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1

Short-range structure of ?-V2D: Pair distribution function analysis of x-ray and neutron diffraction  

NASA Astrophysics Data System (ADS)

X-ray and neutron diffraction experiments using pair distribution function (PDF) analysis were used to elucidate the short-range structure of ?-V2D. The PDF obtained by x-ray diffraction indicated the displacement of the vanadium atoms from the ideal body-centered-tetragonal lattice positions; the displacement was evaluated to be 0.008(2) nm. Reverse Monte Carlo simulation based on x-ray and neutron PDFs was also used to determine the locations of the deuterium atoms. Results suggest that the deuterium atoms are displaced from the centers of the octahedral sites and are surrounded by four vanadium atoms at equal average distances.

Itoh, Keiji; Fukunaga, Toshiharu

2007-06-01

2

Thermal Evolution of Isolated Neutron Stars: Pairing, Pairing, and Pairing  

SciTech Connect

The thermal evolution of young isolated neutron stars is driven by neutrino emission from matter at the highest densities reached in their inner core. As such, these objects are direct probes of the structure of matter at supranuclear density. However, pairing of the neutrino emitting baryons, or quarks, can significantly alter their emission efficiency and the predicted thermal evolution is very sensitive to assumptions about gap size(s). After a brief description of these physical processes, I compare with present observational data models of cooling neutron stars driven by slow or fast neutrino emission. Depending on the assumed size of the neutron {sup 3}P{sub 2}-{sup 3}F{sub 2} gap, a minimal model of neutron stars can accommodate all present data, with the exception of the cold pulsar J0007.0+7303 in the supernova remnant CTA 1. However, in case this gap is vanishingly small or very large, the estimated surface temperatures of more than a half of the observed young cooling neutron stars would imply the intervention of some form of enhanced neutrino emission. Unfortunately, the present uncertainty on the size of the neutron {sup 3}P{sub 2}-{sup 3}F{sub 2} gap precludes us to draw any definitive conclusion about the state of dense matter from the sole study of isolated neutron stars.

Page, Dany [Departamento de Astrofisica Teorica, Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, 04510 Mexico D.F. (Mexico)

2009-05-07

3

Extracting differential pair distribution functions using MIXSCAT  

SciTech Connect

Differently weighted experimental scattering data have been used to extract partial or differential structure factors or pair distribution functions in studying many materials. However, this is not done routinely partly because of the lack of user-friendly software. This paper presents MIXSCAT, a new member of the DISCUS program package. MIXSCAT allows one to combine neutron and X-ray pair distribution functions and extract their respective differential functions.

Wurden, Caroline; Page, Katharine; Llobet, Anna; White, Claire E.; Proffen, Thomas (LANL)

2010-08-27

4

Local atomic strain in ZnSe{sub 1-x}Te{sub x} from high real-space resolution neutron pair distribution function measurements  

SciTech Connect

High real-space resolution atomic pair distribution functions (PDF's) have been obtained from ZnSe{sub 1-x}Te{sub x} using neutron powder diffraction. Distinct Zn-Se and Zn-Te nearest-neighbor (nn) bonds, differing in length by {Delta}r=0.14 Aa, are resolved in the measured PDF's, allowing the evolution with composition of the individual bond lengths to be studied. The local bond lengths change much more slowly with doping than the average bond length obtained crystallographically. The nn bond-length distributions are constant with doping, but higher-neighbor pair distributions broaden significantly, indicating that most of the strain from the alloying is accommodated by bond-bending forces in the alloy. PDF's of alloys across the whole doping range are well fit using a model based on the Kirkwood potential. The resulting PDF's give excellent agreement with the measured PDF's over the entire alloy range with no adjustable parameters.

Peterson, P. F.; Proffen, Th.; Jeong, I.-K.; Billinge, S. J. L.; Choi, K.-S.; Kanatzidis, M. G.; Radaelli, P. G.

2001-04-15

5

TLD pairs, as thermal neutron detectors in neutron multisphere spectrometry  

Microsoft Academic Search

Pairs of thermoluminescence dosimeters, TLD600 and TLD700, have been used as a thermal neutron detector in a multisphere neutron spectrometer. The neutron spectra from a bare 252Cf and a D2O moderated 252Cf sources were measured with the spectrometer with thermoluminescence dosimeters and with a 6LiI(Eu) scintillator. With the neutron spectra the total flux, average neutron energy, dose and equivalent dose

Héctor René Vega-Carrillo

2002-01-01

6

Isovector neutron-proton pairing with particle number projected BCS  

NASA Astrophysics Data System (ADS)

The particle number projected BCS (PBCS) approximation is tested against the exact solution of the SO(5) Richardson-Gaudin model for isovector pairing in a system of nondegenerate single-particle orbits. Two isovector PBCS wave functions are considered. One is constructed as a single proton-neutron pair condensate; the other corresponds to a product of a neutron pair condensate and a proton pair condensate. The PBCS equations are solved using a recurrence method and the analysis is performed for systems with an equal number of neutrons and protons distributed in a sequence of equally spaced fourfold (spin-isospin) degenerate levels. The results show that although PBCS offers significant improvement over BCS, the agreement of PBCS with the exact solution is less satisfactory than in the case of the SU(2) Richardson model for pairing between like particles.

Sandulescu, N.; Errea, B.; Dukelsky, J.

2009-10-01

7

Pair distribution function computed tomography.  

PubMed

An emerging theme of modern composites and devices is the coupling of nanostructural properties of materials with their targeted arrangement at the microscale. Of the imaging techniques developed that provide insight into such designer materials and devices, those based on diffraction are particularly useful. However, to date, these have been heavily restrictive, providing information only on materials that exhibit high crystallographic ordering. Here we describe a method that uses a combination of X-ray atomic pair distribution function analysis and computed tomography to overcome this limitation. It allows the structure of nanocrystalline and amorphous materials to be identified, quantified and mapped. We demonstrate the method with a phantom object and subsequently apply it to resolving, in situ, the physicochemical states of a heterogeneous catalyst system. The method may have potential impact across a range of disciplines from materials science, biomaterials, geology, environmental science, palaeontology and cultural heritage to health. PMID:24077398

Jacques, Simon D M; Di Michiel, Marco; Kimber, Simon A J; Yang, Xiaohao; Cernik, Robert J; Beale, Andrew M; Billinge, Simon J L

2013-09-30

8

New model of the average neutron and proton pairing gaps  

NASA Astrophysics Data System (ADS)

By use of the BCS approximation applied to a distribution of dense, equally spaced levels, we derive new expressions for the average neutron pairing gap \\ŻgDn and average proton pairing gap \\ŻgDp. These expressions, which contain exponential terms, take into account the dependencies of \\ŻgDn and \\ŻgDp upon both the relative neutron excess and shape of the nucleus. The three constants that appear are determined by a least-squares adjustment to experimental pairing gaps obtained by use of fourth-order differences of measured masses. For this purpose we use the 1986 Audi-Wapstra mid-stream mass evaluation and take into account experimental uncertainties. Our new model explains not only the dependencies of \\ŻgDn and \\ŻgDp upon relative neutron excess and nuclear shape, but also the experimental result that for medium and heavy nuclei \\ŻgDn is generally smaller than \\ŻgDp. We also introduce a new expression for the average residual neutron-proton interaction energy \\Żgd that appears in the masses of odd-odd nuclei, and determine the constant that appears by an analogous least-squares adjustment to experimental mass differences. Our new expressions for \\ŻgDn, \\ŻgDp and \\Żgd should permit extrapolation of these quantities to heavier nuclei and to nuclei farther removed from the valley of ? stability than do previous parameterizations.

Madland, David G.; Nix, J. Rayford

1988-01-01

9

Nuclear Pairing and Pairing Vibrations in Stable and Neutron-Rich Nuclei  

SciTech Connect

Pairing interactions with various density dependencies (surface/volume mixing) are constrained with the two-neutron separation energy in the Tin isotopic chain. The response associated with pairing vibrations in very neutron-rich nuclei is sensitive to the density dependence of the pairing interaction. Using the same pairing interaction in nuclear matter and in Tin nuclei, the range of densities where the LDA is valid in the pairing channel is also studied.

Grasso, M.; Khan, E.; Margueron, J. [Institut de Physique Nucleaire, Universite Paris-Sud, IN2P3-CNRS, F-91406 Orsay Cedex (France)

2009-08-26

10

Screening of nuclear pairing in nuclear and neutron matter  

SciTech Connect

The screening potential in the {sup 1}S{sub 0} and {sup 3}S{sub 1} pairing channels in neutron and nuclear matter in different approximations is discussed. It is found that the vertex corrections to the potential are much stronger in nuclear matter than in neutron matter.

Shen Caiwan [China Institute of Atomic Energy, P. O. Box 275(18), Beijing 102413 (China); Center of Theoretical Nuclear Physics, National Laboratory of HIC, Lanzhou (China); Lombardo, U. [LNS-INFN, Via Santa Sofia 44, I-95123 Catania (Italy); Dipartimento di Fisica, Via Santa Sofia 64, I-95123 Catania (Italy); Schuck, P. [Institut de Physique Nucleaire, Universite Paris-Sud, F-91406 Orsay Cedex (France)

2005-05-01

11

3PF2 pairing in high-density neutron matter  

NASA Astrophysics Data System (ADS)

The onset of the superfluid phase in high-density neutron matter is studied within the BCS framework with two- and three-body forces. When including the strong correlation effects in the gap equation, the pairing gap turns out to be nonvanishing in a range of densities about 0.1-0.4fm-3 with a peak value a bit less than 0.05 MeV. These results could limit the role of the 3PF2 superfluidity in the interpretation of phenomena occurring in the neutron-star core.

Dong, J. M.; Lombardo, U.; Zuo, W.

2013-06-01

12

Exact solution of the isovector neutron-proton pairing Hamiltonian.  

PubMed

The complete exact solution of the T = 1 neutron-proton pairing Hamiltonian is presented in the context of the SO(5) Richardson-Gaudin model with nondegenerate single-particle levels and including isospin symmetry-breaking terms. The power of the method is illustrated with a numerical calculation for for 64Ge for a pf + g9/2 model space which is out of reach of modern shell-model codes. PMID:16606080

Dukelsky, J; Gueorguiev, V G; Van Isacker, P; Dimitrova, S; Errea, B; Lerma, S

2006-02-23

13

Pair force distributions in simple fluids.  

PubMed

Analytic expressions are derived for the frequency distribution, P(f), of pair forces, f, and those of their ?-Cartesian component, f(?), or P(f(?)), for some typical model simple fluids, expressed in terms of the radial distribution function and known constants. For strongly repulsive inverse power (IP), exponential and Yukawa purely repulsive potentials, P(f) diverges at the origin approximately as ?f(-1), but with different limiting analytic forms. P(f(?)) is also shown to diverge as ?f(-1) as f ? 0 for the IP fluid. For the Lennard-Jones potential fluid, P(f) is finite for all f ? 0 but has two singularities for negative f, corresponding to the zero force limit (i.e., f ? 0(-)) and the point of inflection in the potential. The corresponding component force distribution is singular as f(?) ? 0 from both positive and negative force sides. The large force limit of P(f), which originates from the close neighbor interactions, is nearly exponential for the IP and LJ fluids, as is also found for granular materials. A more complete picture of force distributions in off-lattice particulate systems as a function of force law and state point (particularly the extent of "thermalization" of the particles) is provided. PMID:22047252

Bra?ka, A C; Heyes, D M; Rickayzen, G

2011-10-28

14

Pair cascades in the magnetospheres of strongly magnetized neutron stars  

NASA Astrophysics Data System (ADS)

We present numerical simulations of electron-positron pair cascades in the magnetospheres of magnetic neutron stars for a wide range of surface fields (Bp = 1012-1015 G), rotation periods (0.1-10 s) and field geometries. This has been motivated by the discovery in recent years of a number of radio pulsars with inferred magnetic fields comparable to those of magnetars. Evolving the cascade generated by a primary electron or positron after it has been accelerated in the inner gap of the magnetosphere, we follow the spatial development of the cascade until the secondary photons and electron-positron pairs leave the magnetosphere, and we obtain the pair multiplicity and the energy spectra of the cascade pairs and photons under various conditions. Going beyond previous works, which were restricted to weaker fields (B <~ afew × 1012 G), we have incorporated in our simulations detailed treatments of physical processes that are potentially important (especially in the high-field regime) but were either neglected or crudely treated before, including photon splitting with the correct selection rules for photon polarization modes, one-photon pair production into low Landau levels for the e+/-, and resonant inverse Compton scattering from polar cap hotspots. We find that even for B >> BQ = 4 × 1013 G, photon splitting has a small effect on the multiplicity of the cascade since a majority of the photons in the cascade cannot split. One-photon decay into e+ e- pairs at low Landau levels, however, becomes the dominant pair production channel when B >~ 3 × 1012 G; this tends to suppress synchrotron radiation so that the cascade can develop only at a larger distance from the stellar surface. Nevertheless, we find that the total number of pairs and their energy spectrum produced in the cascade depend mainly on the polar cap voltage BpP-2, and are weakly dependent on Bp (and P) alone. We discuss the implications of our results for the radio pulsar death line and for the hard X-ray emission from magnetized neutron stars.

Medin, Zach; Lai, Dong

2010-08-01

15

Neutron Density Distributions Deduced from Antiprotonic Atoms  

SciTech Connect

The differences between neutron and proton density distributions at large nuclear radii in stable nuclei were determined. Two experimental methods were applied: nuclear spectroscopy analysis of the antiproton annihilation residues one mass unit lighter than the target mass and the measurements of strong-interaction effects on antiprotonic x rays. Assuming the validity of two-parameter Fermi neutron and proton distributions at these large radii, the conclusions are that the two experiments are consistent with each other and that for neutron rich nuclei it is mostly the neutron diffuseness which increases and not the half-density radius. The obtained neutron and proton rms radii differences are in agreement with previous results.

Trzcinska, A.; Jastrze bski, J.; Lubinski, P.; Hartmann, F. J.; Schmidt, R.; von Egidy, T.; Klos, B.

2001-08-20

16

Total scattering analysis of cation coordination and vacancy pair distribution in Yb substituted ?-Bi2O3.  

PubMed

Reverse Monte Carlo (RMC) modelling of neutron total scattering data, combined with conventional Rietveld analysis of x-ray and neutron data, has been used to describe the cation coordination environments and vacancy pair distribution in the oxide ion conducting electrolyte Bi3YbO6. The thermal variation of the cubic fluorite unit cell volume, monitored by variable temperature x-ray and neutron experiments, reveals significant curvature, which is explained by changes in the oxide ion distribution. There is a significant increase in tetrahedral oxide ion vacancy concentration relative to ?-Bi2O3, due to the creation of Frenkel defects associated with the Yb(3+) cation. The tetrahedral oxide ion vacancy concentration increases from room temperature to 800?° C, but little change is observed in the vacancy pair distribution with temperature. The vacancy pair distributions at both temperatures are consistent with a favouring of ?100? vacancy pairs. PMID:24141081

Leszczynska, M; Liu, X; Wrobel, W; Malys, M; Norberg, S T; Hull, S; Krok, F; Abrahams, I

2013-10-18

17

Total scattering analysis of cation coordination and vacancy pair distribution in Yb substituted ?-Bi2O3  

NASA Astrophysics Data System (ADS)

Reverse Monte Carlo (RMC) modelling of neutron total scattering data, combined with conventional Rietveld analysis of x-ray and neutron data, has been used to describe the cation coordination environments and vacancy pair distribution in the oxide ion conducting electrolyte Bi3YbO6. The thermal variation of the cubic fluorite unit cell volume, monitored by variable temperature x-ray and neutron experiments, reveals significant curvature, which is explained by changes in the oxide ion distribution. There is a significant increase in tetrahedral oxide ion vacancy concentration relative to ?-Bi2O3, due to the creation of Frenkel defects associated with the Yb3+ cation. The tetrahedral oxide ion vacancy concentration increases from room temperature to 800?° C, but little change is observed in the vacancy pair distribution with temperature. The vacancy pair distributions at both temperatures are consistent with a favouring of <100> vacancy pairs.

Leszczynska, M.; Liu, X.; Wrobel, W.; Malys, M.; Norberg, S. T.; Hull, S.; Krok, F.; Abrahams, I.

2013-11-01

18

Pair and single neutron transfer with Borromean 8He  

NASA Astrophysics Data System (ADS)

Direct observation of the survival of 199Au residues after 2n transfer in the He8+Au197 system and the absence of the corresponding 67Cu in the He8+Cu65 system at various energies are reported. The measurements of the surprisingly large cross sections for 199Au, coupled with the integral cross sections for the various Au residues, is used to obtain the first model-independent lower limits on the ratio of 2n to 1n transfer cross sections from 8He to a heavy target. A comparison of the transfer cross sections for 6,8He on these targets highlights the differences in the interactions of these Borromean nuclei. These measurements for the most neutron-rich nuclei on different targets highlight the need to probe the reaction mechanism with various targets and represent an experimental advance towards understanding specific features of pairing in the dynamics of dilute nuclear systems.

Lemasson, A.; Navin, A.; Rejmund, M.; Keeley, N.; Zelevinsky, V.; Bhattacharyya, S.; Shrivastava, A.; Bazin, D.; Beaumel, D.; Blumenfeld, Y.; Chatterjee, A.; Gupta, D.; de France, G.; Jacquot, B.; Labiche, M.; Lemmon, R.; Nanal, V.; Nyberg, J.; Pillay, R. G.; Raabe, R.; Ramachandran, K.; Scarpaci, J. A.; Schmitt, C.; Simenel, C.; Stefan, I.; Timis, C. N.

2011-03-01

19

Bremsstrahlung pair-production of positrons with low neutron background.  

SciTech Connect

Minimization of component activation is highly desirable at accelerator-based positron sources. Electrons in the 8- to 14-MeV energy range impinging on a target produce photons energetic enough to create electron-positron pairs; however, few of the photons are energetic enough to produce photoneutrons. Slow positron production by low-energy electrons impinging on a multilayer tungsten target with and without electromagnetic extraction between the layers was studied by simulation. The neutron background from 14-MeV electrons is expected to be significantly lower than that encountered with higher-energy electron beams. Numerical results are presented and some ideas for a low-activation slow-positron source are discussed.

Lessner, E.

1998-09-16

20

Gamma-ray bursts via pair plasma fireballs from heated neutron stars  

SciTech Connect

In this paper the authors model the emission from a relativistically expanding e{sup +}e{sup {minus}} pair plasma fireball originating near the surface of a heated neutron star. This pair fireball is deposited via the annihilation of neutrino pairs emanating from the surface of the hot neutron star. The heating of neutron stars may occur in close neutron star binary systems near their last stable orbit. The authors model the relativistic expansion and subsequent emission of the plasma and find {approximately} 10{sup 51}--10{sup 52} ergs in {gamma}-rays are produced with spectral and temporal properties consistent with observed gamma-ray bursts.

Salmonson, J D; Wilson, J R; Matthews, G J

2000-01-11

21

Crystal structure solution from experimentally determined atomic pair distribution functions  

Microsoft Academic Search

The paper describes an extension of the Liga algorithm for structure solution from atomic pair distribution function (PDF), to handle periodic crystal structures with multiple elements in the unit cell. The procedure is performed in 2 separate steps - at first the Liga algorithm is used to find unit cell sites consistent with pair distances extracted from the experimental PDF.

Pavol Juhas; Luke Granlund; Saurabh R. Gujarathi; Phillip M. Duxbury; Simon J. L. Billinge

2010-01-01

22

Hydrogen distribution measurements by neutrons.  

PubMed

The paper describes how hydrogenous materials can be investigated with state-of-the-art neutron radiography detection methods. The methodical problems for a precise quantification and steps towards their solution are demonstrated. Based on several practical examples, the diversity of problems to be solved by neutron imaging is illustrated. PMID:15246390

Lehmann, E H; Vontobel, P; Kardjilov, N

2004-10-01

23

Moments of the Bhatia Thornton partial pair-distribution functions  

NASA Astrophysics Data System (ADS)

Topological versus chemical ordering in disordered binary systems is investigated by using the Bhatia-Thornton formalism. The moments of the partial pair-distribution functions are considered and are related to relevant thermodynamic and other properties of the system. The results are illustrated by using the measured partial-pair distribution functions for the network forming glasses ZnCl2 and GeSe2.

Salmon, Philip S.

2005-11-01

24

Pairing in exotic neutron-rich nuclei near the drip line and in the crust of neutron stars  

NASA Astrophysics Data System (ADS)

Exotic and drip-line nuclei as well as nuclei immersed in a low-density gas of neutrons in the inner crust of neutron stars are systematically investigated with respect to their neutron pairing properties. This is done using Skyrme density-functional and different pairing forces such as a density-dependent contact interaction and a separable form of a finite-range Gogny interaction. Hartree-Fock-Bogoliubov (HFB) and Bardeen-Cooper-Schrieffer (BCS) theories are compared. It is found that neutron pairing is reduced towards the drip line while overcast by strong shell effects. Furthermore, resonances in the continuum can have an important effect counterbalancing the tendency of reduction and leading to a persistence of pairing at the drip line. It is also shown that in these systems the difference between HFB and BCS approaches can be quantitatively large.

Pastore, A.; Margueron, J.; Schuck, P.; Vińas, X.

2013-09-01

25

Coauthor pairs' frequencies distribution in journals of gender studies  

Microsoft Academic Search

Previous studies have presented well-ordered collaboration structures of co-author pairs. Kretschmer and Kretschmer have shown that, for high impact SCI journals, the distributions of co-author pairs' frequencies can be considered to be a reflection of a social Gestalt. This study is an extension of that work to the social sciences, namely eleven journals in women's and gender studies. After overlapping

Ramesh Kundra; Hildrun Kretschmer; Theo Kretschmer

26

Neutron dose distribution at the GSI fragment separator.  

PubMed

GSI is operating a facility for the production of rare isotopes. Nuclei are produced by fragmentation or fission of the impinging heavy ions with energies of approximately 1 GeV per nucleon. The major part of the primary beam and the produced nuclei is deposited in the components of the Fragment Separator (FRS) and generates neutron radiation. Thermoluminescence dosemeters (TLDs) (6LiF/7LiF pairs in PE spheres) were exposed in neutron fields produced by uranium beams with energies between 100 and 1000 MeV per nucleon during an irradiation period in the year 2002. Two-dimensional dose distributions are obtained using these TL measurements in combination with model calculations. The applied model describes the dose distribution as a superposition of dose patterns of 20 single sources equally distributed along the FRS. The single source distribution is based on a measured double differential neutron distribution for a 1 GeV per nucleon uranium beam. PMID:15353740

Fehrenbacher, G; Festag, J G

2004-01-01

27

Experimental wavelength-division-multiplexed photon-pair distribution.  

PubMed

We have experimentally implemented the distribution of photon pairs produced by spontaneous parametric downconversion through telecom dense-wavelength-division-multiplexing filters. Using the measured counts and coincidences between symmetric channels, we evaluate the maximum fringe visibility that can be obtained with polarization-entangled photons and compare different filter technologies. PMID:23282829

Ghalbouni, Joe; Agha, Imad; Frey, Robert; Diamanti, Eleni; Zaquine, Isabelle

2013-01-01

28

BCS-BEC crossover of neutron pairs in symmetric and asymmetric nuclear matter  

SciTech Connect

We propose new types of density-dependent contact pairing interactions which reproduce the pairing gaps in symmetric and neutron matters obtained by a microscopic treatment based on realistic nucleon nucleon interaction. These interactions are able to simulate the pairing gaps of either the bare interaction or the interaction screened by the medium polarization effects. It is shown that the medium polarization effects cannot be cast into the usual density power law function of the contact interaction and require the introduction of another isoscalar term. The BCS-BEC crossover of neutron pairs in symmetric and asymmetric nuclear matters is studied by using these contact interactions. This work shows that the bare and screened pairing interactions lead to different features of the BCS-BEC crossover in symmetric nuclear matter. For the screened pairing interaction, a two-neutron BEC state is formed in symmetric matter at k{sub Fn}{approx}0.2 fm{sup -1} (neutron density {rho}{sub n}/{rho}{sub 0}{approx}10{sup -3}). In contrast, the bare interaction does not form the BEC state at any neutron density.

Margueron, J. [Institut de Physique Nucleaire, Universite Paris-Sud, IN2P3-CNRS, F-91406 Orsay Cedex (France); Center for Mathematical Sciences, University of Aizu, Aizu-Wakamatsu, 965-8580 Fukushima (Japan); Sagawa, H. [Center for Mathematical Sciences, University of Aizu, Aizu-Wakamatsu, 965-8580 Fukushima (Japan); Hagino, K. [Department of Physics, Tohoku University, Sendai, e980-8578 (Japan)

2007-12-15

29

Optimization of a Modular Neutron Detector Array for the Detection of Halo Neutron Pairs using GEANT4  

NASA Astrophysics Data System (ADS)

The study of halo neutrons in light nuclei may require the detection of multiple neutrons in a neutron detector array. The detection of multiple neutrons is especially challenging due to the ``false-positives'' induced by cross-talk events between detectors. In this work, we report on the development of a cross-talk filter used to efficiently identify true neutron pairs while rejecting cross-talk events based on time of flight considerations. The classic method of neutron detection in the MeV range involves elastic scattering interactions with the hydrogen contained in organic scintillators, either plastic or liquid. To improve the performance of the cross-talk filter, it is possible to take into account the energy loss of the scattered neutrons. In this context, we are also investigating the possibility of using deuterated liquid scintillators, which can potentially provide better energy loss discrimination than in normal scintillators. This work is done by simulating the interactions of neutron pairs in various detector configurations using the simulation package GEANT4.

Walter, David; Sarazin, Frederic; Smalley, Duane; Ilyushkin, Sergey

2013-04-01

30

Development of multi-moderator neutron spectrometer using a pair of 6Li and 7Li glass scintillators  

Microsoft Academic Search

A multi-moderator spectrometer using a pair of 6Li and 7Li glass scintillators has been developed. This new type of neutron spectrometer can measure the neutron spectrum in a mixed field of neutrons, charged particles and gamma-rays. The particle identification capability was investigated in neutron–gamma-ray and neutron–proton mixed fields and the neutron response functions of the spectrometer were obtained by calculations

Shingo Taniguchi; Masashi Takada; Takashi Nakamura

2001-01-01

31

Sangam: a distributed pair programming plug-in for Eclipse  

Microsoft Academic Search

In pair programming, two programmers traditionally work side-by-side at one computer. However, in globally distributed organizations, long-distance collaboration is frequently necessary. Sangam is an Eclipse plug-in that allows Eclipse users in different locations to share a workspace so that they may work as if they were using the same computer. In this paper, we discuss the Sangam plug-in, and our

Chih-Wei Ho; Somik Raha; Edward F. Gehringer; Laurie Williams

2004-01-01

32

Optimal pair density functional for the description of nuclei with large neutron excess  

SciTech Connect

Toward a universal description of pairing properties in nuclei far from stability, we extend the energy density functional by enriching the isovector density dependence in the particle-particle channel (pair density functional, pair-DF). We emphasize the necessity of both the linear and quadratic isovector density terms. The parameters are optimized by the Hartree-Fock-Bogoliubov calculation for 156 nuclei of mass number A=118 to 196 and asymmetry parameter (N-Z)/A<0.25. We clarify that the pair-DF should include the isovector density dependence in order to take into account in a consistent manner the effect of the isoscalar and isovector effective masses in the particle-hole channel. The different Skyrme forces can give the small difference in the pairing gaps toward the neutron drip line if the optimal pair-DF, consistent with the particle-hole channel, is employed.

Yamagami, M. [Department of Computer Science and Engineering, University of Aizu, Aizu-Wakamatsu, Fukushima 965-8580 (Japan); RIKEN Nishina Center, RIKEN, Hirosawa 2-1, Wako, Saitama 351-0198 (Japan); Shimizu, Y. R. [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); Nakatsukasa, T. [RIKEN Nishina Center, RIKEN, Hirosawa 2-1, Wako, Saitama 351-0198 (Japan)

2009-12-15

33

Multistep shell model description of spin-aligned neutron-proton pair coupling  

NASA Astrophysics Data System (ADS)

The recently proposed spin-aligned neutron-proton pair coupling scheme is studied within a non-orthogonal basis in term of the multistep shell model. This allows us to identify simultaneously the roles played by other configurations such as the normal pairing term. The model is applied to four-, six- and eight-hole N=Z nuclei below the core 100Sn.

Xu, Z. X.; Qi, C.; Blomqvist, J.; Liotta, R. J.; Wyss, R.

2012-03-01

34

Neutron-proton pairing in light nuclei and two-neutrino double-beta decay  

Microsoft Academic Search

We have investigated neutron-proton (np) pairing in light nuclei (2p-lf shell) using a specialized Hartree-Fock-Bogoliubov (HFB) method. For the pairing interaction we used the constant Kisslinger-Sorensen interaction and the realistic G-matrix obtained by solving the Bethe-Goldstone equation with the Bonn one-boson-exchange potential. Our results show that there are at least two minima of the total energy corresponding to two solutions

M. K. Cheoun; A. Bobyk; Amand Faessler; F. Simkovic; G. Teneva

1993-01-01

35

Development of multi-moderator neutron spectrometer using a pair of 6Li and 7Li glass scintillators  

NASA Astrophysics Data System (ADS)

A multi-moderator spectrometer using a pair of 6Li and 7Li glass scintillators has been developed. This new type of neutron spectrometer can measure the neutron spectrum in a mixed field of neutrons, charged particles and gamma-rays. The particle identification capability was investigated in neutron-gamma-ray and neutron-proton mixed fields and the neutron response functions of the spectrometer were obtained by calculations and experiments up to 200 MeV. This spectrometer has been applied to measure neutron spectrum in a neutron-proton mixed field, produced by bombarding a Be target by 70 MeV protons from the cyclotron.

Taniguchi, S.; Takada, M.; Nakamura, T.

2001-03-01

36

Electron-positron energy deposition rate from neutrino pair annihilation on the rotation axis of neutron and quark stars  

NASA Astrophysics Data System (ADS)

We investigate the deposition of energy due to the annihilations of neutrinos and antineutrinos on the rotation axis of rotating neutron and quark stars, respectively. The source of the neutrinos is assumed to be a neutrino-cooled accretion disc around the compact object. Under the assumption of the separability of the neutrino null geodesic equation of motion, we obtain the general relativistic expression of the energy deposition rate for arbitrary stationary and axisymmetric space-times. The neutrino trajectories are obtained by using a ray tracing algorithm, based on numerically solving the Hamilton-Jacobi equation for neutrinos by reversing the proper time evolution. We obtain the energy deposition rates for several classes of rotating neutron stars, described by different equations of state of the neutron matter, and for quark stars, described by the MIT bag model equation of state and in the colour-flavour-locked phase, respectively. The electron-positron energy deposition rate on the rotation axis of rotating neutron and quark stars is studied for two accretion disc models (isothermal disc and accretion disc in thermodynamical equilibrium). Rotation and general relativistic effects modify the total annihilation rate of the neutrino-antineutrino pairs on the rotation axis of compact stellar general relativistic objects, as measured by an observer at infinity. The differences in the equations of state for neutron and quark matter also have important effects on the spatial distribution of the energy deposition rate by neutrino-antineutrino annihilation.

Kovács, Z.; Cheng, K. S.; Harko, T.

2011-03-01

37

General relativistic ray-tracing algorithm for the determination of the electron-positron energy deposition rate from neutrino pair annihilation around rotating neutron and quark stars  

NASA Astrophysics Data System (ADS)

We present a full general relativistic numerical code for estimating the energy-momentum deposition rate (EMDR) from neutrino pair annihilation (?). The source of the neutrinos is assumed to be a neutrino-cooled accretion disc around neutron and quark stars. We calculate the neutrino trajectories by using a ray-tracing algorithm with the general relativistic Hamilton's equations for neutrinos and derive the spatial distribution of the EMDR due to the annihilations of neutrinos and antineutrinos around rotating neutron and quark stars. We obtain the EMDR for several classes of rotating neutron stars, described by different equations of state of the neutron matter, and for quark stars, described by the Massachusetts Institute of Technology (MIT) bag model equation of state and in the colour-flavour-locked (CFL) phase. The distribution of the total annihilation rate of the neutrino-antineutrino pairs around rotating neutron and quark stars is studied for isothermal discs and accretion discs in thermodynamical equilibrium. We demonstrate both the differences in the equations of state for neutron and quark matter and rotation with the general relativistic effects significantly modify the EMDR of the electrons and positrons generated by the neutrino-antineutrino pair annihilation around compact stellar objects, as measured at infinity.

Kovács, Z.; Harko, T.

2011-11-01

38

Spin-aligned neutron-proton pair mode in atomic nuclei  

SciTech Connect

Shell-model calculations using realistic interactions reveal that the ground and low-lying yrast states of the N=Z nucleus {sub 46}{sup 92}Pd are mainly built upon isoscalar neutron-proton pairs, each carrying the maximum angular momentum J=9 allowed by the shell 0g{sub 9/2}, which is dominant in this nuclear region. This structure is different from that found in the ground and low-lying yrast states of all other even-even nuclei studied so far. The low-lying spectrum of excited states generated by such correlated neutron-proton pairs has two distinctive features: (i) the levels are almost equidistant at low energies and (ii) the transition probability I{yields}I-2 is approximately constant and strongly selective. This unique mode is shown to replace normal isovector pairing as the dominant coupling scheme in N=Z nuclei approaching the doubly magic nucleus {sup 100}Sn.

Qi, C.; Blomqvist, J.; Baeck, T.; Cederwall, B.; Johnson, A.; Liotta, R. J.; Wyss, R. [Department of Physics, Royal Institute of Technology, SE-10691 Stockholm (Sweden)

2011-08-15

39

Particle temperature measurement using pair distribution function in complex plasmas  

NASA Astrophysics Data System (ADS)

In order to obtain more reliable particle temperature of complex plasmas, a new method of obtaining it in a solid phase is investigated. Since a conventional method uses a velocity distribution function (VDF), both high spacial resolution and sufficiently large observation area are required for sufficient measurement accuracy. It is often difficult, however, to satisfy them simultaneously due to necessities of highly magnified observation for the former requirement and low magnified one for the latter one. Therefore, we investigate another method of estimating particle temperature in the solid phase by use of a pair distribution function (PDF). This method has a feature that only one observation magnification is required. From comparison between the experimentally obtained PDF's and calculated ones, mean square displacement (MSD) is determined. The temperature is estimated by using the MSD if the particle motion is regarded as harmonic oscillation. It is found that the obtained temperature from the PDF is consistent with that from the VDF.

Adachi, S.; Totsuji, H.; Takahashi, K.; Hayashi, Y.; Takayanagi, M.

2011-12-01

40

Nuclear ?+/EC decays in covariant density functional theory and the impact of isoscalar proton-neutron pairing  

NASA Astrophysics Data System (ADS)

Self-consistent proton-neutron quasiparticle random phase approximation based on the spherical nonlinear point-coupling relativistic Hartree-Bogoliubov theory is established and used to investigate the ?+/electron-capture (EC)-decay half-lives of neutron-deficient Ar, Ca, Ti, Fe, Ni, Zn, Cd, and Sn isotopes. The isoscalar proton-neutron pairing is found to play an important role in reducing the decay half-lives, which is consistent with the same mechanism in the ? decays of neutron-rich nuclei. The experimental ?+/EC-decay half-lives can be well reproduced by a universal isoscalar proton-neutron pairing strength.

Niu, Z. M.; Niu, Y. F.; Liu, Q.; Liang, H. Z.; Guo, J. Y.

2013-05-01

41

Neutron chain length distributions in subcritical systems  

SciTech Connect

In this paper, the authors present the results of the chain-length distribution as a function of k in subcritical systems. These results were obtained from a point Monte Carlo code and a three-dimensional Monte Carlo code, MC++. Based on these results, they then attempt to explain why several of the common neutron noise techniques, such as the Rossi-{alpha} and Feynman's variance-to-mean techniques, are difficult to perform in highly subcritical systems using low-efficiency detectors.

Nolen, S.D.; Spriggs, G.

1999-09-27

42

Bound-neutrino sphere and spontaneous neutrino-pair creation in cold neutron stars  

SciTech Connect

It is shown that neutrinos (massless or massive), produced with kinetic energies below {similar to}50 eV in a supernova, have bound orbits in the remnant neutron star. The binding is mediated by a radial weak-interaction force, caused by a gradient in the collective weak potential of the neutrons in the star. This force is also able to create spontaneously neutrino-antineutrino pairs. If the bound-neutrino sphere is not fully degenerate at low momenta, a cold neutron star will shine continuously antineutrinos with energies {approx lt}50 eV, as a result of the density gradient in it. In principle, these effects can also be realized at smaller (e.g., solid) densities for sufficiently low neutrino energies.

Loeb, A. (The Institute for Advanced Study, Princeton, New Jersey 08540 (US))

1990-01-08

43

Exploring Scaling Laws of Valence Neutron Distributions for Medium Nuclei  

Microsoft Academic Search

The root-mean-square radii of the valence neutron distributions for many nuclei in He-Mo mass range are calculated in the framework of the single-particle potential model. The scaling laws of valence neutron distributions are obtained by analyzing the relations between the radii and the binding energies of the valence neutrons. Based on these scaling laws, the necessary conditions for the occurrence

Yan-Qing Guo; Zhong-Zhou Ren

2010-01-01

44

Spin-aligned neutron-proton pairs in N=Z nuclei  

SciTech Connect

A study is carried out on the role of the aligned neutron-proton pair with angular momentum J=9 and isospin T=0 in the low-energy spectroscopy of the N=Z nuclei {sup 96}Cd, {sup 94}Ag, and {sup 92}Pd. Shell-model wave functions resulting from realistic interactions are analyzed in terms of a variety of two-nucleon pairs corresponding to different choices of their coupled angular momentum J and isospin T. The analysis is performed exactly for four holes ({sup 96}Cd) and carried further for six and eight holes ({sup 94}Ag and {sup 92}Pd) by means of a mapping to an appropriate version of the interacting boson model. The study allows the identification of the strengths and deficiencies of the aligned-pair approximation.

Zerguine, S. [Department of Physics, PRIMALAB Laboratory, University of Batna, Avenue Boukhelouf M El Hadi, 05000 Batna (Algeria); Van Isacker, P. [Grand Accelerateur National d'Ions Lourds, CEA/DSM-CNRS/IN2P3, B.P. 55027, F-14076 Caen Cedex 5 (France)

2011-06-15

45

Dependence of two-neutron momentum densities on total pair momentum  

SciTech Connect

Two-nucleon momentum distributions are calculated for the ground states of {sup 3}He and {sup 4}He as a function of the nucleons' relative and total momenta. We use variational Monte Carlo wave functions derived from a realistic Hamiltonian with two- and three-nucleon potentials. The momentum distribution of pp pairs is found to be much smaller than that of pn pairs for values of the relative momentum in the range (300--500) MeV/c and vanishing total momentum. Howeer, as the totalmomentum increases to 400 MeV/c, the ratio of pp to pn pairs in this relative momentum range grows and approaches the limit 1/2 for {sup 3}He and 1/4 for {sup 4}He, corresponding to the ratio of pp to pn pairs in these nuclei. This behavior should be easily observable in two-nucleon knock-out processes, such as A(e, e'pN).

Carlson, Joseph A [Los Alamos National Laboratory; Wiringa, R B [ANL; Schiavilla, R [JEFFERSON LAB; Pieper, Steven C [ANL

2008-01-01

46

Pair distribution function study on compression of liquid gallium  

SciTech Connect

Integrating a hydrothermal diamond anvil cell (HDAC) and focused high energy x-ray beam from the superconductor wiggler X17 beamline at the National Synchrotron Light Source (NSLS) at the Brookhaven National Laboratory (BNL), we have successfully collected high quality total x-ray scattering data of liquid gallium. The experiments were conducted at a pressure range from 0.1GPa up to 2GPa at ambient temperature. For the first time, pair distribution functions (PDF) for liquid gallium at high pressure were derived up to 10 {angstrom}. Liquid gallium structure has been studied by x-ray absorption (Di Cicco & Filipponi, 1993; Wei et al., 2000; Comez et al., 2001), x-ray diffraction studies (Waseda & Suzuki, 1972), and molecular dynamics simulation (Tsay, 1993; Hui et al., 2002). These previous reports have focused on the 1st nearest neighbor structure, which tells us little about the atomic arrangement outside the first shell in non- crystalline materials. This study focuses on the structure of liquid gallium and the atomic structure change due to compression. The PDF results show that the observed atomic distance of the first nearest neighbor at 2.78 {angstrom} (first G(r) peak and its shoulder at the higher Q position) is consistent with previous studies by x-ray absorption (2.76 {angstrom}, Comez et al., 2001). We have also observed that the first nearest neighbor peak position did not change with pressure increasing, while the farther peaks positions in the intermediate distance range decreased with pressure increasing. This leads to a conclusion of the possible existence of 'locally rigid units' in the liquid. With the addition of reverse Monte Carlo modeling, we have observed that the coordination number in the local rigit unit increases with pressure. The bulk modulus of liquid gallium derived from the volume compression curve at ambient temperature (300K) is 12.1(6) GPa.

Luo, Shengnian [Los Alamos National Laboratory; Yu, Tony [SUNY-SB; Chen, Jiuhua [SUNY-SB; Ehm, Lars [SUNY-SB; Guo, Quanzhong [SUNY-SB; Parise, John [SUNY-SB

2008-01-01

47

On the Mass Distribution and Birth Masses of Neutron Stars  

NASA Astrophysics Data System (ADS)

We investigate the distribution of neutron star masses in different populations of binaries, employing Bayesian statistical techniques. In particular, we explore the differences in neutron star masses between sources that have experienced distinct evolutionary paths and accretion episodes. We find that the distribution of neutron star masses in non-recycled eclipsing high-mass binaries as well as of slow pulsars, which are all believed to be near their birth masses, has a mean of 1.28 M ? and a dispersion of 0.24 M ?. These values are consistent with expectations for neutron star formation in core-collapse supernovae. On the other hand, double neutron stars, which are also believed to be near their birth masses, have a much narrower mass distribution, peaking at 1.33 M ?, but with a dispersion of only 0.05 M ?. Such a small dispersion cannot easily be understood and perhaps points to a particular and rare formation channel. The mass distribution of neutron stars that have been recycled has a mean of 1.48 M ? and a dispersion of 0.2 M ?, consistent with the expectation that they have experienced extended mass accretion episodes. The fact that only a very small fraction of recycled neutron stars in the inferred distribution have masses that exceed ~2 M ? suggests that only a few of these neutron stars cross the mass threshold to form low-mass black holes.

Özel, Feryal; Psaltis, Dimitrios; Narayan, Ramesh; Santos Villarreal, Antonio

2012-09-01

48

Evolution of a merging pair of C + O white dwarfs to form a single neutron star  

NASA Astrophysics Data System (ADS)

The authors investigate the evolution of a merging pair of C+O white dwarfs which constitutes a close binary system. The merging process is simulated as a rapid mass transfer from a less massive white dwarf to a more massive one at a rate of 1×10-5M_sun;yr-1. Such a rapid accretion ignites an off-center carbon flash. The authors found that the carbon burning front propagates inward all the way through the central region and hence the CO white dwarf is completely changed into an ONeMg white dwarf in a quiescent manner. Therefore, the ultimate outcome of the system will not be a type I supernova explosion induced by the carbon deflagration but a collapse triggered by electron captures on 24Mg and 20Ne to form a single neutron star. This class of neutron star might be an origin of a single millisecond pulsar.

Saio, H.; Nomoto, K.

1985-09-01

49

Angular-distribution neutron-emission spectra of niobium following bombardment by fast neutrons  

SciTech Connect

Neutron-emission spectra at ten angles between 20 and 160/sup 0/ and incident neutron energies of 5.9, 7.1 and 8.4 MeV were measured relative to the neutron field emitted after spontaneous fission of /sup 252/Cf. The angular distribution of inelastically scattered neutrons appears to be essentially isotropic where it can be separated from the dominant elastic scattering peak. Above an excitation energy of 4 MeV the spectra are well described by a Maxwellian temperature distribution.

Guenther, P.T.; Smith, A.B.

1985-01-01

50

Equation of State of Superfluid Neutron Matter and the Calculation of the S01 Pairing Gap  

NASA Astrophysics Data System (ADS)

We present a quantum Monte Carlo study of the zero-temperature equation of state of neutron matter and the computation of the S01 pairing gap in the low-density regime with ?<0.04fm-3. The system is described by a nonrelativistic nuclear Hamiltonian including both two- and three-nucleon interactions of the Argonne and Urbana type. This model interaction provides very accurate results in the calculation of the binding energy of light nuclei. A suppression of the gap with respect to the pure BCS theory is found, but sensibly weaker than in other works that attempt to include polarization effects in an approximate way.

Gandolfi, S.; Illarionov, A. Yu.; Fantoni, S.; Pederiva, F.; Schmidt, K. E.

2008-09-01

51

Coherence features of the spin-aligned neutron-proton pair coupling scheme  

NASA Astrophysics Data System (ADS)

The seniority scheme has been shown to be extremely useful for the classification of nuclear states in semi-magic nuclei. The neutron-proton (np) correlation breaks the seniority symmetry in a major way. As a result, the corresponding wave function is a mixture of many components with different seniority quantum numbers. In this paper, we show that the np interaction may favor a new kind of coupling in N=Z nuclei, i.e. the so-called isoscalar spin-aligned np pair mode. Shell model calculations reveal that the ground and low-lying yrast states of the N=Z nuclei 92Pd and 96Cd may be mainly built upon such spin-aligned np pairs, each carrying the maximum angular momentum J=9 allowed by the shell 0?g9/2 which is dominant in this nuclear region.

Qi, C.; Blomqvist, J.; Bäck, T.; Cederwall, B.; Johnson, A.; Liotta, R. J.; Wyss, R.

2012-10-01

52

Hyperdimensional Analysis of Amino Acid Pair Distributions in Proteins  

PubMed Central

Our manuscript presents a novel approach to protein structure analyses. We have organized an 8-dimensional data cube with protein 3D-structural information from 8706 high-resolution non-redundant protein-chains with the aim of identifying packing rules at the amino acid pair level. The cube contains information about amino acid type, solvent accessibility, spatial and sequence distance, secondary structure and sequence length. We are able to pose structural queries to the data cube using program ProPack. The response is a 1, 2 or 3D graph. Whereas the response is of a statistical nature, the user can obtain an instant list of all PDB-structures where such pair is found. The user may select a particular structure, which is displayed highlighting the pair in question. The user may pose millions of different queries and for each one he will receive the answer in a few seconds. In order to demonstrate the capabilities of the data cube as well as the programs, we have selected well known structural features, disulphide bridges and salt bridges, where we illustrate how the queries are posed, and how answers are given. Motifs involving cysteines such as disulphide bridges, zinc-fingers and iron-sulfur clusters are clearly identified and differentiated. ProPack also reveals that whereas pairs of Lys residues virtually never appear in close spatial proximity, pairs of Arg are abundant and appear at close spatial distance, contrasting the belief that electrostatic repulsion would prevent this juxtaposition and that Arg-Lys is perceived as a conservative mutation. The presented programs can find and visualize novel packing preferences in proteins structures allowing the user to unravel correlations between pairs of amino acids. The new tools allow the user to view statistical information and visualize instantly the structures that underpin the statistical information, which is far from trivial with most other SW tools for protein structure analysis.

Henriksen, Svend B.; Arnason, Omar; Soring, Jon; Petersen, Steffen B.

2011-01-01

53

Electron-positron energy deposition rate from neutrino pair annihilation in the equatorial plane of rapidly rotating neutron and quark stars  

NASA Astrophysics Data System (ADS)

The neutrino-antineutrino annihilation into electron-positron pairs near the surface of compact general relativistic stars could play an important role in supernova explosions, neutron star collapse, or for close neutron star binaries near their last stable orbit. General relativistic effects increase the energy deposition rates due to the annihilation process. We investigate the deposition of energy and momentum due to the annihilations of neutrinos and antineutrinos in the equatorial plane of the rapidly rotating neutron and quark stars, respectively. We analyse the influence of general relativistic effects, and obtain the general relativistic corrections to the energy and momentum deposition rates for arbitrary stationary and axisymmetric space-times. We obtain the energy and momentum deposition rates for several classes of rapidly rotating neutron stars, described by different equations of state of the neutron matter, and for quark stars, described by the Massachusetts Institute of Technology bag model equation of state and in the colour-flavour-locked phase, respectively. Compared to the Newtonian calculations, rotation and general relativistic effects increase the total annihilation rate measured by an observer at infinity. The differences in the equations of state for neutron and quark matter also have important effects on the spatial distribution of the energy deposition rate by neutrino-antineutrino annihilation.

Kovács, Z.; Cheng, K. S.; Harko, T.

2010-03-01

54

Relativistic Hartree-Bogoliubov Theory with Finite Range Pairing Forces in Coordinate Space: Neutron Halo in Light Nuclei  

SciTech Connect

The relativistic Hartree Bogoliubov model is applied in the self-consistent mean-field approximation to the description of the neutron halo in the mass region above the s-d shell. Pairing correlations and the coupling to particle continuum states are described by finite range two-body forces. Finite element methods are used in the coordinate space discretization of the coupled system of Dirac-Hartree-Bogoliubov integro-differential eigenvalue equations, and Klein-Gordon equations for the meson fields. Calculations are performed for the isotopic chains of Ne and C nuclei. We find evidence for the occurrence of neutron halo in heavier Ne isotopes. The properties of the 1f-2p orbitals near the Fermi level and the neutron pairing interaction play a crucial role in the formation of the halo. Our calculations display no evidence for the neutron halo phenomenon in C isotopes. {copyright} {ital 1997} {ital The American Physical Society}

Poeschl, W.; Vretenar, D.; Lalazissis, G.A.; Ring, P. [Physics Department, Technische Universitaet Muenchen, D-85748 Garching (Germany)

1997-11-01

55

Proton recoil energy and angular distribution of neutron radiative ?- decay  

NASA Astrophysics Data System (ADS)

We analyze the proton recoil energy and angular distribution of the radiative ?- decay of the neutron to leading order in the large baryon mass expansion by taking into account the contributions of the proton-photon correlations. We show that the account for the proton-photon correlations does not contradict the description of the radiative corrections to the lifetime of the neutron and the proton recoil energy spectrum of the neutron ?- decay in terms of the functions (?/?)gn(Ee) and (?/?)fn(Ee), where Ee is the electron energy. In addition we find that the contributions of the proton-photon correlations in the radiative ?- decay of the neutron to the proton recoil asymmetry C are of order 10-4. They make the contributions of the radiative corrections to the proton recoil asymmetry C symmetric with respect to a change A0?B0, where A0 and B0 are the correlation coefficients of the neutron ?- decay.

Ivanov, A. N.; Höllwieser, R.; Troitskaya, N. I.; Wellenzohn, M.

2013-09-01

56

Effect of three-body interactions on pairing in neutron-star matter  

NASA Astrophysics Data System (ADS)

We extend the standard BCS theory to derive the generic three-body gap equation for neutron matter, which includes a three-nucleon pairing interaction as well as the two-nucleon interaction. Working with a suitably truncated second- quantized Hamiltonian, the gap equation in the presence of three-body forces is expressed in the partial-wave representation such that it can be easily applied to any channel. This equation is used in numerical studies of superfluid phases of neutron matter, specifically the cases of singlet S-wave pairing and triplet P-wave pairing that are relevant at low and high densities, respectively. The realistic Argonne V18 potential is assumed for the two-nucleon interaction, and the phenomenological Urbana IX form is chosen for the three-nucleon interaction. In the singlet-S problem, we find results comparable to those of an earlier study in which the three-body interaction is replaced by an effective two-body force. An efficient numerical strategy is developed for and applied to the much more challenging problem of solving the gap equation in the triplet-P channel. Our results demonstrate a strong sensitivity of the existence of a solution as well as the value of the gap, to the parameters of the Urbana IX interaction. The differing sets of parameters chosen in two state-the-art microscopic many-body studies of nucleonic matter are found to yield dramatically different predictions. The parameter values used in a Brueckner-Hartree-Fock study provide for a solution of the gap equation, with a gap value that is significantly increased by the three-body force, whereas the parameters adopted in a variational study based on elaborate correlated wave functions introduce too much repulsion for a solution of the triplet gap equation to exist. It must be concluded that the present state of our understanding of the fundamental three-nucleon force and the limited precision of current microscopic many-body methods preclude even a definite qualitative statement on the effect of this interaction on nucleonic pairing.

Yuan, Lingfeng

57

Production, Distribution, and Applications of Californium-252 Neutron Sources  

SciTech Connect

The radioisotope {sup 252}Cf is routinely encapsulated into compact, portable, intense neutron sources with a 2.6-year half-life. A source the size of a person's little finger can emit up to 10{sup 11} neutrons/s. Californium-252 is used commercially as a reliable, cost-effective neutron source for prompt gamma neutron activation analysis (PGNAA) of coal, cement, and minerals, as well as for detection and identification of explosives, laud mines, and unexploded military ordnance. Other uses are neutron radiography, nuclear waste assays, reactor start-up sources, calibration standards, and cancer therapy. The inherent safety of source encapsulations is demonstrated by 30 years of experience and by U.S. Bureau of Mines tests of source survivability during explosions. The production and distribution center for the U. S Department of Energy (DOE) Californium Program is the Radiochemical Engineering Development Center (REDC) at Oak Ridge National Laboratory (ORNL). DOE sells The radioisotope {sup 252}Cf is routinely encapsulated into compact, portable, intense neutron sources with a 2.6- year half-life. A source the size of a person's little finger can emit up to 10 neutrons/s. Californium-252 is used commercially as a reliable, cost-effective neutron source for prompt gamma neutron activation analysis (PGNAA) of coal, cement, and minerals, as well as for detection and identification of explosives, laud mines, and unexploded military ordnance. Other uses are neutron radiography, nuclear waste assays, reactor start-up sources, calibration standards, and cancer therapy. The inherent safety of source encapsulations is demonstrated by 30 years of experience and by U.S. Bureau of Mines tests of source survivability during explosions. The production and distribution center for the U. S Department of Energy (DOE) Californium Program is the Radiochemical Engineering Development Center (REDC) at Oak Ridge National Laboratory(ORNL). DOE sells {sup 252}Cf to commercial reencapsulators domestically and internationally. Sealed {sup 252}Cf sources are also available for loan to agencies and subcontractors of the U.S. government and to universities for educational, research, and medical applications. The REDC has established the Californium User Facility (CUF) for Neutron Science to make its large inventory of {sup 252}Cf sources available to researchers for irradiations inside uncontaminated hot cells. Experiments at the CUF include a land mine detection system, neutron damage testing of solid-state detectors, irradiation of human cancer cells for boron neutron capture therapy experiments, and irradiation of rice to induce genetic mutations.

Balo, P.A.; Knauer, J.B.; Martin, R.C.

1999-10-03

58

Bioeffect modeling of nonuniform dose distributions for paired organs  

Microsoft Academic Search

Evaluating treatment plans on the basis of risk\\/benefit to the patient depends on accurate characterization of dose-response distributions from clinical data. Typically, response data is defined as a binary complication variable according to a pre-determined threshold value. This binning of the data into two groups can mask gradual dose-response changes, and may make the dose-response model overly sensitive to the

J. Markman; J. O. Deasy; K. S. Chao; D. A. Low

2000-01-01

59

The equilibrium pair distribution function of a gas: Aspects associated with the presence of bound states  

SciTech Connect

At thermal equilibrium the momentum distribution of atoms in a gas is an atom is bound in a diatomic molecule, the atom's momentum distribution is non-Maxwellian. This paper explores the consequent singlet and pair particle distribution functions in a gas having both unbound atoms and bound pairs of atoms. Comment is made on the range of behavior associated with whether the chemical equilibrium constant for diatom formation is small or large. Calculations of distribution functions and their moments for atoms which are members of dimers are presented for some specific model potentials.

Rainwater, J.C. (Thermophysics Division, National Institute of Standards and Technology ( ))

1993-12-01

60

Extracting generalized neutron parton distributions from 3He data  

NASA Astrophysics Data System (ADS)

An impulse-approximation (IA) analysis of the generalized parton distributions (GPDs) H and E of the 3He nucleus, quantities which are accessible in hard exclusive processes, such as coherent deeply virtual Compton scattering (DVCS), is described. The calculation is based on the Av18 interaction. The electromagnetic form factors are correctly recovered in the proper limits. The sum of the GPDs H and E of 3He, at low momentum transfer, is largely dominated by the neutron contribution, thanks to the unique spin structure of 3He. This nucleus is therefore very promising for the extraction of the neutron information. By increasing the momentum transfer, however, this conclusion is somehow hindered by the the fast growing proton contribution. Besides, even when the neutron contribution to the GPDs of 3He is largely dominating, the procedure of extracting the neutron GPDs from it could be, in principle, nontrivial. A technique is therefore proposed, independent of both the nuclear potential and the nucleon model used in the calculation, able to take into account the nuclear effects included in the IA analysis and to safely extract the neutron information at values of the momentum transfer large enough to allow the measurements. Thanks to this observation, coherent DVCS should be considered a key experiment to access the neutron GPDs and, in turn, the orbital angular momentum of the partons in the neutron.

Rinaldi, M.; Scopetta, S.

2013-03-01

61

Four-nucleon ?-type correlations and proton-neutron pairing away from the N=Z line  

NASA Astrophysics Data System (ADS)

We study the competition between ?-type and conventional pair condensation in the ground state of nuclei with neutrons and protons interacting via a charge-independent pairing interaction. The ground state is described by a product of two condensates, one of ?-like quartets and the other one of pairs in excess relative to the isotope with N=Z. It is shown that this ansatz for the ground state gives very accurate pairing correlation energies for nuclei with the valence nucleons above the closed cores 16O, 40Ca, and 100Sn. These results indicate that ?-type correlations are important not only for the self-conjugate nuclei but also for nuclei away from the N=Z line. In the latter case ?-like quartets coexist with the collective Cooper pairs formed by the nucleons in excess.

Sandulescu, N.; Negrea, D.; Johnson, C. W.

2012-10-01

62

Impact of self-consistent pairing correlations; spatial structure change of quasiparticles and enhanced low-lying collectivity in neutron drip line nuclei  

NASA Astrophysics Data System (ADS)

Role of pairing correlations unique in low-frequency vibrational excitations of neutron drip line nuclei is discussed. Self-consistent pairing correlations in Hartree-Fock-Bogoliubov (HFB) theory cause the change of the spatial structure of the quasiparticle wave functions; the pairing anti-halo effect in the lower component and the broadening effect in the upper component. By performing HFB plus quasiparticle random phase approximation (QRPA) calculation for the isoscalar quadrupole response in 86Ni, we discuss the role of self-consistent pairing correlations for emergency of low-frequency vibrational excitations in neutron drip line nuclei paying special attention to neutrons with small orbital angular momentum ell.

Yamagami, Masayuki

2005-01-01

63

Water distribution measurement for a PEMFC through neutron radiography  

Microsoft Academic Search

Neutron radiography has been used for in situ and non-destructive visualization and measurement technique for liquid water in a working proton exchange membrane fuel cell (PEMFC). In an attempt to differentiate water distribution in the anode side from that in the cathode side, a specially designed cell was machined and used for the experiment. The major difference between our design

Yong-Song Chen; Huei Peng; Daniel S. Hussey; David L. Jacobson; Doanh T. Tran; Tarek Abdel-Baset; Mark Biernacki

2007-01-01

64

Angular distribution and rotations of frame in vector meson decays into lepton pairs  

SciTech Connect

We discuss how the angular distribution of lepton pairs from decays of vector mesons depends on the choice of reference frame, and provide a geometrical description of the transformations of the coefficients of the angular distribution. Invariant expressions involving all coefficients are discussed, together with bounds and consistency relations.

Palestini, Sandro [CERN, 1211 Geneva 23 (Switzerland)

2011-02-01

65

Neutron pair correlations in A=100 nuclei involved in neutrinoless double-? decay  

NASA Astrophysics Data System (ADS)

The pairing properties of the neutrinoless double-? decay (0?2?) candidate 100Mo have been studied, along with its daughter 100Ru, to provide input for nuclear matrix element calculations relevant to the decay. The (p,t) two-neutron transfer reaction was measured on nuclei of 102,100Ru and 100,98Mo. The experiment was designed to have particular sensitivity to 0+ states up to excitation energies of ˜3 MeV with high energy resolution. Measurements were made at two angles and L=0 transitions identified by the ratio of yields between the two angles. For the reactions leading to and from 100Ru, greater than 95% of the L=0 (p,t) strength was in the ground state, but in 100Mo about 20% was in excited 0+ states. The measured (p,t) data, together with existing (t,p) data, suggest that 100Mo is a shape-transitional nucleus while 100Ru is closer to the spherical side of that transition. Theoretical calculations of the 0?2? nuclear matrix element may be complicated by this difference in shape.

Thomas, J. S.; Freeman, S. J.; Deibel, C. M.; Faestermann, T.; Hertenberger, R.; Kay, B. P.; McAllister, S. A.; Mitchell, A. J.; Schiffer, J. P.; Sharp, D. K.; Wirth, H.-F.

2012-10-01

66

NEUTRON FLUX AND VOID DISTRIBUTION IN BWR  

Microsoft Academic Search

Different methods are introduced to solve the two group diffusion ; equations, which involve the mutual interaction of the power, void, and control ; rod distribution in the BWR. In the numerical examples by digital com puter ; (HIPAC-1 and IBM-650) calculations given, the results of one-dimensional forward ; method, backward methcd, and two-dimensional backward method are compared. The ;

T. Kawai; K. Arai; S. Terasawa; T. Kanai

1959-01-01

67

Yield, variance and spatial distribution of electron–hole pairs in CsI  

SciTech Connect

A Monte Carlo (MC) method previously developed has been applied to simulate the interaction of photons, with energies ranging from 50 eV to ~ 1 MeV, with CsI and the subsequent electron cascades. The MC model has been employed to compute nano-scale spatial distributions of electron-hole pairs and important intrinsic properties, including W, the mean energy per electron-hole pair, and the Fano factor, F. W exhibits discontinuities at the shell edges that follow the photoionization cross sections and decreases with increasing photon energy (from ~19 to 15 eV), with an asymptotic value of 15.2 eV at high energy. This decrease may contribute the initial rise in relative light yield with incident energy observed experimentally for CsI, thus suggesting that nonlinearity may be associated with intrinsic properties of the material at low energies. F is calculated to increase with increasing energy and has an asymptotic value of 0.28. A significant number of electron-hole pairs are produced through the different ionization channels of core shells and corresponding relaxation processes, which may explain why F is larger for CsI than for Si or Ge. Finally, the calculated spatial distributions show that the electron-hole pairs are primarily distributed along fast electron tracks. These spatial distributions constitute important input for large-scale simulations of electron-hole pair transport.

Gao, Fei; Xie, YuLong; Kerisit, Sebastien N.; Campbell, Luke W.; Weber, William J.

2011-10-01

68

Modeling the spatial distribution of neutron stars in the Galaxy  

NASA Astrophysics Data System (ADS)

In this paper we investigate the space and velocity distributions of old neutron stars (aged 109 to 1010 yr) in our Galaxy. Galactic old Neutron Stars (NSs) population fills a torus-like area extending to a few tens kiloparsecs above the galactic plane. The initial velocity distribution of NSs is not well known, in this work we adopt a three component initial distribution, as given by the contribution of kick velocities, circular velocities and Maxwellian velocities. For the spatial initial distribution we use a ? function. We then use Monte Carlo simulations to follow the evolution of the NSs under the influence of the Paczy?ski Galactic gravitational potential. Our calculations show that NS orbits have a very large Galactic radial expansion and that their radial distribution peak is quite close to their progenitors' one. We also study the NS vertical distribution and find that it can well be described by a double exponential low. Finally, we investigate the correlation of the vertical and radial distribution and study the radial dependence of scale-heights.

Taani, Ali; Naso, Luca; Wei, Yingchun; Zhang, Chengmin; Zhao, Yongheng

2012-10-01

69

Investigation of the pairing effect using newly evaluated empirical studies for 14 15 MeV neutron reaction cross sections  

Microsoft Academic Search

The asymmetry term effects for the cross sections of (n, charged particle) and (n,2n) reactions at 14 15 MeV neutron incident energy have been investigated. The effects of pairing and odd-even nucleon numbers in new data and in the formula of Tel [J. Phys. G. 29, 2169 (2003)] are discussed. We have determined three different parameters groups by the classification

E. Tel; A. Aydin; G. Tanir

2007-01-01

70

Relativistic Hartree-Bogoliubov Theory with Finite Range Pairing Forces in Coordinate Space: Neutron Halo in Light Nuclei  

Microsoft Academic Search

The relativistic Hartree Bogoliubov model is applied in the self-consistent mean-field approximation to the description of the neutron halo in the mass region above the s-d shell. Pairing correlations and the coupling to particle continuum states are described by finite range two-body forces. Finite element methods are used in the coordinate space discretization of the coupled system of Dirac-Hartree-Bogoliubov integro-differential

W. Poeschl; D. Vretenar; G. A. Lalazissis; P. Ring

1997-01-01

71

The epithermal neutron flux distribution in a nuclear reactor and its effect on epithermal neutron activation analysis  

Microsoft Academic Search

The shape of the epithermal neutron energy distribution has been determined in two irradiation positions of the University\\u000a of London CONSORT II reactor. The method applied involves cadmium ratio measurements using a series of resonance detectors.\\u000a Principles of the method and some considerations relative to epithermal neutron activation analysis in connection with the\\u000a deviation of the epithermal neutron flux distribution

T. Bereznai; T. D. Mac Mahon

1978-01-01

72

Neutron density distribution and the halo structure of C22  

NASA Astrophysics Data System (ADS)

The recently measured reaction cross sections for the neutron-rich carbon isotopes (C19, C20, and C22) on a proton target at 40 A MeV are analyzed using the finite range Glauber model (FRGM) and the microscopic optical potential calculated within the Brueckner-Hartree-Fock formalism (BHF). In FRGM nucleon-nucleon cross sections are used, while in the latter (BHF), Hamada-Johnston, Urbana v-14, and the Argonne v-18 internucleon potentials are employed to calculate the microscopic optical potential. The required nucleon density distributions are calculated within the relativistic mean-field (RMF) framework. To test the halo structure, the extended neutron density distribution for C22 is also used. The analysis reveals that the BHF results of all three internucleon potentials are very close to each other, and also agree with the corresponding results of the FRGM. Our results, using RMF densities, are in agreement with the experimental data for all isotopes of carbon except C22, for which we require extended neutron density distribution, indicating a halo structure.

Sharma, Manjari; Bhagwat, A.; Khan, Z. A.; Haider, W.; Gambhir, Y. K.

2011-03-01

73

The determination of pair distance distributions by pulsed ESR using Tikhonov regularization  

Microsoft Academic Search

Pulsed ESR techniques with the aid of site-directed spin labeling have proven useful in providing unique structural information about proteins. The determination of distance distributions in electron spin pairs directly from the dipolar time evolution of the pulsed ESR signals by means of the Tikhonov regularization method is reported. The difficulties connected with numerically inverting this ill-posed mathematical problem are

Yun-Wei Chiang; Peter P. Borbat; Jack H. Freed

2005-01-01

74

New formula for the bulk viscosity constructed from the interatomic potential and the pair distribution function  

NASA Astrophysics Data System (ADS)

We provide a physical insight into the mechanism of the bulk viscosity ? and construct a new formula for ? directly from microscopic information such as the interatomic potential and the pair distribution function. This is an outstanding advantage when compared to the previously proposed formulas in all of which ? is expressed only in terms of a macroscopic quantity, i.e., pressure. In other words, our new formula makes it possible for the first time to discuss the relation between the macroscopic quantity ? and the microscopic properties such as the interatomic potential and the pair distribution function. This new formula is derived by solving the time development equation of the pair distribution function. Among some of the previously proposed formulas, we prove that the Green-Kubo formula and the Heyes formula are both equivalent to our new formula when the macroscopic quantity-pressure-in their expressions is described by means of interatomic potentials and pair distribution functions under appropriate conditions. This fact confirms the validity of our formula, which reinforces the aforementioned advantage. We calculate ? near the triple point of the Lennard-Jones fluid using our formula, the Green-Kubo formula, and the Heyes formula. The obtained values of ? are in good agreement with each other.

Okumura, Hisashi; Yonezawa, Fumiko

2002-05-01

75

Reconstruction of axisymmetric strain distributions via neutron strain tomography  

NASA Astrophysics Data System (ADS)

Predicting the behaviour of structural components under a particular set of loading conditions requires knowledge of the residual elastic strain distribution throughout the bulk of these components. Characterising the 3D strain state at any particular point involves the measurement of six independent components which make up the second order strain tensor. Mapping the complete strain distribution throughout large volumes thus presents significant practical challenges. One possible solution to this problem is to reconstruct the 3D variation of strain components using tomographic techniques. The basic principle underpinning this idea is that the multi-component strain tensor can be reconstructed from a redundant set of lower order projection data. Here we demonstrate this fundamental concept for two samples: a shrink fit 'ring-and-plug' sample, and a spray-quenched circular cylinder, both possessing axially symmetric internal strain distribution. We present and contrast different approaches to the strain tomography problem. The methods described here can also be readily applied to high-energy X-ray diffraction measurements and represent an important step toward developing the tomographic reconstruction framework for strain tensor distributions of arbitrary complexity. The major benefit of neutron strain tomography is that the incident beam flux is utilised more fully, greatly reducing the data collection times. Using micro-channel plate (MCP) neutron detectors, a spatial resolution of the order of 0.1 mm can be achieved [1].

Abbey, Brian; Zhang, Shu Yan; Vorster, Wim; Korsunsky, Alexander M.

2012-01-01

76

Spatial Two-neutron Correlations Induced by Pairing in Finite Nuclei  

SciTech Connect

We study spatial properties induced by pairing correlations, within the HFB approach employing the finite range D1S Gogny interaction. Local and non-local quantities, such as pairing tensor, are discussed as well as the coherence length. We show that a generic feature occurs at the surface of nuclei, namely Cooper pair of small size characterized by a coherence length xiapprox2 fm.

Pillet, N.; Berger, J.-F. [CEA, DAM, DIF, F-91297 Arpajon (France); Sandulescu, N. [Institute of Physics and Nuclear Engineering, 76900 Bucharest (Romania); Schuck, P. [Institut de Physique Nucleaire, CNRS, UMR8608, Orsay F-91406 (France) and Universite Paris-Sud, Orsay, F-91505 (France)

2009-08-26

77

Electron density distribution in Si and Ge using multipole, maximum entropy method and pair distribution function analysis  

NASA Astrophysics Data System (ADS)

The local, average and electronic structure of the semiconducting materials Si and Ge has been studied using multipole, maximum entropy method (MEM) and pair distribution function (PDF) analyses, using X-ray powder data. The covalent nature of bonding and the interaction between the atoms are clearly revealed by the two-dimensional MEM maps plotted on (1 0 0) and (1 1 0) planes and one-dimensional density along [1 0 0], [1 1 0] and [1 1 1] directions. The mid-bond electron densities between the atoms are 0.554 e/Ĺ^{3} and 0.187 e/Ĺ^{3} for Si and Ge respectively. In this work, the local structural information has also been obtained by analyzing the atomic pair distribution function. An attempt has been made in the present work to utilize the X-ray powder data sets to refine the structure and electron density distribution using the currently available versatile methods, MEM, multipole analysis and determination of pair distribution function for these two systems.

Saravanan, R.; Syed Ali, K. S.; Israel, S.

2008-04-01

78

Experimental verification of improved depth-dose distribution using hyper-thermal neutron incidence in neutron capture therapy.  

PubMed

We have proposed the utilization of 'hyper-thermal neutrons' for neutron capture therapy (NCT) from the viewpoint of the improvement in the dose distribution in a human body. In order to verify the improved depth-dose distribution due to hyper-thermal neutron incidence, two experiments were carried out using a test-type hyper-thermal neutron generator at a thermal neutron irradiation field in Kyoto University Reactor (KUR), which is actually utilized for NCT clinical irradiation. From the free-in-air experiment for the spectrum-shift characteristics, it was confirmed that the hyper-thermal neutrons of approximately 860 K at maximum could be obtained by the generator. From the phantom experiment, the improvement effect and the controllability for the depth-dose distribution were confirmed. For example, it was found that the relative neutron depth-dose distribution was about 1 cm improved with the 860 K hyper-thermal neutron incidence, compared to the normal thermal neutron incidence. PMID:11197667

Sakurai, Y; Kobayashi, T

2001-01-01

79

Electron density distribution in Si and Ge using multipole, maximum entropy method and pair distribution function analysis  

Microsoft Academic Search

The local, average and electronic structure of the semiconducting materials Si and Ge has been studied using multipole, maximum\\u000a entropy method (MEM) and pair distribution function (PDF) analyses, using X-ray powder data. The covalent nature of bonding\\u000a and the interaction between the atoms are clearly revealed by the two-dimensional MEM maps plotted on (100) and (110) planes\\u000a and one-dimensional density

R. Saravanan; K. S. Syed Ali; S. Israel

2008-01-01

80

Fission-product gamma-ray line pairs sensitive to fissile material and neutron energy  

Microsoft Academic Search

The beta-delayed gamma-ray spectra from the fission of 235U, 238U, and 239Pu by thermal and near-14-MeV neutrons have been measured for delay times ranging from 1 min to 14 h. Spectra at all delay times contain sets of prominent gamma-ray lines with intensity ratios that identify the fissile material and distinguish between fission induced by low-energy or high-energy neutrons.

R. E. Marrs; E. B. Norman; J. T. Burke; R. A. Macri; H. A. Shugart; E. Browne; A. R. Smith

2008-01-01

81

Fission-product gamma-ray line pairs sensitive to fissile material and neutron energy  

NASA Astrophysics Data System (ADS)

The beta-delayed gamma-ray spectra from the fission of 235U, 238U, and 239Pu by thermal and near-14-MeV neutrons have been measured for delay times ranging from 1 min to 14 h. Spectra at all delay times contain sets of prominent gamma-ray lines with intensity ratios that identify the fissile material and distinguish between fission induced by low-energy or high-energy neutrons.

Marrs, R. E.; Norman, E. B.; Burke, J. T.; Macri, R. A.; Shugart, H. A.; Browne, E.; Smith, A. R.

2008-07-01

82

Fission-product gamma-ray line pairs sensitive to fissile material and neutron energy  

Microsoft Academic Search

The beta-delayed gamma-ray spectra from the fission of 235U, 238U, and 239Pu by thermal and near-14-MeV neutrons have been measured for delay times ranging from 1min to 14h. Spectra at all delay times contain sets of prominent gamma-ray lines with intensity ratios that identify the fissile material and distinguish between fission induced by low-energy or high-energy neutrons.

R. E. Marrs; E. B. Norman; J. T. Burke; R. A. Macri; H. A. Shugart; E. Browne; A. R. Smith

2008-01-01

83

Time distribution of muon Pairs detected at 40 m.w.e  

Microsoft Academic Search

Experimental results are reported on the distribution of arrival time intervals between pairs of atmospheric muons detected at 40 m.w.e. underground and generated in interactions of primary nuclei with average energy about 600 GeV. A total number of 72,220 single muons was recorded with a total frequency of 7.1 muons per second, in good agreement with previous measurements at the

G. Badino; W. Fulgione; L. Periale; M. Dardo; P. Galeotti; O. Saavedra

1982-01-01

84

Genetic algorithm for the pair distribution function of the electron gas.  

PubMed

The pair distribution function of the electron gas is calculated using a parameterized generalization of hypernetted chain approximation with the parameters being obtained by optimizing the system energy with a genetic algorithm. The functions so obtained are compared with Monte Carlo simulations performed by other authors in its variational and di_usion versions showing a very good agreement especially with the di_usion Monte Carlo results. PMID:22179762

Vericat, Fernando; Stoico, César O; Carlevaro, C Manuel; Renzi, Danilo G

2011-12-18

85

Neutron-Proton Pairing Correlations in Single l and Single j Models.  

NASA Astrophysics Data System (ADS)

The roles of isoscalar (T=0) and isovector (T=1) pairing correlations at the N=Z line have recently received renewed attention. In this work we review the experimental data on binding energy differences between odd-odd and even-even nuclei along the N=Z line and interpret the results with calculations based on single l and single j shell models. In spite of their simplicity, these models incorporate the main ingredients of the np pairing correlations and provide a firm basis to support some general arguments that can be used to probe the formation of a condensate of isoscalar np pairs

Macchiavelli, A. O.; Fallon, P.; Clark, R. M.; Cromaz, M.; Deleplanque, M. A.; Diamond, R. M.; Görgen, A.; Lee, I. Y.; Stephens, F. S.; Ward, D.; Harris, Z.

2002-04-01

86

Leading neutron energy and p distributions in deep inelastic scattering and photoproduction at HERA  

NASA Astrophysics Data System (ADS)

The production of energetic neutrons in ep collisions has been studied with the ZEUS detector at HERA. The neutron energy and pT2 distributions were measured with a forward neutron calorimeter and tracker in a 40 pb sample of inclusive deep inelastic scattering (DIS) data and a 6 pb sample of photoproduction data. The neutron yield in photoproduction is suppressed relative to DIS for the lower neutron energies and the neutrons have a steeper pT2 distribution, consistent with the expectation from absorption models. The distributions are compared to HERA measurements of leading protons. The neutron energy and transverse-momentum distributions in DIS are compared to Monte Carlo simulations and to the predictions of particle exchange models. Models of pion exchange incorporating absorption and additional secondary meson exchanges give a good description of the data.

ZEUS Collaboration; Chekanov, S.; Derrick, M.; Magill, S.; Miglioranzi, S.; Musgrave, B.; Nicholass, D.; Repond, J.; Yoshida, R.; Mattingly, M. C. K.; Jechow, M.; Pavel, N.; Yagües Molina, A. G.; Antonelli, S.; Antonioli, P.; Bari, G.; Basile, M.; Bellagamba, L.; Bindi, M.; Boscherini, D.; Bruni, A.; Bruni, G.; Cifarelli, L.; Cindolo, F.; Contin, A.; Corradi, M.; de Pasquale, S.; Iacobucci, G.; Margotti, A.; Nania, R.; Polini, A.; Rinaldi, L.; Sartorelli, G.; Zichichi, A.; Bartsch, D.; Brock, I.; Goers, S.; Hartmann, H.; Hilger, E.; Jakob, H.-P.; Jüngst, M.; Kind, O. M.; Paul, E.; Renner, R.; Samson, U.; Schönberg, V.; Shehzadi, R.; Wlasenko, M.; Brook, N. H.; Heath, G. P.; Morris, J. D.; Namsoo, T.; Capua, M.; Fazio, S.; Mastroberardino, A.; Schioppa, M.; Susinno, G.; Tassi, E.; Kim, J. Y.; Ma, K. J.; Ibrahim, Z. A.; Kamaluddin, B.; Wan Abdullah, W. A. T.; Ning, Y.; Ren, Z.; Sciulli, F.; Chwastowski, J.; Eskreys, A.; Figiel, J.; Galas, A.; Gil, M.; Olkiewicz, K.; Stopa, P.; Zawiejski, L.; Adamczyk, L.; Bo?d, T.; Grabowska-Bo?d, I.; Kisielewska, D.; ?ukasik, J.; Przybycie?, M.; Suszycki, L.; Kota?ski, A.; S?omi?ski, W.; Adler, V.; Behrens, U.; Bloch, I.; Blohm, C.; Bonato, A.; Borras, K.; Coppola, N.; Dossanov, A.; Fourletova, J.; Geiser, A.; Gladkov, D.; Göttlicher, P.; Gregor, I.; Haas, T.; Hain, W.; Horn, C.; Kahle, B.; Klein, U.; Kötz, U.; Kowalski, H.; Lobodzinska, E.; Löhr, B.; Mankel, R.; Melzer-Pellmann, I.-A.; Montanari, A.; Notz, D.; Nuncio-Quiroz, A. E.; Rubinsky, I.; Santamarta, R.; Schneekloth, U.; Spiridonov, A.; Stadie, H.; Szuba, D.; Szuba, J.; Theedt, T.; Wolf, G.; Wrona, K.; Youngman, C.; Zeuner, W.; Lohmann, W.; Schlenstedt, S.; Barbagli, G.; Gallo, E.; Pelfer, P. G.; Bamberger, A.; Dobur, D.; Karstens, F.; Vlasov, N. N.; Bussey, P. J.; Doyle, A. T.; Dunne, W.; Ferrando, J.; Saxon, D. H.; Skillicorn, I. O.; Gialas, I.; Gosau, T.; Holm, U.; Klanner, R.; Lohrmann, E.; Salehi, H.; Schleper, P.; Schörner-Sadenius, T.; Sztuk, J.; Wichmann, K.; Wick, K.; Foudas, C.; Fry, C.; Long, K. R.; Tapper, A. D.; Kataoka, M.; Matsumoto, T.; Nagano, K.; Tokushuku, K.; Yamada, S.; Yamazaki, Y.; Barakbaev, A. N.; Boos, E. G.; Pokrovskiy, N. S.; Zhautykov, B. O.; Son, D.; de Favereau, J.; Piotrzkowski, K.; Barreiro, F.; Glasman, C.; Jimenez, M.; Labarga, L.; Del Peso, J.; Ron, E.; Soares, M.; Terrón, J.; Zambrana, M.; Corriveau, F.; Liu, C.; Walsh, R.; Zhou, C.; Tsurugai, T.; Antonov, A.; Dolgoshein, B. A.; Sosnovtsev, V.; Stifutkin, A.; Suchkov, S.; Dementiev, R. K.; Ermolov, P. F.; Gladilin, L. K.; Katkov, I. I.; Khein, L. A.; Korzhavina, I. A.; Kuzmin, V. A.; Levchenko, B. B.; Lukina, O. Yu.; Proskuryakov, A. S.; Shcheglova, L. M.; Zotkin, D. S.; Zotkin, S. A.; Abt, I.; Büttner, C.; Caldwell, A.; Kollar, D.; Schmidke, W. B.; Sutiak, J.; Grigorescu, G.; Keramidas, A.; Koffeman, E.; Kooijman, P.; Pellegrino, A.; Tiecke, H.; Vázquez, M.; Wiggers, L.; Brümmer, N.; Bylsma, B.; Durkin, L. S.; Lee, A.; Ling, T. Y.; Allfrey, P. D.; Bell, M. A.; Cooper-Sarkar, A. M.; Cottrell, A.; Devenish, R. C. E.; Foster, B.; Korcsak-Gorzo, K.; Patel, S.; Roberfroid, V.; Robertson, A.; Straub, P. B.; Uribe-Estrada, C.; Walczak, R.; Bellan, P.; Bertolin, A.; Brugnera, R.; Carlin, R.; Ciesielski, R.; Dal Corso, F.; Dusini, S.; Garfagnini, A.; Limentani, S.; Longhin, A.; Stanco, L.; Turcato, M.; Oh, B. Y.; Raval, A.; Ukleja, J.; Whitmore, J. J.; Iga, Y.; D'Agostini, G.; Marini, G.; Nigro, A.; Cole, J. E.; Hart, J. C.; Abramowicz, H.; Gabareen, A.; Ingbir, R.; Kananov, S.; Levy, A.; Kuze, M.; Hori, R.; Kagawa, S.; Okazaki, N.; Shimizu, S.; Tawara, T.; Hamatsu, R.; Kaji, H.; Kitamura, S.; Ota, O.; Ri, Y. D.; Ferrero, M. I.; Monaco, V.; Sacchi, R.; Solano, A.; Arneodo, M.; Ruspa, M.; Fourletov, S.; Martin, J. F.; Boutle, S. K.; Butterworth, J. M.; Gwenlan, C.; Jones, T. W.; Loizides, J. H.; Sutton, M. R.; Targett-Adams, C.; Wing, M.; Brzozowska, B.; Ciborowski, J.; Grzelak, G.; Kulinski, P.; ?u?niak, P.; Malka, J.; Nowak, R. J.; Pawlak, J. M.; Tymieniecka, T.; Ukleja, A.; ?arnecki, A. F.; Adamus, M.; Plucinski, P.; Eisenberg, Y.; Giller, I.; Hochman, D.; Karshon, U.; Rosin, M.; Brownson, E.; Danielson, T.; Everett, A.; Kçira, D.; Reeder, D. D.; Ryan, P.; Savin, A. A.; Smith, W. H.; Wolfe, H.; Bhadra, S.; Catterall, C. D.; Cui, Y.; Hartner, G.; Menary, S.; Noor, U.; Standage, J.; Whyte, J.

2007-07-01

87

Phase transitions of dense neutron matter with generalized Skyrme interaction to superfluid states with triplet pairing in strong magnetic field  

NASA Astrophysics Data System (ADS)

A generalized non-relativistic Fermi-liquid approach was used to find analytical formulas for temperatures Tc1(n, H) and Tc2(n, H) (which are functions nonlinear of density n and linear of magnetic field H) of phase transitions in spatially uniform dense pure neutron matter from normal to superfluid states with spin-triplet p-wave pairing (similar to anisotropic superfluid phases 3He-A1 and 3He-A2) in steady and homogeneous strong magnetic field (but |?n| H ll Ec < ?F(n), where ?n is the magnetic dipole moment of a neutron, Ec is the cutoff energy and ?F(n) is the Fermi energy in neutron matter). General formulas for Tc1, 2 (n, H) (valid for arbitrary parameterization of the effective Skyrme interaction in neutron matter) are specified here for generalized BSk18 parameterization of the Skyrme forces (with additional terms dependent on density n) on the interval 0.3 n0 < n < nc (BSk18) ? 2.7952 ˇ n0, where n0 = 0.17 fm-3 is nuclear density and at critical density nc(BSk18) triplet superfluidity disappears, Tc0(n, cH = 0) = 0. Expressions for phase transition temperatures Tc0(n)<0.09MeV (at Ec = 10MeV) and Tc1, 2(n, H) are realistic non-monotone functions of density n for BSk18 parameterization of the Skyrme forces (contrary to their monotone increase for all previous BSk parameterizations). Phase transitions to superfluid states of such type might occur in liquid outer core of magnetars (strongly magnetized neutron stars).

Tarasov, A. N.

2012-12-01

88

Fission Product Gamma-Ray Line Pairs Sensitive to Fissile Material and Neutron Energy  

Microsoft Academic Search

The beta-delayed gamma-ray spectra from the fission of ²³⁾U, ²³⁸U, and ²³⁚Pu by thermal and near-14-MeV neutrons have been measured for delay times ranging from 1 minute to 14 hours. Spectra at all delay times contain sets of prominent gamma-ray lines with intensity ratios that identify the fissile material and distinguish between fission induced by low-energy or high-energy neutrons.

R E Marrs; E B Norman; J T Burke; R A Macri; H A Shugart; E Browne; A R Smith

2007-01-01

89

Pair distribution function (PDF) analysis of mesoporous ?-Fe2O3 and Cr2O3.  

PubMed

We have measured atomic pair distribution functions of novel mesoporous metal oxides, ?-Fe2O3 and Cr2O3. These have an ordered pore mosaic as well as crystalline structure within the pore walls, making them an interesting class of materials to characterise. Comparison of "bulk" and mesoporous data sets has allowed an estimate of long range structural coherence to be derived; ?125 Ĺ and ?290 Ĺ for ?-Fe2O3 and Cr2O3 respectively. Further "box-car" analysis has shown that above ?40 Ĺ both mesoporous samples deviate greatly from their bulk counterparts. This is attributed to the pores of the mesoporous structure creating voids in the pair-correlations, disrupting long range order. PMID:23619834

Hill, Adrian H; Allieta, Mattia

2013-04-25

90

Towards a robust ad hoc data correction approach that yields reliable atomic pair distribution functions from powder diffraction data  

NASA Astrophysics Data System (ADS)

We examine the equations to obtain atomic pair distribution functions (PDFs) from x-ray, neutron and electron powder diffraction data with a view to obtaining reliable and accurate PDFs from the raw data using a largely ad hoc correction process. We find that this should be possible under certain circumstances that hold, to a reasonably good approximation, in many modern experiments. We describe a variational approach that could be applied to find data correction parameters that is highly automatable and should require little in the way of user inputs yet results in quantitatively reliable PDFs, modulo unknown scale factors that are often not of scientific interest when profile fitting models are applied to the data with scale factor as a parameter. We have worked on a particular implementation of these ideas and demonstrate that it yields PDFs that are of comparable quality to those obtained with the existing x-ray data reduction program PDFgetX2. This opens the door to rapid and highly automated processing of raw data to obtain PDFs.

Billinge, Simon J. L.; Farrow, Christopher L.

2013-11-01

91

Towards a robust ad hoc data correction approach that yields reliable atomic pair distribution functions from powder diffraction data.  

PubMed

We examine the equations to obtain atomic pair distribution functions (PDFs) from x-ray, neutron and electron powder diffraction data with a view to obtaining reliable and accurate PDFs from the raw data using a largely ad hoc correction process. We find that this should be possible under certain circumstances that hold, to a reasonably good approximation, in many modern experiments. We describe a variational approach that could be applied to find data correction parameters that is highly automatable and should require little in the way of user inputs yet results in quantitatively reliable PDFs, modulo unknown scale factors that are often not of scientific interest when profile fitting models are applied to the data with scale factor as a parameter. We have worked on a particular implementation of these ideas and demonstrate that it yields PDFs that are of comparable quality to those obtained with the existing x-ray data reduction program PDFgetX2. This opens the door to rapid and highly automated processing of raw data to obtain PDFs. PMID:24140913

Billinge, Simon J L; Farrow, Christopher L

2013-10-18

92

Pairing correlations and soft dipole excitations in nuclei on the neutron-drip line  

SciTech Connect

Paring correlations and soft dipole excitations in weakly bound nuclei on the edge of neutron drip line are studied by using a three-body model. A density-dependent contact interaction is employed to calculate the ground state of halo nuclei {sup 6}He and {sup 11}Li, as well as a skin nucleus {sup 24}O. Dipole excitations in these nuclei are also studied within the same model. We point out that the dineutron-type correlation plays a dominant role in the halo nuclei {sup 6}He and {sup 11}Li having the coupled spin of the two neutrons S = 0, while the correlation similar to the BCS type is important in {sup 24}O. Contributions of the spin S = 1 and S = 0 configurations are separately discussed in the low-energy dipole excitations. The calculated results are compared with recent experimental data of {sup 6}He and {sup 11}Li.

Sagawa, H. [University of Aizu, Center for Mathematical Sciences (Japan)], E-mail: sagawa@u-aizu.ac.jp; Hagino, K. [Tohoku University, Department of Physics (Japan)], E-mail: hagino@nucl.phys.tohoku.ac.jp

2007-08-15

93

Finite Size Effects on the Real-Space Pair Distribution Function of Nanoparticles  

SciTech Connect

The pair distribution function (PDF) method is a powerful approach for the analysis of the structure of nanoparticles. An important approximation used in nanoparticle PDF simulations is the incorporation of a form factor describing nanoparticle size and shape. The precise effect of the form factor on the PDF is determined by both particle shape and structure if these characteristics are both anisotropic and correlated. The correct incorporation of finite size effects is important for distinguishing and quantifying the structural consequences of small particle size in nanomaterials.

Gilbert, Benjamin

2008-10-01

94

Data Requirements for the Reliable Use of Atomic Pair Distribution Functions in Amorphous Pharmaceutical Fingerprinting  

Microsoft Academic Search

Purpose  To determine the optimal measurement strategy for fingerprinting condensed phases of pharmaceutical systems using atomic pair\\u000a distribution functions (PDFs) obtained from data collected using several types of x-ray diffraction instruments.\\u000a \\u000a \\u000a \\u000a \\u000a Methods  PDFs of crystalline and amorphous-phase molecular systems derived from data accessible to copper-, molybdenum-, and silver-anode\\u000a laboratory sources were compared to one another and synchrotron data using qualitative and quantitative

Timur Dykhne; Ryan Taylor; Alastair Florence; Simon J. L. Billinge

2011-01-01

95

Differential Pair Distribution Function Study of the Structure of Arsenate Adsorbed on Nanocrystalline [gamma]-Alumina  

SciTech Connect

Structural information is important for understanding surface adsorption mechanisms of contaminants on metal (hydr)oxides. In this work, a novel technique was employed to study the interfacial structure of arsenate oxyanions adsorbed on {gamma}-alumina nanoparticles, namely, differential pair distribution function (d-PDF) analysis of synchrotron X-ray total scattering. The d-PDF is the difference of properly normalized PDFs obtained for samples with and without arsenate adsorbed, otherwise identically prepared. The real space pattern contains information on atomic pair correlations between adsorbed arsenate and the atoms on {gamma}-alumina surface (Al, O, etc.). PDF results on the arsenate adsorption sample on {gamma}-alumina prepared at 1 mM As concentration and pH 5 revealed two peaks at 1.66 {angstrom} and 3.09 {angstrom}, corresponding to As-O and As-Al atomic pair correlations. This observation is consistent with those measured by extended X-ray absorption fine structure (EXAFS) spectroscopy, which suggests a first shell of As-O at 1.69 {+-} 0.01 {angstrom} with a coordination number of 4 and a second shell of As-Al at 3.13 {+-} 0.04 {angstrom} with a coordination number of 2. These results are in agreement with a bidentate binuclear coordination environment to the octahedral Al of {gamma}-alumina as predicted by density functional theory (DFT) calculation.

Li, Wei; Harrington, Richard; Tang, Yuanzhi; Kubicki, James D.; Aryanpour, Masoud; Reeder, Richard J.; Parise, John B.; Phillips, Brian L. (SBU); (Penn)

2012-03-15

96

In situ observation of the water distribution across a PEFC using high resolution neutron radiography  

Microsoft Academic Search

The water distribution across the membrane electrolyte assembly (MEA) of a working polymer electrolyte fuel cell (PEFC) was observed in situ using neutron radiography. In order to resolve the distribution between the different layers of the MEA, in plane imaging (cell membrane parallel to the beam) was used. Unprecedented spatial resolution for neutron radiography was obtained using a new detector

P. Boillat; D. Kramer; B. C. Seyfang; G. Frei; E. Lehmann; G. G. Scherer; A. Wokaun; Y. Ichikawa; Y. Tasaki; K. Shinohara

2008-01-01

97

Neutron momentum distribution from ''core break-up'' reactions of halo nuclei.  

National Technical Information Service (NTIS)

Neutron angular distributions from violent break-up reactions of Li-11 and Be-11 have been measured at 28 MeV/u and 280 MeV/u and at 41 MeV/u and 460 MeV/u, respectively. The derived neutron momentum distributions show a narrow component in transverse mom...

T. Nilsson T. Blaich M. J. G. Borge L. V. Chulkov T. W. Elze

1995-01-01

98

Personnel Neutron Dosimetry Applications of Track-Size Distributions on Electrochemically Etched CR-39 Foils.  

National Technical Information Service (NTIS)

The track-size distribution on electrochemically etched CR-39 foils can be used to obtain some limited information on the incident neutron spectra. Track-size distributions on CR-39 foils can also be used to determine if the tracks were caused by neutrons...

D. E. Hankins S. G. Homann J. Westermark

1988-01-01

99

Distribution of nonrandom associations between pairs of protein loci along the third chromosome of Drosophila melanogaster.  

PubMed Central

The within-chromosome distribution of gametic disequilibrium (GD) between protein loci, and the underlying evolutionary factors of this distribution, are still largely unknown. Here, we report a detailed study of GD between a large number of protein loci (15) spanning 87% of the total length of the third chromosome of Drosophila melanogaster in a large sample of haplotypes (600) drawn from a single natural population. We used a sign-based GD estimation method recently developed for multiallelic systems, which considerably increases both the statistical power and the accuracy of estimation of the intensity of GD. We found that strong GD between pairs of protein loci was widespread throughout the chromosome. In total, 22% of both the pairs of alleles and pairs of loci were in significant GD, with mean intensities (as measured by D' coefficients) of 0.43 and 0.31, respectively. In addition, strong GD often occurs between loci that are far apart. By way of illustration, 32% of the allele pairs in significant GD occurred within pairs of loci separated by effective frequencies of recombination (EFRs) of 15-20 cM, the mean D' value being 0.49. These observations are in sharp contrast with previous studies showing that GD between protein loci is rarely found in natural populations of outcrossing species, even between very closely linked loci. Interestingly, we found that most instances of significant interallelic GD (68%) involved functionally related protein loci. Specifically, GD was markedly more frequent between protein loci related by the functions of hormonal control, molybdenum control, antioxidant defense system, and reproduction than between loci without known functional relationship, which is indicative of epistatic selection. Furthermore, long-distance GD between functionally related loci (mean EFR 9 cM) suggests that epistatic interactions must be very strong along the chromosome. This evidence is hardly compatible with the neutral theory and has far-reaching implications for understanding the multilocus architecture of the functional genome. Our findings also suggest that GD may be a useful tool for discovering networks of functionally interacting proteins.

Zapata, Carlos; Nunez, Concepcion; Velasco, Teresa

2002-01-01

100

In-phantom two-dimensional thermal neutron distribution for intraoperative boron neutron capture therapy of brain tumours  

NASA Astrophysics Data System (ADS)

The aim of this study was to determine the in-phantom thermal neutron distribution derived from neutron beams for intraoperative boron neutron capture therapy (IOBNCT). Gold activation wires arranged in a cylindrical water phantom with (void-in-phantom) or without (standard phantom) a cylinder styrene form placed inside were irradiated by using the epithermal beam (ENB) and the mixed thermal-epithermal beam (TNB-1) at the Japan Research Reactor No 4. With ENB, we observed a flattened distribution of thermal neutron flux and a significantly enhanced thermal flux delivery at a depth compared with the results of using TNB-1. The thermal neutron distribution derived from both the ENB and TNB-1 was significantly improved in the void-in-phantom, and a double high dose area was formed lateral to the void. The flattened distribution in the circumference of the void was observed with the combination of ENB and the void-in-phantom. The measurement data suggest that the ENB may provide a clinical advantage in the form of an enhanced and flattened dose delivery to the marginal tissue of a post-operative cavity in which a residual and/or microscopically infiltrating tumour often occurs. The combination of the epithermal neutron beam and IOBNCT will improve the clinical results of BNCT for brain tumours.

Yamamoto, T.; Matsumura, A.; Yamamoto, K.; Kumada, H.; Shibata, Y.; Nose, T.

2002-07-01

101

Conditional pair distributions in many-body systems: Exact results for Poisson ensembles  

NASA Astrophysics Data System (ADS)

We introduce a conditional pair distribution function (CPDF) which characterizes the probability density of finding an object (e.g., a particle in a fluid) to within a certain distance of each other, with each of these two having a nearest neighbor to a fixed but otherwise arbitrary distance. This function describes special four-body configurations, but also contains contributions due to the so-called mutual nearest neighbor (two-body) and shared neighbor (three-body) configurations. The CPDF is introduced to improve a Helmholtz free energy method based on space partitions. We derive exact expressions of the CPDF and various associated quantities for randomly distributed, noninteracting points at Euclidean spaces of one, two, and three dimensions. Results may be of interest in many diverse scientific fields, from fluid physics to social and biological sciences.

Rohrmann, René D.; Zurbriggen, Ernesto

2012-05-01

102

Casimir dependence of transverse distribution of pairs produced from a strong constant chromoelectric background field  

SciTech Connect

The transverse distribution of gluon and quark-antiquark pairs produced from a strong constant chromoelectric field depends on two gauge invariant quantities, C{sub 1}=E{sup a}E{sup a} and C{sub 2}=[d{sub abc}E{sup a}E{sup b}E{sup c}]{sup 2}, as shown earlier in [G. C. Nayak and P. van Nieuwenhuizen, Phys. Rev. D 71, 125001 (2005)] for gluons and in [G. C. Nayak, Phys. Rev. D 72, 125010 (2005)] for quarks. Here, we discuss the explicit dependence of the distribution on the second Casimir invariant C{sub 2} and show the dependence is at most a 15% effect.

Cooper, Fred [National Science Foundation, 4201 Wilson Blvd., Arlington, Virginia 22230 (United States); Santa Fe Institute, Santa Fe, New Mexico 87501 (United States); Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Dawson, John F. [Department of Physics, University of New Hampshire, Durham, New Hampshire 03824 (United States); Mihaila, Bogdan [Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2008-12-01

103

Investigation of the pairing effect using newly evaluated empirical studies for 14 15 MeV neutron reaction cross sections  

NASA Astrophysics Data System (ADS)

The asymmetry term effects for the cross sections of (n, charged particle) and (n,2n) reactions at 14 15 MeV neutron incident energy have been investigated. The effects of pairing and odd-even nucleon numbers in new data and in the formula of Tel [J. Phys. G. 29, 2169 (2003)] are discussed. We have determined three different parameters groups by the classification of nuclei into even-even, even-odd, and odd-even (n,d) reactions. In addition, since there are not enough experimental data available, we have considered two different parameters groups by the classification of nuclei into odd-A and even-A (n,t) reaction cross sections. The empirical formulas with two parameters for the evaluation of the (n,d) and (n,t) reactions cross sections are discussed in the present study.

Tel, E.; Aydin, A.; Tanir, G.

2007-03-01

104

Distinguishing są and s++ electron pairing symmetries by neutron spin resonance in superconducting NaFe0.935Co0.045As  

NASA Astrophysics Data System (ADS)

A determination of the superconducting (SC) electron pairing symmetry forms the basis for establishing a microscopic mechanism for superconductivity. For iron pnictide superconductors, the są-pairing symmetry theory predicts the presence of a sharp neutron spin resonance at an energy below the sum of hole and electron SC gap energies (E?2?) below Tc. On the other hand, the s++-pairing symmetry expects a broad spin excitation enhancement at an energy above 2? below Tc. Although the resonance has been observed in iron pnictide superconductors at an energy below 2? consistent with the są-pairing symmetry, the mode has also been interpreted as arising from the s++-pairing symmetry with E?2? due to its broad energy width and the large uncertainty in determining the SC gaps. Here we use inelastic neutron scattering to reveal a sharp resonance at E=7 meV in SC NaFe0.935Co0.045As (Tc=18 K). On warming towards Tc, the mode energy hardly softens while its energy width increases rapidly. By comparing with calculated spin-excitation spectra within the są and s++-pairing symmetries, we conclude that the ground-state resonance in NaFe0.935Co0.045As is only consistent with the są pairing, and is inconsistent with the s++-pairing symmetry.

Zhang, Chenglin; Li, H.-F.; Song, Yu; Su, Yixi; Tan, Guotai; Netherton, Tucker; Redding, Caleb; Carr, Scott V.; Sobolev, Oleg; Schneidewind, Astrid; Faulhaber, Enrico; Harriger, L. W.; Li, Shiliang; Lu, Xingye; Yao, Dao-Xin; Das, Tanmoy; Balatsky, A. V.; Brückel, Th.; Lynn, J. W.; Dai, Pengcheng

2013-08-01

105

Prediction of In-Phantom Dose Distribution Using In-Air Neutron Beam Characteristics for Boron Neutron Capture Synovectomy  

SciTech Connect

A monoenergetic neutron beam simulation study was carried out to determine the optimal neutron energy range for treatment of rheumatoid arthritis using radiation synovectomy. The goal of the treatment is the ablation of diseased synovial membranes in joints such as knees and fingers. This study focuses on human knee joints. Two figures of merit are used to measure the neutron beam quality, the ratio of the synovium-absorbed dose to the skin-absorbed dose, and the ratio of the synovium-absorbed dose to the bone-absorbed dose. It was found that (a) thermal neutron beams are optimal for treatment and that (b) similar absorbed dose rates and therapeutic ratios are obtained with monodirectional and isotropic neutron beams. Computation of the dose distribution in a human knee requires the simulation of particle transport from the neutron source to the knee phantom through the moderator. A method was developed to predict the dose distribution in a knee phantom from any neutron and photon beam spectra incident on the knee. This method was revealed to be reasonably accurate and enabled one to reduce the particle transport simulation time by a factor of 10 by modeling the moderator only.

Verbeke, Jerome M. [University of California, Berkeley (United States); Chen, Allen S. [University of California, Berkeley (United States); Vujic, Jasmina L. [University of California, Berkeley (United States); Leung, Ka-Ngo [Lawrence Berkeley National Laboratory (United States)

2000-08-15

106

Pairing phenomenon in doubly odd neutron rich {sup 136}Sb nucleus  

SciTech Connect

Based on p-n and n-n pairing gap energies giving by K. Kaneko et al. (2003), we make modifications on the kh5082 interaction. Calculations and study of some nuclear properties for {sup 136}Sb nucleus are developed in the framework of the nuclear shell model by means of OXBASH structure code. We get the same energetic sequence as the recent experimental values of single particle energies. The effective charge values e{sub p}=1.35e and e{sub n}=0.9e, and factors given by V. I. Isakov are used to evaluate multipole electromagnetic moments.

Laouet, N.; Benrachi, F. [Laboratoire de Physique Mathematique et Subatomique Mentouri University, Constantine (Algeria)

2012-06-27

107

Force distribution in a randomly perturbed lattice of identical particles with 1/r2 pair interaction.  

PubMed

We study the statistics of the force felt by a particle in the class of a spatially correlated distribution of identical pointlike particles, interacting via a 1/r2 pair force (i.e., gravitational or Coulomb), and obtained by randomly perturbing an infinite perfect lattice. We specify the conditions under which the force on a particle is a well-defined stochastic quantity. We then study the small displacements approximation, giving both the limitations of its validity and, when it is valid, an expression for the force variance. The method introduced by Chandrasekhar to find the force probability density function for the homogeneous Poisson particle distribution is extended to shuffled lattices of particles. In this way, we can derive an approximate expression for the probability distribution of the force over the full range of perturbations of the lattice, i.e., from very small (compared to the lattice spacing) to very large where the Poisson limit is recovered. We show in particular the qualitative change in the large-force tail of the force distribution between these two limits. Excellent accuracy of our analytic results is found on detailed comparison with results from numerical simulations. These results provide basic statistical information about the fluctuations of the interactions (i) of the masses in self-gravitating systems like those encountered in the context of cosmological N -body simulations, and (ii) of the charges in the ordered phase of the one-component plasma, the so-called Coulomb or Wigner crystal. PMID:17025396

Gabrielli, Andrea; Baertschiger, Thierry; Joyce, Michael; Marcos, Bruno; Labini, Francesco Sylos

2006-08-09

108

Development of a wide-range paired scintillator with optical fiber neutron monitor for BNCT irradiation field study  

Microsoft Academic Search

A wide range thermal neutron detector was developed based on the Scintillator with Optical Fiber (SOF) detector which has been previously used for thermal neutron monitoring during boron neutron capture therapy irradiation. With this new detector system we intended to address the issues of real-time thermal neutron flux measurement and the simultaneous measurement of a wide range of thermal neutron

Masayori Ishikawa; Hiroaki Kumada; Kazuyoshi Yamamoto; Junichi Kaneko; Gerard Bengua; Hironobu Unesaki; Yoshinori Sakurai; Kenichi Tanaka; Toshiso Kosako

2005-01-01

109

Personnel neutron dosimetry applications of track-size distributions on electrochemically etched CR39 foils  

Microsoft Academic Search

The track-size distribution on electrochemically etched CR-39 foils can be used to obtain some limited information on the incident neutron spectra. Track-size distributions on CR-39 foils can also be used to determine if the tracks were caused by neutrons or if they are merely background tracks (which have a significantly different track-size distribution). Identifying and discarding the high-background foils reduces

D. E. Hankins; S. G. Homann; J. Westermark

1988-01-01

110

Evaluation of sodium activation distribution in the PMMA water phantom after fast neutron irradiation.  

PubMed

(24)Na produced by the neutron activation of stable sodium in the body is commonly used to assess neutron doses after criticality accidents. However, the (24)Na distribution is not uniform owing to the interaction with the human body. In this study, we experimentally evaluated the (24)Na distribution in a PMMA water phantom and 60 polyethylene vials. The vials were analyzed to evaluate the sodium activation distribution in the PMMA water phantom by employing a correction factor. PMID:23548694

Ha, Wi-Ho; Park, Seyong; Yoo, Jaeryong; Yoon, Seokwon; Lee, Seung-Sook; Kim, Jong Kyung

2013-03-16

111

Occurrence, distribution, dereplication and efficient discovery of thiazolyl peptides by sensitive-resistant pair screening.  

PubMed

Natural products have been major sources of antibacterial agents and remain very promising. Frequent rediscoveries of known compounds hampers progress of new discoveries and demands development and utilization of new methods for rapid biological and chemical dereplication. This paper describes an efficient approach for discovery of new thiazolyl peptides by sensitive-resistant pair screening and dereplication in a time and cost-effective manner at industrial scale. A highly effective library-based dereplication of thiazolyl peptides by high resolution fourier transform liquid chromatography mass spectrometry (HRFTLCMS) has been developed, which can detect and dereplicate very low levels of thiazolyl peptides particularly when combined with miniaturized high-throughput 96-well solid-phase extraction separation, and as well can be automated. Combination of sensitive (susceptible)-resistant pair screening, diversified screening collection and miniaturized high-throughput SPE and HRFTLCMS techniques were applied for discovery of new thiazolyl peptides. The combined approach allowed for identification of over 24 thiazolyl peptides represented by three of the five structural subgroups, including three novel compounds. In addition, it is possible for the first time to mechanistically group three structural subgroups of over 24 thiazolyl peptides. Furthermore, these studies helped to understand natural frequency of distribution of these compounds and helped in discovery of new producing strains of many thiazolyl compounds. PMID:23801187

Singh, Sheo B; Zhang, Chaowei; Zink, Deborah L; Herath, Kithsiri; Ondeyka, John; Masurekar, Prakash; Jayasuriya, Hiranthi; Goetz, Michael A; Tormo, Jose Rubén; Vicente, Francisca; Martín, Jesús; González, Ignacio; Genilloud, Olga

2013-06-26

112

Understanding the limits of pair-distribution functions for nanoscale correlation function measurement  

NASA Astrophysics Data System (ADS)

We explore the ability of the pair-distribution function (pdf) to accurately measure medium-range correlation lengths in nanoscale crystalline materials. Through simple computer simulations of disordered fcc metals, we find that the presence of quadratic displacement fields is sufficient to mask topological order (mro) at the medium-range (1 3 nm). This reconciles previous measurements and modeling on amorphous silicon—which showed that paracrystalline structures give pair correlation functions which are almost indistinguishable from random networks—with the wide use of pdfs to measure correlation lengths in nanoscale crystalline materials. Through simple analytical considerations, we identify conditions when the pdf method can be trusted for mro measurements in nanocrystalline materials. We show that while the reliability of the technique is dependent on the nature of materials studied, in general the technique fails for sufficiently small grain size in compact materials. When the pdf method does not work, we have previously shown that fluctuation microscopy is a powerful tool to give information on mro.

Gibson, J. Murray

2007-11-01

113

Neutron-Proton Pairing Effect on One-Proton and Two-Proton Separation Energies in Rare-Earth Proton-Rich Nuclei  

NASA Astrophysics Data System (ADS)

The one-proton and two-proton separation energies are studied for "ordinary" and rare-earth proton-rich nuclei by including the isovector neutron-proton (np) pairing correlations using the BCS approximation. Even-even as well as odd nuclei are considered. In the latter case, the wave function is defined using the blocked-level technique. The single-particle energies used are those of a deformed Woods-Saxon mean field. It is shown that the np isovector pairing effects on the one-proton and two-proton separation energies are non-negligible. However, the only isovector BCS approximation seems to be inadequate for a good description of these quantities when including the np pairing effects: either a particle-number projection or the inclusion of the isoscalar pairing effect seems to be necessary. Another possible improvement would be a more realistic choice of the pairing strengths.

Hammache, F.; Allal, N. H.; Fellah, M.

2012-12-01

114

Nanostructure determination from the pair distribution function: a parametric study of the INVERT approach  

NASA Astrophysics Data System (ADS)

We present a detailed study of the mechanism by which the INVERT method (Cliffe et al 2010 Phys. Rev. Lett. 104 125501) guides structure refinement of disordered materials. We present a number of different possible implementations of the central algorithm and explore the question of algorithm weighting. Our analysis includes quantification of the relative contributions of variance and fit-to-data terms during structure refinement, which leads us to study the roles of density fluctuations and configurational jamming in the RMC fitting process. We present a parametric study of the pair distribution function solution space for C60, a-Si and a-SiO2, which serves to highlight the difficulties faced in developing a transferable weighting scheme.

Cliffe, Matthew J.; Goodwin, Andrew L.

2013-11-01

115

Nanostructure determination from the pair distribution function: a parametric study of the INVERT approach.  

PubMed

We present a detailed study of the mechanism by which the INVERT method (Cliffe et al 2010 Phys. Rev. Lett. 104 125501) guides structure refinement of disordered materials. We present a number of different possible implementations of the central algorithm and explore the question of algorithm weighting. Our analysis includes quantification of the relative contributions of variance and fit-to-data terms during structure refinement, which leads us to study the roles of density fluctuations and configurational jamming in the RMC fitting process. We present a parametric study of the pair distribution function solution space for C60, a-Si and a-SiO2, which serves to highlight the difficulties faced in developing a transferable weighting scheme. PMID:24140797

Cliffe, Matthew J; Goodwin, Andrew L

2013-10-18

116

High-energy neutron depth-dose distribution experiment.  

PubMed

A unique set of high-energy neutron depth-dose benchmark experiments were performed at the Los Alamos Neutron Science Center/Weapons Neutron Research (LANSCE/WNR) complex. The experiments consisted of filtered neutron beams with energies up to 800 MeV impinging on a 30 x 30 x 30 cm3 liquid, tissue-equivalent phantom. The absorbed dose was measured in the phantom at various depths with tissue-equivalent ion chambers. This experiment is intended to serve as a benchmark experiment for the testing of high-energy radiation transport codes for the international radiation protection community. PMID:14756177

Ferenci, M S; Hertel, N E

2003-01-01

117

Neutron spectra evaluation obtained from the track-size distribution on electrochemically etched CR-39 foils  

SciTech Connect

We are studying the relationship between neutron energy and track-size distribution on electrochemically etched CR-39 foils using a two-stage etching procedure. Although the electrochemical etching process alters the track size, we now find that the track diameter is related to the neutron energy even after the second stage (blowup) is completed. This relationship is complex, being effected by the etching parameters, including oven temperature, etching high voltage, and etching time. Current studies are directed at establishing the effect of each of these parameters on the track-size distribution and at determining an optimal etching procedure for neutron spectra evaluation. If neutron spectral information can be determined from the track-size distribution, dose can be calculated directly from the neutron fluence and spectrum.

Hankins, D.E.; Westermark, J.

1987-05-01

118

Investigation of the neutron energy distribution of the IRSN 241Am-Be(alpha,n) source.  

PubMed

The neutron energy distribution of the IRSN standard 241Am-Be(alpha,n) source was measured using a proton recoil liquid scintillator, BC501A, >1.65 MeV. The experimental data were compared with the ISO recommended neutron energy distribution for an Am-Be source and some significant discrepancies were observed. Monte Carlo simulations were then performed to investigate on the neutron source term in order to consider the different parameters between the IRSN Am-Be source and the one used to establish the neutron emission spectrum recommended by the ISO standard. The variation of the parameters of the source did not explain the remaining discrepancies. A good agreement with the experimental results was observed when the theoretical neutron energy distribution from Geiger and Van der Zwan was introduced in the study as new source term. These investigations showed that the ISO recommended Am-Be distribution might not be well suited to represent the neutron energy distribution of all Am-Be sources, and that the manufacturing of the sources might play a major role in the neutron fluence energy distribution. PMID:17276999

Magalotti, N; Lacoste, V; Lebreton, L; Gressier, V

2007-02-02

119

Production, Distribution, and Applications of Californium-252 Neutron Sources.  

National Technical Information Service (NTIS)

The radioisotope 252Cf is routinely encapsulated into compact, portable, intense neutron sources with a 2.6-year half-life. A source the size of a persons little finger can emit up to 1011 neutrons/s. Californ...

P. A. Balo J. B. Knauer R. C. Martin

1999-01-01

120

Electron-pair distributions in the C=C double bond. Effects of a push-pull substitution  

SciTech Connect

By application of a recently developed method, the populations of ionic and spin-alternant electron-pair distributions are calculated in ethylene, aminoethylene, nitroethylene, and 2-nitroethenamine, one of the simplest push-pull ethylenes. Occupation numbers, giving a measure of the existence of an ionic electron pair in one carbon atom and of a spin-alternant electron pair in the two carbon atoms of the ethylenic double bond, are investigated from ab initio MO wave functions. The effects of either an electron-donating or an electron-withdrawing group and the cooperative push-pull substitution are discussed.

Marcos, E.S.; Sanz, J.F. (Univ. of Sevilla (Spain)); Karafiloglou, P. (Aristotelian Univ. of Thessaloniki (Greece))

1990-04-05

121

Distinguishing S-plus-minus and S-plus-plus electron pairing symmetries by neutron spin resonances in superconducting Sodium-Iron-Cobalt-Arsenic (transitional temperature = 18 Kelvin)  

SciTech Connect

A determination of the superconducting (SC) electron pairing symmetry forms the basis for establishing a microscopic mechansim for superconductivity. For iron pnictide superconductors, the s{sup {+-}}-pairing symmetry theory predicts the presence of a sharp neutron spin resonance at an energy below the sum of hole and electron SC gap energies (E {le} 2{Delta}). Although the resonances have been observed for various iron pnictide superconductors, they are broad in energy and can also be interpreted as arising from the s{sup ++}-pairing symmetry with E {ge} 2{Delta}. Here we use inelastic neutron scattering to reveal a sharp resonance at E = 7 meV in the SC NaFe{sub 0.935}Co{sub 0.045}As (T{sub c} = 18 K). By comparing our experiments with calculated spin-excitations spectra within the s{sup {+-}} and s{sup ++}-pairing symmetries, we conclude that the resonance in NaFe{sub 0.935}Co{sub 0.045}As is consistent with the s{sup {+-}}-pairing symmetry, thus eliminating s{sup ++}-pairing symmetry as a candidate for superconductivity.

Das, Tanmoy [Los Alamos National Laboratory; Balatsky, Alexander V. [Los Alamos National Laboratory; Zhang, Chenglin [University of Tennessee, Knoxville, Tennessee; Li, Haifeng [Institut fur Festkorperforschung, Julich, Germany; Su, Yiki [The University of Tennessee, Knoxville, Tennessee; Nethertom, Tucker [The University of Tennessee, Knoxville, Tennessee; Redding, Caleb [The University of Tennessee, Knoxville, Tennessee; Carr, Scott [The University of Tennessee, Knoxville, Tennessee; Schneidewind, Astrid [Forschungsneutronenquelle Heinz, Garching, Germany; Faulhaber, Enrico [Gemeinsame Forschergruppe HZB, Berlin, Germany; Li, Shiliang [Institute of Physics, Chinese Academy of Sciences, Beijing, China; Yao, Daoxin [Sun Yat-Sen University, Guangzhou, China; Bruckel, Thomas [Institut fur Festkorperforschung, Julich, Germany; Dai, Pengchen [Institute of Physics, Chinese Academy of Sciences, Beijing, China; Sobolev, Oleg [Forschungsneutronenquelle Heinz, Garching, Germany

2012-06-05

122

Elastic and quasielastic barrier distributions for light neutron-rich nuclei: The role of neutron stripping channels  

NASA Astrophysics Data System (ADS)

Recent interest in the elastic and quasielastic barrier distributions of systems involving weakly bound light projectiles has concentrated on the influence of coupling to breakup. We show that, for light neutron-rich radioactive beams, single-neutron stripping also has an important effect on the calculated barrier distribution. We also show that the recent suggestion that for such systems the quasielastic barrier distribution will not be exactly equivalent to the true fusion barrier distribution seems to hold true, although in the particular case investigated here the discrepancy in the barrier peak position, 0.25 MeV, is considerably smaller than that found experimentally for the Li6+Sm144 system, 1.5 MeV, where breakup is considered to be most important.

Keeley, N.

2009-12-01

123

Elastic and quasielastic barrier distributions for light neutron-rich nuclei: The role of neutron stripping channels  

SciTech Connect

Recent interest in the elastic and quasielastic barrier distributions of systems involving weakly bound light projectiles has concentrated on the influence of coupling to breakup. We show that, for light neutron-rich radioactive beams, single-neutron stripping also has an important effect on the calculated barrier distribution. We also show that the recent suggestion that for such systems the quasielastic barrier distribution will not be exactly equivalent to the true fusion barrier distribution seems to hold true, although in the particular case investigated here the discrepancy in the barrier peak position, 0.25 MeV, is considerably smaller than that found experimentally for the {sup 6}Li+{sup 144}Sm system, 1.5 MeV, where breakup is considered to be most important.

Keeley, N. [Department of Nuclear Reactions, Andrzej Soltan Institute for Nuclear Studies, ul. Hoza 69, PL-00-681 Warsaw (Poland)

2009-12-15

124

Experimental comparison of 241Am-Be neutron fluence energy distributions.  

PubMed

(241)Am-Be(alpha,n) neutron sources provide one of the most commonly used neutron fields for routine calibration of neutron sensitive devices. The neutron energy distribution of the IRSN standard (241)Am-Be source was measured in the energy region above 1.65 MeV using a BC501A proton-recoil liquid scintillator. The experimental data were compared to the ISO-recommended neutron energy distribution for an (241)Am-Be source. Some differences in shape were observed, with large variations mainly within the energy interval 3-6 MeV and around 8 MeV. Within the framework of a collaboration between three national metrological institutes (PTB, Germany; NPL, UK and LNE-IRSN, France), the neutron energy distributions of (241)Am-Be sources at each laboratory have been compared. The IRSN-BC501A proton-recoil scintillator was used to measure all the sources. The results show different energy distributions a priori influenced by the origin of the source, i.e. the manufacturing process. The maximum deviation observed for the integral dose equivalent, in the measured BC501A energy range, is within the 4% uncertainty recommended by ISO standard 8529-2 to allow for variations of the neutron spectrum among different (241)Am-Be sources. However, knowledge of the energy distribution of an (241)Am-Be source provides a way to reduce the uncertainty in the dose equivalent rate delivered by such a source. PMID:17510201

Lebreton, L; Zimbal, A; Thomas, D

2007-05-17

125

Study of the Performance of Collision Short Time Approximation for Neutron Scattering Using Discrete Frequency Distribution.  

National Technical Information Service (NTIS)

Double differential cross sections for thermal neutrons, based on incoherent approximation, using continum distribution as discrete frequency set are theoretically estimated, regarding two models previously done. The FASTT computer program is used in orde...

A. B. D'Oliveira E. S. do Amorim O. B. Galvao

1981-01-01

126

Fission Fragment Distributions and Delayed Neutron Yields from Photon-Induced-Fission  

SciTech Connect

Fission fragment distributions and delayed neutron yields for 235U and 238U are provided by a complete modelization of the photofission process below 25 MeV. The absorption cross-section parameterization and the fission fragment distributions are given and compared to experimental data. The delayed neutron yields and the half-lives in terms of six groups are presented and compared to data obtained with a bremsstrahlung spectrum of 15 MeV.

David, J.-C.; Dore, D.; Giacri-Mauborgne, M.-L.; Ridikas, D.; Lauwe, A. van [DSM/DAPNIA/SPhN, CEA/Saclay, F-91191 Gif-sur-Yvette cedex (France)

2005-05-24

127

EFFECTS OF NUCLEAR SHELL ON THE DISTRIBUTION OF KINETIC ENERGY FRAGMENTS IN FAST NEUTRON FISSION  

Microsoft Academic Search

A double ionization chamber was used in finding the complete kinetic ; energy distribution of U²³⁸ fragments produced by 14.9-Mev neutron fission ; The obtained data were plotted and compared to the data on the kinetic energy ; distribution of fragments from the U²³⁾ fission by 14.1-Mev neutrons and to ; the calculated dispersion It was found that E and

A. N. Protopopov; I. A. Baranov; Yu. A. Selitskii; V. P. Eismont

1959-01-01

128

Neutron Momentum Distributions from ``Core Break-Up'' Reactions of Halo Nuclei  

Microsoft Academic Search

Neutron angular distributions from violent break-up reactions of 11Li and 11Be have been measured at 28 MeV\\/u and 280 MeV\\/u and at 41 MeV\\/u and 460 MeV\\/u, respectively. The derived neutron momentum distributions show a narrow component in transverse momentum that is within uncertainties independent of beam energy and target charge. This component is suggested to be simply related to

T. Nilsson; Th. Blaich; M. J. G. Borge; L. V. Chulkov; Th. W. Elze; H. Emling; H. Geissel; K. Grimm; D. Guillemaud-Mueller; P. G. Hansen; R. Holzmann; P. Hornshřj; F. Humbert; H. Irnich; L. Johannsen; B. Jonson; M. Keim; J. G. Keller; H. Klingler; J. V. Kratz; R. Kulessa; D. Lambrecht; Y. Leifels; M. Lewitowicz; A. Magel; M. F. Mohar; A. C. Mueller; G. Münzenberg; R. Neugart; F. Nickel; G H Nyman; A. Richter; K. Riisager; M.-G. Saint-Laurent; C. Scheidenberger; G. Schrieder; W. Schwab; B. M. Sherrill; H. Simon; O. Sorlin; K. Stelzer; J. Stroth; O. Tengblad; E. Wajda; K. Wilhelmsen Rolander; M. Zinser; E. Zude

1995-01-01

129

Neutron multiplicities and yields of correlated Zr-Ce and Mo-Ba fragment pairs in spontaneous fission of 252Cf  

NASA Astrophysics Data System (ADS)

High resolution ?-? and ?-?-? coincidences in the spontaneous fission of 252Cf were measured. Relative yields and neutron multiplicities from zero up to 10 were extracted directly for the first time in fission for the Zr-Ce and Mo-Ba correlated fragments pairs. The 0, 8, and the new 10 neutron emission yields for Mo-Ba are significantly larger than those reported previously for total 252Cf spontaneous fission. Our results demonstrate that the use of this high resolution ?-?-? coincidence technique can provide important, previously inaccessible data on fission.

Ter-Akopian, G. M.; Hamilton, J. H.; Oganessian, Yu. Ts.; Kormicki, J.; Popeko, G. S.; Daniel, A. V.; Ramayya, A. V.; Lu, Q.; Butler-Moore, K.; Ma, W.-C.; Deng, J. K.; Shi, D.; Kliman, J.; Polhorshy, V.; Morhac, M.; Greiner, W.; Sandelescu, A.; Cole, J. D.; Aryaeinejad, R.; Johnson, N. R.; Lee, I. Y.; McGowan, F. K.

1994-09-01

130

High pressure pair distribution function studies of Green River oil shale.  

SciTech Connect

The compression behavior of a silicate-rich oil shale from the Green River formation in the pressure range 0.0-2.4 GPa was studied using in situ high pressure X-ray pair distribution function (PDF) measurements for the sample contained within a Paris-Edinburgh cell. The real-space local structural information in the PDF, G(r), was used to evaluate the compressibility of the oil shale. Specifically, the pressure-induced reduction in the medium- to long-range atom distances ({approx}6-20 {angstrom}) yielded an average sample compressibility corresponding to a bulk modulus of ca. 61-67 GPa. A structural model consisting of a three phase mixture of the principal crystalline oil shale components (quartz, albite and Illite) provided a good fit to the ambient pressure PDF data (R {approx} 30.7%). Indeed the features in the PDF beyond {approx} {angstrom}, were similarly well fit by a single phase model of the highest symmetry, highly crystalline quartz component. The factors influencing the observed compression behavior are discussed.

Chapman, K. W.; Chupas, P. J.; Locke, D. R.; Winans, R. E.; Pugmire, R. J.; Univ. of Utah

2008-01-01

131

Properties and distribution of paired candidate stony meteorites at Meridiani Planum, Mars  

NASA Astrophysics Data System (ADS)

The Mars Exploration Rover Opportunity investigated four rocks, informally dubbed Barberton, Santa Catarina, Santorini, and Kasos, that are possible stony meteorites. Their chemical and mineralogical composition is similar to the howardite, eucrite, and diogenite group but with additional metal, similar to mesosiderite silicate clasts. Because of their virtually identical composition and because they appear to represent a relatively rare group of meteorites, they are probably paired. The four rocks were investigated serendipitously several kilometers apart, suggesting that Opportunity is driving across a larger population of similar rock fragments, maybe a meteorite strewn field. Small amounts of ferric Fe are a result of weathering. We did not observe evidence for fusion crusts. Four iron meteorites were found across the same area. Although mesosiderites are stony irons, a genetic link to these irons is unlikely. The stony meteorites probably fell later than the irons. The current atmosphere is sufficiently dense to land such meteorites at shallow entry angles, and it would disperse fragments over several kilometers upon atmospheric breakup. Alternatively, dispersion by spallation from an impacting meteoroid may have occurred. Santa Catarina and a large accumulation of similar rocks were found at the rim of Victoria crater. It is possible that they are associated with the impactor that created Victoria crater, but our limited knowledge about their distribution cannot exclude mere coincidence.

Schröder, Christian; Herkenhoff, Kenneth E.; Farrand, William H.; Chappelow, John E.; Wang, Wei; Nittler, Larry R.; Ashley, James W.; Fleischer, Iris; Gellert, Ralf; Golombek, Matthew P.; Johnson, Jeffrey R.; Klingelhöfer, Göstar; Li, Ron; Morris, Richard V.; Squyres, Steven W.

2010-11-01

132

Formalism for obtaining nuclear momentum distributions by the deep inelastic neutron scattering technique  

SciTech Connect

We present a formalism to obtain momentum distributions in condensed matter from neutron Compton profiles measured by the deep inelastic neutron scattering technique. The formalism describes exactly the neutron Compton profiles as an integral in the momentum variable y. As a result we obtain a Volterra equation of the first kind that relates the experimentally measured magnitude with the momentum distributions of the nuclei in the sample. The integration kernel is related with the incident neutron spectrum, the total cross section of the filter analyzer, and the detectors efficiency function. A comparison of the present formalism with the customarily employed approximation based on a convolution of the momentum distribution with a resolution function is presented. We describe the inaccuracies that the use of this approximation produces, and propose a data treatment procedure based on the present formalism.

Blostein, J.J.; Dawidowski, J.; Granada, J. R. [Consejo Nacional de Investigaciones Cientificas y Tecnicas, Centro Atomico Bariloche and Instituto Balseiro, Comision Nacional de Energia Atomica, Universidad Nacional de Cuyo (8400) Bariloche (Argentina)

2005-02-01

133

Impact of prompt-neutron corrections on final fission-fragment distributions  

NASA Astrophysics Data System (ADS)

Background: One important quantity in nuclear fission is the average number of prompt neutrons emitted from the fission fragments, the prompt neutron multiplicity, ?Ż. The total number of prompt fission neutrons, ?Żtot, increases with increasing incident neutron energy. The prompt-neutron multiplicity is also a function of the fragment mass and the total kinetic energy of the fragmentation. Those data are only known in sufficient detail for a few thermal-neutron-induced fission reactions on, for example, 233,235U and 239Pu. The enthralling question has always been asked how the additional excitation energy is shared between the fission fragments. The answer to this question is important in the analysis of fission-fragment data taken with the double-energy technique. Although in the traditional approach the excess neutrons are distributed equally across the mass distribution, a few experiments showed that those neutrons are predominantly emitted by the heavy fragments.Purpose: We investigated the consequences of the ?(A,TKE,En) distribution on the fission fragment observables.Methods: Experimental data obtained for the 234U(n,f) reaction with a Twin Frisch Grid Ionization Chamber, were analyzed assuming two different methods for the neutron evaporation correction. The effect of the two different methods on the resulting fragment mass and energy distributions is studied.Results: We found that the preneutron mass distributions obtained via the double-energy technique become slightly more symmetric, and that the impact is larger for postneutron fission-fragment distributions. In the most severe cases, a relative yield change up to 20-30% was observed.Conclusions: We conclude that the choice of the prompt-neutron correction method has strong implications on the understanding and modeling of the fission process and encourages new experiments to measure fission fragments in coincidence with prompt fission neutrons. Even more, the correct determination of postneutron fragment yields has an impact on the reliable assessment of the nuclear waste inventory, as well as on the correct prediction of delayed neutron precursor yields.

Al-Adili, A.; Hambsch, F.-J.; Pomp, S.; Oberstedt, S.

2012-11-01

134

Neutrino scattering off pair-breaking and collective excitations in superfluid neutron matter and in color-flavor-locked quark matter  

Microsoft Academic Search

We calculate the correlation functions needed to describe the linear response of superfluid matter, and go on to calculate the differential cross section for neutral-current neutrino scattering in superfluid neutron matter and in color-flavor-locked quark matter. We report the first calculation of scattering rates that includes neutrino interactions with both pair-breaking excitations and low-lying collective excitations (Goldstone modes). Our results

Joydip Kundu; Sanjay Reddy

2004-01-01

135

Calculation of neutron flux distributions in BNCT using removal-diffusion theory  

SciTech Connect

Boron neutron capture therapy (BNCT) is under investigation as a treatment modality for brain tumors. Successful routine use of BNCT will require a knowledge of the radiation dose distribution in a patient`s head prior to treatment. This will allow optimization of the treatment to fit the needs of individual patients. Determination of the dose distribution begins with calculation of the neutron flux distribution in the head. Most efforts to date have relied on Monte Carlo or discrete ordinates techniques to calculate this flux distribution. Use of removal-diffusion theory has the advantage of a relatively short computer time to complete a calculation. Previous work by our group has shown good agreement between neutron flux distributions calculated using removal-diffusion theory and Monte Carlo methods for parallel incident neutrons and a rectangular parallelepiped water phantom. This work compares neutron flux distributions calculated using removal-diffusion theory and Monte Carlo methods for a homogeneous ellipsoidal water phantom that models the human head.

Niemkiewicz, J.; Blue, T.E.; Gupta, N.

1994-12-31

136

In situ X-ray pair distribution function analysis of geopolymer gel nanostructure formation kinetics.  

PubMed

With the ever-increasing environmentally-driven demand for technologically advanced structural materials, geopolymer cement is fast becoming a viable alternative to traditional cements due to its proven engineering characteristics and the reduction in CO2 emitted during manufacturing (as much as 80% less CO2 emitted in manufacture, compared to ordinary Portland cement). Nevertheless, much remains unknown regarding the kinetics of reaction responsible for nanostructural evolution during the geopolymerisation process. Here, in situ X-ray total scattering measurements and pair distribution function (PDF) analysis are used to quantify the extent of reaction as a function of time for alkali-activated metakaolin/slag geopolymer binders, including the impact of various activators (alkali hydroxide/silicate) on the kinetics of the geopolymerisation reaction. Quantifying the reaction process in situ from X-ray PDF data collected during the initial ten hours can provide an estimate of the total reaction extent, but when combined with data obtained at longer times (128 days here) enables more accurate determination of the overall rate of reaction. To further assess the initial stages of the geopolymerisation reaction process, a pseudo-single step first order rate equation is fitted to the extent of reaction data, which reveals important mechanistic information regarding the role of free silica in the activators in the evolution of the binder systems. Hence, it is shown that in situ X-ray PDF analysis is an ideal experimental local structure tool to probe the reaction kinetics of complex reacting systems involving transitions between disordered/amorphous phases, of which geopolymerisation is an important example. PMID:23450172

White, Claire E; Provis, John L; Bloomer, Breaunnah; Henson, Neil J; Page, Katharine

2013-02-28

137

Theoretical modeling for neutron elastic scattering angular distribution in the fast energy range  

SciTech Connect

One of the major issues of neutron scattering modeling in the fast energy range is the contribution of compound elastic and inelastic scattering to the total scattering process. The compound component may become large at very low energies where the angular distribution becomes 90-degree symmetric in the center-of-mass system. Together with the shape elastic component, the elastic scattering gives slightly forward-peaked angular distributions in the fast energy range. This anisotropic angular distribution gives high sensitivities to many important nuclear reactor characteristics, such as criticality and neutron shielding. In this talk we describe how the anisotropic angular distributions are calculated within the statistical model framework, including the case where strongly coupled channels exist, by combining the coupled-channels theory with the Hauser-Feshbach model. This unique capability extension will have significant advantages in understanding the neutron scattering process for deformed nuclei, like uranium or plutonium, on which advanced nuclear energy applications center.

Kawano, Toshihiko [Los Alamos National Laboratory

2010-12-07

138

Prediction of in-phantom dose distribution using in-air neutron beam characteristics for BNCS  

SciTech Connect

A monoenergetic neutron beam simulation study is carried out to determine the optimal neutron energy range for treatment of rheumatoid arthritis using radiation synovectomy. The goal of the treatment is the ablation of diseased synovial membranes in joints, such as knees and fingers. This study focuses on human knee joints. Two figures-of-merit are used to measure the neutron beam quality, the ratio of the synovium absorbed dose to the skin absorbed dose, and the ratio of the synovium absorbed dose to the bone absorbed dose. It was found that (a) thermal neutron beams are optimal for treatment, (b) similar absorbed dose rates and therapeutic ratios are obtained with monodirectional and isotropic neutron beams. Computation of the dose distribution in a human knee requires the simulation of particle transport from the neutron source to the knee phantom through the moderator. A method was developed to predict the dose distribution in a knee phantom from any neutron and photon beam spectra incident on the knee. This method was revealed to be reasonably accurate and enabled one to reduce by a factor of 10 the particle transport simulation time by modeling the moderator only.

Verbeke, Jerome M.

1999-12-14

139

Angular distribution of neutrons from deuterated cluster explosions driven by femtosecond laser pulses  

SciTech Connect

We have studied experimentally the angular distributions of fusion neutrons from plasmas of multi-keV ion temperature, created by 40 fs, multi-TW laser pulses in dense plumes of D{sub 2} and CD{sub 4} clusters. A slight anisotropy in the neutron emission is observed. We attribute this anisotropy to the fact that the differential cross section for DD fusion is anisotropic even at low collision energies, and this, coupled with the geometry of the gas jet target, leads to beam-target neutrons that are slightly directed. The qualitative features of this anisotropy are confirmed by Monte Carlo simulations.

Buersgens, F.; Madison, K. W.; Symes, D. R.; Hartke, R.; Osterhoff, J.; Grigsby, W.; Dyer, G.; Ditmire, T. [The Texas Center for High Intensity Laser Science, Department of Physics, University of Texas at Austin, Austin, Texas 78712 (United States)

2006-07-15

140

Angular distribution of neutrons from deuterated cluster explosions driven by femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

We have studied experimentally the angular distributions of fusion neutrons from plasmas of multi-keV ion temperature, created by 40fs , multi-TW laser pulses in dense plumes of D2 and CD4 clusters. A slight anisotropy in the neutron emission is observed. We attribute this anisotropy to the fact that the differential cross section for DD fusion is anisotropic even at low collision energies, and this, coupled with the geometry of the gas jet target, leads to beam-target neutrons that are slightly directed. The qualitative features of this anisotropy are confirmed by Monte Carlo simulations.

Buersgens, F.; Madison, K. W.; Symes, D. R.; Hartke, R.; Osterhoff, J.; Grigsby, W.; Dyer, G.; Ditmire, T.

2006-07-01

141

Measurement of neutron and ?-ray intensity distributions with an optical fiber-scintillator detector  

Microsoft Academic Search

On the tip of an optical fiber, a very small amount of ZnS(Ag) scintillator mixed with neutron converter and adhesive paste was painted, which can be inserted into a narrow space and moved by a fiber-driving unit controlled with a personal computer. The presented method made it possible to measure neutron flux distributions in critical assemblies, research reactors or other

C. Mori; A. Uritani; H. Miyahara; T. Iguchi; S. Shiroya; K. Kobayashi; E. Takada; R. F. Fleming; Y. K. Dewaraja; D. Stuenkel; G. F. Knoll

1999-01-01

142

Interpreting the neutron's electric form factor: Rest frame charge distribution or foldy term?  

SciTech Connect

The neutron's electric form factor contains vital information on nucleon structure, but its interpretation within many models has been obscured by relativistic effects. The author demonstrates that, to leading order in the relativistic expansion of a constituent quark model, the Foldy term cancels exactly against a contribution to the Dirac form factor F{sub 1} to leave intact the naive interpretation of G{sup n}{sub E} as arising from the neutron's rest frame charge distribution.

Nathan Isgur

1998-12-01

143

Neutron spectra evaluation obtained from the track-size distribution on electrochemically etched CR39 foils  

Microsoft Academic Search

We are studying the relationship between neutron energy and track-size distribution on electrochemically etched CR-39 foils using a two-stage etching procedure. Although the electrochemical etching process alters the track size, we now find that the track diameter is related to the neutron energy even after the second stage (blowup) is completed. This relationship is complex, being effected by the etching

D. E. Hankins; J. Westermark

1987-01-01

144

Distribution of fission yields for fission spectrum neutron-induced fission of uranium-238  

Microsoft Academic Search

The mass-yield distribution for the neutron-induced fission of ²³⁸U by degraded fission spectrum neutrons with an average energy of 1.52 MeV has been measured radiochemically for 26 mass chains in the region A = 89 to 153. Germanium-lithium gamma-ray spectroscopy coupled with beta-particle counting techniques was used to determine the absolute activities of each nuclide measured. The absolute cumulative fission

D. C. Harris; J. N. Beck; W. L. Raines; J. T. Harvey; J. L. Meason; H. L. Wright

1977-01-01

145

Nuclear matter distributions of neutron-rich halo nuclei from intermediate energy elastic proton scattering in inverse kinematics  

Microsoft Academic Search

Neutron-rich light nuclei near or at the neutron drip line have attracted much attention in recent years since there is clear evidence that they reveal a qualitatively new type of nuclear structure, namely an extended distribution of valence neutrons surrounding a compact nuclear core. A brief overview is given on this phenomenon, and on the various methods which gave first

P. Egelhof

2001-01-01

146

Solid state NMR and pair distribution function studies of silicon electrodes for lithium-ion batteries  

NASA Astrophysics Data System (ADS)

The universally used negative electrode material in a LIB is carbon, because of its moderate capacity (372 mAhg-1 for graphite), cyclability and high rate capability. However, new, low cost, safe electrode materials with higher capacities are still urgently required for both portable and transportation applications. Silicon anodes are particularly attractive alternatives to carbon with extremely high gravimetric energy densities (3572 mAhg-1). Compared to graphite, silicon has a massive volumetric capacity of 8322 mAhcm-3 (calculated based on the original volume of silicon) which is approximately ten times that graphite. At room temperature, upon electrochemical lithiation, silicon undergoes a crystalline to amorphous phase transition forming a lithiated amorphous silicide phase. Unfortunately, due to the amorphous nature of the lithiated silicides, it is not possible to monitor all the structural changes that occur during lithium insertion/removal with conventional methods such as diffraction. The short range order of the amorphous materials remains unknown, preventing attempts to optimize performance based on electrochemical-structure correlations. In this work, a combination of local structure probes, ex-situ 7Li nuclear magnetic resonance (NMR) studies and pair distribution function (PDF) analysis of X-ray data was applied to investigate the changes in short range order that occur during the initial charge and discharge cycles. The distinct electrochemical profiles observed subsequent to the 1 st discharge have been shown to be associated with the formation of distinct amorphous lithiated silicide structures. A (de)lithiation model consisting of four different mechanisms, each being valid for regions of the charge or discharge process is proposed to explain the hysteresis and the steps in the electrochemical profile observed during lithiation and delithiation of Si. A spontaneous reaction of the fully lithiated lithium silicide with the electrolyte is directly observed in the in situ NMR experiments; this mechanism results in self-discharge, and potentially capacity loss. The rate of this self-discharge process is much slower when CMC (carboxymethylcellulose) is used as the binder. Previous work has shown that the electrochemical performance of nanoparticulate crystalline silicon is different from the bulk. The lithiation and delithiation mechanisms of nano-Si for lithium ion batteries are studied by using ex-situ solid state MAS NMR and PDF analysis. The main differences vs. bulk lithiation and delithiation are identified by characterizing the amorphous phases formed.

Key, Baris

147

Mars Odyssey neutron data: 1. Data processing and models of water-equivalent-hydrogen distribution  

NASA Astrophysics Data System (ADS)

For more than 7 years, the Los Alamos built Mars Odyssey Neutron Spectrometer (MONS) has measured the neutron albedo from Mars in three consecutive energy bands: thermal, epithermal, and fast neutron ranges. This paper synthesizes the teamwork on the optimization of the signal extraction, the corrections for observational biases and instrument specific characteristics. Results are presented for neutron time series with an emphasis on seasonal variations at the poles. Frost-free data are mapped on to the surface, and the apparent random nature of the counting-rate distribution per pixel is analyzed: for epithermal neutrons, the relative standard deviation is less than 0.5% equatorward of 45° and up to 2.5% above this latitude limit; for thermal neutrons it is 1% and 2.5% respectively; and for fast neutrons it is 3% and 5.5%, respectively. New science results are obtained with regards to the distribution of water-equivalent hydrogen (WEH) on Mars. Under the assumption of a single uniform distribution of hydrogen with depth, WEH abundances range from 2% near the equator to 80% at the poles, with ą2% to 4.5% relative error bars. A best approximation to a two-layered global distribution of a lower-level hydrogen-rich substrate beneath an upper layer of varying thicknesses is generated using an average hydration level of an upper layer of 2 wt %, derived in the paper by Feldman et al. (2011). Such results are discussed and compared with regard to previous publications on the MONS instrument.

Maurice, S.; Feldman, W.; Diez, B.; Gasnault, O.; Lawrence, D. J.; Pathare, A.; Prettyman, T.

2011-11-01

148

Theory for Site-Site Pair Distribution Functions of Molecular Fluids. Ii. Approximations for the Percus--Yevick Site-Site Direct Correlation Functions.  

National Technical Information Service (NTIS)

A theory for site-site pair distribution functions of molecular fluids is derived from the Ornstein-Zernike equation. Atom-atom pair distribution functions of this theory which were obtained by using different approximations for the Percus-Yevick site-sit...

E. Johnson

1977-01-01

149

Personnel neutron dosimetry applications of track-size distributions on electrochemically etched CR-39 foils  

SciTech Connect

The track-size distribution on electrochemically etched CR-39 foils can be used to obtain some limited information on the incident neutron spectra. Track-size distributions on CR-39 foils can also be used to determine if the tracks were caused by neutrons or if they are merely background tracks (which have a significantly different track-size distribution). Identifying and discarding the high-background foils reduces the number of foils that must be etched. This also lowers the detection limit of the dosimetry system. We have developed an image analyzer program that can more efficiently determine the track density and track-size distribution, as well as read the laser-cut identification numbers on each foil. This new image analyzer makes the routine application of track-size distributions on CR-39 foils feasible. 2 refs., 3 figs.

Hankins, D.E.; Homann, S.G.; Westermark, J.

1988-09-01

150

Derivation of partial pair distribution functions for amorphous FeTb from electron scattering data based on a new concept  

Microsoft Academic Search

In this work we present pair distribution functions (PDFs) of amorphous Fe1-xTbx (x=0.1-0.5) with a high spatial resolution better than 0.02 nm obtained from electron diffraction experiments. The short-range order of FeTb alloys with up to 32 at.% Tb content is described quantitatively as an arrangement of the known crystalline FeTb phases with various concentrations and structures by superposing PDFs

M. Tewes; J. Zweck; H. Hoffmann

1994-01-01

151

Distribution of Prompt Neutron Emission Probability for Fission Fragments in Spontaneous Fission of 252Cf and 244,248Cm  

NASA Astrophysics Data System (ADS)

Neutrons emitted in fission events were measured separately for each complementary fragment in correlation with fission fragment energies. Two high-efficiency Gd-loaded liquid scintillator tanks were used for neutron registration. Fission fragment energies were measured using a twin Frisch gridded ionization chamber with a pinhole collimator. The neutron multiplicity distributions were obtained for each value of the fission fragment mass and energy and corrected for neutron registration efficiency, background, and pile-up. The dependency of these distributions on fragment mass and energy for different energy and mass bins as well as mass and energy distribution of fission fragments are presented and discussed.

Vorobyev, A. S.; Dushin, V. N.; Hambsch, F.-J.; Jakovlev, V. A.; Kalinin, V. A.; Laptev, A. B.; Petrov, B. F.; Shcherbakov, O. A.

2005-05-01

152

Revised prompt neutron emission multiplicity distributions for 236,238Pu  

NASA Astrophysics Data System (ADS)

The prompt neutron emission multiplicity distributions and average values (P and , respectively) for nuclei which decay via spontaneous fission have been reevaluated. In the cases of 236Pu and 238Pu, inconsistencies were found in the recommended values for P and that were given in the most recent compilation of neutron emission multiplicity distributions from the fission of uranium and transuranium nuclides. In correcting for these inconsistencies, the values of for 236Pu and 238Pu have now been revised to 2.07ą0.13 and 2.19ą0.07, respectively. The corresponding neutron emission probabilities for these two nuclei have also been revised in order to take into account the new recommended values.

Santi, P.; Beddingfield, D. H.; Mayo, D. R.

2005-07-01

153

Measurement of dose distributions of linear energy transfer in matter irradiated by fast neutrons  

SciTech Connect

A detector has been developed and used to measure dose distributions versus linear energy transfer to thin gas targets in spherical geometry from fast neutron irradiation of tissue-equivalent plastic and carbon. The detector is a hemispherical proportional counter with a Cs(T1) scintillator at the center of the hemisphere. The coincidence of the proportional counter signals constrain the measurements to charged particles traversing the radius of the hemisphere. The charged particle energy deposition distributions are directly measured for a known pathlength. The A-150 kerma factor was measured at a neutron energy of 14.8 MeV and is in agreement with tabulated values. The carbon kerma factor measurements are less than the tabulated value at 14.8 MeV. The alpha-particle production in carbon was measured for neutron energies from 14.1 to 14.8 MeV and is compared with existing data.

Schell, M.C. (Cleveland Clinic Foundation, Department of Radiation Therapy, Cleveland, Ohio 44195 (US)); Pearson, D.W.; DeLuca, P.M. Jr. (University of Wisconsin, Madison, Wisconsin 53706 (USA)); Haight, R.C. (Lawrence Livermore National Laboratory, Livermore, California 94550 (USA))

1990-01-01

154

Hyperfine anomaly in Be isotopes in the cluster model and the neutron spatial distribution  

SciTech Connect

The study of the hyperfine anomaly of neutron rich nuclei, in particular, neutron halo nuclei, can give a very specific and unique way to measure their neutron distribution and confirm a halo structure. The hyperfine structure anomaly in Be{sup +} ions is calculated with a realistic electronic wave function, obtained as a solution of the Dirac equation. In the calculations, the Coulomb potential modified by the charge distribution of the clustered nucleus and three electrons in the 1s{sup 2}2s configuration is used. The nuclear wave function is obtained in the core+nucleon model of {sup 9,11}Be. The aim of this study is to test whether the hyperfine structure anomaly reflects a halo structure in {sup 11}Be.

Parfenova, Y.; Leclercq-Willain, Ch. [Physique Nucleaire Theorique et Physique Mathematique, CP229, Universite Libre de Bruxelles, B-1050 Brussels (Belgium)

2005-08-01

155

Effects of Fluid Temperature and Velocity Distributions on Neutron Spectra  

NASA Astrophysics Data System (ADS)

We commonly summarize the spectrum of 14 MeV neutrons produced by a laser fusion capsule by just a yield and a temperature, as if it were a uniform stationary fluid element. However, burn in a real fusion capsule occurs over a wide range of temperatures, and the velocity of the burning fuel is not negligible compared to thermal velocities. Even at low ?r, absent any scattering, these effects cause the shape of the 14 MeV peak to depart significantly from a Gaussian, and cause its width, that is, the observed burn temperature, to vary depending on viewing direction. We describe our ongoing efforts to cope with these complexities in the analysis of data from the National Ignition Facility. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Munro, D. H.; Hatchett, S. P.; Spears, B. K.

2011-11-01

156

LETTER: Ion distribution function and radial profile of neutron production rate in spherical inertial electrostatic confinement plasmas  

Microsoft Academic Search

The radial profile of the neutron production rate in spherical inertial electrostatic confinement plasmas is investigated. The electrostatic potential is obtained by solving the Poisson equation, and by using the potential; the fuel ion velocity distribution function is determined at each radial point. From the velocity distribution function, the neutron production rate is accurately evaluated. Numerical results show that if

H. Matsuura; T. Takaki; K. Funakoshi; Y. Nakao; K. Kudo

2000-01-01

157

Correlation between ion\\/electron distribution functions and neutron production rate in spherical inertial electrostatic confinement plasmas  

Microsoft Academic Search

Correlation between ion\\/electron distribution functions and device performance, i.e. potential structure, density profile and neutron production rate, in spherical inertial electrostatic confinement plasmas is studied by solving the Poisson equation for various deuteron and electron distribution functions. For several combinations of the ion and electron convergences, dependence of the total neutron production rate on discharged current is discussed. It is

H. Matsuura; K. Funakoshi; Y. Nakao

2003-01-01

158

Neutron coincidence counting based on time interval analysis with dead time corrected one and two dimensional Rossi-alpha distributions: an application for passive neutron waste assay.  

National Technical Information Service (NTIS)

The report describes a new neutron multiplicity counting method based on Rossi-alpha distributions. The report also gives the necessary dead time correction formulas for the multiplicity counting method. The method was tested numerically using a Monte Car...

M. Bruggeman P. Baeten W. De Boeck R. Carchon

1996-01-01

159

Fast-ion distributions from third harmonic ICRF heating studied with neutron emission spectroscopy  

NASA Astrophysics Data System (ADS)

The fast-ion distribution from third harmonic ion cyclotron resonance frequency (ICRF) heating on the Joint European Torus is studied using neutron emission spectroscopy with the time-of-flight spectrometer TOFOR. The energy dependence of the fast deuteron distribution function is inferred from the measured spectrum of neutrons born in DD fusion reactions, and the inferred distribution is compared with theoretical models for ICRF heating. Good agreements between modelling and measurements are seen with clear features in the fast-ion distribution function, that are due to the finite Larmor radius of the resonating ions, replicated. Strong synergetic effects between ICRF and neutral beam injection heating were also seen. The total energy content of the fast-ion population derived from TOFOR data was in good agreement with magnetic measurements for values below 350 kJ.

Hellesen, C.; Gatu Johnson, M.; Andersson Sundén, E.; Conroy, S.; Ericsson, G.; Eriksson, J.; Sjöstrand, H.; Weiszflog, M.; Johnson, T.; Gorini, G.; Nocente, M.; Tardocchi, M.; Kiptily, V. G.; Pinches, S. D.; Sharapov, S. E.; EFDA Contributors, JET

2013-11-01

160

Energy distribution of muon pairs: A signal for the creation of a baryon-rich quark-gluon plasma in relativistic heavy-ion collisions  

SciTech Connect

A study of the energy distribution of muon pairs and photon pairs produced in ultrarelativistic heavy-ion collisions shows that muon pairs may be better signatures than photon pairs for the detection of a baryon-rich quark-gluon plasma (QGP). The value of the transverse mass of the muon pairs at which the {rho}-meson peak disappears from their invariant-mass spectrum is sensitive to the equation of state of the QGP. Hence dimuons are useful not only for the detection of a QGP but also for a study of its equation of state.

Janhavi, G.; Sakthi Murugesan, K.; Raja, K.; Subramanian, P.R. (Department of Nuclear Physics, University of Madras, Madras 600 025 (India))

1992-12-01

161

Proton and neutron density distributions for A=16-58 nuclei  

Microsoft Academic Search

A new method of calculating nuclear charge and matter distributions is described. It uses the sum of the squares of single-particle wavefunctions to give a first approximation and then iterates the proton and neutron densities in a formalism that takes into account the interaction between these densities and between the valence and core nucleons. The single-particle potentials are adjusted to

B. A. Brown; S. E. Massen; P. E. Hodgson

1979-01-01

162

Post-Neutron Mass Distribution for Sup 232 U(Nsub(Th),F).  

National Technical Information Service (NTIS)

The post-neutron absolute mass yields of 35 products from 25 mass chains for sup 232 U(nsub(th),f) have been determined by gamma -ray spectroscopy. The resulting mass distribution for sup 232 U is compared with the corresponding existing data on sup 233 U...

M. Haddad M. Asghar J. Crancon C. Hamelin G. Lhospice

1985-01-01

163

Critical experiments with strong neutron absorbers heterogeneously distributed throughout uranyl nitrate solution  

Microsoft Academic Search

Several critical experiments were performed for a number of strong neutron absorbers periodically distributed throughout a tank filled with high-concentration fissile solution, These experiments served as a pilot study for a novel means of storing fissile solutions at a nuclear production plant handling such solutions. The configuration also approximates one commonly used method (Raschig rings) of assuring criticality safety in

1991-01-01

164

Distribution of trace elements in the human body determined by neutron activation analysis  

Microsoft Academic Search

Neutron activation analysis and instrumental semiconductor gamma-ray spectrometry were used for analysis of 20 trace elements in 10 autopsied human organs and tissues (liver, kidney, cerebrum, cerebellum, heart, muscle, pancreas, spleen, lung, and aorta) from 63 Japanese persons, whose ages ranged from 15 days to 85 yr. Distributions of aluminum, bromine, magnesium, manganese, rubidium, selenium, and vanadium in human body

M. Yukawa; M. Suzuki-Yasumoto; K. Amano; M. Terai

1980-01-01

165

Depth distribution of boron determined by slow neutron induced lithium ion emission  

Microsoft Academic Search

Neutron Depth Profiling (NDP) has been established as a non-destructive technique to determine the near surface distribution of light elements, particularly boron. By analyzing the residual energy spectrum of the emitted particles of known initial energy as a result of nuclear capture within the target material, information about the site and amount of the reactions can be deduced. In the

Huaiyu H. Chen-Mayer; George P Lamaze

1998-01-01

166

Determination of momentum distributions from deep inelastic neutron scattering experiments: A Bayesian study  

SciTech Connect

A Bayesian analysis shows that the determination of momentum distributions in quantum fluids and solids by deep inelastic neutron scattering is an extremely ill-posed problem. The argument is illustrated with the issue of the Bose condensate fraction in superfluid /sup 4/He. 10 refs., 4 figs.

Sivia, D.S.; Silver, R.N.

1988-01-01

167

Measurement of Dose Distributions in let Produced in Matter by Fast Neutron Irradiation  

NASA Astrophysics Data System (ADS)

A detector has been developed and used to measure the dose distributions vs. LET in thin gas targets is spherical geometry from fast neutron irradiation of tissue equivalent plastic and carbon. These data are a physical characterization of the fast neutron interactions with the detector wall material and provide the physical basis for material damage studies in fusion technology. The LET Detector could measure charged particle types and make available data for the predictions of radiobiological effect with the Track Structure Model of Katz. The detector is a hemispherical proportional counter with an inorganic scintillator at the center of the hemisphere. The coincidence of the proportional counter and scintillator signals constrain the measurements to the charged particles traversing only the radius of the hemispherical proportional counter. The charged particle energy deposition distributions are directly measured for a known pathlength. The measured charged particle energy loss distributions are compared with theoretical linear energy transfer spectra and both measured and calculated event size distributions. The kerma in the wall material from fast neutron irradiation is inferred from the dose in the gas by means of the Bragg -Gray cavity theory. The measured kerma in carbon and A -150 plastic from fast neutron bombardment are compared with the calculated kerma based on microscopic cross sections.

Schell, Michael Charles

168

Productivity of Pair Programming in a Distributed Environment - Results from Two Controlled Case Studies  

Microsoft Academic Search

Several methods and techniques have surfaced to address the ongoing concerns of quality and productivity of software development.\\u000a Among these is the Pair Programming (PP) method, which has gained a lot off attention through being an essential part of an\\u000a agile software development methodology called the eXtreme Programming (XP). In this paper, we present the results of two controlled\\u000a case

Sami Pietinen; Vesa Tenhunen; Markku Tukiainen

2008-01-01

169

Nonreciprocal elastic scattering of unpolarized neutrons by magnetic systems with the noncoplanar magnetization distribution  

SciTech Connect

It is shown that the elastic scattering of unpolarized neutrons by systems with the noncoplanar spatial magnetic induction distribution in nonreciprocal. Two systems with the noncoplanar distribution of the magnetic field are proposed and calculated, i.e., a nanoparticle with vortex magnetization and a system of three magnetic mirrors. It is shown that, under certain conditions, the nonreciprocity is rather large and can be observed experimentally.

Tatarskiy, D. A., E-mail: tatarsky@ipmras.ru; Udalov, O. G.; Fraerman, A. A. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

2012-10-15

170

Distribution patterns of firearm discharge residues as revealed by neutron activation analysis  

Microsoft Academic Search

A systematic investigation using a variety of handguns has revealed the existence of distinguishable distribution patterns\\u000a of firearm discharge residues on surfaces below the flight path of a bullet. The residues are identifiable even at distances\\u000a of 12 meters from the gun using nondestructive neutron activation analysis. The results of these investigations show that\\u000a the distribution pattern for a gun

K. K. S. Pillay; D. C. Driscoll; W. A. Jester

1975-01-01

171

New method for measurement of energy and angular distributions of prompt fission neutrons  

NASA Astrophysics Data System (ADS)

The energy (E) and the angle (?) dependent emission probabilities N(E, ?) of prompt fission neutrons are measured by neutron time-of-flight spectroscopy as well as by a direction-sensitive method of fragment spectroscopy based on two parallel-plate avalanche counters (PPAC, one position-sensitive). Due to the determination of ? by the measurement of fragment direction for a fixed neutron detector position systematic errors are considerably reduced. The arrangement permits the precise measurement of neutron angular distributions depending on E for the whole angular range (180°) with a rather high angle point density (up to 120 per 180°). The angular resolution amounts to >~3° depending on the chosen geometry. Pulse shape discrimination is used for background (?-rays, cosmic muons) suppression when employing NE213 scintillators for neutron detection (1-10 MeV range). 6Li-glass scintillators serve for the N(E, ?) measurement at low energy. The experimental setup, the multiparameter data handling, and the analysis procedures including corrections are described. Results on 252Cf(sf) neutron emission covering the energy range 0.1-10 MeV (up to 18 MeV in the polar direction) are presented and discussed in comparison with previous data.

Märten, Horst; Richter, Dietmar; Seeliger, Dieter; Fromm, Wolf Dietrich; Neubert, Waldemar; Lajtai, Albert

1988-02-01

172

The Differential cross section distribution of Drell-Yan dielectron pairs in the z boson mass region  

SciTech Connect

We report on a measurement of the rapidity distribution, d{sigma}/dy, for Z=Drell-Yan {yields} ee events produced in p{bar p} collisions at {radical}s = 1.96 TeV. The data sample consists of 2.13 fb{sup -1} corresponding to about 160,000 Z/Drell-Yan {yields} ee candidates in the Z boson mass region collected by the Collider Detector at Fermilab. The d{sigma}/dy distribution, which is measured over the full kinematic range for e{sup +}e{sup -} pairs in the invariant mass range 66 < M{sub ee} < 116 GeV/c{sup 2}, is compared with theory predictions. There is good agreement between the data and predictions of Quantum Chromodynamics in Next to Leading Order with the CTEQ6.1M Parton Distribution Functions.

Han, Jiyeon; /Rochester U.

2008-11-01

173

Calculation of the angular distribution of delay times in neutron scattering on {sup 58}Ni nuclei  

SciTech Connect

Angular distributions of average delay times and time variances are calculated for resonance-neutron scattering on {sup 58}Ni nuclei at neutron energies in the range E = 600-700 keV. The effect of the energy spectrum and polarization of the beam on the scattering-process time is discussed. The angular dependence of the time law is also considered for the decay of an intermediate compound nuclear system. It is shown that the results of stationary and nonstationary calculations are in good agreement.

Prokopets, G. A., E-mail: gaprok@uos.net.ua [National University of Kyiv-Mohyla Academy (Ukraine)

2011-05-15

174

Spherical momentum distribution of the protons in hexagonal ice from modeling of inelastic neutron scattering data.  

PubMed

The spherical momentum distribution of the protons in ice is extracted from a high resolution deep inelastic neutron scattering experiment. Following a recent path integral Car-Parrinello molecular dynamics study, data were successfully interpreted in terms of an anisotropic Gaussian model, with a statistical accuracy comparable to that of the model independent scheme used previously, but providing more detailed information on the three dimensional potential energy surface experienced by the proton. A recently proposed theoretical concept is also employed to directly calculate the mean force from the experimental neutron Compton profile, and to evaluate the accuracy required to unambiguously resolve and extract the effective proton potential from the experimental data. PMID:22260600

Flammini, D; Pietropaolo, A; Senesi, R; Andreani, C; McBride, F; Hodgson, A; Adams, M A; Lin, L; Car, R

2012-01-14

175

Reverse Monte Carlo Modeling of Pair Distribution Function Data as a Tool for Separating the Coordination Environments of Multiple Atoms Disordered Over a Single Site  

NASA Astrophysics Data System (ADS)

The local structures of 8 perovskite compounds which contain equal concentrations of 2 transition metal cations disordered over the B-sites have been investigated using reverse Monte Carlo (RMC) modeling of neutron pair distribution function (PDF) data. Such compounds are known to display a number of interesting magnetic and electronic properties which, due to the cation disorder, cannot be correlated with the average long range structure and so remain poorly understood. In compounds with B=Mn/Ru there exists a valence degeneracy between Mn^3+/Ru^5+ and Mn^4+/Ru^4+. We demonstrate that the RMC method can be used as an effective tool to separate out the individual coordination environments of these cations and also to monitor the relative concentrations of the different oxidation states. We find that the valency ratio is governed by the size of the A-site cations. In a different series of Sr2FeMnO6-x perovskites we find that locally the structures are quite different from the average cubic structures, with the local coordination environments more closely resembling those of the brownmillerite structure. In all compounds the octahedra containing Mn^3+ are Jahn-Teller distorted, even if this distortion is not evident in the average structure.

King, Graham; Llobet, Anna; Ricciardo, Rebecca; Soliz, Jennifer; Woodward, Patrick; Ramezanipour, Farshid; Greedan, John

2012-02-01

176

Neutron Signatures of Non-Thermal Ion Distributions in Z-Pinch Driven ICF Plasmas  

NASA Astrophysics Data System (ADS)

In preparation for upcoming ICF experiments on the 26 MA Z machine (e.g., D2 gas puff, MagLIF [1]), we are studying the neutron energy spectra produced by magnetically-driven loads beyond the archetypal single temperature, uniform plasma. Z-pinch sources frequently exhibit evidence of unusual neutron spectra [2], which can be attributed to three-dimensional turbulent motion, high-energy beams, and other phenomena leading to non-Maxwellian ion distributions. Understanding the nature of our plasma neutron sources is critical for understanding how they scale with increasing current. We will show Monte Carlo and analytic calculations for plausible scenarios and discuss the corresponding signatures for the existing set of time-of-flight diagnostics on Z.[4pt] [1] S. A. Slutz et al. Phys. Plasmas 17, 056303 (2010)[0pt] [2] V.V. Vikhrev and V.D. Korolev, Plasma Dynamics, Vol. 33, No. 5 (2007)

Knapp, Patrick; Jennings, Christopher; Sinars, Daniel

2012-10-01

177

Neutron-activation study of phasewise element distribution in common chondrites  

SciTech Connect

This paper studies the possibility of selective dissolution of the individual phases of common chondrites by treating them with solutions at elevated temperatures (80-100 C). Water, solution of Cu(NO/sub 3/)/sub 2/ + NH/sub 4/NO/sub 3/ (metallic phase), bromine water (troilite), and 0.2 M HCl (olivine) are used as media. It is shown that under the chosen conditions the yield of the desired phase in the appropriate fraction lies within 90-98% with less than 5% going into other fractions. Irradiation of most of the minerals by an integral neutron flux of up to 4 X 10/sup 19/ neutrons/cm/sup 2/ does not affect their solubility. Only olivine and troilite, after strong irradiation with neutrons, exhibit heightened solubility. The influence of the recoil nucleus effect on the element distribution is studied.

Kuznetsov, R.A.; Ortega, J.; Panichev, N.A.; Pankratov, V.B.

1986-05-01

178

Plans for a Collaboratively Developed Distributed Control System for the Spallation Neutron Source  

SciTech Connect

The Spallation Neutron Source (SNS) is an accelerator-based pulsed neutron source to be built in Oak Ridge, Tennessee. The facility has five major sections - a ''front end'' consisting of a 65 keV H{sup -} ion source followed by a 2.5 MeV RFQ; a 1 GeV linac; a storage ring; a 1MW spallation neutron target (upgradeable to 2 MW); the conventional facilities to support these machines and a suite of neutron scattering instruments to exploit them. These components will be designed and implemented by five collaborating institutions: Lawrence Berkeley National Laboratory (Front End), Los Alamos National Laboratory (Linac); Brookhaven National Laboratory (Storage Ring); Argonne National Laboratory (Instruments); and Oak Ridge National Laboratory (Neutron Source and Conventional Facilities). It is proposed to implement a fully integrated control system for all aspects of this complex. The system will be developed collaboratively, with some degree of local autonomy for distributed systems, but centralized accountability. Technical integration will be based upon the widely-used EPICS control system toolkit, and a complete set of hardware and software standards. The scope of the integrated control system includes site-wide timing and synchronization, networking and machine protection. This paper discusses the technical and organizational issues of planning a large control system to be developed collaboratively at five different institutions, the approaches being taken to address those issues, as well as some of the particular technical challenges for the SNS control system.

DeVan, W.R.; Gurd, D.P.; Hammonds, J.; Lewis, S.A.; Smith, J.D.

1999-03-29

179

Acquired Drive Strength as a Joint Function of Ucs Intensity and Number of Cs-Ucs Pairings: The Effect of Massed and Distributed Cs-Ucs Pairings  

Microsoft Academic Search

The empirical law relating acquired drive strength, as measured by the latency of a hurdle-jump response, to UCS intensity and number of CS-UCS pairings was investigated. The effect on acquired drive strength of varying the intervals between successive CS-UCS pairings was also investigated. Ss were 150 male albino rats, 125–160 days old. The apparatus was the classically conditioned fear apparatus.

Melvin L. Goldstein

1976-01-01

180

Calculation of the light pulse distributions induced by fast neutrons in organic scintillation detectors  

NASA Astrophysics Data System (ADS)

We develop a fully analytic and self-contained description of the amplitude distribution of light pulses in an organic scintillation detector due to a monoenergetic source of fast neutrons. To this end, two classes of problems have to be handled. One is a formula for the light pulse amplitude distribution for the complete life history of neutrons slowing down in a mixture of hydrogen and carbon as a statistical average over all collision sequences that can occur, accounting also for neutron leakage. A complete solution is given in terms of a non-recursive convolution integral expansion with respect to the various possible collision histories. These latter are dependent on the collision probabilities of neutrons of a given energy. The second is the calculation of this collision probability from analytical expressions for the geometry of the detector, in the present case a right cylinder. This quantity was taken from Monte Carlo simulations in previous work. Recursive formulae are derived for the probabilities of arbitrary collision sequences, and quantitative results are given for up to five consecutive collisions of all combinations. These probabilities can be used to determine how to truncate the non-recursive expansion of the full light amplitude distribution in quantitative work. The calculational method serves to lend insight and understanding into the structure of the pulse height spectra, as well as it provides a computationally cheap method of generating a large number of such spectra for various detector compositions, sizes and neutron energies, for the development and test of new spectrum unfolding techniques.

Enqvist, Andreas; Pázsit, Imre

2010-06-01

181

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

Microsoft Academic Search

Neutron Fluence rate of a low intense Pu-Be source is measured by Neutron Activation Analysis (NAA) of 197Au foils. Also, the neutron fluence rate distribution versus energy is calculated using the MCNP-4B code based on ENDF\\/B-V library. Theoretical simulation as well as our experimental performance are a new experience for Iranians to make reliability with the code for further researches.

F. Faghihi; S. Mehdizadeh; K. Hadad

2006-01-01

182

Pair Distribution Functions and Attenuation Rates for Sticky Particles in Dense Media.  

National Technical Information Service (NTIS)

This paper considers scattering from systems of densely distributed, non tenuous spheres that exhibit surface adhesion. The Percus-Yevlck sticky particle pail function is used to describe the clustering nature of the particles and to include this in low f...

K. H. Ding L. M. Zurk L. Tsang

1994-01-01

183

Observation of a vh{sub 11/2} pair alignment in neutron-rich {sup 118}Pd  

SciTech Connect

The yrast band was significantly extended to 14{sup +} and the {gamma} band to 5{sup +} in neutron-rich {sup 118}Pd by measuring the {gamma}-{gamma}-{gamma} coincidences emitted from the spontaneous fission of {sup 252}Cf with Gammasphere. The first band crossing was observed in the yrast band in {sup 118}Pd at a frequency of {Dirac_h}{omega}{approx}0.36 MeV at the starting point of the backbending, which is similar to that found in {sup 112-116}Pd. The first bandbending in the yrast cascade in {sup 118}Pd is interpreted to be built on a two h{sub 11/2} neutron configuration based on its similarity to the yrast bands in even-even {sup 112-116}Pd. Our result indicates {sup 118}Pd still maintains a prolate shape. The quasineutron Routhian calculations indicate a lower crossing frequency for the h{sub 11/2} level.

Zhang, X. Q.; Hamilton, J. H.; Ramayya, A. V.; Zhu, S. J.; Hwang, J. K.; Beyer, C. J.; Kormicki, J.; Jones, E. F.; Gore, P. M.; Babu, B. R. S. (and others)

2001-02-01

184

The importance of the direction distribution of neutron fluence, and methods of determination  

NASA Astrophysics Data System (ADS)

For the estimation of non-isotropic quantities such as personal dose equivalent and effective dose, and for the interpretation of the readings of personal dosemeters, it is necessary to determine both the energy and direction distributions of the neutron fluence. In fact, for workplace fields, the fluence and dose-equivalent responses of dosemeters and the relationships of operational and protection quantities, are frequently more dependent on the direction than on the energy distribution. In general, the direction distribution will not be independent of the energy distribution, and simultaneous determination of both may be required, which becomes a complex problem. The extent to which detailed information can be obtained depends on the spectrometric properties and on the angle dependence of the response of the detectors used. Methods for the determination of direction distributions of workplace fields are described.

Bartlett, D. T.; Drake, P.; d'Errico, F.; Luszik-Bhadra, M.; Matzke, M.; Tanner, R. J.

2002-01-01

185

Neutron diffraction analysis of residual strain/stress distribution in the vicinity of high strength welds  

NASA Astrophysics Data System (ADS)

Residual stresses resulting from non homogeneous heat distribution during welding process belong to most significant factor influencing behavior of welded structures. These stresses are responsible for defect occurrence during welding and they are also responsible for crack initiation and propagation at the either static or dynamic load. The significant effect of weld metal chemical composition as well as the effect of fatigue load and local plastic deformation on residual stress distribution and fatigue life have been recognized for high strength steels welds. The changes in residual stress distribution have then positive effect on cold cracking behavior and also on fatigue properties of the welds [1-3]. Several experimental methods, both destructive and non-destructive, such as hole drilling method, X-ray diffraction, neutron diffraction and others, have been used to examine residual stress distribution in all three significant orientations in the vicinity of the welds. The present contribution summarizes the results of neutron diffraction measurements of residual stress distribution in the vicinity of single-pass high-strength-steel welds having different chemical composition as well as the influence of fatigue load and local plastic deformation. It has been observed that the chemical composition of the weld metal has a significant influence on the stress distribution around the weld. Similarly, by aplying both cyclic load or pre-stress load on the specimens, stress relaxation was observed even in the region of approximately 40 mm far from the weld toe.

Mráz, L.; Karlsson, L.; Hamák, I.; Vrána, M.; Mikula, P.

2010-06-01

186

Structure of Barrier Distributions:. Probing the Role of Neutron-Transfer Channels  

Microsoft Academic Search

In view of its large deformation, which should give rise to strong barrier structures, the 20Ne projectile has been used to study the influence of neutron-transfer channels on the distribution of barrier heights. A previous experiment with a combination of projectiles 20,22Ne suggested that the role of alpha-particle transfer channels is small. By an appropriate choice of targets (90Zr and

E. Piasecki; L. Swiderski; K. Rusek; M. Kisielinski; J. Jastrzebski; A. Kordyasz; M. Kowalczyk; M. Mutterer; T. Krogulski; K. Piasecki; P. Russotto; A. M. Stefanini; N. Rowley

2007-01-01

187

The Spatial Distribution of Coalescing Neutron Star Binaries: Implications for Gamma-Ray Bursts  

Microsoft Academic Search

We find the distribution of coalescence times, birthrates, spatial\\u000avelocities, and subsequent radial offsets of coalescing neutron stars (NSs) in\\u000avarious galactic potentials accounting for large asymmetric kicks introduced\\u000aduring a supernovae. The birthrates of bound NS-NS binaries are quite sensitive\\u000ato the magnitude of the kick velocities but are, nevertheless, similar (~10 per\\u000aGalaxy per Myr) to previous population

Joshua S. Bloom; Steinn Sigurdsson; Onno R. Pols

1998-01-01

188

Comprehensive neutron cross-section and secondary energy distribution uncertainty analysis for a fusion reactor  

Microsoft Academic Search

On the example of General Atomic's well-documented Power Generating Fusion Reactor (PGFR) design, this report exercises a comprehensive neutron cross-section and secondary energy distribution (SED) uncertainty analysis. The LASL sensitivity and uncertainty analysis code SENSIT is used to calculate reaction cross-section sensitivity profiles and integral SED sensitivity coefficients. These are then folded with covariance matrices and integral SED uncertainties to

S. A. W. Gerstl; R. J. LaBauve; P. G. Young

1980-01-01

189

Neutron density distribution and the halo structure of {sup 22}C  

SciTech Connect

The recently measured reaction cross sections for the neutron-rich carbon isotopes ({sup 19}C, {sup 20}C, and {sup 22}C) on a proton target at 40 A MeV are analyzed using the finite range Glauber model (FRGM) and the microscopic optical potential calculated within the Brueckner-Hartree-Fock formalism (BHF). In FRGM nucleon-nucleon cross sections are used, while in the latter (BHF), Hamada-Johnston, Urbana v-14, and the Argonne v-18 internucleon potentials are employed to calculate the microscopic optical potential. The required nucleon density distributions are calculated within the relativistic mean-field (RMF) framework. To test the halo structure, the extended neutron density distribution for {sup 22}C is also used. The analysis reveals that the BHF results of all three internucleon potentials are very close to each other, and also agree with the corresponding results of the FRGM. Our results, using RMF densities, are in agreement with the experimental data for all isotopes of carbon except {sup 22}C, for which we require extended neutron density distribution, indicating a halo structure.

Sharma, Manjari; Khan, Z. A.; Haider, W. [Department of Physics, Aligarh Muslim University, Aligarh 202 002 (India); Bhagwat, A. [UM-DAE Centre for Excellence in Basic Sciences, Mumbai 400 098 (India); Gambhir, Y. K. [Department of Physics, I.I.T. Powai, Mumbai 400 076 (India); Manipal University, Manipal 576104 (India)

2011-03-15

190

Clamping stiffness and its influence on load distribution between paired internal spinal fixation devices.  

PubMed

The load distribution between two internal spinal fixation devices depends, besides other factors, on their stiffness. The stiffness ranges were determined experimentally for the clamps of the AO internal fixator with lateral nut and with posterior nut as well as for the clamps of the SOCON fixator. The stiffness of eight devices each differed by a factor of 3.1 for the clamp with lateral nut, by a factor of 1.5 for the clamp with posterior nut, and by a factor of 1.4 for the clamp of the SOCON fixator. For the AO clamp with lateral nut, the influence of the nut-tightening torque on the stiffness was determined. Using instrumented internal spinal fixation devices mounted to plastic vertebrae and simulating a corpectomy, the load distribution between the implants was measured for different tightening torques. It could be shown that, for the AO internal fixator whose clamps have a lateral nut, a nut-tightening torque > 5 Nm has only a negligible influence on load-sharing between the implants. Tooth damage occurs when the teeth of the clamp body and clamping jaw of the clamp with lateral nut do not gear together exactly, which leads to changes in the clamping stiffness and load-sharing between the two implants. PMID:8854279

Rohlmann, A; Calisse, J; Bergmann, G; Radvan, J; Mayer, H M

1996-06-01

191

Detection of prokaryotic promoters from the genomic distribution of hexanucleotide pairs  

PubMed Central

Background In bacteria, sigma factors and other transcriptional regulatory proteins recognize DNA patterns upstream of their target genes and interact with RNA polymerase to control transcription. As a consequence of evolution, DNA sequences recognized by transcription factors are thought to be enriched in intergenic regions (IRs) and depleted from coding regions of prokaryotic genomes. Results In this work, we report that genomic distribution of transcription factors binding sites is biased towards IRs, and that this bias is conserved amongst bacterial species. We further take advantage of this observation to develop an algorithm that can efficiently identify promoter boxes by a distribution-dependent approach rather than a direct sequence comparison approach. This strategy, which can easily be combined with other methodologies, allowed the identification of promoter sequences in ten species and can be used with any annotated bacterial genome, with results that rival with current methodologies. Experimental validations of predicted promoters also support our approach. Conclusion Considering that complete genomic sequences of over 1000 bacteria will soon be available and that little transcriptional information is available for most of them, our algorithm constitutes a promising tool for the prediction of promoter sequences. Importantly, our methodology could also be adapted to identify DNA sequences recognized by other regulatory proteins.

Jacques, Pierre-Etienne; Rodrigue, Sebastien; Gaudreau, Luc; Goulet, Jean; Brzezinski, Ryszard

2006-01-01

192

Gas Distribution and Starburst Activity in the Widely Separated Interacting Galaxy Pair NGC 6670  

NASA Astrophysics Data System (ADS)

We present high-resolution H I 21 cm line, 20 cm radio continuum, and CO (1-0) line observations of the luminous infrared galaxy pair NGC 6670. NGC 6670 consists of two edge-on disk galaxies (NGC 6670E and NGC 6670W) with a projected nuclear separation of ~16 kpc. While there are no optically identified tidal features and the molecular disks are not distorted much, we have detected a 90 kpc long H I tail, which suggests that the galaxies are interacting and have already experienced at least one close encounter. The galaxies appear to be gravitationally bound and in a prograde-prograde orbit, which is the most efficient for producing tidal tails. Our observations suggest that the H I at larger galactic radii has been ejected to form the tails and the remnant H I disks have been perturbed by the interaction. In particular, we find that the H I disk of NGC 6670E appears to have been nearly destroyed. We conclude that the previous encounter between the galaxies had a large impact parameter and that the system is still in an early stage of interaction. Even though NGC 6670 is in an early stage of interaction, we find that there is evidence for nuclear starbursts already present. The CO (1-0) observations show large molecular gas reservoirs in the central regions, and the 20 cm radio continuum observations reveal enhanced star formation activity in the nuclear regions of both galaxies. The spatial extent of the 20 cm emission and the far-infrared-radio correlation further rule out active galactic nuclei as the source of the IR luminosity from NGC 6670. We estimate the ratio LIR/MH2, which is often used as an indicator of star formation efficiency, in the nuclear regions of NGC 6670E and NGC 6670W to be 18 and 11 Lsolar/Msolar, respectively. The nuclear star formation efficiency of these two galaxies has been elevated to the level observed in other nearby starburst galaxies (LIR/MH2>10 Lsolar/Msolar). Other indicators of starburst activity, such as CO brightness temperature and infrared surface brightness, are also observed.

Wang, Wei-Hao; Lo, K. Y.; Gao, Yu; Gruendl, Robert A.

2001-07-01

193

The Effect of Neutron Source Distribution on Subcriticality Measurement of Pressurized Water Reactors Using the Modified Neutron Source Multiplication Method  

Microsoft Academic Search

A modified neutron source multiplication method has been investigated for application to subcriticality measurement in commercial Pressurized Water Reactors (PWRs). This method is based on the extraction of the fundamental mode from measured neutron signals and corrections for spatial effects. In commercial reactors, mainly two types of neutron sources are expected, one from burnt fuels and the other from in-core

Win Naing; Masashi TSUJI; Yoichiro SHIMAZU

2003-01-01

194

Three-dimensional visualization of void fraction distribution in steady two-phase flow by thermal neutron radiography  

Microsoft Academic Search

Three-dimensional void fraction distributions of a steady air–water two-phase flow in a 4×4 rod-bundle with circular ferrule type spacers were measured by neutron radiography using a CT method. The high flux thermal neutron radiography system at JRR-3M in JAERI was used. Two-phase flow was visualized with a SIT tube camera and time-averaged one-dimensional cross sectional averaged void fraction distributions were

N Takenaka; H Asano; T Fujii; M Matsubayashi

1998-01-01

195

Transverse momentum distribution in Drell-Yan pair and W and Z boson production  

NASA Astrophysics Data System (ADS)

We exhibit and discuss the QCD prediction for the transverse momentum distribution of W bosons, Z bosons and high-mass virtual photons produced in high-energy hadron-hadron collisions. Recent work has shown that this prediction is consistent with the structure of leading twist initial state interactions. The expression we present is expected to give results correct up to order ?sN(Q) for any QT when the boson mass Q is very large (> 108 GeV!), given only input from perturbative calculations at order ?sN+2 and deeply inelastic scattering structure functions. We specify the required N = 0 coefficients, employing the order ?s2 results of Kodaira and Trentadue and of Davies and Stirling. We then show how the expression should be modified to deal with current energy scales. We also discuss the connection between low-QT and high-QT formulae.

Collins, J. C.; Soper, Davison E.; Sterman, George

196

Pulse-height distributions of neutron and gamma rays from plutonium-oxide samples  

NASA Astrophysics Data System (ADS)

We present new results on neutron and gamma-ray pulse-height distributions (PHDs) measured with liquid scintillators from five plutonium-oxide samples of varying mass and burnup and a 252Cf isotopic source. We show that the analysis of the pulse-height distributions can be used to easily distinguish the fissile material (plutonium oxide) from the 252Cf source. Moreover, the slope of the measured pulse-height distributions can be analyzed to distinguish the burnup of the samples, independent of their masses. Finally, the measurement scenarios are modeled using the MCNP-PoliMi code and good agreement is observed between the measured and the simulated pulse-height distributions.

Pozzi, S. A.; Clarke, S. D.; Flaska, M.; Peerani, P.

2009-09-01

197

Neutron scattering studies of short-range order, atomic displacements, and effective pair interactions in a null-matrix Ni0.5262Pt0.48 crystal  

NASA Astrophysics Data System (ADS)

The best known exception to the Heine-Sampson and Bieber-Gauthier arguments for ordering effects in transition metal alloys (similar to the Hume-Rothery rules) is a NiPt alloy, whose phase diagram is similar to that of the CuAu system. Using neutron scattering we have investigated the local atomic order in a null-matrix Ni0.5262Pt0.48 single crystal. In a null-matrix alloy, the isotopic composition is adjusted so that the average neutron scattering length vanishes ( Ni62 has a negative scattering length nearly equal in magnitude to that of Pt). Consequently, all contributions to the total scattering depending on the average lattice are suppressed. The only remaining components of the elastic scattering are the short-range order (SRO) and size effect terms. These data permit the extraction of the SRO parameters (concentration-concentration correlations) as well as the displacement parameters (concentration-displacement correlations). Using the Krivoglaz-Clapp-Moss theory, we obtain the effective pair interactions (EPIs) between near neighbors in the alloy. The results can be used by theorists to model the alloy in the context of the electronic theory of alloy phase stability, including a preliminary evaluation of the local species-dependent displacements. Our maps of V(q) , the Fourier transform of the EPIs, show very similar shapes in the experimental and reconstructed data. This is of importance when comparing to electronic structure calculations.

Rodriguez, J. A.; Moss, S. C.; Robertson, J. L.; Copley, J. R. D.; Neumann, D. A.; Major, J.

2006-09-01

198

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

NASA Astrophysics Data System (ADS)

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

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

199

Detecting phase separation of freeze-dried binary amorphous systems using pair-wise distribution function and multivariate data analysis.  

PubMed

The purpose of this study is to investigate the use of multivariate data analysis for powder X-ray diffraction-pair-wise distribution function (PXRD-PDF) data to detect phase separation in freeze-dried binary amorphous systems. Polymer-polymer and polymer-sugar binary systems at various ratios were freeze-dried. All samples were analyzed by PXRD, transformed to PDF and analyzed by principal component analysis (PCA). These results were validated by differential scanning calorimetry (DSC) through characterization of glass transition of the maximally freeze-concentrate solute (Tg'). Analysis of PXRD-PDF data using PCA provides a more clear 'miscible' or 'phase separated' interpretation through the distribution pattern of samples on a score plot presentation compared to residual plot method. In a phase separated system, samples were found to be evenly distributed around the theoretical PDF profile. For systems that were miscible, a clear deviation of samples away from the theoretical PDF profile was observed. Moreover, PCA analysis allows simultaneous analysis of replicate samples. Comparatively, the phase behavior analysis from PXRD-PDF-PCA method was in agreement with the DSC results. Overall, the combined PXRD-PDF-PCA approach improves the clarity of the PXRD-PDF results and can be used as an alternative explorative data analytical tool in detecting phase separation in freeze-dried binary amorphous systems. PMID:23872303

Chieng, Norman; Trnka, Hjalte; Boetker, Johan; Pikal, Michael; Rantanen, Jukka; Grohganz, Holger

2013-07-18

200

Synthesis and structural characterisation using Rietveld and pair distribution function analysis of layered mixed titanium-zirconium phosphates  

NASA Astrophysics Data System (ADS)

Crystalline metal (IV) phosphates with variable zirconium-to-titanium molar ratios of general formula (Ti1-xZrx)(HPO4)2ˇH2O have been prepared by precipitation of soluble salts of the metals with phosphoric acid and heating the amorphous solids in 12 M H3PO4 in an autoclave. The new materials are structurally characterised by Rietveld analysis of synchrotron X-ray powder diffraction data and pair distribution function (PDF) analysis of high energy synchrotron X-ray total scattering data. A broad range of zirconium-titanium phosphate solid solutions were formed showing isomorphous substitution of titanium by zirconium in the ?-titanium phosphate lattice and vice versa for titanium substitution into the ?-zirconium phosphate lattice. In both cases the solubility is partial with the coexistence of two substituted phases observed in samples with nominal compositions between the solubility limits.

Burnell, Victoria A.; Readman, Jennifer E.; Tang, Chiu C.; Parker, Julia E.; Thompson, Stephen P.; Hriljac, Joseph A.

2010-09-01

201

Determining the radial pair distribution function from X-ray absorption spectra by use of the Landweber iteration method.  

PubMed

The Landweber iteration approach is used to construct the radial pair distribution function (RPDF) from an X-ray absorption (EXAFS) spectrum. The physical motivation for the presented investigation is the possibility to also reconstruct asymmetric RPDFs from the EXAFS spectra. From the methodical point of view the shell fit analysis in the case of complicated spectra would be much more eased if the RPDF for the first shell(s) are computed precisely and independently. The RPDF, as a solution of the fundamental EXAFS integral equation, is examined for theoretical examples, and a detailed noise analysis is performed. As a real example the EXAFS spectrum of curium(III) hydrate is evaluated in a stable way without supplementary conditions by the proposed iteration, i.e. by a recursive application of the EXAFS kernel. PMID:20157284

Rossberg, André; Funke, Harald

2010-01-16

202

Confirmation of disordered structure of ultrasmall CdSe nanoparticles from X-ray atomic pair distribution function analysis.  

PubMed

The atomic pair distribution function (PDF) analysis of X-ray powder diffraction data has been used to study the structure of small and ultra-small CdSe nanoparticles. A method is described that uses a wurtzite and zinc-blende mixed phase model to account for stacking faults in CdSe particles. The mixed-phase model successfully describes the structure of nanoparticles larger than 2 nm yielding a stacking fault density of about 30%. However, for ultrasmall nanoparticles smaller than 2 nm, the models cannot fit the experimental PDF showing that the structure is significantly modified from that of larger particles and the bulk. The observation of a significant change in the average structure at ultra-small size is likely to explain the unusual properties of the ultrasmall particles such as their white light emitting ability. PMID:23525376

Yang, Xiaohao; Masadeh, Ahmad S; McBride, James R; Božin, Emil S; Rosenthal, Sandra J; Billinge, Simon J L

2013-03-25

203

Pair-distribution Function Analysis of the Structural Valence Transition in Cp?2Yb(4,4?-Me2-bipy)  

SciTech Connect

The Cp*{sub 2}Yb(L) class of compounds, where Cp* = pentamethylcyclopentadienyl = C{sub 5}Me{sub 5} and L is either a 1,4-diazabutadiene or bipy = 2,2'-bipyridine related ligand, have provided excellent analogies to the Kondo state on the nanoscale. Cp*{sub 2}Yb(4,4'-Me{sub 2}-bipy) furthers this analogy by demonstrating a valence transition as the sample is cooled below 200 K. Here, pair-distribution function (PDF) analysis of x-ray powder diffraction data demonstrate that the Cp*{sub 2}Yb(4,4'-Me{sub 2}-bipy) molecule is virtually unchanged through the valence transition. However, the molecule's stacking arrangement is altered through the valence transition.

Billinge, S.J.; Booth, C.H.; Bauer, E.D.; Bozin, E.S.; Walter, M.D.

2011-02-24

204

Structural study of biotic and abiotic poorly-crystalline manganese oxides using atomic pair distribution function analysis  

NASA Astrophysics Data System (ADS)

Manganese (Mn) oxides are among the most reactive natural minerals and play an important role in elemental cycling in oceanic and terrestrial environments. A large portion of naturally-occurring Mn oxides tend to be poorly-crystalline and/or nanocrystalline, with not fully resolved crystal structures. In this study, the crystal structures of their synthetic analogs including acid birnessite (AcidBir), ?-MnO2, polymeric MnO2 (PolyMnO2) and a bacteriogenic Mn oxide (BioMnOx), have been revealed using atomic pair distribution function (PDF) analysis. Results unambiguously verify that these Mn oxides are layered materials. The best models that accurately allow simulation of pair distribution functions (PDFs) belong to the monoclinic C12/m1 space group with a disk-like shape. The single MnO6 layers in the average structures deviate significantly from hexagonal symmetry, in contrast to the results of previous studies based on X-ray diffraction analysis in reciprocal space. Manganese occupancies in MnO6 layers are estimated to be 0.936, 0.847, 0.930 and 0.935, for AcidBir, BioMnOx, ?-MnO2 and PolyMnO2, respectively; however, occupancies of interlayer cations and water molecules cannot be accurately determined using the models in this study. The coherent scattering domains (CSDs) of PolyMnO2, ?-MnO2 and BioMnOx are at the nanometer scale, comprising one to three MnO6 layers stacked with a high disorder in the crystallographic c-axis direction. Overall, the results of this study advance our understanding of the mineralogy of Mn oxide minerals in the environment.

Zhu, Mengqiang; Farrow, Christopher L.; Post, Jeffrey E.; Livi, Kenneth J. T.; Billinge, Simon J. L.; Ginder-Vogel, Matthew; Sparks, Donald L.

2012-03-01

205

Structural study of biotic and abiotic poorly-crystalline manganese oxides using atomic pair distribution function analysis  

SciTech Connect

Manganese (Mn) oxides are among the most reactive natural minerals and play an important role in elemental cycling in oceanic and terrestrial environments. A large portion of naturally-occurring Mn oxides tend to be poorly-crystalline and/or nanocrystalline, with not fully resolved crystal structures. In this study, the crystal structures of their synthetic analogs including acid birnessite (AcidBir), {delta}-MnO{sub 2}, polymeric MnO{sub 2} (PolyMnO{sub 2}) and a bacteriogenic Mn oxide (BioMnO{sub x}), have been revealed using atomic pair distribution function (PDF) analysis. Results unambiguously verify that these Mn oxides are layered materials. The best models that accurately allow simulation of pair distribution functions (PDFs) belong to the monoclinic C12/m1 space group with a disk-like shape. The single MnO{sub 6} layers in the average structures deviate significantly from hexagonal symmetry, in contrast to the results of previous studies based on X-ray diffraction analysis in reciprocal space. Manganese occupancies in MnO{sub 6} layers are estimated to be 0.936, 0.847, 0.930 and 0.935, for AcidBir, BioMnOx, {delta}-MnO{sub 2} and PolyMnO{sub 2}, respectively; however, occupancies of interlayer cations and water molecules cannot be accurately determined using the models in this study. The coherent scattering domains (CSDs) of PolyMnO{sub 2}, {delta}-MnO{sub 2} and BioMnO{sub x} are at the nanometer scale, comprising one to three MnO{sub 6} layers stacked with a high disorder in the crystallographic c-axis direction. Overall, the results of this study advance our understanding of the mineralogy of Mn oxide minerals in the environment.

Zhu, Mengqiang; Farrow, Christopher L.; Post, Jeffrey E.; Livi, Kenneth J.T.; Billinge, Simon J.L.; Ginder-Vogel, Matthew; Sparks, Donald L. (Delaware); (Columbia); (JHU); (Smithsonian)

2012-03-15

206

Structural Study of Biotic and Abiotic Poorly-crystalline Manganese Oxides Using Atomic Pair Distribution Function Analysis  

SciTech Connect

Manganese (Mn) oxides are among the most reactive natural minerals and play an important role in elemental cycling in oceanic and terrestrial environments. A large portion of naturally-occurring Mn oxides tend to be poorly-crystalline and/or nanocrystalline, with not fully resolved crystal structures. In this study, the crystal structures of their synthetic analogs including acid birnessite (AcidBir), {delta}-MnO{sub 2}, polymeric MnO{sub 2} (PolyMnO{sub 2}) and a bacteriogenic Mn oxide (BioMnO{sub x}), have been revealed using atomic pair distribution function (PDF) analysis. Results unambiguously verify that these Mn oxides are layered materials. The best models that accurately allow simulation of pair distribution functions (PDFs) belong to the monoclinic C12/m1 space group with a disk-like shape. The single MnO{sub 6} layers in the average structures deviate significantly from hexagonal symmetry, in contrast to the results of previous studies based on X-ray diffraction analysis in reciprocal space. Manganese occupancies in MnO{sub 6} layers are estimated to be 0.936, 0.847, 0.930 and 0.935, for AcidBir, BioMnO{sub x}, {delta}-MnO{sub 2} and PolyMnO{sub 2}, respectively; however, occupancies of interlayer cations and water molecules cannot be accurately determined using the models in this study. The coherent scattering domains (CSDs) of PolyMnO{sub 2}, {delta}-MnO{sub 2} and BioMnO{sub x} are at the nanometer scale, comprising one to three MnO{sub 6} layers stacked with a high disorder in the crystallographic c-axis direction. Overall, the results of this study advance our understanding of the mineralogy of Mn oxide minerals in the environment.

Billinge S. J.; Zhu, M.; Farrow, C.L.; Post, J.E.; Livi, K.J.T.; Ginder-Vogel, M.; Sparks, D.L.

2012-03-15

207

Casimir dependence of transverse distribution of pairs produced from a strong constant chromo-electric background field  

SciTech Connect

Recently the transverse distribution of particle production from strong constant chromo-electric fields has been explicitly calculated in Ref. 1 for soft-gluon production and in Ref. 2 for quark (antiquark) production. This particle production method, originally discussed by Heisenberg and Euler, Schwinger and Weisskopf, has a long history as a model of the production of the quark gluon plasma following a relativistic heavy ion collision. The physical picture considered here is that of two relativistic heavy nuclei colliding and leaving behind a semi-classical gluon field which then non-perturbatively produces gluon and quark-antiquark pairs via the Schwinger mechanism. At high energy large hadron colliders, such as RHIC (Au-Au collisions at {radical}{ovr s} = 200 GeV) and LHC (Pb-Pb collisions at {radical}{ovr s} = 5.5 TeV), about half the total center-of-mass energy, E{sub cm}, goes into the production of a semi-classical gluon field, which can be thought to be initially in a Lorentz contracted disc. The gluon field in SU(3) is described by two Casimir invariants, the first one, C{sub 1} = E{sup a}E{sup a}, being related to the energy density of the initial field, where the second one, C{sub 2} = [d{sub abc}E{sup a}E{sup b}E{sup c}]{sup 2}, is related to the SU(3) color hypercharge left behind by the leading particles. So the question we want to study in this short note is how sensitive the transverse distribution is to this second Casimir invariant C{sub 2}. We have considered the dependence of the pair production rate of quarks and gluons from a strong chromo-electric field and have discovered that the effect of the second Casimir invariant of SU(3), which was not present in the electric field problem, effects the distribution by less than 15%. This event by event dependence of the transverse momentum distribution of jets on C{sub 2} may be something of interest at heavy ion colliders.

Cooper, Fred M [Los Alamos National Laboratory; Mihaila, Bogdan [Los Alamos National Laboratory; Dawson, John F [UNIV OF NH

2008-01-01

208

3D Core-Collapse Supernova Simulations: Neutron Star Kicks and Nickel Distribution  

NASA Astrophysics Data System (ADS)

We perform a set of neutrino-driven core-collapse supernova (CCSN) simulations studying the hydrodynamical neutron star kick mechanism in three-dimensions. Our simulations produce neutron star (NS) kick velocities in a range between ~100-600 km/s resulting mainly from the anisotropic gravitational tug by the asymmetric mass distribution behind the supernova shock. This stochastic kick mechanism suggests that a NS kick velocity of more than 1000 km/s may as well be possible. An enhanced production of heavy elements in the direction roughly opposite to the NS recoil direction is also observed as a result of the asymmetric explosion. This large scale asymmetry might be detectable and can be used to constrain the NS kick mechanism.

Wongwathanarat, Annop; Janka, Hans-Thomas; Müller, Ewald

2012-09-01

209

Vertical distribution of hydrogen at high northern latitudes on Mars: The Mars Odyssey Neutron Spectrometer  

NASA Astrophysics Data System (ADS)

Neutron leakage currents measured using the Mars Odyssey Neutron Spectrometer are used to develop a two-layer model of the distribution of hydrogen (here parameterized as water-equivalent hydrogen, WEH) at high northern latitudes. The WEH abundance in the upper layer, Wup, was found to range between 1% and about 5%. The maximum value of the apparent thickness, D, of this upper layer peaks at about 60° latitude, giving the appearance of zonal bands of enhanced D in both hemispheres. This maximum is consistent with an expected transition from WEH contained solely in hydrous minerals at lower latitudes, to WEH contained both in the forms of water ice and water of hydration at high latitudes. A strong anti-correlation between the WEH concentration in the lower layer and apparent depth, D, at high latitudes is observed and may provide clues to the origin of these deposits.

Feldman, W. C.; Mellon, M. T.; Gasnault, O.; Diez, B.; Elphic, R. C.; Hagerty, J. J.; Lawrence, D. J.; Maurice, S.; Prettyman, T. H.

2007-03-01

210

Elliptic Phantom Measurements and Calculations of Neutron Spectra and Dose Distributions for exp 252 Cf and Heavy-Water-Moderated exp 252 Cf Sources.  

National Technical Information Service (NTIS)

Calculations and measurements for the dose distribution in a water-filled elliptical phantom when irradiated with neutrons of bare and heavy-water moderated Californium neutron sources are presented. The calculations were performed by a Monte-Carlo code, ...

J. Palfalvi

1983-01-01

211

A Theoretical Scheme for Multi-user Quantum Key Distribution with N Einstein-Podolsky-Rosen Pairs on a Passive Optical Network  

Microsoft Academic Search

We propose a theoretical scheme for any-to-any multi-user quantum key distribution on a passive optical network with ordered N Einstein-Podolsky-Rosen pairs. This scheme is safe and more efficient than those with single photons. Its efficiency approaches 100% in the limit that the number of pairs used in the eavesdropping check becomes negligible. It also has high capacity and is convenient

Fu-Guo Deng; Xiao-Shu Liu; Ying-Jun Ma; Li Xiao; Gui-Lu Long

2002-01-01

212

Distinction between Proton and Neutron-Density Distributions of Halo Nuclei at the Nuclear Surface via Reaction Cross Sections  

Microsoft Academic Search

The halo and skin structures at the nuclear surface have attracted much interest for their exotic nature. By utilizing the isospin asymmetry of nucleon-nucleon total cross sections in the intermediate energy region, in principle, the proton- and neutron-density distributions can be determined independently. To demonstrate this isospin asymmetric effect, we have studied sigmaR for the neutron-halo nucleus ^11 Be and

Daiki Nishimura; M. Fukuda; M. Takechi; M. Mihara; D. Ishikawa; K. Matsuta; R. Matsumiya; T. Kuboki; T. Suzuki; T. Yamaguchi; I. Hachiuma; K. Namihira; T. Ohtsubo; Y. Shinbara; Y. Ohkuma; T. Izumikawa; K. Tanaka; A. Ozawa; Y. Yasuda; T. Moriguchi; S. Momota; S. Fukuda; S. Sato; M. Kanazawa; A. Kitagawa

2009-01-01

213

On the Angular Distribution of Neutrons Protons and X-Rays from a Small Dense Plasma Focus Machine  

SciTech Connect

Time integrated measurements of the angular distributions of neutrons, protons and X-rays are made, inside the discharge chamber of the FN-II device, using passive detectors. A set of detectors was placed on a semi-circular Teflon registered holder, 13 cm. around the plasma column, and covered with 15 {mu}m Al filters, thus eliminating energetic ions from the expansion of the discharge, as well as tritium and helium-3 ions, but not protons and neutrons. A second set was placed on the opposite side of the holder, eliminating protons. It is found that the detectors on the upper side of the holder show two distinctively different distributions of track diameters. The distribution of the smaller ones, is sharper than that of the larger ones, and are presumably originated by a wide angle beam of protons. The distribution of the ones on the lower side of the holder, which can only be attributed to charged particles which result as a recoil of neutron collisions, are slightly shifted to larger diameters. The angular distribution of X-rays is also studied within the chamber with TLD-200 dosimeters. While the neutron and proton angular distributions can be fitted by single maximum distributions, the X-ray one shows two maxima around the axis.

Herrera, J.J.E.; Castillo, F.; Gamboa, I.; Rangel, R.; Espinosa, G.; Golzarri, J. I. [Instituto de Ciencias Nucleares, Universidad National Autonoma de Mexico, A.P. 70-543. 04511 Mexico, D.F. (Mexico); Instituto de Fisica, Universidad National Autonoma de Mexico, A.P. 20-364, 01000, Mexico, D.F. (Mexico)

2006-01-05

214

Galactic neutron stars. I. Space and velocity distributions in the disk and in the halo  

NASA Astrophysics Data System (ADS)

Aims: Neutron stars (NSs) produced in the Milky Way are supposedly ten to the eighth - ten to the ninth - of which only ~2 ×103 are observed. Constraining the phase space distribution of NSs may help to characterize the yet undetected population of stellar remnants. Methods: We performed Monte Carlo simulations of NS orbits, under different assumptions concerning the Galactic potential and the distribution of progenitors and birth velocities. We study the resulting phase space distributions, focusing on the statistical properties of the NS populations in the disk and in the solar neighbourhood. Results: It is shown that ~80 percent of NSs are in bound orbits. The fraction of NSs located in a disk of radius 20 kpc and width 0.4 kpc is ?20 percent. Therefore the majority of NSs populate the halo. Fits for the surface density of the disk, the distribution of heights on the Galactic plane and the velocity distribution of the disk are given. We also provide sky maps of the projected number density in heliocentric Galactic coordinates (l, b). Our results are compared with previous ones reported in the literature. Conclusions: Obvious applications of our modeling are in the revisiting of accretion luminosities of old isolated NSs, the issue of the observability of the nearest NS and the NS optical depth for microlensing events. These will be the scope of further studies.

Sartore, N.; Ripamonti, E.; Treves, A.; Turolla, R.

2010-02-01

215

Combining pair distribution function and computational methods to understand lithium insertion in brookite (TiO{sub 2}).  

SciTech Connect

X-ray pair distribution function (PDF) methods and first-principles calculations have been combined to probe the structure of electrochemically lithiated TiO{sub 2} Brookite. Traditional powder diffraction studies suggest that Brookite amorphizes upon lithium insertion, with the Bragg reflections disappearing. However, PDF analysis indicates that the TiO{sub 2} framework connectivity is maintained throughout lithium intercalation, with expansions along the a and b axes. The Li{sup +} ions within the framework are poorly observed in the X-ray PDF, which is dominated by contributions from the more strongly scattering Ti and O atoms. First-principles calculations were used to identify energetically favorable Li{sup +} sites within the Brookite lattice and to develop a complete structural model of the lithiated material. This model replicates the local structure and decreased intermediate range order observed in the PDF data. The analysis suggests that local structural distortions of the TiO{sub 2} lattice accommodate lithium in five-coordinate sites. This structural model is consistent with the observed electrochemical behavior.

Dambournet, D.; Chapman, K. W.; Koudriachova, M. V.; Chupas, P. J.; Belharouak, I.; Amine, K. (X-Ray Science Division); ( CSE); (Univ. Coll. London)

2011-07-04

216

Synthesis and structural characterisation using Rietveld and pair distribution function analysis of layered mixed titanium?zirconium phosphates  

SciTech Connect

Crystalline metal (IV) phosphates with variable zirconium-to-titanium molar ratios of general formula (Ti{sub 1-x}Zr{sub x})(HPO{sub 4}){sub 2} {center_dot} H{sub 2}O have been prepared by precipitation of soluble salts of the metals with phosphoric acid and heating the amorphous solids in 12 M H{sub 3}PO{sub 4} in an autoclave. The new materials are structurally characterised by Rietveld analysis of synchrotron X-ray powder diffraction data and pair distribution function (PDF) analysis of high energy synchrotron X-ray total scattering data. A broad range of zirconium-titanium phosphate solid solutions were formed showing isomorphous substitution of titanium by zirconium in the {alpha}-titanium phosphate lattice and vice versa for titanium substitution into the {alpha}-zirconium phosphate lattice. In both cases the solubility is partial with the coexistence of two substituted phases observed in samples with nominal compositions between the solubility limits.

Burnell, Victoria A.; Readman, Jennifer E.; Tang, Chiu C.; Parker, Julia E.; Thompson, Stephen P.; Hriljac, Joseph A. (Birmingham UK); (DLS)

2010-12-01

217

Subcellular distribution of trace elements in kidney of a mother-fetus pair of Dall's porpoises (Phocoenoides dalli).  

PubMed

Total and subcellular renal Zn, Cu, Se, Mn, V, Hg, Cd and Ag were determined by a mother-fetus pair of Dall's porpoises (Phocoenoides dalli). All element concentrations in the maternal individual were higher than those in the fetal individual. Most of total renal elements studied were present in the cytosol of both animals. In maternal cytosol, Mn, Hg and Ag were present in high molecular weight substances (HMW); Se was in low molecular weight substances (LMW); Zn, Cu, and Cd were in metallothionein (MT), mostly; and the distribution of V in percentage among the three renal cytosolic fractions was similar. In fetal cytosol, Zn, Mn, Hg, V, Cd, and Ag were present in HMW, Cu was present in MT, mostly. In contrast, Se was observed mostly in both LMW and HMW. MT isoforms were characterized. Three obvious peaks in retention time were found in either the maternal or fetal MT. The highest elemental ion intensities were in the 7.8min peak for the mother, and in the 4.3min peak for the fetus, respectively, implying that different MT isoforms may be closely associated with elemental accumulation between maternal and fetal renal cytosols. PMID:17889254

Yang, Jian; Kunito, Takashi; Anan, Yasumi; Tanabe, Shinsuke; Miyazaki, Nobuyuki

2007-09-21

218

Assessment of crystalline disorder in cryo-milled samples of indomethacin using atomic pair-wise distribution functions.  

PubMed

The aim of this study was to investigate the usefulness of the atomic pair-wise distribution function (PDF) to detect the extension of disorder/amorphousness induced into a crystalline drug using a cryo-milling technique, and to determine the optimal milling times to achieve amorphisation. The PDF analysis was performed on samples of indomethacin obtained by cryogenic ball milling (cryo-milling) for different periods of time. X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), polarised light microscopy (PLM) and solid state nuclear magnetic resonances (ss-NMR) were also used to analyse the cryo-milled samples. The high similarity between the ?-indomethacin cryogenic ball milled samples and the crude ?-indomethacin indicated that milled samples retained residual order of the ?-form. The PDF analysis encompassed the capability of achieving a correlation with the physical properties determined from DSC, ss-NMR and stability experiments. Multivariate data analysis (MVDA) was used to visualize the differences in the PDF and XRPD data. The MVDA approach revealed that PDF is more efficient in assessing the introduced degree of disorder in ?-indomethacin after cryo-milling than MVDA of the corresponding XRPD diffractograms. The PDF analysis was able to determine the optimal cryo-milling time that facilitated the highest degree of disorder in the samples. Therefore, it is concluded that the PDF technique may be used as a complementary tool to other solid state methods and that further investigations are warranted to elucidate the capabilities of this technique. PMID:21182911

Břtker, Johan P; Karmwar, Pranav; Strachan, Clare J; Cornett, Claus; Tian, Fang; Zujovic, Zoran; Rantanen, Jukka; Rades, Thomas

2010-12-21

219

Inversion of radial distribution functions to pair forces by solving the Yvon-Born-Green equation iteratively.  

PubMed

We develop a new method to invert the target profiles of radial distribution functions (RDFs) to the pair forces between particles. The target profiles of RDFs can be obtained from all-atom molecular dynamics (MD) simulations or experiments and the inverted pair forces can be used in molecular simulations at a coarse-grained (CG) scale. Our method is based on a variational principle that determines the mean forces between CG sites after integrating out the unwanted degrees of freedom. The solution of this variational principle has been shown to correspond to the Yvon-Born-Green (YBG) equation [Noid et al., J. Phys. Chem. B 111, 4116 (2007)]. To invert RDFs, we solve the YBG equation iteratively by running a CG MD simulation at each step of iteration. A novelty of the iterative-YBG method is that during iteration, CG forces are updated according to the YBG equation without imposing any approximation as is required by other methods. As a result, only three to ten iterations are required to achieve convergence for all cases tested in this work. Furthermore, we show that not only are the target RDFs reproduced by the iterative solution; the profiles of the three-body correlation function in the YBG equation computed from all-atom and CG simulations also have a better agreement. The iterative-YBG method is applied to compute the CG forces of four molecular liquids to illustrate its efficiency and robustness: water, ethane, ethanol, and a water/methanol mixture. Using the resulting CG forces, all of the target RDFs observed in all-atom MD simulations are reproduced. We also show that the iterative-YBG method can be applied with a virial constraint to expand the representability of a CG force field. The iterative-YBG method thus provides a general and robust framework for computing CG forces from RDFs and could be systematically generalized to go beyond pairwise forces and to include higher-body interactions in a CG force field by applying the aforementioned variational principle to derive the corresponding YBG equation for iterative solution. PMID:19814543

Cho, Hyung Min; Chu, Jhih-Wei

2009-10-01

220

Invariant Mass Distribution of Jet Pairs Produced in Association with a W Boson in ppŻ Collisions at s=1.96TeV  

NASA Astrophysics Data System (ADS)

We report a study of the invariant mass distribution of jet pairs produced in association with a W boson using data collected with the CDF detector which correspond to an integrated luminosity of 4.3fb-1. The observed distribution has an excess in the 120-160GeV/c2 mass range which is not described by current theoretical predictions within the statistical and systematic uncertainties. In this Letter, we report studies of the properties of this excess.

Aaltonen, T.; Álvarez González, B.; Amerio, S.; Amidei, D.; Anastassov, A.; Annovi, A.; Antos, J.; Apollinari, G.; Appel, J. A.; Apresyan, A.; Arisawa, T.; Artikov, A.; Asaadi, J.; Ashmanskas, W.; Auerbach, B.; Aurisano, A.; Azfar, F.; Badgett, W.; Barbaro-Galtieri, A.; Barnes, V. E.; Barnett, B. A.; Barria, P.; Bartos, P.; Bauce, M.; Bauer, G.; Bedeschi, F.; Beecher, D.; Behari, S.; Bellettini, G.; Bellinger, J.; Benjamin, D.; Beretvas, A.; Bhatti, A.; Binkley, M.; Bisello, D.; Bizjak, I.; Bland, K. R.; Blumenfeld, B.; Bocci, A.; Bodek, A.; Bortoletto, D.; Boudreau, J.; Boveia, A.; Brau, B.; Brigliadori, L.; Brisuda, A.; Bromberg, C.; Brucken, E.; Bucciantonio, M.; Budagov, J.; Budd, H. S.; Budd, S.; Burkett, K.; Busetto, G.; Bussey, P.; Buzatu, A.; Calancha, C.; Camarda, S.; Campanelli, M.; Campbell, M.; Canelli, F.; Canepa, A.; Carls, B.; Carlsmith, D.; Carosi, R.; Carrillo, S.; Carron, S.; Casal, B.; Casarsa, M.; Castro, A.; Catastini, P.; Cauz, D.; Cavaliere, V.; Cavalli-Sforza, M.; Cerri, A.; Cerrito, L.; Chen, Y. C.; Chertok, M.; Chiarelli, G.; Chlachidze, G.; Chlebana, F.; Cho, K.; Chokheli, D.; Chou, J. P.; Chung, W. H.; Chung, Y. S.; Ciobanu, C. I.; Ciocci, M. A.; Clark, A.; Clarke, C.; Compostella, G.; Convery, M. E.; Conway, J.; Corbo, M.; Cordelli, M.; Cox, C. A.; Cox, D. J.; Crescioli, F.; Cuenca Almenar, C.; Cuevas, J.; Culbertson, R.; Dagenhart, D.; D'Ascenzo, N.; Datta, M.; de Barbaro, P.; de Cecco, S.; de Lorenzo, G.; Dell'Orso, M.; Deluca, C.; Demortier, L.; Deng, J.; Deninno, M.; Devoto, F.; D'Errico, M.; di Canto, A.; di Ruzza, B.; Dittmann, J. R.; D'Onofrio, M.; Donati, S.; Dong, P.; Dorigo, M.; Dorigo, T.; Ebina, K.; Elagin, A.; Eppig, A.; Erbacher, R.; Errede, D.; Errede, S.; Ershaidat, N.; Eusebi, R.; Fang, H. C.; Farrington, S.; Feindt, M.; Fernandez, J. P.; Ferrazza, C.; Field, R.; Forrest, R.; Frank, M. J.; Franklin, M.; Freeman, J. C.; Funakoshi, Y.; Furic, I.; Gallinaro, M.; Galyardt, J.; Garcia, J. E.; Garfinkel, A. F.; Garosi, P.; Gerberich, H.; Gerchtein, E.; Giagu, S.; Giakoumopoulou, V.; Giannetti, P.; Gibson, K.; Ginsburg, C. M.; Giokaris, N.; Giromini, P.; Giunta, M.; Giurgiu, G.; Glagolev, V.; Gold, M.; Goldin, D.; Goldschmidt, N.; Golossanov, A.; Gomez, G.; Gomez-Ceballos, G.; Goncharov, M.; González, O.; Gorelov, I.; Goshaw, A. T.; Goulianos, K.; Grinstein, S.; Grosso-Pilcher, C.; Group, R. C.; Guimaraes da Costa, J.; Gunay-Unalan, Z.; Haber, C.; Hahn, S. R.; Halkiadakis, E.; Hamaguchi, A.; Han, J. Y.; Happacher, F.; Hara, K.; Hare, D.; Hare, M.; Harr, R. F.; Hatakeyama, K.; Hays, C.; Heck, M.; Heinrich, J.; Herndon, M.; Hewamanage, S.; Hidas, D.; Hocker, A.; Hopkins, W.; Horn, D.; Hou, S.; Hughes, R. E.; Hurwitz, M.; Husemann, U.; Hussain, N.; Hussein, M.; Huston, J.; Introzzi, G.; Iori, M.; Ivanov, A.; James, E.; Jang, D.; Jayatilaka, B.; Jeon, E. J.; Jha, M. K.; Jindariani, S.; Johnson, W.; Jones, M.; Joo, K. K.; Jun, S. Y.; Junk, T. R.; Kamon, T.; Karchin, P. E.; Kasmi, A.; Kato, Y.; Ketchum, W.; Keung, J.; Khotilovich, V.; Kilminster, B.; Kim, D. H.; Kim, H. S.; Kim, H. W.; Kim, J. E.; Kim, M. J.; Kim, S. B.; Kim, S. H.; Kim, Y. K.; Kimura, N.; Kirby, M.; Klimenko, S.; Kondo, K.; Kong, D. J.; Konigsberg, J.; Kotwal, A. V.; Kreps, M.; Krop, D.; Krumnack, N.; Kruse, M.; Krutelyov, V.; Kuhr, T.; Kurata, M.; Kwang, S.; Laasanen, A. T.; Lami, S.; Lancaster, M.; Lander, R. L.; Lannon, K.; Lath, A.; Latino, G.; Lecompte, T.; Lee, E.; Lee, H. S.; Lee, J. S.; Lee, S. W.; Leo, S.; Leone, S.; Lewis, J. D.; Limosani, A.; Lin, C.-J.; Linacre, J.; Lindgren, M.; Lipeles, E.; Lister, A.; Litvintsev, D. O.; Liu, C.; Liu, Q.; Liu, T.; Lockwitz, S.; Lockyer, N. S.; Loginov, A.; Lucchesi, D.; Lueck, J.; Lujan, P.; Lukens, P.; Lungu, G.; Lys, J.; Lysak, R.; Madrak, R.; Maeshima, K.; Makhoul, K.; Maksimovic, P.; Malik, S.; Manca, G.; Manousakis-Katsikakis, A.; Margaroli, F.; Marino, C.; Martínez, M.; Martínez-Ballarín, R.; Mastrandrea, P.; Mathis, M.; Mattson, M. E.; Mazzanti, P.; McFarland, K. S.; McIntyre, P.; McNulty, R.; Mehta, A.; Mehtala, P.; Menzione, A.; Mesropian, C.; Miao, T.; Mietlicki, D.; Mitra, A.; Miyake, H.; Moed, S.; Moggi, N.; Mondragon, M. N.; Moon, C. S.; Moore, R.; Morello, M. J.; Morlock, J.; Movilla Fernandez, P.; Mukherjee, A.; Muller, Th.; Mussini, M.; Nachtman, J.; Nagai, Y.; Naganoma, J.; Nakano, I.; Napier, A.; Nett, J.; Neu, C.; Neubauer, M. S.; Nielsen, J.; Nodulman, L.; Norniella, O.; Nurse, E.; Oakes, L.; Oh, S. H.; Oh, Y. D.; Oksuzian, I.; Okusawa, T.; Orava, R.; Ortolan, L.; Pagan Griso, S.; Pagliarone, C.; Palencia, E.; Papadimitriou, V.; Paramonov, A. A.; Patrick, J.; Pauletta, G.; Paulini, M.; Paus, C.; Pellett, D. E.; Penzo, A.; Phillips, T. J.; Piacentino, G.; Pianori, E.; Pilot, J.; Pitts, K.; Plager, C.; Pondrom, L.; Potamianos, K.; Poukhov, O.

2011-04-01

221

Three-dimensional observation of water distribution in PEFC by neutron CT  

NASA Astrophysics Data System (ADS)

A polymer electrolyte fuel cell (PEFC) consists of a membrane electrode assembly (MEA), gas diffusion layers (GDL), hydrogen and oxygen supply channels. At the anode, protons and electrons are generated, while at the cathode the protons and electrons combine to form water. The condensed water may affect the fuel cell performance. In order to clarify the effect of water distribution on the PEFC performance, three-dimensional water distribution in the PEFC was visualized by using a neutron radiography facility at JRR-3 in JAEA. For observing the detailed water distribution, a small sized PEFC was designed. Size of the gas channel is 1 mm width and 0.5 mm depth. Thickness of the MEA and the GDL are about 50 and 200 ?m. The electrode area is 0.35×3.5 cm2. The PEFC was set on an automatic rotating stage, and a picture was taken every 2.25° by using a cooled CCD camera with grey scale of 16 bit. The exposure time was set at 15 s. Using the 80 pictures which correspond to 180°, a computed tomography (CT) was carried out. In order to observe water distribution with high spatial resolution, the LiF scintillator with a thickness of 50 ?m was used. From the water distributions parallel and perpendicular to the MEA, existence of water around O-ring can be confirmed. However, the detailed distribution in the PEFC is difficult to obtain from the two-dimensional pictures. On the other hand, CT pictures make possible to obtain the three-dimensional water distribution. In this study, the spatial resolution of 76.5 ?m was achieved, and existence of water in the PEFC could be confirmed.

Sakata, I.; Ueda, T.; Murakawa, H.; Sugimoto, K.; Asano, H.; Takenaka, N.; Yasuda, R.; Tomura, T.; Shiozawa, M.

2009-06-01

222

Methods for radiation dose distribution analysis and treatment planning in boron neutron capture therapy  

SciTech Connect

This article presents a survey of recent progress in the development and application of analytical methods for calculating macroscopic and microscopic radiation dose distributions for Boron Neutron Capture Therapy (BNCT). Such calculations are an essential component of in vivo BNCT research and will ultimately also be required for human BNCT treatment planning. Calculations of macroscopic absorbed dose distributions for BNCT are more complex than for photon therapy. There are several different dose components, each of which has its own characteristic spatial distribution, linear energy transfer, and relative biological effectiveness (RBE). Three-dimensional (3-D) energy-dependent radiation transport models with a detailed treatment of particle scattering are required. Geometric descriptions for such models are typically constructed directly from medical image data and both the Monte Carlo stochastic simulation method and the discrete-ordinates deterministic approach have been successfully used to perform the necessary radiation transport calculations. Microdosimetric effects can profoundly influence the therapeutic benefit that may be attainable in BNCT. These effects must be carefully taken into account in the interpretation dose. Calculations of microdosimetric parameters for BNCT are typically performed using the Monte Carlo method to generate single-event energy deposition frequency distributions for critical targets in various cell types of interest. This information is useful in the development of apparent RBE factors, or [open quotes]compound factors[close quotes] for the various dose components in BNCT. 31 refs., 15 figs., 1 tab.

Nigg, D.W. (Idaho National Engineering Lab. EG G, Idaho Falls, ID (United States))

1994-03-30

223

Single and multi-deadtime parameter corrections of one- and two-dimensional Rossi-alpha distributions for time interval analysis in neutron coincidence counting  

Microsoft Academic Search

Advanced neutron coincidence counting techniques applied for the assay of special nuclear materials additionally also determine the factorial moments of the detected neutron multiplicity distribution. From these factorial moments the actual neutron detection efficiency or neutron multiplication can be inferred via a so-called three-parameter-analysis in which the spontaneous fission rate together with two other unknowns can be determined. The factorial

P. Baeten; M. Bruggeman; R. Carchon

1997-01-01

224

Neutron Capture from ^87Sr  

NASA Astrophysics Data System (ADS)

The neutron-capture resonances of the reaction ^87Sr(n,?)^88Sr are significant to nuclear astrophysics to estimate the neutron density during the s process, whose path is split by the branching nucleus ^85Kr, and for a possible use of the ^87Rb-^87Sr chronometric pair to measure the age of our Galaxy. In addition, the ? rays of the product nucleus ^88Sr are of importance to nuclear structure and the study of the pygmy resonance observed earlier in (,') measurements. We report results from a neutron-capture experiment on ^87Sr carried out with the 4? BaF2 array, DANCE, at LANL. Spin values of neutron resonances have been deduced using the multiplicity and angular distributions of the cascade ? rays following the neutron capture.

Rusev, G.; Raut, R.; Tonchev, A. P.; Tornow, W.; Baramsai, B.; Kelley, J. H.; Mitchell, G.; Bredeweg, T.; Couture, A.; Jandel, M.; O'Donnell, J.; Rundberg, R.; Ullmann, J. L.; Chyzh, A.; Kwan, E.

2011-10-01

225

Neutron Scattering Measurements of Hydrogen Distribution in a Zircaloy-4 Alloy Charged with Hydrogen Gas  

SciTech Connect

Neutron incoherent scattering measurements were conducted on Zircaloy-4 round bars. The specimens were charged in a tube furnace at 430 C, using a 12.5 vol. % hydrogen in an argon mixture for 30, 60, and 90 minutes at 13.8 kPa pressure. The volume-average neutron diffraction measurements showed the presence of the face-centered-cubic delta zirconium hydride ({delta}-ZrH{sub 2}) phase in the hydrogenated specimens. The assessment of the background in the diffraction profiles due to the incoherent scattering from the hydrogen atoms was carried out by performing inelastic scans around zero energy transfer and at a fixed two-theta value for which there was only flat background and no coherent scattering. To estimate the relative amount of hydrogen in the Zircaloy-4 samples, the increase in incoherent scattering intensities with hydrogen content was calibrated using samples for which the hydrogen content was known. Measurement of the background scattering from locations within the round bar was also performed to map the distribution of hydrogen content.

Garlea, Elena [ORNL; Garlea, Vasile O [ORNL; Choo, Hahn [ORNL; Hubbard, Camden R [ORNL; Liaw, Peter K [University of Tennessee, Knoxville (UTK); Rack, P. D. [University of Tennessee, Knoxville (UTK)

2007-01-01

226

Critical experiments with strong neutron absorbers heterogeneously distributed throughout uranyl nitrate solution  

SciTech Connect

Several critical experiments were performed for a number of strong neutron absorbers periodically distributed throughout a tank filled with high-concentration fissile solution, These experiments served as a pilot study for a novel means of storing fissile solutions at a nuclear production plant handling such solutions. The configuration also approximates one commonly used method (Raschig rings) of assuring criticality safety in such plants, Still, the configuration is heterogeneous, and so, easily susceptible to modeling with modern computer codes. The fissile solution was uranyl nitrate at about 363 gU/liter with the uranium enriched to 93.2% U{sup 235}. One important neutron absorber studied consisted of borosilicate glass rods, containing the same 12.5{percent} boron oxide found in Raschig rings used throughout the industry. Another consisted of rubber sheet containing 0.1 mg/mm{sup 2} boron (as B{sub 4}C) glued to thin-walled steel tubing. Cadmium sheet metal (1.6 mm thick) wrapped around steel rods formed yet another absorber; and solid polyvinyl chloride rods were also studied. Four loose powders packed into paper tubes completed the list of absorbers: cadmium oxide, anhydrous boric acid, sodium tetraborate pentahydrate, and a very inexpensive mixture of two common minerals-colmanite (calcium borate) and ulexite (sodium-calcium borate). The spacing between tubes containing each absorber was varied widely in both square and triangular patterns,

Rothe, R.E.

1991-01-01

227

Benchmark Experiments of Thermal Neutron and Capture Gamma-Ray Distributions in Concrete Using {sup 252}Cf  

SciTech Connect

The distributions of thermal neutrons and capture gamma rays in ordinary concrete were investigated by using {sup 252}Cf. Two subjects are considered. One is the benchmark experiments for the thermal neutron and the capture gamma-ray distributions in ordinary concrete. The thermal neutron and the capture gamma-ray distributions were measured by using gold-foil activation detectors and thermoluminescence detectors. These were compared with the simulations by using the discrete ordinates code ANISN with two different group structure types of cross-section library of a new Japanese version, JENDL-3.3, showing reasonable agreement with both fine and rough structure groups of thermal neutron energy. The other is a comparison of the simulations with two different cross-section libraries, JENDL-3.3 and ENDF/B-VI, for the deep penetration of neutrons in the concrete, showing close agreement in 0- to 100-cm-thick concrete. However, the differences in flux grow with an increase in concrete thickness, reaching up to approximately eight times near 4-m thickness.

Asano, Yoshihiro [Japan Atomic Energy Research Institute (Japan); Sugita, Takeshi [Science and System Laboratory, Ltd. (Japan); Hirose, Hideyuki [Japan Atomic Energy Research Institute (Japan); Suzaki, Takenori [Japan Atomic Energy Research Institute (Japan)

2005-10-15

228

Determination of the magnetization distribution in Cr2O3 using spherical neutron polarimetry  

NASA Astrophysics Data System (ADS)

The magnetization distribution due to the Cr3+ ion in Cr2O3 has been determined using spherical neutron polarimetry. The magnetic structure factors of h 0 l reflections have been measured out to sin ?/? = 0.75 Ĺ-1. The results show that the Cr3+ magnetic moment is reduced by the zero-point spin deviation and by covalent mixing to 2.48 ľB. They are consistent with the Cr d electrons being in the trigonally symmetric a1 and e orbitals derived from the cubic orbitals with t2g symmetry. There is a small but significant magnetization which is not accounted for by these orbitals, which is attributed to covalent overlap. Its symmetry is consistent with the magneto-electric susceptibility.

Brown, P. J.; Forsyth, J. B.; Leličvre-Berna, E.; Tasset, F.

2002-03-01

229

Partial-wave contributions to pairing in nuclei  

SciTech Connect

We present a detailed study of partial-wave contributions of nuclear forces to pairing in nuclei. For T=1,J=0 pairing, partial waves beyond the standard {sup 1}S{sub 0} channel play an interesting role for the pair formation in nuclei. The additional contributions are dominated by the repulsive {sup 3}P{sub 1} partial wave. Their effects, and generally spin-triplet nuclear forces between paired nucleons, are influenced by the interplay of spin-orbit partners. We explore the impact of including partial waves beyond the {sup 1}S{sub 0} channel on neutron-neutron pairing gaps in semimagic isotopic chains. In addition, we show that nuclear forces favor T=1,J=0 over T=0,J=1 pairing, except in low-j orbitals. This is in contrast to the free-space motivation that suggests the formation of deuteron-like T=0 pairs in N=Z nuclei. The suppression of T=0 pairing is because the {sup 3}S{sub 1} strength is distributed on spin-orbit partners and because of the effects of the repulsive {sup 1}P{sub 1} channel and of D waves.

Baroni, Simone [Institute for Nuclear Theory, University of Washington, Box 351550, Seattle, Washington 98195 (United States); TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3 (Canada); Macchiavelli, Augusto O. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Schwenk, Achim [TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3 (Canada); ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, 64291 Darmstadt (Germany); Institut fuer Kernphysik, Technische Universitaet Darmstadt, 64289 Darmstadt (Germany)

2010-06-15

230

Feasibility of boron neutron capture therapy (BNCT) for malignant pleural mesothelioma from a viewpoint of dose distribution analysis  

Microsoft Academic Search

Purpose: To investigate the feasibility of boron neutron capture therapy (BNCT) for malignant pleural mesothelioma (MPM) from a viewpoint of dose distribution analysis using Simulation Environment for Radiotherapy Applications (SERA), a currently available BNCT treatment planning system. Methods and Materials: The BNCT treatment plans were constructed for 3 patients with MPM using the SERA system, with 2 opposed anterior-posterior beams.

Minoru. Suzuki; Yoshinori Sakurai; Shinichiro Masunaga; Yuko Kinashi; Kenji Nagata; Akira Maruhashi; Koji Ono

2006-01-01

231

Neutrons, Markets, Cities, and Empires: A 1000Year Perspective on Ceramic Production and Distribution in the Postclassic Basin of Mexico  

Microsoft Academic Search

We use instrumental neutron activation analysis (INAA) of ceramics from three centers, Cerro Portezuelo, Chalco, and Xaltocan, in the Basin of Mexico, whose occupations span the Postclassic to examine the changing role of markets and evaluate models of political economy. Our results suggest that production and distribution of Epiclassic serving wares was highly localized conforming closely to a solar market

Deborah L. Nichols; Elizabeth M. Brumfiel; Hector Neff; Mary Hodge; Thomas H. Charlton; Michael D. Glascock

2002-01-01

232

Proton elastic scattering from tin isotopes at 295 MeV and systematic change of neutron density distributions  

Microsoft Academic Search

Cross sections and analyzing powers for proton elastic scattering from Sn116,118,120,122,124 at 295 MeV have been measured for a momentum transfer of up to about 3.5 fm-1 to deduce systematic changes of the neutron density distribution. We tuned the relativistic Love-Franey interaction to explain the proton elastic scattering of a nucleus whose density distribution is well known. Then, we applied

S. Terashima; H. Sakaguchi; H. Takeda; T. Ishikawa; M. Itoh; T. Kawabata; T. Murakami; M. Uchida; Y. Yasuda; M. Yosoi; J. Zenihiro; H. P. Yoshida; T. Noro; T. Ishida; S. Asaji; T. Yonemura

2008-01-01

233

Proton elastic scattering from tin isotopes at 295 MeV and systematic change of neutron density distributions  

Microsoft Academic Search

Cross sections and analyzing powers for proton elastic scattering from {sup 116,118,120,122,124}Sn at 295 MeV have been measured for a momentum transfer of up to about 3.5 fmš to deduce systematic changes of the neutron density distribution. We tuned the relativistic Love-Franey interaction to explain the proton elastic scattering of a nucleus whose density distribution is well known. Then, we

S. Terashima; H. Sakaguchi; H. Takeda; T. Ishikawa; M. Itoh; T. Kawabata; T. Murakami; M. Uchida; Y. Yasuda; J. Zenihiro; M. Yosoi; H. P. Yoshida; T. Noro; T. Ishida; S. Asaji; T. Yonemura

2008-01-01

234

The effects of high-velocity supernova kicks on the orbital properties and sky distributions of neutron-star binaries  

Microsoft Academic Search

We systematically investigate the effects of high supernova kick velocities on the orbital parameters of post-supernova neutron-star binaries. Using Monte Carlo simulations, we determine the post-supernova distributions of orbital parameters (orbital period, eccentricity, system velocity, spin inclination, ratio of spin to orbital angular momentum) for progenitors of high-mass X-ray binaries (HMXBs) and low-mass X-ray binaries (LMXBs). With the recent distribution

Niel Brandt; Philipp Podsiadlowski

1995-01-01

235

The Effects of High-Velocity Supernova Kicks on the Orbital Properties and Sky Distributions of Neutron Star Binaries  

Microsoft Academic Search

We systematically investigate the effects of high supernova kick velocities on the orbital parameters of post-supernova neutron-star binaries. Using Monte- Carlo simulations, we determine the post-supernova distributions of orbital parameters for progeneitors of HMXBs and LMXBs. With the recent distribution of pulsar birth velocities by Lyne & Lorimer (1994), only about 27% of massive systems remain bound after the supernova,

W. N. Brandt; Ph. Podsiadlowski

1994-01-01

236

Distinction between Proton-Neutron Density Distribution of Halo Nuclei at the Nuclear Surface via Reaction Cross Sections  

Microsoft Academic Search

Reaction cross sections (?R) for 11Be and 8B on proton targets at 50A?120AMeV have been measured to distinguish between the proton- and neutron- density distributions at the nuclear surface. The ?R is connected with the nucleon density distributions by the Glauber theory. Since the nucleon-nucleon total cross sections in that energy region have a large isospin dependence, the ?R on

D. Nishimura; M. Fukuda; M. Takechi; M. Mihara; D. Ishikawa; J. Komurasaki; K. Matsuta; R. Matsumiya; T. Kuboki; M. Yoshitake; T. Suzuki; T. Yamaguchi; S. Nakajima; K. Saito; M. Miura; I. Hachiuma; K. Namihira; T. Ohtsubo; Y. Shimbara; R. Watanabe; Y. Ohkuma; T. Izumikawa; K. Tanaka; T. Suda; A. Ozawa; Y. Yasuda; T. Moriguchi; S. Momota; S. Fukuda; S. Sato; M. Kanazawa; A. Kitagawa

2010-01-01

237

BNCT dose distribution in liver with epithermal D-D and D-T fusion-based neutron beams.  

PubMed

Recently, a new application of boron neutron capture therapy (BNCT) treatment has been introduced. Results have indicated that liver tumors can be treated by BNCT after removal of the liver from the body. At Lawrence Berkeley National Laboratory, compact neutron generators based on (2)H(d,n)(3)He (D-D) or (3)H(t,n)(4)He (D-T) fusion reactions are being developed. Preliminary simulations of the applicability of 2.45 MeV D-D fusion and 14.1 MeV D-T fusion neutrons for in vivo liver tumor BNCT, without removing the liver from the body, have been carried out. MCNP simulations were performed in order to find a moderator configuration for creating a neutron beam of optimal neutron energy and to create a source model for dose calculations with the simulation environment for radiotherapy applications (SERA) treatment planning program. SERA dose calculations were performed in a patient model based on CT scans of the body. The BNCT dose distribution in liver and surrounding healthy organs was calculated with rectangular beam aperture sizes of 20 cm x 20 cm and 25 cm x 25 cm. Collimator thicknesses of 10 and 15 cm were used. The beam strength to obtain a practical treatment time was studied. In this paper, the beam shaping assemblies for D-D and D-T neutron generators and dose calculation results are presented. PMID:15308157

Koivunoro, H; Bleuel, D L; Nastasi, U; Lou, T P; Reijonen, J; Leung, K-N

2004-11-01

238

Neutron skins in spherical and deformed nuclei from Skyrme Hartree-Fock calculations  

NASA Astrophysics Data System (ADS)

The development of neutron skins as a function of the neutron number is investigated within a self-consistent framework based on deformed Hartree-Fock calculations with density dependent Skyrme forces and pairing correlations in BCS approximation. We study several isotopic chains and consider all the experimentally observed isotopes from neutron-deficient to neutron-rich. We discuss various possibilities to define the neutron skin thickness based on the differences between neutron and proton radii as well as definitions based on comparison of the tails of the neutron and proton density distributions. We finally discuss the effects of deformation on the neutron skin based on the example of Kr isotopes. We study the neutron skins in different directions for oblate and prolate shapes and discuss it in terms of the quadrupole components of the density distributions.

Sarriguren, P.; Gaidarov, M. K.; de Guerra, E. Moya; Antonov, A. N.

2008-05-01

239

Determination of fast neutron flux distribution in irradiation sites of the Malaysian Nuclear Agency research reactor.  

PubMed

Determination of thermal to fast neutron flux ratio (f(fast)) and fast neutron flux (?(fast)) is required for fast neutron reactions, fast neutron activation analysis, and for correcting interference reactions. The f(fast) and subsequently ?(fast) were determined using the absolute method. The f(fast) ranged from 48 to 155, and the ?(fast) was found in the range 1.03×10(10)-4.89×10(10) n cm(-2) s(-1). These values indicate an acceptable conformity and applicable for installation of the fast neutron facility at the MNA research reactor. PMID:21295987

Yavar, A R; Sarmani, S B; Wood, A K; Fadzil, S M; Radir, M H; Khoo, K S

2011-01-13

240

Neutronic analysis stochastic distribution of fuel particles in Very High Temperature Gas-Cooled Reactors  

NASA Astrophysics Data System (ADS)

The Very High Temperature Gas-Cooled Reactor (VHTR) is a promising candidate for Generation IV designs due to its inherent safety, efficiency, and its proliferation-resistant and waste minimizing fuel cycle. A number of these advantages stem from its unique fuel design, consisting of a stochastic mixture of tiny (0.78mm diameter) microspheres with multiple coatings. However, the microsphere fuel regions represent point absorbers for resonance energy neutrons, resulting in the "double heterogeneity" for particle fuel. Special care must be taken to analyze this fuel in order to predict the spatial and spectral dependence of the neutron population in a steady-state reactor configuration. The challenges are considerable and resist brute force computation: there are over 1010 microspheres in a typical reactor configuration, with no hope of identifying individual microspheres in this stochastic mixture. Moreover, when individual microspheres "deplete" (e.g., burn the fissile isotope U-235 or transmute the fertile isotope U-238 (eventually) to Pu-239), the stochastic time-dependent nature of the depletion compounds the difficulty posed by the stochastic spatial mixture of the fuel, resulting in a prohibitive computational challenge. The goal of this research is to develop a methodology to analyze particle fuel randomly distributed in the reactor, accounting for the kernel absorptions as well as the stochastic depletion of the fuel mixture. This Ph.D. dissertation will address these challenges by developing a methodology for analyzing particle fuel that will be accurate enough to properly model stochastic particle fuel in both static and time-dependent configurations and yet be efficient enough to be used for routine analyses. This effort includes creation of a new physical model, development of a simulation algorithm, and application to real reactor configurations.

Ji, Wei

241

Pair-correlation properties and momentum distribution of finite number of interacting trapped bosons in three dimensions  

SciTech Connect

We study the ground state pair-correlation properties of a weakly interacting trapped Bose gas in three dimensions by using a correlated many-body method. The use of the van der Waals interaction potential and an external trapping potential shows realistic features. We also test the validity of shape-independent approximation in the calculation of correlation properties.

Biswas, Anindya; Das, Tapan Kumar [Department of Physics, University of Calcutta, 92 A.P.C. Road, Kolkata 700009 (India); Chakrabarti, Barnali [Abdus Salam International Centre for Theoretical Physics, 34100 Trieste (Italy) and Department of Physics, Lady Brabourne College, P-1/2 Suhrawardy Avenue, Kolkata 700017 (India)

2010-09-14

242

A distribution pattern of cadmium, gadolinium and samarium in Phaseolus vulgaris (L) plants as assessed by dynamic neutron radiography  

NASA Astrophysics Data System (ADS)

The qualitative and semi-quantitative distributions, presumably apoplast transport patterns for the Gd, Sm and Cd were investigated in the primordial leaf tissues of the bean using dynamic neutron radiography. According to the applied 3D, 2D images and the pixel count distribution histograms of the considered gray levels, peculiar distribution patterns were postulated for the elements. Main and lateral vascular systems for Gd, the cell walls as well as intercellular spaces for Sm and the main leaf vein for Cd assumed to be the apoplast transport spaces and volumes.

K?rösi, F.; Balaskó, M.; Sváb, E.

1999-11-01

243

A new approach to measure momentum distributions and production cross-sections of neutron rich nuclei using fragment separators  

NASA Astrophysics Data System (ADS)

The longitudinal momentum distributions of 34 neutron-rich isotopes of elements produced by fragmentation of a 76Ge beam at 132 MeV/u with 13?Z?27 were scanned using a novel experimental approach where a variety of targets with different thicknesses was used with the fragment separator at constant magnetic rigidity. In comparison to models that describe the shape and centroid of fragment momentum distributions, a parametrization based on the measured data was derived. Details of the transmission calculations, the analysis of their uncertainties, as well as the general analysis of momentum distributions and deduced cross-sections obtained with this approach are presented.

Tarasov, O. B.; Bazin, D.; Baumann, T.; Gade, A.; Ginter, T. N.; Hausmann, M.; Morrissey, D. J.; Pereira, J.; Portillo, M.; Sherrill, B. M.; Stolz, A.; Thoennessen, M.

2010-08-01

244

Lunar prospector epithermal neutrons from impact craters and landing sites: Implications for surface maturity and hydrogen distribution  

USGS Publications Warehouse

Initial studies of neutron spectrometer data returned by Lunar Prospector concentrated on the discovery of enhanced hydrogen abundances near both lunar poles. However, the nonpolar data exhibit intriguing patterns that appear spatially correlated with surface features such as young impact craters (e.g., Tycho). Such immature crater materials may have low hydrogen contents because of their relative lack of exposure to solar wind-implanted volatiles. We tested this hypothesis by comparing epithermal* neutron counts (i.e., epithermal -0.057 ?? thermal neutrons) for Copernican-age craters classified as relatively young, intermediate, and old (as determined by previous studies of Clementine optical maturity variations). The epithermal* counts of the crater and continuous ejecta regions suggest that the youngest impact materials are relatively devoid of hydrogen in the upper 1 m of regolith. We also show that the mean hydrogen contents measured in Apollo and Luna landing site samples are only moderately well correlated to the epithermal* neutron counts at the landing sites, likely owing to the effects of rare earth elements. These results suggest that further work is required to define better how hydrogen distribution can be revealed by epithermal neutrons in order to understand more fully the nature and sources (e.g., solar wind, meteorite impacts) of volatiles in the lunar regolith.

Johnson, J. R.; Feldman, W. C.; Lawrence, D. J.; Maurice, S.; Swindle, T. D.; Lucey, P. G.

2002-01-01

245

New method for measurement of energy and angular distributions of prompt fission neutrons  

Microsoft Academic Search

The energy (E) and the angle (theta) dependent emission probabilities N(E, theta) of prompt fission neutrons are measured by neutron time-of-flight spectroscopy as well as by a direction-sensitive method of fragment spectroscopy based on two parallel-plate avalanche counters (PPAC, one position-sensitive). Due to the determination of theta by the measurement of fragment direction for a fixed neutron detector position systematic

Horst Märten; Dietmar Richter; Dieter Seeliger; Wolf Dietrich Fromm; Waldemar Neubert; Albert Lajtai

1988-01-01

246

Distribution of Drug Molecules in Lipid Membranes: Neutron Diffraction and MD Simulations.  

NASA Astrophysics Data System (ADS)

Non-steroidal anti-inflammatory drugs (NSAIDs) e.g. Aspirin and Ibuprofen, with chronic usage cause gastro intestinal (GI) toxicity. It has been shown experimentally that NSAIDs pre-associated with phospholipids reduce the GI toxicity and also increase the therapeutic activity of these drugs compared to the unmodified ones. In this study, using neutron diffraction, the DOPC lipid bilayer structure (with and without drug) as well as the distribution of a model NSAID (Ibuprofen) as a function of its position along the membrane normal was obtained at sub-nanometer resolution. It was found that the bilayer thickness reduces as the drug is added. Further, the results are successfully compared with atomistic Molecular Dynamics simulations. Based on this successful comparison and motivated by atomic details from MD, quasi-molecular modeling of the lipid membrane is being carried out and will be presented. The above study is expected to provide an effective methodology to design drug delivery nanoparticles based on a variety of soft condensed matter such as lipids or polymers.

Boggara, Mohan; Mihailescu, Ella; Krishnamoorti, Ramanan

2009-03-01

247

Calculations and measurements of neutron moderation time distributions for multisphere LiI detectors and AB remmeter at 20-MeV electron linac  

SciTech Connect

Neutron moderation time distribution is an important factor for the dead-time correction for moderator type neutron detectors used at pulsed neutron fields. Measurements of the neutron moderation time distributions for multisphere (bare, 2 inch, 3 inch, 5 inch, 8 inch, 10 inch and 12 inch diameter) LiI detectors and AB remmeter have been successfully made inside a ANL 20-MeV electron Linac room. Equivalent calculations were also made using MCNP4a. First, the neutron energy spectrum at the detector position was calculated using a coupled EGS4-MORSE code with a giant-resonant photoneutron generation algorithm. The calculated spectrum agrees with the multisphere detector measurements from the unfolding. Then, neutrons arriving at the detector surface were scored as a function of energy and time using MCNP4a. Finally, the above neutron fluence as a function of energy and time was used as the source term and the neutrons detected by {sup 6}Li or {sup 10}B in the sensor were scored as a function of the moderation time for each detector. The calculations are in good agreement with the measurements. The results also show that the moderation time distributions for large detectors, e.g., the 12 inch detector and AB remmeter, depend mainly on the neutron spectrum and moderator thickness. However, for small detectors, the neutron travel time from the source target to the detector surface in the radiation field is also crucial. Therefore, all four factors (neutron spectrum, neutron travel time in the field, detector moderator thickness and detector response function) play interrelated roles in the time distribution of a moderator type detector.

Liu, J.C.; Rokni, S.; Vylet, V. [SLAC, Stanford, CA (United States)] [and others

1996-06-01

248

Yields of correlated fragment pairs in spontaneous fission of 252Cf  

Microsoft Academic Search

Independent yields of 139 individual secondary (appearing after neutron evaporation) fragment pairs of five different charge splits (ZL\\/ZH=46\\/52, 44\\/54, 42\\/56, 40\\/58, and 38\\/60) have been experimentally measured by detecting the coincidences between prompt gamma rays emitted in the spontaneous fission of 252Cf. Nuclear charge and mass distributions of fission fragments that follow from the measured yields of individual fragment pairs

G. M. Ter-Akopian; J. H. Hamilton; Yu. Ts. Oganessian; A. V. Daniel; J. Kormicki; A. V. Ramayya; G. S. Popeko; B. R. Babu; Q.-H. Lu; K. Butler-Moore; W.-C. Ma; E. F. Jones; J. K. Deng; D. Shi; J. Kliman; M. Morhác; J. D. Cole; R. Aryaeinejad; N. R. Johnson; I. Y. Lee; F. K. McGowan

1997-01-01

249

Pairing correlations in exotic nuclei  

NASA Astrophysics Data System (ADS)

The BCS and HFB theories which can accommodate the pairing correlations in the ground states of atomic nuclei are presented. As an application of the pairing theories, we investigate the spatial extension of weakly bound Ne and C isotopes by taking into account the pairing correlation with the Hartree-Fock-Bogoliubov (HFB) method and a 3-body model, respectively. We show that the odd-even staggering in the reaction cross sections of 30,31,32Ne and 14,15,16C are successfully reproduced, and thus the staggering can be attributed to the unique role of pairing correlations in nuclei far from the stability line. A correlation between a one-neutron separation energy and the anti-halo effect is demonstrated for s- and p-waves using the HFB wave functions. We also propose effective density-dependent pairing interactions which reproduce both the neutron-neutron (nn) scattering length at zero density and the neutron pairing gap in uniform matter. Then, we apply these interactions to study pairing gaps in semi-magic finite nuclei, such as Ca, Ni, Sn and Pb isotopic chains.

Sagawa, H.; Hagino, K.

2013-02-01

250

The distribution of some trace elements in iron meteorites, as determined by neutron activation  

Microsoft Academic Search

The ten trace elements germanium, arsenic, antimony, copper, chromium molybdenum, silver, indium, zinc and palladium have been determined in sixty-seven different meteorites, using neutron activation and radiochemical separations. In addition the meteorites have been analysed for gallium using either neutron activation or colorimetric methods. The sulphur content of twenty-five of the meteorites has also been measured, using an evolution and

A. A. Smales; D. Mapper; K. F. Fouché

1967-01-01

251

Temperature distribution in nuclear fuel rod and variation of the neutronic performance parameters in (D–T) driven hybrid reactor system  

Microsoft Academic Search

Temperature distribution in nuclear fuel rod and variation of the neutronic performance parameters are investigated for different coolants under various first wall loads (Pw=2, 5, 7, 8, 9, and 10 MW m?2) in (D, T) (deuterium and tritium) driven and fueled with UO2 hybrid reactors. Plasma chamber dimension, DR, with a line fusion neutron source is 300 cm. The fissile

Hüseyin Yap?c?; Osman ?pek; Veysel Özceyhan

2001-01-01

252

PULSAR PAIR CASCADES IN MAGNETIC FIELDS WITH OFFSET POLAR CAPS  

SciTech Connect

Neutron star magnetic fields may have polar caps (PCs) that are offset from the dipole axis, through field-line sweepback near the light cylinder or non-symmetric currents within the star. The effects of such offsets on electron-positron pair cascades are investigated, using simple models of dipole magnetic fields with small distortions that shift the PCs by different amounts or directions. Using a Monte Carlo pair cascade simulation, we explore the changes in the pair spectrum, multiplicity, and energy flux across the PC, as well as the trends in pair flux and pair energy flux with spin-down luminosity, L{sub sd}. We also give an estimate of the distribution of heating flux from returning positrons on the PC for different offsets. We find that even modest offsets can produce significant increases in pair multiplicity, especially for pulsars that are near or beyond the pair death lines for centered PCs, primarily because of higher accelerating fields. Pair spectra cover several decades in energy, with the spectral range of millisecond pulsars (MSPs) two orders of magnitude higher than for normal pulsars, and PC offsets allow significant extension of all spectra to lower pair energies. We find that the total PC pair luminosity L{sub pair} is proportional to L{sub sd}, with L{sub pair} {approx} 10{sup -3} L{sub sd} for normal pulsars and L{sub pair} {approx} 10{sup -2} L{sub sd} for MSPs. Remarkably, the total PC heating luminosity for even large offsets increases by less than a factor of two, even though the PC area increases by much larger factors, because most of the heating occurs near the magnetic axis.

Harding, Alice K.; Muslimov, Alex G. [Astrophysics Science Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2011-12-20

253

Cation Ordering in Li[NixMnxCo(1-2x)]O2-Layered Cathode Materials: A Nuclear Magnetic Resonance (NMR), Pair Distribution Function, X-ray Absorption Spectroscopy, and Electrochemical Study  

SciTech Connect

Several members of the compositional series Li[NixMnxCo(1-2x)]O2 (0.01 = x = 1/3) were synthesized and characterized. X-ray diffraction results confirm the presence of the layered a-NaFeO2-type structure, while X-ray absorption near-edge spectroscopy experiments verify the presence of Ni2+, Mn4+, and Co3+. Their local environment and short-range ordering were investigated by using a combination of 6Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and neutron pair distribution function (PDF) analysis, associated with reverse Monte Carlo (RMC) calculations. The 6Li MAS NMR spectra of compounds with low Ni/Mn contents (x = 0.10) show several well-resolved resonances, which start to merge when the amount of Ni and Mn increases, finally forming a broad resonance at high Ni/Mn contents. Analysis of the 6Li MAS NMR 6Li[Ni0.02Mn0.02Co0.96]O2 spectrum, is consistent with the formation of Ni2+ and Mn4+ clusters within the transition-metal layers, even at these low-doping levels. The oxidation state of Ni in this high Co content sample strongly depends upon the Li/transition metal ratio of the starting materials. Neutron PDF analysis of the highest Ni/Mn content sample Li[Ni1/3Mn1/3Co1/3]O2 shows a tendency for Ni cations to be close to Mn cations in the first coordination shell; however, the Co3+ ions are randomly distributed. Analysis of the intensity of the 'LiCoO2' resonance, arising from Li surrounded by Co3+ in its first two cation coordination shells, for the whole series provides further evidence for a nonrandom distribution of the transition-metal cations. The presence of the insulator-to-metal transition seen in the electrochemical profiles of these materials upon charging correlates strongly with the concentration of the 'LiCoO2' resonance.

Zeng,D.; Cabana, J.; Breger, J.; Yoon, W.; Grey, C.

2007-01-01

254

Assessment of cortical and trabecular bone distribution in the beagle skeleton by neutron activation analysis  

SciTech Connect

The distribution of bone calcium between morphologically identifiable cortical and trabecular bone obtained by dissection and quantitated by neutron activation analysis (NAA) is described. The skeleton of a female beagle dog was dissected into approximately 400 pieces and assayed for /sup 49/Ca produced in the University of California, Irvine TRIGA reactor. For each of the skeletal sections, we give the initial weight of the alcohol-fixed tissue, which includes cortical bone, trabecular bone, marrow, and cartilage, and a final tissue weight after the marrow and trabecular bone have been dissected away; total section and cortical section calcium weights are reported. The level of detail is represented, for example, by the vertebrae, which were divided into three parts (body, spine, and transverse processes) and by the long bones, which were divided into 10-12 parts such that characterization of the epiphysis, metaphysis, and diaphysis was accomplished. The median percentage cortical calcium values for cervical, thoracic, and lumbar vertebrae were 82%, 56%, and 66%, respectively; however, variation within these groups and among individual vertebral sections was about a factor of 2. For long bones, the median percentage cortical calcium varied from 90-100% in the midshaft to below 50% in the proximal and distal sections. The final calculated cortical tissue-to-calcium mass ratio (TCR) varied from about 4.5 for midshafts of the long bones to about 9 for thoracic vertebral bodies and indicated that the mineral fraction of cortical bone is not constant throughout the skeleton. The ratio of cortical to trabecular calcium in the skeleton was 79.6:20.4.

Parks, N.J.; Jee, W.S.; Dell, R.B.; Miller, G.E.

1986-07-01

255

Imaging of a spatial distribution of preferred orientation of crystallites by pulsed neutron Bragg edge transmission  

NASA Astrophysics Data System (ADS)

A pulsed neutron transmission coupled with a two-dimensional position sensitive neutron detector gives a time-of-flight spectrum at each pixel of the detector, which depends on the total cross-sections of materials. In order to extract quantitative information of the preferred orientation included in the Bragg scattering total cross-section data, a spectral analysis software for the 2D imaging has been developed, and the transmission data of an unbent iron plate were analyzed. The 2D images with respect to the preferred orientation were successfully obtained, and the effectiveness of spectroscopic neutron transmission imaging was indicated.

Sato, H.; Takada, O.; Iwase, K.; Kamiyama, T.; Kiyanagi, Y.

2010-11-01

256

Distributions of glass-transition temperature and thermal expansivity in multilayered polystyrene thin films studied by neutron reflectivity  

NASA Astrophysics Data System (ADS)

We performed neutron reflectivity measurements on multilayered polymer thin films consisting of alternatively stacked deuterated polystyrene (d-PS) and hydrogenated polystyrene (h-PS) layers ˜200 Ĺ thick as a function of temperature covering the glass-transition temperature Tg, and we found a wide distribution of Tg as well as a distribution of the thermal expansivity ? within the thin films, implying the dynamic heterogeneity of the thin films along the depth direction. The reported anomalous film thickness dependences of Tg and ? were reasonably understood in terms of the distributions, showing that the surface mobile layer and the bottom hard interfacial layer are, respectively, responsible for the depressions of Tg and ? with decreasing film thickness. The molecular mobility in each layer is also discussed in relation to the distribution of Tg, based on the results on mutual diffusion at the layer interface.

Inoue, Rintaro; Kawashima, Kazuko; Matsui, Kazuya; Kanaya, Toshiji; Nishida, Koji; Matsuba, Go; Hino, Masahiro

2011-02-01

257

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

PubMed

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

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

2011-04-22

258

Study of the Fluence and Neutron Dose Energy Distribution at Large Distances from Accelerators.  

National Technical Information Service (NTIS)

The transport to large distances of neutrons produced by high-energy accelerators is studied experimentally and theoretically for the Dubna synchrocyclotron. This accelerator uses superposition of the point monodirectional and point isotopic sources with ...

M. M. Komochkov A. L. Shishkin B. V. Man'ko B. S. Sychev

1979-01-01

259

Measurements and calculations of neutron scattering angular distributions over a wide mass and energy range  

SciTech Connect

Neutron elastic and inelastic differential cross sections for targets between /sup 9/Be and /sup 239/Pu at energies, E > 14 MeV have been measured using the Livermore and Ohio University neutron time-of-flight facilities. We review here the data and the analyses based on two local microscopic optical potentials: that of Jeukenne, Lejeune and Mahaux, and that of Brieva and Rook. The results are also compared with calculations using global potentials. Coupled channel formalism has been used in the analysis of targets with strong deformations, such as Be, C, Ta, and actinides. The value of the microscopic optical potentials as a tool to predict elastic and inelastic neutron cross sections over a wide mass and energy range is discussed. The need for neutron measurements up to higher energies and their analysis in conjunction with (p,p) and charge exchange (p,n) data is addressed. 17 refs.

Hansen, L.F.

1985-05-01

260

Mass distributions in monoenergetic-neutron-induced fission of /sup 239/Pu  

SciTech Connect

Fission product yields for 24 masses were determined for the fission of /sup 239/Pu with essentially monoenergetic neutrons of 0.17, 1.0, 2.0, 3.4, 4.5, 6.1, and 7.9 MeV. Fission product activities were measured by Ge(Li) ..gamma..-ray spectrometry of irradiated /sup 239/Pu targets and by chemical separation of the fission product elements followed by ..beta.. counting. Yields of near symmetric (valley) fission products increase nearly monotonically with incident neutron energy and do not exhibit a break in the slope of the yield versus neutron energy curve in the energy region where second-chance fission begins. This is in contrast to the curves for /sup 232/Th, /sup 235/U, and /sup 238/U neutron-induced fission.

Gindler, J.E.; Glendenin, L.E.; Henderson, D.J.; Meadows, J.W.

1983-05-01

261

Neutron multiplicity distributions for 1.94 to 5 GeV/c proton-, antiproton-, pion-, kaon-, and deuteron-induced spallation reactions on thin and thick targets  

SciTech Connect

Measurements of neutron multiplicity distributions of 1.94 to 5.0 GeV/ c proton-, antiproton-, pion-, kaon-, and deuteron-induced spallation reactions on thin (few mm thick) and thick (35{endash}40 cm thick) targets are presented. The 4{pi} neutron detector employed for the first time to measure neutron multiplicity distributions from thick targets is described. Results for thin and thick targets are compared with intra- and internuclear cascade model calculations. {copyright} {ital 1997} {ital The American Physical Society}

Pienkowski, L.; Goldenbaum, F.; Hilscher, D.; Jahnke, U. [Hahn-Meitner-Institut Berlin, Glienickerstrasse 100, D-14109 Berlin (Germany); Galin, J.; Lott, B. [GANIL (IN2P3-CNRS, DSM-CEA), BP 5027, F-14021 Caen-Cedex (France)

1997-10-01

262

Effective pairing interactions with isospin density dependence  

SciTech Connect

We perform Hartree-Fock-Bogoliubov (HFB) calculations for semi-magic calcium, nickel, tin, and lead isotopes and N=20,28,50, and 82 isotones using density-dependent pairing interactions recently derived from a microscopic nucleon-nucleon interaction. These interactions have an isovector component so that the pairing gaps in symmetric and neutron matter are reproduced. Our calculations well account for the experimental data for the neutron number dependence of binding energy, two-neutron separation energy, and odd-even mass staggering of these isotopes. This result suggests that by introducing the isovector term in the pairing interaction, one can construct a global effective pairing interaction that is applicable to nuclei in a wide range of the nuclear chart. It is also shown with the local density approximation that the pairing field deduced from the pairing gaps in infinite matter reproduces qualitatively well the pairing field for finite nuclei obtained with the HFB method.

Margueron, J. [Institut de Physique Nucleaire, IN2P3-CNRS and Universite Paris-Sud, F-91406 Orsay Cedex (France); Center for Mathematical Sciences, University of Aizu, Aizu-Wakamatsu, 965-8580 Fukushima (Japan); Sagawa, H. [Center for Mathematical Sciences, University of Aizu, Aizu-Wakamatsu, 965-8580 Fukushima (Japan); Hagino, K. [Department of Physics, Tohoku University, Sendai, 980-8578 (Japan)

2008-05-15

263

Earthquake interevent time distributions reflect the proportion of dependent and independent events pairs and are therefore not universal  

NASA Astrophysics Data System (ADS)

Seismic activity is routinely quantified using event rates or their inverse, interevent times, which are more stable to extreme events [1]. It is common practice to model regional earthquake interevent times using a gamma distribution [2]. However, the use of this gamma distribution is empirically based, not physical. Our recent work has shown that the gamma distribution is an approximation that drops out of a physically based model after the commonly applied filtering of the raw data [3]. We show that in general, interevent time distributions have a fundamentally bimodal shape caused by the mixing of two contributions: correlated aftershocks, which have short interevent times and produce a gamma distribution; and independent events, which tend to be separated by longer intervals and are described by a Poisson distribution. The power-law segment of the gamma distribution arises at the cross over between these distributions. This physically based model is transferable to other fields to explain the form of cascading interevent time series with varying proportions of independent and dependent daughter events. We have found that when the independent or background rate of earthquakes is high, as is the case for earthquake catalogues spanning large regions, significant overlapping of separate aftershock sequences within the time series "masks" the effects of these aftershock sequences on the temporal statistics. The time series qualitatively appears more random; this is confirmed in the interevent time distribution, in the convergence of the mean interevent time, and in the poor performance of temporal ETAS parameter inversions on synthetic catalogues within this regime [4]. The aftershock-triggering characteristics within the data are thus hidden from observation in the time series by a high independent rate of events; spatial information about event occurrence is needed in this case to uncover the triggering structure in the data. We show that earthquake interevent time data from the Kilauea volcano can be explained by this physical model and demonstrate that the form of the interevent time distributions separated in space reflect the diversity of processes across the volcano [5]. [1] Naylor, M., Main, I.G. & Touati, S. (2009) Quantifying uncertainty in mean earthquake interevent times for a finite sample, J. Geophys. Res, 114, B01316. [2] Corral, A. (2004) Long-Term Clustering, Scaling, and Universality in the Temporal Occurrence of Earthquakes Phys. Rev. Lett. 92, 108501 [3] Touati, S., Naylor, M. & Main, I.G., (2009) Origin and nonuniversality of the earthquake interevent time distribution, Phys. Rev. Lett .102, 168501 [4] S. Touati, M. Naylor, I.G. Main and M. Christie (Submitted) Masking of earthquake triggering behaviour by a high spontaneous rate and implications for ETAS inversions [5] A. Bell, S. Touati, M. Naylor and I. Main, (Submitted) The structure of earthquake interevent-time distributions at Kilauea volcano, Hawaii

Naylor, Mark; Touati, Sarah; Main, Ian; Bell, Andrew

2010-05-01

264

Calculations of the anisotropy of the fission fragment angular distribution and neutron emission multiplicities prescission from Langevin dynamics  

SciTech Connect

The anisotropy of the fission fragment angular distribution defined at the saddle point and the neutron multiplicities emitted prior to scission for fissioning nuclei {sup 224}Th, {sup 229}Np, {sup 248}Cf, and {sup 254}Fm are calculated simultaneously by using a set of realistic coupled two-dimensional Langevin equations, where the (c,h,{alpha}=0) nuclear parametrization is employed. In comparison with the one-dimensional stochastic model without neck variation, our two-dimensional model produces results that are in better agreement with the experimental data, and the one-dimensional model is available only for low excitation energies. Indeed, to determine the temperature of the nucleus at the saddle point, we investigate the neutron emission during nucleus oscillation around the saddle point for different friction mechanisms. It is shown that the neutrons emitted during the saddle oscillation cause the temperature of a fissioning nuclear system at the saddle point to decrease and influence the fission fragment angular distribution.

Jia Ying; Bao Jingdong [Department of Physics, Beijing Normal University, Beijing 100875 (China)

2007-03-15

265

Measures of daily distribution patterns of cow calf pairs using global positioning systems on both cows and calves  

Technology Transfer Automated Retrieval System (TEKTRAN)

GPS collars were used to describe the daily distribution patterns of cows and their calves from 18 to 60 days postpartum on pinyon juniper-shortgrass rangeland in central New Mexico. Eighteen, 3 year old cows and their calves were fitted weekly with GPS collars for seven consecutive weeks. Twenty da...

266

MCNP modeling of the Swiss LWRs for the calculation of the in- and ex-vessel neutron flux distributions  

SciTech Connect

MCNP models of all Swiss Nuclear Power Plants have been developed by the National Cooperative for the Disposal of Radioactive Waste (Nagra), in collaboration with the utilities and ETH Zurich, for the 2011 decommissioning cost study. The estimation of the residual radionuclide inventories and corresponding activity levels of irradiated structures and components following the NPP shut-down is of crucial importance for the planning of the dismantling process, the waste packaging concept and, consequently, for the estimation of the decommissioning costs. Based on NPP specific data, the neutron transport simulations lead to the best yet knowledge of the neutron spectra necessary for the ensuing activation calculations. In this paper, the modeling concept towards the MCNP-NPPs is outlined and the resulting flux distribution maps are presented. (authors)

Pantelias, M.; Volmert, B.; Caruso, S. [National Cooperative for the Disposal of Radioactive Waste Nagra, Hardstrasse 73, 5430, Wettingen (Switzerland); Zvoncek, P. [Laboratory for Nuclear Energy Systems, ETH Zurich, Sonneggstrasse 3, 8092, Zurich (Switzerland); Bitterli, B. [Kernkraftwerk Goesgen-Daeniken AG, 4658 Daeniken (Switzerland); Neukaeter, E.; Nissen, W. [BKW FMB Energie AG-Kernkraftwerk Muehleberg, 3203 Muehleberg (Switzerland); Ledergerber, G. [Kernkraftwerk Leibstadt AG, 5325 Leibstadt (Switzerland); Vielma, R. [Axpo AG-Kernkraftwerk Beznau, 5312 Doettingen (Switzerland)

2012-07-01

267

Spatial distribution of thorium fission rate in a fast spallation and fission neutron field: An experimental and Monte Carlo study  

NASA Astrophysics Data System (ADS)

The Energy plus Transmutation (EpT) set-up of the Joint Institute for Nuclear Research (JINR), Dubna, Russia is composed of a lead spallation target surrounded by a blanket of natural uranium. The resultant neutron spectrum is a combination of spallation and fission spectra, modified by a reflective external layer of polyethylene and an internal absorbing layer of cadmium. The EpT set-up was irradiated with a beam of 4 GeV deuterons from the Nuclotron Accelerator at JINR. The spatial distribution of thorium fission rate within the assembly was determined experimentally, using a fission track detector technique, and compared with Monte Carlo predictions of the MCNPX code. Contributions of neutrons, protons, deuterons, photons and pions to total fission were taken into account. Close agreement between the experimental and calculated results was found.

Borger, J. J.; Hashemi-Nezhad, S. R.; Alexiev, D.; Brandt, R.; Westmeier, W.; Thomauske, B.; Adam, J.; Kadykov, M.; Tiutiunnikov, S.

2012-02-01

268

Probing the Room Temperature Spatial Distribution of Hydrogen in Nanoporous Carbon by Use of Small-Angle Neutron Scattering  

SciTech Connect

The spatial distribution of hydrogen physically adsorbed in a nanoporous carbon at room temperature (RT) as a function of H2 gas pressure is investigated for the first time using small-angle neutron scattering (SANS). A hierarchical pore structure consisting of micropores and a fractal mesopore network of the used activated carbon is also studied to correlate the relationship between the spatial distribution of hydrogen and the pore confinement. The cylinder-like cluster of aggregated hydrogen is formed and is confined in the disklike micropore. The evolution of spatial structures of adsorbed hydrogen with hydrogen pressure is elucidated. A direct experimental observation of the spatial distribution and the behavior of hydrogen adsorbed in the porous materials at RT is still scarce to date. The analysis results obtained by SANS provide new information for the future investigations of the RT storage mechanism of hydrogen in the nanoporous materials developed for the purpose of on-board hydrogen storage.

Tsao, Cheng-Si [Massachusetts Institute of Technology (MIT); Li, Mingda [ORNL; Zhang, Yang [ORNL; Leao, Juscelino B [ORNL; Chiang, Wei-Shan [ORNL; Chung, Tsui-Yun [Institute of Nuclear Energy Research, Taiwan; Tzeng, Yi-Ren [Institute of Nuclear Energy Research, Taiwan; Chen, Sow-hsin H [ORNL

2010-01-01

269

Measurement of energy spectra and spatial distributions of neutron beams provided by the ANNRI beamline for capture cross-section measurements at the J-PARC/MLF  

NASA Astrophysics Data System (ADS)

We measured the energy spectra and spatial distributions of the neutron beam of Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) at the Japan Proton Accelerator Research Complex/Materials and Life Science Experimental Facility (J-PARC/MLF). Our research team designed and built ANNRI to measure nuclear data with high precision. The measurements of the neutron beam were performed on three types of beams provided by ANNRI in the neutron energy range from 1.5 meV to 10 keV. The energy spectra show a typical feature of para-hydrogen moderator, and the absolute intensities almost agree with predictions based on both a simulation calculation of the Japan Spallation Neutron Source (JSNS) and a neutron transmission calculation of the beamline. The available neutron intensities at 21.5 m are 7.5×105, 1.6×104, and 1.1×105 n/cm2/s in the energy ranges 1.5-25 meV, 0.9-1.1 eV, and 0.9-1.1 keV, respectively, under the 17.5 kW JSNS operation. The measured spatial distributions of the beams formed by three different collimators are consistent with those expected from the collimator-system design of the beamline. The beam sizes in FWHM are about 29, 14, and 11 mm for the three different beam collimators. The edges of the spatial distributions are relatively sharp, enabling us to measure the nuclear data successfully.

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

2011-01-01

270

Measuring subsurface water distribution using the Dynamic Albedo of Neutrons instrument on Mars Science Laboratory  

NASA Astrophysics Data System (ADS)

The Dynamic Albedo of Neutrons (DAN) instrument, a neutron scattering instrument currently being constructed by IKI, is a component of the science payload of the 2009 Mars Science Laboratory (MSL) mission. Based on simulations using the Monte-Carlo N-Particle Extended (MCNPX) particle physics code, DAN is able to measure bulk water content and to detect variations in water concentration up to ˜50 cm beneath the ground surface, assuming perfect detector performance. Data from DAN, combined with measurements from other instruments on MSL, allow derivation of profiles of water content to a depth of ˜15 cm.

Busch, Michael W.; Aharonson, Oded

2008-07-01

271

Pick a Pair. Pancake Pairs  

ERIC Educational Resources Information Center

|Cold February weather and pancakes are a traditional pairing. Pancake Day began as a way to eat up the foods that were abstained from in Lent--traditionally meat, fat, eggs and dairy products. The best-known pancake event is The Pancake Day Race in Buckinghamshire, England, which has been run since 1445. This column describes pairs of books that…

Miller, Pat

2005-01-01

272

Radiowave dielectric investigation of boron compounds distribution in cultured tumour cells: relevance to boron neutron capture therapy  

NASA Astrophysics Data System (ADS)

The distribution of two main Boron neutron capture therapy (BNCT) agents, borocaptate sodium ( BSH) and borono-phenylalanine ( BPA), in C6 rat glioma cells has been investigated by means of radiowave dielectric spectroscopy measurements. Significant differences between cells treated with the two different boron carriers were found in the magnitude of passive electrical cell parameters. This technique offers a new procedure for the measurement of boron compounds interactions with different biological environments at cellular level and is suggested to have the potentiality for becoming an attractive tool for biodistribution studies of BNCT compounds in biological tissues.

Capuani, S.; Gili, T.; Cametti, C.; Maraviglia, B.; Colasanti, M.; Muolo, M.; Venturini, G.

2002-07-01

273

NEUTRON SPECTRUM TEMPERATURE DISTRIBUTION IN HETEROGENEOUS MEDIA WITH ENERGY DEPENDENT ABSORPTION  

Microsoft Academic Search

The problem of neutron thermalization in heavy gas was solved in Pâ; approximation by means of the expansion in Laguerre polynomials. The absorption ; cross section was assumed to be energy-dependent. More detailed calculations ; were performed for 1\\/v absorption. A system of coupled equations was obtained ; for the energy moments of the spectrum. The number of equations is

1961-01-01

274

Phase separation and nanostructuring in the thermoelectric material PbTe[subscript 1?x]S[subscript x] studied using the atomic pair distribution function technique  

SciTech Connect

The average and local structures of the (PbTe){sub 1-x}(PbS){sub x} system of thermoelectric materials has been studied using the Rietveld and atomic pair distribution function methods. Samples with 0.25 {le} x are macroscopically phase separated. Phase separation was suppressed in a quenched x=0.5 sample which, nonetheless, exhibited a partial spinodal decomposition. The promising thermoelectric material with x=0.16 showed intermediate behavior. Combining TEM and bulk scattering data suggests that the sample is a mixture of PbTe-rich material and a partially spinodally decomposed phase similar to the quenched 50% sample. This confirms that, in the bulk, this sample is inhomogeneous on a nanometer length scale, which may account for its enhanced thermoelectric figure of merit.

Lin, He; Bož in, E.S.; Billinge, S.J.L.; Androulakis, J.; Malliakas, C.D.; Lin, C.H.; Kanatzidis, M.G.; (MSU); (NWU); (BNL)

2009-08-13

275

Accurate structure analysis of Mo[subscript 6]S[subscript y]I[subscript z] nanowires from atomic pair distribution function (PDF) analysis  

SciTech Connect

The structure of the recently discovered systematically reproducible Mo{sub 6}S{sub y}I{sub z} nanowires has been determined from the atomic pair distribution function (PDF) analysis of powder X-ray diffraction data. This total scattering approach was required because the nanowires are not perfectly crystalline and, therefore, the structure cannot be obtained crystallographically. Several nanotube and nanowire models were fit to the PDF data. The resulting best-fit model structure consists of nanowires of Mo{sub 6} octahedra that are bridged by sulfur and terminated on the outside by iodine. This demonstrates the power of total scattering methods in accurately resolving structural issues in nanostructured materials where traditional crystallographic methods fail.

Paglia, G.; Bozin, E.S.; Vengust, D.; Mihailovic, D.; Billinge, S.J.L. (Joseph Stefan Inst.); (MSU)

2010-12-03

276

Neutron multiplicity distributions and the role of transfer and breakup in quasielastic heavy-ion reactions at 15 MeV/nucleon  

SciTech Connect

A new tool for the study of heavy-ion reactions is obtained by adapting a 4..pi..-neutron-multiplicity counter to accelerator experiments. The instrument registers almost all neutrons emitted in each single reaction event. For quasielastic reactions of 290-MeV /sup 20/Ne + /sup 197/Au the measured neutron multiplicity distributions allow a quantitative decomposition of the cross section into two contributions: one with higher Q value from transfer reactions, one with lower Q value due to the decay of the projectilelike fragments.

Jahnke, U.; Ingold, G.; Homeyer, H.; Buergel, M.; Egelhaaf, C.; Fuchs, H.; Hilscher, D.

1983-04-25

277

Precision and Bias of a Normal Finite Mixture Distribution Model to Analyze Twin Data When Zygosity is Unknown: Simulations and Application to IQ Phenotypes on a Large Sample of Twin Pairs  

Microsoft Academic Search

The classification of twin pairs based on zygosity into monozygotic (MZ) or dizygotic (DZ) twins is the basis of most twin analyses. When zygosity information is unavailable, a normal finite mixture distribution (mixture distribution) model can be used to estimate components of variation for continuous traits. The main assumption of this model is that the observed phenotypes on a twin

Beben Benyamin; Ian J. Deary; Peter M. Visscher

2006-01-01

278

Two R Process Components in Ultra-Metal-Poor Stars: The Neutron-Capture Element Distribution of CS 22892-052  

Microsoft Academic Search

The abundance patterns of neutron-capture elements in very metal-poor halo stars play a crucial role in guiding and constraining\\u000a theoretical models of nucleosynthesis. Many studies have suggested that the abundance patterns of the heavier (Z? 56) stable neutron-capture elements in very metal-poor halo stars are consistent with the solar system r-process abundance distribution, but this concordance breaks down for the

Bo Zhang; Ji Li; Yue-Xiang Wang; Yan-Xia Zhang; Jun-Hong Liu; Qiu-He Peng

2002-01-01

279

Quark momentum-space charge distribution in deuteron and neutron\\/proton structure functions ratio  

Microsoft Academic Search

.  The aim of the present article is to extract the free neutron structure function, which is experimentally unknown, form proton\\u000a and deuteron deep inelastic scattering (DIS) data in the deep valence region. We begin by using the quark-exchange formalism,\\u000a deuteron wave function and Fermi motion effect to investigate the deep inelastic electron scattering from the deuteron. The\\u000a up- and down-quark

M. Modarres; M. M. Yazdanpanah; F. Zolfagharpour

2007-01-01

280

THE ULTRAVIOLET SPECTRAL ENERGY DISTRIBUTIONS OF QUIESCENT BLACK HOLES AND NEUTRON STARS  

SciTech Connect

We present Hubble Space Telescope/Advanced Camera for Surveys ultraviolet photometry of three quiescent black hole X-ray transients, X-ray Nova Muscae 1991 (GU Mus), GRO J0422+32 (V518 Per), and X-ray Nova Vel 1993 (MM Vel), and one neutron star system, Aql X-1. These are the first quiescent UV detections of these objects. All are detected at a much higher level than expected from their companion stars alone and are significant detections of the accretion flow. Three of the four UV excesses can be characterized by a blackbody of temperature 5000-13, 000 K, hotter than expected for the quiescent outer disk. A good fit could not be found for MM Vel. The source of the blackbody-like emission is most likely a heated region of the inner disk. Contrary to initial indications from spectroscopy, there does not appear to be a systematic difference in the UV luminosity or spectral shape between black holes and neutron star systems. However, combining our new data with earlier spectroscopy and published X-ray luminosities, there is a significant difference in the X-ray to UV flux ratios, with the neutron stars exhibiting L{sub X}/L{sub UV} about 10 times higher than the black hole systems. This is consistent with earlier comparisons based on estimating non-stellar optical light, but since both bandpasses we use are expected to be dominated by accretion light, we present a cleaner comparison. This suggests that the difference in X-ray luminosities cannot simply reflect differences in quiescent accretion rates and so the UV/X-ray ratio is a more robust discriminator between the black hole and neutron star populations than the comparison of X-ray luminosities alone.

Hynes, R. I. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Robinson, E. L., E-mail: rih@phys.lsu.edu, E-mail: elr@astro.as.utexas.edu [Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712 (United States)

2012-04-10

281

Calculating Method and Characteristics of the Distribution of Neutron Exposures in the Radiative S-process Nucleosynthesis Model for AGB Stars  

NASA Astrophysics Data System (ADS)

A study on the distribution of neutron exposures in a low-mass asymptotic giant branch (AGB) star is presented, according to the s-process nucleosynthesis model with the 12C(?, n)16O reaction occurred under radiative conditions in the interpulse phases. The model parameters, such as the over- lap factor r of two successive convective thermal pulses, the mass ratio q of the 13C shell with respect to the He intershell, and the effective mass of 13C in the 13C shell, vary with the pulse number. Considering these factors, a calculating method for the distribution of neutron exposures in the He intershell has been presented. This method has the features of simplicity and universality. Using this method, the exposure distribution for the stellar model of a star with the mass of 3 M? and the solar metallicity has been calculated. The results suggest that under the reasonable assumption that the number density of neutrons is uniform in the 13C shell, the ?nal exposure distribution approaches to an exponential distribution. For a stellar model with the de?nite initial mass and metallicity, there is a de?nite relation between the mean neutron exposure ?0 and the neutron exposure ?? of each pulse, namely ?0 = 0.434?(q1, q2, …, qmmax +1, …, r1, r2, …, rmmax +1)??, where mmax is the total number of thermal pulses with the third dredge-up episode, and the proportional coeffcient ?(q1, q2, …, qmmax +1, …, r1, r2, …, rmmax +1) can be determined by an exponential curve ?tting to the ?nal exposure distribution. This new formula quantitatively uni?es the classical model with the s-process nu- cleosynthesis model by means of neutron exposure distribution, and makes the classical model continue to offer guidance and constraints to the s-process nu- merical calculations of stellar models.

Feng-hua, Zhang; Gui-de, Zhou; Wen-yuan, Cui; Bo, Zhang

2013-10-01

282

Fission fragment mass and energy distributions as a function of incident neutron energy measured in a lead slowing-down spectrometer  

SciTech Connect

A new method of measuring fission fragment mass and energy distributions as a function of incident neutron energy in the range from below 0.1 eV to 1 keV has been developed. The method involves placing a double-sided Frisch-gridded fission chamber in Rensselaer Polytechnic Institute's lead slowing-down spectrometer (LSDS). The high neutron flux of the LSDS allows for the measurement of the energy-dependent, neutron-induced fission cross sections simultaneously with the mass and kinetic energy of the fission fragments of various small samples. The samples may be isotopes that are not available in large quantities (submicrograms) or with small fission cross sections (microbarns). The fission chamber consists of two anodes shielded by Frisch grids on either side of a single cathode. The sample is located in the center of the cathode and is made by depositing small amounts of actinides on very thin films. The chamber was successfully tested and calibrated using 0.41+-0.04 ng of {sup 252}Cf and the resulting mass distributions were compared to those of previous work. As a proof of concept, the chamber was placed in the LSDS to measure the neutron-induced fission cross section and fragment mass and energy distributions of 25.3+-0.5 mug of {sup 235}U. Changes in the mass distributions as a function of incident neutron energy are evident and are examined using the multimodal fission mode model.

Romano, C.; Danon, Y.; Block, R.; Thompson, J.; Blain, E. [Rensselaer Polytechnic Institute, Department of Mechanical, Aerospace, and Nuclear Engineering, NES 1-25, 110 8th Street, Troy, New York 12180 (United States); Bond, E. [Los Alamos National Lab, Los Alamos, New Mexico 87545 (United States)

2010-01-15

283

Pairing anti-halo effect  

NASA Astrophysics Data System (ADS)

We discuss pairing correlations in weakly bound neutron rich nuclei, by using the coordinate-space Hartree-Fock-Bogolyubov approach which allows to take into account the coupling to particle continuum. We show that the additional pairing binding energy acts against a development of an infinite rms radius that characterizes standard /l=0 mean-field eigenfunctions in the limit of vanishing binding energy. As a result, neutron radii of even-/N nuclei do not diverge in the limit of vanishing Fermi energy. Only the broken-pair ground states of odd-/N nuclei can exhibit diverging neutron radii, provided an /l=0 (or 1) quasiparticle state appears near the Fermi surface. We also show that the pairing-increased (although not infinite) rms radii of even-/N nuclei result from the coupling to low-lying /l=0 continuum, which is always available for virtual pair excitations, independently of what are the angular momenta of least-bound single-particle levels.

Bennaceur, K.; Dobaczewski, J.; Ploszajczak, M.

2000-12-01

284

Number Pairs  

NSDL National Science Digital Library

With this interactive Flash applet students make use of complements of 10 to develop fluency with addition within 100. Users "repair" a water slide by selecting pairs of numbers that add to 20 in the first round, and then to 100. In successive rounds they may choose to practice with any multiple of 10 from 30 to 90.

Bunker, Dan

2010-01-01

285

Residual stress distribution in steel butt welds measured using neutron and synchrotron diffraction.  

SciTech Connect

70 keV synchrotron radiation and thermal neutrons have been employed to investigate the residual stress characteristics in a fully restrained, steel, butt weld. The focus is on the values of the subsurface and through-thickness strain/stress variation in the middle of the weld. The advantages and limitations of the techniques have been addressed, in relation to the gauge volume, the stress-free reference sample and positioning. The measurement of residual stress around the weld achieved in this work significantly improves the resolution at which residual stress in welded components has been determined.

Paradowska, A. M.; Price, J. W. H.; Finlayson, T. R.; Lienert, U.; Walls, P.; Ibrahim, R.; X-Ray Science Division; Rutherford Appleton Lab.; Monash Univ.; Univ. of Melborne; ANSTO

2009-01-01

286

Energy Distribution Function of Fast Neutral Atoms and Neutron Production Rate in Inertial Electrostatic Confinement Device  

Microsoft Academic Search

Fast-neutral energy distribution function in inertial electrostatic confinement (IEC) plasmas is studied by solving the Boltzmann equation for fast neutral, which is produced by several kinds of charge-exchange reac- tions, for various presumed ion distribution functions. From the obtained fast-neutral distribution functions, the Doppler-shift spectrum (energy spectrum) of fast-neutral in IEC devices is evaluated. By comparing the spectra between the

YOSHINAGA Sho; MATSUURA Hideaki; NAKAO Yasuyuki; KUDO Kazuhiko

2006-01-01

287

Improvement of dose distribution in phantom by using epithermal neutron source based on the Be(p,n) reaction using a 30 MeV proton cyclotron accelerator.  

PubMed

In order to generate epithermal neutrons for boron neutron capture therapy (BNCT), we proposed the method of filtering and moderating fast neutrons, which are emitted from the reaction between a beryllium target and 30 MeV protons accelerated by a cyclotron, using an optimum moderator system composed of iron, lead, aluminum, calcium fluoride, and enriched (6)LiF ceramic filter. At present, the epithermal-neutron source is under construction since June 2008 at Kyoto University Research Reactor Institute. This system consists of a cyclotron to supply a proton beam of about 1 mA at 30 MeV, a beam transport system, a beam scanner system for heat reduction on the beryllium target, a target cooling system, a beam shaping assembly, and an irradiation bed for patients. In this article, an overview of the cyclotron-based neutron source (CBNS) and the properties of the treatment neutron beam optimized by using the MCNPX Monte Carlo code are presented. The distribution of the RBE (relative biological effectiveness) dose in a phantom shows that, assuming a (10)B concentration of 13 ppm for normal tissue, this beam could be employed to treat a patient with an irradiation time less than 30 min and a dose less than 12.5 Gy-eq to normal tissue. The CBNS might be an alternative to the reactor-based neutron sources for BNCT treatments. PMID:19376720

Tanaka, H; Sakurai, Y; Suzuki, M; Takata, T; Masunaga, S; Kinashi, Y; Kashino, G; Liu, Y; Mitsumoto, T; Yajima, S; Tsutsui, H; Takada, M; Maruhashi, A; Ono, K

2009-03-31

288

Continuous distribution of defect states and band gap narrowing in neutron irradiated GaAs  

SciTech Connect

We find that fast neutron irradiated n- and p-GaAs diodes both show a broad feature in deep level transient spectroscopy (DLTS) previously studied primarily in n-GaAs and termed the ''U-band.'' The high temperature edge of the broad DLTS feature cuts off at the same temperature in both n- and p-GaAs suggesting that the cut off is due to the DLTS behavior expected for a continuous density of defect states that spans midgap. The band gap implied by the DLTS midgap cut off is 1.36 eV, as compared to the bulk GaAs band gap 1.52 eV. Band gap narrowing is consistent with previous measurements of lattice expansion in neutron irradiated GaAs. This leads to a model of defect cascades that are regions of narrowed band gap with defect levels that are inhomogeneously broadened. We observe, in addition, that the damage cascades are surrounded by large Coulomb barriers that prevent the complete filling of traps in the damaged regions.

Fleming, R. M.; Lang, D. V.; Seager, C. H.; Bielejec, E.; Patrizi, G. A.; Campbell, J. M. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1415 (United States)

2010-06-15

289

Calculation of the neutron source distribution in the venus PWR engineering mock-up and comparison with experimental measurements  

SciTech Connect

The VENUS experiment is sponsored by the USNRC in conjunction with CEN/SCK in Mol, Belgium. The VENUS configuration consists of a central water hole, surrounded by a 2.888 cm thick inner sheet baffle. The inner core zone in the immediate vicinity of the inner baffle contains 752 3.3% /sup 235/U, zircalloy fuel cells, with 48 pyrex rods interspersed among them. The outer core zone contains 1800 4.0% /sup 235/U, steel clad fuel cells. The core itself is surrounded by a 2.858 cm thick outer steel baffle, a water reflector, a 4.972 cm thick steel core barrel, a water gap, a neutron pad, and the pressure vessel. The primary aim of this study is to calculate the VENUS neutron source distribution, as part of the USNRC's overall program goal of benchmarking RPV fluence calculations. Of particular concern is the accuracy of the source calculation near the core-baffle interface, which is the important region for contributing to RPV fluence. The accuracy of the calculations is evaluated by comparison with gamma scan measurements performed by CEN/SCK.

Morakinyo, P.; Williams, M.L.; Kam, F.B.K.

1984-01-01

290

Neutron coincidence counting based on time interval analysis with one- and two-dimensional Rossi-alpha distributions: an application for passive neutron waste assay  

Microsoft Academic Search

Neutron coincidence counting is commonly used for the non-destructive assay of plutonium bearing waste or for safeguards verification measurements. A major drawback of conventional coincidence counting is related to the fact that a valid calibration is needed to convert a neutron coincidence count rate to a 240Pu equivalent mass (240Pueq). In waste assay, calibrations are made for representative waste matrices

M. Bruggeman; P. Baeten; W De Boeck; R. Carchon

1996-01-01

291

Neutron removal cross section as a measure of neutron skin  

SciTech Connect

We study the relation between neutron removal cross section (sigma{sub -N}) and neutron skin thickness for finite neutron-rich nuclei using the statistical abrasion ablation model. Different sizes of neutron skin are obtained by adjusting the diffuseness parameter of neutrons in the Fermi distribution. It is demonstrated that there is a good linear correlation between sigma{sub -N} and the neutron skin thickness for neutron-rich nuclei. Further analysis suggests that the relative increase of neutron removal cross section could be used as a quantitative measure for neutron skin thickness in neutron-rich nuclei.

Fang, D. Q.; Ma, Y. G.; Cai, X. Z.; Tian, W. D.; Wang, H. W. [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Post Office Box 800-204, Shanghai 201800 (China)

2010-04-15

292

Quantitative spatial magnetization distribution in iron oxide nanocubes and nanospheres by polarized small-angle neutron scattering  

SciTech Connect

By means of polarized small-angle neutron scattering, we have resolved the long-standing challenge of determining the magnetization distribution in magnetic nanoparticles in absolute units. The reduced magnetization, localized in non-interacting nanoparticles, indicates strongly particle shape- dependent surface spin canting with a 0.3(1) and 0.5(1) nm thick surface shell of reduced magnetization found for {approx}9 nm nanospheres and {approx}8.5 nm nanocubes, respectively. Further, the reduced macroscopic magnetization in nanoparticles results not only from surface spin canting, but also from drastically reduced magnetization inside the uniformly magnetized core as compared to the bulk material. Our microscopic results explain the low macroscopic magnetization commonly found in nanoparticles.

Disch, S.; Wetterskog, E.; Hermann, R.P.; Wiedenmann, A.; Vainio, U.; Salazar-Alvarez, G.; Bergström, L.; Brückel, Th. (Julich); (StockholmU); (HASYLAB); (Liege)

2012-09-19

293

Measurement of absorbed dose distributions in a plastic phantom irradiated by 40- and 65-MeV quasi-monoenergetic neutrons  

NASA Astrophysics Data System (ADS)

In order to validate dose evaluation methods for radiation shielding design of accelerator facilities, absorbed dose distributions in a plastic phantom of 30×30×30cm3 slab were measured for 40- and 65-MeV quasi-monoenergetic neutrons with a tissue-equivalent proportional counter and a tissue-equivalent ionization chamber. The measured distributions were compared with the calculated ones from the energy deposition of charged particles and neutron energy spectra by using the Monte Carlo codes, HETC-3STEP and MORSE-CG/KFA, respectively. As a result, it was revealed that the calculation method used in the present work was applicable to absorbed dose evaluation for intermediate energy neutrons with high accuracy.

Nakane, Y.; Sakamoto, Y.

2001-03-01

294

In-situ investigation water distribution in polymer electrolyte fuel cell using neutron radiography  

SciTech Connect

This paper investigates the water content within operating polymer electrolyte membrane (PEM) fuel cells using neutron radiography. We consider fuel cells with various PTFE loadings in their gas diffusion layers (GDL) and microporous layers (MPL), and examine the impacts of MPL/GDL properties on the liquid water behavior and fuel cell performance. Fuel cells are tested at both dry and fully hydrated conditions with different serpentine flow fields. Water contents in the projected areas of channel and land regions are probed. The fuel cell may be subject to more flooding at low current-density operation. Both MPL and GDL wetting properties have substantial impacts on the water content in fuel cell. Cell performance also varies on different scenarios of the MPL/GDL wetting properties. A quad-serpentine channel flow field exhibits higher water content without remarkable change in performance at low current densities. Liquid water profile along the channel is presented and on-set clearly indicated.

Mishler, Jeffrey H [Los Alamos National Laboratory; Mukundan, Rangachary [Los Alamos National Laboratory; Borup, Rodney L [Los Alamos National Laboratory; Wang, Eunkyoung Y [UC/RIVERSIDE; Hussey, Daniel S [NIST; Jacobson, David L [NIST

2010-01-01

295

An atomistic MD simulation and pair-distribution-function study of disorder and reactivity of [alpha]-AlF[subscript 3] nanoparticles  

SciTech Connect

Cubic nanoparticles of {alpha}-AlF{sub 3} containing 864 and 2048 atoms were investigated by using molecular dynamics simulations. Significant structural rearrangements of these particles occurred, primarily at the edges and corners of the particles, and 3 and 5 membered (Al-F-){sub n} ring structures were observed in addition to the 4-membered rings seen in bulk {alpha}-AlF{sub 3}. These 3 and 5 membered ring structures are, however, present in other metastable forms of AlF{sub 3}, which are formed at low temperatures from high surface area precursors. The surfaces of the nanoparticles were very dynamic on the timescale of the MD run, Al-F bonds being continually broken and formed, resulting in the movement of the low coordinate Lewis acid Al sites on the surfaces of the particles. The Lewis acid sites, which represent the catalytically active sites for F/Cl exchange reactions, are largely present at the corners and edges of the particles. The particles show larger rhombohedral distortions than present in the bulk phase and do not undergo a rhombohedral to cubic phase transition at elevated temperatures. The results are compared with pair distribution function (PDF) analysis results from fluorinated {gamma}-Al{sub 2}O{sub 3}, nanoparticles of AlF{sub 3} prepared by plasma routes and {alpha}- and {beta}-AlF{sub 3}. Broad peaks between 3.3 and 4.5 {angstrom} in the PDF plots of the fluorinated Al{sub 2}O{sub 3} and the nanoparticles indicate a distribution of Al-F distances arising from Al and F atoms in connected AlF{sub 6} octahedra; this is consistent with the presence of ring structures other than those found in {alpha}-AlF{sub 3}.

Chaudhuri, Santanu; Chupas, Peter; Morgan, Benjamin J.; Madden, Paul A.; Grey, Clare P. (Edinburgh); (SBU); (Dublin)

2008-06-18

296

An atomistic MD simulation and pair-distribution-function study of disorder and reactivity of alpha-AlF3 nanoparticles.  

PubMed

Cubic nanoparticles of alpha-AlF(3) containing 864 and 2048 atoms were investigated by using molecular dynamics simulations. Significant structural rearrangements of these particles occurred, primarily at the edges and corners of the particles, and 3 and 5 membered (Al-F-)(n) ring structures were observed in addition to the 4-membered rings seen in bulk alpha-AlF(3). These 3 and 5 membered ring structures are, however, present in other metastable forms of AlF(3), which are formed at low temperatures from high surface area precursors. The surfaces of the nanoparticles were very dynamic on the timescale of the MD run, Al-F bonds being continually broken and formed, resulting in the movement of the low coordinate Lewis acid Al sites on the surfaces of the particles. The Lewis acid sites, which represent the catalytically active sites for F/Cl exchange reactions, are largely present at the corners and edges of the particles. The particles show larger rhombohedral distortions than present in the bulk phase and do not undergo a rhombohedral to cubic phase transition at elevated temperatures. The results are compared with pair distribution function (PDF) analysis results from fluorinated gamma-Al(2)O(3), nanoparticles of AlF(3) prepared by plasma routes and alpha- and beta-AlF(3). Broad peaks between 3.3 and 4.5 A in the PDF plots of the fluorinated Al(2)O(3) and the nanoparticles indicate a distribution of Al-F distances arising from Al and F atoms in connected AlF(6) octahedra; this is consistent with the presence of ring structures other than those found in alpha-AlF(3). PMID:17091155

Chaudhuri, Santanu; Chupas, Peter; Morgan, Benjamin J; Madden, Paul A; Grey, Clare P

2006-07-11

297

Efficient simultaneous reverse Monte Carlo modeling of pair-distribution functions and extended x-ray-absorption fine structure spectra of crystalline disordered materials  

NASA Astrophysics Data System (ADS)

An efficient implementation of simultaneous reverse Monte Carlo (RMC) modeling of pair distribution function (PDF) and EXAFS spectra is reported. This implementation is an extension of the technique established by Krayzman et al. [J. Appl. Cryst. 42, 867 (2009)] in the sense that it enables simultaneous real-space fitting of x-ray PDF with accurate treatment of Q-dependence of the scattering cross-sections and EXAFS with multiple photoelectron scattering included. The extension also allows for atom swaps during EXAFS fits thereby enabling modeling the effects of chemical disorder, such as migrating atoms and vacancies. Significant acceleration of EXAFS computation is achieved via discretization of effective path lengths and subsequent reduction of operation counts. The validity and accuracy of the approach is illustrated on small atomic clusters and on 5500-9000 atom models of bcc-Fe and ?-Fe2O3. The accuracy gains of combined simultaneous EXAFS and PDF fits are pointed out against PDF-only and EXAFS-only RMC fits. Our modeling approach may be widely used in PDF and EXAFS based investigations of disordered materials.

Németh, Károly; Chapman, Karena W.; Balasubramanian, Mahalingam; Shyam, Badri; Chupas, Peter J.; Heald, Steve M.; Newville, Matt; Klingler, Robert J.; Winans, Randall E.; Almer, Jonathan D.; Sandi, Giselle; Srajer, George

2012-02-01

298

Pair Distribution Function Analysis and Solid State NMR Studies of Silicon Electrodes for Lithium Ion Batteries: Understanding the (De)lithiation Mechanisms  

NASA Astrophysics Data System (ADS)

The crystalline-to-amorphous phase transition that occurs on electrochemical Li insertion into crystalline Si, during the first discharge, hinders attempts to link the structure with electrochemical performance. We apply a combination of local structure probes, in situ and ex situ 7Li nuclear magnetic resonance (NMR) studies, and pair distribution function (PDF) analysis of X-ray data to investigate the changes in short-range order that occur during the initial charge and discharge cycles. The distinct electrochemical profiles observed subsequent to the first discharge have been shown to be associated with the formation of distinct amorphous lithiated silicide structures. The first process seen on the second discharge is associated with the lithiation of the amorphous Si, forming small clusters. These clusters are broken in the second process to form isolated silicon anions. The (de)lithiation model helps explain the hysteresis and the steps in the electrochemical profile observed during the lithiation and delithiation of silicon. At deep discharge states a highly reactive lithium excess Li15Si4 phase is detected by in situ NMR which undergoes a self-discharge process in electrolyte.

Key, Baris

2012-02-01

299

Quantification of subclonal distributions of recurrent genomic aberrations in paired pre-treatment and relapse samples from patients with B-cell chronic lymphocytic leukemia  

PubMed Central

Genome-wide array approaches and sequencing analyses are powerful tools for identifying genetic aberrations in cancers, including leukemias and lymphomas. However, the clinical and biological significance of such aberrations and their subclonal distribution are poorly understood. Here, we present the first genome-wide array based study of pre-treatment and relapse samples from patients with B-cell chronic lymphocytic leukemia (B-CLL) that uses the computational statistical tool OncoSNP. We show that quantification of the proportion of copy number alterations (CNAs) and copy neutral loss of heterozygosity regions (cnLOHs) in each sample is feasible. Furthermore, we (i) reveal complex changes in the subclonal architecture of paired samples at relapse compared with pre-treatment, (ii) provide evidence supporting an association between increased genomic complexity and poor clinical outcome (iii) report previously undefined, recurrent CNA/cnLOH regions that expand or newly occur at relapse and therefore might harbor candidate driver genes of relapse and/or chemotherapy resistance. Our findings are likely to impact on future therapeutic strategies aimed towards selecting effective and individually tailored targeted therapies.

Knight, S J L; Yau, C; Clifford, R; Timbs, A T; Sadighi Akha, E; Dreau, H M; Burns, A; Ciria, C; Oscier, D G; Pettitt, A R; Dutton, S; Holmes, C C; Taylor, J; Cazier, J-B; Schuh, A

2012-01-01

300

Efficient simultaneous reverse Monte Carlo modeling of pair-distribution functions and extended x-ray-absorption fine structure spectra of crystalline disordered materials.  

PubMed

An efficient implementation of simultaneous reverse Monte Carlo (RMC) modeling of pair distribution function (PDF) and EXAFS spectra is reported. This implementation is an extension of the technique established by Krayzman et al. [J. Appl. Cryst. 42, 867 (2009)] in the sense that it enables simultaneous real-space fitting of x-ray PDF with accurate treatment of Q-dependence of the scattering cross-sections and EXAFS with multiple photoelectron scattering included. The extension also allows for atom swaps during EXAFS fits thereby enabling modeling the effects of chemical disorder, such as migrating atoms and vacancies. Significant acceleration of EXAFS computation is achieved via discretization of effective path lengths and subsequent reduction of operation counts. The validity and accuracy of the approach is illustrated on small atomic clusters and on 5500-9000 atom models of bcc-Fe and ?-Fe(2)O(3). The accuracy gains of combined simultaneous EXAFS and PDF fits are pointed out against PDF-only and EXAFS-only RMC fits. Our modeling approach may be widely used in PDF and EXAFS based investigations of disordered materials. PMID:22360234

Németh, Károly; Chapman, Karena W; Balasubramanian, Mahalingam; Shyam, Badri; Chupas, Peter J; Heald, Steve M; Newville, Matt; Klingler, Robert J; Winans, Randall E; Almer, Jonathan D; Sandi, Giselle; Srajer, George

2012-02-21

301

Applications of an amorphous silicon-based area detector for high resolution, high sensitivity and fast time-resolved pair distribution function measurements.  

SciTech Connect

The application of a large-area (41 x 41 cm, 2048 x 2048 or 1024 x 1024 pixel) high-sensitivity (detective quantum efficiency > 65%) fast-readout (up to 7.5 or 30 Hz) flat-panel detector based on an amorphous silicon array system to the collection of high-energy X-ray scattering data for quantitative pair distribution function (PDF) analysis is evaluated and discussed. Data were collected over a range of exposure times (0.13 s-7 min) for benchmark PDF samples: crystalline nickel metal and amorphous silica (SiO2). The high real-space resolution of the resultant PDFs (with Q{sub max} up to {approx} 40 Angstroms{sup -1})and the high quality of fits to data [RNi(0.13s) = 10.5%, RNi(1.3s) = 6.3%] obtained in short measurement times indicate that this detector is well suited to studies of materials disorder. Further applications of the detector to locate weakly scattering H2 molecules within the porous Prussian blue system, Mn{sup II}{sub 3}[CoIII(CN)6]2 x xH2, and to follow the in situ reduction of PtIVO2 to Pt0 at 30 Hz, confirm the high sensitivity of the detector and demonstrate a new potential for fast time-resolved studies.

Chupas, P. J.; Chapman, K. W.; Lee, P. L.; X-Ray Science Division

2007-01-01

302

Pair distribution function-derived mechanism of a single-crystal to disordered to single-crystal transformation in a hemilabile metal-organic framework  

SciTech Connect

Flexible metal-organic frameworks (MOFs) are materials of great current interest. A small class of MOFs show flexibility driven by reversible bonding rearrangements that lead directly to unusual properties. Cu-SIP-3 is a MOF based on the 5-sulfoisophthalate ligand, where the strong copper-carboxylate bonds ensure that the three-dimensional integrity of the structure is retained while allowing bonding changes to occur at the more weakly bonding sulfonate group leading to unusual properties such as the ultra-selective adsorption of only certain gases. While the integrity of the framework remains intact during bonding changes, crystalline order is not retained at all times during the transformations. X-Ray diffraction reveals that highly crystalline single crystals lose order during the transformation before regaining crystallinity once it is complete. Here we show how X-ray pair distribution function analysis can be used to reveal the mechanism of the transformations in Cu-SIP-3, identifying the sequence of atomic displacements that occur in the disordered phase. A similar approach reveals the underlying mechanism of Cu-SIP-3's ultra-selective gas adsorption.

Allan, P. K.; Chapman, K. W.; Chupas, P. J.; Hriljac, J. A.; Renouf, C. L.; Lucas, T. C. A.; Morris, R. E. (X-Ray Science Division); (Univ. of St. Andrews); (Univ. of Birmingham)

2012-01-01

303

Local structures of Sr2FeMnO5+y (y=0, 0.5) and Sr2Fe1.5Cr0.5O5 from reverse Monte Carlo modeling of pair distribution function data and implications for magnetic order  

NASA Astrophysics Data System (ADS)

The local structures of the oxygen deficient perovskites Sr2FeMnO5, Sr2FeMnO5.5, and Sr2Fe1.5Cr0.5O5 have been analyzed using neutron pair distribution function data. The results show that locally all three structures are more complex than implied by their average cubic structures and that the distributions of oxygen vacancies are not completely random on a local level. For both Sr2FeMnO5+y compounds it is found that there is no short range ordering of the Fe and Mn cations. For Sr2Fe1.5Cr0.5O5 there is evidence to suggest that the Fe/Cr distribution is not completely random and is locally ordered such that there are fewer Fe?Fe nearest neighbor pairs than in a random distribution. Reverse Monte Carlo modeling of the pair distribution function data has provided the Fe?O, Mn?O, and Cr?O bond length distributions and information on the coordination numbers of the Fe, Mn, and Cr cations. In Sr2FeMnO5 it is found that the Fe3+ cations are most often in 4-fold coordination but there is also a large amount of Fe3+ in 5-fold coordination and a small amount in 6-fold coordination. The Mn3+ is split between 5-fold and 6-fold coordination. The Mn?O bond length distributions indicate that the Mn3+O6 octahedra and Mn3+O5 square pyramids are locally Jahn-Teller distorted. In Sr2FeMnO5.5 the Fe3+ is almost entirely 5 coordinate while the Mn4+ is almost entirely 6 coordinate. The Cr3+ in Sr2Fe1.5Cr0.5O5 is almost entirely 6-fold coordinated, giving the Fe3+ an average coordination number of 4.67. In Sr2FeMnO5 and Sr2Fe1.5Cr0.5O5 the Fe3+ and Sr2+ cations undergo local displacements which are driven by the oxygen vacancies, while the Mn3+ and Cr3+ cations remain near their positions in the average structures. In Sr2FeMnO5.5 these cations are not significantly displaced. The local coordination geometries are used to explain previously observed but yet poorly understood magnetic properties of these materials.

King, Graham; Ramezanipour, Farshid; Llobet, Anna; Greedan, John E.

2013-02-01

304

Depth Distribution of Lithium in Oxidized Binary Al-Li Alloys Determined by Secondary Ion Mass Spectrometry and Neutron Depth Profiling  

Microsoft Academic Search

Oxidation of binary Al-Li alloys during short exposures at 530 C and long exposures at 200 C was studied with regard to the Li distribution. Secondary ion mass spectrometry (SIMS) and neutron depth profiling (NDP) were used to obtain quantitative Li depth profiles across the surface oxide layer and the underlying alloy. The underlying alloy was depleted in Li as

K. K. Soni; G. K. Lamaza; D. B. Williams; D. E. Newbury; R. G. Downing; P. K. Chi

1993-01-01

305

Distribution & Solubility of Radionuclides & Neutron Absorbers in Waste Forms for Disposition of Plutonium Ash & Scraps, Excess Plutonium, and Miscellaneous Spent Nuclear Fuels  

SciTech Connect

The objective of this research is to develop a basic understanding of the distribution and solubility of radionuclides and neutron absorbers in waste forms and their release from waste forms by studying the local structural environments of these constituents in representative materials.

Strachan, Denis M.; Vance, Eric R.; Shuh, David K.; Ewing, Rodney C.

1999-06-01

306

Study of the Spin/Orbit Term of the Spherical Optical Model Potential by Means of Large Angle Fast Neutron Elastic Scattering Angular Distribution Measurements.  

National Technical Information Service (NTIS)

The study of differential cross section angular distributions for neutron elastic scattering at large angles is a sensitive method for testing the effect of the choice of the numerical value of the spin-orbit term of the optical model potential. This is o...

E. Ramstroem B. Trostell

1978-01-01

307

Calculations of the Transverse Spatial Distribution of NE102 Scintillation Light Made by Recoil Protons from Collimated 14-MeV Neutrons.  

National Technical Information Service (NTIS)

A calculation has been made of the spatial distribution of NE102 scintillation light produced by recoil protons from collimated 14-MeV neutron illumination. Results were then averaged over offset circles of various radii, thus determining the fraction of ...

D. R. Goosman

1979-01-01

308

What Can We Learn From a Detailed Study of the Temperature Dependence of Omega, the Width of the Pair Distribution Function?  

SciTech Connect

In many systems there is a significant coupling between the local structure and other properties of the system such as magnetism, electrical and thermal transport, metal/insulator transitions etc. In such materials, a detailed temperature-dependent study of the width of the Pair Distribution Function (PDF), {sigma}, can separate different contributions and provide a connection between the observed macroscopic observations and the underlying atomic interactions that produce them. The usual model for simple systems is that the T-dependence of {sigma}{sup 2} is described by an Einstein or Correlated Debye model, with one characteristic temperature for the system; in such models {sigma}{sup 2}(T) increases smoothly with T and has a slowly increasing slope. However that is not always the case: in structures with large unit cells containing several types of atoms, some atoms in the crystal can have a low Einstein temperature while others have a very high correlated Debye temperature as observed in a number of thermoelectric systems (skutterudites and clathrates). In others systems such as the negative thermal expansion material ZrW{sub 2}O{sub 8}, the same atom cam be involved in both low and high temperature Einstein modes. Vibrations of atoms (or molecular unit) described by a low Einstein temperature often control/determine the lattice properties. In other systems there are deviations from the T-dependence expected for either the Einstein or correlated Debye models -- such as a small increase in {sigma}{sup 2} at low temperatures for the Ru-Ru pair in PrRu{sub 4}Sb{sub 12} which has a metal/insulator transition near 60K, or a very sharp step in {sigma}{sup 2}(T) observed in the bilayer colossal magnetoresistance system La{sub 2-2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} at the ferromagnetic transition. We discuss broadening of the PDF in more complex systems, show some simulations and then present several recent examples.

Bridges, F.; Downward, L.; Jiang, Y.; O'Brien, T.

2009-06-04

309

Elastic two-neutron transfer reactions of 58Ni+60Ni and 62Ni+64Ni around the Coulomb barrier  

Microsoft Academic Search

We have measured elastic scattering angular distributions for 58Ni+60Ni at E58Ni =204, 220, 236, and 250 MeV and for 62Ni+64Ni at E64Ni =250 MeV. The measured angular distributions show bell-shaped structures at backward angles for both systems at Elab=250 MeV which are due to the neutron pair exchange between identical cores for the projectile and target. The pair exchange has

Y. Sugiyama; Y. Tomita; Y. Yamanouti; S. Hamada; T. Ikuta; H. Fujita; D. R. Napoli

1997-01-01

310

Measurement and analysis of the energy–angular distribution of secondary neutrons for 9Be at 5.9 and 6.4 MeV incident neutrons  

Microsoft Academic Search

The energy-angle double-differential neutron emission cross-sections of beryllium have been measured using the time of flight technique for 5.9 and 6.4MeV incident neutrons, respectively, at 10 laboratory angles between 25° and 150°. The measured results are compared with model calculations based on the LUNF code and those of other authors and the ENDF\\/B-VII data. The estimation of the inelastic scattering

Jinxiang Chen; Pei Zhu; Xiaoyong Mao; Xiangqing Li; Guanren Shen; Jingshang Zhang; Yinlu Han

2009-01-01

311

The effects of high-velocity supernova kicks on the orbital properties and sky distributions of neutron-star binaries  

NASA Astrophysics Data System (ADS)

We systematically investigate the effects of high supernova kick velocities on the orbital parameters of post-supernova neutron-star binaries. Using Monte Carlo simulations, we determine the post-supernova distributions of orbital parameters (orbital period, eccentricity, system velocity, spin inclination, ratio of spin to orbital angular momentum) for progenitors of high-mass X-ray binaries (HMXBs) and low-mass X-ray binaries (LMXBs). With the recent distribution of pulsar birth velocities by Lyne & Lorimer, only about 27 per cent of massive systems remain bound after the supernova, of which ~26 per cent immediately experience dynamical mass transfer and possibly merge to become Thorne-Zytkow objects. The correlations between various orbital parameters can be compared with observational samples to yield information about supernova kick velocities and pre-supernova orbital-period distributions. After the supernova, the spins of most stars in massive systems have large inclinations with respect to their orbital axes, and a significant fraction of systems (~20 per cent) contain stars with retrograde spins. This may have important implications for the interpretation of those HMXBs that seem to have tilted, `precessing' accretion discs. We estimate that the spin angular momentum in the massive components of most HMXBs is a significant fraction (0.1-0.4) of the total orbital angular momentum. Therefore spin-orbit coupling effects may be important in many HMXBs. In the case of low-mass companions, we find that ~19 per cent of systems remain bound after the supernova, of which ~57 per cent experience immediate dynamical mass transfer. The systems that survive as binaries and become LMXB progenitors attain a very large system velocity of 180+/-80 km s^-1 after the supernova. There is a relatively tight correlation between the eccentricity and the post-supernova orbital period in these systems. All LMXBs with post-supernova periods longer than a few days initially have very large eccentricities. This may suggest that there should be a special class of LMXBs with periodic outbursts, of which Cir X-1 may be an extreme representative. We also use the results of these calculations to simulate the sky distributions of HMXBs and LMXBs. The simulated distributions agree with observed samples. Most importantly, the distribution of Galactic LMXBs is consistent with an ordinary Galactic disc population that has been widened because of large supernova kicks and does not require a special population of progenitors. The observed LMXB distribution does not provide a strong constraint on the age of LMXBs since the supernova, although there may be a weak hint that they are relatively young, with ages less than ~10^8 yr.

Brandt, Niel; Podsiadlowski, Philipp

1995-05-01

312

In-situ investigation of water distribution in polymer electrolyte fuel cell using neutron radiography  

SciTech Connect

This paper investigates the water content within operating polymer electrolyte membrane (PEM) fuel cells using neutron radiography. We consider fuel cells with various PTFE loadings in their gas diffusion layers (GDL) and microporous layers (MPL), and examine the impacts of MPL/GDL properties on the liquid water behavior and fuel cell performance. Fuel cells are tested at both dry and fully hydrated conditions with different serpentine flow fields. Water contents in the projected areas of channel and land regions are probed. We find that the fuel cell may be subject to more flooding at low current-density operation. In addition, both MPL and GDL wetting properties have substantial impacts on the water content in fuel cell. The cell performance also varies on different scenarios of the MPL/GDL wetting properties. The quad-channel flow field exhibits higher water content without remarkable change in performance at low current densities. Liquid water profile along the channel is presented and liquid water on-set clearly indicated.

Mishler, Jeffrey H [Los Alamos National Laboratory; Mukundan, Rangachary [Los Alamos National Laboratory; Borup, Rodney L [Los Alamos National Laboratory; Wang, Yun [UC IRVINE; Hussey, Daniel S [NIST; Jacobson, David L [NIST

2010-01-01

313

Autoradiography of californium-252 wire neutron sources. [To determine uniformity of distribution of Cf 252  

Microsoft Academic Search

A technique for measuring the distribution of Cf 252 in a wire is discussed. An autograph was produced by placing the wire on a photographic plate sensitive to gamma radiation. The radiograph was read by a computer automated densitometer. A brief discussion of the accuracy of the technique is presented. (DDA)

B. Tiffany; K. W. MacMurdo; R. H. Gaddy

1976-01-01

314

Neutron diffraction analysis of residual strain\\/stress distribution in the vicinity of high strength welds  

Microsoft Academic Search

Residual stresses resulting from non homogeneous heat distribution during welding process belong to most significant factor influencing behavior of welded structures. These stresses are responsible for defect occurrence during welding and they are also responsible for crack initiation and propagation at the either static or dynamic load. The significant effect of weld metal chemical composition as well as the effect

L. Mráz; L. Karlsson; I. Hamák; M. Vrána; P. Mikula

2010-01-01

315

Toward prompt gamma spectrometry for monitoring boron distributions during extra corporal treatment of liver metastases by boron neutron capture therapy: a Monte Carlo simulation study.  

PubMed

A Monte Carlo calculation was carried out for boron neutron capture therapy (BNCT) of extra corporal liver phantom. The present paper describes the basis for a subsequent clinical application of the prompt gamma spectroscopy set-up aimed at in vivo monitoring of boron distribution. MCNP code was used first to validate the homogeneity in thermal neutron field in the liver phantom and simulate the gamma ray detection system (collimator and detector) in the treatment room. The gamma ray of 478 keV emitted by boron in small specific region can be detected and a mathematical formalism was used for the tomography image reconstruction. PMID:19394243

Khelifi, R; Nievaart, V A; Bode, P; Moss, R L; Krijger, G C

2009-04-02

316

Co-localized or randomly distributed? Pair cross correlation of in vivo grown subgingival biofilm bacteria quantified by digital image analysis.  

PubMed

The polymicrobial nature of periodontal diseases is reflected by the diversity of phylotypes detected in subgingival plaque and the finding that consortia of suspected pathogens rather than single species are associated with disease development. A number of these microorganisms have been demonstrated in vitro to interact and enhance biofilm integration, survival or even pathogenic features. To examine the in vivo relevance of these proposed interactions, we extended the spatial arrangement analysis tool of the software daime (digital image analysis in microbial ecology). This modification enabled the quantitative analysis of microbial co-localization in images of subgingival biofilm species, where the biomass was confined to fractions of the whole-image area, a situation common for medical samples. Selected representatives of the disease-associated red and orange complexes that were previously suggested to interact with each other in vitro (Tannerella forsythia with Fusobacterium nucleatum and Porphyromonas gingivalis with Prevotella intermedia) were chosen for analysis and labeled with specific fluorescent probes via fluorescence in situ hybridization. Pair cross-correlation analysis of in vivo grown biofilms revealed tight clustering of F. nucleatum/periodonticum and T. forsythia at short distances (up to 6 ľm) with a pronounced peak at 1.5 ľm. While these results confirmed previous in vitro observations for F. nucleatum and T. forsythia, random spatial distribution was detected between P. gingivalis and P. intermedia in the in vivo samples. In conclusion, we successfully employed spatial arrangement analysis on the single cell level in clinically relevant medical samples and demonstrated the utility of this approach for the in vivo validation of in vitro observations by analyzing statistically relevant numbers of different patients. More importantly, the culture-independent nature of this approach enables similar quantitative analyses for "as-yet-uncultured" phylotypes which cannot be characterized in vitro. PMID:22655057

Schillinger, Claudia; Petrich, Annett; Lux, Renate; Riep, Birgit; Kikhney, Judith; Friedmann, Anton; Wolinsky, Lawrence E; Göbel, Ulf B; Daims, Holger; Moter, Annette

2012-05-24

317

Effect of ion speed distribution on the spectral shape of the 2. 5 MeV neutron line produced by DD fusion  

SciTech Connect

Ion mean energy may be determined from Doppler broadening of the 2.5 MeV neutron line in Maxwellian deuterium plasma. Since many plasmas are non-Maxwellian a Monte Carlo simulation has been used to predict the spectral shape produced by a variety of simple speed distributions with mean energies in the range 1 to 100 keV. The results are Gaussian to high order and their width varies as the square root of the mean ion energy. However, the line width varies substantially among different ion speed distributions with the same mean energy. The similarity in shape of these spectra prevent the determination of the speed distribution type from detailed measurements of the neutron spectrum. 24 refs., 4 figs., 2 tabs.

Slaughter, D.

1986-02-01

318

Cytological analysis on the distribution and origin of the alien chromosome pair conferring blue aleurone color in several European common wheat ( Triticum aestivum L.) strains  

Microsoft Academic Search

Meiotic chromosome pairing and Giemsa C-banding analyses in crosses of several European blue-grained wheat strains with Chinese Spring double ditelosomic and other aneuploid lines showed that Triticum aestivum Blaukorn strains “Berlin,” “Probstdorf,” “Tschermak,” and “Weihenstephan” are chromosome substitutions, in which the complete wheat chromosome 4A pair is replaced, whereas the strains “Brünn” and “Moskau” are 4B substitutions. The alien chromosome

F. J. Zeller; M. C. Cermeńo; T. E. Miller

1991-01-01

319

[Paired hemodiafiltration].  

PubMed

Paired hemodiafiltration (PHF) is a dialysis modality where an ultrafilter and a filter with hollow-fiber membranes are used in series for on-line infusion of ultrapure fluid. PHF is a on-line hemodiafiltration modality which allows reinfusion using the dialysate prepared by the monitor. The dialysate is infused by retrofiltration, which takes place in the filter positioned in series with regard to the filter where ultrafiltration and the diffusive/convective exchange of solutes occur. The indications and contraindications of the method are the same as those of standard on-line hemodiafiltration, but PHF minimizes the inflammatory response of the patient. This is the result of the increased number of ultrafiltration stages (three), two of which in the monitor and the third by the filter in series, where the retrofiltration takes place. The method can also be carried out with acetate-free dialysate; this reduces the side effects of acetate used to stabilize pH in bicarbonate dialysate, resulting in better cardiovascular stability during dialysis. PMID:22723148

Conti, Paolo

320

Investigation of neutron and proton distributions of He, Li, and Be isotopes using the new Skyrme-Force parameters  

SciTech Connect

The proton and neutron densities, root-mean-square (rms) radii of proton density and neutron density, and neutron skin thickness of {sup 4-10}He, {sup 6-11}Li, and {sup 7-12}Be isotopes are calculated using Skyrme-Hartree-Fock method with SLy4, SLy5, SLy6, and SLy7 force parameters. The evaluated results are compared with experimental data. Also, the results of halo nuclei ({sup 6,8}He, {sup 11}Li, and {sup 11}Be) are compared with the results of other isotopes for selected nuclei having the same neutron configuration.

Baldik, R.; Aytekin, H., E-mail: huseyinaytekin@gmail.co [Zonguldak Karaelmas University, Department of Physics (Turkey); Tel, E. [Gazi University, Department of Physics (Turkey)

2010-01-15

321

Nuclear reaction secondary particle dose distributions and dose enhancement by boron neutron capture in proton beam therapy evaluated using the LAHET code system  

NASA Astrophysics Data System (ADS)

The objective of this study was to use the LAHET Code System (LCS), which has recently been used in shielding calculations for proton therapy, to model the proton, neutron and photon dose and equivalent dose distributions created in tissue during proton beam cancer therapy. Proton beams used for therapy have shown distinct advantages over other therapeutic radiation treatments due to the rapid distal dose falloff in the region of the Bragg Peak. Nuclear reactions caused by the primary proton beam in beam modifying devices and patient tissues create secondary particles which contribute to the dose received by the patient inside and outside of the targeted region. The spatial distribution of the dose created by these secondary particles is an important consideration in the choice of beam modification methods and treatment volume planning, since a goal of radiation therapy is to minimize dose to normal tissue while maximizing dose to the tumor. The photon dose was found to be negligible in all target regions. The neutron dose and dose equivalent were found to be negligible in the tissue volume targeted for proton beam therapy, but contributed a majority of the dose outside of the treatment volume. Finally, LAHET was used to evaluate the utility of exploiting the secondary neutrons for supplemental boron neutron capture therapy during proton beam therapy. These results indicate that the additional useful dose due to BNCT is negligible.

Laky, Peter Gyula

322

Disk accretion in the gravitational field of a rapidly rotating neutron star with a rotationally induced quadrupole mass distribution  

NASA Astrophysics Data System (ADS)

We analyze the effect of the quadrupole component in the mass distribution of a rapidly rotating neutron star on the energy release in the equatorial (or boundary) layer on the surface of the accreting star and in the accretion disk in the cases where the stellar radius is smaller (or larger) than the radius of the last stable circular orbit. We calculate the velocities and trajectories of the particles that fall on the stellar surface from the marginally stable orbit for a low-luminosity accreting source. The corresponding external gravitational field of the star is modeled by a new exact solution of the Einstein equations in vacuum. The parameters of this solution are adjusted by reconciling the numerical data for the radius of the marginally stable orbit and the gravitational redshift of Cook et al. (1994) with the corresponding data in the analytical solution. For various equations of state, we consider 1.4M_solar normal sequences and maximum-mass normal sequences which become unstable in the static limit.

Sibgatullin, N. R.; Sunyaev, R. A.

1998-11-01

323

Feasibility of boron neutron capture therapy (BNCT) for malignant pleural mesothelioma from a viewpoint of dose distribution analysis  

SciTech Connect

Purpose: To investigate the feasibility of boron neutron capture therapy (BNCT) for malignant pleural mesothelioma (MPM) from a viewpoint of dose distribution analysis using Simulation Environment for Radiotherapy Applications (SERA), a currently available BNCT treatment planning system. Methods and Materials: The BNCT treatment plans were constructed for 3 patients with MPM using the SERA system, with 2 opposed anterior-posterior beams. The {sup 1}B concentrations in the tumor and normal lung in this study were assumed to be 84 and 24 ppm, respectively, and were derived from data observed in clinical trials. The maximum, mean, and minimum doses to the tumors and the normal lung were assessed for each plan. The doses delivered to 5% and 95% of the tumor volume, D{sub 05} and D{sub 95}, were adopted as the representative dose for the maximum and minimum dose, respectively. Results: When the D{sub 05} to the normal ipsilateral lung was 5 Gy-Eq, the D{sub 95} and mean doses delivered to the normal lung were 2.2-3.6 and 3.5-4.2 Gy-Eq, respectively. The mean doses delivered to the tumors were 22.4-27.2 Gy-Eq. The D{sub 05} and D{sub 95} doses to the tumors were 9.6-15.0 and 31.5-39.5 Gy-Eq, respectively. Conclusions: From a viewpoint of the dose-distribution analysis, BNCT has the possibility to be a promising treatment for MPM patients who are inoperable because of age and other medical illnesses.

Suzuki, Minoru [Particle Oncology Research Center, Osaka (Japan)]. E-mail: msuzuki@rri.kyoto-u.ac.jp; Sakurai, Yoshinori [Division of Medical Physics, Department of Radiation Life Science, Research Reactor Institute, Kyoto University, Osaka (Japan); Masunaga, Shinichiro [Particle Oncology Research Center, Osaka (Japan); Kinashi, Yuko [Particle Oncology Research Center, Osaka (Japan); Nagata, Kenji [Particle Oncology Research Center, Osaka (Japan); Maruhashi, Akira [Division of Medical Physics, Department of Radiation Life Science, Research Reactor Institute, Kyoto University, Osaka (Japan); Ono, Koji [Particle Oncology Research Center, Osaka (Japan)

2006-12-01

324

Fingerprinting analysis of non-crystalline pharmaceutical compounds using high energy X-rays and the total scattering pair distribution function  

NASA Astrophysics Data System (ADS)

In the development of new medicinal products, poor oral bioavailability, due to the low solubilities of many active pharmaceutical ingredients (APIs), is increasingly a barrier for treatments to be administered using tablet or capsule formulations and one of the main challenges facing the pharmaceutical industry. Non-crystalline phases such as the amorphous and nanostructured states can confer increased solubility to a drug, and therefore, have recently garnered a lot of interest from pharmaceutical researchers. However, little is known about local ordering in non-crystalline pharmaceuticals due to the lack of reliable experimental probes, hindering the clinical application of these compounds. The powerful tools of crystallography begin to lose their potency for structures on the nanoscale; conventional X-ray powder diffraction (XRPD) patterns become broad and featureless in these cases and are not useful for differentiating between different local molecular packing arrangements. In this thesis, we introduce the use of high energy X-rays coupled with total scattering pair distribution function (TSPDF) and fingerprinting analysis to investigate the local structures of non-crystalline pharmaceutical compounds. The high energy X-rays allow us to experimentally collect diffuse scattering intensities, which contain information about a sample's local ordering, in addition to the Bragg scattering available in conventional XRPD experiments, while the TSPDF allows us to view the intra- and inter-molecular correlations in real space. The goal of this study was to address some fundamental problems involving fingerprinting non-crystalline APIs using TSPDF in order to lay the groundwork for the proper use of the technique by the pharmaceutical community. We achieved this by developing the methodology as well as the exploring the scientific implications. On the methodology side, we introduced PDFGetX3, a new software program for calculating TSPDFs that simplifies the procedure and reduces user interaction. We also set a baseline for the minimum X-ray energy that is needed for fingerprinting analysis, which had implications on the type of X-ray diffractometers that can be used. On the science side, we investigated the local structures of nanocrystalline and amorphous materials as well mixtures containing crystalline and amorphous phases. First, we identified a non-crystalline sample of the mood-stabilizing drug carbamazepine as a nanocrystalline version of one of its polymorphs. Next, we found that amorphous forms created by spray drying and cryomilling a proprietary compound have the same local structure. Finally, we quantified the phase fractions of polymorphic and amorphous components in a sample of the antibiotic sulfamerazine that was recrystallizing from a cryomilling-induced amorphous state.

Davis, Timur D.

325

Neutron diffraction plus molecular dynamics: a powerful approach for understanding liquid structure  

Microsoft Academic Search

The local order present in liquids gives rise to features in the pair distribution function (pdf) derived from neutron diffraction that cannot be interpreted directly. One powerful approach to deriving structural information from the intermolecular region of the pdf is to simulate the liquid by means of molecular dynamics.The quality of such simulations is normally tested by the extent of

A. N Burgess; K. A Mort; K. A Johnson; D. L Cooper; S. C Rogers; W. S Howells

1995-01-01

326

Pairing Learners in Pair Work Activity  

ERIC Educational Resources Information Center

|Although pair work is advocated by major theories of second language (L2) learning and research findings suggest that pair work facilitates L2 learning, what is unclear is how to best pair students in L2 classes of mixed L2 proficiency. This study investigated the nature of pair work in an English as a Foreign Language (EFL) class in a college in…

Storch, Neomy; Aldosari, Ali

2013-01-01

327

Pairing Learners in Pair Work Activity  

ERIC Educational Resources Information Center

Although pair work is advocated by major theories of second language (L2) learning and research findings suggest that pair work facilitates L2 learning, what is unclear is how to best pair students in L2 classes of mixed L2 proficiency. This study investigated the nature of pair work in an English as a Foreign Language (EFL) class in a college in…

Storch, Neomy; Aldosari, Ali

2013-01-01

328

FAST NEUTRON SPECTROMETER USING SPACED SEMICONDUCTORS FOR MEASURING TOTAL ENERGY OF NEUTRONS CAPTURED  

DOEpatents

A fast neutron spectrometer was designed, which utilizes a pair of opposed detectors having a layer of /sup 6/LiF between to produce alpha and T pair for each neutron captured to provide signals, which, when combined, constitute a measure of neutron energy. (AEC)

Love, T.A.; Murray, R.B.

1964-04-14

329

Dependence of charge collection distributions and dose on the gas type filling the ionization chamber for a p(66)Be(49) clinical neutron beam  

SciTech Connect

Measurements of central axis depth charge distributions (CADCD) in a p(66)Be(49) clinical neutron beam using A-150 TE plastic ionization chambers (IC) have shown that these distributions are dependent on the gas type filling the ICs. IC volumes from 0.1 to 8 cm/sup 3/ and nine different gases were investigated. Off axis ratios and build-up measurements do not seem to be as sensitive to gas type. The gas dosimetry constants given in the AAPM Protocol for Neutron Beam Dosimetry for air and methane based TE gases were tested for consistency in water and in TE solution filled phantoms at depths of 10 cm, when used in conjunction with an IC having 5 mm thick walls of A-150. 29 refs., 7 figs., 1 tab.

Awschalom, M.; Haken, R.K.T.

1985-01-01

330

Three-dimensional implantation distribution of lithium implanted into pyrographite, as revealed by solid state tomography in combination with neutron depth profiling  

Microsoft Academic Search

We have studied the three-dimensional distribution of 2.5 MeV Li implanted into pyrographite at room temperature by means of modified tomography in combination with neutron depth profiling. Our new findings essentially reconfirm earlier results (D. Fink et al., J. Appl. Phys. 58 (1985) 668 [1]; Radiat. Eff. and Def. in Solids 114 (1990) 21 [2]) which indicated the presence of

D. Fink; M. Müller; R. Klett; J. Vacik; V. Hnatowicz; J. Cervena

1995-01-01

331

Visualization and void fraction distribution of downward gas–liquid two-phase flow in a plate heat exchanger by neutron radiography  

Microsoft Academic Search

Adiabatic vertically downward air–water two-phase flows in a commercial plate heat exchanger were visualized by a neutron radiography method as a non-destructive test in order to clarify the flow characteristics and the differences of the liquid distributions from those of the vertically upward flows. Flow behaviors in a single channel and a multi-channel plate heat exchanger were investigated. From the

Hitoshi Asano; Nobuyuki Takenaka; Toshiaki Wakabayashi; Terushige Fujii

2005-01-01

332

Synchrotron radiation from giant e+/- pair halos  

NASA Astrophysics Data System (ADS)

A giant e+/- pair halo is formed by electromagnetic cascades developing around an AGN under the intergalactic magnetic field (1nG - 1?G). Many studies have been focussed on the pair halos in the gamma band because it has been predicted that the e+/-s in the pair halos up-scatter the Cosmic Microwave Background (CMB) to be gamma-rays. However, the pair halos do not emit only gamma photons but also X-ray photons via synchrotron radiation. In this paper, the Spectral Energy Distributions (SEDs) and the angular distributions of the synchrotron radiation of the pair halos from the Monte Carlo simulations will be discussed.

Eungwanichayapant, A.; Maithong, W.; Ruffolo, D.

2012-08-01

333

Three-body force effect on P3 F2 neutron superfluidity in neutron matter, neutron star matter, and neutron stars  

NASA Astrophysics Data System (ADS)

We investigate the effect of microscopic three-body forces on the P3 F2 neutron superfluidity in neutron matter, ?-stable neutron star matter, and neutron stars by using the BCS theory and the Brueckner-Hartree-Fock approach. We adopt the Argonne V18 potential supplemented with a microscopic three-body force as the realistic nucleon-nucleon interaction. We have concentrated on studying the three-body force effect on the P3 F2 neutron pairing gap. It is found that the three-body force effect considerably enhances the P3 F2 neutron superfluidity in neutron star matter and neutron stars.

Zuo, W.; Cui, C. X.; Lombardo, U.; Schulze, H.-J.

2008-07-01

334

A combinatorial analysis of pair breaking in fission  

Microsoft Academic Search

We develop a model for pair-breaking in order to explain the behavior of the even-odd effects displayed both by the fragment yields and the fragments' kinetic energies in low energy nuclear fission. Neutron and proton pair breaking are taken into acount. Two pair-breaking mechanisms are considered. In the first, pairs are broken at the saddle point and the individual members

H. Nifenecker; G. Mariolopoulos; J. P. Bocquet; R. Brissot; Mme Ch. Hamelin; J. Crançon; Ch. Ristori

1982-01-01

335

BNCT dose distribution in liver with epithermal D–D and D–T fusion-based neutron beams  

Microsoft Academic Search

Recently, a new application of boron neutron capture therapy (BNCT) treatment has been introduced. Results have indicated that liver tumors can be treated by BNCT after removal of the liver from the body. At Lawrence Berkeley National Laboratory, compact neutron generators based on 2H(d,n)3He (D–D) or 3H(t,n)4He (D–T) fusion reactions are being developed. Preliminary simulations of the applicability of 2.45MeV

H. Koivunoro; D. L. Bleuel; U. Nastasi; T. P. Lou; J. Reijonen; K.-N. Leung

2004-01-01

336

Mars low-latitude neutron distribution: Possible remnant near-surface water ice and a mechanism for its recent emplacement  

Microsoft Academic Search

The Mars Odyssey Gamma-Ray Spectrometer\\/Neutron Spectrometer\\/High Energy Neutron Detector has provided measurements of near-surface hydrogen, generally interpreted as resulting from water, in the equatorial and mid-latitudes. Water abundances as great as 10% by mass are inferred. Although such high abundances could be present as adsorbed water in clays or water of hydration of magnesium salts, other measurements suggest that this

Bruce M. Jakosky; Michael T. Mellon; E. Stacy Varnesa; William C. Feldman; William V. Boynton; Robert M. Haberle

2005-01-01

337

Measurement of thermal neutron fluence distribution with use of 23 Na radioactivation around a medical compact cyclotron  

Microsoft Academic Search

A medical compact cyclotron produces about 1015 neutrons per day along with 100 GBq of 18F. Therefore, it is important to establish radiation safety guidelines on residual radioactivity for routine operation, maintenance\\u000a work, and decommissioning. Thus, we developed a simple method for measuring the thermal neutrons in a cyclotron room. In order\\u000a to verify the feasibility of our proposed method, we

Toshioh Fujibuchi; Ichiro Yamaguchi; Tetsuharu Kasahara; Takashi Iimori; Yoshitada Masuda; Ken-ichi Kimura; Hiroshi Watanabe; Tomonori Isobe; Takeji Sakae

2009-01-01

338

Development of a high-speed camera system for neutron imaging at a pulsed neutron source  

NASA Astrophysics Data System (ADS)

A neutron energy resolved imaging system with a time-of-flight technique has been newly developed and installed at Japan Proton Accelerator Research Complex (J-PARC) with the aim to investigate more preciously and rapidly a spatial distribution of several elements and crystals in various kinds of materials or substances. A high-speed video camera (CMOS, 1300 k frame/s) equipped system allows to obtain TOF images consecutively resolved into narrow energy ranges with a single pulsed neutrons while conventional CCD camera imaging system could obtain only one TOF image in an arbitral neutron energy region in the pulsed neutron energy region from 0.01 eV to a few keV. Qualities of the images obtained with the system, such as spatial resolution (defined by modulation transfer function, 0.8 line-pairs/mm at En˜0.01 eV), dependence of the brightness on the neutron energy and measurement errors (˜2%) of the system were examined experimentally and evaluated by comparison with those of conventional imaging system. The results obtained in the experiments show that the system can visualize the neutron energy resolved images within a small error even at high speed.

Segawa, M.; Kai, T.; Sakai, T.; Ooi, M.; Kureta, M.

2013-01-01

339

Alu pair exclusions in the human genome  

PubMed Central

Background The human genome contains approximately one million Alu elements which comprise more than 10% of human DNA by mass. Alu elements possess direction, and are distributed almost equally in positive and negative strand orientations throughout the genome. Previously, it has been shown that closely spaced Alu pairs in opposing orientation (inverted pairs) are found less frequently than Alu pairs having the same orientation (direct pairs). However, this imbalance has only been investigated for Alu pairs separated by 650 or fewer base pairs (bp) in a study conducted prior to the completion of the draft human genome sequence. Results We performed a comprehensive analysis of all (> 800,000) full-length Alu elements in the human genome. This large sample size permits detection of small differences in the ratio between inverted and direct Alu pairs (I:D). We have discovered a significant depression in the full-length Alu pair I:D ratio that extends to repeat pairs separated by ? 350,000 bp. Within this imbalance bubble (those Alu pairs separated by ? 350,000 bp), direct pairs outnumber inverted pairs. Using PCR, we experimentally verified several examples of inverted Alu pair exclusions that were caused by deletions. Conclusions Over 50 million full-length Alu pairs reside within the I:D imbalance bubble. Their collective impact may represent one source of Alu element-related human genomic instability that has not been previously characterized.

2011-01-01

340

Positron-Electron Pair Creation Near Threshold  

SciTech Connect

Positron-electron pair creation near the threshold energy is extremely difficult to investigate by both experiments and theory. First test experiments were performed at the ILL to determine the cross sections for positron-electron pair creation near threshold using prompt {gamma}-rays from different targets after neutron capture and conventional radioactive sources. Pair creation was studied in a Ge detector, which simultaneously acted as sample and detector. First results are presented which show a significant deviation from theoretical values near threshold.

Frahm, Ronald; Luetzenkirchen-Hecht, Dirk [Fachgruppe Physik, Bergische Universitaet Wuppertal, Gaussstr. 20, 42097 Wuppertal (Germany); Jentschel, Michael; Urban, Waldemar; Krempel, Jochen [Institut Laue-Langevin, 6 rue Jules Horowitz, 38000 Grenoble (France); Schreckenbach, Klaus [Physik-Department E21, Technische Univ. Muenchen, James-Franck-Str., 85748 Garching (Germany)

2009-01-28

341

Direction distribution of ambient neutron dose equivalent from 20 MeV protons incident on thick Be and Cu targets.  

PubMed

Ambient neutron dose equivalent from 20 MeV protons incident on thick Be and Cu targets are measured at 0 degrees, 30 degrees, 60 degrees and 90 degrees with respect to the beam direction using a conventional dose equivalent meter. The neutron spectra calculated using nuclear reaction model codes ALICE, PRECO and earlier reported empirical expressions are converted to the ambient dose equivalent using the ICRP fluence-to-dose conversion coefficients and are compared with the measured values. The experimental energy spectra reported in the literature for 19.08 MeV protons incident on a thick Be target are also converted to ambient neutron dose equivalent and are compared with the present experimental results. It is observed that the values estimated from the neutron spectra obtained from the nuclear reaction codes are unable to predict the measured values. The results obtained from the reported experimental energy spectra compare well with the results obtained here. An empirical relation that was used to calculate the directional dependence of the measured neutron dose equivalent from heavy ion-induced reactions is used in this study to check its effectiveness for proton-induced reactions. PMID:19700498

Sunil, C; Shanbhag, A A; Nandy, M; Maiti, M; Bandyopadhyay, T; Sarkar, P K

2009-08-21

342

Neutron tomography of the root-soil interface: water distribution around different parts of the root structure  

NASA Astrophysics Data System (ADS)

Although the importance of the root-soil interface in water uptake by plant roots has been acknowledged in many studies, there is a gap of knowledge on how water enters the roots. The main reason for this gap is the technical difficulties in resolving soil moisture dynamics in the vicinity of roots. Spatially and temporally resolved data on water flow across soil-root interface is needed to improve our understanding of mechanisms controlling water uptake by roots. We used neutron tomography to image soil water distribution around roots in-situ. We grew chick peas and lupines in sand-filled cylinders for 10 days at a water potential of -20 hPa. The samples were tomographed for 4 days over day and night and during a drying period and after rewetting. We observed that water content near the root surface was higher than in the bulk soil during the whole course of measurement for all the samples. Our hypothesis is that this increase of water content next to roots was due to the distinct water retention curve of the soil next to roots, the rhizosphere. Our hypothesis is that the rhizosphere water retention curve is caused by mucilage exuded by roots. Mucilage contains more than 90% water even at low water potentials, consequently increasing the water holding capacity of the rhizosphere. In another words, the roots modify the physical and chemical properties of their rhizosphere. The thickness of the area of increasing water, rhizosphere, varied along the root length. It ranged from slightly less than 1.5 mm in the distal part of the roots to more than 3 mm around the root tip. Also, it was slightly thicker around the main root compared to the lateral roots. As the soil water was being consumed by the roots, the extent of the rhizosphere decreased slightly, and then increased again after rewetting. We expect that the high water-holding capacity of the rhizosphere favors root water uptake, especially in dry soils. Most of the present modeling approaches neglect this effect.

Moradi, A. B.; Carminati, A.

2009-12-01

343

Collective excitations induced by pairing anti-halo effect  

NASA Astrophysics Data System (ADS)

We emphasize a special interplay of loosely-bound neutrons with small orbital angular momentum ? and self-consistent pairing correlations for low-lying collective vibrational excitations in neutron drip line nuclei. Change of the spatial structure in quasiparticle wave functions by self-consistent pairing correlations leads to the broad localization of two-quasiparticle states with low-? neutrons. We show that the broad localization can cause the enhancement of the low-lying collectivity. By performing HFB plus quasiparticle random phase approximation (QRPA) calculation for the first 2+ states in neutron rich Ni isotopes, the unique role of self-consistent pairing correlations is examined. Finally we make a comment on deformation effects for low-lying vibrational excitations in neutron drip line nuclei.

Yamagami, M.

2005-09-01

344

Energy mode distribution: An analysis of the ratio of anti-Stokes to Stokes amplitudes generated by a pair of counterpropagating Langmuir waves  

NASA Astrophysics Data System (ADS)

Results from plasma wave experiments in spacecrafts give support to nonlinear interactions involving Langmuir, electromagnetic, and ion-acoustic waves in association with type III solar radio bursts. Starting from a general form of Zakharov equation (Zakharov, V.E., 1985. Collapse and self-focusing of Langmuir waves. Hand-book of Plasma Physics Cap.2, 81 121) the equations for electric fields and density fluctuations (density gratings) induced by a pair of counterpropagating Langmuir waves are obtained. We consider the coupling of four triplets. Each two triplets have in common the Langmuir pump wave (forward or backward wave) and a pair of independent density gratings. We numerically solve the dispersion relation for the system, extending the work of (Alves, M.V., Chian, A.C.L., Moraes, M.A.E., Abalde, J.R., Rizzato, F.B., 2002. A theory of the fundamental plasma emission of type- III solar radio bursts. Astronomy and Astrophysics 390, 351 357). The ratio of anti-Stokes (AS) (?0+?) to Stokes (S) (?0-?) electromagnetic mode amplitudes is obtained as a function of the pump wave frequency, wave number, and energy. We notice that the simultaneous excitation of AS and S distinguishable modes, i.e., with Re{?}=??0, only occurs when the ratio between the pump wave amplitudes, r is ?1 and the pump wave vector k0 is <(13)W01/2, W0 being the forward pump wave energy. We also observe that the S mode always receives more energy.

Simőes Júnior, F. J. R.; Alves, M. V.; Rizzato, F. B.

2005-12-01

345

Atomic-scale structure of nanocrystals by high-energy x-ray diffraction and atomic pair distribution function analysis : study of Fe{sub x}Pd{sub 100-x} (x=0, 26, 28, 48) nanoparticles.  

SciTech Connect

Knowledge of the atomic-scale structure is an important prerequisite to understanding and predicting properties of materials. With bulk crystals it is routinely obtained by X-ray diffraction. With nanocrystals, however, traditional X-ray crystallography fails because of their substantially limited length of structural coherence. Here we illustrate, step by step, how a nontraditional approach involving high-energy X-ray diffraction and atomic pair distribution function analysis is applied to determine the atomic-scale structure of a typical nanocrystalline material-Fe{sub x}Pd{sub 100-x} (x = 0, 26, 28, 48) nanoparticles exhibiting useful magnetic properties.

Petkov, V.; Ohta, T.; Hou, Y.; Ren, Y.; Central Michigan Univ.; Univ. of Tokyo; Brown National Lab.

2006-12-07

346

Evaluation of the neutron energy spectrum, angular distribution, and yield of the 9Be(d,n) reaction with a thick beryllium target  

NASA Astrophysics Data System (ADS)

A mathematical model and a computer program are developed to calculate the neutron energy spectrum, angular distribution, and integrated yield of the 9Be(d,n) reaction on a thick beryllium target as an accelerator-based neutron source in the incident-deuteron-energy range from 0.5 to 20.0 MeV. The double-differential cross section computed by the talys code and the stopping power derived from the SRIM-2010 code are adopted in the program. Typical computational results are presented, and are compared with the previous experimental data to evaluate the computing model as well as the characteristics of the 9Be(d,n) reaction with a thick Be target. Moreover, the developed theory and calculation methods can also provide a reasonable evaluation for calculating data of double-differential cross sections and stopping power. This model and the program can predict the above characteristics parameters of the 9Be(d,n) reaction for a thick beryllium target as a neutron source in the incident-deuteron-energy range from 0.5 to 20.0 MeV.

Wei, Z.; Yan, Y.; Yao, Z. E.; Lan, C. L.; Wang, J.

2013-05-01

347

Lunar Prospector epithermal neutrons from impact craters and landing sites: Implications for surface maturity and hydrogen distribution  

Microsoft Academic Search

Initial studies of neutron spectrometer data returned by Lunar Prospector concentrated on the discovery of enhanced hydrogen abundances near both lunar poles. However, the nonpolar data exhibit intriguing patterns that appear spatially correlated with surface features such as young impact craters (e.g., Tycho). Such immature crater materials may have low hydrogen contents because of their relative lack of exposure to

Jeffrey R. Johnson; William C. Feldman; David J. Lawrence; Sylvestre Maurice; Timothy D. Swindle; Paul G. Lucey

2002-01-01

348

The Probability Distribution of Binary Pulsar Coalescence Rates. I. Double Neutron Star Systems in the Galactic Field  

Microsoft Academic Search

Estimates of the Galactic coalescence rate (R) of close binaries with two neutron stars (NS-NS) are known to be uncertain by large factors (about 2 orders of magnitude) mainly because of the small number of systems detected as binary radio pulsars. We present an analysis method that allows us to estimate the Galactic NS-NS coalescence rate using the current observed

C. Kim; V. Kalogera; D. R. Lorimer

2003-01-01

349

Superfluidity in the Core of Neutron Stars  

NASA Astrophysics Data System (ADS)

The year (1958) after the publication of the BCS theory, Bohr, Mottelson & Pines showed that nuclei should also contain superfluid neutrons and superconducting protons. In 1959, A. Migdal proposed that neutron superfluidity should also occur in the interior of neutron stars. Pairing in nuclei forms Cooper pairs with zero spin, but the relevant component of the nuclear interaction becomes repulsive at densities larger than the nuclear matter density. It has been proposed that neutron-neutron interaction in the spin-triplet state, and L=1 orbital angular momentum, that is known to be attractive from laboratory experiments, may result in a new form of neutron superfluidity in the neutron star interior. I will review our present understanding of the structure of neutron stars and describe how superfluidity strongly affects their thermal evolution. I will show how a ``Minimal Model'' that excludes the presence of ``exotic'' matter (Bose condensates, quarks, etc.) is compatible with most observations of the surface temperatures of young isolated neutron stars in the case this neutron superfluid exists. Compared to the case of isotropic spin-zero Cooper pairs, the formation of anisotropic spin-one Cooper pairs results in a strong neutrino emission that leads to an enhanced cooling of neutron stars after the onset of the pairing phase transition and allows the Minimal Cooling scenario to be compatible with most observations. In the case the pairing critical temperature Tc is less than about 6 x10^8 K, the resulting rapid cooling of the neutron star may be observable. It was recently reported that 10 years of Chandra observations of the 333 year young neutron star in the Cassiopeia A supernova remnant revealed that its temperature has dropped by about 5%. This result indicates that neutrons in this star are presently becoming superfluid and, if confirmed, provides us with the first direct observational evidence for neutron superfluidity at supra-nuclear densities.

Page, Dany

2013-04-01

350

Two-neutron transfer probabilities and spatial-localization effects at the drip line  

NASA Astrophysics Data System (ADS)

We examine Cr isotopes at the drip line, where surface effects related to the existence of a weakly bound s1/2 state are known to be important and tightly connected with the pairing phenomenon (antihalo effect). For these weakly bound isotopes, we evaluate the ground state to ground state two-neutron transfer probabilities within a mean-field-based approach. An important part of the discussion is devoted to the analysis of several procedures that can be employed to constrain the parameters of a phenomenological pairing interaction. The parameters are first adjusted to reproduce the experimental gaps evaluated with the five-point formula. This choice has, however, some consequences on the evolution of the pairing correlations along the isotopic chains and, in particular, at shell closures. Other procedures are then followed (adjustment on a theoretical pairing gap at mid-shell and on the two-neutron separation energies). For the transfer probabilities, we discuss the effects associated with different choices of the spatial localization of the pairing interaction. We indicate that the analysis of pair-transfer reactions for such cases (where the last bound state is a low-l state in a weakly bound nucleus) may improve our understanding of two aspects: the spatial distribution of pairing correlations in nuclei and the general problem of the persistence of pairing at the drip lines.

Grasso, Marcella

2013-06-01

351

Non-Statistical Effects in Neutron Capture  

SciTech Connect

There have been many reports of non-statistical effects in neutron-capture measurements. However, reports of deviations of reduced-neutron-width ({gamma}{sub n}{sup 0}) distributions from the expected Porter-Thomas (PT) shape largely have been ignored. Most of these deviations have been reported for odd-A nuclides. Because reliable spin (J) assignments have been absent for most resonances for such nuclides, it is possible that reported deviations from PT might be due to incorrect J assignments. We recently developed a new method for measuring spins of neutron resonances by using the DANCE detector at the Los Alamos Neutron Science Center (LANSCE). Measurements made with a {sup 147}Sm sample allowed us to determine spins of almost all known resonances below 1 keV. Furthermore, analysis of these data revealed that the {gamma}{sub n}{sup 0} distribution was in good agreement with PT for resonances below 350 eV, but in disagreement with PT for resonances between 350 and 700 eV. Our previous (n,{alpha}) measurements had revealed that the {alpha} strength function also changes abruptly at this energy. There currently is no known explanation for these two non-statistical effects. Recently, we have developed another new method for determining the spins of neutron resonances. To implement this technique required a small change (to record pulse-height information for coincidence events) to a much simpler apparatus: A pair of C{sub 6}D{sub 6}{gamma}-ray detectors which we have employed for many years to measure neutron-capture cross sections at the Oak Ridge Electron Linear Accelerator (ORELA). Measurements with a {sup 95}Mo sample revealed that not only does the method work very well for determining spins, but it also makes possible parity assignments. Taken together, these new techniques at LANSCE and ORELA could be very useful for further elucidation of non-statistical effects.

Koehler, P. E.; Guber, K. H.; Harvey, J. A.; Wiarda, D. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); Bredeweg, T. A.; O'Donnell, J. M.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wouters, J. M. [Los Alamos National Laboratory, Los Alamos, NM (United States); Reifarth, R. [GSI, Planckstr. 1, 64291 Darmstadt (Germany)

2009-01-28

352

Non-Statistical Effects in Neutron Capture  

SciTech Connect

There have been many reports of non-statistical effects in neutron-capture measurements. However, reports of deviations of reduced-neutron-width ({Gamma}n{sup 0}) distributions from the expected Porter-Thomas (PT) shape largely have been ignored. Most of these deviations have been reported for odd-A nuclides. Because reliable spin (J) assignments have been absent for most resonances for such nuclides, it is possible that reported deviations from PT might be due to incorrect J assignments. We recently developed a new method for measuring spins of neutron resonances by using the DANCE detector at the Los Alamos Neutron Science Center (LANSCE). Measurements made with a 147Sm sample allowed us to determine spins of almost all known resonances below 1 keV. Furthermore, analysis of these data revealed that the {Gamma}n{sup 0} distribution was in good agreement with PT for resonances below 350 eV, but in disagreement with PT for resonances between 350 and 700 eV. Our previous (n,{alpha}) measurements had revealed that the {alpha} strength function also changes abruptly at this energy. There currently is no known explanation for these two non-statistical effects. Recently, we have developed another new method for determining the spins of neutron resonances. To implement this technique required a small change (to record pulse-height information for coincidence events) to a much simpler apparatus: A pair of C6D6 ?-ray detectors which we have employed for many years to measure neutron-capture cross sections at the Oak Ridge Electron Linear Accelerator (ORELA). Measurements with a 95Mo sample revealed that not only does the method work very well for determining spins, but it also makes possible parity assignments. Taken together, these new techniques at LANSCE and ORELA could be very useful for further elucidation of non-statistical effects.

Koehler, Paul Edward [ORNL; Bredeweg, t a [Los Alamos National Laboratory (LANL); Guber, Klaus H [ORNL; Harvey, John A [ORNL; O'Donnell, J. M. [Los Alamos National Laboratory (LANL); Reifarth, R. [Los Alamos National Laboratory (LANL); Rundberg, R. S. [Los Alamos National Laboratory (LANL); Ullmann, J. L. [Los Alamos National Laboratory (LANL); Vieira, D. J. [Los Alamos National Laboratory (LANL); Wiarda, Dorothea [ORNL; Wouters, J. M. [Los Alamos National Laboratory (LANL)

2009-01-01

353

Cation distribution in a Fe-bearing K-feldspar from Itrongay,Madagascar. A combined neutron- and X-ray single crystal diffractionstudy  

SciTech Connect

We determined the cation distribution and ordering of Si, Al and Fe on the tetrahedral sites of a monoclinic low-sanidine from Itrongay, Madagascar, by combined neutron- and X-ray single-crystal diffraction. The cation distribution was determined by means of a simultaneous refinement using neutron- and X-ray data, as well as by combining scattering densities obtained from separate refinements with chemical data from a microprobe experiment. The two methods give the same results and show that Fe is fully ordered on T1, whereas Al shows a high degree of disorder. Based on this and previously published temperature-dependent X-ray data, we conclude that it is preferential ordering of Fe on T1 even at high temperature, rather than a high diffusion kinetics of Fe, which causes this asymmetry in ordering behavior between Al and Fe. The preferential ordering of Fe3+ relative to Al3+ in T1 is consistent with its 25 percent larger ionic radius.

Ackermann, Sonia; Kunz, Martin; Armbruster, Thomas; Schefer,Jurg; Hanni, Henry

2005-05-02

354

Measurement and analysis of energy and angular distributions of thick target neutron yields from 110 MeV F19 on Al27  

NASA Astrophysics Data System (ADS)

Energy distributions of emitted neutrons were measured for 110 MeV F19 ions incident on a thick Al27 target. Measurements were done at 0°, 30°, 60°, 90°, and 120° with respect to the projectile direction employing the time-of-flight technique using a proton recoil scintillation detector. Comparison with calculated results from equilibrium nuclear reaction model codes like PACE-2 and EMPIRE 2.18 using various level-density options was carried out. It is observed that the dynamic level-density approach in EMPIRE 2.18 gives the closest approximation to the measured data. In the Fermi-gas level-density approach the best approximation of the level-density parameter is a=A/12.0, where A is the mass number of the composite system. The trend in the angular distribution of emitted neutrons is well reproduced by the projection of the angular momentum on the recoil axis as done in the PACE-2 code.

C, Sunil; Nandy, Maitreyee; Sarkar, P. K.

2008-12-01

355

Atom-pair correlations in Fe-13.5% V  

NASA Astrophysics Data System (ADS)

Diffuse neutron scattering data were used to determine the atom-pair correlations for Fe-13.5% V in terms of both the Warren-Cowley ASRO parameters and the Krivoglaz-Clapp-Moss pair potentials. These agree reasonably well with those calculated by Hennion from alloy band structure parameters. Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan

Cable, J. W.; Child, H. R.; Nakai, Y.

1989-01-01

356

Atom-pair correlations in Fe-13. 5% V  

SciTech Connect

Diffuse neutron scattering data were used to determine the atom-pair correlations for Fe-13.5% V in terms of both the Warren-Cowley ASRO parameters and the Krivoglaz-Clapp-Moss pair-potentials. These agree reasonably well with those calculated by Hennion from alloy band structure parameters. 9 refs., 2 figs., 1 tab.

Cable, J.W.; Child, H.R.; Nakai, Y.

1988-01-01

357

Experimental determination of moisture distributions in fired clay brick using a 252Cf source: a neutron transmission study.  

PubMed

A neutron transmission method was proposed to study liquid transport in porous media. It was applied to study water penetration into two kinds of fired clay bricks. The results showed that the diffusion processes in the investigated samples are different. Water diffusivities and capillary absorption coefficients characterizing both the flow process and the brick samples were determined and compared. The proposed method is simple, accurate and reliable in studying water diffusion in porous media, in real time. PMID:23410613

El Abd, A; Abdel-Monem, A M; Kansouh, W A

2013-01-16

358

A background-free direction-sensitive neutron detector  

Microsoft Academic Search

We show data from a new type of detector that can be used to determine neutron flux, energy distribution, and direction of neutron motion for both fast and thermal neutrons. Many neutron detectors are plagued by large backgrounds from x-rays and gamma rays, and most current neutron detectors lack single-event energy sensitivity or any information on neutron directionality. Even the

Alvaro Roccaro; H. Tomita; S. Ahlen; D. Avery; A. Inglis; J. Battat; D. Dujmic; P. Fisher; S. Henderson; A. Kaboth; G. Kohse; R. Lanza; J. Monroe; G. Sciolla; N. Skvorodnev; H. Wellenstein; R. Yamamoto

2009-01-01

359

A bounding estimate of neutron dose based on measured photon dose around single pass reactors at the Hanford site.  

PubMed

Neutron and photon radiation survey records have been used to evaluate and develop a neutron to photon (NP) ratio to reconstruct neutron doses to workers around Hanford's single pass reactors that operated from 1945 to 1972. A total of 5,773 paired neutron and photon measurements extracted from 57 boxes of survey records were used in the development of the NP ratio. The development of the NP ratio enables the use of the recorded dose from an individual's photon dosimeter badge to be used to estimate the unmonitored neutron dose. The Pearson rank correlation between the neutron and photon measurements was 0.71. The NP ratio best fit a lognormal distribution with a geometric mean (GM) of 0.8, a geometric standard deviation (GSD) of 2.95, and the upper 95 th % of this distribution was 4.75. An estimate of the neutron dose based on this NP ratio is considered bounding due to evidence that up to 70% of the total photon exposure received by workers around the single pass reactors occurs during shutdown maintenance and refueling activities when there is no significant neutron exposure. Thus when this NP ratio is applied to the total measured photon dose from an individual film badge dosimeter, the resulting neutron dose is considered bounded. PMID:20539122

Taulbee, Timothy D; Glover, Samuel E; Macievic, Gregory V; Hunacek, Mickey; Smith, Cheryl; DeBord, Gary W; Morris, Donald; Fix, Jack

2010-07-01

360

Counting the number of correlated pairs in a nucleus  

SciTech Connect

We suggest that the number of correlated nucleon pairs in an arbitrary nucleus can be estimated by counting the number of proton-neutron, proton-proton, and neutron-neutron pairs residing in a relative S state. We present numerical calculations of those amounts for the nuclei {sup 4}He, {sup 9}Be, {sup 12}C, {sup 27}Al, {sup 40}Ca, {sup 48}Ca, {sup 56}Fe, {sup 63}Cu, {sup 108}Ag, and {sup 197}Au. The results are used to predict the values of the ratios of the per-nucleon electron-nucleus inelastic scattering cross section to the deuteron in the kinematic regime where correlations dominate.

Vanhalst, Maarten; Cosyn, Wim; Ryckebusch, Jan [Department of Physics and Astronomy, Ghent University, Proeftuinstraat 86, B-9000 Gent (Belgium)

2011-09-15

361

Development of a new type multi-moderator neutron spectrometer  

Microsoft Academic Search

A multi-moderator spectrometer on which is mounted a pair of 6Li and 7Li glass scintillators has been developed as a new type neutron spectrometer which can measure the neutron spectrum in a mixed field of neutrons, charged particles and gamma-rays realized in space. The particle identification capability was investigated in neutron-gamma-ray and neutron-proton mixed fields and the neutron response functions

Shingo Taniguchi; Masashi Takada; Takashi Nakamura

2001-01-01

362

Fast Neutron Resonance Radiography in a Pulsed Neutron Beam  

Microsoft Academic Search

The feasibility of performing fast neutron resonance radiography at the PTB accelerator facility is studied. A neutron beam of a broad spectral distribution is produced by a pulsed 13 MeV deuterium beam hitting a thick Be target. The potential of 3 different neutron imaging detectors with time-of flight capability are investigated. The applied methods comprise wire chambers with hydrogenous converter

V. Dangendorf; G. Laczko; C. Kersten; O. Jagutzki; U. Spillmann

2003-01-01

363

The Neutron Star Census  

Microsoft Academic Search

The paucity of old isolated accreting neutron stars in ROSAT observations is used to derive a lower limit on the mean velocity of neutron stars at birth. The secular evolution of the population is simulated following the paths of a statistical sample of stars for different values of the initial kick velocity, drawn from an isotropic Gaussian distribution with mean

S. B. Popov; M. Colpi; A. Treves; R. Turolla; V. M. Lipunov; M. E. Prokhorov

2000-01-01

364

Electron pair emission in nuclear pion capture  

SciTech Connect

We report the first observation of the rare pion capture mode in beryllium consisting in the emission of an electron-positron pair. Rate, angular distribution, and energy-spectrum are in quantitative agreement with the ones expected assuming internal pair-creation from single radiative capture.

Lebrun, M.; Deutsch, J.; Favart, D.; Lipnik, P.; Macq, P.; Prieels, R.

1981-08-01

365

Odd-even mass difference and isospin dependent pairing interaction  

SciTech Connect

The neutron and proton odd-even mass differences are studied with Hartree-Fock + BCS (HF+BCS) calculations with Skyrme interactions and an isospin dependent contact pairing interaction, which is recently derived from a microscopic nucleon-nucleon interaction. To this end, we perform HF+BCS calculations for even and odd semi-magic tin and lead isotopes together with even and odd Z isotones with N=50 and 82. The filling approximation is applied to the last unoccupied particle in odd nuclei. Comparisons with the experimental data show a clear manifestation of the isospin dependent pairing correlations in both proton and neutron pairing gaps.

Bertulani, C. A. [Department of Physics, Texas A and M University-Commerce, Commerce, Texas 75429 (United States); Lue, H. F. [College of Science, China Agricultural University, Beijing (China); Sagawa, H. [Center for Mathematics and Physics, University of Aizu, Aizu-Wakamatsu, 965-8580 Fukushima (Japan)

2009-08-15

366

Electron-pair excitations and the molecular Coulomb continuum  

SciTech Connect

Electron-pair excitations in the molecular hydrogen continuum are described by quantizing rotations of the momentum plane of the electron pair about by the pair's relative momentum. A helium-like description of the molecular pi.Joto double ionization is thus extended to higher angular momenta of the electron pair. A simple three-state superposition is found to account surprisingly well for recent observations of noncoplanar electron-pair, molecular-axis angular distributions.

Colgan, James [Los Alamos National Laboratory

2009-01-01

367

Detailed mapping of the local Ir{sup 4+} dimers through the metal-insulator transitions of CuIr{sub 2}S{sub 4} thiospinel by x-ray atomic pair distribution function measurements.  

SciTech Connect

The evolution of the short-range structural signature of the Ir{sup 4+} dimer state in CuIr{sub 2}S{sub 4} thiospinel has been studied across the metal-insulator phase transitions as the metallic state is induced by temperature, Cr doping, and x-ray fluence. An atomic pair distribution function (PDF) approach reveals that there are no local dimers that survive into the metallic phase when this is invoked by temperature and doping. The PDF shows Ir{sup 4+} dimers when they exist, regardless of whether or not they are long-range ordered. At 100 K, exposure to a 98 keV x-ray beam melts the long-range dimer order within a few seconds, though the local dimers remain intact. This shows that the metallic state accessed on warming and doping is qualitatively different from the state obtained under x-ray irradiation.

Bozin, E. S.; Masadeh, A. S.; Hor, Y. S.; Mitchell, J. F.; Billinge, S. J. L.; Materials Science Division; BNL; Michigan State Univ.; Univ. of Jordan; Columbia Univ.

2011-01-24

368

Momentum distributions in medium and heavy exotic nuclei  

SciTech Connect

We study nucleon momentum distributions of even-even isotopes of Ni, Kr, and Sn in the framework of deformed self-consistent mean-field Skyrme HF + BCS method, as well as of theoretical correlation methods based on light-front dynamics and local density approximation. The isotopic sensitivities of the calculated neutron and proton momentum distributions are investigated together with the effects of pairing and nucleon-nucleon correlations. The role of deformation on the momentum distributions in even-even Kr isotopes is discussed. For comparison, the results for the momentum distribution in nuclear matter are also presented.

Gaidarov, M. K.; Antonov, A. N.; Ivanov, M. V. [Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Sofia 1784 (Bulgaria); Krumova, G. Z. [University of Ruse, Ruse 7017 (Bulgaria); Sarriguren, P. [Instituto de Estructura de la Materia, CSIC, Serrano 123, E-28006 Madrid (Spain); Moya de Guerra, E. [Departamento de Fisica Atomica, Molecular y Nuclear, Facultad de Ciencias Fisicas, Universidad Complutense de Madrid, E-28040 Madrid (Spain)

2009-11-15

369

Studies on the periodicity and intravascular distribution of Wuchereria bancrofti microfilariae in paired samples of capillary and venous blood from Recife, Brazil.  

PubMed

We examined the periodicity and intravascular distribution of Wuchereria bancrofti microfilariae (mf) and determined the effect of these parasite properties on the accuracy of blood filming and filtration methods for diagnosis of bancroftian filariasis in the endemic area of Recife, Brazil. Microfilariae in both venous and capillary blood exhibited a nocturnal periodicity pattern with a relatively high amplitude. Overall, capillary blood contained approximately 1.25 times the number of mf present at the same time in the same volume of venous blood. However, the ratio of mf present in capillary and venous blood varied over a 24-hour period, so that the fewest mf were present in the capillary bed of the skin at the time when biting activity of the local Culex vector is the lowest. Twenty or 60 microliters blood films did not reliably detect carriers with fewer than 100 or 60 mf/ml venous blood, respectively, and were thus inadequate for the identification of low density mf carriers. In contrast, all carriers with > 1 mf/20 or 60 microliters blood smear at night could be identified during daytime hours by filtration of 1 micromilligram venous blood. PMID:8665395

Dreyer, G; Pimentael, A; Medeiros, Z; Béliz, F; Moura, I; Coutinho, A; de Andrade, L D; Rocha, A; da Silva, L M; Piessens, W F

1996-04-01

370

Fast neutrons from annihilation  

NASA Astrophysics Data System (ADS)

We analyzed experimental data on fast neutron production in Żp+64Cu and Żp+238U annihilation and the ratio of231Th/231Ac isotopes from Żp+232Th annihilation at rest. The contributions from standard reaction channels are calculated by cascade model. The annihilation pion rescattering and absorption in nuclear medium as well as the preequilibrium nucleon emission were analyzed. The calculation based on the assumption that neutron density distribution ?uals the proton one multiplied by factor N/Z does not reproduce the experimental data. We discussed the influence of the neutron density distribution on fast neutron and isotope production. It was found that the hypothesis of the neutron halo allows one to get a reasonable description of the experimental data.

Sibirtsev, A.

1994-09-01

371

Gelina neutron target optimisation.  

PubMed

A study is being performed on the properties of the Geel Electron Linear Accelerator (GELINA), a powerful white neutron source, designed for the high-energy resolution time-of-flight measurements. The main aim of this study is to reduce the time spread of neutrons of the given energy without compromising the neutron yield. Both time spread and neutron intensity influence the experimental accuracy of high-resolution neutron cross section measurements, which are particularly important in the resonance region. The quantities of interest have been simulated with coupled electron-photon-neutron steady state and transient MCNP4C3 calculations. Following benchmarking of the code to the properties of the existing target, neutron yield, energy spectra, resolution functions, and neutron and heat spatial distributions have been determined for various alternative geometries and materials. At a fixed accelerator power, actinides deliver the highest neutron yield and a small target provides the best time resolution. The resulting high-power density requires a joint optimisation of the thermal hydraulics and neutronics properties. PMID:16381756

Flaska, M; Plompen, A J M; Mondelaers, W; Lathouwers, D; van der Hagen, T H J J; van Dam, H

2005-01-01

372

Advanced setup for high-pressure and low-temperature neutron diffraction at hydrostatic conditions  

SciTech Connect

We describe a design of the experimental setup for neutron diffraction studies at low temperatures and hydrostatic pressure. The significant benefit of the setup, compared to the previous methods, is that it makes possible the simultaneous collection of neutrons diffracted at the 30 deg. -150 deg. range with no contamination by the primary scattering from the sample surroundings and without cutting out the incident and diffracted beams. The suggested design is most useful for third-generation time-of-flight diffractometers and constant wavelength instruments. Application of the setup expands the capabilities of high-pressure neutron diffraction, allowing time-resolved kinetics and structural studies, multihistogram Rietveld, and pair distribution function and texture analyses. The high efficiency of the setup was proven for the HIPPO diffractometer at Los Alamos Neutron Science Center under pressures up to 10 kbar and temperatures from 4 to 300 K.

Lokshin, Konstantin A.; Zhao Yusheng [LANSCE-12, Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States)

2005-06-15

373

Neutron degeneracy and plasma physics effects on radiative neutron captures in neutron star crust  

NASA Astrophysics Data System (ADS)

We consider the astrophysical reaction rates for radiative neutron capture reactions (n,?) in the crust of a neutron star. The presence of degenerate neutrons at high densities (mainly in the inner crust) can drastically affect the reaction rates. Standard rates assuming a Maxwell-Boltzmann distribution for neutrons can underestimate the rates by several orders of magnitude. We derive simple analytical expressions for reaction rates at a variety of conditions with account for neutron degeneracy. We also discuss the plasma effects on the outgoing radiative transition channel in neutron radiative capture reactions and show that these effects can also increase the reaction rates by a few orders of magnitude. In addition, using detailed balance, we analyze the effects of neutron degeneracy and plasma physics on reverse (?,n) photodisintegration. We discuss the dependence of the reaction rates on temperature and neutron chemical potential and outline the efficiency of these reactions in the neutron star crust.

Shternin, P. S.; Beard, M.; Wiescher, M.; Yakovlev, D. G.

2012-07-01

374

Induced Pairing Interaction in 11Li  

NASA Astrophysics Data System (ADS)

If neutrons are progressively added to a normal nucleus, the Pauli principle forces them into states of higher momentum. When the core becomes neutron-saturated, the nucleus expels most of the wavefunction of the last neutrons outside to form a halo, which because of its large size can have lower momentum. It is an open question how nature stabilizes such a fragile system and provides the glue needed to bind the halo neutrons to the core. Here we show that this problem is similar to that of the instability of the normal state of an electron system at zero temperature solved by Cooper, solution which is at the basis of BCS theory of superconductivity. By mimicking this approach using the long wavelength vibrations of the nucleus 11Li, the best known halo nucleus, as tailored glues of the least bound neutrons, we are able to obtain a unified and quantitative picture of the observed properties of 11Li. This result suggests a strategy for designing nuclei at the edges of the neutron drip line, and thus probing the limits of nuclear stability. It also provides evidence of the limits of validity of BCS theory in finite systems: a single Cooper pair.

Broglia, R. A.; Barranco, F.; Bortignon, P. F.; Colň, G.; Vigezzi, E.

2002-04-01

375

Experimental extraction of an entangled photon pair from two identically decohered pairs.  

PubMed

Entanglement is considered to be one of the most important resources in quantum information processing schemes, including teleportation, dense coding and entanglement-based quantum key distribution. Because entanglement cannot be generated by classical communication between distant parties, distribution of entangled particles between them is necessary. During the distribution process, entanglement between the particles is degraded by the decoherence and dissipation processes that result from unavoidable coupling with the environment. Entanglement distillation and concentration schemes are therefore needed to extract pairs with a higher degree of entanglement from these less-entangled pairs; this is accomplished using local operations and classical communication. Here we report an experimental demonstration of extraction of a polarization-entangled photon pair from two decohered photon pairs. Two polarization-entangled photon pairs are generated by spontaneous parametric down-conversion and then distributed through a channel that induces identical phase fluctuations to both pairs; this ensures that no entanglement is available as long as each pair is manipulated individually. Then, through collective local operations and classical communication we extract from the two decohered pairs a photon pair that is observed to be polarization-entangled. PMID:12540894

Yamamoto, Takashi; Koashi, Masato; Ozdemir, Sahin Kaya; Imoto, Nobuyuki

2003-01-23

376

Matched-pair classification  

SciTech Connect

Following an analogous distinction in statistical hypothesis testing, we investigate variants of machine learning where the training set comes in matched pairs. We demonstrate that even conventional classifiers can exhibit improved performance when the input data has a matched-pair structure. Online algorithms, in particular, converge quicker when the data is presented in pairs. In some scenarios (such as the weak signal detection problem), matched pairs can be generated from independent samples, with the effect not only doubling the nominal size of the training set, but of providing the structure that leads to better learning. A family of 'dipole' algorithms is introduced that explicitly takes advantage of matched-pair structure in the input data and leads to further performance gains. Finally, we illustrate the application of matched-pair learning to chemical plume detection in hyperspectral imagery.

Theiler, James P [Los Alamos National Laboratory

2009-01-01

377

Neutron dosimetry, moderated energy spectrum, and neutron capture therapy for californium-252 medical sources  

NASA Astrophysics Data System (ADS)

Examination of neutron dosimetry for 252Cf has been conducted using calculative and experimental means. Monte Carlo N-Particle (MCNP) transport code was used in a distributed computing environment as a parallel virtual machine (PVM) to determine the absorbed neutron dose and neutron energy spectrum from 252Cf in a variety of clinically relevant materials. Herein, a Maxwellian spectrum was used to model the 252Cf neutron emissions within these materials. 252Cf mixed-field dosimetry of Applicator Tube (AT) type sources was measured using 1.0 and 0.05 cm3 tissue-equivalent ion chambers and a miniature GM counter. A dosimetry protocol was formulated similar that of ICRU 45. The 252Cf AT neutron dosimetry was determined in the cylindrical coordinate system formalism recommended by the AAPM Task Group 43. These results demonstrated the overwhelming dependence of dosimetry on the source geometry factor as there was no significant neutron attenuation within the source or encapsulation. Gold foils and TLDs were used to measure the thermal flux in the vicinity of 252Cf AT sources to compare with the results calculated using MCNP. As the fast neutron energy spectrum did not markedly changed at increasing distances from the AT source, neutron dosimetry results obtained with paired ion chambers using fixed sensitivity factors agreed well with MCNP results and those in the literature. Calculations of moderated 252Cf neutron energy spectrum with various loadings of 10B and 157Gd were performed, in addition to analysis of neutron capture therapy dosimetry with these isotopes. Radiological concerns such as personnel exposure and shielding of 252Cf emissions were examined. Feasibility of a high specific-activity 252Cf HDR source was investigated through radiochemical and metallurgical studies using stand-ins such as Tb, Gd and 249Cf. Issues such as capsule burst strength due to helium production for a variety of proposed HDR sources were addressed. A recommended 252Cf source strength of at least 1mg was necessary for fabrication of a 252Cf HDR source.

Rivard, Mark Joseph

378

Evolution of local structures in polycrystalline Zn1?xMgxO (0<=x<=0.15) studied by Raman spectroscopy and synchrotron x-ray pair-distribution-function analysis  

SciTech Connect

The local structures of Zn{sub 1-x}Mg{sub x}O alloys have been studied by Raman spectroscopy and by synchrotron x-ray pair-distribution-function (PDF) analysis. Within the solid solution range (0 {le} x {le} 0.15) of Zn{sub 1-x}Mg{sub x}O, the wurtzite framework is maintained with Mg homogeneously distributed throughout the wurtzite lattice. The E{sub 2}{sup high} Raman line of Zn{sub 1-x}Mg{sub x}O displays systematic changes in response to the evolution of the crystal lattice upon the Mg substitution. The redshift and broadening of the E{sub 2}{sup high} mode are explained by the expansion of hexagonal ab dimensions and compositional disorder of Zn/Mg, respectively. Synchrotron x-ray PDF analyses of Zn{sub 1-x}Mg{sub x}O reveal that the Mg atoms have a slightly reduced wurtzite parameter u and more regular tetrahedral bond distances than the Zn atoms. For both Zn and Mg, the internal tetrahedral geometries are independent of the alloy composition.

Kim, Young-Il; Page, Katharine; Limarga, Andi M.; Clarke, David R.; Seshadri, Ram (UCSB)

2008-09-18

379

Evolution of local structures in polycrystalline Zn{sub 1-x}Mg{sub x}O (0{<=}x{<=}0.15) studied by Raman spectroscopy and synchrotron x-ray pair-distribution-function analysis  

SciTech Connect

The local structures of Zn{sub 1-x}Mg{sub x}O alloys have been studied by Raman spectroscopy and by synchrotron x-ray pair-distribution-function (PDF) analysis. Within the solid solution range (0{<=}x{<=}0.15) of Zn{sub 1-x}Mg{sub x}O, the wurtzite framework is maintained with Mg homogeneously distributed throughout the wurtzite lattice. The E{sub 2}{sup high} Raman line of Zn{sub 1-x}Mg{sub x}O displays systematic changes in response to the evolution of the crystal lattice upon the Mg substitution. The redshift and broadening of the E{sub 2}{sup high} mode are explained by the expansion of hexagonal ab dimensions and compositional disorder of Zn/Mg, respectively. Synchrotron x-ray PDF analyses of Zn{sub 1-x}Mg{sub x}O reveal that the Mg atoms have a slightly reduced wurtzite parameter u and more regular tetrahedral bond distances than the Zn atoms. For both Zn and Mg, the internal tetrahedral geometries are independent of the alloy composition.

Kim, Young-Il; Page, Katharine; Limarga, Andi M.; Clarke, David R.; Seshadri, Ram [Materials Department and Materials Research Laboratory, University of California, Santa Barbara, California 93106 (United States)

2007-09-15

380

Measurement and model prediction of proton-recoil track length distributions in NTA film dosimeters for neutron energy spectroscopy and retrospective dose assessment  

Microsoft Academic Search

The goal of this research was to determine whether neutron dose reconstruction could be improved through re-analysis of historic NTA films worn by workers in the 1950 through the 1970s. To improve neutron dose reconstruction, the underlying neutron energy spectra is critical in determining the organ dose due to energy dependence of the dose conversion factor as well as the

Timothy D. Taulbee

2009-01-01

381

Vortex pairs on surfaces  

SciTech Connect

A pair of infinitesimally close opposite vortices moving on a curved surface moves along a geodesic, according to a conjecture by Kimura. We outline a proof. Numerical simulations are presented for a pair of opposite vortices at a close but nonzero distance on a surface of revolution, the catenoid. We conjecture that the vortex pair system on a triaxial ellipsoid is a KAM perturbation of Jacobi's geodesic problem. We outline some preliminary calculations required for this study. Finding the surfaces for which the vortex pair system is integrable is in order.

Koiller, Jair [Centro de Matematica Aplicada, FGV/RJ, Praia de Botafogo 190 Rio de Janeiro, RJ, 22250-40 (Brazil); Boatto, Stefanella [Instituto de Matematica da UFRJ, C.P. 68530, Cidade Universitaria Rio de Janeiro, RJ 21945-970 (Brazil)

2009-05-06

382

Neutron Radiography.  

National Technical Information Service (NTIS)

Thermal neutron output from a moderated 14 Mev D-T reaction is discussed as applicable to neutron radiography. Detectors for radiography are evaluated and the results using the thermal beam of the Naval Ordnance Laboratory's Neutron Diffraction Facility a...

P. W. Hesse

1970-01-01

383

Laser generated neutron source for neutron resonance spectroscopy  

SciTech Connect

A neutron source for neutron resonance spectroscopy has been developed using high-intensity, short-pulse lasers. This technique will allow robust measurement of interior ion temperature of laser-shocked materials and provide insight into material equation of state. The neutron generation technique uses laser-accelerated protons to create neutrons in LiF through (p,n) reactions. The incident proton beam has been diagnosed using radiochromic film. This distribution is used as the input for a (p,n) neutron prediction code which is validated with experimentally measured neutron yields. The calculation infers a total fluence of 1.8x10{sup 9} neutrons, which are expected to be sufficient for neutron resonance spectroscopy temperature measurements.

Higginson, D. P.; Bartal, T. [Department of Mechanical and Aerospace Engineering, University of California-San Diego, La Jolla, California 92093 (United States); Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); McNaney, J. M.; Swift, D. C.; Hey, D. S.; Le Pape, S.; Mackinnon, A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Kodama, R.; Tanaka, K. A. [Institute of Laser Engineering, Osaka University, 2-6, Yamada-oka, Suita, Osaka 565-0871 (Japan); Graduate School of Engineering, Osaka University, 2-1, Yamada-oka, Suita, Osaka 565-0871 (Japan); Mariscal, D.; Beg, F. N. [Department of Mechanical and Aerospace Engineering, University of California-San Diego, La Jolla, California 92093 (United States); Nakamura, H. [Institute of Laser Engineering, Osaka University, 2-6, Yamada-oka, Suita, Osaka 565-0871 (Japan); Nakanii, N. [Department of Mechanical and Aerospace Engineering, University of California-San Diego, La Jolla, California 92093 (United States); Institute of Laser Engineering, Osaka University, 2-6, Yamada-oka, Suita, Osaka 565-0871 (Japan); Graduate School of Engineering, Osaka University, 2-1, Yamada-oka, Suita, Osaka 565-0871 (Japan)

2010-10-15

384

Laser generated neutron source for neutron resonance spectroscopy  

NASA Astrophysics Data System (ADS)

A neutron source for neutron resonance spectroscopy has been developed using high-intensity, short-pulse lasers. This technique will allow robust measurement of interior ion temperature of laser-shocked materials and provide insight into material equation of state. The neutron generation technique uses laser-accelerated protons to create neutrons in LiF through (p,n) reactions. The incident proton beam has been diagnosed using radiochromic film. This distribution is used as the input for a (p,n) neutron prediction code which is validated with experimentally measured neutron yields. The calculation infers a total fluence of 1.8×109 neutrons, which are expected to be sufficient for neutron resonance spectroscopy temperature measurements.

Higginson, D. P.; McNaney, J. M.; Swift, D. C.; Bartal, T.; Hey, D. S.; Kodama, R.; Le Pape, S.; MacKinnon, A.; Mariscal, D.; Nakamura, H.; Nakanii, N.; Tanaka, K. A.; Beg, F. N.

2010-10-01

385

Neutron Exposure Accelerator System For Biological Effect Experiments (NASBEE)  

SciTech Connect

The neutron exposure accelerator system for biological effect experiments (NASBEE) was developed to study biological effects of fast neutrons. We have characterized the NASBEE neutron beams with neutron energy spectrum, absorbed dose energy distributions, and space distributions. The neutron energy spectrum shows 2.3 MeV as mean energy and 3.0 MeV as kerma of tissue-equivalent-plastic (A150) weighted mean energy, and the maximum neutron energy was determined to be 9 MeV. Neutron absorbed doses occupy 82% of the NASBEE neutron beam. NASBEE has been used to learn some of the outcomes of the biological effects of fast neutrons.

Takada, Masashi; Suda, Mitsuo; Kamada, So; Hagiwara, Takuya; Imaseki, Hitoshi; Hamano, Tsuyoshi [National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage-ku Chiba, Japan 263-8555 (Japan)

2011-06-01

386

Galaxy pairs in the Local Group  

NASA Astrophysics Data System (ADS)

Current models of galaxy formation predict that galaxy pairs of comparable magnitudes should become increasingly rare with decreasing luminosity. This seems at odds with the relatively high frequency of pairings among dwarf galaxies in the Local Group. We use literature data to show that ˜30 per cent of all the satellites of the Milky Way and Andromeda galaxies brighter than MV = -8 are found in likely physical pairs of comparable luminosity. Besides the previously recognized pairings of the Magellanic Clouds and of NGC 147/NGC 185, other candidate pairs include the Ursa Minor and Draco dwarf spheroidals, as well as the And I/And III satellites of M31. These pairs are much closer than expected by chance if the radial and angular distributions of satellites were uncorrelated; in addition, they have very similar line-of-sight velocities and luminosities that differ by less than three magnitudes. In contrast, the same criteria pair fewer than 4 per cent of satellites in N-body/semi-analytic models that match the radial distribution and luminosity function of Local Group satellites. If confirmed in studies of larger samples, the high frequency of dwarf galaxy pairings may provide interesting clues to the formation of faint galaxies in the current cosmological paradigm.

Fattahi, Azadeh; Navarro, Julio F.; Starkenburg, Else; Barber, Christopher R.; McConnachie, Alan W.

2013-04-01

387

New Optical/UV Counterparts, Astrometry and the Spectral Energy Distributions of Nearby, Thermally Emitting, Isolated Neutron Stars  

NASA Astrophysics Data System (ADS)

Seven of the nearby isolated neutron stars (INS) known till date show predominantly thermal spectrum with 106 K temperatures. Being relatively nearby and isolated makes them particularly attractive to constrain important NS properties such as mass, radius, cooling and possibly the equation of state of matter at ultra-high densities. However, interpreting their thermal spectra has turned out to be far more difficult than thought initially : The blackbody radius inferred from X-ray spectra, while ignoring optical/UV measurements, turns out to be too small to be a NS - even leading to immature speculations that the object might be a 'quark star'. Therefore, we carried out HST observations of these INSs to identify their optical/UV counterparts. We now have clearly identified optical and UV counterparts to all seven INSs. When compared to their X-ray spectra most of these sources appear to be brighter in optical/UV, in one case by a factor of 40 ! We find that the optical/UV SEDs show a range of slopes that are inconsistent with that expected from thermal (Rayleigh-Jeans) emission. We consider several explanations for this ranging from atmospheric effects, magnetospheric emission, and resonant scattering, but find that none is sufficient. These observations show that the puzzle of INSs, and possibly of all NSs, is far from over. Support for this work was provided by NASA (HST award GO-11564.05), and NSF (under grants PHY 05-51164 and AST 07-07633).

Kamble, Atish; Kaplan, D. L.; Kerkwijk, M. H. v.; Ho, W. C. G.

2011-09-01

388

Nuclear-matter density distribution in the neutron-rich nuclei 12,14Be from proton elastic scattering in inverse kinematics  

NASA Astrophysics Data System (ADS)

In the present work, the differential cross sections for small-angle proton elastic scattering on the 12,14Be nuclei were measured in inverse kinematics, using secondary radioactive beams with energies near 700 MeV/u produced with the fragment separator FRS at GSI. The main part of the experimental setup was the active target IKAR, which was used simultaneously as a target and a detector for the recoil protons. Auxiliary detectors for projectile tracking and isotope identification completed the setup. The measured differential cross sections were analyzed using the Glauber multiple-scattering theory. For the evaluation of the data several phenomenological nuclear-matter density parametrizations and a sum of Gaussian parametrization were used. The nuclear-matter radii and radial density distributions of the isotopes 12,14Be were deduced. Extended nuclear-matter density distributions were observed in both isotopes, and the halo structure of 14Be was confirmed. The results were also compared with microscopic few-body and fermionic molecular dynamics model calculations concerning the structure of these neutron-rich nuclei.

Ilieva, S.; Aksouh, F.; Alkhazov, G. D.; Chulkov, L.; Dobrovolsky, A. V.; Egelhof, P.; Geissel, H.; Gorska, M.; Inglessi, A.; Kanungo, R.; Khanzadeev, A. V.; Kiselev, O. A.; Korolev, G. A.; Le, X. C.; Litvinov, Yu. A.; Nociforo, C.; Seliverstov, D. M.; Sergeev, L. O.; Simon, H.; Volkov, V. A.; Vorobyov, A. A.; Weick, H.; Yatsoura, V. I.; Zhdanov, A. A.

2012-02-01

389

Aspects of nuclear pairing  

NASA Astrophysics Data System (ADS)

Pairing correlations between nucleons are known to be one of the major driving forces behind the nuclear many-body dynamics. The collective effects resulting from pairing play a crucial role in many nuclear properties. Despite a long history the methods of treating pairing along with corresponding questions and problems have constantly evolved. The role of pairing in exotic nuclei where superconducting phase competes with particle instability will be addressed in this presentation. Apart from this, the mesoscopic nature of the problem also accentuates other problems such as interplay of pairing and collective effects including rotations and deformations. The extended pairing phase transition, instability to large fluctuations and related thermodynamical properties are inseparable components of nuclear superconductivity. In this presentation I will explore these questions highlighting simultaneously the novel methods and techniques. The method of Exact Pairing (EP) is based on the algebraic treatment of pairing that relies on quasispin algebra. Recently the EP has evolved into a powerful technique that provides an exact numerical solution to the many-body problem. The EP serves as a foundation for understanding of manifestations of pairing in mesoscopic systems, and provides some answers to the above questions. The method allows for far-reaching extensions such as inclusion of collective dynamics within Random Phase Approximation, treatment of interactions beyond pairing and exploration of continuum of reaction states. Considering pairing within a rotating deformed proton emitter I will address its effect on particle emission. The kinematical suppression of the recoil, known as Coriolis attenuation, due to the superfluid nature of the rotating core is of special interest.

Volya, Alexander

2006-10-01

390

Hard photodisintegration of a proton pair  

NASA Astrophysics Data System (ADS)

We present a study of high energy photodisintegration of proton-pairs through the ?+He3?p+p+n channel. Photon energies, E, from 0.8 to 4.7 GeV were used in kinematics corresponding to a proton pair with high relative momentum and a neutron nearly at rest. The s-11 scaling of the cross section, as predicted by the constituent counting rule for two nucleon photodisintegration, was observed for the first time. The onset of the scaling is at a higher energy and the cross section is significantly lower than for deuteron (pn pair) photodisintegration. For E below the scaling region, the scaled cross section was found to present a strong energy-dependent structure not observed in deuteron photodisintegration.

Pomerantz, I.; Bubis, N.; Allada, K.; Beck, A.; Beck, S.; Berman, B. L.; Boeglin, W.; Camsonne, A.; Canan, M.; Chirapatpimol, K.; Cisbani, E.; Cusanno, F.; de Jager, C. W.; Dutta, C.; Garibaldi, F.; Geagla, O.; Gilman, R.; Glister, J.; Higinbotham, D. W.; Jiang, X.; Katramatou, A. T.; Khrosinkova, E.; Lee, B. W.; Lerose, J. J.; Lindgren, R.; McCullough, E.; Meekins, D.; Michaels, R.; Moffit, B.; Petratos, G. G.; Piasetzky, E.; Qian, X.; Qiang, Y.; Rodriguez, I.; Ron, G.; Saha, A.; Sarty, A. J.; Sawatzky, B.; Schulte, E.; Shneor, R.; Sparveris, N.; Subedi, R.; Strauch, S.; Sulkosky, V.; Wang, Y.; Wojtsekhowski, B.; Yan, X.; Yao, H.; Zhan, X.; Zheng, X.

2010-02-01

391

Coulombic effect and renormalization in nuclear pairing  

SciTech Connect

We investigate the effects of the Coulomb force on the nuclear pairing properties by performing the Gogny Hartree-Fock-Bogolyubov calculations for the N=20, 28, 50, 82, and 126 nuclei. The Coulomb force reduces the proton pair energy and the even-odd mass difference by about 25%, except for nuclei at and around the proton shell or subshell closure. We then propose a renormalization scheme via a reduction factor {gamma}{sub p} for the proton pairing channel. It is found that a single value {gamma}{sub p}=0.90 accounts well for the Coulombic effect for nuclei covering a wide range of the mass number and the neutron excess, including the nuclei around the shell or subshell closure.

Nakada, H.; Yamagami, M. [Department of Physics, Graduate School of Science, Chiba University, Yayoi-cho 1-33, Inage, Chiba 263-8522 (Japan); Department of Computer Science and Engineering, University of Aizu, Aizu-Wakamatsu, Fukushima 965-8580 (Japan)

2011-03-15

392

Distribution  

Microsoft Academic Search

e're closer than you think: Portland's geographic location and Oregon's transportation infra - structure offer unmatched con - nectivity and time savings to international and domestic markets. Our economic development practices combine project-ready property with efficient, high-capacity infrastructure to create today's logistics advantages. Connecting people, places and products is the core of Portland's distribution and logistics industry sec - tor.

F. Gregory; B. Boyd; R. Bridges; D. Mitchell; J. Halsell; S. Fancher; D. King; R. Fore; E. Mango; D. Berlinrut; M. Leinbach; M. Maier; M. Wetmore; H. Herring; J. Guidi; M. Coolidge; J. Heald; T. Knox; D. Bartine; R. Bailey; H. Delgado; P. Conant; J. Madura; R. Thomas; F. Merceret; G. Allen; E. Bensman; R. Dittemore; N. Feldman; C. Boykin; H. Tileston; F. Brody; L. Hagerman; S. Pearson; L. Uccellini; W. Vaughan; J. Golden; D. Johnson; J. McQueen; B. Roberts; L. Freeman; G. Jasper; B. Hagemeyer; A. McCool; X. W. Proenza; S. Glover

2006-01-01

393

The Ephemeral Pairing Problem  

Microsoft Academic Search

In wireless ad-hoc broadcast networks the pairing problem con- sists of establishing a (long-term) connection between two specic phys- ical nodes in the network that do not yet know each other. We focus on the ephemeral version of this problem. Ephemeral pairings occur, for ex- ample, when electronic business cards are exchanged between two people that meet, or when one

Jaap-henk Hoepman

2004-01-01

394

Neutron Compound Refractive Prisms - DOE SBIR Phase II Final Report  

SciTech Connect

The results of the research led to a pulsed electromagnetic periodic magnetic field array (PMF), which coupled with a pair of collimation slits, and a mechanical chopper slit, were able to deflect spin-up neutrons to a band of line-fused neutrons a focal plane heights that correspond to the time-varying magnetic field amplitude. The electromagnetic field PMF produced 5.4 pulses per minute in which each pulse was 50 msec in duration with a full width half maximum (FWHM) of 7.5 msec. The calculated 7.7 mm vertical height of the band of focused spin-up neutrons corresponded closely to the measured 7.5 mm height of the center line of the imaged band of neutrons. The band of deflected spin-up neutrons was 5 mm in vertical width and the bottom of the band was 5 mm above the surface of the PMF pole. The limited exposure time of 3 hours and the smaller 0.78 T magnetic field allowed focused and near focused neutrons of 1.8 ���� to 2.6 ���� neutrons, which were in the tails of the McClellan Nuclear Radiation Center Bay 4 Maxwell Boltzmann distribution of neutrons with peak flux at 1.1-1.2 ����. The electromagnetic PMF was expected to produces a 2.0 T peak magnetic field amplitude, which would be operational at a higher duty factor, rather than the as built 7.5 msec FWHM with pulse repetition frequency of 5.4 pulses per minute. The fabricated pulsed electromagnetic PMF with chopper is expected to perform well on a cold, very cold or ultra cold beam line as a spectrometer or monochromator source of spin-up polarized neutron. In fact there may be a possible use of the PMF to do ultra-cold neutron trapping, see paper by A. I. Frank1, V. G. Nosov, Quantum Effects in a One-Dimensional Magnetic Gravitational Trap for Ultracold Neutrons, JETP Letters, Vol. 79, No. 7, 2004, pp. 313�¢����315. The next step is to find a cold or very cold neutron facility, where further testing or use of the pulsed magnetic field PMF can be pursued.

Dr. Jay Theodore Cremer, Jr

2011-06-25

395

Cooper Pairs in Insulators?!  

SciTech Connect

Nearly 50 years elapsed between the discovery of superconductivity and the emergence of the microscopic theory describing this zero resistance state. The explanation required a novel phase of matter in which conduction electrons joined in weakly bound pairs and condensed with other pairs into a single quantum state. Surprisingly, this Cooper pair formation has also been invoked to account for recently uncovered high-resistance or insulating phases of matter. To address this possibility, we have used nanotechnology to create an insulating system that we can probe directly for Cooper pairs. I will present the evidence that Cooper pairs exist and dominate the electrical transport in these insulators and I will discuss how these findings provide new insight into superconductor to insulator quantum phase transitions.

Valles, James (Brown University)

2008-07-23

396

Pair contact process with diffusion of pairs  

NASA Astrophysics Data System (ADS)

The pair contact process (PCP) is a nonequilibrium stochastic model which, like the basic contact process (CP), exhibits a phase transition to an absorbing state. The two models belong to the directed percolation (DP) universality class, despite the fact that the PCP possesses infinitely many absorbing configurations whereas the CP has but one. The critical behavior of the PCP with hopping by particles (PCPD) is as yet unclear. Here we study a version of the PCP in which nearest-neighbor particle pairs can hop but individual particles cannot. Using quasistationary simulations for three values of the diffusion probability (D = 0.1, 0.5 and 0.9), we find convincing evidence of DP-like critical behavior.

Santos, F. L.; Dickman, Ronald; Fulco, U. L.

2011-03-01

397

Asymmetric pair distribution functions in catalysts  

Microsoft Academic Search

The structural parameters, i.e., coordination numbers, bond distances and disorder obtained from the analysis of EXAFS spectra\\u000a may sometimes be significantly influenced by errors introduced due to the inadequacy of the analysis method applied. Especially\\u000a in the case of heterogeneous catalysts it has been realized that often there is a need to use an improved EXAFS data analysis\\u000a compared to

Bjerne S. Clausen; Jens K. Nřrskov

2000-01-01

398

Calculation of Prompt Neutron Multiplicities and Spectra for Several Actinides  

SciTech Connect

The prompt fission neutron multiplicity and spectra of actinides are nuclear data of crucial importance. Based on experimental fission yield and total kinetic energy data, new calculations for the prompt neutron multiplicity and spectra for 238U(n,f), 237Np(n,f) in the incident neutron energy range up to the second chance fission threshold, for 238U(n,f), up to 50 MeV, and for 252Cf(SF) have been performed.For the first time the multi-modality of the fission process was taken into account up to the second fission chance (about 6 MeV). Additionally, for some isotopes a more realistic fission fragment residual temperature distribution as well as an anisotropy of the prompt neutron emission led to improved agreement between the calculation and experimental results. Also, the range of fission fragment pairs entering in the multiplicity and spectrum model was extended over the entire experimental fission-fragment mass range. This led to an improved version of the Los Alamos (LA) model and especially to an improved determination of the input model parameters. In addition the LA model is extended towards higher incident neutron energy, where the fission of compound nuclei formed by charged particle emission occurs.

Hambsch, Franz-Josef; Oberstedt, Stephan [EC-JRC-Institute for Reference Materials and Measurements, Retieseweg 111, B-2440 Geel (Belgium); Tudora, Anabella; Vladuca, Gheorghita [Faculty of Physics, Bucharest University, RO-76900 Bucharest (Romania)

2005-05-24

399

Simulated workplace neutron fields  

NASA Astrophysics Data System (ADS)

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.

Lacoste, V.; Taylor, G.; Röttger, S.

2011-12-01

400

Prompt Neutron Multiplicities for the Transplutonium Nuclides.  

National Technical Information Service (NTIS)

The direct determination of the average prompt neutron emission values is reviewed, and a method of comparing different sites of neutron emission multiplicity distribution values is described. Measured and recommended values are tabulated for these nuclid...

N. E. Holden M. S. Zucker

1985-01-01

401

Pair correlations in the neutrinoless double-? decay candidate Te130  

NASA Astrophysics Data System (ADS)

Pair correlations in the ground state of Te130 have been investigated using pair-transfer experiments to explore the validity of approximations in calculating the matrix element for neutrinoless double-? decay. This nucleus is a candidate for the observation of such decay, and a good understanding of its structure is crucial for eventual calculations of the neutrino mass, should such a decay indeed be observed. For proton-pair adding, strong transitions to excited 0+ states had been observed in the Te isotopes by Alford [Nucl. Phys. ANUPABL0375-947410.1016/0375-9474(79)90114-3 323, 339 (1979)], indicating a breaking of the BCS approximation for protons in the ground state. We measured the neutron-pair removing (p,t) reaction on Te130 and found no indication of a corresponding splitting of the BCS nature of the ground state for neutrons.

Bloxham, T.; Kay, B. P.; Schiffer, J. P.; Clark, J. A.; Deibel, C. M.; Freeman, S. J.; Freedman, S. J.; Howard, A. M.; McAllister, S. A.; Parker, P. D.; Sharp, D. K.; Thomas, J. S.

2010-08-01

402

Observation of Structures in the Mass-Tke Distributions of Fission Fragments in Spontaneous Fission  

NASA Astrophysics Data System (ADS)

The number of prompt neutrons emitted in the fission event has been measured separately for each complementary fragment in coincidence with fragment mass and kinetic energies in spontaneous fission of 252Cf and 248Cm. Two high efficient Gd-loaded liquid scintillator tanks were used for the neutron registration. Approximately 3ˇ106 fission events coincident with prompt neutron emission have been accumulated for each isotope. Two-dimensional neutron multiplicity distributions corrected for efficiency, background and pile-up have been reconstructed for each value of the fission fragment mass and total kinetic energy (TKE). Based on these unfolded multiplicity distributions fragment mass and TKE distributions for specific numbers of emitted neutrons from each of the complementary fragments have been obtained. These distributions exhibit pronounced structures reflecting the fine structures in the potential-energy surface. Structures showing a periodicity of two-masses at the edges of the mass-TKE distributions corresponding to the odd-even effect of the neutron pairing in the fissioning nucleus have been observed for the first time at large values of the fragment total excitation energy.

Kalinin, V. A.; Dushin, V. N.; Jakovlev, V. A.; Petrov, B. F.; Vorobyev, A. S.; Laptev, A. B.; Shcherbakov, O. A.; Hambsch, F.-J.

2004-02-01

403

Subradiant Split Cooper Pairs  

NASA Astrophysics Data System (ADS)

We suggest a way to characterize the coherence of the split Cooper pairs emitted by a double-quantum-dot based Cooper pair splitter (CPS), by studying the radiative response of such a CPS inside a microwave cavity. The coherence of the split pairs manifests in a strongly nonmonotonic variation of the emitted radiation as a function of the parameters controlling the coupling of the CPS to the cavity. The idea to probe the coherence of the electronic states using the tools of cavity quantum electrodynamics could be generalized to many other nanoscale circuits.

Cottet, Audrey; Kontos, Takis; Yeyati, Alfredo Levy

2012-04-01

404

Pairing in two dimensions  

SciTech Connect

A two-dimensional Fermi gas with an attractive {ital s}-wave interaction is shown to display a finite number of bound fermion pairs at all densities and temperatures. We study the chemical equilibrium between bound and ionized fermion pairs by including single-pair fluctuations in the free energy. While this turns out to be sufficient to drive the critical temperature for the onset of long-range order to zero, higher-order processes must be invoked to describe correctly the low-temperature regime.

Schmitt-Rink, S.; Varma, C.M. (AT T Bell Laboratories, Murray Hill, New Jersey 07974 (US)); Ruckenstein, A.E. (Institute for Theoretical Physics, University of California, Santa Barbara, California 93106)

1989-07-24

405

Et{sub 3}NH{sup +}Co(CO){sub 4}{sup -}: Hydrogen-bonded adduct or simple ion pair? Single-crystal neutron diffraction study at 15 K  

SciTech Connect

Et{sub 3}NH{sup +}Co(CO){sub 4}{sup -} contains a short N-N{hor_ellipsis}Co contact, which provides the closest approach between the anion and cation. Accurate structural characterization by neutron diffraction at 15 K shows the N-H{hor_ellipsis}Co interaction to be linear with a long N-H bond length and a relatively short Co{hor_ellipsis}H separation (Co{hor_ellipsis} = 2.613 (2){Angstrom}, N-H = 1.054 (1) {Angstrom}, N-H{hor_ellipsis}Co = 180.0{degrees}). This evidence is consistent with the presence of a three-center-four-electron hydrogen-bond-like N-H{hor_ellipsis}Co interaction, though it does not rule out simple electrostatic attraction as the principal driving force behind association of the Et{sub 3}NH{sup +} and Co(CO){sub 4}{sup -} ions. 17 refs., 2 figs.

Brammer, L.; McCann, M.C. [Univ. of Missouri, St. Louis, MO (United States); Bullock, R.M.; McMullan, R.K. [Brookhaven National Lab., Upton, NY (United States)

1992-07-01

406

Probing local structure in the yellow phosphor LaSr[subscript 2]AlO[subscript 5]:Ce[superscript 3+], by the maximum entropy method and pair distribution function analysis  

SciTech Connect

The compound LaSr{sub 2}AlO{sub 5} was recently introduced as a competitive Ce{sup 3+} host material for blue-pumped yellow phosphors for use in white light emitting diodes. A crucial feature of the crystal structure of LaSr{sub 2}AlO{sub 5} is that La, which is the host site for Ce{sup 3+}, is located in the 8h positions of the I4/mcm crystal structure, a site equally shared with Sr. While the average crystal structure of LaSr{sub 2}AlO{sub 5} as revealed by Rietveld analysis of laboratory and synchrotron X-ray diffraction data suggests nothing untoward, maximum entropy method analysis of the synchrotron X-ray data reveals the existence of conspicuous non-sphericity of the electron density. Pair distribution function analysis of the data suggests that despite their occupying the same crystallographic site, La and Sr possess distinct coordination environments, and the environment around La is more compact and regular than the environment suggested by the Rietveld refinement of the average structure. The absorption and emission from Ce{sup 3+} centers is controlled by the local coordination and symmetry, and the use of powerful new tools in unraveling details of these strengthens the rational search for new phosphors for solid state white lighting.

Im, Won Bin; Page, Katharine; DenBaars, Steven P.; Seshadri, Ram (UCSB); (LANL)

2011-08-04

407

The Neutron Stars Census  

Microsoft Academic Search

The paucity of old isolated accreting neutron stars in ROSAT observations is\\u000aused to derive a lower limit on the mean velocity of neutron stars at birth.\\u000aThe secular evolution of the population is simulated following the paths of a\\u000astatistical sample of stars for different values of the initial kick velocity,\\u000adrawn from an isotropic Gaussian distribution with mean

S. B. Popov; M. Colpi; A. Treves; R. Turolla; V. M. Lipunov; M. E. Prokhorov

1999-01-01

408

Pairing effects in low density domain of nuclear matter  

Microsoft Academic Search

Using equations, governing np pairing correlations in S=1, T=0 pairing channel (PRC 63 (2001) 021304(R)), it is shown that at low densities equations for the energy gap in the spectrum of quasiparticles and chemical potentials of protons and neutrons allow solutions with negative chemical potential. This corresponds to appearance of Bose–Einstein condensate (BEC) of deuterons in low density region of

A. A. Isayev; S. I. Bastrukov; J. Yang

2004-01-01

409

Pairing theory of the symmetry energy  

SciTech Connect

A model is investigated that displays a picture of the symmetry energy as an energy of rotation in isospace of a Cooper pair condensate, briefly 'superfluid isorotation'. The Hamiltonian is isobarically invariant and has a one- and a two-nucleon term, where the two-nucleon interaction is composed of an isovector pairing force and an interaction of isospins. It is analyzed in the Hartree-Bogolyubov plus random-phase approximation (RPA). The Hartree-Bogolyubov energy minus Lagrangian multiplier terms proportional to the number of valence nucleons and the z component of the isospin is shown to be locally minimized by a product of neutron and proton Bardeen-Cooper-Schrieffer states. The equations of the RPA can be reduced to independent equations for two-neutron, two-proton, and neutron-proton quasiparticle pairs. In each of these spaces, they have a Nambu-Goldstone solution due to the global gauge invariance and isobaric invariance of the Hamiltonian. Except for the Nambu-Goldstone solutions, the RPA solutions are independent of the strength of the isospin interaction. If, in one space, the pertinent single-nucleon spectrum has a particle-hole symmetry, the RPA solutions are twofold degenerate except for the Nambu-Goldstone solution and one more solution. In an idealized case of infinitely many equidistant single-nucleon levels, the one-nucleon term in the Hamiltonian and the isospin interaction contribute terms in the symmetry energy quadratic in the isospin T. The pairing force and the two-neutron and two-proton RPA correlation energies do not contribute. The contribution of the neutron-proton correlation energy is dominated by the Nambu-Goldstone solution, which gives a linear term that makes the total symmetry energy proportional to T(T+1). The rest of this contribution is negative and can be written as the difference of two terms of the form {radical}((aT){sup 2}+b{sup 2})-b. Observations reported from Skyrme force calculations are discussed in the light of these results. Calculations with deformed Woods-Saxon single-nucleon levels give results similar to those of the idealized case. In calculations for the mass numbers A=56 and A=100 with spherical Woods-Saxon levels, the promotion of nucleons across magic gaps in the single-nucleon spectrum and the onset of superfluidity with the departure from magicity give rise to large linear terms in the symmetry energy. The calculations with Woods-Saxon single-nucleon levels reproduce surprisingly well the empirical symmetry energy. An experimental signature of superfluid isorotation is discussed.

Neergaard, K. [Fjordtoften 17, DK-4700 Naestved (Denmark)

2009-10-15

410

Field distributions and particle optics in main bending dipoles of Oak Ridge Spallation Neutron Source accumulator ring  

NASA Astrophysics Data System (ADS)

The SNS accumulator ring employs 32 electro-magnetic dipoles to bend proton beams. The dipoles are typical sector magnets with relatively large aperture and short length. Thus, how to correctly treat magnetic fringe fields in the devices remains as a question. We have performed 3D computer simulations to study magnetic field distributions in the dipoles. Further, we have analyzed particle optics based on the space-dependent curvature and focusing functions in the magnets. The effect of magnetic fringe fields on the particle motion, especially the focusing/defocusing and dispersion, is investigated. The lens parameters, including the second-order aberrations, are derived and compared with the design hard-edge parameters used in the ring lattice calculations.

Wang, J. G.

2013-09-01

411

Treatment of the like-particle pairing of quartets  

NASA Astrophysics Data System (ADS)

The ground state correlations induced by a general pairing Hamiltonian in a finite system of like fermions are described in terms of four-body correlated structures (quartets). These are real superpositions of the products of two pairs of particles in time-reversed states. Quartets are determined variationally through an iterative sequence of diagonalizations of the Hamiltonian in restricted model spaces and are, in principle, all distinct from one another. The ground state is represented as a product of quartets to which, depending on the number of particles (supposed to be even, in any case), an extra collective pair is added. The extra pair is also determined variationally. In the case of pairing in a spherically symmetric mean field, both the quartets and the extra pair (if any) are characterized by a total angular momentum J = 0. Realistic applications of the quartet formalism are carried out for Sn isotopes with valence neutrons in the 50-82 neutron shell. The exact ground state correlation energies, occupation numbers and pair transfer matrix elements are reproduced to a very high degree of precision. The formalism also lends itself to a straightforward and accurate description of the lowest seniority 0 and 2 excited states of the pairing Hamiltonian. A simplified representation of the ground state as a product of identical quartets is eventually discussed and found to improve considerably upon the more traditional particle-number projected BCS approach.

Sambataro, M.; Sandulescu, N.

2013-05-01

412

Photoproduction of charm pairs  

SciTech Connect

A large sample of events containing fully and partially reconstructed pairs of charmed D mesons has been studied by the Fermilab photoproduction experiment FOCUS (FNAL-E831). Correlations between photoproduced D and {bar D} mesons are used to study heavy quark production dynamics. Correlation results are presented for fully and partially reconstructed pairs of charmed D mesons. The results are compared to Monte Carlo predictions based on a recent version of PYTHIA with default settings.

Erik E Gottschalk

2003-09-02

413

Measurement of 241Am-Be spectra (bare and Pb-covered) using TLD pairs in multi-spheres: Spectrum unfolding by different methods  

NASA Astrophysics Data System (ADS)

The neutron spectra from a Pb-covered and a bare (without Pb-cover) 241Am-Be (?,n) source were measured using thermoluminescent detector (TLD) pairs of 6LiF and 7LiF with high-density polyethylene (HDPE) multi-spheres of seven different diameters. A total of 8 distinct neutron response signals (including a bare mode exposure) were obtained from which the energy distribution for the entire energy range was generated with the help of different neutron spectrum unfolding methods, viz. BUNKI, BUNKIUT and Frascati unfolding interactive tool (FRUIT). Shape of these spectra are matching very well and is also comparable with the standard IAEA 241Am-Be spectrum, thus, validating the unfolding methods used in this work. The effect of Pb-cover on the spectrum and the unfolding details are reported in the paper.

Tripathy, S. P.; Bakshi, A. K.; Sathian, V.; Tripathi, S. M.; Vega-Carrillo, H. R.; Nandy, M.; Sarkar, P. K.; Sharma, D. N.

2009-01-01

414

Investigating concentration distributions of arsenic, gold and antimony in grain-size fractions of gold ore using instrumental neutron activation analysis.  

PubMed

Instrumental neutron activation analysis (INAA) has been used to quantify concentrations of arsenic (As), gold (Au) and antimony (Sb) in grain-size fractions of a gold ore. The ore, which was taken from the Ahafo project site of Newmont Ghana Gold Ltd., was fractionated into 14 grain-size fractions using state-of-the-art analytical sieve machine. The minimum sieve mesh size used was 36mum and grains >2000mum were not considered for analysis. Result of the sieving was analysed with easysieve(R) software. The<36mum subfraction was found to be the optimum, hosting bulk of all three elements. Arsenic was found to be highly concentrated in<36-100mum size fractions and erratically distributed in from 150mum fraction and above. For gold, with the exception of the subfraction <36mum which had exceptionally high concentration, the element was found to be approximately equally distributed in all the size fractions but slightly "played out" in 150-400mum size fractions. Antimony occurrence in the sample was relatively high in <36mum size fraction followed by 600, 800, 400 and 36mum size fractions in that order. Gold content in the sample was comparatively far greater than arsenic and antimony; this is indicative of level of gold mineralization in the concession where the sample ore was taken. The concentration of gold in the composite sample was in the range 564-8420ppm as compared to 14.33-186.92ppm for arsenic and 1.09-9.48ppm for antimony. Elemental concentrations were correlated with each other and with grain-size fractions and the relationships between these descriptive parameters were established. PMID:19896855

Nyarku, M; Nyarko, B J B; Serfor-Armah, Y; Osae, S

2009-10-17

415

Neutron cross sections: Volume 2, Neutron cross section curves  

Microsoft Academic Search

Data is presented only for total (i.e., integrated) reaction cross sections (and related fission parameters) as a function of incident-neutron energy. The energy range has been limited to 0.01 eV to 200 MeV in order to exclude crystalline and magnetic effects for slow neutrons and relativistic effects for high energy neutrons. Angular distributions and partial reaction cross sections to specific

V. McLane; C. L. Dunford; P. F. Rose

1988-01-01

416

La structure des verres étudiée par diffraction des neutrons  

NASA Astrophysics Data System (ADS)

La diffraction des neutrons est une méthode largement utilisée pour déterminer la structure des matériaux amorphes et en particulier des verres. L'utilisation de la méthode de substitution isotopique permet d'extraire les fonctions de distribution de paires partielles centrées autour d'un élément choisi. Nous présentons quelques exemples récents d'études par diffraction des neutrons sur des verres qui ont permis de mieux comprendre ŕ la fois le réseau polymérique de la matrice vitreuse et l'environnement local et ŕ moyenne distance autour des cations. Ces études ont révélées un ordre structural s'étendant au delŕ des premiers voisins, jusque vers de distances d'environ 10Ĺ. Le couplage avec d'autres méthodes expérimentales (diffraction anormale des rayons X) et des techniques de simulations (dynamique moléculaire, Monte Carlo Inverse ou RMC) sont indispensables pour affiner nos connaissances de la structure des verres.

Cormier, L.

2003-09-01

417

Local Structure of La1-xSrxCoO3 determined from EXAFS and neutron PDF studies  

SciTech Connect

The combined local structure techniques, extended x-ray absorption fine structure (EXAFS) and neutron pair distribution function analysis, have been used for temperatures 4<= T<= 330 K to rule out a large Jahn-Teller (JT) distortion of the Co-O bond in La1?xSrxCoO3 for a significant fraction of Co sites (x<= 0.35), indicating few, if any, JT-active, singly occupied eg Co sites exist.

Sundaram, N.; Jiang, Y.; Anderson, I. E.; Belanger, D. P.; Booth, C. H.; Bridges, F.; Mitchell, J. F.; Proffen, Th.; Zheng, H.

2009-01-26

418

Neutron multiplicities in spontaneous fission and nuclear structure studies  

SciTech Connect

New insights into the fission process can be gained by better quantitative knowledge of how the energy released in fission is distributed between the kinetic energy of the two fragments, the excitation energy of the two fragments and the number of neutrons emitted. Studies of prompt gamma-rays emitted in spontaneous fission (SF) with large arrays of Compton suppressed Ge detector arrays are providing new quantitative answers to longstanding questions concerning fission as well as new insights into the structure of neutron-rich nuclei. For the first time the triple gamma coincidence technique was employed in spontaneous fission studies. Studies of SF of {sup 252}Cf and {sup 242}Pu have been carried out. These {gamma}-{gamma}-{gamma} data provide powerful ways to identify uniquely gamma rays from a particular nucleus in the very complex gamma-ray spectra given off by the over 100 different nuclei produced. The emphasis of this paper is on the first quantitative measurements of the multiplicities of the neutrons emitted in SF and the energy levels populated in the fragments. Indeed, in the break up into Mo-Ba pairs, we have identified for the first time fragments associated with from zero up to ten neutrons emitted and observed the excited energy states populated in these nuclei. The zero neutron emission pairs like {sup 104}Mo- {sup 148}Ba, {sup 106}Mo- {sup 146}Ba and {sup 104}Zr- {sup 148}Ce observed in this work are particularly interesting because they represent a type of cold fission or a new mode of cluster radioactivity as proposed by Greiner, Sandulescu and co-workers. These data provide new insights into the processes of cluster radioactivity and cold fission.

Hamilton, J.H.; Kormicki, J.; Lu, Q. [Vanderbilt Univ., Nashville, TN (United States). Dept. of Physics and Astronomy] [and others

1993-12-31

419

Neutron multiplication in beryllium  

SciTech Connect

Integral neutron multiplication experiments have been performed using spherical shells of beryllium metal of 4.6-, 6.99-, 7.87-, 9.38-, 13.8-, and 19.9-cm thickness. Neutron leakage, from {sup 252}Cf and a DT neutron source normalized with an associated particle detector, were measured with a Bonner sphere spectrometer system. The neutron fluence was obtained by processing the room-returned and air-scattered corrected count-rate data with a Bonner sphere spectrum unfolding routine and a weighted Bonner sphere technique. The neutron multiplication was obtained directly by comparing the normalized neutron leakage fluence with and without beryllium present. The neutron leakage spectra were calculated for each shell using the discrete ordinates codes ANISN and ONEDANT with ENDF/B-IV and ENDF/B-V respectively. The cross sections from ENDF/B-V included the most current cross section revisions from the Los Alamos National Laboratory. A comparison of the leakage multiplication, calculated using the two versions of evaluated nuclear data, indicate that corrections have been made to the energy-angle distribution of the secondary neutrons in ENDF/B-V resulting in a lower neutron leakage multiplication for shells greater than 9.38-cm thickness. The measured {sup 252}Cf neutron leakage multiplication is 22% higher than the ANISN-ENDF/B-IV calculated leakage multiplication for the 4.6-cm shell thickness, within 4% for the 6.99-cm thickness, and at least 29% lower than the calculated leakage multiplication for the 19.9-cm shell thickness.

Hartley, R.S.

1987-01-01

420

Cross-sectional void fraction distribution measurements in a vertical annulus two-phase flow by high speed X-ray computed tomography and real-time neutron radiography techniques  

Microsoft Academic Search

A real-time neutron radiography (RTNR) system and a high speed X-ray computed tomography (X-CT) system are compared for measurement of two-phase flow. Each system is used to determine the flow regime, and the void fraction distribution in a vertical annulus flow channel with particular attention on the temporal resolution of the systems and the time behaviour of the two-phase flow.

G. D. Harvel; K. Hori; K. Kawanishi; J. S. Chang

1999-01-01

421

Kidney paired donation.  

PubMed

Kidney paired donation (KPD) was first suggested in 1986, but it was not until 2000 when the first paired donation transplant was performed in the USA. In the past decade, KPD has become the fastest growing source of transplantable kidneys, overcoming the barrier faced by living donors deemed incompatible with their intended recipients. This review provides a basic overview of the concepts and challenges faced by KPD as we prepare for a national pilot program with the United Network for Organ Sharing. Several different algorithms have been creatively implemented in the USA and elsewhere to transplant paired donors, each method uniquely contributing to the success of KPD. As the paired donor pool grows, the problem of determining allocation strategies that maximize equity and utility will become increasingly important as the transplant community seeks to balance quality and quantity in choosing the best matches. Financing for paired donation is a major issue, as philanthropy alone cannot support the emerging national system. We also discuss the advent of altruistic or non-directed donors in KPD, and the important role of chains in addition to exchanges. This review is designed to provide insight into the challenges that face the emerging national KPD system in the USA, now 5 years into its development. PMID:21454351

Wallis, C Bradley; Samy, Kannan P; Roth, Alvin E; Rees, Michael A

2011-03-31

422

Neutron coincidence imaging for active and passive neutron assays  

Microsoft Academic Search

Neutron multiplicity assay algorithms for ˛°Pu assume a point source of fission neutrons that are detected in a single detector channel. The ˛°Pu in real waste, however, is more likely to be distributed throughout the container in some random way. For different reasons, this leads to significant errors when using either multiplicity or simpler coincidence analyses. Reduction of these errors

R. J. Estep; G. S. Brunson; S. G. Melton

2001-01-01

423

New Insights into the Crystal and Electronic Structures of Li[subscript 1+x]V[subscript 1?x]O[subscript 2] from Solid State NMR, Pair Distribution Function Analyses, and First Principles Calculations  

SciTech Connect

Pair distribution function (PDF) analyses of synchrotron data obtained for the anode materials Li{sub 1+x}V{sub 1-x}O{sub 2} (0 {le} x {le} 0.1) have been performed to characterize the short to medium range structural ordering. The data show clear evidence for the magnetically-induced distortion of the V sublattice to form trimers, the distortion persisting at even the highest excess Li content considered of x = 0.1. At least three distinct local environments were observed for the stoichiometric material LiVO{sub 2} in {sup 6}Li nuclear magnetic resonance (NMR) spectroscopy, the environments becoming progressively more disordered as the Li content increases. A two-dimensional Li-Li correlation NMR experiment (POST-C7) was used to identify the resonances corresponding to Li within the same layers. NMR spectra were acquired as a function of the state of charge, a distinct environment for Li in Li{sub 2}VO{sub 2} being observed. The results suggest that disorder within the Li layers (in addition to the presence of Li within the V layers as proposed by Armstrong et al. Nat. Mater.2011, 10, 223-229) may aid the insertion of Li into the Li{sub 1+x}V{sub 1-x}O{sub 2} phase. The previously little-studied Li{sub 2}VO{sub 2} phase was also investigated by hybrid density functional theory (DFT) calculations, providing insights into magnetic interactions, spin-lattice coupling, and Li hyperfine parameters.

Pourpoint, Frédérique; Hua, Xiao; Middlemiss, Derek S.; Adamson, Paul; Wang, Da; Bruce, Peter G.; Grey, Clare P. (SBU); (Cambridge); (St Andrews)

2012-10-29

424

Extended pairing model revisited  

NASA Astrophysics Data System (ADS)

The mean-field plus extended pairing model proposed by the authors for describing well-deformed nuclei (F. Pan, V.G. Gueorguiev, J.P. Draayer, Phys. Rev. Lett. 92, 112503 (2004)) is revisited. Eigenvalues of the model can be determined by solving a single transidental equation. Results to date show that even through the model includes many-body interactions, the one- and two-body terms continue to dominate the dynamics for small values of the pairing strength; however, as the strength of the pairing interaction grows, the higher-order terms grow in importance and ultimately dominate. Attempts to extend the theory to the prediction of excited zero plus states did not produce expected results and therefore requires additional consideration.

Draayer, J. P.; Pan, Feng; Gueorguiev, V. G.

2005-09-01