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Sample records for neutron reference field

  1. Monoenergetic fast neutron reference fields: II. Field characterization

    NASA Astrophysics Data System (ADS)

    Nolte, Ralf; Thomas, David J.

    2011-12-01

    Monoenergetic neutron reference fields are required for the calibration of neutron detectors and dosemeters for various applications ranging from nuclear physics and nuclear data measurements to radiation protection. In a series of two separate publications the metrological aspects of the production and measurement of fast neutrons are reviewed. In the first part, requirements for the nuclear reactions used to produce neutron fields as well as methods for target characterization and the general layout of reference facilities were discussed. This second part focuses on the most important techniques for field characterization and includes the determination of the neutron fluence as well as the spectral neutron distribution and the determination of the fluence of contaminating photons. The measurements are usually carried out relative to reference cross sections which are reviewed in a separate contribution, but for certain conditions 'absolute' methods for neutron measurements can be used which are directly traceable to the international system of units (SI).

  2. Neutron Reference Benchmark Field Specification: ACRR Free-Field Environment (ACRR-FF-CC-32-CL).

    SciTech Connect

    Vega, Richard Manuel; Parma, Edward J.; Griffin, Patrick J.; Vehar, David W.

    2015-07-01

    This report was put together to support the International Atomic Energy Agency (IAEA) REAL- 2016 activity to validate the dosimetry community’s ability to use a consistent set of activation data and to derive consistent spectral characterizations. The report captures details of integral measurements taken in the Annular Core Research Reactor (ACRR) central cavity free-field reference neutron benchmark field. The field is described and an “a priori” calculated neutron spectrum is reported, based on MCNP6 calculations, and a subject matter expert (SME) based covariance matrix is given for this “a priori” spectrum. The results of 31 integral dosimetry measurements in the neutron field are reported.

  3. Characterization of neutron reference fields at US Department of Energy calibration fields.

    PubMed

    Olsher, R H; McLean, T D; Mallett, M W; Seagraves, D T; Gadd, M S; Markham, Robin L; Murphy, R O; Devine, R T

    2007-01-01

    The Health Physics Measurements Group at the Los Alamos National Laboratory (LANL) has initiated a study of neutron reference fields at selected US Department of Energy (DOE) calibration facilities. To date, field characterisation has been completed at five facilities. These fields are traceable to the National Institute for Standards and Technology (NIST) through either a primary calibration of the source emission rate or through the use of a secondary standard. However, neutron spectral variation is caused by factors such as room return, scatter from positioning tables and fixtures, source anisotropy and spectral degradation due to source rabbits and guide tubes. Perturbations from the ideal isotropic point source field may impact the accuracy of instrument calibrations. In particular, the thermal neutron component of the spectrum, while contributing only a small fraction of the conventionally true dose, can contribute a significant fraction of a dosemeter's response with the result that the calibration becomes facility-specific. A protocol has been developed to characterise neutron fields that relies primarily on spectral measurements with the Bubble Technology Industries (BTI) rotating neutron spectrometer (ROSPEC) and the LANL Bonner sphere spectrometer. The ROSPEC measurements were supplemented at several sites by the BTI Simple Scintillation Spectrometer probe, which is designed to extend the ROSPEC upper energy range from 5 to 15 MeV. In addition, measurements were performed with several rem meters and neutron dosemeters. Detailed simulations were performed using the LANL MCNPX Monte Carlo code to calculate the magnitude of source anisotropy and scatter factors. PMID:17496290

  4. Characterisation of three high-energy photon and fast neutron reference radiation fields.

    PubMed

    Behrens, R; Röttger, S

    2008-01-01

    Three reference radiation fields for the purpose of radiation protection were characterised: (1) radiation field R-F, consisting of photons in the energy range of about 6 and 7 MeV and a small neutron contamination; (2) radiation field R-C, consisting of photons with energies of about 4.4 MeV and neutrons with energies up to 2.65 MeV; (3) radiation field R-CF, consisting of photons in the energy range of about 1 and 7 MeV and neutrons with energies about 1.5 MeV. The radiation fields R-F and R-C have previously been defined in the ISO standard 4037. Their neutron components, however, have never been described accurately in the past. The new radiation field R-CF is proposed for the first time. This radiation field can, e.g., be used to calibrate tissue-equivalent proportional counters instruments for measurements at flight altitudes. PMID:19131379

  5. The neutron component of two high-energy photon reference fields.

    PubMed

    Röttger, S; Schäler, K; Behrens, R; Nolte, R; Wissmann, F

    2007-01-01

    The 4.4 MeV photon reference field described in ISO 4037 is produced by the (12)C(p,p')(12)C (E(x) = 4.4389 MeV) reaction using a thick elemental carbon target and a proton beam with an energy of 5.7 MeV. The relative abundance of the isotope (13)C in elemental carbon is 1.10%. Therefore, the 4.4 MeV photon field is contaminated by neutrons produced by the (13)C(p,n) (13)N reaction (Q = -3.003 MeV). The ambient dose equivalent H*(10) produced by these neutrons is of the same order of magnitude as the ambient dose equivalent produced by the 4.4 MeV photons. For the calibration of dosemeters, especially those also sensitive to neutrons, the spectral fluence distribution of these neutrons has to be known in detail. On the other hand, a mixed photon/neutron field is very useful for the calibration of tissue-equivalent proportional counters (TEPC), if this field combines a high-linear energy transfer (LET) component produced by low-energy neutrons and a low-LET component resulting from photons with about the same ambient dose equivalent and energies up to 7 MeV. Such a mixed field was produced at the PTB accelerator facility using a thin CaF(2) + (nat)C target and a 5.7 MeV proton beam. PMID:17675300

  6. Reference neutron fields of the KIGAM for the neutron energy range between 144 keV and 2.5 MeV

    NASA Astrophysics Data System (ADS)

    Kim, G. D.; Woo, H. J.; Choi, H. W.; Park, J. W.; Trinh, T. A.

    2012-08-01

    The Korea Institute of Geoscience and Mineral Resources (KIGAM) is constructing a reference neutron field facility as a national project. Neutron fields consist of mono-energetic sources of 144 keV, 250 keV, 565 keV, and 2.5 MeV have a fluence range from 102 neutrons/cm2/sec to 103 neutrons/cm2/sec. The systems for the reference neutron fields, such as a duo-plasmatron ion source, a 4-MHz beam bunching system, a neutron chamber, an irradiation room, a neutron time-of-flight (n-TOF) system, a long-counter, and a sample moving system, were designed and fabricated. The neutron energies of the reference neutron fields and their spreads were observed by using the n-TOF system. The neutron fluence was measured by using a long-counter for energies below 1 MeV and a proton-recoil counter for 2.5 MeV. The long-counter efficiency was calibrated by the Japan Atomic Energy Agency (JAEA) which had a traceability of mono-energetic neutron sources to both Japanese and international standards. The efficiency of the proton-recoil counter was obtained by using a calculation with detailed construction information.

  7. Validation of IRDFF in 252Cf Standard and IRDF-2002 Reference Neutron Fields

    NASA Astrophysics Data System (ADS)

    Simakov, Stanislav; Capote, Roberto; Greenwood, Lawrence; Griffin, Patrick; Kahler, Albert; Pronyaev, Vladimir; Trkov, Andrej; Zolotarev, Konstantin

    2016-02-01

    The results of validation of the latest release of International Reactor Dosimetry and Fusion File, IRDFF-1.03, in the standard 252Cf(s.f.) and reference 235U(nth,f) neutron benchmark fields are presented. The spectrum-averaged cross sections were shown to confirm IRDFF-1.03 in the 252Cf standard spontaneous fission spectrum; that was not the case for the current recommended spectra for 235U(nth,f). IRDFF was also validated in the spectra of the research reactor facilities ISNF, Sigma-Sigma and YAYOI, which are available in the IRDF-2002 collection. The ISNF facility was re-simulated to remove unphysical oscillations in the spectrum. IRDFF-1.03 was shown to reproduce reasonably well the spectrum-averaged data measured in these fields except for the case of YAYOI.

  8. Neutron Reference Benchmark Field Specifications: ACRR Polyethylene-Lead-Graphite (PLG) Bucket Environment (ACRR-PLG-CC-32-CL).

    SciTech Connect

    Vega, Richard Manuel; Parm, Edward J.; Griffin, Patrick J.; Vehar, David W.

    2015-07-01

    This report was put together to support the International Atomic Energy Agency (IAEA) REAL- 2016 activity to validate the dosimetry community’s ability to use a consistent set of activation data and to derive consistent spectral characterizations. The report captures details of integral measurements taken in the Annular Core Research Reactor (ACRR) central cavity with the Polyethylene-Lead-Graphite (PLG) bucket, reference neutron benchmark field. The field is described and an “a priori” calculated neutron spectrum is reported, based on MCNP6 calculations, and a subject matter expert (SME) based covariance matrix is given for this “a priori” spectrum. The results of 37 integral dosimetry measurements in the neutron field are reported.

  9. Direction distributions of neutrons and reference values of the personal dose equivalent in workplace fields.

    PubMed

    Luszik-Bhadra, M; Bolognese-Milsztajn, T; Boschung, M; Coeck, M; Curzio, G; d'Errico, F; Fiechtner, A; Lacoste, V; Lindborg, L; Reginatto, M; Schuhmacher, H; Tanner, R; Vanhavere, F

    2007-01-01

    Within the EC project EVIDOS, double-differential (energy and direction) fluence spectra were determined by means of novel direction spectrometers. By folding the spectra with fluence-to-dose equivalent conversion coefficients, contributions to H*(10) for 14 directions, and values of the personal dose equivalent Hp(10) and the effective dose E for 6 directions of a person's orientation in the field were determined. The results of the measurements and calculations obtained within the EVIDOS project in workplace fields in nuclear installations in Europe, i.e., at Krümmel (boiling water reactor and transport cask), at Mol (Venus research reactor and fuel facility Belgonucléaire) and at Ringhals (pressurised reactor and transport cask) are presented. PMID:17369265

  10. Neutron Reference Benchmark Field Specification: ACRR 44 Inch Lead-Boron (LB44) Bucket Environment (ACRR-LB44-CC-32-CL).

    SciTech Connect

    Vega, Richard Manuel; Parma, Edward J.; Griffin, Patrick J.; Vehar, David W.

    2015-07-01

    This report was put together to support the International Atomic Energy Agency (IAEA) REAL- 2016 activity to validate the dosimetry community’s ability to use a consistent set of activation data and to derive consistent spectral characterizations. The report captures details of integral measurements taken in the Annular Core Research Reactor (ACRR) central cavity with the 44 inch Lead-Boron (LB44) bucket, reference neutron benchmark field. The field is described and an “a priori” calculated neutron spectrum is reported, based on MCNP6 calculations, and a subject matter expert (SME) based covariance matrix is given for this “a priori” spectrum. The results of 31 integral dosimetry measurements in the neutron field are reported.

  11. 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.

  12. Experimental test of a newly developed single-moderator, multi-detector, directional neutron spectrometer in reference monochromatic fields from 144 keV to 16.5 MeV

    NASA Astrophysics Data System (ADS)

    Bedogni, R.; Gómez-Ros, J. M.; Pola, A.; Bortot, D.; Gentile, A.; Introini, M. V.; Buonomo, B.; Lorenzoli, M.; Mazzitelli, M.; Sacco, D.

    2015-05-01

    A new directional neutron spectrometer called CYSP (CYlindrical SPectrometer) was developed within the NESCOFI@BTF (2011-2013) collaboration. The device, composed by seven active thermal neutron detectors located along the axis of a cylindrical moderator, was designed to simultaneously respond from the thermal domain up to hundreds of MeV neutrons. The new spectrometer condenses the performance of the Bonner Sphere Spectrometer in a single moderator; thus requiring only one exposure to determine the whole spectrum. The CYSP response matrix, determined with MCNP, has been experimentally evaluated with monochromatic reference neutron fields from 144 keV to 16.5 MeV, plus a 252Cf source, available at NPL (Teddington, UK). The results of the experiment confirmed the correctness of the response matrix within an overall uncertainty of ±2.5%. The new active spectrometer CYSP offers an innovative option for real-time monitoring of directional neutron fields as those produced in neutron beam-lines.

  13. Neutron field characteristics of Ciemat's Neutron Standards Laboratory.

    PubMed

    Guzman-Garcia, Karen A; Mendez-Villafañe, Roberto; Vega-Carrillo, Hector Rene

    2015-06-01

    Monte Carlo calculations were carried out to characterize the neutron field produced by the calibration neutron sources of the Neutron Standards Laboratory at the Research Center for Energy, Environment, and Technology (CIEMAT) in Spain. For (241)AmBe and (252)Cf neutron sources, the neutron spectra, the ambient dose equivalent rates and the total neutron fluence rates were estimated. In the calibration hall, there are several items that modify the neutron field. To evaluate their effects different cases were used, from point-like source in vacuum up to the full model. Additionally, using the full model, the neutron spectra were estimated to different distances along the bench; with these spectra, the total neutron fluence and the ambient dose equivalent rates were calculated. The hall walls induce the largest changes in the neutron spectra and the respective integral quantities. The free-field neutron spectrum is modified due the room return effect. PMID:25468287

  14. Characterisation of neutron fields at Cernavoda NPP.

    PubMed

    Cauwels, Vanessa; Vanhavere, Filip; Dumitrescu, Dorin; Chirosca, Alecsandru; Hager, Luke; Million, Marc; Bartz, James

    2013-04-01

    Near a nuclear reactor or a fuel container, mixed neutron/gamma fields are very common, necessitating routine neutron dosimetry. Accurate neutron dosimetry is complicated by the fact that the neutron effective dose is strongly dependent on the neutron energy and the direction distribution of the neutron fluence. Neutron field characterisation is indispensable if one wants to obtain a reliable estimate for the neutron dose. A measurement campaign at CANDU nuclear power plant located in Cernavoda, Romania, was set up to characterise the neutron fields in four different locations and to investigate the behaviour of different neutron personal dosemeters. This investigation intends to assist in choosing a suitable neutron dosimetry system at this nuclear power plant. PMID:22874895

  15. Reference Dosimetry for Fast Neutron and Proton Therapy

    SciTech Connect

    Jones, D.T.L.

    2005-05-24

    Fast neutrons and protons undergo fundamentally different interactions in tissue. The former interact with nuclei, while the latter, as in the case of photons, interact mainly with atomic electrons. Protons do, however, also undergo some nuclear interactions, the probability of which increases with energy. For both modalities the practical instruments for determining the reference absorbed dose in a patient are ionization chambers. These provide indirect determination of absorbed dose because calibration factors measured in standard radiation fields, as well as conversion factors that require knowledge of various physical data, have to be applied. All dosimetry protocols recommend that reference absorbed dose measurements in the clinical situation be made with ionization chambers having 60Co calibration factors traceable to standards laboratories. Neutron doses determined with the current internationally accepted protocol (ICRU Report 45 [1989]) have a relative uncertainty of {+-}4.3% (1{sigma}), while proton doses determined with the two protocols (ICRU Report 59 [1998] and IAEA Report TRS 398 [2000]) presently in use have relative uncertainties (1{sigma}) of {+-}2.6 % and {+-}2.0%, respectively.

  16. Magnetic fields in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Viganò, D.; Pons, J. A.; Miralles, J. A.; Rea, N.

    2015-05-01

    Isolated neutron stars show a diversity in timing and spectral properties, which has historically led to a classification in different sub-classes. The magnetic field plays a key role in many aspects of the neutron star phenomenology: it regulates the braking torque responsible for their timing properties and, for magnetars, it provides the energy budget for the outburst activity and high quiescent luminosities (usually well above the rotational energy budget). We aim at unifying this observational variety by linking the results of the state-of-the-art 2D magneto-thermal simulations with observational data. The comparison between theory and observations allows to place two strong constraints on the physical properties of the inner crust. First, strong electrical currents must circulate in the crust, rather than in the star core. Second, the innermost part of the crust must be highly resistive, which is in principle in agreement with the presence of a novel phase of matter so-called nuclear pasta phase.

  17. Benchmark field study of deep neutron penetration

    NASA Astrophysics Data System (ADS)

    Morgan, J. F.; Sale, K.; Gold, R.; Roberts, J. H.; Preston, C. C.

    1991-06-01

    A unique benchmark neutron field has been established at the Lawrence Livermore National Laboratory (LLNL) to study deep penetration neutron transport. At LLNL, a tandem accelerator is used to generate a monoenergetic neutron source that permits investigation of deep neutron penetration under conditions that are virtually ideal to model, namely the transport of mono-energetic neutrons through a single material in a simple geometry. General features of the Lawrence Tandem (LATAN) benchmark field are described with emphasis on neutron source characteristics and room return background. The single material chosen for the first benchmark, LATAN-1, is a steel representative of Light Water Reactor (LWR) Pressure Vessels (PV). Also included is a brief description of the Little Boy replica, a critical reactor assembly designed to mimic the radiation doses from the atomic bomb dropped on Hiroshima, and its us in neutron spectrometry.

  18. Benchmark field study of deep neutron penetration

    SciTech Connect

    Morgan, J.F.; Sale, K. ); Gold, R.; Roberts, J.H.; Preston, C.C. )

    1991-06-10

    A unique benchmark neutron field has been established at the Lawrence Livermore National Laboratory (LLNL) to study deep penetration neutron transport. At LLNL, a tandem accelerator is used to generate a monoenergetic neutron source that permits investigation of deep neutron penetration under conditions that are virtually ideal to model, namely the transport of mono-energetic neutrons through a single material in a simple geometry. General features of the Lawrence Tandem (LATAN) benchmark field are described with emphasis on neutron source characteristics and room return background. The single material chosen for the first benchmark, LATAN-1, is a steel representative of Light Water Reactor (LWR) Pressure Vessels (PV). Also included is a brief description of the Little Boy replica, a critical reactor assembly designed to mimic the radiation doses from the atomic bomb dropped on Hiroshima, and its us in neutron spectrometry. 18 refs.

  19. International Geomagnetic Reference Field: the third generation.

    USGS Publications Warehouse

    Peddie, N.W.

    1982-01-01

    In August 1981 the International Association of Geomagnetism and Aeronomy revised the International Geomagnetic Reference Field (IGRF). It is the second revision since the inception of the IGRF in 1968. The revision extends the earlier series of IGRF models from 1980 to 1985, introduces a new series of definitive models for 1965-1976, and defines a provisional reference field for 1975- 1980. The revision consists of: 1) a model of the main geomagnetic field at 1980.0, not continuous with the earlier series of IGRF models together with a forecast model of the secular variation of the main field during 1980-1985; 2) definitive models of the main field at 1965.0, 1970.0, and 1975.0, with linear interpolation of the model coefficients specified for intervening dates; and 3) a provisional reference field for 1975-1980, defined as the linear interpolation of the 1975 and 1980 main-field models.-from Author

  20. Cold Neutrons Trapped in External Fields

    SciTech Connect

    Gandolfi, S.; Carlson, J.; Pieper, Steven C.

    2011-01-07

    The properties of inhomogeneous neutron matter are crucial to the physics of neutron-rich nuclei and the crust of neutron stars. Advances in computational techniques now allow us to accurately determine the binding energies and densities of many neutrons interacting via realistic microscopic interactions and confined in external fields. We perform calculations for different external fields and across several shells to place important constraints on inhomogeneous neutron matter, and hence the large isospin limit of the nuclear energy density functionals that are used to predict properties of heavy nuclei and neutron star crusts. We find important differences between microscopic calculations and current density functionals; in particular, the isovector gradient terms are significantly more repulsive than in traditional models, and the spin-orbit and pairing forces are comparatively weaker.

  1. Cold neutrons trapped in external fields.

    SciTech Connect

    Gandolfi, S.; Carlson, J.; Pieper, S. C.

    2011-01-05

    The properties of inhomogeneous neutron matter are crucial to the physics of neutron-rich nuclei and the crust of neutron stars. Advances in computational techniques now allow us to accurately determine the binding energies and densities of many neutrons interacting via realistic microscopic interactions and confined in external fields. We perform calculations for different external fields and across several shells to place important constraints on inhomogeneous neutron matter, and hence the large isospin limit of the nuclear energy density functionals that are used to predict properties of heavy nuclei and neutron star crusts. We find important differences between microscopic calculations and current density functionals; in particular, the isovector gradient terms are significantly more repulsive than in traditional models, and the spin-orbit and pairing forces are comparatively weaker.

  2. High Flux Isotope Reactor cold neutron source reference design concept

    SciTech Connect

    Selby, D.L.; Lucas, A.T.; Hyman, C.R.

    1998-05-01

    In February 1995, Oak Ridge National Laboratory`s (ORNL`s) deputy director formed a group to examine the need for upgrades to the High Flux Isotope Reactor (HFIR) system in light of the cancellation of the Advanced neutron Source Project. One of the major findings of this study was that there was an immediate need for the installation of a cold neutron source facility in the HFIR complex. In May 1995, a team was formed to examine the feasibility of retrofitting a liquid hydrogen (LH{sub 2}) cold source facility into an existing HFIR beam tube. The results of this feasibility study indicated that the most practical location for such a cold source was the HB-4 beam tube. This location provides a potential flux environment higher than the Institut Laue-Langevin (ILL) vertical cold source and maximizes the space available for a future cold neutron guide hall expansion. It was determined that this cold neutron beam would be comparable, in cold neutron brightness, to the best facilities in the world, and a decision was made to complete a preconceptual design study with the intention of proceeding with an activity to install a working LH{sub 2} cold source in the HFIR HB-4 beam tube. During the development of the reference design the liquid hydrogen concept was changed to a supercritical hydrogen system for a number of reasons. This report documents the reference supercritical hydrogen design and its performance. The cold source project has been divided into four phases: (1) preconceptual, (2) conceptual design and testing, (3) detailed design and procurement, and (4) installation and operation. This report marks the conclusion of the conceptual design phase and establishes the baseline reference concept.

  3. One directional polarized neutron reflectometry with optimized reference layer method

    NASA Astrophysics Data System (ADS)

    Masoudi, S. Farhad; Jahromi, Saeed S.

    2012-09-01

    In the past decade, several neutron reflectometry methods for determining the modulus and phase of the complex reflection coefficient of an unknown multilayer thin film have been worked out among which the method of variation of surroundings and reference layers are of highest interest. These methods were later modified for measurement of the polarization of the reflected beam instead of the measurement of the intensities. In their new architecture, these methods not only suffered from the necessity of change of experimental setup but also another difficulty was added to their experimental implementations. This deficiency was related to the limitations of the technology of the neutron reflectometers that could only measure the polarization of the reflected neutrons in the same direction as the polarization of the incident beam. As the instruments are limited, the theory has to be optimized so that the experiment could be performed. In a recent work, we developed the method of variation of surroundings for one directional polarization analysis. In this new work, the method of reference layer with polarization analysis has been optimized to determine the phase and modulus of the unknown film with measurement of the polarization of the reflected neutrons in the same direction as the polarization of the incident beam.

  4. Magnetic field decay in isolated neutron stars

    NASA Technical Reports Server (NTRS)

    Goldreich, Peter; Reisenegger, Andreas

    1992-01-01

    Three mechanisms that promote the loss of magnetic flux from an isolated neutron star - Ohmic decay, ambipolar diffusion, and Hall drift - are investigated. Equations of motions are solved for charged particles in the presence of a magnetic field and a fixed background of neutrons, while allowing for the creation and destruction of particles by weak interactions. Although these equations apply to normal neutrons and protons, the present interpretations of their solutions are extended to cover cases of neutron superfluidity and proton superconductivity. The equations are manipulated to prove that, in the presence of a magnetic force, the charged particles cannot be simultaneously in magnetostatic equilibrium and chemical equilibrium with the neutrons. The application of the results to real neutron stars is discussed.

  5. Polarized neutron reflectometry in high magnetic fields

    SciTech Connect

    Fritzsche, H.

    2005-11-15

    A simple method is described to maintain the polarization of a neutron beam on its way through the large magnetic stray fields produced by a vertical field of a cryomagnet with a split-coil geometry. The two key issues are the proper shielding of the neutron spin flippers and an additional radial field component in order to guide the neutron spin through the region of the null point (i.e., point of reversal for the vertical field component). Calculations of the neutron's spin rotation as well as polarized neutron reflectometry experiments on an ErFe{sub 2}/DyFe{sub 2} multilayer show the perfect performance of the used setup. The recently commissioned cryomagnet M5 with a maximum vertical field of up to 7.2 T in asymmetric mode for polarized neutrons and 9 T in symmetric mode for unpolarized neutrons was used on the C5 spectrometer in reflectometry mode, at the NRU reactor in Chalk River, Canada.

  6. Magnetic Fields in Superconducting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Lander, S. K.

    2013-02-01

    The interior of a neutron star is likely to be predominantly a mixture of superfluid neutrons and superconducting protons. This results in the quantization of the star’s magnetic field into an array of thin flux tubes, producing a macroscopic force very different from the Lorentz force of normal matter. We show that in an axisymmetric superconducting equilibrium the behavior of a magnetic field is governed by a single differential equation. Solving this, we present the first self-consistent superconducting neutron star equilibria with poloidal and mixed poloidal-toroidal fields and also give the first quantitative results for the corresponding magnetically induced distortions to the star. The poloidal component is dominant in all our configurations. We suggest that the transition from normal to superconducting matter in a young neutron star may cause a large-scale field rearrangement.

  7. Review of neutron calibration facilities and monitoring techniques: new needs for emerging fields.

    PubMed

    Gressier, V

    2014-10-01

    Neutron calibration facilities and monitoring techniques have been developed since the middle of the 20th century to support research and nuclear power energy development. The technical areas needing reference neutron fields and related instruments were mainly cross section measurements, radiation protection, dosimetry and fission reactors, with energy ranging from a few millielectronvolts to about 20 MeV. The reference neutron fields and calibration techniques developed for these purposes will be presented in this paper. However, in recent years, emerging fields have brought new needs for calibration facilities and monitoring techniques. These new challenges for neutron metrology will be exposed with their technical difficulties. PMID:24344349

  8. Characterization of a Pulse Neutron Source Yield under Field Conditions

    SciTech Connect

    Barzilov, Alexander; Novikov, Ivan; Womble, Phillip C.; Hopper, Lindsay

    2009-03-10

    Technique of rapid evaluation of a pulse neutron sources such as neutron generators under field conditions has been developed. The phoswich sensor and pulse-shape discrimination techniques have been used for the simultaneous measurements of fast neutrons, thermal neutrons, and photons. The sensor has been calibrated using activation neutron detectors and a pulse deuterium-tritium fusion neutron source.

  9. Intercomparison of radiation protection instrumentation in a pulsed neutron field

    NASA Astrophysics Data System (ADS)

    Caresana, M.; Denker, A.; Esposito, A.; Ferrarini, M.; Golnik, N.; Hohmann, E.; Leuschner, A.; Luszik-Bhadra, M.; Manessi, G.; Mayer, S.; Ott, K.; Röhrich, J.; Silari, M.; Trompier, F.; Volnhals, M.; Wielunski, M.

    2014-02-01

    In the framework of the EURADOS working group 11, an intercomparison of active neutron survey meters was performed in a pulsed neutron field (PNF). The aim of the exercise was to evaluate the performances of various neutron instruments, including commercially available rem-counters, personal dosemeters and instrument prototypes. The measurements took place at the cyclotron of the Helmholtz-Zentrum Berlin für Materialien und Energie GmbH. The cyclotron is routinely used for proton therapy of ocular tumours, but an experimental area is also available. For the therapy the machine accelerates protons to 68 MeV. The interaction of the proton beam with a thick tungsten target produces a neutron field with energy up to about 60 MeV. One interesting feature of the cyclotron is that the beam can be delivered in bursts, with the possibility to modify in a simple and flexible way the burst length and the ion current. Through this possibility one can obtain radiation bursts of variable duration and intensity. All instruments were placed in a reference position and irradiated with neutrons delivered in bursts of different intensity. The analysis of the instrument response as a function of the burst charge (the total electric charge of the protons in the burst shot onto the tungsten target) permitted to assess for each device the dose underestimation due to the time structure of the radiation field. The personal neutron dosemeters were exposed on a standard PMMA slab phantom and the response linearity was evaluated.

  10. The International Geomagnetic Reference Field, 2005

    USGS Publications Warehouse

    Rukstales, Kenneth S.; Love, Jeffrey J.

    2007-01-01

    This is a set of five world charts showing the declination, inclination, horizontal intensity, vertical component, and total intensity of the Earth's magnetic field at mean sea level at the beginning of 2005. The charts are based on the International Geomagnetic Reference Field (IGRF) main model for 2005 and secular change model for 2005-2010. The IGRF is referenced to the World Geodetic System 1984 ellipsoid. Additional information about the USGS geomagnetism program is available at: http://geomag.usgs.gov/

  11. Use of Neutron Benchmark Fields for the Validation of Dosimetry Cross Sections

    NASA Astrophysics Data System (ADS)

    Griffin, Patrick

    2016-02-01

    The evolution of validation metrics for dosimetry cross sections in neutron benchmark fields is explored. The strength of some of the metrics in providing validation evidence is examined by applying them to the 252Cf spontaneous fission standard neutron benchmark field, the 235U thermal neutron fission reference benchmark field, the ACRR pool-type reactor central cavity reference benchmark fields, and the SPR-III fast burst reactor central cavity. The IRDFF dosimetry cross section library is used in the validation study and observations are made on the amount of coverage provided to the library contents by validation data available in these benchmark fields.

  12. Magnetic field evolution in superconducting neutron stars

    NASA Astrophysics Data System (ADS)

    Graber, Vanessa; Andersson, Nils; Glampedakis, Kostas; Lander, Samuel K.

    2015-10-01

    The presence of superconducting and superfluid components in the core of mature neutron stars calls for the rethinking of a number of key magnetohydrodynamical notions like resistivity, the induction equation, magnetic energy and flux-freezing. Using a multifluid magnetohydrodynamics formalism, we investigate how the magnetic field evolution is modified when neutron star matter is composed of superfluid neutrons, type-II superconducting protons and relativistic electrons. As an application of this framework, we derive an induction equation where the resistive coupling originates from the mutual friction between the electrons and the vortex/fluxtube arrays of the neutron and proton condensates. The resulting induction equation allows the identification of two time-scales that are significantly different from those of standard magnetohydrodynamics. The astrophysical implications of these results are briefly discussed.

  13. Icy Schwedeneck field may provide reference

    SciTech Connect

    Not Available

    1985-05-01

    Situated in an icy region of the Baltic Sea, Germany's first offshore field may provide the nation with the reference needed to encroach the arctic market. Production began last winter from one platform in the Schwedeneck-See field, located about three miles off the Baltic Coast. Total reserves have been estimated at more than 18 million bbl. Yearly production by the end of 1986 has been estimated at 294,000 bbl. The first two production platforms were installed in late 1983 in water depths ranging from 50 to 80 ft. Because of the ice hazards inherent in the Baltic, the platforms are concrete designed with steel decks.

  14. Anomalies of neutron field of the Earth.

    NASA Astrophysics Data System (ADS)

    Plotnikova, Natalia

    This work is devoted to the researches of time and spatial heterogeneity of thermal neurtron flux (Fn) density in the troposphere of the Earth. We had already received the values of thermal neutron flux density on the surface of the Earth in the European part of Russia. The large-scale monitoring of thermal neutron flux density was carried out on structural cross-section from Drake Strait in the Atlantic Ocean to the high latitudes of Arctic. We observe the increase of Fn from 44о N to 59о N, from 0,4 to 2,9 •10-3 н/(c•cм2). The values of Fn were received in latitude Novorossiysk (0,4•10-3 n/(c•sm2)) , Moskow (0,7-1,5•10-3 n/(c•sm2)), Arhangelsk (1,3•10-3 n/(c•sm2)). High-rise dependance of the thermal neutron flux density on the surface of the Earth and in troposphere during transcontinental flights was researched. With the increasing of height from 0 to 8000 m the thermal neutron flux density rises to 180•10-3 н/(c•cм2) The measurements were carried out in latitude of Spitsbergen. The value of thermal neutron flux density on the North pole was measured. Fn is equal to 0,7•10-3 n/(c•sm2)) 890 20/ in North latitude. Recently it has been shown, that thermal neutrons render appreciable influence on alive organisms [Matveeva and etc., 2004, Masunaga S., 2001]. Abmormal increases of thermal neutron flux density are revealed in flora biogeocenosis. Daily background Fn demonstrate the specific abnormal flares for every biocenosis or biotope long-lasting (for tens of minutes) Fn - meaning during the «flares» in biogeocenosis depends on the contains of flora community and can reach 104 n/(с m2). [Plotnikova N.V., Siroeshkin A.V., 2005]. The researches of the neutron field in the World Ocean were received at the time of transatlantic expedition by the programme of RAS «Meridian» (2006, 2008). Abnormal increasing Fn had being observed in the area of equator and between 310N to 540N and 330S to 530S Moreover, the coordinates of these

  15. Dosimetry in mixed neutron-gamma fields

    SciTech Connect

    Remec, I.

    1998-04-01

    The gamma field accompanying neutrons may, in certain circumstances, play an important role in the analysis of neutron dosimetry and even in the interpretation of radiation induced steel embrittlement. At the High Flux Isotope Reactor pressure vessel the gamma induced reactions dominate the responses of {sup 237}Np and {sup 238}U dosimeters, and {sup 9}Be helium accumulation fluence monitors. The gamma induced atom displacement rate in steel is higher than corresponding neutron rate, and is the cause of ``accelerated embrittlement`` of HFIR materials. In a large body of water, adjacent to a fission plate, photofissions contribute significantly to the responses of fission monitors and need to be taken into account if the measurements are used for the qualification of the transport codes and cross-section libraries.

  16. Physics in Strong Magnetic Fields Near Neutron Stars.

    ERIC Educational Resources Information Center

    Harding, Alice K.

    1991-01-01

    Discussed are the behaviors of particles and energies in the magnetic fields of neutron stars. Different types of possible research using neutron stars as a laboratory for the study of strong magnetic fields are proposed. (CW)

  17. Electromagnetic field dynamics in Binary Neutron Stars

    NASA Astrophysics Data System (ADS)

    Palenzuela, Carlos; Anderson, Matthew; Hirschmann, Eric; Lehner, Luis; Liebling, Steven; Neilsen, David; Motl, Patrick

    2011-04-01

    Neutron star mergers represent one of the most promising sources of gravitational waves (GW) within the bandwidth of advLIGO. In addition to GW, strong magnetic fields may offer the possibility of a characteristic electromagnetic signature allowing for concurrent detection. In this talk we present results from numerical evolutions of such mergers, studying the dynamics of both the gravitational and electromagnetic degrees of freedom.

  18. Neutron field measurements for alara purposes around a Van de Graaff accelerator building.

    PubMed

    Kockerols, P; Lebacq, A L; Gasparro, J; Hult, M; Janssens, H; Lövestam, G; Vanhavere, F

    2004-01-01

    The Institute for Reference Materials and Measurements operates a 7.0 MV Van de Graaff accelerator to generate monoenergetic neutron radiation for experimental applications. Owing to increased intensities of generated neutron fields and the more stringent regulation related to the maximum dose for the public, a concrete shielding wall surrounding the experimental building was constructed. This paper presents a study aiming at evaluating the effect of the shielding on the neutron field outside the wall. For this purpose, the following measurements were carried out around the building: (1) cartography of the neutron field for different experimental conditions; (2) measurement of neutron spectra using multiple Bonner spheres; (3) activation measurements using gold discs followed by low-level gamma spectrometry. From the measurements, it can be concluded that the wall fulfils its purpose to reduce the neutron dose rate to the surrounding area to an acceptable level. PMID:15353736

  19. Characterization of neutron calibration fields at the TINT's 50 Ci americium-241/beryllium neutron irradiator

    NASA Astrophysics Data System (ADS)

    Liamsuwan, T.; Channuie, J.; Ratanatongchai, W.

    2015-05-01

    Reliable measurement of neutron radiation is important for monitoring and protection in workplace where neutrons are present. Although Thailand has been familiar with applications of neutron sources and neutron beams for many decades, there is no calibration facility dedicated to neutron measuring devices available in the country. Recently, Thailand Institute of Nuclear Technology (TINT) has set up a multi-purpose irradiation facility equipped with a 50 Ci americium-241/beryllium neutron irradiator. The facility is planned to be used for research, nuclear analytical techniques and, among other applications, calibration of neutron measuring devices. In this work, the neutron calibration fields were investigated in terms of neutron energy spectra and dose equivalent rates using Monte Carlo simulations, an in-house developed neutron spectrometer and commercial survey meters. The characterized neutron fields can generate neutron dose equivalent rates ranging from 156 μSv/h to 3.5 mSv/h with nearly 100% of dose contributed by neutrons of energies larger than 0.01 MeV. The gamma contamination was less than 4.2-7.5% depending on the irradiation configuration. It is possible to use the described neutron fields for calibration test and routine quality assurance of neutron dose rate meters and passive dosemeters commonly used in radiation protection dosimetry.

  20. Neutron field characterisation at mixed oxide fuel plant.

    PubMed

    Passmore, C; Million, M; Kirr, M; Bartz, J; Akselrod, M S; Devita, A; Berard, J

    2012-06-01

    A neutron field characterisation was conducted at the AREVA Melox Plant to determine the response of passive and active neutron dosemeters for several stages in the mixed oxide fuel manufacturing process. Landauer Europe provides radiation dosimetry to many contractors working at the Melox site. The studies were conducted to assist in determining the neutron radiation fields the workers are exposed to routinely, evaluate the need for specific neutron correction factors and to ensure that the most accurate neutron dose is reported for the Melox Plant workers. PMID:22028415

  1. An in-phantom comparison of neutron fields for BNCT

    SciTech Connect

    Woollard, J.E.; Blue, T.E.; Capala, J.

    1998-01-01

    Previously, the authors have developed the in-phantom neutron field assessment parameters T and D (Tumor) for the evaluation of epithermal neutron fields for use in BNCT. These parameters are based on an energy-spectrum-dependent neutron normal-tissue RBE and the treatment planning methodology of Gahbauer and his co-workers, which includes the effects of dose fractionation. In this paper, these neutron field assessment parameters were applied to The Ohio State University (OSU) design of an Accelerator Based Neutron Source (ABNS) (hereafter called the OSU-ABNS) and the Brookhaven Medical Research Reactor (BMRR) epithermal neutron beam (hereafter called the BMRR-ENB), in order to judge the suitability of the OSU-ABNS for BNCT. The BMRR-ENB was chosen as the basis for comparison because it is presently being used in human clinical trials of BNCT and because it is the standard to which other neutron beams are most often compared.

  2. Reference data file for neutron spectrum adjustment and related radiation damage calculations

    SciTech Connect

    Zsolnay, E.M. ); Nolthenius, H.J.; Greenwood, L.R.; Szondi, E.J. )

    1990-08-01

    The REAL-88 interlaboratory exercise organized by IAEA resulted in a neutron metrology file. (NMF-90) comprising problem dependent data for benchmark neutron fields, furthermore, nuclear data and computer programs for neutron spectrum adjustment and radiation damage parameter calculations for the service life assessment of nuclear facilities. Calculation results of some experienced laboratories are also present. This paper describes and analyses the content of the neutron metrology file and outlines the most important problems and tasks to be solved in the field of radiation damage parameter calculations. 14 refs., 2 figs., 1 tab.

  3. Magnetic field induced differential neutron phase contrast imaging

    SciTech Connect

    Strobl, M.; Treimer, W.; Walter, P.; Keil, S.; Manke, I.

    2007-12-17

    Besides the attenuation of a neutron beam penetrating an object, induced phase changes have been utilized to provide contrast in neutron and x-ray imaging. In analogy to differential phase contrast imaging of bulk samples, the refraction of neutrons by magnetic fields yields image contrast. Here, it will be reported how double crystal setups can provide quantitative tomographic images of magnetic fields. The use of magnetic air prisms adequate to split the neutron spin states enables a distinction of field induced phase shifts and these introduced by interaction with matter.

  4. The Neutron Imaging System Fielded at the National Ignition Facility

    SciTech Connect

    Fittinghoff, D N; Atkinson, D P; Bower, D E; Drury, O B; Dzenitis, J M; Felker, B; Frank, M; Liddick, S N; Moran, M J; Roberson, G P; Weiss, P B; Grim, G P; Aragonez, R J; Archuleta, T N; Batha, S H; Clark, D D; Clark, D J; Danly, C R; Day, R D; Fatherley, V E; Finch, J P; Garcia, F P; Gallegos, R A; Guler, N; Hsu, A H; Jaramillo, S A; Loomis, E N; Mares, D; Martinson, D D; Merrill, F E; Morgan, G L; Munson, C; Murphy, T J; Oertel, J A; Polk, P J; Schmidt, D W; Tregillis, I L; Valdez, A C; Volegov, P L; Wang, T F; Wilde, C H; Wilke, M D; Wilson, D C; Buckles, R A; Cradick, J R; Kaufman, M I; Lutz, S S; Malone, R M; Traille, A

    2011-10-24

    We have fielded a neutron imaging system at the National Ignition Facility to collect images of fusion neutrons produced in the implosion of inertial confinement fusion experiments and scattered neutrons from (n, n') reactions of the source neutrons in the surrounding dense material. A description of the neutron imaging system will be presented, including the pinhole array aperture, the line-of-sight collimation, the scintillator-based detection system and the alignment systems and methods. Discussion of the alignment and resolution of the system will be presented. We will also discuss future improvements to the system hardware.

  5. The neutron imaging system fielded at the National Ignition Facility

    NASA Astrophysics Data System (ADS)

    Fittinghoff, D. N.; Atkinson, D. P.; Bower, D. E.; Drury, O. B.; Dzenitis, J. M.; Frank, M.; Liddick, S. N.; Moran, M. J.; Roberson, G. P.; Weiss, P. B.; Grim, G. P.; Aragonez, R. J.; Archuleta, T. N.; Batha, S. H.; Clark, D. D.; Clark, D. J.; Danly, C. R.; Day, R. D.; Fatherley, V. E.; Finch, J. P.; Garcia, F. P.; Gallegos, R. A.; Guler, N.; Hsu, A. H.; Jaramillo, S. A.; Loomis, E. N.; Mares, D.; Martinson, D. D.; Merrill, F. E.; Morgan, G. L.; Munson, C.; Murphy, T. J.; Oertel, J. A.; Polk, P. J.; Schmidt, D. W.; Tregillis, I. L.; Valdez, A. C.; Volegov, P. L.; Wang, T. F.; Wilde, C. H.; Wilke, M. D.; Wilson, D. C.; Buckles, R. A.; Cradick, J. R.; Kaufman, M. I.; Lutz, S. S.; Malone, R. M.; Traille, A.

    2013-11-01

    We have fielded a neutron imaging system at the National Ignition Facility to collect images of fusion neutrons produced in the implosion of inertial confinement fusion experiments and scattered neutrons from (n, n') reactions of the source neutrons in the surrounding dense material. A description of the neutron imaging system is presented, including the pinhole array aperture, the line-of-sight collimation, the scintillator-based detection system and the alignment systems and methods. Discussion of the alignment and resolution of the system is presented. We also discuss future improvements to the system hardware.

  6. Does mass accretion lead to field decay in neutron stars

    NASA Technical Reports Server (NTRS)

    Shibazaki, N.; Murakami, T.; Shaham, Jacob; Nomoto, K.

    1989-01-01

    The recent discovery of cyclotron lines from gamma-ray bursts indicates that the strong magnetic fields of isolated neutron stars might not decay. The possible inverse correlation between the strength of the magnetic field and the mass accreted by the neutron star suggests that mass accretion itself may lead to the decay of the magnetic field. The spin and magnetic field evolution of the neutron star was calculated under the hypothesis of the accretion-induced field decay. It is shown that the calculated results are consistent with the observations of binary and millisecond radio pulsars.

  7. Personnel neutron dose assessment upgrade: Volume 2, Field neutron spectrometer for health physics applications

    SciTech Connect

    Brackenbush, L.W.; Reece, W.D.; Miller, S.D.; Endres, G.W.R.; Durham, J.S.; Scherpelz, R.I.; Tomeraasen, P.L.; Stroud, C.M.; Faust, L.G.; Vallario, E.J.

    1988-07-01

    Both the (ICRP) and the (NCPR) have recommended an increase in neutron quality factors and the adoption of effective dose equivalent methods. The series of reports entitled Personnel Neutron Dose Assessment Upgrade (PNL-6620) addresses these changes. Volume 1 in this series of reports (Personnel Neutron Dosimetry Assessment) provided guidance on the characteristics, use, and calibration of personnel neutron dosimeters in order to meet the new recommendations. This report, Volume 2: Field Neutron Spectrometer for Health Physics Applications describes the development of a portable field spectrometer which can be set up for use in a few minutes by a single person. The field spectrometer described herein represents a significant advance in improving the accuracy of neutron dose assessment. It permits an immediate analysis of the energy spectral distribution associated with the radiation from which neutron quality factor can be determined. It is now possible to depart from the use of maximum Q by determining and realistically applying a lower Q based on spectral data. The field spectrometer is made up of two modules: a detector module with built-in electronics and an analysis module with a IBM PC/reg sign/-compatible computer to control the data acquisition and analysis of data in the field. The unit is simple enough to allow the operator to perform spectral measurements with minimal training. The instrument is intended for use in steady-state radiation fields with neutrons energies covering the fission spectrum range. The prototype field spectrometer has been field tested in plutonium processing facilities, and has been proven to operate satisfactorily. The prototype field spectrometer uses a /sup 3/He proportional counter to measure the neutron energy spectrum between 50 keV and 5 MeV and a tissue equivalent proportional counter (TEPC) to measure absorbed neutron dose.

  8. Methods of approximation of reference fields of different classes

    NASA Astrophysics Data System (ADS)

    Kolesova, Valentina I.

    1993-11-01

    The summary geomagnetic field on the reference field for the regional anomalies is surface of the Earth consists of the follow- the sum of the main geomagnetic field and ing components: the intermediate anomalies. Since the components mentioned above have the F0 = Fm + Fim + Fr + F1 + F (1) different space-spectral characteristics, different methods are used for the analytiwhere cal descriptions. The main geomagnetic field, being the global reference field, is approximated by F0 - the observed geomagnetic field the optimal way as a spherical harmonic Fm - the main geomagnetic field series [1]: Fim - the field of the intermediate anoma- n lies Fr - the field of the regional anomalies X = (g cosm\\ + n=i m=O F1 - the field of the local anomalies, - the external geomagnetic field.

  9. Rotational and magnetic field instabilities in neutron stars

    SciTech Connect

    Kokkotas, Kostas D.

    2014-01-14

    In this short review we present recent results on the dynamics of neutron stars and their magnetic fields. We discuss the progress that has been made, during the last 5 years, in understanding the rotational instabilities with emphasis to the one due to the f-mode, the possibility of using gravitational wave detection in constraining the parameters of neutron stars and revealing the equation of state as well as the detectability of gravitational waves produced during the unstable phase of a neutron star’s life. In addition we discuss the dynamics of extremely strong magnetic fields observed in a class of neutron stars (magnetars). Magnetic fields of that strength are responsible for highly energetic phenomena (giant flares) and we demonstrate that the analysis of the emitted electromagnetic radiation can lead in constraining the parameters of neutron stars. Furthermore, we present our results from the study of such violent phenomena in association with the emission of gravitational radiation.

  10. GCR Simulator Reference Field and a Spectral Approach for Laboratory Simulation

    NASA Technical Reports Server (NTRS)

    Slaba, Tony C.; Blattnig, Steve R.; Norbury, John W.; Rusek, Adam; La Tessa, Chiara; Walker, Steven A.

    2015-01-01

    The galactic cosmic ray (GCR) simulator at the NASA Space Radiation Laboratory (NSRL) is intended to deliver the broad spectrum of particles and energies encountered in deep space to biological targets in a controlled laboratory setting. In this work, certain aspects of simulating the GCR environment in the laboratory are discussed. Reference field specification and beam selection strategies at NSRL are the main focus, but the analysis presented herein may be modified for other facilities. First, comparisons are made between direct simulation of the external, free space GCR field and simulation of the induced tissue field behind shielding. It is found that upper energy constraints at NSRL limit the ability to simulate the external, free space field directly (i.e. shielding placed in the beam line in front of a biological target and exposed to a free space spectrum). Second, variation in the induced tissue field associated with shielding configuration and solar activity is addressed. It is found that the observed variation is likely within the uncertainty associated with representing any GCR reference field with discrete ion beams in the laboratory, given current facility constraints. A single reference field for deep space missions is subsequently identified. Third, an approach for selecting beams at NSRL to simulate the designated reference field is presented. Drawbacks of the proposed methodology are discussed and weighed against alternative simulation strategies. The neutron component and track structure characteristics of the simulated field are discussed in this context.

  11. Reference Materials for Reactor Neutron Fluence Rate and Temperature Measurements

    NASA Astrophysics Data System (ADS)

    Ingelbrecht, C.

    2003-06-01

    Certified reference materials are distributed by the European Commission through the BCR® programme (over 500 CRMs) including a series of activation and fission monitor materials originally proposed by the Euratom Working Group on Reactor Dosimetry. The current range (18 CRMs) includes materials to cover the complete energy spectrum, and suitable for different irradiation times. Fission monitors are 238UO2 or 237NpO2 in the form of microspheres. Activation monitors are high purity metals (Ni, Cu, Al, Fe, Nb, Rh, or Ti), certified for interfering trace impurities, or dilute aluminium-based alloys. Reference materials newly certified are IRMM-530R A1-0.1%Au, replacing the exhausted IRMM-530 material, used as comparator for k0- standardisation, and three new Al-Co alloys (0.01, 0.1 and 1.0%Co). Others in the process of certification are A1-0.1%Ag and A1-2%Sc for thermal and epithermal fluence rate measurements and two uranium-doped glass materials intended for dosimetry by the fission-track technique. Various alloy compositions have been prepared for use as melt-wire temperature monitors with melting points ranging from 198 to 327ºC.

  12. Evaluation of neutron radiation field in carbon ion therapy

    NASA Astrophysics Data System (ADS)

    Xu, Jun-Kui; Su, You-Wu; Li, Wu-Yuan; Yan, Wei-Wei; Chen, Xi-Meng; Mao, Wang; Pang, Cheng-Guo

    2016-01-01

    Carbon ions have significant advantages in tumor therapy because of their physical and biological properties. In view of the radiation protection, the safety of patients is the most important issue in therapy processes. Therefore, the effects of the secondary particles produced by the carbon ions in the tumor therapy should be carefully considered, especially for the neutrons. In the present work, the neutron radiation field induced by carbon ions was evaluated by using the FLUKA code. The simulated results of neutron energy spectra and neutron dose was found to be in good agreement with the experiment data. In addition, energy deposition of carbon ions and neutrons in tissue-like media was studied, it is found that the secondary neutron energy deposition is not expected to exceed 1% of the carbon ion energy deposition in a typical treatment.

  13. Field parameters and dosimetric characteristics of a fast neutron calibration facility: experimental and Monte Carlo evaluations

    NASA Astrophysics Data System (ADS)

    Bedogni, R.; Gualdrini, G.; Monteventi, F.

    2002-01-01

    At the ENEA Institute for Radiation Protection (IRP) the fast neutron calibration facility consists of a remote control device which allows locating different sources (Am-Be, Pu-Li, bare and D 2O moderated 252Cf) at the reference position, at the desired height from the floor, inside a 10×10×3 m 3 irradiation room. Either the ISO reference sources or the Pu-Li source have been characterised in terms of uncollided H*(10) and neutron fluence according to the ISO calibration procedures. A spectral fluence mapping, carried out with the Monte Carlo Code MCNP TM, allowed characterising the calibration point, in scattered field conditions, according to the most recent international recommendations. Moreover, the irradiation of personal dosemeters on the ISO water filled slab phantom was simulated to determine the field homogeneity of the calibration area and the variability of the neutron field (including the backscattered component) along the phantom surface. At the ENEA Institute for Radiation Protection the calibration of neutron area monitors as well as personal dosemeters can now be performed according to the international standards, at the same time guaranteeing suitable conditions for research and qualification purposes in the field of neutron dosimetry.

  14. A proposed International Geomagnetic Reference Field for 1965- 1985.

    USGS Publications Warehouse

    Peddie, N.W.; Fabiano, E.B.

    1982-01-01

    A set of spherical harmonic models describing the Earth's main magnetic field from 1965 to 1985 has been developed and is proposed as the next revision of the International Geomagnetic Reference Field (IGRF). A tenth degree and order spherical harmonic model of the main field was derived from Magsat data. A series of eighth degree and order spherical harmonic models of the secular variation of the main field was derived from magnetic observatory annual mean values. Models of the main field at 1965, 1970, 1975, and 1980 were obtained by extrapolating the main-field model using the secular variation models.-Authors spherical harmonic models Earth main magnetic field Magsat data

  15. Physics in strong magnetic fields near neutron stars

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    1991-01-01

    Electromagnetic phenomena occurring in the strong magnetic fields of neutron stars are currently of great interest in high-energy astrophysics. Observations of rotation rate changes and cyclotron lines in pulsars and gamma-ray bursts indicate that surface magnetic fields of neutron stars often exceed a trillion gauss. In fields this strong, where electrons behave much as if they were in bound atomic states, familiar processes undergo profound changes, and exotic processes become important. Strong magnetic fields affect the physics in several fundamental ways: energies perpendicular to the field are quantized, transverse momentum is not conserved, and electron-positron spin is important. Neutron stars therefore provide a unique laboratory for the study of physics in extremely high fields that cannot be generated on earth.

  16. A method for evaluating personal dosemeters in workplace with neutron fields.

    PubMed

    de Freitas Nascimento, Luana; Cauwels, Vanessa; Vanhavere, Filip

    2012-04-01

    Passive detectors, as albedo or track-etch, still dominate the field of neutron personal dosimetry, mainly due to their low-cost, high-reliability and elevated throughput. However, the recent appearance in the market of electronic personal dosemeters for neutrons presents a new option for personal dosimetry. In addition to passive detectors, electronic personal dosemeters necessitate correction factors, concerning their energy and angular response dependencies. This paper reports on the results of a method to evaluate personal dosemeters for workplace where neutrons are present. The approach here uses few instruments and does not necessitate a large mathematical workload. Qualitative information on the neutron energy spectrum is acquired using a simple spectrometer (Nprobe), reference values for H*(10) are derived from measurements with ambient detectors (Studsvik, Berthold and Harwell) and angular information is measured using personal dosemeters (electronic and bubbles dosemeters) disposed in different orientations on a slab phantom. PMID:21565843

  17. Temperature compensated current sensor using reference magnetic field

    DOEpatents

    Yakymyshyn, Christopher Paul; Brubaker, Michael Allen; Yakymyshyn, Pamela Jane

    2007-10-09

    A method is described to provide temperature compensation and self-calibration of a current sensor based on a plurality of magnetic field sensors positioned around a current carrying conductor. A reference magnetic field generated within the current sensor housing is detected by a separate but identical magnetic field sensor and is used to correct variations in the output signal due to temperature variations and aging.

  18. Precise determination of Cr and Co in certified reference material of silicon nitride by neutron activation analysis using internal standardization.

    PubMed

    Miura, Tsutomu; Matsue, Hideaki; Kuroiwa, Takayoshi; Chiba, Koichi

    2009-07-01

    Neutron activation analysis with an internal standard correction was applied to the determination of Cr and Co in a ceramics certified reference material (NMIJ CRM 8004-a silicon nitride powder). Cesium was used as an internal standard to compensate for any inhomogeneity of the neutron flux through an irradiation capsule and to improve the repeatability of gamma-ray measurements. It was found that the linearity of the calibration curves of Cr and Co was improved by using an internal standard. The analytical results of Cr and Co in NMIJ CRM 8004-a were in good agreement with those obtained by ICP-OES, ICP-sector field mass spectrometry (ICP-SFMS), and isotope dilution/ICP-SFMS for Cr. The relative expanded uncertainties (k = 2) were 1.9% for Cr and 1.5% for Co. The uncertainties were comparable to those of atomic spectrometric methods. PMID:19609027

  19. The Covariance and Biocovariance of the Stochartic Neutron Field

    SciTech Connect

    Perez, R.B.

    1998-01-01

    The use of stochastic neutron field theory (neutron noise) for the measurement of reactor physics parameters goes back to the early work of Serber, Feynmann, and Orndoff. Since then, a large variety of methods and applications has been developed. In the majority of these methods, some form of modified one-point reactor kinetics was used for the interpretation of the measurements. In fact, the high level of sophistication of the instrumentation used was not matched by the theory. In 1965, Bell developed a general theory of the stochastic neutron field, and in 1987, Munoz-Cobo et al enlarged this treatment to include the effect of the detectors in the neutron field. In both instances, the complexity of the theoretical results were beyond the computing capabilities then available thus, the mismatch between experimental and theoretical methods remained in existence because the powerful Monte-Carlo methods then at work, were only applicable to static neutron fields. This problem was eliminated by the development of a time-dependent Monte-Carlo code specially written by T. E. Valentine for the analysis of stochastic measurements that gave them relevance to the results of the general theory. The purpose of this work is to illustrate the derivation of observables of the stochastic neutron filed from its general treatment.

  20. Determination of elements in National Bureau of Standards' geological Standard Reference Materials by neutron activation analysis

    SciTech Connect

    Graham, C.C.; Glascock, M.D.; Carni, J.J.; Vogt, J.R.; Spalding, T.G.

    1982-08-01

    Instrumental neutron activation analysis (INAA) and prompt gamma neutron activation analysis (PGNAA) have been used to determine elemental concentrations in two recently issued National Bureau of Standards (NBS) Standard Reference Materials (SRM's). The results obtained are in good agreement with the certified and information values reported by NBS for those elements in each material for which comparisons are available. Average concentrations of 35 elements in SRM 278 obsidian rock and 32 elements in SRM 688 basalt rock are reported for comparison with results that may be obtained by other laboratories.

  1. Relativistic mean field calculations in neutron-rich nuclei

    SciTech Connect

    Gangopadhyay, G.; Bhattacharya, Madhubrata; Roy, Subinit

    2014-08-14

    Relativistic mean field calculations have been employed to study neutron rich nuclei. The Lagrange's equations have been solved in the co-ordinate space. The effect of the continuum has been effectively taken into account through the method of resonant continuum. It is found that BCS approximation performs as well as a more involved Relativistic Continuum Hartree Bogoliubov approach. Calculations reveal the possibility of modification of magic numbers in neutron rich nuclei. Calculation for low energy proton scattering cross sections shows that the present approach reproduces the density in very light neutron rich nuclei.

  2. Magnetic field effects on gravitational waves from binary neutron stars

    NASA Astrophysics Data System (ADS)

    Anderson, Matthew; Hirschmann, Eric; Lehner, Luis; Liebling, Steven; Motl, Patrick; Neilsen, David; Palenzuela, Carlos; Tohline, Joel

    2008-04-01

    Observational evidence indicates that a fair number of neutron star binaries and neutron star-black hole binaries have a sizable magnetic field which can be responsible for powering pulsars and colimating jets. Magnetic field effects additionally can have a strong influence on the dynamics of the fluid by redistributing angular momentum through different mechanisms (magnetic winding and braking, magneto-rotational instabilities) depending on the strength of the magnetic field and the typical time scales involved in the process. These processes can affect the multipolar structure of the source and consequently the produced gravitational wave. We present results of neutron star binary mergers both with and without magnetic field and discuss the magnetic effects on the gravitational waves, fluid structure, and merger timescale.

  3. The alanine detector in BNCT dosimetry: Dose response in thermal and epithermal neutron fields

    SciTech Connect

    Schmitz, T.; Bassler, N.; Blaickner, M.; Ziegner, M.; Hsiao, M. C.; Liu, Y. H.; Koivunoro, H.; Auterinen, I.; Serén, T.; Kotiluoto, P.; Palmans, H.; Sharpe, P.; Langguth, P.; Hampel, G.

    2015-01-15

    Purpose: The response of alanine solid state dosimeters to ionizing radiation strongly depends on particle type and energy. Due to nuclear interactions, neutron fields usually also consist of secondary particles such as photons and protons of diverse energies. Various experiments have been carried out in three different neutron beams to explore the alanine dose response behavior and to validate model predictions. Additionally, application in medical neutron fields for boron neutron capture therapy is discussed. Methods: Alanine detectors have been irradiated in the thermal neutron field of the research reactor TRIGA Mainz, Germany, in five experimental conditions, generating different secondary particle spectra. Further irradiations have been made in the epithermal neutron beams at the research reactors FiR 1 in Helsinki, Finland, and Tsing Hua open pool reactor in HsinChu, Taiwan ROC. Readout has been performed with electron spin resonance spectrometry with reference to an absorbed dose standard in a {sup 60}Co gamma ray beam. Absorbed doses and dose components have been calculated using the Monte Carlo codes FLUKA and MCNP. The relative effectiveness (RE), linking absorbed dose and detector response, has been calculated using the Hansen and Olsen alanine response model. Results: The measured dose response of the alanine detector in the different experiments has been evaluated and compared to model predictions. Therefore, a relative effectiveness has been calculated for each dose component, accounting for its dependence on particle type and energy. Agreement within 5% between model and measurement has been achieved for most irradiated detectors. Significant differences have been observed in response behavior between thermal and epithermal neutron fields, especially regarding dose composition and depth dose curves. The calculated dose components could be verified with the experimental results in the different primary and secondary particle fields. Conclusions: The

  4. Neutron Limit on the Strongly-Coupled Chameleon Field

    NASA Astrophysics Data System (ADS)

    Pushin, Dmitry

    2016-03-01

    One of the major open questions of cosmology is the physical origin of the dark energy. There are a few sets of theories which might explain this origin that could be tested experimentally. The chameleon dark energy theory postulates self-interacting scalar field that couples to matter. This coupling induces a screening mechanism chosen so that the field amplitude is nonzero in empty space but is greatly suppressed in regions of terrestrial matter density. On behalf of the INDEX collaboration, I will report the most stringent upper bound on the free neutron-chameleon coupling in the strongly-coupled limit of the chameleon theory using neutron interferometric techniques. In our experiment we measure neutron phase induced by chameleon field. We report a 95 % confidence level upper bound on the neutron-chameleon coupling ranging from β < 4 . 7 ×106 for a Ratra-Peebles index of n = 1 in the nonlinear scalar field potential to β < 2 . 4 ×107 for n = 6 , one order of magnitude more sensitive than the most recent free neutron limit for intermediate n. This work was supported by NIST; NSF Grants: PHY-1205342, PHY-1068712, PHY-1307426; DOE award DE-FG02-97ER41042; NSERC CREATE and DISCOVERY programs; CERC; IUCSS and IU FRS program.

  5. Gamma-ray bursts and neutron star field decay

    NASA Technical Reports Server (NTRS)

    Hartmann, Dieter; Blumenthal, George; Chuang, Kuan-Wen; Hurley, Kevin; Kargatis, Vincent; Liang, Edison; Linder, Eric

    1992-01-01

    Assuming a Galactic origin of gamma-ray bursts, we use pulsar data to calculate the spatial distribution of neutron stars and determine the sampling depths of current detectors. Based on these distance limits, we calculate the corresponding age distribution of Galactic neutron stars and apply an exponential field decay model to test whether the observed high incidence rate of cyclotron lines is consistent with suggested field decay time scales of order 10 exp 7 years. We find that the properties of the observed population of gamma-ray bursts are inconsistent with the idea that bursts originate at arbitrary times on neutron stars whose fields decay on time scales shorter than about 10 exp 9 years. Possible interpretations of this inconsistency are discussed.

  6. Second Research Coordination Meeting on Reference Database for Neutron Activation Analysis -- Summary Report

    SciTech Connect

    Firestone, Richard B.; Kellett, Mark A.

    2008-03-19

    The second meeting of the Co-ordinated Research Project on"Reference Database for Neutron Activation Analysis" was held at the IAEA, Vienna from 7-9 May, 2007. A summary of the presentations made by participants is given, along with reports on specifically assigned tasks and subsequent discussions. In order to meet the overall objectives of this CRP, the outputs have been reiterated and new task assignments made.

  7. Neutron activation analysis for reference determination of the implantation dose of cobalt ions

    SciTech Connect

    Garten, R.P.H.; Bubert, H.; Palmetshofer, L.

    1992-05-15

    The authors prepared depth profilling reference materials by cobalt ion implantation at an ion energy of 300 keV into n-type silicon. The implanted Co dose was then determined by instrumental neutron activation analysis (INAA) giving an analytical dynamic range of almost 5 decades and uncertainty of 1.5%. This form of analysis allows sources of error (beam spreading, misalignment) to be corrected. 70 refs., 3 tabs.

  8. Evaluation of homogeneity of a certified reference material by instrumental neutron activation analysis

    SciTech Connect

    Kratochvil, B.; Duke, M.J.M.; Ng, D.

    1986-01-01

    The homogeneity of the marine reference material TORT-1, a spray-dried and acetone-extracted hepatopancreatic material from the lobster, was tested for 26 elements by instrumental neutron activation analysis (INAA). Through a one-way analysis of variance based on six analyses on each of six bottles of TORT-1, it was concluded that the between-bottle heterogeneity is no greater than the within-bottle heterogeneity. The analytical results for those elements for which values were provided by NRC agree with the NRC values within 95% confidence limits. 8 references, 6 tables.

  9. Neutron limit on the strongly-coupled chameleon field

    NASA Astrophysics Data System (ADS)

    Li, K.; Arif, M.; Cory, D. G.; Haun, R.; Heacock, B.; Huber, M. G.; Nsofini, J.; Pushin, D. A.; Saggu, P.; Sarenac, D.; Shahi, C. B.; Skavysh, V.; Snow, W. M.; Young, A. R.; Index Collaboration

    2016-03-01

    The physical origin of the dark energy that causes the accelerated expansion rate of the Universe is one of the major open questions of cosmology. One set of theories postulates the existence of a self-interacting scalar field for dark energy coupling to matter. In the chameleon dark energy theory, this coupling induces a screening mechanism such that the field amplitude is nonzero in empty space but is greatly suppressed in regions of terrestrial matter density. However measurements performed under appropriate vacuum conditions can enable the chameleon field to appear in the apparatus, where it can be subjected to laboratory experiments. Here we report the most stringent upper bound on the free neutron-chameleon coupling in the strongly coupled limit of the chameleon theory using neutron interferometric techniques. Our experiment sought the chameleon field through the relative phase shift it would induce along one of the neutron paths inside a perfect crystal neutron interferometer. The amplitude of the chameleon field was actively modulated by varying the millibar pressures inside a dual-chamber aluminum cell. We report a 95% confidence level upper bound on the neutron-chameleon coupling β ranging from β <4.7 ×106 for a Ratra-Peebles index of n =1 in the nonlinear scalar field potential to β <2.4 ×107 for n =6 , one order of magnitude more sensitive than the most recent free neutron limit for intermediate n . Similar experiments can explore the full parameter range for chameleon dark energy in the foreseeable future.

  10. A compact neutron scatter camera for field deployment.

    PubMed

    Goldsmith, John E M; Gerling, Mark D; Brennan, James S

    2016-08-01

    We describe a very compact (0.9 m high, 0.4 m diameter, 40 kg) battery operable neutron scatter camera designed for field deployment. Unlike most other systems, the configuration of the sixteen liquid-scintillator detection cells are arranged to provide omnidirectional (4π) imaging with sensitivity comparable to a conventional two-plane system. Although designed primarily to operate as a neutron scatter camera for localizing energetic neutron sources, it also functions as a Compton camera for localizing gamma sources. In addition to describing the radionuclide source localization capabilities of this system, we demonstrate how it provides neutron spectra that can distinguish plutonium metal from plutonium oxide sources, in addition to the easier task of distinguishing AmBe from fission sources. PMID:27587113

  11. Determination of TFTR far-field neutron detector efficiencies by local neutron flux spectrum measurement

    NASA Astrophysics Data System (ADS)

    Jassby, D. L.; Ascione, G.; Kugel, H. W.; Roquemore, A. L.; Barcelo, T. W.; Kumar, A.

    1997-01-01

    Neutron detectors have often been located on the tokamak fusion test reactor (TFTR) test cell floor 3 m or more from the vacuum vessel for ease of detector access, to reduce radiation damage, minimize count saturation problems, and to avoid high magnetic fields. These detectors include Si surface-barrier diodes, fission chambers, natural diamond detectors, and T2 production in a moderated 3He cell. To evaluate the performance of these detectors during deuterium-tritium (D-T) operation, we determined the neutron flux spectrum incident on the principal detector enclosure using nuclide sample sets containing Al, Ti, Fe, Co, Cu, Zn, Ni, Zr, Nb, In, and Au activation foils. Foils were installed and then removed after ample exposure to TFTR D-T neutrons. High efficiency, high purity Ge detectors were used for gamma spectroscopy of the irradiated foils. The incident neutron fluence and spectral distribution were unfolded from the measured results, and used to derive absolute detector efficiencies.

  12. 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. PMID:20511404

  13. A compact neutron generator using a field ionization source

    SciTech Connect

    Persaud, Arun; Waldmann, Ole; Schenkel, Thomas; Kapadia, Rehan; Takei, Kuniharu; Javey, Ali

    2012-02-15

    Field ionization as a means to create ions for compact and rugged neutron sources is pursued. Arrays of carbon nano-fibers promise the high field-enhancement factors required for efficient field ionization. We report on the fabrication of arrays of field emitters with a density up to 10{sup 6} tips/cm{sup 2} and measure their performance characteristics using electron field emission. The critical issue of uniformity is discussed, as are efforts towards coating the nano-fibers to enhance their lifetime and surface properties.

  14. A compact neutron generator using a field ionization source

    SciTech Connect

    Persaud, Arun; Waldmann, Ole; Kapadia, Rehan; Takei, Kuniharu; Javey, Ali; Schenkel, Thomas

    2012-02-15

    We study field ionization as a means to create ions for compact and rugged neutron source. Arrays of carbon nano-fibers promise the high field-enhancement factors required for efficient field ionization. We report on the fabrication of arrays of field emitters with a density up to 106 tips/cm2 and measure their performance characteristics using electron field emission. Lastly, the critical issue of uniformity is discussed, as are efforts towards coating the nano-fibers to enhance their lifetime and surface properties.

  15. Application of an ultraminiature thermal neutron monitor for irradiation field study of accelerator-based neutron capture therapy

    PubMed Central

    Ishikawa, Masayori; Tanaka, Kenichi; Endo, Satrou; Hoshi, Masaharu

    2015-01-01

    Phantom experiments to evaluate thermal neutron flux distribution were performed using the Scintillator with Optical Fiber (SOF) detector, which was developed as a thermal neutron monitor during boron neutron capture therapy (BNCT) irradiation. Compared with the gold wire activation method and Monte Carlo N-particle (MCNP) calculations, it was confirmed that the SOF detector is capable of measuring thermal neutron flux as low as 105 n/cm2/s with sufficient accuracy. The SOF detector will be useful for phantom experiments with BNCT neutron fields from low-current accelerator-based neutron sources. PMID:25589504

  16. International Geomagnetic Reference Field: the 12th generation

    NASA Astrophysics Data System (ADS)

    Thébault, Erwan; Finlay, Christopher C.; Beggan, Ciarán D.; Alken, Patrick; Aubert, Julien; Barrois, Olivier; Bertrand, Francois; Bondar, Tatiana; Boness, Axel; Brocco, Laura; Canet, Elisabeth; Chambodut, Aude; Chulliat, Arnaud; Coïsson, Pierdavide; Civet, François; Du, Aimin; Fournier, Alexandre; Fratter, Isabelle; Gillet, Nicolas; Hamilton, Brian; Hamoudi, Mohamed; Hulot, Gauthier; Jager, Thomas; Korte, Monika; Kuang, Weijia; Lalanne, Xavier; Langlais, Benoit; Léger, Jean-Michel; Lesur, Vincent; Lowes, Frank J.; Macmillan, Susan; Mandea, Mioara; Manoj, Chandrasekharan; Maus, Stefan; Olsen, Nils; Petrov, Valeriy; Ridley, Victoria; Rother, Martin; Sabaka, Terence J.; Saturnino, Diana; Schachtschneider, Reyko; Sirol, Olivier; Tangborn, Andrew; Thomson, Alan; Tøffner-Clausen, Lars; Vigneron, Pierre; Wardinski, Ingo; Zvereva, Tatiana

    2015-05-01

    The 12th generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2014 by the Working Group V-MOD appointed by the International Association of Geomagnetism and Aeronomy (IAGA). It updates the previous IGRF generation with a definitive main field model for epoch 2010.0, a main field model for epoch 2015.0, and a linear annual predictive secular variation model for 2015.0-2020.0. Here, we present the equations defining the IGRF model, provide the spherical harmonic coefficients, and provide maps of the magnetic declination, inclination, and total intensity for epoch 2015.0 and their predicted rates of change for 2015.0-2020.0. We also update the magnetic pole positions and discuss briefly the latest changes and possible future trends of the Earth's magnetic field.

  17. Microdosimetry of epithermal neutron field at the Kyoto University reactor.

    PubMed

    Onizuka, Y; Endo, S; Ishikawa, M; Hoshi, M; Takada, M; Kobayashi, T; Sakurai, Y; Utsumi, H; Uehara, S; Hayabuchi, N; Maeda, N; Takatuji, T; Fujika, K

    2002-01-01

    Microdosimetric spectra were measured in order to gain the microdosimetric parameters of some epithermal neutron fields. Changes in dose mean lineal energy YD as a function of depth of heavy water showed a trend of softening with heavy water of the beam. The neutron absorbed dose was obtained by using the frequency mean lineal energy. Results show good agreement with measurements with the activation method using gold foil. This study demonstrated how microdosimetric parameters change in radiation quality as a function of heavy water depth. PMID:12194334

  18. Small-Angle Neutron Scattering study of the NIST mAb reference material

    NASA Astrophysics Data System (ADS)

    Castellanos, Maria Monica; Liu, Yun; Krueger, Susan; Curtis, Joseph

    Monoclonal antibodies (mAbs) are of great interest to the biopharmaceutical industry because they can be engineered to target specific antigens. Due to their importance, the biomanufacturing initiative at NIST is developing an IgG1 mAb reference material `NIST mAb', which can be used by industry, academia, and regulatory authorities. As part of this collaborative effort, we aim at characterizing the reference material using neutron scattering techniques. We have studied the small-angle scattering profile of the NIST mAb in a histidine buffer at 0 and 150 mM NaCl. Using Monte Carlo simulations, we generate an ensemble of structures and calculate their theoretical scattering profile, which can be directly compared with experimental data. Moreover, we analyze the structure factor to understand the effect of solution conditions on the protein-protein interactions. Finally, we have measured the solution scattering of the NIST mAb, while simultaneously performing freeze/thaw cycles, in order to investigate if the solution structure was affected upon freezing. The results from neutron scattering not only support the development of the reference material, but also provide insights on its stability and guide efforts for its development under different formulations.

  19. EPR dosimetry in a mixed neutron and gamma radiation field.

    PubMed

    Trompier, F; Fattibene, P; Tikunov, D; Bartolotta, A; Carosi, A; Doca, M C

    2004-01-01

    Suitability of Electron Paramagnetic Resonance (EPR) spectroscopy for criticality dosimetry was evaluated for tooth enamel, mannose and alanine pellets during the 'international intercomparison of criticality dosimetry techniques' at the SILENE reactor held in Valduc in June 2002, France. These three materials were irradiated in neutron and gamma-ray fields of various relative intensities and spectral distributions in order to evaluate their neutron sensitivity. The neutron response was found to be around 10% for tooth enamel, 45% for mannose and between 40 and 90% for alanine pellets according their type. According to the IAEA recommendations on the early estimate of criticality accident absorbed dose, analyzed results show the EPR potentiality and complementarity with regular criticality techniques. PMID:15353687

  20. Characterisation of neutron fields: challenges in assessing the directional distribution.

    PubMed

    Cauwels, Vanessa; Vanhavere, Filip; Reginatto, Marcel

    2014-10-01

    The SCK·CEN has carried out neutron field characterisation campaigns at several nuclear reactors. The main goal of these measurement campaigns was to evaluate the performance of different neutron personal dosemeters. To be able to evaluate the performance of neutron personal dosemeters in terms of Hp(10), knowledge of the directional distribution is indispensable. This distribution was estimated by placing several personal dosemeters on all six sides of a slab phantom. The interpretation and conversion of this information into a reliable value for Hp(10) requires great care. The data were analysed using three methods. In the first approach, a linear interpolation was performed on three perpendicular axes. In the other two approaches, an icosahedron was used to model the angle of incidence of the neutrons and a linear interpolation or a Bayesian analysis was performed. This study describes the limitations and advantages of each of these methods and provides recommendations for their use to estimate the personal dose equivalent Hp(10) for neutron dosimetry. PMID:24966340

  1. Measurement of neutron and gamma radiation in a mixed field.

    PubMed

    Kronenberg, S; Bechtel, E; Brucker, G J

    1995-10-01

    This paper describes a study of dosimeters with a range of 0 to 0.2 mGy that were developed by the authors and built by the Federal Emergency Management Agency (FEMA). These instruments are a type of air-filled ion chamber that is self-reading by means of an internal carbon fiber electrometer. Two types of these dosimeters were constructed: one with an ion chamber wall made of a conductive hydrogenous material, and the other device made with a conductive wall lining of non-hydrogenous material. Both types of dosimeters have the same sensitivity for gamma radiation, but greatly different sensitivities for fast neutrons, thus making it possible to measure gamma radiation and neutron doses separately in a mixed radiation field. The results indicate that such pairs of dosimeters can be used for the first time to accurately monitor personnel for gamma ray and neutron doses in real time. Since the difference in neutron sensitivities is due to the properties of wall materials, periodic calibrations of the dosimeter system can be accomplished using only gamma rays after the material constants are measured. The absolute number of neutron induced transmutations in sulfur was required for this work. Methods and techniques which were applied to determine this quantity are described in the text. This approach was one of several dosimetric procedures utilized in this investigation. PMID:7558835

  2. Neutron field measurements at the Aladdin Synchrotron Light Source.

    PubMed

    Yang, Y; Li, Y; DeLuca, P M; Otte, R; Rowe, E M

    1986-01-01

    The neutron field near the inflector of the 800-MeV electron storage ring was studied. Photon-induced neutrons are produced by 100-MeV electrons bombarding the inflector during injection into the synchrotron ring. Neutrons were measured with moderating detectors made of 15 X 15 X 20 cm Lucite blocks and Au activation foils. Detector response was established with a Pu-Be neutron source and a 25.4-cm polyethylene sphere and Au foil detector. The neutron yield was 0.97 +/- 0.14 X 10(12) kJ-1. For 1.38 W of electron pulse power, the dose equivalent rate 1 m aside and 1 m above the inflector was 4.35 +/- 0.47 mu Sv s-1 and 3.13 +/- 0.23 mu Sv s-1, respectively. A measured dose equivalent transmission curve for polyethylene yielded an attenuation coefficient of 15.7 m-1. PMID:3943962

  3. Neutron interference in the gravitational field of a ring laser

    NASA Astrophysics Data System (ADS)

    Fischetti, Robert D.; Mallett, Ronald L.

    2015-07-01

    The neutron split-beam interferometer has proven to be particularly useful in measuring Newtonian gravitational effects such as those studied by Colella, Overhauser, and Werner (COW). The development of the ring laser has led to numerous applications in many areas of physics including a recent general relativistic prediction of frame dragging in the gravitational field produced by the electromagnetic radiation in a ring laser. This paper introduces a new general technique based on a canonical transformation of the Dirac equation for the gravitational field of a general linearized spacetime. Using this technique it is shown that there is a phase shift in the interference of two neutron beams due to the frame-dragging nature of the gravitational field of a ring laser.

  4. Simulation of the Magnetic Field Evolution in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Hoyos, J.; Reisenegger, A.; Valdivia, J. A.

    Using a numerical simulation, we study the effects of ambipolar diffusion and ohmic diffusion on the magnetic field evolution in the interior of an isolated neutron star (Goldreich & Reisenegger 1992; Reisenegger et al. 2005; Hoyos et al. 2007). We are interested in the behavior of the magnetic field on a long time scale, over which all Alfven and sound waves have been damped. We model the stellar interior as an electrically neutral plasma composed of neutrons, protons and electrons, which can interact with each other through collisions and electromagnetic forces. Weak interactions convert neutrons and charged particles into each other, erasing chemical imbalances. As a first step, we assume that the magnetic field points in one fixed Cartesian direction but can vary along an orthogonal direction. We start with a uniform-density background threaded by a homogeneous magnetic field and study the evolution of a magnetic perturbation as well as the density fluctuations it induces in the particles. We show that the system evolves through different quasi-equilibrium states and estimate the characteristic time scales on which these quasi-equilibria occur as a function of the magnetic field intensity, the collisional strength between the particles, the weak interaction rate, and the ohmic resistivity. We intend in a near future to extend this simulation to two dimensions in order to study an axially symmetric star geometry.

  5. Search for strongly coupled Chameleon scalar field with neutron interferometry

    NASA Astrophysics Data System (ADS)

    Li, K.; Arif, M.; Cory, D.; Haun, R.; Heacock, B.; Huber, M.; Nsofini, J.; Pushin, D. A.; Saggu, P.; Sarenac, D.; Shahi, C.; Skavysh, V.; Snow, M.; Young, A.

    2015-04-01

    The dark energy proposed to explain the observed accelerated expansion of the universe is not understood. A chameleon scalar field proposed as a dark energy candidate can explain the accelerated expansion and evade all current gravity experimental bounds. It features an effective range of the chameleon scalar field that depends on the local mass density. Hence a perfect crystal neutron interferometer, that measures relative phase shift between two paths, is a prefect tool to search for the chameleon field. We are preparing a two-chamber helium gas cell for the neutron interferometer. We can lower the pressure in one cell so low that the chameleon field range expands into the cell and causes a measurable neutron phase shift while keeping the pressure difference constant. We expect to set a new upper limit of the Chameleon field by at least one order of magnitude. This work is supported by NSF Grant 1205977, DOE Grant DE-FG02-97ER41042, Canadian Excellence Research Chairs program, Natural Sciences and Engineering Research Council of Canada and Collaborative Research and Training Experience Program

  6. A Reference Field for GCR Simulation and an LET-Based Implementation at NSRL

    NASA Technical Reports Server (NTRS)

    Slaba, Tony C.; Blattnig, Steve R.; Walker, Steven A.; Norbury, John W.

    2015-01-01

    Exposure to galactic cosmic rays (GCR) on long duration deep space missions presents a serious health risk to astronauts, with large uncertainties connected to the biological response. In order to reduce the uncertainties and gain understanding about the basic mechanisms through which space radiation initiates cancer and other endpoints, radiobiology experiments are performed. Some of the accelerator facilities supporting such experiments have matured to a point where simulating the broad range of particles and energies characteristic of the GCR environment in a single experiment is feasible from a technology, usage, and cost perspective. In this work, several aspects of simulating the GCR environment in the laboratory are discussed. First, comparisons are made between direct simulation of the external, free space GCR field and simulation of the induced tissue field behind shielding. It is found that upper energy constraints at the NASA Space Radiation Laboratory (NSRL) limit the ability to simulate the external, free space field directly (i.e. shielding placed in the beam line in front of a biological target and exposed to a free space spectrum). Second, variation in the induced tissue field associated with shielding configuration and solar activity is addressed. It is found that the observed variation is within physical uncertainties, allowing a single reference field for deep space missions to be defined. Third, an approach for simulating the reference field at NSRL is presented. The approach allows for the linear energy transfer (LET) spectrum of the reference field to be approximately represented with discrete ion and energy beams and implicitly maintains a reasonably accurate charge spectrum (or, average quality factor). Drawbacks of the proposed methodology are discussed and weighed against alternative simulation strategies. The neutron component and track structure characteristics of the proposed strategy are discussed in this context.

  7. The neutron standard fields at the BR1 reactor at SCK.CEN

    SciTech Connect

    Wagemans, J.; Malambu, E.; Borms, L.

    2011-07-01

    The BR1 research reactor at SCK-CEN is characterized by a wide variety of irradiation possibilities, a large reactor core, and strong flexibility in its operation. A full MCNP model of BR1 has been recently developed in order to complement the results that can be obtained from activation dosimetry. After a general presentation of the reactor, this paper pays particular attention to its standard {sup 235}U(n,f) fast neutron field MARK III. This irradiation field is a useful tool for integral measurements and for detector calibrations. With the support of MCNP calculations, irradiations in MARK III can be directly referred to the pure {sup 235}U(n,f) fast neutron spectrum. (authors)

  8. Determination of multielements in a typical Japanese diet certified reference material by instrumental neutron activation analysis.

    PubMed

    Suzuki, Shogo; Okada, Yukiko; Hirai, Shoji

    2003-08-01

    Multielements in a typical Japanese diet certified reference material prepared at the National Institute for Environmental Studies (NIES) of Japan, in collaboration with the National Institute of Radiological Sciences (NIRS) of Japan were determined by instrumental neutron activation analysis (INAA). Five samples (ca. 510-1000 mg) and comparative standards were irradiated for a short time (10 s) at a thermal neutron flux of 1.5 x 10(12) n cm(-2) s(-1) (pneumatic transfer) and for a long time (6 h) at a thermal neutron flux of 3.7 x 10(12) n cm(-2) s(-1) (central thimble) in the Rikkyo University Research Reactor (TRIGA Mark-II, 100 kW). The irradiated samples were measured by conventional gama-ray spectrometry using a coaxial Ge detector, and by anti-coincidence and coincidence gamma-ray spectrometry with a coaxial Ge detector and a well-type NaI(Tl) detector. The concentrations of 38 elements were determined by these methods. PMID:12945682

  9. Thermal neutron irradiation field design for boron neutron capture therapy of human explanted liver

    SciTech Connect

    Bortolussi, S.; Altieri, S.

    2007-12-15

    The selective uptake of boron by tumors compared to that by healthy tissue makes boron neutron capture therapy (BNCT) an extremely advantageous technique for the treatment of tumors that affect a whole vital organ. An example is represented by colon adenocarcinoma metastases invading the liver, often resulting in a fatal outcome, even if surgical resection of the primary tumor is successful. BNCT can be performed by irradiating the explanted organ in a suitable neutron field. In the thermal column of the Triga Mark II reactor at Pavia University, a facility was created for this purpose and used for the irradiation of explanted human livers. The neutron field distribution inside the organ was studied both experimentally and by means of the Monte Carlo N-particle transport code (MCNP). The liver was modeled as a spherical segment in MCNP and a hepatic-equivalent solution was used as an experimental phantom. In the as-built facility, the ratio between maximum and minimum flux values inside the phantom ({phi}{sub max}/{phi}{sub min}) was 3.8; this value can be lowered to 2.3 by rotating the liver during the irradiation. In this study, the authors proposed a new facility configuration to achieve a uniform thermal neutron flux distribution in the liver. They showed that a {phi}{sub max}/{phi}{sub min} ratio of 1.4 could be obtained without the need for organ rotation. Flux distributions and dose volume histograms were reported for different graphite configurations.

  10. Thermal neutron irradiation field design for boron neutron capture therapy of human explanted liver.

    PubMed

    Bortolussi, S; Altieri, S

    2007-12-01

    The selective uptake of boron by tumors compared to that by healthy tissue makes boron neutron capture therapy (BNCT) an extremely advantageous technique for the treatment of tumors that affect a whole vital organ. An example is represented by colon adenocarcinoma metastases invading the liver, often resulting in a fatal outcome, even if surgical resection of the primary tumor is successful. BNCT can be performed by irradiating the explanted organ in a suitable neutron field. In the thermal column of the Triga Mark II reactor at Pavia University, a facility was created for this purpose and used for the irradiation of explanted human livers. The neutron field distribution inside the organ was studied both experimentally and by means of the Monte Carlo N-particle transport code (MCNP). The liver was modeled as a spherical segment in MCNP and a hepatic-equivalent solution was used as an experimental phantom. In the as-built facility, the ratio between maximum and minimum flux values inside the phantom ((phi(max)/phi(min)) was 3.8; this value can be lowered to 2.3 by rotating the liver during the irradiation. In this study, the authors proposed a new facility configuration to achieve a uniform thermal neutron flux distribution in the liver. They showed that a phi(max)/phi(min) ratio of 1.4 could be obtained without the need for organ rotation. Flux distributions and dose volume histograms were reported for different graphite configurations. PMID:18196797

  11. Dose homogeneity specification for reference dosimetry of nonstandard fields

    SciTech Connect

    Chung, Eunah; Soisson, Emilie; Seuntjens, Jan

    2012-01-15

    Purpose: To investigate the sensitivity of the plan-class specific correction factor to dose distributions in composite nonstandard field dosimetry. Methods: A cylindrical water-filled PMMA phantom was constructed at the center of which reference absorbed dose could be measured. Ten different TomoTherapy-based IMRT fields were created on the CT images of the phantom. The dose distribution for each IMRT field was estimated at the position of a radiation detector or ionization chamber. The dose in each IMRT field normalized to that in a reference 10 x 10 cm{sup 2} field was measured using a PTW micro liquid ion chamber. Based on the new dosimetry formalism, a plan-class specific correction factor k{sub Q{sub p{sub c{sub s{sub r,Q}{sup f{sub p}{sub c}{sub s}{sub r},f{sub r}{sub e}{sub f}}}}}} for each field was measured for two Farmer-type chambers, Exradin A12 and NE2571, as well as for a smaller Exradin A1SL chamber. The dependence of the measured correction factor on parameters characterizing dose distribution was analyzed. Results: Uncertainty on the plan-class specific correction factor measurement was in the range of 0.3%-0.5% and 0.3%-0.8% for the Farmer-type chambers and the Exradin A1SL, respectively. When the heterogeneity of the central region of the target volume was less than 5%, the correction factor did not differ from unity by more than 0.7% for the three air-filled ionization chambers. For more heterogeneous dose deliveries, the correction factor differed from unity by up to 2.4% for the Farmer-type chambers. For the Exradin A1SL, the correction factor was closer to unity due to the reduced effect of dose gradients, while it was highly variable in different IMRT fields because of a more significant impact of positioning uncertainties on the response of this chamber. Conclusions: The authors have shown that a plan-class specific correction factor can be specified as a function of plan evaluation parameters especially for Farmer-type chambers. This work

  12. Reference dosimetry calculations for neutron capture therapy with comparison of analytical and voxel models.

    PubMed

    Goorley, J T; Kiger, W S; Zamenhof, R G

    2002-02-01

    As clinical trials of Neutron Capture Therapy (NCT) are initiated in the U.S. and other countries, new treatment planning codes are being developed to calculate detailed dose distributions in patient-specific models. The thorough evaluation and comparison of treatment planning codes is a critical step toward the eventual standardization of dosimetry, which, in turn, is an essential element for the rational comparison of clinical results from different institutions. In this paper we report development of a reference suite of computational test problems for NCT dosimetry and discuss common issues encountered in these calculations to facilitate quantitative evaluations and comparisons of NCT treatment planning codes. Specifically, detailed depth-kerma rate curves were calculated using the Monte Carlo radiation transport code MCNP4B for four different representations of the modified Snyder head phantom, an analytic, multishell, ellipsoidal model, and voxel representations of this model with cubic voxel sizes of 16, 8, and 4 mm. Monoenergetic and monodirectional beams of 0.0253 eV, 1, 2, 10, 100, and 1000 keV neutrons, and 0.2, 0.5, 1, 2, 5, and 10 MeV photons were individually simulated to calculate kerma rates to a statistical uncertainty of <1% (1 std. dev.) in the center of the head model. In addition, a "generic" epithermal neutron beam with a broad neutron spectrum, similar to epithermal beams currently used or proposed for NCT clinical trials, was computed for all models. The thermal neutron, fast neutron, and photon kerma rates calculated with the 4 and 8 mm voxel models were within 2% and 4%, respectively, of those calculated for the analytical model. The 16 mm voxel model produced unacceptably large discrepancies for all dose components. The effects from different kerma data sets and tissue compositions were evaluated. Updating the kerma data from ICRU 46 to ICRU 63 data produced less than 2% difference in kerma rate profiles. The depth-dose profile data

  13. The freedom to choose neutron star magnetic field equilibria

    NASA Astrophysics Data System (ADS)

    Glampedakis, Kostas; Lasky, Paul D.

    2016-08-01

    Our ability to interpret and glean useful information from the large body of observations of strongly magnetised neutron stars rests largely on our theoretical understanding of magnetic field equilibria. We answer the following question: is one free to arbitrarily prescribe magnetic equilibria such that fluid degrees of freedom can balance the equilibrium equations? We examine this question for various models for neutron star matter; from the simplest single-fluid barotrope to more realistic non-barotropic multifluid models with superfluid/superconducting components, muons and entropy. We do this for both axi- and non-axisymmetric equilibria, and in Newtonian gravity and general relativity. We show that, in axisymmetry, the most realistic model allows complete freedom in choosing a magnetic field equilibrium whereas non-axisymmetric equilibria are never completely arbitrary.

  14. Fission of 232Th in a spallation neutron field

    NASA Astrophysics Data System (ADS)

    Yurevich, V. I.; Nikolaev, V. A.; Yakovlev, R. M.

    2016-03-01

    The spatial distributions of thorium fission reaction rate in a spallation neutron field of thick lead target bombarded by protons or deuterons with energy between 1.0 and 3.7 GeV were measured. Approximately a linear dependence of the thorium fission rate on the beam energy is observed. The mean fission cross section of 232Th <σ f > ≈ 123 mb and it does not depend on energy and type of the beam particles.

  15. Dynamical model of the magnetic field of neutron stars

    NASA Astrophysics Data System (ADS)

    Cummings, F. W.; Dixon, D. D.; Kaus, P. E.

    1992-02-01

    Attention is given to a dynamical model of the magnetization of a neutron star. The model exhibits three distinct behaviors, as characterized in the 2D parameter space of the two relevant parameters. In one region of the parameter space, the magnetization, and correspondingly the magnetic field, behaves erratically and nonperiodically, occasionally producing large pulses of the directional electric and magnetic field. It is suggested that this field is associated with 'bursters', very energetic gamma-rich pulses of the order of 1-s duration, and believed to emanate from solo neutron stars. A second region of parameter space shows the magnetization precessing at a constant period around the spin or conserved angular momentum direction. The third region is a 'dead' region, where the magnetization is aligned with the spin axis, and the star is nonradiating. The model suggests a life history of a neutron star in which the star typically evolves initially from a burster, later becoming a pulsar, and ending as a dead star.

  16. Torsional oscillations of neutron stars with highly tangled magnetic fields

    NASA Astrophysics Data System (ADS)

    Sotani, Hajime

    2015-11-01

    To determine the frequencies of magnetic oscillations in neutron stars with highly tangled magnetic fields, we derive the perturbation equations. We assume that the field strength of the global magnetic structure is so small that such fields are negligible compared with tangled fields, which may still be far from a realistic configuration. Then, we systematically examine the spectra of the magnetic oscillations, as varying the magnetic field strength and stellar mass. The frequencies without crust elasticity are completely proportional to the strength of the magnetic field, whose proportionality constant depends strongly on the stellar mass. On the other hand, the oscillation spectra with crust elasticity become more complicated, where the frequencies even for weak magnetic fields are different from the crustal torsional oscillations without magnetic fields. For discussing spectra, the critical field strength can play an important role, and it is determined in such a way that the shear velocity is equivalent to the Alfvén velocity at the crust basis. Additionally, we find that the effect of the crust elasticity can be seen strongly in the fundamental oscillations with a lower harmonic index, ℓ. Unlike the stellar models with a pure dipole magnetic field, we also find that the spectra with highly tangled magnetic fields become discrete, where one can expect many of the eigenfrequencies. Maybe these frequencies could be detected after the violent phenomena breaking the global magnetic field structure.

  17. High electric field deuterium ion sources for neutron generators

    NASA Astrophysics Data System (ADS)

    Reichenbach, Birk

    Active interrogation systems for highly enriched uranium require improved fieldable neutron sources. The target technology for deuterium-tritium neutron generators is well understood and the most significant improvement can be achieved by improving the deuterium ion source through increased output and, in some cases, lifetime of the ion source. We are developing a new approach to a deuterium ion sources based upon the field desorption/evaporation of deuterium from the surfaces of metal tips. Electrostatic field desorption (EFD) desorbs previously adsorbed deuterium as ions under the influence of high electric fields (several V/A), without removing tip material. Single etched wire tip experiments have been performed and have shown that this is difficult but can be achieved with molybdenum and tungsten tips. Electrostatic field evaporation (EFE) evaporates ultra thin deuterated titanium films as ions. It has been shown that several 10s of atomic layers can be removed within a few nanoseconds from etched tungsten tips. In the course of these studies titanium deposition and deuteration methods were studied and new detection methods developed. Space charge effects resulting from the large ion currents were identified to be the most likely cause of some unusual ion emission characteristics. In addition, on W < 110 > oriented substrates a surprising body-centered cubic crystal structure of the titanium film was found and studied. The ion currents required for neutron generator applications can be achieved by microfabrication of metal tip arrays. Field desorption studies of microfabricated field emitter tip arrays have been conducted for the first time. Maximum fields of 3 V/A have been applied to the array tip surfaces to date, although fields of ˜ 2 V/A to ˜ 2.5 V/A are more typical. Desorption of atomic deuterium ions has been observed at fields of roughly 2 V/A at room temperature. The desorption of common surface adsorbates, such as hydrogen, carbon, water, and

  18. A militarily fielded thermal neutron activation sensor for landmine detection

    NASA Astrophysics Data System (ADS)

    Clifford, E. T. H.; McFee, J. E.; Ing, H.; Andrews, H. R.; Tennant, D.; Harper, E.; Faust, A. A.

    2007-08-01

    The Canadian Department of National Defence has developed a teleoperated, vehicle-mounted, multi-sensor system to detect anti-tank landmines on roads and tracks in peacekeeping operations. A key part of the system is a thermal neutron activation (TNA) sensor which is placed above a suspect location to within a 30 cm radius and confirms the presence of explosives via detection of the 10.835 MeV gamma ray associated with thermal neutron capture on 14N. The TNA uses a 100 μg252Cf neutron source surrounded by four 7.62 cm×7.62 cm NaI(Tl) detectors. The system, consisting of the TNA sensor head, including source, detectors and shielding, the high-rate, fast pulse processing electronics and the data processing methodology are described. Results of experiments to characterize detection performance are also described. The experiments have shown that anti-tank mines buried 10 cm or less can be detected in roughly a minute or less, but deeper mines and mines significantly displaced horizontally take considerably longer time. Mines as deep as 30 cm can be detected for long count times (1000 s). Four TNA detectors are now in service with the Canadian Forces as part of the four multi-sensor systems, making it the first militarily fielded TNA sensor and the first militarily fielded confirmation sensor for landmines. The ability to function well in adverse climatic conditions has been demonstrated, both in trials and operations.

  19. Neutron Interference in the Gravitational Field of a Ring Laser

    NASA Astrophysics Data System (ADS)

    Fischetti, Robert

    2013-04-01

    A number of analyses of neutron interference effects due to various metric perturbations have been found in the literature [1,2]. However, the approach of each author depends on a specific metric. I will present a new general technique giving the Foldy-Wouthuysen transformed Hamiltonian for a Dirac particle in the most general linearized space-time metric. I will then apply this new technique to calculate the phase shift on a neutron beam interferometer due to the gravitational field of a ring laser [3].[4pt] [1] D. M Greenberger and A. W. Overhauser, Rev. Mod. Phys. 51, 43--78 (1979).[0pt] [2] F. W. Hehl and W. T. Ni, Phys. Rev. D, vol 42, no. 6, pp. 2045-2048, 1990.[0pt] [3] R. L. Mallett, Phys. Lett. A 269, 214 (2000).

  20. Long-term evolution of crustal neutron star magnetic fields

    NASA Technical Reports Server (NTRS)

    Urpin, V. A.; Chanmugam, G.; Sang, Yeming

    1994-01-01

    We have derived an analytic solution to the asymptotic behavior of dipolar magnetic fields that are generated in the crusts of neutron stars. We show that if the conductivity is due to impurity scattering, as expected for late stages of evolution, the surface field strength at the magnetic pole declines with the power law B(sub p) approximately = (t/t(sub 0))(exp -2/3). The results are shown to be qualitatively consistent with detailed numerical calculations. These latter results are consistent with some recent analyses of pulsar statistics and the magnetic fields of several binary pulsars with white dwarf companions whose ages have been determined. The dependence of the surface magnetic field on spin period of the pulsar is derived.

  1. Neutron-activation analysis of several US Geological Survey and National Bureau of Standards reference materials

    SciTech Connect

    Daly, A.T.

    1981-01-01

    In this work, several US Geological Survey (U.S.G.S.) and National Bureau of Standards (N.B.S.) reference samples have been analyzed in an effort to improve the quality of elemental concentration data available on these materials, so they can be used in a program of verification of factor analysis source resolution procedures. The analyses of these samples were performed by instrumental neutron activation analysis (INAA). The samples analyzed were: U.S.G.S. Green River Shale, N.B.S. 45b Homogeneous River Sediment, U.S.G.S. Analyzed Peridotite N.B.S. 1579 Powdered Lead-based Paint, U.S.G.S. Hawaian Basalt U.S.G.S. Marine Mud, U.S.G.S. Analyzed Cody Shale U.S.G.S. Glass Mountain Rhyolite, N.B.S. Argillaceous Limestone No. 1, and a sample of Spex ultrapure graphite. Neutron activation analysis was employed because of the high sensitivity that can be attained in determining elemental concentrations. Although INAA is a relatively simple method and the reproducibility of the data is good, the method shows some inaccuracies. The basic theory and technique are reviewed in an attempt to show where problems can arise and how they can be dealt with.

  2. A field evaporation deuterium ion source for neutron generators

    SciTech Connect

    Reichenbach, Birk; Solano, I.; Schwoebel, P. R.

    2008-05-01

    Proof-of-principle experiments have demonstrated an electrostatic field evaporation based deuterium ion source for use in compact, high-output deuterium-tritium neutron generators. The ion source produces principally atomic deuterium and titanium ions. More than 100 ML of deuterated titanium thin film can be removed and ionized from a single tip in less than 20 ns. The measurements indicate that with the use of microfabricated tip arrays the deuterium ion source could provide sufficient ion current to produce 10{sup 9}-10{sup 10} n/cm{sup 2} of tip array area.

  3. A field evaporation deuterium ion source for neutron generators

    NASA Astrophysics Data System (ADS)

    Reichenbach, Birk; Solano, I.; Schwoebel, P. R.

    2008-05-01

    Proof-of-principle experiments have demonstrated an electrostatic field evaporation based deuterium ion source for use in compact, high-output deuterium-tritium neutron generators. The ion source produces principally atomic deuterium and titanium ions. More than 100 ML of deuterated titanium thin film can be removed and ionized from a single tip in less than 20 ns. The measurements indicate that with the use of microfabricated tip arrays the deuterium ion source could provide sufficient ion current to produce 109-1010 n/cm2 of tip array area.

  4. Development and characteristics of the HANARO neutron irradiation facility for applications in the boron neutron capture therapy field

    NASA Astrophysics Data System (ADS)

    Kim, Myong-Seop; Lee, Byung-Chul; Hwang, Sung-Yul; Kim, Heonil; Jun, Byung-Jin

    2007-05-01

    The HANARO neutron irradiation facility for various applications in the boron neutron capture therapy (BNCT) field was developed, and its characteristics were investigated. In order to obtain the sufficient thermal neutron flux with a low level of contamination by fast neutrons and gamma rays, a radiation filtering method was adopted. The radiation filter was designed by using a silicon single crystal, cooled by liquid nitrogen, and a bismuth crystal. The installation of the main components of the irradiation facility and the irradiation room was finished. Neutron beam characteristics were measured by using bare and cadmium-covered gold foils and wires. The in-phantom neutron flux distribution was measured for flux mapping inside the phantom. The gamma-ray dose was determined by using TLD-700 thermoluminescence dosimeters. The thermal and fast neutron fluxes and the gamma-ray dose were calculated by using the MCNP code, and they were compared with experimental data. The thermal neutron flux and Cd ratio available at this facility were confirmed to be 1.49 × 109 n cm-2 s-1 and 152, respectively. The maximum neutron flux inside the phantom was measured to be 2.79 × 109 n cm-2 s-1 at a depth of 3 mm in the phantom. The two-dimensional in-phantom neutron flux distribution was determined, and significant neutron irradiation was observed within 20 mm from the phantom surface. The gamma-ray dose rate for the free beam condition was expected to be about 80 cGy h-1. These experimental results were reasonably well supported by calculation using the facility design code. This HANARO thermal neutron facility can be used not only for clinical trials, but also for various pre-clinical studies in the BNCT field.

  5. Development and characteristics of the HANARO neutron irradiation facility for applications in the boron neutron capture therapy field.

    PubMed

    Kim, Myong-Seop; Lee, Byung-Chul; Hwang, Sung-Yul; Kim, Heonil; Jun, Byung-Jin

    2007-05-01

    The HANARO neutron irradiation facility for various applications in the boron neutron capture therapy (BNCT) field was developed, and its characteristics were investigated. In order to obtain the sufficient thermal neutron flux with a low level of contamination by fast neutrons and gamma rays, a radiation filtering method was adopted. The radiation filter was designed by using a silicon single crystal, cooled by liquid nitrogen, and a bismuth crystal. The installation of the main components of the irradiation facility and the irradiation room was finished. Neutron beam characteristics were measured by using bare and cadmium-covered gold foils and wires. The in-phantom neutron flux distribution was measured for flux mapping inside the phantom. The gamma-ray dose was determined by using TLD-700 thermoluminescence dosimeters. The thermal and fast neutron fluxes and the gamma-ray dose were calculated by using the MCNP code, and they were compared with experimental data. The thermal neutron flux and Cd ratio available at this facility were confirmed to be 1.49 x 10(9) n cm(-2) s(-1) and 152, respectively. The maximum neutron flux inside the phantom was measured to be 2.79 x 10(9) n cm(-2) s(-1) at a depth of 3 mm in the phantom. The two-dimensional in-phantom neutron flux distribution was determined, and significant neutron irradiation was observed within 20 mm from the phantom surface. The gamma-ray dose rate for the free beam condition was expected to be about 80 cGy h(-1). These experimental results were reasonably well supported by calculation using the facility design code. This HANARO thermal neutron facility can be used not only for clinical trials, but also for various pre-clinical studies in the BNCT field. PMID:17440252

  6. Measurement and modeling of polarized specular neutron reflectivity in large magnetic fields

    PubMed Central

    Maranville, Brian B.; Kirby, Brian J.; Grutter, Alexander J.; Kienzle, Paul A.; Majkrzak, Charles F.; Liu, Yaohua; Dennis, Cindi L.

    2016-01-01

    The presence of a large applied magnetic field removes the degeneracy of the vacuum energy states for spin-up and spin-down neutrons. For polarized neutron reflectometry, this must be included in the reference potential energy of the Schrödinger equation that is used to calculate the expected scattering from a magnetic layered structure. For samples with magnetization that is purely parallel or antiparallel to the applied field which defines the quantization axis, there is no mixing of the spin states (no spin-flip scattering) and so this additional potential is constant throughout the scattering region. When there is non-collinear magnetization in the sample, however, there will be significant scattering from one spin state into the other, and the reference potentials will differ between the incoming and outgoing wavefunctions, changing the angle and intensities of the scattering. The theory of the scattering and recommended experimental practices for this type of measurement are presented, as well as an example measurement. PMID:27504074

  7. Measurement and modeling of polarized specular neutron reflectivity in large magnetic fields

    DOE PAGESBeta

    Maranville, Brian B.; Kirby, Brian J.; Grutter, Alexander J.; Kienzle, Paul A.; Majkrzak, Charles F.; Liu, Yaohua; Dennis, Cindi L.

    2016-06-09

    The presence of a large applied magnetic field removes the degeneracy of the vacuum energy states for spin-up and spin-down neutrons. For polarized neutron reflectometry, this must be included in the reference potential energy of the Schrödinger equation that is used to calculate the expected scattering from a magnetic layered structure. For samples with magnetization that is purely parallel or antiparallel to the applied field which defines the quantization axis, there is no mixing of the spin states (no spin-flip scattering) and so this additional potential is constant throughout the scattering region. When there is non-collinear magnetization in the sample,more » however, there will be significant scattering from one spin state into the other, and the reference potentials will differ between the incoming and outgoing wavefunctions, changing the angle and intensities of the scattering. In conclusion, the theory of the scattering and recommended experimental practices for this type of measurement are presented, as well as an example measurement.« less

  8. Simulated magnetic field expulsion in neutron star cores

    NASA Astrophysics Data System (ADS)

    Elfritz, J. G.; Pons, J. A.; Rea, N.; Glampedakis, K.; Viganò, D.

    2016-03-01

    The study of long-term evolution of neutron star (NS) magnetic fields is key to understanding the rich diversity of NS observations, and to unifying their nature despite the different emission mechanisms and observed properties. Such studies in principle permit a deeper understanding of the most important parameters driving their apparent variety, e.g. radio pulsars, magnetars, X-ray dim isolated NSs, gamma-ray pulsars. We describe, for the first time, the results from self-consistent magnetothermal simulations considering not only the effects of the Hall-driven field dissipation in the crust, but also adding a complete set of proposed driving forces in a superconducting core. We emphasize how each of these core-field processes drive magnetic evolution and affect observables, and show that when all forces are considered together in vectorial form, the net expulsion of core magnetic flux is negligible, and will have no observable effect in the crust (consequently in the observed surface emission) on megayear time-scales. Our new simulations suggest that strong magnetic fields in NS cores (and the signatures on the NS surface) will persist long after the crustal magnetic field has evolved and decayed, due to the weak combined effects of dissipation and expulsion in the stellar core.

  9. Effects of hole doping by neutron irradiation of magnetic field induced electronic phase transitions in graphite

    SciTech Connect

    Singleton, John; Yaguchi, Hiroshi

    2008-01-01

    We have investigated effects of hole doping by fast-neutron irradiation on the magnetic-field induced phase transitions in graphite using specimens irradiated with fast neutrons. Resistance measurements have been done in magnetic fields of up to above 50 T and at temperatures down to about 1.5 K. The neutron irradiation creates lattice defects acting as acceptors, affecting the imbalance of the electron and hole densities and the Fermi level. We have found that the reentrant field from the field induced state back to the normal state shifts towards a lower field with hole doping, suggestive of the participation of electron subbands in the magnetic-field induced state.

  10. Characterization of extended range Bonner Sphere Spectrometers in the CERF high-energy broad neutron field at CERN

    NASA Astrophysics Data System (ADS)

    Agosteo, S.; Bedogni, R.; Caresana, M.; Charitonidis, N.; Chiti, M.; Esposito, A.; Ferrarini, M.; Severino, C.; Silari, M.

    2012-12-01

    The accurate determination of the ambient dose equivalent in the mixed neutron-photon fields encountered around high-energy particle accelerators still represents a challenging task. The main complexity arises from the extreme variability of the neutron energy, which spans over 10 orders of magnitude or more. Operational survey instruments, which response function attempts to mimic the fluence-to-ambient dose equivalent conversion coefficient up to GeV neutrons, are available on the market, but their response is not fully reliable over the entire energy range. Extended range rem counters (ERRC) do not require the exact knowledge of the energy distribution of the neutron field and the calibration can be done with a source spectrum. If the actual neutron field has an energy distribution different from the calibration spectrum, the measurement is affected by an added uncertainty related to the partial overlap of the fluence-to-ambient dose equivalent conversion curve and the response function. For this reason their operational use should always be preceded by an "in-field" calibration, i.e. a calibration made against a reference instrument exposed in the same field where the survey-meter will be employed. In practice the extended-range Bonner Sphere Spectrometer (ERBSS) is the only device which can serve as reference instrument in these fields, because of its wide energy range and the possibility to assess the neutron fluence and the ambient dose equivalent (H*(10)) values with the appropriate accuracy. Nevertheless, the experience gained by a number of experimental groups suggests that mandatory conditions for obtaining accurate results in workplaces are: (1) the use of a well-established response matrix, thus implying validation campaigns in reference monochromatic neutrons fields, (2) the expert and critical use of suitable unfolding codes, and (3) the performance test of the whole system (experimental set-up, elaboration and unfolding procedures) in a well

  11. Conditions for jet formation in accreting neutron stars: the magnetic field decay

    NASA Astrophysics Data System (ADS)

    García, Federico; Aguilera, Deborah N.; Romero, Gustavo E.

    2011-02-01

    Accreting neutron stars can produce jets only if they are weakly magnetized (B ~ 108 G). On the other hand, neutron stars are compact objects born with strong surface magnetic fields (B ~ 1012 G). In this work we study the conditions for jet formation in a binary system formed by a neutron star and a massive donor star once the magnetic field has decayed due to accretion. We solve the induction equation for the magnetic field diffusion in a realistic neutron star crust and discuss the possibility of jet launching in systems like the recently detected Supergiant Fast X-ray Transients.

  12. Characterisation of mixed neutron photon workplace fields at nuclear facilities by spectrometry (energy and direction) within the EVIDOS project.

    PubMed

    Luszik-Bhadra, M; Bartlett, D; Bolognese-Milsztajn, T; Boschung, M; Coeck, M; Curzio, G; d'Errico, F; Fiechtner, A; Lacoste, V; Lindborg, L; Reginatto, M; Schuhmacher, H; Tanner, R; Vanhavere, F

    2007-01-01

    Within the EC project EVIDOS, 17 different mixed neutron-photon workplace fields at nuclear facilities (boiling water reactor, pressurised water reactor, research reactor, fuel processing, storage of spent fuel) were characterised using conventional Bonner sphere spectrometry and newly developed direction spectrometers. The results of the analysis, using Bayesian parameter estimation methods and different unfolding codes, some of them especially adapted to simultaneously unfold energy and direction distributions of the neutron fluence, showed that neutron spectra differed strongly at the different places, both in energy and direction distribution. The implication of the results for the determination of reference values for radiation protection quantities (ambient dose equivalent, personal dose equivalent and effective dose) and the related uncertainties are discussed. PMID:17890781

  13. Monitoring Neutron Generator Output in a Mixed Neutron-Gamma Field Using a Plastic Scintillator.

    SciTech Connect

    Mitra,S.; Wielopolski, L.

    2007-10-28

    Quantitative neutron-induced gamma-ray spectroscopy employing neutron generators (NGs) entails monitoring them for possible fluctuations in their neutron output. We accomplished this using a plastic scintillator and recording a spectrum from which we selected a neutron region-of-interest (nROI) to discriminate between neutrons and the accompanying high-energy gamma-rays. We show that the selected nROI is insensitive to changes in the gamma-ray background, thus allowing satisfactory normalization of the gamma-ray spectra of an in-situ system for analyzing soil carbon.

  14. FIELD VALIDATION OF EPA (ENVIRONMENTAL PROTECTION AGENCY) REFERENCE METHOD 23

    EPA Science Inventory

    The accuracy and precision of U.S. Environmental Protection Agency Reference Method 23 was evaluated at a trichloroethylene degreasing facility and an ethylene dichloride plant. The method consists of a procedure for obtaining an integrated sample followed by gas chromatographic ...

  15. Neutron star cooling: A challenge to the nuclear mean field

    SciTech Connect

    Hoang Sy Than; Nguyen Van Giai

    2009-12-15

    The two recent density-dependent versions of the finite-range M3Y interaction (CDM3Yn and M3Y-Pn) have been probed against the bulk properties of asymmetric nuclear matter (NM) in the nonrelativistic Hartree-Fock (HF) formalism. The same HF study has also been done with the famous Skyrme (SLy4) and Gogny (D1S and D1N) interactions that were well tested in the nuclear structure calculations. Our HF results are compared with those given by other many-body calculations like the Dirac-Brueckner Hartree-Fock approach or ab initio variational calculations using free nucleon-nucleon interaction and by both the nonrelativistic and relativistic mean-field studies using different model parameters. Although the two considered density-dependent versions of the M3Y interaction were proven to be quite realistic in the nuclear structure or reaction studies, they give two distinct behaviors of the NM symmetry energy at high densities, like the Asy-soft and Asy-stiff scenarios found earlier with other mean-field interactions. As a consequence, we obtain two different behaviors of the proton fraction in the {beta}-equilibrium that in turn can imply two drastically different mechanisms for the neutron star cooling. While some preference of the Asy-stiff scenario was found based on predictions of the latest microscopic many-body calculations or empirical NM pressure and isospin diffusion data deduced from heavy-ion collisions, a consistent mean-field description of nuclear structure database is more often given by some Asy-soft type interaction like the Gogny or M3Y-Pn ones. Such a dilemma poses an interesting challenge to the modern mean-field approaches.

  16. EuTEPC: measurements in gamma and neutron fields.

    PubMed

    Moro, D; Chiriotti, S

    2015-09-01

    The EuTEPC (European TEPC) is a novel spherical tissue-equivalent gas-proportional single-wire counter that has been designed and constructed at the National Laboratories of Legnaro of Italian Nuclear Physics Institute in collaboration with the University of Padova, the DLR (German Aerospace Centre) and Austrian Institute of Technology. Its peculiarity is the spherical A-150 cathode wall which is sub-divided in nine sectors. Each sector is properly and differently biased, in order to obtain a uniform electric field along the anode wire, for reaching a good isotropic response and energy resolution. The counter components can be easily replaced and reassembled including the anode wire. The counter could be used as a monitor area inside the International Space Station. This paper describes first microdosimetric measurements in (60)Co, (137)Cs and (241)Am-Be(α,n) gamma and neutron fields performed with the EuTEPC filled with pure propane gas. Measurements have been performed simulating sites sizes, ranging from 0.05 up to 0.25 mg cm(-2) in pure propane, which correspond from 0.7 up to 3.3 µm equivalent site sizes in propane-TE gas. Comparisons with some literature spectra are presented. PMID:25877529

  17. Application of the TLD albedo technique for monitoring and interpretation of neutron stray radiation fields

    NASA Astrophysics Data System (ADS)

    Piesch, E.; Burgkhardt, B.

    1980-09-01

    A single sphere albedo technique with TLD 600/TLD 700 detectors has been applied in neutron monitoring to calibrate albedo dosimeters and to interpret neutron stray radiation fields in terms of neutron dose equivalent separated for the energy groups below 0.4 eV, 0.4-10 keV and 10 keV-10 MeV, and Eeff for fast neutrons. The paper describes the technique for field and personnel monitoring under the aspect of an on-line computer program for data recording and processing.

  18. Characteristics of Neutron Fields for Radiation Protection and Other Applications at the Kinki University Reactor

    NASA Astrophysics Data System (ADS)

    Ogawa, Yoshihiro; Fujiwara, Tatsuya; Morishima, Hiroshige; Urabe, Itsumasa; Sagawa, Hiroyuki

    2003-06-01

    In order to get useful information about neutron energy spectrum and neutron dose, a versatile and accurate reactor model of the Kinki University Reactor (UTR-KINKI) was developed under the three-dimensional continuous-energy MCNP Monte Carlo code. The agreement between MCNP predictions and the experimentally determined values was very good. This paper describes characteristics of neutron fields at the Kinki University Reactor calculated with the present MCNP model of the UTR-KINKI. From the results obtained it was clear that these neutron fields are applicable to development and performance evaluation of personnel dosimeters and experimental studies on biological effects of low levels of radiation.

  19. Calculation verification of the utilization of LR-0 for reference neutron spectra

    NASA Astrophysics Data System (ADS)

    Ján, Milčák; Michal, Košťál; Marie, Švadlenková; Michal, Koleška; Vojtěch, Rypar

    2014-11-01

    Well-defined neutron spectrum is crucial for calibration and testing of detectors for spectrometry and dosimetry purposes. As a possible source of neutrons nuclear reactors can be utilized. In reactor core most of the neutrons are originated from fission and neutron spectra is usually some form of moderated spectra of fast neutrons. The reactor LR-0 is an experimental light-water zero-power pool-type reactor originally designed for research of the VVER type reactor cores, spent-fuel storage lattices and benchmark experiments. The main reactor feature that influences the performance of experiments is the flexible arrangement of the core. Special types of the possible core arrangements on the reactor LR-0 can provide different neutron spectra in special experimental channels. These neutron spectra are modified by inserting different materials around the channel and whole core is driven by standard fuel assemblies. Fast, epithermal or thermal spectra can be simulated using graphite, H2O, D2O insertions, air, Cd foils or fuel with different enrichment.

  20. Internal composition of proto-neutron stars under strong magnetic fields

    NASA Astrophysics Data System (ADS)

    Franzon, B.; Dexheimer, V.; Schramm, S.

    2016-08-01

    In this work, we study the effects of magnetic fields and rotation on the structure and composition of proto-neutron stars. A hadronic chiral SU(3) model is applied to cold neutron stars and proto-neutron stars with trapped neutrinos and at fixed entropy per baryon. We obtain general relativistic solutions for neutron and proto-neutron stars endowed with a poloidal magnetic field by solving Einstein-Maxwell field equations in a self-consistent way. As the neutrino chemical potential decreases in value over time, this alters the chemical equilibrium and the composition inside the star, leading to a change in the structure and in the particle population of these objects. We find that the magnetic field deforms the star and significantly alters the number of trapped neutrinos in the stellar interior, together with strangeness content and temperature in each evolution stage.

  1. Neutron Star Magnetic Field Evolution, Crust Movement, and Glitches: Erratum

    NASA Astrophysics Data System (ADS)

    Ruderman, Malvin; Zhu, Tianhua; Chen, Kaiyou

    1998-08-01

    In the paper "Neutron Star Magnetic Field Evolution, Crust Movement, and Glitches" by Malvin Ruderman, Tianhua Zhu, and Kaiyou Chen (ApJ, 492, 267 [1998]), the following corrections should be made: Four lines below equation (24), "with v_phi still the same as that of the Vela" should be replaced by "with each vortex line-flux-tube intersection force still the same as that in Vela." Just after equation (25), "as long as 3 - n is less than 1, but 3 - n = 1 otherwise" should be inserted. There is no change in Table 1. The authors also note that a new analysis of observations of the period history of PSR 0540-69 gives a most probable spin-down index n = 2.5 (S. Eikenberg, G. Fazio, and S. Ransom, ApJ, 492, 754 [1998]), which removes the major discrepancy between the observed and model spin-down indices and makes the remarks about it below equation (25) no longer relevant.

  2. Radiation fields from neutron generators shielded with different materials

    NASA Astrophysics Data System (ADS)

    Chichester, D. L.; Blackburn, B. W.

    2007-08-01

    As a general guide for assessing radiological conditions around a DT neutron generator numerical modeling has been performed to assess neutron and photon dose profiles for a variety of shield materials ranging from 1 to 100 cm thick. In agreement with accepted radiation safety practices high-Z materials such as bismuth and lead have been found to be ineffective biological shield materials, owing in part to the existence of (n,2n) reaction channels available with 14.1 MeV DT neutrons, while low-Z materials serve as effective shields for these sources. Composite materials such as a mixture of polyethylene and bismuth, or regular concrete, are ideal shield materials for neutron generator radiation because of their ability to attenuate internally generated photon radiation resulting from neutron scattering and capture within the shields themselves.

  3. Neutron Scattering at Highest Magnetic Fields at the Helmholtz Centre Berlin

    NASA Astrophysics Data System (ADS)

    Smeibidl, P.; Tennant, A.; Ehmler, H.; Bird, M.

    2010-04-01

    The Helmholtz Centre Berlin (HZB), formerly Hahn-Meitner Institute is a user facility for the study of structure and dynamics with neutrons and synchrotron radiation with special emphasis on experiments under extreme conditions. Neutron scattering is uniquely suited to study magnetic properties on a microscopic length scale, because neutrons have comparable wavelengths and, due to their magnetic moment, they interact with the atomic magnetic moments. At HZB a dedicated instrument for neutron scattering at extreme fields is under construction, the Extreme Environment Diffractometer ExED. It is projected according to the “time-of-flight” principle for elastic and inelastic neutron scattering and for the special geometric constraints of analysing samples in a high field magnet. The new magnet will not only allow for novel experiments, it will be at the forefront of development in magnet technology itself. The design of the magnet will follow the Series Connected Hybrid System Technology (SCH) developed at the National High Magnetic Field Laboratory (NHMFL) in Tallahassee, Florida. To compromise between the needs of the magnet design for highest fields and the concept of the neutron instrument, the magnetic field will be generated by means of a coned solenoid with horizontal field orientation. By using resistive insert coils, which are mounted in the room temperature bore of a superconducting cable-in-conduit (CIC) magnet, fields above 30 Tesla can be obtained in a geometry optimised for the demands of neutron scattering.

  4. 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.

  5. Compact deuterium-tritium neutron generator using a novel field ionization source

    SciTech Connect

    Ellsworth, J. L. Falabella, S.; Sanchez, J.; Tang, V.; Wang, H.

    2014-11-21

    Active interrogation using neutrons is an effective method for detecting shielded nuclear material. A lightweight, lunch-box-sized, battery-operated neutron source would enable new concepts of operation in the field. We have developed at-scale components for a highly portable, completely self-contained, pulsed Deuterium-Tritium (DT) neutron source producing 14 MeV neutrons with average yields of 10{sup 7} n/s. A gated, field ionization ion source using etched electrodes has been developed that produces pulsed ion currents up to 500 nA. A compact Cockcroft-Walton high voltage source is used to accelerate deuterons into a metal hydride target for neutron production. The results of full scale DT tests using the field ionization source are presented.

  6. Quantification of the sensitivity range in neutron dark-field imaging

    SciTech Connect

    Betz, B.; Harti, R. P.; Hovind, J.; Kaestner, A.; Lehmann, E.; Grünzweig, C.; Strobl, M.; Van Swygenhoven, H.

    2015-12-15

    In neutron grating interferometry, the dark-field image visualizes the scattering properties of samples in the small-angle and ultra-small-angle scattering range. These angles correspond to correlation lengths from several hundred nanometers up to several tens of micrometers. In this article, we present an experimental study that demonstrates the potential of quantitative neutron dark-field imaging. The dark-field signal for scattering from different particle sizes and concentrations of mono-dispersive polystyrene particles in aqueous solution is compared to theoretical predictions and the good agreement between measurements and calculations underlines the quantitative nature of the measured values and reliability of the technique with neutrons.

  7. Quantification of the sensitivity range in neutron dark-field imaging

    NASA Astrophysics Data System (ADS)

    Betz, B.; Harti, R. P.; Strobl, M.; Hovind, J.; Kaestner, A.; Lehmann, E.; Van Swygenhoven, H.; Grünzweig, C.

    2015-12-01

    In neutron grating interferometry, the dark-field image visualizes the scattering properties of samples in the small-angle and ultra-small-angle scattering range. These angles correspond to correlation lengths from several hundred nanometers up to several tens of micrometers. In this article, we present an experimental study that demonstrates the potential of quantitative neutron dark-field imaging. The dark-field signal for scattering from different particle sizes and concentrations of mono-dispersive polystyrene particles in aqueous solution is compared to theoretical predictions and the good agreement between measurements and calculations underlines the quantitative nature of the measured values and reliability of the technique with neutrons.

  8. Gamma ray bursts from comet neutron star magnetosphere interaction, field twisting and E sub parallel formation

    SciTech Connect

    Colgate, S.A.

    1990-01-01

    Consider the problem of a comet in a collision trajectory with a magnetized neutron star. The question addressed in this paper is whether the comet interacts strongly enough with a magnetic field such as to capture at a large radius or whether in general the comet will escape a magnetized neutron star. 6 refs., 4 figs.

  9. Polarisation Analysis Neutron Spectrometer, POLANO, at J-PARC - Concept and Magnetic Field Optimisation

    NASA Astrophysics Data System (ADS)

    Ohoyama, K.; Yokoo, T.; Itoh, S.; Nanbu, M.; Iwasa, K.; Ohkawara, M.; Kaneko, N.; Ino, T.; Hayashida, H.; Oku, T.; Kira, H.; Tasaki, S.; Takeda, M.; Kimura, H.; Sato, T. J.

    2016-04-01

    The status of the polarised neutron spectrometer constructed at the Japan Proton Accelerator Research Complex through a collaboration between Tohoku University and KEK will be reported. In particular, the optimisation of magnetic fields to minimise neutron- beam depolarisation using the finite element method will be discussed on the basis of several simulations using the finite element method.

  10. Neutron Star Structure in the Presence of Conformally Coupled Scalar Fields

    NASA Technical Reports Server (NTRS)

    Sultana, Joseph; Bose, Benjamin; Kazanas, Demosthenes

    2014-01-01

    Neutron star models are studied in the context of scalar-tensor theories of gravity in the presence of a conformally coupled scalar field, using two different numerical equations of state (EoS) representing different degrees of stiffness. In both cases we obtain a complete solution by matching the interior numerical solution of the coupled Einstein-scalar field hydrostatic equations, with an exact metric on the surface of the star. These are then used to find the effect of the scalar field and its coupling to geometry, on the neutron star structure, particularly the maximum neutron star mass and radius. We show that in the presence of a conformally coupled scalar field, neutron stars are less dense and have smaller masses and radii than their counterparts in the minimally coupled case, and the effect increases with the magnitude of the scalar field at the center of the star.

  11. Neutron star structure in the presence of conformally coupled scalar fields

    NASA Astrophysics Data System (ADS)

    Sultana, Joseph; Bose, Benjamin; Kazanas, Demosthenes

    2014-10-01

    Neutron star models are studied in the context of scalar-tensor theories of gravity in the presence of a conformally coupled scalar field, using two different numerical equations of state (EoS) representing different degrees of stiffness. In both cases we obtain a complete solution by matching the interior numerical solution of the coupled Einstein-scalar field hydrostatic equations, with an exact metric on the surface of the star. These are then used to find the effect of the scalar field and its coupling to geometry, on the neutron star structure, particularly the maximum neutron star mass and radius. We show that in the presence of a conformally coupled scalar field, neutron stars are less dense and have smaller masses and radii than their counterparts in the minimally coupled case, and the effect increases with the magnitude of the scalar field at the center of the star.

  12. A method for comparing degradation of boron trifluoride and helium detectors in neutron and gamma fields

    SciTech Connect

    Qian, T.; Tonner, P.; Keller, N.; Buyers, W.J.L.

    1998-06-01

    A method developed to measure the degradation of neutron detectors in neutron and gamma fields has been applied to five models of boron trifluoride (BF{sub 3}) detectors from major suppliers, and to a special helium ({sup 3}He) detector model. The detectors tested all have about the same nominal thermal neutron sensitivity and overall dimensions. The results showed widely different neutron and gamma durability for BF{sub 3} models, an undesirable time-dependent gamma degradation followed by recovery for some BF{sub 3} models, and very robust performance of the modified {sup 3}He detector.

  13. Proton and neutron skins of light nuclei within the relativistic mean field theory

    NASA Astrophysics Data System (ADS)

    Geng, L. S.; Toki, H.; Ozawa, A.; Meng, J.

    2004-01-01

    The relativistic mean field (RMF) theory is applied to the analysis of ground-state properties of Ne, Na, Cl and Ar isotopes. In particular, we study the recently established proton skin in Ar isotopes and neutron skin in Na isotopes as a function of the difference between the proton and the neutron separation energy. We use the TMA effective interaction in the RMF Lagrangian, and describe pairing correlation by the density-independent delta-function interaction. We calculate single neutron and proton separation energies, quadrupole deformations, nuclear matter radii and differences between proton radii and neutron radii, and compare these results with the recent experimental data.

  14. Topological currents in neutron stars: kicks, precession, toroidal fields, and magnetic helicity

    SciTech Connect

    Charbonneau, James; Zhitnitsky, Ariel E-mail: arz@phas.ubc.ca

    2010-08-01

    The effects of anomalies in high density QCD are striking. We consider a direct application of one of these effects, namely topological currents, on the physics of neutron stars. All the elements required for topological currents are present in neutron stars: degenerate matter, large magnetic fields, and parity violating processes. These conditions lead to the creation of vector currents capable of carrying momentum and inducing magnetic fields. We estimate the size of these currents for many representative states of dense matter in the neutron star and argue that they could be responsible for the large proper motion of neutron stars (kicks), the toroidal magnetic field and finite magnetic helicity needed for stability of the poloidal field, and the resolution of the conflict between type-II superconductivity and precession. Though these observational effects appear unrelated, they likely originate from the same physics — they are all P-odd phenomena that stem from a topological current generated by parity violation.

  15. Field Testing Near-IR and Neutron Spectrometer Prospecting: Applications to Resource Prospector on the Moon

    NASA Astrophysics Data System (ADS)

    Elphic, R. C.; Colaprete, A.; Heldmann, J. L.; Deans, M. C.

    2015-10-01

    The Resource Prospector payload includes a near-infrared spectrometer and neutron spectrometer for surficial and near-surface volatile prospecting. Here we describe results from a field test in the Mojave Desert using the two instruments.

  16. Improvement of depth dose distribution using multiple-field irradiation in boron neutron capture therapy.

    PubMed

    Fujimoto, N; Tanaka, H; Sakurai, Y; Takata, T; Kondo, N; Narabayashi, M; Nakagawa, Y; Watanabe, T; Kinashi, Y; Masunaga, S; Maruhashi, A; Ono, K; Suzuki, M

    2015-12-01

    It is important that improvements are made to depth dose distribution in boron neutron capture therapy, because the neutrons do not reach the innermost regions of the human body. Here, we evaluated the dose distribution obtained using multiple-field irradiation in simulation. From a dose volume histogram analysis, it was found that the mean and minimum tumor doses were increased using two-field irradiation, because of improved dose distribution for deeper-sited tumors. PMID:26282566

  17. Neutron field measurements of the CRNA OB26 irradiator using a Bonner sphere spectrometer for radiation protection purposes.

    PubMed

    Mazrou, H; Allab, M

    2012-08-01

    The present work deals with the Bonner sphere spectrometer (BSS) measurements performed, to support the authors' Monte-Carlo calculations, to estimate accurately the main characteristics of the neutron field of the (241)Am-Be-based OB26 irradiator acquired for radiation protection purposes by the Nuclear Research Centre of Algiers. The measurements were performed at a reference irradiation position selected at 150 cm from the geometrical centre of the neutron source. The spectrometric system in use is based on a central spherical (3)He thermal neutron proportional counter. The response matrix of the present spectrometer has been taken to be similar to the original Physikalisch-Technische Bundesanstalt (PTB) (Braunschweig, Germany) BSS's response matrix, with a five bins per decade energy group structure, as there is no significant difference in the BSS's physical characteristics. Thereafter, the authors' BSS measurements were used together with MCNP5 results to unfold the neutron spectrum by means of MAXED and GRAVEL computer codes from the U.M.G. 3.3 package, developed at PTB. Besides, sensitivity analysis has been performed to test the consistency of the unfolding procedure. It reveals that no significant discrepancy was observed in the total neutron fluence and total ambient dose values following the perturbation of some pertinent unfolding parameters except for the case where a 10 bins energy structure was assumed for the guess spectrum. In this latter case, a 5 % difference was observed in the ambient dose equivalent compared with the reference case. Finally, a comparative study performed between different counting systems together with MCNP5 and predictive formulas results shows that they were globally satisfactory, highlighting thereby the relevance of the unfolding procedure and the reliability of the obtained results. PMID:22345213

  18. The effect of thermal neutron field slagging caused by cylindrical BF3 counters in diffusion media

    NASA Technical Reports Server (NTRS)

    Gorshkov, G. V.; Tsvetkov, O. S.; Yakovlev, R. M.

    1975-01-01

    Computations are carried out in transport approximation (first collision method) for the attenuation of the field of thermal neutrons formed in counters of the CHM-8 and CHMO-5 type. The deflection of the thermal neutron field is also obtained near the counters and in the air (shade effect) and in various decelerating media (water, paraffin, plexiglas) for which the calculations are carried out on the basis of diffusion theory. To verify the calculations, the distribution of the density of the thermal neutrons at various distances from the counter in the water is measured.

  19. Development of a compact neutron source based on field ionization processes

    SciTech Connect

    Persaud, Arun; Allen, Ian; Dickinson, Michael R.; Schenkel, Thomas; Kapadia, Rehan; Takei, Kuniharu; Javey, Ali

    2010-11-25

    The authors report on the use of carbon nanofiber nanoemitters to ionize deuterium atoms for the generation of neutrons in a deuterium-deuterium reaction in a preloaded target. Acceleration voltages in the range of 50-80 kV are used. Field emission of electrons is investigated to characterize the emitters. The experimental setup and sample preparation are described and first data of neutron production are presented. Ongoing experiments to increase neutron production yields by optimizing the field emitter geometry and surface conditions are discussed.

  20. Periodic magnetic field as a polarized and focusing thermal neutron spectrometer and monochromator

    SciTech Connect

    Cremer, J. T.; Williams, D. L.; Fuller, M. J.; Gary, C. K.; Piestrup, M. A.; Pantell, R. H.; Feinstein, J.; Flocchini, R. G.; Boussoufi, M.; Egbert, H. P.; Kloh, M. D.; Walker, R. B.

    2010-01-15

    A novel periodic magnetic field (PMF) optic is shown to act as a prism, lens, and polarizer for neutrons and particles with a magnetic dipole moment. The PMF has a two-dimensional field in the axial direction of neutron propagation. The PMF alternating magnetic field polarity provides strong gradients that cause separation of neutrons by wavelength axially and by spin state transversely. The spin-up neutrons exit the PMF with their magnetic spins aligned parallel to the PMF magnetic field, and are deflected upward and line focus at a fixed vertical height, proportional to the PMF period, at a downstream focal distance that increases with neutron energy. The PMF has no attenuation by absorption or scatter, as with material prisms or crystal monochromators. Embodiments of the PMF include neutron spectrometer or monochromator, and applications include neutron small angle scattering, crystallography, residual stress analysis, cross section measurements, and reflectometry. Presented are theory, experimental results, computer simulation, applications of the PMF, and comparison of its performance to Stern-Gerlach gradient devices and compound material and magnetic refractive prisms.

  1. Temperature compensated and self-calibrated current sensor using reference magnetic field

    DOEpatents

    Yakymyshyn, Christopher Paul; Brubaker, Michael Allen; Yakymyshyn, Pamela Jane

    2007-10-09

    A method is described to provide temperature compensation and self-calibration of a current sensor based on a plurality of magnetic field sensors positioned around a current carrying conductor. A reference magnetic field generated within the current sensor housing is detected by the magnetic field sensors and is used to correct variations in the output signal due to temperature variations and aging.

  2. Characterization of the IRSN neutron multisphere spectrometer (HERMEIS) at European standard calibration fields

    NASA Astrophysics Data System (ADS)

    Cheminet, A.; Lacoste, V.; Gressier, V.; Hubert, G.; Martin, A.; Pépino, M.

    2012-04-01

    The Institute for Radiological Protection and Nuclear Safety (IRSN) has developed a new spectrometry system for neutron energies from 10-9 MeV to 10 GeV. This high energy range multisphere extended IRSN system (HERMEIS) is a high gas pressure3He-based Bonner spheres set. It is adapted to low neutron fluence rate measurements and one of its main application concerns the determination of cosmic-ray-induced neutron spectra at ground level and mountain altitudes. The neutron fluence response matrix of the set of 13 Bonner spheres, including three extended ones with tungsten and lead shells, was calculated with the radiation transport code MCNPX-2.6f. Reliable fluence responses being mandatory for a correct evaluation of the atmospheric neutron spectra, HERMEIS was characterized at standard monoenergetic, quasi-monoenergetic and realistic neutron fields facilities. Measurements with monoenergetic neutron beams of 144 keV, 565 keV, 5 MeV and 17 MeV were performed at the NPL standard Van de Graaff facility. For the characterization of the response functions at higher energies, measurements were done at the Svedberg Laboratory, with 46 MeV and 144 MeV quasi-monoenergetic neutrons. Finally, to demonstrate the suitability of the system for broad cosmic-ray neutron spectra, measurements were performed at the TSL Atmospheric-like Neutrons from thIck TArget (ANITA) and also at the CERN European Realistic Field (CERF) facilities. Data from the realistic spectra were unfolded with the GRAVEL unfolding code and as a whole, a good agreement was found between the experimental and Monte-Carlo calculated neutron fluence energy distributions.

  3. Summary Report: First Research Coordination Meeting on ReferenceDatabase for Neutron Activation Analysis

    SciTech Connect

    Firestone, Richard B.; Trkov, Andrej

    2005-10-31

    Potential problems associated with nuclear data for neutronactivation analysis were identified, the scope of the work to beundertaken was defined together with its priorities, and tasks wereassigned to participants. Data testing and measurements refer to gammaspectrum peak evaluations, detector efficiency calibration, neutronspectrum characteristics and reference materials analysis.

  4. Summary Report: First Research Coordination Meeting on ReferenceDatabase for Neutron Activation Analysis

    SciTech Connect

    Firestone, Richard B.; Trkov, Andrej

    2005-10-01

    Potential problems associated with nuclear data for neutronactivation analysis were identified, the scope of the work to beundertaken was defined together with its priorities, and tasks wereassigned to participants. Data testing and measurements refer to gammaspectrumpeak evaluations, detector efficiency calibration, neutronspectrum characteristics and reference materials analysis.

  5. Effects of Magnetic Field Topology on Secondary Neutron Spectra in MagLIF

    NASA Astrophysics Data System (ADS)

    Appelbe, Brian; Chittenden, Jeremy

    2015-11-01

    Ignition in Magneto-Inertial Fusion schemes requires both inertial and magnetic confinement of the fuel and charged fusion products. Recent theoretical and experimental work has demonstrated the confinement of charged fusion products by magnetic fields in Magnetized Liner Inertial Fusion (MagLIF) experiments. This confinement can be inferred from the ratio of secondary to primary neutron yields and the shape of secondary neutron spectra. In this work we investigate the effects of magnetic field topology on the shape of secondary neutron spectra. The MagLIF design has a cylindrical geometry and includes both axial and azimuthal magnetic fields. The azimuthal field is initially in the liner surrounding the fuel but instability growth may cause it to penetrate into the fuel. Charged fusion products (such as tritons or alpha particles) that are isotropically emitted and then confined by an axial field will flow parallel and anti-parallel to the field with equal intensities. In the case of tritons, this motion results in a secondary neutron spectrum emitted in the axial direction that is symmetric. However, in an azimuthal field such particles exhibit singular orbits and there is a net ion drift along the axis. This ion drift can cause the secondary neutron spectrum to be asymmetric. We examine the effects on the spectrum shape of confinement by a combination of axial and azimuthal fields.

  6. Estimating field scale root zone soil moisture using the cosmic-ray neutron probe

    NASA Astrophysics Data System (ADS)

    Peterson, A. M.; Helgason, W. D.; Ireson, A. M.

    2015-12-01

    Many practical hydrological, meteorological and agricultural management problems require estimates of soil moisture with an areal footprint equivalent to "field scale", integrated over the entire root zone. The cosmic-ray neutron probe is a promising instrument to provide field scale areal coverage, but these observations are shallow and require depth scaling in order to be considered representative of the entire root zone. A study to identify appropriate depth-scaling techniques was conducted at a grazing pasture site in central Saskatchewan, Canada over a two year period. Area-averaged soil moisture was assessed using a cosmic-ray neutron probe. Root zone soil moisture was measured at 21 locations within the 5002 m2 area, using a down-hole neutron probe. The cosmic-ray neutron probe was found to provide accurate estimates of field scale surface soil moisture, but accounted for less than 40 % of the seasonal change in root zone storage due to its shallow measurement depth. The root zone estimation methods evaluated were: (1) the coupling of the cosmic-ray neutron probe with a time stable neutron probe monitoring location, (2) coupling the cosmic-ray neutron probe with a representative landscape unit monitoring approach, and (3) convolution of the cosmic-ray neutron probe measurements with the exponential filter. The time stability method provided the best estimate of root zone soil moisture (RMSE = 0.004 cm3 cm-3), followed by the exponential filter (RMSE = 0.012 cm3 cm-3). The landscape unit approach, which required no calibration, had a negative bias but estimated the cumulative change in storage reasonably. The feasibility of applying these methods to field sites without existing instrumentation is discussed. It is concluded that the exponential filter method has the most potential for estimating root zone soil moisture from cosmic-ray neutron probe data.

  7. Estimating field-scale root zone soil moisture using the cosmic-ray neutron probe

    NASA Astrophysics Data System (ADS)

    Peterson, Amber M.; Helgason, Warren D.; Ireson, Andrew M.

    2016-04-01

    Many practical hydrological, meteorological, and agricultural management problems require estimates of soil moisture with an areal footprint equivalent to field scale, integrated over the entire root zone. The cosmic-ray neutron probe is a promising instrument to provide field-scale areal coverage, but these observations are shallow and require depth-scaling in order to be considered representative of the entire root zone. A study to identify appropriate depth-scaling techniques was conducted at a grazing pasture site in central Saskatchewan, Canada over a 2-year period. Area-averaged soil moisture was assessed using a cosmic-ray neutron probe. Root zone soil moisture was measured at 21 locations within the 500 m × 500 m study area, using a down-hole neutron probe. The cosmic-ray neutron probe was found to provide accurate estimates of field-scale surface soil moisture, but measurements represented less than 40 % of the seasonal change in root zone storage due to its shallow measurement depth. The root zone estimation methods evaluated were: (a) the coupling of the cosmic-ray neutron probe with a time-stable neutron probe monitoring location, (b) coupling the cosmic-ray neutron probe with a representative landscape unit monitoring approach, and (c) convolution of the cosmic-ray neutron probe measurements with the exponential filter. The time stability method provided the best estimate of root zone soil moisture (RMSE = 0.005 cm3 cm-3), followed by the exponential filter (RMSE = 0.014 cm3 cm-3). The landscape unit approach, which required no calibration, had a negative bias but estimated the cumulative change in storage reasonably. The feasibility of applying these methods to field sites without existing instrumentation is discussed. Based upon its observed performance and its minimal data requirements, it is concluded that the exponential filter method has the most potential for estimating root zone soil moisture from cosmic-ray neutron probe data.

  8. Asymmetric neutrino production in magnetized proto-neutron stars in fully relativistic mean-field approach

    SciTech Connect

    Maruyama, Tomoyuki; Kajino, Toshitaka; Hidaka, Jun; Takiwaki, Tomoya; Yasutake, Nobutoshi; Kuroda, Takami; Cheoun, Myung-Ki; Ryu, Chung-Yeol; Mathews, Grant J.

    2014-05-02

    We calculate the neutrino production cross-section in the proto-neutron-star matter under a strong magnetic field in the relativistic mean-field approach. We introduce a new parameter-set which can reproduce the 1.96 solar mass neutron star. We find that the production process increases emitted neutrinos along the direction parallel to the magnetic field and decrease those along its opposite direction. It means that resultant asymmetry due to the neutrino absorption and scattering process in the magnetic field becomes larger by the addition of the neutrino production process.

  9. Effects of neutrino emissivity on the cooling of neutron stars in the presence of a strong magnetic field

    NASA Astrophysics Data System (ADS)

    Coelho, Eduardo Lenho; Chiapparini, Marcelo; Negreiros, Rodrigo Picanço

    2015-12-01

    One of the most interesting kind of neutron stars are the pulsars, which are highly magnetized neutron stars with fields up to 1014 G at the surface. The strength of magnetic field in the center of a neutron star remains unknown. According to the scalar virial theorem, magnetic field in the core could be as large as 1018 G. In this work we study the influence of strong magnetic fields on the cooling of neutron stars coming from direct Urca process. Direct Urca process is an extremely efficient mechanism for cooling a neutron star after its formation. The matter is described using a relativistic mean-field model at zero temperature with eight baryons (baryon octet), electrons and muons. We obtain the relative population of each species of particles as function of baryon density for different magnetic fields. We calculate numerically the cooling of neutron stars for a parametrized magnetic field and compare the results for the case without a magnetic field.

  10. An evaluation of thermal and epithermal neutron activation analysis compton suppression methods for biological reference materials.

    PubMed

    Landsberger, S; Wu, D

    1999-01-01

    For neutron activation analysis (NAA), the usual matrix problems of sodium, chlorine, and bromine are well known to give rise to high backgrounds that inhibit the determination of several trace elements for short-lived or medium-lived NAA. For long counting times in long-lived NAA, very low backgrounds are required to achieve good sensitivities. We have investigated the use of thermal and epithermal NAA in conjunction with Compton suppression to determine several elements such as arsenic, antimony, cadmium, and mercury, at the level of a few nanograms. The values of these techniques are discussed in contrast to the standard radiochemical methods. PMID:10676521

  11. Spin precession of slow neutrons in Einstein-Cartan gravity with torsion, chameleon, and magnetic field

    NASA Astrophysics Data System (ADS)

    Ivanov, A. N.; Wellenzohn, M.

    2016-02-01

    We analyze a spin precession of slow neutrons in the Einstein-Cartan gravity with torsion, chameleon and magnetic field. For the derivation of the Heisenberg equation of motion of the neutron spin we use the effective low-energy potential, derived by Ivanov and Wellenzohn [Phys. Rev. D 92, 125004 (2015)] for slow neutrons, coupled to gravitational, chameleon, and torsion fields to order 1 /m , where m is the neutron mass. In addition to these low-energy interactions we switch on the interaction of slow neutrons with a magnetic field. We show that to linear order approximation with respect to gravitational, chameleon, and torsion fields the Dirac Hamilton operator for fermions (neutrons), moving in spacetimes created by rotating coordinate systems, contains the anti-Hermitian operators of torsion-fermion (neutron) interactions, caused by torsion scalar and tensor space-space-time and time-space-space degrees of freedom. Such anti-Hermitian operators violate C P and T invariance. In the low-energy approximation the C P and T violating torsion-fermion (neutron) interactions appear only to order O (1 /m ). One may assume that in the rotating Universe and galaxies the obtained anti-Hermitian torsion-fermion interactions might be an origin of (i) violation of C P and T invariance in the Universe and (ii) of baryon asymmetry. We show that anti-Hermitian torsion-fermion interactions of relativistic fermions, violating C P and T invariance, (i) cannot be removed by nonunitary transformations of the Dirac fermion wave functions and (ii) are conformal invariant. According to general requirements of conformal invariance of massive particle theories in gravitational fields [see R. H. Dicke, Phys. Rev. 125, 2163 (1962) and A. J. Silenko, Phys. Rev. D 91, 065012 (2015)], conformal invariance of anti-Hermitian torsion-fermion interactions is valid only if the fermion mass is changed by a conformal factor.

  12. Calibration approaches of cosmic-ray neutron sensing for soil moisture measurement in cropped fields

    NASA Astrophysics Data System (ADS)

    Rivera Villarreyes, C. A.; Baroni, G.; Oswald, S. E.

    2013-04-01

    Measurement of soil moisture at the plot or hill-slope scale is an important link between local vadose-zone hydrology and catchment hydrology. This study evaluates the applicability of the cosmic-ray neutron sensing for soil moisture in cropped fields. Measurements of cosmic-ray neutrons (fast neutrons) were performed at a lowland farmland in Bornim (Brandenburg, Germany) cropped with sunflower and winter rye. Three field calibration approaches and four different ways of integration the soil moisture profile to an integral value for cosmic-ray neutron sensing were evaluated in this study. The cosmic-ray sensing (CRS) probe was calibrated against a network of classical point-scale soil moisture measurements. A large CRS parameter variability was observed by choosing calibration periods within the different growing stages of sunflower and winter rye. Therefore, it was not possible to identify a single set of parameters perfectly estimating soil moisture for both sunflower and winter rye periods. On the other hand, CRS signal and its parameter variability could be understood by some crop characteristics and by predicting the attenuated neutrons by crop presence. This study proves the potentiality of the cosmic-ray neutron sensing at the field scale; however, its calibration needs to be adapted for seasonal vegetation in cropped fields.

  13. Performance of a PADC personal neutron dosemeter at simulated and real workplace fields of the nuclear industry.

    PubMed

    Fiechtner, A; Boschung, M; Wernli, C

    2007-01-01

    In the framework of the EVIDOS (Evaluation of Individual Dosimetry in Mixed Neutron and Photon Radiation Fields) project, funded by the EC, measurements with PADC personal neutron dosemeters were carried out at several workplace fields of the nuclear industry and at simulated workplace fields. The measured personal neutron dose equivalents of the PADC personal neutron dosemeter are compared with values that were assessed within the EVIDOS project by other partners. The detection limits for different spectra types are given. In cases were the neutron dose was too low to be measured by the PADC personal neutron dosemeter, the response is estimated by convoluting the responses to monoenergetic neutrons with the dose energy distribution measured within EVIDOS. The advantages and limitations of the PADC personal neutron dosemeter are discussed. PMID:17578876

  14. ON THE MAGNETIC FIELD OF PULSARS WITH REALISTIC NEUTRON STAR CONFIGURATIONS

    SciTech Connect

    Belvedere, R.; Rueda, Jorge A.; Ruffini, R. E-mail: jorge.rueda@icra.it

    2015-01-20

    We have recently developed a neutron star model fulfilling global and not local charge neutrality, both in the static and in the uniformly rotating cases. The model is described by the coupled Einstein-Maxwell-Thomas-Fermi equations, in which all fundamental interactions are accounted for in the framework of general relativity and relativistic mean field theory. Uniform rotation is introduced following Hartle's formalism. We show that the use of realistic parameters of rotating neutron stars, obtained from numerical integration of the self-consistent axisymmetric general relativistic equations of equilibrium, leads to values of the magnetic field and radiation efficiency of pulsars that are very different from estimates based on fiducial parameters that assume a neutron star mass M = 1.4 M {sub ☉}, radius R = 10 km, and moment of inertia I = 10{sup 45} g cm{sup 2}. In addition, we compare and contrast the magnetic field inferred from the traditional Newtonian rotating magnetic dipole model with respect to the one obtained from its general relativistic analog, which takes into account the effect of the finite size of the source. We apply these considerations to the specific high-magnetic field pulsar class and show that, indeed, all of these sources can be described as canonical pulsars driven by the rotational energy of the neutron star, and have magnetic fields lower than the quantum critical field for any value of the neutron star mass.

  15. On the Magnetic Field of Pulsars with Realistic Neutron Star Configurations

    NASA Astrophysics Data System (ADS)

    Belvedere, R.; Rueda, Jorge A.; Ruffini, R.

    2015-01-01

    We have recently developed a neutron star model fulfilling global and not local charge neutrality, both in the static and in the uniformly rotating cases. The model is described by the coupled Einstein-Maxwell-Thomas-Fermi equations, in which all fundamental interactions are accounted for in the framework of general relativity and relativistic mean field theory. Uniform rotation is introduced following Hartle's formalism. We show that the use of realistic parameters of rotating neutron stars, obtained from numerical integration of the self-consistent axisymmetric general relativistic equations of equilibrium, leads to values of the magnetic field and radiation efficiency of pulsars that are very different from estimates based on fiducial parameters that assume a neutron star mass M = 1.4 M ⊙, radius R = 10 km, and moment of inertia I = 1045 g cm2. In addition, we compare and contrast the magnetic field inferred from the traditional Newtonian rotating magnetic dipole model with respect to the one obtained from its general relativistic analog, which takes into account the effect of the finite size of the source. We apply these considerations to the specific high-magnetic field pulsar class and show that, indeed, all of these sources can be described as canonical pulsars driven by the rotational energy of the neutron star, and have magnetic fields lower than the quantum critical field for any value of the neutron star mass.

  16. Elucidating High Field Phases of the Multiferroic MnWO4 with a Pulsed Magnetic Field and Time of Flight Neutron Laue Diffraction

    SciTech Connect

    Nojiri, H; Yoshii, Shunsuke; Yasui, Motoyoshi; Okada, Kyoko; Matsuda, M.; Santodonato, Louis J; Granroth, Garrett E; Ross, Kathyrn; Carlo, Jeremy P; Gaulin, Bruce D.

    2011-01-01

    We have combined time-of-flight neutron Laue diffraction and pulsed high magnetic fields at the Spallation Neutron Source to study the phase diagram of the multiferroic material MnWO4. The control of the field-pulse timing enabled an exploration of magnetic Bragg scattering through the time dependence of both the neutron wavelength and the pulsed magnetic field. This allowed us to observe several magnetic Bragg peaks in different field-induced phases of MnWO4 with a single instrument configuration. These phases were not previously amenable to neutron diffraction studies due to the large fields involved.

  17. Gravitationally enhanced depolarization of ultracold neutrons in magnetic-field gradients

    NASA Astrophysics Data System (ADS)

    Harris, P. G.; Pendlebury, J. M.; Devenish, N. E.

    2014-01-01

    Trapped ultracold neutrons (UCNs) have for many years been the mainstay of experiments to search for the electric dipole moment (EDM) of the neutron, a critical parameter in constraining scenarios of new physics beyond the Standard Model. Because their energies are so low, UCNs preferentially populate the lower region of their physical enclosure and do not sample uniformly the ambient magnetic field throughout the storage volume. This leads to a substantial increase in the rate of depolarization, as well as to shifts in the measured frequency of the stored neutrons. Consequences for EDM measurements are discussed.

  18. Radiative Neutron β-Decay in Effective Field Theory

    PubMed Central

    Gardner, Susan; Bernard, Véronique; Meißner, Ulf-G.; Zhang, Chi

    2005-01-01

    We consider radiative β-decay of the neutron in heavy baryon chiral perturbation theory. Nucleon-structure effects not encoded in the weak coupling constants gA and gV are determined at next-to-leading order in the chiral expansion, and enter at the O(0.5%)-level, making a sensitive test of the Dirac structure of the weak currents possible. PMID:27308159

  19. APPLICATION OF A "VITURAL FIELD REFERENCE DATABASE" TO ASSESS LAND-COVER MAP ACCURACIES

    EPA Science Inventory

    An accuracy assessment was performed for the Neuse River Basin, NC land-cover/use
    (LCLU) mapping results using a "Virtual Field Reference Database (VFRDB)". The VFRDB was developed using field measurement and digital imagery (camera) data collected at 1,409 sites over a perio...

  20. AN ASSESSMENT OF GROUND TRUTH VARIABILITY USING A "VIRTUAL FIELD REFERENCE DATABASE"

    EPA Science Inventory



    A "Virtual Field Reference Database (VFRDB)" was developed from field measurment data that included location and time, physical attributes, flora inventory, and digital imagery (camera) documentation foy 1,01I sites in the Neuse River basin, North Carolina. The sampling f...

  1. A remarkable focusing property of a parabolic mirror for neutrons in the gravitational field: Geometric proof

    NASA Astrophysics Data System (ADS)

    Masalovich, S.

    2014-11-01

    An extraordinary focusing property of a parabolic mirror for ultracold neutrons in the presence of the gravitational field was first reported by Steyerl and co-authors. It was shown that all neutrons emitted from the focus of the mirror will be reflected back upon the same focus passing a point of return in the gravitational field in between. The present note offers a complementary geometric proof of this feature and discusses its application to many-mirror systems. The results can also be applied to electrons and ions in an electric field.

  2. Comparison of photon-photon and photon-magnetic field pair production rates. [in neutron stars

    NASA Technical Reports Server (NTRS)

    Burns, M. L.; Harding, A. K.

    1983-01-01

    Neutron stars were proposed as the site of gamma-ray burst activity and the copious supply of MeV photons admits the possibility of electron-positron pair production. If the neutron star magnetic field is sufficiently intense (10 to the 12th power G), both photon-photon (2 gamma) and photon-magnetic field (gamma) pair production should be important mechanisms. Rates for the two processes were calculated using a Maxwellian distribution for the photons. The ratio of 1 gamma to 2 gamma pair production rates was obtained as a function of photon temperature and magnetic field strength.

  3. Neutron stars in the Bogomol'nyi-Prasad-Sommerfield Skyrme model: Mean-field limit versus full field theory

    NASA Astrophysics Data System (ADS)

    Adam, C.; Naya, C.; Sanchez-Guillen, J.; Vazquez, R.; Wereszczynski, A.

    2015-08-01

    Using a solitonic model of nuclear matter, the Bogomol'nyi-Prasad-Sommerfield (BPS) Skyrme model, we compare neutron stars obtained in the full field theory, where gravitational backreaction is completely taken into account, with calculations in a mean-field approximation using the Tolman-Oppenheimer-Volkoff approach. In the latter case, a mean-field-theory equation of state is derived from the original BPS field theory. We show that in the full field theory, where the energy density is nonconstant even at equilibrium, there is no universal and coordinate-independent equation of state of nuclear matter, in contrast to the mean-field approximation. We also study how neutron star properties are modified by going beyond mean-field theory and find that the differences between mean-field theory and exact results can be considerable. Further, we compare both exact and mean-field results with some theoretical and phenomenological constraints on neutron star properties, demonstrating thus the relevance of our model even in its most simple version.

  4. New high field magnet for neutron scattering at Hahn-Meitner Institute

    NASA Astrophysics Data System (ADS)

    Steiner, M.; Tennant, D. A.; Smeibidl, P.

    2006-11-01

    The Berlin Neutron Scattering Center BENSC at the Hahn-Meitner-Institute (HMI) is a user facility for the study of structure and dynamics of condensed matter with neutrons and synchrotron radiation with special emphasis on experiments under extreme conditions. Neutron scattering is uniquely suited to study magnetic properties on a microscopic length scale, because neutrons have comparable wavelengths and, due to their magnetic moment, they interact with the atomic magnetic moments. Magnetic interactions and magnetic phenomena depend on thermodynamic parameters like magnetic field, temperature and pressure. At HMI special efforts are being made to offer outstanding sample environments such as very low temperatures or high magnetic fields or combination of both. For the future a dedicated instrument for neutron scattering at extreme fields is under construction, the Extreme Environment Diffractometer ExED. For this instrument the existing superconducting magnets as well as a future hybrid system can be used. The highest fields, above 30 T will be produced by the planned series-connected hybrid magnet system, designed and constructed in collaboration with the National High Magnetic Field Laboratory, Tallahassee, FL.

  5. Quantification of the sensitivity range in neutron dark-field imaging.

    PubMed

    Betz, B; Harti, R P; Strobl, M; Hovind, J; Kaestner, A; Lehmann, E; Van Swygenhoven, H; Grünzweig, C

    2015-12-01

    In neutron grating interferometry, the dark-field image visualizes the scattering properties of samples in the small-angle and ultra-small-angle scattering range. These angles correspond to correlation lengths from several hundred nanometers up to several tens of micrometers. In this article, we present an experimental study that demonstrates the potential of quantitative neutron dark-field imaging. The dark-field signal for scattering from different particle sizes and concentrations of mono-dispersive polystyrene particles in aqueous solution is compared to theoretical predictions and the good agreement between measurements and calculations underlines the quantitative nature of the measured values and reliability of the technique with neutrons. PMID:26724039

  6. Possible theoretical explanations for occasional days of non-field-aligned diffusion at neutron monitor energies

    NASA Technical Reports Server (NTRS)

    Forman, M. A.

    1975-01-01

    It has been shown previously (Anath et al., 1973 and Kane, 1974) that 20 to 25% of days, the diffusion component of the cosmic-ray neutron diurnal anisotropy is directed more than 30 degrees away from the ecliptic projection of the interplanetary magnetic field averaged over the same 24 hours. A number of explanations for this deviation are discussed and it is concluded that transverse gradient drifts due to gradients perpendicular to the ecliptic are likely, that diurnal variations in the diffusion component of the neutron anisotropy may affect results from single stations and that the 24 hour mean interplanetary magnetic field may not be the field appropriate to the streaming equation at neutron monitor energies.

  7. Determination of the gamma-ray spectrum in a strong neutron/gamma-ray mixed field

    NASA Astrophysics Data System (ADS)

    Liu, Yuan-Hao; Lin, Yi-Chun; Nievaart, Sander; Chou, Wen-Tsae; Liu, Hong-Ming; Jiang, Shiang-Huei

    2011-10-01

    The knowledge of gamma-ray spectrum highly affects the accuracy of the correspondingly derived gamma-ray dose and the correctness of calculated neutron dose in the neutron/gamma-ray mixed field dosimetry when using the paired ionization chambers technique. It is of our interest to develop a method to determine the gamma-ray spectrum in a strong neutron/gamma-ray mixed field. The current type detector, Mg(Ar) ionization chamber with 6 different thick caps incorporated with the unfolding technique, was used to determine the gamma-ray spectrum in the THOR epithermal neutron beam, which contains intense neutrons and gamma rays. The applied caps had nominal thicknesses from 1 to 6 mm. Detector response functions of the applied Mg(Ar) chamber with different caps were calculated using MCNP5 with a validated chamber model. The spectrum unfolding process was performed using the well-known SAND-II algorithm. The unfolded result was found much softer than the originally calculated spectrum at the design stage. A large portion of low energy continuum was shown in the adjusted spectrum. This work gave us a much deeper insight into the THOR epithermal neutron beam and also showed a way to determine the gamma-ray spectrum.

  8. Reference field specification and preliminary beam selection strategy for accelerator-based GCR simulation

    NASA Astrophysics Data System (ADS)

    Slaba, Tony C.; Blattnig, Steve R.; Norbury, John W.; Rusek, Adam; La Tessa, Chiara

    2016-02-01

    The galactic cosmic ray (GCR) simulator at the NASA Space Radiation Laboratory (NSRL) is intended to deliver the broad spectrum of particles and energies encountered in deep space to biological targets in a controlled laboratory setting. In this work, certain aspects of simulating the GCR environment in the laboratory are discussed. Reference field specification and beam selection strategies at NSRL are the main focus, but the analysis presented herein may be modified for other facilities and possible biological considerations. First, comparisons are made between direct simulation of the external, free space GCR field and simulation of the induced tissue field behind shielding. It is found that upper energy constraints at NSRL limit the ability to simulate the external, free space field directly (i.e. shielding placed in the beam line in front of a biological target and exposed to a free space spectrum). Second, variation in the induced tissue field associated with shielding configuration and solar activity is addressed. It is found that the observed variation is likely within the uncertainty associated with representing any GCR reference field with discrete ion beams in the laboratory, given current facility constraints. A single reference field for deep space missions is subsequently identified. Third, a preliminary approach for selecting beams at NSRL to simulate the designated reference field is presented. This approach is not a final design for the GCR simulator, but rather a single step within a broader design strategy. It is shown that the beam selection methodology is tied directly to the reference environment, allows facility constraints to be incorporated, and may be adjusted to account for additional constraints imposed by biological or animal care considerations. The major biology questions are not addressed herein but are discussed in a companion paper published in the present issue of this journal. Drawbacks of the proposed methodology are discussed

  9. Reference field specification and preliminary beam selection strategy for accelerator-based GCR simulation.

    PubMed

    Slaba, Tony C; Blattnig, Steve R; Norbury, John W; Rusek, Adam; La Tessa, Chiara

    2016-02-01

    The galactic cosmic ray (GCR) simulator at the NASA Space Radiation Laboratory (NSRL) is intended to deliver the broad spectrum of particles and energies encountered in deep space to biological targets in a controlled laboratory setting. In this work, certain aspects of simulating the GCR environment in the laboratory are discussed. Reference field specification and beam selection strategies at NSRL are the main focus, but the analysis presented herein may be modified for other facilities and possible biological considerations. First, comparisons are made between direct simulation of the external, free space GCR field and simulation of the induced tissue field behind shielding. It is found that upper energy constraints at NSRL limit the ability to simulate the external, free space field directly (i.e. shielding placed in the beam line in front of a biological target and exposed to a free space spectrum). Second, variation in the induced tissue field associated with shielding configuration and solar activity is addressed. It is found that the observed variation is likely within the uncertainty associated with representing any GCR reference field with discrete ion beams in the laboratory, given current facility constraints. A single reference field for deep space missions is subsequently identified. Third, a preliminary approach for selecting beams at NSRL to simulate the designated reference field is presented. This approach is not a final design for the GCR simulator, but rather a single step within a broader design strategy. It is shown that the beam selection methodology is tied directly to the reference environment, allows facility constraints to be incorporated, and may be adjusted to account for additional constraints imposed by biological or animal care considerations. The major biology questions are not addressed herein but are discussed in a companion paper published in the present issue of this journal. Drawbacks of the proposed methodology are discussed

  10. Investigation of the Neutron Quantum States in the Earth’s Gravitational Field

    PubMed Central

    Nesvizhevsky, V. V.; Petukhov, A. K.; Börner, H. G.; Baranova, T. A.; Gagarski, A. M.; Petrov, G. A.; Protasov, K. V.; Voronin, A. Yu.; Baeßler, S.; Abele, H.; Westphal, A.; Lucovac, L.

    2005-01-01

    We studied the neutron quantum states in the potential well formed by the Earth’s gravitational field and a horizontal mirror. The estimated characteristic sizes of the neutron wave functions in two lowest quantum states correspond to their expectations with an accuracy of ≈25 %. The spatial density distribution in a standing neutron wave above a mirror was measured for a set of a few lowest quantum states. A position-sensitive neutron detector with an extra high spatial resolution of 1 μm to 2 μm was developed and tested for this particular task. Although this experiment was not designed or optimized to search for an additional short-range force, nevertheless it allowed us to slightly improve the published boundary in the nanometer range of characteristic distances. We studied systematical uncertainties in the chosen “flow-through” method as well as the feasibility to improve further the accuracy in this experiment. PMID:27308133

  11. Benchmarking of activation reaction distribution in an intermediate energy neutron field.

    PubMed

    Ogawa, Tatsuhiko; Morev, Mikhail N; Hirota, Masahiro; Abe, Takuya; Koike, Yuya; Iwai, Satoshi; Iimoto, Takeshi; Kosako, Toshiso

    2011-07-01

    Neutron-induced reaction rate depth profiles inside concrete shield irradiated by intermediate energy neutron were calculated using a Monte-Carlo code and compared with an experiment. An irradiation field of intermediate neutron produced in the forward direction from a thick (stopping length) target bombarded by 400 MeV nucleon(-1) carbon ions was arranged at the heavy ion medical accelerator in Chiba. Ordinary concrete shield of 90 cm thickness was installed 50 cm downstream the iron target. Activation detectors of aluminum, gold and gold covered with cadmium were inserted at various depths. Irradiated samples were extracted after exposure and gamma-ray spectrometry was performed for each sample. Comparison of experimental and calculated shows good agreement for both low- and high-energy neutron-induced reaction except for (27)Al(n,X)(24)Na reaction at the surface. PMID:21515619

  12. SU-E-T-471: Small Field Jaw/MLC Reference Data

    SciTech Connect

    Kerns, J; Alvarez, P; Followill, D; Lowenstein, J; Molineu, A; Summers, P; Kry, S

    2014-06-01

    Purpose: In recent years the need for small field data of MLCs has increased due to the use of intensity-modulated radiation (IMRT), but moreover the use of stereotactic body radiation (SBRT) has increased, which uses not simply small field sizes, but small jaw and field sizes together. Having reference data for these small fields that is reliable would be invaluable to the physics community. Our study has gathered these values and the data distributions from the Radiological Physics Center's (RPC) site visits between 1990 and the present. Methods: For all measurements, the RPC used a 25 × 25 × 25cm water phantom placed at 100cm SSD. All measurements were made with an Exradin A16 cylindrical ion chamber at an effective depth of 10 cm. A total of 42 Varian machine measurements were used to compose the data for a 6 MV beam and 5 TrueBeam 6 MV flattening filter free (FFF) beams were used for FFF data. Results: Jaw/MLC fields were measured for both 6 MV and 6 MF FFF beams with the jaws and MLCs both at the following field sizes: 6×6, 4×4, 3×3, and 2×2cm. Measurements were normalized to the 10×10 field readings (defined by the jaws and MLC). Spread in the data was minimal and demonstrates a high level of accuracy of acquired data. Conclusion: Small field Jaw/MLC reference data for Varian 6MV and 6 MV FFF beams has been analyzed and presented here, composed of the aggregation of numerous RPC site visits. Obtaining reliable small field data remains difficult, however the RPC has collected high fidelity small field Jaw/MLC data. The data are presented as a reference along with their distributions, in such a way that the physicist can act based upon their own desired agreement with the reference data.

  13. Accessing Interior Vector Magnetic Field Components in Neutron EDM Experiments via Boundary Value Techniques

    NASA Astrophysics Data System (ADS)

    Plaster, Brad

    2012-10-01

    We propose a new technique for the determination and monitoring of the interior vector magnetic field components during the operation of neutron EDM experiments. If a suitable three-dimensional volume surrounding the fiducial volume of an experiment can be defined which contains no interior currents or magnetization, each of the interior vector field components will satisfy the Laplace Equation within this volume. Therefore, if the field components can be measured on the boundary, the interior vector field components can be determined uniquely via numerical solution of the Laplace Equation. We discuss the applicability of this technique to the determination of the magnetic field components and magnetic field gradients in the fiducial volumes of neutron EDM experiments.

  14. Slowly rotating neutron stars in scalar-tensor theories with a massive scalar field

    NASA Astrophysics Data System (ADS)

    Yazadjiev, Stoytcho S.; Doneva, Daniela D.; Popchev, Dimitar

    2016-04-01

    In the scalar-tensor theories with a massive scalar field, the coupling constants, and the coupling functions in general, which are observationally allowed, can differ significantly from those in the massless case. This fact naturally implies that the scalar-tensor neutron stars with a massive scalar field can have rather different structure and properties in comparison with their counterparts in the massless case and in general relativity. In the present paper, we study slowly rotating neutron stars in scalar-tensor theories with a massive gravitational scalar. Two examples of scalar-tensor theories are examined—the first example is the massive Brans-Dicke theory and the second one is a massive scalar-tensor theory indistinguishable from general relativity in the weak-field limit. In the latter case, we study the effect of the scalar field mass on the spontaneous scalarization of neutron stars. Our numerical results show that the inclusion of a mass term for the scalar field indeed changes the picture drastically compared to the massless case. It turns out that mass, radius, and moment of inertia for neutron stars in massive scalar-tensor theories can differ drastically from the pure general relativistic solutions if sufficiently large masses of the scalar field are considered.

  15. Field-theory calculation of the electric dipole moment of the neutron and paramagnetic atoms

    NASA Astrophysics Data System (ADS)

    Blundell, S. A.; Griffith, J.; Sapirstein, J.

    2012-07-01

    Electric dipole moments (edms) of bound states that arise from the constituents having edms are studied with field-theoretic techniques. The systems treated are the neutron and a set of paramagnetic atoms. In the latter case it is well known that the atomic edm differs greatly from the electron edm when the internal electric fields of the atom are taken into account. In the nonrelativistic limit these fields lead to a complete suppression, but for heavy atoms large enhancement factors are present. A general bound-state field theory approach applicable to both the neutron and paramagnetic atoms is set up. It is applied first to the neutron, treating the quarks as moving freely in a confining spherical well. It is shown that the effect of internal electric fields is small in this case. The atomic problem is then revisited using field-theory techniques in place of the usual Hamiltonian methods, and the atomic enhancement factor is shown to be consistent with previous calculations. Possible application of bound-state techniques to other sources of the neutron edm is discussed.

  16. Crystal-field levels in UBr 3 determined by neutron spectroscopy

    NASA Astrophysics Data System (ADS)

    Murasik, A.; Furrer, A.; Szczepaniak, W.

    1980-03-01

    Inelastic neutron scattering experiments have been performed in UBr 3 in order to determine the crystal-field levels. Four transitions between the ground state and all excited states have been observed, thus the crystal-field level scheme could be unambigously assigned. The Russell-Saunders coupling scheme has been used to derive the crystal-field parameters which cannot be accounted for by a simple point charge calculation.

  17. Inelastic neutron scattering investigation of crystal-field splittings in UBr 3

    NASA Astrophysics Data System (ADS)

    Murasik, A.; Furrer, A.

    1980-10-01

    An inelastic neutron scattering technique was used to measure the crystal-field splittings in UBr 3 at various temperatures and momentum transfers. In the interpretation of the observed energy spectra it turns out that the Russell-Saunders coupling scheme is a reasonable approximation. The crystal-field level scheme could be unambiguously assigned. The detailed nature of the crystal-field transition from the ground state to the first-excited state is not yet fully understood.

  18. Signatures of field induced spin polarization of neutron star matter in seismic vibrations of paramagnetic neutron star

    NASA Astrophysics Data System (ADS)

    Bastrukov, S. I.; Yang, J.; Podgainy, D. V.; Weber, F.

    2003-04-01

    A macroscopic model of the dissipative magneto-elastic dynamics of viscous spin polarized nuclear matter is discussed in the context of seismic activity of a paramagnetic neutron star. The source of the magnetic field of such a star is attributed to Pauli paramagnetism of baryon matter promoted by a seed magnetic field frozen into the star in the process of gravitational collapse of a massive progenitor. Particular attention is given to the effect of shear viscosity of incompressible stellar material on the timing of non-radial torsional magneto-elastic pulsations of the star triggered by starquakes. By accentuating the fact that this kind of vibration is unique to the seismology of a paramagnetic neutron star we show that the high-frequency modes decay faster than the low-frequency modes. The obtained analytic expressions for the period and relaxation time of this mode, in which the magnetic susceptibility and viscosity enter as input parameters, are then quantified by numerical estimates for these parameters taken from early and current works on transport coefficients of dense matter. It is found that the effect of viscosity is crucial for the lifetime of magneto-torsion vibrations but it does not appreciably affect the periods of this seismic mode which fall in the realm of periods of pulsed emission of soft gamma-ray repeaters and anomalous x-ray pulsars - young super-magnetized neutron stars, radiating, according to the magnetar model, at the expense of the magnetic energy release. Finally, we present arguments that the long periodic pulsed emission of these stars in a quiescent regime of radiation can be interpreted as a manifestation of weakly damped seismic magneto-torsion vibrations exhibiting the field induced spin polarization of baryon matter.

  19. Monte Carlo simulation of the operational quantities at the realistic mixed neutron-photon radiation fields CANEL and SIGMA.

    PubMed

    Lacoste, V; Gressier, V

    2007-01-01

    The Institute for Radiological Protection and Nuclear Safety owns two facilities producing realistic mixed neutron-photon radiation fields, CANEL, an accelerator driven moderator modular device, and SIGMA, a graphite moderated americium-beryllium assembly. These fields are representative of some of those encountered at nuclear workplaces, and the corresponding facilities are designed and used for calibration of various instruments, such as survey meters, personal dosimeters or spectrometric devices. In the framework of the European project EVIDOS, irradiations of personal dosimeters were performed at CANEL and SIGMA. Monte Carlo calculations were performed to estimate the reference values of the personal dose equivalent at both facilities. The Hp(10) values were calculated for three different angular positions, 0 degrees, 45 degrees and 75 degrees, of an ICRU phantom located at the position of irradiation. PMID:17578872

  20. Quantitative Neutron Dark-field Imaging through Spin-Echo Interferometry

    PubMed Central

    Strobl, Markus; Sales, Morten; Plomp, Jeroen; Bouwman, Wim G.; Tremsin, Anton S.; Kaestner, Anders; Pappas, Catherine; Habicht, Klaus

    2015-01-01

    Neutron dark-field imaging constitutes a seminal progress in the field of neutron imaging as it combines real space resolution capability with information provided by one of the most significant neutron scattering techniques, namely small angle scattering. The success of structural characterizations bridging the gap between macroscopic and microscopic features has been enabled by the introduction of grating interferometers so far. The induced interference pattern, a spatial beam modulation, allows for mapping of small-angle scattering signals and hence addressing microstructures beyond direct spatial resolution of the imaging system with high efficiency. However, to date the quantification in the small angle scattering regime is severely limited by the monochromatic approach. To overcome such drawback we here introduce an alternative and more flexible method of interferometric beam modulation utilizing a spin-echo technique. This novel method facilitates straightforward quantitative dark-field neutron imaging, i.e. the required quantitative microstructural characterization combined with real space image resolution. For the first time quantitative microstructural reciprocal space information from small angle neutron scattering becomes available together with macroscopic image information creating the potential to quantify several orders of magnitude in structure sizes simultaneously. PMID:26560644

  1. Quantitative Neutron Dark-field Imaging through Spin-Echo Interferometry.

    PubMed

    Strobl, Markus; Sales, Morten; Plomp, Jeroen; Bouwman, Wim G; Tremsin, Anton S; Kaestner, Anders; Pappas, Catherine; Habicht, Klaus

    2015-01-01

    Neutron dark-field imaging constitutes a seminal progress in the field of neutron imaging as it combines real space resolution capability with information provided by one of the most significant neutron scattering techniques, namely small angle scattering. The success of structural characterizations bridging the gap between macroscopic and microscopic features has been enabled by the introduction of grating interferometers so far. The induced interference pattern, a spatial beam modulation, allows for mapping of small-angle scattering signals and hence addressing microstructures beyond direct spatial resolution of the imaging system with high efficiency. However, to date the quantification in the small angle scattering regime is severely limited by the monochromatic approach. To overcome such drawback we here introduce an alternative and more flexible method of interferometric beam modulation utilizing a spin-echo technique. This novel method facilitates straightforward quantitative dark-field neutron imaging, i.e. the required quantitative microstructural characterization combined with real space image resolution. For the first time quantitative microstructural reciprocal space information from small angle neutron scattering becomes available together with macroscopic image information creating the potential to quantify several orders of magnitude in structure sizes simultaneously. PMID:26560644

  2. Field ionization characteristics of an ion source array for neutron generators

    SciTech Connect

    B. Bargsten Johnson; P. R. Schwoebel; P. J. Resnick; C. E. Holland; L. Hertz; D. L. Chichester

    2013-11-01

    A new deuterium ion source is being developed to improve the performance of existing compact neutron generators. The ion source is a microfabricated array of metal tips with an integrated gate (i.e., grid) and produces deuterium ions by field ionizing (or field desorbing) a supply of deuterium gas. Deuterium field ion currents from arrays at source temperatures of 77?K and 293?K are studied. Ion currents from single etched-wire tips operating under the same conditions are used to help understand array results. I-F characteristics of the arrays were found to follow trends similar to those of the better understood single etched-wire tip results; however, the fields achieved by the arrays are limited by electrical breakdown of the structure. Neutron production by field ionization at 293?K was demonstrated for the first time from microfabricated array structures with integrated gates.

  3. Field ionization characteristics of an ion source array for neutron generators

    SciTech Connect

    Bargsten Johnson, B.; Schwoebel, P. R.; Resnick, P. J.; Holland, C. E.; Hertz, K. L.; Chichester, D. L.

    2013-11-07

    A new deuterium ion source is being developed to improve the performance of existing compact neutron generators. The ion source is a microfabricated array of metal tips with an integrated gate (i.e., grid) and produces deuterium ions by field ionizing (or field desorbing) a supply of deuterium gas. Deuterium field ion currents from arrays at source temperatures of 77 K and 293 K are studied. Ion currents from single etched-wire tips operating under the same conditions are used to help understand array results. I-F characteristics of the arrays were found to follow trends similar to those of the better understood single etched-wire tip results; however, the fields achieved by the arrays are limited by electrical breakdown of the structure. Neutron production by field ionization at 293 K was demonstrated for the first time from microfabricated array structures with integrated gates.

  4. Exploring the Magnetic field and Black Hole Spin in Black Hole--Neutron star mergers

    NASA Astrophysics Data System (ADS)

    Chawla, Sarvnipun; Anderson, Matthew; Lehner, Luis; Liebling, Steven; Megevand, Miguel; Motl, Patrick; Neilsen, David; Palenzuela, Carlos

    2010-02-01

    A sizable magnetic field in neutron star-black hole binaries can have a strong influence on the merger dynamics of the fluid by redistributing angular momentum through different mechanisms. The magnetic field can also be responsible for collimating jets. BH spin can increase the number of orbits before merger as compared to a binary with a non-spinning BH. The corresponding decrease in ISCO can alter the tidal disruption suffered by the NS. We present results of fully relativistic black hole--neutron star simulations proceeding from quasi-circular initial data generated with the Lorene libraries. We explore the effect of magnetic field and spin by evolving four sets of nearly identical initial data which differ in their magnetic field and spin values. We examine the gravitational wave signature through direct simulation. Finally, we compare the fluid structure and explore the magnetic field configuration in the post-merger remnant disk. )

  5. Comparison of DD, DT and Cf-252 neutron excitation of light and medium mass nuclei for field PGNAA applications

    NASA Astrophysics Data System (ADS)

    Seabury, E. H.; Blackburn, B. W.; Chichester, D. L.; Wharton, C. J.; Caffrey, A. J.

    2007-08-01

    Prompt Gamma Ray Neutron activation analysis can offer significant cost and safety advantages in the identification of explosives and toxic chemicals. As an example, the US military examined over a thousand suspect chemical munitions with Idaho National Laboratory's PINS Chemical Assay System last year. PGNAA requires, of course, a neutron source to excite the atomic nuclei of the item under test via neutron capture and inelastic neutron scattering reactions and the choice of neutron source can drastically affect PGNAA system performance. We have carried out Monte Carlo and laboratory experiments comparing DD, DT and Cf-252 neutrons incident on light and medium mass chemical elements, toward optimizing the design of future neutron-generator-based PGNAA systems for field use. We report the excitation of (n, γ) and (n, n‧) gamma rays from these elements by each type of neutron source.

  6. Neutron production using a pyroelectric driven target coupled with a gated field ionization source

    SciTech Connect

    Ellsworth, J. L.; Tang, V.; Falabella, S.; Naranjo, B.; Putterman, S.

    2013-04-19

    A palm sized, portable neutron source would be useful for widespread implementation of detection systems for shielded, special nuclear material. We present progress towards the development of the components for an ultracompact neutron generator using a pulsed, meso-scale field ionization source, a deuterated (or tritiated) titanium target driven by a negative high voltage lithium tantalate crystal. Neutron production from integrated tests using an ion source with a single, biased tungsten tip and a 3 Multiplication-Sign 1 cm, vacuum insulated crystal with a plastic deuterated target are presented. Component testing of the ion source with a single tip produces up to 3 nA of current. Dielectric insulation of the lithium tantalate crystals appears to reduce flashover, which should improve the robustness. The field emission losses from a 3 cm diameter crystal with a plastic target and 6 cm diameter crystal with a metal target are compared.

  7. Four-hair relations for differentially rotating neutron stars in the weak-field limit

    NASA Astrophysics Data System (ADS)

    Bretz, Joseph; Yagi, Kent; Yunes, Nicolas

    2016-03-01

    The opportunity to study physics at supra-nuclear densities through x-ray observations of neutron stars has led to in-depth investigations of certain approximately universal relations that can remove degeneracies in pulse profile models. One such set of relations, the three-hair relations, were found to hold in neutron stars that rotate rigidly, but neutron stars can also rotate differentially, as is the case for proto-neutron stars and hypermassive transient remnants of binary mergers. We extend the three-hair relations to differentially rotating stars for the first time with a generic rotation law using two approximations: a weak-field scheme (an expansion in powers of the neutron star compactness) and a perturbative differential rotation scheme (an expansion about rigid rotation). The resulting relations include the fourth moment, hence deemed the four-hair relations for differentially rotating neutron stars, and are found to be approximately independent of the equation of state to a higher degree than the three-hair relations for uniformly rotating stars. Our results can be instrumental in the development of four-hair relations for rapidly differentially rotating stars in full general relativity using numerical simulations.

  8. Researching Refugee and Forced Migration Studies: An Introduction to the Field and the Reference Literature.

    ERIC Educational Resources Information Center

    Mason, Elisa

    1999-01-01

    Describes the evolution of refugee and forced migration studies, identifies factors that render it a challenging field to research, and highlights a variety of Internet-based and other electronic resources that can be used to locate monographs, periodicals, grey literature, and current information. Provides a bibliography of reference materials in…

  9. Religious Studies: The Shaping of a Field and a Guide to Reference Resources.

    ERIC Educational Resources Information Center

    Lippy, Charles H.

    1992-01-01

    Discusses the development of religious studies as an academic discipline. Examines the work of leading thinkers in the field, including anthropologists Sir James Fraser and Edward Burnett Taylor, sociologist Max Weber, and psychologist Erik Erikson. Identifies some of the many reference works that deal with religious studies. (SG)

  10. Evaluation of models proposed for the 1991 revision of the International Geomagnetic Reference Field

    USGS Publications Warehouse

    Peddie, N.W.

    1992-01-01

    The 1991 revision of the International Geomagnetic Reference Field (IGRF) comprises a definitive main-field model for 1985.0, a main-field model for 1990.0, and a forecast secular-variation model for the period 1990-1995. The five 1985.0 main-field models and five 1990.0 main-field models that were proposed have been evaluated by comparing them with one another, with magnetic observatory data, and with Project MAGNET aerial survey data. The comparisons indicate that the main-field models proposed by IZMIRAN, and the secular-variation model proposed jointly by the British Geological Survey and the US Naval Oceanographic Office, should be assigned relatively lower weight in the derivation of the new IGRF models. -Author

  11. Magnetic Field R&D for the neutron EDM experiment at TRIUMF

    NASA Astrophysics Data System (ADS)

    Mammei, Russell R.

    2014-09-01

    The neutron EDM experiment at TRIUMF aims to constrain the EDM with a precision of 1 ×10-27 e-cm by 2018. The experiment will use a spallation ultracold neutron (UCN) source employing superfluid helium coupled to a room-temperature EDM apparatus. In the previous best experiment, conducted at ILL, effects related to magnetic field homogeneity and instability were found to dominate the systematic error. This presentation will cover our R&D efforts on passive and active magnetic shielding, magnetic field generation within shielded volumes, and precision magnetometry. The neutron EDM experiment at TRIUMF aims to constrain the EDM with a precision of 1 ×10-27 e-cm by 2018. The experiment will use a spallation ultracold neutron (UCN) source employing superfluid helium coupled to a room-temperature EDM apparatus. In the previous best experiment, conducted at ILL, effects related to magnetic field homogeneity and instability were found to dominate the systematic error. This presentation will cover our R&D efforts on passive and active magnetic shielding, magnetic field generation within shielded volumes, and precision magnetometry. Supported by the Canada Foundation for Innovation, the Natural Sciences and Engineering Research Council of Canada, and the Canada Research Chairs program.

  12. Dependence of TLD thermoluminescence yield on absorbed dose in a thermal neutron field.

    PubMed

    Gambarini, G; Roy, M S

    1997-01-01

    The emission from 6LiF and 7LiF thermoluminescence dosimeters (TLDs) exposed to the mixed field of thermal neutrons and gamma-rays of the thermal facility of a TRIGA MARK II nuclear reactor has been investigated for various thermal neutron fluences of the order of magnitude of those utilised in radiotherapy, with the purpose of investigating the reliability of TLD readouts in such radiation fields and of giving some information for better obtainment of the absorbed dose values. The emission after exposure in this mixed field is compared with the emission after gamma-rays only. The glow curves have been deconvoluted into gaussian peaks, and the differences in the characteristics of the peaks observed for the two radiation fields, having different linear energy transfers, and for different doses are shown. Irreversible radiation damage in dosimeters having high sensitivity to thermal neutrons is also reported, showing a memory effect of the previous thermal neutron irradiation history which is not restored by anneal treatment. PMID:9463872

  13. Extension of the VITESS polarized neutron suite towards the use of imported magnetic field distributions

    NASA Astrophysics Data System (ADS)

    Manoshin, S.; Rubtsov, A.; Bodnarchuk, V.; Mattauch, S.; Ioffe, A.

    2014-07-01

    Latest developments of the polarized neutron suite in the VITESS simulation package allowed for simulations of time-dependent spin handling devices (e.g. radio-frequency (RF) flippers, adiabatic gradient RF-flippers) and the instrumentation built upon them (NRSE, SESANS, MIEZE, etc.). However, till now the magnetic field distribution in such devices have been considered as "ideal" (sinusoidal, triangular or rectangular), when the main practical interest is in the use of arbitrary magnetic field distributions (either obtained by the field mapping or by FEM calculations) that may significantly influence the performance of real polarized neutron instruments and is the key issue in the practical use of the simulation packages. Here we describe modified VITESS modules opening the possibility to load the magnetic field 3-dimensional space map from an external source (file). Such a map can be either obtained by direct measurements or calculated by dedicated FEM programs (such as ANSYS, MagNet, Maxwell or similar). The successful use of these new modules is demonstrated by a very good agreement of neutron polarimetric experiments with performance of the spin turner with rotating magnetic field and an adiabatic gradient RF-flipper simulated by VITESS using calculated 3-dimensional field maps (using MagNet) and magnetic field mapping, respectively.

  14. HYPERCRITICAL ACCRETION ONTO A NEWBORN NEUTRON STAR AND MAGNETIC FIELD SUBMERGENCE

    SciTech Connect

    Bernal, Cristian G.; Page, Dany; Lee, William H. E-mail: page@astro.unam.mx

    2013-06-20

    We present magnetohydrodynamic numerical simulations of the late post-supernova hypercritical accretion to understand its effect on the magnetic field of the newborn neutron star. We consider as an example the case of a magnetic field loop protruding from the star's surface. The accreting matter is assumed to be non-magnetized, and, due to the high accretion rate, matter pressure dominates over magnetic pressure. We find that an accretion envelope develops very rapidly, and once it becomes convectively stable, the magnetic field is easily buried and pushed into the newly forming neutron star crust. However, for low enough accretion rates the accretion envelope remains convective for an extended period of time and only partial submergence of the magnetic field occurs due to a residual field that is maintained at the interface between the forming crust and the convective envelope. In this latter case, the outcome should be a weakly magnetized neutron star with a likely complicated field geometry. In our simulations we find the transition from total to partial submergence to occur around M-dot {approx}10 M{sub sun} yr{sup -1}. Back-diffusion of the submerged magnetic field toward the surface, and the resulting growth of the dipolar component, may result in a delayed switch-on of a pulsar on timescales of centuries to millennia.

  15. Development and application of setup for ac magnetic field in neutron scattering experiments.

    PubMed

    Klimko, Sergey; Zhernenkov, Kirill; Toperverg, Boris P; Zabel, Hartmut

    2010-10-01

    We report on a new setup developed for neutron scattering experiments in periodically alternating magnetic fields at the sample position. The assembly consisting of rf generator, amplifier, wide band transformer, and resonance circuit. It allows to generate homogeneous ac magnetic fields over a volume of a few cm(3) and variable within a wide range of amplitudes and frequencies. The applicability of the device is exemplified by ac polarized neutron reflectometry (PNR): a new method established to probe remagnetization kinetics in soft ferromagnetic films. Test experiments with iron films demonstrate that the ac field within the accessible range of frequencies and amplitudes produces a dramatic effect on the PNR signal. This shows that the relevant ac field parameters generated by the device match well with the scales involved in the remagnetization processes. Other possible applications of the rf unit are briefly discussed. PMID:21034083

  16. Development and application of setup for ac magnetic field in neutron scattering experiments

    SciTech Connect

    Klimko, Sergey; Zhernenkov, Kirill; Toperverg, Boris P.; Zabel, Hartmut

    2010-10-15

    We report on a new setup developed for neutron scattering experiments in periodically alternating magnetic fields at the sample position. The assembly consisting of rf generator, amplifier, wide band transformer, and resonance circuit. It allows to generate homogeneous ac magnetic fields over a volume of a few cm{sup 3} and variable within a wide range of amplitudes and frequencies. The applicability of the device is exemplified by ac polarized neutron reflectometry (PNR): a new method established to probe remagnetization kinetics in soft ferromagnetic films. Test experiments with iron films demonstrate that the ac field within the accessible range of frequencies and amplitudes produces a dramatic effect on the PNR signal. This shows that the relevant ac field parameters generated by the device match well with the scales involved in the remagnetization processes. Other possible applications of the rf unit are briefly discussed.

  17. Constraints on Neutron Star Radii Based on Chiral Effective Field Theory Interactions

    SciTech Connect

    Hebeler, K.; Lattimer, J. M.; Pethick, C. J.; Schwenk, A.

    2010-10-15

    We show that microscopic calculations based on chiral effective field theory interactions constrain the properties of neutron-rich matter below nuclear densities to a much higher degree than is reflected in commonly used equations of state. Combined with observed neutron star masses, our results lead to a radius R=9.7-13.9 km for a 1.4M{sub {center_dot}} star, where the theoretical range is due, in about equal amounts, to uncertainties in many-body forces and to the extrapolation to high densities.

  18. Neutron field for activation experiments in horizontal channel of training reactor VR-1

    NASA Astrophysics Data System (ADS)

    Stefanik, Milan; Katovsky, Karel; Vins, Miroslav; Soltes, Jaroslav; Zavorka, Lukas

    2014-11-01

    The experimental channels of nuclear reactors often serve for nuclear data measurement and validation. The dosimetry-foils activation technique was employed to measure neutron field parameters in the horizontal radial channel of the training reactor VR-1, and to test the possibility of using the reactor for scientific purposes. The reaction rates, energy spectral indexes, and neutron spectrum at several irradiation positions of the experimental channel were determined. The experimental results show the feasibility of the radial channel for irradiating experiments and open new possibilities for data validation by using this nuclear facility.

  19. Neutron Imaging and Applications

    SciTech Connect

    Anderson, Ian S; McGreevy, Robert L; Bilheux, Hassina Z

    2009-04-01

    Neutron Imaging and Applications offers an introduction to the basics of neutron beam production and instrumentation in addition to the wide scope of techniques that provide unique imaging capabilities over a broad and diverse range of applications. An instructional overview of neutron sources, optics and detectors, allows readers to delve more deeply into the discussions of radiography, tomography, phase contrast imaging and prospective applications using advanced neutron holography techniques and polarized beams. A section devoted to overviews in a growing range of applications describes imaging of fuel cells and hydrogen storage devices for a robust hydrogen economy; new directions in material science and engineering; the investigation of precious artifacts of cultural heritage importance; determination of plant physiology and growth processes; imaging of biological tissues and macromolecules, and the practical elements of neutron imaging for homeland security and contraband detection. Written by key experts in the field, researchers and engineers involved with imaging technologies will find Neutron Imaging and Applications a valuable reference.

  20. Sensitivity Reach of the Neutron EDM Experiment: The Electric Field Strength

    NASA Astrophysics Data System (ADS)

    Hennings-Yeomans, R.; Cooper, M.; Currie, S. A.; Makela, M. F.; Ramsey, J. C.; Tajima, S.; Womack, T. L.; Long, J. C.; Stanislaus, S.

    2010-08-01

    The search for an electric dipole moment of the neutron tests physics beyond the Standard Model such as new sources of CP-violation and Supersymmetry. The nEDM experiment aims to improve the sensitivity on the current limit of the electric dipole moment of the neutron to <10-27 eṡcm. The experiment will use a flux of Ultra Cold Neutrons (UCNs) produced and stored in a bath of superfluid He-II. A change in precession frequency is expected for a non-zero EDM when an electric field is applied parallel and antiparallel to a magnetic field across the neutron storage cell. A dominant parameter in terms of reducing the statistical uncertainty of this measurement is the strength of the applied electric field. An experiment to measure if superfluid He-II can sustain up to 50 kV/cm for a volume and electrode spacings comparable to the nEDM experiment has been constructed at Los Alamos National Laboratory. It consists in a large-area parallel plate capacitor immersed in a 200 liter central volume inside a suitable cryostat that in turn is connected to a dilution refrigerator unit. A description of test runs and the status of the experiment is presented.

  1. Sensitivity Reach of the Neutron EDM Experiment: The Electric Field Strength

    SciTech Connect

    Hennings-Yeomans, R.; Cooper, M.; Currie, S. A.; Makela, M. F.; Ramsey, J. C.; Tajima, S.; Womack, T. L.; Long, J. C.; Stanislaus, S.

    2010-08-04

    The search for an electric dipole moment of the neutron tests physics beyond the Standard Model such as new sources of CP-violation and Supersymmetry. The nEDM experiment aims to improve the sensitivity on the current limit of the electric dipole moment of the neutron to <10{sup -27} e{center_dot}cm. The experiment will use a flux of Ultra Cold Neutrons (UCNs) produced and stored in a bath of superfluid He-II. A change in precession frequency is expected for a non-zero EDM when an electric field is applied parallel and antiparallel to a magnetic field across the neutron storage cell. A dominant parameter in terms of reducing the statistical uncertainty of this measurement is the strength of the applied electric field. An experiment to measure if superfluid He-II can sustain up to 50 kV/cm for a volume and electrode spacings comparable to the nEDM experiment has been constructed at Los Alamos National Laboratory. It consists in a large-area parallel plate capacitor immersed in a 200 liter central volume inside a suitable cryostat that in turn is connected to a dilution refrigerator unit. A description of test runs and the status of the experiment is presented.

  2. Magnetic field dependence of the neutron spin resonance in CeB6

    NASA Astrophysics Data System (ADS)

    Portnichenko, P. Y.; Demishev, S. V.; Semeno, A. V.; Ohta, H.; Cameron, A. S.; Surmach, M. A.; Jang, H.; Friemel, G.; Dukhnenko, A. V.; Shitsevalova, N. Yu.; Filipov, V. B.; Schneidewind, A.; Ollivier, J.; Podlesnyak, A.; Inosov, D. S.

    2016-07-01

    In zero magnetic field, the famous neutron spin resonance in the f -electron superconductor CeCoIn5 is similar to the recently discovered exciton peak in the nonsuperconducting CeB6. A magnetic field splits the resonance in CeCoIn5 into two components, indicating that it is a doublet. Here we employ inelastic neutron scattering (INS) to scrutinize the field dependence of spin fluctuations in CeB6. The exciton shows a markedly different behavior without any field splitting. Instead, we observe a second field-induced magnon whose energy increases with field. At the ferromagnetic zone center, however, we find only a single mode with a nonmonotonic field dependence. At low fields, it is initially suppressed to zero together with the antiferromagnetic order parameter, but then reappears at higher fields inside the hidden-order phase, following the energy of an electron spin resonance (ESR). This is a unique example of a ferromagnetic resonance in a heavy-fermion metal seen by both ESR and INS consistently over a broad range of magnetic fields.

  3. A comprehensive spectrometry study of a stray neutron radiation field in scanning proton therapy.

    PubMed

    Mares, Vladimir; Romero-Expósito, Maite; Farah, Jad; Trinkl, Sebastian; Domingo, Carles; Dommert, Martin; Stolarczyk, Liliana; Van Ryckeghem, Laurent; Wielunski, Marek; Olko, Pawel; Harrison, Roger M

    2016-06-01

    The purpose of this study is to characterize the stray neutron radiation field in scanning proton therapy considering a pediatric anthropomorphic phantom and a clinically-relevant beam condition. Using two extended-range Bonner sphere spectrometry systems (ERBSS), Working Group 9 of the European Radiation Dosimetry Group measured neutron spectra at ten different positions around a pediatric anthropomorphic phantom irradiated for a brain tumor with a scanning proton beam. This study compares the different systems and unfolding codes as well as neutron spectra measured in similar conditions around a water tank phantom. The ten spectra measured with two ERBSS systems show a generally similar thermal component regardless of the position around the phantom while high energy neutrons (above 20 MeV) were only registered at positions near the beam axis (at 0°, 329° and 355°). Neutron spectra, fluence and ambient dose equivalent, H (*)(10), values of both systems were in good agreement (<15%) while the unfolding code proved to have a limited effect. The highest H (*)(10) value of 2.7 μSv Gy(-1) was measured at 329° to the beam axis and 1.63 m from the isocenter where high-energy neutrons (E  ⩾  20 MeV) contribute with about 53%. The neutron mapping within the gantry room showed that H (*)(10) values significantly decreased with distance and angular position with respect to the beam axis dropping to 0.52 μSv Gy(-1) at 90° and 3.35 m. Spectra at angles of 45° and 135° with respect to the beam axis measured here with an anthropomorphic phantom showed a similar peak structure at the thermal, fast and high energy range as in the previous water-tank experiments. Meanwhile, at 90°, small differences at the high-energy range were observed. Using ERBSS systems, neutron spectra mapping was performed to characterize the exposure of scanning proton therapy patients. The ten measured spectra provide precise information about the exposure of healthy organs to

  4. A comprehensive spectrometry study of a stray neutron radiation field in scanning proton therapy

    NASA Astrophysics Data System (ADS)

    Mares, Vladimir; Romero-Expósito, Maite; Farah, Jad; Trinkl, Sebastian; Domingo, Carles; Dommert, Martin; Stolarczyk, Liliana; Van Ryckeghem, Laurent; Wielunski, Marek; Olko, Pawel; Harrison, Roger M.

    2016-06-01

    The purpose of this study is to characterize the stray neutron radiation field in scanning proton therapy considering a pediatric anthropomorphic phantom and a clinically-relevant beam condition. Using two extended-range Bonner sphere spectrometry systems (ERBSS), Working Group 9 of the European Radiation Dosimetry Group measured neutron spectra at ten different positions around a pediatric anthropomorphic phantom irradiated for a brain tumor with a scanning proton beam. This study compares the different systems and unfolding codes as well as neutron spectra measured in similar conditions around a water tank phantom. The ten spectra measured with two ERBSS systems show a generally similar thermal component regardless of the position around the phantom while high energy neutrons (above 20 MeV) were only registered at positions near the beam axis (at 0°, 329° and 355°). Neutron spectra, fluence and ambient dose equivalent, H *(10), values of both systems were in good agreement (<15%) while the unfolding code proved to have a limited effect. The highest H *(10) value of 2.7 μSv Gy‑1 was measured at 329° to the beam axis and 1.63 m from the isocenter where high-energy neutrons (E  ⩾  20 MeV) contribute with about 53%. The neutron mapping within the gantry room showed that H *(10) values significantly decreased with distance and angular position with respect to the beam axis dropping to 0.52 μSv Gy‑1 at 90° and 3.35 m. Spectra at angles of 45° and 135° with respect to the beam axis measured here with an anthropomorphic phantom showed a similar peak structure at the thermal, fast and high energy range as in the previous water-tank experiments. Meanwhile, at 90°, small differences at the high-energy range were observed. Using ERBSS systems, neutron spectra mapping was performed to characterize the exposure of scanning proton therapy patients. The ten measured spectra provide precise information about the exposure of healthy organs to thermal

  5. Exterior field of slowly and rapidly rotating neutron stars: Rehabilitating spacetime metrics involving hyperextreme objects

    NASA Astrophysics Data System (ADS)

    Manko, V. S.; Ruiz, E.

    2016-05-01

    The 4-parameter exact solution presumably describing the exterior gravitational field of a generic neutron star is presented in a concise explicit form defined by only three potentials. In the equatorial plane, the metric functions of the solution are found to be given by particularly simple expressions that make them very suitable for the use in concrete applications. Following Pappas and Apostolatos, we perform a comparison of the multipole structure of the solution with the multipole moments of the known physically realistic Berti-Stergioulas numerical models of neutron stars to argue that the hyperextreme sectors of the solution are not less (but are possibly even more) important for the correct description of rapidly rotating neutron stars than the subextreme sector involving exclusively the black-hole constituents. We have also worked out in explicit form an exact analog of the well-known Hartle-Thorne approximate metric.

  6. Neutron field parameter measurements on the JET tokamak by means of super-heated fluid detectors.

    PubMed

    Gherendi, M; Zoita, V L; Craciunescu, T; Johnson, M Gatu; Pantea, A; Baltog, I; Edlington, T; Hellesen, C; Kiptily, V; Conroy, S; Murari, A; Popovichev, S

    2012-10-01

    The neutron field parameters (fluence and energy distribution) at a specific location outside the JET Torus Hall have been measured by means of super-heated fluid detectors (or "bubble detectors") in combination with an independent, time-of-flight, technique. The bubble detector assemblies were placed at the end of a vertical line of sight at about 16 m from the tokamak mid plane. Spatial distributions of the neutron fluence along the radial and toroidal directions have been obtained using two-dimensional arrays of bubble detectors. Using a set of three bubble detector spectrometers the neutron energy distribution was determined over a broad energy range, from about 10 keV to above 10 MeV, with an energy resolution of about 30% at 2.5 MeV. The very broad energy response allowed for the identification of energy features far from the main fusion component (around 2.45 MeV for deuterium discharges). PMID:23130800

  7. Inelastic neutron scttering study o fcrystal field levels in PrOs4As12

    SciTech Connect

    Chi, Songxue; Dai, Pengcheng; Barnes, Ted {F E }; Kang, H. J.; Lynn, J. W.; Ye, Feng; Maple, M. B.

    2008-01-01

    We use neutron scattering to study the Pr$^{3+}$ crystalline electric field (CEF) excitations in the filled skutterudite PrOs$_4$As$_{12}$. By comparing the observed levels and their strengths under neutron excitation with the theoretical spectrum and neutron excitation intensities, we identify the Pr$^{3+}$ CEF levels, and show that the ground state is a magnetic $\\Gamma_4^{(2)}$ triplet, and the excited states $\\Gamma_1$, $\\Gamma_4^{(1)}$ and $\\Gamma_{23}$ are at 0.4, 13 and 23~meV, respectively. A comparison of the observed CEF levels in PrOs$_4$As$_{12}$ with the heavy fermion superconductor PrOs$_4$Sb$_{12}$ reveals the microscopic origin of the differences in the ground states of these two filled skutterudites.

  8. Neutron field parameter measurements on the JET tokamak by means of super-heated fluid detectors

    SciTech Connect

    Gherendi, M.; Craciunescu, T.; Pantea, A.; Zoita, V. L.; Johnson, M. Gatu; Hellesen, C.; Conroy, S.; Baltog, I.; Edlington, T.; Kiptily, V.; Popovichev, S.; Murari, A.; Collaboration: JET EFDA Contributors

    2012-10-15

    The neutron field parameters (fluence and energy distribution) at a specific location outside the JET Torus Hall have been measured by means of super-heated fluid detectors (or 'bubble detectors') in combination with an independent, time-of-flight, technique. The bubble detector assemblies were placed at the end of a vertical line of sight at about 16 m from the tokamak mid plane. Spatial distributions of the neutron fluence along the radial and toroidal directions have been obtained using two-dimensional arrays of bubble detectors. Using a set of three bubble detector spectrometers the neutron energy distribution was determined over a broad energy range, from about 10 keV to above 10 MeV, with an energy resolution of about 30% at 2.5 MeV. The very broad energy response allowed for the identification of energy features far from the main fusion component (around 2.45 MeV for deuterium discharges).

  9. X-ray studies of neutron stars and their magnetic fields

    NASA Astrophysics Data System (ADS)

    Makishima, K.

    2016-05-01

    Utilizing results obtained over the past quarter century mainly with Japanese X-ray astronomy satellites, a review is given to some aspects of neutron stars (NSs), with a particular emphasis on the magnetic fields (MFs) of mass-accreting NSs and magnetars. Measurements of electron cyclotron resonance features in binary X-ray pulsars, using the Ginga and Suzaku observatories, clarified that their surface MFs are concentrated in a narrow range of (1?7) × 10^8 T. Extensive studies of magnetars with Suzaku reinforced their nature as neutron stars with truly strong MFs, and revealed several important clues to their formation, evolution, and physical states. Taking all these results into account, a discussion is made on the origin and evolution of these strong MFs. One possible scenario is that the MF of NSs is a manifestation of some fundamental physics, e.g., neutron spin alignment or chirality violation, and the MF makes transitions from strong to weak states.

  10. Four-hair relations for differentially rotating neutron stars in the weak-field limit

    NASA Astrophysics Data System (ADS)

    Bretz, Joseph; Yagi, Kent; Yunes, Nicolás

    2015-10-01

    The opportunity to study physics at supra-nuclear densities through x-ray observations of neutron stars has led to in-depth investigations of certain approximately universal relations that can remove degeneracies in pulse profile models. One such set of relations determines all of the multipole moments of a neutron star just from the first three (the mass monopole, the current dipole and the mass quadrupole moment) approximately independently of the equation of state. These three-hair relations were found to hold in neutron stars that rotate rigidly, as is the case in old pulsars, but neutron stars can also rotate differentially, as is the case for proto-neutron stars and hypermassive transient remnants of binary mergers. We here extend the three-hair relations to differentially rotating stars for the first time with a generic rotation law using two approximations: a weak-field scheme (an expansion in powers of the neutron star compactness) and a perturbative differential rotation scheme (an expansion about rigid rotation). These approximations allow us to analytically derive approximately universal relations that allow us to determine all of the multipole moments of a (perturbative) differentially rotating star in terms of only the first four moments. These new four-hair relations for differentially rotating neutron stars are found to be approximately independent of the equation of state to a higher degree than the three-hair relations for uniformly rotating stars. Our results can be instrumental in the development of four-hair relations for rapidly differentially rotating stars in full general relativity using numerical simulations.

  11. FOREWORD: Neutron metrology Neutron metrology

    NASA Astrophysics Data System (ADS)

    Thomas, David J.; Nolte, Ralf; Gressier, Vincent

    2011-12-01

    covered, particularly as a compendium of papers on spectrometry for radiation protection has been published relatively recently [1]. The CIPM Mutual Recognition Arrangement (CIPM MRA), whereby national measurement standards and certificates issued by different national metrology institutes (NMIs) can be recognized internationally, is covered only briefly, although the key comparisons which underpin the CIPM MRA are highlighted. The papers included in this issue concentrate on the primary physical quantities—neutron source emission rate and neutron fluence, papers on the latter quantity covering the wide range of neutron energies for which standards are required. Neutron cross sections are fundamental to neutron physics and their importance in neutron metrology is also covered. A large amount of work by acknowledged experts in neutron metrology has gone into the preparation of this special issue and we are indebted to them for their time and effort. The list of contributors begins with the authors of the papers but also includes the referees who provided invisible but invaluable input. We are grateful for the support and encouragement of Professor Georgio Moscati, president of the CCRI when the work was proposed, Dr Kim Carneiro the current president, and Dr Penny Allisy-Roberts the executive secretary of the CCRI. When this work was first proposed a list of potential topics was drawn up by the then chairman of Section (III) Dr Horst Klein. It is a measure of his insight and knowledge of the field that the resulting document matches almost exactly the original plan he drew up. This special issue is thus a tribute to his very extensive contribution to the field. We sincerely hope its contents provide an accurate picture of the present state of neutron metrology in view of Dr Klein's conviction of the importance in metrology of getting things right. Reference [1] Thomas D J and Klein H (ed) 2003 Neutron and photon spectrometry techniques for radiation protection Radiat

  12. Multipolar electromagnetic fields around neutron stars: exact vacuum solutions and related properties

    NASA Astrophysics Data System (ADS)

    Pétri, J.

    2015-06-01

    The magnetic field topology in the surrounding of neutron stars is one of the key questions in pulsar magnetospheric physics. A very extensive literature exists about the assumption of a dipolar magnetic field but very little progress has been made in attempts to include multipolar components in a self-consistent way. In this paper, we study the effect of multipolar electromagnetic fields anchored in the star. We give exact analytical solutions in closed form for any order l and apply them to the retarded point quadrupole (l = 2), hexapole (l = 3) and octopole (l = 4), a generalization of the retarded point dipole (l = 1). We also compare the Poynting flux from each multipole and show that the spin-down luminosity depends on the ratio R/rL, R being the neutron star radius and rL the light-cylinder radius. Therefore the braking index also depends on R/rL. As such multipole fields possess very different topology, most importantly smaller length scales compared to the dipolar field, especially close to the neutron star, we investigate the deformation of the polar caps induced by these multipolar fields. Such fields could have a strong impact on the interpretation of the pulsed radio emission suspected to emanate from these polar caps as well as on the inferred geometry deduced from the high-energy light-curve fitting and on the magnetic field strength. Discrepancies between the two-pole caustic model and our new multipole caustic model are emphasized with the quadrupole field. To this respect, we demonstrate that working with only a dipole field can be very misleading.

  13. The design of the inelastic neutron scattering mode for the Extreme Environment Diffractometer with the 26 T High Field Magnet

    NASA Astrophysics Data System (ADS)

    Bartkowiak, Maciej; Stüßer, Norbert; Prokhnenko, Oleksandr

    2015-10-01

    The Extreme Environment Diffractometer is a neutron time-of-flight instrument, designed to work with a constant-field hybrid magnet capable of reaching fields over 26 T, unprecedented in neutron science; however, the presence of the magnet imposes both spatial and technical limitations on the surrounding instrument components. In addition to the existing diffraction and small-angle neutron scattering modes, the instrument will operate also in an inelastic scattering mode, as a direct time-of-flight spectrometer. In this paper we present the Monte Carlo ray-tracing simulations, the results of which illustrate the performance of the instrument in the inelastic-scattering mode. We describe the focussing neutron guide and the chopper system of the existing instrument and the planned design for the instrument upgrade. The neutron flux, neutron spatial distribution, divergence distribution and energy resolution are calculated for standard instrument configurations.

  14. Effect of Reference Scheme on Power and Phase of the Local Field Potential.

    PubMed

    Shirhatti, Vinay; Borthakur, Ayon; Ray, Supratim

    2016-05-01

    Brain signals are often analyzed in the spectral domain, where the power spectral density (PSD) and phase differences and consistency can reveal important information about the network. However, for proper interpretation, it is important to know whether these measures depend on stimulus/behavioral conditions or the reference scheme used to analyze data. We recorded local field potential (LFP) from an array of microelectrodes chronically implanted in area V1 of monkeys under different stimulus/behavioral conditions and computed PSD slopes, coherence, and phase difference between LFPs as a function of frequency and interelectrode distance while using four reference schemes: single wire, average, bipolar, and current source density. PSD slopes were dependent on reference scheme at low frequencies (below 200 Hz) but became invariant at higher frequencies. Average phase differences between sites also depended critically on referencing, switching from 0 degrees for single-wire to 180 degrees for average reference. Results were consistent across different stimulus/behavioral conditions. We were able to account for these results based on the coherence profile across sites and properties of the spectral estimator. Our results show that using different reference schemes can have drastic effects on phase differences and PSD slopes and therefore must be interpreted carefully to gain insights about network properties. PMID:26942748

  15. Use of D-T-produced fast neutrons for in vivo body composition analysis: a reference method for nutritional assessment in the elderly.

    PubMed

    Kehayias, J J

    2004-05-01

    Body composition has become the main outcome of many nutritional intervention studies including osteoporosis, malnutrition, obesity, AIDS, and aging. Traditional indirect body composition methods developed with healthy young adults do not apply to the elderly or diseased. Fast neutron activation (for N and P) and neutron inelastic scattering (for C and O) are used to assess in vivo elements characteristic of specific body compartments. Non-bone phosphorus for muscle is measured by the (31)P(n, alpha)(28)Al reaction, and nitrogen for protein via the (14)N(n,2n)(13)N fast neutron reaction. Inelastic neutron scattering is used to measure total body carbon and oxygen. Body fat is derived from carbon after correcting for contributions from protein, bone, and glycogen. Carbon-to-oxygen ratio (C/O) is used to measure the distribution of fat and lean tissue in the body and to monitor small changes of lean mass. A sealed, D-T neutron generator is used for the production of fast neutrons. Carbon and oxygen mass and their ratio are measured in vivo at a radiation exposure of less than 0.06 mSv. Gamma-ray spectra are collected using large BGO detectors and analyzed for the 4.43 MeV state of carbon and 6.13 MeV state of oxygen, simultaneously with the irradiation. P and N analysis by delayed fast neutron activation is performed by transferring the patient to a shielded room equipped with an array of NaI(Tl) detectors. A combination of measurements makes possible the assessment of the "quality" of fat-free mass. The neutron generator system is used to evaluate the efficacy of new treatments, to study mechanisms of lean tissue depletion with aging, and to investigate methods for preserving function and quality of life in the elderly. It is also used as a reference method for the validation of portable instruments of nutritional assessment. PMID:14747891

  16. Experimental setup for the determination of the correction factors of the neutron doseratemeters in fast neutron fields

    SciTech Connect

    Iliescu, Elena; Bercea, Sorin; Dudu, Dorin; Celarel, Aurelia

    2013-12-16

    The use of the U-120 Cyclotron of the IFIN-HH allowed to perform a testing bench with fast neutrons in order to determine the correction factors of the doseratemeters dedicated to neutron measurement. This paper deals with researchers performed in order to develop the irradiation facility testing the fast neutrons flux generated at the Cyclotron. This facility is presented, together with the results obtain in determining the correction factor for a doseratemeter dedicated to the neutron dose equivalent rate measurement.

  17. DOSIMETRIC response of a REM-500 in low energy neutron fields typical of nuclear power plants.

    PubMed

    Aslam; Matysiak, W; Atanackovic, J; Waker, A J

    2012-06-01

    This study investigates the response of a REM-500 to assess neutron quality factor and dose equivalent in low energy neutron fields, which are commonly encountered in the workplace environment of nuclear power stations. The McMaster University 3 MV Van de Graaff accelerator facility was used to measure the response of the instrument in monoenergetic neutron fields in the energy range 51 to 727 keV by bombarding a thin LiF target with 1.93-2.50 MeV protons. The energy distribution of the neutron fields produced in the facility was measured by a (3)He filled gas ionization chamber. The MCA mode of the REM-500 instrument was used to collect lineal energy distributions at varying neutron energies and to calculate the frequency and dose-mean lineal energies. The effective quality factor, Q-, was also calculated using the values of Q(y)listed in the REM-500 operation manual and compared with those of ICRP 60. The authors observed a continuously increasing trend in y - F, y-D, and Q-with an increase in neutron energy. It is interesting to note that standard tissue equivalent proportional counters (TEPCs) filled with tissue equivalent(TE) gas give rise to a similar trend for these microdosimetric quantities of interest in the same energy range; however, the averages calculated in this study are larger by about 15%compared to a TEPC filled with propane-based TE gas probably because of the larger stopping power of protons in propane compared to TE gas. These somewhat larger event sizes did not result in any significant increase in the Q-compared to those obtained from a TEPC filled with TE gas and were found to be in good agreement with other measurements reported earlier at corresponding neutron energies. The instrument quality factor response, R(Q), defined as the ratio of measured quality factor to the calculated quality factor in an ICRU tissue sphere,was found to vary with neutron energy. The instrument response,R(Q), was ~0.6 at 727 keV, which deteriorates further to

  18. Implications of X-ray tube parameter deviations in X-ray reference fields.

    PubMed

    Behnke, B; Hupe, O; Ambrosi, P

    2016-02-01

    For the purpose of radiation protection, ICRU Report 57/ICRP Publication 74 provides a list of monoenergetic conversion coefficients to be used with, among others, photon reference fields generated with X-ray tubes. A comprehensive definition of these photon reference fields can be found in international standard ISO 4037; however, it lacks thorough indication of the allowed deviations of essential parameters that influence these X-ray reference fields. These parameters are the high-voltage tube potential, the thickness of the beryllium window and the purity and thickness of the filter materials used to create different radiation qualities. Small variations of these parameters can lead to significant changes in the created X-ray spectra and, hence, the spectra-dependent conversion coefficients for phantom-related radiation-protection quantities. This can lead to situations in which the conversion coefficients listed in ISO 4037 cannot be used, resulting in time-consuming spectrometry measurements. In this work, the impact on the resulting conversion coefficients is investigated using a simplified mathematical approximation model. The findings are validated with an independent X-ray spectra calculation programme. As a result, well-founded upper limit values on the allowed deviations of the essential X-ray tube parameters are proposed to be used in a future revision of ISO 4037. PMID:25889609

  19. Neutron detection in a high-gamma field using solution-grown stilbene

    NASA Astrophysics Data System (ADS)

    Bourne, M. M.; Clarke, S. D.; Adamowicz, N.; Pozzi, S. A.; Zaitseva, N.; Carman, L.

    2016-01-01

    A solution-based technique for growing large-volume stilbene scintillators was developed in 2013; crystals up to diameters of 10 cm, or larger, have been grown while preserving excellent pulse shape discrimination (PSD) properties. The goal of this study is to evaluate the PSD capabilities of 5.08 by 5.08-cm stilbene crystals grown by Lawrence Livermore National Laboratory and Inrad Optics when exposed to a 1000 to 1 gamma ray-neutron ratio and operating at a 100-kHz count rate. Results were compared to an equivalent EJ-309 liquid scintillation detector. 252Cf neutron pulses were recorded in two experiments where 60Co and 137Cs sources created the high-gamma field. The high count rate created numerous double pulses that were cleaned using fractional and template approaches designed to remove double pulses while preserving neutron counts. PSD was performed at a threshold of 42 keVee (440-keV proton) for stilbene and 60 keVee (610-keV proton) for EJ-309 liquid. The lower threshold in stilbene resulted in a neutron intrinsic efficiency of approximately 14.5%, 10% higher than EJ-309 liquid, for bare 252Cf and 13% for 252Cf in the high-gamma field. Despite the lower threshold, the gamma misclassification rate in stilbene was approximately 3×10-6, nearly a factor-of-five lower than what we found with the EJ-309 liquid.

  20. Comparison of different MC techniques to evaluate BNCT dose profiles in phantom exposed tovarious neutron fields.

    PubMed

    Durisi, E; Koivunoro, H; Visca, L; Borla, O; Zanini, A

    2010-03-01

    The absorbed dose in BNCT (boron neutron capture therapy) consists of several radiation components with different physical properties and biological effectiveness. In order to assess the clinical efficacy of the beams, determining the dose profiles in tissues, Monte Carlo (MC) simulations are used. This paper presents a comparison between dose profiles calculated in different phantoms using two techniques: MC radiation transport code, MCNP-4C2 and BNCT MC treatment planning program, SERA (simulation environment for radiotherapy application). In this study MCNP is used as a reference tool. A preliminary test of SERA is performed using six monodirectional and monoenergetic beams directed onto a simple water phantom. In order to deeply investigate the effect of the different cross-section libraries and of the dose calculation methodology, monoenergetic and monodirectional beams directed toward a standard Snyder phantom are simulated. Neutron attenuation curves and dose profiles are calculated with both codes and the results are compared. PMID:19939825

  1. Field calibration of PADC track etch detectors for local neutron dosimetry in man using different radiation qualities

    NASA Astrophysics Data System (ADS)

    Hälg, Roger A.; Besserer, Jürgen; Boschung, Markus; Mayer, Sabine; Clasie, Benjamin; Kry, Stephen F.; Schneider, Uwe

    2012-12-01

    In order to quantify the dose from neutrons to a patient for contemporary radiation treatment techniques, measurements inside phantoms, representing the patient, are necessary. Published reports on neutron dose measurements cover measurements performed free in air or on the surface of phantoms and the doses are expressed in terms of personal dose equivalent or ambient dose equivalent. This study focuses on measurements of local neutron doses inside a radiotherapy phantom and presents a field calibration procedure for PADC track etch detectors. An initial absolute calibration factor in terms of Hp(10) for personal dosimetry is converted into neutron dose equivalent and additional calibration factors are derived to account for the spectral changes in the neutron fluence for different radiation therapy beam qualities and depths in the phantom. The neutron spectra used for the calculation of the calibration factors are determined in different depths by Monte Carlo simulations for the investigated radiation qualities. These spectra are used together with the energy dependent response function of the PADC detectors to account for the spectral changes in the neutron fluence. The resulting total calibration factors are 0.76 for a photon beam (in- and out-of-field), 1.00 (in-field) and 0.84 (out-of-field) for an active proton beam and 1.05 (in-field) and 0.91 (out-of-field) for a passive proton beam, respectively. The uncertainty for neutron dose measurements using this field calibration method is less than 40%. The extended calibration procedure presented in this work showed that it is possible to use PADC track etch detectors for measurements of local neutron dose equivalent inside anthropomorphic phantoms by accounting for spectral changes in the neutron fluence.

  2. Different resistance patterns of reference and field strains of Brucella abortus

    PubMed Central

    Miranda, Karina L.; Dorneles, Elaine M. S.; Poester, Fernando P.; Martins, Paulo S.; Pauletti, Rebeca B.; Lage, Andrey P.

    2015-01-01

    The aim of this study was to evaluate the growth of the B. abortus reference strains and field isolates on media containing different inhibitor agents. Reference strains were seeded on tryptose agar containing: i-erythritol (1.0 mg/mL), fuchsin (20 μg/mL and 80 μg/mL), thionin (2.5 μg/mL and 10 μg/mL), rifampicin (200 μg/mL) and safranin O (200 μg/mL). Field isolates were tested only on media containing i-erythritol, rifampicin and thionin. Furthermore, each suspension was also inoculated on tryptose agar incubated in air, to test its ability to grow without CO 2 . Sensitivity to fuchsin was similar among reference strains evaluated. Growth of S19, 544 and 2308 but not RB51 were inhibited on media containing rifampicin. Medium with safranin O showed no inhibition for RB51, 544 and 2308, but it partially inhibited the S19 growth as well as medium containing i-erythritol. Treatment/control growth ratio for 2308 on tryptose agar containing thionin (2.5 μg/mL) was approximatelly 1.0, whereas S19 and RB51 showed 0.85 and 0.89 ratios, respectively. Growth of 544, S19 and RB51 but not 2308 was completely inhibited on medium with thionin (10 μg/mL). All field strains grew on medium containing i-erythritol, but were completelly inhibited by rifampicin. With exception of A1 ( B. abortus biovar 3) all field isolates grew on medium with thionin, although some strains showed a treatment/control growth ratio of 0.75–0.80 (10 μg/mL). These results showed that tryptose agar with thionin, i-erythritol or rifampicin could be useful for differentiating vaccine, challenge and field strains of B. abortus. PMID:26221116

  3. Different resistance patterns of reference and field strains of Brucella abortus.

    PubMed

    Miranda, Karina L; Dorneles, Elaine M S; Poester, Fernando P; Martins Filho, Paulo S; Pauletti, Rebeca B; Lage, Andrey P

    2015-03-01

    The aim of this study was to evaluate the growth of the B. abortus reference strains and field isolates on media containing different inhibitor agents. Reference strains were seeded on tryptose agar containing: i-erythritol (1.0 mg/mL), fuchsin (20 μg/mL and 80 μg/mL), thionin (2.5 μg/mL and 10 μg/mL), rifampicin (200 μg/mL) and safranin O (200 μg/mL). Field isolates were tested only on media containing i-erythritol, rifampicin and thionin. Furthermore, each suspension was also inoculated on tryptose agar incubated in air, to test its ability to grow without CO 2 . Sensitivity to fuchsin was similar among reference strains evaluated. Growth of S19, 544 and 2308 but not RB51 were inhibited on media containing rifampicin. Medium with safranin O showed no inhibition for RB51, 544 and 2308, but it partially inhibited the S19 growth as well as medium containing i-erythritol. Treatment/control growth ratio for 2308 on tryptose agar containing thionin (2.5 μg/mL) was approximatelly 1.0, whereas S19 and RB51 showed 0.85 and 0.89 ratios, respectively. Growth of 544, S19 and RB51 but not 2308 was completely inhibited on medium with thionin (10 μg/mL). All field strains grew on medium containing i-erythritol, but were completelly inhibited by rifampicin. With exception of A1 ( B. abortus biovar 3) all field isolates grew on medium with thionin, although some strains showed a treatment/control growth ratio of 0.75-0.80 (10 μg/mL). These results showed that tryptose agar with thionin, i-erythritol or rifampicin could be useful for differentiating vaccine, challenge and field strains of B. abortus. PMID:26221116

  4. NOAA/NGDC candidate models for the 12th generation International Geomagnetic Reference Field

    NASA Astrophysics Data System (ADS)

    Alken, Patrick; Maus, Stefan; Chulliat, Arnaud; Manoj, Chandrasekharan

    2015-05-01

    The International Geomagnetic Reference Field (IGRF) is a model of the geomagnetic main field and its secular variation, produced every 5 years from candidate models proposed by a number of international research institutions. For this 12th generation IGRF, three candidate models were solicited: a main field model for the 2010.0 epoch, a main field model for the 2015.0 epoch, and the predicted secular variation for the five-year period 2015 to 2020. The National Geophysical Data Center (NGDC), part of the National Oceanic and Atmospheric Administration (NOAA), has produced three candidate models for consideration in IGRF-12. The 2010 main field candidate was produced from Challenging Minisatellite Payload (CHAMP) satellite data, while the 2015 main field and secular variation candidates were produced from Swarm and Ørsted satellite data. Careful data selection was performed to minimize the influence of magnetospheric and ionospheric fields. The secular variation predictions of our parent models, from which the candidate models were derived, have been validated against independent ground observatory data.

  5. Quark-hadron phase transition in a neutron star under strong magnetic fields

    NASA Astrophysics Data System (ADS)

    Rabhi, A.; Pais, H.; Panda, P. K.; Providência, C.

    2009-11-01

    We study the effect of a strong magnetic field on the properties of neutron stars with a quark-hadron phase transition. It is shown that the magnetic field prevents the appearance of a quark phase, enhances the leptonic fraction, decreases the baryonic density extension of the mixed phase and stiffens the total equation of state, including both the stellar matter and the magnetic field contributions. Two parametrizations of a density-dependent static magnetic field, increasing, respectively, fast and slowly with the density and reaching 2-4 × 1018 G in the centre of the star, are considered. The compact stars with strong magnetic fields have maximum mass configurations with larger masses and radii and smaller quark fractions. The parametrization of the magnetic field with density has a strong influence on the star properties.

  6. Hydrogen Concentration and Strain Fields Near Fatigue Cracks in Pipeline Steel Measured Via Neutron Imaging

    NASA Astrophysics Data System (ADS)

    Connolly, Matthew; Slifka, Andrew; Drexler, Elizabeth; Hydrogen Pipeline Safety Team

    Hydrogen (H2) is desirable for energy storage as it is cleaner burning and can store a larger amount of energy than an equal mass of gasoline. One problem in the development of a hydrogen economy is to find or develop materials that ensure the safe, reliable, and cost-effective flow of energy from the source to the user. It is expected steels will be needed to serve this function. However, the existing network of natural gas pipeline, for example, is constructed of ferrous materials which are susceptible to embrittlement and subsequent increased fatigue crack growth rates after exposure to hydrogen. In order to improve current modeling efforts, experimental determination of hydrogen concentration, hydrogen diffusion rates, and strain fields are required to inform and validate the model. Here we report neutron imaging measurements of the hydrogen concentration near a fatigue crack and the corresponding strain field, measured via neutron transmission Bragg edge spectroscopy. Nist Materials Measurement Laboratory, Applied Chemicals and Materials Division.

  7. Field-dependent neutron depolarization study of the ferrite formation in medium-carbon steels

    SciTech Connect

    Te Velthuis, S.G.E.; Van Dijk, N.H.; Rekveldt, M.T.; Sietsma, J.; Van Der Zwaag, S.

    2000-03-14

    Neutron depolarization experiments have been performed on the ferrite and pearlite phase transformations of the medium-carbon C60 and C35 steels. The interaction of the polarized neutron beam with the ferromagnetic ferrite grains gives information on the mean magnetization and the magnetic correlation length. From these parameters the ferrite fraction and the mean ferrite grain size are determined in situ as a function of time and temperature during the phase transformation. The applied magnetic field was varied periodically in order to record a full hysteresis curve of the magnetization, which gives essential information on the microstructure of the ferromagnetic ferrite grains. The field dependence of the mean particle size during the early stages of the pearlite formation is a strong indication of multi-domain behavior, which is absent in the austenite-ferrite transformation and at the end of the pearlite formation.

  8. Neutron-skin thickness of finite nuclei in relativistic mean-field models with chiral limits

    SciTech Connect

    Jiang Weizhou; Li Baoan; Chen Liewen

    2007-11-15

    We study several structure properties of finite nuclei using relativistic mean-field Lagrangians constructed according to the Brown-Rho scaling due to the chiral symmetry restoration at high densities. The models are consistent with current experimental constraints for the equations of state of symmetric matter at both normal and supranormal densities and of asymmetric matter at subsaturation densities. It is shown that these models can successfully describe the binding energies and charge radii of finite nuclei. Compared to calculations with usual relativistic mean-field models, these models give a reduced thickness of neutron skin in {sup 208}Pb between 0.17 fm and 0.21 fm. The reduction of the predicted neutron skin thickness is found to be due to not only the softening of the symmetry energy but also the scaling property of {rho} meson required by the partial restoration of chiral symmetry.

  9. Neutron stars in a perturbative f(R) gravity model with strong magnetic fields

    SciTech Connect

    Cheoun, Myung-Ki; Deliduman, Cemsinan; Güngör, Can; Keleş, Vildan; Ryu, C.Y.; Kajino, Toshitaka; Mathews, Grant J. E-mail: cemsinan@msgsu.edu.tr E-mail: kelesvi@itu.edu.tr E-mail: kajino@nao.ac.jp

    2013-10-01

    In Kaluza-Klein electromagnetism it is natural to associate modified gravity with strong electromagnetic fields. Hence, in this paper we investigate the combined effects of a strong magnetic field and perturbative f(R) gravity on the structure of neutron stars. The effect of an interior strong magnetic field of about 10{sup 17−18} G on the equation of state is derived in the context of a quantum hadrodynamics (QHD) equation of state (EoS) including effects of the magnetic pressure and energy along with occupied Landau levels. Adopting a random orientation of interior field domains, we solve the modified spherically symmetric hydrostatic equilibrium equations derived for a gravity model with f(R) = R+αR{sup 2}. Effects of both the finite magnetic field and the modified gravity are detailed for various values of the magnetic field and the perturbation parameter α along with a discussion of their physical implications. We show that there exists a parameter space of the modified gravity and the magnetic field strength, in which even a soft equation of state can accommodate a large ( > 2 M{sub s}un) maximum neutron star mass.

  10. Interior Vector Magnetic Field Monitoring for the SNS Neutron EDM Experiment

    NASA Astrophysics Data System (ADS)

    Nouri, Nima; Plaster, Brad

    2014-09-01

    A concept has been developed which provides for a real-time determination of the spatial dependence of the vector components of the magnetic field (and, hence, the ∂Bi / ∂xj field gradients) within the interior fiducial volume of the SNS neutron EDM experiment solely from exterior measurements at fixed discrete locations. This technique will be especially important during the operation of the experiment, when direct measurements of the field gradients present within the fiducial volume will not be physically possible. Our method, which is based on the solution to the Laplace Equation, is completely general and does not require the field to possess any type of symmetry. We describe the concept and our systematic approach for optimizing the locations of these exterior measurements. We also present results from prototyping studies of a field monitoring system deployed within a half-scale prototype of the experiment's magnetic field environment. A concept has been developed which provides for a real-time determination of the spatial dependence of the vector components of the magnetic field (and, hence, the ∂Bi / ∂xj field gradients) within the interior fiducial volume of the SNS neutron EDM experiment solely from exterior measurements at fixed discrete locations. This technique will be especially important during the operation of the experiment, when direct measurements of the field gradients present within the fiducial volume will not be physically possible. Our method, which is based on the solution to the Laplace Equation, is completely general and does not require the field to possess any type of symmetry. We describe the concept and our systematic approach for optimizing the locations of these exterior measurements. We also present results from prototyping studies of a field monitoring system deployed within a half-scale prototype of the experiment's magnetic field environment. This work was supported in part by the U.S. Department of Energy Office of

  11. Assessment of models proposed for the 1985 revision of the international geomagnetic reference field

    USGS Publications Warehouse

    Peddie, N.W.; Zunde, A.K.

    1987-01-01

    Geomagnetic measurements from land, marine and aerial surveys conducted in the years 1945-1964 were used to test the 14 models proposed as additions, for that period, to the series of definitive geomagnetic reference field (DGRF) models. Overall, NASA's 'SFAS' models and the BGS (British Geological Survey) models agree best with these data. Comparisons of the two proposed definitive main-field models for 1980.0, with each other and with the existing IGRF 1980 main-field model, show mostly close agreement, with the greatest absolute differences (several tens of nanotesla) occurring in the region of Antarctica. Comparison of the the three proposed forecast secular-variation models for 1985-1990 with estimates of recent rates of change at 148 magnetic observatories shows that the IZMIRAN (U.S.S.R.) and USGS models are in closest agreement with these data. ?? 1987.

  12. Reference-ellipsoid and the normal gravity field in post-Newtonian geodesy

    NASA Astrophysics Data System (ADS)

    Kopeikin, Sergei; Mazurova, Elena

    2016-07-01

    We apply general relativity to construct the post-Newtonian background manifold that serves as a reference spacetime in relativistic geodesy for conducting relativistic calculation of the geoid undulation and the deflection of the plumb line from the vertical. We chose an axisymmetric ellipsoidal body made up of a perfect homogeneous fluid uniformly rotating around a fixed axis, as a source generating the reference geometry. We reformulate and extend hydrodynamic calculations of rotating fluids done by previous researchers to the realm of relativistic geodesy to set up the algebraic equations defining the shape of the post-Newtonian reference ellipsoid. We explicitly perform all integrals characterizing gravitational field inside and outside the fluid body and represent them in terms of the elementary functions depending on its eccentricity. We fully explore the coordinate freedom of the equations describing the post-Newtonian ellipsoid and evaluate the deviation of the post-Newtonian level surface from the Newtonian (Maclaurin) ellipsoid. We also derive the post-Newtonian normal gravity field of the rotating fluid in terms of the parameters characterizing the post-Newtonian ellipsoid including relativistic mass, angular velocity and eccentricity. We formulate the post-Newtonian theorems of Pizzetti and Clairaut that are used in geodesy to connect the geometric parameters of the Earth figure to physically measurable force of gravity at its pole and equator.

  13. The role of the brain's frontal eye fields in constructing frame of reference.

    PubMed

    Wallentin, Mikkel

    2012-08-01

    Establishing contextual reference during discourse is a vital part of language function. Personal pronouns (e.g., he/she/it) are used to refer to previously experienced objects, utterances and events. These items, however, are often no longer present in the environment and have to be maintained and manipulated in working memory (WM). One aspect of this is the construction of a spatial frame of reference (e.g., "He was in front of it" where "he" is established as figure and "it" is the ground). The WM processes underlying this function may be different from those involved in establishing a non-spatial relation (e.g., "He was older than her"). The brain's frontal eye fields (FEFs), responsible for eye movement control, are known to be involved in processing spatial WM. This paper reviews both functional magnetic resonance imaging experiments and a subsequent behavioral interference study demonstrating a specific role for the FEFs and the brain's eye movement control system in manipulation of WM content for establishing object-centered spatial reference frames during verbally cued recall of recent visual and linguistic experiences. PMID:22806655

  14. Spectra of photons and neutrons generated in a heterogeneous head of a 15 MV LINAC at differents field sizes

    SciTech Connect

    Benites-Rengifo, J. L.; Vega-Carrillo, H. R.; Velazquez-Fernandez, J. B.

    2012-10-23

    Spectra of photons and neutrons were calculated, using the Monte Carlo code MCNP-5 using the e/p/n mode. A heterogeneous model was used to define the linac head where the collimators were modeled to produce five different treatment fields at the isocenter. Photon and neutron spectra were estimated in several points along two directions from the isocenter. The total photon fluence beyond 60 cm behaves according to 1/r{sup 2} rule, while total neutron fluence, beyond 80 cm, can be described by diffusion theory using an infinite plane as a neutron source.

  15. Advances in Neutron Spectroscopy and High Magnetic Field Instrumentation for studies of Correlated Electron Systems

    SciTech Connect

    Granroth, Garrett E

    2011-01-01

    Neutron Spectroscopy has provided critical information on the magnetism in correlated electron systems. Specifically quantum magnets, superconductors, and multi-ferroics are areas of productive research. A discussion of recent measurements on the SEQUOIA spectrometer will provide examples of how novel instrumentation concepts are used on the latest generation of spectrometers to extend our knowledge in such systems. The now ubiquitous function of sample rotation allows for full mapping of volumes of $Q$ and $\\omega$ space. An instrument focused on low angles could extend these maps to cover more of the first Brillioun zone. Innovative chopper cascades allow two unique modes of operation. Multiplexed measurements allow the simultaneous measurement of high and low energy features in an excitation spectrum. Alternatively by limiting the neutron bandwidth incident on the Fermi Chopper, background from subsequent time frames is removed, enabling the observation of weak, large energy transfer features. Finally the implementation of event-based detection for neutron experiments is time correlated experiments. Diffraction studies of the high field spin states in MnWO$_4$ using magnetic fields up to 30 T, provided by a pulsed magnet, illustrate this method. Expanding the high field studies to spectroscopy will require a novel instrument, focused around a world class DC magnet, like Zeemans proposed for the SNS.

  16. Spin-Down Mechanisms in Neutron Stars with ``Anomalous'' Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Rogers, Adam; Safi-Harb, Samar

    2015-08-01

    Energy losses from isolated neutron stars are attributed to a number of factors, the most common assumption being the emission of electromagnetic radiation from a rotating point-like magnetic dipole in vacuum. This energy loss mechanism predicts a braking index n = 3, which is not observed in highly magnetized neutron stars. Despite this fact, the assumptions of a dipole field and rapid early rotation are often assumed a priori. This typically causes a discrepancy in the characteristic age of these objects and the age of their associated Supernova Remnants (SNRs). In this work we consider neutron stars with ``anomalous'' magnetic fields - namely magnetars, high-B radio pulsars, and the Central Compact Objects (proposed to be `anti-magnetars’) that are securely associated with SNRs. Without making any assumptions about the initial spin periods of these objects and by constraining the SNR ages to match their associated pulsar ages, we compare the predictions of distinct energy loss mechanisms, such as field decay and the emission of relativistic winds using all observed data on the braking indices. This study has important implications on the proposed emission models for these exotic objects and helps in resolving the PSR-SNR age discrepancy.

  17. Effects of neutrino emissivity on the cooling of neutron stars in the presence of a strong magnetic field

    SciTech Connect

    Coelho, Eduardo Lenho; Chiapparini, Marcelo; Negreiros, Rodrigo Picanço

    2015-12-17

    One of the most interesting kind of neutron stars are the pulsars, which are highly magnetized neutron stars with fields up to 10{sup 14} G at the surface. The strength of magnetic field in the center of a neutron star remains unknown. According to the scalar virial theorem, magnetic field in the core could be as large as 10{sup 18} G. In this work we study the influence of strong magnetic fields on the cooling of neutron stars coming from direct Urca process. Direct Urca process is an extremely efficient mechanism for cooling a neutron star after its formation. The matter is described using a relativistic mean-field model at zero temperature with eight baryons (baryon octet), electrons and muons. We obtain the relative population of each species of particles as function of baryon density for different magnetic fields. We calculate numerically the cooling of neutron stars for a parametrized magnetic field and compare the results for the case without a magnetic field.

  18. Fluence measurement of fast neutron fields with a highly efficient recoil proton telescope using active pixel sensors.

    PubMed

    Taforeau, J; Higueret, S; Husson, D; Kachel, M; Lebreton, L

    2014-10-01

    The spectrometer ATHENA (Accurate Telescope for High-Energy Neutron metrology Applications) is being developed at the LNE-IRSN and aims at characterising energy and fluence of fast neutron fields. The detector is a recoil proton telescope and measures neutron fields in the range of 5-20 MeV. This telescope is intended to become a primary standard for both energy and fluence measurements. The neutron detection is achieved by a polyethylene radiator for n-p conversion, three 50-µm-thick silicon sensors that use CMOS technology for proton tracking and a 3-mm-thick silicon diode to measure the residual proton energy. The use of CMOS sensors and silicon diode, owing to a large detection solid angle, increases the intrinsic efficiency of the detector by a factor of 10 compared with conventional designs. The ability of the spectrometer to determine the neutron energy was demonstrated and reported elsewhere. This paper focuses on the fluence measurement of monoenergetic neutron fields in the range of 5-20 MeV. Experimental investigations, performed at the AMANDE facility, indicate a good estimation of neutron fluence at various energies. In addition, a complete description of uncertainties budget is presented in this paper and a Monte Carlo propagation of uncertainty sources leads to a fluence measurement with a precision ∼3-5 % depending on the neutron energy. PMID:24243312

  19. Transient particle acceleration in strongly magnetized neutron stars. II - Effects due to a dipole field geometry

    NASA Technical Reports Server (NTRS)

    Fatuzzo, Marco; Melia, Fulvio

    1991-01-01

    Sheared Alfven waves generated by nonradial crustal disturbances above the polar cap of a strongly magnetized neutron star induce an electric field component parallel to B. An attempt is made to determine the manner in which the strong radial dependence of B affects the propagation of these sheared Alfven waves, and whether this MHD process is still an effective particle accelerator. It is found that although the general field equation is quite complicated, a simple wavelike solution can still be obtained under the conditions of interest for which the Alfven phase velocity decouples from the wave equation. The results may be applicable to gamma-ray burst sources.

  20. The use of passive personal neutron dosemeters to determine the neutron dose equivalent component of radiation fields in spacecraft.

    PubMed

    Bartlett, D T; Hager, L G; Tanner, R J

    2004-01-01

    For the altitude range and inclination of the International Space Station (ISS), secondary neutrons can be a major contributor to dose equivalent inside a spacecraft. The exact proportion is very dependent on the amount of shielding of the primary galactic cosmic radiation and trapped particles, but is likely to lie in the range of 10-50%. Personal neutron dosemeters of simple design, processed using simple techniques developed for personal dosimetry, may be used to estimate this neutron component. PMID:15353682

  1. Constraints on Non-Newtonian Gravity From the Experiment on Neutron Quantum States in the Earth’s Gravitational Field

    PubMed Central

    Nesvizhevsky, V. V.; Protasov, K. V.

    2005-01-01

    An upper limit to non-Newtonian attractive forces is obtained from the measurement of quantum states of neutrons in the Earth’s gravitational field. This limit improves the existing constraints in the nanometer range. PMID:27308134

  2. Neutron scattering studies of crude oil viscosity reduction with electric field

    NASA Astrophysics Data System (ADS)

    Du, Enpeng

    topic. Dr. Tao with his group at Temple University, using his electro or magnetic rheological viscosity theory has developed a new technology, which utilizes electric or magnetic fields to change the rheology of complex fluids to reduce the viscosity, while keeping the temperature unchanged. After we successfully reduced the viscosity of crude oil with field and investigated the microstructure changing in various crude oil samples with SANS, we have continued to reduce the viscosity of heavy crude oil, bunker diesel, ultra low sulfur diesel, bio-diesel and crude oil and ultra low temperature with electric field treatment. Our research group developed the viscosity electrorheology theory and investigated flow rate with laboratory and field pipeline. But we never visualize this aggregation. The small angle neutron scattering experiment has confirmed the theoretical prediction that a strong electric field induces the suspended nano-particles inside crude oil to aggregate into short chains along the field direction. This aggregation breaks the symmetry, making the viscosity anisotropic: along the field direction, the viscosity is significantly reduced. The experiment enables us to determine the induced chain size and shape, verifies that the electric field works for all kinds of crude oils, paraffin-based, asphalt-based, and mix-based. The basic physics of such field induced viscosity reduction is applicable to all kinds of suspensions.

  3. Neutron scattering facility for continuous high magnetic fields up to 40 T at Hahn-Meitner-Institut Berlin

    NASA Astrophysics Data System (ADS)

    Smeibidl, P.; Mezei, F.; Meissner, M.; Prokes, K.; Schröder-Smeibidl, B.; Steiner, M.

    2003-05-01

    The neutron scattering facility BENSC at Hahn-Meitner-Institut offers outstanding research opportunities to the international scientific user community. Experiments on an advanced suite of instruments can be performed in uniquely high magnetic fields up to 17.5 T at temperatures down to 30 mK simultaneously. To further extend the range of continuous magnetic fields for neutron scattering, HMI has proposed a new facility with resistive magnets up to 40 T.

  4. Relativistic mean field model for entrainment in general relativistic superfluid neutron stars

    NASA Astrophysics Data System (ADS)

    Comer, G. L.; Joynt, R.

    2003-07-01

    General relativistic superfluid neutron stars have a significantly more intricate dynamics than their ordinary fluid counterparts. Superfluidity allows different superfluid (and superconducting) species of particles to have independent fluid flows, a consequence of which is that the fluid equations of motion contain as many fluid element velocities as superfluid species. Whenever the particles of one superfluid interact with those of another, the momentum of each superfluid will be a linear combination of both superfluid velocities. This leads to the so-called entrainment effect whereby the motion of one superfluid will induce a momentum in the other superfluid. We have constructed a fully relativistic model for entrainment between superfluid neutrons and superconducting protons using a relativistic σ-ω mean field model for the nucleons and their interactions. In this context there are two notions of “relativistic”: relativistic motion of the individual nucleons with respect to a local region of the star (i.e. a fluid element containing, say, an Avogadro’s number of particles), and the motion of fluid elements with respect to the rest of the star. While it is the case that the fluid elements will typically maintain average speeds at a fraction of that of light, the supranuclear densities in the core of a neutron star can make the nucleons themselves have quite high average speeds within each fluid element. The formalism is applied to the problem of slowly rotating superfluid neutron star configurations, a distinguishing characteristic being that the neutrons can rotate at a rate different from that of the protons.

  5. Cooling of neutron stars and emissivity of neutrinos by the direct Urca process under influence of a strong magnetic field

    NASA Astrophysics Data System (ADS)

    Coelho, E. L.; Chiapparini, M.; Negreiros, R. P.

    2016-04-01

    Neutron stars are born with high temperatures and during a few seconds suffer rapid cooling by emission of neutrinos. The direct Urca process is the main mechanism to explain this loss of energy. In this work we study the influence of a strong magnetic field on the composition of nuclear matter at high densities and zero temperature. We describe the matter through a relativistic mean-field model with eight light baryons (baryon octet), electrons, muons magnetic field. As output of the numerical calculations, we obtain the relative population for a parametrized magnetic field. We calculate the cooling of neutron stars with different mass and magnetic fields due to direct Urca process.

  6. Astronomers Use X-Rays To Probe Gravitational Field Of A Neutron Star

    NASA Astrophysics Data System (ADS)

    2002-06-01

    With NASA's Chandra X-ray Observatory, astronomers have detected features that may be the first direct evidence of the effect of gravity on radiation from a neutron star. This finding, if confirmed, could enable scientists to measure the gravitational field of neutron stars and determine whether they contain exotic forms of matter not seen on Earth. A team led by George Pavlov of Penn State University in University Park observed 1E 1207.4-5209, a neutron star in the center of a supernova remnant about 7,000 light years from Earth. The results were presented on June 6, 2002, at the American Astronomical Society in Albuquerque, NM. Pavlov's group found two dips, or absorption features, in the spectrum of X-rays from the star. If these dips are due to the absorption of X-rays near the star by helium ions in a strong magnetic field, they indicate that the gravitational field reduces the energies of X-rays escaping from near the surface of a neutron star. "This interpretation is consistent with the data," said Pavlov, "but the features may be a blend of many other features. More precise measurements, preferably with Chandra's grating spectrometer, are needed." "These absorption features may be the first evidence of the effect of gravity on radiation near the surface of an isolated neutron star," said Pavlov. "This is particularly important because it would allow us to set limits on the type of matter that comprises this star." Neutron stars are formed when a massive star runs out of fuel and its core collapses. A supernova explosion occurs and the collapsed core is compressed to a hot object about 12 miles in diameter, with a thin atmosphere of hydrogen and possibly heavier ions in a gravitational field 100 billion times as strong as Earth's. These objects, which have a density of more than 1 billion tons per teaspoonful, are called neutron stars because they have been thought to be composed mostly of neutrons. Although neutron stars have been studied extensively for

  7. Surface temperature of a magnetized neutron star and interpretation of the ROSAT data. 1: Dipole fields

    NASA Technical Reports Server (NTRS)

    Page, Dany

    1995-01-01

    We model the temperature distribution at the surface of a magnetized neutron star and study the effects on the observed X-ray spectra and light curves. Generalrelativistic effects, i.e., redshift and lensing, are fully taken into account. Atmospheric effects on the emitted spectral flux are not included: we consider only blackbody emission at the local effective temperature. In this first paper we restrict ourselves to dipole fields. General features are studied and compared with the ROSAT data from the pulsars 0833 - 45 (Vela), 0656 + 14, 0630 + 178 (Geminga), and 1055 - 52, the four cases for which there is strong evidence that thermal radiation from the stellar surface is detected. The composite spectra we obtain are not very different from a blackbody spectrum at the star's effective temperature. We conclude that, as far as blackbody spectra are considered, temperature estimates using single-temperature models give results practically identical to our composite models. The change of the (composite blackbody) spectrum with the star's rotational phase is also not very large and may be unobservable inmost cases. Gravitational lensing strongly suppresses the light curve pulsations. If a dipole field is assumed, pulsed fractions comparable to the observed ones can be obtained only with stellar radii larger than those which are predicted by current models of neutron star struture, or with low stellar masses. Moreover, the shapes of the theoretical light curves with dipole fields do not correspond to the observations. The use of magnetic spectra may raise the pulsed fraction sufficiently but will certainly make the discrepancy with the light curve shapes worse: dipole fields are not sufficient to interpret the data. Many neutron star models with a meson condensate or hypersons predict very small radii, and hence very strong lensing, which will require highly nondipolar fields to be able to reproduce the observed pulsed fractions, if possible at all: this may be a new

  8. Disordered Nuclear Pasta, Magnetic Field Decay, and Crust Cooling in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Horowitz, C. J.; Berry, D. K.; Briggs, C. M.; Caplan, M. E.; Cumming, A.; Schneider, A. S.

    2015-01-01

    Nuclear pasta, with nonspherical shapes, is expected near the base of the crust in neutron stars. Large-scale molecular dynamics simulations of pasta show long lived topological defects that could increase electron scattering and reduce both the thermal and electrical conductivities. We model a possible low-conductivity pasta layer by increasing an impurity parameter Qimp . Predictions of light curves for the low-mass x-ray binary MXB 1659-29, assuming a large Qimp, find continued late time cooling that is consistent with Chandra observations. The electrical and thermal conductivities are likely related. Therefore, observations of late time crust cooling can provide insight on the electrical conductivity and the possible decay of neutron star magnetic fields (assuming these are supported by currents in the crust).

  9. Disordered nuclear pasta, magnetic field decay, and crust cooling in neutron stars

    NASA Astrophysics Data System (ADS)

    Horowitz, C. J.; Berry, D. K.; Briggs, C. M.; Caplan, M. E.; Cumming, A.; Schneider, A. S.

    2015-04-01

    Nuclear pasta, with non-spherical shapes, is expected near the base of the crust in neutron stars. Large scale molecular dynamics simulations of pasta show long lived topological defects that could increase electron scattering and reduce both the thermal and electrical conductivities. We model a possible low conductivity pasta layer by increasing an impurity parameter Qimp. Predictions of light curves for the low mass X-ray binary MXB 1659-29, assuming a large Qimp, find continued late time cooling that is consistent with Chandra observations. The electrical and thermal conductivities are likely related. Therefore observations of late time crust cooling can provide insight on the electrical conductivity and the possible decay of neutron star magnetic fields (assuming these are supported by currents in the crust). This research was supported in part by DOE Grants DE-FG02-87ER40365 (Indiana University) and DE-SC0008808 (NUCLEI SciDAC Collaboration).

  10. Quantification of the neutron dark-field imaging signal in grating interferometry

    NASA Astrophysics Data System (ADS)

    Grünzweig, C.; Kopecek, J.; Betz, B.; Kaestner, A.; Jefimovs, K.; Kohlbrecher, J.; Gasser, U.; Bunk, O.; David, C.; Lehmann, E.; Donath, T.; Pfeiffer, F.

    2013-09-01

    Here we report on a mathematical description for the neutron dark-field image (DFI) contrast based on the influence of the thickness-dependent beam broadening caused by scattering interactions and multiple refraction in the sample. We conduct radiography experiments to verify that the DFI signal exponentially decays as a function of thickness for both magnetic and nonmagnetic materials. Here we introduce a material-dependent parameter, the so-called linear diffusion coefficient Ω. This allows us to perform a quantitative DFI-computed tomography. Additionally, we conduct correlative small-angle neutron-scattering experiments and validate the mathematical assumption that the angular broadening of the direct beam is proportional to the square root of the number of discrete layers.