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 664 (2012) 304-309.) and the results obtained from similar computer codes like SCINFUL, NRESP7 and Geant4. The simulated gamma pulse height distribution for a 137Cs source is also compared with the experimental data.

Neutron production from beam-modifying devices in a modern double scattering proton therapy beam delivery system

PubMed Central

Pérez-Andújar, Angélica; Newhauser, Wayne D; DeLuca, Paul M

2014-01-01

In this work the neutron production in a passive beam delivery system was investigated. Secondary particles including neutrons are created as the proton beam interacts with beam shaping devices in the treatment head. Stray neutron exposure to the whole body may increase the risk that the patient develops a radiogenic cancer years or decades after radiotherapy. We simulated a passive proton beam delivery system with double scattering technology to determine the neutron production and energy distribution at 200 MeV proton energy. Specifically, we studied the neutron absorbed dose per therapeutic absorbed dose, the neutron absorbed dose per source particle and the neutron energy spectrum at various locations around the nozzle. We also investigated the neutron production along the nozzle's central axis. The absorbed doses and neutron spectra were simulated with the MCNPX Monte Carlo code. The simulations revealed that the range modulation wheel (RMW) is the most intense neutron source of any of the beam spreading devices within the nozzle. This finding suggests that it may be helpful to refine the design of the RMW assembly, e.g., by adding local shielding, to suppress neutron-induced damage to components in the nozzle and to reduce the shielding thickness of the treatment vault. The simulations also revealed that the neutron dose to the patient is predominated by neutrons produced in the field defining collimator assembly, located just upstream of the patient. PMID:19147903

The "neutron channel design"—A method for gaining the desired neutrons

NASA Astrophysics Data System (ADS)

Hu, G.; Hu, H. S.; Wang, S.; Pan, Z. H.; Jia, Q. G.; Yan, M. F.

2016-12-01

The neutrons with desired parameters can be obtained after initial neutrons penetrating various structure and component of the material. A novel method, the "neutron channel design", is proposed in this investigation for gaining the desired neutrons. It is established by employing genetic algorithm (GA) combining with Monte Carlo software. This method is verified by obtaining 0.01eV to 1.0eV neutrons from the Compact Accelerator-driven Neutron Source (CANS). One layer polyethylene (PE) moderator was designed and installed behind the beryllium target in CANS. The simulations and the experiment for detection the neutrons were carried out. The neutron spectrum at 500cm from the PE moderator was simulated by MCNP and PHITS software. The counts of 0.01eV to 1.0eV neutrons were simulated by MCNP and detected by the thermal neutron detector in the experiment. These data were compared and analyzed. Then this method is researched on designing the complex structure of PE and the composite material consisting of PE, lead and zirconium dioxide.

Status and Perspectives of Neutron Imaging Facilities

NASA Astrophysics Data System (ADS)

Lehmann, E.; Trtik, P.; Ridikas, D.

The methodology and the application range of neutron imaging techniques have been significantly improved at numerous facilities worldwide in the last decades. This progress has been achieved by new detector systems, the setup of dedicated, optimized and flexible beam lines and the much better understanding of the complete imaging process thanks to complementary simulations. Furthermore, new applications and research topics were found and implemented. However, since the quality and the number of neutron imaging facilities depend much on the access to suitable beam ports, there is still an enormous potential to implement state-of-the-art neutron imaging techniques at many more facilities. On the one hand, there are prominent and powerful sources which do not intend/accept the implementation of neutron imaging techniques due to the priorities set for neutron scattering and irradiation techniques exclusively. On the other hand, there are modern and useful devices which remain under-utilized and have either not the capacity or not the know-how to develop attractive user programs and/or industrial partnerships. In this overview of the international status of neutron imaging facilities, we will specify details about the current situation.

Research on a Neutron Detector With a Boron-Lined Honeycomb Neutron Converter

NASA Astrophysics Data System (ADS)

Fang, Zhujun; Yang, Yigang; Li, Yulan; Zhang, Zhi; Wang, Xuewu

2017-04-01

A new design of the boron-lined gaseous neutron detector composed of a boron-lined honeycomb neutron converter and an electron multiplier is proposed in this paper. The motivation for this research was to decrease the manufacturing difficulty and improve the robustness of the boron-lined gaseous neutron detector. The numerous anode wires in the traditional designs were removed, and the gas electron multiplier (GEM) was used as the electron multiplier. To drive the ionized electrons produced inside the honeycomb structure out to the incident surface of the GEM, a drift electric field was applied inside the holes of the honeycomb structure. The design principles of this detector were discussed. Geant4, Maxwell11, and Garfield9 were used to estimate the neutron absorption efficiency and the electron migration process. A prototype detector was constructed and experimentally evaluated. Both the simulation and experimental results indicate that this detector has the potential to be used in the applications of small angle neutron scattering for scientific research, and to replace the currently used 3He detectors, which have the trouble of very limited supply of 3He gas.

ENERGY RESPONSE OF FLUORESCENT NUCLEAR TRACK DETECTORS OF VARIOUS COLORATIONS TO MONOENERGETIC NEUTRONS.

PubMed

Fomenko, V; Moreno, B; Million, M; Harrison, J; Akselrod, M

2017-10-25

The neutron-energy dependence of the track-counting sensitivity of fluorescent nuclear track detectors (FNTDs) at two ranges of Mg doping, resulting in different crystal colorations, was investigated. The performance of FNTDs was studied with the following converters: Li-glass for thermal to intermediate-energy neutrons, polyethylene for fast neutrons, and polytetrafluoroethylene (Teflon™) for photon- and radon-background subtraction. The irradiations with monoenergetic neutrons were performed at the National Physics Laboratory (NPL), UK. The energy range was varied from 144 keV to 16.5 MeV in the personal dose equivalent range from 1 to 3 mSv. Monte Carlo simulations were performed to model the response of FNTDs to monoenergetic neutrons. A good agreement with the experimental data was observed suggesting the development of a basic model for future MC studies. Further work will focus on increasing FNTD sensitivity to low-energy neutrons and developing a faster imaging technique for scanning larger areas to improve counting statistics. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Structural and mechanical properties of cardiolipin lipid bilayers determined using neutron spin echo, small angle neutron and X-ray scattering, and molecular dynamics simulations

DOE PAGES

Pan, Jianjun; Cheng, Xiaolin; Sharp, Melissa; ...

2014-10-29

We report that the detailed structural and mechanical properties of a tetraoleoyl cardiolipin (TOCL) bilayer were determined using neutron spin echo (NSE) spectroscopy, small angle neutron and X-ray scattering (SANS and SAXS, respectively), and molecular dynamics (MD) simulations. We used MD simulations to develop a scattering density profile (SDP) model, which was then utilized to jointly refine SANS and SAXS data. In addition to commonly reported lipid bilayer structural parameters, component distributions were obtained, including the volume probability, electron density and neutron scattering length density.

Simulation of neutron production using MCNPX+MCUNED.

PubMed

Erhard, M; Sauvan, P; Nolte, R

2014-10-01

In standard MCNPX, the production of neutrons by ions cannot be modelled efficiently. The MCUNED patch applied to MCNPX 2.7.0 allows to model the production of neutrons by light ions down to energies of a few kiloelectron volts. This is crucial for the simulation of neutron reference fields. The influence of target properties, such as the diffusion of reactive isotopes into the target backing or the effect of energy and angular straggling, can be studied efficiently. In this work, MCNPX/MCUNED calculations are compared with results obtained with the TARGET code for simulating neutron production. Furthermore, MCUNED incorporates more effective variance reduction techniques and a coincidence counting tally. This allows the simulation of a TCAP experiment being developed at PTB. In this experiment, 14.7-MeV neutrons will be produced by the reaction T(d,n)(4)He. The neutron fluence is determined by counting alpha particles, independently of the reaction cross section. © The Author 2013. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Design of thermal neutron beam based on an electron linear accelerator for BNCT.

PubMed

Zolfaghari, Mona; Sedaghatizadeh, Mahmood

2016-12-01

An electron linear accelerator (Linac) can be used for boron neutron capture therapy (BNCT) by producing thermal neutron flux. In this study, we used a Varian 2300 C/D Linac and MCNPX.2.6.0 code to simulate an electron-photoneutron source for use in BNCT. In order to decelerate the produced fast neutrons from the photoneutron source, which optimize the thermal neutron flux, a beam-shaping assembly (BSA) was simulated. After simulations, a thermal neutron flux with sharp peak at the beam exit was obtained in the order of 3.09×10 8 n/cm 2 s and 6.19×10 8 n/cm 2 s for uranium and enriched uranium (10%) as electron-photoneutron sources respectively. Also, in-phantom dose analysis indicates that the simulated thermal neutron beam can be used for treatment of shallow skin melanoma in time of about 85.4 and 43.6min for uranium and enriched uranium (10%) respectively. Copyright © 2016. Published by Elsevier Ltd.

Measurement and simulation for a complementary imaging with the neutron and X-ray beams

NASA Astrophysics Data System (ADS)

Hara, Kaoru Y.; Sato, Hirotaka; Kamiyama, Takashi; Shinohara, Takenao

2017-09-01

By using a composite source system, we measured radiographs of the thermal neutron and keV X-ray in the 45-MeV electron linear accelerator facility at Hokkaido University. The source system provides the alternative beam of neutron and X-ray by switching the production target onto the electron beam axis. In the measurement to demonstrate a complementary imaging, the detector based on a vacuum-tube type neutron color image intensifier was applied to the both beams for dual-purpose. On the other hand, for reducing background in a neutron transmission spectrum, test measurements using a gadolinium-type neutron grid were performed with a cold neutron source at Hokkaido University. In addition, the simulations of the neutron and X-ray transmissions for various substances were performed using the PHITS code. A data analysis procedure for estimating the substance of sample was investigated through the simulations.

PENTrack - a versatile Monte Carlo tool for ultracold neutron sources and experiments

NASA Astrophysics Data System (ADS)

Picker, Ruediger; Chahal, Sanmeet; Christopher, Nicolas; Losekamm, Martin; Marcellin, James; Paul, Stephan; Schreyer, Wolfgang; Yapa, Pramodh

2016-09-01

Ultracold neutrons have energies in the hundred nano eV region. They can be stored in traps for hundreds of seconds. This makes them the ideal tool to study the neutron itself. Measurements of neutron decay correlations, lifetime or electric dipole moment are ideally suited for ultracold neutrons, as well as experiments probing the neutron's gravitational levels in the earth's field. We have developed a Monte Carlo simulation tool that can serve to design and optimize these experiments, and possibly correct results: PENTrack is a C++ based simulation code that tracks neutrons, protons and electrons or atoms, as well as their spins, in gravitational and electromagnetic fields. In addition wall interactions of neutrons due to strong interaction are modeled with a Fermi-potential formalism and take surface roughness into account. The presentation will introduce the physics behind the simulation and provide examples of its application.

Energy resolution of pulsed neutron beam provided by the ANNRI beamline at the J-PARC/MLF

NASA Astrophysics Data System (ADS)

Kino, K.; Furusaka, M.; Hiraga, F.; Kamiyama, T.; Kiyanagi, Y.; Furutaka, K.; Goko, S.; Hara, K. Y.; Harada, H.; Harada, M.; Hirose, K.; Kai, T.; Kimura, A.; Kin, T.; Kitatani, F.; Koizumi, M.; Maekawa, F.; Meigo, S.; Nakamura, S.; Ooi, M.; Ohta, M.; Oshima, M.; Toh, Y.; Igashira, M.; Katabuchi, T.; Mizumoto, M.; Hori, J.

2014-02-01

We studied the energy resolution of the pulsed neutron beam of the Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) at the Japan Proton Accelerator Research Complex/Materials and Life Science Experimental Facility (J-PARC/MLF). A simulation in the energy region from 0.7 meV to 1 MeV was performed and measurements were made at thermal (0.76-62 meV) and epithermal energies (4.8-410 eV). The neutron energy resolution of ANNRI determined by the time-of-flight technique depends on the time structure of the neutron pulse. We obtained the neutron energy resolution as a function of the neutron energy by the simulation in the two operation modes of the neutron source: double- and single-bunch modes. In double-bunch mode, the resolution deteriorates above about 10 eV because the time structure of the neutron pulse splits into two peaks. The time structures at 13 energy points from measurements in the thermal energy region agree with those of the simulation. In the epithermal energy region, the time structures at 17 energy points were obtained from measurements and agree with those of the simulation. The FWHM values of the time structures by the simulation and measurements were found to be almost consistent. In the single-bunch mode, the energy resolution is better than about 1% between 1 meV and 10 keV at a neutron source operation of 17.5 kW. These results confirm the energy resolution of the pulsed neutron beam produced by the ANNRI beamline.

Perspectives in biological physics: the nDDB project for a neutron Dynamics Data Bank for biological macromolecules.

PubMed

Rusevich, Leonid; García Sakai, Victoria; Franzetti, Bruno; Johnson, Mark; Natali, Francesca; Pellegrini, Eric; Peters, Judith; Pieper, Jörg; Weik, Martin; Zaccai, Giuseppe

2013-07-01

Neutron spectroscopy provides experimental data on time-dependent trajectories, which can be directly compared to molecular dynamics simulations. Its importance in helping us to understand biological macromolecules at a molecular level is demonstrated by the results of a literature survey over the last two to three decades. Around 300 articles in refereed journals relate to neutron scattering studies of biological macromolecular dynamics, and the results of the survey are presented here. The scope of the publications ranges from the general physics of protein and solvent dynamics, to the biologically relevant dynamics-function relationships in live cells. As a result of the survey we are currently setting up a neutron Dynamics Data Bank (nDDB) with the aim to make the neutron data on biological systems widely available. This will benefit, in particular, the MD simulation community to validate and improve their force fields. The aim of the database is to expose and give easy access to a body of experimental data to the scientific community. The database will be populated with as much of the existing data as possible. In the future it will give value, as part of a bigger whole, to high throughput data, as well as more detailed studies. A range and volume of experimental data will be of interest in determining how quantitatively MD simulations can reproduce trends across a range of systems and to what extent such trends may depend on sample preparation and data reduction and analysis methods. In this context, we strongly encourage researchers in the field to deposit their data in the nDDB.

Benchmarking of neutron production of heavy-ion transport codes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Remec, I.; Ronningen, R. M.; Heilbronn, L.

Document available in abstract form only, full text of document follows: Accurate prediction of radiation fields generated by heavy ion interactions is important in medical applications, space missions, and in design and operation of rare isotope research facilities. In recent years, several well-established computer codes in widespread use for particle and radiation transport calculations have been equipped with the capability to simulate heavy ion transport and interactions. To assess and validate these capabilities, we performed simulations of a series of benchmark-quality heavy ion experiments with the computer codes FLUKA, MARS15, MCNPX, and PHITS. We focus on the comparisons of secondarymore » neutron production. Results are encouraging; however, further improvements in models and codes and additional benchmarking are required. (authors)« less

A scintillator-based approach to monitor secondary neutron production during proton therapy.

PubMed

Clarke, S D; Pryser, E; Wieger, B M; Pozzi, S A; Haelg, R A; Bashkirov, V A; Schulte, R W

2016-11-01

The primary objective of this work is to measure the secondary neutron field produced by an uncollimated proton pencil beam impinging on different tissue-equivalent phantom materials using organic scintillation detectors. Additionally, the Monte Carlo code mcnpx-PoliMi was used to simulate the detector response for comparison to the measured data. Comparison of the measured and simulated data will validate this approach for monitoring secondary neutron dose during proton therapy. Proton beams of 155- and 200-MeV were used to irradiate a variety of phantom materials and secondary particles were detected using organic liquid scintillators. These detectors are sensitive to fast neutrons and gamma rays: pulse shape discrimination was used to classify each detected pulse as either a neutron or a gamma ray. The mcnpx-PoliMi code was used to simulate the secondary neutron field produced during proton irradiation of the same tissue-equivalent phantom materials. An experiment was performed at the Loma Linda University Medical Center proton therapy research beam line and corresponding models were created using the mcnpx-PoliMi code. The authors' analysis showed agreement between the simulations and the measurements. The simulated detector response can be used to validate the simulations of neutron and gamma doses on a particular beam line with or without a phantom. The authors have demonstrated a method of monitoring the neutron component of the secondary radiation field produced by therapeutic protons. The method relies on direct detection of secondary neutrons and gamma rays using organic scintillation detectors. These detectors are sensitive over the full range of biologically relevant neutron energies above 0.5 MeV and allow effective discrimination between neutron and photon dose. Because the detector system is portable, the described system could be used in the future to evaluate secondary neutron and gamma doses on various clinical beam lines for commissioning and prospective data collection in pediatric patients treated with proton therapy.

The response of a bonner sphere spectrometer to charged hadrons.

PubMed

Agosteo, S; Dimovasili, E; Fassò, A; Silari, M

2004-01-01

Bonner sphere spectrometers (BSSs) are employed in neutron spectrometry and dosimetry since many years. Recent developments have seen the addition to a conventional BSS of one or more detectors (moderator plus thermal neutron counter) specifically designed to improve the overall response of the spectrometer to neutrons above 10 MeV. These additional detectors employ a shell of material with a high mass number (such as lead) within the polyethylene moderator, in order to slow down high-energy neutrons via (n,xn) reactions. A BSS can be used to measure neutron spectra both outside accelerator shielding and from an unshielded target. Measurements were recently performed at CERN of the neutron yield and spectral fluence at various angles from unshielded, semi-thick copper, silver and lead targets, bombarded by a mixed proton/pion beam with 40 GeV per c momentum. These experiments have provided evidence that under certain circumstances, the use of lead-enriched moderators may present a problem: these detectors were found to have a significant response to the charged hadron component accompanying the neutrons emitted from the target. Conventional polyethylene moderators show a similar behaviour but less pronounced. These secondary hadrons interact with the moderator and generate neutrons, which are in turn detected by the counter. To investigate this effect and determine a correction factor to be applied to the unfolding procedure, a series of Monte Carlo simulations were performed with the FLUKA code. These simulations aimed at determining the response of the BSS to charged hadrons under the specific experimental situation. Following these results, a complete response matrix of the extended BSS to charged pions and protons was calculated with FLUKA. An experimental verification was carried out with a 120 GeV per c hadron beam at the CERF facility at CERN.

A kinematically complete, interdisciplinary, and co-institutional measurement of the 19F(α,n) cross section for nuclear safeguards science

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peters, W. A.; Smith, M. S.; Pittman, S.

2016-05-01

Alpha particles emitted from the decay of uranium in a UF 6 matrix can interact with fluorine and generate neutrons via the 19F(α,n) 22Na reaction. These neutrons can be used to determine the uranium content in a UF 6 storage cylinder. The accuracy of this self-interrogating, non-destructive assay (NDA) technique is, however, limited by the uncertainty of the 19F(α,n) 22Na cross section. We have performed complementary measurements of the 19F(α,n) 22Na reaction with both 4He and 19F beams to improve the precision of the 19F(α,n) 22Na cross section over the alpha energy range that encompasses common actinide alpha decay neededmore » for NDA studies. We have determined an absolute cross section for the 19F(α,n) 22Na reaction to an average precision of 7.6% over the alpha energy range of 3.9 – 6.7 MeV. We utilized this cross section in a simulation of a 100 g spherical UF 6 assembly and obtained a change in neutron emission rate values of approximately 10-12%, and a significant (factor of 3.6) decrease in the neutron emission rate uncertainty (from 50-51% to 13-14%), compared to simulations using the old cross section. Our new absolute cross section enables improved interpretations of NDAs of containers of arbitrary size and configuration.« less

JPRS Report, Science & Technology, China

DTIC Science & Technology

1991-09-12

original Sanyo 183-cm television projector; its perfor- air-cushion seat; the hydraulic action tube and the air mance has been improved in terms of...is amplified to control the motion of the hydraulic action tube and the air cushion to simulate the sensation of Simulator Cockpit overload motion...Academy has detected face science, measurement science, microscope tech- obvious neutrons in a vacuum using a palladium elec- nology, ultra- microfine

A comparative study of history-based versus vectorized Monte Carlo methods in the GPU/CUDA environment for a simple neutron eigenvalue problem

NASA Astrophysics Data System (ADS)

Liu, Tianyu; Du, Xining; Ji, Wei; Xu, X. George; Brown, Forrest B.

2014-06-01

For nuclear reactor analysis such as the neutron eigenvalue calculations, the time consuming Monte Carlo (MC) simulations can be accelerated by using graphics processing units (GPUs). However, traditional MC methods are often history-based, and their performance on GPUs is affected significantly by the thread divergence problem. In this paper we describe the development of a newly designed event-based vectorized MC algorithm for solving the neutron eigenvalue problem. The code was implemented using NVIDIA's Compute Unified Device Architecture (CUDA), and tested on a NVIDIA Tesla M2090 GPU card. We found that although the vectorized MC algorithm greatly reduces the occurrence of thread divergence thus enhancing the warp execution efficiency, the overall simulation speed is roughly ten times slower than the history-based MC code on GPUs. Profiling results suggest that the slow speed is probably due to the memory access latency caused by the large amount of global memory transactions. Possible solutions to improve the code efficiency are discussed.

Fully kinetic simulations of dense plasma focus Z-pinch devices.

PubMed

Schmidt, A; Tang, V; Welch, D

2012-11-16

Dense plasma focus Z-pinch devices are sources of copious high energy electrons and ions, x rays, and neutrons. The mechanisms through which these physically simple devices generate such high-energy beams in a relatively short distance are not fully understood. We now have, for the first time, demonstrated a capability to model these plasmas fully kinetically, allowing us to simulate the pinch process at the particle scale. We present here the results of the initial kinetic simulations, which reproduce experimental neutron yields (~10(7)) and high-energy (MeV) beams for the first time. We compare our fluid, hybrid (kinetic ions and fluid electrons), and fully kinetic simulations. Fluid simulations predict no neutrons and do not allow for nonthermal ions, while hybrid simulations underpredict neutron yield by ~100x and exhibit an ion tail that does not exceed 200 keV. Only fully kinetic simulations predict MeV-energy ions and experimental neutron yields. A frequency analysis in a fully kinetic simulation shows plasma fluctuations near the lower hybrid frequency, possibly implicating lower hybrid drift instability as a contributor to anomalous resistivity in the plasma.

Object kinetic Monte Carlo model for neutron and ion irradiation in tungsten: Impact of transmutation and carbon impurities

NASA Astrophysics Data System (ADS)

Castin, N.; Bonny, G.; Bakaev, A.; Ortiz, C. J.; Sand, A. E.; Terentyev, D.

2018-03-01

We upgrade our object kinetic Monte Carlo (OKMC) model, aimed at describing the microstructural evolution in tungsten (W) under neutron and ion irradiation. Two main improvements are proposed based on recently published atomistic data: (a) interstitial carbon impurities, and their interaction with radiation-induced defects (point defect clusters and loops), are more accurately parameterized thanks to ab initio findings; (b) W transmutation to rhenium (Re) upon neutron irradiation, impacting the diffusivity of radiation defects, is included, also relying on recent atomistic data. These essential amendments highly improve the portability of our OKMC model, providing a description for the formation of SIA-type loops under different irradiation conditions. The model is applied to simulate neutron and ion irradiation in pure W samples, in a wide range of fluxes and temperatures. We demonstrate that it performs a realistic prediction of the population of TEM-visible voids and loops, as compared to experimental evidence. The impact of the transmutation of W to Re, and of carbon trapping, is assessed.

ENDF/B-VII.0: Next Generation Evaluated Nuclear Data Library for Nuclear Science and Technology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chadwick, M B; Oblozinsky, P; Herman, M

2006-10-02

We describe the next generation general purpose Evaluated Nuclear Data File, ENDF/B-VII.0, of recommended nuclear data for advanced nuclear science and technology applications. The library, released by the U.S. Cross Section Evaluation Working Group (CSEWG) in December 2006, contains data primarily for reactions with incident neutrons, protons, and photons on almost 400 isotopes. The new evaluations are based on both experimental data and nuclear reaction theory predictions. The principal advances over the previous ENDF/B-VI library are the following: (1) New cross sections for U, Pu, Th, Np and Am actinide isotopes, with improved performance in integral validation criticality and neutronmore » transmission benchmark tests; (2) More precise standard cross sections for neutron reactions on H, {sup 6}Li, {sup 10}B, Au and for {sup 235,238}U fission, developed by a collaboration with the IAEA and the OECD/NEA Working Party on Evaluation Cooperation (WPEC); (3) Improved thermal neutron scattering; (4) An extensive set of neutron cross sections on fission products developed through a WPEC collaboration; (5) A large suite of photonuclear reactions; (6) Extension of many neutron- and proton-induced reactions up to an energy of 150 MeV; (7) Many new light nucleus neutron and proton reactions; (8) Post-fission beta-delayed photon decay spectra; (9) New radioactive decay data; and (10) New methods developed to provide uncertainties and covariances, together with covariance evaluations for some sample cases. The paper provides an overview of this library, consisting of 14 sublibraries in the same, ENDF-6 format, as the earlier ENDF/B-VI library. We describe each of the 14 sublibraries, focusing on neutron reactions. Extensive validation, using radiation transport codes to simulate measured critical assemblies, show major improvements: (a) The long-standing underprediction of low enriched U thermal assemblies is removed; (b) The {sup 238}U, {sup 208}Pb, and {sup 9}Be reflector biases in fast systems are largely removed; (c) ENDF/B-VI.8 good agreement for simulations of highly enriched uranium assemblies is preserved; (d) The underprediction of fast criticality of {sup 233,235}U and {sup 239}Pu assemblies is removed; and (e) The intermediate spectrum critical assemblies are predicted more accurately. We anticipate that the new library will play an important role in nuclear technology applications, including transport simulations supporting national security, nonproliferation, advanced reactor and fuel cycle concepts, criticality safety, medicine, space applications, nuclear astrophysics, and nuclear physics facility design. The ENDF/B-VII.0 library is archived at the National Nuclear Data Center, BNL. The complete library, or any part of it, may be retrieved from www.nndc.bnl.gov.« less

Validation of MCNP NPP Activation Simulations for Decommissioning Studies by Analysis of NPP Neutron Activation Foil Measurement Campaigns

NASA Astrophysics Data System (ADS)

Volmert, Ben; Pantelias, Manuel; Mutnuru, R. K.; Neukaeter, Erwin; Bitterli, Beat

2016-02-01

In this paper, an overview of the Swiss Nuclear Power Plant (NPP) activation methodology is presented and the work towards its validation by in-situ NPP foil irradiation campaigns is outlined. Nuclear Research and consultancy Group (NRG) in The Netherlands has been given the task of performing the corresponding neutron metrology. For this purpose, small Aluminium boxes containing a set of circular-shaped neutron activation foils have been prepared. After being irradiated for one complete reactor cycle, the sets have been successfully retrieved, followed by gamma-spectrometric measurements of the individual foils at NRG. Along with the individual activities of the foils, the reaction rates and thermal, intermediate and fast neutron fluence rates at the foil locations have been determined. These determinations include appropriate corrections for gamma self-absorption and neutron self-shielding as well as corresponding measurement uncertainties. The comparison of the NPP Monte Carlo calculations with the results of the foil measurements is done by using an individual generic MCNP model functioning as an interface and allowing the simulation of individual foil activation by predetermined neutron spectra. To summarize, the comparison between calculation and measurement serve as a sound validation of the Swiss NPP activation methodology by demonstrating a satisfying agreement between measurement and calculation. Finally, the validation offers a chance for further improvements of the existing NPP models by ensuing calibration and/or modelling optimizations for key components and structures.

Neutrons Flux Distributions of the Pu-Be Source and its Simulation by the MCNP-4B Code

NASA Astrophysics Data System (ADS)

Faghihi, F.; Mehdizadeh, S.; Hadad, K.

Neutron Fluence rate of a low intense Pu-Be source is measured by Neutron Activation Analysis (NAA) of 197Au foils. Also, the neutron fluence rate distribution versus energy is calculated using the MCNP-4B code based on ENDF/B-V library. Theoretical simulation as well as our experimental performance are a new experience for Iranians to make reliability with the code for further researches. In our theoretical investigation, an isotropic Pu-Be source with cylindrical volume distribution is simulated and relative neutron fluence rate versus energy is calculated using MCNP-4B code. Variation of the fast and also thermal neutrons fluence rate, which are measured by NAA method and MCNP code, are compared.

Simulations of neutron transport at low energy: a comparison between GEANT and MCNP.

PubMed

Colonna, N; Altieri, S

2002-06-01

The use of the simulation tool GEANT for neutron transport at energies below 20 MeV is discussed, in particular with regard to shielding and dose calculations. The reliability of the GEANT/MICAP package for neutron transport in a wide energy range has been verified by comparing the results of simulations performed with this package in a wide energy range with the prediction of MCNP-4B, a code commonly used for neutron transport at low energy. A reasonable agreement between the results of the two codes is found for the neutron flux through a slab of material (iron and ordinary concrete), as well as for the dose released in soft tissue by neutrons. These results justify the use of the GEANT/MICAP code for neutron transport in a wide range of applications, including health physics problems.

Benchmarking shielding simulations for an accelerator-driven spallation neutron source

DOE PAGES

Cherkashyna, Nataliia; Di Julio, Douglas D.; Panzner, Tobias; ...

2015-08-09

The shielding at an accelerator-driven spallation neutron facility plays a critical role in the performance of the neutron scattering instruments, the overall safety, and the total cost of the facility. Accurate simulation of shielding components is thus key for the design of upcoming facilities, such as the European Spallation Source (ESS), currently in construction in Lund, Sweden. In this paper, we present a comparative study between the measured and the simulated neutron background at the Swiss Spallation Neutron Source (SINQ), at the Paul Scherrer Institute (PSI), Villigen, Switzerland. The measurements were carried out at several positions along the SINQ monolithmore » wall with the neutron dosimeter WENDI-2, which has a well-characterized response up to 5 GeV. The simulations were performed using the Monte-Carlo radiation transport code Geant4, and include a complete transport from the proton beam to the measurement locations in a single calculation. An agreement between measurements and simulations is about a factor of 2 for the points where the measured radiation dose is above the background level, which is a satisfactory result for such simulations spanning many energy regimes, different physics processes and transport through several meters of shielding materials. The neutrons contributing to the radiation field emanating from the monolith were confirmed to originate from neutrons with energies above 1 MeV in the target region. The current work validates Geant4 as being well suited for deep-shielding calculations at accelerator-based spallation sources. We also extrapolate what the simulated flux levels might imply for short (several tens of meters) instruments at ESS.« less

In situ calibration of neutron activation system on the large helical device

NASA Astrophysics Data System (ADS)

Pu, N.; Nishitani, T.; Isobe, M.; Ogawa, K.; Kawase, H.; Tanaka, T.; Li, S. Y.; Yoshihashi, S.; Uritani, A.

2017-11-01

In situ calibration of the neutron activation system on the Large Helical Device (LHD) was performed by using an intense 252Cf neutron source. To simulate a ring-shaped neutron source, we installed a railway inside the LHD vacuum vessel and made a train loaded with the 252Cf source run along a typical magnetic axis position. Three activation capsules loaded with thirty pieces of indium foils stacked with total mass of approximately 18 g were prepared. Each capsule was irradiated over 15 h while the train was circulating. The activation response coefficient (9.4 ± 1.2) × 10-8 of 115In(n, n')115mIn reaction obtained from the experiment is in good agreement with results from three-dimensional neutron transport calculations using the Monte Carlo neutron transport simulation code 6. The activation response coefficients of 2.45 MeV birth neutron and secondary 14.1 MeV neutron from deuterium plasma were evaluated from the activation response coefficient obtained in this calibration experiment with results from three-dimensional neutron calculations using the Monte Carlo neutron transport simulation code 6.

Designing a new type of neutron detector for neutron and gamma-ray discrimination via GEANT4.

PubMed

Shan, Qing; Chu, Shengnan; Ling, Yongsheng; Cai, Pingkun; Jia, Wenbao

2016-04-01

Design of a new type of neutron detector, consisting of a fast neutron converter, plastic scintillator, and Cherenkov detector, to discriminate 14-MeV fast neutrons and gamma rays in a pulsed n-γ mixed field and monitor their neutron fluxes is reported in this study. Both neutrons and gamma rays can produce fluorescence in the scintillator when they are incident on the detector. However, only the secondary charged particles of the gamma rays can produce Cherenkov light in the Cherenkov detector. The neutron and gamma-ray fluxes can be calculated by measuring the fluorescence and Cherenkov light. The GEANT4 Monte Carlo simulation toolkit is used to simulate the whole process occurring in the detector, whose optimum parameters are known. Analysis of the simulation results leads to a calculation method of neutron flux. This method is verified by calculating the neutron fluxes using pulsed n-γ mixed fields with different n/γ ratios, and the results show that the relative errors of all calculations are <5%. Copyright © 2016 Elsevier Ltd. All rights reserved.

Development of a reliable estimation procedure of radioactivity inventory in a BWR plant due to neutron irradiation for decommissioning

NASA Astrophysics Data System (ADS)

Tanaka, Ken-ichi; Ueno, Jun

2017-09-01

Reliable information of radioactivity inventory resulted from the radiological characterization is important in order to plan decommissioning planning and is also crucial in order to promote decommissioning in effectiveness and in safe. The information is referred to by planning of decommissioning strategy and by an application to regulator. Reliable information of radioactivity inventory can be used to optimize the decommissioning processes. In order to perform the radiological characterization reliably, we improved a procedure of an evaluation of neutron-activated materials for a Boiling Water Reactor (BWR). Neutron-activated materials are calculated with calculation codes and their validity should be verified with measurements. The evaluation of neutron-activated materials can be divided into two processes. One is a distribution calculation of neutron-flux. Another is an activation calculation of materials. The distribution calculation of neutron-flux is performed with neutron transport calculation codes with appropriate cross section library to simulate neutron transport phenomena well. Using the distribution of neutron-flux, we perform distribution calculations of radioactivity concentration. We also estimate a time dependent distribution of radioactivity classification and a radioactive-waste classification. The information obtained from the evaluation is utilized by other tasks in the preparatory tasks to make the decommissioning plan and the activity safe and rational.

Monte Carlo simulation of secondary neutron dose for scanning proton therapy using FLUKA

PubMed Central

Lee, Chaeyeong; Lee, Sangmin; Lee, Seung-Jae; Song, Hankyeol; Kim, Dae-Hyun; Cho, Sungkoo; Jo, Kwanghyun; Han, Youngyih; Chung, Yong Hyun

2017-01-01

Proton therapy is a rapidly progressing field for cancer treatment. Globally, many proton therapy facilities are being commissioned or under construction. Secondary neutrons are an important issue during the commissioning process of a proton therapy facility. The purpose of this study is to model and validate scanning nozzles of proton therapy at Samsung Medical Center (SMC) by Monte Carlo simulation for beam commissioning. After the commissioning, a secondary neutron ambient dose from proton scanning nozzle (Gantry 1) was simulated and measured. This simulation was performed to evaluate beam properties such as percent depth dose curve, Bragg peak, and distal fall-off, so that they could be verified with measured data. Using the validated beam nozzle, the secondary neutron ambient dose was simulated and then compared with the measured ambient dose from Gantry 1. We calculated secondary neutron dose at several different points. We demonstrated the validity modeling a proton scanning nozzle system to evaluate various parameters using FLUKA. The measured secondary neutron ambient dose showed a similar tendency with the simulation result. This work will increase the knowledge necessary for the development of radiation safety technology in medical particle accelerators. PMID:29045491

Three-dimensional simulations of National Ignition Facility implosions: Insight into experimental observablesa)

NASA Astrophysics Data System (ADS)

Spears, Brian K.; Munro, David H.; Sepke, Scott; Caggiano, Joseph; Clark, Daniel; Hatarik, Robert; Kritcher, Andrea; Sayre, Daniel; Yeamans, Charles; Knauer, James; Hilsabeck, Terry; Kilkenny, Joe

2015-05-01

We simulate in 3D both the hydrodynamics and, simultaneously, the X-ray and neutron diagnostic signatures of National Ignition Facility (NIF) implosions. We apply asymmetric radiation drive to study the impact of low mode asymmetry on diagnostic observables. We examine X-ray and neutron images as well as neutron spectra for these perturbed implosions. The X-ray images show hot spot evolution on small length scales and short time scales, reflecting the incomplete stagnation seen in the simulation. The neutron images show surprising differences from the X-ray images. The neutron spectra provide additional measures of implosion asymmetry. Flow in the hot spot alters the neutron spectral peak, namely, the peak location and width. The changes in the width lead to a variation in the apparent temperature with viewing angle that signals underlying hot spot asymmetry. We compare our new expectations based on the simulated data with NIF data. We find that some recent cryogenic layered experiments show appreciable temperature anisotropy indicating residual flow in the hot spot. We also find some trends in the data that do not reflect our simulation and theoretical understanding.

Interfacing MCNPX and McStas for simulation of neutron transport

NASA Astrophysics Data System (ADS)

Klinkby, Esben; Lauritzen, Bent; Nonbøl, Erik; Kjær Willendrup, Peter; Filges, Uwe; Wohlmuther, Michael; Gallmeier, Franz X.

2013-02-01

Simulations of target-moderator-reflector system at spallation sources are conventionally carried out using Monte Carlo codes such as MCNPX (Waters et al., 2007 [1]) or FLUKA (Battistoni et al., 2007; Ferrari et al., 2005 [2,3]) whereas simulations of neutron transport from the moderator and the instrument response are performed by neutron ray tracing codes such as McStas (Lefmann and Nielsen, 1999; Willendrup et al., 2004, 2011a,b [4-7]). The coupling between the two simulation suites typically consists of providing analytical fits of MCNPX neutron spectra to McStas. This method is generally successful but has limitations, as it e.g. does not allow for re-entry of neutrons into the MCNPX regime. Previous work to resolve such shortcomings includes the introduction of McStas inspired supermirrors in MCNPX. In the present paper different approaches to interface MCNPX and McStas are presented and applied to a simple test case. The direct coupling between MCNPX and McStas allows for more accurate simulations of e.g. complex moderator geometries, backgrounds, interference between beam-lines as well as shielding requirements along the neutron guides.

Neutron collimator design of neutron radiography based on the BNCT facility

NASA Astrophysics Data System (ADS)

Yang, Xiao-Peng; Yu, Bo-Xiang; Li, Yi-Guo; Peng, Dan; Lu, Jin; Zhang, Gao-Long; Zhao, Hang; Zhang, Ai-Wu; Li, Chun-Yang; Liu, Wan-Jin; Hu, Tao; Lü, Jun-Guang

2014-02-01

For the research of CCD neutron radiography, a neutron collimator was designed based on the exit of thermal neutron of the Boron Neutron Capture Therapy (BNCT) reactor. Based on the Geant4 simulations, the preliminary choice of the size of the collimator was determined. The materials were selected according to the literature data. Then, a collimator was constructed and tested on site. The results of experiment and simulation show that the thermal neutron flux at the end of the neutron collimator is greater than 1.0×106 n/cm2/s, the maximum collimation ratio (L/D) is 58, the Cd-ratio(Mn) is 160 and the diameter of collimator end is 10 cm. This neutron collimator is considered to be applicable for neutron radiography.

Geant4 simulations of NIST beam neutron lifetime experiment

NASA Astrophysics Data System (ADS)

Valete, Daniel; Crawford, Bret; BL2 Collaboration Collaboration

2017-09-01

A free neutron is unstable and its decay is described by the Standard Model as the transformation of a down quark into an up quark through the weak interaction. Precise measurements of the neutron lifetime test the validity of the theory of the weak interaction and provide useful information for the predictions of the theory of Big Bang nucleosynthesis of the primordial helium abundance in the universe and the number of different types of light neutrinos Nν. The predominant experimental methods for determination of the neutron lifetime are commonly called `beam' and `bottle' methods, and the most recent uses of each method do not agree with each other within their stated uncertainties. An improved experiment of the beam technique, which uses magnetic and electric fields to trap and guide the decay protons of a beam of cold neutrons to a detector, is in progress at the National Institute of Standards and Technology, Gaithersburg, MD with a precision goal of 0.1. I acknowledge the support of the Cross-Diciplinary Institute at Gettysburg College.

ASNC upgrade for nuclear material accountancy of ACPF

NASA Astrophysics Data System (ADS)

Seo, Hee; Ahn, Seong-Kyu; Lee, Chaehun; Oh, Jong-Myeong; Yoon, Seonkwang

2018-02-01

A safeguards neutron coincidence counter for nuclear material accountancy of the Advanced spent-fuel Conditioning Process Facility (ACPF), known as the ACP Safeguards Neutron Counter (ASNC), was upgraded to improve its remote-handling and maintenance capabilities. Based on the results of the previous design study, the neutron counter was completely rebuilt, and various detector parameters for neutron coincidence counting (i.e., high-voltage plateau, efficiency profile, dead time, die-away time, gate length, doubles gate fraction, and stability) were experimentally determined. The measurement data showed good agreement with the MCNP simulation results. To the best of the authors' knowledge, the ASNC is the only safeguards neutron coincidence counter in the world that is installed and operated in a hot-cell. The final goals to be achieved were (1) to evaluate the uncertainty level of the ASNC in nuclear material accountancy of the process materials of the oxide-reduction process for spent fuels and (2) to evaluate the applicability of the neutron coincidence counting technique within a strong radiation field (e.g., in a hot-cell environment).

Development of a detector in order to investigate (n,γ)-cross sections by ToF method with a very short flight path

NASA Astrophysics Data System (ADS)

Wolf, C.; Glorius, J.; Reifarth, R.; Weigand, M.

2018-01-01

The determination of neutron capture cross sections of some radioactive isotopes like 85Kr is very important to improve the knowledge about the s process. Based on its own radioactive decay these isotopes can only be used in small samples inside a TOF facility, which is why the neutron flux of these facilities has to be very high. Unfortunately the neutron flux of the FRANZ setup at Goethe University Frankfurt, which will offer the highest neutron flux in astrophysical energy regions (keV region) [1], is still to low to investigate isotopes like 85Kr. Therefore a new setup called NAUTILUS is under development, which will reduce the flight path from 80 cm to a few centimeter to enhance the angular coverage of the sample and therefore increase the neutron flux by a factor of nearly 100. This implies a higher intensity of the γ-flash energy inside the detector and the neutron induced background. Hence the geometry, the scintillator material and the moderator were optimized by GEANT3 simulations.

High intensity multi beam design of SANS instrument for Dhruva reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abbas, Sohrab, E-mail: abbas@barc.gov.in; Aswal, V. K.; Désert, S.

A new and versatile design of Small Angle Neutron Scattering (SANS) instrument based on utilization of multi-beam is presented. The multi-pinholes and multi-slits as SANS collimator for medium flux Dhruva rearctor have been proposed and their designs have been validated using McStas simulations. Various instrument configurations to achieve different minimum wave vector transfers in scattering experiments are envisioned. These options enable smooth access to minimum wave vector transfers as low as ~ 6×10{sup −4} Å{sup −1} with a significant improvement in neutron intensity, allowing faster measurements. Such angularly well defined and intense neutron beam will allow faster SANS studies ofmore » agglomerates larger than few tens of nm.« less

EBR-II Static Neutronic Calculations by PHISICS / MCNP6 codes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paolo Balestra; Carlo Parisi; Andrea Alfonsi

2016-02-01

The International Atomic Energy Agency (IAEA) launched a Coordinated Research Project (CRP) on the Shutdown Heat Removal Tests (SHRT) performed in the '80s at the Experimental fast Breeder Reactor EBR-II, USA. The scope of the CRP is to improve and validate the simulation tools for the study and the design of the liquid metal cooled fast reactors. Moreover, training of the next generation of fast reactor analysts is being also considered the other scope of the CRP. In this framework, a static neutronic model was developed, using state-of-the art neutron transport codes like SCALE/PHISICS (deterministic solution) and MCNP6 (stochastic solution).more » Comparison between both solutions is briefly illustrated in this summary.« less

Unfolding neutron spectra from simulated response of thermoluminescence dosimeters inside a polyethylene sphere using GRNN neural network

NASA Astrophysics Data System (ADS)

Lotfalizadeh, F.; Faghihi, R.; Bahadorzadeh, B.; Sina, S.

2017-07-01

Neutron spectrometry using a single-sphere containing dosimeters has been developed recently, as an effective replacement for Bonner sphere spectrometry. The aim of this study is unfolding the neutron energy spectra using GRNN artificial neural network, from the response of thermoluminescence dosimeters, TLDs, located inside a polyethylene sphere. The spectrometer was simulated using MCNP5. TLD-600 and TLD-700 dosimeters were simulated at different positions in all directions. Then the GRNN was used for neutron spectra prediction, using the TLDs' readings. Comparison of spectra predicted by the network with the real spectra, show that the single-sphere dosimeter is an effective instrument in unfolding neutron spectra.

The specific purpose Monte Carlo code McENL for simulating the response of epithermal neutron lifetime well logging tools

NASA Astrophysics Data System (ADS)

Prettyman, T. H.; Gardner, R. P.; Verghese, K.

1993-08-01

A new specific purpose Monte Carlo code called McENL for modeling the time response of epithermal neutron lifetime tools is described. The weight windows technique, employing splitting and Russian roulette, is used with an automated importance function based on the solution of an adjoint diffusion model to improve the code efficiency. Complete composition and density correlated sampling is also included in the code, and can be used to study the effect on tool response of small variations in the formation, borehole, or logging tool composition and density. An illustration of the latter application is given for the density of a thermal neutron filter. McENL was benchmarked against test-pit data for the Mobil pulsed neutron porosity tool and was found to be very accurate. Results of the experimental validation and details of code performance are presented.

Time-Dependent Hartree-Fock Approach to Nuclear Pasta at Finite Temperature

NASA Astrophysics Data System (ADS)

Schuetrumpf, B.; Klatt, M. A.; Iida, K.; Maruhn, J. A.; Mecke, K.; Reinhard, P.-G.

2013-03-01

We present simulations of neutron-rich matter at subnuclear densities, like supernova matter, with the time-dependent Hartree-Fock approximation at temperatures of several MeV. The initial state consists of α particles randomly distributed in space that have a Maxwell-Boltzmann distribution in momentum space. Adding a neutron background initialized with Fermi distributed plane waves the calculations reflect a reasonable approximation of astrophysical matter. This matter evolves into spherical, rod-like, and slab-like shapes and mixtures thereof. The simulations employ a full Skyrme interaction in a periodic three-dimensional grid. By an improved morphological analysis based on Minkowski functionals, all eight pasta shapes can be uniquely identified by the sign of only two valuations, namely the Euler characteristic and the integral mean curvature.

CAFNA{reg{underscore}sign}, coded aperture fast neutron analysis for contraband detection: Preliminary results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, L.; Lanza, R.C.

1999-12-01

The authors have developed a near field coded aperture imaging system for use with fast neutron techniques as a tool for the detection of contraband and hidden explosives through nuclear elemental analysis. The technique relies on the prompt gamma rays produced by fast neutron interactions with the object being examined. The position of the nuclear elements is determined by the location of the gamma emitters. For existing fast neutron techniques, in Pulsed Fast Neutron Analysis (PFNA), neutrons are used with very low efficiency; in Fast Neutron Analysis (FNS), the sensitivity for detection of the signature gamma rays is very low.more » For the Coded Aperture Fast Neutron Analysis (CAFNA{reg{underscore}sign}) the authors have developed, the efficiency for both using the probing fast neutrons and detecting the prompt gamma rays is high. For a probed volume of n{sup 3} volume elements (voxels) in a cube of n resolution elements on a side, they can compare the sensitivity with other neutron probing techniques. As compared to PFNA, the improvement for neutron utilization is n{sup 2}, where the total number of voxels in the object being examined is n{sup 3}. Compared to FNA, the improvement for gamma-ray imaging is proportional to the total open area of the coded aperture plane; a typical value is n{sup 2}/2, where n{sup 2} is the number of total detector resolution elements or the number of pixels in an object layer. It should be noted that the actual signal to noise ratio of a system depends also on the nature and distribution of background events and this comparison may reduce somewhat the effective sensitivity of CAFNA. They have performed analysis, Monte Carlo simulations, and preliminary experiments using low and high energy gamma-ray sources. The results show that a high sensitivity 3-D contraband imaging and detection system can be realized by using CAFNA.« less

A study to compute integrated dpa for neutron and ion irradiation environments using SRIM-2013

NASA Astrophysics Data System (ADS)

Saha, Uttiyoarnab; Devan, K.; Ganesan, S.

2018-05-01

Displacements per atom (dpa), estimated based on the standard Norgett-Robinson-Torrens (NRT) model, is used for assessing radiation damage effects in fast reactor materials. A computer code CRaD has been indigenously developed towards establishing the infrastructure to perform improved radiation damage studies in Indian fast reactors. We propose a method for computing multigroup neutron NRT dpa cross sections based on SRIM-2013 simulations. In this method, for each neutron group, the recoil or primary knock-on atom (PKA) spectrum and its average energy are first estimated with CRaD code from ENDF/B-VII.1. This average PKA energy forms the input for SRIM simulation, wherein the recoil atom is taken as the incoming ion on the target. The NRT-dpa cross section of iron computed with "Quick" Kinchin-Pease (K-P) option of SRIM-2013 is found to agree within 10% with the standard NRT-dpa values, if damage energy from SRIM simulation is used. SRIM-2013 NRT-dpa cross sections applied to estimate the integrated dpa for Fe, Cr and Ni are in good agreement with established computer codes and data. A similar study carried out for polyatomic material, SiC, shows encouraging results. In this case, it is observed that the NRT approach with average lattice displacement energy of 25 eV coupled with the damage energies from the K-P option of SRIM-2013 gives reliable displacement cross sections and integrated dpa for various reactor spectra. The source term of neutron damage can be equivalently determined in the units of dpa by simulating self-ion bombardment. This shows that the information of primary recoils obtained from CRaD can be reliably applied to estimate the integrated dpa and damage assessment studies in accelerator-based self-ion irradiation experiments of structural materials. This study would help to advance the investigation of possible correlations between the damages induced by ions and reactor neutrons.

Methodology for testing infrared focal plane arrays in simulated nuclear radiation environments

NASA Astrophysics Data System (ADS)

Divita, E. L.; Mills, R. E.; Koch, T. L.; Gordon, M. J.; Wilcox, R. A.; Williams, R. E.

1992-07-01

This paper summarizes test methodology for focal plane array (FPA) testing that can be used for benign (clear) and radiation environments, and describes the use of custom dewars and integrated test equipment in an example environment. The test methodology, consistent with American Society for Testing Materials (ASTM) standards, is presented for the total accumulated gamma dose, transient dose rate, gamma flux, and neutron fluence environments. The merits and limitations of using Cobalt 60 for gamma environment simulations and of using various fast-neutron reactors and neutron sources for neutron simulations are presented. Test result examples are presented to demonstrate test data acquisition and FPA parameter performance under different measurement conditions and environmental simulations.

Extracting equation of state parameters from black hole-neutron star mergers: Aligned-spin black holes and a preliminary waveform model

NASA Astrophysics Data System (ADS)

Lackey, Benjamin D.; Kyutoku, Koutarou; Shibata, Masaru; Brady, Patrick R.; Friedman, John L.

2014-02-01

Information about the neutron-star equation of state is encoded in the waveform of a black hole-neutron star system through tidal interactions and the possible tidal disruption of the neutron star. During the inspiral this information depends on the tidal deformability Λ of the neutron star, and we find that the best-measured parameter during the merger and ringdown is consistent with Λ as well. We performed 134 simulations where we systematically varied the equation of state as well as the mass ratio, neutron star mass, and aligned spin of the black hole. Using these simulations we develop an analytic representation of the full inspiral-merger-ringdown waveform calibrated to these numerical waveforms; we use this analytic waveform and a Fisher matrix analysis to estimate the accuracy to which Λ can be measured with gravitational-wave detectors. We find that although the inspiral tidal signal is small, coherently combining this signal with the merger-ringdown matter effect improves the measurability of Λ by a factor of ˜3 over using just the merger-ringdown matter effect alone. However, incorporating correlations between all the waveform parameters then decreases the measurability of Λ by a factor of ˜3. The uncertainty in Λ increases with the mass ratio, but decreases as the black hole spin increases. Overall, a single Advanced LIGO detector can only marginally measure Λ for mass ratios Q =2-5, black hole spins JBH/MBH2=-0.5-0.75, and neutron star masses MNS=1.2M⊙-1.45M⊙ at an optimally oriented distance of 100 Mpc. For the proposed Einstein Telescope, however, the uncertainty in Λ is an order of magnitude smaller.

SU-F-T-657: In-Room Neutron Dose From High Energy Photon Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Christ, D; Ding, G

Purpose: To estimate neutron dose inside the treatment room from photodisintegration events in high energy photon beams using Monte Carlo simulations and experimental measurements. Methods: The Monte Carlo code MCNP6 was used for the simulations. An Eberline ESP-1 Smart Portable Neutron Detector was used to measure neutron dose. A water phantom was centered at isocenter on the treatment couch, and the detector was placed near the phantom. A Varian 2100EX linear accelerator delivered an 18MV open field photon beam to the phantom at 400MU/min, and a camera captured the detector readings. The experimental setup was modeled in the Monte Carlomore » simulation. The source was modeled for two extreme cases: a) hemispherical photon source emitting from the target and b) cone source with an angle of the primary collimator cone. The model includes the target, primary collimator, flattening filter, secondary collimators, water phantom, detector and concrete walls. Energy deposition tallies were measured for neutrons in the detector and for photons at the center of the phantom. Results: For an 18MV beam with an open 10cm by 10cm field and the gantry at 180°, the Monte Carlo simulations predict the neutron dose in the detector to be 0.11% of the photon dose in the water phantom for case a) and 0.01% for case b). The measured neutron dose is 0.04% of the photon dose. Considering the range of neutron dose predicted by Monte Carlo simulations, the calculated results are in good agreement with measurements. Conclusion: We calculated in-room neutron dose by using Monte Carlo techniques, and the predicted neutron dose is confirmed by experimental measurements. If we remodel the source as an electron beam hitting the target for a more accurate representation of the bremsstrahlung fluence, it is feasible that the Monte Carlo simulations can be used to help in shielding designs.« less

Triple pulse shape discrimination and capture-gated spectroscopy in a composite heterogeneous scintillator

NASA Astrophysics Data System (ADS)

Sharma, M.; Nattress, J.; Wilhelm, K.; Jovanovic, I.

2017-06-01

We demonstrate an all-solid-state design for a composite heterogeneous scintillation detector sensitive to interactions with high-energy photons (gammas), fast neutrons, and thermal neutrons. The scintillator exhibits triple pulse shape discrimination, effectively separating electron recoils, fast neutron recoils, and neutron captures. This is accomplished by combining the properties of two distinct scintillators, whereby a 51-mm diameter, 51-mm tall cylinder of pulse shape discriminating plastic is wrapped by a 320-μm thick sheet of 6LiF:ZnS(Ag), optically coupling the scintillators to each other and to the photomultiplier tube. In this way, the sensitivity to neutron captures is achieved without the need to load the plastic scintillator with a capture agent. We demonstrate a figure of merit of up to 1.2 for fast neutrons/gammas and 5.7 for thermal neutrons/gammas. Intrinsic capture efficiency is found to be 0.46±0.05% and is in good agreement with simulation, while gamma rejection was 10-6 with respect to the capture region and 10-4 with respect to the recoil region using a 300 keVee threshold. Finally, we show an improvement in capture-gated neutron spectroscopy by rejecting accidental gamma coincidences using pulse shape discrimination in the plastic scintillator.

GEANT4 and PHITS simulations of the shielding of neutrons from the 252Cf source

NASA Astrophysics Data System (ADS)

Shin, Jae Won; Hong, Seung-Woo; Bak, Sang-In; Kim, Do Yoon; Kim, Chong Yeal

2014-09-01

Monte Carlo simulations are performed by using the GEANT4 and the PHITS for studying the neutron-shielding abilities of several materials, such as graphite, iron, polyethylene, NS-4-FR and KRAFTON-HB. As a neutron source, 252Cf is considered. For the Monte Carlo simulations by using the GEANT4, high precision (G4HP) models with the G4NDL 4.2 based on ENDF/B-VII data are used. For the simulations by using the PHITS, the JENDL-4.0 library is used. The neutron-dose-equivalent rates with or without five different shielding materials are estimated and compared with the experimental values. The differences between the shielding abilities calculated by using the GEANT4 with the G4NDL 4.2 and the PHITS with the JENDL-4.0 are found not to be significant for all the cases considered in this work. The neutron-dose-equivalent rates obtained by using the GEANT4 and the PHITS are compared with experimental data and other simulation results. Our neutron-dose-equivalent rates agree well with the experimental dose-equivalent rates, within 20% errors, except for polyethylene. For polyethylene, the discrepancies between our calculations and the experiments are less than 40%, as observed in other simulation results.

Neutronic calculation of fast reactors by the EUCLID/V1 integrated code

NASA Astrophysics Data System (ADS)

Koltashev, D. A.; Stakhanova, A. A.

2017-01-01

This article considers neutronic calculation of a fast-neutron lead-cooled reactor BREST-OD-300 by the EUCLID/V1 integrated code. The main goal of development and application of integrated codes is a nuclear power plant safety justification. EUCLID/V1 is integrated code designed for coupled neutronics, thermomechanical and thermohydraulic fast reactor calculations under normal and abnormal operating conditions. EUCLID/V1 code is being developed in the Nuclear Safety Institute of the Russian Academy of Sciences. The integrated code has a modular structure and consists of three main modules: thermohydraulic module HYDRA-IBRAE/LM/V1, thermomechanical module BERKUT and neutronic module DN3D. In addition, the integrated code includes databases with fuel, coolant and structural materials properties. Neutronic module DN3D provides full-scale simulation of neutronic processes in fast reactors. Heat sources distribution, control rods movement, reactivity level changes and other processes can be simulated. Neutron transport equation in multigroup diffusion approximation is solved. This paper contains some calculations implemented as a part of EUCLID/V1 code validation. A fast-neutron lead-cooled reactor BREST-OD-300 transient simulation (fuel assembly floating, decompression of passive feedback system channel) and cross-validation with MCU-FR code results are presented in this paper. The calculations demonstrate EUCLID/V1 code application for BREST-OD-300 simulating and safety justification.

Monte Carlo simulation of neutron backscattering from concrete walls in the dense plasma focus laboratory of Bologna University.

PubMed

Frignani, M; Mostacci, D; Rocchi, F; Sumini, M

2005-01-01

Between 2001 and 2003 a 3.2 kJ dense plasma focus (DPF) device has been built at the Montecuccolino Laboratory of the Department of Energy, Nuclear and Environmental Control Engineering (DIENCA) of the University of Bologna. A DPF is a pulsed device in which deuterium nuclear fusion reactions can be obtained through the pinching effects of electromagnetic fields upon a dense plasma. The empirical scale law that governs the total D-D neutron yield from a single pulse of a DPF predicts for this machine a figure of approximately 10(7) fast neutrons per shot. The aim of the present work is to evaluate the role of backscattering of neutrons from the concrete walls surrounding the Montecuccolino DPF in total neutron yield measurements. The evaluation is performed by MCNP-5 simulations that are aimed at estimating the neutron spectra at a few points of interest in the laboratory, where neutron detectors will be placed during the experimental campaigns. Spectral information from the simulations is essential because the response of detectors is influenced by neutron energy. Comparisons are made with the simple r(-2) law, which holds for a DPF in infinite vacuum. The results from the simulations will ultimately be used both in the design and optimisation of the neutron detectors and in their final calibration and placement inside the laboratory.

Simulating an Exploding Fission-Bomb Core

NASA Astrophysics Data System (ADS)

Reed, Cameron

2016-03-01

A time-dependent desktop-computer simulation of the core of an exploding fission bomb (nuclear weapon) has been developed. The simulation models a core comprising a mixture of two isotopes: a fissile one (such as U-235) and an inert one (such as U-238) that captures neutrons and removes them from circulation. The user sets the enrichment percentage and scattering and fission cross-sections of the fissile isotope, the capture cross-section of the inert isotope, the number of neutrons liberated per fission, the number of ``initiator'' neutrons, the radius of the core, and the neutron-reflection efficiency of a surrounding tamper. The simulation, which is predicated on ordinary kinematics, follows the three-dimensional motions and fates of neutrons as they travel through the core. Limitations of time and computer memory render it impossible to model a real-life core, but results of numerous runs clearly demonstrate the existence of a critical mass for a given set of parameters and the dramatic effects of enrichment and tamper efficiency on the growth (or decay) of the neutron population. The logic of the simulation will be described and results of typical runs will be presented and discussed.

Coupled multi-group neutron photon transport for the simulation of high-resolution gamma-ray spectroscopy applications

NASA Astrophysics Data System (ADS)

Burns, Kimberly Ann

The accurate and efficient simulation of coupled neutron-photon problems is necessary for several important radiation detection applications. Examples include the detection of nuclear threats concealed in cargo containers and prompt gamma neutron activation analysis for nondestructive determination of elemental composition of unknown samples. In these applications, high-resolution gamma-ray spectrometers are used to preserve as much information as possible about the emitted photon flux, which consists of both continuum and characteristic gamma rays with discrete energies. Monte Carlo transport is the most commonly used modeling tool for this type of problem, but computational times for many problems can be prohibitive. This work explores the use of coupled Monte Carlo-deterministic methods for the simulation of neutron-induced photons for high-resolution gamma-ray spectroscopy applications. RAdiation Detection Scenario Analysis Toolbox (RADSAT), a code which couples deterministic and Monte Carlo transport to perform radiation detection scenario analysis in three dimensions [1], was used as the building block for the methods derived in this work. RADSAT was capable of performing coupled deterministic-Monte Carlo simulations for gamma-only and neutron-only problems. The purpose of this work was to develop the methodology necessary to perform coupled neutron-photon calculations and add this capability to RADSAT. Performing coupled neutron-photon calculations requires four main steps: the deterministic neutron transport calculation, the neutron-induced photon spectrum calculation, the deterministic photon transport calculation, and the Monte Carlo detector response calculation. The necessary requirements for each of these steps were determined. A major challenge in utilizing multigroup deterministic transport methods for neutron-photon problems was maintaining the discrete neutron-induced photon signatures throughout the simulation. Existing coupled neutron-photon cross-section libraries and the methods used to produce neutron-induced photons were unsuitable for high-resolution gamma-ray spectroscopy applications. Central to this work was the development of a method for generating multigroup neutron-photon cross-sections in a way that separates the discrete and continuum photon emissions so the neutron-induced photon signatures were preserved. The RADSAT-NG cross-section library was developed as a specialized multigroup neutron-photon cross-section set for the simulation of high-resolution gamma-ray spectroscopy applications. The methodology and cross sections were tested using code-to-code comparison with MCNP5 [2] and NJOY [3]. A simple benchmark geometry was used for all cases compared with MCNP. The geometry consists of a cubical sample with a 252Cf neutron source on one side and a HPGe gamma-ray spectrometer on the opposing side. Different materials were examined in the cubical sample: polyethylene (C2H4), P, N, O, and Fe. The cross sections for each of the materials were compared to cross sections collapsed using NJOY. Comparisons of the volume-averaged neutron flux within the sample, volume-averaged photon flux within the detector, and high-purity gamma-ray spectrometer response (only for polyethylene) were completed using RADSAT and MCNP. The code-to-code comparisons show promising results for the coupled Monte Carlo-deterministic method. The RADSAT-NG cross-section production method showed good agreement with NJOY for all materials considered although some additional work is needed in the resonance region and in the first and last energy bin. Some cross section discrepancies existed in the lowest and highest energy bin, but the overall shape and magnitude of the two methods agreed. For the volume-averaged photon flux within the detector, typically the five most intense lines agree to within approximately 5% of the MCNP calculated flux for all of materials considered. The agreement in the code-to-code comparisons cases demonstrates a proof-of-concept of the method for use in RADSAT for coupled neutron-photon problems in high-resolution gamma-ray spectroscopy applications. One of the primary motivators for using the coupled method over pure Monte Carlo method is the potential for significantly lower computational times. For the code-to-code comparison cases, the run times for RADSAT were approximately 25--500 times shorter than for MCNP, as shown in Table 1. This was assuming a 40 mCi 252Cf neutron source and 600 seconds of "real-world" measurement time. The only variance reduction technique implemented in the MCNP calculation was forward biasing of the source toward the sample target. Improved MCNP runtimes could be achieved with the addition of more advanced variance reduction techniques.

Application of the SHARP Toolkit to Sodium-Cooled Fast Reactor Challenge Problems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shemon, E. R.; Yu, Y.; Kim, T. K.

The Simulation-based High-efficiency Advanced Reactor Prototyping (SHARP) toolkit is under development by the Nuclear Energy Advanced Modeling and Simulation (NEAMS) Campaign of the U.S. Department of Energy, Office of Nuclear Energy. To better understand and exploit the benefits of advanced modeling simulations, the NEAMS Campaign initiated the “Sodium-Cooled Fast Reactor (SFR) Challenge Problems” task, which include the assessment of hot channel factors (HCFs) and the demonstration of zooming capability using the SHARP toolkit. If both challenge problems are resolved through advanced modeling and simulation using the SHARP toolkit, the economic competitiveness of a SFR can be significantly improved. The effortsmore » in the first year of this project focused on the development of computational models, meshes, and coupling procedures for multi-physics calculations using the neutronics (PROTEUS) and thermal-hydraulic (Nek5000) components of the SHARP toolkit, as well as demonstration of the HCF calculation capability for the 100 MWe Advanced Fast Reactor (AFR-100) design. Testing the feasibility of the SHARP zooming capability is planned in FY 2018. The HCFs developed for the earlier SFRs (FFTF, CRBR, and EBR-II) were reviewed, and a subset of these were identified as potential candidates for reduction or elimination through high-fidelity simulations. A one-way offline coupling method was used to evaluate the HCFs where the neutronics solver PROTEUS computes the power profile based on an assumed temperature, and the computational fluid dynamics solver Nek5000 evaluates the peak temperatures using the neutronics power profile. If the initial temperature profile used in the neutronics calculation is reasonably accurate, the one-way offline method is valid because the neutronics power profile has weak dependence on small temperature variation. In order to get more precise results, the proper temperature profile for initial neutronics calculations was obtained from the STAR-CCM+ calculations. The HCFs of the peak temperatures at cladding outer surface, cladding inner wall surface, and fuel centerline induced by cladding manufacturing tolerance and uncertainties on the cladding, coolant, and fuel properties were evaluated for the AFR-100. Some assessment on the effect of wire wrap configuration and size of the bundle shows that it is practical to use the 7-pin bare rod bundle to calculate the HCFs. The resulting HCFs obtained from the high-fidelity SHARP calculations are generally smaller than those developed for the earlier SFRs because the most uncertainties involved in the modeling and simulations were disappeared. For completeness, additional investigations are planned in FY 2018, which will use random sampling techniques.« less

Research and development of a dedicated collimator for 14.2 MeV fast neutrons for imaging using a D-T generator

NASA Astrophysics Data System (ADS)

Sabo-Napadensky, I.; Weiss-Babai, R.; Gayer, A.; Vartsky, D.; Bar, D.; Mor, I.; Chacham-Zada, R.; Cohen, M.; Tamim, N.

2012-06-01

One of the main problems in neutron imaging is the scattered radiation that accompanies the direct neutrons that reach the imaging detectors and affect the image quality. We have developed a dedicated collimator for 14.2 MeV fast neutrons. The collimator optimizes the amount of scattered radiation to primary neutrons that arrive at the imaging plane. We have used different materials within the collimator in order to lower the scattered radiation that arrives at the scanned object. The image quality and the signal to noise ratios that are measured show that a mixture of BORAX (Na2B4O7ṡ10H2O) and water in the experimental beam collimator give the best results. We have used GEANT4 to simulate the collimator performance, the simulations predict the optimized material looking on the ratios of the scattered to primary neutrons that contribute in the detector. We present our experimental setup, report the results of the experimental and related simulation studies with neutrons beam generated by a 14.2 MeV D-T neutron generator.

Hierarchical optimization for neutron scattering problems

DOE PAGES

Bao, Feng; Archibald, Rick; Bansal, Dipanshu; ...

2016-03-14

In this study, we present a scalable optimization method for neutron scattering problems that determines confidence regions of simulation parameters in lattice dynamics models used to fit neutron scattering data for crystalline solids. The method uses physics-based hierarchical dimension reduction in both the computational simulation domain and the parameter space. We demonstrate for silicon that after a few iterations the method converges to parameters values (interatomic force-constants) computed with density functional theory simulations.

Hierarchical optimization for neutron scattering problems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bao, Feng; Archibald, Rick; Bansal, Dipanshu

In this study, we present a scalable optimization method for neutron scattering problems that determines confidence regions of simulation parameters in lattice dynamics models used to fit neutron scattering data for crystalline solids. The method uses physics-based hierarchical dimension reduction in both the computational simulation domain and the parameter space. We demonstrate for silicon that after a few iterations the method converges to parameters values (interatomic force-constants) computed with density functional theory simulations.

Optimization of 6LiF:ZnS(Ag) scintillator light yield using GEANT4

NASA Astrophysics Data System (ADS)

Yehuda-Zada, Y.; Pritchard, K.; Ziegler, J. B.; Cooksey, C.; Siebein, K.; Jackson, M.; Hurlbut, C.; Kadmon, Y.; Cohen, Y.; Ibberson, R. M.; Majkrzak, C. F.; Maliszewskyj, N. C.; Orion, I.; Osovizky, A.

2018-06-01

A new cold neutron detector has been developed at the NIST Center for Neutron Research (NCNR) for the CANDoR (Chromatic Analysis Neutron Diffractometer or Reflectometer) project. Geometric and performance constraints dictate that this detector be exceptionally thin (∼ 2 mm). For this reason, the design of the detector consists of a 6LiF:ZnS(Ag) scintillator with embedded wavelength shifting (WLS) fibers. We used the GEANT4 package to simulate neutron capture and light transport in the detector to optimize the composition and arrangement of materials to satisfy the competing requirements of high neutron capture probability and light production and transport. In the process, we have developed a method for predicting light collection and total neutron detection efficiency for different detector configurations. The simulation was performed by adjusting crucial parameters such as the scintillator stoichiometry, light yield, component grain size, WLS fiber geometry, and reflectors at the outside edges of the scintillator volume. Three different detector configurations were fabricated and their test results were correlated with the simulations. Through this correlation we have managed to find a common photon threshold for the different detector configurations which was then used to simulate and predict the efficiencies for many other detector configurations. New detectors that have been fabricated based on simulation results yielding the desired sensitivity of 90% for 3.27 meV (5 Å) cold neutrons. The simulation has proven to be a useful tool by dramatically reducing the development period and the required number of detector prototypes. It can be used to test new designs with different thicknesses and different target neutron energies.

Investigating a cyclotron HM-30 based neutron source for BNCT of deep-seated tumors by using shifting method

NASA Astrophysics Data System (ADS)

Suharyana; Riyatun; Octaviana, E. F.

2016-11-01

We have successfully proposed a simulation of a neutron beam-shaping assembly using MCNPX Code. This simulation study deals with designing a compact, optimized, and geometrically simple beam shaping assembly for a neutron source based on a proton cyclotron for BNCT purpose. Shifting method was applied in order to lower the fast neutron energy to the epithermal energy range by choosing appropriate materials. Based on a set of MCNPX simulations, it has been found that the best materials for beam shaping assembly are 3 cm Ni layered with 7 cm Pb as the reflector and 13 cm AlF3 the moderator. Our proposed beam shaping assembly configuration satisfies 2 of 5 of the IAEA criteria, namely the epithermal neutron flux 1.25 × 109 n.cm-2 s-1 and the gamma dose over the epithermal neutron flux is 0.18×10 -13 Gy.cm 2 n -1. However, the ratio of the fast neutron dose rate over neutron epithermal flux is still too high. We recommended that the shifting method must be accompanied by the filter method to reduce the fast neutron flux.

Measurement and simulation of thermal neutron flux distribution in the RTP core

NASA Astrophysics Data System (ADS)

Rabir, Mohamad Hairie B.; Jalal Bayar, Abi Muttaqin B.; Hamzah, Na'im Syauqi B.; Mustafa, Muhammad Khairul Ariff B.; Karim, Julia Bt. Abdul; Zin, Muhammad Rawi B. Mohamed; Ismail, Yahya B.; Hussain, Mohd Huzair B.; Mat Husin, Mat Zin B.; Dan, Roslan B. Md; Ismail, Ahmad Razali B.; Husain, Nurfazila Bt.; Jalil Khan, Zareen Khan B. Abdul; Yakin, Shaiful Rizaide B. Mohd; Saad, Mohamad Fauzi B.; Masood, Zarina Bt.

2018-01-01

The in-core thermal neutron flux distribution was determined using measurement and simulation methods for the Malaysian’s PUSPATI TRIGA Reactor (RTP). In this work, online thermal neutron flux measurement using Self Powered Neutron Detector (SPND) has been performed to verify and validate the computational methods for neutron flux calculation in RTP calculations. The experimental results were used as a validation to the calculations performed with Monte Carlo code MCNP. The detail in-core neutron flux distributions were estimated using MCNP mesh tally method. The neutron flux mapping obtained revealed the heterogeneous configuration of the core. Based on the measurement and simulation, the thermal flux profile peaked at the centre of the core and gradually decreased towards the outer side of the core. The results show a good agreement (relatively) between calculation and measurement where both show the same radial thermal flux profile inside the core: MCNP model over estimation with maximum discrepancy around 20% higher compared to SPND measurement. As our model also predicts well the neutron flux distribution in the core it can be used for the characterization of the full core, that is neutron flux and spectra calculation, dose rate calculations, reaction rate calculations, etc.

Single crystal to polycrystal neutron transmission simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dessieux, Luc Lucius; Stoica, Alexandru Dan; Bingham, Philip R.

A collection of routines for calculation of the total cross section that determines the attenuation of neutrons by crystalline solids is presented. The total cross section is calculated semi-empirically as a function of crystal structure, neutron energy, temperature, and crystal orientation. The semi-empirical formula includes the contribution of parasitic Bragg scattering to the total cross section using both the crystal’s mosaic spread value and its orientation with respect to the neutron beam direction as parameters. These routines allow users to enter a distribution of crystal orientations for calculation of total cross sections of user defined powder or pseudo powder distributions,more » which enables simulation of non-uniformities such as texture and strain. In conclusion, the spectra for neutron transmission simulations in the neutron thermal energy range (2 meV–100 meV) are presented for single crystal and polycrystal samples and compared to measurements.« less

Simulations towards optimization of a neutron/anti-neutron oscillation experiment at the European Spallation Source

NASA Astrophysics Data System (ADS)

Frost, Matthew; Kamyshkov, Yuri; Castellanos, Luis; Klinkby, Esben; US NNbar Collaboration

2015-04-01

The observation of Neutron/Anti-neutron oscillation would prove the existence of Baryon Number Violation (BNV), and thus an explanation for the dominance of matter over anti-matter in the universe. The latest experiments have shown the oscillation time to be greater than 8.6 x 107 seconds, whereas current theoretical predictions suggest times on the order of 108 to 109 seconds. A neutron oscillation experiment proposed at the European Spallation Source (ESS) would provide sensitivity of more than 1000 times previous experiments performed, thus providing a result well-suited to confirm or deny current theory. A conceptual design of the proposed experiment will be presented, as well as the optimization of key experiment components using Monte-Carlo simulation methods, including the McStas neutron ray-trace simulation package. This work is supported by the Organized Research Units Program funded by The University of Tennessee, Knoxville Office of Research and Engagement.

Radiative GRMHD simulations of accretion and outflow in non-magnetized neutron stars and ultraluminous X-ray sources

NASA Astrophysics Data System (ADS)

Abarca, David; Kluźniak, Wlodek; Sądowski, Aleksander

2018-06-01

We run two GRRMHD simulations of super-Eddington accretion disks around a black hole and a non-magnetized, non-rotating neutron star. The neutron star was modeled using a reflective inner boundary condition. We observe the formation of a transition layer in the inner region of the disk in the neutron star simulation which leads to a larger mass outflow rate and a lower radiative luminosity over the black hole case. Sphereization of the flow leads to an observable luminosity at infinity around the Eddington value when viewed from all directions for the neutron star case, contrasting to the black hole case where collimation of the emission leads to observable luminosities about an order of magnitude higher when observed along the disk axis. We find the outflow to be optically thick to scattering, which would lead to the obscuring of any neutron star pulsations observed in corresponding ULXs.

Single crystal to polycrystal neutron transmission simulation

DOE PAGES

Dessieux, Luc Lucius; Stoica, Alexandru Dan; Bingham, Philip R.

2018-02-02

A collection of routines for calculation of the total cross section that determines the attenuation of neutrons by crystalline solids is presented. The total cross section is calculated semi-empirically as a function of crystal structure, neutron energy, temperature, and crystal orientation. The semi-empirical formula includes the contribution of parasitic Bragg scattering to the total cross section using both the crystal’s mosaic spread value and its orientation with respect to the neutron beam direction as parameters. These routines allow users to enter a distribution of crystal orientations for calculation of total cross sections of user defined powder or pseudo powder distributions,more » which enables simulation of non-uniformities such as texture and strain. In conclusion, the spectra for neutron transmission simulations in the neutron thermal energy range (2 meV–100 meV) are presented for single crystal and polycrystal samples and compared to measurements.« less

Coupled multi-group neutron photon transport for the simulation of high-resolution gamma-ray spectroscopy applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burns, Kimberly A.

2009-08-01

The accurate and efficient simulation of coupled neutron-photon problems is necessary for several important radiation detection applications. Examples include the detection of nuclear threats concealed in cargo containers and prompt gamma neutron activation analysis for nondestructive determination of elemental composition of unknown samples.

Monte Carlo simulations of safeguards neutron counter for oxide reduction process feed material

NASA Astrophysics Data System (ADS)

Seo, Hee; Lee, Chaehun; Oh, Jong-Myeong; An, Su Jung; Ahn, Seong-Kyu; Park, Se-Hwan; Ku, Jeong-Hoe

2016-10-01

One of the options for spent-fuel management in Korea is pyroprocessing whose main process flow is the head-end process followed by oxide reduction, electrorefining, and electrowining. In the present study, a well-type passive neutron coincidence counter, namely, the ACP (Advanced spent fuel Conditioning Process) safeguards neutron counter (ASNC), was redesigned for safeguards of a hot-cell facility related to the oxide reduction process. To this end, first, the isotopic composition, gamma/neutron emission yield and energy spectrum of the feed material ( i.e., the UO2 porous pellet) were calculated using the OrigenARP code. Then, the proper thickness of the gammaray shield was determined, both by irradiation testing at a standard dosimetry laboratory and by MCNP6 simulations using the parameters obtained from the OrigenARP calculation. Finally, the neutron coincidence counter's calibration curve for 100- to 1000-g porous pellets, in consideration of the process batch size, was determined through simulations. Based on these simulation results, the neutron counter currently is under construction. In the near future, it will be installed in a hot cell and tested with spent fuel materials.

Numerical study on determining formation porosity using a boron capture gamma ray technique and MCNP.

PubMed

Liu, Juntao; Zhang, Feng; Wang, Xinguang; Han, Fei; Yuan, Zhelong

2014-12-01

Formation porosity can be determined using the boron capture gamma ray counting ratio with a near to far detector in a pulsed neutron-gamma element logging tool. The thermal neutron distribution, boron capture gamma spectroscopy and porosity response for formations with different water salinity and wellbore diameter characteristics were simulated using the Monte Carlo method. We found that a boron lining improves the signal-to-noise ratio and that the boron capture gamma ray counting ratio has a higher sensitivity for determining porosity than total capture gamma. Copyright © 2014 Elsevier Ltd. All rights reserved.

Improvement on Fermionic properties and new isotope production in molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Wang, Ning; Wu, Tong; Zeng, Jie; Yang, Yongxu; Ou, Li

2016-06-01

By considering momentum transfer in the Fermi constraint procedure, the stability of the initial nuclei and fragments produced in heavy-ion collisions can be further improved in quantum molecular dynamics simulations. The case of a phase-space occupation probability larger than one is effectively reduced with the proposed procedure. Simultaneously, the energy conservation can be better described for both individual nuclei and heavy-ion reactions. With the revised version of the improved quantum molecular dynamics model, the fusion excitation functions of 16O+186W and the central collisions of Au+Au at 35 AMeV are re-examined. The fusion cross sections at sub-barrier energies and the charge distribution of fragments are relatively better reproduced due to the reduction of spurious nucleon emission. The charge and isotope distribution of fragments in Xe+Sn, U+U and Zr+Sn at intermediate energies are also predicted. More unmeasured extremely neutron-rich fragments with Z = 16-28 are observed in the central collisions of 238U+238U than that of 96Zr+124Sn, which indicates that multi-fragmentation of U+U may offer a fruitful pathway to new neutron-rich isotopes.

Measurements of the thermal neutron flux for an accelerator-based photoneutron source.

PubMed

Taheri, Ali; Pazirandeh, Ali

2016-12-01

To have access to an appropriate neutron source is one of the most demanding requirements for neutron studies. This is important specially in laboratory and clinical applications, which need more compact and accessible sources. The most known neutron sources are fission reactors and natural isotopes, but there is an increasing interest for using accelerator based neutron sources because of their advantages. In this paper, we shall present a photo-neutron source prototype which is designed and fabricated to be used for different neutron researches including in-laboratory neutron activation analysis and neutron imaging, and also preliminary studies in boron neutron capture therapy (BNCT). Series of experimental tests were conducted to examine the intensity and quality of the neutron field produced by this source. Monte-Carlo simulations were also utilized to provide more detailed evaluation of the neutron spectrum, and determine the accuracy of the experiments. The experiments demonstrated a thermal neutron flux in the order of 10 7 (n/cm 2 .s), while simulations affirmed this flux and showed a neutron spectrum with a sharp peak at thermal energy region. According to the results, about 60 % of produced neutrons are in the range of thermal to epithermal neutrons.

"Measurements of the neutron spectrum in transit to Mars on the Mars Science Laboratory", Köhler et al.

NASA Astrophysics Data System (ADS)

Miller, Jack

2015-04-01

The Mars Science Laboratory (MSL) spacecraft carried the Curiosity rover to Mars. While the dramatic, successful landing of Curiosity and its subsequent exploration of the Martian surface have justifiably generated great excitement, from the standpoint of the health of crewmembers on missions to Mars, knowledge of the environment between Earth and Mars is critical. This paper reports data taken during the cruise phase of the MSL by the Radiation Assessment Detector (RAD). The results are of great interest for several reasons. They are a direct measurement of the radiation environment during what will be a significant fraction of the duration of a proposed human mission to Mars; they were made behind the de facto shielding provided by various spacecraft components; and, in particular, they are a measurement of the contribution to radiation dose by neutrons. The neutron environment inside spacecraft is produced primarily by galactic cosmic ray ions interacting in shielding materials, and given the high biological effectiveness of neutrons and the increased contribution of neutrons to dose with increased depth in shielding, accurate knowledge of the neutron energy spectrum behind shielding is vital. The results show a relatively modest contribution from neutrons and gammas compared to that from charged particles, but also a discrepancy in both dose and dose rate between the data and simulations. The failure of the calculations to accurately reproduce the data is significant, given that future manned spacecraft will be more heavily shielded (and thus produce more secondary neutrons) and that spacecraft design will rely on simulations and model calculations of radiation transport. The methodology of risk estimation continues to evolve, and incorporates our knowledge of both the physical and biological effects of radiation. The relatively large uncertainties in the biological data, and the difficulties in reducing those uncertainties, makes it all the more important to improve both the accuracy and the precision of the physics data.

Jets from Merging Neutron Stars

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-06-01

With the recent discovery of gravitational waves from the merger of two black holes, its especially important to understand the electromagnetic signals resulting from mergers of compact objects. New simulations successfully follow a merger of two neutron stars that produces a short burst of energy via a jet consistent with short gamma-ray burst (sGRB) detections.Still from the authors simulation showing the two neutron stars, and their magnetic fields, before merger. [Adapted from Ruiz et al. 2016]Challenging SystemWe have long suspected that sGRBs are produced by the mergers of compact objects, but this model has been difficult to prove. One major hitch is that modeling the process of merger and sGRB launch is very difficult, due to the fact that these extreme systems involve magnetic fields, fluids and full general relativity.Traditionally, simulations are only able to track such mergers over short periods of time. But in a recent study, Milton Ruiz (University of Illinois at Urbana-Champaign and Industrial University of Santander, Colombia) and coauthors Ryan Lang, Vasileios Paschalidis and Stuart Shapiro have modeled a binary neutron star system all the way through the process of inspiral, merger, and the launch of a jet.A Merger TimelineHow does this happen? Lets walk through one of the teams simulations, in which dipole magnetic field lines thread through the interior of each neutron star and extend beyond its surface(like magnetic fields found in pulsars). In this example, the two neutron stars each have a mass of 1.625 solar masses.Simulation start (0 ms)Loss of energy via gravitational waves cause the neutron stars to inspiral.Merger (3.5 ms)The neutron stars are stretched by tidal effects and make contact. Their merger produces a hypermassive neutron star that is supported against collapse by its differential (nonuniform) rotation.Delayed collapse into a black hole (21.5 ms)Once the differential rotation is redistributed by magnetic fields and partially radiated away in gravitational waves, the hypermassive neutron star loses its support and collapses to a black hole.Plasma velocities turn around (51.5 ms)Initially the plasma was falling inward, but as the disk of neutron-star debris is accreted onto the black hole, energy is released. This turns the plasma near the black hole poles around and flings it outward.Magnetic field forms a helical funnel (62.5 ms)The fields near the poles of the black hole amplify as they are wound around, creating a funnel that provides the wall of the jet.Jet outflow extends to heights greater than 445 km (64.5 ms)The disk is all accreted and, since the fuel is exhausted, the outflow shuts off (within 100ms)Neutron-Star SuccessPlot showing the gravitational wave signature for one of the authors simulations. The moments of merger of the neutron stars and collapse to a black hole are marked. [Adapted from Ruiz et al. 2016]These simulations show that no initial black hole is needed to launch outflows; a merger of two neutron stars can result in an sGRB-like jet. Another interesting result is that the magnetic field configuration doesnt affect the formation of a jet: neutron stars with magnetic fields confined to their interiors launch jets as effectively as those with pulsar-like magnetic fields. The accretion timescale for both cases is consistent with the duration of an sGRB.While this simulation models milliseconds of real time, its enormously computationally challenging and takes months to simulate. The successes of this simulation represent exciting advances in numerical relativity, as well as in our understanding of the electromagnetic counterparts that may accompany gravitational waves.BonusCheck out this awesome video of the authors simulations. The colors differentiate the plasma density and the white lines depict the pulsar-like magnetic field that initially threads the two merging neutron stars. Watch as the neutron stars evolve through the different stages outlined above, eventually forming a black hole and launching a powerful jet.[Simulations and visualization by M. Ruiz, R. Lang, V. Paschalidis, S. Shapiro and the Illinois Relativity Group REU team: S. Connelly, C. Fan, A. Khan, and P. Wongsutthikoson]CitationMilton Ruiz et al 2016 ApJ 824 L6. doi:10.3847/2041-8205/824/1/L6

DOE Office of Scientific and Technical Information (OSTI.GOV)

Milovich, J. L., E-mail: milovich1@llnl.gov; Robey, H. F.; Clark, D. S.

Experimental results from indirectly driven ignition implosions during the National Ignition Campaign (NIC) [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] achieved a record compression of the central deuterium-tritium fuel layer with measured areal densities up to 1.2 g/cm{sup 2}, but with significantly lower total neutron yields (between 1.5 × 10{sup 14} and 5.5 × 10{sup 14}) than predicted, approximately 10% of the 2D simulated yield. An order of magnitude improvement in the neutron yield was subsequently obtained in the “high-foot” experiments [O. A. Hurricane et al., Nature 506, 343 (2014)]. However, this yield was obtained at the expensemore » of fuel compression due to deliberately higher fuel adiabat. In this paper, the design of an adiabat-shaped implosion is presented, in which the laser pulse is tailored to achieve similar resistance to ablation-front instability growth, but with a low fuel adiabat to achieve high compression. Comparison with measured performance shows a factor of 3–10× improvement in the neutron yield (>40% of predicted simulated yield) over similar NIC implosions, while maintaining a reasonable fuel compression of >1 g/cm{sup 2}. Extension of these designs to higher laser power and energy is discussed to further explore the trade-off between increased implosion velocity and the deleterious effects of hydrodynamic instabilities.« less

Differential Die-Away Instrument: Report on Benchmark Measurements and Comparison with Simulation for the Effects of Neutron Poisons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goodsell, Alison Victoria; Swinhoe, Martyn Thomas; Henzl, Vladimir

2015-03-30

In this report, new experimental data and MCNPX simulation results of the differential die-away (DDA) instrument response to the presence of neutron absorbers are evaluated. In our previous fresh nuclear fuel experiments and simulations, no neutron absorbers or poisons were included in the fuel definition. These new results showcase the capability of the DDA instrument to acquire data from a system that better mimics spent nuclear fuel.

Conception of a New Recoil Proton Telescope for Real-Time Neutron Spectrometry in Proton-Therapy

NASA Astrophysics Data System (ADS)

Combe, Rodolphe; Arbor, Nicolas; el Bitar, Ziad; Higueret, Stéphane; Husson, Daniel

2018-01-01

Neutrons are the main type of secondary particles emitted in proton-therapy. Because of the risk of secondary cancer and other late occurring effects, the neutron dose should be included in the out-of-field dose calculations. A neutron spectrometer has to be used to take into account the energy dependence of the neutron radiological weighting factor. Due to its high dependence on various parameters of the irradiation (beam, accelerator, patient), the neutron spectrum should be measured independently for each treatment. The current reference method for the measurement of the neutron energy, the Bonner Sphere System, consists of several homogeneous polyethylene spheres with increasing diameters equipped with a proportional counter. It provides a highresolution reconstruction of the neutron spectrum but requires a time-consuming work of signal deconvolution. New neutron spectrometers are being developed, but the main experimental limitation remains the high neutron flux in proton therapy treatment rooms. A new model of a real-time neutron spectrometer, based on a Recoil Proton Telescope technology, has been developed at the IPHC. It enables a real-time high-rate reconstruction of the neutron spectrum from the measurement of the recoil proton trajectory and energy. A new fast-readout microelectronic integrated sensor, called FastPixN, has been developed for this specific purpose. A first prototype, able to detect neutrons between 5 and 20 MeV, has already been validated for metrology with the AMANDE facility at Cadarache. The geometry of the new Recoil Proton Telescope has been optimized via extensive Geant4 Monte Carlo simulations. Uncertainty sources have been carefully studied in order to improve simultaneously efficiency and energy resolution, and solutions have been found to suppress the various expected backgrounds. We are currently upgrading the prototype for secondary neutron detection in proton therapy applications.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, C; Kim, J; Park, S

Purpose: Photon beams with energy higher than 10 MV interact with metal material in the primary barriers, where lead or steel have been widely used, neutrons can be generated. Monte Carlo simulations were performed to simulate the production of photoneutrons and the neutron shielding effect. Methods: For two photon beam energies, 15 MV and 18 MV, we simulated to strike metal sheets (steel and lead), and the ambient dose equivalents were calculated at the isocenter (in the patient plane) while delivering 1 Gy to the patient. For these cases, the thickness of the neutron shielding materials (Borated polyethylene (BPE) andmore » concrete) were simulated to reduce the patient exposure by neutron doses. Results: When 18 MV photons interact with the metal sheets in the primary barrier, the evaluated neutron doses at the isocenter inside the treatment vault were 48.7 µSv and 7.3 µSv for lead and steel, respectively. In case of 15 MV photons, the calculated neutron doses were 18.6 µSv and 0.6 µSv for lead and steel, respectively. The neutron dose delivered to the patient can be reduced to negligible levels by including a 10 cm thick sheet of BPE or 22 cm thick sheet of concrete. Conclusion: When bunker shielding is designed with a primary barrier including a metal sheet inside the wall for a high energy machine, proper neutron shielding should be constructed to avoid undesirable extra dose.« less

Neutrons in active proton therapy: Parameterization of dose and dose equivalent.

PubMed

Schneider, Uwe; Hälg, Roger A; Lomax, Tony

2017-06-01

One of the essential elements of an epidemiological study to decide if proton therapy may be associated with increased or decreased subsequent malignancies compared to photon therapy is an ability to estimate all doses to non-target tissues, including neutron dose. This work therefore aims to predict for patients using proton pencil beam scanning the spatially localized neutron doses and dose equivalents. The proton pencil beam of Gantry 1 at the Paul Scherrer Institute (PSI) was Monte Carlo simulated using GEANT. Based on the simulated neutron dose and neutron spectra an analytical mechanistic dose model was developed. The pencil beam algorithm used for treatment planning at PSI has been extended using the developed model in order to calculate the neutron component of the delivered dose distribution for each treated patient. The neutron dose was estimated for two patient example cases. The analytical neutron dose model represents the three-dimensional Monte Carlo simulated dose distribution up to 85cm from the proton pencil beam with a satisfying precision. The root mean square error between Monte Carlo simulation and model is largest for 138MeV protons and is 19% and 20% for dose and dose equivalent, respectively. The model was successfully integrated into the PSI treatment planning system. In average the neutron dose is increased by 10% or 65% when using 160MeV or 177MeV instead of 138MeV. For the neutron dose equivalent the increase is 8% and 57%. The presented neutron dose calculations allow for estimates of dose that can be used in subsequent epidemiological studies or, should the need arise, to estimate the neutron dose at any point where a subsequent secondary tumour may occur. It was found that the neutron dose to the patient is heavily increased with proton energy. Copyright © 2016. Published by Elsevier GmbH.

The need for precise and well-documented experimental data on prompt fission neutron spectra from neutron-induced fission of 239Pu

DOE PAGES

Neudecker, Denise; Taddeucci, Terry Nicholas; Haight, Robert Cameron; ...

2016-01-06

The spectrum of neutrons emitted promptly after 239Pu(n,f)—a so-called prompt fission neutron spectrum (PFNS)—is a quantity of high interest, for instance, for reactor physics and global security. However, there are only few experimental data sets available that are suitable for evaluations. In addition, some of those data sets differ by more than their 1-σ uncertainty boundaries. We present the results of MCNP studies indicating that these differences are partly caused by underestimated multiple scattering contributions, over-corrected background, and inconsistent deconvolution methods. A detailed uncertainty quantification for suitable experimental data was undertaken including these effects, and test-evaluations were performed with themore » improved uncertainty information. The test-evaluations illustrate that the inadequately estimated effects and detailed uncertainty quantification have an impact on the evaluated PFNS and associated uncertainties as well as the neutron multiplicity of selected critical assemblies. A summary of data and documentation needs to improve the quality of the experimental database is provided based on the results of simulations and test-evaluations. Furthermore, given the possibly substantial distortion of the PFNS by multiple scattering and background effects, special care should be taken to reduce these effects in future measurements, e.g., by measuring the 239Pu PFNS as a ratio to either the 235U or 252Cf PFNS.« less

Concealed nuclear material identification via combined fast-neutron/γ-ray computed tomography (FNGCT): a Monte Carlo study

NASA Astrophysics Data System (ADS)

Licata, M.; Joyce, M. J.

2018-02-01

The potential of a combined and simultaneous fast-neutron/γ-ray computed tomography technique using Monte Carlo simulations is described. This technique is applied on the basis of a hypothetical tomography system comprising an isotopic radiation source (americium-beryllium) and a number (13) of organic scintillation detectors for the production and detection of both fast neutrons and γ rays, respectively. Via a combination of γ-ray and fast neutron tomography the potential is demonstrated to discern nuclear materials, such as compounds comprising plutonium and uranium, from substances that are used widely for neutron moderation and shielding. This discrimination is achieved on the basis of the difference in the attenuation characteristics of these substances. Discrimination of a variety of nuclear material compounds from shielding/moderating substances (the latter comprising lead or polyethylene for example) is shown to be challenging when using either γ-ray or neutron tomography in isolation of one another. Much-improved contrast is obtained for a combination of these tomographic modalities. This method has potential applications for in-situ, non-destructive assessments in nuclear security, safeguards, waste management and related requirements in the nuclear industry.

An Updated Nuclear Equation of State for Neutron Stars and Supernova Simulations

NASA Astrophysics Data System (ADS)

Meixner, M. A.; Mathews, G. J.; Dalhed, H. E.; Lan, N. Q.

2011-10-01

We present an updated and improved Equation of State based upon the framework originally developed by Bowers & Wilson. The details of the EoS and improvements are described along with a description of how to access this EOS for numerical simulations. Among the improvements are an updated compressibility based upon recent measurements, the possibility of the formation of proton excess (Ye> 0.5) material and an improved treatment of the nuclear statistical equilibrium and the transition to pasta nuclei as the density approaches nuclear matter density. The possibility of a QCD chiral phase transition is also included at densities above nuclear matter density. We show comparisons of this EOS with the other two publicly available equations of state used in supernova collapse simulations. The advantages of the present EoS is that it is easily amenable to phenomenological parameterization to fit observed explosion properties and to accommodate new physical parameters.

SU-F-T-183: Design of a Beam Shaping Assembly of a Compact DD-Based Boron Neutron Capture Therapy System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsieh, M; Liu, Y; Nie, L

Purpose: To design a beam shaping assembly (BSA) to shape the 2.45-MeV neutrons produced by a deuterium-deuterium (DD) neutron generator and to optimize the beam output for boron neutron capture therapy of brain tumors Methods: MCNP is used for this simulation study. The simulation model consists of a neutron surface source that resembles an actual DD source and is surrounded by a BSA. The neutron source emits 2.45-MeV neutrons isotropically. The BSA is composed of a moderator, reflector, collimator and filter. Various types of materials and geometries are tested for each component to optimize the neutron output. Neutron characteristics aremore » measured with an 2×2×2-cm{sup 3} air-equivalent cylinder at the beam exit. The ideal BSA is determined by evaluating the in-air parameters, which include epithermal neutron per source neutron, fast neutron dose per epithermal neutron, and photon dose per epithermal neutron. The parameter values are compared to those recommended by the IAEA. Results: The ideal materials for reflector and thermal neutron filter were lead and cadmium, respectively. The thickness for reflector was 43 cm and for filter was 0.5 mm. At present, the best-performing moderator has 25 cm of AlF{sub 3} and 5 cm of MgF{sub 2}. This layout creates a neutron spectrum that has a peak at approximately 10 keV and produces 1.35E-4 epithermal neutrons per source neutron per cm{sup 2}. Additional neutron characteristics, fast neutrons per epithermal neutron and photon per epithermal neutron, are still under investigation. Conclusion: Working is ongoing to optimize the final layout of the BSA. The neutron spectrum at the beam exit window of the final configuration will have the maximum number of epithermal neutrons and limited photon and fast neutron contaminations within the recommended values by IAEA. Future studies will also include phantom experiments to validate the simulation results.« less

Recently measured large AN for forward neutrons in p↑A collisions at √{sN N}=200 GeV explained through simulations of ultraperipheral collisions and hadronic interactions

NASA Astrophysics Data System (ADS)

Mitsuka, Gaku

2017-04-01

The PHENIX experiment at the BNL Relativistic Heavy Ion Collider recently reported transverse single-spin asymmetry, AN, for forward neutrons in p↑A collisions at √{sNN}=200 GeV . AN in p↑Al and p↑Au collisions were measured as -0.015 and 0.18, respectively. These values are clearly different from the measured AN=-0.08 in p↑p collisions. In this paper, I propose that a large AN for forward neutrons in ultraperipheral p↑A collisions may explain the PHENIX measurements. The proposed model is demonstrated using two Monte Carlo simulations. In the ultraperipheral collision simulation, I use the starlight event generator for the simulation of the virtual photon flux and then use the maid2007 unitary isobar model for the simulation of neutron production in the interactions of a virtual photon with a polarized proton. In the p↑A hadronic interaction simulation, the differential cross sections for forward neutron production are predicted by a simple one-pion exchange model and the Glauber model. The simulated AN values for both the contribution of ultraperipheral collisions and the hadronic interactions are in good agreement with the PHENIX results.

Coupling of TRAC-PF1/MOD2, Version 5.4.25, with NESTLE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knepper, P.L.; Hochreiter, L.E.; Ivanov, K.N.

1999-09-01

A three-dimensional (3-D) spatial kinetics capability within a thermal-hydraulics system code provides a more correct description of the core physics during reactor transients that involve significant variations in the neutron flux distribution. Coupled codes provide the ability to forecast safety margins in a best-estimate manner. The behavior of a reactor core and the feedback to the plant dynamics can be accurately simulated. For each time step, coupled codes are capable of resolving system interaction effects on neutronics feedback and are capable of describing local neutronics effects caused by the thermal hydraulics and neutronics coupling. With the improvements in computational technology,more » modeling complex reactor behaviors with coupled thermal hydraulics and spatial kinetics is feasible. Previously, reactor analysis codes were limited to either a detailed thermal-hydraulics model with simplified kinetics or multidimensional neutron kinetics with a simplified thermal-hydraulics model. The authors discuss the coupling of the Transient Reactor Analysis Code (TRAC)-PF1/MOD2, Version 5.4.25, with the NESTLE code.« less

Development of a technique using MCNPX code for determination of nitrogen content of explosive materials using prompt gamma neutron activation analysis method

NASA Astrophysics Data System (ADS)

Nasrabadi, M. N.; Bakhshi, F.; Jalali, M.; Mohammadi, A.

2011-12-01

Nuclear-based explosive detection methods can detect explosives by identifying their elemental components, especially nitrogen. Thermal neutron capture reactions have been used for detecting prompt gamma 10.8 MeV following radioactive neutron capture by 14N nuclei. We aimed to study the feasibility of using field-portable prompt gamma neutron activation analysis (PGNAA) along with improved nuclear equipment to detect and identify explosives, illicit substances or landmines. A 252Cf radio-isotopic source was embedded in a cylinder made of high-density polyethylene (HDPE) and the cylinder was then placed in another cylindrical container filled with water. Measurements were performed on high nitrogen content compounds such as melamine (C3H6N6). Melamine powder in a HDPE bottle was placed underneath the vessel containing water and the neutron source. Gamma rays were detected using two NaI(Tl) crystals. The results were simulated with MCNP4c code calculations. The theoretical calculations and experimental measurements were in good agreement indicating that this method can be used for detection of explosives and illicit drugs.

Synergistic effect of mixed neutron and gamma irradiation in bipolar operational amplifier OP07

NASA Astrophysics Data System (ADS)

Yan, Liu; Wei, Chen; Shanchao, Yang; Xiaoming, Jin; Chaohui, He

2016-09-01

This paper presents the synergistic effects in bipolar operational amplifier OP07. The radiation effects are studied by neutron beam, gamma ray, and mixed neutron/gamma ray environments. The characterateristics of the synergistic effects are studied through comparison of different experiment results. The results show that the bipolar operational amplifier OP07 exhibited significant synergistic effects in the mixed neutron and gamma irradiation. The bipolar transistor is identified as the most radiation sensitive unit of the operational amplifier. In this paper, a series of simulations are performed on bipolar transistors in different radiation environments. In the theoretical simulation, the geometric model and calculations based on the Medici toolkit are built to study the radiation effects in bipolar components. The effect of mixed neutron and gamma irradiation is simulated based on the understanding of the underlying mechanisms of radiation effects in bipolar transistors. The simulated results agree well with the experimental data. The results of the experiments and simulation indicate that the radiation effects in the bipolar devices subjected to mixed neutron and gamma environments is not a simple combination of total ionizing dose (TID) effects and displacement damage. The data suggests that the TID effect could enhance the displacement damage. The synergistic effect should not be neglected in complex radiation environments.

Mass Yields and Average Total Kinetic Energy Release in Fission for 235U, 238U, and 239Pu

NASA Astrophysics Data System (ADS)

Duke, Dana

2015-10-01

Mass yield distributions and average total kinetic energy (TKE) in neutron induced fission of 235U, 238U, and 239Pu targets were measured with a gridded ionization chamber. Despite decades of fission research, our understanding of how fragment mass yields and TKE depend on incident neutron energy is limited, especially at higher energies (above 5-10 MeV). Improved accuracy in these quantities is important for nuclear technology as it enhances our simulation capabilities and increases the confidence in diagnostic tools. The data can also guide and validate theoretical fission models where the correlation between the fragment mass and TKE is of particular value for constraining models. The Los Alamos Neutron Science Center - Weapons Neutron Research (LANSCE - WNR) provides a neutron beam with energies from thermal to hundreds of MeV, well-suited for filling in the gaps in existing data and exploring fission behavior in the fast neutron region. The results of the studies on target nuclei 235U, 238U, and 239Pu will be presented with a focus on exploring data trends as a function of neutron energy from thermal through 30 MeV. Results indicate clear evidence of structure due to multi-chance fission in the TKE . LA-UR-15-24761.

Beam-contamination-induced compositional alteration and its neutron-atypical consequences in ion simulation of neutron-induced void swelling

DOE PAGES

Gigax, Jonathan G.; Kim, Hyosim; Aydogan, Eda; ...

2017-05-16

Although accelerator-based ion irradiation has been widely accepted to simulate neutron damage, neutron-atypical features need to be carefully investigated. In this study, we have shown that Coulomb force drag by ion beams can introduce significant amounts of carbon, nitrogen, and oxygen into target materials even under ultra-high vacuum conditions. The resulting compositional and microstructural changes dramatically suppress void swelling. By applying a beam-filtering technique, introduction of vacuum contaminants is greatly minimized and the true swelling resistance of the alloys is revealed and matches neutron behavior closely. These findings are a significant step toward developing standardized procedures for emulating neutron damage.

Comparison with simulations to experimental data for photo-neutron reactions using SPring-8 Injector

NASA Astrophysics Data System (ADS)

Asano, Yoshihiro

2017-09-01

Simulations of photo-nuclear reactions by using Monte Carlo codes PHITS and FLUKA have been performed to compare to the measured data at the SPring-8 injector with 250MeV and 961MeV electrons. Measurement data of Bismuth-206 productions due to photo-nuclear reactions of 209Bi(γ,3n) 206Bi and high energy neutron reactions of 209Bi(n,4n)206 Bi at the beam dumps have been compared with the simulations. Neutron leakage spectra outside the shield wall are also compared between experiments and simulations.

Simulations and experiments on RITA-2 at PSI

NASA Astrophysics Data System (ADS)

Klausen, S. N.; Lefmann, K.; McMorrow, D. F.; Altorfer, F.; Janssen, S.; Lüthy, M.

The cold-neutron triple-axis spectrometer RITA-2 designed and built at Riso National Laboratory was installed at the neutron source SINQ at Paul Scherrer Institute in April/May 2001. In connection with the installation of RITA-2, computer simulations were performed using the neutron ray-tracing package McStas. The simulation results are compared to real experimental results obtained with a powder sample. Especially, the flux at the sample position and the resolution function of the spectrometer are investigated.

Focusing adaptive-optics for neutron spectroscopy at extreme conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simeoni, G. G., E-mail: ggsimeoni@outlook.com; Physics Department E13, Technical University of Munich, D-85748 Garching; Valicu, R. G.

2015-12-14

Neutron Spectroscopy employing extreme-conditions sample environments is nowadays a crucial tool for the understanding of fundamental scientific questions as well as for the investigation of materials and chemical-physical properties. For all these kinds of studies, an increased neutron flux over a small sample area is needed. The prototype of a focusing neutron guide component, developed and produced completely at the neutron source FRM II in Garching (Germany), has been installed at the time-of-flight (TOF) disc-chopper neutron spectrometer TOFTOF and came into routine-operation. The design is based on the compressed Archimedes' mirror concept for finite-size divergent sources. It represents a uniquemore » device combining the supermirror technology with Adaptive Optics, suitable for broad-bandwidth thermal-cold TOF neutron spectroscopy (here optimized for 1.4–10 Å). It is able to squeeze the beam cross section down to a square centimeter, with a more than doubled signal-to-background ratio, increased efficiency at high scattering angles, and improved symmetry of the elastic resolution function. We present a comparison between the simulated and measured beam cross sections, as well as the performance of the instrument within real experiments. This work intends to show the unprecedented opportunities achievable at already existing instruments, along with useful guidelines for the design and construction of next-generation neutron spectrometers.« less

Monte Carlo simulation of explosive detection system based on a Deuterium-Deuterium (D-D) neutron generator.

PubMed

Bergaoui, K; Reguigui, N; Gary, C K; Brown, C; Cremer, J T; Vainionpaa, J H; Piestrup, M A

2014-12-01

An explosive detection system based on a Deuterium-Deuterium (D-D) neutron generator has been simulated using the Monte Carlo N-Particle Transport Code (MCNP5). Nuclear-based explosive detection methods can detect explosives by identifying their elemental components, especially nitrogen. Thermal neutron capture reactions have been used for detecting prompt gamma emission (10.82MeV) following radiative neutron capture by (14)N nuclei. The explosive detection system was built based on a fully high-voltage-shielded, axial D-D neutron generator with a radio frequency (RF) driven ion source and nominal yield of about 10(10) fast neutrons per second (E=2.5MeV). Polyethylene and paraffin were used as moderators with borated polyethylene and lead as neutron and gamma ray shielding, respectively. The shape and the thickness of the moderators and shields are optimized to produce the highest thermal neutron flux at the position of the explosive and the minimum total dose at the outer surfaces of the explosive detection system walls. In addition, simulation of the response functions of NaI, BGO, and LaBr3-based γ-ray detectors to different explosives is described. Copyright © 2014 Elsevier Ltd. All rights reserved.

Single-view 3D reconstruction of correlated gamma-neutron sources

DOE PAGES

Monterial, Mateusz; Marleau, Peter; Pozzi, Sara A.

2017-01-05

We describe a new method of 3D image reconstruction of neutron sources that emit correlated gammas (e.g. Cf- 252, Am-Be). This category includes a vast majority of neutron sources important in nuclear threat search, safeguards and non-proliferation. Rather than requiring multiple views of the source this technique relies on the source’s intrinsic property of coincidence gamma and neutron emission. As a result only a single-view measurement of the source is required to perform the 3D reconstruction. In principle, any scatter camera sensitive to gammas and neutrons with adequate timing and interaction location resolution can perform this reconstruction. Using a neutronmore » double scatter technique, we can calculate a conical surface of possible source locations. By including the time to a correlated gamma we further constrain the source location in three-dimensions by solving for the source-to-detector distance along the surface of said cone. As a proof of concept we applied these reconstruction techniques on measurements taken with the the Mobile Imager of Neutrons for Emergency Responders (MINER). Two Cf-252 sources measured at 50 and 60 cm from the center of the detector were resolved in their varying depth with average radial distance relative resolution of 26%. To demonstrate the technique’s potential with an optimized system we simulated the measurement in MCNPX-PoliMi assuming timing resolution of 200 ps (from 2 ns in the current system) and source interaction location resolution of 5 mm (from 3 cm). Furthermore, these simulated improvements in scatter camera performance resulted in radial distance relative resolution decreasing to an average of 11%.« less

Single-view 3D reconstruction of correlated gamma-neutron sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Monterial, Mateusz; Marleau, Peter; Pozzi, Sara A.

We describe a new method of 3D image reconstruction of neutron sources that emit correlated gammas (e.g. Cf- 252, Am-Be). This category includes a vast majority of neutron sources important in nuclear threat search, safeguards and non-proliferation. Rather than requiring multiple views of the source this technique relies on the source’s intrinsic property of coincidence gamma and neutron emission. As a result only a single-view measurement of the source is required to perform the 3D reconstruction. In principle, any scatter camera sensitive to gammas and neutrons with adequate timing and interaction location resolution can perform this reconstruction. Using a neutronmore » double scatter technique, we can calculate a conical surface of possible source locations. By including the time to a correlated gamma we further constrain the source location in three-dimensions by solving for the source-to-detector distance along the surface of said cone. As a proof of concept we applied these reconstruction techniques on measurements taken with the the Mobile Imager of Neutrons for Emergency Responders (MINER). Two Cf-252 sources measured at 50 and 60 cm from the center of the detector were resolved in their varying depth with average radial distance relative resolution of 26%. To demonstrate the technique’s potential with an optimized system we simulated the measurement in MCNPX-PoliMi assuming timing resolution of 200 ps (from 2 ns in the current system) and source interaction location resolution of 5 mm (from 3 cm). Furthermore, these simulated improvements in scatter camera performance resulted in radial distance relative resolution decreasing to an average of 11%.« less

Neutron detection devices with 6LiF converter layers

NASA Astrophysics Data System (ADS)

Finocchiaro, Paolo; Cosentino, Luigi; Meo, Sergio Lo; Nolte, Ralf; Radeck, Desiree

2018-01-01

The demand for new thermal neutron detectors as an alternative to 3He tubes in research, industrial, safety and homeland security applications, is growing. These needs have triggered research and development activities about new generations of thermal neutron detectors, characterized by reasonable efficiency and gamma rejection comparable to 3He tubes. In this paper we show the state of art of a promising lowcost technique, based on commercial solid state silicon detectors coupled with thin neutron converter layers of 6LiF deposited onto carbon fiber substrates. Several configurations were studied with the GEANT4 simulation code, and then calibrated at the PTB Thermal Neutron Calibration Facility. The results show that the measured detection efficiency is well reproduced by the simulations, therefore validating the simulation tool in view of new designs. These neutron detectors have also been tested at neutron beam facilities like ISIS (Rutherford Appleton Laboratory, UK) and n_TOF (CERN) where a few samples are already in operation for beam flux and 2D profile measurements. Forthcoming applications are foreseen for the online monitoring of spent nuclear fuel casks in interim storage sites.

Sci-Sat AM: Brachy - 04: Neutron production around a radiation therapy linac bunker - monte carlo simulations and physical measurements.

PubMed

Khatchadourian, R; Davis, S; Evans, M; Licea, A; Seuntjens, J; Kildea, J

2012-07-01

Photoneutrons are a major component of the equivalent dose in the maze and near the door of linac bunkers. Physical measurements and Monte Carlo (MC) calculations of neutron dose are key for validating bunker design with respect to health regulations. We attempted to use bubble detectors and a 3 He neutron spectrometer to measure neutron equivalent dose and neutron spectra in the maze and near the door of one of our bunkers. We also ran MC simulations with MCNP5 to measure the neutron fluence in the same region. Using a point source of neutrons, a Clinac 1800 linac operating at 10 MV was simulated and the fluence measured at various locations of interest. We describe the challenges faced when measuring dose with bubble detectors in the maze and the complexity of photoneutron spectrometry with linacs operating in pulsed mode. Finally, we report on the development of a userfriendly GUI for shielding calculations based on the NCRP 151 formalism. © 2012 American Association of Physicists in Medicine.

Computational Transport Modeling of High-Energy Neutrons Found in the Space Environment

NASA Technical Reports Server (NTRS)

Cox, Brad; Theriot, Corey A.; Rohde, Larry H.; Wu, Honglu

2012-01-01

The high charge and high energy (HZE) particle radiation environment in space interacts with spacecraft materials and the human body to create a population of neutrons encompassing a broad kinetic energy spectrum. As an HZE ion penetrates matter, there is an increasing chance of fragmentation as penetration depth increases. When an ion fragments, secondary neutrons are released with velocities up to that of the primary ion, giving some neutrons very long penetration ranges. These secondary neutrons have a high relative biological effectiveness, are difficult to effectively shield, and can cause more biological damage than the primary ions in some scenarios. Ground-based irradiation experiments that simulate the space radiation environment must account for this spectrum of neutrons. Using the Particle and Heavy Ion Transport Code System (PHITS), it is possible to simulate a neutron environment that is characteristic of that found in spaceflight. Considering neutron dosimetry, the focus lies on the broad spectrum of recoil protons that are produced in biological targets. In a biological target, dose at a certain penetration depth is primarily dependent upon recoil proton tracks. The PHITS code can be used to simulate a broad-energy neutron spectrum traversing biological targets, and it account for the recoil particle population. This project focuses on modeling a neutron beamline irradiation scenario for determining dose at increasing depth in water targets. Energy-deposition events and particle fluence can be simulated by establishing cross-sectional scoring routines at different depths in a target. This type of model is useful for correlating theoretical data with actual beamline radiobiology experiments. Other work exposed human fibroblast cells to a high-energy neutron source to study micronuclei induction in cells at increasing depth behind water shielding. Those findings provide supporting data describing dose vs. depth across a water-equivalent medium. This poster presents PHITS data suggesting an increase in dose, up to roughly 10 cm depth, followed by a continual decrease as neutrons come to a stop in the target.

Monte Carlo calculations of lung dose in ORNL phantom for boron neutron capture therapy.

PubMed

Krstic, D; Markovic, V M; Jovanovic, Z; Milenkovic, B; Nikezic, D; Atanackovic, J

2014-10-01

Monte Carlo simulations were performed to evaluate dose for possible treatment of cancers by boron neutron capture therapy (BNCT). The computational model of male Oak Ridge National Laboratory (ORNL) phantom was used to simulate tumours in the lung. Calculations have been performed by means of the MCNP5/X code. In this simulation, two opposite neutron beams were considered, in order to obtain uniform neutron flux distribution inside the lung. The obtained results indicate that the lung cancer could be treated by BNCT under the assumptions of calculations. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Energy and direction distribution of neutrons in workplace fields: implication of the results from the EVIDOS project for the set-up of simulated workplace fields.

PubMed

Luszik-Bhadra, M; Lacoste, V; Reginatto, M; Zimbal, A

2007-01-01

Workplace neutron spectra from nuclear facilities obtained within the European project EVIDOS are compared with those of the simulated workplace fields CANEL and SIGMA and fields set-up with radionuclide sources at the PTB. Contributions of neutrons to ambient dose equivalent and personal dose equivalent are given in three energy intervals (for thermal, intermediate and fast neutrons) together with the corresponding direction distribution, characterised by three different types of distributions (isotropic, weakly directed and directed). The comparison shows that none of the simulated workplace fields investigated here can model all the characteristics of the fields observed at power reactors.

Secondary Neutron Doses to Pediatric Patients During Intracranial Proton Therapy: Monte Carlo Simulation of the Neutron Energy Spectrum and its Organ Doses.

PubMed

Matsumoto, Shinnosuke; Koba, Yusuke; Kohno, Ryosuke; Lee, Choonsik; Bolch, Wesley E; Kai, Michiaki

2016-04-01

Proton therapy has the physical advantage of a Bragg peak that can provide a better dose distribution than conventional x-ray therapy. However, radiation exposure of normal tissues cannot be ignored because it is likely to increase the risk of secondary cancer. Evaluating secondary neutrons generated by the interaction of the proton beam with the treatment beam-line structure is necessary; thus, performing the optimization of radiation protection in proton therapy is required. In this research, the organ dose and energy spectrum were calculated from secondary neutrons using Monte Carlo simulations. The Monte Carlo code known as the Particle and Heavy Ion Transport code System (PHITS) was used to simulate the transport proton and its interaction with the treatment beam-line structure that modeled the double scattering body of the treatment nozzle at the National Cancer Center Hospital East. The doses of the organs in a hybrid computational phantom simulating a 5-y-old boy were calculated. In general, secondary neutron doses were found to decrease with increasing distance to the treatment field. Secondary neutron energy spectra were characterized by incident neutrons with three energy peaks: 1×10, 1, and 100 MeV. A block collimator and a patient collimator contributed significantly to organ doses. In particular, the secondary neutrons from the patient collimator were 30 times higher than those from the first scatter. These results suggested that proactive protection will be required in the design of the treatment beam-line structures and that organ doses from secondary neutrons may be able to be reduced.

Improvements in Gravitational-wave Sky Localization with Expanded Networks of Interferometers

NASA Astrophysics Data System (ADS)

Pankow, Chris; Chase, Eve A.; Coughlin, Scott; Zevin, Michael; Kalogera, Vassiliki

2018-02-01

A milestone of multi-messenger astronomy has been achieved with the detection of gravitational waves from a binary neutron star merger accompanied by observations of several associated electromagnetic counterparts. Joint observations can reveal details of the engines that drive the electromagnetic and gravitational-wave emission. However, locating and identifying an electromagnetic counterpart to a gravitational-wave event is heavily reliant on localization of the source through gravitational-wave information. We explore the sky localization of a simulated set of neutron star mergers as the worldwide network of gravitational-wave detectors evolves through the next decade, performing the first such study for neutron star–black hole binary sources. Currently, three detectors are observing with additional detectors in Japan and India expected to become operational in the coming years. With three detectors, we recover a median neutron star–black hole binary sky localization of 60 deg2 at the 90% credible level. As all five detectors become operational, sources can be localized to a median of 11 deg2 on the sky.

The Application of Neutron Transport Green's Functions to Threat Scenario Simulation

NASA Astrophysics Data System (ADS)

Thoreson, Gregory G.; Schneider, Erich A.; Armstrong, Hirotatsu; van der Hoeven, Christopher A.

2015-02-01

Radiation detectors provide deterrence and defense against nuclear smuggling attempts by scanning vehicles, ships, and pedestrians for radioactive material. Understanding detector performance is crucial to developing novel technologies, architectures, and alarm algorithms. Detection can be modeled through radiation transport simulations; however, modeling a spanning set of threat scenarios over the full transport phase-space is computationally challenging. Previous research has demonstrated Green's functions can simulate photon detector signals by decomposing the scenario space into independently simulated submodels. This paper presents decomposition methods for neutron and time-dependent transport. As a result, neutron detector signals produced from full forward transport simulations can be efficiently reconstructed by sequential application of submodel response functions.

Applications of a Fast Neutron Detector System to Verification of Special Nuclear Materials

NASA Astrophysics Data System (ADS)

Mayo, Douglas R.; Byrd, Roger C.; Ensslin, Norbert; Krick, Merlyn S.; Mercer, David J.; Miller, Michael C.; Prettyman, Thomas H.; Russo, Phyllis A.

1998-04-01

An array of boron-loaded plastic optically coupled to bismuth germanate scintillators has been developed to detect neutrons for measurement of special nuclear materials. The phoswiched detection system has the advantage of a high neutron detection efficiency and short die-away time. This is achieved by mixing the moderator (plastic) and the detector (^10B) at the molecular level. Simulations indicate that the neutron capture probabilities equal or exceed those of the current thermal neutron multiplicity techniques which have the moderator (polyethylene) and detectors (^3He gas proportional tubes) macroscopically separate. Experiments have been performed to characterize the response of these detectors and validate computer simulations. The fast neutron detection system may be applied to the quantitative assay of plutonium in high (α,n) backgrounds, with emphasis on safeguards and enviromental scenarios. Additional applications of the insturment, in a non-quantative mode, has been tested for possible verification activities involving dismantlement of nuclear weapons. A description of the detector system, simulations and preliminary data will be presented.

Production of neutron-rich nuclei approaching r-process by gamma-induced fission of 238U at ELI-NP

NASA Astrophysics Data System (ADS)

Mei, Bo; Balabanski, Dimiter; Constantin, Paul; Anh Le, Tuan; Viet Cuong, Phan

2018-05-01

The investigation of neutron-rich exotic nuclei is crucial not only for nuclear physics but also for nuclear astrophysics. Experimentally, only few neutron-rich nuclei near the stability have been studied, however, most neutron-rich nuclei have not been measured due to their small production cross sections as well as short half-lives. At ELI-NP, gamma beams with high intensities will open new opportunities to investigate very neutron-rich fragments produced by photofission of 238U targets in a gas cell. Based on some simulations, a novel gas cell has been designed to produce, stop and extract 238U photofission fragments. The extraction time and efficiency of photofission fragments have been optimized by using SIMION simulations. According to these simulations, a high extraction efficiency and a short extraction time can be achieved for 238U photofission fragments in the gas cell, which will allow one to measure very neutron-rich fragments with short half-lives by using the IGISOL facility proposed at ELI-NP.

Thermal Neutron Radiography using a High-flux Compact Neutron Generator

NASA Astrophysics Data System (ADS)

Taylor, Michael; Sengbusch, Evan; Seyfert, Chris; Moll, Eli; Radel, Ross

A novel neutron imaging system has been designed and constructed by Phoenix Nuclear Labs to investigate specimens when conventional X-ray imaging will not suffice. A first-generation electronic neutron generator is actively being used by the United States Army and is coupled with activation films for neutron radiography to inspect munitions and other critical defence and aerospace components. A second-generation system has been designed to increase the total neutron output from an upgraded gaseous deuterium target to 5×1011 DD n/s, generating higher neutron flux at the imaging plane and dramatically reducing interrogation time, while maintaining high spatial resolution and low geometric unsharpness. A description of the neutron generator and imaging system, including the beamline, target and detector platform, is given in this paper. State of the art neutron moderators, collimators and imaging detector components are also discussed in the context of increasing specimen throughput and optimizing image quality. Neutron radiographs captured with the neutron radiography system will be further compared against simulated images using the MCNP nuclear simulation code.

Performance verification of an epithermal neutron flux monitor using accelerator-based BNCT neutron sources

NASA Astrophysics Data System (ADS)

Guan, X.; Murata, I.; Wang, T.

2017-09-01

The performance of an epithermal neutron flux monitor developed for boron neutron capture therapy (BNCT) is verified by Monte Carlo simulations using accelerator-based neutron sources (ABNSs). The results indicate that the developed epithermal neutron flux monitor works well and it can be efficiently used in practical applications to measure the epithermal neutron fluxes of ABNSs in a high accuracy.

Monte-Carlo gamma response simulation of fast/thermal neutron interactions with soil elements

USDA-ARS?s Scientific Manuscript database

Soil elemental analysis using characteristic gamma rays induced by neutrons is an effective method of in situ soil content determination. The nuclei of soil elements irradiated by neutrons issue characteristic gamma rays due to both inelastic neutron scattering (e.g., Si, C) and thermal neutron capt...

A D-D/D-T fusion reaction based neutron generator system for liver tumor BNCT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koivunoro, H.; Lou, T.P.; Leung, K. N.

2003-04-02

Boron-neutron capture therapy (BNCT) is an experimental radiation treatment modality used for highly malignant tumor treatments. Prior to irradiation with low energetic neutrons, a 10B compound is located selectively in the tumor cells. The effect of the treatment is based on the high LET radiation released in the {sup 10}B(n,{alpha}){sup 7}Li reaction with thermal neutrons. BNCT has been used experimentally for brain tumor and melanoma treatments. Lately applications of other severe tumor type treatments have been introduced. Results have shown that liver tumors can also be treated by BNCT. At Lawrence Berkeley National Laboratory, various compact neutron generators based onmore » D-D or D-T fusion reactions are being developed. The earlier theoretical studies of the D-D or D-T fusion reaction based neutron generators have shown that the optimal moderator and reflector configuration for brain tumor BNCT can be created. In this work, the applicability of 2.5 MeV neutrons for liver tumor BNCT application was studied. The optimal neutron energy for external liver treatments is not known. Neutron beams of different energies (1eV < E < 100 keV) were simulated and the dose distribution in the liver was calculated with the MCNP simulation code. In order to obtain the optimal neutron energy spectrum with the D-D neutrons, various moderator designs were performed using MCNP simulations. In this article the neutron spectrum and the optimized beam shaping assembly for liver tumor treatments is presented.« less

Simulation study of accelerator based quasi-mono-energetic epithermal neutron beams for BNCT.

PubMed

Adib, M; Habib, N; Bashter, I I; El-Mesiry, M S; Mansy, M S

2016-01-01

Filtered neutron techniques were applied to produce quasi-mono-energetic neutron beams in the energy range of 1.5-7.5 keV at the accelerator port using the generated neutron spectrum from a Li (p, n) Be reaction. A simulation study was performed to characterize the filter components and transmitted beam lines. The feature of the filtered beams is detailed in terms of optimal thickness of the primary and additive components. A computer code named "QMNB-AS" was developed to carry out the required calculations. The filtered neutron beams had high purity and intensity with low contamination from the accompanying thermal, fast neutrons and γ-rays. Copyright © 2015 Elsevier Ltd. All rights reserved.

Superconducting magnetic Wollaston prism for neutron spin encoding

NASA Astrophysics Data System (ADS)

Li, F.; Parnell, S. R.; Hamilton, W. A.; Maranville, B. B.; Wang, T.; Semerad, R.; Baxter, D. V.; Cremer, J. T.; Pynn, R.

2014-05-01

A magnetic Wollaston prism can spatially split a polarized neutron beam into two beams with different neutron spin states, in a manner analogous to an optical Wollaston prism. Such a Wollaston prism can be used to encode the trajectory of neutrons into the Larmor phase associated with their spin degree of freedom. This encoding can be used for neutron phase-contrast radiography and in spin echo scattering angle measurement (SESAME). In this paper, we show that magnetic Wollaston prisms with highly uniform magnetic fields and low Larmor phase aberration can be constructed to preserve neutron polarization using high temperature superconducting (HTS) materials. The Meissner effect of HTS films is used to confine magnetic fields produced electromagnetically by current-carrying HTS tape wound on suitably shaped soft iron pole pieces. The device is cooled to ˜30 K by a closed cycle refrigerator, eliminating the need to replenish liquid cryogens and greatly simplifying operation and maintenance. A HTS film ensures that the magnetic field transition within the prism is sharp, well-defined, and planar due to the Meissner effect. The spin transport efficiency across the device was measured to be ˜98.5% independent of neutron wavelength and energizing current. The position-dependent Larmor phase of neutron spins was measured at the NIST Center for Neutron Research facility and found to agree well with detailed simulations. The phase varies linearly with horizontal position, as required, and the neutron beam shows little depolarization. Consequently, the device has advantages over existing devices with similar functionality and provides the capability for a large neutron beam (20 mm × 30 mm) and an increase in length scales accessible to SESAME to beyond 10 μm. With further improvements of the external coupling guide field in the prototype device, a larger neutron beam could be employed.

Superconducting magnetic Wollaston prism for neutron spin encoding.

PubMed

Li, F; Parnell, S R; Hamilton, W A; Maranville, B B; Wang, T; Semerad, R; Baxter, D V; Cremer, J T; Pynn, R

2014-05-01

A magnetic Wollaston prism can spatially split a polarized neutron beam into two beams with different neutron spin states, in a manner analogous to an optical Wollaston prism. Such a Wollaston prism can be used to encode the trajectory of neutrons into the Larmor phase associated with their spin degree of freedom. This encoding can be used for neutron phase-contrast radiography and in spin echo scattering angle measurement (SESAME). In this paper, we show that magnetic Wollaston prisms with highly uniform magnetic fields and low Larmor phase aberration can be constructed to preserve neutron polarization using high temperature superconducting (HTS) materials. The Meissner effect of HTS films is used to confine magnetic fields produced electromagnetically by current-carrying HTS tape wound on suitably shaped soft iron pole pieces. The device is cooled to ~30 K by a closed cycle refrigerator, eliminating the need to replenish liquid cryogens and greatly simplifying operation and maintenance. A HTS film ensures that the magnetic field transition within the prism is sharp, well-defined, and planar due to the Meissner effect. The spin transport efficiency across the device was measured to be ~98.5% independent of neutron wavelength and energizing current. The position-dependent Larmor phase of neutron spins was measured at the NIST Center for Neutron Research facility and found to agree well with detailed simulations. The phase varies linearly with horizontal position, as required, and the neutron beam shows little depolarization. Consequently, the device has advantages over existing devices with similar functionality and provides the capability for a large neutron beam (20 mm × 30 mm) and an increase in length scales accessible to SESAME to beyond 10 μm. With further improvements of the external coupling guide field in the prototype device, a larger neutron beam could be employed.

Blandford's argument: The strongest continuous gravitational wave signal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knispel, Benjamin; Allen, Bruce

2008-08-15

For a uniform population of neutron stars whose spin-down is dominated by the emission of gravitational radiation, an old argument of Blandford states that the expected gravitational-wave amplitude of the nearest source is independent of the deformation and rotation frequency of the objects. Recent work has improved and extended this argument to set upper limits on the expected amplitude from neutron stars that also emit electromagnetic radiation. We restate these arguments in a more general framework, and simulate the evolution of such a population of stars in the gravitational potential of our galaxy. The simulations allow us to test themore » assumptions of Blandford's argument on a realistic model of our galaxy. We show that the two key assumptions of the argument (two dimensionality of the spatial distribution and a steady-state frequency distribution) are in general not fulfilled. The effective scaling dimension D of the spatial distribution of neutron stars is significantly larger than two, and for frequencies detectable by terrestrial instruments the frequency distribution is not in a steady state unless the ellipticity is unrealistically large. Thus, in the cases of most interest, the maximum expected gravitational-wave amplitude does have a strong dependence on the deformation and rotation frequency of the population. The results strengthen the previous upper limits on the expected gravitational-wave amplitude from neutron stars by a factor of 6 for realistic values of ellipticity.« less

Neutron dose estimation in a zero power nuclear reactor

NASA Astrophysics Data System (ADS)

Triviño, S.; Vedelago, J.; Cantargi, F.; Keil, W.; Figueroa, R.; Mattea, F.; Chautemps, A.; Santibañez, M.; Valente, M.

2016-10-01

This work presents the characterization and contribution of neutron and gamma components to the absorbed dose in a zero power nuclear reactor. A dosimetric method based on Fricke gel was implemented to evaluate the separation between dose components in the mixed field. The validation of this proposed method was performed by means of direct measurements of neutron flux in different positions using Au and Mg-Ni activation foils. Monte Carlo simulations were conversely performed using the MCNP main code with a dedicated subroutine to incorporate the exact complete geometry of the nuclear reactor facility. Once nuclear fuel elements were defined, the simulations computed the different contributions to the absorbed dose in specific positions inside the core. Thermal/epithermal contributions of absorbed dose were assessed by means of Fricke gel dosimetry using different isotopic compositions aimed at modifying the sensitivity of the dosimeter for specific dose components. Clear distinctions between gamma and neutron capture dose were obtained. Both Monte Carlo simulations and experimental results provided reliable estimations about neutron flux rate as well as dose rate during the reactor operation. Simulations and experimental results are in good agreement in every positions measured and simulated in the core.

Generation of nanosecond neutron pulses in vacuum accelerating tubes

NASA Astrophysics Data System (ADS)

Didenko, A. N.; Shikanov, A. E.; Rashchikov, V. I.; Ryzhkov, V. I.; Shatokhin, V. L.

2014-06-01

The generation of neutron pulses with a duration of 1-100 ns using small vacuum accelerating tubes is considered. Two physical models of acceleration of short deuteron bunches in pulse neutron generators are described. The dependences of an instantaneous neutron flux in accelerating tubes on the parameters of pulse neutron generators are obtained using computer simulation. The results of experimental investigation of short-pulse neutron generators based on the accelerating tube with a vacuum-arc deuteron source, connected in the circuit with a discharge peaker, and an accelerating tube with a laser deuteron source, connected according to the Arkad'ev-Marx circuit, are given. In the experiments, the neutron yield per pulse reached 107 for a pulse duration of 10-100 ns. The resultant experimental data are in satisfactory agreement with the results of computer simulation.

Precise calculations in simulations of the interaction of low energy neutrons with nano-dispersed media

NASA Astrophysics Data System (ADS)

Artem'ev, V. A.; Nezvanov, A. Yu.; Nesvizhevsky, V. V.

2016-01-01

We discuss properties of the interaction of slow neutrons with nano-dispersed media and their application for neutron reflectors. In order to increase the accuracy of model simulation of the interaction of neutrons with nanopowders, we perform precise quantum mechanical calculation of potential scattering of neutrons on single nanoparticles using the method of phase functions. We compare results of precise calculations with those performed within first Born approximation for nanodiamonds with the radius of 2-5 nm and for neutron energies 3 × 10-7-10-3 eV. Born approximation overestimates the probability of scattering to large angles, while the accuracy of evaluation of integral characteristics (cross sections, albedo) is acceptable. Using Monte-Carlo method, we calculate albedo of neutrons from different layers of piled up diamond nanopowder.

Impedance measurements of the extraction kicker system for the rapid cycling synchrotron of China Spallation Neutron Source

NASA Astrophysics Data System (ADS)

Huang, Liang-Sheng; Wang, Sheng; Liu, Yu-Dong; Li, Yong; Liu, Ren-Hong; Xiao, Ou-Zheng

2016-04-01

The fast extraction kicker system is one of the most important accelerator components and the main source of impedance in the Rapid Cycling Synchrotron of the China Spallation Neutron Source. It is necessary to understand the kicker impedance before its installation into the tunnel. Conventional and improved wire methods are employed in the impedance measurement. The experimental results for the kicker impedance are explained by comparison with simulation using CST PARTICLE STUDIO. The simulation and measurement results confirm that the window-frame ferrite geometry and the end plate are the important structures causing coupling impedance. It is proved in the measurements that the mismatching from the power form network to the kicker leads to a serious oscillation sideband of the longitudinal and vertical impedance and the oscillation can be reduced by ferrite absorbing material. Supported by National Natural Science Foundation of China (11175193, 11275221)

Enhanced Dynamics of Hydrated tRNA on Nanodiamond Surfaces: A Combined Neutron Scattering and MD Simulation Study.

PubMed

Dhindsa, Gurpreet K; Bhowmik, Debsindhu; Goswami, Monojoy; O'Neill, Hugh; Mamontov, Eugene; Sumpter, Bobby G; Hong, Liang; Ganesh, Panchapakesan; Chu, Xiang-Qiang

2016-09-14

Nontoxic, biocompatible nanodiamonds (ND) have recently been implemented in rational, systematic design of optimal therapeutic use in nanomedicines. However, hydrophilicity of the ND surface strongly influences structure and dynamics of biomolecules that restrict in situ applications of ND. Therefore, fundamental understanding of the impact of hydrophilic ND surface on biomolecules at the molecular level is essential. For tRNA, we observe an enhancement of dynamical behavior in the presence of ND contrary to generally observed slow motion at strongly interacting interfaces. We took advantage of neutron scattering experiments and computer simulations to demonstrate this atypical faster dynamics of tRNA on ND surface. The strong attractive interactions between ND, tRNA, and water give rise to unlike dynamical behavior and structural changes of tRNA in front of ND compared to without ND. Our new findings may provide new design principles for safer, improved drug delivery platforms.

The study of in vivo quantification of aluminum (Al) in human bone with a compact DD generator-based neutron activation analysis (NAA) system.

PubMed

Byrne, Patrick; Mostafaei, Farshad; Liu, Yingzi; Blake, Scott P; Koltick, David; Nie, Linda H

2016-05-01

The feasibility and methodology of using a compact DD generator-based neutron activation analysis system to measure aluminum in hand bone has been investigated. Monte Carlo simulations were used to simulate the moderator, reflector, and shielding assembly and to estimate the radiation dose. A high purity germanium (HPGe) detector was used to detect the Al gamma ray signals. The minimum detectable limit (MDL) was found to be 11.13 μg g(-1) dry bone (ppm). An additional HPGe detector would improve the MDL by a factor of 1.4, to 7.9 ppm. The equivalent dose delivered to the irradiated hand was calculated by Monte Carlo to be 11.9 mSv. In vivo bone aluminum measurement with the DD generator was found to be feasible among general population with an acceptable dose to the subject.

Time-dependent Hartree-Fock approach to nuclear ``pasta'' at finite temperature

NASA Astrophysics Data System (ADS)

Schuetrumpf, B.; Klatt, M. A.; Iida, K.; Maruhn, J. A.; Mecke, K.; Reinhard, P.-G.

2013-05-01

We present simulations of neutron-rich matter at subnuclear densities, like supernova matter, with the time-dependent Hartree-Fock approximation at temperatures of several MeV. The initial state consists of α particles randomly distributed in space that have a Maxwell-Boltzmann distribution in momentum space. Adding a neutron background initialized with Fermi distributed plane waves the calculations reflect a reasonable approximation of astrophysical matter. This matter evolves into spherical, rod-like, and slab-like shapes and mixtures thereof. The simulations employ a full Skyrme interaction in a periodic three-dimensional grid. By an improved morphological analysis based on Minkowski functionals, all eight pasta shapes can be uniquely identified by the sign of only two valuations, namely the Euler characteristic and the integral mean curvature. In addition, we propose the variance in the cell density distribution as a measure to distinguish pasta matter from uniform matter.

High Fidelity Ion Beam Simulation of High Dose Neutron Irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Was, Gary; Wirth, Brian; Motta, Athur

The objective of this proposal is to demonstrate the capability to predict the evolution of microstructure and properties of structural materials in-reactor and at high doses, using ion irradiation as a surrogate for reactor irradiations. “Properties” includes both physical properties (irradiated microstructure) and the mechanical properties of the material. Demonstration of the capability to predict properties has two components. One is ion irradiation of a set of alloys to yield an irradiated microstructure and corresponding mechanical behavior that are substantially the same as results from neutron exposure in the appropriate reactor environment. Second is the capability to predict the irradiatedmore » microstructure and corresponding mechanical behavior on the basis of improved models, validated against both ion and reactor irradiations and verified against ion irradiations. Taken together, achievement of these objectives will yield an enhanced capability for simulating the behavior of materials in reactor irradiations.« less

A Monte Carlo simulation study for the gamma-ray/neutron dual-particle imager using rotational modulation collimator (RMC).

PubMed

Kim, Hyun Suk; Choi, Hong Yeop; Lee, Gyemin; Ye, Sung-Joon; Smith, Martin B; Kim, Geehyun

2018-03-01

The aim of this work is to develop a gamma-ray/neutron dual-particle imager, based on rotational modulation collimators (RMCs) and pulse shape discrimination (PSD)-capable scintillators, for possible applications for radioactivity monitoring as well as nuclear security and safeguards. A Monte Carlo simulation study was performed to design an RMC system for the dual-particle imaging, and modulation patterns were obtained for gamma-ray and neutron sources in various configurations. We applied an image reconstruction algorithm utilizing the maximum-likelihood expectation-maximization method based on the analytical modeling of source-detector configurations, to the Monte Carlo simulation results. Both gamma-ray and neutron source distributions were reconstructed and evaluated in terms of signal-to-noise ratio, showing the viability of developing an RMC-based gamma-ray/neutron dual-particle imager using PSD-capable scintillators.

The CIELO collaboration: Progress in international evaluations of neutron reactions on Oxygen, Iron, Uranium and Plutonium

DOE PAGES

Chadwick, M. B.; Capote, R.; Trkov, A.; ...

2017-01-01

The CIELO collaboration has studied neutron cross sections on nuclides that significantly impact criticality in nuclear technologies - 16O, 56Fe, 235;8U and 239Pu - with the aim of improving the accuracy of the data and resolving previous discrepancies in our understanding. This multi-laboratory pilot project, coordinated via the OECD/NEA Working Party on Evaluation Cooperation (WPEC) Subgroup 40 with support also from the IAEA, has motivated experimental and theoretical work and led to suites of new evaluated libraries that accurately reflect measured data and also perform well in integral simulations of criticality.

The CIELO collaboration: Progress in international evaluations of neutron reactions on Oxygen, Iron, Uranium and Plutonium

NASA Astrophysics Data System (ADS)

Chadwick, M. B.; Capote, R.; Trkov, A.; Kahler, A. C.; Herman, M. W.; Brown, D. A.; Hale, G. M.; Pigni, M.; Dunn, M.; Leal, L.; Plompen, A.; Schillebeeck, P.; Hambsch, F.-J.; Kawano, T.; Talou, P.; Jandel, M.; Mosby, S.; Lestone, J.; Neudecker, D.; Rising, M.; Paris, M.; Nobre, G. P. A.; Arcilla, R.; Kopecky, S.; Giorginis, G.; Cabellos, O.; Hill, I.; Dupont, E.; Danon, Y.; Jing, Q.; Zhigang, G.; Tingjin, L.; Hanlin, L.; Xichao, R.; Haicheng, W.; Sin, M.; Bauge, E.; Romain, P.; Morillon, B.; Noguere, G.; Jacqmin, R.; Bouland, O.; De Saint Jean, C.; Pronyaev, V. G.; Ignatyuk, A.; Yokoyama, K.; Ishikawa, M.; Fukahori, T.; Iwamoto, N.; Iwamoto, O.; Kuneada, S.; Lubitz, C. R.; Palmiotti, G.; Salvatores, M.; Kodeli, I.; Kiedrowski, B.; Roubtsov, D.; Thompson, I.; Quaglioni, S.; Kim, H. I.; Lee, Y. O.; Koning, A. J.; Carlson, A.; Fischer, U.; Sirakov, I.

2017-09-01

The CIELO collaboration has studied neutron cross sections on nuclides that significantly impact criticality in nuclear technologies - 16O, 56Fe, 235,8U and 239Pu - with the aim of improving the accuracy of the data and resolving previous discrepancies in our understanding. This multi-laboratory pilot project, coordinated via the OECD/NEA Working Party on Evaluation Cooperation (WPEC) Subgroup 40 with support also from the IAEA, has motivated experimental and theoretical work and led to suites of new evaluated libraries that accurately reflect measured data and also perform well in integral simulations of criticality.

A study on the optimum fast neutron flux for boron neutron capture therapy of deep-seated tumors.

PubMed

Rasouli, Fatemeh S; Masoudi, S Farhad

2015-02-01

High-energy neutrons, named fast neutrons which have a number of undesirable biological effects on tissue, are a challenging problem in beam designing for Boron Neutron Capture Therapy, BNCT. In spite of this fact, there is not a widely accepted criterion to guide the beam designer to determine the appropriate contribution of fast neutrons in the spectrum. Although a number of researchers have proposed a target value for the ratio of fast neutron flux to epithermal neutron flux, it can be shown that this criterion may not provide the optimum treatment condition. This simulation study deals with the determination of the optimum contribution of fast neutron flux in the beam for BNCT of deep-seated tumors. Since the dose due to these high-energy neutrons damages shallow tissues, delivered dose to skin is considered as a measure for determining the acceptability of the designed beam. To serve this purpose, various beam shaping assemblies that result in different contribution of fast neutron flux are designed. The performances of the neutron beams corresponding to such configurations are assessed in a simulated head phantom. It is shown that the previously used criterion, which suggests a limit value for the contribution of fast neutrons in beam, does not necessarily provide the optimum condition. Accordingly, it is important to specify other complementary limits considering the energy of fast neutrons. By analyzing various neutron spectra, two limits on fast neutron flux are proposed and their validity is investigated. The results show that considering these limits together with the widely accepted IAEA criteria makes it possible to have a more realistic assessment of sufficiency of the designed beam. Satisfying these criteria not only leads to reduction of delivered dose to skin, but also increases the advantage depth in tissue and delivered dose to tumor during the treatment time. The Monte Carlo Code, MCNP-X, is used to perform these simulations. Copyright © 2014 Elsevier Ltd. All rights reserved.

McStas 1.1: a tool for building neutron Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Lefmann, K.; Nielsen, K.; Tennant, A.; Lake, B.

2000-03-01

McStas is a project to develop general tools for the creation of simulations of neutron scattering experiments. In this paper, we briefly introduce McStas and describe a particular application of the program: the Monte Carlo calculation of the resolution function of a standard triple-axis neutron scattering instrument. The method compares well with the analytical calculations of Popovici.

Epithermal neutron formation for boron neutron capture therapy by adiabatic resonance crossing concept

NASA Astrophysics Data System (ADS)

Khorshidi, A.; Ghafoori-Fard, H.; Sadeghi, M.

2014-05-01

Low-energy protons from the cyclotron in the range of 15-30 MeV and low current have been simulated on beryllium (Be) target with a lead moderator around the target. This research was accomplished to design an epithermal neutron beam for Boron Neutron Capture Therapy (BNCT) using the moderated neutron on the average produced from 9Be target via (p, xn) reaction in Adiabatic Resonance Crossing (ARC) concept. Generation of neutron to proton ratio, energy distribution, flux and dose components in head phantom have been simulated by MCNP5 code. The reflector and collimator were designed in prevention and collimation of derivation neutrons from proton bombarding. The scalp-skull-brain phantom consisting of bone and brain equivalent material has been simulated in order to evaluate the dosimetric effect on the brain. Results of this analysis demonstrated while the proton energy decreased, the dose factor altered according to filters thickness. The maximum epithermal flux revealed using fluental, Fe and bismuth (Bi) filters with thicknesses of 9.4, 3 and 2 cm, respectively and also the epithermal to thermal neutron flux ratio was 103.85. The potential of the ARC method to replace or complement the current reactor-based supply sources of BNCT purposes.

Monte carlo simulations of the n_TOF lead spallation target with the Geant4 toolkit: A benchmark study

NASA Astrophysics Data System (ADS)

Lerendegui-Marco, J.; Cortés-Giraldo, M. A.; Guerrero, C.; Quesada, J. M.; Meo, S. Lo; Massimi, C.; Barbagallo, M.; Colonna, N.; Mancussi, D.; Mingrone, F.; Sabaté-Gilarte, M.; Vannini, G.; Vlachoudis, V.; Aberle, O.; Andrzejewski, J.; Audouin, L.; Bacak, M.; Balibrea, J.; Bečvář, F.; Berthoumieux, E.; Billowes, J.; Bosnar, D.; Brown, A.; Caamaño, M.; Calviño, F.; Calviani, M.; Cano-Ott, D.; Cardella, R.; Casanovas, A.; Cerutti, F.; Chen, Y. H.; Chiaveri, E.; Cortés, G.; Cosentino, L.; Damone, L. A.; Diakaki, M.; Domingo-Pardo, C.; Dressler, R.; Dupont, E.; Durán, I.; Fernández-Domínguez, B.; Ferrari, A.; Ferreira, P.; Finocchiaro, P.; Göbel, K.; Gómez-Hornillos, M. B.; García, A. R.; Gawlik, A.; Gilardoni, S.; Glodariu, T.; Gonçalves, I. F.; González, E.; Griesmayer, E.; Gunsing, F.; Harada, H.; Heinitz, S.; Heyse, J.; Jenkins, D. G.; Jericha, E.; Käppeler, F.; Kadi, Y.; Kalamara, A.; Kavrigin, P.; Kimura, A.; Kivel, N.; Kokkoris, M.; Krtička, M.; Kurtulgil, D.; Leal-Cidoncha, E.; Lederer, C.; Leeb, H.; Lonsdale, S. J.; Macina, D.; Marganiec, J.; Martínez, T.; Masi, A.; Mastinu, P.; Mastromarco, M.; Maugeri, E. A.; Mazzone, A.; Mendoza, E.; Mengoni, A.; Milazzo, P. M.; Musumarra, A.; Negret, A.; Nolte, R.; Oprea, A.; Patronis, N.; Pavlik, A.; Perkowski, J.; Porras, I.; Praena, J.; Radeck, D.; Rauscher, T.; Reifarth, R.; Rout, P. C.; Rubbia, C.; Ryan, J. A.; Saxena, A.; Schillebeeckx, P.; Schumann, D.; Smith, A. G.; Sosnin, N. V.; Stamatopoulos, A.; Tagliente, G.; Tain, J. L.; Tarifeño-Saldivia, A.; Tassan-Got, L.; Valenta, S.; Variale, V.; Vaz, P.; Ventura, A.; Vlastou, R.; Wallner, A.; Warren, S.; Woods, P. J.; Wright, T.; Žugec, P.

2017-09-01

Monte Carlo (MC) simulations are an essential tool to determine fundamental features of a neutron beam, such as the neutron flux or the γ-ray background, that sometimes can not be measured or at least not in every position or energy range. Until recently, the most widely used MC codes in this field had been MCNPX and FLUKA. However, the Geant4 toolkit has also become a competitive code for the transport of neutrons after the development of the native Geant4 format for neutron data libraries, G4NDL. In this context, we present the Geant4 simulations of the neutron spallation target of the n_TOF facility at CERN, done with version 10.1.1 of the toolkit. The first goal was the validation of the intra-nuclear cascade models implemented in the code using, as benchmark, the characteristics of the neutron beam measured at the first experimental area (EAR1), especially the neutron flux and energy distribution, and the time distribution of neutrons of equal kinetic energy, the so-called Resolution Function. The second goal was the development of a Monte Carlo tool aimed to provide useful calculations for both the analysis and planning of the upcoming measurements at the new experimental area (EAR2) of the facility.

General relativistic viscous hydrodynamics of differentially rotating neutron stars

NASA Astrophysics Data System (ADS)

Shibata, Masaru; Kiuchi, Kenta; Sekiguchi, Yu-ichiro

2017-04-01

Employing a simplified version of the Israel-Stewart formalism for general-relativistic shear-viscous hydrodynamics, we perform axisymmetric general-relativistic simulations for a rotating neutron star surrounded by a massive torus, which can be formed from differentially rotating stars. We show that with our choice of a shear-viscous hydrodynamics formalism, the simulations can be stably performed for a long time scale. We also demonstrate that with a possibly high shear-viscous coefficient, not only viscous angular momentum transport works but also an outflow could be driven from a hot envelope around the neutron star for a time scale ≳100 ms with the ejecta mass ≳10-2 M⊙ , which is comparable to the typical mass for dynamical ejecta of binary neutron-star mergers. This suggests that massive neutron stars surrounded by a massive torus, which are typical outcomes formed after the merger of binary neutron stars, could be the dominant source for providing neutron-rich ejecta, if the effective shear viscosity is sufficiently high, i.e., if the viscous α parameter is ≳10-2. The present numerical result indicates the importance of a future high-resolution magnetohydrodynamics simulation that is the unique approach to clarify the viscous effect in the merger remnants of binary neutron stars by the first-principle manner.

X-ray and neutron total scattering analysis of Hy·(Bi0.2Ca0.55Sr0.25)(Ag0.25Na0.75)Nb3O10·xH2O perovskite nanosheet booklets with stacking disorder

DOE Office of Scientific and Technical Information (OSTI.GOV)

Metz, Peter; Koch, Robert; Cladek, Bernadette

Ion-exchanged Aurivillius materials form perovskite nanosheet booklets wherein well-defined bi-periodic sheets, with ~11.5 Å thickness, exhibit extensive stacking disorder. The perovskite layer contents were defined initially using combined synchrotron X-ray and neutron Rietveld refinement of the parent Aurivillius structure. The structure of the subsequently ion-exchanged material, which is disordered in its stacking sequence, is analyzed using both pair distribution function (PDF) analysis and recursive method simulations of the scattered intensity. Combined X-ray and neutron PDF refinement of supercell stacking models demonstrates sensitivity of the PDF to both perpendicular and transverse stacking vector components. Further, hierarchical ensembles of stacking models weightedmore » by a standard normal distribution are demonstrated to improve PDF fit over 1–25 Å. Recursive method simulations of the X-ray scattering profile demonstrate agreement between the real space stacking analysis and more conventional reciprocal space methods. The local structure of the perovskite sheet is demonstrated to relax only slightly from the Aurivillius structure after ion exchange.« less

Monte Carlo calculations of thermal neutron capture in gadolinium: a comparison of GEANT4 and MCNP with measurements.

PubMed

Enger, Shirin A; Munck af Rosenschöld, Per; Rezaei, Arash; Lundqvist, Hans

2006-02-01

GEANT4 is a Monte Carlo code originally implemented for high-energy physics applications and is well known for particle transport at high energies. The capacity of GEANT4 to simulate neutron transport in the thermal energy region is not equally well known. The aim of this article is to compare MCNP, a code commonly used in low energy neutron transport calculations and GEANT4 with experimental results and select the suitable code for gadolinium neutron capture applications. To account for the thermal neutron scattering from chemically bound atoms [S(alpha,beta)] in biological materials a comparison of thermal neutron fluence in tissue-like poly(methylmethacrylate) phantom is made with MCNP4B, GEANT4 6.0 patch1, and measurements from the neutron capture therapy (NCT) facility at the Studsvik, Sweden. The fluence measurements agreed with MCNP calculated results considering S(alpha,beta). The location of the thermal neutron peak calculated with MCNP without S(alpha,beta) and GEANT4 is shifted by about 0.5 cm towards a shallower depth and is 25%-30% lower in amplitude. Dose distribution from the gadolinium neutron capture reaction is then simulated by MCNP and compared with measured data. The simulations made by MCNP agree well with experimental results. As long as thermal neutron scattering from chemically bound atoms are not included in GEANT4 it is not suitable for NCT applications.

The Need for Precise and Well-documented Experimental Data on Prompt Fission Neutron Spectra from Neutron-induced Fission of {sup 239}Pu

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neudecker, D., E-mail: dneudecker@lanl.gov; Taddeucci, T.N.; Haight, R.C.

2016-01-15

The spectrum of neutrons emitted promptly after {sup 239}Pu(n,f)—a so-called prompt fission neutron spectrum (PFNS)—is a quantity of high interest, for instance, for reactor physics and global security. However, there are only few experimental data sets available that are suitable for evaluations. In addition, some of those data sets differ by more than their 1-σ uncertainty boundaries. We present the results of MCNP studies indicating that these differences are partly caused by underestimated multiple scattering contributions, over-corrected background, and inconsistent deconvolution methods. A detailed uncertainty quantification for suitable experimental data was undertaken including these effects, and test-evaluations were performed withmore » the improved uncertainty information. The test-evaluations illustrate that the inadequately estimated effects and detailed uncertainty quantification have an impact on the evaluated PFNS and associated uncertainties as well as the neutron multiplicity of selected critical assemblies. A summary of data and documentation needs to improve the quality of the experimental database is provided based on the results of simulations and test-evaluations. Given the possibly substantial distortion of the PFNS by multiple scattering and background effects, special care should be taken to reduce these effects in future measurements, e.g., by measuring the {sup 239}Pu PFNS as a ratio to either the {sup 235}U or {sup 252}Cf PFNS.« less

Absolute efficiency calibration of 6LiF-based solid state thermal neutron detectors

NASA Astrophysics Data System (ADS)

Finocchiaro, Paolo; Cosentino, Luigi; Lo Meo, Sergio; Nolte, Ralf; Radeck, Desiree

2018-03-01

The demand for new thermal neutron detectors as an alternative to 3He tubes in research, industrial, safety and homeland security applications, is growing. These needs have triggered research and development activities about new generations of thermal neutron detectors, characterized by reasonable efficiency and gamma rejection comparable to 3He tubes. In this paper we show the state of the art of a promising low-cost technique, based on commercial solid state silicon detectors coupled with thin neutron converter layers of 6LiF deposited onto carbon fiber substrates. A few configurations were studied with the GEANT4 simulation code, and the intrinsic efficiency of the corresponding detectors was calibrated at the PTB Thermal Neutron Calibration Facility. The results show that the measured intrinsic detection efficiency is well reproduced by the simulations, therefore validating the simulation tool in view of new designs. These neutron detectors have also been tested at neutron beam facilities like ISIS (Rutherford Appleton Laboratory, UK) and n_TOF (CERN) where a few samples are already in operation for beam flux and 2D profile measurements. Forthcoming applications are foreseen for the online monitoring of spent nuclear fuel casks in interim storage sites.

Effects of Neutron-Star Dynamic Tides on Gravitational Waveforms within the Effective-One-Body Approach

NASA Astrophysics Data System (ADS)

Hinderer, Tanja; Taracchini, Andrea; Foucart, Francois; Buonanno, Alessandra; Steinhoff, Jan; Duez, Matthew; Kidder, Lawrence E.; Pfeiffer, Harald P.; Scheel, Mark A.; Szilagyi, Bela; Hotokezaka, Kenta; Kyutoku, Koutarou; Shibata, Masaru; Carpenter, Cory W.

2016-05-01

Extracting the unique information on ultradense nuclear matter from the gravitational waves emitted by merging neutron-star binaries requires robust theoretical models of the signal. We develop a novel effective-one-body waveform model that includes, for the first time, dynamic (instead of only adiabatic) tides of the neutron star as well as the merger signal for neutron-star-black-hole binaries. We demonstrate the importance of the dynamic tides by comparing our model against new numerical-relativity simulations of nonspinning neutron-star-black-hole binaries spanning more than 24 gravitational-wave cycles, and to other existing numerical simulations for double neutron-star systems. Furthermore, we derive an effective description that makes explicit the dependence of matter effects on two key parameters: tidal deformability and fundamental oscillation frequency.

Study of low energy neutron beam formation based on GEANT4 simulations

NASA Astrophysics Data System (ADS)

Avagyan, R.; Avetisyan, R.; Ivanyan, V.; Kerobyan, I.

2017-07-01

The possibility of obtaining thermal/epithermal energy neutron beams using external protons from cyclotron C18/18 is studied based on GEANT4 simulations. This study will be the basis of the Beam Shaped Assembly (BSA) development for future Boron Neutron Capture Therapy (BNCT). Proton induced reactions on 9Be target are considered as a neutron source, and dependence of neutron yield on target thickness is investigated. The problem of reducing the ratio of gamma to neutron yields by inserting a lead sheet after the beryllium target is studied as well. By GEANT4 modeling the optimal thicknesses of 9Be target and lead absorber are determined and the design characteristics of beam shaping assembly, including the materials and thicknesses of reflector and moderator are considered.

Effects of Neutron-Star Dynamic Tides on Gravitational Waveforms within the Effective-One-Body Approach.

PubMed

Hinderer, Tanja; Taracchini, Andrea; Foucart, Francois; Buonanno, Alessandra; Steinhoff, Jan; Duez, Matthew; Kidder, Lawrence E; Pfeiffer, Harald P; Scheel, Mark A; Szilagyi, Bela; Hotokezaka, Kenta; Kyutoku, Koutarou; Shibata, Masaru; Carpenter, Cory W

2016-05-06

Extracting the unique information on ultradense nuclear matter from the gravitational waves emitted by merging neutron-star binaries requires robust theoretical models of the signal. We develop a novel effective-one-body waveform model that includes, for the first time, dynamic (instead of only adiabatic) tides of the neutron star as well as the merger signal for neutron-star-black-hole binaries. We demonstrate the importance of the dynamic tides by comparing our model against new numerical-relativity simulations of nonspinning neutron-star-black-hole binaries spanning more than 24 gravitational-wave cycles, and to other existing numerical simulations for double neutron-star systems. Furthermore, we derive an effective description that makes explicit the dependence of matter effects on two key parameters: tidal deformability and fundamental oscillation frequency.

Double difference method in deep inelastic neutron scattering on the VESUVIO spectrometer

NASA Astrophysics Data System (ADS)

Andreani, C.; Colognesi, D.; Degiorgi, E.; Filabozzi, A.; Nardone, M.; Pace, E.; Pietropaolo, A.; Senesi, R.

2003-02-01

The principles of the Double Difference (DD) method, applied to the neutron spectrometer VESUVIO, are discussed. VESUVIO, an inverse geometry spectrometer operating at the ISIS pulsed neutron source in the eV energy region, has been specifically designed to measure the single particle dynamical properties in condensed matter. The width of the nuclear resonance of the absorbing filter, used for the neutron energy analysis, provides the most important contribution to the energy resolution of the inverse geometry instruments. In this paper, the DD method, which is based on a linear combination of two measurements recorded with filter foils of the same resonance material but of different thickness, is shown to improve significantly the instrumental energy resolution, as compared with the Single Difference (SD) method. The asymptotic response functions, derived through Monte-Carlo simulations for polycrystalline Pb and ZrH 2 samples, are analysed in both DD and SD methods, and compared with the experimental ones for Pb sample. The response functions have been modelled for two distinct experimental configurations of the VESUVIO spectrometer, employing 6Li-glass neutron detectors and NaI γ detectors revealing the γ-ray cascade from the ( n,γ) reaction, respectively. The DD method appears to be an effective experimental procedure for Deep Inelastic Neutron Scattering measurements on VESUVIO spectrometer, since it reduces the experimental resolution of the instrument in both 6Li-glass neutron detector and γ detector configurations.

SU-F-T-217: A Comprehensive Monte-Carlo Study of Out-Of-Field Secondary Neutron Spectra in a Scanned-Beam Proton Therapy Treatment Room

DOE Office of Scientific and Technical Information (OSTI.GOV)

Englbrecht, F; Parodi, K; Trinkl, S

2016-06-15

Purpose: To simulate secondary neutron radiation-fields produced at different positions during phantom irradiation inside a scanning proton therapy gantry treatment room. Further, to identify origin, energy distribution and angular emission as function of proton beam energy. Methods: GEANT4 and FLUKA Monte-Carlo codes were used to model the relevant parts of the treatment room in a gantry-equipped pencil beam scanning proton therapy facility including walls, floor, metallic gantry-components, patient table and the homogeneous PMMA target. The proton beams were modeled based on experimental beam ranges in water and spot shapes in air. Neutron energy spectra were simulated at 0°, 45°, 90°more » and 135° relative to the beam axis at 2m distance from isocenter, as well as 11×11 cm2 fields for 75MeV, 140MeV, 200MeV and for 118MeV with 5cm PMMA range-shifter. The total neutron energy distribution was recorded for these four positions and proton energies. Additionally, the room-components generating secondary neutrons in the room and their contributions to the total spectrum were identified and quantified. Results: FLUKA and GEANT4 simulated neutron spectra showed good general agreement in the whole energy range of 10{sup −}9 to 10{sup 2} MeV. Comparison of measured spectra with the simulated contributions of the various room components helped to limit the complexity of the room model, by identifying the dominant contributions to the secondary neutron spectrum. The iron of the bending magnet and counterweight were identified as sources of secondary evaporation-neutrons, which were lacking in simplified room models. Conclusion: Thorough Monte-Carlo simulations have been performed to complement Bonner-sphere spectrometry measurements of secondary neutrons in a clinical proton therapy treatment room. Such calculations helped disentangling the origin of secondary neutrons and their dominant contributions to measured spectra, besides providing a useful validation of widely used Monte-Carlo packages in comparison to experimental data. Cluster of Excellence of the German Research Foundation (DFG) “Munich-Centre for Advanced Photonics (MAP)”.« less

Simulations of GCR interactions within planetary bodies using GEANT4

NASA Astrophysics Data System (ADS)

Mesick, K.; Feldman, W. C.; Stonehill, L. C.; Coupland, D. D. S.

2017-12-01

On planetary bodies with little to no atmosphere, Galactic Cosmic Rays (GCRs) can hit the body and produce neutrons primarily through nuclear spallation within the top few meters of the surfaces. These neutrons undergo further nuclear interactions with elements near the planetary surface and some will escape the surface and can be detected by landed or orbiting neutron radiation detector instruments. The neutron leakage signal at fast neutron energies provides a measure of average atomic mass of the near-surface material and in the epithermal and thermal energy ranges is highly sensitive to the presence of hydrogen. Gamma-rays can also escape the surface, produced at characteristic energies depending on surface composition, and can be detected by gamma-ray instruments. The intra-nuclear cascade (INC) that occurs when high-energy GCRs interact with elements within a planetary surface to produce the leakage neutron and gamma-ray signals is highly complex, and therefore Monte Carlo based radiation transport simulations are commonly used for predicting and interpreting measurements from planetary neutron and gamma-ray spectroscopy instruments. In the past, the simulation code that has been widely used for this type of analysis is MCNPX [1], which was benchmarked against data from the Lunar Neutron Probe Experiment (LPNE) on Apollo 17 [2]. In this work, we consider the validity of the radiation transport code GEANT4 [3], another widely used but open-source code, by benchmarking simulated predictions of the LPNE experiment to the Apollo 17 data. We consider the impact of different physics model options on the results, and show which models best describe the INC based on agreement with the Apollo 17 data. The success of this validation then gives us confidence in using GEANT4 to simulate GCR-induced neutron leakage signals on Mars in relevance to a re-analysis of Mars Odyssey Neutron Spectrometer data. References [1] D.B. Pelowitz, Los Alamos National Laboratory, LA-CP-05-0369, 2005. [2] G.W. McKinney et al, Journal of Geophysics Research, 111, E06004, 2006. [3] S. Agostinelli et al, Nuclear Instrumentation and Methods A, 506, 2003.

Deploying Solid Targets in Dense Plasma Focus Devices for Improved Neutron Yields

NASA Astrophysics Data System (ADS)

Podpaly, Y. A.; Chapman, S.; Povilus, A.; Falabella, S.; Link, A.; Shaw, B. H.; Cooper, C. M.; Higginson, D.; Holod, I.; Sipe, N.; Gall, B.; Schmidt, A. E.

2017-10-01

We report on recent progress in using solid targets in dense plasma focus (DPF) devices. DPFs have been observed to generate energetic ion beams during the pinch phase; these beams interact with the dense plasma in the pinch region as well as the background gas and are believed to be the primary neutron generation mechanism for a D2 gas fill. Targets can be placed in the beam path to enhance neutron yield and to shorten the neutron pulse if desired. In this work, we measure yields from placing titanium deuteride foils, deuterated polyethylene, and non-deuterated control targets in deuterium filled DPFs at both megajoule and kilojoule scales. Furthermore, we have deployed beryllium targets in a helium gas-filled, kilojoule scale DPF for use as a potential AmBe radiological source replacement. Neutron yield, neutron time of flight, and optical images are used to diagnose the effectiveness of target deployments relative to particle-in-cell simulation predictions. A discussion of target holder engineering for material compatibility and damage control will be shown as well. Prepared by LLNL under Contract DE-AC52-07NA27344. Supported by the Office of Defense Nuclear Nonproliferation Research and Development within U.S. DOE's National Nuclear Security Administration and the LLNL Institutional Computing Grand Challenge program.

Hexagonal Uniformly Redundant Arrays (HURAs) for scintillator based coded aperture neutron imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gamage, K.A.A.; Zhou, Q.

2015-07-01

A series of Monte Carlo simulations have been conducted, making use of the EJ-426 neutron scintillator detector, to investigate the potential of using hexagonal uniformly redundant arrays (HURAs) for scintillator based coded aperture neutron imaging. This type of scintillator material has a low sensitivity to gamma rays, therefore, is of particular use in a system with a source that emits both neutrons and gamma rays. The simulations used an AmBe source, neutron images have been produced using different coded-aperture materials (boron- 10, cadmium-113 and gadolinium-157) and location error has also been estimated. In each case the neutron image clearly showsmore » the location of the source with a relatively small location error. Neutron images with high resolution can be easily used to identify and locate nuclear materials precisely in nuclear security and nuclear decommissioning applications. (authors)« less

Neutron flux measurements on a mock-up of a storage cask for high-level nuclear waste using 2.5 MeV neutrons.

PubMed

Suárez, H Saurí; Becker, F; Klix, A; Pang, B; Döring, T

2018-06-07

To store and dispose spent nuclear fuel, shielding casks are employed to reduce the emitted radiation. To evaluate the exposure of employees handling such casks, Monte Carlo radiation transport codes can be employed. Nevertheless, to assess the reliability of these codes and nuclear data, experimental checks are required. In this study, a neutron generator (NG) producing neutrons of 2.5 MeV was employed to simulate neutrons produced in spent nuclear fuel. Different configurations of shielding layers of steel and polyethylene were positioned between the target of the NG and a NE-213 detector. The results of the measurements of neutron and γ radiation and the corresponding simulations with the code MCNP6 are presented. Details of the experimental set-up as well as neutron and photon flux spectra are provided as reference points for such NG investigations with shielding structures.

A Dosimetry Study of Deuterium-Deuterium Neutron Generator-based In Vivo Neutron Activation Analysis.

PubMed

Sowers, Daniel; Liu, Yingzi; Mostafaei, Farshad; Blake, Scott; Nie, Linda H

2015-12-01

A neutron irradiation cavity for in vivo neutron activation analysis (IVNAA) to detect manganese, aluminum, and other potentially toxic elements in human hand bone has been designed and its dosimetric specifications measured. The neutron source is a customized deuterium-deuterium neutron generator that produces neutrons at 2.45 MeV by the fusion reaction 2H(d, n)3He at a calculated flux of 7 × 10(8) ± 30% s(-1). A moderator/reflector/shielding [5 cm high density polyethylene (HDPE), 5.3 cm graphite and 5.7 cm borated (HDPE)] assembly has been designed and built to maximize the thermal neutron flux inside the hand irradiation cavity and to reduce the extremity dose and effective dose to the human subject. Lead sheets are used to attenuate bremsstrahlung x rays and activation gammas. A Monte Carlo simulation (MCNP6) was used to model the system and calculate extremity dose. The extremity dose was measured with neutron and photon sensitive film badges and Fuji electronic pocket dosimeters (EPD). The neutron ambient dose outside the shielding was measured by Fuji NSN3, and the photon dose was measured by a Bicron MicroREM scintillator. Neutron extremity dose was calculated to be 32.3 mSv using MCNP6 simulations given a 10-min IVNAA measurement of manganese. Measurements by EPD and film badge indicate hand dose to be 31.7 ± 0.8 mSv for neutrons and 4.2 ± 0.2 mSv for photons for 10 min; whole body effective dose was calculated conservatively to be 0.052 mSv. Experimental values closely match values obtained from MCNP6 simulations. These are acceptable doses to apply the technology for a manganese toxicity study in a human population.

Distributions of neutron yields and doses around a water phantom bombarded with 290-MeV/nucleon and 430-MeV/nucleon carbon ions

NASA Astrophysics Data System (ADS)

Satoh, D.; Kajimoto, T.; Shigyo, N.; Itashiki, Y.; Imabayashi, Y.; Koba, Y.; Matsufuji, N.; Sanami, T.; Nakao, N.; Uozumi, Y.

2016-11-01

Double-differential neutron yields from a water phantom bombarded with 290-MeV/nucleon and 430-MeV/nucleon carbon ions were measured at emission angles of 15°, 30°, 45°, 60°, 75°, and 90°, and angular distributions of neutron yields and doses around the phantom were obtained. The experimental data were compared with results of the Monte-Carlo simulation code PHITS. The PHITS results showed good agreement with the measured data. On the basis of the PHITS simulation, we estimated the angular distributions of neutron yields and doses from 0° to 180° including thermal neutrons.

Application of Simulated Reactivity Feedback in Nonnuclear Testing of a Direct-Drive Gas-Cooled Reactor

NASA Technical Reports Server (NTRS)

Bragg-Sitton, S. M.; Webster, K. L.

2007-01-01

Nonnuclear testing can be a valuable tool in the development of an in-space nuclear power or propulsion system. In a nonnuclear test facility, electric heaters are used to simulate heat from nuclear fuel. Standard testing allows one to fully assess thermal, heat transfer, and stress related attributes of a given system but fails to demonstrate the dynamic response that would be present in an integrated, fueled reactor system. The integration of thermal hydraulic hardware tests with simulated neutronic response provides a bridge between electrically heated testing and full nuclear testing. By implementing a neutronic response model to simulate the dynamic response that would be expected in a fueled reactor system, one can better understand system integration issues, characterize integrated system response times and response and response characteristics, and assess potential design improvements with a relatively small fiscal investment. Initial system dynamic response testing was demonstrated on the integrated SAFE 100a heat pipe cooled, electrically heated reactor and heat exchanger hardware. This Technical Memorandum discusses the status of the planned dynamic test methodology for implementation in the direct-drive gas-cooled reactor testing and assesses the additional instrumentation needed to implement high-fidelity dynamic testing.

Variations in AmLi source spectra and their estimation utilizing the 5 Ring Multiplicity Counter

NASA Astrophysics Data System (ADS)

Weinmann-Smith, R.; Beddingfield, D. H.; Enqvist, A.; Swinhoe, M. T.

2017-06-01

Active-mode assay systems are widely used for the safeguards of uranium items to verify compliance with the Non-Proliferation Treaty. Systems such as the Active-Well Coincidence Counter (AWCC) and the Uranium Neutron Coincidence Collar (UNCL) use americium-lithium (AmLi) neutron sources to induce fissions which are measured to determine the sample mass. These systems have historically relied on calibrations derived from well-defined standards. Recently, restricted access to standards or more difficult measurements have resulted in a reliance on modeling and simulation for the calibration of systems, which introduces potential simulation biases. The AmLi source energy spectra commonly used in the safeguards community do not accurately represent measurement results and the spectrum uncertainty can represent a large contribution to the total modeling uncertainty in active-mode systems. The 5-Ring Multiplicity Counter (5RMC) has been used to measure 17 AmLi sources. The measurements showed a significant spectral variation between different sources. Utilization of a spectrum that is specific to an individual source or a series of sources will give improved results over historical general spectra when modeling AmLi sources. Candidate AmLi neutron spectra were calculated in MCNP and SOURCES4C for a range of physical AmLi characteristics. The measurement and simulation data were used to fit reliable and accurate AmLi spectra for use in the simulation of active-mode systems. Spectra were created for average Gammatron C, Gammatron N, and MRC series sources, and for individual sources. The systematic uncertainty introduced by physical aspects of the AmLi source were characterized through simulations. The accuracy of spectra from the literature was compared.

Advanced Instrumentation for Transient Reactor Testing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Corradini, Michael L.; Anderson, Mark; Imel, George

Transient testing involves placing fuel or material into the core of specialized materials test reactors that are capable of simulating a range of design basis accidents, including reactivity insertion accidents, that require the reactor produce short bursts of intense highpower neutron flux and gamma radiation. Testing fuel behavior in a prototypic neutron environment under high-power, accident-simulation conditions is a key step in licensing nuclear fuels for use in existing and future nuclear power plants. Transient testing of nuclear fuels is needed to develop and prove the safety basis for advanced reactors and fuels. In addition, modern fuel development and designmore » increasingly relies on modeling and simulation efforts that must be informed and validated using specially designed material performance separate effects studies. These studies will require experimental facilities that are able to support variable scale, highly instrumented tests providing data that have appropriate spatial and temporal resolution. Finally, there are efforts now underway to develop advanced light water reactor (LWR) fuels with enhanced performance and accident tolerance. These advanced reactor designs will also require new fuel types. These new fuels need to be tested in a controlled environment in order to learn how they respond to accident conditions. For these applications, transient reactor testing is needed to help design fuels with improved performance. In order to maximize the value of transient testing, there is a need for in-situ transient realtime imaging technology (e.g., the neutron detection and imaging system like the hodoscope) to see fuel motion during rapid transient excursions with a higher degree of spatial and temporal resolution and accuracy. There also exists a need for new small, compact local sensors and instrumentation that are capable of collecting data during transients (e.g., local displacements, temperatures, thermal conductivity, neutron flux, etc.).« less

Neutron-fragment and Neutron-neutron Correlations in Low-energy Fission

NASA Astrophysics Data System (ADS)

Lestone, J. P.

2016-01-01

A computational method has been developed to simulate neutron emission from thermal-neutron induced fission of 235U and from spontaneous fission of 252Cf. Measured pre-emission mass-yield curves, average total kinetic energies and their variances, both as functions of mass split, are used to obtain a representation of the distribution of fragment velocities. Measured average neutron multiplicities as a function of mass split and their dependence on total kinetic energy are used. Simulations can be made to reproduce measured factorial moments of neutron-multiplicity distributions with only minor empirical adjustments to some experimental inputs. The neutron-emission spectra in the rest-frame of the fragments are highly constrained by ENDF/B-VII.1 prompt-fission neutron-spectra evaluations. The n-f correlation measurements of Vorobyev et al. (2010) are consistent with predictions where all neutrons are assumed to be evaporated isotropically from the rest frame of fully accelerated fragments. Measured n-f and n-n correlations of others are a little weaker than the predictions presented here. These weaker correlations could be used to infer a weak scission-neutron source. However, the effect of neutron scattering on the experimental results must be studied in detail before moving away from a null hypothesis that all neutrons are evaporated from the fragments.

Photonuclear activation of pure isotopic mediums.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grohman, Mark A.; Lukosi, Eric Daniel

2010-06-01

This work simulated the response of idealized isotopic U-235, U-238, Th-232, and Pu-239 mediums to photonuclear activation with various photon energies. These simulations were conducted using MCNPX version 2.6.0. It was found that photon energies between 14-16 MeV produce the highest response with respect to neutron production rates from all photonuclear reactions. In all cases, Pu-239 responds the highest, followed by U-238. Th-232 produces more overall neutrons at lower photon energies then U-235 when material thickness is above 3.943 centimeters. The time it takes each isotopic material to reach stable neutron production rates in time is directly proportional to themore » material thickness and stopping power of the medium, where thicker mediums take longer to reach stable neutron production rates and thinner media display a neutron production plateau effect, due to the lack of significant attenuation of the activating photons in the isotopic mediums. At this time, no neutron sensor system has time resolutions capable of verifying these simulations, but various indirect methods are possible and should be explored for verification of these results.« less

Development of a Geant4 application to characterise a prototype neutron detector based on three orthogonal 3He tubes inside an HDPE sphere.

PubMed

Gracanin, V; Guatelli, S; Prokopovich, D; Rosenfeld, A B; Berry, A

2017-01-01

The Bonner Sphere Spectrometer (BSS) system is a well-established technique for neutron dosimetry that involves detection of thermal neutrons within a range of hydrogenous moderators. BSS detectors are often used to perform neutron field surveys in order to determine the ambient dose equivalent H*(10) and estimate health risk to personnel. There is a potential limitation of existing neutron survey techniques, since some detectors do not consider the direction of the neutron field, which can result in overly conservative estimates of dose in neutron fields. This paper shows the development of a Geant4 simulation application to characterise a prototype neutron detector based on three orthogonal 3 He tubes inside a single HDPE sphere built at the Australian Nuclear Science and Technology Organisation (ANSTO). The Geant4 simulation has been validated with respect to experimental measurements performed with an Am-Be source. Crown Copyright © 2016. Published by Elsevier Ltd. All rights reserved.

Thermal neutron calibration channel at LNMRI/IRD.

PubMed

Astuto, A; Salgado, A P; Leite, S P; Patrão, K C S; Fonseca, E S; Pereira, W W; Lopes, R T

2014-10-01

The Brazilian Metrology Laboratory of Ionizing Radiations (LNMRI) standard thermal neutron flux facility was designed to provide uniform neutron fluence for calibration of small neutron detectors and individual dosemeters. This fluence is obtained by neutron moderation from four (241)Am-Be sources, each with 596 GBq, in a facility built with blocks of graphite/paraffin compound and high-purity carbon graphite. This study was carried out in two steps. In the first step, simulations using the MCNPX code on different geometric arrangements of moderator materials and neutron sources were performed. The quality of the resulting neutron fluence in terms of spectrum, cadmium ratio and gamma-neutron ratio was evaluated. In the second step, the system was assembled based on the results obtained on the simulations, and new measurements are being made. These measurements will validate the system, and other intercomparisons will ensure traceability to the International System of Units. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Prompt gamma-ray imaging for small animals

NASA Astrophysics Data System (ADS)

Xu, Libai

Small animal imaging is recognized as a powerful discovery tool for small animal modeling of human diseases, which is providing an important clue to complete understanding of disease mechanisms and is helping researchers develop and test new treatments. The current small animal imaging techniques include positron emission tomography (PET), single photon emission tomography (SPECT), computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound (US). A new imaging modality called prompt gamma-ray imaging (PGI) has been identified and investigated primarily by Monte Carlo simulation. Currently it is suggested for use on small animals. This new technique could greatly enhance and extend the present capabilities of PET and SPECT imaging from ingested radioisotopes to the imaging of selected non-radioactive elements, such as Gd, Cd, Hg, and B, and has the great potential to be used in Neutron Cancer Therapy to monitor neutron distribution and neutron-capture agent distribution. This approach consists of irradiating small animals in the thermal neutron beam of a nuclear reactor to produce prompt gamma rays from the elements in the sample by the radiative capture (n, gamma) reaction. These prompt gamma rays are emitted in energies that are characteristic of each element and they are also produced in characteristic coincident chains. After measuring these prompt gamma rays by surrounding spectrometry array, the distribution of each element of interest in the sample is reconstructed from the mapping of each detected signature gamma ray by either electronic collimations or mechanical collimations. In addition, the transmitted neutrons from the beam can be simultaneously used for very sensitive anatomical imaging, which provides the registration for the elemental distributions obtained from PGI. The primary approach is to use Monte Carlo simulation methods either with the specific purpose code CEARCPG, developed at NC State University or with the general purpose codes GEANT4 or MCNP5, to predict results and investigate the feasibility of this new imaging idea. Benchmark experiments have been conducted to test the capability of the code to simulate prompt gamma rays, which are produced by following the nuclear structures of each irradiated isotope, and coincidence counting techniques, which are considered the most important improvement in neutron-related gamma-ray detection applications to reduce gamma background and improve system signal-to-noise ratios. With coincidence prompt gamma rays available, two major imaging techniques, electronic collimations and mechanic collimations, are implemented in the simulation to illustrate the feasibility of imaging elemental distribution by this new technique. The expectation maximization algorithm is employed in electronic collimation to reconstruct images. The common SPECT imaging algorithms are used in mechanical collimation to get an image. Several critical topics concerning practical applications have already been discussed, such as the radiation dose to the mouse and the detection efficiency of high-energy gamma rays. The funding of this work is provided by the Center for Engineering Application of Radioisotopes (CEAR) at North Carolina State University (NCSU) and Nuclear Engineering Education Research.

Generation of the neutron response function of an NE213 scintillator for fusion applications

NASA Astrophysics Data System (ADS)

Binda, F.; Eriksson, J.; Ericsson, G.; Hellesen, C.; Conroy, S.; Nocente, M.; Sundén, E. Andersson; JET Contributors

2017-09-01

In this work we present a method to evaluate the neutron response function of an NE213 liquid scintillator. This method is particularly useful when the proton light yield function of the detector has not been measured, since it is based on a proton light yield function taken from literature, MCNPX simulations, measurements of gamma-rays from a calibration source and measurements of neutrons from fusion experiments with ohmic plasmas. The inclusion of the latter improves the description of the proton light yield function in the energy range of interest (around 2.46 MeV). We apply this method to an NE213 detector installed at JET, inside the radiation shielding of the magnetic proton recoil (MPRu) spectrometer, and present the results from the calibration along with some examples of application of the response function to perform neutron emission spectroscopy (NES) of fusion plasmas. We also investigate how the choice of the proton light yield function affects the NES analysis, finding that the result does not change significantly. This points to the fact that the method for the evaluation of the neutron response function is robust and gives reliable results.

Effective Elastic and Neutron Capture Cross Section Calculations Corresponding to Simulated Fluid Properties from CO2 Push-Pull Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chugunov, Nikita; Altundas, Bilgin

The submission contains a .xls files consisting of 10 excel sheets, which contain combined list of pressure, saturation, salinity, temperature profiles from the simulation of CO2 push-pull using Brady reservoir model and the corresponding effective compressional and shear velocity, bulk density, and fluid and time-lapse neutron capture cross section profiles of rock at times 0 day (baseline) through 14 days. First 9 sheets (each named after the corresponding CO2 push-pull simulation time) contains simulated pressure, saturation, temperature, salinity profiles and the corresponding effective elastic and neutron capture cross section profiles of rock matrix at the time of CO2 injection. Eachmore » sheet contains two sets of effective compressional velocity profiles of the rock, one based on Gassmann and the other based on Patchy saturation model. Effective neutron capture cross section calculations are done using a proprietary neutron cross-section simulator (SNUPAR) whereas for the thermodynamic properties of CO2 and bulk density of rock matrix filled with fluid, a standalone fluid substitution tool by Schlumberger is used. Last sheet in the file contains the bulk modulus of solid rock, which is inverted from the rock properties (porosity, sound speed etc) based on Gassmann model. Bulk modulus of solid rock in turn is used in the fluid substitution.« less

SU-E-T-108: Development of a Novel Clinical Neutron Dose Monitor for Proton Therapy Based On Twin TLD500 Chips in a Small PE Moderator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hentschel, R; Mukherjee, B

2014-06-01

Purpose: In proton therapy, it could be desirable to measure out-of-field fast neutron doses at critical locations near and outside the patient body. Methods: The working principle of a novel clinical neutron dose monitor is verified by MCNPX simulation. The device is based on a small PE moderator of just 5.5cm side length for easy handling covered with a thermal neutron suppression layer. In the simulation, a polystyrene phantom is bombarded with a standard proton beam. The secondary thermal neutron flux produced inside the moderator by the impinging fast neutrons from the treatment volume is estimated by pairs of α-Al2O3:Cmore » (TLD500) chips which are evaluated offline after the treatment either by TL or OSL methods. The first chip is wrapped with 0.5mm natural Gadolinium foil converting the thermal neutrons to gammas via (n,γ) reaction. The second chip is wrapped with a dummy material. The chip centers have a distance of 2cm from each other. Results: The simulation shows that the difference of gamma doses in the TLD500 chips is correlated to the mean fast neutron dose delivered to the moderator material. Different outer shielding materials have been studied. 0.5mm Cadmium shielding is preferred for cost reasons and convenience. Replacement of PE moderator material by other materials like lead or iron at any place is unfavorable. The spatial orientation of the moderator cube is uncritical. Using variance reduction techniques like splitting/Russian roulette, the TLD500 gamma dose simulation give positive differences up to distances of 0.5m from the treatment volume. Conclusion: Applicability and basic layout of a novel clinical neutron dose monitor are demonstrated. The monitor measures PE neutron doses at locations outside the patient body up to distances of 0.5m from the treatment volume. Tissue neutron doses may be calculated using neutron kerma factors.« less

Feasibility of Small Animal Anatomical and Functional Imaging with Neutrons: A Monte Carlo Simulation Study

NASA Astrophysics Data System (ADS)

Medich, David C.; Currier, Blake H.; Karellas, Andrew

2014-10-01

A novel technique is presented for obtaining a single in-vivo image containing both functional and anatomical information in a small animal model such as a mouse. This technique, which incorporates appropriate image neutron-scatter rejection and uses a neutron opaque contrast agent, is based on neutron radiographic technology and was demonstrated through a series of Monte Carlo simulations. With respect to functional imaging, this technique can be useful in biomedical and biological research because it could achieve a spatial resolution orders of magnitude better than what presently can be achieved with current functional imaging technologies such as nuclear medicine (PET, SPECT) and fMRI. For these studies, Monte Carlo simulations were performed with thermal (0.025 eV) neutrons in a 3 cm thick phantom using the MCNP5 simulations software. The goals of these studies were to determine: 1) the extent that scattered neutrons degrade image contrast; 2) the contrasts of various normal and diseased tissues under conditions of complete scatter rejection; 3) the concentrations of Boron-10 and Gadolinium-157 required for contrast differentiation in functional imaging; and 4) the efficacy of collimation for neutron scatter image rejection. Results demonstrate that with proper neutron-scatter rejection, a neutron fluence of 2 ×107 n/cm2 will provide a signal to noise ratio of at least one ( S/N ≥ 1) when attempting to image various 300 μm thick tissues placed in a 3 cm thick phantom. Similarly, a neutron fluence of only 1 ×107 n/cm2 is required to differentiate a 300 μm thick diseased tissue relative to its normal tissue counterpart. The utility of a B-10 contrast agent was demonstrated at a concentration of 50 μg/g to achieve S/N ≥ 1 in 0.3 mm thick tissues while Gd-157 requires only slightly more than 10 μg/g to achieve the same level of differentiation. Lastly, neutron collimator with an L/D ratio from 50 to 200 were calculated to provide appropriate scatter rejection for thick tissue biological imaging with neutrons.

Analysis of JKT01 Neutron Flux Detector Measurements In RSG-GAS Reactor Using LabVIEW

NASA Astrophysics Data System (ADS)

Rokhmadi; Nur Rachman, Agus; Sujarwono; Taryo, Taswanda; Sunaryo, Geni Rina

2018-02-01

The RSG-GAS Reactor, one of the Indonesia research reactors and located in Serpong, is owned by the National Nuclear Energy Agency (BATAN). The RSG-GAS reactor has operated since 1987 and some instrumentation and control systems are considered to be degraded and ageing. It is therefore, necessary to evaluate the safety of all instrumentation and controls and one of the component systems to be evaluated is the performance of JKT01 neutron flux detector. Neutron Flux Detector JKT01 basically detects neutron fluxes in the reactor core and converts it into electrical signals. The electrical signal is then forwarded to the amplifier (Amplifier) to become the input of the reactor protection system. One output of it is transferred to the Main Control Room (RKU) showing on the analog meter as an indicator used by the reactor operator. To simulate all of this matter, a program to simulate the output of the JKT01 Neutron Flux Detector using LabVIEW was developed. The simulated data is estimated using a lot of equations also formulated in LabVIEW. The calculation results are also displayed on the interface using LabVIEW available in the PC. By using this simulation program, it is successful to perform anomaly detection experiments on the JKT01 detector of RSG-GAS Reactor. The simulation results showed that the anomaly JKT01 neutron flux using electrical-current-base are respectively, 1.5×,1.7× and 2.0×.

Improved Convergence Rate of Multi-Group Scattering Moment Tallies for Monte Carlo Neutron Transport Codes

NASA Astrophysics Data System (ADS)

Nelson, Adam

Multi-group scattering moment matrices are critical to the solution of the multi-group form of the neutron transport equation, as they are responsible for describing the change in direction and energy of neutrons. These matrices, however, are difficult to correctly calculate from the measured nuclear data with both deterministic and stochastic methods. Calculating these parameters when using deterministic methods requires a set of assumptions which do not hold true in all conditions. These quantities can be calculated accurately with stochastic methods, however doing so is computationally expensive due to the poor efficiency of tallying scattering moment matrices. This work presents an improved method of obtaining multi-group scattering moment matrices from a Monte Carlo neutron transport code. This improved method of tallying the scattering moment matrices is based on recognizing that all of the outgoing particle information is known a priori and can be taken advantage of to increase the tallying efficiency (therefore reducing the uncertainty) of the stochastically integrated tallies. In this scheme, the complete outgoing probability distribution is tallied, supplying every one of the scattering moment matrices elements with its share of data. In addition to reducing the uncertainty, this method allows for the use of a track-length estimation process potentially offering even further improvement to the tallying efficiency. Unfortunately, to produce the needed distributions, the probability functions themselves must undergo an integration over the outgoing energy and scattering angle dimensions. This integration is too costly to perform during the Monte Carlo simulation itself and therefore must be performed in advance by way of a pre-processing code. The new method increases the information obtained from tally events and therefore has a significantly higher efficiency than the currently used techniques. The improved method has been implemented in a code system containing a new pre-processor code, NDPP, and a Monte Carlo neutron transport code, OpenMC. This method is then tested in a pin cell problem and a larger problem designed to accentuate the importance of scattering moment matrices. These tests show that accuracy was retained while the figure-of-merit for generating scattering moment matrices and fission energy spectra was significantly improved.

Neutron kinetics in moderators and SNM detection through epithermal-neutron-induced fissions

NASA Astrophysics Data System (ADS)

Gozani, Tsahi; King, Michael J.

2016-01-01

Extension of the well-established Differential Die Away Analysis (DDAA) into a faster time domain, where more penetrating epithermal neutrons induce fissions, is proposed and demonstrated via simulations and experiments. In the proposed method the fissions stimulated by thermal, epithermal and even higher-energy neutrons are measured after injection of a narrow pulse of high-energy 14 MeV (d,T) or 2.5 MeV (d,D) source neutrons, appropriately moderated. The ability to measure these fissions stems from the inherent correlation of neutron energy and time ("E-T" correlation) during the process of slowing down of high-energy source neutrons in common moderating materials such as hydrogenous compounds (e.g., polyethylene), heavy water, beryllium and graphite. The kinetic behavior following injection of a delta-function-shaped pulse (in time) of 14 MeV neutrons into such moderators is studied employing MCNPX simulations and, when applicable, some simple "one-group" models. These calculations served as a guide for the design of a source moderator which was used in experiments. Qualitative relationships between slowing-down time after the pulse and the prevailing neutron energy are discussed. A laboratory system consisting of a 14 MeV neutron generator, a polyethylene-reflected Be moderator, a liquid scintillator with pulse-shape discrimination (PSD) and a two-parameter E-T data acquisition system was set up to measure prompt neutron and delayed gamma-ray fission signatures in a 19.5% enriched LEU sample. The measured time behavior of thermal and epithermal neutron fission signals agreed well with the detailed simulations. The laboratory system can readily be redesigned and deployed as a mobile inspection system for SNM in, e.g., cars and vans. A strong pulsed neutron generator with narrow pulse (<75 ns) at a reasonably high pulse frequency could make the high-energy neutron induced fission modality a realizable SNM detection technique.

Intrinsic neutron background of nuclear emulsions for directional Dark Matter searches

NASA Astrophysics Data System (ADS)

Alexandrov, A.; Asada, T.; Buonaura, A.; Consiglio, L.; D'Ambrosio, N.; De Lellis, G.; Di Crescenzo, A.; Di Marco, N.; Di Vacri, M. L.; Furuya, S.; Galati, G.; Gentile, V.; Katsuragawa, T.; Laubenstein, M.; Lauria, A.; Loverre, P. F.; Machii, S.; Monacelli, P.; Montesi, M. C.; Naka, T.; Pupilli, F.; Rosa, G.; Sato, O.; Strolin, P.; Tioukov, V.; Umemoto, A.; Yoshimoto, M.

2016-07-01

Recent developments of the nuclear emulsion technology led to the production of films with nanometric silver halide grains suitable to track low energy nuclear recoils with submicrometric length. This improvement opens the way to a directional Dark Matter detection, thus providing an innovative and complementary approach to the on-going WIMP searches. An important background source for these searches is represented by neutron-induced nuclear recoils that can mimic the WIMP signal. In this paper we provide an estimation of the contribution to this background from the intrinsic radioactive contamination of nuclear emulsions. We also report the neutron-induced background as a function of the read-out threshold, by using a GEANT4 simulation of the nuclear emulsion, showing that it amounts to about 0.06 per year per kilogram, fully compatible with the design of a 10 kg × year exposure.

Development of a polarized neutron beam line at Algerian research reactors using McStas software

NASA Astrophysics Data System (ADS)

Makhloufi, M.; Salah, H.

2017-02-01

Unpolarized instrumentation has long been studied and designed using McStas simulation tool. But, only recently new models were developed for McStas to simulate polarized neutron scattering instruments. In the present contribution, we used McStas software to design a polarized neutron beam line, taking advantage of the available spectrometers reflectometer and diffractometer in Algeria. Both thermal and cold neutron was considered. The polarization was made by two types of supermirrors polarizers FeSi and CoCu provided by the HZB institute. For sake of performance and comparison, the polarizers were characterized and their characteristics reproduced. The simulated instruments are reported. Flipper and electromagnets for guide field are developed. Further developments including analyzers and upgrading of the existing spectrometers are underway.

fissioncore: A desktop-computer simulation of a fission-bomb core

NASA Astrophysics Data System (ADS)

Cameron Reed, B.; Rohe, Klaus

2014-10-01

A computer program, fissioncore, has been developed to deterministically simulate the growth of the number of neutrons within an exploding fission-bomb core. The program allows users to explore the dependence of criticality conditions on parameters such as nuclear cross-sections, core radius, number of secondary neutrons liberated per fission, and the distance between nuclei. Simulations clearly illustrate the existence of a critical radius given a particular set of parameter values, as well as how the exponential growth of the neutron population (the condition that characterizes criticality) depends on these parameters. No understanding of neutron diffusion theory is necessary to appreciate the logic of the program or the results. The code is freely available in FORTRAN, C, and Java and is configured so that modifications to accommodate more refined physical conditions are possible.

ANTS — a simulation package for secondary scintillation Anger-camera type detector in thermal neutron imaging

NASA Astrophysics Data System (ADS)

Morozov, A.; Defendi, I.; Engels, R.; Fraga, F. A. F.; Fraga, M. M. F. R.; Guerard, B.; Jurkovic, M.; Kemmerling, G.; Manzin, G.; Margato, L. M. S.; Niko, H.; Pereira, L.; Petrillo, C.; Peyaud, A.; Piscitelli, F.; Raspino, D.; Rhodes, N. J.; Sacchetti, F.; Schooneveld, E. M.; Van Esch, P.; Zeitelhack, K.

2012-08-01

A custom and fully interactive simulation package ANTS (Anger-camera type Neutron detector: Toolkit for Simulations) has been developed to optimize the design and operation conditions of secondary scintillation Anger-camera type gaseous detectors for thermal neutron imaging. The simulation code accounts for all physical processes related to the neutron capture, energy deposition pattern, drift of electrons of the primary ionization and secondary scintillation. The photons are traced considering the wavelength-resolved refraction and transmission of the output window. Photo-detection accounts for the wavelength-resolved quantum efficiency, angular response, area sensitivity, gain and single-photoelectron spectra of the photomultipliers (PMTs). The package allows for several geometrical shapes of the PMT photocathode (round, hexagonal and square) and offers a flexible PMT array configuration: up to 100 PMTs in a custom arrangement with the square or hexagonal packing. Several read-out patterns of the PMT array are implemented. Reconstruction of the neutron capture position (projection on the plane of the light emission) is performed using the center of gravity, maximum likelihood or weighted least squares algorithm. Simulation results reproduce well the preliminary results obtained with a small-scale detector prototype. ANTS executables can be downloaded from http://coimbra.lip.pt/~andrei/.

Recent Research applications at the Athens Neutron Monitor Station

NASA Astrophysics Data System (ADS)

Mavromichalaki, H.; Gerontidou, M.; Paschalis, P.; Papaioannou, A.; Paouris, E.; Papailiou, M.; Souvatzoglou, G.

2015-08-01

The ground based neutron monitor measurements play a key role in the field of space physics, solar-terrestrial relations, and space weather applications. The Athens cosmic ray group has developed several research applications such as an optimized automated Ground Level Enhancement Alert (GLE Alert Plus) and a web interface, providing data from multiple Neutron Monitor stations (Multi-Station tool). These services are actually available via the Space Weather Portal operated by the European Space Agency (http://swe.ssa.esa.int). In addition, two simulation tools, based on Geant4, have also been implemented. The first one is for the simulation of the cosmic ray showers in the atmosphere (DYASTIMA) and the second one is for the simulation of the 6NM-64 neutron monitor. The contribution of the simulation tools to the calculations of the radiation dose received by air crews and passengers within the Earth's atmosphere and to the neutron monitor study is presented as well. Furthermore, the accurate calculation of the barometric coefficient and the primary data processing by filtering algorithms, such as the well known Median Editor and the developed by the Athens group ANN Algorithm and Edge Editor which contribute to the provision of high quality neutron monitor data are also discussed. Finally, a Space Weather Forecasting Center which provides a three day geomagnetic activity report on a daily basis has been set up and has been operating for the last two years at the Athens Neutron Monitor Station.

Aperture tolerances for neutron-imaging systems in inertial confinement fusion.

PubMed

Ghilea, M C; Sangster, T C; Meyerhofer, D D; Lerche, R A; Disdier, L

2008-02-01

Neutron-imaging systems are being considered as an ignition diagnostic for the National Ignition Facility (NIF) [Hogan et al., Nucl. Fusion 41, 567 (2001)]. Given the importance of these systems, a neutron-imaging design tool is being used to quantify the effects of aperture fabrication and alignment tolerances on reconstructed neutron images for inertial confinement fusion. The simulations indicate that alignment tolerances of more than 1 mrad would introduce measurable features in a reconstructed image for both pinholes and penumbral aperture systems. These simulations further show that penumbral apertures are several times less sensitive to fabrication errors than pinhole apertures.

The Unbiased Velocity Distribution of Neutron Stars from a Simulation of Pulsar Surveys

NASA Astrophysics Data System (ADS)

Arzoumanian, Z.; Cordes, J. M.; Chernoff, D.

1997-12-01

We present the results of a new simulation of the Galactic population of neutron stars: their birthrate, velocity distribution, luminosities, beaming characteristics, and spin evolution. The many simulations in the literature differ from one another primarily in their treatment of the selection effects associated with pulsar detection. Our method, the most realistic to date, goes beyond earlier efforts by retaining the full kinematic, rotational, luminosity, and beaming evolution of each simulated star: ``Monte-Carlo'' neutron stars are created according to assumed distributions (at birth) in spatial coordinates, kick velocity, and magnitudes and orientations of the spin and magnetic field vectors. The neutron stars spin down following an assumed braking law, and their Galactic trajectories are traced to the present epoch. For each star, a pulse waveform is generated using a phenomenological radio-beam model, obviating the need for an arbitrary beaming fraction. Luminosity is assumed to be a parameterized function of period and spin-down rate, with no intrinsic spread, and a parameterized death-line is applied. Interstellar dispersion and scattering consistent with survey instrumentation and the galactic locales of the neutron stars are applied to the pulse waveforms, which are Fourier analyzed and tested for detection following the techniques of real-world surveys. A unique algorithm is used to compare the populations of simulated and known, non-millisecond, pulsars in the multi-dimensional space of observables (any subset of galactic coordinates, dispersion measure, period, spin-down rate, flux, and proper motion). Model parameters are varied, and statistically independent neutron star populations are created until a maximum likelihood model is found. The highlight of this effort is an unbiased determination of the velocity distribution of neutron stars. We discuss the implications of our results for supernova physics, binary evolution, and the nature of gamma -ray transients.

Thick-foils activation technique for neutron spectrum unfolding with the MINUIT routine-Comparison with GEANT4 simulations

NASA Astrophysics Data System (ADS)

Vagena, E.; Theodorou, K.; Stoulos, S.

2018-04-01

Neutron activation technique has been applied using a proposed set of twelve thick metal foils (Au, As, Cd, In, Ir, Er, Mn, Ni, Se, Sm, W, Zn) for off-site measurements to obtain the neutron spectrum over a wide energy range (from thermal up to a few MeV) in intense neutron-gamma mixed fields such as around medical Linacs. The unfolding procedure takes into account the activation rates measured using thirteen (n , γ) and two (n , p) reactions without imposing a guess solution-spectrum. The MINUIT minimization routine unfolds a neutron spectrum that is dominated by fast neutrons (70%) peaking at 0.3 MeV, while the thermal peak corresponds to the 15% of the total neutron fluence equal to the epithermal-resonances area. The comparison of the unfolded neutron spectrum against the simulated one with the GEANT4 Monte-Carlo code shows a reasonable agreement within the measurement uncertainties. Therefore, the proposed set of activation thick-foils could be a useful tool in order to determine low flux neutrons spectrum in intense mixed field.

Progress in the development of the neutron flux monitoring system of the French GEN-IV SFR: simulations and experimental validations [ANIMMA--2015-IO-98

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jammes, C.; Filliatre, P.; De Izarra, G.

The neutron flux monitoring system of the French GEN-IV sodium-cooled fast reactor will rely on high temperature fission chambers installed in the reactor vessel and capable of operating over a wide-range neutron flux. The definition of such a system is presented and the technological solutions are justified with the use of simulation and experimental results. (authors)

Opportunities afforded by the intense nanosecond neutron pulses from a plasma focus source for neutron capture therapy and the preliminary simulation results

NASA Astrophysics Data System (ADS)

Giannini, G.; Gribkov, V.; Longo, F.; Ramos Aruca, M.; Tuniz, C.

2012-11-01

The use of short and powerful neutron pulses for boron neutron capture therapy (BNCT) can potentially increase selectivity and reduce the total dose absorbed by the patient. The biological effects of radiation depend on the dose, the dose power and the spatial distribution of the microscopic energy deposition. A dense plasma focus (DPF) device emits very short (in the nanosecond range) and extremely intense pulses of fast neutrons (2.5 or 14 MeV neutrons—from D-D or D-T nuclear reactions) and x-rays. Optimal spectra of neutrons formed for use in BNCT must contain an epithermal part to ensure a reasonable penetration depth into tissues at high enough cross-section on boron. So the powerful nanosecond pulses of fast neutrons generated by DPF must be moderated. After this moderation, the pulse duration must be shorter compared with the duration of the reaction with free radicals, that is, ⩾1 μs. In this work we focus on the development of a detailed simulation of interaction of short-pulse radiation from a DPF with the device's materials and with different types of moderators to estimate the dose power at the cells for this dynamic case. The simulation was carried out by means of the Geant4 toolkit in two main steps: the modeling of the pulsed neutron source device itself; the study of the interaction of fast mono-energetic neutrons with a moderator specific for BNCT.

MONDO: a neutron tracker for particle therapy secondary emission characterisation

NASA Astrophysics Data System (ADS)

Marafini, M.; Gasparini, L.; Mirabelli, R.; Pinci, D.; Patera, V.; Sciubba, A.; Spiriti, E.; Stoppa, D.; Traini, G.; Sarti, A.

2017-04-01

Tumour control is performed in particle therapy using particles and ions, whose high irradiation precision enhances the effectiveness of the treatment, while sparing the healthy tissue surrounding the target volume. Dose range monitoring devices using photons and charged particles produced by the beam interacting with the patient’s body have already been proposed, but no attempt has been made yet to exploit the detection of the abundant neutron component. Since neutrons can release a significant dose far away from the tumour region, precise measurements of their flux, production energy and angle distributions are eagerly sought in order to improve the treatment planning system (TPS) software. It will thus be possible to predict not only the normal tissue toxicity in the target region, but also the risk of late complications in the whole body. The aforementioned issues underline the importance of an experimental effort devoted to the precise characterisation of neutron production, aimed at the measurement of their abundance, emission point and production energy. The technical challenges posed by a neutron detector aimed at high detection efficiency and good backtracking precision are addressed within the MONDO (monitor for neutron dose in hadrontherapy) project, whose main goal is to develop a tracking detector that can target fast and ultrafast neutrons. A full reconstruction of two consecutive elastic scattering interactions undergone by the neutrons inside the detector material will be used to measure their energy and direction. The preliminary results of an MC simulation performed using the FLUKA software are presented here, together with the DSiPM (digital SiPM) readout implementation. New detector readout implementations specifically tailored to the MONDO tracker are also discussed, and the neutron detection efficiency attainable with the proposed neutron tracking strategy are reported.

The neutron channeling phenomenon.

PubMed

Khanouchi, A; Sabir, A; Boulkheir, M; Ichaoui, R; Ghassoun, J; Jehouani, A

1997-01-01

Shields, used for protection against radiation, are often pierced with vacuum channels for passing cables and other instruments for measurements. The neutron transmission through these shields is an unavoidable phenomenon. In this work we study and discuss the effect of channels on neutron transmission through shields. We consider an infinite homogeneous slab, with a fixed thickness (20 lambda, with lambda the mean free path of the neutron in the slab), which contains a vacuum channel. This slab is irradiated with an infinite source of neutrons on the left side and on the other side (right side) many detectors with windows equal to 2 lambda are placed in order to evaluate the neutron transmission probabilities (Khanouchi, A., Aboubekr, A., Ghassoun, J. and Jehouani, A. (1994) Rencontre Nationale des Jeunes Chercheurs en Physique. Casa Blanca Maroc; Khanouchi, A., Sabir, A., Ghassoun, J. and Jehouani, A. (1995) Premier Congré International des Intéractions Rayonnements Matière. Eljadida Maroc). The neutron history within the slab is simulated by the Monte Carlo method (Booth, T. E. and Hendricks, J. S. (1994) Nuclear Technology 5) and using the exponential biasing technique in order to improve the Monte Carlo calculation (Levitt, L. B. (1968) Nuclear Science and Engineering 31, 500-504; Jehouani, A., Ghassoun, J. and Aboubker, A. (1994) In Proceedings of the 6th International Symposium on Radiation Physics, Rabat, Morocco). Then different geometries of the vacuum channel have been studied. For each geometry we have determined the detector response and calculated the neutron transmission probability for different detector positions. This neutron transmission probability presents a peak for the detectors placed in front of the vacuum channel. This study allowed us to clearly identify the neutron channeling phenomenon. One application of our study is to detect vacuum defects in materials.

MONDO: a neutron tracker for particle therapy secondary emission characterisation.

PubMed

Marafini, M; Gasparini, L; Mirabelli, R; Pinci, D; Patera, V; Sciubba, A; Spiriti, E; Stoppa, D; Traini, G; Sarti, A

2017-04-21

Tumour control is performed in particle therapy using particles and ions, whose high irradiation precision enhances the effectiveness of the treatment, while sparing the healthy tissue surrounding the target volume. Dose range monitoring devices using photons and charged particles produced by the beam interacting with the patient's body have already been proposed, but no attempt has been made yet to exploit the detection of the abundant neutron component. Since neutrons can release a significant dose far away from the tumour region, precise measurements of their flux, production energy and angle distributions are eagerly sought in order to improve the treatment planning system (TPS) software. It will thus be possible to predict not only the normal tissue toxicity in the target region, but also the risk of late complications in the whole body. The aforementioned issues underline the importance of an experimental effort devoted to the precise characterisation of neutron production, aimed at the measurement of their abundance, emission point and production energy. The technical challenges posed by a neutron detector aimed at high detection efficiency and good backtracking precision are addressed within the MONDO (monitor for neutron dose in hadrontherapy) project, whose main goal is to develop a tracking detector that can target fast and ultrafast neutrons. A full reconstruction of two consecutive elastic scattering interactions undergone by the neutrons inside the detector material will be used to measure their energy and direction. The preliminary results of an MC simulation performed using the FLUKA software are presented here, together with the DSiPM (digital SiPM) readout implementation. New detector readout implementations specifically tailored to the MONDO tracker are also discussed, and the neutron detection efficiency attainable with the proposed neutron tracking strategy are reported.

Optimization of the Efficiency of a Neutron Detector to Measure (α, n) Reaction Cross-Section

NASA Astrophysics Data System (ADS)

Perello, Jesus; Montes, Fernando; Ahn, Tony; Meisel, Zach; Joint InstituteNuclear Astrophysics Team

2015-04-01

Nucleosynthesis, the origin of elements, is one of the greatest mysteries in physics. A recent particular nucleosynthesis process of interest is the charge-particle process (cpp). In the cpp, elements form by nuclear fusion reactions during supernovae. This process of nuclear fusion, (α,n), will be studied by colliding beam elements produced and accelerated at the National Superconducting Cyclotron Laboratory (NSCL) to a helium-filled cell target. The elements will fuse with α (helium nuclei) and emit neutrons during the reaction. The neutrons will be detected for a count of fused-elements, thus providing us the probability of such reactions. The neutrons will be detected using the Neutron Emission Ratio Observer (NERO). Currently, NERO's efficiency varies for neutrons at the expected energy range (0-12 MeV). To study (α,n), NERO's efficiency must be near-constant at these energies. Monte-Carlo N-Particle Transport Code (MCNP6), a software package that simulates nuclear processes, was used to optimize NERO configuration for the experiment. MCNP6 was used to simulate neutron interaction with different NERO configurations at the expected neutron energies. By adding additional 3He detectors and polyethylene, a near-constant efficiency at these energies was obtained in the simulations. With the new NERO configuration, study of the (α,n) reactions can begin, which may explain how elements are formed in the cpp. SROP MSU, NSF, JINA, McNair Society.

Design of the radiation shielding for the time of flight enhanced diagnostics neutron spectrometer at Experimental Advanced Superconducting Tokamak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, T. F.; Chen, Z. J.; Peng, X. Y.

A radiation shielding has been designed to reduce scattered neutrons and background gamma-rays for the new double-ring Time Of Flight Enhanced Diagnostics (TOFED). The shielding was designed based on simulation with the Monte Carlo code MCNP5. Dedicated model of the EAST tokamak has been developed together with the emission neutron source profile and spectrum; the latter were simulated with the Nubeam and GENESIS codes. Significant reduction of background radiation at the detector can be achieved and this satisfies the requirement of TOFED. The intensities of the scattered and direct neutrons in the line of sight of the TOFED neutron spectrometermore » at EAST are studied for future data interpretation.« less

MEASUREMENTS OF NEUTRON SPECTRA IN 0.8-GEV AND 1.6-GEV PROTON-IRRADIATED<2 OF 2>NA THICK TARGETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Titarenko, Y. E.; Batyaev, V. F.; Zhivun, V. M.

2001-01-01

Measurements of neutron spectra in W, and Na targets irradiated by 0.8 GeV and 1.6 GeV protons are presented. Measurements were made by the TOF techniques using the proton beam from ITEP U-10 synchrotron. Neutrons were detected with BICRON-511 liquid scintillator-based detectors. The neutron detection efficiency was calculated via the SCINFUL and CECIL codes. The W results are compared with the similar data obtained elsewhere. The measured neutron spectra are compared with the LAHET and CEM2k code simulations results. Attempt is made to explain some observed disagreements between experiments and simulations. The presented results are of interest both in termsmore » of nuclear data buildup and as a benchmark of the up-to-date predictive power of the simulation codes used in designing the hybrid accelerator-driven system (ADS) facilities with sodium-cooled tungsten targets.« less

Gravitational waveforms for neutron star binaries from binary black hole simulations

NASA Astrophysics Data System (ADS)

Barkett, Kevin; Scheel, Mark; Haas, Roland; Ott, Christian; Bernuzzi, Sebastiano; Brown, Duncan; Szilagyi, Bela; Kaplan, Jeffrey; Lippuner, Jonas; Muhlberger, Curran; Foucart, Francois; Duez, Matthew

2016-03-01

Gravitational waves from binary neutron star (BNS) and black-hole/neutron star (BHNS) inspirals are primary sources for detection by the Advanced Laser Interferometer Gravitational-Wave Observatory. The tidal forces acting on the neutron stars induce changes in the phase evolution of the gravitational waveform, and these changes can be used to constrain the nuclear equation of state. Current methods of generating BNS and BHNS waveforms rely on either computationally challenging full 3D hydrodynamical simulations or approximate analytic solutions. We introduce a new method for computing inspiral waveforms for BNS/BHNS systems by adding the post-Newtonian (PN) tidal effects to full numerical simulations of binary black holes (BBHs), effectively replacing the non-tidal terms in the PN expansion with BBH results. Comparing a waveform generated with this method against a full hydrodynamical simulation of a BNS inspiral yields a phase difference of < 1 radian over ~ 15 orbits. The numerical phase accuracy required of BNS simulations to measure the accuracy of the method we present here is estimated as a function of the tidal deformability parameter λ.

Gravitational waveforms for neutron star binaries from binary black hole simulations

NASA Astrophysics Data System (ADS)

Barkett, Kevin; Scheel, Mark A.; Haas, Roland; Ott, Christian D.; Bernuzzi, Sebastiano; Brown, Duncan A.; Szilágyi, Béla; Kaplan, Jeffrey D.; Lippuner, Jonas; Muhlberger, Curran D.; Foucart, Francois; Duez, Matthew D.

2016-02-01

Gravitational waves from binary neutron star (BNS) and black hole/neutron star (BHNS) inspirals are primary sources for detection by the Advanced Laser Interferometer Gravitational-Wave Observatory. The tidal forces acting on the neutron stars induce changes in the phase evolution of the gravitational waveform, and these changes can be used to constrain the nuclear equation of state. Current methods of generating BNS and BHNS waveforms rely on either computationally challenging full 3D hydrodynamical simulations or approximate analytic solutions. We introduce a new method for computing inspiral waveforms for BNS/BHNS systems by adding the post-Newtonian (PN) tidal effects to full numerical simulations of binary black holes (BBHs), effectively replacing the nontidal terms in the PN expansion with BBH results. Comparing a waveform generated with this method against a full hydrodynamical simulation of a BNS inspiral yields a phase difference of <1 radian over ˜15 orbits. The numerical phase accuracy required of BNS simulations to measure the accuracy of the method we present here is estimated as a function of the tidal deformability parameter λ .

Geant4 Modifications for Accurate Fission Simulations

NASA Astrophysics Data System (ADS)

Tan, Jiawei; Bendahan, Joseph

Monte Carlo is one of the methods to simulate the generation and transport of radiation through matter. The most widely used radiation simulation codes are MCNP and Geant4. The simulation of fission production and transport by MCNP has been thoroughly benchmarked. There is an increasing number of users that prefer using Geant4 due to the flexibility of adding features. However, it has been found that Geant4 does not have the proper fission-production cross sections and does not produce the correct fission products. To achieve accurate results for studies in fissionable material applications, Geant4 was modified to correct these inaccuracies and to add new capabilities. The fission model developed by the Lawrence Livermore National Laboratory was integrated into the neutron-fission modeling package. The photofission simulation capability was enabled using the same neutron-fission library under the assumption that nuclei fission in the same way, independent of the excitation source. The modified fission code provides the correct multiplicity of prompt neutrons and gamma rays, and produces delayed gamma rays and neutrons with time and energy dependencies that are consistent with ENDF/B-VII. The delayed neutrons are now directly produced by a custom package that bypasses the fragment cascade model. The modifications were made for U-235, U-238 and Pu-239 isotopes; however, the new framework allows adding new isotopes easily. The SLAC nuclear data library is used for simulation of isotopes with an atomic number above 92 because it is not available in Geant4. Results of the modified Geant4.10.1 package of neutron-fission and photofission for prompt and delayed radiation are compared with ENDFB-VII and with results produced with the original package.

A Computational Approach for Modeling Neutron Scattering Data from Lipid Bilayers

DOE PAGES

Carrillo, Jan-Michael Y.; Katsaras, John; Sumpter, Bobby G.; ...

2017-01-12

Biological cell membranes are responsible for a range of structural and dynamical phenomena crucial to a cell's well-being and its associated functions. Due to the complexity of cell membranes, lipid bilayer systems are often used as biomimetic models. These systems have led to signficant insights into vital membrane phenomena such as domain formation, passive permeation and protein insertion. Experimental observations of membrane structure and dynamics are, however, limited in resolution, both spatially and temporally. Importantly, computer simulations are starting to play a more prominent role in interpreting experimental results, enabling a molecular under- standing of lipid membranes. Particularly, the synergymore » between scattering experiments and simulations offers opportunities for new discoveries in membrane physics, as the length and time scales probed by molecular dynamics (MD) simulations parallel those of experiments. We also describe a coarse-grained MD simulation approach that mimics neutron scattering data from large unilamellar lipid vesicles over a range of bilayer rigidity. Specfically, we simulate vesicle form factors and membrane thickness fluctuations determined from small angle neutron scattering (SANS) and neutron spin echo (NSE) experiments, respectively. Our simulations accurately reproduce trends from experiments and lay the groundwork for investigations of more complex membrane systems.« less

Soil Moisture Estimation Across Scales with Mobile Sensors for Cosmic-Ray Neutrons from the Ground and Air

NASA Astrophysics Data System (ADS)

Schrön, Martin; Köhler, Mandy; Bannehr, Lutz; Köhli, Markus; Fersch, Benjamin; Rebmann, Corinna; Mai, Juliane; Cuntz, Matthias; Kögler, Simon; Schröter, Ingmar; Wollschläger, Ute; Oswald, Sascha; Dietrich, Peter; Zacharias, Steffen

2016-04-01

Soil moisture is a key variable for environmental sciences, but its determination at various scales and depths is still an open challenge. Cosmic-ray neutron sensing has become a well accepted and unique method to monitor an effective soil water content, covering tens of hectares in area and tens of centimeters in depth. The technology is famous for its low maintanance, non-invasiveness, continous measurement, and most importantly its large footprint and penetration depth. Beeing more representative than point data, and finer resolved plus deeper penetrating than remote-sensing products, cosmic-ray neutron derived soil moisture products provide unrivaled advantage for agriculture, regional hydrologic and land surface models. The method takes advantage of omnipresent neutrons which are extraordinarily sensitive to hydrogen in soil, plants, snow and air. Unwanted hydrogen sources in the footprint can be excluded by local calibration to extract the pure soil water information. However, this procedure is not feasible for mobile measurements, where neutron detectors are mounted on a car to do catchment-scale surveys. As a solution to that problem, we suggest strategies to correct spatial neutron data with the help of available spatial data of soil type, landuse and vegetation. We further present results of mobile rover campaigns at various scales and conditions, covering small sites from 0.2 km2 to catchments of 100 km2 area, and complex terrain from agricultural fields, urban areas, forests, to snowy alpine sites. As the rover is limited to accessible roads, we further investigated the applicability of airborne measurements. First tests with a gyrocopter at 150 to 200m heights proofed the concept of airborne neutron detection for environmental sciences. Moreover, neutron transport simulations confirm an improved areal coverage during these campaigns. Mobile neutron measurements at the ground or air are a promising tool for the detection of water sources across many scales. The method has a great potential to improve spatial performance of hydrological models, and help to assess regional soil moisture states for agriculture and flood risk management.

Modeling of ground albedo neutrons to investigate seasonal cosmic ray-induced neutron variations measured at high-altitude stations

NASA Astrophysics Data System (ADS)

Hubert, G.; Pazianotto, M. T.; Federico, C. A.

2016-12-01

This paper investigates seasonal cosmic ray-induced neutron variations measured over a long-term period (from 2011 to 2016) in both the high-altitude stations located in medium geomagnetic latitude and Antarctica (Pic-du-Midi and Concordia, respectively). To reinforce analysis, modeling based on ground albedo neutrons simulations of extensive air showers and the solar modulation potential was performed. Because the local environment is well known and stable over time in Antarctica, data were used to validate the modeling approach. A modeled scene representative to the Pic-du-Midi was simulated with GEANT4 for various hydrogen properties (composition, density, and wet level) and snow thickness. The orders of magnitudes of calculated thermal fluence rates are consistent with measurements obtained during summers and winters. These variations are dominant in the thermal domain (i.e., En < 0.5 eV) and lesser degree in epithermal and evaporation domains (i.e., 0.5 eV < En < 0.1 MeV and 0.1 MeV < En < 20 MeV, respectively). Cascade neutron (En > 20 MeV) is weakly impacted. The role of hydrogen content on ground albedo neutron generation was investigated with GEANT4 simulations. These investigations focused to mountain environment; nevertheless, they demonstrate the complexity of the local influences on neutron fluence rates.

Development of Measurement Methods for Detection of Special Nuclear Materials using D-D Pulsed Neutron Source

NASA Astrophysics Data System (ADS)

Misawa, Tsuyoshi; Takahashi, Yoshiyuki; Yagi, Takahiro; Pyeon, Cheol Ho; Kimura, Masaharu; Masuda, Kai; Ohgaki, Hideaki

2015-10-01

For detection of hidden special nuclear materials (SNMs), we have developed an active neutron-based interrogation system combined with a D-D fusion pulsed neutron source and a neutron detection system. In the detection scheme, we have adopted new measurement techniques simultaneously; neutron noise analysis and neutron energy spectrum analysis. The validity of neutron noise analysis method has been experimentally studied in the Kyoto University Critical Assembly (KUCA), and was applied to a cargo container inspection system by simulation.

Neutron reflecting supermirror structure

DOEpatents

Wood, J.L.

1992-12-01

An improved neutron reflecting supermirror structure comprising a plurality of stacked sets of bilayers of neutron reflecting materials. The improved neutron reflecting supermirror structure is adapted to provide extremely good performance at high incidence angles, i.e. up to four time the critical angle of standard neutron mirror structures. The reflection of neutrons striking the supermirror structure at a high critical angle provides enhanced neutron throughput, and hence more efficient and economical use of neutron sources. 2 figs.

Neutron reflecting supermirror structure

DOEpatents

Wood, James L.

1992-01-01

An improved neutron reflecting supermirror structure comprising a plurality of stacked sets of bilayers of neutron reflecting materials. The improved neutron reflecting supermirror structure is adapted to provide extremely good performance at high incidence angles, i.e. up to four time the critical angle of standard neutron mirror structures. The reflection of neutrons striking the supermirror structure at a high critical angle provides enhanced neutron throughput, and hence more efficient and economical use of neutron sources.

MCNP SIMULATION OF THE HP(10) ENERGY RESPONSE OF A BRAZILIAN TLD ALBEDO NEUTRON INDIVIDUAL DOSEMETER, FROM THERMAL TO 20 MeV.

PubMed

Freitas, B M; Martins, M M; Pereira, W W; da Silva, A X; Mauricio, C L P

2016-09-01

The Brazilian Instituto de Radioproteção e Dosimetria (IRD) runs a neutron individual monitoring system with a home-made TLD albedo dosemeter. It has already been characterised and calibrated in some reference fields. However, the complete energy response of this dosemeter is not known, and the calibration factors for all monitored workplace neutron fields are difficult to be obtained experimentally. Therefore, to overcome such difficulties, Monte Carlo simulations have been used. This paper describes the simulation of the HP(10) neutron response of the IRD TLD albedo dosemeter using the MCNPX transport code, for energies from thermal to 20 MeV. The validation of the MCNPX modelling is done comparing the simulated results with the experimental measurements for ISO standard neutron fields of (241)Am-Be, (252)Cf, (241)Am-B and (252)Cf(D2O) and also for (241)Am-Be source moderated with paraffin and silicone. Bare (252)Cf are used for normalisation. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Upgrade of the compact neutron spectrometer for high flux environments

NASA Astrophysics Data System (ADS)

Osipenko, M.; Bellucci, A.; Ceriale, V.; Corsini, D.; Gariano, G.; Gatti, F.; Girolami, M.; Minutoli, S.; Panza, F.; Pillon, M.; Ripani, M.; Trucchi, D. M.

2018-03-01

In this paper new version of the 6Li-based neutron spectrometer for high flux environments is described. The new spectrometer was built with commercial single crystal Chemical Vapour Deposition diamonds of electronic grade. These crystals feature better charge collection as well as higher radiation hardness. New metal contacts approaching ohmic conditions were deposited on the diamonds suppressing build-up of space charge observed in the previous prototypes. New passive preamplification of the signal at detector side was implemented to improve its resolution. This preamplification is based on the RF transformer not sensitive to high neutron flux. The compact mechanical design allowed to reduce detector size to a tube of 1 cm diameter and 13 cm long. The spectrometer was tested in the thermal column of TRIGA reactor and at the DD neutron generator. The test results indicate an energy resolution of 300 keV (FWHM), reduced to 72 keV (RMS) excluding energy loss, and coincidence timing resolution of 160 ps (FWHM). The measured data are in agreement with Geant4 simulations except for larger energy loss tail presumably related to imperfections of metal contacts and glue expansion.

Neutron capture therapy with deep tissue penetration using capillary neutron focusing

DOEpatents

Peurrung, Anthony J.

1997-01-01

An improved method for delivering thermal neutrons to a subsurface cancer or tumor which has been first doped with a dopant having a high cross section for neutron capture. The improvement is the use of a guide tube in cooperation with a capillary neutron focusing apparatus, or neutron focusing lens, for directing neutrons to the tumor, and thereby avoiding damage to surrounding tissue.

Discrete-Event Simulation Unmasks the Quantum Cheshire Cat

NASA Astrophysics Data System (ADS)

Michielsen, Kristel; Lippert, Thomas; Raedt, Hans De

2017-05-01

It is shown that discrete-event simulation accurately reproduces the experimental data of a single-neutron interferometry experiment [T. Denkmayr {\\sl et al.}, Nat. Commun. 5, 4492 (2014)] and provides a logically consistent, paradox-free, cause-and-effect explanation of the quantum Cheshire cat effect without invoking the notion that the neutron and its magnetic moment separate. Describing the experimental neutron data using weak-measurement theory is shown to be useless for unravelling the quantum Cheshire cat effect.

The effects of nuclear data library processing on Geant4 and MCNP simulations of the thermal neutron scattering law

NASA Astrophysics Data System (ADS)

Hartling, K.; Ciungu, B.; Li, G.; Bentoumi, G.; Sur, B.

2018-05-01

Monte Carlo codes such as MCNP and Geant4 rely on a combination of physics models and evaluated nuclear data files (ENDF) to simulate the transport of neutrons through various materials and geometries. The grid representation used to represent the final-state scattering energies and angles associated with neutron scattering interactions can significantly affect the predictions of these codes. In particular, the default thermal scattering libraries used by MCNP6.1 and Geant4.10.3 do not accurately reproduce the ENDF/B-VII.1 model in simulations of the double-differential cross section for thermal neutrons interacting with hydrogen nuclei in a thin layer of water. However, agreement between model and simulation can be achieved within the statistical error by re-processing ENDF/B-VII.I thermal scattering libraries with the NJOY code. The structure of the thermal scattering libraries and sampling algorithms in MCNP and Geant4 are also reviewed.

Influence of surface oxidation on ion dynamics and capacitance in porous and nonporous carbon electrodes

DOE PAGES

Dyatkin, Boris; Zhang, Yu; Mamontov, Eugene; ...

2016-04-07

Here, we investigate the influence of surface chemistry and ion confinement on capacitance and electrosorption dynamics of room-temperature ionic liquids (RTILs) in supercapacitors. Using air oxidation and vacuum annealing, we produced defunctionalized and oxygen-rich surfaces of carbide-derived carbons (CDCs) and graphene nanoplatelets (GNPs). While oxidized surfaces of porous CDCs improve capacitance and rate handling abilities of ions, defunctionalized nonporous GNPs improve charge storage densities on planar electrodes. Quasi-elastic neutron scattering (QENS) and inelastic neutron scattering (INS) probed the structure, dynamics, and orientation of RTIL ions confined in divergently functionalized pores. Oxidized, ionophilic surfaces draw ions closer to pore surfaces andmore » enhance potential-driven ion transport during electrosorption. Molecular dynamics (MD) simulations corroborated experimental data and demonstrated the significance of surface functional groups on ion orientations, accumulation densities, and capacitance.« less

Detailed high-resolution three-dimensional simulations of OMEGA separated reactants inertial confinement fusion experiments

DOE PAGES

Haines, Brian Michael; Grim, Gary P.; Fincke, James R.; ...

2016-07-29

Here, we present results from the comparison of high-resolution three-dimensional (3D) simulations with data from the implosions of inertial confinement fusion capsules with separated reactants performed on the OMEGA laser facility. Each capsule, referred to as a “CD Mixcap,” is filled with tritium and has a polystyrene (CH) shell with a deuterated polystyrene (CD) layer whose burial depth is varied. In these implosions, fusion reactions between deuterium and tritium ions can occur only in the presence of atomic mix between the gas fill and shell material. The simulations feature accurate models for all known experimental asymmetries and do not employmore » any adjustable parameters to improve agreement with experimental data. Simulations are performed with the RAGE radiation-hydrodynamics code using an Implicit Large Eddy Simulation (ILES) strategy for the hydrodynamics. We obtain good agreement with the experimental data, including the DT/TT neutron yield ratios used to diagnose mix, for all burial depths of the deuterated shell layer. Additionally, simulations demonstrate good agreement with converged simulations employing explicit models for plasma diffusion and viscosity, suggesting that the implicit sub-grid model used in ILES is sufficient to model these processes in these experiments. In our simulations, mixing is driven by short-wavelength asymmetries and longer-wavelength features are responsible for developing flows that transport mixed material towards the center of the hot spot. Mix material transported by this process is responsible for most of the mix (DT) yield even for the capsule with a CD layer adjacent to the tritium fuel. Consistent with our previous results, mix does not play a significant role in TT neutron yield degradation; instead, this is dominated by the displacement of fuel from the center of the implosion due to the development of turbulent instabilities seeded by long-wavelength asymmetries. Through these processes, the long-wavelength asymmetries degrade TT yield more than the DT yield and thus bring DT/TT neutron yield ratios into agreement with experiment. Finally, we present a detailed comparison of the flows in 2D and 3D simulations.« less

Detailed high-resolution three-dimensional simulations of OMEGA separated reactants inertial confinement fusion experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haines, Brian M., E-mail: bmhaines@lanl.gov; Fincke, James R.; Shah, Rahul C.

We present results from the comparison of high-resolution three-dimensional (3D) simulations with data from the implosions of inertial confinement fusion capsules with separated reactants performed on the OMEGA laser facility. Each capsule, referred to as a “CD Mixcap,” is filled with tritium and has a polystyrene (CH) shell with a deuterated polystyrene (CD) layer whose burial depth is varied. In these implosions, fusion reactions between deuterium and tritium ions can occur only in the presence of atomic mix between the gas fill and shell material. The simulations feature accurate models for all known experimental asymmetries and do not employ anymore » adjustable parameters to improve agreement with experimental data. Simulations are performed with the RAGE radiation-hydrodynamics code using an Implicit Large Eddy Simulation (ILES) strategy for the hydrodynamics. We obtain good agreement with the experimental data, including the DT/TT neutron yield ratios used to diagnose mix, for all burial depths of the deuterated shell layer. Additionally, simulations demonstrate good agreement with converged simulations employing explicit models for plasma diffusion and viscosity, suggesting that the implicit sub-grid model used in ILES is sufficient to model these processes in these experiments. In our simulations, mixing is driven by short-wavelength asymmetries and longer-wavelength features are responsible for developing flows that transport mixed material towards the center of the hot spot. Mix material transported by this process is responsible for most of the mix (DT) yield even for the capsule with a CD layer adjacent to the tritium fuel. Consistent with our previous results, mix does not play a significant role in TT neutron yield degradation; instead, this is dominated by the displacement of fuel from the center of the implosion due to the development of turbulent instabilities seeded by long-wavelength asymmetries. Through these processes, the long-wavelength asymmetries degrade TT yield more than the DT yield and thus bring DT/TT neutron yield ratios into agreement with experiment. Finally, we present a detailed comparison of the flows in 2D and 3D simulations.« less

Detailed high-resolution three-dimensional simulations of OMEGA separated reactants inertial confinement fusion experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haines, Brian Michael; Grim, Gary P.; Fincke, James R.

Here, we present results from the comparison of high-resolution three-dimensional (3D) simulations with data from the implosions of inertial confinement fusion capsules with separated reactants performed on the OMEGA laser facility. Each capsule, referred to as a “CD Mixcap,” is filled with tritium and has a polystyrene (CH) shell with a deuterated polystyrene (CD) layer whose burial depth is varied. In these implosions, fusion reactions between deuterium and tritium ions can occur only in the presence of atomic mix between the gas fill and shell material. The simulations feature accurate models for all known experimental asymmetries and do not employmore » any adjustable parameters to improve agreement with experimental data. Simulations are performed with the RAGE radiation-hydrodynamics code using an Implicit Large Eddy Simulation (ILES) strategy for the hydrodynamics. We obtain good agreement with the experimental data, including the DT/TT neutron yield ratios used to diagnose mix, for all burial depths of the deuterated shell layer. Additionally, simulations demonstrate good agreement with converged simulations employing explicit models for plasma diffusion and viscosity, suggesting that the implicit sub-grid model used in ILES is sufficient to model these processes in these experiments. In our simulations, mixing is driven by short-wavelength asymmetries and longer-wavelength features are responsible for developing flows that transport mixed material towards the center of the hot spot. Mix material transported by this process is responsible for most of the mix (DT) yield even for the capsule with a CD layer adjacent to the tritium fuel. Consistent with our previous results, mix does not play a significant role in TT neutron yield degradation; instead, this is dominated by the displacement of fuel from the center of the implosion due to the development of turbulent instabilities seeded by long-wavelength asymmetries. Through these processes, the long-wavelength asymmetries degrade TT yield more than the DT yield and thus bring DT/TT neutron yield ratios into agreement with experiment. Finally, we present a detailed comparison of the flows in 2D and 3D simulations.« less

Detailed high-resolution three-dimensional simulations of OMEGA separated reactants inertial confinement fusion experiments

NASA Astrophysics Data System (ADS)

Haines, Brian M.; Grim, Gary P.; Fincke, James R.; Shah, Rahul C.; Forrest, Chad J.; Silverstein, Kevin; Marshall, Frederic J.; Boswell, Melissa; Fowler, Malcolm M.; Gore, Robert A.; Hayes-Sterbenz, Anna C.; Jungman, Gerard; Klein, Andreas; Rundberg, Robert S.; Steinkamp, Michael J.; Wilhelmy, Jerry B.

2016-07-01

We present results from the comparison of high-resolution three-dimensional (3D) simulations with data from the implosions of inertial confinement fusion capsules with separated reactants performed on the OMEGA laser facility. Each capsule, referred to as a "CD Mixcap," is filled with tritium and has a polystyrene (CH) shell with a deuterated polystyrene (CD) layer whose burial depth is varied. In these implosions, fusion reactions between deuterium and tritium ions can occur only in the presence of atomic mix between the gas fill and shell material. The simulations feature accurate models for all known experimental asymmetries and do not employ any adjustable parameters to improve agreement with experimental data. Simulations are performed with the RAGE radiation-hydrodynamics code using an Implicit Large Eddy Simulation (ILES) strategy for the hydrodynamics. We obtain good agreement with the experimental data, including the DT/TT neutron yield ratios used to diagnose mix, for all burial depths of the deuterated shell layer. Additionally, simulations demonstrate good agreement with converged simulations employing explicit models for plasma diffusion and viscosity, suggesting that the implicit sub-grid model used in ILES is sufficient to model these processes in these experiments. In our simulations, mixing is driven by short-wavelength asymmetries and longer-wavelength features are responsible for developing flows that transport mixed material towards the center of the hot spot. Mix material transported by this process is responsible for most of the mix (DT) yield even for the capsule with a CD layer adjacent to the tritium fuel. Consistent with our previous results, mix does not play a significant role in TT neutron yield degradation; instead, this is dominated by the displacement of fuel from the center of the implosion due to the development of turbulent instabilities seeded by long-wavelength asymmetries. Through these processes, the long-wavelength asymmetries degrade TT yield more than the DT yield and thus bring DT/TT neutron yield ratios into agreement with experiment. Finally, we present a detailed comparison of the flows in 2D and 3D simulations.

Investigating the response of Micromegas detector to low-energy neutrons using Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Khezripour, S.; Negarestani, A.; Rezaie, M. R.

2017-08-01

Micromegas detector has recently been used for high-energy neutron (HEN) detection, but the aim of this research is to investigate the response of the Micromegas detector to low-energy neutron (LEN). For this purpose, a Micromegas detector (with air, P10, BF3, 3He and Ar/BF3 mixture) was optimized for the detection of 60 keV neutrons using the MCNP (Monte Carlo N Particle) code. The simulation results show that the optimum thickness of the cathode is 1 mm and the optimum of microgrid location is 100 μm above the anode. The output current of this detector for Ar (3%) + BF3 (97%) mixture is greater than the other ones. This mixture is considered as the appropriate gas for the Micromegas neutron detector providing the output current for 60 keV neutrons at the level of 97.8 nA per neutron. Consecuently, this detector can be introduced as LEN detector.

Theoretical neutron damage calculations in industrial robotic manipulators used for non-destructive imaging applications

DOE PAGES

Hashem, Joseph; Schneider, Erich; Pryor, Mitch; ...

2017-01-01

Our paper describes how to use MCNP to evaluate the rate of material damage in a robot incurred by exposure to a neutron flux. The example used in this work is that of a robotic manipulator installed in a high intensity, fast, and collimated neutron radiography beam port at the University of Texas at Austin's TRIGA Mark II research reactor. Our effort includes taking robotic technologies and using them to automate non-destructive imaging tasks in nuclear facilities where the robotic manipulator acts as the motion control system for neutron imaging tasks. Simulated radiation tests are used to analyze the radiationmore » damage to the robot. Once the neutron damage is calculated using MCNP, several possible shielding materials are analyzed to determine the most effective way of minimizing the neutron damage. Furthermore, neutron damage predictions provide users the means to simulate geometrical and material changes, thus saving time, money, and energy in determining the optimal setup for a robotic system installed in a radiation environment.« less

Multi-layer plastic scintillation detector for intermediate- and high-energy neutrons with n- γ discrimination capability

NASA Astrophysics Data System (ADS)

Yu, L.; Terashima, S.; Ong, H. J.; Chan, P. Y.; Tanihata, I.; Iwamoto, C.; Tran, D. T.; Tamii, A.; Aoi, N.; Fujioka, H.; Gey, G.; Sakaguchi, H.; Sakaue, A.; Sun, B. H.; Tang, T. L.; Wang, T. F.; Watanabe, Y. N.; Zhang, G. X.

2017-09-01

A new type of neutron detector, named Stack Structure Solid organic Scintillator (S4), consisting of multi-layer plastic scintillators with capability to suppress low-energy γ rays under high-counting rate has been constructed and tested. To achieve n- γ discrimination, we exploit the difference in the ranges of the secondary charged particles produced by the interactions of neutrons and γ rays in the scintillator material. The thickness of a plastic scintillator layer was determined based on the results of Monte Carlo simulations using the Geant4 toolkit. With layer thicknesses of 5 mm, we have achieved a good separation between neutrons and γ rays at 5 MeVee threshold setting. We have also determined the detection efficiencies using monoenergetic neutrons at two energies produced by the d + d → n+3He reaction. The results agree well with the Geant4 simulations implementing the Li e ̀ge Intranuclear Cascade hadronic model (INCL++) and the high-precision model of low-energy neutron interactions (NeutronHP).

Theoretical neutron damage calculations in industrial robotic manipulators used for non-destructive imaging applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hashem, Joseph; Schneider, Erich; Pryor, Mitch

Our paper describes how to use MCNP to evaluate the rate of material damage in a robot incurred by exposure to a neutron flux. The example used in this work is that of a robotic manipulator installed in a high intensity, fast, and collimated neutron radiography beam port at the University of Texas at Austin's TRIGA Mark II research reactor. Our effort includes taking robotic technologies and using them to automate non-destructive imaging tasks in nuclear facilities where the robotic manipulator acts as the motion control system for neutron imaging tasks. Simulated radiation tests are used to analyze the radiationmore » damage to the robot. Once the neutron damage is calculated using MCNP, several possible shielding materials are analyzed to determine the most effective way of minimizing the neutron damage. Furthermore, neutron damage predictions provide users the means to simulate geometrical and material changes, thus saving time, money, and energy in determining the optimal setup for a robotic system installed in a radiation environment.« less

The help of simulation codes in designing waste assay systems using neutron measurement methods: Application to the alpha low level waste assay system PROMETHEE 6

NASA Astrophysics Data System (ADS)

Mariani, A.; Passard, C.; Jallu, F.; Toubon, H.

2003-11-01

The design of a specific nuclear assay system for a dedicated application begins with a phase of development, which relies on information from the literature or on knowledge resulting from experience, and on specific experimental verifications. The latter ones may require experimental devices which can be restricting in terms of deadline, cost and safety. One way generally chosen to bypass these difficulties is to use simulation codes to study particular aspects. This paper deals with the potentialities offered by the simulation in the case of a passive-active neutron (PAN) assay system for alpha low level waste characterization; this system has been carried out at the Nuclear Measurements Development Laboratory of the French Atomic Energy Commission. Due to the high number of parameters to be taken into account for its development, this is a particularly sophisticated example. Since the PAN assay system, called PROMETHEE (prompt epithermal and thermal interrogation experiment), must have a detection efficiency of more than 20% and preserve a high level of modularity for various applications, an improved version has been studied using the MCNP4 (Monte Carlo N-Particle) transport code. Parameters such as the dimensions of the assay system, of the cavity and of the detection blocks, and the thicknesses of the nuclear materials of neutronic interest have been optimised. Therefore, the number of necessary experiments was reduced.

MCNP simulation to optimise in-pile and shielding parts of the Portuguese SANS instrument.

PubMed

Gonçalves, I F; Salgado, J; Falcão, A; Margaça, F M A; Carvalho, F G

2005-01-01

A Small Angle Neutron Scattering instrument is being installed at one end of the tangential beam tube of the Portuguese Research Reactor. The instrument is fed using a neutron scatterer positioned in the middle of the beam tube. The scatterer consists of circulating H2O contained in a hollow disc of Al. The in-pile shielding components and the shielding installed around the neutron selector have been the object of an MCNP simulation study. The quantities calculated were the neutron and gamma-ray fluxes in different positions, the energy deposited in the material by the neutron and gamma-ray fields, the material activation resulting from the neutron field and radiation doses at the exit wall of the shutter and around the shielding. The MCNP results are presented and compared with results of an analytical approach and with experimental data collected after installation.

The Multi-Step CADIS method for shutdown dose rate calculations and uncertainty propagation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ibrahim, Ahmad M.; Peplow, Douglas E.; Grove, Robert E.

2015-12-01

Shutdown dose rate (SDDR) analysis requires (a) a neutron transport calculation to estimate neutron flux fields, (b) an activation calculation to compute radionuclide inventories and associated photon sources, and (c) a photon transport calculation to estimate final SDDR. In some applications, accurate full-scale Monte Carlo (MC) SDDR simulations are needed for very large systems with massive amounts of shielding materials. However, these simulations are impractical because calculation of space- and energy-dependent neutron fluxes throughout the structural materials is needed to estimate distribution of radioisotopes causing the SDDR. Biasing the neutron MC calculation using an importance function is not simple becausemore » it is difficult to explicitly express the response function, which depends on subsequent computational steps. Furthermore, the typical SDDR calculations do not consider how uncertainties in MC neutron calculation impact SDDR uncertainty, even though MC neutron calculation uncertainties usually dominate SDDR uncertainty.« less

Neutron capture therapy with deep tissue penetration using capillary neutron focusing

DOEpatents

Peurrung, A.J.

1997-08-19

An improved method is disclosed for delivering thermal neutrons to a subsurface cancer or tumor which has been first doped with a dopant having a high cross section for neutron capture. The improvement is the use of a guide tube in cooperation with a capillary neutron focusing apparatus, or neutron focusing lens, for directing neutrons to the tumor, and thereby avoiding damage to surrounding tissue. 1 fig.

Main drive optimization of a high-foot pulse shape in inertial confinement fusion implosions

NASA Astrophysics Data System (ADS)

Wang, L. F.; Ye, W. H.; Wu, J. F.; Liu, Jie; Zhang, W. Y.; He, X. T.

2016-12-01

While progress towards hot-spot ignition has been made achieving an alpha-heating dominated state in high-foot implosion experiments [Hurricane et al., Nat. Phys. 12, 800 (2016)] on the National Ignition Facility, improvements are needed to increase the fuel compression for the enhancement of the neutron yield. A strategy is proposed to improve the fuel compression through the recompression of a shock/compression wave generated by the end of the main drive portion of a high-foot pulse shape. Two methods for the peak pulse recompression, namely, the decompression-and-recompression (DR) and simple recompression schemes, are investigated and compared. Radiation hydrodynamic simulations confirm that the peak pulse recompression can clearly improve fuel compression without significantly compromising the implosion stability. In particular, when the convergent DR shock is tuned to encounter the divergent shock from the capsule center at a suitable position, not only the neutron yield but also the stability of stagnating hot-spot can be noticeably improved, compared to the conventional high-foot implosions [Hurricane et al., Phys. Plasmas 21, 056314 (2014)].

An automated analysis workflow for optimization of force-field parameters using neutron scattering data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lynch, Vickie E.; Borreguero, Jose M.; Bhowmik, Debsindhu

Graphical abstract: - Highlights: • An automated workflow to optimize force-field parameters. • Used the workflow to optimize force-field parameter for a system containing nanodiamond and tRNA. • The mechanism relies on molecular dynamics simulation and neutron scattering experimental data. • The workflow can be generalized to any other experimental and simulation techniques. - Abstract: Large-scale simulations and data analysis are often required to explain neutron scattering experiments to establish a connection between the fundamental physics at the nanoscale and data probed by neutrons. However, to perform simulations at experimental conditions it is critical to use correct force-field (FF) parametersmore » which are unfortunately not available for most complex experimental systems. In this work, we have developed a workflow optimization technique to provide optimized FF parameters by comparing molecular dynamics (MD) to neutron scattering data. We describe the workflow in detail by using an example system consisting of tRNA and hydrophilic nanodiamonds in a deuterated water (D{sub 2}O) environment. Quasi-elastic neutron scattering (QENS) data show a faster motion of the tRNA in the presence of nanodiamond than without the ND. To compare the QENS and MD results quantitatively, a proper choice of FF parameters is necessary. We use an efficient workflow to optimize the FF parameters between the hydrophilic nanodiamond and water by comparing to the QENS data. Our results show that we can obtain accurate FF parameters by using this technique. The workflow can be generalized to other types of neutron data for FF optimization, such as vibrational spectroscopy and spin echo.« less

Explosives detection using photoneutrons produced by X-rays

NASA Astrophysics Data System (ADS)

Yang, Yigang; Li, Yuanjing; Wang, Haidong; Li, Tiezhu; Wu, Bin

2007-08-01

The detection of explosives has become a critical issue after recent terrorist attacks. This paper describes research on explosives detection using photoneutrons from a photoneutron convertor that consists of 20 kg heavy water in an aluminum container whose shape was optimized to most effectively convert X-rays to photoneutrons. The X-rays were produced by a 9 MeV electron accelerator with an average electron current of 100 μA, resulted in a photoneutron yield of >10 11 n/s. Monte-Carlo simulations show that the radiation field is composed of X-ray pulses, fast neutron pulses and thermal neutrons. Both the X-ray and fast neutron pulses are 5 μs wide with a 300 Hz repetition frequency. The thermal neutron flux, which is higher than 10 4 n/cm 2/s, is essentially time invariant. A time shielding circuit was developed for the spectrometry system to halt the sampling process during the intense X-ray pulses. Paraffin, boron carbide and lead were used to protect the detector from interference from the X-rays, fast neutrons, thermal neutrons and background γ-rays coming from the system materials induced by photoneutrons. 5″×5″ NaI (Tl) scintillators were chosen as the detectors to detect the photoneutrons induced γ-rays from the inspected explosive simulant. Nitrogen (6.01 cps) 10.828 MeV γ-rays were detected with one detector from a 50 kg carbamide block placed 60 cm in front of the detector. A collimator was used to reduce the number of background 10.828 MeV γ-rays coming from the nitrogen in the air to improve the signal to background ratio from 0.136 to 1.81. A detector array of seven 5″×5″ NaI (Tl) detectors was used to measure the 2-D distributions of N and H in the sample. The combination of photoneutron analysis and X-ray imaging shows promise for enhancing explosives detection capabilities.

Neutrons in proton pencil beam scanning: parameterization of energy, quality factors and RBE

NASA Astrophysics Data System (ADS)

Schneider, Uwe; Hälg, Roger A.; Baiocco, Giorgio; Lomax, Tony

2016-08-01

The biological effectiveness of neutrons produced during proton therapy in inducing cancer is unknown, but potentially large. In particular, since neutron biological effectiveness is energy dependent, it is necessary to estimate, besides the dose, also the energy spectra, in order to obtain quantities which could be a measure of the biological effectiveness and test current models and new approaches against epidemiological studies on cancer induction after proton therapy. For patients treated with proton pencil beam scanning, this work aims to predict the spatially localized neutron energies, the effective quality factor, the weighting factor according to ICRP, and two RBE values, the first obtained from the saturation corrected dose mean lineal energy and the second from DSB cluster induction. A proton pencil beam was Monte Carlo simulated using GEANT. Based on the simulated neutron spectra for three different proton beam energies a parameterization of energy, quality factors and RBE was calculated. The pencil beam algorithm used for treatment planning at PSI has been extended using the developed parameterizations in order to calculate the spatially localized neutron energy, quality factors and RBE for each treated patient. The parameterization represents the simple quantification of neutron energy in two energy bins and the quality factors and RBE with a satisfying precision up to 85 cm away from the proton pencil beam when compared to the results based on 3D Monte Carlo simulations. The root mean square error of the energy estimate between Monte Carlo simulation based results and the parameterization is 3.9%. For the quality factors and RBE estimates it is smaller than 0.9%. The model was successfully integrated into the PSI treatment planning system. It was found that the parameterizations for neutron energy, quality factors and RBE were independent of proton energy in the investigated energy range of interest for proton therapy. The pencil beam algorithm has been extended using the developed parameterizations in order to calculate the neutron energy, quality factor and RBE.

Monte Carlo simulation of a very high resolution thermal neutron detector composed of glass scintillator microfibers.

PubMed

Song, Yushou; Conner, Joseph; Zhang, Xiaodong; Hayward, Jason P

2016-02-01

In order to develop a high spatial resolution (micron level) thermal neutron detector, a detector assembly composed of cerium doped lithium glass microfibers, each with a diameter of 1 μm, is proposed, where the neutron absorption location is reconstructed from the observed charged particle products that result from neutron absorption. To suppress the cross talk of the scintillation light, each scintillating fiber is surrounded by air-filled glass capillaries with the same diameter as the fiber. This pattern is repeated to form a bulk microfiber detector. On one end, the surface of the detector is painted with a thin optical reflector to increase the light collection efficiency at the other end. Then the scintillation light emitted by any neutron interaction is transmitted to one end, magnified, and recorded by an intensified CCD camera. A simulation based on the Geant4 toolkit was developed to model this detector. All the relevant physics processes including neutron interaction, scintillation, and optical boundary behaviors are simulated. This simulation was first validated through measurements of neutron response from lithium glass cylinders. With good expected light collection, an algorithm based upon the features inherent to alpha and triton particle tracks is proposed to reconstruct the neutron reaction position in the glass fiber array. Given a 1 μm fiber diameter and 0.1mm detector thickness, the neutron spatial resolution is expected to reach σ∼1 μm with a Gaussian fit in each lateral dimension. The detection efficiency was estimated to be 3.7% for a glass fiber assembly with thickness of 0.1mm. When the detector thickness increases from 0.1mm to 1mm, the position resolution is not expected to vary much, while the detection efficiency is expected to increase by about a factor of ten. Copyright © 2015 Elsevier Ltd. All rights reserved.

Neutrons in proton pencil beam scanning: parameterization of energy, quality factors and RBE.

PubMed

Schneider, Uwe; Hälg, Roger A; Baiocco, Giorgio; Lomax, Tony

2016-08-21

The biological effectiveness of neutrons produced during proton therapy in inducing cancer is unknown, but potentially large. In particular, since neutron biological effectiveness is energy dependent, it is necessary to estimate, besides the dose, also the energy spectra, in order to obtain quantities which could be a measure of the biological effectiveness and test current models and new approaches against epidemiological studies on cancer induction after proton therapy. For patients treated with proton pencil beam scanning, this work aims to predict the spatially localized neutron energies, the effective quality factor, the weighting factor according to ICRP, and two RBE values, the first obtained from the saturation corrected dose mean lineal energy and the second from DSB cluster induction. A proton pencil beam was Monte Carlo simulated using GEANT. Based on the simulated neutron spectra for three different proton beam energies a parameterization of energy, quality factors and RBE was calculated. The pencil beam algorithm used for treatment planning at PSI has been extended using the developed parameterizations in order to calculate the spatially localized neutron energy, quality factors and RBE for each treated patient. The parameterization represents the simple quantification of neutron energy in two energy bins and the quality factors and RBE with a satisfying precision up to 85 cm away from the proton pencil beam when compared to the results based on 3D Monte Carlo simulations. The root mean square error of the energy estimate between Monte Carlo simulation based results and the parameterization is 3.9%. For the quality factors and RBE estimates it is smaller than 0.9%. The model was successfully integrated into the PSI treatment planning system. It was found that the parameterizations for neutron energy, quality factors and RBE were independent of proton energy in the investigated energy range of interest for proton therapy. The pencil beam algorithm has been extended using the developed parameterizations in order to calculate the neutron energy, quality factor and RBE.

Superconducting magnetic Wollaston prism for neutron spin encoding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, F., E-mail: fankli@indiana.edu; Parnell, S. R.; Wang, T.

2014-05-15

A magnetic Wollaston prism can spatially split a polarized neutron beam into two beams with different neutron spin states, in a manner analogous to an optical Wollaston prism. Such a Wollaston prism can be used to encode the trajectory of neutrons into the Larmor phase associated with their spin degree of freedom. This encoding can be used for neutron phase-contrast radiography and in spin echo scattering angle measurement (SESAME). In this paper, we show that magnetic Wollaston prisms with highly uniform magnetic fields and low Larmor phase aberration can be constructed to preserve neutron polarization using high temperature superconducting (HTS)more » materials. The Meissner effect of HTS films is used to confine magnetic fields produced electromagnetically by current-carrying HTS tape wound on suitably shaped soft iron pole pieces. The device is cooled to ∼30 K by a closed cycle refrigerator, eliminating the need to replenish liquid cryogens and greatly simplifying operation and maintenance. A HTS film ensures that the magnetic field transition within the prism is sharp, well-defined, and planar due to the Meissner effect. The spin transport efficiency across the device was measured to be ∼98.5% independent of neutron wavelength and energizing current. The position-dependent Larmor phase of neutron spins was measured at the NIST Center for Neutron Research facility and found to agree well with detailed simulations. The phase varies linearly with horizontal position, as required, and the neutron beam shows little depolarization. Consequently, the device has advantages over existing devices with similar functionality and provides the capability for a large neutron beam (20 mm × 30 mm) and an increase in length scales accessible to SESAME to beyond 10 μm. With further improvements of the external coupling guide field in the prototype device, a larger neutron beam could be employed.« less

Neutron energy measurement for practical applications

NASA Astrophysics Data System (ADS)

Roshan, M. V.; Sadeghi, H.; Ghasabian, M.; Mazandarani, A.

2018-03-01

Industrial demand for neutrons constrains careful energy measurements. Elastic scattering of monoenergetic α -particles from neutron collision enables neutron energy measurement by calculating the amount of deviation from the position where collision takes place. The neutron numbers with specific energy is obtained by counting the number of α -particles in the corresponding location on the charged particle detector. Monte Carlo simulation and COMSOL Multiphysics5.2 are used to account for one-to-one collision of neutrons with α -particles.

Indoor Fast Neutron Generator for Biophysical and Electronic Applications

NASA Astrophysics Data System (ADS)

Cannuli, A.; Caccamo, M. T.; Marchese, N.; Tomarchio, E. A.; Pace, C.; Magazù, S.

2018-05-01

This study focuses the attention on an indoor fast neutron generator for biophysical and electronic applications. More specifically, the findings obtained by several simulations with the MCNP Monte Carlo code, necessary for the realization of a shield for indoor measurements, are presented. Furthermore, an evaluation of the neutron spectrum modification caused by the shielding is reported. Fast neutron generators are a valid and interesting available source of neutrons, increasingly employed in a wide range of research fields, such as science and engineering. The employed portable pulsed neutron source is a MP320 Thermo Scientific neutron generator, able to generate 2.5 MeV neutrons with a neutron yield of 2.0 x 106 n/s, a pulse rate of 250 Hz to 20 KHz and a duty factor varying from 5% to 100%. The neutron generator, based on Deuterium-Deuterium nuclear fusion reactions, is employed in conjunction with a solid-state photon detector, made of n-type high-purity germanium (PINS-GMX by ORTEC) and it is mainly addressed to biophysical and electronic studies. The present study showed a proposal for the realization of a shield necessary for indoor applications for MP320 neutron generator, with a particular analysis of the transport of neutrons simulated with Monte Carlo code and described the two main lines of research in which the source will be used.

Benchmarking of Neutron Flux Parameters at the USGS TRIGA Reactor in Lakewood, Colorado

NASA Astrophysics Data System (ADS)

Alzaabi, Osama E.

The USGS TRIGA Reactor (GSTR) located at the Denver Federal Center in Lakewood Colorado provides opportunities to Colorado School of Mines students to do experimental research in the field of neutron activation analysis. The scope of this thesis is to obtain precise knowledge of neutron flux parameters at the GSTR. The Colorado School of Mines Nuclear Physics group intends to develop several research projects at the GSTR, which requires the precise knowledge of neutron fluxes and energy distributions in several irradiation locations. The fuel burn-up of the new GSTR fuel configuration and the thermal neutron flux of the core were recalculated since the GSTR core configuration had been changed with the addition of two new fuel elements. Therefore, a MCNP software package was used to incorporate the burn up of reactor fuel and to determine the neutron flux at different irradiation locations and at flux monitoring bores. These simulation results were compared with neutron activation analysis results using activated diluted gold wires. A well calibrated and stable germanium detector setup as well as fourteen samplers were designed and built to achieve accuracy in the measurement of the neutron flux. Furthermore, the flux monitoring bores of the GSTR core were used for the first time to measure neutron flux experimentally and to compare to MCNP simulation. In addition, International Atomic Energy Agency (IAEA) standard materials were used along with USGS national standard materials in a previously well calibrated irradiation location to benchmark simulation, germanium detector calibration and sample measurements to international standards.

Nonspinning black hole-neutron star mergers: A model for the amplitude of gravitational waveforms

NASA Astrophysics Data System (ADS)

Pannarale, Francesco; Berti, Emanuele; Kyutoku, Koutarou; Shibata, Masaru

2013-10-01

Black hole-neutron star binary mergers display a much richer phenomenology than black hole-black hole mergers, even in the relatively simple case—considered in this paper—in which both the black hole and the neutron star are nonspinning. When the neutron star is tidally disrupted, the gravitational wave emission is radically different from the black hole-black hole case and it can be broadly classified in two groups, depending on the spatial extent of the disrupted material. We present a phenomenological model for the gravitational waveform amplitude in the frequency domain that encompasses the three possible outcomes of the merger: no tidal disruption, “mild,” and “strong” tidal disruption. The model is calibrated to general relativistic numerical simulations using piecewise polytropic neutron star equations of state. It should prove useful to extract information on the nuclear equation of state from future gravitational-wave observations, and also to obtain more accurate estimates of black hole-neutron star merger event rates in second- and third-generation interferometric gravitational-wave detectors. We plan to extend and improve the model as longer and more accurate gravitational waveforms become available, and we will make it publicly available online as a Mathematica package. We also present in the Appendix analytical fits of the projected KAGRA noise spectral density, which should be useful in data analysis applications.

SU-E-T-132: Assess the Shielding of Secondary Neutrons From Patient Collimator in Proton Therapy Considering Secondary Photons Generated in the Shielding Process with Monte Carlo Simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamanaka, M; Takashina, M; Kurosu, K

Purpose: In this study we present Monte Carlo based evaluation of the shielding effect for secondary neutrons from patient collimator, and secondary photons emitted in the process of neutron shielding by combination of moderator and boron-10 placed around patient collimator. Methods: The PHITS Monte Carlo Simulation radiation transport code was used to simulate the proton beam (Ep = 64 to 93 MeV) from a proton therapy facility. In this study, moderators (water, polyethylene and paraffin) and boron (pure {sup 10}B) were placed around patient collimator in this order. The rate of moderator and boron thicknesses was changed fixing the totalmore » thickness at 3cm. The secondary neutron and photons doses were evaluated as the ambient dose equivalent per absorbed dose [H*(10)/D]. Results: The secondary neutrons are shielded more effectively by combination moderators and boron. The most effective combination of shielding neutrons is the polyethylene of 2.4 cm thick and the boron of 0.6 cm thick and the maximum reduction rate is 47.3 %. The H*(10)/D of secondary photons in the control case is less than that of neutrons by two orders of magnitude and the maximum increase of secondary photons is 1.0 µSv/Gy with the polyethylene of 2.8 cm thick and the boron of 0.2 cm thick. Conclusion: The combination of moderators and boron is beneficial for shielding secondary neutrons. Both the secondary photons of control and those emitted in the shielding neutrons are very lower than the secondary neutrons and photon has low RBE in comparison with neutron. Therefore the secondary photons can be ignored in the shielding neutrons.This work was supported by JSPS Core-to-Core Program (No.23003). This work was supported by JSPS Core-to-Core Program (No.23003)« less

Directional Antineutrino Detection

NASA Astrophysics Data System (ADS)

Safdi, B. R.; Suerfu, J.

2014-12-01

We propose the first truly directional antineutrino detector for antineutrinos near the threshold for the inverse beta decay (IBD) of hydrogen, with potential applications including the spatial mapping of geo-neutrinos, searches for stellar antineutrinos, and the monitoring of nuclear reactors. The detector consists of adjacent and separated target and neutron-capture layers. The IBD events, which result in a neutron and a positron, take place in the target layers. These layers are thin enough so that the neutrons escape without scattering elastically. The neutrons are detected in the thicker neutron-capture layers. The location of the IBD event is determined from the energy deposited by the positron as it slows in the medium and from the two gamma rays that come from the positron annihilation. Since the neutron recoils in the direction of the antineutrino's motion, a line may then be drawn between the IBD event location and the neutron-capture location to approximate the antineutrino's velocity. In some events, we may even measure the positron's velocity, which further increases our ability to reconstruct the antineutrino's direction of motion. Our method significantly improves upon previous methods by allowing the neutron to freely travel a long distance before diffusing and being captured. Moreover, our design is a straightforward modification of existing antineutrino detectors; a prototype could easily be built with existing technology. We verify our design through Monte Carlo simulations in Geant4, using commercially-available boron-loaded plastic scintillators for the target and neutron-capture layer materials. We are able to discriminate from background using multiple coincidence signatures within a short, ~microsecond time interval. We conclude that the detector could likely operate above ground with minimal shielding.

Analysis and Implementation of Accident Tolerant Nuclear Fuels

NASA Astrophysics Data System (ADS)

Prewitt, Benjamin Joseph

To improve the reliability and robustness of LWR, accident tolerant nuclear fuels and cladding materials are being developed to possibly replace the current UO2/zirconium system. This research highlights UN and U3Si 2, two of the most favorable accident tolerant fuels being developed. To evaluate the commercial feasiblilty of these fuels, two areas of research were conducted. Chemical fabrication routes for both fuels were investigated in detail, considering UO2 and UF6 as potential starting materials. Potential pathways for industrial scale fabrication using these methods were discussed. Neutronic performance of 70%UN-30%U3Si2 composite was evaluated in MNCP using PWR assembly and core models. The results showed comparable performance to an identical UO2 fueled simulation with the same configuration. The parameters simulated for composite and oxide fuel include the following: fuel to moderator ratio curves; energy dependent flux spectra; temperature coefficients for fuel and moderator; delayed neutron fractions; power peaking factors; axial and radial flux profiles in 2D and 3D; burnup; critical boron concentration; and shutdown margin. Overall, the neutronic parameters suggest that the transition from UO2 to composite in existing nuclear systems will not require significant changes in operating procedures or modifications to standards and regulations.

Applying Monte-Carlo simulations to optimize an inelastic neutron scattering system for soil carbon analysis

USDA-ARS?s Scientific Manuscript database

Computer Monte-Carlo (MC) simulations (Geant4) of neutron propagation and acquisition of gamma response from soil samples was applied to evaluate INS system performance characteristic [sensitivity, minimal detectable level (MDL)] for soil carbon measurement. The INS system model with best performanc...

Enhanced dynamics of hydrated tRNA on nanodiamond surfaces: A combined neutron scattering and MD simulation study

DOE PAGES

Dhindsa, Gurpreet K.; Bhowmik, Debsindhu; Goswami, Monojoy; ...

2016-09-01

Nontoxic, biocompatible nanodiamonds (ND) have recently been implemented in rational, systematic design of optimal therapeutic use in nanomedicines. However, hydrophilicity of the ND surface strongly influences structure and dynamics of biomolecules that restrict in situ applications of ND. Therefore, fundamental understanding of the impact of hydrophilic ND surface on biomolecules at the molecular level is essential. For tRNA, we observe an enhancement of dynamical behavior in the presence of ND contrary to generally observed slow motion at strongly interacting interfaces. We took advantage of neutron scattering experiments and computer simulations to demonstrate this atypical faster dynamics of tRNA on NDmore » surface. The strong attractive interactions between ND, tRNA, and water give rise to unlike dynamical behavior and structural changes of tRNA in front of ND compared to without ND. As a result, our new findings may provide new design principles for safer, improved drug delivery platforms.« less

The neutron flux monitors from 20 keV to 1 MeV for BNCT: performance study using accelerator-based neutron sources

NASA Astrophysics Data System (ADS)

Guan, X. C.; Gong, Y.; Murata, I.; Wang, T. S.

2018-05-01

The performance of the neutron flux monitors from 20 keV to 1 MeV developed for boron neutron capture therapy (BNCT) is studied by Monte Carlo simulations using accelerator-based neutron sources (ABNSs). The results show that the performance of the neutron flux monitors is very satisfactory and they can be efficiently used in practical applications to measure the neutron fluxes from 20 keV to 1 MeV of ABNSs for BNCT to high accuracy.

Assessment of radiation shield integrity of DD/DT fusion neutron generator facilities by Monte Carlo and experimental methods

NASA Astrophysics Data System (ADS)

Srinivasan, P.; Priya, S.; Patel, Tarun; Gopalakrishnan, R. K.; Sharma, D. N.

2015-01-01

DD/DT fusion neutron generators are used as sources of 2.5 MeV/14.1 MeV neutrons in experimental laboratories for various applications. Detailed knowledge of the radiation dose rates around the neutron generators are essential for ensuring radiological protection of the personnel involved with the operation. This work describes the experimental and Monte Carlo studies carried out in the Purnima Neutron Generator facility of the Bhabha Atomic Research Center (BARC), Mumbai. Verification and validation of the shielding adequacy was carried out by measuring the neutron and gamma dose-rates at various locations inside and outside the neutron generator hall during different operational conditions both for 2.5-MeV and 14.1-MeV neutrons and comparing with theoretical simulations. The calculated and experimental dose rates were found to agree with a maximum deviation of 20% at certain locations. This study has served in benchmarking the Monte Carlo simulation methods adopted for shield design of such facilities. This has also helped in augmenting the existing shield thickness to reduce the neutron and associated gamma dose rates for radiological protection of personnel during operation of the generators at higher source neutron yields up to 1 × 1010 n/s.

Analysis of energy resolution in the KURRI-LINAC pulsed neutron facility

NASA Astrophysics Data System (ADS)

Sano, Tadafumi; Hori, Jun-ichi; Takahashi, Yoshiyuki; Yashima, Hiroshi; Lee, Jaehong; Harada, Hideo

2017-09-01

In this study, we carried out Monte Carlo simulations to obtain the energy resolution of the neutron flux for TOF measurements in the KURRI-LINAC pulsed neutron facility. The simulation was performed on the moderated neutron flux from the pac-man type moderator at the energy range from 0.1 eV to 10 keV. As the result, we obtained the energy resolutions (ΔE/E) of about 0.7% to 1.3% between 0.1 eV to 10 keV. The energy resolution obtained from Monte Carlo simulation agreed with the resolution using the simplified evaluation formula. In addition, we compared the energy resolution among KURRI-LINAC and other TOF facilities, the energy dependency of the energy resolution with the pac-man type moderator in KURRI-LINAC was similar to the J-PARC ANNRI for the single-bunch mode.

Standardization of accelerator irradiation procedures for simulation of neutron induced damage in reactor structural materials

NASA Astrophysics Data System (ADS)

Shao, Lin; Gigax, Jonathan; Chen, Di; Kim, Hyosim; Garner, Frank A.; Wang, Jing; Toloczko, Mychailo B.

2017-10-01

Self-ion irradiation is widely used as a method to simulate neutron damage in reactor structural materials. Accelerator-based simulation of void swelling, however, introduces a number of neutron-atypical features which require careful data extraction and, in some cases, introduction of innovative irradiation techniques to alleviate these issues. We briefly summarize three such atypical features: defect imbalance effects, pulsed beam effects, and carbon contamination. The latter issue has just been recently recognized as being relevant to simulation of void swelling and is discussed here in greater detail. It is shown that carbon ions are entrained in the ion beam by Coulomb force drag and accelerated toward the target surface. Beam-contaminant interactions are modeled using molecular dynamics simulation. By applying a multiple beam deflection technique, carbon and other contaminants can be effectively filtered out, as demonstrated in an irradiation of HT-9 alloy by 3.5 MeV Fe ions.

An analytical model of leakage neutron equivalent dose for passively-scattered proton radiotherapy and validation with measurements.

PubMed

Schneider, Christopher; Newhauser, Wayne; Farah, Jad

2015-05-18

Exposure to stray neutrons increases the risk of second cancer development after proton therapy. Previously reported analytical models of this exposure were difficult to configure and had not been investigated below 100 MeV proton energy. The purposes of this study were to test an analytical model of neutron equivalent dose per therapeutic absorbed dose  at 75 MeV and to improve the model by reducing the number of configuration parameters and making it continuous in proton energy from 100 to 250 MeV. To develop the analytical model, we used previously published H/D values in water from Monte Carlo simulations of a general-purpose beamline for proton energies from 100 to 250 MeV. We also configured and tested the model on in-air neutron equivalent doses measured for a 75 MeV ocular beamline. Predicted H/D values from the analytical model and Monte Carlo agreed well from 100 to 250 MeV (10% average difference). Predicted H/D values from the analytical model also agreed well with measurements at 75 MeV (15% average difference). The results indicate that analytical models can give fast, reliable calculations of neutron exposure after proton therapy. This ability is absent in treatment planning systems but vital to second cancer risk estimation.

Simulations of super-ellipse hohlraum targets as a path to high neutron yields

NASA Astrophysics Data System (ADS)

Milovich, Jose; Amendt, Peter; Storm, Erik; Robey, Harry; Haan, Steve; Landen, Otto; Meezan, Nathan; Lindl, John

2017-10-01

Recently neutron yields in excess of 1016 have been achieved at the National Ignition Facility (NIF) using a low-density gas fill hohlraum and a subscale high-density-carbon capsule. The laser power used was near the current maximum level allowed on the inner cones of the NIF laser. While more energy can be extracted from the laser to provide additional improvement on the neutron yield, a more efficient design is desired. A new effort has begun to investigate alternatives to the current cylinder-shaped hohlraum for driving larger capsules (1.1 mm outer radius). If these new hohlraums can preserve the implosion symmetry, the additional absorbed energy is expected to provide a path to high neutron yield and potential ignition. Super-ellipse hohlraums, a generalization of an earlier rugby hohlraum design, have the advantage of a larger waist diameter and reduced parasitic energy losses from the corners of cylindrical hohlraums while still being able to produce the required capsule drive at the current energy and power limits available at the NIF. We will present plausible designs of these hohlraums based on the Lamé mathematical construction, and discuss their prospects to reach high neutron gains. Prepared by LLNL under Contract DE-AC52-07NA27344.

Neutron Scattering and Diffraction Studies of Fluids and Fluid-Solid Interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cole, David R; Herwig, Kenneth W; Mamontov, Eugene

2006-01-01

There can be no disputing the fact that neutron diffraction and scattering have made a clear contribution to our current understanding of the structural and dynamical characteristics of liquid water and water containing dissolved ions at ambient conditions and to a somewhat lesser degree other state conditions involving a change in temperature and pressure. Indeed, a molecular-level understanding of how fluids (e.g., water, CO{sub 2}, CH{sub 4}, higher hydrocarbons, etc.) interact with and participate in reactions with other solid earth materials are central to the development of predictive models that aim to quantify a wide array of geochemical processes. Inmore » the context of natural systems, interrogation of fluids and fluid-solid interactions at elevated temperatures and pressures is an area requiring much more work, particularly for complex solutions containing geochemically relevant cations, anions, and other important dissolved species such as CO{sub 2} or CH{sub 4}. We have tried to describe a series of prototypical interfacial and surface problems using neutron scattering to stimulate the thinking of earth scientists interested applying some of these approaches to confined systems of mineralogical importance. Our ability to predict the molecular-level properties of fluids and fluid-solid interactions relies heavily on the synergism between experiments such as neutron diffraction or inelastic neutron scattering and molecular-based simulations. Tremendous progress has been made in closing the gap between experimental observations and predicted behavior based on simulations due to improvements in the experimental methodologies and instrumentation on the one hand, and the development of new potential models of water and other simple and complex fluids on the other. For example there has been an emergence of studies taking advantage of advanced computing power that can accommodate the demands of ab initio molecular dynamics. On the neutron instrumentation side while much of the quasielastic work described has been performed using instrumentation located at reactor based sources, the advent of 2{sup nd} generation spallation neutron sources like ISIS, new generation sources like the SNS at the Oak Ridge National Laboratory and the low repetition rate 2{sup nd} target station at ISIS offer significant opportunities for the study of interfacial and entrained liquids. At the very least, an improvement of the counting statistics by one to two orders of magnitude on many instruments such as vibrational and time-of-flight spectrometers at SNS will allow parametric studies of many systems which otherwise would be prohibitively time consuming. The extended-Q SANS diffractometer at SNS will offer very high intensity and unparalleled Q-range to extend the accessible length scale in the real space, from 0. 05 nm to150 nm. The backscattering spectrometer will provide very high intensity and excellent energy resolution through unprecedented range of energy transfers, thereby allowing simultaneous studies of translational and rotational diffusion components in various systems. The vibrational spectrometer with two orders of magnitude improvement in performance and the capability to perform simultaneous structural measurements should present exciting opportunities to and engender an entire new population of users in the neutron community.« less

Simulation and optimization of a new focusing polarizing bender for the diffuse neutrons scattering spectrometer DNS at MLZ

NASA Astrophysics Data System (ADS)

Nemkovski, K.; Ioffe, A.; Su, Y.; Babcock, E.; Schweika, W.; Brückel, Th

2017-06-01

We present the concept and the results of the simulations of a new polarizer for the diffuse neutron scattering spectrometer DNS at MLZ. The concept of the polarizer is based on the idea of a bender made from the stack of the silicon wafers with a double-side supermirror polarizing coating and absorbing spacers in between. Owing to its compact design, such a system provides more free space for the arrangement of other instrument components. To reduce activation of the polarizer in the high intensity neutron beam of the DNS spectrometer we plan to use the Fe/Si supermirrors instead of currently used FeCoV/Ti:N ones. Using the VITESS simulation package we have performed simulations for horizontally focusing polarizing benders with different geometries in the combination with the double-focusing crystal monochromator of DNS. Neutron transmission and polarization efficiency as well as the effects of the focusing for convergent conventional C-benders and S-benders have been analyzed both for wedge-like and plane-parallel convergent geometries of the channels. The results of these simulations and the advantages/disadvantages of the various configurations are discussed.

Quasielastic neutron scattering measurements and ab initio MD-simulations on single ion motions in molten NaF

DOE Office of Scientific and Technical Information (OSTI.GOV)

Demmel, F.; Mukhopadhyay, S.; Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ

2016-01-07

The ionic stochastic motions in the molten alkali halide NaF are investigated by quasielastic neutron scattering and first principles molecular dynamics simulation. Quasielastic neutron scattering was employed to extract the diffusion behavior of the sodium ions in the melt. An extensive first principles based simulation on a box of up to 512 particles has been performed to complement the experimental data. From that large box, a smaller 64-particle box has then been simulated over a runtime of 60 ps. A good agreement between calculated and neutron data on the level of spectral shape has been obtained. The obtained sodium diffusionmore » coefficients agree very well. The simulation predicts a fluorine diffusion coefficient similar to the sodium one. Applying the Nernst-Einstein equation, a remarkable large cross correlation between both ions can be deduced. The velocity cross correlations demonstrate a positive correlation between the ions over a period of 0.1 ps. That strong correlation is evidence that the unlike ions do not move completely statistically independent and have a strong association over a short period of time.« less

Cosmic-ray neutron simulations and measurements in Taiwan.

PubMed

Chen, Wei-Lin; Jiang, Shiang-Huei; Sheu, Rong-Jiun

2014-10-01

This study used simulations of galactic cosmic ray in the atmosphere to investigate the neutron background environment in Taiwan, emphasising its altitude dependence and spectrum variation near interfaces. The calculated results were analysed and compared with two measurements. The first measurement was a mobile neutron survey from sea level up to 3275 m in altitude conducted using a car-mounted high-sensitivity neutron detector. The second was a previous measured result focusing on the changes in neutron spectra near air/ground and air/water interfaces. The attenuation length of cosmic-ray neutrons in the lower atmosphere was estimated to be 163 g cm(-2) in Taiwan. Cosmic-ray neutron spectra vary with altitude and especially near interfaces. The determined spectra near the air/ground and air/water interfaces agree well with measurements for neutrons below 10 MeV. However, the high-energy portion of spectra was observed to be much higher than our previous estimation. Because high-energy neutrons contribute substantially to a dose evaluation, revising the annual sea-level effective dose from cosmic-ray neutrons at ground level in Taiwan to 35 μSv, which corresponds to a neutron flux of 5.30 × 10(-3) n cm(-2) s(-1), was suggested. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Development of a Research Reactor Protocol for Neutron Multiplication Measurements

DOE PAGES

Arthur, Jennifer Ann; Bahran, Rian Mustafa; Hutchinson, Jesson D.; ...

2018-03-20

A new series of subcritical measurements has been conducted at the zero-power Walthousen Reactor Critical Facility (RCF) at Rensselaer Polytechnic Institute (RPI) using a 3He neutron multiplicity detector. The Critical and Subcritical 0-Power Experiment at Rensselaer (CaSPER) campaign establishes a protocol for advanced subcritical neutron multiplication measurements involving research reactors for validation of neutron multiplication inference techniques, Monte Carlo codes, and associated nuclear data. There has been increased attention and expanded efforts related to subcritical measurements and analyses, and this work provides yet another data set at known reactivity states that can be used in the validation of state-of-the-art Montemore » Carlo computer simulation tools. The diverse (mass, spatial, spectral) subcritical measurement configurations have been analyzed to produce parameters of interest such as singles rates, doubles rates, and leakage multiplication. MCNP ®6.2 was used to simulate the experiment and the resulting simulated data has been compared to the measured results. Comparison of the simulated and measured observables (singles rates, doubles rates, and leakage multiplication) show good agreement. This work builds upon the previous years of collaborative subcritical experiments and outlines a protocol for future subcritical neutron multiplication inference and subcriticality monitoring measurements on pool-type reactor systems.« less

Development of a Research Reactor Protocol for Neutron Multiplication Measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arthur, Jennifer Ann; Bahran, Rian Mustafa; Hutchinson, Jesson D.

A new series of subcritical measurements has been conducted at the zero-power Walthousen Reactor Critical Facility (RCF) at Rensselaer Polytechnic Institute (RPI) using a 3He neutron multiplicity detector. The Critical and Subcritical 0-Power Experiment at Rensselaer (CaSPER) campaign establishes a protocol for advanced subcritical neutron multiplication measurements involving research reactors for validation of neutron multiplication inference techniques, Monte Carlo codes, and associated nuclear data. There has been increased attention and expanded efforts related to subcritical measurements and analyses, and this work provides yet another data set at known reactivity states that can be used in the validation of state-of-the-art Montemore » Carlo computer simulation tools. The diverse (mass, spatial, spectral) subcritical measurement configurations have been analyzed to produce parameters of interest such as singles rates, doubles rates, and leakage multiplication. MCNP ®6.2 was used to simulate the experiment and the resulting simulated data has been compared to the measured results. Comparison of the simulated and measured observables (singles rates, doubles rates, and leakage multiplication) show good agreement. This work builds upon the previous years of collaborative subcritical experiments and outlines a protocol for future subcritical neutron multiplication inference and subcriticality monitoring measurements on pool-type reactor systems.« less

Effect of driver impedance on dense plasma focus Z-pinch neutron yield

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sears, Jason, E-mail: sears8@llnl.gov, E-mail: schmidt36@llnl.gov; Link, Anthony, E-mail: sears8@llnl.gov, E-mail: schmidt36@llnl.gov; Schmidt, Andrea, E-mail: sears8@llnl.gov, E-mail: schmidt36@llnl.gov

2014-12-15

The Z-pinch phase of a dense plasma focus (DPF) heats the plasma by rapid compression and accelerates ions across its intense electric fields, producing neutrons through both thermonuclear and beam-target fusion. Driver characteristics have empirically been shown to affect performance, as measured by neutron yield per unit of stored energy. We are exploring the effect of driver characteristics on DPF performance using particle-in-cell (PIC) simulations of a kJ scale DPF. In this work, our PIC simulations are fluid for the run-down phase and transition to fully kinetic for the pinch phase, capturing kinetic instabilities, anomalous resistivity, and beam formation duringmore » the pinch. The anode-cathode boundary is driven by a circuit model of the capacitive driver, including system inductance, the load of the railgap switches, the guard resistors, and the coaxial transmission line parameters. It is known that the driver impedance plays an important role in the neutron yield: first, it sets the peak current achieved at pinch time; and second, it affects how much current continues to flow through the pinch when the pinch inductance and resistance suddenly increase. Here we show from fully kinetic simulations how total neutron yield depends on the impedance of the driver and the distributed parameters of the transmission circuit. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability for neutron source applications.« less

New thermal neutron calibration channel at LNMRI/IRD

NASA Astrophysics Data System (ADS)

Astuto, A.; Patrão, K. C. S.; Fonseca, E. S.; Pereira, W. W.; Lopes, R. T.

2016-07-01

A new standard thermal neutron flux unit was designed in the National Ionizing Radiation Metrology Laboratory (LNMRI) for calibration of neutron detectors. Fluence is achieved by moderation of four 241Am-Be sources with 0.6 TBq each, in a facility built with graphite and paraffin blocks. The study was divided into two stages. First, simulations were performed using MCNPX code in different geometric arrangements, seeking the best performance in terms of fluence and their uncertainties. Last, the system was assembled based on the results obtained on the simulations. The simulation results indicate quasi-homogeneous fluence in the central chamber and H*(10) at 50 cm from the front face with the polyethylene filter.

Coupled neutronics and thermal-hydraulics numerical simulations of a Molten Fast Salt Reactor (MFSR)

NASA Astrophysics Data System (ADS)

Laureau, A.; Rubiolo, P. R.; Heuer, D.; Merle-Lucotte, E.; Brovchenko, M.

2014-06-01

Coupled neutronics and thermalhydraulic numerical analyses of a molten salt fast reactor are presented. These preliminary numerical simulations are carried-out using the Monte Carlo code MCNP and the Computation Fluid Dynamic code OpenFOAM. The main objectives of this analysis performed at steady-reactor conditions are to confirm the acceptability of the current neutronic and thermalhydraulic designs of the reactor, to study the effects of the reactor operating conditions on some of the key MSFR design parameters such as the temperature peaking factor. The effects of the precursor's motion on the reactor safety parameters such as the effective fraction of delayed neutrons have been evaluated.

Progress toward the development and testing of source reconstruction methods for NIF neutron imaging.

PubMed

Loomis, E N; Grim, G P; Wilde, C; Wilson, D C; Morgan, G; Wilke, M; Tregillis, I; Merrill, F; Clark, D; Finch, J; Fittinghoff, D; Bower, D

2010-10-01

Development of analysis techniques for neutron imaging at the National Ignition Facility is an important and difficult task for the detailed understanding of high-neutron yield inertial confinement fusion implosions. Once developed, these methods must provide accurate images of the hot and cold fuels so that information about the implosion, such as symmetry and areal density, can be extracted. One method under development involves the numerical inversion of the pinhole image using knowledge of neutron transport through the pinhole aperture from Monte Carlo simulations. In this article we present results of source reconstructions based on simulated images that test the methods effectiveness with regard to pinhole misalignment.

Effects of inhomogeneity at stagnation in 3D simulations of ICF implosions

NASA Astrophysics Data System (ADS)

Appelbe, Brian

2016-10-01

The stagnation phase of an ICF implosion is characterized by a hotspot and dense fuel layer that are spatially and temporally inhomogeneous. Perturbation growth during the implosion results in significant asymmetry at stagnation while the hotspot size, density and temperature change rapidly, even in non-igniting capsules. Diagnosing these inhomogeneities is necessary to increase yield in ICF experiments. In this work, 3D radiation hydrodynamic simulations of perturbed indirect drive ICF capsules are carried out using the CHIMERA code. During the stagnation phase a suite of novel and computationally efficient simulation tools are used to produce synthetic time-resolved neutron spectra and images. These tools allow a detailed study of the effects of hotspot inhomogeneities on diagnostic signals. Results show that the burn-averaged ion temperature drops rapidly during thermonuclear burn as the hotspot evolves from a localised, shock-heated region to a more massive, non-uniform plasma. Primary DD and DT neutron spectra show that there is significant residual bulk fluid motion at stagnation, complicating the measurement of ion temperature. Different perturbation modes cause different levels of anisotropic spectra shifts and broadening. However, in all cases the discrepancies between the DD and DT spectra are a reliable indicator of residual motion at stagnation. The simulations are used to examine the relationship between neutron scattering and areal density (ρR). Three measures of areal density are simulated: downscattered neutron ratio, attenuated primary neutron yield and nT backscatter edge. Each of these diagnoses the magnitude and anisotropy of the ρR with varying success, with accuracy decreasing for higher mode perturbations. Contributions to the neutron energy spectra from T +T reactions, secondary DT reactions and deuteron break-up are also evaluated.

LiquidLib: A comprehensive toolbox for analyzing classical and ab initio molecular dynamics simulations of liquids and liquid-like matter with applications to neutron scattering experiments

NASA Astrophysics Data System (ADS)

Walter, Nathan P.; Jaiswal, Abhishek; Cai, Zhikun; Zhang, Yang

2018-07-01

Neutron scattering is a powerful experimental technique for characterizing the structure and dynamics of materials on the atomic or molecular scale. However, the interpretation of experimental data from neutron scattering is oftentimes not trivial, partly because scattering methods probe ensemble-averaged information in the reciprocal space. Therefore, computer simulations, such as classical and ab initio molecular dynamics, are frequently used to unravel the time-dependent atomistic configurations that can reproduce the scattering patterns and thus assist in the understanding of the microscopic origin of certain properties of materials. LiquidLib is a post-processing package for analyzing the trajectory of atomistic simulations of liquids and liquid-like matter with application to neutron scattering experiments. From an atomistic simulation, LiquidLib provides the computation of various statistical quantities including the pair distribution function, the weighted and unweighted structure factors, the mean squared displacement, the non-Gaussian parameter, the four-point correlation function, the velocity auto correlation function, the self and collective van Hove correlation functions, the self and collective intermediate scattering functions, and the bond orientational order parameter. LiquidLib analyzes atomistic trajectories generated from packages such as LAMMPS, GROMACS, and VASP. It also offers an extendable platform to conveniently integrate new quantities into the library and integrate simulation trajectories of other file formats for analysis. Weighting the quantities by element-specific neutron-scattering lengths provides results directly comparable to neutron scattering measurements. Lastly, LiquidLib is independent of dimensionality, which allows analysis of trajectories in two, three, and higher dimensions. The code is beginning to find worldwide use.

Simulations of a PSD Plastic Neutron Collar for Assaying Fresh Fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hausladen, Paul; Newby, Jason; McElroy, Robert Dennis

The potential performance of a notional active coincidence collar for assaying uranium fuel based on segmented detectors constructed from the new PSD plastic fast organic scintillator with pulse shape discrimination capability was investigated in simulation. Like the International Atomic Energy Agency's present Uranium Neutron Collar for LEU (UNCL), the PSD plastic collar would also function by stimulating fission in the 235U content of the fuel with a moderated 241Am/Li neutron source and detecting instances of induced fission via neutron coincidence counting. In contrast to the moderated detectors of the UNCL, the fast time scale of detection in the scintillator eliminatesmore » statistical errors due to accidental coincidences that limit the performance of the UNCL. However, the potential to detect a single neutron multiple times historically has been one of the properties of organic scintillator detectors that has prevented their adoption for international safeguards applications. Consequently, as part of the analysis of simulated data, a method was developed by which true neutron-neutron coincidences can be distinguished from inter-detector scatter that takes advantage of the position and timing resolution of segmented detectors. Then, the performance of the notional simulated coincidence collar was evaluated for assaying a variety of fresh fuels, including some containing burnable poisons and partial defects. In these simulations, particular attention was paid to the analysis of fast mode measurements. In fast mode, a Cd liner is placed inside the collar to shield the fuel from the interrogating source and detector moderators, thereby eliminating the thermal neutron flux that is most sensitive to the presence of burnable poisons that are ubiquitous in modern nuclear fuels. The simulations indicate that the predicted precision of fast mode measurements is similar to what can be achieved by the present UNCL in thermal mode. For example, the statistical accuracy of a ten-minute measurement of fission coincidences collected in fast mode will be approximately 1% for most fuels of interest, yielding a ~1.4% error after subtraction of a five minute measurement of the spontaneous fissions from 238U in the fuel, a ~2% error in analyzed linear density after accounting for the slope of the calibration curve, and a ~2.9% total error after addition of an assumed systematic error of 2%.« less

Application and Development of Microstructured Solid-State Neutron Detectors

NASA Astrophysics Data System (ADS)

Weltz, Adam D.

Neutron detectors are useful for a number of applications, including the identification of nuclear weapons, radiation dosimetry, and nuclear reactor monitoring, among others. Microstructured solid-state neutron detectors (SSNDs) developed at RPI have the potential to reinvent a variety of neutron detection systems due to their compact size, zero bias requirement, competitive thermal neutron detection efficiency (up to 29%), low gamma sensitivity (below the PNNL recommendation of 10-6 corresponding to a 10 mR/hr gamma exposure), and scalability to large surface areas with a single preamplifier (<20% loss in relative efficiency from 1 to 16 cm2). These microstructured SSNDs have semiconducting substrate etched with a repeated, three-dimensional microstructure of high aspect ratio holes filled with 10B. MCNP simulations optimized the dimensions of each microstructure geometry for each detector application, improving the overall performance. This thesis outlines the development of multiple, novel neutron detection applications using microstructured SSNDs developed at RPI. The Directional and Spectral Neutron Detection System (DSNDS) is a modular and portable system that uses rings of microstructured SSNDs embedded in polyethylene in order to gather real-time information about the directionality and spectrum of an unidentified neutron source. This system can be used to identify the presence of diverted special nuclear material (SNM), determine its position, and gather spectral information in real-time. The compact and scalable zero-bias SSNDs allow for customization and modularity of the detector array, which provides design flexibility and enhanced portability. Additionally, a real-time personal neutron dosimeter is a wearable device that uses a combination of fast and thermal microstructured SSNDs in order to determine an individual's neutron dose rate. This system demonstrates that neutron detection systems utilizing microstructured SSNDs are applicable for personal neutron dosimetry. The development of these systems using the compact, zero-bias microstructured SSNDs lays the groundwork for a new generation of neutron detection tools, outlines the challenges and design considerations associated with the implementation of these devices, and demonstrates the value that these detectors bring to the future of neutron detection systems.

Detection of hidden explosives by using tagged neutron beams: Status and perspectives

NASA Astrophysics Data System (ADS)

Viesti, Giuseppe; Pesente, Silvia; Nebbia, Giancarlo; Lunardon, Marcello; Sudac, Davorin; Nađ, Karlo; Blagus, Sasha; Valković, Vladivoj

2005-12-01

Non-destructive inspections have been simulated in laboratory conditions by using our tagged neutron inspection system (TNIS), using YAP:Ce scintillators to tag the neutron beam and an array of BaF2 crystals to detect the γ-rays. The system has been operated up to 2 × 108 neutron/s. Further developments of the TNIS concept are discussed in the light of our current projects for cargo container inspections.

Development of a transportable neutron activation analysis system to quantify manganese in bone in vivo: feasibility and methodology.

PubMed

Liu, Yingzi; Koltick, David; Byrne, Patrick; Wang, Haoyu; Zheng, Wei; Nie, Linda H

2013-12-01

This study was conducted to investigate the methodology and feasibility of developing a transportable neutron activation analysis (NAA) system to quantify manganese (Mn) in bone using a portable deuterium-deuterium (DD) neutron generator as the neutron source. Since a DD neutron generator was not available in our laboratory, a deuterium-tritium (DT) neutron generator was used to obtain experimental data and validate the results from Monte Carlo (MC) simulations. After validation, MC simulations using a DD generator as the neutron source were then conducted. Different types of moderators and reflectors were simulated, and the optimal thicknesses for the moderator and reflector were determined. To estimate the detection limit (DL) of the system, and to observe the interference of the magnesium (Mg) γ line at 844 keV to the Mn γ line at 847 keV, three hand phantoms with Mn concentrations of 30 parts per million (ppm), 150 ppm, and 500 ppm were made and irradiated by the DT generator system. The Mn signals in these phantoms were then measured using a 50% high-efficiency high-purity germanium (HPGe) detector. The DL was calculated to be about 4.4 ppm for the chosen irradiation, decay, and measurement time. This was calculated to be equivalent to a DL of about 3.3 ppm for the DD generator system. To achieve this DL with one 50% high-efficiency HPGe detector, the dose to the hand was simulated to be about 37 mSv, with the total body equivalent dose being about 23µSv. In conclusion, it is feasible to develop a transportable NAA system to quantify Mn in bone in vivo with an acceptable radiation exposure to the subject.

Development of a transportable neutron activation analysis system to quantify manganese in bone in vivo: feasibility and methodology

PubMed Central

Liu, Yingzi; Koltick, David; Byrne, Patrick; Wang, Haoyu; Zheng, Wei; Nie, Linda H

2014-01-01

This study was conducted to investigate the methodology and feasibility of developing a transportable neutron activation analysis (NAA) system to quantify manganese (Mn) in bone using a portable deuterium–deuterium (DD) neutron generator as the neutron source. Since a DD neutron generator was not available in our laboratory, a deuterium–tritium (DT) neutron generator was used to obtain experimental data and validate the results from Monte Carlo (MC) simulations. After validation, MC simulations using a DD generator as the neutron source were then conducted. Different types of moderators and reflectors were simulated, and the optimal thicknesses for the moderator and reflector were determined. To estimate the detection limit (DL) of the system, and to observe the interference of the magnesium (Mg) γ line at 844 keV to the Mn γ line at 847 keV, three hand phantoms with Mn concentrations of 30 parts per million (ppm), 150 ppm, and 500 ppm were made and irradiated by the DT generator system. The Mn signals in these phantoms were then measured using a 50% high-efficiency high-purity germanium (HPGe) detector. The DL was calculated to be about 4.4 ppm for the chosen irradiation, decay, and measurement time. This was calculated to be equivalent to a DL of about 3.3 ppm for the DD generator system. To achieve this DL with one 50% high-efficiency HPGe detector, the dose to the hand was simulated to be about 37 mSv, with the total body equivalent dose being about 23μSv. In conclusion, it is feasible to develop a transportable NAA system to quantify Mn in bone in vivo with an acceptable radiation exposure to the subject. PMID:24165395

Measuring and monitoring KIPT Neutron Source Facility Reactivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, Yan; Gohar, Yousry; Zhong, Zhaopeng

2015-08-01

Argonne National Laboratory (ANL) of USA and Kharkov Institute of Physics and Technology (KIPT) of Ukraine have been collaborating on developing and constructing a neutron source facility at Kharkov, Ukraine. The facility consists of an accelerator-driven subcritical system. The accelerator has a 100 kW electron beam using 100 MeV electrons. The subcritical assembly has k eff less than 0.98. To ensure the safe operation of this neutron source facility, the reactivity of the subcritical core has to be accurately determined and continuously monitored. A technique which combines the area-ratio method and the flux-to-current ratio method is purposed to determine themore » reactivity of the KIPT subcritical assembly at various conditions. In particular, the area-ratio method can determine the absolute reactivity of the subcritical assembly in units of dollars by performing pulsed-neutron experiments. It provides reference reactivities for the flux-to-current ratio method to track and monitor the reactivity deviations from the reference state while the facility is at other operation modes. Monte Carlo simulations are performed to simulate both methods using the numerical model of the KIPT subcritical assembly. It is found that the reactivities obtained from both the area-ratio method and the flux-to-current ratio method are spatially dependent on the neutron detector locations and types. Numerical simulations also suggest optimal neutron detector locations to minimize the spatial effects in the flux-to-current ratio method. The spatial correction factors are calculated using Monte Carlo methods for both measuring methods at the selected neutron detector locations. Monte Carlo simulations are also performed to verify the accuracy of the flux-to-current ratio method in monitoring the reactivity swing during a fuel burnup cycle.« less

How Well Do We Know The Supernova Equation of State?

NASA Astrophysics Data System (ADS)

Hempel, Matthias; Oertel, Micaela; Typel, Stefan; Klähn, Thomas

We give an overview about equations of state (EOS) which are currently available for simulations of core-collapse supernovae and neutron star mergers. A few selected important aspects of the EOS, such as the symmetry energy, the maximum mass of neutron stars, and cluster formation, are confronted with constraints from experiments and astrophysical observations. There are just very few models which are compatible even with this very restricted set of constraints. These remaining models illustrate the uncertainty of the uniform nuclear matter EOS at high densities. In addition, at finite temperatures the medium modifications of nuclear clusters represent a conceptual challenge. In conclusion, there has been significant development in the recent years, but there is still need for further improved general purpose EOS tables.

Towards an In-Beam Measurement of the Neutron Lifetime to 1 Second

NASA Astrophysics Data System (ADS)

Mulholland, Jonathan

2014-03-01

A precise value for the neutron lifetime is required for consistency tests of the Standard Model and is an essential parameter in the theory of Big Bang Nucleosynthesis. A new measurement of the neutron lifetime using the in-beam method is planned at the National Institute of Standards and Technology Center for Neutron Research. The systematic effects associated with the in-beam method are markedly different than those found in storage experiments utilizing ultracold neutrons. Experimental improvements, specifically recent advances in the determination of absolute neutron fluence, should permit an overall uncertainty of 1 second on the neutron lifetime. The dependence of the primordial mass fraction on the neutron lifetime, technical improvements of the in-beam technique, and the path toward improving the precision of the new measurement will be discussed.

A Monte Carlo Library Least Square approach in the Neutron Inelastic-scattering and Thermal-capture Analysis (NISTA) process in bulk coal samples

NASA Astrophysics Data System (ADS)

Reyhancan, Iskender Atilla; Ebrahimi, Alborz; Çolak, Üner; Erduran, M. Nizamettin; Angin, Nergis

2017-01-01

A new Monte-Carlo Library Least Square (MCLLS) approach for treating non-linear radiation analysis problem in Neutron Inelastic-scattering and Thermal-capture Analysis (NISTA) was developed. 14 MeV neutrons were produced by a neutron generator via the 3H (2H , n) 4He reaction. The prompt gamma ray spectra from bulk samples of seven different materials were measured by a Bismuth Germanate (BGO) gamma detection system. Polyethylene was used as neutron moderator along with iron and lead as neutron and gamma ray shielding, respectively. The gamma detection system was equipped with a list mode data acquisition system which streams spectroscopy data directly to the computer, event-by-event. A GEANT4 simulation toolkit was used for generating the single-element libraries of all the elements of interest. These libraries were then used in a Linear Library Least Square (LLLS) approach with an unknown experimental sample spectrum to fit it with the calculated elemental libraries. GEANT4 simulation results were also used for the selection of the neutron shielding material.

Radiation environment on board Foton-M 3: the neutron component

NASA Astrophysics Data System (ADS)

Falzetta, Giuseppe; Zanini, Alba; Chiorra, Katia; Briccarello, Mauro; Belluco, Maurizio; Longo, Francesco; Jerse, Giovanna

The recoverable capsule Foton-M 3 (ESA mission) was launched from Baikonur on 2007 September 14 and landed on the Russian-Kazakh border 12 days later. The spacecraft carried on board several ESA experiments. During this space mission a study has been performed on the neutron component of the radiation environment inside the capsule. Neutrons are a not avoidable component of the secondary radiation produced by interaction of primary radiation with the spacecraft shielding. Because of their high LET, neutrons could represent a main risk for both the electronic instruments and the health of the astronauts during space missions. Monte Carlo simulations performed by Geant4 code have been carried out using as input primary proton and alpha spectra, obtained by various tools (i.e. Creme 96, Omere, etc . . . ) and the neutron fluxes and doses, as a function of neutron energies, have been evaluated. The simulation results are compared with experimental data obtained by passive neutron detectors. In this study the effectiveness of various shielding materials useful in space mission has been also investigated.

Characterization and MCNP simulation of neutron energy spectrum shift after transmission through strong absorbing materials and its impact on tomography reconstructed image.

PubMed

Hachouf, N; Kharfi, F; Boucenna, A

2012-10-01

An ideal neutron radiograph, for quantification and 3D tomographic image reconstruction, should be a transmission image which exactly obeys to the exponential attenuation law of a monochromatic neutron beam. There are many reasons for which this assumption does not hold for high neutron absorbing materials. The main deviations from the ideal are due essentially to neutron beam hardening effect. The main challenges of this work are the characterization of neutron transmission through boron enriched steel materials and the observation of beam hardening. Then, in our work, the influence of beam hardening effect on neutron tomographic image, for samples based on these materials, is studied. MCNP and FBP simulation are performed to adjust linear attenuation coefficients data and to perform 2D tomographic image reconstruction with and without beam hardening corrections. A beam hardening correction procedure is developed and applied based on qualitative and quantitative analyses of the projections data. Results from original and corrected 2D reconstructed images obtained shows the efficiency of the proposed correction procedure. Copyright © 2012 Elsevier Ltd. All rights reserved.

Cross-correlation measurements with the EJ-299-33 plastic scintillator

NASA Astrophysics Data System (ADS)

Bourne, Mark M.; Whaley, Jeff; Dolan, Jennifer L.; Polack, John K.; Flaska, Marek; Clarke, Shaun D.; Tomanin, Alice; Peerani, Paolo; Pozzi, Sara A.

2015-06-01

New organic-plastic scintillation compositions have demonstrated pulse-shape discrimination (PSD) of neutrons and gamma rays. We present cross-correlation measurements of 252Cf and mixed uranium-plutonium oxide (MOX) with the EJ-299-33 plastic scintillator. For comparison, equivalent measurements were performed with an EJ-309 liquid scintillator. Offline, digital PSD was applied to each detector. These measurements show that EJ-299-33 sacrifices a factor of 5 in neutron-neutron efficiency relative to EJ-309, but could still utilize the difference in neutron-neutron efficiency and neutron single-to-double ratio to distinguish 252Cf from MOX. These measurements were modeled with MCNPX-PoliMi, and MPPost was used to convert the detailed collision history into simulated cross-correlation distributions. MCNPX-PoliMi predicted the measured 252Cf cross-correlation distribution for EJ-309 to within 10%. Greater photon uncertainty in the MOX sample led to larger discrepancy in the simulated MOX cross-correlation distribution. The modeled EJ-299-33 plastic also gives reasonable agreement with measured cross-correlation distributions, although the MCNPX-PoliMi model appears to under-predict the neutron detection efficiency.

Study of neutron spectra in a water bath from a Pb target irradiated by 250 MeV protons

NASA Astrophysics Data System (ADS)

Li, Yan-Yan; Zhang, Xue-Ying; Ju, Yong-Qin; Ma, Fei; Zhang, Hong-Bin; Chen, Liang; Ge, Hong-Lin; Wan, Bo; Luo, Peng; Zhou, Bin; Zhang, Yan-Bin; Li, Jian-Yang; Xu, Jun-Kui; Wang, Song-Lin; Yang, Yong-Wei; Yang, Lei

2015-04-01

Spallation neutrons were produced by the irradiation of Pb with 250 MeV protons. The Pb target was surrounded by water which was used to slow down the emitted neutrons. The moderated neutrons in the water bath were measured by using the resonance detectors of Au, Mn and In with a cadmium (Cd) cover. According to the measured activities of the foils, the neutron flux at different resonance energies were deduced and the epithermal neutron spectra were proposed. Corresponding results calculated with the Monte Carlo code MCNPX were compared with the experimental data to check the validity of the code. The comparison showed that the simulation could give a good prediction for the neutron spectra above 50 eV, while the finite thickness of the foils greatly effected the experimental data in low energy. It was also found that the resonance detectors themselves had great impact on the simulated energy spectra. Supported by National Natural Science Foundation and Strategic Priority Research Program of the Chinese Academy of Sciences (11305229, 11105186, 91226107, 91026009, XDA03030300)

Towards a programme of testing and qualification for structural and plasma-facing materials in ‘fusion neutron’ environments

NASA Astrophysics Data System (ADS)

Stork, D.; Heidinger, R.; Muroga, T.; Zinkle, S. J.; Moeslang, A.; Porton, M.; Boutard, J.-L.; Gonzalez, S.; Ibarra, A.

2017-09-01

Materials damage by 14.1MeV neutrons from deuterium-tritium (D-T) fusion reactions can only be characterised definitively by subjecting a relevant configuration of test materials to high-intensity ‘fusion-neutron spectrum sources’, i.e. those simulating closely D-T fusion-neutron spectra. This provides major challenges to programmes to design and construct a demonstration fusion reactor prior to having a large-scale, high-intensity source of such neutrons. In this paper, we discuss the different aspects related to these ‘relevant configuration’ tests, including: • generic issues in materials qualification/validation, comparing safety requirements against those of investment protection; • lessons learned from the fission programme, enabling a reduced fusion materials testing programme; • the use and limitations of presently available possible irradiation sources to optimise a fusion neutron testing program including fission-neutron irradiation of isotopically and chemically tailored steels, ion damage by high-energy helium ions and self-ion beams, or irradiation studies with neutron sources of non-fusion spectra; and • the different potential sources of simulated fusion neutron spectra and the choice using stripping reactions from deuterium-beam ions incident on light-element targets.

A neutron diagnostic for high current deuterium beams.

PubMed

Rebai, M; Cavenago, M; Croci, G; Dalla Palma, M; Gervasini, G; Ghezzi, F; Grosso, G; Murtas, F; Pasqualotto, R; Cippo, E Perelli; Tardocchi, M; Tollin, M; Gorini, G

2012-02-01

A neutron diagnostic for high current deuterium beams is proposed for installation on the spectral shear interferometry for direct electric field reconstruction (SPIDER, Source for Production of Ion of Deuterium Extracted from RF plasma) test beam facility. The proposed detection system is called Close-contact Neutron Emission Surface Mapping (CNESM). The diagnostic aims at providing the map of the neutron emission on the beam dump surface by placing a detector in close contact, right behind the dump. CNESM uses gas electron multiplier detectors equipped with a cathode that also serves as neutron-proton converter foil. The cathode is made of a thin polythene film and an aluminium film; it is designed for detection of neutrons of energy >2.2 MeV with an incidence angle < 45°. CNESM was designed on the basis of simulations of the different steps from the deuteron beam interaction with the beam dump to the neutron detection in the nGEM. Neutron scattering was simulated with the MCNPX code. CNESM on SPIDER is a first step towards the application of this diagnostic technique to the MITICA beam test facility, where it will be used to resolve the horizontal profile of the beam intensity.

A neutron diagnostic for high current deuterium beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rebai, M.; Perelli Cippo, E.; Cavenago, M.

2012-02-15

A neutron diagnostic for high current deuterium beams is proposed for installation on the spectral shear interferometry for direct electric field reconstruction (SPIDER, Source for Production of Ion of Deuterium Extracted from RF plasma) test beam facility. The proposed detection system is called Close-contact Neutron Emission Surface Mapping (CNESM). The diagnostic aims at providing the map of the neutron emission on the beam dump surface by placing a detector in close contact, right behind the dump. CNESM uses gas electron multiplier detectors equipped with a cathode that also serves as neutron-proton converter foil. The cathode is made of a thinmore » polythene film and an aluminium film; it is designed for detection of neutrons of energy >2.2 MeV with an incidence angle < 45 deg. CNESM was designed on the basis of simulations of the different steps from the deuteron beam interaction with the beam dump to the neutron detection in the nGEM. Neutron scattering was simulated with the MCNPX code. CNESM on SPIDER is a first step towards the application of this diagnostic technique to the MITICA beam test facility, where it will be used to resolve the horizontal profile of the beam intensity.« less

Neutron-beam-shaping assembly for boron neutron-capture therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaidi, L.; Kashaeva, E. A.; Lezhnin, S. I.

A neutron-beam-shaping assembly consisting of a moderator, a reflector, and an absorber is used to form a therapeutic neutron beam for the boron neutron-capture therapy of malignant tumors at accelerator neutron sources. A new structure of the moderator and reflector is proposed in the present article, and the results of a numerical simulation of the neutron spectrum and of the absorbed dose in a modified Snyder head phantom are presented. The application of a composite moderator and of a composite reflector and the implementation of neutron production at the proton energy of 2.3MeV are shown to permit obtaining a high-qualitymore » therapeutic neutron beam.« less

Designing of the 14 MeV neutron moderator for BNCT

NASA Astrophysics Data System (ADS)

Cheng, Dao-Wen; Lu, Jing-Bin; Yang, Dong; Liu, Yu-Min; Wang, Hui-Dong; Ma, Ke-Yan

2012-09-01

In boron neutron capture therapy (BNCT), the ratio of the fast neutron flux to the neutron flux in the tumor (RFNT) must be less than 3%. If a D-T neutron generator is used in BNCT, the 14 MeV neutron moderator must be optimized to reduce the RFNT. Based on the neutron moderation theory and the simulation results, tungsten, lead and diamond were used to moderate the 14 MeV neutrons. Satisfying RFNT of less than 3%, the maximum neutron flux in the tumor was achieved with a three-layer moderator comprised of a 3 cm thick tungsten layer, a 14 cm thick lead layer and a 21 cm thick diamond layer.

A study on the sensitivity of self-powered neutron detectors (SPNDs)

NASA Astrophysics Data System (ADS)

Lee, Wanno; Cho, Gyuseong; Kim, Kwanghyun; Kim, Hee Joon; choi, Yuseon; Park, Moon Chu; Kim, Soongpyung

2001-08-01

Self-powered neutron detectors (SPNDs) are widely used in reactors to monitor neutron flux, while they have several advantages such as small size, and relatively simple electronics required in conjunction with those usages, they have some intrinsic problems of the low level of output current-a slow response time and the rapid change of sensitivity-that make it difficult to use for a long term. Monte Carlo simulation was used to calculate the escape probability as a function of the birth position of emitted beta particle for geometry of rhodium-based SPNDs. A simple numerical method calculated the initial generation rate of beta particles and the change of generation rate due to rhodium burnup. Using results of the simulation and the simple numerical method, the burnup profile of rhodium number density and the neutron sensitivity were calculated as a function of burnup time in reactors. This method was verified by the comparison of this and other papers, and data of YGN3.4 (Young Gwang Nuclear plant 3, 4) about the initial sensitivity. In addition, for improvement of some properties of rhodium-based SPNDs, which are currently used, a modified geometry is proposed. The proposed geometry, which is tube-type, is able to increase the initial sensitivity due to increase of the escape probability. The escape probability was calculated by changing the thickness of the insulator and compared solid-type with tube-type about each insulator thickness. The method used here can be applied to the analysis and design of other types of SPNDs.

Evaluation of radioisotope tracer and activation analysis techniques for contamination monitoring in space environment simulation chambers

NASA Technical Reports Server (NTRS)

Smathers, J. B.; Kuykendall, W. E., Jr.; Wright, R. E., Jr.; Marshall, J. R.

1973-01-01

Radioisotope measurement techniques and neutron activation analysis are evaluated for use in identifying and locating contamination sources in space environment simulation chambers. The alpha range method allows the determination of total contaminant concentration in vapor state and condensate state. A Cf-252 neutron activation analysis system for detecting oils and greases tagged with stable elements is described. While neutron activation analysis of tagged contaminants offers specificity, an on-site system is extremely costly to implement and provides only marginal detection sensitivity under even the most favorable conditions.

Preliminary On-Orbit Neutron Dose Equivalent and Energy Spectrum Results from the ISS-RAD Fast Neutron Detector (FND)

NASA Technical Reports Server (NTRS)

Semones, Edward; Leitgab, Martin

2016-01-01

The ISS-RAD instrument was activated on ISS on February 1st, 2016. Integrated in ISS-RAD, the Fast Neutron Detector (FND) performs, for the first time on ISS, routine and precise direct neutron measurements between 0.5 and 8 MeV. Preliminary results for neutron dose equivalent and neutron flux energy distributions from online/on-board algorithms and offline ground analyses will be shown, along with comparisons to simulated data and previously measured neutron spectral data. On-orbit data quality and pre-launch analysis validation results will be discussed as well.

Simulating a High-Spin Black Hole-Neutron Star Binary

NASA Astrophysics Data System (ADS)

Derby, John; Lovelace, Geoffrey; Duez, Matt; Foucart, Francois; Simulating Extreme Spacetimes (SXS) Collaboration

2017-01-01

During their first observing run (fall 2015) Advanced LIGO detected gravitational waves from merging black holes. In its future observations LIGO could detect black hole neutron star binaries (BHNS). It is important to have numerical simulations to predict these waves, to help find as many of these waves as possible and to estimate the sources properties, because at times near merger analytic approximations fail. Also, numerical models of the disk formed when the black hole tears apart the neutron star can help us learn about these systems' potential electromagnetic counterparts. One area of the parameter space for BHNS systems that is particularly challenging is simulations with high black hole spin. I will present results from a new BHNS simulation that has a black hole spin of 90% of the theoretical maximum. We are part of SXS but not all.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dehart, Mark; Mausolff, Zander; Goluoglu, Sedat

This report summarizes university research activities performed in support of TREAT modeling and simulation research. It is a compilation of annual research reports from four universities: University of Florida, Texas A&M University, Massachusetts Institute of Technology and Oregon State University. The general research topics are, respectively, (1) 3-D time-dependent transport with TDKENO/KENO-VI, (2) implementation of the Improved Quasi-Static method in Rattlesnake/MOOSE for time-dependent radiation transport approximations, (3) improved treatment of neutron physics representations within TREAT using OpenMC, and (4) steady state modeling of the minimum critical core of the Transient Reactor Test Facility (TREAT).

Radiation shielding evaluation of the BNCT treatment room at THOR: a TORT-coupled MCNP Monte Carlo simulation study.

PubMed

Chen, A Y; Liu, Y-W H; Sheu, R J

2008-01-01

This study investigates the radiation shielding design of the treatment room for boron neutron capture therapy at Tsing Hua Open-pool Reactor using "TORT-coupled MCNP" method. With this method, the computational efficiency is improved significantly by two to three orders of magnitude compared to the analog Monte Carlo MCNP calculation. This makes the calculation feasible using a single CPU in less than 1 day. Further optimization of the photon weight windows leads to additional 50-75% improvement in the overall computational efficiency.

Capture-gated Spectroscopic Measurements of Monoenergetic Neutrons with a Composite Scintillation Detector

NASA Astrophysics Data System (ADS)

Nattress, Jason; Mayer, M.; Foster, A.; Meddeb, A. Barhoumi; Trivelpiece, C.; Ounaies, Z.; Jovanovic, I.

2016-04-01

We report on the measurements of monoenergetic neutrons from DD and DT fusion reactions by use of the capture gating method in a heterogeneous plastic-glass composite scintillation detector. The cylindrical detector is 5.08 cm in diameter and 5.05 cm in height and was fabricated using 1-mm diameter Li-doped glass rods (GS20) and scintillating polyvinyl toluene (EJ-290). Different scintillation decay constants are used to identify energy depositions in two materials constituting the composite scintillator. Geant4 simulations of the neutron thermalization and capture process were conducted, finding a mean capture time of approximately 2.6 μs for both DD and DT neutrons. A capture gating time acceptance window based on simulation results was used to identify the neutron thermalization pulses. The total scintillation light yield produced in neutron thermalization was measured and found to show consistency on event-by-event basis despite the variety of neutron thermalization histories prior to capture. The ratio of light yields from thermalization of 14.1 MeV and 2.45 MeV neutrons in the EJ-290 scintillator was determined to be 14.6, and the light output from 2.45 MeV neutrons was also correlated to its electron equivalent, obtaining a value of 0.58±0.05 MeVee.

Development in the SONNE Instrument, a Solar Neutron Spectrometer for Solar Orbiter and Solar Sentinels

NASA Astrophysics Data System (ADS)

Ryan, J. M.; Bravar, U.; Macri, J. R.; McConnell, M. L.; Woolf, R.; Moser, M.; Flueckiger, E.; Pirard, B.; MacKinnon, A.; Mallik, P.; Bruillard, P.

2007-12-01

We report on the technical development of SONNE (Solar Neutron Experiment), a solar neutron spectrometer intended for use on the ESA Solar Orbiter and/or the NASA Solar Sentinels Missions. Development has taken place on three fronts, (1) simulations of a flight instrument, including the spacecraft radiation environment, (2) calibrating a prototype instrument in a monoenergetic neutron beam and (3) mechanical and electrical design of a deep space mission instrument. SONNE will be sensitive to fast neutrons up to 20 MeV, using double scatter imaging techniques to dramatically reduce background. Preliminary beam measurement analysis, conducted just before this abstract, supports advertised design goals in terms of sensitivity and energy resolution, meaning that time stamping neutron emission from the Sun will be possible. Combined with gamma ray measurements, new insight into particle acceleration will emerge when deployed on an inner heliospheric mission. Progress will be reported on simulations and physical design as well as calibrations.

Structure of single-supported DMPC lipid bilayer membranes as a function of hydration level studied by neutron reflectivity and Atomic Force Microscopy

NASA Astrophysics Data System (ADS)

Miskowiec, A.; Schnase, P.; Bai, M.; Taub, H.; Hansen, F. Y.; Dubey, M.; Singh, S.; Majewski, J.

2012-02-01

We have recently been investigating the diffusion of water on single-supported DMPC lipid bilayer membranes at different levels of hydration, using high-resolution quasielastic neutron scattering (QNS). To aid in the interpretation of these QNS studies, we have conducted neutron reflectivity (NR) measurements on SPEAR at LANSCE to characterize the structure of similarly prepared samples. Protonated DMPC membranes were deposited onto SiO2-coated Si(100) substrates and characterized by Atomic Force Microscopy (AFM) at different levels of hydration. We find reasonable agreement between the membrane thickness determined by NR and AFM at room temperature. We also find consistency between the scattering length density (SLD) profile in the vicinity of the upper leaflet of the supported DMPC membrane and that found in a molecular dynamics simulation of a freestanding membrane at 303 K. However, the fit to the reflectivity curve can be improved by modifying the SLD profile near the leaflet closest to the SiO2 surface.

Study of microdosimetric energy deposition patterns in tissue-equivalent medium due to low-energy neutron fields using a graphite-walled proportional counter.

PubMed

Waker, A J; Aslam

2011-06-01

To improve radiation protection dosimetry for low-energy neutron fields encountered in nuclear power reactor environments, there is increasing interest in modeling neutron energy deposition in metrological instruments such as tissue-equivalent proportional counters (TEPCs). Along with these computational developments, there is also a need for experimental data with which to benchmark and test the results obtained from the modeling methods developed. The experimental work described in this paper is a study of the energy deposition in tissue-equivalent (TE) medium using an in-house built graphite-walled proportional counter (GPC) filled with TE gas. The GPC is a simple model of a standard TEPC because the response of the counter at these energies is almost entirely due to the neutron interactions in the sensitive volume of the counter. Energy deposition in tissue spheres of diameter 1, 2, 4 and 8 µm was measured in low-energy neutron fields below 500 keV. We have observed a continuously increasing trend in microdosimetric averages with an increase in neutron energy. The values of these averages decrease as we increase the simulated diameter at a given neutron energy. A similar trend for these microdosimetric averages has been observed for standard TEPCs and the Rossi-type, TE, spherical wall-less counter filled with propane-based TE gas in the same energy range. This implies that at the microdosimetric level, in the neutron energy range we employed in this study, the pattern of average energy deposited by starter and insider proton recoil events in the gas is similar to those generated cumulatively by crosser and stopper events originating from the counter wall plus starter and insider recoil events originating in the sensitive volume of a TEPC.

First measurement of the VESUVIO neutron spectrum in the 30-80 MeV energy range using a Proton Recoil Telescope technique

NASA Astrophysics Data System (ADS)

Cazzaniga, C.; Tardocchi, M.; Croci, G.; Frost, C.; Giacomelli, L.; Grosso, G.; Hjalmarsson, A.; Rebai, M.; Rhodes, N. J.; Schooneveld, E. M.; Gorini, G.

2013-11-01

Measurements of the fast neutron energy spectrum at the ISIS spallation source are reported. The measurements were performed with a Proton Recoil Telescope consisting of a thin plastic foil placed in the neutron beam and two scintillator detectors. Results in the neutron energy range 30 MeV < En < 80 MeV are in good agreement with Monte Carlo simulations of the neutron spectrum.

Characterization of emergent leakage neutrons from multiple layers of hydrogen/water in the lunar regolith by Monte Carlo simulation

NASA Astrophysics Data System (ADS)

SU, J.; Sagdeev, R.; Usikov, D.; Chin, G.; Boyer, L.; Livengood, T. A.; McClanahan, T. P.; Murray, J.; Starr, R. D.

2013-12-01

Introduction: The leakage flux of lunar neutrons produced by precipitation of galactic cosmic ray (GCR) particles in the upper layer of the lunar regolith and measured by orbital instruments such as the Lunar Exploration Neutron Detector (LEND) is investigated by Monte Carlo simulation. Previous Monte Carlo (MC) simulations have been used to investigate neutron production and leakage from the lunar surface to assess the elemental composition of lunar soil [1-6] and its effect on the leakage neutron flux. We investigate effects on the emergent flux that depend on the physical distribution of hydrogen within the regolith. We use the software package GEANT4 [7] to calculate neutron production from spallation by GCR particles [8,9] in the lunar soil. Multiple layers of differing hydrogen/water at different depths in the lunar regolith model are introduced to examine enhancement or suppression of leakage neutron flux. We find that the majority of leakage thermal and epithermal neutrons are produced in 25 cm to 75 cm deep from the lunar surface. Neutrons produced in the shallow top layer retain more of their original energy due to fewer scattering interactions and escape from the lunar surface mostly as fast neutrons. This provides a diagnostic tool in interpreting leakage neutron flux enhancement or suppression due to hydrogen concentration distribution in lunar regolith. We also find that the emitting angular distribution of thermal and epithermal leakage neutrons can be described by cos3/2(theta) where the fast neutrons emitting angular distribution is cos(theta). The energy sensitivity and angular response of the LEND detectors SETN and CSETN are investigated using the leakage neutron spectrum from GEANT4 simulations. A simplified LRO model is used to benchmark MCNPX[10] and GEANT4 on CSETN absolute count rate corresponding to neutron flux from bombardment of 120MV solar potential GCR particles on FAN lunar soil. We are able to interpret the count rates of SETN and CSETN from the leakage neutron spectrum, emission angle, detector energy sensitivity and angular response. Reference: [1] W. C. Feldman, et al., Science 4 September 1998: Vol. 281 no. 5382 pp. 1496-1500. [2] Gasnault, O., et al., (2000) J. Geophys. Res., 105(E2), 4263-4271. [3] Little, R. C., et al. (2003), J. Geophys. Res., 108(E5), 5046. [4] McKinney et al., (2006), J. Geophys. Res., 111, E06004. [5] Lawrence et al., (2006), J. Geophys. Res., 111, E08001. [6] Looper et al, (2013), Space Weather, VOL. 11, 142-152. [7] J. Allison, et al, (2006) IEEE TRANS. ON NUCL SCI, VOL. 53, NO. 1. [8] J. Masarik and R. Reedy (1996), J. Geophys. Res., 101, 18,891-18,912. [9] P. O'Neil (2010) IEEE Trans. Nucl. Sci., 57(6), 3148-3153. [10] D. Pelowitz, (2005), Rep. LA-CP-05-0369, LANL, Los Alamos, NM.

Unambiguous determination of H-atom positions: comparing results from neutron and high-resolution X-ray crystallography.

PubMed

Gardberg, Anna S; Del Castillo, Alexis Rae; Weiss, Kevin L; Meilleur, Flora; Blakeley, Matthew P; Myles, Dean A A

2010-05-01

The locations of H atoms in biological structures can be difficult to determine using X-ray diffraction methods. Neutron diffraction offers a relatively greater scattering magnitude from H and D atoms. Here, 1.65 A resolution neutron diffraction studies of fully perdeuterated and selectively CH(3)-protonated perdeuterated crystals of Pyrococcus furiosus rubredoxin (D-rubredoxin and HD-rubredoxin, respectively) at room temperature (RT) are described, as well as 1.1 A resolution X-ray diffraction studies of the same protein at both RT and 100 K. The two techniques are quantitatively compared in terms of their power to directly provide atomic positions for D atoms and analyze the role played by atomic thermal motion by computing the sigma level at the D-atom coordinate in simulated-annealing composite D-OMIT maps. It is shown that 1.65 A resolution RT neutron data for perdeuterated rubredoxin are approximately 8 times more likely overall to provide high-confidence positions for D atoms than 1.1 A resolution X-ray data at 100 K or RT. At or above the 1.0sigma level, the joint X-ray/neutron (XN) structures define 342/378 (90%) and 291/365 (80%) of the D-atom positions for D-rubredoxin and HD-rubredoxin, respectively. The X-ray-only 1.1 A resolution 100 K structures determine only 19/388 (5%) and 8/388 (2%) of the D-atom positions above the 1.0sigma level for D-rubredoxin and HD-rubredoxin, respectively. Furthermore, the improved model obtained from joint XN refinement yielded improved electron-density maps, permitting the location of more D atoms than electron-density maps from models refined against X-ray data only.

Ultra Low Level Environmental Neutron Measurements Using Superheated Droplet Detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fernandes, A.C.; Centro de Fisica Nuclear, Universidade de Lisboa. Av. Prof. Gama Pinto, 2, 1649- 003 Lisboa; Felizardo, M.

2015-07-01

Through the application of superheated droplet detectors (SDDs), the SIMPLE project for the direct search for dark matter (DM) reached the most restrictive limits on the spin-dependent sector to date. The experiment is based on the detection of recoils following WIMP-nuclei interaction, mimicking those from neutron scattering. The thermodynamic operation conditions yield the SDDs intrinsically insensitive to radiations with linear energy transfer below ∼150 keVμm{sup -1} such as photons, electrons, muons and neutrons with energies below ∼40 keV. Underground facilities are increasingly employed for measurements in a low-level radiation background (DM search, gamma-spectroscopy, intrinsic soft-error rate measurements, etc.), where themore » rock overburden shields against cosmic radiation. In this environment the SDDs are sensitive only to α-particles and neutrons naturally emitted from the surrounding materials. Recently developed signal analysis techniques allow discrimination between neutron and α-induced signals. SDDs are therefore a promising instrument for low-level neutron and α measurements, namely environmental neutron measurements and α-contamination assays. In this work neutron measurements performed in the challenging conditions of the latest SIMPLE experiment (1500 mwe depth with 50-75 cm water shield) are reported. The results are compared with those obtained by detailed Monte Carlo simulations of the neutron background induced by {sup 238}U and {sup 232}Th traces in the facility, shielding and detector materials. Calculations of the neutron energy distribution yield the following neutron fluence rates (in 10{sup -8} cm{sup -2}s{sup -1}): thermal (<0.5 eV): 2.5; epithermal (0.5 eV-100 keV): 2.2; fast (>1 MeV): 3.9. Signal rates were derived using standard cross sections and codes routinely employed in reactor dosimetry. The measured and calculated neutron count rates per unit of active mass were 0.15 ct/kgd and 0.33 ct/kg-d respectively. As the major signal contribution (98%) originates from radio-impurities in the detector container, alternative materials will be employed in future devices. Latest results regarding the improvement of the detector characterization accuracy towards its application in environmental neutron detection are in progress and will be described. (authors)« less

Phase I - Final report: Improved position sensitive detectors for thermal neutrons. Design, fabrication, and results of testing the Phase I - Proof-of-Principal Improved Position Sensitive Thermal Neutron Detector Prototype in the laboratory and at the Intense Pulsed Neutron Source (IPNS), Argonne National Laboratory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hull, Carter D.

A position sensitive neutron detector was designed and fabricated with bundles of individual detector elements with diameters of 120 mm. These neutron scintillating fibers were coupled with optoelectronic arrays to produce a ''Fiber Detector.'' A fiber position sensitive detector was completed and tested with scattered and thermal neutrons. Deployment of improved 2D PSDs with high signal to noise ratios at lower costs per area was the overall objective of the project.

Radiological Protection and Nuclear Engineering Studies in Multi-MW Target Systems

NASA Astrophysics Data System (ADS)

Luis, Raul Fernandes

Several innovative projects involving nuclear technology have emerged around the world in recent years, for applications such as spallation neutron sources, accelerator-driven systems for the transmutation of nuclear waste and radioactive ion beam (RIB) production. While the available neutron Wuxes from nuclear reactors did not increase substantially in intensity over the past three decades, the intensities of neutron sources produced in spallation targets have increased steadily, and should continue to do so during the 21st century. Innovative projects like ESS, MYRRHA and EURISOL lie at the forefront of the ongoing pursuit for increasingly bright neutron sources; driven by proton beams with energies up to 2 GeV and intensities up to several mA, the construction of their proposed facilities involves complex Nuclear Technology and Radiological Protection design studies executed by multidisciplinary teams of scientists and engineers from diUerent branches of Science. The intense neutron Wuxes foreseen for those facilities can be used in several scientiVc research Velds, such as Nuclear Physics and Astrophysics, Medicine and Materials Science. In this work, the target systems of two facilitites for the production of RIBs using the Isotope Separation On-Line (ISOL) method were studied in detail: ISOLDE, operating at CERN since 1967, and EURISOL, the next-generation ISOL facility to be built in Europe. For the EURISOL multi-MW target station, a detailed study of Radiological Protection was carried out using the Monte Carlo code FLUKA. Simulations were done to assess neutron Wuences, Vssion rates, ambient dose equivalent rates during operation and after shutdown and the production of radioactive nuclei in the targets and surrounding materials. DiUerent materials were discussed for diUerent components of the target system, aiming at improving its neutronics performance while keeping the residual activities resulting from material activation as low as possible. The second goal of this work was to perform an optimisation study for the ISOLDE neutron converter and Vssion target system. The target system was simulated using FLUKA and the cross section codes TALYS and ABRABLA, with the objective of maximising the performance of the system for the production of pure beams of neutron-rich isotopes, suppressing the contaminations by undesired neutron-deficient isobars. Two alternative target systems were proposed in the optimisation studies; the simplest of the two, with some modiVcations, was built as a prototype and tested at ISOLDE. The experimental results clearly show that it is possible, with simple changes in the layouts of the target systems, to produce purer beams of neutron-rich isotopes around the doubly magic nuclei 78Ni and 132Sn. A study of Radiological Protection was also performed, comparing the performances of the prototype target system and the standard ISOLDE target system. None

Neutron Energy Spectra and Yields from the 7Li(p,n) Reaction for Nuclear Astrophysics

NASA Astrophysics Data System (ADS)

Tessler, M.; Friedman, M.; Schmidt, S.; Shor, A.; Berkovits, D.; Cohen, D.; Feinberg, G.; Fiebiger, S.; Krása, A.; Paul, M.; Plag, R.; Plompen, A.; Reifarth, R.

2016-01-01

Neutrons produced by the 7Li(p, n)7Be reaction close to threshold are widely used to measure the cross section of s-process nucleosynthesis reactions. While experiments have been performed so far with Van de Graaff accelerators, the use of RF accelerators with higher intensities is planned to enable investigations on radioactive isotopes. In parallel, high-power Li targets for the production of high-intensity neutrons at stellar energies are developed at Goethe University (Frankfurt, Germany) and SARAF (Soreq NRC, Israel). However, such setups pose severe challenges for the measurement of the proton beam intensity or the neutron fluence. In order to develop appropriate methods, we studied in detail the neutron energy distribution and intensity produced by the thick-target 7Li(p,n)7Be reaction and compared them to state-of- the-art simulation codes. Measurements were performed with the bunched and chopped proton beam at the Van de Graaff facility of the Institute for Reference Materials and Measurements (IRMM) using the time-of-flight (TOF) technique with thin (1/8") and thick (1") detectors. The importance of detailed simulations of the detector structure and geometry for the conversion of TOF to a neutron energy is stressed. The measured neutron spectra are consistent with those previously reported and agree well with Monte Carlo simulations that include experimentally determined 7Li(p,n) cross sections, two-body kinematics and proton energy loss in the Li-target.

Real time spectrometer for thermal neutrons from radiotherapic accelerators

NASA Astrophysics Data System (ADS)

Mozzanica, A.; Bartesaghi, G.; Bolognini, D.; Conti, V.; Mascagna, V.; Prest, M.; Scazzi, S.; Cappelletti, P.; Frigerio, M.; Gelosa, S.; Monti, A.; Ostinelli, A.; Bevilacqua, R.; Giannini, G.; Totaro, P.; Vallazza, E.

2007-10-01

Radiotherapy accelerators can produce high energy photon beams for deep tumour treatments. Photons with energies greater than 8 MeV produce neutrons via photoproduction. The PHONES (PHOto NEutron Source) project is developing a neutron moderator to use the photoproduced neutrons for BNCT (Boron Neutron Capture Therapy) in hospital environments. In this framework we are developing a real time spectrometer for thermal neutrons exploiting the bunch structure of the beam. Since the beam is produced by a linear accelerator, in fact, particles are sent to the patient in bunches with a rate of 150-300 Hz depending on the beam type and energy. The neutron spectrum is usually measured with integrating detectors such as bubble dosimeters or TLDs, which integrate over a time interval and an energy one. We are developing a scintillator detector to measure the neutron spectrum in real time in the interval between bunches, that is in the thermal region. The signals from the scintillator are discriminated and sampled by a dedicated clock in a Cyclone II FPGA by Altera, thus obtaining the neutron time of flight spectrum. The exploited physical process in ordinary plastic scintillators is neutron capture by H with a subsequent γ emission. The measured TOF spectrum has been compared with a BF 3 counter one. A dedicated simulation with MCNP is being developed to extract the energy spectrum from the TOF one. The paper will present the results of the prototype measurements and the status of the simulation.

Monte Carlo analysis of tagged neutron beams for cargo container inspection.

PubMed

Pesente, S; Lunardon, M; Nebbia, G; Viesti, G; Sudac, D; Valkovic, V

2007-12-01

Fast neutrons produced via D+T reactions and tagged by the associated particle technique have been recently proposed to inspect cargo containers. The general characteristics of this technique are studied with Monte Carlo simulations by determining the properties of the tagged neutron beams as a function of the relevant design parameters (energy and size of the deuteron beam, geometry of the charged particle detector). Results from simulations, validated by experiments, show that the broadening of the correlation between the alpha-particle and the neutron, induced by kinematical as well as geometrical (beam and detector size) effects, is important and limits the dimension of the minimum voxel to be inspected. Moreover, the effect of the container filling is explored. The material filling produces a sizeable loss of correlation between alpha-particles and neutrons due to scattering and absorption. Conditions in inspecting cargo containers are discussed.

GEM detectors development for radiation environment: neutron tests and simulations

NASA Astrophysics Data System (ADS)

Chernyshova, Maryna; Jednoróg, Sławomir; Malinowski, Karol; Czarski, Tomasz; Ziółkowski, Adam; Bieńkowska, Barbara; Prokopowicz, Rafał; Łaszyńska, Ewa; Kowalska-Strzeciwilk, Ewa; Poźniak, Krzysztof T.; Kasprowicz, Grzegorz; Zabołotny, Wojciech; Wojeński, Andrzej; Krawczyk, Rafał D.; Linczuk, Paweł; Potrykus, Paweł; Bajdel, Barcel

2016-09-01

One of the requests from the ongoing ITER-Like Wall Project is to have diagnostics for Soft X-Ray (SXR) monitoring in tokamak. Such diagnostics should be focused on tungsten emission measurements, as an increased attention is currently paid to tungsten due to a fact that it became a main candidate for the plasma facing material in ITER and future fusion reactor. In addition, such diagnostics should be able to withstand harsh radiation environment at tokamak during its operation. The presented work is related to the development of such diagnostics based on Gas Electron Multiplier (GEM) technology. More specifically, an influence of neutron radiation on performance of the GEM detectors is studied both experimentally and through computer simulations. The neutron induced radioactivity (after neutron source exposure) was found to be not pronounced comparing to an impact of other secondary neutron reaction products (during the exposure).

Thermal Neutron Point Source Imaging using a Rotating Modulation Collimator (RMC)

DTIC Science & Technology

2010-03-01

Source Details.........................................................................................37 3.5 Simulation of RMC in MCNP ...passed through the masks at each rotation angle. ................................. 42 19. Figure 19: MCNP Generate Modulation Profile for Cadmium. The...Cadmium. The multi-energetic neutron source simulation from MCNP is used for this plot. The energy is values are shown per energy bin. The

Monte Carlo source simulation technique for solution of interference reactions in INAA experiments: a preliminary report

NASA Astrophysics Data System (ADS)

Allaf, M. Athari; Shahriari, M.; Sohrabpour, M.

2004-04-01

A new method using Monte Carlo source simulation of interference reactions in neutron activation analysis experiments has been developed. The neutron spectrum at the sample location has been simulated using the Monte Carlo code MCNP and the contributions of different elements to produce a specified gamma line have been determined. The produced response matrix has been used to measure peak areas and the sample masses of the elements of interest. A number of benchmark experiments have been performed and the calculated results verified against known values. The good agreement obtained between the calculated and known values suggests that this technique may be useful for the elimination of interference reactions in neutron activation analysis.

SU-G-IeP4-04: DD-Neutron Source Collimation for Neutron Stimulated Emission Computed Tomography: A Monte Carlo Simulation Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fong, G; Kapadia, A

Purpose: To optimize collimation and shielding for a deuterium-deuterium (DD) neutron generator for an inexpensive and compact clinical neutron imaging system. The envisioned application is cancer diagnosis through Neutron Stimulated Emission Computed Tomography (NSECT). Methods: Collimator designs were tested with an isotropic 2.5 MeV neutron source through GEANT4 simulations. The collimator is a 52×52×52 cm{sup 3} polyethylene block coupled with a 1 cm lead sheet in sequence. Composite opening was modeled into the collimator to permit passage of neutrons. The opening varied in shape (cylindrical vs. tapered), size (1–5 cm source-side and target-side openings) and aperture placements (13–39 cm frommore » source-side). Spatial and energy distribution of neutrons and gammas were tracked from each collimator design. Parameters analyzed were primary beam width (FWHM), divergence, and efficiency (percent transmission) for different configurations of the collimator. Select resultant outputs were then used for simulated NSECT imaging of a virtual breast phantom containing a 2.5 cm diameter tumor to assess the effect of the collimator on spatial resolution, noise, and scan time. Finally, composite shielding enclosure made of polyethylene and lead was designed and evaluated to block 99.99% of neutron and gamma radiation generated in the system. Results: Analysis of primary beam indicated the beam-width is linear to the aperture size. Increasing source-side opening allowed at least 20% more neutron throughput for all designs relative to the cylindrical openings. Maximum throughput for all designs was 364% relative to cylindrical openings. Conclusion: The work indicates potential for collimating and shielding a DD neutron generator for use in a clinical NSECT system. The proposed collimator designs produced a well-defined collimated neutron beam that can be used to image samples of interest with millimeter resolution. Balance in output efficiency, noise reduction, and scan time should be considered to determine the optimal design for specific NSECT applications.« less

rf improvements for Spallation Neutron Source H- ion sourcea)

NASA Astrophysics Data System (ADS)

Kang, Y. W.; Fuja, R.; Goulding, R. H.; Hardek, T.; Lee, S.-W.; McCarthy, M. P.; Piller, M. C.; Shin, K.; Stockli, M. P.; Welton, R. F.

2010-02-01

The Spallation Neutron Source at Oak Ridge National Laboratory is ramping up the accelerated proton beam power to 1.4 MW and just reached 1 MW. The rf-driven multicusp ion source that originates from the Lawrence Berkeley National Laboratory has been delivering ˜38 mA H- beam in the linac at 60 Hz, 0.9 ms. To improve availability, a rf-driven external antenna multicusp ion source with a water-cooled ceramic aluminum nitride (AlN) plasma chamber is developed. Computer modeling and simulations have been made to analyze and optimize the rf performance of the new ion source. Operational statistics and test runs with up to 56 mA medium energy beam transport beam current identify the 2 MHz rf system as a limiting factor in the system availability and beam production. Plasma ignition system is under development by using a separate 13 MHz system. To improve the availability of the rf power system with easier maintenance, we tested a 70 kV isolation transformer for the 80 kW, 6% duty cycle 2 MHz amplifier to power the ion source from a grounded solid-state amplifier.

rf improvements for Spallation Neutron Source H- ion source.

PubMed

Kang, Y W; Fuja, R; Goulding, R H; Hardek, T; Lee, S-W; McCarthy, M P; Piller, M C; Shin, K; Stockli, M P; Welton, R F

2010-02-01

The Spallation Neutron Source at Oak Ridge National Laboratory is ramping up the accelerated proton beam power to 1.4 MW and just reached 1 MW. The rf-driven multicusp ion source that originates from the Lawrence Berkeley National Laboratory has been delivering approximately 38 mA H(-) beam in the linac at 60 Hz, 0.9 ms. To improve availability, a rf-driven external antenna multicusp ion source with a water-cooled ceramic aluminum nitride (AlN) plasma chamber is developed. Computer modeling and simulations have been made to analyze and optimize the rf performance of the new ion source. Operational statistics and test runs with up to 56 mA medium energy beam transport beam current identify the 2 MHz rf system as a limiting factor in the system availability and beam production. Plasma ignition system is under development by using a separate 13 MHz system. To improve the availability of the rf power system with easier maintenance, we tested a 70 kV isolation transformer for the 80 kW, 6% duty cycle 2 MHz amplifier to power the ion source from a grounded solid-state amplifier.

Improved Delayed-Neutron Spectroscopy Using Trapped Ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Norman, Eric B.

The neutrons emitted following the β decay of fission fragments (known as delayed neutrons because they are emitted after fission on a timescale of the β-decay half-lives) play a crucial role in reactor performance and control. Reviews of delayed-neutron properties highlight the need for high-quality data for a wide variety of delayed-neutron emitters to better understand the time dependence and energy spectrum of the neutrons as these properties are essential for a detailed understanding of reactor kinetics needed for reactor safety and to understand the behavior of these reactors under various accident and component-failure scenarios. For fast breeder reactors, criticalitymore » calculations require accurate delayed-neutron energy spectra and approximations that are acceptable for light-water reactors such as assuming the delayed-neutron and fission-neutron energy spectra are identical are not acceptable and improved β-delayed neutron data is needed for safety and accident analyses for these reactors. With improved nuclear data, the delayed neutrons flux and energy spectrum could be calculated from the contributions from individual isotopes and therefore could be accurately modeled for any fuel-cycle concept, actinide mix, or irradiation history. High-quality β-delayed neutron measurements are also critical to constrain modern nuclear-structure calculations and empirical models that predict the decay properties for nuclei for which no data exists and improve the accuracy and flexibility of the existing empirical descriptions of delayed neutrons from fission such as the six-group representation« less

Cross Calibration of Omnidirectional Orbital Neutron Detectors of Lunar Prospector (LP) and Lunar Exploration Neutron Detector (LEND) by Monte Carlo Simulation

NASA Astrophysics Data System (ADS)

Murray, J.; SU, J. J.; Sagdeev, R.; Chin, G.

2014-12-01

Introduction:Monte Carlo (MC) simulations have been used to investigate neutron production and leakage from the lunar surface to assess the composition of the lunar soil [1-3]. Orbital measurements of lunar neutron flux have been made by the Lunar Prospector Neutron Spectrometer (LPNS)[4] of the Lunar Prospector mission and the Lunar Exploration Neutron Detector (LEND)[5] of the Lunar Reconnaissance Orbiter mission. While both are cylindrical helium-3 detectors, LEND's SETN (Sensor EpiThermal Neutrons) instrument is shorter, with double the helium-3 pressure than that of LPNS. The two instruments therefore have different angular sensitivities and neutron detection efficiencies. Furthermore, the Lunar Prospector's spin-stabilized design makes its detection efficiency latitude-dependent, while the SETN instrument faces permanently downward toward the lunar surface. We use the GEANT4 Monte Carlo simulation code[6] to investigate the leakage lunar neutron energy spectrum, which follows a power law of the form E-0.9 in the epithermal energy range, and the signals detected by LPNS and SETN in the LP and LRO mission epochs, respectively. Using the lunar neutron flux reconstructed for LPNS epoch, we calculate the signal that would have been observed by SETN at that time. The subsequent deviation from the actual signal observed during the LEND epoch is due to the significantly higher intensity of Galactic Cosmic Rays during the anomalous Solar Minimum of 2009-2010. References: [1] W. C. Feldman, et al., (1998) Science Vol. 281 no. 5382 pp. 1496-1500. [2] Gasnault, O., et al.,(2000) J. Geophys. Res., 105(E2), 4263-4271. [3] Little, R. C., et al. (2003), J. Geophys. Res., 108(E5), 5046. [4]W. C. Feldman, et al., (1999) Nucl. Inst. And Method in Phys. Res. A 422, [5] M. L. Litvak, et al., (2012) J.Geophys. Res. 117, E00H32 [6] J. Allison, et al, (2006) IEEE Trans. on Nucl Sci, Vol 53, No 1.

Introducing single-crystal scattering and optical potentials into MCNPX: Predicting neutron emission from a convoluted moderator

DOE PAGES

Gallmeier, F. X.; Iverson, E. B.; Lu, W.; ...

2016-01-08

Neutron transport simulation codes are an indispensable tool used for the design and construction of modern neutron scattering facilities and instrumentation. It has become increasingly clear that some neutron instrumentation has started to exploit physics that is not well-modelled by the existing codes. Particularly, the transport of neutrons through single crystals and across interfaces in MCNP(X), Geant4 and other codes ignores scattering from oriented crystals and refractive effects, and yet these are essential ingredients for the performance of monochromators and ultra-cold neutron transport respectively (to mention but two examples). In light of these developments, we have extended the MCNPX codemore » to include a single-crystal neutron scattering model and neutron reflection/refraction physics. Furthermore, we have also generated silicon scattering kernels for single crystals of definable orientation with respect to an incoming neutron beam. As a first test of these new tools, we have chosen to model the recently developed convoluted moderator concept, in which a moderating material is interleaved with layers of perfect crystals to provide an exit path for neutrons moderated to energies below the crystal s Bragg cut off at locations deep within the moderator. Studies of simple cylindrical convoluted moderator systems of 100 mm diameter and composed of polyethylene and single crystal silicon were performed with the upgraded MCNPX code and reproduced the magnitude of effects seen in experiments compared to homogeneous moderator systems. Applying different material properties for refraction and reflection, and by replacing the silicon in the models with voids, we show that the emission enhancements seen in recent experiments are primarily caused by the transparency of the silicon/void layers. Finally the convoluted moderator experiments described by Iverson et al. were simulated and we find satisfactory agreement between the measurement and the results of simulations performed using the tools we have developed.« less

Direct comparison of elastic incoherent neutron scattering experiments with molecular dynamics simulations of DMPC phase transitions.

PubMed

Aoun, Bachir; Pellegrini, Eric; Trapp, Marcus; Natali, Francesca; Cantù, Laura; Brocca, Paola; Gerelli, Yuri; Demé, Bruno; Marek Koza, Michael; Johnson, Mark; Peters, Judith

2016-04-01

Neutron scattering techniques have been employed to investigate 1,2-dimyristoyl-sn -glycero-3-phosphocholine (DMPC) membranes in the form of multilamellar vesicles (MLVs) and deposited, stacked multilamellar-bilayers (MLBs), covering transitions from the gel to the liquid phase. Neutron diffraction was used to characterise the samples in terms of transition temperatures, whereas elastic incoherent neutron scattering (EINS) demonstrates that the dynamics on the sub-macromolecular length-scale and pico- to nano-second time-scale are correlated with the structural transitions through a discontinuity in the observed elastic intensities and the derived mean square displacements. Molecular dynamics simulations have been performed in parallel focussing on the length-, time- and temperature-scales of the neutron experiments. They correctly reproduce the structural features of the main gel-liquid phase transition. Particular emphasis is placed on the dynamical amplitudes derived from experiment and simulations. Two methods are used to analyse the experimental data and mean square displacements. They agree within a factor of 2 irrespective of the probed time-scale, i.e. the instrument utilized. Mean square displacements computed from simulations show a comparable level of agreement with the experimental values, albeit, the best match with the two methods varies for the two instruments. Consequently, experiments and simulations together give a consistent picture of the structural and dynamical aspects of the main lipid transition and provide a basis for future, theoretical modelling of dynamics and phase behaviour in membranes. The need for more detailed analytical models is pointed out by the remaining variation of the dynamical amplitudes derived in two different ways from experiments on the one hand and simulations on the other.

Progress toward a new measurement of the neutron lifetime

NASA Astrophysics Data System (ADS)

Grammer, Kyle

2015-10-01

Free neutron decay is the simplest nuclear beta decay. A precise value for the neutron lifetime is valuable for standard model consistency tests and Big Bang Nucleosynthesis models. There is a disagreement between the measured neutron lifetime from cold neutron beam experiments and ultracold neutron storage experiments. A new measurement of the neutron lifetime using the beam method is planned at the National Institute of Standards and Technology Center for Neutron Research. Experimental improvements should result in a 1s uncertainty measurement of the neutron lifetime. The technical improvements, recent apparatus tests, and the path towards the new measurement will be discussed. This work is supported by DOE Office of Science, NIST, and NSF.

Progress toward a new measurement of the neutron lifetime

NASA Astrophysics Data System (ADS)

Grammer, Kyle

2015-04-01

Free neutron decay is the simplest nuclear beta decay. A precise value for the neutron lifetime is valuable for standard model consistency tests and Big Bang Nucleosynthesis models. There is a disagreement between the measured neutron lifetime from cold neutron beam experiments and ultracold neutron storage experiments. A new measurement of the neutron lifetime using the beam method is planned at the National Institute of Standards and Technology Center for Neutron Research. Experimental improvements should result in a 1s uncertainty measurement of the neutron lifetime. The technical improvements and the path towards the new measurement will be discussed. This work is supported by DOE Office of Science, NIST, and NSF.

Accelerator driven neutron source design via beryllium target and 208Pb moderator for boron neutron capture therapy in alternative treatment strategy by Monte Carlo method.

PubMed

Khorshidi, Abdollah

2017-01-01

The reactor has increased its area of application into medicine especially boron neutron capture therapy (BNCT); however, accelerator-driven neutron sources can be used for therapy purposes. The present study aimed to discuss an alternative method in BNCT functions by a small cyclotron with low current protons based on Karaj cyclotron in Iran. An epithermal neutron spectrum generator was simulated with 30 MeV proton energy for BNCT purposes. A low current of 300 μA of the proton beam in spallation target concept via 9Be target was accomplished to model neutron spectrum using 208Pb moderator around the target. The graphite reflector and dual layer collimator were planned to prevent and collimate the neutrons produced from proton interactions. Neutron yield per proton, energy distribution, flux, and dose components in the simulated head phantom were estimated by MCNPX code. The neutron beam quality was investigated by diverse filters thicknesses. The maximum epithermal flux transpired using Fluental, Fe, Li, and Bi filters with thicknesses of 7.4, 3, 0.5, and 4 cm, respectively; as well as the epithermal to thermal neutron flux ratio was 161. Results demonstrated that the induced neutrons from a low energy and low current proton may be effective in tumor therapy using 208Pb moderator with average lethargy and also graphite reflector with low absorption cross section to keep the generated neutrons. Combination of spallation-based BNCT and proton therapy can be especially effective, if a high beam intensity cyclotron becomes available.

Neutron-neutron angular correlations in spontaneous fission of 252Cf and 240Pu

NASA Astrophysics Data System (ADS)

Verbeke, J. M.; Nakae, L. F.; Vogt, R.

2018-04-01

Background: Angular anisotropy has been observed between prompt neutrons emitted during the fission process. Such an anisotropy arises because the emitted neutrons are boosted along the direction of the parent fragment. Purpose: To measure the neutron-neutron angular correlations from the spontaneous fission of 252Cf and 240Pu oxide samples using a liquid scintillator array capable of pulse-shape discrimination. To compare these correlations to simulations combining the Monte Carlo radiation transport code MCNPX with the fission event generator FREYA. Method: Two different analysis methods were used to study the neutron-neutron correlations with varying energy thresholds. The first is based on setting a light output threshold while the second imposes a time-of-flight cutoff. The second method has the advantage of being truly detector independent. Results: The neutron-neutron correlation modeled by FREYA depends strongly on the sharing of the excitation energy between the two fragments. The measured asymmetry enabled us to adjust the FREYA parameter x in 240Pu, which controls the energy partition between the fragments and is so far inaccessible in other measurements. The 240Pu data in this analysis was the first available to quantify the energy partition for this isotope. The agreement between data and simulation is overall very good for 252Cf(sf ) and 240Pu(sf ) . Conclusions: The asymmetry in the measured neutron-neutron angular distributions can be predicted by FREYA. The shape of the correlation function depends on how the excitation energy is partitioned between the two fission fragments. Experimental data suggest that the lighter fragment is disproportionately excited.

Molecular dynamics simulations of amphiphilic graft copolymer molecules at a water/air interface.

PubMed

Anderson, Philip M; Wilson, Mark R

2004-11-01

Fully atomistic molecular dynamics simulations of amphiphilic graft copolymer molecules have been performed at a range of surface concentrations at a water/air interface. These simulations are compared to experimental results from a corresponding system over a similar range of surface concentrations. Neutron reflectivity data calculated from the simulation trajectories agrees well with experimentally acquired profiles. In particular, excellent agreement in neutron reflectivity is found for lower surface concentration simulations. A simulation of a poly(ethylene oxide) (PEO) chain in aqueous solution has also been performed. This simulation allows the conformational behavior of the free PEO chain and those tethered to the interface in the previous simulations to be compared. (c) 2004 American Institute of Physics.

A Monte Carlo Simulation for Understanding Energy Measurements of Beta Particles Detected by the UCNb Experiment

NASA Astrophysics Data System (ADS)

Feng, Chi; UCNb Collaboration

2011-10-01

It is theorized that contributions to the Fierz interference term from scalar interaction beyond the Standard Model could be detectable in the spectrum of neutron beta-decay. The UCNb experiment run at the Los Alamos Neutron Science Center aims to accurately measure the neutron beta-decay energy spectrum to detect a nonzero interference term. The instrument consists of a cubic ``integrating sphere'' calorimeter attached with up to 4 photomultiplier tubes. The inside of the calorimeter is coated with white paint and a thin UV scintillating layer made of deuterated polystyrene to contain the ultracold neutrons. A Monte Carlo simulation using the Geant4 toolkit is developed in order to provide an accurate method of energy reconstruction. Offline calibration with the Kellogg Radiation Laboratory 140 keV electron gun and conversion electron sources will be used to validate the Monte Carlo simulation to give confidence in the energy reconstruction methods and to better understand systematics in the experiment data.

Stability and accuracy of 3D neutron transport simulations using the 2D/1D method in MPACT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collins, Benjamin, E-mail: collinsbs@ornl.gov; Stimpson, Shane, E-mail: stimpsonsg@ornl.gov; Kelley, Blake W., E-mail: kelleybl@umich.edu

2016-12-01

A consistent “2D/1D” neutron transport method is derived from the 3D Boltzmann transport equation, to calculate fuel-pin-resolved neutron fluxes for realistic full-core Pressurized Water Reactor (PWR) problems. The 2D/1D method employs the Method of Characteristics to discretize the radial variables and a lower order transport solution to discretize the axial variable. This paper describes the theory of the 2D/1D method and its implementation in the MPACT code, which has become the whole-core deterministic neutron transport solver for the Consortium for Advanced Simulations of Light Water Reactors (CASL) core simulator VERA-CS. Several applications have been performed on both leadership-class and industry-classmore » computing clusters. Results are presented for whole-core solutions of the Watts Bar Nuclear Power Station Unit 1 and compared to both continuous-energy Monte Carlo results and plant data.« less

Stability and accuracy of 3D neutron transport simulations using the 2D/1D method in MPACT

DOE PAGES

Collins, Benjamin; Stimpson, Shane; Kelley, Blake W.; ...

2016-08-25

We derived a consistent “2D/1D” neutron transport method from the 3D Boltzmann transport equation, to calculate fuel-pin-resolved neutron fluxes for realistic full-core Pressurized Water Reactor (PWR) problems. The 2D/1D method employs the Method of Characteristics to discretize the radial variables and a lower order transport solution to discretize the axial variable. Our paper describes the theory of the 2D/1D method and its implementation in the MPACT code, which has become the whole-core deterministic neutron transport solver for the Consortium for Advanced Simulations of Light Water Reactors (CASL) core simulator VERA-CS. We also performed several applications on both leadership-class and industry-classmore » computing clusters. Results are presented for whole-core solutions of the Watts Bar Nuclear Power Station Unit 1 and compared to both continuous-energy Monte Carlo results and plant data.« less

A Monte Carlo Simulation of Prompt Gamma Emission from Fission Fragments

NASA Astrophysics Data System (ADS)

Regnier, D.; Litaize, O.; Serot, O.

2013-03-01

The prompt fission gamma spectra and multiplicities are investigated through the Monte Carlo code FIFRELIN which is developed at the Cadarache CEA research center. Knowing the fully accelerated fragment properties, their de-excitation is simulated through a cascade of neutron, gamma and/or electron emissions. This paper presents the recent developments in the FIFRELIN code and the results obtained on the spontaneous fission of 252Cf. Concerning the decay cascades simulation, a fully Hauser-Feshbach model is compared with a previous one using a Weisskopf spectrum for neutron emission. A particular attention is paid to the treatment of the neutron/gamma competition. Calculations lead using different level density and gamma strength function models show significant discrepancies of the slope of the gamma spectra at high energy. The underestimation of the prompt gamma spectra obtained regardless our de-excitation cascade modeling choice is discussed. This discrepancy is probably linked to an underestimation of the post-neutron fragments spin in our calculation.

Neutron reflecting supermirror structure

DOEpatents

Wood, James L.

1992-01-01

An improved neutron reflecting supermirror structure comprising a plurality of stacked sets of bilayers of neutron reflecting materials. The improved neutron reflecting supermirror structure is adapted to provide extremely good performance at high incidence angles, i.e. up to four time the critical angle of standard neutron mirror structures. The reflection of neutrons striking the supermirror structure at a high critical angle provides enhanced neutron throughput, and hence more efficient and economical use of neutron sources. One layer of each set of bilayers consist of titanium, and the second layer of each set of bilayers consist of an alloy of nickel with carbon interstitially present in the nickel alloy.

Standardization of accelerator irradiation procedures for simulation of neutron induced damage in reactor structural materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Lin; Gigax, Jonathan; Chen, Di

Self-ion irradiation is widely used as a method to simulate neutron damage in reactor structural materials. Accelerator-based simulation of void swelling, however, introduces a number of neutron-atypical features which require careful data extraction and in some cases introduction of innovative irradiation techniques to alleviate these issues. We briefly summarize three such atypical features: defect imbalance effects, pulsed beam effects, and carbon contamination. The latter issue has just been recently recognized as being relevant to simulation of void swelling and is discussed here in greater detail. It is shown that carbon ions are entrained in the ion beam by Coulomb forcemore » drag and accelerated toward the target surface. Beam-contaminant interactions are modeled using molecular dynamics simulation. By applying a multiple beam deflection technique, carbon and other contaminants can be effectively filtered out, as demonstrated in an irradiation of HT-9 alloy by 3.5 MeV Fe ions.« less

Standardization of accelerator irradiation procedures for simulation of neutron induced damage in reactor structural materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Lin; Gigax, Jonathan; Chen, Di

Self-ion irradiation is widely used as a method to simulate neutron damage in reactor structural materials. Accelerator-based simulation of void swelling, however, introduces a number of neutron-atypical features which require careful data extraction and, in some cases, introduction of innovative irradiation techniques to alleviate these issues. In this paper, we briefly summarize three such atypical features: defect imbalance effects, pulsed beam effects, and carbon contamination. The latter issue has just been recently recognized as being relevant to simulation of void swelling and is discussed here in greater detail. It is shown that carbon ions are entrained in the ion beammore » by Coulomb force drag and accelerated toward the target surface. Beam-contaminant interactions are modeled using molecular dynamics simulation. Finally, by applying a multiple beam deflection technique, carbon and other contaminants can be effectively filtered out, as demonstrated in an irradiation of HT-9 alloy by 3.5 MeV Fe ions.« less

Standardization of accelerator irradiation procedures for simulation of neutron induced damage in reactor structural materials

DOE PAGES

Shao, Lin; Gigax, Jonathan; Chen, Di; ...

2017-06-12

Self-ion irradiation is widely used as a method to simulate neutron damage in reactor structural materials. Accelerator-based simulation of void swelling, however, introduces a number of neutron-atypical features which require careful data extraction and, in some cases, introduction of innovative irradiation techniques to alleviate these issues. In this paper, we briefly summarize three such atypical features: defect imbalance effects, pulsed beam effects, and carbon contamination. The latter issue has just been recently recognized as being relevant to simulation of void swelling and is discussed here in greater detail. It is shown that carbon ions are entrained in the ion beammore » by Coulomb force drag and accelerated toward the target surface. Beam-contaminant interactions are modeled using molecular dynamics simulation. Finally, by applying a multiple beam deflection technique, carbon and other contaminants can be effectively filtered out, as demonstrated in an irradiation of HT-9 alloy by 3.5 MeV Fe ions.« less

Measuring The Neutron Lifetime to One Second Using in Beam Techniques

NASA Astrophysics Data System (ADS)

Mulholland, Jonathan; NIST In Beam Lifetime Collaboration

2013-10-01

The decay of the free neutron is the simplest nuclear beta decay and is the prototype for charged current semi-leptonic weak interactions. A precise value for the neutron lifetime is required for consistency tests of the Standard Model and is an essential parameter in the theory of Big Bang Nucleosynthesis. A new measurement of the neutron lifetime using the in-beam method is planned at the National Institute of Standards and Technology Center for Neutron Research. The systematic effects associated with the in-beam method are markedly different than those found in storage experiments utilizing ultracold neutrons. Experimental improvements, specifically recent advances in the determination of absolute neutron fluence, should permit an overall uncertainty of 1 second on the neutron lifetime. The technical improvements in the in-beam technique, and the path toward improving the precision of the new measurement will be discussed.

Designing an upgrade of the Medley setup for light-ion production and fission cross-section measurements

NASA Astrophysics Data System (ADS)

Jansson, K.; Gustavsson, C.; Al-Adili, A.; Hjalmarsson, A.; Andersson-Sundén, E.; Prokofiev, A. V.; Tarrío, D.; Pomp, S.

2015-09-01

Measurements of neutron-induced fission cross-sections and light-ion production are planned in the energy range 1-40 MeV at the upcoming Neutrons For Science (NFS) facility. In order to prepare our detector setup for the neutron beam with continuous energy spectrum, a simulation software was written using the Geant4 toolkit for both measurement situations. The neutron energy range around 20 MeV is troublesome when it comes to the cross-sections used by Geant4 since data-driven cross-sections are only available below 20 MeV but not above, where they are based on semi-empirical models. Several customisations were made to the standard classes in Geant4 in order to produce consistent results over the whole simulated energy range. Expected uncertainties are reported for both types of measurements. The simulations have shown that a simultaneous precision measurement of the three standard cross-sections H(n,n), 235U(n,f) and 238U(n,f) relative to each other is feasible using a triple layered target. As high resolution timing detectors for fission fragments we plan to use Parallel Plate Avalanche Counters (PPACs). The simulation results have put some restrictions on the design of these detectors as well as on the target design. This study suggests a fissile target no thicker than 2 μm (1.7 mg/cm2) and a PPAC foil thickness preferably less than 1 μm. We also comment on the usability of Geant4 for simulation studies of neutron reactions in this energy range.

Dosimetric and microdosimetric analyses for blood exposed to reactor-derived thermal neutrons.

PubMed

Ali, F; Atanackovic, J; Boyer, C; Festarini, A; Kildea, J; Paterson, L C; Rogge, R; Stuart, M; Richardson, R B

2018-06-06

Thermal neutrons are found in reactor, radiotherapy, aircraft, and space environments. The purpose of this study was to characterise the dosimetry and microdosimetry of thermal neutron exposures, using three simulation codes, as a precursor to quantitative radiobiological studies using blood samples. An irradiation line was designed employing a pyrolytic graphite crystal or-alternatively-a super mirror to expose blood samples to thermal neutrons from the National Research Universal reactor to determine radiobiological parameters. The crystal was used when assessing the relative biological effectiveness for dicentric chromosome aberrations, and other biomarkers, in lymphocytes over a low absorbed dose range of 1.2-14 mGy. Higher exposures using a super mirror will allow the additional quantification of mitochondrial responses. The physical size of the thermal neutron fields and their respective wavelength distribution was determined using the McStas Monte Carlo code. Spinning the blood samples produced a spatially uniform absorbed dose as determined from Monte Carlo N-Particle version 6 simulations. The major part (71%) of the total absorbed dose to blood was determined to be from the 14 N(n,p) 14 C reaction and the remainder from the 1 H(n,γ) 2 H reaction. Previous radiobiological experiments at Canadian Nuclear Laboratories involving thermal neutron irradiation of blood yielded a relative biological effectiveness of 26 ± 7. Using the Particle and Heavy Ion Transport Code System, a similar value of ∼19 for the quality factor of thermal neutrons initiating the 14 N(n,p) 14 C reaction in soft tissue was determined by microdosimetric simulations. This calculated quality factor is of similar high value to the experimentally-derived relative biological effectiveness, and indicates the potential of thermal neutrons to induce deleterious health effects in superficial organs such as cataracts of the eye lens.

Monte carlo simulation of innovative neutron and photon shielding material composing of high density concrete, waste rubber, lead and boron carbide

NASA Astrophysics Data System (ADS)

Aim-O, P.; Wongsawaeng, D.; Phruksarojanakun, P.; Tancharakorn, S.

2017-06-01

High-density concrete exhibits high strength and can perform an important role of gamma ray attenuation. In order to upgrade this material’s radiation-shielding performance, hydrogen-rich material can be incorporated. Waste rubber from vehicles has high hydrogen content which is the prominent characteristic to attenuate neutron. The objective of this work was to evaluate the radiation-shielding properties of this composite material against neutron and photon radiations. Monte Carlo transport simulation was conducted to simulate radiation through the composite material. Am-241/Be was utilized for neutron source and Co-60 for photon source. Parameters of the study included volume percentages of waste rubber, lead and boron carbide and thickness of the shielding material. These designs were also fabricated and the radiation shielding properties were experimentally evaluated. The best neutron and gamma ray shielding material was determined to be high-density concrete mixed with 5 vol% crumb rubber and 5 vol% lead powder. This shielding material increased the neutron attenuation by 64% and photon attenuation by 68% compared to ordinary concrete. Also, increasing the waste rubber content to greater than 5% resulted in a decrease in the radiation attenuation. This innovative composite radiation shielding material not only benefits nuclear science and engineering applications, but also helps solve the environmental issue of waste rubber.

Optimization of beam shaping assembly based on D-T neutron generator and dose evaluation for BNCT

NASA Astrophysics Data System (ADS)

Naeem, Hamza; Chen, Chaobin; Zheng, Huaqing; Song, Jing

2017-04-01

The feasibility of developing an epithermal neutron beam for a boron neutron capture therapy (BNCT) facility based on a high intensity D-T fusion neutron generator (HINEG) and using the Monte Carlo code SuperMC (Super Monte Carlo simulation program for nuclear and radiation process) is proposed in this study. The Monte Carlo code SuperMC is used to determine and optimize the final configuration of the beam shaping assembly (BSA). The optimal BSA design in a cylindrical geometry which consists of a natural uranium sphere (14 cm) as a neutron multiplier, AlF3 and TiF3 as moderators (20 cm each), Cd (1 mm) as a thermal neutron filter, Bi (5 cm) as a gamma shield, and Pb as a reflector and collimator to guide neutrons towards the exit window. The epithermal neutron beam flux of the proposed model is 5.73 × 109 n/cm2s, and other dosimetric parameters for the BNCT reported by IAEA-TECDOC-1223 have been verified. The phantom dose analysis shows that the designed BSA is accurate, efficient and suitable for BNCT applications. Thus, the Monte Carlo code SuperMC is concluded to be capable of simulating the BSA and the dose calculation for BNCT, and high epithermal flux can be achieved using proposed BSA.

Evaluation of Am–Li neutron spectra data for active well type neutron multiplicity measurements of uranium

DOE PAGES

Goddard, Braden; Croft, Stephen; Lousteau, Angela; ...

2016-05-25

Safeguarding nuclear material is an important and challenging task for the international community. One particular safeguards technique commonly used for uranium assay is active neutron correlation counting. This technique involves irradiating unused uranium with ( α,n) neutrons from an Am-Li source and recording the resultant neutron pulse signal which includes induced fission neutrons. Although this non-destructive technique is widely employed in safeguards applications, the neutron energy spectra from an Am-Li sources is not well known. Several measurements over the past few decades have been made to characterize this spectrum; however, little work has been done comparing the measured spectra ofmore » various Am-Li sources to each other. This paper examines fourteen different Am-Li spectra, focusing on how these spectra affect simulated neutron multiplicity results using the code Monte Carlo N-Particle eXtended (MCNPX). Two measurement and simulation campaigns were completed using Active Well Coincidence Counter (AWCC) detectors and uranium standards of varying enrichment. The results of this work indicate that for standard AWCC measurements, the fourteen Am-Li spectra produce similar doubles and triples count rates. Finally, the singles count rates varied by as much as 20% between the different spectra, although they are usually not used in quantitative analysis.« less

MCNP-REN - A Monte Carlo Tool for Neutron Detector Design Without Using the Point Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abhold, M.E.; Baker, M.C.

1999-07-25

The development of neutron detectors makes extensive use of the predictions of detector response through the use of Monte Carlo techniques in conjunction with the point reactor model. Unfortunately, the point reactor model fails to accurately predict detector response in common applications. For this reason, the general Monte Carlo N-Particle code (MCNP) was modified to simulate the pulse streams that would be generated by a neutron detector and normally analyzed by a shift register. This modified code, MCNP - Random Exponentially Distributed Neutron Source (MCNP-REN), along with the Time Analysis Program (TAP) predict neutron detector response without using the pointmore » reactor model, making it unnecessary for the user to decide whether or not the assumptions of the point model are met for their application. MCNP-REN is capable of simulating standard neutron coincidence counting as well as neutron multiplicity counting. Measurements of MOX fresh fuel made using the Underwater Coincidence Counter (UWCC) as well as measurements of HEU reactor fuel using the active neutron Research Reactor Fuel Counter (RRFC) are compared with calculations. The method used in MCNP-REN is demonstrated to be fundamentally sound and shown to eliminate the need to use the point model for detector performance predictions.« less

Improved neutron-gamma discrimination for a 3He neutron detector using subspace learning methods

DOE PAGES

Wang, C. L.; Funk, L. L.; Riedel, R. A.; ...

2017-02-10

3He gas based neutron linear-position-sensitive detectors (LPSDs) have been applied for many neutron scattering instruments. Traditional Pulse-Height Analysis (PHA) for Neutron-Gamma Discrimination (NGD) resulted in the neutron-gamma efficiency ratio on the orders of 10 5-10 6. The NGD ratios of 3He detectors need to be improved for even better scientific results from neutron scattering. Digital Signal Processing (DSP) analyses of waveforms were proposed for obtaining better NGD ratios, based on features extracted from rise-time, pulse amplitude, charge integration, a simplified Wiener filter, and the cross-correlation between individual and template waveforms of neutron and gamma events. Fisher linear discriminant analysis (FLDA)more » and three multivariate analyses (MVAs) of the features were performed. The NGD ratios are improved by about 10 2-10 3 times compared with the traditional PHA method. Finally, our results indicate the NGD capabilities of 3He tube detectors can be significantly improved with subspace-learning based methods, which may result in a reduced data-collection time and better data quality for further data reduction.« less

SU-E-T-168: Characterization of Neutrons From the TrueBeam Treatment Head

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sawkey, D; Svatos, M

2015-06-15

Purpose: Calculate neutron production and transport in the TrueBeam treatment head, as input for vault design and phantom dose calculations. Methods: A detailed model of the treatment head, including shielding components off the beam axis, was created from manufacturer’s engineering drawings. Simulations were done with Geant4 for the 18X, 15X, 10X and 10FFF beams, tuned to match measured dose distributions inside the treatment field. Particles were recorded on a 70 cm radius sphere surrounding the treatment head enabling input into simulations of vaults. Results: For the 18X beam, 11×10{sup 9} neutrons/MU were observed. The energy spectrum was a broad peakmore » with average energy 0.37 MeV. With jaws closed, 48% of the neutrons were generated in the primary collimator, 18% in the jaws, 12% in the target, and 10% in the flattening filter. With wide open jaws, few neutrons were produced in the jaws and consequently total neutron production dropped to 8.5×10{sup 9} neutrons/MU. Angular distributions were greatest along the beam axis (12×10{sup 9} neutrons/MU/sr, within 2 deg of the beam axis) and antiparallel to the beam axis (7×10{sup 9} neutrons/MU/sr). Peaks were observed in the neutron energy spectrum, corresponding to elastic scattering resonances in the shielding materials. Neutron production was lower for the other beams studied: 4.1×10{sup 9} neutrons/MU for 15X, 0.38×10{sup 9} neutrons/MU for 10X, and 0.22×10{sup 9} neutrons/MU for 10FFF. Despite dissimilar treatment head geometries and materials, the neutron production and energy spectrum were similar to those reported for Clinac accelerators. Conclusion: Detailed neutron production and leakage calculations for the TrueBeam treatment head were done. Unlike other studies, results are independent of the surrounding vault, enabling vault design calculations.« less

Determination of the optimum-size californium-252 neutron source for borehole capture gamma-ray analysis

USGS Publications Warehouse

Senftle, F.E.; Macy, R.J.; Mikesell, J.L.

1979-01-01

The fast- and thermal-neutron fluence rates from a 3.7 ??g 252Cf neutron source in a simulated borehole have been measured as a function of the source-to-detector distance using air, water, coal, iron ore-concrete mix, and dry sand as borehole media. Gamma-ray intensity measurements were made for specific spectral lines at low and high energies for the same range of source-to-detector distances in the iron ore-concrete mix and in coal. Integral gamma-ray counts across the entire spectrum were also made at each source-to-detector distance. From these data, the specific neutron-damage rate, and the critical count-rate criteria, we show that in an iron ore-concrete mix (low hydrogen concentration), 252Cf neutron sources of 2-40 ??g are suitable. The source size required for optimum gamma-ray sensitivity depends on the energy of the gamma ray being measured. In a hydrogeneous medium such as coal, similar measurements were made. The results show that sources from 2 to 20 ??g are suitable to obtain the highest gamma-ray sensitivity, again depending on the energy of the gamma ray being measured. In a hydrogeneous medium, significant improvement in sensitivity can be achieved by using faster electronics; in iron ore, it cannot. ?? 1979 North-Holland Publishing Co.

Neutron spectrometry for UF 6 enrichment verification in storage cylinders

DOE PAGES

Mengesha, Wondwosen; Kiff, Scott D.

2015-01-29

Verification of declared UF 6 enrichment and mass in storage cylinders is of great interest in nuclear material nonproliferation. Nondestructive assay (NDA) techniques are commonly used for safeguards inspections to ensure accountancy of declared nuclear materials. Common NDA techniques used include gamma-ray spectrometry and both passive and active neutron measurements. In the present study, neutron spectrometry was investigated for verification of UF 6 enrichment in 30B storage cylinders based on an unattended and passive measurement approach. MCNP5 and Geant4 simulated neutron spectra, for selected UF 6 enrichments and filling profiles, were used in the investigation. The simulated neutron spectra weremore » analyzed using principal component analysis (PCA). The PCA technique is a well-established technique and has a wide area of application including feature analysis, outlier detection, and gamma-ray spectral analysis. Results obtained demonstrate that neutron spectrometry supported by spectral feature analysis has potential for assaying UF 6 enrichment in storage cylinders. Thus the results from the present study also showed that difficulties associated with the UF 6 filling profile and observed in other unattended passive neutron measurements can possibly be overcome using the approach presented.« less

Neutron-gamma flux and dose calculations for feasibility study of DISCOMS instrumentation in case of severe accident in a GEN 3 reactor

NASA Astrophysics Data System (ADS)

Brovchenko, Mariya; Duhamel, Isabelle; Dechenaux, Benjamin

2017-09-01

The present paper presents the study carried out in the frame of the DISCOMS project, which stands for "DIstributed Sensing for COrium Monitoring and Safety". This study concerns the calculation of the neutron and gamma radiations received by the considered instrumentation during the normal reactor operation as well as in case of a severe accident for the EPR reactor, outside the reactor pressure vessel and in the containment basemat. This paper summarizes the methods and hypotheses used for the particle transport simulation outside the vessel during normal reactor operation. The results of the simulations are then presented including the responses for distributed Optical Fiber Sensors (OFS), such as the gamma dose and the fast neutron fluence, and for Self Powered Neutron Detectors (SPNDs), namely the neutron and gamma spectra. Same responses are also evaluated for severe accident situations in order to design the SPNDs being sensitive to the both types of received neutron-gamma radiation. By contrast, fibers, involved as transducers in distributed OFS have to resist to the total radiation gamma dose and neutron fluence received during normal operation and the severe accident.

Comparison between proton boron fusion therapy (PBFT) and boron neutron capture therapy (BNCT): a monte carlo study.

PubMed

Jung, Joo-Young; Yoon, Do-Kun; Barraclough, Brendan; Lee, Heui Chang; Suh, Tae Suk; Lu, Bo

2017-06-13

The aim of this study is to compare between proton boron fusion therapy (PBFT) and boron neutron capture therapy (BNCT) and to analyze dose escalation using a Monte Carlo simulation. We simulated a proton beam passing through the water with a boron uptake region (BUR) in MCNPX. To estimate the interaction between neutrons/protons and borons by the alpha particle, the simulation yielded with a variation of the center of the BUR location and proton energies. The variation and influence about the alpha particle were observed from the percent depth dose (PDD) and cross-plane dose profile of both the neutron and proton beams. The peak value of the maximum dose level when the boron particle was accurately labeled at the region was 192.4% among the energies. In all, we confirmed that prompt gamma rays of 478 keV and 719 keV were generated by the nuclear reactions in PBFT and BNCT, respectively. We validated the dramatic effectiveness of the alpha particle, especially in PBFT. The utility of PBFT was verified using the simulation and it has a potential for application in radiotherapy.

Comparison between proton boron fusion therapy (PBFT) and boron neutron capture therapy (BNCT): a Monte Carlo study

PubMed Central

Barraclough, Brendan; Lee, Heui Chang; Suh, Tae Suk; Lu, Bo

2017-01-01

The aim of this study is to compare between proton boron fusion therapy (PBFT) and boron neutron capture therapy (BNCT) and to analyze dose escalation using a Monte Carlo simulation. We simulated a proton beam passing through the water with a boron uptake region (BUR) in MCNPX. To estimate the interaction between neutrons/protons and borons by the alpha particle, the simulation yielded with a variation of the center of the BUR location and proton energies. The variation and influence about the alpha particle were observed from the percent depth dose (PDD) and cross-plane dose profile of both the neutron and proton beams. The peak value of the maximum dose level when the boron particle was accurately labeled at the region was 192.4% among the energies. In all, we confirmed that prompt gamma rays of 478 keV and 719 keV were generated by the nuclear reactions in PBFT and BNCT, respectively. We validated the dramatic effectiveness of the alpha particle, especially in PBFT. The utility of PBFT was verified using the simulation and it has a potential for application in radiotherapy. PMID:28427153

Simulating irradiation hardening in tungsten under fast neutron irradiation including Re production by transmutation

NASA Astrophysics Data System (ADS)

Huang, Chen-Hsi; Gilbert, Mark R.; Marian, Jaime

2018-02-01

Simulations of neutron damage under fusion energy conditions must capture the effects of transmutation, both in terms of accurate chemical inventory buildup as well as the physics of the interactions between transmutation elements and irradiation defect clusters. In this work, we integrate neutronics, primary damage calculations, molecular dynamics results, Re transmutation calculations, and stochastic cluster dynamics simulations to study neutron damage in single-crystal tungsten to mimic divertor materials. To gauge the accuracy and validity of the simulations, we first study the material response under experimental conditions at the JOYO fast reactor in Japan and the High Flux Isotope Reactor at Oak Ridge National Laboratory, for which measurements of cluster densities and hardening levels up to 2 dpa exist. We then provide calculations under expected DEMO fusion conditions. Several key mechanisms involving Re atoms and defect clusters are found to govern the accumulation of irradiation damage in each case. We use established correlations to translate damage accumulation into hardening increases and compare our results to the experimental measurements. We find hardening increases in excess of 5000 MPa in all cases, which casts doubts about the integrity of W-based materials under long-term fusion exposure.

Comparing Simulated and Experimental Data from UCN τ

NASA Astrophysics Data System (ADS)

Howard, Dezrick; Holley, Adam

2017-09-01

The UCN τ experiment is designed to measure the average lifetime of a free neutron (τn) by trapping ultracold neutrons (UCN) in a magneto-gravitational trap and allowing them to β-decay, with the ultimate goal of minimizing the uncertainty to approximately 0.01% (0.1 s). Understanding the systematics of the experiment at the level necessary to reach this high precision may help to better understand the disparity between measurements from cold neutron beam and UCN bottle experiments (τn 888 s and τn 878 s, respectively). To assist in evaluating systemics that might conceivably contribute at this level, a neutron spin-tracking Monte Carlo simulation, which models a UCN population's behavior throughout a run, is currently under development. The simulation will utilize an empirical map of the magnetic field in the trap (see poster by K. Hoffman) by interpolating the field between measured points (see poster by J. Felkins) in order to model the depolarization mechanism with high fidelity. As a preliminary step, I have checked that the Monte Carlo model can reasonably reproduce the observed behavior of the experiment. In particular, I will present a comparison between simulated data and data acquired from the 2016-2017 UCN τ run cycle.

Simulation of Thermal Neutron Transport Processes Directly from the Evaluated Nuclear Data Files

NASA Astrophysics Data System (ADS)

Androsenko, P. A.; Malkov, M. R.

The main idea of the method proposed in this paper is to directly extract thetrequired information for Monte-Carlo calculations from nuclear data files. The met od being developed allows to directly utilize the data obtained from libraries and seehs to be the most accurate technique. Direct simulation of neutron scattering in themmal energy range using file 7 ENDF-6 format in terms of code system BRAND has beer achieved. Simulation algorithms have been verified using the criterion x2

CIELO Collaboration Summary Results: International Evaluations of Neutron Reactions on Uranium, Plutonium, Iron, Oxygen and Hydrogen

DOE PAGES

Chadwick, M. B.; Capote, R.; Trkov, A.; ...

2018-03-07

The CIELO collaboration has studied neutron cross sections on nuclides that significantly impact criticality in nuclear technologies - 235,238U, 239Pu, 56Fe, 16O and 1H - with the aim of improving the accuracy of the data and resolving previous discrepancies in our understanding. This multi-laboratory pilot project, coordinated via the OECD/NEA Working Party on Evaluation Cooperation (WPEC) Subgroup 40 with support also from the IAEA, has motivated experimental and theoretical work and led to suites of new evaluated libraries that accurately reflect measured data and also perform well in integral simulations of criticality. This report summarizes our results on cross sectionsmore » and preliminary work on covariances, and outlines plans for the next phase of this collaboration.« less

CIELO Collaboration Summary Results: International Evaluations of Neutron Reactions on Uranium, Plutonium, Iron, Oxygen and Hydrogen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chadwick, M. B.; Capote, R.; Trkov, A.

The CIELO collaboration has studied neutron cross sections on nuclides that significantly impact criticality in nuclear technologies - 235,238U, 239Pu, 56Fe, 16O and 1H - with the aim of improving the accuracy of the data and resolving previous discrepancies in our understanding. This multi-laboratory pilot project, coordinated via the OECD/NEA Working Party on Evaluation Cooperation (WPEC) Subgroup 40 with support also from the IAEA, has motivated experimental and theoretical work and led to suites of new evaluated libraries that accurately reflect measured data and also perform well in integral simulations of criticality. This report summarizes our results on cross sectionsmore » and preliminary work on covariances, and outlines plans for the next phase of this collaboration.« less

Investigating inertial confinement fusion target fuel conditions through x-ray spectroscopya)

NASA Astrophysics Data System (ADS)

Hansen, Stephanie B.

2012-05-01

Inertial confinement fusion (ICF) targets are designed to produce hot, dense fuel in a neutron-producing core that is surrounded by a shell of compressing material. The x-rays emitted from ICF plasmas can be analyzed to reveal details of the temperatures, densities, gradients, velocities, and mix characteristics of ICF targets. Such diagnostics are critical to understand the target performance and to improve the predictive power of simulation codes.

Numerical relativity simulations of neutron star merger remnants using conservative mesh refinement

NASA Astrophysics Data System (ADS)

Dietrich, Tim; Bernuzzi, Sebastiano; Ujevic, Maximiliano; Brügmann, Bernd

2015-06-01

We study equal- and unequal-mass neutron star mergers by means of new numerical relativity simulations in which the general relativistic hydrodynamics solver employs an algorithm that guarantees mass conservation across the refinement levels of the computational mesh. We consider eight binary configurations with total mass M =2.7 M⊙, mass ratios q =1 and q =1.16 , four different equations of state (EOSs) and one configuration with a stiff EOS, M =2.5 M⊙ and q =1.5 , which is one of the largest mass ratios simulated in numerical relativity to date. We focus on the postmerger dynamics and study the merger remnant, the dynamical ejecta, and the postmerger gravitational wave spectrum. Although most of the merger remnants are a hypermassive neutron star collapsing to a black hole+disk system on dynamical time scales, stiff EOSs can eventually produce a stable massive neutron star. During the merger process and on very short time scales, about ˜10-3- 10-2M⊙ of material become unbound with kinetic energies ˜1050 erg . Ejecta are mostly emitted around the orbital plane and favored by large mass ratios and softer EOS. The postmerger wave spectrum is mainly characterized by the nonaxisymmetric oscillations of the remnant neutron star. The stiff EOS configuration consisting of a 1.5 M⊙ and a 1.0 M⊙ neutron star, simulated here for the first time, shows a rather peculiar dynamics. During merger the companion star is very deformed; about ˜0.03 M⊙ of the rest mass becomes unbound from the tidal tail due to the torque generated by the two-core inner structure. The merger remnant is a stable neutron star surrounded by a massive accretion disk of rest mass ˜0.3 M⊙. This and similar configurations might be particularly interesting for electromagnetic counterparts. Comparing results obtained with and without the conservative mesh refinement algorithm, we find that postmerger simulations can be affected by systematic errors if mass conservation is not enforced in the mesh refinement strategy. However, mass conservation also depends on grid details and on the artificial atmosphere setup; the latter are particularly significant in the computation of the dynamical ejecta.

Analytical functions to predict cosmic-ray neutron spectra in the atmosphere.

PubMed

Sato, Tatsuhiko; Niita, Koji

2006-09-01

Estimation of cosmic-ray neutron spectra in the atmosphere has been an essential issue in the evaluation of the aircrew doses and the soft-error rates of semiconductor devices. We therefore performed Monte Carlo simulations for estimating neutron spectra using the PHITS code in adopting the nuclear data library JENDL-High-Energy file. Excellent agreements were observed between the calculated and measured spectra for a wide altitude range even at the ground level. Based on a comprehensive analysis of the simulation results, we propose analytical functions that can predict the cosmic-ray neutron spectra for any location in the atmosphere at altitudes below 20 km, considering the influences of local geometries such as ground and aircraft on the spectra. The accuracy of the analytical functions was well verified by various experimental data.

DETECTORS AND EXPERIMENTAL METHODS: Measurement of the response function and the detection efficiency of an organic liquid scintillator for neutrons between 1 and 30 MeV

NASA Astrophysics Data System (ADS)

Huang, Han-Xiong; Ruan, Xi-Chao; Chen, Guo-Chang; Zhou, Zu-Ying; Li, Xia; Bao, Jie; Nie, Yang-Bo; Zhong, Qi-Ping

2009-08-01

The light output function of a varphi50.8 mm × 50.8 mm BC501A scintillation detector was measured in the neutron energy region of 1 to 30 MeV by fitting the pulse height (PH) spectra for neutrons with the simulations from the NRESP code at the edge range. Using the new light output function, the neutron detection efficiency was determined with two Monte-Carlo codes, NEFF and SCINFUL. The calculated efficiency was corrected by comparing the simulated PH spectra with the measured ones. The determined efficiency was verified at the near threshold region and normalized with a Proton-Recoil-Telescope (PRT) at the 8-14 MeV energy region.

A Bonner Sphere Spectrometer for pulsed fields

PubMed Central

Aza, E.; Dinar, N.; Manessi, G. P.; Silari, M.

2016-01-01

The use of conventional Bonner Sphere Spectrometers (BSS) in pulsed neutron fields (PNF) is limited by the fact that proportional counters, usually employed as the thermal neutron detectors, suffer from dead time losses and show severe underestimation of the neutron interaction rate, which leads to strong distortion of the calculated spectrum. In order to avoid these limitations, an innovative BSS, called BSS-LUPIN, has been developed for measuring in PNF. This paper describes the physical characteristics of the device and its working principle, together with the results of Monte Carlo simulations of its response matrix. The BSS-LUPIN has been tested in the stray neutron field at the CERN Proton Synchrotron, by comparing the spectra obtained with the new device, the conventional CERN BSS and via Monte Carlo simulations. PMID:25948828

Monte-Carlo Application for Nondestructive Nuclear Waste Analysis

NASA Astrophysics Data System (ADS)

Carasco, C.; Engels, R.; Frank, M.; Furletov, S.; Furletova, J.; Genreith, C.; Havenith, A.; Kemmerling, G.; Kettler, J.; Krings, T.; Ma, J.-L.; Mauerhofer, E.; Neike, D.; Payan, E.; Perot, B.; Rossbach, M.; Schitthelm, O.; Schumann, M.; Vasquez, R.

2014-06-01

Radioactive waste has to undergo a process of quality checking in order to check its conformance with national regulations prior to its transport, intermediate storage and final disposal. Within the quality checking of radioactive waste packages non-destructive assays are required to characterize their radio-toxic and chemo-toxic contents. The Institute of Energy and Climate Research - Nuclear Waste Management and Reactor Safety of the Forschungszentrum Jülich develops in the framework of cooperation nondestructive analytical techniques for the routine characterization of radioactive waste packages at industrial-scale. During the phase of research and development Monte Carlo techniques are used to simulate the transport of particle, especially photons, electrons and neutrons, through matter and to obtain the response of detection systems. The radiological characterization of low and intermediate level radioactive waste drums is performed by segmented γ-scanning (SGS). To precisely and accurately reconstruct the isotope specific activity content in waste drums by SGS measurement, an innovative method called SGSreco was developed. The Geant4 code was used to simulate the response of the collimated detection system for waste drums with different activity and matrix configurations. These simulations allow a far more detailed optimization, validation and benchmark of SGSreco, since the construction of test drums covering a broad range of activity and matrix properties is time consuming and cost intensive. The MEDINA (Multi Element Detection based on Instrumental Neutron Activation) test facility was developed to identify and quantify non-radioactive elements and substances in radioactive waste drums. MEDINA is based on prompt and delayed gamma neutron activation analysis (P&DGNAA) using a 14 MeV neutron generator. MCNP simulations were carried out to study the response of the MEDINA facility in terms of gamma spectra, time dependence of the neutron energy spectrum, neutron flux distribution. The validation of the measurements simulations with Mont-Carlo transport codes for the design, optimization and data analysis of further P&DGNAA facilities is performed in collaboration with LMN CEA Cadarache. The performance of the prompt gamma neutron activation analysis (PGNAA) for the nondestructive determination of actinides in small samples is investigated. The quantitative determination of actinides relies on the precise knowledge of partial neutron capture cross sections. Up to today these cross sections are not very accurate for analytical purpose. The goal of the TANDEM (Trans-uranium Actinides' Nuclear Data - Evaluation and Measurement) Collaboration is the evaluation of these cross sections. Cross sections are measured using prompt gamma activation analysis facilities in Budapest and Munich. Geant4 is used to optimally design the detection system with Compton suppression. Furthermore, for the evaluation of the cross sections it is strongly needed to correct the results to the self-attenuation of the prompt gammas within the sample. In the framework of cooperation RWTH Aachen University, Forschungszentrum Jülich and the Siemens AG will study the feasibility of a compact Neutron Imaging System for Radioactive waste Analysis (NISRA). The system is based on a 14 MeV neutron source and an advanced detector system (a-Si flat panel) linked to an exclusive converter/scintillator for fast neutrons. For shielding and radioprotection studies the codes MCNPX and Geant4 were used. The two codes were benchmarked in processing time and accuracy in the neutron and gamma fluxes. Also the detector response was simulated with Geant4 to optimize components of the system.

Obtaining higher-accuracy estimates of water-rich rocks and water-poor sand dunes on Mars in active neutron experiments

NASA Astrophysics Data System (ADS)

Gabriel, T. S. J.; Hardgrove, C.; Litvak, M. L.; Nowicki, S.; Mitrofanov, I. G.; Boynton, W. V.; Fedosov, F.; Golovin, D.; Jun, I.; Mischna, M.; Tate, C. G.; Moersch, J.; Harshman, K.; Kozyrev, A.; Malakhov, A. V.; Mokrousov, M.; Nikiforov, S.; Sanin, A. B.; Vostrukhin, A.; Thompson, L. M.

2017-12-01

The Dynamic Albedo of Neutrons (DAN) experiment on the Mars Science Laboratory Curiosity Rover delivers high-energy (14.1 MeV) pulses of neutrons into the surface when operating in "active" mode. Neutrons are moderated in the subsurface and return to two detectors to provide a time-of-flight profile in 64 time-bins in epithermal and thermal energy ranges. Results are compared to simulations of the experiment in the Monte Carlo N-Particle Transport Code where several aspects are modeled including the DAN detectors, neutron source, rover components, and underlying rock. Models can be improved by increasing the fidelity of the rock geochemistry as informed by instruments including the Alpha Particle X-Ray Spectrometer (APXS). Furthermore, increasing the fidelity of the rock morphology in models is enabled by the suite of imaging instruments on the rover.To rapidly interpret DAN data a set of pre-simulated generic rock density and bulk geochemistry models are compared to several DAN active observations. While, to first order, this methodology provides an indication of significant geochemical changes in the subsurface, higher-fidelity models should be used to provide accurate constraints on water content, depth of geologic layers, or abundance of neutron absorbers. For example, in high-silicon, low-iron rocks observed along the rover's traverse, generic models can differ by several wt%H2O from models that use APXS measurements of nearby drill samples. Accurate measurements of high-silicon targets are necessary in outlining the extent of aqueous alteration and hydrothermal activity in Gale Crater. Additionally, we find that for DAN active experiments over sand dunes best-fit models can differ by greater than 0.5 wt%HO when the upper layer density is reduced by 0.6 g/cm3 to account for the low-bulk density of sand. In areas where the rock geochemistry differs little from generic models the difference in results is expectedly less disparate. We report refined wt%HO values for high-silicon, aqueously-altered rock and comparatively dry sand dunes along the rover traverse. We also outline the methodology for providing accurate geochemical and morphological constraints using DAN active measurements.

Assessment of Neutron Contamination Originating from the Presence of Wedge and Block in Photon Beam Radiotherapy.

PubMed

Bahreyni Toossi, M T; Khajetash, B; Ghorbani, M

2018-03-01

One of the main causes of induction of secondary cancer in radiation therapy is neutron contamination received by patients during treatment. Objective: In the present study the impact of wedge and block on neutron contamination production is investigated. The evaluations are conducted for a 15 MV Siemens Primus linear accelerator. Simulations were performed using MCNPX Monte Carlo code. 30˚, 45˚ and 60˚ wedges and a cerrobend block with dimensions of 1.5 × 1.5 × 7 cm 3 were simulated. The investigation were performed in the 10 × 10 cm 2 field size at source to surface distance of 100 cm for depth of 0.5, 2, 3 and 4 cm in a water phantom. Neutron dose was calculated using F4 tally with flux to dose conversion factors and F6 tally. Results showed that the presence of wedge increases the neutron contamination when the wedge factor was considered. In addition, 45˚ wedge produced the most amount of neutron contamination. If the block is in the center of the field, the cerrobend block caused less neutron contamination than the open field due to absorption of neutrons and photon attenuation. The results showed that neutron contamination is less in steeper depths. The results for two tallies showed practically equivalent results. Wedge causes neutron contamination hence should be considered in therapeutic protocols in which wedge is used. In terms of clinical aspects, the results of this study show that superficial tissues such as skin will tolerate more neutron contamination than the deep tissues.

Monte-Carlo simulation of soil carbon measurements by inelastic neutron scattering

USDA-ARS?s Scientific Manuscript database

Measuring soil carbon is critical for assessing the potential impact of different land management practices on carbon sequestration. The inelastic neutron scattering (INS) of fast neutrons (with energy around 14 MeV) on carbon-12 nuclei produces gamma rays with energy of 4.43 MeV; this gamma flux ca...

Modeling the tagged-neutron UXO identification technique using the Geant4 toolkit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou Y.; Mitra S.; Zhu X.

2011-10-16

It is proposed to use 14 MeV neutrons tagged by the associated particle neutron time-of-flight technique (APnTOF) to identify the fillers of unexploded ordnances (UXO) by characterizing their carbon, nitrogen and oxygen contents. To facilitate the design and construction of a prototype system, a preliminary simulation model was developed, using the Geant4 toolkit. This work established the toolkit environment for (a) generating tagged neutrons, (b) their transport and interactions within a sample to induce emission and detection of characteristic gamma-rays, and (c) 2D and 3D-image reconstruction of the interrogated object using the neutron and gamma-ray time-of-flight information. Using the modeling,more » this article demonstrates the novelty of the tagged-neutron approach for extracting useful signals with high signal-to-background discrimination of an object-of-interest from that of its environment. Simulations indicated that an UXO filled with the RDX explosive, hexogen (C{sub 3}H{sub 6}O{sub 6}N{sub 6}), can be identified to a depth of 20 cm when buried in soil.« less

Simulation of the neutron response matrix of an EJ309 liquid scintillator

NASA Astrophysics Data System (ADS)

Bai, Huaiyong; Wang, Zhimin; Zhang, Luyu; Jiang, Haoyu; Lu, Yi; Chen, Jinxiang; Zhang, Guohui

2018-04-01

The neutron response matrix is the basis for measuring the neutron energy spectrum through unfolding the pulse height spectrum detected with a liquid scintillator. Based on the light output of the EJ309 liquid scintillator and the related reaction cross sections, a Monte Carlo code is developed to obtain the neutron response matrix. The effects of the related reactions, the contributions of different number of neutron interactions and the wall effect of the recoil proton are discussed. With the obtained neutron response matrix and the GRAVEL iterative unfolding method, the neutron energy spectra of the 252Cf and the 241AmBe neutron sources are measured, and the results are respectively compared with the theoretical prediction of the 252Cf neutron energy spectrum and the previous results of the 241AmBe neutron energy spectra.

General Relativistic Radiation MHD Simulations of Supercritical Accretion onto a Magnetized Neutron Star: Modeling of Ultraluminous X-Ray Pulsars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takahashi, Hiroyuki R.; Ohsuga, Ken, E-mail: takahashi@cfca.jp, E-mail: ken.ohsuga@nao.ac.jp

By performing 2.5-dimensional general relativistic radiation magnetohydrodynamic simulations, we demonstrate supercritical accretion onto a non-rotating, magnetized neutron star, where the magnetic field strength of dipole fields is 10{sup 10} G on the star surface. We found the supercritical accretion flow consists of two parts: the accretion columns and the truncated accretion disk. The supercritical accretion disk, which appears far from the neutron star, is truncated at around ≃3 R {sub *} ( R {sub *} = 10{sup 6} cm is the neutron star radius), where the magnetic pressure via the dipole magnetic fields balances with the radiation pressure of themore » disks. The angular momentum of the disk around the truncation radius is effectively transported inward through magnetic torque by dipole fields, inducing the spin up of a neutron star. The evaluated spin-up rate, ∼−10{sup −11} s s{sup −1}, is consistent with the recent observations of the ultraluminous X-ray pulsars. Within the truncation radius, the gas falls onto a neutron star along the dipole fields, which results in a formation of accretion columns onto the northern and southern hemispheres. The net accretion rate and the luminosity of the column are ≃66 L {sub Edd}/ c {sup 2} and ≲10 L {sub Edd}, where L {sub Edd} is the Eddington luminosity and c is the light speed. Our simulations support a hypothesis whereby the ultraluminous X-ray pulsars are powered by the supercritical accretion onto the magnetized neutron stars.« less

Using neutrons to measure keV temperatures in highly compressed plastic at multi-Gbar pressures

NASA Astrophysics Data System (ADS)

Nilsen, J.; Bachmann, B.; Zimmerman, G. B.; Hatarik, R.; Döppner, T.; Swift, D.; Hawreliak, J.; Collins, G. W.; Falcone, R. W.; Glenzer, S. H.; Kraus, D.; Landen, O. L.; Kritcher, A. L.

2016-12-01

We have designed an experiment for the National Ignition Facility to measure the Hugoniot of materials such as plastic at extreme pressures. The design employs a strong spherically converging shock launched through a solid ball of material using a hohlraum radiation drive. The shock front conditions can be characterized using X-ray radiography until background from shock coalescence overtakes the backlit signal. Shock coalescence at the center is predicted to reach tens of Gbars and can be further characterized by measuring the X-ray self-emission and 2.45 MeV neutrons emitted from the shock flash region. In this simulation design work the standard plastic sphere is replaced with a deuterated polyethylene sphere, CD2, that reaches sufficiently high densities and temperatures in the central hot spot to produce neutrons from Deuterium-Deuterium (DD) fusion reactions that can be measured by a neutron time of flight spectrometer (nTOF) and act as a temperature diagnostic. This paper focuses on the design of these experiments, based on an extensive suite of radiation-hydrodynamics simulations, and the interpretation of the predicted DD neutron signals. The simulations predict mean temperatures of 1 keV in the central hot spot with mean densities of 33 g/cc and mean pressures of 25 Gbar. A preliminary comparison with early experimental results looks promising with an average ion temperature of 1.06 ± 0.15 keV in the central hot spot estimated from the nTOF spectral width and measured neutron yield of 7.0 (±0.5) × 109 DD neutrons.

Moderator design studies for a new neutron reference source based on the D-T fusion reaction

NASA Astrophysics Data System (ADS)

Mozhayev, Andrey V.; Piper, Roman K.; Rathbone, Bruce A.; McDonald, Joseph C.

2016-06-01

The radioactive isotope Californium-252 (252Cf) is relied upon internationally as a neutron calibration source for ionizing radiation dosimetry because of its high specific activity. The source may be placed within a heavy-water (D2O) moderating sphere to produce a softened spectrum representative of neutron fields common to commercial nuclear power plant environments, among others. Due to termination of the U.S. Department of Energy loan/lease program in 2012, the expense of obtaining 252Cf sources has undergone a significant increase, rendering high output sources largely unattainable. On the other hand, the use of neutron generators in research and industry applications has increased dramatically in recent years. Neutron generators based on deuteriumtritium (D-T) fusion reaction provide high neutron fluence rates and, therefore, could possibly be used as a replacement for 252Cf. To be viable, the 14 MeV D-T output spectrum must be significantly moderated to approximate common workplace environments. This paper presents the results of an effort to select appropriate moderating materials and design a configuration to reshape the primary neutron field toward a spectrum approaching that from a nuclear power plant workplace. A series of Monte-Carlo (MCNP) simulations of single layer high- and low-Z materials are used to identify initial candidate moderators. Candidates are refined through a similar series of simulations involving combinations of 2-5 different materials. The simulated energy distribution using these candidate moderators are rated in comparison to a target spectrum. Other properties, such as fluence preservation and/or enhancement, prompt gamma production and other characteristics are also considered.

Soft error rate simulation and initial design considerations of neutron intercepting silicon chip (NISC)

NASA Astrophysics Data System (ADS)

Celik, Cihangir

Advances in microelectronics result in sub-micrometer electronic technologies as predicted by Moore's Law, 1965, which states the number of transistors in a given space would double every two years. The most available memory architectures today have submicrometer transistor dimensions. The International Technology Roadmap for Semiconductors (ITRS), a continuation of Moore's Law, predicts that Dynamic Random Access Memory (DRAM) will have an average half pitch size of 50 nm and Microprocessor Units (MPU) will have an average gate length of 30 nm over the period of 2008-2012. Decreases in the dimensions satisfy the producer and consumer requirements of low power consumption, more data storage for a given space, faster clock speed, and portability of integrated circuits (IC), particularly memories. On the other hand, these properties also lead to a higher susceptibility of IC designs to temperature, magnetic interference, power supply, and environmental noise, and radiation. Radiation can directly or indirectly affect device operation. When a single energetic particle strikes a sensitive node in the micro-electronic device, it can cause a permanent or transient malfunction in the device. This behavior is called a Single Event Effect (SEE). SEEs are mostly transient errors that generate an electric pulse which alters the state of a logic node in the memory device without having a permanent effect on the functionality of the device. This is called a Single Event Upset (SEU) or Soft Error . Contrary to SEU, Single Event Latchup (SEL), Single Event Gate Rapture (SEGR), or Single Event Burnout (SEB) they have permanent effects on the device operation and a system reset or recovery is needed to return to proper operations. The rate at which a device or system encounters soft errors is defined as Soft Error Rate (SER). The semiconductor industry has been struggling with SEEs and is taking necessary measures in order to continue to improve system designs in nano-scale technologies. Prevention of SEEs has been studied and applied in the semiconductor industry by including radiation protection precautions in the system architecture or by using corrective algorithms in the system operation. Decreasing 10B content (20%of natural boron) in the natural boron of Borophosphosilicate glass (BPSG) layers that are conventionally used in the fabrication of semiconductor devices was one of the major radiation protection approaches for the system architecture. Neutron interaction in the BPSG layer was the origin of the SEEs because of the 10B (n,alpha) 7Li reaction products. Both of the particles produced have the capability of ionization in the silicon substrate region, whose thickness is comparable to the ranges of these particles. Using the soft error phenomenon in exactly the opposite manner of the semiconductor industry can provide a new neutron detection system based on the SERs in the semiconductor memories. By investigating the soft error mechanisms in the available semiconductor memories and enhancing the soft error occurrences in these devices, one can convert all memory using intelligent systems into portable, power efficient, directiondependent neutron detectors. The Neutron Intercepting Silicon Chip (NISC) project aims to achieve this goal by introducing 10B-enriched BPSG layers to the semiconductor memory architectures. This research addresses the development of a simulation tool, the NISC Soft Error Analysis Tool (NISCSAT), for soft error modeling and analysis in the semiconductor memories to provide basic design considerations for the NISC. NISCSAT performs particle transport and calculates the soft error probabilities, or SER, depending on energy depositions of the particles in a given memory node model of the NISC. Soft error measurements were performed with commercially available, off-the-shelf semiconductor memories and microprocessors to observe soft error variations with the neutron flux and memory supply voltage. Measurement results show that soft errors in the memories increase proportionally with the neutron flux, whereas they decrease with increasing the supply voltages. NISC design considerations include the effects of device scaling, 10B content in the BPSG layer, incoming neutron energy, and critical charge of the node for this dissertation. NISCSAT simulations were performed with various memory node models to account these effects. Device scaling simulations showed that any further increase in the thickness of the BPSG layer beyond 2 mum causes self-shielding of the incoming neutrons due to the BPSG layer and results in lower detection efficiencies. Moreover, if the BPSG layer is located more than 4 mum apart from the depletion region in the node, there are no soft errors in the node due to the fact that both of the reaction products have lower ranges in the silicon or any possible node layers. Calculation results regarding the critical charge indicated that the mean charge deposition of the reaction products in the sensitive volume of the node is about 15 fC. It is evident that the NISC design should have a memory architecture with a critical charge of 15 fC or less to obtain higher detection efficiencies. Moreover, the sensitive volume should be placed in close proximity to the BPSG layers so that its location would be within the range of alpha and 7Li particles. Results showed that the distance between the BPSG layer and the sensitive volume should be less than 2 mum to increase the detection efficiency of the NISC. Incoming neutron energy was also investigated by simulations and the results obtained from these simulations showed that NISC neutron detection efficiency is related with the neutron cross-sections of 10B (n,alpha) 7Li reaction, e.g., ratio of the thermal (0.0253 eV) to fast (2 MeV) neutron detection efficiencies is approximately equal to 8000:1. Environmental conditions and their effects on the NISC performance were also studied in this research. Cosmic rays were modeled and simulated via NISCSAT to investigate detection reliability of the NISC. Simulation results show that cosmic rays account for less than 2 % of the soft errors for the thermal neutron detection. On the other hand, fast neutron detection by the NISC, which already has a poor efficiency due to the low neutron cross-sections, becomes almost impossible at higher altitudes where the cosmic ray fluxes and their energies are higher. NISCSAT simulations regarding soft error dependency of the NISC for temperature and electromagnetic fields show that there are no significant effects in the NISC detection efficiency. Furthermore, the detection efficiency of the NISC decreases with both air humidity and use of moderators since the incoming neutrons scatter away before reaching the memory surface.

MCNP Simulations of Measurement of Insulation Compaction in the Cryogenic Rocket Fuel Tanks at Kennedy Space Center by Fast/Thermal Neutron Techniques

NASA Technical Reports Server (NTRS)

Livingston, R. A.; Schweitzer, J. S.; Parsons, A. M.; Arens, E. E.

2010-01-01

MCNP simulations have been run to evaluate the feasibility of using a combination of fast and thermal neutrons as a nondestructive method to measure of the compaction of the perlite insulation in the liquid hydrogen and oxygen cryogenic storage tanks at John F. Kennedy Space Center (KSC). Perlite is a feldspathic volcanic rock made up of the major elements Si, AI, Na, K and 0 along with some water. When heated it expands from four to twenty times its original volume which makes it very useful for thermal insulation. The cryogenic tanks at Kennedy Space Center are spherical with outer diameters of 69-70 feet and lined with a layer of expanded perlite with thicknesses on the order of 120 cm. There is evidence that some of the perlite has compacted over time since the tanks were built 1965, affecting the thermal properties and possibly also the structural integrity of the tanks. With commercially available portable neutron generators it is possible to produce simultaneously fluxes of neutrons in two energy ranges: fast (14 Me V) and thermal (25 me V). The two energy ranges produce complementary information. Fast neutrons produce gamma rays by inelastic scattering, which is sensitive to Fe and O. Thermal neutrons produce gamma rays by prompt gamma neutron activation (PGNA) and this is sensitive to Si, Al, Na, K and H. The compaction of the perlite can be measured by the change in gamma ray signal strength which is proportional to the atomic number densities of the constituent elements. The MCNP simulations were made to determine the magnitude of this change. The tank wall was approximated by a I-dimensional slab geometry with an 11/16" outer carbon steel wall, an inner stainless wall and 120 cm thick perlite zone. Runs were made for cases with expanded perlite, compacted perlite or with various void fractions. Runs were also made to simulate the effect of adding a moderator. Tallies were made for decay-time analysis from t=0 to 10 ms; total detected gamma-rays; detected gamma-rays from thermal neutron reactions d. detected gamma-rays from non-thermal neutron reactions and total detected gamma-rays as a function of depth into the annulus volume. These indicated a number of possible independent metrics of perlite compaction. For example the count rate for perlite elements increased from 3600 to 8500 cps for an increase in perlite density from 6 lbs/lcf to 16.5 lbs/cf. Thus the MCNP simulations have confirmed the feasibility of using neutron methods to map the compaction of perlite in the walls of the cryogenic tanks.

Correlated Production and Analog Transport of Fission Neutrons and Photons using Fission Models FREYA, FIFRELIN and the Monte Carlo Code TRIPOLI-4® .

NASA Astrophysics Data System (ADS)

Verbeke, Jérôme M.; Petit, Odile; Chebboubi, Abdelhazize; Litaize, Olivier

2018-01-01

Fission modeling in general-purpose Monte Carlo transport codes often relies on average nuclear data provided by international evaluation libraries. As such, only average fission multiplicities are available and correlations between fission neutrons and photons are missing. Whereas uncorrelated fission physics is usually sufficient for standard reactor core and radiation shielding calculations, correlated fission secondaries are required for specialized nuclear instrumentation and detector modeling. For coincidence counting detector optimization for instance, precise simulation of fission neutrons and photons that remain correlated in time from birth to detection is essential. New developments were recently integrated into the Monte Carlo transport code TRIPOLI-4 to model fission physics more precisely, the purpose being to access event-by-event fission events from two different fission models: FREYA and FIFRELIN. TRIPOLI-4 simulations can now be performed, either by connecting via an API to the LLNL fission library including FREYA, or by reading external fission event data files produced by FIFRELIN beforehand. These new capabilities enable us to easily compare results from Monte Carlo transport calculations using the two fission models in a nuclear instrumentation application. In the first part of this paper, broad underlying principles of the two fission models are recalled. We then present experimental measurements of neutron angular correlations for 252Cf(sf) and 240Pu(sf). The correlations were measured for several neutron kinetic energy thresholds. In the latter part of the paper, simulation results are compared to experimental data. Spontaneous fissions in 252Cf and 240Pu are modeled by FREYA or FIFRELIN. Emitted neutrons and photons are subsequently transported to an array of scintillators by TRIPOLI-4 in analog mode to preserve their correlations. Angular correlations between fission neutrons obtained independently from these TRIPOLI-4 simulations, using either FREYA or FIFRELIN, are compared to experimental results. For 240Pu(sf), the measured correlations were used to tune the model parameters.

Superfluid Fermi atomic gas as a quantum simulator for the study of the neutron-star equation of state in the low-density region

NASA Astrophysics Data System (ADS)

van Wyk, Pieter; Tajima, Hiroyuki; Inotani, Daisuke; Ohnishi, Akira; Ohashi, Yoji

2018-01-01

We propose a theoretical idea to use an ultracold Fermi gas as a quantum simulator for the study of the low-density region of a neutron-star interior. Our idea is different from the standard quantum simulator that heads for perfect replication of another system, such as the Hubbard model discussed in high-Tc cuprates. Instead, we use the similarity between two systems and theoretically make up for the difference between them. That is, (1) we first show that the strong-coupling theory developed by Nozières and Schmitt-Rink (NSR) can quantitatively explain the recent experiment on the equation of state (EoS) in a 6Li superfluid Fermi gas in the BCS (Bardeen-Cooper-Schrieffer) unitary limit far below the superfluid phase-transition temperature Tc. This region is considered to be very similar to the low-density region (crust regime) of a neutron star (where a nearly unitary s -wave neutron superfluid is expected). (2) We then theoretically compensate the difference that, while the effective range reff is negligibly small in a superfluid 6Li Fermi gas, it cannot be ignored (reff=2.7 fm) in a neutron star, by extending the NSR theory to include effects of reff. The calculated EoS when reff=2.7 fm is shown to agree well with the previous neutron-star EoS in the low-density region predicted in nuclear physics. Our idea indicates that an ultracold atomic gas may more flexibly be used as a quantum simulator for the study of other complicated quantum many-body systems, when we use not only the experimental high tunability, but also the recent theoretical development in this field. Since it is difficult to directly observe a neutron-star interior, our idea would provide a useful approach to the exploration for this mysterious astronomical object.

Evaluation of equivalent dose from neutrons and activation products from a 15-MV X-ray LINAC

PubMed Central

Israngkul-Na-Ayuthaya, Isra; Suriyapee, Sivalee; Pengvanich, Phongpheath

2015-01-01

A high-energy photon beam that is more than 10 MV can produce neutron contamination. Neutrons are generated by the [γ,n] reactions with a high-Z target material. The equivalent neutron dose and gamma dose from activation products have been estimated in a LINAC equipped with a 15-MV photon beam. A Monte Carlo simulation code was employed for neutron and photon dosimetry due to mixed beam. The neutron dose was also experimentally measured using the Optically Stimulated Luminescence (OSL) under various conditions to compare with the simulation. The activation products were measured by gamma spectrometer system. The average neutron energy was calculated to be 0.25 MeV. The equivalent neutron dose at the isocenter obtained from OSL measurement and MC calculation was 5.39 and 3.44 mSv/Gy, respectively. A gamma dose rate of 4.14 µSv/h was observed as a result of activations by neutron inside the treatment machine. The gamma spectrum analysis showed 28Al, 24Na, 54Mn and 60Co. The results confirm that neutrons and gamma rays are generated, and gamma rays remain inside the treatment room after the termination of X-ray irradiation. The source of neutrons is the product of the [γ,n] reactions in the machine head, whereas gamma rays are produced from the [n,γ] reactions (i.e. neutron activation) with materials inside the treatment room. The most activated nuclide is 28Al, which has a half life of 2.245 min. In practice, it is recommended that staff should wait for a few minutes (several 28Al half-lives) before entering the treatment room after the treatment finishes to minimize the dose received. PMID:26265661

Key achievements in elementary R&D on water-cooled solid breeder blanket for ITER test blanket module in JAERI

NASA Astrophysics Data System (ADS)

Suzuki, S.; Enoeda, M.; Hatano, T.; Hirose, T.; Hayashi, K.; Tanigawa, H.; Ochiai, K.; Nishitani, T.; Tobita, K.; Akiba, M.

2006-02-01

This paper presents the significant progress made in the research and development (R&D) of key technologies on the water-cooled solid breeder blanket for the ITER test blanket modules in JAERI. Development of module fabrication technology, bonding technology of armours, measurement of thermo-mechanical properties of pebble beds, neutronics studies on a blanket module mockup and tritium release behaviour from a Li2TiO3 pebble bed under neutron-pulsed operation conditions are summarized. With the improvement of the heat treatment process for blanket module fabrication, a fine-grained microstructure of F82H can be obtained by homogenizing it at 1150 °C followed by normalizing it at 930 °C after the hot isostatic pressing process. Moreover, a promising bonding process for a tungsten armour and an F82H structural material was developed using a solid-state bonding method based on uniaxial hot compression without any artificial compliant layer. As a result of high heat flux tests of F82H first wall mockups, it has been confirmed that a fatigue lifetime correlation, which was developed for the ITER divertor, can be made applicable for the F82H first wall mockup. As for R&D on the breeder material, Li2TiO3, the effect of compression loads on effective thermal conductivity of pebble beds has been clarified for the Li2TiO3 pebble bed. The tritium breeding ratio of a simulated multi-layer blanket structure has successfully been measured using 14 MeV neutrons with an accuracy of 10%. The tritium release rate from the Li2TiO3 pebble has also been successfully measured with pulsed neutron irradiation, which simulates ITER operation.

Model for Generation of Neutrons in a Compact Diode with Laser-Plasma Anode and Suppression of Electron Conduction Using a Permanent Cylindrical Magnet

NASA Astrophysics Data System (ADS)

Shikanov, A. E.; Vovchenko, E. D.; Kozlovskii, K. I.; Rashchikov, V. I.; Shatokhin, V. L.

2018-04-01

A model for acceleration of deuterons and generation of neutrons in a compact laser-plasma diode with electron isolation using magnetic field generated by a hollow cylindrical permanent magnet is presented. Experimental and computer-simulated neutron yields are compared for the diode structure under study. An accelerating neutron tube with a relatively high neutron generation efficiency can be constructed using suppression of electron conduction with the aid of a magnet placed in the vacuum volume.

Assessment of the neutron dose field around a biomedical cyclotron: FLUKA simulation and experimental measurements.

PubMed

Infantino, Angelo; Cicoria, Gianfranco; Lucconi, Giulia; Pancaldi, Davide; Vichi, Sara; Zagni, Federico; Mostacci, Domiziano; Marengo, Mario

2016-12-01

In the planning of a new cyclotron facility, an accurate knowledge of the radiation field around the accelerator is fundamental for the design of shielding, the protection of workers, the general public and the environment. Monte Carlo simulations can be very useful in this process, and their use is constantly increasing. However, few data have been published so far as regards the proper validation of Monte Carlo simulation against experimental measurements, particularly in the energy range of biomedical cyclotrons. In this work a detailed model of an existing installation of a GE PETtrace 16.5MeV cyclotron was developed using FLUKA. An extensive measurement campaign of the neutron ambient dose equivalent H ∗ (10) in marked positions around the cyclotron was conducted using a neutron rem-counter probe and CR39 neutron detectors. Data from a previous measurement campaign performed by our group using TLDs were also re-evaluated. The FLUKA model was then validated by comparing the results of high-statistics simulations with experimental data. In 10 out of 12 measurement locations, FLUKA simulations were in agreement within uncertainties with all the three different sets of experimental data; in the remaining 2 positions, the agreement was with 2/3 of the measurements. Our work allows to quantitatively validate our FLUKA simulation setup and confirms that Monte Carlo technique can produce accurate results in the energy range of biomedical cyclotrons. Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Fast Monte Carlo simulation of a dispersive sample on the SEQUOIA spectrometer at the SNS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Granroth, Garrett E; Chen, Meili; Kohl, James Arthur

2007-01-01

Simulation of an inelastic scattering experiment, with a sample and a large pixilated detector, usually requires days of time because of finite processor speeds. We report simulations on an SNS (Spallation Neutron Source) instrument, SEQUOIA, that reduce the time to less than 2 hours by using parallelization and the resources of the TeraGrid. SEQUOIA is a fine resolution (∆E/Ei ~ 1%) chopper spectrometer under construction at the SNS. It utilizes incident energies from Ei = 20 meV to 2 eV and will have ~ 144,000 detector pixels covering 1.6 Sr of solid angle. The full spectrometer, including a 1-D dispersivemore » sample, has been simulated using the Monte Carlo package McStas. This paper summarizes the method of parallelization for and results from these simulations. In addition, limitations of and proposed improvements to current analysis software will be discussed.« less

Efficiency of depleted UO2 based semiconductor neutron detectors in direct and indirect configuration—A GEANT4 simulation study

NASA Astrophysics Data System (ADS)

Parida, M. K.; Prabakar, K.; Sundari, S. T.

2018-03-01

In the present work, Monte Carlo simulations using GEANT4 are carried out to estimate the efficiency of semiconductor neutron detectors with depleted UO2 (DUO2) as converter material, in both planar (direct and indirect) and 3D geometry (cylindrical perforation and trenches structure) configurations. The simulations were conducted for neutrons of variable energy viz., thermal (25 meV) and fast (1 to 10 MeV) that were incident on varying thicknesses (0.25 μm to 1000 μm), diameters (1 μm to 9 μm) and widths (1 μm to 9 μm) along with depths (50 μm to 275 μm) of DUO2 for planar, cylindrical perforated and trench structures, respectively. In the case of direct planar detectors, efficiency was found to increase with the thickness of DUO2 and the rate at which efficiency increased was found to follow the macroscopic fission cross section at the corresponding neutron energy. In the case of indirect planar detector, efficiency was lower as compared to direct configuration and was found to saturate beyond a thickness of ~3 μm. This saturation is explained on the basis of mean free path of neutrons in the DUO2 material. For the 3D perforated silicon detectors of cylindrical (trench) geometry, backfilled with DUO2, the efficiency for detection of thermal neutrons ~25 meV and fast neutrons ~ typical energy of 10 MeV was found to be ~0.0159% (~0.0177%) and ~0.0088% (0.0098%), respectively. These efficiency values were two (one) order values higher than planar indirect detector for thermal (fast) neutrons. Histogram plots were also obtained from the GEANT4 simulations to monitor the energy distribution of fission products in planar (direct and indirect) and 3D geometry (cylindrical and trench) configurations. These plots revealed that, for all the detector configurations, the energy deposited by the fission products are higher as compared to the typical gamma ray background. Thus, for detectors with DUO2 as converter material, higher values of low level discriminator (LLD) can be set, so as to achieve good background discrimination.

The Fate of Merging Neutron Stars

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-08-01

A rapidly spinning, highly magnetized neutron star is one possible outcome when two smaller neutron stars merge. [Casey Reed/Penn State University]When two neutron stars collide, the new object that they make can reveal information about the interior physics of neutron stars. New theoretical work explores what we should be seeing, and what it can teach us.Neutron Star or Black Hole?So far, the only systems from which weve detected gravitational waves are merging black holes. But other compact-object binaries exist and are expected to merge on observable timescales in particular, binary neutron stars. When two neutron stars merge, the resulting object falls into one of three categories:a stable neutron star,a black hole, ora supramassive neutron star, a large neutron star thats supported by its rotation but will eventually collapse to a black hole after it loses angular momentum.Histograms of the initial (left) and final (right) distributions of objects in the authors simulations, for five different equations of state. Most cases resulted primarily in the formation of neutron stars (NSs) or supramassive neutron stars (sNSs), not black holes (BHs). [Piro et al. 2017]Whether a binary-neutron-star merger results in another neutron star, a black hole, or a supramassive neutron star depends on the final mass of the remnant and what the correct equation of state is that describes the interiors of neutron stars a longstanding astrophysical puzzle.In a recent study, a team of scientists led by Anthony Piro (Carnegie Observatories) estimated which of these outcomes we should expect for mergers of binary neutron stars. The teams results along with future observations of binary neutron stars may help us to eventually pin down the equation of state for neutron stars.Merger OutcomesPiro and collaborators used relativistic calculations of spinning and non-spinning neutron stars to estimate the mass range that neutron stars would have for several different realistic equations of state. They then combined this information with Monte Carlo simulations based on the mass distribution of neutron-star binaries in our galaxy. From these simulations, Piro and collaborators could predict the distribution of fates expected for merging neutron-star binaries, given different equations of state.The authors found that the fate of the merger could vary greatly depending on the equation of state you assume. Intriguingly, all equations of state resulted in a surprisingly high fraction of systems that merged to form a neutron star or a supramassive neutron star in fact, four out of the five equations of state predicted that 80100% of systems would result in a neutron star or a supermassive neutron star.Lessons from ObservationsThe frequency bands covered by various current and planned gravitational wave observatories. Advanced LIGO has the right frequency coverage to be able to explore a neutron-star remnant if the signal is loud enough. [Christopher Moore, Robert Cole and Christopher Berry]These results have important implications for our future observations. The high predicted fraction of neutron stars resulting from these mergers tells us that its especially important for gravitational-wave observatories to probe 14 kHz emission. This frequency range will enable us to study the post-merger neutron-star or supramassive-neutron-star remnants.Even if we cant observe the remnants behavior after it forms, we can still compare the distribution of remnants that we observe in the future to the predictions made by Piro and collaborators. This will potentially allow us to constrain the neutron-star equation of state, revealing the physics of neutron-star interiors even without direct observations.CitationAnthony L. Piro et al 2017 ApJL 844 L19. doi:10.3847/2041-8213/aa7f2f

Assessment of the Neutronic and Fuel Cycle Performance of the Transatomic Power Molten Salt Reactor Design

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robertson, Sean; Dewan, Leslie; Massie, Mark

This report presents results from a collaboration between Transatomic Power Corporation (TAP) and Oak Ridge National Laboratory (ORNL) to provide neutronic and fuel cycle analysis of the TAP core design through the Department of Energy Gateway for Accelerated Innovation in Nuclear (GAIN) Nuclear Energy Voucher program. The TAP concept is a molten salt reactor using configurable zirconium hydride moderator rod assemblies to shift the neutron spectrum in the core from mostly epithermal at beginning of life to thermal at end of life. Additional developments in the ChemTriton modeling and simulation tool provide the critical moderator-to-fuel ratio searches and time-dependent parametersmore » necessary to simulate the continuously changing physics in this complex system. The implementation of continuous-energy Monte Carlo transport and depletion tools in ChemTriton provide for full-core three-dimensional modeling and simulation. Results from simulations with these tools show agreement with TAP-calculated performance metrics for core lifetime, discharge burnup, and salt volume fraction, verifying the viability of reducing actinide waste production with this concept. Additional analyses of mass feed rates and enrichments, isotopic removals, tritium generation, core power distribution, core vessel helium generation, moderator rod heat deposition, and reactivity coeffcients provide additional information to make informed design decisions. This work demonstrates capabilities of ORNL modeling and simulation tools for neutronic and fuel cycle analysis of molten salt reactor concepts.« less

A suspended boron foil multi-wire proportional counter neutron detector

NASA Astrophysics Data System (ADS)

Nelson, Kyle A.; Edwards, Nathaniel S.; Hinson, Niklas J.; Wayant, Clayton D.; McGregor, Douglas S.

2014-12-01

Three natural boron foils, approximately 1.0 cm in diameter and 1.0 μm thick, were obtained from The Lebow Company and suspended in a multi-wire proportional counter. Suspending the B foils allowed the alpha particle and Li ion reaction products to escape simultaneously, one on each side of the foil, and be measured concurrently in the gas volume. The thermal neutron response pulse-height spectrum was obtained and two obvious peaks appear from the 94% and 6% branches of the 10B(n,α)7Li neutron reaction. Scanning electron microscope images were collected to obtain the exact B foil thicknesses and MCNP6 simulations were completed for those same B thicknesses. Pulse-height spectra obtained from the simulations were compared to experimental data and matched well. The theoretical intrinsic thermal-neutron detection efficiency for enriched 10B foils was calculated and is presented. Additionally, the intrinsic thermal neutron detection efficiency of the three natural B foils was calculated to be 3.2±0.2%.

Constraining the Origin of Phobos with the Elpasolite Planetary Ice and Composition Spectrometer (EPICS) - Simulated Performance

NASA Astrophysics Data System (ADS)

Nowicki, S. F.; Mesick, K.; Coupland, D. D. S.; Dallmann, N. A.; Feldman, W. C.; Stonehill, L. C.; Hardgrove, C.; Dibb, S.; Gabriel, T. S. J.; West, S.

2017-12-01

Elpasolites are a promising new family of inorganic scintillators that can detect both gamma rays and neutrons within a single detector volume, reducing the instrument size, weight, and power (SWaP), all of which are critical for planetary science missions. The ability to distinguish between neutron and gamma events is done through pulse shape discrimination (PSD). The Elpasolite Planetary Ice and Composition Spectrometer (EPICS) utilizes elpasolites in a next-generation, highly capable, low-SWaP gamma-ray and neutron spectrometer. We present simulated capabilities of EPICS sensitivities to neutron and gamma-rays, and demonstrate how EPICS can constrain the origin of Phobos between the following three main hypotheses: 1) accretion after a giant impact with Mars, 2) co-accretion with Mars, and 3) capture of an external body. The MCNP6 code was used to calculate the neutron and gamma-ray flux that escape the surface of Phobos, and GEANT4 to model the response of the EPICS instrument on orbit around Phobos.

Progress toward a new beam measurement of the neutron lifetime

NASA Astrophysics Data System (ADS)

Hoogerheide, Shannon Fogwell

2016-09-01

Neutron beta decay is the simplest example of nuclear beta decay. A precise value of the neutron lifetime is important for consistency tests of the Standard Model and Big Bang Nucleosysnthesis models. The beam neutron lifetime method requires the absolute counting of the decay protons in a neutron beam of precisely known flux. Recent work has resulted in improvements in both the neutron and proton detection systems that should permit a significant reduction in systematic uncertainties. A new measurement of the neutron lifetime using the beam method will be performed at the National Institute of Standards and Technology Center for Neutron Research. The projected uncertainty of this new measurement is 1 s. An overview of the measurement and the technical improvements will be discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

James, S St.; Argento, D; Stewart, R

Purpose: The University of Washington Medical Center offers neutron therapy for the palliative and definitive treatment of selected cancers. In vivo field verification has the potential to improve the safe and effective delivery of neutron therapy. We propose a portal imaging method that relies on the creation of positron emitting isotopes (11C and 15O) through (n, 2n) reactions with a PMMA plate placed below the patient. After field delivery, the plate is retrieved from the vault and imaged using a reader that detects annihilation photons. The spatial pattern of activity produced in the PMMA plate provides information to reconstruct themore » neutron fluence map needed to confirm treatment delivery. Methods: We used MCNP to simulate the accumulation of 11C activity in a slab of PMMA 2 mm thick, and GATE was used to simulate the sensitivity and spatial resolution of a prototype imaging system. BGO crystal thicknesses of 1 cm, 2 cm and 3 cm were simulated with detector separations of 2 cm. Crystal pitches of 2 mm and 4 mm were evaluated. Back-projection of the events was used to create a planar image. The spatial resolution was taken to be the FWHM of the reconstructed point source image. Results: The system sensitivity for a point source in the center of the field of view was found to range from 58% for 1 cm thick BGO with 2 mm crystal pitch to 74% for the 3 cm thick BGO crystals with 4 mm crystal pitch. The spatial resolution at the center of the field of view was found to be 1.5 mm for the system with 2 mm crystal pitch and 2.8 mm for the system with the 4 mm crystal pitch. Conclusion: BGO crystals with 4 mm crystal pitch and 3 cm length would offer the best sensitivity reader.« less

Neutron Tomography of a Fuel Cell: Statistical Learning Implementation of a Penalized Likelihood Method

NASA Astrophysics Data System (ADS)

Coakley, Kevin J.; Vecchia, Dominic F.; Hussey, Daniel S.; Jacobson, David L.

2013-10-01

At the NIST Neutron Imaging Facility, we collect neutron projection data for both the dry and wet states of a Proton-Exchange-Membrane (PEM) fuel cell. Transmitted thermal neutrons captured in a scintillator doped with lithium-6 produce scintillation light that is detected by an amorphous silicon detector. Based on joint analysis of the dry and wet state projection data, we reconstruct a residual neutron attenuation image with a Penalized Likelihood method with an edge-preserving Huber penalty function that has two parameters that control how well jumps in the reconstruction are preserved and how well noisy fluctuations are smoothed out. The choice of these parameters greatly influences the resulting reconstruction. We present a data-driven method that objectively selects these parameters, and study its performance for both simulated and experimental data. Before reconstruction, we transform the projection data so that the variance-to-mean ratio is approximately one. For both simulated and measured projection data, the Penalized Likelihood method reconstruction is visually sharper than a reconstruction yielded by a standard Filtered Back Projection method. In an idealized simulation experiment, we demonstrate that the cross validation procedure selects regularization parameters that yield a reconstruction that is nearly optimal according to a root-mean-square prediction error criterion.

Anomalous neutron yield in indirect-drive inertial-confinement-fusion due to the formation of collisionless shocks in the corona

NASA Astrophysics Data System (ADS)

Zhang, Wen-Shuai; Cai, Hong-Bo; Shan, Lian-Qiang; Zhang, Hua-Sen; Gu, Yu-Qiu; Zhu, Shao-Ping

2017-06-01

Observations of anomalous neutron yield in the indirect-drive inertial confinement fusion implosion experiments conducted at SG-III prototype and SG-II upgrade laser facilities are interpreted. The anomalous mechanism results in a neutron yield which is 100-times higher than that predicted by 1D radiation-hydrodynamic simulations. 2D radiation-hydrodynamic simulations show that the supersonic, radially directed gold (Au) plasma jets arising from the laser-hohlraum interactions can collide with the carbon-deuterium (CD) corona plasma of the compressed pellet. It is found that in the interaction front of the high-Z jet with the low-Z corona, with low density  ˜{{10}20}~\\text{c}{{\\text{m}}-3} and high temperature  ˜keV, kinetic effects become important. Particle-in-cell simulations indicate that an electrostatic shock wave can be driven when the high-temperature Au jet expands into the low-temperature CD corona. Deuterium ions with an amount of  ˜1015 can be accelerated to  ˜25 keV by the collisionless shock wave, thus causing efficient neutron productions though the beam-target method by stopping these energetic ions in the corona. The evaluated neutron yield is consistent with the experiments conducted at SG laser facilities.

Calcium ions in aqueous solutions: Accurate force field description aided by ab initio molecular dynamics and neutron scattering

NASA Astrophysics Data System (ADS)

Martinek, Tomas; Duboué-Dijon, Elise; Timr, Štěpán; Mason, Philip E.; Baxová, Katarina; Fischer, Henry E.; Schmidt, Burkhard; Pluhařová, Eva; Jungwirth, Pavel

2018-06-01

We present a combination of force field and ab initio molecular dynamics simulations together with neutron scattering experiments with isotopic substitution that aim at characterizing ion hydration and pairing in aqueous calcium chloride and formate/acetate solutions. Benchmarking against neutron scattering data on concentrated solutions together with ion pairing free energy profiles from ab initio molecular dynamics allows us to develop an accurate calcium force field which accounts in a mean-field way for electronic polarization effects via charge rescaling. This refined calcium parameterization is directly usable for standard molecular dynamics simulations of processes involving this key biological signaling ion.

Compact D-D/D-T neutron generators and their applications

NASA Astrophysics Data System (ADS)

Lou, Tak Pui

2003-10-01

Neutron generators based on the 2H(d,n)3He and 3H(d,n)4He fusion reactions are the most commonly available neutron sources. The applications of current commercial neutron generators are often limited by their low neutron yield and their short operational lifetime. A new generation of D-D/D-T fusion-based neutron generators has been designed at Lawrence Berkeley National Laboratory (LBNL) by using high current ion beams hitting on a self-loading target that has a large surface area to dissipate the heat load. This thesis describes the rationale behind the new designs and their potential applications. A survey of other neutron sources is presented to show their advantages and disadvantages compared to the fusion-based neutron generator. A prototype neutron facility was built at LBNL to test these neutron generators. High current ion beams were extracted from an RF-driven ion source to produce neutrons. With an average deuteron beam current of 24 mA and an energy of 100 keV, a neutron yield of >109 n/s has been obtained with a D-D coaxial neutron source. Several potential applications were investigated by using computer simulations. The computer code used for simulations and the variance reduction techniques employed were discussed. A study was carried out to determine the neutron flux and resolution of a D-T neutron source in thermal neutron scattering applications for condensed matter experiments. An error analysis was performed to validate the scheme used to predict the resolution. With a D-T neutron yield of 1014 n/s, the thermal neutron flux at the sample was predicted to be 7.3 x 105 n/cm2s. It was found that the resolution of cold neutrons was better than that of thermal neutrons when the duty factor is high. This neutron generator could be efficiently used for research and educational purposes at universities. Additional applications studied were positron production and Boron Neutron Capture Therapy (BNCT). The neutron flux required for positron production could not be provided with a single D-T neutron generator. Therefore, a subcritical fission multiplier was designed to increase the neutron yield. The neutron flux was increased by a factor of 25. A D-D driven fission multiplier was also studied for BNCT and a gain of 17 was obtained. The fission multiplier system gain was shown to be limited by the neutron absorption in the fuel and the reduction of source brightness. A brief discussion was also given regarding the neutron generator applications for fast neutron brachytherapy and neutron interrogation systems. It was concluded that new designs of compact D-D/D-T neutron generators are feasible and that superior quality neutron beams could be produced and used for various applications.

Benchmark test of neutron transport calculations: indium, nickel, gold, europium, and cobalt activation with and without energy moderated fission neutrons by iron simulating the Hiroshima atomic bomb casing.

PubMed

Iwatani, K; Hoshi, M; Shizuma, K; Hiraoka, M; Hayakawa, N; Oka, T; Hasai, H

1994-10-01

A benchmark test of the Monte Carlo neutron and photon transport code system (MCNP) was performed using a bare- and energy-moderated 252Cf fission neutron source which was obtained by transmission through 10-cm-thick iron. An iron plate was used to simulate the effect of the Hiroshima atomic bomb casing. This test includes the activation of indium and nickel for fast neutrons and gold, europium, and cobalt for thermal and epithermal neutrons, which were inserted in the moderators. The latter two activations are also to validate 152Eu and 60Co activity data obtained from the atomic bomb-exposed specimens collected at Hiroshima and Nagasaki, Japan. The neutron moderators used were Lucite and Nylon 6 and the total thickness of each moderator was 60 cm or 65 cm. Measured activity data (reaction yield) of the neutron-irradiated detectors in these moderators decreased to about 1/1,000th or 1/10,000th, which corresponds to about 1,500 m ground distance from the hypocenter in Hiroshima. For all of the indium, nickel, and gold activity data, the measured and calculated values agreed within 25%, and the corresponding values for europium and cobalt were within 40%. From this study, the MCNP code was found to be accurate enough for the bare- and energy-moderated 252Cf neutron activation calculations of these elements using moderators containing hydrogen, carbon, nitrogen, and oxygen.

New developments in the McStas neutron instrument simulation package

NASA Astrophysics Data System (ADS)

Willendrup, P. K.; Knudsen, E. B.; Klinkby, E.; Nielsen, T.; Farhi, E.; Filges, U.; Lefmann, K.

2014-07-01

The McStas neutron ray-tracing software package is a versatile tool for building accurate simulators of neutron scattering instruments at reactors, short- and long-pulsed spallation sources such as the European Spallation Source. McStas is extensively used for design and optimization of instruments, virtual experiments, data analysis and user training. McStas was founded as a scientific, open-source collaborative code in 1997. This contribution presents the project at its current state and gives an overview of the main new developments in McStas 2.0 (December 2012) and McStas 2.1 (expected fall 2013), including many new components, component parameter uniformisation, partial loss of backward compatibility, updated source brilliance descriptions, developments toward new tools and user interfaces, web interfaces and a new method for estimating beam losses and background from neutron optics.

CORE-COLLAPSE SUPERNOVA EQUATIONS OF STATE BASED ON NEUTRON STAR OBSERVATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steiner, A. W.; Hempel, M.; Fischer, T.

2013-09-01

Many of the currently available equations of state for core-collapse supernova simulations give large neutron star radii and do not provide large enough neutron star masses, both of which are inconsistent with some recent neutron star observations. In addition, one of the critical uncertainties in the nucleon-nucleon interaction, the nuclear symmetry energy, is not fully explored by the currently available equations of state. In this article, we construct two new equations of state which match recent neutron star observations and provide more flexibility in studying the dependence on nuclear matter properties. The equations of state are also provided in tabularmore » form, covering a wide range in density, temperature, and asymmetry, suitable for astrophysical simulations. These new equations of state are implemented into our spherically symmetric core-collapse supernova model, which is based on general relativistic radiation hydrodynamics with three-flavor Boltzmann neutrino transport. The results are compared with commonly used equations of state in supernova simulations of 11.2 and 40 M{sub Sun} progenitors. We consider only equations of state which are fitted to nuclear binding energies and other experimental and observational constraints. We find that central densities at bounce are weakly correlated with L and that there is a moderate influence of the symmetry energy on the evolution of the electron fraction. The new models also obey the previously observed correlation between the time to black hole formation and the maximum mass of an s = 4 neutron star.« less

Measuring muon-induced neutrons with liquid scintillation detector at Soudan mine

NASA Astrophysics Data System (ADS)

Zhang, C.; Mei, D.-M.

2014-12-01

We report a direct detection of muon-induced high-energy neutrons with a 12-liter neutron detector fabricated with EJ-301 liquid scintillator operating at Soudan mine for about two years. The detector response to energy from a few MeV up to ˜20 MeV has been calibrated using radioactive sources and cosmic-ray muons. Subsequently, we have calculated the scintillation efficiency for nuclear recoils, up to a few hundred MeV, using Birks' law in the Monte Carlo simulation. Data from an exposure of 655.1 days were analyzed and neutron-induced recoil events were observed in the energy region from 4 to 50 MeV, corresponding to fast neutrons with kinetic energy up to a few hundred MeV, depending on the scattering angle. Combining with the Monte Carlo simulation, the measured muon-induced fast neutron flux is determined to be (2.23 ±0.52 (sta)±0.99 (sys))×10-9 cm-2 s-1 (En >20 MeV ), in a reasonable agreement with the model prediction. The muon flux is found to be (1.65 ±0.02 (sta)±0.1 (sys))×10-7 cm-2 s-1 (Eμ >1 GeV ), consistent with other measurements. As a result, the muon-induced high-energy gamma-ray flux is simulated to be 7.08 ×10-7 cm-2 s-1 (Eγ > 1 MeV ) for the depth of Soudan.

Neutron detection by scintillation of noble-gas excimers

NASA Astrophysics Data System (ADS)

McComb, Jacob Collin

Neutron detection is a technique essential to homeland security, nuclear reactor instrumentation, neutron diffraction science, oil-well logging, particle physics and radiation safety. The current shortage of helium-3, the neutron absorber used in most gas-filled proportional counters, has created a strong incentive to develop alternate methods of neutron detection. Excimer-based neutron detection (END) provides an alternative with many attractive properties. Like proportional counters, END relies on the conversion of a neutron into energetic charged particles, through an exothermic capture reaction with a neutron absorbing nucleus (10B, 6Li, 3He). As charged particles from these reactions lose energy in a surrounding gas, they cause electron excitation and ionization. Whereas most gas-filled detectors collect ionized charge to form a signal, END depends on the formation of diatomic noble-gas excimers (Ar*2, Kr*2,Xe* 2) . Upon decaying, excimers emit far-ultraviolet (FUV) photons, which may be collected by a photomultiplier tube or other photon detector. This phenomenon provides a means of neutron detection with a number of advantages over traditional methods. This thesis investigates excimer scintillation yield from the heavy noble gases following the boron-neutron capture reaction in 10B thin-film targets. Additionally, the thesis examines noble-gas excimer lifetimes with relationship to gas type and gas pressure. Experimental data were collected both at the National Institute of Standards and Technology (NIST) Center for Neutron Research, and on a newly developed neutron beamline at the Maryland University Training Reactor. The components of the experiment were calibrated at NIST and the University of Maryland, using FUV synchrotron radiation, neutron imaging, and foil activation techniques, among others. Computer modeling was employed to simulate charged-particle transport and excimer photon emission within the experimental apparatus. The observed excimer scintillation yields from the 10B( n, alpha)7Li reaction are comparable to the yields of many liquid and solid neutron scintillators. Additionally, the observed slow triplet-state decay of neutron-capture-induced excimers may be used in a practical detector to discriminate neutron interactions from gamma-ray interactions. The results of these measurements and simulations will contribute to the development and optimization of a deployable neutron detector based on noble-gas excimer scintillation.

Neutron Stars Rip Each Other Apart to Form Black Hole

NASA Image and Video Library

2014-05-13

Simulation frames from this NASA Goddard neutron star merger animation: bit.ly/1jolBYY Credit: NASA's Goddard Space Flight Center This supercomputer simulation shows one of the most violent events in the universe: a pair of neutron stars colliding, merging and forming a black hole. A neutron star is the compressed core left behind when a star born with between eight and 30 times the sun's mass explodes as a supernova. Neutron stars pack about 1.5 times the mass of the sun — equivalent to about half a million Earths — into a ball just 12 miles (20 km) across. As the simulation begins, we view an unequally matched pair of neutron stars weighing 1.4 and 1.7 solar masses. They are separated by only about 11 miles, slightly less distance than their own diameters. Redder colors show regions of progressively lower density. As the stars spiral toward each other, intense tides begin to deform them, possibly cracking their crusts. Neutron stars possess incredible density, but their surfaces are comparatively thin, with densities about a million times greater than gold. Their interiors crush matter to a much greater degree densities rise by 100 million times in their centers. To begin to imagine such mind-boggling densities, consider that a cubic centimeter of neutron star matter outweighs Mount Everest. By 7 milliseconds, tidal forces overwhelm and shatter the lesser star. Its superdense contents erupt into the system and curl a spiral arm of incredibly hot material. At 13 milliseconds, the more massive star has accumulated too much mass to support it against gravity and collapses, and a new black hole is born. The black hole's event horizon — its point of no return — is shown by the gray sphere. While most of the matter from both neutron stars will fall into the black hole, some of the less dense, faster moving matter manages to orbit around it, quickly forming a large and rapidly rotating torus. This torus extends for about 124 miles (200 km) and contains the equivalent of 1/5th the mass of our sun. Scientists think neutron star mergers like this produce short gamma-ray bursts (GRBs). Short GRBs last less than two seconds yet unleash as much energy as all the stars in our galaxy produce over one year. The rapidly fading afterglow of these explosions presents a challenge to astronomers. A key element in understanding GRBs is getting instruments on large ground-based telescopes to capture afterglows as soon as possible after the burst. The rapid notification and accurate positions provided by NASA's Swift mission creates a vibrant synergy with ground-based observatories that has led to dramatically improved understanding of GRBs, especially for short bursts. This video is public domain and can be downloaded at: svs.gsfc.nasa.gov/vis/a010000/a011500/a011530/index.html NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Neutron Stars Rip Each Other Apart to Form Black Hole

NASA Image and Video Library

2017-12-08

Simulation frames from this NASA Goddard neutron star merger animation: bit.ly/1jolBYY Credit: NASA's Goddard Space Flight Center This supercomputer simulation shows one of the most violent events in the universe: a pair of neutron stars colliding, merging and forming a black hole. A neutron star is the compressed core left behind when a star born with between eight and 30 times the sun's mass explodes as a supernova. Neutron stars pack about 1.5 times the mass of the sun — equivalent to about half a million Earths — into a ball just 12 miles (20 km) across. As the simulation begins, we view an unequally matched pair of neutron stars weighing 1.4 and 1.7 solar masses. They are separated by only about 11 miles, slightly less distance than their own diameters. Redder colors show regions of progressively lower density. As the stars spiral toward each other, intense tides begin to deform them, possibly cracking their crusts. Neutron stars possess incredible density, but their surfaces are comparatively thin, with densities about a million times greater than gold. Their interiors crush matter to a much greater degree densities rise by 100 million times in their centers. To begin to imagine such mind-boggling densities, consider that a cubic centimeter of neutron star matter outweighs Mount Everest. By 7 milliseconds, tidal forces overwhelm and shatter the lesser star. Its superdense contents erupt into the system and curl a spiral arm of incredibly hot material. At 13 milliseconds, the more massive star has accumulated too much mass to support it against gravity and collapses, and a new black hole is born. The black hole's event horizon — its point of no return — is shown by the gray sphere. While most of the matter from both neutron stars will fall into the black hole, some of the less dense, faster moving matter manages to orbit around it, quickly forming a large and rapidly rotating torus. This torus extends for about 124 miles (200 km) and contains the equivalent of 1/5th the mass of our sun. Scientists think neutron star mergers like this produce short gamma-ray bursts (GRBs). Short GRBs last less than two seconds yet unleash as much energy as all the stars in our galaxy produce over one year. The rapidly fading afterglow of these explosions presents a challenge to astronomers. A key element in understanding GRBs is getting instruments on large ground-based telescopes to capture afterglows as soon as possible after the burst. The rapid notification and accurate positions provided by NASA's Swift mission creates a vibrant synergy with ground-based observatories that has led to dramatically improved understanding of GRBs, especially for short bursts. This video is public domain and can be downloaded at: svs.gsfc.nasa.gov/vis/a010000/a011500/a011530/index.html NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Latitude Variation of the Subsurface Lunar Temperature: Lunar Prospector Thermal Neutrons

NASA Astrophysics Data System (ADS)

Little, R. C.; Feldman, W. C.; Maurice, S.; Genetay, I.; Lawrence, D. J.; Lawson, S. L.; Gasnault, O.; Barraclough, B. L.; Elphic, R. C.; Prettyman, T. H.; Binder, A. B.

2001-05-01

Planetary thermal neutron fluxes provide a sensitive proxy for mafic and feldspathic terranes, and are also necessary for translating measured gamma-ray line strengths to elemental abundances. Both functions require a model for near surface temperatures and a knowledge of the dependence of thermal neutron flux on temperature. We have explored this dependence for a representative sample of lunar soil compositions and surface temperatures using MCNP. For all soil samples, the neutron density is found to be independent of temperature, in accord with neutron moderation theory. The thermal neutron flux, however, does vary with temperature in a way that depends on D, the ratio of macroscopic absorption to energy-loss cross sections of soil compositions. The weakest dependence is for the largest D (which corresponds to the Apollo 17 high Ti basalt in our soil selection), and the largest dependence is for the lowest D (which corresponds to ferroan anorthosite, [FAN] in our selection). For the lunar model simulated, the depth at which the thermal neutron population is most sensitive to temperature is ~30 g/cm**2. These simulations were compared with the flux of thermal neutrons measured using the Lunar Prospector neutron spectrometer over the lunar highlands using a sub-surface temperature profile that varies with latitude, L, as (Cos L)**0.25. The fit is excellent. The best fitting equatorial temperature is determined to be, Teq=224+/-40 K. This temperature range brackets the average temperature measured below the thermal wave at the equator, Tmeas = 252+/-3K [Langseth and Keihm, 1977]. The present result represents the first measurement of subsurface temperature from orbit using neutrons.

Intercomparison of Monte Carlo radiation transport codes to model TEPC response in low-energy neutron and gamma-ray fields.

PubMed

Ali, F; Waker, A J; Waller, E J

2014-10-01

Tissue-equivalent proportional counters (TEPC) can potentially be used as a portable and personal dosemeter in mixed neutron and gamma-ray fields, but what hinders this use is their typically large physical size. To formulate compact TEPC designs, the use of a Monte Carlo transport code is necessary to predict the performance of compact designs in these fields. To perform this modelling, three candidate codes were assessed: MCNPX 2.7.E, FLUKA 2011.2 and PHITS 2.24. In each code, benchmark simulations were performed involving the irradiation of a 5-in. TEPC with monoenergetic neutron fields and a 4-in. wall-less TEPC with monoenergetic gamma-ray fields. The frequency and dose mean lineal energies and dose distributions calculated from each code were compared with experimentally determined data. For the neutron benchmark simulations, PHITS produces data closest to the experimental values and for the gamma-ray benchmark simulations, FLUKA yields data closest to the experimentally determined quantities. © The Author 2013. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

The MCNP Simulation of a PGNAA System at TRR-1/M1

NASA Astrophysics Data System (ADS)

Sangaroon, S.; Ratanatongchai, W.; Picha, R.; Khaweerat, S.; Channuie, J.

2017-06-01

The prompt-gamma neutron activation analysis system (PGNAA) has been installed at Thai Research Reactor-1/Modified 1 (TRR-1/M1) since 1999. The purpose of the system is for elemental and isotopic analyses. The system mainly consists of a series of the moderator and collimator, neutron and gamma-ray shielding and the HPGe detector. In this work, the condition of the system is carried out based on the Monte Carlo method using Monte Carlo N-Particle transport code and the experiment. The flux ratios (Φthermal/Φepithermal and Φthermal/Φfast) and thermal neutron flux have been obtained. The simulated prompt gamma rays of the Portland cement sample have been carried out. The simulation provides significant contribution in upgrading the PGNAA station to be available in various applications.

Corrigendum to "Monte Carlo simulations of the secondary neutron ambient and effective dose equivalent rates from surface to suborbital altitudes and low Earth orbit".

PubMed

El-Jaby, Samy

2016-06-01

A recent paper published in Life Sciences in Space Research (El-Jaby and Richardson, 2015) presented estimates of the secondary neutron ambient and effective dose equivalent rates, in air, from surface altitudes up to suborbital altitudes and low Earth orbit. These estimates were based on MCNPX (LANL, 2011) (Monte Carlo N-Particle eXtended) radiation transport simulations of galactic cosmic radiation passing through Earth's atmosphere. During a recent review of the input decks used for these simulations, a systematic error was discovered that is addressed here. After reassessment, the neutron ambient and effective dose equivalent rates estimated are found to be 10 to 15% different, though, the essence of the conclusions drawn remains unchanged. Crown Copyright © 2016. Published by Elsevier Ltd. All rights reserved.

A novel laser-collider used to produce monoenergetic 13.3 MeV 7Li (d, n) neutrons

PubMed Central

Zhao, J. R.; Zhang, X. P.; Yuan, D. W.; Li, Y. T.; Li, D. Z.; Rhee, Y. J.; Zhang, Z.; Li, F.; Zhu, B. J.; Li, Yan F.; Han, B.; Liu, C.; Ma, Y.; Li, Yi F.; Tao, M. Z.; Li, M. H.; Guo, X.; Huang, X. G.; Fu, S. Z.; Zhu, J. Q.; Zhao, G.; Chen, L. M.; Fu, C. B.; Zhang, J.

2016-01-01

Neutron energy is directly correlated with the energy of the incident ions in experiments involving laser-driven nuclear reactions. Using high-energy incident ions reduces the energy concentration of the generated neutrons. A novel “laser-collider” method was used at the Shenguang II laser facility to produce monoenergetic neutrons via 7Li (d, n) nuclear reactions. The specially designed K-shaped target significantly increased the numbers of incident d and Li ions at the keV level. Ultimately, 13.3 MeV neutrons were obtained. Considering the time resolution of the neutron detector, we demonstrated that the produced neutrons were monoenergetic. Interferometry and a Multi hydro-dynamics simulation confirmed the monoenergetic nature of these neutrons. PMID:27250660

Neutron assay in mixed radiation fields with a 6Li-loaded plastic scintillator

NASA Astrophysics Data System (ADS)

Balmer, M. J. I.; Gamage, K. A. A.; Taylor, G. C.

2015-08-01

A novel technique for assay of thermal and fast neutrons in a 6Li-loaded plastic scintillator is presented. Existing capture-gated thermal neutron detection techniques were evaluated with the 6Li-loaded plastic scintillator studied in this work. Using simulations and experimental work, shortcomings in its performance were highlighted. As a result, it was proposed that by separating the combined fast and thermal neutron events from gamma events, using established pulse shape discrimination techniques, the thermal neutron events could then be assayed. Experiments were conducted at the National Physical Laboratory, Teddington, performing neutron assays with seven different neutron fields using the proposed technique. For each field, thermal and fast neutron content was estimated and were shown to corroborate with the seven synthesised fields.

Observation of Neutron Skyshine from an Accelerator Based Neutron Source

NASA Astrophysics Data System (ADS)

Franklyn, C. B.

2011-12-01

A key feature of neutron based interrogation systems is the need for adequate provision of shielding around the facility. Accelerator facilities adapted for fast neutron generation are not necessarily suitably equipped to ensure complete containment of the vast quantity of neutrons generated, typically >1011 nṡs-1. Simulating the neutron leakage from a facility is not a simple exercise since the energy and directional distribution can only be approximated. Although adequate horizontal, planar shielding provision is made for a neutron generator facility, it is sometimes the case that vertical shielding is minimized, due to structural and economic constraints. It is further justified by assuming the atmosphere above a facility functions as an adequate radiation shield. It has become apparent that multiple neutron scattering within the atmosphere can result in a measurable dose of neutrons reaching ground level some distance from a facility, an effect commonly known as skyshine. This paper describes a neutron detection system developed to monitor neutrons detected several hundred metres from a neutron source due to the effect of skyshine.

An improved target velocity sampling algorithm for free gas elastic scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Romano, Paul K.; Walsh, Jonathan A.

We present an improved algorithm for sampling the target velocity when simulating elastic scattering in a Monte Carlo neutron transport code that correctly accounts for the energy dependence of the scattering cross section. The algorithm samples the relative velocity directly, thereby avoiding a potentially inefficient rejection step based on the ratio of cross sections. Here, we have shown that this algorithm requires only one rejection step, whereas other methods of similar accuracy require two rejection steps. The method was verified against stochastic and deterministic reference results for upscattering percentages in 238U. Simulations of a light water reactor pin cell problemmore » demonstrate that using this algorithm results in a 3% or less penalty in performance when compared with an approximate method that is used in most production Monte Carlo codes« less

An improved target velocity sampling algorithm for free gas elastic scattering

DOE PAGES

Romano, Paul K.; Walsh, Jonathan A.

2018-02-03

We present an improved algorithm for sampling the target velocity when simulating elastic scattering in a Monte Carlo neutron transport code that correctly accounts for the energy dependence of the scattering cross section. The algorithm samples the relative velocity directly, thereby avoiding a potentially inefficient rejection step based on the ratio of cross sections. Here, we have shown that this algorithm requires only one rejection step, whereas other methods of similar accuracy require two rejection steps. The method was verified against stochastic and deterministic reference results for upscattering percentages in 238U. Simulations of a light water reactor pin cell problemmore » demonstrate that using this algorithm results in a 3% or less penalty in performance when compared with an approximate method that is used in most production Monte Carlo codes« less

Symmetry Parameter Constraints from a Lower Bound on Neutron-matter Energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tews, Ingo; Lattimer, James M.; Ohnishi, Akira

We propose the existence of a lower bound on the energy of pure neutron matter (PNM) on the basis of unitary-gas considerations. We discuss its justification from experimental studies of cold atoms as well as from theoretical studies of neutron matter. We demonstrate that this bound results in limits to the density-dependent symmetry energy, which is the difference between the energies of symmetric nuclear matter and PNM. In particular, this bound leads to a lower limit to the volume symmetry energy parameter S {sub 0}. In addition, for assumed values of S {sub 0} above this minimum, this bound impliesmore » both upper and lower limits to the symmetry energy slope parameter L , which describes the lowest-order density dependence of the symmetry energy. A lower bound on neutron-matter incompressibility is also obtained. These bounds are found to be consistent with both recent calculations of the energies of PNM and constraints from nuclear experiments. Our results are significant because several equations of state that are currently used in astrophysical simulations of supernovae and neutron star mergers, as well as in nuclear physics simulations of heavy-ion collisions, have symmetry energy parameters that violate these bounds. Furthermore, below the nuclear saturation density, the bound on neutron-matter energies leads to a lower limit to the density-dependent symmetry energy, which leads to upper limits to the nuclear surface symmetry parameter and the neutron-star crust–core boundary. We also obtain a lower limit to the neutron-skin thicknesses of neutron-rich nuclei. Above the nuclear saturation density, the bound on neutron-matter energies also leads to an upper limit to the symmetry energy, with implications for neutron-star cooling via the direct Urca process.« less

Experimental characterization of the Advanced Liquid Hydrogen Cold Neutron Source spectrum of the NBSR reactor at the NIST Center for Neutron Research

NASA Astrophysics Data System (ADS)

Cook, J. C.; Barker, J. G.; Rowe, J. M.; Williams, R. E.; Gagnon, C.; Lindstrom, R. M.; Ibberson, R. M.; Neumann, D. A.

2015-08-01

The recent expansion of the National Institute of Standards and Technology (NIST) Center for Neutron Research facility has offered a rare opportunity to perform an accurate measurement of the cold neutron spectrum at the exit of a newly-installed neutron guide. Using a combination of a neutron time-of-flight measurement, a gold foil activation measurement, and Monte Carlo simulation of the neutron guide transmission, we obtain the most reliable experimental characterization of the Advanced Liquid Hydrogen Cold Neutron Source brightness to date. Time-of-flight measurements were performed at three distinct fuel burnup intervals, including one immediately following reactor startup. Prior to the latter measurement, the hydrogen was maintained in a liquefied state for an extended period in an attempt to observe an initial radiation-induced increase of the ortho (o)-hydrogen fraction. Since para (p)-hydrogen has a small scattering cross-section for neutron energies below 15 meV (neutron wavelengths greater than about 2.3 Å), changes in the o- p hydrogen ratio and in the void distribution in the boiling hydrogen influence the spectral distribution. The nature of such changes is simulated with a continuous-energy, Monte Carlo radiation-transport code using 20 K o and p hydrogen scattering kernels and an estimated hydrogen density distribution derived from an analysis of localized heat loads. A comparison of the transport calculations with the mean brightness function resulting from the three measurements suggests an overall o- p ratio of about 17.5(±1) % o- 82.5% p for neutron energies<15 meV, a significantly lower ortho concentration than previously assumed.

Symmetry Parameter Constraints from a Lower Bound on Neutron-matter Energy

NASA Astrophysics Data System (ADS)

Tews, Ingo; Lattimer, James M.; Ohnishi, Akira; Kolomeitsev, Evgeni E.

2017-10-01

We propose the existence of a lower bound on the energy of pure neutron matter (PNM) on the basis of unitary-gas considerations. We discuss its justification from experimental studies of cold atoms as well as from theoretical studies of neutron matter. We demonstrate that this bound results in limits to the density-dependent symmetry energy, which is the difference between the energies of symmetric nuclear matter and PNM. In particular, this bound leads to a lower limit to the volume symmetry energy parameter S 0. In addition, for assumed values of S 0 above this minimum, this bound implies both upper and lower limits to the symmetry energy slope parameter L ,which describes the lowest-order density dependence of the symmetry energy. A lower bound on neutron-matter incompressibility is also obtained. These bounds are found to be consistent with both recent calculations of the energies of PNM and constraints from nuclear experiments. Our results are significant because several equations of state that are currently used in astrophysical simulations of supernovae and neutron star mergers, as well as in nuclear physics simulations of heavy-ion collisions, have symmetry energy parameters that violate these bounds. Furthermore, below the nuclear saturation density, the bound on neutron-matter energies leads to a lower limit to the density-dependent symmetry energy, which leads to upper limits to the nuclear surface symmetry parameter and the neutron-star crust-core boundary. We also obtain a lower limit to the neutron-skin thicknesses of neutron-rich nuclei. Above the nuclear saturation density, the bound on neutron-matter energies also leads to an upper limit to the symmetry energy, with implications for neutron-star cooling via the direct Urca process.

Forward Propagation Analysis for determining the 16O(n,α)13C Reaction Cross Section at LANSCE

NASA Astrophysics Data System (ADS)

Purcell, Zachary; Lee, Hye Young; Davison, Jacob

2017-09-01

Oxygen is present in many materials and the uncertainties in its nuclear data can have a significant impact on applications. In particular, neutron-absorption reactions reduceavailable neutrons in applications. Thus,high precision in knowledge of this reaction cross sectionis required. To decreasethe systematic uncertainty, we developed a framework that uses Forward Propagation Analysis (FPA) for determining the 16O(n,α)13C reaction cross section from data measured at LANSCE. The Low Energy NZ (LENZ) instrument was used to detectreaction alphas on the Ta2 O5 solid target with silicon strip detectors. The FPA was performed in GEANT4. The geometry, efficiency, and resolution functions of LENZ werevalidated by comparing with the alpha emitting Th-229 source measurement. To reproduce experimental yields in silicon strip detectors, the energy dependent neutron beam flux distribution, the 16O(n,a) reaction differential cross sections, and the 2-body kinematics calculations were implemented in the simulation. We present results from the FPA on LENZ data anddiscuss the improved data analysis [LA-UR-17-26436]. This work has benefited from the use of the Los Alamos Neutron Science Center, is funded by the US Department of Energy and operated by Los Alamos National Security, LLC under Contract DE-AC52-06NA25396.

Reliability Design for Neutron Induced Single-Event Burnout of IGBT

NASA Astrophysics Data System (ADS)

Shoji, Tomoyuki; Nishida, Shuichi; Ohnishi, Toyokazu; Fujikawa, Touma; Nose, Noboru; Hamada, Kimimori; Ishiko, Masayasu

Single-event burnout (SEB) caused by cosmic ray neutrons leads to catastrophic failures in insulated gate bipolar transistors (IGBTs). It was found experimentally that the incident neutron induced SEB failure rate increases as a function of the applied collector voltage. Moreover, the failure rate increased sharply with an increase in the applied collector voltage when the voltage exceeded a certain threshold value (SEB cutoff voltage). In this paper, transient device simulation results indicate that impact ionization at the n-drift/n+ buffer boundary is a crucially important factor in the turning-on of the parasitic pnp transistor, and eventually latch-up of the parasitic thyristor causes SEB. In addition, the device parameter dependency of the SEB cutoff voltage was analytically derived from the latch-up condition of the parasitic thyristor. As a result, it was confirmed that reducing the current gain of the parasitic transistor, such as by increasing the n-drift region thickness d was effective in increasing the SEB cutoff voltage. Furthermore, `white' neutron-irradiation experiments demonstrated that suppressing the inherent parasitic thyristor action leads to an improvement of the SEB cutoff voltage. It was confirmed that current gain optimization of the parasitic transistor is a crucial factor for establishing highly reliable design against chance failures.

1983 international intercomparison of nuclear accident dosimetry systems at Oak Ridge National Laboratory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swaja, R.E.; Greene, R.T.; Sims, C.S.

1985-04-01

An international intercomparison of nuclear accident dosimetry systems was conducted during September 12-16, 1983, at Oak Ridge National Laboratory (ORNL) using the Health Physics Research Reactor operated in the pulse mode to simulate criticality accidents. This study marked the twentieth in a series of annual accident dosimetry intercomparisons conducted at ORNL. Participants from ten organizations attended this intercomparison and measured neutron and gamma doses at area monitoring stations and on phantoms for three different shield conditions. Results of this study indicate that foil activation techniques are the most popular and accurate method of determining accident-level neutron doses at area monitoringmore » stations. For personnel monitoring, foil activation, blood sodium activation, and thermoluminescent (TL) methods are all capable of providing accurate dose estimates in a variety of radiation fields. All participants in this study used TLD's to determine gamma doses with very good results on the average. Chemical dosemeters were also shown to be capable of yielding accurate estimates of total neutron plus gamma doses in a variety of radiation fields. While 83% of all neutron measurements satisfied regulatory standards relative to reference values, only 39% of all gamma results satisfied corresponding guidelines for gamma measurements. These results indicate that continued improvement in accident dosimetry evaluation and measurement techniques is needed.« less

ENDF/B-VII.1 Nuclear Data for Science and Technology: Cross Sections, Covariances, Fission Product Yields and Decay Data

NASA Astrophysics Data System (ADS)

Chadwick, M. B.; Herman, M.; Obložinský, P.; Dunn, M. E.; Danon, Y.; Kahler, A. C.; Smith, D. L.; Pritychenko, B.; Arbanas, G.; Arcilla, R.; Brewer, R.; Brown, D. A.; Capote, R.; Carlson, A. D.; Cho, Y. S.; Derrien, H.; Guber, K.; Hale, G. M.; Hoblit, S.; Holloway, S.; Johnson, T. D.; Kawano, T.; Kiedrowski, B. C.; Kim, H.; Kunieda, S.; Larson, N. M.; Leal, L.; Lestone, J. P.; Little, R. C.; McCutchan, E. A.; MacFarlane, R. E.; MacInnes, M.; Mattoon, C. M.; McKnight, R. D.; Mughabghab, S. F.; Nobre, G. P. A.; Palmiotti, G.; Palumbo, A.; Pigni, M. T.; Pronyaev, V. G.; Sayer, R. O.; Sonzogni, A. A.; Summers, N. C.; Talou, P.; Thompson, I. J.; Trkov, A.; Vogt, R. L.; van der Marck, S. C.; Wallner, A.; White, M. C.; Wiarda, D.; Young, P. G.

2011-12-01

The ENDF/B-VII.1 library is our latest recommended evaluated nuclear data file for use in nuclear science and technology applications, and incorporates advances made in the five years since the release of ENDF/B-VII.0. These advances focus on neutron cross sections, covariances, fission product yields and decay data, and represent work by the US Cross Section Evaluation Working Group (CSEWG) in nuclear data evaluation that utilizes developments in nuclear theory, modeling, simulation, and experiment. The principal advances in the new library are: (1) An increase in the breadth of neutron reaction cross section coverage, extending from 393 nuclides to 423 nuclides; (2) Covariance uncertainty data for 190 of the most important nuclides, as documented in companion papers in this edition; (3) R-matrix analyses of neutron reactions on light nuclei, including isotopes of He, Li, and Be; (4) Resonance parameter analyses at lower energies and statistical high energy reactions for isotopes of Cl, K, Ti, V, Mn, Cr, Ni, Zr and W; (5) Modifications to thermal neutron reactions on fission products (isotopes of Mo, Tc, Rh, Ag, Cs, Nd, Sm, Eu) and neutron absorber materials (Cd, Gd); (6) Improved minor actinide evaluations for isotopes of U, Np, Pu, and Am (we are not making changes to the major actinides 235,238U and 239Pu at this point, except for delayed neutron data and covariances, and instead we intend to update them after a further period of research in experiment and theory), and our adoption of JENDL-4.0 evaluations for isotopes of Cm, Bk, Cf, Es, Fm, and some other minor actinides; (7) Fission energy release evaluations; (8) Fission product yield advances for fission-spectrum neutrons and 14 MeV neutrons incident on 239Pu; and (9) A new decay data sublibrary. Integral validation testing of the ENDF/B-VII.1 library is provided for a variety of quantities: For nuclear criticality, the VII.1 library maintains the generally-good performance seen for VII.0 for a wide range of MCNP simulations of criticality benchmarks, with improved performance coming from new structural material evaluations, especially for Ti, Mn, Cr, Zr and W. For Be we see some improvements although the fast assembly data appear to be mutually inconsistent. Actinide cross section updates are also assessed through comparisons of fission and capture reaction rate measurements in critical assemblies and fast reactors, and improvements are evident. Maxwellian-averaged capture cross sections at 30 keV are also provided for astrophysics applications. We describe the cross section evaluations that have been updated for ENDF/B-VII.1 and the measured data and calculations that motivated the changes, and therefore this paper augments the ENDF/B-VII.0 publication [M. B. Chadwick, P. Obložinský, M. Herman, N. M. Greene, R. D. McKnight, D. L. Smith, P. G. Young, R. E. MacFarlane, G. M. Hale, S. C. Frankle, A. C. Kahler, T. Kawano, R. C. Little, D. G. Madland, P. Moller, R. D. Mosteller, P. R. Page, P. Talou, H. Trellue, M. C. White, W. B. Wilson, R. Arcilla, C. L. Dunford, S. F. Mughabghab, B. Pritychenko, D. Rochman, A. A. Sonzogni, C. R. Lubitz, T. H. Trumbull, J. P. Weinman, D. A. Br, D. E. Cullen, D. P. Heinrichs, D. P. McNabb, H. Derrien, M. E. Dunn, N. M. Larson, L. C. Leal, A. D. Carlson, R. C. Block, J. B. Briggs, E. T. Cheng, H. C. Huria, M. L. Zerkle, K. S. Kozier, A. Courcelle, V. Pronyaev, and S. C. van der Marck, "ENDF/B-VII.0: Next Generation Evaluated Nuclear Data Library for Nuclear Science and Technology," Nuclear Data Sheets 107, 2931 (2006)].

Designing an extended energy range single-sphere multi-detector neutron spectrometer

NASA Astrophysics Data System (ADS)

Gómez-Ros, J. M.; Bedogni, R.; Moraleda, M.; Esposito, A.; Pola, A.; Introini, M. V.; Mazzitelli, G.; Quintieri, L.; Buonomo, B.

2012-06-01

This communication describes the design specifications for a neutron spectrometer consisting of 31 thermal neutron detectors, namely Dysprosium activation foils, embedded in a 25 cm diameter polyethylene sphere which includes a 1 cm thick lead shell insert that degrades the energy of neutrons through (n,xn) reactions, thus allowing to extension of the energy range of the response up to hundreds of MeV neutrons. The new spectrometer, called SP2 (SPherical SPectrometer), relies on the same detection mechanism as that of the Bonner Sphere Spectrometer, but with the advantage of determining the whole neutron spectrum in a single exposure. The Monte Carlo transport code MCNPX was used to design the spectrometer in terms of sphere diameter, number and position of the detectors, position and thickness of the lead shell, as well as to obtain the response matrix for the final configuration. This work focuses on evaluating the spectrometric capabilities of the SP2 design by simulating the exposure of SP2 in neutron fields representing different irradiation conditions (test spectra). The simulated SP2 readings were then unfolded with the FRUIT unfolding code, in the absence of detailed pre-information, and the unfolded spectra were compared with the known test spectra. The results are satisfactory and allowed approving the production of a prototypal spectrometer.

Experimental and simulation studies of neutron-induced single-event burnout in SiC power diodes

NASA Astrophysics Data System (ADS)

Shoji, Tomoyuki; Nishida, Shuichi; Hamada, Kimimori; Tadano, Hiroshi

2014-01-01

Neutron-induced single-event burnouts (SEBs) of silicon carbide (SiC) power diodes have been investigated by white neutron irradiation experiments and transient device simulations. It was confirmed that a rapid increase in lattice temperature leads to formation of crown-shaped aluminum and cracks inside the device owing to expansion stress when the maximum lattice temperature reaches the sublimation temperature. SEB device simulation indicated that the peak lattice temperature is located in the vicinity of the n-/n+ interface and anode contact, and that the positions correspond to a hammock-like electric field distribution caused by the space charge effect. Moreover, the locations of the simulated peak lattice temperature agree closely with the positions of the observed destruction traces. Furthermore, it was theoretically demonstrated that the period of temperature increase of a SiC power device is two orders of magnitude less than that of a Si power device, using a thermal diffusion equation.

A Simplified Model of Local Structure in Aqueous Proline Amino Acid Revealed by First-Principles Molecular Dynamics Simulations

PubMed Central

Troitzsch, Raphael Z.; Tulip, Paul R.; Crain, Jason; Martyna, Glenn J.

2008-01-01

Aqueous proline solutions are deceptively simple as they can take on complex roles such as protein chaperones, cryoprotectants, and hydrotropic agents in biological processes. Here, a molecular level picture of proline/water mixtures is developed. Car-Parrinello ab initio molecular dynamics (CPAIMD) simulations of aqueous proline amino acid at the B-LYP level of theory, performed using IBM's Blue Gene/L supercomputer and massively parallel software, reveal hydrogen-bonding propensities that are at odds with the predictions of the CHARMM22 empirical force field but are in better agreement with results of recent neutron diffraction experiments. In general, the CPAIMD (B-LYP) simulations predict a simplified structural model of proline/water mixtures consisting of fewer distinct local motifs. Comparisons of simulation results to experiment are made by direct evaluation of the neutron static structure factor S(Q) from CPAIMD (B-LYP) trajectories as well as to the results of the empirical potential structure refinement reverse Monte Carlo procedure applied to the neutron data. PMID:18790850

A simplified model of local structure in aqueous proline amino acid revealed by first-principles molecular dynamics simulations.

PubMed

Troitzsch, Raphael Z; Tulip, Paul R; Crain, Jason; Martyna, Glenn J

2008-12-01

Aqueous proline solutions are deceptively simple as they can take on complex roles such as protein chaperones, cryoprotectants, and hydrotropic agents in biological processes. Here, a molecular level picture of proline/water mixtures is developed. Car-Parrinello ab initio molecular dynamics (CPAIMD) simulations of aqueous proline amino acid at the B-LYP level of theory, performed using IBM's Blue Gene/L supercomputer and massively parallel software, reveal hydrogen-bonding propensities that are at odds with the predictions of the CHARMM22 empirical force field but are in better agreement with results of recent neutron diffraction experiments. In general, the CPAIMD (B-LYP) simulations predict a simplified structural model of proline/water mixtures consisting of fewer distinct local motifs. Comparisons of simulation results to experiment are made by direct evaluation of the neutron static structure factor S(Q) from CPAIMD (B-LYP) trajectories as well as to the results of the empirical potential structure refinement reverse Monte Carlo procedure applied to the neutron data.

Neutron Particle Effects on a Quad-Redundant Flight Control Computer

NASA Technical Reports Server (NTRS)

Eure, Kenneth; Belcastro, Celeste M.; Gray, W Steven; Gonzalex, Oscar

2003-01-01

This paper describes a single-event upset experiment performed at the Los Alamos National Laboratory. A closed-loop control system consisting of a Quad-Redundant Flight Control Computer (FCC) and a B737 simulator was operated while the FCC was exposed to a neutron beam. The purpose of this test was to analyze the effects of neutron bombardment on avionics control systems operating at altitudes where neutron strikes are probable. The neutron energy spectrum produced at the Los Alamos National Laboratory is similar in shape to the spectrum of atmospheric neutrons but much more intense. The higher intensity results in accelerated life tests that are representative of the actual neutron radiation that a FCC may receive over a period of years.

Using neutrons to measure keV temperatures in highly compressed plastic at multi-Gbar pressures

DOE PAGES

Nilsen, J.; Bachmann, B.; Zimmerman, G. B.; ...

2016-10-27

In this study, we have designed an experiment for the National Ignition Facility to measure the Hugoniot of materials such as plastic at extreme pressures. The design employs a strong spherically converging shock launched through a solid ball of material using a hohlraum radiation drive. The shock front conditions can be characterized using X-ray radiography until background from shock coalescence overtakes the backlit signal. Shock coalescence at the center is predicted to reach tens of Gbars and can be further characterized by measuring the X-ray self-emission and 2.45 MeV neutrons emitted from the shock flash region. In this simulation designmore » work the standard plastic sphere is replaced with a deuterated polyethylene sphere, CD 2, that reaches sufficiently high densities and temperatures in the central hot spot to produce neutrons from Deuterium-Deuterium (DD) fusion reactions that can be measured by a neutron time of flight spectrometer (nTOF) and act as a temperature diagnostic. This paper focuses on the design of these experiments, based on an extensive suite of radiation-hydrodynamics simulations, and the interpretation of the predicted DD neutron signals. The simulations predict mean temperatures of 1 keV in the central hot spot with mean densities of 33 g/cc and mean pressures of 25 Gbar. Lastly, a preliminary comparison with early experimental results looks promising with an average ion temperature of 1.06 ± 0.15 keV in the central hot spot estimated from the nTOF spectral width and measured neutron yield of 7.0 (±0.5) × 10 9 DD neutrons.« less

Development of Monte Carlo based real-time treatment planning system with fast calculation algorithm for boron neutron capture therapy.

PubMed

Takada, Kenta; Kumada, Hiroaki; Liem, Peng Hong; Sakurai, Hideyuki; Sakae, Takeji

2016-12-01

We simulated the effect of patient displacement on organ doses in boron neutron capture therapy (BNCT). In addition, we developed a faster calculation algorithm (NCT high-speed) to simulate irradiation more efficiently. We simulated dose evaluation for the standard irradiation position (reference position) using a head phantom. Cases were assumed where the patient body is shifted in lateral directions compared to the reference position, as well as in the direction away from the irradiation aperture. For three groups of neutron (thermal, epithermal, and fast), flux distribution using NCT high-speed with a voxelized homogeneous phantom was calculated. The three groups of neutron fluxes were calculated for the same conditions with Monte Carlo code. These calculated results were compared. In the evaluations of body movements, there were no significant differences even with shifting up to 9mm in the lateral directions. However, the dose decreased by about 10% with shifts of 9mm in a direction away from the irradiation aperture. When comparing both calculations in the phantom surface up to 3cm, the maximum differences between the fluxes calculated by NCT high-speed with those calculated by Monte Carlo code for thermal neutrons and epithermal neutrons were 10% and 18%, respectively. The time required for NCT high-speed code was about 1/10th compared to Monte Carlo calculation. In the evaluation, the longitudinal displacement has a considerable effect on the organ doses. We also achieved faster calculation of depth distribution of thermal neutron flux using NCT high-speed calculation code. Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Monte Carlo simulations of the secondary neutron ambient and effective dose equivalent rates from surface to suborbital altitudes and low Earth orbit

NASA Astrophysics Data System (ADS)

El-Jaby, Samy; Richardson, Richard B.

2015-07-01

Occupational exposures from ionizing radiation are currently regulated for airline travel (<20 km) and for missions to low-Earth orbit (∼300-400 km). Aircrew typically receive between 1 and 6 mSv of occupational dose annually, while aboard the International Space Station, the area radiation dose equivalent measured over just 168 days was 106 mSv at solar minimum conditions. It is anticipated that space tourism vehicles will reach suborbital altitudes of approximately 100 km and, therefore, the annual occupational dose to flight crew during repeated transits is expected to fall somewhere between those observed for aircrew and astronauts. Unfortunately, measurements of the radiation environment at the high altitudes reached by suborbital vehicles are sparse, and modelling efforts have been similarly limited. In this paper, preliminary MCNPX radiation transport code simulations are developed of the secondary neutron flux profile in air from surface altitudes up to low Earth orbit at solar minimum conditions and excluding the effects of spacecraft shielding. These secondary neutrons are produced by galactic cosmic radiation interacting with Earth's atmosphere and are among the sources of radiation that can pose a health risk. Associated estimates of the operational neutron ambient dose equivalent, used for radiation protection purposes, and the neutron effective dose equivalent that is typically used for estimates of stochastic health risks, are provided in air. Simulations show that the neutron radiation dose rates received at suborbital altitudes are comparable to those experienced by aircrew flying at 7 to 14 km. We also show that the total neutron dose rate tails off beyond the Pfotzer maximum on ascension from surface up to low Earth orbit.

Monte Carlo simulations of the secondary neutron ambient and effective dose equivalent rates from surface to suborbital altitudes and low Earth orbit.

PubMed

El-Jaby, Samy; Richardson, Richard B

2015-07-01

Occupational exposures from ionizing radiation are currently regulated for airline travel (<20 km) and for missions to low-Earth orbit (∼300-400 km). Aircrew typically receive between 1 and 6 mSv of occupational dose annually, while aboard the International Space Station, the area radiation dose equivalent measured over just 168 days was 106 mSv at solar minimum conditions. It is anticipated that space tourism vehicles will reach suborbital altitudes of approximately 100 km and, therefore, the annual occupational dose to flight crew during repeated transits is expected to fall somewhere between those observed for aircrew and astronauts. Unfortunately, measurements of the radiation environment at the high altitudes reached by suborbital vehicles are sparse, and modelling efforts have been similarly limited. In this paper, preliminary MCNPX radiation transport code simulations are developed of the secondary neutron flux profile in air from surface altitudes up to low Earth orbit at solar minimum conditions and excluding the effects of spacecraft shielding. These secondary neutrons are produced by galactic cosmic radiation interacting with Earth's atmosphere and are among the sources of radiation that can pose a health risk. Associated estimates of the operational neutron ambient dose equivalent, used for radiation protection purposes, and the neutron effective dose equivalent that is typically used for estimates of stochastic health risks, are provided in air. Simulations show that the neutron radiation dose rates received at suborbital altitudes are comparable to those experienced by aircrew flying at 7 to 14 km. We also show that the total neutron dose rate tails off beyond the Pfotzer maximum on ascension from surface up to low Earth orbit. Crown Copyright © 2015. Published by Elsevier Ltd. All rights reserved.

Moderator design studies for a new neutron reference source based on the D–T fusion reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mozhayev, Andrey V.; Piper, Roman K.; Rathbone, Bruce A.

2016-06-01

The radioactive isotope Californium-252 (252Cf) is relied upon internationally as a neutron calibration source for ionizing radiation dosimetry because of its high specific activity. The source may be placed within a heavy-water (D2O) moderating sphere to produce a softened spectrum representative of neutron fields common to commercial nuclear power plant environments, among others. Due to termination of the U.S. Department of Energy loan/lease program in 2012, the expense of obtaining 252Cf sources has undergone a significant increase, rendering high output sources largely unattainable. On the other hand, the use of neutron generators in research and industry applications has increased dramaticallymore » in recent years. Neutron generators based on deuterium-tritium (D-T) fusion reaction provide high neutron fluence rates and, therefore, could possibly be used as a replacement for 252Cf. To be viable, the 14.6 MeV D-T output spectrum must be significantly moderated to approximate common workplace environments. This paper presents the results of an effort to select appropriate moderating materials and design a configuration to reshape the primary neutron field toward a spectrum approaching that from a nuclear power plant workplace. A series of Monte-Carlo (MCNP) simulations of single layer high- and low-Z materials are used to identify initial candidate moderators. Candidates are refined through a similar series of simulations involving combinations of 2 to 5 different materials. The simulated energy distribution using these candidate moderators are rated in comparison to a target spectrum. Other properties, such as fluence preservation and/or enhancement, prompt gamma production and other characteristics are also considered.« less

Progress toward a new beam measurement of the neutron lifetime

NASA Astrophysics Data System (ADS)

Hoogerheide, Shannon Fogwell; BL2 Collaboration

2017-01-01

Neutron beta decay is the simplest example of nuclear beta decay. A precise value of the neutron lifetime is important for consistency tests of the Standard Model and Big Bang Nucleosynthesis models. The beam neutron lifetime method requires the absolute counting of the decay protons in a neutron beam of precisely known flux. Recent work has resulted in improvements in both the neutron and proton detection systems that should permit a significant reduction in systematic uncertainties. A new measurement of the neutron lifetime using the beam method is underway at the National Institute of Standards and Technology Center for Neutron Research. The projected uncertainty of this new measurement is 1 s. An overview of the measurement, its current status, and the technical improvements will be discussed.

Active-Interrogation Measurements of Induced-Fission Neutrons from Low-Enriched Uranium

DOE Office of Scientific and Technical Information (OSTI.GOV)

J. L. Dolan; M. J. Marcath; M. Flaska

2012-07-01

Protection and control of nuclear fuels is paramount for nuclear security and safeguards; therefore, it is important to develop fast and robust controlling mechanisms to ensure the safety of nuclear fuels. Through both passive- and active-interrogation methods we can use fast-neutron detection to perform real-time measurements of fission neutrons for process monitoring. Active interrogation allows us to use different ranges of incident neutron energy to probe for different isotopes of uranium. With fast-neutron detectors, such as organic liquid scintillation detectors, we can detect the induced-fission neutrons and photons and work towards quantifying a sample’s mass and enrichment. Using MCNPX-PoliMi, amore » system was designed to measure induced-fission neutrons from U-235 and U-238. Measurements were then performed in the summer of 2010 at the Joint Research Centre in Ispra, Italy. Fissions were induced with an associated particle D-T generator and an isotopic Am-Li source. The fission neutrons, as well as neutrons from (n, 2n) and (n, 3n) reactions, were measured with five 5” by 5” EJ-309 organic liquid scintillators. The D-T neutron generator was available as part of a measurement campaign in place by Padova University. The measurement and data-acquisition systems were developed at the University of Michigan utilizing a CAEN V1720 digitizer and pulse-shape discrimination algorithms to differentiate neutron and photon detections. Low-enriched uranium samples of varying mass and enrichment were interrogated. Acquired time-of-flight curves and cross-correlation curves are currently analyzed to draw relationships between detected neutrons and sample mass and enrichment. In the full paper, the promise of active-interrogation measurements and fast-neutron detection will be assessed through the example of this proof-of-concept measurement campaign. Additionally, MCNPX-PoliMi simulation results will be compared to the measured data to validate the MCNPX-PoliMi code when used for active-interrogation simulations.« less

Nuclear accident dosimetry intercomparison studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sims, C.S.

1989-09-01

Twenty-two nuclear accident dosimetry intercomparison studies utilizing the fast-pulse Health Physics Research Reactor at the Oak Ridge National Laboratory have been conducted since 1965. These studies have provided a total of 62 different organizations a forum for discussion of criticality accident dosimetry, an opportunity to test their neutron and gamma-ray dosimetry systems under a variety of simulated criticality accident conditions, and the experience of comparing results with reference dose values as well as with the measured results obtained by others making measurements under identical conditions. Sixty-nine nuclear accidents (27 with unmoderated neutron energy spectra and 42 with eight different shieldedmore » spectra) have been simulated in the studies. Neutron doses were in the 0.2-8.5 Gy range and gamma doses in the 0.1-2.0 Gy range. A total of 2,289 dose measurements (1,311 neutron, 978 gamma) were made during the intercomparisons. The primary methods of neutron dosimetry were activation foils, thermoluminescent dosimeters, and blood sodium activation. The main methods of gamma dose measurement were thermoluminescent dosimeters, radiophotoluminescent glass, and film. About 68% of the neutron measurements met the accuracy guidelines (+/- 25%) and about 52% of the gamma measurements met the accuracy criterion (+/- 20%) for accident dosimetry.« less

Signatures of asymmetry in neutron spectra and images predicted by three-dimensional radiation hydrodynamics simulations of indirect drive implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chittenden, J. P., E-mail: j.chittenden@imperial.ac.uk; Appelbe, B. D.; Manke, F.

2016-05-15

We present the results of 3D simulations of indirect drive inertial confinement fusion capsules driven by the “high-foot” radiation pulse on the National Ignition Facility. The results are post-processed using a semi-deterministic ray tracing model to generate synthetic deuterium-tritium (DT) and deuterium-deuterium (DD) neutron spectra as well as primary and down scattered neutron images. Results with low-mode asymmetries are used to estimate the magnitude of anisotropy in the neutron spectra shift, width, and shape. Comparisons of primary and down scattered images highlight the lack of alignment between the neutron sources, scatter sites, and detector plane, which limits the ability tomore » infer the ρr of the fuel from a down scattered ratio. Further calculations use high bandwidth multi-mode perturbations to induce multiple short scale length flows in the hotspot. The results indicate that the effect of fluid velocity is to produce a DT neutron spectrum with an apparently higher temperature than that inferred from the DD spectrum and which is also higher than the temperature implied by the DT to DD yield ratio.« less

On the possible use of the MASURCA reactor as a flexible, high-intensity, fast neutron beam facility

NASA Astrophysics Data System (ADS)

Dioni, Luca; Jacqmin, Robert; Sumini, Marco; Stout, Brian

2017-09-01

In recent work [1, 2], we have shown that the MASURCA research reactor could be used to deliver a fairly-intense continuous fast neutron beam to an experimental room located next to the reactor core. As a consequence of the MASURCA favorable characteristics and diverse material inventories, the neutron beam intensity and spectrum can be further tailored to meet the users' needs, which could be of interest for several applications. Monte Carlo simulations have been performed to characterize in detail the extracted neutron (and photon) beam entering the experimental room. These numerical simulations were done for two different bare cores: A uranium metallic core (˜30% 235U enriched) and a plutonium oxide core (˜25% Pu fraction, ˜78% 239Pu). The results show that the distinctive resonance energy structures of the two core leakage spectra are preserved at the channel exit. As the experimental room is large enough to house a dedicated set of neutron spectrometry instruments, we have investigated several candidate neutron spectrum measurement techniques, which could be implemented to guarantee well-defined, repeatable beam conditions to users. Our investigation also includes considerations regarding the gamma rays in the beams.

Neutron Stars Rip Each Other Apart to Form Black Hole

NASA Image and Video Library

2014-05-13

This supercomputer simulation shows one of the most violent events in the universe: a pair of neutron stars colliding, merging and forming a black hole. A neutron star is the compressed core left behind when a star born with between eight and 30 times the sun's mass explodes as a supernova. Neutron stars pack about 1.5 times the mass of the sun — equivalent to about half a million Earths — into a ball just 12 miles (20 km) across. As the simulation begins, we view an unequally matched pair of neutron stars weighing 1.4 and 1.7 solar masses. They are separated by only about 11 miles, slightly less distance than their own diameters. Redder colors show regions of progressively lower density. As the stars spiral toward each other, intense tides begin to deform them, possibly cracking their crusts. Neutron stars possess incredible density, but their surfaces are comparatively thin, with densities about a million times greater than gold. Their interiors crush matter to a much greater degree densities rise by 100 million times in their centers. To begin to imagine such mind-boggling densities, consider that a cubic centimeter of neutron star matter outweighs Mount Everest. By 7 milliseconds, tidal forces overwhelm and shatter the lesser star. Its superdense contents erupt into the system and curl a spiral arm of incredibly hot material. At 13 milliseconds, the more massive star has accumulated too much mass to support it against gravity and collapses, and a new black hole is born. The black hole's event horizon — its point of no return — is shown by the gray sphere. While most of the matter from both neutron stars will fall into the black hole, some of the less dense, faster moving matter manages to orbit around it, quickly forming a large and rapidly rotating torus. This torus extends for about 124 miles (200 km) and contains the equivalent of 1/5th the mass of our sun. Scientists think neutron star mergers like this produce short gamma-ray bursts (GRBs). Short GRBs last less than two seconds yet unleash as much energy as all the stars in our galaxy produce over one year. The rapidly fading afterglow of these explosions presents a challenge to astronomers. A key element in understanding GRBs is getting instruments on large ground-based telescopes to capture afterglows as soon as possible after the burst. The rapid notification and accurate positions provided by NASA's Swift mission creates a vibrant synergy with ground-based observatories that has led to dramatically improved understanding of GRBs, especially for short bursts. This video is public domain and can be downloaded at: : svs.gsfc.nasa.gov/goto?11530

Novel Multidimensional Cross-Correlation Data Comparison Techniques for Spectroscopic Discernment in a Volumetrically Sensitive, Moderating Type Neutron Spectrometer

NASA Astrophysics Data System (ADS)

Hoshor, Cory; Young, Stephan; Rogers, Brent; Currie, James; Oakes, Thomas; Scott, Paul; Miller, William; Caruso, Anthony

2014-03-01

A novel application of the Pearson Cross-Correlation to neutron spectral discernment in a moderating type neutron spectrometer is introduced. This cross-correlation analysis will be applied to spectral response data collected through both MCNP simulation and empirical measurement by the volumetrically sensitive spectrometer for comparison in 1, 2, and 3 spatial dimensions. The spectroscopic analysis methods discussed will be demonstrated to discern various common spectral and monoenergetic neutron sources.

Measurements of the total cross section of natBe with thermal neutrons from a photo-neutron source

NASA Astrophysics Data System (ADS)

Liu, L. X.; Wang, H. W.; Ma, Y. G.; Cao, X. G.; Cai, X. Z.; Chen, J. G.; Zhang, G. L.; Han, J. L.; Zhang, G. Q.; Hu, J. F.; Wang, X. H.; Li, W. J.; Yan, Z.; Fu, H. J.

2017-11-01

The total neutron cross sections of natural beryllium in the neutron energy region of 0.007 to 0.1 eV were measured by using a time-of-flight (TOF) technique at the Shanghai Institute of Applied Physics (SINAP). The low energy neutrons were obtained by moderating the high energy neutrons from a pulsed photo-neutron source generated from a 16 MeV electron linac. The time dependent neutron background component was determined by employing the 12.8 cm boron-loaded polyethylene (PEB) (5% w.t.) to block neutron TOF path and using the Monte Carlo simulation methods. The present data was compared with the fold Harvey data with the response function of the photo-neutron source (PNS, phase-1). The present measurement of total cross section of natBe for thermal neutrons based on PNS has been developed for the acquisition of nuclear data needed for the Thorium Molten Salt Reactor (TMSR).

Neutron production for 250 MeV protons bombarding on thick grain-made tungsten target

NASA Astrophysics Data System (ADS)

Zhang, Xueying; Zhang, Yanbin; Ma, Fei; Ju, Yongqin; Chen, Liang; Zhang, Hongbin; Li, Yanyan; Wan, Bo; Wang, Jianguo; Ge, Honglin

2015-08-01

Neutron yield for 250 MeV protons incident on a tungsten target has been measured using the water bath method. The target was made of many randomly placed tungsten grains. Through analyzing the activity of Au foils, the neutron flux distribution in water was obtained. The neutrons slowing down process shows that the neutrons from tungsten have an average energy lower than neutrons from the lead target. The neutron yield was experimentally determined to be 2.02 ± 0.15 neutron/proton. Detailed simulation was also performed with the Geant4 toolkit. Comparison has been made with the experimentally derived neutron yield. It was found that, around 250 MeV, experimental results were described satisfactorily with a combination of high-energy spallation, low-energy neutron reaction and scattering. It was shown that the grain-packed target does not affect much the main neutronic properties, which are of crucial importance for the design of the spallation target.

Applicability of a Bonner Shere technique for pulsed neutron in 120 GeV proton facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanami, T.; Hagiwara, M.; Iwase, H.

2008-02-01

The data on neutron spectra and intensity behind shielding are important for radiation safety design of high-energy accelerators since neutrons are capable of penetrating thick shielding and activating materials. Corresponding particle transport codes--that involve physics models of neutron and other particle production, transportation, and interaction--have been developed and used world-wide [1-8]. The results of these codes have been ensured through plenty of comparisons with experimental results taken in simple geometries. For neutron generation and transport, several related experiments have been performed to measure neutron spectra, attenuation length and reaction rates behind shielding walls of various thicknesses and materials in energymore » range up to several hundred of MeV [9-11]. The data have been used to benchmark--and modify if needed--the simulation modes and parameters in the codes, as well as the reference data for radiation safety design. To obtain such kind of data above several hundred of MeV, Japan-Fermi National Accelerator Laboratory (FNAL) collaboration for shielding experiments has been started in 2007, based on suggestion from the specialist meeting of shielding, Shielding Aspects of Target, Irradiation Facilities (SATIF), because of very limited data available in high-energy region (see, for example, [12]). As a part of this shielding experiment, a set of Bonner sphere (BS) was tested at the antiproton production target facility (pbar target station) at FNAL to obtain neutron spectra induced by a 120-GeV proton beam in concrete and iron shielding. Generally, utilization of an active detector around high-energy accelerators requires an improvement on its readout to overcome burst of secondary radiation since the accelerator delivers an intense beam to a target in a short period after relatively long acceleration period. In this paper, we employ BS for a spectrum measurement of neutrons that penetrate the shielding wall of the pbar target station in FNAL.« less

Development of a generalized perturbation theory method for sensitivity analysis using continuous-energy Monte Carlo methods

DOE PAGES

Perfetti, Christopher M.; Rearden, Bradley T.

2016-03-01

The sensitivity and uncertainty analysis tools of the ORNL SCALE nuclear modeling and simulation code system that have been developed over the last decade have proven indispensable for numerous application and design studies for nuclear criticality safety and reactor physics. SCALE contains tools for analyzing the uncertainty in the eigenvalue of critical systems, but cannot quantify uncertainty in important neutronic parameters such as multigroup cross sections, fuel fission rates, activation rates, and neutron fluence rates with realistic three-dimensional Monte Carlo simulations. A more complete understanding of the sources of uncertainty in these design-limiting parameters could lead to improvements in processmore » optimization, reactor safety, and help inform regulators when setting operational safety margins. A novel approach for calculating eigenvalue sensitivity coefficients, known as the CLUTCH method, was recently explored as academic research and has been found to accurately and rapidly calculate sensitivity coefficients in criticality safety applications. The work presented here describes a new method, known as the GEAR-MC method, which extends the CLUTCH theory for calculating eigenvalue sensitivity coefficients to enable sensitivity coefficient calculations and uncertainty analysis for a generalized set of neutronic responses using high-fidelity continuous-energy Monte Carlo calculations. Here, several criticality safety systems were examined to demonstrate proof of principle for the GEAR-MC method, and GEAR-MC was seen to produce response sensitivity coefficients that agreed well with reference direct perturbation sensitivity coefficients.« less

Impact parameter smearing effects on isospin sensitive observables in heavy ion collisions

NASA Astrophysics Data System (ADS)

Li, Li; Zhang, Yingxun; Li, Zhuxia; Wang, Nan; Cui, Ying; Winkelbauer, Jack

2018-04-01

The validity of impact parameter estimation from the multiplicity of charged particles at low-intermediate energies is checked within the framework of the improved quantum molecular dynamics model. The simulations show that the multiplicity of charged particles cannot estimate the impact parameter of heavy ion collisions very well, especially for central collisions at the beam energies lower than ˜70 MeV/u due to the large fluctuations of the multiplicity of charged particles. The simulation results for the central collisions defined by the charged particle multiplicity are compared to those by using impact parameter b =2 fm and it shows that the charge distribution for 112Sn+112Sn at the beam energy of 50 MeV/u is different evidently for two cases; and the chosen isospin sensitive observable, the coalescence invariant single neutron to proton yield ratio, reduces less than 15% for neutron-rich systems Sn,132124+124Sn at Ebeam=50 MeV/u, while the coalescence invariant double neutron to proton yield ratio does not have obvious difference. The sensitivity of the chosen isospin sensitive observables to effective mass splitting is studied for central collisions defined by the multiplicity of charged particles. Our results show that the sensitivity is enhanced for 132Sn+124Sn relative to that for 124Sn+124Sn , and this reaction system should be measured in future experiments to study the effective mass splitting by heavy ion collisions.

3D reconstruction of carbon nanotube networks from neutron scattering experiments

DOE PAGES

Mahdavi, Mostafa; Baniassadi, Majid; Baghani, Mostafa; ...

2015-09-03

Structure reconstruction from statistical descriptors, such as scattering data obtained using x-rays or neutrons, is essential in understanding various properties of nanocomposites. Scattering based reconstruction can provide a realistic model, over various length scales, that can be used for numerical simulations. In this study, 3D reconstruction of a highly loaded carbon nanotube (CNT)-conducting polymer system based on small and ultra-small angle neutron scattering (SANS and USANS, respectively) data was performed. These light-weight and flexible materials have recently shown great promise for high-performance thermoelectric energy conversion, and their further improvement requires a thorough understanding of their structure-property relationships. The first stepmore » in achieving such understanding is to generate models that contain the hierarchy of CNT networks over nano and micron scales. The studied system is a single walled carbon nanotube (SWCNT)/poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS). SANS and USANS patterns of the different samples containing 10, 30, and 50 wt% SWCNTs were measured. These curves were then utilized to calculate statistical two-point correlation functions of the nanostructure. These functions along with the geometrical information extracted from SANS data and scanning electron microscopy images were used to reconstruct a representative volume element (RVE) nanostructure. Generated RVEs can be used for simulations of various mechanical and physical properties. This work, therefore, introduces a framework for the reconstruction of 3D RVEs of high volume faction nanocomposites containing high aspect ratio fillers from scattering experiments.« less

3D reconstruction of carbon nanotube networks from neutron scattering experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahdavi, Mostafa; Baniassadi, Majid; Baghani, Mostafa

Structure reconstruction from statistical descriptors, such as scattering data obtained using x-rays or neutrons, is essential in understanding various properties of nanocomposites. Scattering based reconstruction can provide a realistic model, over various length scales, that can be used for numerical simulations. In this study, 3D reconstruction of a highly loaded carbon nanotube (CNT)-conducting polymer system based on small and ultra-small angle neutron scattering (SANS and USANS, respectively) data was performed. These light-weight and flexible materials have recently shown great promise for high-performance thermoelectric energy conversion, and their further improvement requires a thorough understanding of their structure-property relationships. The first stepmore » in achieving such understanding is to generate models that contain the hierarchy of CNT networks over nano and micron scales. The studied system is a single walled carbon nanotube (SWCNT)/poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS). SANS and USANS patterns of the different samples containing 10, 30, and 50 wt% SWCNTs were measured. These curves were then utilized to calculate statistical two-point correlation functions of the nanostructure. These functions along with the geometrical information extracted from SANS data and scanning electron microscopy images were used to reconstruct a representative volume element (RVE) nanostructure. Generated RVEs can be used for simulations of various mechanical and physical properties. This work, therefore, introduces a framework for the reconstruction of 3D RVEs of high volume faction nanocomposites containing high aspect ratio fillers from scattering experiments.« less