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1

Isovector neutron-proton pairing with particle number projected BCS  

SciTech Connect

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. [Institute of Physics and Nuclear Engineering, Post Office Box MG-6, R-76900 Bucharest-Magurele (Romania); Instituto de Estructura de la Materia, CSIC, Serrano 123, E-28006 Madrid (Spain)

2009-10-15

2

Induced Pairing Interaction in Neutron Star Matter  

NASA Astrophysics Data System (ADS)

The three superfluid phases supposed to occur in neutron stars are reviewed in the framework of the generalized BCS theory with the induced interaction. The structure of neutron stars characterized by beta-stable asymmetric nuclear matter in equilibrium with the gravitational force discloses new aspects of the pairing mechanism. Some of them are discussed in this report, in particular the formation in dense matter of Cooper pairs in the presence of three-body forces and the interplay between repulsive and attractive polarization effects on isospin T = 1 Cooper pairs embedded into the neutron and proton environment. Quantitative estimates of the energy gaps are reported and their sensitivity to the medium effects, i.e., interaction and polarization, is explored.

Lombardo, U.; Schulze, H.-J.; Zuo, W.

2013-01-01

3

Pair-vibrational states in the presence of neutron-proton pairing  

E-print Network

Pair vibrations are studied for a Hamiltonian with neutron-neutron, proton-proton and neutron-proton pairing. The spectrum is found to be rich in strongly correlated, low-lying excited states. Changing theratio of diagonal to off-diagonal pairing matrix elements is found to have a large impact on the excited-state spectrum. The variational configuration interaction (VCI) method, used to calculate the excitation spectrum, is found to be in very good agreement with exact solutions for systems with large degeneracies having equal T=0 and T=1 pairing strengths.

R. R. Chasman; P. Van Isacker

2010-01-18

4

Distribution of neutron resonance widths  

E-print Network

Recent data on neutron resonance widths indicate disagreement with the Porter-Thomas distribution (PTD). I discuss the theoretical arguments for the PTD, possible theoretical modifications, and I summarize the experimantal evidence.

Hans A. Weidenmueller

2011-10-28

5

A pair distribution function analysis of zeolite beta  

SciTech Connect

We describe the structural refinement of zeolite beta using the local structure obtained with the pair distribution function (PDF) method. A high quality synchrotron and two neutron scattering datasets were obtained on two samples of siliceous zeolite beta. The two polytypes that make up zeolite beta have the same local structure; therefore refinement of the two structures was possible using the same experimental PDF. Optimized structures of polytypes A and B were used to refine the structures using the program PDFfit. Refinements using only the synchrotron or the neutron datasets gave results inconsistent with each other but a cyclic refinement with the two datasets gave a good fit to both PDFs. The results show that the PDF method is a viable technique to analyze the local structure of disordered zeolites. However, given the complexity of most zeolite frameworks, the use of both X-ray and neutron radiation and high-resolution patterns is essential to obtain reliable refinements.

Martinez-Inesta, M.M.; Peral, I.; Proffen, T.; Lobo, R.F. (Delaware); (LANL)

2010-07-20

6

Neutrino-pair bremsstrahlung in a neutron star crust  

NASA Astrophysics Data System (ADS)

Based on the formalism by Kaminker et al. (Astron. Astrophys., 343 (1999) 1009) we derive an analytic approximation for neutrino-pair bremsstrahlung emissivity due to scattering of electrons by atomic nuclei in a neutron star crust of any realistic composition. The emissivity is expressed through the generalized Coulomb logarithm which we fit by introducing an effective potential of electron-nucleus scattering. In addition, we study the conditions at which the neutrino bremsstrahlung in the crust is affected by strong magnetic fields. The results can be applied for modelling of many phenomena in neutron stars, such as thermal relaxation in young isolated neutron stars and in accreting neutron stars with overheated crust in soft X-ray transients.

Ofengeim, D. D.; Kaminker, A. D.; Yakovlev, D. G.

2014-11-01

7

S10 pairing for neutrons in dense neutron matter induced by a soft pion  

NASA Astrophysics Data System (ADS)

The possibility of neutron pairing in the S10 channel is studied for dense neutron matter in a vicinity of the ?0 condensation point. The S10 pairing gap ? is shown to occur in a model with a pairing force induced by the exchange of a soft neutral pionic mode. The soft pion induced potential V?(r ) is characterized by an attenuating oscillatory behavior in coordinate space, while in momentum space all S -wave matrix elements V?(p ,p') are positive. The solution of the gap equation reveals strong momentum dependence.

Pankratov, S. S.; Baldo, M.; Saperstein, E. E.

2015-01-01

8

Singlet pairing gaps of neutrons and protons in hyperonic neutron stars  

E-print Network

The $^{1}S_{0}$ nucleonic superfluids are investigated within the relativistic mean-field model and Bardeen-Cooper-Schrieffer theory in hyperonic neutron stars. The $^{1}S_{0}$ pairing gaps of neutrons and protons are calculated based on the Reid soft-core interaction as the nucleon-nucleon interaction. We have studied particularly the influence of hyperons degrees of freedom on the $^{1}S_{0}$ nucleonic pairing gap in neutron star matter. It is found that the appearance of hyperons has little impact on baryonic density range and size for the $^{1}S_{0}$ neutronic pairing gap, the $^{1}S_{0}$ protonic pairing gap also decreases slightly in this region $\\rho_B=0.0-0.393$ fm$^{-3}$. However, if baryonic density becomes greater than 0.393 fm${^{-3}}$, the $^{1}S_{0}$ protonic pairing gap obviously increases. In addition, the protonic superfluid range is obviously enlarged due to the presence of hyperons. In our results, the hyperons change the $^{1}S_{0}$ protonic pairing gap which must change the cooling properties of neutron stars.

Yan Xu; Cheng-Zhi Liu; Cun-Bo Fan; Xing-Wei Han; Xiao-Jun Zhang; Ming-Feng Zhu; Hong-Yan Wang; Guang-Zhou Liu

2014-08-13

9

Pairing and Shell Evolution in Neutron Rich Nuclei  

NASA Astrophysics Data System (ADS)

From the experimental data on odd-even staggering of masses, it has been shown that variation of pairing as a function of neutron number plays an important role in many distinctive features like occurrence of new shell closures, shell erosion, anomalous reduction of the energy of the first 2+ state and slower increase in the B(E2,21^ + -> 01^ + ) in the neutron-rich even-even nuclei in different mass regions. New predictions have been made in a model independent way.

Sarkar, Maitreyee Saha; Sarkar, Sukhendusekhar

2014-09-01

10

Exact Solution of the Isovector Proton Neutron Pairing Hamiltonian  

SciTech Connect

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 non-degenerate single-particle levels and including isospin-symmetry breaking terms. The power of the method is illustrated with a numerical calculation for {sup 64}Ge for a pf + g{sub 9/2} model space which is out of reach of modern shell-model codes.

Dukelsky, J; Gueorguiev, V G; Van Isacker, P; Dimitrova, S S; Errea, B; H., S L

2005-12-02

11

Exact Solution of the Isovector Neutron-Proton Pairing Hamiltonian  

SciTech Connect

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 {sup 64}Ge for a pf+g{sub 9/2} model space which is out of reach of modern shell-model codes.

Dukelsky, J.; Errea, B.; Lerma, S.H. [Instituto de Estructura de la Materia, CSIC. Serrano 123, 28006 Madrid (Spain); Gueorguiev, V.G. [Lawrence Livermore National Laboratory, Livermore, California (United States); Institute of Nuclear Research and Nuclear Energy, BAS, Sofia 1784 (Bulgaria); Van Isacker, P. [Grand Accelerateur National d'Ions Lourds, BP 55027, F-14076 Caen Cedex 5 (France); Dimitrova, S. [Institute of Nuclear Research and Nuclear Energy, BAS, Sofia 1784 (Bulgaria)

2006-02-24

12

Pair force distributions in simple fluids  

NASA Astrophysics Data System (ADS)

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.

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

2011-10-01

13

Proton-neutron pairing vibrations in N=Z nuclei: Precursory soft mode of isoscalar pairing condensation  

E-print Network

L=0 proton-neutron ($pn$) pair-addition and pair-removal strengths in $^{40}$Ca and $^{56}$Ni are investigated by means of the $pn$ particle-particle random-phase approximation employing a Skyrme energy-density functional. It is found that the collectivity of the lowest $J^\\pi = 1^+$ state in the adjacent odd-odd nuclei becomes stronger as the strength of the isoscalar (T=0) pairing interaction increases. The results suggest the emergence of the T=0 $pn$-pairing vibrational mode as a possible critical phenomenon toward the T=0 pairing condensation.

Kenichi Yoshida

2014-09-17

14

Neutron density distribution and neutron skin thickness of $^{208}$Pb  

E-print Network

We present and discuss numerical predictions for the neutron density distribution of $^{208}$Pb using various non-relativistic and relativistic mean-field models for the nuclear structure. Our results are compared with the very recent pion photoproduction data from Mainz. The parity-violating asymmetry parameter for elastic electron scattering at the kinematics of the PREX experiment at JLab and the neutron skin thickness are compared with the available data. We consider also the dependence between the neutron skin and the parameters of the expansion of the symmetry energy.

Meucci, Andrea; Giusti, Carlotta; Finelli, Paolo

2014-01-01

15

Gamma-Ray Bursts via Pair Plasma Fireballs from Heated Neutron Stars  

E-print Network

In this paper we model the emission from a relativistically expanding electron-positron 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. We model the relativistic expansion and subsequent emission of the plasma and find 10^51 to 10^52 ergs in gamma-rays are produced with spectral and temporal properties consistent with observed gamma-ray bursts.

Jay D. Salmonson; James R. Wilson; Grant J. Mathews

2000-01-22

16

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

17

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

18

Superfluid phases of triplet pairing and rapid cooling of the neutron star in Cassiopeia A  

E-print Network

In a simple model it is demonstrated that the neutron star surface temperature evolution is sensitive to the phase state of the triplet superfluid condensate. A multicomponent triplet pairing of superfluid neutrons in the core of a neutron star with participation of several magnetic quantum numbers leads to neutrino energy losses exceeding the losses from the unicomponent pairing. A phase transition of the neutron condensate into the multicomponent state triggers more rapid cooling of superfluid core in neutron stars. This makes it possible to simulate an anomalously rapid cooling of neutron stars within the minimal cooling paradigm without employing any exotic scenarios suggested earlier for rapid cooling of isolated neutron star in Cassiopeia A.

Lev B. Leinson

2014-11-25

19

Nucleon and nucleon-pair momentum distributions in A?12 nuclei  

SciTech Connect

We report variational Monte Carlo calculations of single-nucleon momentum distributions for A?12 nuclei and nucleon-pair and nucleon-cluster momentum distributions for A?8. The wave functions have been generated for a Hamiltonian containing the Argonne ?18 two-nucleon and Urbana X three-nucleon potentials. The single-nucleon and nucleon-pair momentum distributions exhibit universal features attributable to the one-pion-exchange tensor interaction The single-nucleon distributions are broken down into proton and neutron components and spin-up and spin-down components where appropriate. The nucleon-pair momentum distributions are given separately for pp and pn pairs. The nucleon-cluster momentum distributions include dp in 3He, tp and dd in S4He, ?d in 6Li,?t in 7Li, and ?? in 8Be. Detailed tables are provided on-line for download.

Wiringa, Robert B. [ANL; Schiavilla, Rocco [ODU, JLAB; Pieper, Steven C. [ANL; Carlson, Joseph A. [LANL

2014-02-01

20

Pairing properties and specific heat of the inner crust of a neutron star  

NASA Astrophysics Data System (ADS)

I investigate the pairing properties at finite temperature of the Wigner-Seitz cells in the inner crust of a neutron star obtained with the recent Brussels-Montreal Skyrme functional BSk21. In particular I analyze the phenomena of persistence and reentrance of pairing correlations and their impact on the specific heat in the low-density region of the inner crust.

Pastore, A.

2015-01-01

21

Proton-Neutron Pairing Amplitude as a Generator Coordinate for Double-Beta Decay  

E-print Network

We treat proton-neutron pairing amplitudes, in addition to the nuclear deformation, as generator coordinates in a calculation of the neutrinoless double-beta decay of 76Ge. We work in two oscillator shells, with a Hamiltonian that includes separable terms in the quadrupole, spin-isospin, and pairing (isovector and isoscalar) channels. Our approach allows larger single-particle spaces than the shell model and includes the important physics of the proton-neutron quasiparticle random-phase approximation (QRPA) without instabilities near phase transitions. After comparing the results of a simplified calculation that neglects deformation with those of the QRPA, we present a more realistic calculation with both deformation and proton-neutron pairing amplitudes as generator coordinates. The future should see proton-neutron coordinates used together with energy-density functionals.

Nobuo Hinohara; Jonathan Engel

2014-06-03

22

Proton-Neutron Pairing Amplitude as a Generator Coordinate for Double-Beta Decay  

E-print Network

We treat proton-neutron pairing amplitudes, in addition to the nuclear deformation, as generator coordinates in a calculation of the neutrinoless double-beta decay of 76Ge. We work in two oscillator shells, with a Hamiltonian that includes separable terms in the quadrupole, spin-isospin, and pairing (isovector and isoscalar) channels. Our approach allows larger single-particle spaces than the shell model and includes the important physics of the proton-neutron quasiparticle random-phase approximation (QRPA) without instabilities near phase transitions. After comparing the results of a simplified calculation that neglects deformation with those of the QRPA, we briefly present a more realistic calculation with both deformation and proton-neutron pairing amplitudes as generator coordinates. The future should see proton-neutron generator coordinates used together with energy-density functionals.

Hinohara, Nobuo

2014-01-01

23

Super Distributions, Analytic and Algebraic Super Harish-Chandra pairs  

E-print Network

The purpose of this paper is to extend the theory of Super Harish-Chandra pairs, originally developed by Koszul for Lie supergroups, to analytic and algebraic supergroups, in order to obtain information also about their representations. We also define the distribution superalgebra for algebraic and analytic supergroups and study its relation with the universal enveloping superalgebra

C. Carmeli; R. Fioresi

2011-06-06

24

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

25

Single and pair neutron transfers at sub-barrier energies  

SciTech Connect

Multinucleon transfer cross sections in the {sup 96}Zr+{sup 40}Ca system have been measured, in inverse kinematics, at bombarding energies ranging from the Coulomb barrier to {approx}25% below. Targetlike recoils have been identified in A, Z and velocity with the large solid angle magnetic spectrometer PRISMA. The experimental data for one- and two-neutron transfer channels have been compared with semiclassical microscopic calculations. For the two-neutron transfer channels the relevance of the transitions to the ground state and to the 0{sup +} excited states of {sup 42}Ca are discussed by employing, for the reaction mechanism, the successive approximation. It is found that the transition to the 0{sup +} state at {approx}6 MeV, whose wave function is dominated by the two neutrons in the 2p{sub 3/2} shell, is much larger than the ground state one. The comparison with the inclusive data reveals that transitions to states with high multipolarity and non-natural parity are important. This suggests that more complex two-particle correlations have to be incorporated in the treatment of the transfer process.

Corradi, L.; Fioretto, E.; Michelagnoli, C.; Stefanini, A. M.; Valiente-Dobon, J. J. [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, I-35020 Legnaro (Italy); Szilner, S. [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, I-35020 Legnaro (Italy); Ruder Boskovic Institute, HR-10 001 Zagreb (Croatia); Pollarolo, G. [Dipartimento di Fisica Teorica, Universita di Torino, and Istituto Nazionale di Fisica Nucleare, I-10125 Torino (Italy); Colo, G. [Dipartimento di Fisica, Universita degli Studi di Milano and Istituto Nazionale di Fisica Nucleare, I-20133 Milano (Italy); Mason, P.; Farnea, E.; Montagnoli, G.; Montanari, D.; Scarlassara, F.; Ur, C. A. [Dipartimento di Fisica, Universita di Padova, and Istituto Nazionale di Fisica Nucleare, I-35131 Padova (Italy); Gadea, A. [IFIC, CSIC-Universidad de Valencia, E-46071 Valencia (Spain); Haas, F. [Institut Pluridisciplinaire Hubert Curien, CNRS-IN2P3, Universite de Strasbourg, F-67037 Strasbourg (France); Jelavic-Malenica, D.; Soic, N. [Ruder Boskovic Institute, HR-10 001 Zagreb (Croatia); Marginean, N. [Horia Hulubei National Institute of Physics and Nuclear Engineering, R-077125, Bucharest-Magurele (Romania)

2011-09-15

26

Dosimetry of mixed neutron and gamma radiation with paired Fricke solutions in light and heavy water.  

PubMed

Paired Fricke solutions, made up from light water or heavy water and 0.8N in H2SO4 and 1 mM in Fe(NH4)2(SO4)2 and NaCl, were calibrated with 60Co gamma rays and with mixed neutron and gamma radiation from a 252Cf source. Absorbance increases, AL and AH, in light- and heavy-water Fricke dosimeters, respectively, increased with fast-neutron and gamma-ray tissue doses, Dn (GY) and D gamma (GY), of the mixed radiation as follows: AL = 0.00178Dn + 0.00371D gamma; AH = 0.00121Dn + 0.00442 D gamma. G-values of 7.2 and 5.5 were obtained for 252Cf neutrons in light- and heavy-water Fricke dosimeters, respectively. When we applied the pair of equations to AL and AH values observed after exposure to mixed radiation in a nuclear reactor, resulting Dn and D gamma values agreed within 10% to doses measured with paired ionization chambers. Doses required for Fricke dosimeters were 5 Gy or more. In contrast, we found that micronuclear yields in onion roots can measure the neutron component of mixed radiation fields at the order of 10 cGy with reasonable accuracy even if the neutron to gamma-ray dose ratio is unknown. PMID:8840720

Himit, M; Itoh, T; Endo, S; Fujikawa, K; Hoshi, M

1996-06-01

27

Pair distribution functions of bacteriorhodopsin and rhodopsin in model bilayers.  

PubMed Central

The pair distribution functions have been measured from freeze-fracture pictures of bacteriorhodopsin and rhodopsin recombinants with diacyl phosphatidylcholines (PC) of various hydrocarbon chain lengths. Pictures were used of samples that had been frozen from above the phase transition temperature of the lipid. Measured functions were compared with those calculated from two model interparticle potential energy functions, (a) a hard-disk repulsion only, and (b) a hard-disk repulsion plus electrostatic repulsion for a point charge buried in the membrane. The measured functions for bacteriorhodopsin di 12:0 PC, di 14:0 PC, and di 16:0 PC recombinants can be simulated using an interparticle hard-disk repulsion only. Bleached rhodopsin di 12:0 PC and di 18:1 trans-PC recombinants, and dark-adapted rhodopsin di 10:0 PC recombinants yield functions that are better simulated by assuming an additional repulsive interaction. The measured functions resemble those calculated using the hard-disk plus electrostatic repulsion model. The picture of dark-adapted rhodopsin in di 18:1 trans-PC frozen from 20 degrees C shows partial aggregation that is apparent in the measured pair distribution function. This attractive interaction persists even at 37 degrees C, where the measured function shows deviations from the hard-disk repulsive model, indicative of an attractive interparticle interaction. Implications of these results are discussed in terms of protein-lipid interactions. Images FIGURE 1 PMID:6616005

Pearson, L T; Chan, S I; Lewis, B A; Engelman, D M

1983-01-01

28

Role of pairing interaction in neutron rich odd and even Zr nuclei  

SciTech Connect

Neutron rich Zr nuclei with number of neutrons between N=50 and 82 are investigated in the relativistic mean field approach in coordinate space. The resonant levels in the positive energy continuum have been explicitly included in the calculation. Odd nuclei have been treated in the blocking approximation. Our calculation indicates that the dripline for odd mass isotopes is far away from that for the even mass ones. Pairing interaction plays a significant role in stabilizing the even isotopes, thus extending the dripline for them.

Bhattacharya, Madhubrata; Gangopadhyay, G. [Department of Physics, University of Calcutta 92, Acharya Prafulla Chandra Road, Kolkata-700 009 (India)

2007-01-15

29

Comparison of MCNP6 and experimental results for neutron counts, Rossi-{alpha}, and Feynman-{alpha} distributions  

SciTech Connect

MCNP6, the general-purpose Monte Carlo N-Particle code, has the capability to perform time-dependent calculations by tracking the time interval between successive events of the neutron random walk. In fixed-source calculations for a subcritical assembly, the zero time value is assigned at the moment the neutron is emitted by the external neutron source. The PTRAC and F8 cards of MCNP allow to tally the time when a neutron is captured by {sup 3}He(n, p) reactions in the neutron detector. From this information, it is possible to build three different time distributions: neutron counts, Rossi-{alpha}, and Feynman-{alpha}. The neutron counts time distribution represents the number of neutrons captured as a function of time. The Rossi-a distribution represents the number of neutron pairs captured as a function of the time interval between two capture events. The Feynman-a distribution represents the variance-to-mean ratio, minus one, of the neutron counts array as a function of a fixed time interval. The MCNP6 results for these three time distributions have been compared with the experimental data of the YALINA Thermal facility and have been found to be in quite good agreement. (authors)

Talamo, A.; Gohar, Y. [Argonne National Laboratory, 9700 S. Cass Ave., Lemont, IL 60439 (United States); Sadovich, S.; Kiyavitskaya, H.; Bournos, V.; Fokov, Y.; Routkovskaya, C. [Joint Institute for Power and Nuclear Research-Sosny, 99 Academician A.K. Krasin Str., Minsk 220109 (Belarus)

2013-07-01

30

Optimized pair distribution function analysis of gold nanoparticles  

NASA Astrophysics Data System (ADS)

A fast and efficient method for creating quantitative pair distribution functions (PDFs) was developed for use on a range of sample types. A volume correction was modelled in parallel with work on an optimized PDF calculation method. It was shown that the optimized calculation method eliminated the need for specific physical corrections which otherwise contaminate PDFs, thus greatly improving the efficiency of PDF calculation. Proof of this principle and of the PDF's quantitative accuracy was demonstrated using a standard sample, bulk gold. To demonstrate the versatility and power of the new PDF analysis method, non standard samples consisting of gold nanopartic1es of various sizes were analyzed. For the first time, properties such as thermal expansion, lattice constant and Debye-Waller factors of these nanopartic1es were measured via the optimized PDF method and are presented here.

Pritchard, Bayden

31

Role of proton pairing in a semimicroscopic treatment of the inner crust of neutron stars  

NASA Astrophysics Data System (ADS)

The TETFSI (temperature-dependent extended Thomas-Fermi plus Strutinsky integral) method for calculating the properties of the inner crust of neutron stars is here extended in the zero-temperature limit to include proton pairing. The main effect is to smooth out the proton shell effects, although the energetically favored value of Z , the number of protons per Wigner-Seitz cell, remains at, or close to, 40.

Pearson, J. M.; Chamel, N.; Pastore, A.; Goriely, S.

2015-01-01

32

Neutron Pair Transfer in Ni60+Sn116 Far below the Coulomb Barrier  

NASA Astrophysics Data System (ADS)

An excitation function of one- and two-neutron transfer channels for the Ni60+Sn116 system has been measured with the magnetic spectrometer PRISMA in a wide energy range, from the Coulomb barrier to far below it. The experimental transfer probabilities are well reproduced, for the first time with heavy ions, in absolute values and in slope by microscopic calculations which incorporate nucleon-nucleon pairing correlations.

Montanari, D.; Corradi, L.; Szilner, S.; Pollarolo, G.; Fioretto, E.; Montagnoli, G.; Scarlassara, F.; Stefanini, A. M.; Courtin, S.; Goasduff, A.; Haas, F.; Jelavi? Malenica, D.; Michelagnoli, C.; Mijatovi?, T.; Soi?, N.; Ur, C. A.; Varga Pajtler, M.

2014-08-01

33

Fission meter and neutron detection using poisson distribution comparison  

DOEpatents

A neutron detector system and method for discriminating fissile material from non-fissile material wherein a digital data acquisition unit collects data at high rate, and in real-time processes large volumes of data directly into information that a first responder can use to discriminate materials. The system comprises counting neutrons from the unknown source and detecting excess grouped neutrons to identify fission in the unknown source. Comparison of the observed neutron count distribution with a Poisson distribution is performed to distinguish fissile material from non-fissile material.

Rowland, Mark S; Snyderman, Neal J

2014-11-18

34

Exact Solution of the Spin-Isospin Proton-Neutron Pairing Hamiltonian  

SciTech Connect

The exact solution of the proton-neutron isoscalar-isovector (T=0,1) pairing Hamiltonian with nondegenerate single-particle orbits and equal pairing strengths is presented for the first time. The Hamiltonian is a particular case of a family of integrable SO(8) Richardson-Gaudin models. The exact solution of the T=0,1 pairing Hamiltonian is reduced to a problem of 4 sets of coupled nonlinear equations that determine the spectral parameters of the complete set of eigenstates. The microscopic structure of individual eigenstates is analyzed in terms of evolution of the spectral parameters in the complex plane for a system of A=80 nucleons. The spectroscopic trends of the exact solutions are discussed in terms of generalized rotations in isospace.

Lerma H, S.; Errea, B.; Dukelsky, J. [Instituto de Estructura de la Materia, CSIC, Serrano 123, 28006 Madrid (Spain); Satula, W. [Institute of Theoretical Physics, University of Warsaw, ul. Hoza 69, 00-681 Warsaw (Poland)

2007-07-20

35

An efficient approach to approximating the pair distribution function of the inhomogeneous hard-sphere fluid  

E-print Network

We introduce an approximation for the pair distribution function of the inhomogeneous hard sphere fluid. Our approximation makes use of our recently published averaged pair distribution function at contact which has been shown to accurately reproduce the averaged pair distribution function at contact for inhomogeneous density distributions. This approach achieves greater computational efficiency than previous approaches by enabling the use of exclusively fixed-kernel convolutions and thus allowing an implementation using fast Fourier transforms. We compare results for our pair distribution approximation with two previously published works and Monte-Carlo simulation, showing favorable results.

Paho Lurie-Gregg; Jeff B. Schulte; David Roundy

2014-09-24

36

Approach to approximating the pair distribution function of inhomogeneous hard-sphere fluids  

NASA Astrophysics Data System (ADS)

We introduce an approximation for the pair distribution function of the inhomogeneous hard sphere fluid. Our approximation makes use of our recently published averaged pair distribution function at contact, which has been shown to accurately reproduce the averaged pair distribution function at contact for inhomogeneous density distributions. This approach achieves greater computational efficiency than previous approaches by enabling the use of exclusively fixed-kernel convolutions and thus allowing an implementation using fast Fourier transforms. We compare results for our pair distribution approximation with two previously published works and Monte Carlo simulation, showing favorable results.

Lurie-Gregg, Paho; Schulte, Jeff B.; Roundy, David

2014-10-01

37

AN ASSESSMENT OF WOOD DUCK DISTRIBUTION, ABUNDANCE AND RIPARIAN BREEDING PAIR HABITATS IN SOUTH DAKOTA  

E-print Network

AN ASSESSMENT OF WOOD DUCK DISTRIBUTION, ABUNDANCE AND RIPARIAN BREEDING PAIR HABITATS IN SOUTH #12;AN ASSESSMENT OF WOOD DUCK DISTRIBUTION, ABUNDANCE AND RIPARIAN BREEDING PAIR HABITATS IN SOUTH Wildlife and Fisheries Sciences #12;AN ASSESSMENT OF WOOD DUCK DISTRIBUTION, ABUNDANCE AND RIPARIAN

38

Determination of energetic neutron spatial distribution using neutron induced nuclear recoil events  

Microsoft Academic Search

Neutron induced nuclear recoils were used to determine the spatial distribution of the weakly moderated spallation neutrons produced in the interaction of 1GeV protons with lead and uranium–lead targets. CR39 plastic track detectors were used to record neutron-induced recoil tracks. The track density measurements were carried out using a fully automated optical microscope. The experimental results were compared with Monte

S. R Hashemi-Nezhad; M. Dolleiser; R. Brandt; W. Westmeier; R. Odoj; M. I. Krivopustov; B. A Kulakov; A. N Sosnin

2002-01-01

39

Temperature effects on atomic pair distribution functions of melts  

SciTech Connect

Using molecular dynamics simulations, we investigate the temperature-dependent evolution of the first peak position/shape in pair distribution functions of liquids. For metallic liquids, the peak skews towards the left (shorter distance side) with increasing temperature, similar to the previously reported anomalous peak shift. Making use of constant-volume simulations in the absence of thermal expansion and change in inherent structure, we demonstrate that the apparent shift of the peak maximum can be a result of the asymmetric shape of the peak, as the asymmetry increases with temperature-induced spreading of neighboring atoms to shorter and longer distances due to the anharmonic nature of the interatomic interaction potential. These findings shed light on the first-shell expansion/contraction paradox for metallic liquids, aside from possible changes in local topological or chemical short-range ordering. The melts of covalent materials are found to exhibit an opposite trend of peak shift, which is attributed to an effect of the directionality of the interatomic bonds.

Ding, J., E-mail: ding@jhu.edu; Ma, E. [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States)] [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Xu, M. [I. Physikalisches Institut IA, RWTH Aachen University, Aachen 52056 (Germany)] [I. Physikalisches Institut IA, RWTH Aachen University, Aachen 52056 (Germany); Guan, P. F. [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States) [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Beijing Computational Science Research Center, Beijing 100086 (China); Deng, S. W. [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States) [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Department of Chemistry, East China University of Science and Technology, Shanghai 200237 (China); Cheng, Y. Q. [Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)] [Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

2014-02-14

40

A Statistical Study of the Mass Distribution of Neutron Stars  

NASA Astrophysics Data System (ADS)

By reviewing the methods of mass measurements of neutron stars in four different kinds of systems, i.e., the high-mass X-ray binaries (HMXBs), low-mass X-ray binaries (LMXBs), double neutron star systems (DNSs) and neutron star-white dwarf (NS-WD) binary systems, we have collected the orbital parameters of 40 systems. By using the boot-strap method and the Monte-Carlo method, we have rebuilt the likelihood probability curves of the measured masses of 46 neutron stars. The statistical analysis of the simulation results shows that the masses of neutron stars in the X-ray neutron star systems and those in the radio pulsar systems exhibit different distributions. Besides, the Bayes statistics of these four different kind systems yields the most-probable probability density distributions of these four kind systems to be (1.340 ± 0.230)M8, (1, 505 ± 0.125)M8,(1.335 ± 0.055)M8 and (1.495 ± 0.225)M8, respectively. It is noteworthy that the masses of neutron stars in the HMXB and DNS systems are smaller than those in the other two kind systems by approximately 0.16M8. This result is consistent with the theoretical model of the pulsar to be accelerated to the millisecond order of magnitude via accretion of approximately 0.2M8. If the HMXBs and LMXBs are respectively taken to be the precursors of the BNS and NS-WD systems, then the influence of the accretion effect on the masses of neutron stars in the HMXB systems should be exceedingly small. Their mass distributions should be very close to the initial one during the formation of neutron stars. As for the LMXB and NS-WD systems, they should have already under- gone the process of suffcient accretion, hence there arises rather large deviation from the initial mass distribution.

Cheng, Zheng; Zhang, Cheng-Min; Zhao, Yong-Heng; Wang, De-Hua; Pan, Yuan-Yue; Lei, Ya-Juan

2014-07-01

41

ON THE MASS DISTRIBUTION AND BIRTH MASSES OF NEUTRON STARS  

SciTech Connect

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{sub Sun} and a dispersion of 0.24 M{sub Sun }. 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{sub Sun }, but with a dispersion of only 0.05 M{sub Sun }. 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{sub Sun} and a dispersion of 0.2 M{sub Sun }, 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 {approx}2 M{sub Sun} suggests that only a few of these neutron stars cross the mass threshold to form low-mass black holes.

Oezel, Feryal; Psaltis, Dimitrios; Santos Villarreal, Antonio [Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Narayan, Ramesh [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138,USA (United States)

2012-09-20

42

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

NASA Astrophysics Data System (ADS)

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 flux in a BNCT irradiation field which were difficult to implement with the gold wire activation method. The dynamic range of linearity of the SOF detector was expanded by using a plastic scintillator with a rapid decay time. On the other hand, the contribution of gamma rays and fast neutrons in the measured signals were compensated from those obtained by a pair of SOF detectors, one with a 6LiF neutron converter and the other without. The discrimination level for the measured signals was also optimized to further reduce the contribution of gamma rays and fast neutrons signals. A non-paralyzable system model was applied to correct for the dead-time in the detector system. A good agreement between the thermal neutron flux measured by the gold wire activation method and the paired SOF detector system was observed. However, measurements which would normally take a few days to perform with the gold wire activation method were obtained in just about 15 min using the SOF detector system. We also confirmed the dynamic range of linearity for the SOF detector system to be in the order of magnitude of 10 4.

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

2005-10-01

43

Four energy group neutron flux distributions in the Syrian Miniature Neutron Source Reactor using the WIMSD4 and CITATION codes  

Microsoft Academic Search

A 3-D (R, ?, Z) neutronic model for the Miniature Neutron Source Reactor (MNSR) was developed earlier to conduct the reactor neutronic analysis. The group constants for all the reactor components were generated using the WIMSD4 code. The reactor excess reactivity and the four group neutron flux distributions were calculated using the CITATION code. This model is used in this

K. Khattab; H. Omar; N. Ghazi

2009-01-01

44

Distribution of thermal neutron flux around a PET cyclotron.  

PubMed

The number of positron emission tomography (PET) examinations has greatly increased world-wide. Since positron emission nuclides for the PET examinations have short half-lives, they are mainly produced using on-site cyclotrons. During the production of the nuclides, significant quantities of neutrons are generated from the cyclotrons. Neutrons have potential to activate the materials around the cyclotrons and cause exposure to the staff. To investigate quantities and distribution of the thermal neutrons, thermal neutron fluxes were measured around a PET cyclotron in a laboratory associating with a hospital. The cyclotron accelerates protons up to 18 MeV, and the mean particle current is 20 ?A. The neutron fluxes were measured during both 18F production and C production. Gold foils and thermoluminescent dosimeter (TLD) badges were used to measure the neutron fluxes. The neutron fluxes in the target box averaged 9.3 × 10(6) cm(-2) s(-1) and 1.7 × 10(6) cm(-2) s(-1) during 18F and 11C production, respectively. Those in the cyclotron room averaged 4.1 × 10(5) cm(-2) s(-1) and 1.2 × 10(5) cm(-2) s(-1), respectively. Those outside the concrete wall shielding were estimated as being equal to or less than ?3 cm s, which corresponded to 0.1 ?Sv h(-1) in effective dose. The neutron fluxes outside the concrete shielding were confirmed to be quite low compared to the legal limit. PMID:21451309

Ogata, Yoshimune; Ishigure, Nobuhito; Mochizuki, Shingo; Ito, Kengo; Hatano, Kentaro; Abe, Junichiro; Miyahara, Hiroshi; Masumoto, Kazuyoshi; Nakamura, Hajime

2011-05-01

45

Production, distribution and applications of californium-252 neutron sources.  

PubMed

The radioisotope 252Cf is routinely encapsulated into compact, portable, intense neutron sources with a 2.6-yr half-life. A source the size of a person's little finger can emit up to 10(11) neutrons s(-1). 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, land mines and unexploded military ordinance. 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 yr of experience and by US Bureau of Mines tests of source survivability during explosions. The production and distribution center for the US Department of Energy (DOE) Californium Program is the Radiochemical Engineering Development Center (REDC) at Oak Ridge National Laboratory (ORNL). DOE sells 252Cf to commercial reencapsulators domestically and internationally. Sealed 252Cf sources are also available for loan to agencies and subcontractors of the US 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 252Cf 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. PMID:11003521

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

2000-01-01

46

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

47

Distribution of Primes and of Interval Prime Pairs Based on $?$ Function  

E-print Network

$\\Theta$ function is defined based upon Kronecher symbol. In light of the principle of inclusion-exclusion, $\\Theta$ function of sine function is used to denote the distribution of composites and primes. The structure of Goldbach Conjecture has been analyzed, and $\\Xi$ function is brought forward by the linear diophantine equation; by relating to $\\Theta$ function, the interval distribution of composite pairs and prime pairs (i.e. the Goldbach Conjecture) is thus obtained. In the end, Abel's Theorem (Multiplication of Series) is used to discuss the lower limit of the distribution of the interval prime pairs.

Yifang Fan; Zhiyu Li

2010-04-19

48

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

PubMed

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

Cauwels, Vanessa; Vanhavere, Filip; Reginatto, Marcel

2014-10-01

49

Evidence for a spin-aligned neutron-proton paired phase from the level structure of (92)Pd.  

PubMed

Shell structure and magic numbers in atomic nuclei were generally explained by pioneering work that introduced a strong spin-orbit interaction to the nuclear shell model potential. However, knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers (N = Z), enhanced correlations arise between neutrons and protons (two distinct types of fermions) that occupy orbitals with the same quantum numbers. Such correlations have been predicted to favour an unusual type of nuclear superfluidity, termed isoscalar neutron-proton pairing, in addition to normal isovector pairing. Despite many experimental efforts, these predictions have not been confirmed. Here we report the experimental observation of excited states in the N = Z = 46 nucleus (92)Pd. Gamma rays emitted following the (58)Ni((36)Ar,2n)(92)Pd fusion-evaporation reaction were identified using a combination of state-of-the-art high-resolution ?-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron-proton coupling scheme, different from the previous prediction. We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling) in the ground and low-lying excited states of the heaviest N = Z nuclei. Such strong, isoscalar neutron-proton correlations would have a considerable impact on the nuclear level structure and possibly influence the dynamics of rapid proton capture in stellar nucleosynthesis. PMID:21179086

Cederwall, B; Moradi, F Ghazi; Bäck, T; Johnson, A; Blomqvist, J; Clément, E; de France, G; Wadsworth, R; Andgren, K; Lagergren, K; Dijon, A; Jaworski, G; Liotta, R; Qi, C; Nyakó, B M; Nyberg, J; Palacz, M; Al-Azri, H; Algora, A; de Angelis, G; Ataç, A; Bhattacharyya, S; Brock, T; Brown, J R; Davies, P; Di Nitto, A; Dombrádi, Zs; Gadea, A; Gál, J; Hadinia, B; Johnston-Theasby, F; Joshi, P; Juhász, K; Julin, R; Jungclaus, A; Kalinka, G; Kara, S O; Khaplanov, A; Kownacki, J; La Rana, G; Lenzi, S M; Molnár, J; Moro, R; Napoli, D R; Singh, B S Nara; Persson, A; Recchia, F; Sandzelius, M; Scheurer, J-N; Sletten, G; Sohler, D; Söderström, P-A; Taylor, M J; Timár, J; Valiente-Dobón, J J; Vardaci, E; Williams, S

2011-01-01

50

Kinematic distributions for electron pair production by muons  

NASA Technical Reports Server (NTRS)

Cross sections and kinematic distributions for the trident production process plus or negative muon plus charge yields plus or minus muon plus electron plus positron plus charge (with charge = dipion moment and Fe) are given for beam energies of 100 to 300 GeV at fixed (electron positron) masses from 5 to 15 GeV. This process is interesting as a test of quantum electrodynamics at high energies, and in particular as a test of the form of the photon propagator at large timelike (four-momentum) squared. For this purpose, it is desirable to impose kinematic cuts that favor those Bethe-Heitler graphs which contain a timelike photon propagator. It is found that there are substantial differences between the kinematic distributions for the full Bethe-Heitler matrix element and the distributions for the two timelike-photon graphs alone; these differences can be exploited in the selection of appropriate kinematic cuts.

Linsker, R.

1972-01-01

51

The neutron drip line: single-particle degrees of freedom and pairing properties as sources of theoretical uncertainties  

E-print Network

The sources of theoretical uncertainties in the prediction of the two-neutron drip line are analyzed in the framework of covariant density functional theory. We concentrate on single-particle and pairing properties as potential sources of these uncertainties. The major source of these uncertainties can be traced back to the differences in the underlying single-particle structure of the various covariant energy density functionals (CEDF). It is found that the uncertainties in the description of single-particle energies at the two-neutron drip line are dominated by those existing already in known nuclei. Only approximately one third of these uncertainties are due to the uncertainties in the isovector channel of CEDF's. Thus, improving the CEDF description of single-particle energies in known nuclei will also reduce the uncertainties in the prediction of the position of two-neutron drip line. The predictions of pairing properties in neutron rich nuclei depend on the CEDF. Although pairing properties affect moder...

Afanasjev, A V; Ray, D; Ray, P

2015-01-01

52

Necessary conditions for the N-representability of pair distribution functions  

NASA Astrophysics Data System (ADS)

A necessary condition for the N-representability of the electron pair density proposed by one of the authors (E. R. D.) is generalized. This shows a link between this necessary condition and other, more widely known, N-representability conditions for the second-order density matrix. The extension to spin-resolved electron pair densities is considered, as is the extension to higher-order distribution functions. Although quantum mechanical systems are our primary focus, the results are also applicable to classical systems, where they reduce to an inequality originally derived by Garrod and Percus. As a simple application, bounds to the average angle between an electron pair are derived. It is shown that computational methods based on variational minimization of the energy with respect to the electron pair density can give extremely poor results unless robust N-representability constraints are considered. For reference, constraints for the N-representability of the pair density are summarized.

Ayers, Paul W.; Davidson, Ernest R.

53

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

54

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

SciTech Connect

A Monte Carlo method previously developed has been applied to simulate the interaction of photons with CsI over the energy range from 50 eV to ~ 1 MeV and the subsequent electron cascades, as well as various quantum mechanical processes. The MC model has been employed to investigate the creation and nano-scale spatial distribution of electron-hole pairs and to calculate important intrinsic properties, including the W value, which is the mean energy required to produce an electron-hole pair, and the Fano factor. At energies lower than 10 keV, W generally decreases with increasing photon energy from 19 to 15 eV, whereas it saturates to 15 eV for higher energies. However, W exhibits a sawtooth variation, and discontinuities at the shell edges that follow the photoionization cross sections. The Fano factor, F, generally increases with increasing energy, and has a value of 0.28 at energies higher than 10 keV. The decrease of W value up to 10 keV may account for the initial rise in relative light yield with incident energy, as observed in experiments in CsI, and this suggests that the nonlinearity at low energy range may be associated with intrinsic properties of materials. Also, the spatial distribution of e-h pairs shows that the e-h pairs are primarily distributed along fast electron tracks in CsI, but the density of electron-hole pairs is low. A significant number of electron-hole pairs are produced through the different ionization channels of core shells and corresponding relaxation processes, which may provide an explanation why the Fano factor in CsI is larger than that in Si or Ge. The spatial distribution and density of thermalized electron-hole pairs along the primary and secondary tracks are important for large scale simulations of electron-hole pair transport.

Gao, Fei [Pacific Northwest National Laboratory (PNNL); Xie, Y. [Pacific Northwest National Laboratory (PNNL); Kerisit, S. [Pacific Northwest National Laboratory (PNNL); Campbell, L. W. [Pacific Northwest National Laboratory (PNNL); Weber, William J [ORNL

2011-01-01

55

Radical distributions in ammonium tartrate single crystals exposed to photon and neutron beams.  

PubMed

The radiation therapy carried out by means of heavy charged particles (such as carbon ions) and neutrons is rapidly becoming widespread worldwide. The success of these radiation therapies relies on the high density of energy released by these particles or by secondary particles produced after primary interaction with matter. The biological damages produced by ionising radiations in tissues and cells depend more properly on the energy released per unit pathlength, which is the linear energy transfer and which determines the radiation quality. To improve the therapy effectiveness, it is necessary to grasp the mechanisms of free radical production and distribution after irradiation with these particles when compared with the photon beams. In this work some preliminary results on the analysis of the spatial distributions of the free radicals produced after exposure of ammonium tartrate crystals to various radiation beams ((60)Co gamma photons and thermal neutrons) were reported. Electron spin resonance analyses were performed by the electron spin echo technique, which allows the determination of local spin concentrations and by double electron-electron resonance technique, which is able to measure the spatial distance distribution (range 1.5-8 nm) among pairs of radicals in solids. The results of these analyses are discussed on the basis of the different distributions of free radicals produced by the two different radiation beams used. PMID:24591730

Marrale, M; Longo, A; Barbon, A; Brustolon, M; Brai, M

2014-10-01

56

Probing transverse momentum dependent gluon distribution functions from hadronic quarkonium pair production  

NASA Astrophysics Data System (ADS)

The inclusive hadronic production of ?Q (?c or ?b) pair is proposed to extract the transverse momentum-dependent (TMD) gluon distribution functions. We use nonrelativistic QCD (NRQCD) for the production of ?Q. Under the nonrelativistic limit, the TMD factorization for this process is assumed to make a lowest-order calculation. For unpolarized initial hadrons, unpolarized and linearly polarized gluon distributions can be extracted by studying different angular distributions.

Zhang, Guang-Peng

2014-11-01

57

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

58

Coupled tunnelling motion of a pair of methyl groups in lithium acetate studied by inelastic neutron scattering  

Microsoft Academic Search

The tunnelling and torsional motions of methyl groups in lithium acetate dihydrate (CH3COOLi·2H2O) have been studied in detail by incoherent inelastic neutron scattering. The results are interpreted by a model of pairs of methyl groups performing a coupled tunnelling motion. The strength of the coupling term is estimated to be about twice as strong as the threefold hindering barrier for

S. Clough; A. Heidemann; A. H. Horsewill; M. N. J. Paley

1984-01-01

59

Pair distribution function analysis of La(Fe1-xRux)AsO compounds  

NASA Astrophysics Data System (ADS)

The local structures of La(Fe1-xRux)AsO (0.00?x?0.80) compounds were investigated by means of pair distribution function analysis at room temperature; as a result, no phase separation or clustering takes place. Local distortions are no longer correlated beyond ~15 Å for both pure and substituted samples, indicating that the presence of Ru atoms does not determine a notable variation in the length scale of the local distortion. Different types of short range correlation between Fe and Ru atoms do not produce significant changes in the pair distribution function.

Martinelli, A.; Palenzona, A.; Ferdeghini, C.; Mazzani, M.; Bonfa`, P.; Allodi, G.

2014-12-01

60

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

61

Method and apparatus for determining the content and distribution of a thermal neutron absorbing material in an object  

DOEpatents

The disclosure is directed to an apparatus and method for determining the content and distribution of a thermal neutron absorbing material within an object. Neutrons having an energy higher than thermal neutrons are generated and thermalized. The thermal neutrons are detected and counted. The object is placed between the neutron generator and the neutron detector. The reduction in the neutron flux corresponds to the amount of thermal neutron absorbing material in the object. The object is advanced past the neutron generator and neutron detector to obtain neutron flux data for each segment of the object. The object may comprise a space reactor heat pipe and the thermal neutron absorbing material may comprise lithium.

Crane, Thomas W. (Los Alamos, NM)

1986-01-01

62

Method and apparatus for determining the content and distribution of a thermal neutron absorbing material in an object  

DOEpatents

The disclosure is directed to an apparatus and method for determining the content and distribution of a thermal neutron absorbing material within an object. Neutrons having an energy higher than thermal neutrons are generated and thermalized. The thermal neutrons are detected and counted. The object is placed between the neutron generator and the neutron detector. The reduction in the neutron flux corresponds to the amount of thermal neutron absorbing material in the object. The object is advanced past the neutron generator and neutron detector to obtain neutron flux data for each segment of the object. The object may comprise a space reactor heat pipe and the thermal neutron absorbing material may comprise lithium.

Crane, T.W.

1983-12-21

63

Time dependent worldwide distribution of atmospheric neutrons and of their products. I, II, III.  

NASA Technical Reports Server (NTRS)

Review of the experimental results obtained in a series of measurements of the fast neutron cosmic ray spectrum by means of high-altitude balloons and aircraft. These results serve as a basis for checking a Monte Carlo calculation of the entire neutron distribution and its products. A calculation of neutron production and transport in the earth's atmosphere is then discussed for the purpose of providing a detailed description of the morphology of secondary neutron components. Finally, an analysis of neutron observations during solar particle events is presented. The Monte Carlo output is used to estimate the contribution of flare particles to fluctuations in the steady state neutron distributions.

Merker, M.; Light, E. S.; Verschell, H. J.; Mendell, R. B.; Korff, S. A.

1973-01-01

64

Atomic pair distribution function analysis of materials containing crystalline and amorphous phases  

E-print Network

Abstract. The atomic pair distribution function (PDF) approach has been used to study the local structure materials relies heavily on the precise knowledge of their atomic structure. For more than 100 years in general contains two-body atomic correlations and thus holds the key to the defect or local structure

65

Neutron spectral distribution from a sealed-tube neutron generator by multiple-foil activation unfolding method  

NASA Astrophysics Data System (ADS)

The spectral distribution of 14 MeV neutrons from a KAMAN sealed-tube neutron generator has been determined using threshold-energy monitor reactions in combination with the SULSA unfolding code, in which no input 'guess spectrum' is required except measured reaction rates of threshold monitor reactions. Result indicates that value of mean neutron energy determined in the present study compares well with the value obtained using the Nb-Zr ratio method.

Jonah, S. A.; Ibikunle, K.

2003-04-01

66

Passive and Active Neutron Matrix Correction for Heterogeneous Distributions Utilizing the Neutron Imaging Technique  

SciTech Connect

Classical Non-Destructive Assay (NDA) Passive Neutron Coincidence Counting (PNCC) and Differential Die-Away (DDA) active neutron interrogation techniques [1, 2] are well suited for determining the gross matrix correction factors for homogenous mass distributions of Special Nuclear Material (SNM) within an interfering waste drum matrix. These measured passive and active matrix correction factors are crucial in quantifying the SNM mass, associated Total Measurement Uncertainty (TMU), and Minimum Detectable Activity (MDA) within the drum. When heterogeneous SNM mass distributions are encountered, the measured SNM mass, TMU and MDA biases introduced may be 100%, or greater, especially for dense hydrogenous matrices. The standard matrix correction factors can be adjusted if a coarse spatial image of the SNM mass, relative to the matrix, is available. The image can then be analyzed to determine the spatially-adjusted, matrix correction factors case by case. This image analysis approach was accomplished by modifying the standard Passive-Active Neutron (PAN) counter design [3] to accommodate a unique data acquisition architecture that supports a newly developed image acquisition and analysis application called the Neutron Imaging Technique (NIT). The NIT functionality supports both PNCC and DDA acquisition and analysis modes and exploits the symmetry between a stored set of factory acquired NIT images with those from the unknown PAN assay. The NIT result is then an adjustment to the classical correction factor reducing, if not removing, the SNM mass bias and revealing the true TMU and MDA values. In this paper we describe the NIT for the PAN design from the software and algorithmic perspectives and how this technique accommodates waste matrix drums that are difficult, from the classical standpoint, if not impossible, to extract meaningful SNM mass, TMU and MDA results. (authors)

Villani, M.F.; Croft, St. [Canberra Industries, Inc., Meriden, CT (United States); Alvarez, E.; Wilkins, C.G.; Stamp, D.; Fisher, J. [Canberra Harwell, Ltd., Didcot (United Kingdom); Ambrifi, A.; Simone, G. [Nucleco SpA, Casaccia (Italy); Bourva, L.C. [International Atomic Energy Agency, Dept. of Safeguards, Vienna (Australia)

2008-07-01

67

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

E-print Network

The production of energetic neutrons in $ep$ collisions has been studied with the ZEUS detector at HERA. The neutron energy and $p_T^2$ distributions were measured with a forward neutron calorimeter and tracker in a $40 \\pb^{-1}$ sample of inclusive deep inelastic scattering (DIS) data and a $6 \\pb^{-1}$ 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 $p_T^2$ 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.

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

2007-01-01

68

Local structure study of disordered crystalline materials with the atomic pair distribution function method  

NASA Astrophysics Data System (ADS)

The employed experimental method in this Ph.D. dissertation research is the atomic pair distribution function (PDF) technique specializing in high real space resolution local structure determination. The PDF is obtained via Fourier transform from powder total scattering data including the important local structural information in the diffuse scattering intensities underneath, and in-between, the Bragg peaks. Having long been used to study liquids and amorphous materials, the PDF technique has been recently successfully applied to highly crystalline materials owing to the advances in modern X-ray and neutron sources and computing power. An integral part of this thesis work has been to make the PDF technique accessible to a wider scientific community. We have recently developed the rapid acquisition PDF (RA-PDF) method featuring high energy X-rays coupled with an image plate area detector, allowing three to four orders of magnitude decrease of data collection time. Correspondingly in software development, I have written a complete X-ray data correction program PDFgetX2 (user friendly with GUI, 32,000+ lines). Those developments sweep away many barriers to the wide-spread application of the PDF technique in complex materials. The RA-PDF development also opens up new fields of research such as time-resolved studies, pump-probe measurements and so on, where the PDF analysis can provide unique insights. Two examples of the RA-PDF applications are described: the distorted T12 square nets in the new binary antimonide Ti2Sb and in-situ chemical reduction of CuO to Cu. The most intellectually enriching has been the local structure studies of the colossal magneto-resistive (CMR) manganites with intrinsic inhomogeneities. The strong coupling between electron, spin, orbital, and lattice degrees of freedom result in extremely rich and interesting phase diagrams. We have carried out careful PDF analysis of neutron powder diffraction data to study the local MnO6 octahedral distortions. For example, in the updoped compound LaMnO3, the Jahn-Teller (JT) transition around 750 K is characterized as distorted (JT active) to undistorted MnO6 octahedra transition by the conventional crystallographic analysis. However, our PDF results show local MnO6 octahedral distortions persist above the JT transition, and it is their random orientations that make the existing local distortions invisible to average structure analysis. The nature of the JT transition around 750 K is orbital order to disorder. Our first local structure study of the high temperature rhombohedral phase (T ? 1010 K) additionally discovered the existence of locally JT distorted MnO6 octahedra. More significantly, the range of the orbital order in the high temperature dynamic-JT phases; estimated from the crossover from the local to the average structure, is around 16 A (˜four MnO6 octahedra), suggesting strong nearest neighbor JT anti-ferrodistortive coupling. In the bi-layered La0.92Sr 2.08Mn2O7, we found the shape of MnO6 octahedron changes from oblate (4 long, 2 short Mn-O bonds) to prolate (2 long, 4 short Mn-O bonds) as the material goes from type A anti-ferromagnetic to type CE charge ordered phase. This can be understood as the d x2-y2 to dx,y2-r2 orbital occupancy transition of the Mn3+ e g electrons. Evidences for nano-scale inhomogeneities in the Mn4+ rich region of La2-2xSr 1+2xMn2O7 (0.54 ? x ? 0.80) are also discussed.

Qiu, Xiangyun

69

Differential-phase quantum key distribution experiment using a series of quantum entangled photon pairs.  

PubMed

We report what we believe to be the first differential-phase quantum key distribution experiment using a series of quantum entangled photon pairs. We employed two outstanding techniques. As an entangled photon source, we used a 1.5 microm band entangled photon pair source based on spontaneous four-wave mixing in a cooled dispersion-shifted fiber. As receivers, photon pairs were actively phase modulated with LiNbO3 phase modulators followed by very stable planar light-wave circuit Mach-Zehnder interferometers, which provided two nonorthogonal measurements. As a consequence, we successfully generated sifted keys with a quantum bit error rate of 8.3% and a key generation rate of 0.3 bit/s and revealed the feasibility of this QKD scheme. PMID:17410270

Honjo, Toshimori; Takesue, Hiroki; Inoue, Kyo

2007-05-01

70

Neutrino and Electron-positron Pair Emission from Phase-induced Collapse of Neutron Stars to Quark Stars  

E-print Network

We study the energy released from phase-transition induced collapse of neutron stars, which results in large amplitude stellar oscillations. To model this process we use a Newtonian hydrodynamic code, with a high resolution shock-capturing scheme. The physical process considered is a sudden phase transition from normal nuclear matter to a mixed phase of quark and nuclear matter. We show that both the temperature and the density at the neutrinosphere oscillate with time. However, they are nearly 180 degree out of phase. Consequently, extremely intense, pulsating neutrino/antineutrino and leptonic pair fluxes will be emitted. During this stage several mass ejecta can be ejected from the stellar surface by the neutrinos and antineutrinos. These ejecta can be further accelerated to relativistic speeds by the electron/positron pairs, created by the neutrino and antineutrino annihilation outside the stellar surface. We suggest that this process may be a possible mechanism for short Gamma-Ray Bursts.

Cheng, K S

2010-01-01

71

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

Microsoft Academic Search

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?1 sample of inclusive deep inelastic scattering (DIS) data and a 6 pb?1 sample of photoproduction data. The neutron yield in photoproduction is suppressed relative to DIS

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

2007-01-01

72

Pairing properties of the inner crust of neutron stars at finite temperature  

E-print Network

We investigate the thermal properties of the inner crust of a neutron star using the Hartree-Fock-Bogoliubov (HFB) formalism at finite temperature. We compare our results with the ones obtained solving the same equations, but within the BCS approximation. We observe that for the outermost regions of the inner crust, the two methods can show important differences, in particular when we use them to calculate the neutron specific heat of the system.

A. Pastore

2014-03-20

73

An efficient algorithm for generating random number pairs drawn from a bivariate normal distribution  

NASA Technical Reports Server (NTRS)

An efficient algorithm for generating random number pairs from a bivariate normal distribution was developed. Any desired value of the two means, two standard deviations, and correlation coefficient can be selected. Theoretically the technique is exact and in practice its accuracy is limited only by the quality of the uniform distribution random number generator, inaccuracies in computer function evaluation, and arithmetic. A FORTRAN routine was written to check the algorithm and good accuracy was obtained. Some small errors in the correlation coefficient were observed to vary in a surprisingly regular manner. A simple model was developed which explained the qualities aspects of the errors.

Campbell, C. W.

1983-01-01

74

Radial Flux Distribution of Low-Energy Neutrons.  

ERIC Educational Resources Information Center

Describes an experiment designed to illustrate the basic principle involved in the process of moderation of fast neutrons by water, and the monitoring of the low-energy neutron flux using indium as a probe. (GA)

Higinbotham, J.

1979-01-01

75

Production, distribution and applications of californium-252 neutron sources  

Microsoft Academic Search

The radioisotope 252Cf is routinely encapsulated into compact, portable, intense neutron sources with a 2.6-yr half-life. A source the size of a person’s little finger can emit up to 1011 neutrons s?1. 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

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

2000-01-01

76

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

77

Richardson-Gaudin Algebras and the Exact Solutions of the Proton-Neutron Pairing  

E-print Network

Many exactly solvable models are based on Lie algebras. The pairing interaction is important in nuclear physics and its exact solution for identical particles in non-degenerate single-particle levels was first given by Richardson in 1963. His solution and its generalization to Richardson-Gaudin quasi-exactly solvable models have attracted the attention of many contemporary researchers and resulted in the exact solution of the isovector pn-pairing within the so(5) RG-model and the equal strength spin-isospin pn-pairing within the so(8) RG-model. Basic properties of the RG-models are summarized and possible applications to nuclear physics are emphasized. MSC2010 Classification: 81U15 Exactly and quasi-solvable systems, 17B81 Applications to physics, 81V35 Nuclear physics, 81R40 Symmetry breaking.

V. G. Gueorguiev; J. Dukelsky

2010-11-27

78

Richardson-Gaudin Algebras and the Exact Solutions of the Proton-Neutron Pairing  

E-print Network

Many exactly solvable models are based on Lie algebras. The pairing interaction is important in nuclear physics and its exact solution for identical particles in non-degenerate single-particle levels was first given by Richardson in 1963. His solution and its generalization to Richardson-Gaudin quasi-exactly solvable models have attracted the attention of many contemporary researchers and resulted in the exact solution of the isovector pn-pairing within the so(5) RG-model and the equal strength spin-isospin pn-pairing within the so(8) RG-model. Basic properties of the RG-models are summarized and possible applications to nuclear physics are emphasized. MSC2010 Classification: 81U15 Exactly and quasi-solvable systems, 17B81 Applications to physics, 81V35 Nuclear physics, 81R40 Symmetry breaking.

Gueorguiev, V G

2010-01-01

79

Study of nuclear dynamics of neutron-rich colliding pair at energy of vanishing flow  

E-print Network

We study nuclear dynamics at the energy of vanishing flow of neutron-rich systems having N/Z ratio 1.0, 1.6 and 2.0 throughout the mass range at semi central colliding geometry. In particular we study the behavior of average and maximum density with N/Z dependence of the system.

Sakshi Gautam

2011-07-28

80

Marginal Stability Constrains Force and Pair Distributions at Random Close Packing  

NASA Astrophysics Data System (ADS)

The requirement that packings of frictionless hard spheres, arguably the simplest structural glass, cannot be compressed by rearranging their network of contacts is shown to yield a new constraint on their microscopic structure. This constraint takes the form a bound between the distribution of contact forces P(f) and the pair distribution function g(r): if P(f)˜f? and g(r)˜(r-?0)-?, where ?0 is the particle diameter, one finds that ??1/(2+?). This bound plays a role similar to those found in some glassy materials with long-range interactions, such as the Coulomb gap in Anderson insulators or the distribution of local fields in mean-field spin glasses. There are grounds to believe that this bound is saturated, yielding a mechanism to explain the avalanches of rearrangements with power-law statistics that govern plastic flow in packings.

Wyart, Matthieu

2012-09-01

81

Neutron diffraction study of liquid bromine: Evaluation of the effective pair potential  

Microsoft Academic Search

An analysis of the orientational correlation between neighbouring molecules of liquid bromine is given. Giving proper weighting of parallel and perpendicular orientations, the correlated form factor f2(Q) is determined taking into account the fact that the centre structure factor, Sc(Q) in and around the first peak region should be well produced by hard sphere considerations. The effective pair potential obtained

R. V. Gopala Rao; R. N. Joarder

1978-01-01

82

d sigma/dy Distribution of Drell-Yan Dielectron Pairs  

SciTech Connect

The authors report on the measurement of the rapidity distribution, d{sigma}/dY, over the full kinematic range for e{sup +}e{sup -} pairs produced in p{bar p} collisions at {radical}s = 1.96 TeV in the Z boson region of 66 < M{sub ee} < 116 GeV/c{sup 2}. The data sample consists of 1.1 fb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV taken by the Collider Detector at Fermilab (CDF). The d{sigma}/dy is compared with the NLO theory prediction.

Han, Jiyeon; Bodek, A.; Sakumoto, W.; Chung, Y.; /Rochester U.

2007-11-01

83

Directional pair distribution function for diffraction line profile analysis of atomistic models  

PubMed Central

The concept of the directional pair distribution function is proposed to describe line broadening effects in powder patterns calculated from atomistic models of nano-polycrystalline microstructures. The approach provides at the same time a description of the size effect for domains of any shape and a detailed explanation of the strain effect caused by the local atomic displacement. The latter is discussed in terms of different strain types, also accounting for strain field anisotropy and grain boundary effects. The results can in addition be directly read in terms of traditional line profile analysis, such as that based on the Warren–Averbach method. PMID:23396818

Leonardi, Alberto; Leoni, Matteo; Scardi, Paolo

2013-01-01

84

Quantitative Nanostructure Characterization Using Atomic Pair Distribution Functions Obtained From Laboratory Electron Microscopes  

SciTech Connect

Quantitatively reliable atomic pair distribution functions (PDFs) have been obtained from nanomaterials in a straightforward way from a standard laboratory transmission electron microscope (TEM). The approach looks very promising for making electron derived PDFs (ePDFs) a routine step in the characterization of nanomaterials because of the ubiquity of such TEMs in chemistry and materials laboratories. No special attachments such as energy filters were required on the microscope. The methodology for obtaining the ePDFs is described as well as some opportunities and limitations of the method.

Abeykoon M.; Billinge S.; Malliakas, C.D.; Juhas, P.; Bozin, E.S.; Kanatzidis, M.G.

2012-05-01

85

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

2013-11-01

86

Quantitative study of coherent pairing modes with two-neutron transfer: Sn isotopes  

NASA Astrophysics Data System (ADS)

Pairing rotations and pairing vibrations are collective modes associated with a field, the pair field, which changes the number of particles by two. Consequently, they can be studied at profit with the help of two-particle transfer reactions in superfluid and in normal nuclei, respectively. The advent of exotic beams has opened, for the first time, the possibility to carry out such studies in medium heavy nuclei, within the same isotopic chain. The case studied in the present paper is that of the Sn isotopes [essentially from closed (Z=N=50) to closed (Z=50, N=82) shells]. The static and dynamic off-diagonal, long-range order phase coherence in gauge space displayed by pairing rotations and vibrations, respectively, leads to coherent states which behave almost classically. Consequently, these modes are amenable to an accurate nuclear structure description in terms of simple models containing the right physics, in particular, BCS plus quasiparticle random-phase approximation and Hartree-Fock mean field plus random-phase approximation, respectively. The associated two-nucleon transfer spectroscopic amplitudes predicted by such model calculations can thus be viewed as essentially “exact.” This fact, together with the availability of optical potentials for the different real and virtual channels involved in the reactions considered, namely A+2Sn+p, A+1Sn+d, and ASn+t, allows for the calculation of the associated absolute cross sections without, arguably, free parameters. The numerical predictions of the absolute differential cross sections, obtained making use of the above-mentioned nuclear structure and optical potential inputs, within the framework of second-order distorted-wave Born approximation, taking into account simultaneous, successive, and nonorthogonality contributions, provide, within experimental errors in general, and below 10% uncertainty in particular, an overall account of the experimental findings for all of the measured A+2Sn(p,t)ASn(gs) reactions, for which absolute cross sections have been reported to date.

Potel, G.; Idini, A.; Barranco, F.; Vigezzi, E.; Broglia, R. A.

2013-05-01

87

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

88

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

89

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

90

Water above its boiling point: Study of the temperature and density dependence of the partial pair correlation functions. I. Neutron diffraction experiment  

Microsoft Academic Search

Neutron diffraction data on water, employing the technique of hydrogen\\/deuterium isotope substitution, are reported at three thermodynamic states above the boiling point. The structural information is analyzed in terms of the partial radial distribution functions, OO, OH, and HH, which are extracted from the neutron data. It is found that temperature affects mainly the medium and longer range order in

P. Postorino; M. A. Ricci; A. K. Soper

1994-01-01

91

Neutron density distributions from antiprotonic 208Pb and 209Bi atoms  

E-print Network

The X-ray cascade from antiprotonic atoms was studied for 208Pb and 209Bi. Widths and shifts of the levels due to the strong interaction were determined. Using modern antiproton-nucleus optical potentials the neutron densities in the nuclear periphery were deduced. Assuming two parameter Fermi distributions (2pF) describing the proton and neutron densities the neutron rms radii were deduced for both nuclei. The difference of neutron and proton rms radii /\\r_np equal to 0.16 +-(0.02)_{stat} +- (0.04)_{syst} fm for 208Pb and 0.14 +- (0.04)_{stat} +- (0.04)_{syst} fm for 209Bi were determined and the assigned systematic errors are discussed. The /\\r_np values and the deduced shapes of the neutron distributions are compared with mean field model calculations.

B. Klos; A. Trzcinska; J. Jastrzebski; T. Czosnyka; M. Kisielinski; P. Lubinski; P. Napiorkowski; L. Pienkowski; F. J. Hartmann; B. Ketzer; P. Ring; R. Schmidt; T. von Egidy; R. Smolanczuk; S. Wycech; K. Gulda; W. Kurcewicz; E. Widmann; B. A. Brown

2007-02-08

92

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

93

Fragment yield distribution and the influence of neutron composition and excitation energy in multifragmentation reactions  

NASA Astrophysics Data System (ADS)

The isotopic properties of the primary and secondary fragment yield distribution in the multifragmentation of 58Fe+58Ni and 58Fe+58Fe reactions are studied with respect to the 58Ni+58Ni reaction at 30, 40, and 47 MeV/nucleon. The reduced neutron and proton densities from the observed fragment yield distribution show primary fragment yield distribution to undergo strongly secondary deexcitations. The effect is small at the lowest excitation energy and smallest neutron-to-proton ratio and becomes large at higher excitation energies and higher neutron-to-proton ratio. The symmetry energy of the primary fragments deduced from the reduced neutron density is significantly lower than that for the normal nuclei at saturation density, indicating that the fragments are highly excited and formed at a reduced density. Furthermore, the symmetry energy is also observed to decrease slowly with increasing excitation energy. The observed effect is explained using the statistical multifragmentation model.

Shetty, D. V.; Botvina, A. S.; Yennello, S. J.; Souliotis, G. A.; Bell, E.; Keksis, A.

2005-02-01

94

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

E-print Network

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 (CFL). 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 apply both above and below the critical temperature, allowing use in simulations of neutrino transport in supernovae and neutron stars.

Joydip Kundu; Sanjay Reddy

2004-05-19

95

Pair-flowered cymes in the Lamiales: structure, distribution and origin  

PubMed Central

Background and Aims In the Lamiales, indeterminate thyrses (made up of axillary cymes) represent a significant inflorescence type. However, it has been largely overlooked that there occur two types of cymes: (1) ordinary cymes, and (2) ‘pair-flowered cymes’ (PFCs), with a flower pair (terminal and front flower) topping each cyme unit. PFCs are unique to the Lamiales and their distribution, origin and phylogeny are not well understood. Methods The Lamiales are screened as to the occurrence of PFCs, ordinary cymes and single flowers (constituting racemic inflorescences). Key Results PFCs are shown to exhibit a considerable morphological and developmental diversity and are documented to occur in four neighbouring taxa of Lamiales: Calceolariaceae, Sanango, Gesneriaceae and Plantaginaceae. They are omnipresent in the Calceolariaceae and almost so in the Gesneriaceae. In the Plantaginaceae, PFCs are restricted to the small sister tribes Russelieae and Cheloneae (while the large remainder has single flowers in the leaf/bract axils; ordinary cymes do not occur). Regarding the origin of PFCs, the inflorescences of the genus Peltanthera (unplaced as to family; sister to Calceolariaceae, Sanango and Gesneriaceae in most molecular phylogenies) support the idea that PFCs have originated from paniculate systems, with the front-flowers representing remnant flowers. Conclusions From the exclusive occurrence of PFCs in the Lamiales and the proximity of the respective taxa in molecular phylogenies it may be expected that PFCs have originated once, representing a synapomorphy for this group of taxa and fading out within the Plantaginaceae. However, molecular evidence is ambiguous. Depending on the position of Peltanthera (depending in turn on the kind and number of genes and taxa analysed) a single, a double (the most probable scenario) or a triple origin appears conceivable. PMID:23884395

Weber, Anton

2013-01-01

96

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

97

Neutron angular distribution in a plasma focus obtained using nuclear track detectors.  

PubMed

The dense plasma focus (DPF) is a coaxial plasma gun in which a high-density, high-temperature plasma is obtained in a focused column for a few nanoseconds. When the filling gas is deuterium, neutrons can be obtained from fusion reactions. These are partially due to a beam of deuterons which are accelerated against the background hot plasma by large electric fields originating from plasma instabilities. Due to a beam-target effect, the angular distribution of the neutron emission is anisotropic, peaked in the forward direction along the axis of the gun. The purpose of this work is to illustrate the use of CR-39 nuclear track detectors as a diagnostic tool in the determination of the time-integrated neutron angular distribution. For the case studied in this work, neutron emission is found to have a 70% contribution from isotropic radiation and a 30% contribution from anisotropic radiation. PMID:12382811

Castillo-Mejía, F; Herrera, J J E; Rangel, J; Golzarri, J I; Espinosa, G

2002-01-01

98

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

99

Spatial distribution of moderated neutrons along a Pb target irradiated by high-energy protons  

Microsoft Academic Search

High-energy protons in the range of 0.5–7.4GeV have irradiated an extended Pb target covered with a paraffin moderator. The moderator was used in order to shift the hard Pb spallation neutron spectrum to lower energies and to increase the transmutation efficiency via (n,?) reactions. Neutron distributions along and inside the paraffin moderator were measured. An analysis of the experimental results

M. Fragopoulou; M. Manolopoulou; S. Stoulos; R. Brandt; W. Westmeier; B. A. Kulakov; M. I. Krivopustov; A. N. Sosnin; M. Debeauvais; J. C. Adloff; M. Zamani Valasiadou

2006-01-01

100

Imaging of gamma and neutron dose distributions at LVR-15 epithermal beam by means of FGLDs.  

PubMed

Gamma and fast neutron dose spatial distributions have been measured at the collimator exit of the epithermal neutron beam of LVR-15 reactor (?ež). Measurements were performed by means of optically analyzed Fricke-gel-layer detectors. The separation of the two dose contributions has been achieved by suitable pixel-to-pixel elaboration of the light transmittance images of Fricke-gel-layer detectors prepared with water and heavy water. PMID:21497100

Gambarini, G; Bartesaghi, G; Carrara, M; Negri, A; Paganini, L; Vanossi, E; Burian, J; Marek, M; Viererbl, L; Klupak, V; Rejchrt, J

2011-12-01

101

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

102

Roots Revealed - Neutron imaging insight of spatial distribution, morphology, growth and function  

NASA Astrophysics Data System (ADS)

Root production, distribution and turnover are not easily measured, yet their dynamics are an essential part of understanding and modeling ecosystem response to changing environmental conditions. Root age, order, morphology and mycorrhizal associations all regulate root uptake of water and nutrients, which along with along with root distribution determines plant response to, and impact on its local environment. Our objectives were to demonstrate the ability to non-invasively monitor fine root distribution, root growth and root functionality in Zea mays L. (maize) and Panicum virgatum L. (switchgrass) seedlings using neutron imaging. Plants were propagated in aluminum chambers containing sand then placed into a high flux cold neutron beam line. Dynamics of root distribution and growth were assessed by collecting consecutive CCD radiographs through time. Root functionality was assessed by tracking individual root uptake of water (H2O) or deuterium oxide (D2O) through time. Since neutrons strongly scatter H atoms, but not D atoms, biological materials such as plants are prime candidates for neutron imaging. 2D and 3D neutron radiography readily illuminated root structure, root growth, and relative plant and soil water content. Fungal hyphae associated with the roots were also visible and appeared as dark masses since their diameter was likely several orders of magnitude less than ~100 ?m resolution of the detector. The 2D pulse-chase irrigation experiments with H2O and D2O successfully allowed observation of uptake and mass flow of water within the root system. Water flux within individual roots responded differentially to foliar illumination based on internal water potential gradients, illustrating the ability to track root functionality based on root size, order and distribution within the soil. (L) neutron image of switchgrass growing in sandy soil with 100 ?m diameter roots (R) 3D reconstruction of maize seedling following neutron tomography

Warren, J.; Bilheux, H.; Kang, M.; Voisin, S.; Cheng, C.; Horita, J.; Perfect, E.

2013-05-01

103

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

104

Nyquist-Shannon sampling theorem applied to refinements of the atomic pair distribution function  

SciTech Connect

We have systematically studied the optimal real-space sampling of atomic pair distribution (PDF) data by comparing refinement results from oversampled and resampled data. Based on nickel and a complex perovskite system, we show that not only is the optimal sampling bounded by the Nyquist interval described by the Nyquist-Shannon (NS) sampling theorem as expected, but near this sampling interval, the data points in the PDF are minimally correlated, which results in more reliable uncertainty estimates in the modeling. Surprisingly, we find that PDF refinements quickly become unstable for data on coarser grids. Although the Nyquist-Shannon sampling theorem is well known, it has not been applied to PDF refinements, despite the growing popularity of the PDF method and its adoption in a growing number of communities. Here, we give explicit expressions for the application of NS sampling theorem to the PDF case, and establish through modeling that it is working in practice, which lays the groundwork for this to become more widely adopted. This has implications for the speed and complexity of possible refinements that can be carried out many times faster than currently with no loss of information, and it establishes a theoretically sound limit on the amount of information contained in the PDF that will prevent over-parametrization during modeling.

Farrow, Christopher L.; Shaw, Margaret; Kim, Hyunjeong; Juhás, Pavol; Billinge, Simon J.L. (NIAIST); (Columbia); (Princeton)

2011-12-07

105

Angular distribution of fast neutrons outside iron shielding  

Microsoft Academic Search

where E (g) is the total collision cross section; d is the thickness of the layer. The particles remaining were assigned a weight [2s\\/E](1-P), where ~ is the scattering cross section. Histories were terminated when the particle weight became less than a given quantity, which usually was 0.1% of the penetration probability for unscattered radiation. The angutar neutron spectra outside

I. V. Goryachev; V. A. Dulin; S. M. Ermakov; V. V. kolyzhenkova; A. P. Suvorov; L. A. Trykov

1966-01-01

106

Distribution of elements in biotite-hornblende pairs and in an orthopyroxene-clinopyroxene pair from zoned plutons, northern Sierra Nevada, California  

USGS Publications Warehouse

Distribution of major and minor elements has been determined for five hornblende-biotite pairs from hornblende-biotite quartz diorite and monzotonalite and for a clinopyroxene-orthopyroxene pair from pyroxene diorite collected from the border zones and centers of zoned plutons in the northern Sierra Nevada, California. The distribution coefficients Kd [Mg/Fe] for biotite/hornblende are of the same magnitude (0.61-0.67) for both the mafic border zone and the silicic center. For comparison, KD [Mg/Fe] values for biotite/hornblende from plutonic rocks of the central Sierra Nevada and the southern California batholith were calculated from data published by others. Rocks of the oldest age group (ca. 150 m.y.) in the central Sierra Nevada have an average distribution coefficient, KD, of 0.64, close to the average KD in the study area, where K-Ar dates are 143 to 129 m.y. The intermediate age group has an average KD=0.81, and the youngest group has KD=0.77. KD [Mg/Fe] for biotite/hornblende from the southern California batholith is 0.83, close to the average of the intermediate age group in the central Sierra Nevada. The calculated difference in pressure of crystallization between rocks of the Feather River area and the southern California batholith is 1 kb; the rocks of the Feather River area being crystallized at a higher pressure. This is in good agreement with the low-pressure contact metamorphism in the south (pyroxene hornfels facies), as compared with a medium-pressure metamorphism around the northern plutons, where andalusitesillimanite-cordierite and andalusite-staurolite subfacies of the amphibolite facies indicate pressures of about 4 kb. Trace elements Cr, V, Ni, Co, Ga are distributed equally between biotite and hornblende, whereas Ba and possibly Cu are concentrated in biotite and Sr and Sc and possibly Zr in hornblende. ?? 1971 Springer-Verlag.

Hietanen, A.

1971-01-01

107

J. Mol. Biol. (1975) 91, 101-120 A Neutron Scattering Study of the Distribution of Protein  

E-print Network

J. Mol. Biol. (1975) 91, 101-120 A Neutron Scattering Study of the Distribution of Protein and RNA coli have been measured by neutron scattering experiments on the intact subunit. In addition the radius, 1972; Lutter et al., 1972), and neutron scattering (Engelman & Moore, 1972; Moore et al., 1974

108

Neutron tomographic investigations of water distributions in polymer electrolyte membrane fuel cell stacks  

NASA Astrophysics Data System (ADS)

Neutron tomography was applied to study the 3D water distribution in full polymer electrolyte membrane fuel cell (PEMFC) stacks. The water distribution after switch-off of the fuel cell was analyzed over a period of 36 h. We found a slowly increasing water amount in the fuel cell, but only few changes within a time period of 5 h, which is about the time necessary for neutron tomography. In this way, the requirement for successful tomography was obtained. It is demonstrated how the quasi in-situ tomography technique enables us to study the water content in individual flow field channels of three-fold stacks. Flow field as well as stack design issues are addressed by this visualization method showing weak points due to a non-uniform water distribution that can be identified by means of neutron imaging.

Markötter, Henning; Manke, Ingo; Kuhn, Robert; Arlt, Tobias; Kardjilov, Nikolay; Hentschel, Manfred P.; Kupsch, Andreas; Lange, Axel; Hartnig, Christoph; Scholta, Joachim; Banhart, John

2012-12-01

109

Characterisation of superconducting capillaries for magnetic shielding of twisted-wire pairs in a neutron electric dipole moment experiment  

NASA Astrophysics Data System (ADS)

The cryoEDM neutron electric dipole moment experiment requires a SQUID magnetometry system with pick-up loops inside a magnetically shielded volume connected to SQUID sensors by long (up to 2 m) twisted-wire pairs (TWPs). These wires run outside the main shield, and therefore must run through superconducting capillaries to screen unwanted magnetic pick-up. We show that the average measured transverse magnetic pick-up of a set of lengths of TWPs is equivalent to a loop area of 5.0×10-6 m2/m, or 14 twists per metre. From this we set the requirement that the magnetic shielding factor of the superconducting capillaries used in the cryoEDM system must be greater than 8.0×104. The shielding factor-the ratio of the signal picked-up by an unshielded TWP to that induced in a shielded TWP-was measured for a selection of superconducting capillaries made from solder wire. We conclude the transverse shielding factor of a uniform capillary is greater than 107. The measured pick-up was equal to, or less than that due to direct coupling to the SQUID sensor (measured without any TWP attached). We show that discontinuities in the capillaries substantially impair the magnetic shielding, yet if suitably repaired, this can be restored to the shielding factor of an unbroken capillary. We have constructed shielding assemblies for cryoEDM made from lengths of single core and triple core solder capillaries, joined by a shielded Pb cylinder, incorporating a heater to heat the wires above the superconducting transition as required.

Henry, S.; Pipe, M.; Cottle, A.; Clarke, C.; Divakar, U.; Lynch, A.

2014-11-01

110

Application of gamma-neutron ionization chambers for monitoring the distribution of the neutron flux density, energy release, and energy production in RBMK-1000  

Microsoft Academic Search

A method developed for performing direct measurements of three-dimensional distributions of energy release and energy production\\u000a in RBMK fuel assemblies is described. The method is based on performing measurements with a gamma-neutron chamber and comparing\\u000a the neutron and gamma signals. The results of the measurements of the neutron flux density, energy release, and energy production\\u000a are compared with the values

S. I. Aleksandrov; R. V. Konopatov; V. V. Postnikov; Yu. É. Khandamirov; G. V. Yurkin

2007-01-01

111

Relationship between the Neutron Time Delay Distribution and the Rigidity Spectrum of Primary Cosmic Rays  

NASA Astrophysics Data System (ADS)

Neutron monitors are the premier instruments for precisely tracking time variations in the galactic cosmic ray flux at GeV-range energies above the geomagnetic cutoff at the location of measurement. Recently, a new capability has been developed to record and analyze the neutron time delay distribution (related to neutron multiplicity) to infer variations in the cosmic ray spectrum as well. In particular, we can determine the leader fraction L, defined as the fraction of neutrons that did not follow a previous neutron detection in the same tube from the same nuclear interaction, from time delay histograms. By analyzing data taken during 1995-2007 by a ship-borne neutron monitor latitude survey we confirm a strong dependence of L on the geomagnetic cutoff. We have also developed Monte Carlo simulations of cosmic ray interactions in the atmosphere and in a neutron monitor, and trace cosmic ray trajectories through Earth's magnetic field to model how the cosmic ray spectrum is suppressed at low rigidity at a given geographic location. The simulation results show a variation of L with geomagnetic cutoff as observed by the latitude survey, confirming that these changes in L can reasonably be attributed to changes in the cosmic ray spectrum.

Mangeard, Pierre-Simon; Bieber, John W.; Duldig, Marcus L.; Humble, John E.; Pyle, Roger; Evenson, Paul; Ruffolo, David; Saiz, Alejandro; Nuntiyakul, Waraporn

112

The effect of temperature and control rod position on the spatial neutron flux distribution in the Syrian miniature neutron source reactor  

Microsoft Academic Search

The effect on the spatial neutron flux distribution for both of water and fuel temperature increase as well as the change in the control rod position are presented in the Syrian miniature neutron source reactor (MNSR). The cross-sections of all the reactor components at different temperatures are generated using the WIMSD4 code. These group constants are used then in the

K. Khattab; H. Omar; N. Ghazi

2006-01-01

113

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

2013-06-14

114

Directional Stand-off Detection of Fast Neutrons and Gammas Using Angular Scattering Distributions  

SciTech Connect

We have investigated the response of a DoubleScatter Neutron Spectrometer (DSNS) for sources at long distances (gr than 200 meters). We find that an alternative method for analyzing double scatter data avoids some uncertainties introduced by amplitude measurements in plastic scintillators.Time of flight is used to discriminate between gamma and neutron events, and the kinematic distributions of scattering angles are assumed to apply. Non-relativistic neutrons are most likely to scatter at 45°, while gammas with energies greater than 2 MeV are most likely to be forward scattered. The distribution of scattering angles of fission neutrons arriving from a distant point source generates a 45° cone, which can be back-projected to give the source direction. At the same time, the distribution of Compton-scattered gammas has a maximum in the forward direction, and can be made narrower by selecting events that deposit minimal energy in the first scattering event. We have further determined that the shape of spontaneous fission neutron spectra at ranges gr than 110 m is still significantly different from thecosmic ray background.

Vanier P. e.; Dioszegi, I.; Salwen, C.; Forman, L.

2009-10-25

115

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

SciTech Connect

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.; Shcherbakov, O.A. [Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, 188300 (Russian Federation); Dushin, V.N.; Jakovlev, V.A.; Kalinin, V.A.; Petrov, B.F. [V.G. Khlopin Radium Institute, St. Petersburg, 194021 (Russian Federation); Hambsch, F.-J. [EC-JRC-Institute for Reference Materials and Measurements Retieseweg 111, B-2440, Geel (Belgium); Laptev, A.B. [Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, 188300 (Russian Federation); Japan Nuclear Cycle Development Institute, Tokai-mura, Naka-gun, Ibaraki, 319-1194 (Japan)

2005-05-24

116

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

117

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

118

Structural Study of Poorly Crystalline Layered Manganese Oxides Using the Atomic Pair Distribution Function Technique. Tuesday, November 3, 2009: 11:15 AM  

E-print Network

Structural Study of Poorly Crystalline Layered Manganese Oxides Using the Atomic Pair Distribution. of Delaware, Bear, DE (4)Univ. of Delaware, Newark, DE The atomic pair distribution function (PDF) is a powerful technique to analyze crystal structures of nanoparticulate, poorly crystalline and amorphous

Sparks, Donald L.

119

Effect of water distributions on performances of JARI standard PEFC by using neutron radiography  

Microsoft Academic Search

In order to clarify the effects of water on performances of a Polymer Electrolyte Fuel Cell (PEFC), measurements of water distribution in a Japan Automobile Research Institute (JARI) standard PEFC were carried out by means of neutron radiography. Furthermore, the cell voltage and the pressure drop between inlet and outlet of the air were simultaneously measured. The effects of channel

H. Murakawa; T. Ueda; T. Yoshida; K. Sugimoto; H. Asano; N. Takenaka; K. Mochiki; H. Iikura; R. Yasuda; M. Matsubayashi

2009-01-01

120

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

121

The evolution of the \\\\vec{z} distribution of normal neutron stars in the Galaxy  

Microsoft Academic Search

Under the two initial 1-D one parameter velocity distribution forms (one is normal, the other is exponential), the z direction scale height evolution of normal neutron stars in the Galaxy is studied by numerical simulation. We do statistics for the cases at different time segments, also do statistics for the cumulative cases made of each time segment. The results show

Y.-C. Wei; C.-M. Zhang; Y.-H. Zhao; Q.-H. Peng; X.-J. Wu; J. Wang; Y.-Y. Pan; H.-X. Yin; Y. Yan; T.-S. Yan; H.-J. Tian; A. Esamdin; A. L. Luo; Y. Cai; A. Taani

2010-01-01

122

Spontaneous superfluid unpinning and the inhomogeneous distribution of vortex lines in neutron stars  

NASA Astrophysics Data System (ADS)

The authors study the equation of motion of the pinned superfluid which couples to the crust of neutron stars via thermal vortex creep. An analytical solution can be obtained even when ?cr(r), the maximum value of the lag ?s-?c that can be supported by pinning forces, has large spatial variations. Substantial inhomogeneous distributions of vortex lines will result from this kind of spatial variation. The authors suggest that such structural inhomogeneities in the crust of neutron stars may be responsible for frequent microglitches which lead to pulsar timing noise. Model calculations are compared with observations.

Cheng, K. S.; Pines, D.; Alpar, M. A.; Shaham, J.

1988-07-01

123

Mass distribution in the quasi-mono-energetic neutron-induced fission of 232Th  

NASA Astrophysics Data System (ADS)

The cumulative yields of various fission products in 232Th(n, f) with average neutron energies of 6.35, 8.53 and 10.09 MeV have been determined using an off-line -ray spectrometric technique. The neutron beam was produced from the 7Li(p, n) reaction. From the cumulative fission yields, the mass chain yields were obtained by using charge distribution correction of medium energy. The peak-to-valley () ratio, the average value of light mass (), heavy mass () and the average number of neutrons () at the three different neutron energies of the present work and at other energies from the literature in the 232Th(n, f) reaction were obtained from the mass yield data. The present and the existing literature data in the 232Th(n, f) reaction at various excitation energies were compared with similar data in the 238U(n, f) reaction. The fine structure in the mass yield distribution was interpreted from the point of nuclear structure effect such as shell closure proximity and even-odd effect. The role of standard I and standard II asymmetric mode of fission was discussed. The different types of mass-yield distributions between 232Th(n, f) and 238U(n, f) reactions were explained from different types of the potential energy between the two fissioning systems. The role of excitation energy was also investigated.

Naik, H.; Crasta, Rita; Suryanarayana, S. V.; Prajapati, P. M.; Mulik, V. K.; Shivasankar, B. S.; Jagadeesan, K. C.; Thakare, S. V.; Sharma, S. C.; Goswami, A.

2014-09-01

124

Measurement of thermal neutron fluence distribution with use of 23Na radioactivation around a medical compact cyclotron.  

PubMed

A medical compact cyclotron produces about 10(15) neutrons per day along with 100 GBq of (18)F. Therefore, it is important to establish radiation safety guidelines on residual radioactivity for routine operation, maintenance work, and decommissioning. Thus, we developed a simple method for measuring the thermal neutrons in a cyclotron room. In order to verify the feasibility of our proposed method, we measured the thermal neutron distribution around a cyclotron by using the activation of (23)Na in salt. We installed 78 salt dosimeters in the cyclotron room with a 50 cm mesh. The photopeak of (24)Na was measured, and the neutron flux distribution was estimated. Monitoring the neutron flux distribution in a cyclotron room appears to be useful for not only obtaining an accurate estimate of the distribution of induced radioactivity, but also optimizing the shield design for radiation safety in preparation for the decommissioning process. PMID:20821115

Fujibuchi, Toshioh; Yamaguchi, Ichiro; Kasahara, Tetsuharu; Iimori, Takashi; Masuda, Yoshitada; Kimura, Ken-ichi; Watanabe, Hiroshi; Isobe, Tomonori; Sakae, Takeji

2009-07-01

125

Importance of neutron energy distribution in borehole activation analysis in relatively dry, low-porosity rocks  

USGS Publications Warehouse

To evaluate the importance of variations in the neutron energy distribution in borehole activation analysis, capture gamma-ray measurements were made in relatively dry, low-porosity gabbro of the Duluth Complex. Although sections of over a meter of solid rock were encountered in the borehole, there was significant fracturing with interstitial water leading to a substantial variation of water with depth in the borehole. The linear-correlation coefficients calculated for the peak intensities of several elements compared to the chemical core analyses were generally poor throughout the depth investigated. The data suggest and arguments are given which indicate that the variation of the thermal-to-intermediate-to-fast neutron flux density as a function of borehole depth is a serious source of error and is a major cause of the changes observed in the capture gamma-ray peak intensities. These variations in neutron energy may also cause a shift in the observed capture gamma-ray energy.

Senftle, F.E.; Moxham, R.M.; Tanner, A.B.; Philbin, P.W.; Boynton, G.R.; Wager, R.E.

1977-01-01

126

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

127

Study on detecting spatial distribution of neutrons and gamma rays using a multi-imaging plate system.  

PubMed

In order to measure the spatial distributions of neutrons and gamma rays separately using the imaging plate, the requirement for the converter to enhance specific component was investigated with the PHITS code. Consequently, enhancing fast neutrons using recoil protons from epoxy resin was not effective due to high sensitivity of the imaging plate to gamma rays. However, the converter of epoxy resin doped with (10)B was found to have potential for thermal and epithermal neutrons, and graphite for gamma rays. PMID:24485172

Tanaka, Kenichi; Sakurai, Yoshinori; Endo, Satoru; Takada, Jun

2014-06-01

128

Neutron emission effects on fragment mass and kinetic energy distribution from fission of 239{sup Pu} induced by thermal neutrons  

SciTech Connect

The average of fragment kinetic energy (E-bar sign*) and the multiplicity of prompt neutrons ({nu}(bar sign)) as a function of fragment mass (m*), as well as the fragment mass yield (Y(m*)) from thermal neutron-induced fission of {sup 239}Pu have been measured by Tsuchiya et al.. In that work the mass and kinetic energy are calculated from the measured kinetic energy of one fragment and the difference of time of flight of the two complementary fragments. However they do not present their results about the standard deviation {sigma}{sub E}*(m*). In this work we have made a numerical simulation of that experiment which reproduces its results, assuming an initial distribution of the primary fragment kinetic energy (E(A)) with a constant value of the standard deviation as function of fragment mass ({sigma}{sub E}(A)). As a result of the simulation we obtain the dependence {sigma}{sub E}*(m*) which presents an enhancement between m* = 92 and m* = 110, and a peak at m* = 121.

Montoya, M. [Instituto Peruano de Energia Nuclear, Av. Canada 1470, Lima 41 (Peru); Facultad de Ciencias, Universidad Nacional de Ingenieria, Av. Tupac Amaru 210, Apartado 31-139, Lima (Peru); Rojas, J. [Instituto Peruano de Energia Nuclear, Av. Canada 1470, Lima 41 (Peru); Facultad de Ciencias Fisicas, Universidad Nacional Mayor de San Marcos, Av. Venezuela Cdra 34, Apartado Postal 14-0149, Lima 1 (Peru); Lobato, I. [Facultad de Ciencias, Universidad Nacional de Ingenieria, Av. Tupac Amaru 210, Apartado 31-139, Lima (Peru)

2010-08-04

129

The Distribution of Pairs of Quadratic Residues and Nonresidues of a Special Form  

NASA Astrophysics Data System (ADS)

Nontrivial estimates are obtained for sums of Legendre symbols of a quadratic polynomial over primes in an arithmetic progression. These estimates are used to prove a theorem concerning the number of pairs of the form (p + a, p + b), p \\equiv l (\\operatorname{mod} k), p\\le N, for which p + a is a quadratic residue (nonresidue), p + b is a quadratic residue (nonresidue) modulo the prime q, and N > k^3q^{0.75+\\varepsilon}. Bibliography: 27 titles.

Karatsuba, A. A.

1988-04-01

130

Angular distribution of products of ternary nuclear fission induced by cold polarized neutrons  

NASA Astrophysics Data System (ADS)

Within quantum fission theory, angular distributions of products originating from the ternary fission of nuclei that is induced by polarized cold and thermal neutrons are investigated on the basis of a nonevaporative mechanism of third-particle emission and a consistent description of fission-channel coupling. It is shown that the inclusion of Coriolis interaction both in the region of the discrete and in the region of the continuous spectrum of states of the system undergoing fission leads to T-odd correlations in the aforementioned angular distributions. The properties of the TRI and ROT effects discovered recently, which are due to the interference between the fission amplitudes of neutron resonances, are explored. The results obtained here are compared with their counterparts from classic calculations based on the trajectory method.

Bunakov, V. E.; Kadmensky, S. G.; Kadmensky, S. S.

2008-11-01

131

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

132

Field validation of a cosmic-ray neutron sensor using a distributed sensor network1 Trenton E. Franz*  

E-print Network

Field validation of a cosmic-ray neutron sensor using a distributed sensor network1 Trenton E availability of such6 data is inadequate. Here, we present a comparison of two datasets that provide average7 is from a cosmic-ray neutron sensor placed at the center of10 the study area. We find the cosmic

Zreda, Marek

133

3D mapping of crystallographic phase distribution using energy-selective neutron tomography.  

PubMed

Nondestructive 3D mapping of crystallographic phases is introduced providing distribution of phase fractions within the bulk (centimeter range) of samples with micrometer-scale resolution. The novel neutron tomography based technique overcomes critical limitations of existing techniques and offers a wide range of potential applications. It is demonstrated for steel samples exhibiting phase transformation after being subjected to tensile and torsional deformation. PMID:24692200

Woracek, Robin; Penumadu, Dayakar; Kardjilov, Nikolay; Hilger, Andre; Boin, Mirko; Banhart, John; Manke, Ingo

2014-06-25

134

Use of the diffusion approximation to calculate spatial and energy distributions of fast neutrons  

Microsoft Academic Search

In the design of biological shielding wide use is made of methods based on solution of the kinetic equation in low-order approximations employing spherical harmonics, together with a correction for the spatial distribution of the group of fast neutrons with energy E > 1.4 to 2.0 MeV. This correction is determined either by integrating over the source volume using experimentally

N. A. Artem'eva; D. L. Broder; G. Yu. Nikol'skii; K. K. Popkov

1974-01-01

135

Energy Distribution of Mass97 Fission Fragments from Thermal-Neutron Fission of Uranium235  

Microsoft Academic Search

The energy distribution of mass-97 fragments from thermal neutron induced fission of U235 was measured with a high-resolution magnetic spectrograph. The fragments originate in a thin plating of U235 near the center of the Oak Ridge National Laboratory graphite reactor and travel 16 feet to a wedge magnet which analyzes and focuses them at the focal plane 6 feet beyond.

Bernard L. Cohen; Anna Foner Cohen; Charles D. Coley

1956-01-01

136

Polarized and unpolarized $?$-pair meson-induced Drell--Yan production and the pion distribution amplitude  

E-print Network

We present a detailed analysis of meson-induced massive lepton (muon) Drell--Yan production for the process $\\pi^{-}N\\to\\mu^{+}\\mu^{-}X$, considering both an unpolarized nucleon target and longitudinally polarized protons. Using a QCD framework, we focus on the angular distribution of $\\mu^+$, which is sensitive to the shape of the pion distribution amplitude, the goal being to test corresponding results against available experimental data. Predictions are made, employing various pion distribution amplitudes, for the azimuthal angle dependence of the $\\mu^{+}$ distribution in the polarized case, relevant for the planned COMPASS experiment. QCD evolution is given particular attention in both considered cases.

A. P. Bakulev; N. G. Stefanis; O. V. Teryaev

2007-06-28

137

Stokes and anti-Stokes differential pulse pair based distributed Brillouin fiber sensor with double-sideband probe wave.  

PubMed

We propose and demonstrate a distributed Brillouin fiber sensor using Stokes and anti-Stokes differential pulse pair based on double- sideband probe wave, in which the two sidebands of probe wave are used to balance the power of two pump pulses. The spatial resolution is determined by the slightly width difference of the two balanced pulses, without Brillouin gain spectrum broadening. The pulses perform gain-loss process in optical field before the probe signal being detected, without any post-processing or extra measurement time. The proposed technique can achieve high spatial resolution, natural Brillouin gain spectrum linewidth, normal measurement time and long sensing range simultaneously. PMID:24663580

Yang, Zhisheng; Hong, Xiaobin; Guo, Hongxiang; Wu, Jian; Lin, Jintong

2014-02-10

138

Empirical Bayesian analysis of paired high-throughput sequencing data with a beta-binomial distribution  

E-print Network

coordinately up-regulated in a compendium of mouse embryonic stem cells (ESC) which are shared with the human ESC-like module. 2.22E-16 LI_WILMS_TUMOR_VS_FETAL_KIDNEY _1_DN Genes down-regulated in Wilm's tumor samples compared to fetal kidney. 4.44E-16... of interest in a systematic review of head and neck squamous cell carcinoma transcripts, as ranked by their likelihood of showing differential expression of any kind in the Tuch et al (2010) data. RefSeq ID Gene Symbol Sample Pair 1 (Normal:Tumor...

Hardcastle, Thomas J; Kelly, Krystyna A

2013-04-23

139

High Resolution Quantitative Auto-Radiography to determine microscopic distributions of B-10 in neutron capture therapy  

E-print Network

The success of Boron Neutron Capture Therapy (BNCT) is heavily dependent on the microscopic distribution of B-10 in tissue. High Resolution Quantitative Auto-Radiography (HRQAR) is a potentially valuable analytical tool ...

Harris, Thomas C. (Thomas Cameron)

2006-01-01

140

Experimental and Monte-Carlo studies of the spatial distribution of neutrons around extended Pb-spallation target  

Microsoft Academic Search

The spatial distribution of thermal and fast neutrons on the surface of a paraffin moderator surrounding a cylindrical lead target, irradiated with 1GeV protons was studied. The lead target had 8cm diameter and 20cm length. The thickness of the paraffin around the target was 6cm. The slow and fast neutron distributions were determined using LR 115 2B and CR-39 detectors

S. R. Hashemi-Nezhad; R. Brandt; W. Westmeier; R. Odoj; Kh. M. Hella; M. I. Krivopustov; B. A. Kulakov; A. N. Sosnin

2003-01-01

141

The influence of the deviation from the equilibrium deuteron distribution on the neutron spectra in linear pinch geometries  

NASA Astrophysics Data System (ADS)

In order to analyze the influence of the deviation from the equilibrium distribution of the fast deuterons on the neutron spectrum, the limiting case, corresponding to a two dimensional monoenergetic deuteron distribution, was studied. The appearance of a pronounced peak in the side-on spectra at neutron energy = 2.5 MeV is noted. There is good agreement between theory and experiment, if relaxation processes are taken into account.

Deutsch, R.; Herold, H.; Kaeppeler, H. J.; Schmidt, H.

1982-07-01

142

Measurement of momentum distribution of lightatoms and molecules in condensed matter systems using inelastic neutron scattering  

NASA Astrophysics Data System (ADS)

Studies of single-particle momentum distributions in light atoms and molecules are reviewed with specific emphasis on experimental measurements using the deep inelastic neutron scattering technique at eV energies. The technique has undergone a remarkable development since the mid-1980s, when intense fluxes of epithermal neutrons were made available from pulsed neutron sources. These types of measurements provide a probe of the short-time dynamics of the recoiling atoms or molecules as well as information on the local structure of the materials. The paper introduces both the theoretical framework for the interpretation of deep inelastic neutron scattering experiments and thoroughly illustrates the physical principles underlying the impulse approximation from light atoms and molecules. The most relevant experimental studies performed on a variety of condensed matter systems in the last 20 years are reviewed. The experimental technique is critically presented in the context of a full list of published work. It is shown how, in some cases, these measurements can be used to extract directly the effective Born Oppenheimer potential. A summary of the progress made to date in instrument development is also provided. Current data analysis and the interpretation of the results for a variety of physical systems is chosen to illustrate the scope and power of the method. The review ends with a brief consideration of likely developments in the foreseeable future. Particular discussion is given to the use of the VESUVIO spectrometer at ISIS.

Andreani, C.; Colognesi, D.; Mayers, J.; Reiter, G. F.; Senesi, R.

143

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

144

Neutron capture autoradiographic determination of 10B distributions and concentrations in biological samples for boron neutron capture therapy  

NASA Astrophysics Data System (ADS)

It is necessary for effective boron neutron capture therapy (BNCT) to accumulate 10B atoms in the tumor cells. We prepared a cationic liposome entrapped 10B compound for the delivery system and examined the delivery capacity of 10B atoms to pancreatic cancer cell, AsPC-1, in vivo. It is required to achieve an accurate measurement of 10B distributions and concentrations in biological samples with a sensitivity in the ppm range for BNCT. We applied CR-39 (polyallyldiglycol carbonate) plastic track detectors to ?-autoradiographic measurements of the 10B biodistribution in sliced whole-body samples of mice. To selectively desensitize undesirable proton tracks, we applied PEW (KOH+C 2H 5OH+H 2O) solution to the etching of CR-39 detector. The subsequent use of an alpha-track radiographic image analysis system enabled a discrimination between alpha tracks and recoiled proton tracks by the track size selection method. This enabled us to estimate quantitatively the distributions of 10B concentrations within the tissue sections by comparing with suitable standards.

Yanagie, Hironobu; Ogura, Koichi; Matsumoto, Toshio; Eriguchi, Masazumi; Kobayashi, Hisao

1999-11-01

145

Tomographic analysis of neutron and gamma pulse shape distributions from liquid scintillation detectors at Joint European Torus  

SciTech Connect

The Joint European Torus (JET, Culham, UK) is the largest tokamak in the world devoted to nuclear fusion experiments of magnetic confined Deuterium (D)/Deuterium-Tritium (DT) plasmas. Neutrons produced in these plasmas are measured using various types of neutron detectors and spectrometers. Two of these instruments on JET make use of organic liquid scintillator detectors. The neutron emission profile monitor implements 19 liquid scintillation counters to detect the 2.45 MeV neutron emission from D plasmas. A new compact neutron spectrometer is operational at JET since 2010 to measure the neutron energy spectra from both D and DT plasmas. Liquid scintillation detectors are sensitive to both neutron and gamma radiation but give light responses of different decay time such that pulse shape discrimination techniques can be applied to identify the neutron contribution of interest from the data. The most common technique consists of integrating the radiation pulse shapes within different ranges of their rising and/or trailing edges. In this article, a step forward in this type of analysis is presented. The method applies a tomographic analysis of the 3-dimensional neutron and gamma pulse shape and pulse height distribution data obtained from liquid scintillation detectors such that n/? discrimination can be improved to lower energies and additional information can be gained on neutron contributions to the gamma events and vice versa.

Giacomelli, L. [JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom) [JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Department of Physics, Università degli Studi di Milano-Bicocca, Milano (Italy); Conroy, S. [JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom) [JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Department of Physics and Astronomy, Uppsala University, Uppsala (Sweden); Gorini, G. [Department of Physics, Università degli Studi di Milano-Bicocca, Milano (Italy)] [Department of Physics, Università degli Studi di Milano-Bicocca, Milano (Italy); Horton, L.; Murari, A.; Popovichev, S.; Syme, D. B. [JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom)] [JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom)

2014-02-15

146

Monte Carlo simulation of depth dose distribution in several organic models for boron neutron capture therapy  

NASA Astrophysics Data System (ADS)

Monte Carlo simulations are performed to evaluate depth-dose distributions for possible treatment of cancers by boron neutron capture therapy (BNCT). The ICRU computational model of ADAM & EVA was used as a phantom to simulate tumors at a depth of 5 cm in central regions of the lungs, liver and pancreas. Tumors of the prostate and osteosarcoma were also centered at the depth of 4.5 and 2.5 cm in the phantom models. The epithermal neutron beam from a research reactor was the primary neutron source for the MCNP calculation of the depth-dose distributions in those cancer models. For brain tumor irradiations, the whole-body dose was also evaluated. The MCNP simulations suggested that a lethal dose of 50 Gy to the tumors can be achieved without reaching the tolerance dose of 25 Gy to normal tissue. The whole-body phantom calculations also showed that the BNCT could be applied for brain tumors without significant damage to whole-body organs.

Matsumoto, T.

2007-09-01

147

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

148

Microscopic calculations on pair-condensed states of infinite fermi systems  

Microsoft Academic Search

An analysis of the spatial correlations in the BCS pair-condensed state of strongly interacting Fermi systems is presented. The short-range correlations among the particles are described by state-independent correlations of the Jastrow type. Preliminary results of the Fermi hypernetted chain (FHNC) evaluation of the radial distribution function, the one-particle momentum distribution and the pair distribution of neutron and nuclear matter

S. Fantoni; W. Germany

1981-01-01

149

Optimal prefix codes for pairs of geometrically-distributed random variables  

E-print Network

-called two-dimensional geometric distributions are parameter-singular, in the sense that a prefix code contrast to the one-dimensional case, where codes are optimal for positive-length intervals of the parameter q. Thus, in the two-dimensional case, it is infeasible to give a compact characterization

Bassino, Frédérique

150

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

SciTech Connect

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 et al. [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.; Tanir, G. [Gazi University, Faculty of Art and Science, Department of Physics, Ankara (Turkey); Aydin, A. [Kirikkale University, Faculty of Art and Science, Department of Physics, Kirikkale (Turkey)

2007-03-15

151

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

152

Proton-Neutron Pairing Correlations in the Self-Conjugate Nucleus K38 Probed via a Direct Measurement of the Isomer Shift  

NASA Astrophysics Data System (ADS)

A marked difference in the nuclear charge radius was observed between the I?=3+ ground state and the I?=0+ isomer of K38 and is qualitatively explained using an intuitive picture of proton-neutron pairing. In a high-precision measurement of the isomer shift using bunched-beam collinear laser spectroscopy at CERN-ISOLDE, a change in the mean-square charge radius of ?rc2?(38Km)-?rc2?(38Kg)=0.100(6) fm2 was obtained. This is an order of magnitude more accurate than the result of a previous indirect measurement from which it was concluded that both long-lived states in K38 have similar charge radii. Our observation leads to a substantially different understanding since the difference in charge radius is, moreover, opposite in sign to previously reported theoretical predictions. It is demonstrated that the observed isomer shift can be reproduced by large-scale shell-model calculations including proton and neutron excitations across the N ,Z=20 shell gaps, confirming the significance of cross-shell correlations in the region of Ca40.

Bissell, M. L.; Papuga, J.; Naïdja, H.; Kreim, K.; Blaum, K.; De Rydt, M.; Garcia Ruiz, R. F.; Heylen, H.; Kowalska, M.; Neugart, R.; Neyens, G.; Nörtershäuser, W.; Nowacki, F.; Rajabali, M. M.; Sanchez, R.; Sieja, K.; Yordanov, D. T.

2014-08-01

153

Charge distribution, neutron evaporation, and energy distribution in higher energy binary fission  

Microsoft Academic Search

A computational procedure based on the order-disorder model for predicting independent yields of fission products in higher energy fission is described. Based on the experimental observation that increase in excitation energy of the compound nucleus is used up only in exciting the fragments resulting from fission, a scheme for the distribution of extra excitation between the fragments has been evolved.

D. N. Sharma; M. R. Iyer; A. K. Ganguly

1976-01-01

154

REDETERMINATION OF THE CATION DISTRIBUTION OF SPINEL (MgAl2O4) BY MEANS OF NEUTRON DIFFRACTION  

E-print Network

447. REDETERMINATION OF THE CATION DISTRIBUTION OF SPINEL (MgAl2O4) BY MEANS OF NEUTRON DIFFRACTION The cation distribution of synthetic spinel powder of grain size ~ 50 03BC was redeter- mined by means. The lattice parameter of the unit cell amounts to 8.0832 A, and there are eight molecules per cell. The spinel

Paris-Sud XI, Université de

155

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

2010-03-01

156

Application of total X-ray scattering methods and pair distribution function analysis for study of structure of biominerals.  

PubMed

Total X-ray scattering and pair distribution function (PDF) analysis, using a high-energy synchrotron source, allow direct study of the short- and intermediate-range structure that distinguish amorphous, structurally disordered, and nanocrystalline biominerals. For such samples in which diffuse scatter is a significant component, care must be taken in the experimental procedures to optimize data quality and extract the useful signal necessary to calculate the PDF. General methods are described for data collection and processing, including commonly used software programs. Methods for analysis and interpretation of PDFs are presented, including direct real-space refinement and reverse Monte Carlo methods. Greater application of PDFs to amorphous and poorly crystallized biominerals will provide new insight into structure, especially over length scales that are not probed by other techniques. The rapid data collection available at synchrotron facilities also allows in situ kinetic studies of reactions involving biominerals. PMID:24188779

Reeder, Richard J; Michel, F Marc

2013-01-01

157

Quantitative size-dependent structure and strain determination of CdSe nanoparticles using atomic pair distribution function analysis  

E-print Network

The size-dependent structure of CdSe nanoparticles, with diameters ranging from 2 to 4 nm, has been studied using the atomic pair distribution function (PDF) method. The core structure of the measured CdSe nanoparticles can be described in terms of the wurtzite atomic structure with extensive stacking faults. The density of faults in the nanoparticles ~50% . The diameter of the core region was extracted directly from the PDF data and is in good agreement with the diameter obtained from standard characterization methods suggesting that there is little surface amorphous region. A compressive strain was measured in the Cd-Se bond length that increases with decreasing particle size being 0.5% with respect to bulk CdSe for the 2 nm diameter particles. This study demonstrates the size-dependent quantitative structural information that can be obtained even from very small nanoparticles using the PDF approach.

A. S. Masadeh; E. Bozin; C. L. Farrow; G. Paglia; P. Juhas; A. Karkamkar; M. G. Kanatzidis; S. J. L. Billinge

2007-08-03

158

Muscle-Pair Specific Distribution and Grip-Type Modulation of Neural Common Input to Extrinsic Digit Flexors  

PubMed Central

To gain insight into the synergistic control of hand muscles, we have recently quantified the strength of correlated neural activity across motor units from extrinsic digit flexors during a five-digit object-hold task. We found stronger synchrony and coherence across motor units from thumb and index finger flexor muscle compartment than between the thumb flexor and other finger flexor muscle compartments. The present study of two-digit object hold was designed to determine the extent to which such distribution of common input among thumb-finger flexor muscle compartments, revealed by holding an object with five digits, is preserved when varying the functional role of a given digit pair. We recorded normal force exerted by the digits and electrical activity of single motor units from muscle flexor pollicis longus (FPL) and two compartments of the m. flexor digitorum profundus (FDP2 and FDP3; index and middle finger, respectively). Consistent with our previous results from five-digit grasping, synchrony and coherence across motor units from FPL-FDP2 was significantly stronger than in FPL-FDP3 during object hold with two digits [common input strength: 0.49 ± 0.02 and 0.35 ± 0.02 (means ± SE), respectively; peak coherence: 0.0054 and 0.0038, respectively]. This suggests that the distribution of common neural input is muscle-pair specific regardless of grip type. However, the strength of coherence, but not synchrony, was significantly stronger in two- versus five-digit object hold for both muscle combinations, suggesting the periodicity of common input is sensitive to grip type. PMID:16723414

Winges, Sara A.; Johnston, Jamie A.; Santello, Marco

2007-01-01

159

Quantum key distribution using a series of quantum correlated photon pairs  

SciTech Connect

The differential-phase-shift quantum key distribution (DPS-QKD) is a recently proposed QKD scheme in which a pulse train is transmitted through a quantum channel. This paper extends the ideal of the DPS-QKD to entanglement-based systems. Two schemes are presented. In one, an entanglement source sends pulse trains of signal and idler to two parties (Alice and Bob), respectively, who phase-modulate the incoming pulses and receive them after one-bit delay interferometers. In the other, two entanglement sources are prepared, one between Alice and a repeating node (Charlie) and one between Charlie and Bob, which send signal and idler pulse trains to Alice and Bob and Charlie, respectively. These schemes offer a longer distance between Alice and Bob than the conventional DPS-QKD.

Inoue, Kyo [NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi, 243-0198 (Japan)

2005-03-01

160

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

161

Competition of proton and neutron pair breakings: High-spin structures of $^{124-127}$Te isotopes  

E-print Network

In the present work recently available experimental data for high-spin states of four nuclei, $^{124}_{\\ 52}$Te, $^{125}_{\\ 52}$Te, $^{126}_{\\ 52}$Te, and $^{127}_{\\ 52}$Te have been interpreted using state-of-the-art shell model calculations. The calculations have been performed in the 50-82 valence shell composed of $1g_{7/2}$, $2d_{5/2}$, $1h_{11/2}$, $3s_{1/2}$, and $2d_{3/2}$ orbitals. We have compared our results with the available experimental data for excitation energies and transition probabilities, including high-spin states. The results are in reasonable agreement with the available experimental data. The wave functions, particularly, the specific proton and neutron configurations which are involved to generate the angular momentum along the yrast lines are discussed.

Vikas Kumar; P. C. Srivastava; M. J. Ermamatov; Irving O. Morales

2014-12-28

162

22.101 Applied Nuclear Physics (Fall 2006) Lecture 18 (11/20/06) Neutron Interactions: Energy and Angular Distributions, Thermal Motions  

E-print Network

We will use the expressions relating energy and scattering angles derived in the previous chapter to determine the energy and angular distributions of an elastically scattered neutron. The energy distribution, in particular, is widely used in the analysis of neutron energy moderation in systems where neutrons are produced at high energies (Mev) by nuclear reactions and slow down to thermal energies. This is the problem of neutron slowing down, where the assumption of the target nucleus being initially at rest is justified. When the neutron energy approaches the thermal region ( ~ 0.025 ev), the stationary target assumption is no longer valid. One can relax this assumption and derive a more general distribution which holds for neutron elastic scattering at any energy. This then is the result that should be used for the analysis of the spectrum (energy distribution) of thermal neutrons, a problem known as neutron thermalization. As part of this discussion we will have an opportunity to study the energy dependence of the elastic scattering cross section. We have seen from our study of cross section calculation using the method of phase shift that for low-energy scattering (kro << 1, which is equivalent to neutron energies below about 10-100 kev) only s-wave contribution to the cross section is important, and moreover, the angular distribution of the scattered neutron is spherically symmetric in CMCS. This is the result that we will make use of in deriving the energy distribution of the elastically scattered neutron.

unknown authors

163

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

164

Mode-distribution analysis of quasielastic neutron scattering and application to liquid water.  

PubMed

A quasielastic neutron scattering (QENS) experiment is a particular technique that endeavors to define a relationship between time and space for the diffusion dynamics of atoms and molecules. However, in most cases, analyses of QENS data are model dependent, which may distort attempts to elucidate the actual diffusion dynamics. We have developed a method for processing QENS data without a specific model, wherein all modes can be described as combinations of the relaxations based on the exponential law. By this method, we can obtain a distribution function B(Q,?), which we call the mode-distribution function (MDF), to represent the number of relaxation modes and distributions of the relaxation times in the modes. The deduction of MDF is based on the maximum entropy method and is very versatile in QENS data analysis. To verify this method, reproducibility was checked against several analytical models, such as that with a mode of distributed relaxation time, that with two modes closely located, and that represented by the Kohlrausch-Williams-Watts function. We report the first application to experimental data of liquid water. In addition to the two known modes, the existence of a relaxation mode of water molecules with an intermediate time scale has been discovered. We propose that the fast mode might be assigned to an intermolecular motion and the intermediate motion might be assigned to a rotational motion of the water molecules instead of to the fast mode. PMID:23848682

Kikuchi, Tatsuya; Nakajima, Kenji; Ohira-Kawamura, Seiko; Inamura, Yasuhiro; Yamamuro, Osamu; Kofu, Maiko; Kawakita, Yukinobu; Suzuya, Kentaro; Nakamura, Mitsutaka; Arai, Masatoshi

2013-06-01

165

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

166

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

167

Macroscopic geometric heterogeneity effects in radiation dose distribution analysis for boron neutron capture therapy  

SciTech Connect

Calculations of radiation flux and dose distributions for boron neutron capture therapy (BNCT) of brain tumors are typically performed using sophisticated three-dimensional analytical models based on either a homogeneous approximation or a simplified few-region approximation to the actual highly heterogeneous geometry of the irradiation volume. Such models should be validated by comparison with calculations using detailed models in which all significant macroscopic tissue heterogeneities and geometric structures are explicitly represented as faithfully as possible. This paper describes such a validation exercise for BNCT of canine brain tumors. Geometric measurements of the canine anatomical structures of interest for this work were performed by dissecting and examining two essentially identical Labrador retriever heads. Chemical analyses of various tissue samples taken during the dissections were conducted to obtain measurements of elemental compositions for the tissues of interest. The resulting geometry and tissue composition data were then used to construct a detailed heterogeneous calculational model of the Labrador head. Calculations of three-dimensional radiation flux distributions pertinent to BNCT were performed for this model using the TORT discrete-ordinates radiation transport code. The calculations were repeated for a corresponding volume-weighted homogeneous-tissue model. Comparison of the results showed that peak neutron and photon flux magnitudes were quite similar for the two models (within 5%), but that the spatial flux profiles were shifted in the heterogeneous model such that the fluxes in some locations away from the peak differed from the corresponding fluxes in the homogeneous model by as much as 10%--20%. Differences of this magnitude can be therapeutically significant, emphasizing the need for proper validation of simplified treatment planning models.

Moran, J.M.; Nigg, D.W.; Wheeler, F.J.; Bauer, W.F. (Idaho National Engineering Laboratory, EG G Idaho, Inc., P.O. Box 1625, Idaho Falls, Idaho 83415-3515 (United States))

1992-05-01

168

A Numerical Method for Obtaining Monoenergetic Neutron Flux Distributions and Transmissions in Multiple-Region Slabs  

NASA Technical Reports Server (NTRS)

This method is investigated for semi-infinite multiple-slab configurations of arbitrary width, composition, and source distribution. Isotropic scattering in the laboratory system is assumed. Isotropic scattering implies that the fraction of neutrons scattered in the i(sup th) volume element or subregion that will make their next collision in the j(sup th) volume element or subregion is the same for all collisions. These so-called "transfer probabilities" between subregions are calculated and used to obtain successive-collision densities from which the flux and transmission probabilities directly follow. For a thick slab with little or no absorption, a successive-collisions technique proves impractical because an unreasonably large number of collisions must be followed in order to obtain the flux. Here the appropriate integral equation is converted into a set of linear simultaneous algebraic equations that are solved for the average total flux in each subregion. When ordinary diffusion theory applies with satisfactory precision in a portion of the multiple-slab configuration, the problem is solved by ordinary diffusion theory, but the flux is plotted only in the region of validity. The angular distribution of neutrons entering the remaining portion is determined from the known diffusion flux and the remaining region is solved by higher order theory. Several procedures for applying the numerical method are presented and discussed. To illustrate the calculational procedure, a symmetrical slab ia vacuum is worked by the numerical, Monte Carlo, and P(sub 3) spherical harmonics methods. In addition, an unsymmetrical double-slab problem is solved by the numerical and Monte Carlo methods. The numerical approach proved faster and more accurate in these examples. Adaptation of the method to anisotropic scattering in slabs is indicated, although no example is included in this paper.

Schneider, Harold

1959-01-01

169

Invariant Mass Distribution of Jet Pairs Produced in Association with a W boson in pp? Collisions at ?s= 1.96 TeV  

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 4.3 fb-1. The observed distribution has an excess in the 120-160 GeV/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 [Helsinki Inst. of Phys.; Alvarez Gonzalez, B [Oviedo U.; Cantabria Inst. of Phys.; Amerio, S [INFN, Padua; Amidei, D [Michigan U.; Anastassov, A [Northwestern U.; Annovi, A [Frascati; Antos, J [Comenius U.; Apollinari, G [Fermilab; Appel, J A [Fermilab; Apresyan, A [Purdue U.; Arisawa, T [Waseda U.; Dubna, JINR

2011-04-28

170

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

171

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

172

Pore distributions in nanocrystalline metals from small-angle neutron scattering  

SciTech Connect

Recent upgrades in inert-gas condensation processing equipment have produced nanocrystalline metal samples with high densities and low-impurity levels. Typical Cu and Pd samples have densities {ge}98% of theoretical and oxygen and hydrogen impurity concentrations {le}0.5 at. %. Lower porosity and impurity levels may make it difficult to produce and maintain samples with the smallest nanocrystalline grain sizes. These improved samples were studied by small-angle neutron scattering (SANS) to determine the volume fraction and size distribution of pores. Excellent correlation was obtained between the total volume fraction of pores and the Archimedes density for Pd, signifying that most of the pores were relatively small and in the detectability range of SANS ({approx}1--100 nm). Nanocrystalline Cu is shown to exhibit a wider pore size distribution. For Pd, the average pore sizes were slightly smaller than the average grain size, while for Cu the pore size and grain size were about the same. Both materials exhibited a trend of increasing pore size with increasing grain size. In terms of processing prerequisites, the principal condition for the production of high-density nanocrystalline Cu is an exceptionally clean synthesis environment, while nanocrystalline Pd requires compaction at elevated temperatures. These differences are the result of Cu having both a lower melting point and a greater susceptibility to contamination by gaseous impurities such as oxygen.

Sanders, P.G.; Weertman, J.R. [Northwestern Univ., Evanston, IL (United States). Materials Science and Engineering Dept.] [Northwestern Univ., Evanston, IL (United States). Materials Science and Engineering Dept.; Eastman, J.A. [Argonne National Lab., IL (United States). Materials Science Div.] [Argonne National Lab., IL (United States). Materials Science Div.

1998-07-24

173

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

2011-05-01

174

Relationship between electron delocalization and asymmetry of the pair distribution function as determined by x-ray absorption spectroscopy  

NASA Astrophysics Data System (ADS)

Electron delocalization, whether over an entire solid or a local environment of a few atoms, contributes to many macroscopic properties of materials, including conductivity, malleability, ductility, optical properties, and chemical reactivity. Despite its importance, few existing techniques can directly determine the degree of delocalization within a particular bond. In this work, it is hypothesized that, for otherwise similar systems, asymmetry in the pair distribution function (PDF) as determined by extended x- ray absorption fine structure (EXAFS) spectroscopy is correlated to the degree of electron delocalization. The accuracy of using EXAFS curve-fitting with theoretical standards to determine the asymmetry of the PDF is first established by finding thermal expansion, harmonic Debye-Waller factor, and EXAFS third cumulant for two FCC metals, nickel and copper. The results yield a temperature dependence that agrees well with theory, although the third cumulant shows an offset that indicates that absolute values determined by this method are not reliable. Fortunately, only relative values, which appear to be quite accurate, are necessary for exploring the hypothesis presented. The technique is then used to find the bond responsible for the semiconductor-metal transition of titanium sesquioxide, to establish the presence of charge-transfer in solid iodine, and to rank the relative amount of stabilizing charge available to the carbon-bromine bond of butyl bromide isomers. In the latter case, the role of hyperconjugation and the inductive effect is discussed. In all cases, the EXAFS third cumulant is found to increase with increasing electron delocalization for systems that are otherwise similar. General considerations of EXAFS analysis are also discussed, including background subtraction, constraint schemes for multiple-scattering paths, the effects of the finite and discrete Fourier transforms used, and the effects of sample inhomogeneity.

Calvin, Scott

175

Spatial distribution of nonemissive metastables in a two-frequency capacitively coupled plasma in Ar by using a pair of optical emission lines  

SciTech Connect

When a pair of short- and long-lived excited molecules are coupled with an upper radiative state, it will be possible to derive the number density of the long-lived species from the optical emission spectroscopy of upper-level short-lived species by careful selection of the pair. Two-dimensional density distributions of the long-lived metastable state Ar(1s{sub 5}) and that of the short-lived excited state Ar(2p{sub 2}) are observed and compared in the time-averaged form, using a computerized tomography technique of the emissions from a pair of optical transitions in a two-frequency capacitively coupled plasma in pure Ar.

Ohba, Tomihito; Makabe, Toshiaki [Department of Electronics and Electrical Engineering, Faculty of Science and Technology, Keio University, 3-14-1-Hiyoshi, Yokohama 223-8522 (Japan)

2010-03-15

176

Pairing forces in nuclei  

SciTech Connect

In this contribution, the author mentions some features of pairing forces that are unique to nuclei and cover some areas of major interest in nuclear structure research, that involve pairing. At the level of most nuclear structure studies, nuclei are treated as consisting of two kinds of fermions (protons and neutrons) in a valence space with rather few levels. These features give rise to unique aspects of pairing forces in nuclei: (1) n-p pairing in T = 0 as well as the usual T = 1 pairing that is characteristic of like fermions; (2) a need to correct pairing calculations for the (1/N) effects that can typically be neglected in superconducting solids. An issue of current concern is the nature of the pairing interaction: several recent studies suggest a need for a density dependent form of the pairing interaction. There is a good deal of feedback between the questions of accurate calculations of pairing interactions and the form and magnitude of the pairing interaction. Finally, the authors discuss some many-body wave functions that are a generalization of the BCS wave function form, and apply them to a calculation of energy level spacings in superdeformed rotational bands.

Chasman, R.R. [Argonne National Lab., IL (United States). Physics Div.

1996-12-31

177

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, Ferenc; Balaskó, Márton; Sváb, Erzsébet

1999-11-01

178

Use of Instrumental Neutron Activation Analysis to investigate the distribution of trace elements among subsamples of solid materials  

NASA Astrophysics Data System (ADS)

The results of analytical measurements performed with solid-sampling techniques are affected by the distribution of the analytes within the matrix. The effect becomes significant in the case of determination of trace elements in small subsamples. In this framework we propose a measurement model based on Instrumental Neutron Activation Analysis to determine the relative variability of the amount of an analyte among subsamples of a material. The measurement uncertainty is evaluated and includes the counting statistics, the full-energy gamma peak efficiency and the spatial gradient of the neutron flux at the irradiation position. The data we obtained in a neutron activation experiment and showing the relative variability of As, Au, Ir, Sb and W among subsamples of a highly pure Rh foil are also presented.

D'Agostino, G.; Bergamaschi, L.; Giordani, L.; Oddone, M.; Kipphardt, H.; Richter, S.

2014-02-01

179

Measuring strain and stress distributions along rebar embedded in concrete using time-of-flight neutron diffraction  

NASA Astrophysics Data System (ADS)

In modern society, architectural and civil engineering structures such as reinforced concrete buildings require high seismic performance to minimize the ‘megarisk’ exposed from urban earthquake hazards. In the reinforced concrete structures, the bond resistance between rebar and concrete is one important parameter for discussing its performance and it has been typically evaluated by measuring the strain distribution along the embedded rebar. Here, we present in-situ strain and stress measurements for the rebar in reinforced concrete using time-of-flight neutron diffraction as a novel alternative technique to typical strain gauges. It was demonstrated in this study that the three-dimensional deformation behavior of the embedded rebar in normal-strength concrete, cured in air, can be accurately measured under pull-out loading using time-of-flight neutron diffraction. Wider applications of neutron diffraction in the structural engineering field are expected for advanced understanding of actual phenomena on reinforced concrete structures.

Suzuki, H.; Kusunoki, K.; Hatanaka, Y.; Mukai, T.; Tasai, A.; Kanematsu, M.; Kabayama, K.; Harjo, S.

2014-02-01

180

Atmospheric neutrons  

NASA Technical Reports Server (NTRS)

Contributions to fast neutron measurements in the atmosphere are outlined. The results of a calculation to determine the production, distribution and final disappearance of atmospheric neutrons over the entire spectrum are presented. An attempt is made to answer questions that relate to processes such as neutron escape from the atmosphere and C-14 production. In addition, since variations of secondary neutrons can be related to variations in the primary radiation, comment on the modulation of both radiation components is made.

Korff, S. A.; Mendell, R. B.; Merker, M.; Light, E. S.; Verschell, H. J.; Sandie, W. S.

1979-01-01

181

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

182

Break Point Distribution on Chromosome 3 of Human Epithelial Cells exposed to Gamma Rays, Neutrons and Fe Ions  

NASA Technical Reports Server (NTRS)

Most of the reported studies of break point distribution on the damaged chromosomes from radiation exposure were carried out with the G-banding technique or determined based on the relative length of the broken chromosomal fragments. However, these techniques lack the accuracy in comparison with the later developed multicolor banding in situ hybridization (mBAND) technique that is generally used for analysis of intrachromosomal aberrations such as inversions. Using mBAND, we studied chromosome aberrations in human epithelial cells exposed in vitro to both low or high dose rate gamma rays in Houston, low dose rate secondary neutrons at Los Alamos National Laboratory and high dose rate 600 MeV/u Fe ions at NASA Space Radiation Laboratory. Detailed analysis of the inversion type revealed that all of the three radiation types induced a low incidence of simple inversions. Half of the inversions observed after neutron or Fe ion exposure, and the majority of inversions in gamma-irradiated samples were accompanied by other types of intrachromosomal aberrations. In addition, neutrons and Fe ions induced a significant fraction of inversions that involved complex rearrangements of both inter- and intrachromosome exchanges. We further compared the distribution of break point on chromosome 3 for the three radiation types. The break points were found to be randomly distributed on chromosome 3 after neutrons or Fe ions exposure, whereas non-random distribution with clustering break points was observed for gamma-rays. The break point distribution may serve as a potential fingerprint of high-LET radiation exposure.

Hada, M.; Saganti, P. B.; Gersey, B.; Wilkins, R.; Cucinotta, F. A.; Wu, H.

2007-01-01

183

Effect of water distributions on performances of JARI standard PEFC by using neutron radiography  

NASA Astrophysics Data System (ADS)

In order to clarify the effects of water on performances of a Polymer Electrolyte Fuel Cell (PEFC), measurements of water distribution in a Japan Automobile Research Institute (JARI) standard PEFC were carried out by means of neutron radiography. Furthermore, the cell voltage and the pressure drop between inlet and outlet of the air were simultaneously measured. The effects of channel geometry, i.e. single-serpentine and three-serpentine, and relative humidity of air were investigated. The experimental conditions were current density of 200 mA/cm 2, hydrogen utilization of 9.5% and oxygen utilization of 40%. The membrane electrode assembly (MEA) area was 5×5 cm 2. The pictures were taken every 15 s with an exposure time of 12 s. The spatial resolution was 108 ?m. From the measurements, the relation between cell voltage, pressure drop and movement of the water plug in the channel was confirmed. The PEFC performances were recovered as the water plug evacuated. Condensed water in the channel decreased with the relative humidity of air. However, it may affect the MEA permanence. Therefore, the most appropriate operating conditions should be decided for taking into account both the cell performances and the permanencies.

Murakawa, H.; Ueda, T.; Yoshida, T.; Sugimoto, K.; Asano, H.; Takenaka, N.; Mochiki, K.; Iikura, H.; Yasuda, R.; Matsubayashi, M.

2009-06-01

184

A polarized neutron study of the magnetization distribution in Co?FeSi.  

PubMed

The magnetization distribution in Co2FeSi which has the largest moment per formula unit ?6 ?B of all Heusler alloys, has been determined using polarized neutron diffraction. The experimentally determined magnetization has been integrated over spheres centred on the three sites of the L12 structure giving ? Fe = 3.10(3) ?B and ? Co = 1.43(2) ?B, results which are slightly lower than the moments in atomic spheres of similar radii obtained in recent LDA + U band structure calculations (Li et al 2010 Chin. Phys. B 19 097102). Approximately 50% of the magnetic carriers at the Fe sites were found to be in orbitals with eg symmetry. This was higher, ?65%, at the Co sites. Both Fe and Co were found to have orbital moments that are larger than those predicted. Comparison with similar results obtained for related alloys suggests that there must be a finite density of states in both spin bands at the Fermi energy indicating that Co2FeSi is not a perfect half-metallic ferromagnet. PMID:23612471

Brown, P J; Kainuma, R; Kanomata, T; Neumann, K-U; Okubo, A; Umetsu, R Y; Ziebeck, K R A

2013-05-22

185

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

186

Invariant Mass Distribution of Jet Pairs Produced in Association with a W boson in pp? Collisions at ?s= 1.96 TeV  

SciTech Connect

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 4.3 fb-1. The observed distribution has an excess in the 120-160 GeV/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 [Helsinki Inst. of Phys.; Alvarez Gonzalez, B [Oviedo U.; Cantabria Inst. of Phys.; Amerio, S [INFN, Padua; Amidei, D [Michigan U.; Anastassov, A [Northwestern U.; Annovi, A [Frascati; Antos, J [Comenius U.; Apollinari, G [Fermilab; Appel, J A [Fermilab; Apresyan, A [Purdue U.; Arisawa, T [Waseda U.; Dubna, JINR

2011-04-28

187

Role of neutron transfer on fusion barrier distributions of the Si28,30 + Sn124 systems  

NASA Astrophysics Data System (ADS)

The fusion barrier distributions for Si28,30 + Sn124 systems were extracted from quasielastic excitation function measurements at backward angles. The experimental barrier distributions were then compared with coupled-channel (CC) calculations. The fusion barrier distribution for the Si30 + Sn124 reaction was well reproduced by the CC calculations with the inclusion of projectile and target inelastic couplings and only one possible positive Q-value 2n-transfer channel coupling using the ccfull code. However, CC calculations with similar coupling schemes for inelastic excitation of target and projectile with the 4n-transfer channel corresponding to the highest positive Q value failed to reproduce the barrier distribution for the Si28 + Sn124 reaction, because it has many positive Q-value multi-neutron transfer channels. A better agreement between the experimental fusion barrier distribution for the Si28 + Sn124 system and the prediction of semiempirical CC calculations based on the Zagrebaev framework [V. I. Zagrebaev, Phys. Rev. C 67, 061601(R) (2003), 10.1103/PhysRevC.67.061601] was obtained only after considering positive Q-value multi-neutron transfer couplings. The sensitivity of the fusion barrier distribution to the hexadecapole deformation parameter ?4 of the projectile was also discussed.

Danu, L. S.; Nayak, B. K.; Mirgule, E. T.; Choudhury, R. K.; Garg, U.

2014-04-01

188

Determination of spatial and energy distributions of neutrons in experiments on transmutation of radioactive waste using relativistic protons  

Microsoft Academic Search

The experiments on transmutation of 129I and 237Np using uranium-lead targets surrounded by a paraffin moderator were performed at the Joint Institute for Nuclear Research (JINR, Russia). The targets were irradiated by 1.5 GeV and 7.4 GeV protons at the Synchrophasotron of JINR. In the frame of present work spatial and energy distributions of neutrons on the surface of the

I. V. Zhuk; E. M. Lomonosova; S. F. Boulyga; A. I. Kievitskaia; I. L. Rakhno; S. E. Chigrinov; V. Bradnova; M. I. Krivopustov; B. A. Kulakov; R. Brandt; M. Ochs; J.-S. Wan

1999-01-01

189

Liquidlike Spatial Distribution of Magnetic Droplets Revealed by Neutron Scattering in La1-xCaxMnO3  

Microsoft Academic Search

Elastic neutron scattering experiments, performed in semiconducting La1-xCaxMnO3 single crystals \\\\(x = 0.05,0.08\\\\), reveal new features in the problem of electronic phase separation and metal insulator transition. Below TN, the observation of a broad magnetic modulation in the q-dependent elastic scattering intensity, centered at nearly identical qm whatever the q direction, can be explained by a liquidlike spatial distribution of

M. Hennion; F. Moussa; G. Biotteau; J. Rodríguez-Carvajal; L. Pinsard; A. Revcolevschi

1998-01-01

190

DISTRIBUTION AND SOLUBILITY OF RADIONUCLIDES AND NEUTRON ABSORBERS IN WASTE FORMS FOR DISPOSITION OF PLUTONIUM ASH AND SCRAPS, EXCESS PLUTONIUM, AND MISCELLANEOUS SPENT NUCLEAR FUELS  

EPA Science Inventory

The objective of this multi-institutional, multi-national research effort is to understand the distributions, solubilities, and releases of radionuclides and neutron absorbers in waste forms. The results will provide the underpinning knowledge for developing, evaluating, selectin...

191

FURTHER EVIDENCE FOR THE BIMODAL DISTRIBUTION OF NEUTRON-STAR MASSES  

SciTech Connect

We use a collection of 14 well-measured neutron-star masses to strengthen the case that a substantial fraction of these neutron stars were formed via electron-capture (e-capture) supernovae (SNe) as opposed to Fe core-collapse SNe. The e-capture SNe are characterized by lower resultant gravitational masses and smaller natal kicks, leading to lower orbital eccentricities when the e-capture SN has led to the formation of the second neutron star in a binary system. Based on the measured masses and eccentricities, we identify four neutron stars, which have a mean post-collapse gravitational mass of {approx}1.25 M {sub sun}, as the product of e-capture SNe. We associate the remaining 10 neutron stars, which have a mean mass of {approx}1.35 M {sub sun}, with Fe core-collapse SNe. If the e-capture SN occurs during the formation of the first neutron star, then this should substantially increase the formation probability for double neutron stars, given that more systems will remain bound with the smaller kicks. However, this does not appear to be the case for any of the observed systems and we discuss possible reasons for this.

Schwab, J.; Rappaport, S. [37-602B, M.I.T., Department of Physics and Kavli Institute for Astrophysics and Space Research, 70 Vassar St., Cambridge, MA, 02139 (United States); Podsiadlowski, Ph., E-mail: sar@mit.ed, E-mail: jschwab@mit.ed, E-mail: jwschwab@berkeley.ed, E-mail: podsi@astro.ox.ac.u [Department of Astrophysics, University of Oxford, Oxford OX1 3RH (United Kingdom)

2010-08-10

192

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

193

Prompt neutron emission multiplicity distributions and average values, /bar char/. nu. , at 2200 meter per second for the fissile nuclides  

SciTech Connect

The prompt neutron emission multiplicity distribution, P/sub nu/ is of interest for methods of self-calibration and for auto-correlation to assay fissionable material for nuclear safeguards. /bar char/..nu.., the average value of P/sub nu/, is of interest at neutron thermal energies since it is used as a normalizing point for energy dependent values of /bar char/..nu... Values of P/sub nu/ and /bar char/..nu.. have been determined at the standard neutron energy of 0.0253 ev for the neutron induced fission of the four fissile nuclides, /sup 233,235/U, and /sup 239,241/Pu. Revised /bar char/..nu.. values have been obtained by re-evaluating /bar char/..nu.. experiments measured at 2200 meter/second relative to the /bar char/..nu.. from the spontaneous fission of /sup 252/Cf. These revised values of /bar char/..nu.. been used to renormalize the measured P/sub nu/ values. The revised values of /bar char/..nu.. are all about 1/4% to 1/2% smaller than the corresponding values of ENDF/B-V. 25 refs., 4 tabs.

Holden, N.E.; Zucker, M.S.

1988-01-01

194

Neutron Scattering Angular Distributions for ^159Tb at 570 keV and at 1000 keV  

NASA Astrophysics Data System (ADS)

Neutron elastic and inelastic scattering angular distributions for ^159Tb were measured via the time-of-flight (TOF) technique with incident neutron energies of 570 keV and 1000 keV. Measurements were made at 11 angles from 35^0 to 135^0 in 10-degree steps. Neutrons were generated by the^7Li(p,n)^7Be reaction at the UML Van de Graaff accelerator laboratory, with a pulsed proton beam, Mobley compressed to around 0.5 ns, irradiating a 15-keV thick metallic Li target. The time resolution of the accelerator was controlled by monitoring the width of the prompt target gamma-ray peak in a TOF spectrum with a fast scintillation detector. The terbium scatterer was disk shaped with a thickness of 0.6 cm and a diameter of 3.8 cm. Neutrons were detected by a 0.6-cm thick plastic scintillator. The relative efficiency of the detector was determined by comparison to a calibrated ^235U fission chamber. Measured cross sections are compared with previous work, ENDF/B-VI, JENDL, and JEF.

Seo, P.-N.; Egan, J. J.; Kegel, G. H. R.; Desimone, D. J.; Ko, Y. J.; McKittrick, T.; Ji, C.; Kim, D. S.

2000-10-01

195

First spin-resolved electron distributions in crystals from combined polarized neutron and X-ray diffraction experiments  

PubMed Central

Since the 1980s it has been possible to probe crystallized matter, thanks to X-ray or neutron scattering techniques, to obtain an accurate charge density or spin distribution at the atomic scale. Despite the description of the same physical quantity (electron density) and tremendous development of sources, detectors, data treatment software etc., these different techniques evolved separately with one model per experiment. However, a breakthrough was recently made by the development of a common model in order to combine information coming from all these different experiments. Here we report the first experimental determination of spin-resolved electron density obtained by a combined treatment of X-ray, neutron and polarized neutron diffraction data. These experimental spin up and spin down densities compare very well with density functional theory (DFT) calculations and also confirm a theoretical prediction made in 1985 which claims that majority spin electrons should have a more contracted distribution around the nucleus than minority spin electrons. Topological analysis of the resulting experimental spin-resolved electron density is also briefly discussed. PMID:25075338

Deutsch, Maxime; Gillon, Béatrice; Claiser, Nicolas; Gillet, Jean-Michel; Lecomte, Claude; Souhassou, Mohamed

2014-01-01

196

Diffraction pattern from thermal neutron incoherent elastic scattering and the holographic reconstruction of the coherent scattering length distribution  

SciTech Connect

The diffraction of spherical waves (S waves) interacting with a periodic scattering length distribution produces characteristic intensity patterns known as Kossel and Kikuchi lines (collectively called K lines). The K-line signal can be inverted to give the three-dimensional structure of the coherent scattering length distribution surrounding the source of S waves - a process known as 'Gabor holography' or, simply, 'holography'. This paper outlines a kinematical formulation for the diffraction pattern of monochromatic plane waves scattering from a mixed incoherent and coherent S-wave scattering length distribution. The formulation demonstrates that the diffraction pattern of plane waves incident on a sample with a uniformly random distribution of incoherent scatterers is the same as that from a sample with a single incoherent scatterer per unit cell. In practice, one can therefore reconstruct the holographic data from samples with numerous incoherent S-wave scatterers per unit cell. Thus atomic resolution thermal neutron holography is possible for materials naturally rich in incoherent thermal neutron scatterers, such as hydrogen (e.g., biological and polymeric materials). Additionally, holographic inversions from single-wavelength data have suffered from the so-called conjugate or twin-image problem. The formulation presented for holographic inversion - different from those used previously [e.g., T. Gog et al., Phys. Rev. Lett. 76, 3132 (1996)] - eliminates the twin-image problem for single-wavelength data.

Sur, B.; Anghel, V.N.P. [Atomic Energy of Canada Limited, Chalk River Laboratories, Chalk River, Ontario, K0J 1J0 (Canada); Rogge, R.B.; Katsaras, J. [Steacie Institute for Molecular Sciences, National Research Council, Chalk River, Ontario, K0J 1J0 (Canada)

2005-01-01

197

Fast neutron dosimetry. Progress report, July 1, 1979-June 30, 1980  

SciTech Connect

Progress is reported in: the development and testing of new gas mixtures more suitable for fast neutron dosimetry using the common A150-type Tissue-equivalent plastic ion chambers; comparison of photon doses determined with a graphite-walled proportional counter and with paired dosimeters irradiated by 14.8-MeV neutrons; a detector for the direct measurement of LET distributions from irradiation with fast neutrons; LET distributions from fast neutron irradiation of TE-plastic and graphite measured in a cylindrically symmetric geometry; progress in development of a tandem fast neutron and /sup 60/Co gamma ray source irradiation facility; an approach to the correlation of cellular response with lineal energy; calculated and measured HTO atmospheric dispersion rates within meters of a release site; application of cavity theory to fast neutrons; and fast neutron dosimetry by thermally stimulated currents in Al/sub 2/O/sub 3/. (GHT)

Attix, F.H.

1980-01-01

198

Invariant Mass Distribution of Jet Pairs Produced in Association with a W Boson in p[overbar p] Collisions at [sqrt]s=1.96??TeV  

E-print Network

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 4.3??fb[superscript -1]. ...

Bauer, Gerry P.

199

Observation of the spatial distribution of gravitationally bound quantum states of ultracold neutrons and its derivation using the Wigner function.  

PubMed

Ultracold neutrons (UCNs) can be bound by the potential of terrestrial gravity and a reflecting mirror. The wave function of the bound state has characteristic modulations. We carried out an experiment to observe the vertical distribution of the UCNs above such a mirror at the Institut Laue-Langevin in 2011. The observed modulation is in good agreement with that prediction by quantum mechanics using the Wigner function. The spatial resolution of the detector system is estimated to be 0.7???m. This is the first observation of gravitationally bound states of UCNs with submicron spatial resolution. PMID:24579585

Ichikawa, G; Komamiya, S; Kamiya, Y; Minami, Y; Tani, M; Geltenbort, P; Yamamura, K; Nagano, M; Sanuki, T; Kawasaki, S; Hino, M; Kitaguchi, M

2014-02-21

200

Examination of the Atomic Pair Distribution Function (PDF) of SiC Nanocrystals by In-situ High Pressure Diffraction  

NASA Technical Reports Server (NTRS)

Key properties of nanocrystals are determined by their real atomic structure, therefore a reasonable understanding and meaningful interpretation of their properties requires a realistic model of the structure. In this paper we present an evidence of a complex response of the lattice distances to external pressure indicating a presence of a complex structure of Sic nanopowders. The experiments were performed on nanocrystalline Sic subjected to hydrostatic or isostatic pressure using synchrotron and neutron powder diffraction. Elastic properties of the samples were examined based on X-ray diffraction data using a Diamond Anvil Cell (DAC) in HASYLAB at DESY. The dependence'of the lattice parameters and of the Bragg reflections width with pressure exhibits a ha1 nature of the properties (compressibilities) of the powders and indicates a complex structure of the grains. We interpreted tws behaviour as originating from different elastic properties of the grain interior and surface. Analysis of the dependence of individual interatomic distances on pressure was based on in-situ neutron diffraction measurements done with HbD diffractometer at LANSCE in Los Alamos National Laboratory with the Paris-Edinburgh cell under pressures up to 8 GPa (Qmax = 26/A). Interatomic distances were obtained by PDF analysis using the PDFgetN program. We have found that the interatomic distances undergo a complex, non-monotonic changes. Even under substantial pressures a considerable relaxation of the lattice may take place: some interatomic distances increase with an increase in pressure. We relate this phenomenon to: (1), changes of the microstructure of the densified material, in particular breaking of its fractal chain structure and, (2), its complex structure resembling that of a material composed of two phases, each with its distinct elastic properties.

Grzanka, E.; Stelmakh, S.; Gierlotka, S.; Zhao, Y.; Palosz, B.; Palosz, W.

2003-01-01

201

Electromagnetic dipole strength distribution in $^{124,128,132,134}$Xe below the neutron separation energy  

E-print Network

Dipole strength functions in the chain of xenon isotopes are analyzed on the basis of photon-scatterde experiments with bremsstrahlung at the ELBE facility in Dresden, Germany, and at the HI S facility in Durham, North Carolina, USA. The evolution of dipole strength with neutron excess and nuclear deformation is studied.

Massarczyk, R; Dönau, F; Frauendorf, S; Bemmerer, D; Beyer, R; Butterling, M; Hannaske, R; Junghans, A; Koegler, T; Rusev, G; Schilling, K D; Schramm, G; Tonchev, A P; Tornow, W; Wagner, A

2014-01-01

202

The functional significance of density and distribution of outgrowths on co-opted contact pairs in biological arresting systems.  

PubMed

Microstructures responsible for temporary arresting of contacting surfaces are widely distributed on surfaces in different organisms. Recent morphological studies show that these structures have different density of outgrowths and not ideal distribution pattern on both complementary parts of the contact. One can suggest that this difference is optimized by natural selection to get stronger mechanical arrest within the system. In this paper, we simulate such a system numerically, both in the frames of continuous contact and discrete dynamical models to prove this hypothesis and elucidate other aspects of optimization of such mechanical adhesive systems. PMID:25533090

Filippov, Alexander E; Popov, Valentin L; Gorb, Stanislav N

2015-02-01

203

Analysis of Fragment Mass Distribution in Asymmetric Area at Fission of {sup 235}U Induced by Thermal Neutrons  

SciTech Connect

The fragment mass yields in fission of {sup 235}U induced by thermal neutrons for A=145 - 160 and E{sub K}=50 - 75 MeV were measured using a mass spectrometer. The fine structure is observed at A=153, 154 and E{sub K}=50 - 60 MeV. The obtained results were described in the framework of a model based on the dinuclear system concept. The analyzed correlation between the total kinetic energy and mass distribution of fission fragments is connected with the shell structure of the formed fragments of fission. From this correlation and the time dependence of the calculated mass distribution of the binary reaction products, one can conclude that the descent time from a saddle point to a scission point for the more deformed fragments is longer than that for fragments of more compact shape.

Pikul, V.P.; Koblik, Yu.N.; Khugaev, A.V.; Yuldashev, B.S. [Institute of Nuclear Physics, Tashkent (Uzbekistan); Jovliev, U.Yu.; Muminov, A.I.; Pavliy, K.V. [Heavy-Ion Physics Department, Institute of Nuclear Physics, Tashkent (Uzbekistan); Nasirov, A.K. [Heavy-Ion Physics Department, Institute of Nuclear Physics, Tashkent (Uzbekistan); Bogolyubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 (Russian Federation)

2005-02-01

204

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...

205

Identified particle transverse momentum distributions from AU + AU collisions at 62.4 GeV per nucleon pair  

E-print Network

Transverse momentum (PT) distributions for pions, kaons, protons and antiprotons have been measured near mid-rapidity for Au+Au collisions at sNN = 62.4 GeV using the PHOBOS detector at the Relativistic Heavy-Ion Collider ...

Henderson, Conor, 1977-

2005-01-01

206

ACHIEVING THE REQUIRED COOLANT FLOW DISTRIBUTION FOR THE ACCELERATOR PRODUCTION OF TRITIUM (APT) TUNGSTEN NEUTRON SOURCE  

SciTech Connect

The Accelerator Production of Tritium neutron source consists of clad tungsten targets, which are concentric cylinders with a center rod. These targets are arranged in a matrix of tubes, producing a large number of parallel coolant paths. The coolant flow required to meet thermal-hydraulic design criteria varies with location. This paper describes the work performed to ensure an adequate coolant flow for each target for normal operation and residual heat-removal conditions.

D. SIEBE; K. PASAMEHMETOGLU

2000-11-01

207

Hard Photo-disintegration of proton pairs in ^3He  

NASA Astrophysics Data System (ADS)

Hard deuteron photo-disintegration has been investigated for 20 years, as its cross sections follow the constituent counting rules and it provides insight into the interplay between hadronic and quark-gluon degrees of freedom in high-momentum transfer exclusive reactions. We have now measured for the first time hard pp-pair disintegration in the reaction ?,3 He ->pp + n, using kinematics corresponding to a spectator neutron. Clues to the underlying physics can be found in the comparison of our measurements with deuteron photo-disintegration, the energy dependence of the cross sections at 90^o c.m., the ?n distribution, and the angular distribution.

Gilman, Ronald; Piasetzky, Eli; Pomerantz, Ishay

2007-10-01

208

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

209

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

NASA Astrophysics Data System (ADS)

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 Cf252 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?g of U235. 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.; Bond, E.

2010-01-01

210

Determination of the relative power density distribution in a heterogeneous reactor from the results of measurements of the reactivity effects and the neutron importance function  

NASA Astrophysics Data System (ADS)

A method for experimental determination of the relative power density distribution in a heterogeneous reactor based on measurements of fuel reactivity effects and importance of neutrons from a californium source is proposed. The method was perfected on two critical assembly configurations at the NARCISS facility of the Kurchatov Institute, which simulated a small-size heterogeneous nuclear reactor. The neutron importance measurements were performed on subcritical and critical assemblies. It is shown that, along with traditionally used activation methods, the developed method can be applied to experimental studies of special features of the power density distribution in critical assemblies and reactors.

Bobrov, A. A.; Glushkov, E. S.; Zimin, A. A.; Kapitonova, A. V.; Kompaniets, G. V.; Nosov, V. I.; Petrushenko, R. P.; Smirnov, O. N.

2012-12-01

211

Determination of the relative power density distribution in a heterogeneous reactor from the results of measurements of the reactivity effects and the neutron importance function  

SciTech Connect

A method for experimental determination of the relative power density distribution in a heterogeneous reactor based on measurements of fuel reactivity effects and importance of neutrons from a californium source is proposed. The method was perfected on two critical assembly configurations at the NARCISS facility of the Kurchatov Institute, which simulated a small-size heterogeneous nuclear reactor. The neutron importance measurements were performed on subcritical and critical assemblies. It is shown that, along with traditionally used activation methods, the developed method can be applied to experimental studies of special features of the power density distribution in critical assemblies and reactors.

Bobrov, A. A.; Glushkov, E. S.; Zimin, A. A.; Kapitonova, A. V.; Kompaniets, G. V.; Nosov, V. I., E-mail: rpp@adis.vver.kiae.ru; Petrushenko, R. P.; Smirnov, O. N. [Russian Research Centre Kurchatov Institute (Russian Federation)

2012-12-15

212

The study of disorder and nanocrystallinity in C-S-H, supplementary cementitious materials and geopolymers using pair distribution function analysis  

SciTech Connect

Significant progress was achieved with the application of Rietveld method to characterize the crystalline phases in portland cement paste. However, to obtain detailed information on the amorphous or poorly crystalline phases, it is necessary to analyze the total scattering data. The pair distribution function (PDF) method has been successfully used in the study of liquids and amorphous solids. The method takes the Sine Fourier transform of the measured structure factor over a wide momentum transfer range, providing a direct measure of the probability of finding an atom surrounding a central atom at a radial distance away. The obtained experimental characteristic distances can be also used to validate the predictions by the theoretical models, such as, molecular dynamics, ab initio simulations and density functional theory. The paper summarizes recent results of PDF analysis on silica fume, rice husk ash, fly ash, ASR gel, C-S-H and geopolymers.

Meral, Cagla [Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720 (United States); Benmore, C.J. [X-ray Science Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, Illinois 60439 (United States); Monteiro, Paulo J.M., E-mail: monteiro@berkeley.edu [Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720 (United States)

2011-07-15

213

Pair-distribution function analysis of the structural valence transition in Cp{sub 2}{sup *}Yb(4,4'-Me{sub 2}-bipy)  

SciTech Connect

The Cp{sup ?}{sub 2} Yb(L) class of compounds, where Cp{sup ?}=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{sup ?}{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{sup ?}{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.

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

2010-07-20

214

Experimental kerma coefficients and dose distributions of C, N, O, Mg, Al, Si, Fe, Zr, A-150 plastic, Al203, AlN, SiO2 and ZrO2 for neutron energies up to 66 MeV.  

PubMed

Low-pressure proportional counters (LPPCs) with walls made from the elements C, Mg, Al, Si, Fe and Zr and from the chemical compounds A-150 plastic, AlN, Al2O3, SiO2 and ZrO2 were used to measure neutron fluence-to-kerma conversion coefficients at energies up to 66 MeV. The LPPCs served to measure the absorbed dose deposited in the gas of a cavity surrounded by the counter walls that could be converted to the absorbed dose to the wall on the basis of the Bragg-Gray cavity theory. Numerically the absorbed doses to the walls were almost equal to the corresponding kerma values of the wall materials. The neutron fluence was determined by various experimental methods based on the reference cross sections of the 1H(n, p) scattering and/or the 238U(n, f) reactions. The measurements were performed in monoenergetic neutron fields of energies of 5 MeV, 8 MeV, 15 MeV and 17 MeV and in polyenergetic neutron beams with prominent peaks of energies of 34 MeV, 44 MeV and 66 MeV. For the measurements in the polyenergetic neutron beams, significant corrections for the contributions of the non peak energy neutrons were applied. The fluence-to kerma conversion coefficients of N and O were determined using the difference technique applied with matched pairs of LPPCs made from a chemical compound and a pure element. This paper reports experimental fluence-to-kerma conversion coefficient values of eight elements and four compounds measured for seven neutron energies, and presents a comparison with data from previous measurements and theoretical predictions. The distributions of the absorbed dose as a function of the lineal energy were measured for monoenergetic neutrons or, for polyenergetic neutron fields, deduced by applying iterative unfolding procedures in order to subtract the contributions from non-peak energy neutrons. The dose distributions provide insight into the neutron interaction processes. PMID:10730963

Schrewe, U J; Newhauser, W D; Brede, H J; DeLuca, P M

2000-03-01

215

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

216

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

217

Measurement and model prediction of proton-recoil track length distributions in NTA film dosimeters for neutron energy spectroscopy and retrospective dose assessment  

NASA Astrophysics Data System (ADS)

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 application of radiation weighting factors used in epidemiology and probability of causation calculations. Monte Carlo models of proton-recoil track length distributions were developed and benchmarked against measurement data for both NTA and Ilford films. These models, when applied to several NTA film dosimeter configurations, demonstrated that proton-recoil track length distributions change based upon incident neutron energy. The neutron energy spectra changes that result from the general work environment such as source term and shielding can subsequently be modeled to predict the response of the NTA film dosimeter. An Automatic NTA Film Analyzer has been designed and developed to determine if the difference in proton-recoil track length distributions predicted by the Monte Carlo models could be measured and whether these differences could be correlated to the incident neutron energy spectra. The design required the development of a 2D-3D hybrid track recognition algorithm for a three dimensional analysis of the NTA film in order to accurately determine the proton-recoil track length for subsequent neutron energy determination. NTA films exposed to a plutonium fluoride (PuF4) and polonium boron (PoB) calibration sources were measured and compared. The proton-recoil track lengths were used to reconstruct the incident neutron energy spectra demonstrating the functionality of the analyzer and that reconstruction of the neutron energy spectra from NTA films is feasible. These measurements were compared to the Monte Carlo models and confirmed the applicability of using models to determine the NTA film response. Based on the Monte Carlo Modeling and the Automatic NTA Film Analyzer, the neutron energy spectra to which an individual worker was exposed can be retrospectively determined through re-analysis of historic NTA dosimeter films thus improving retrospective neutron dose assessments.

Taulbee, Timothy D.

218

Hopf algebras, distributive (Laplace) pairings and hash products: a unified approach to tensor product decompositions of group characters  

NASA Astrophysics Data System (ADS)

We show for bicommutative graded connected Hopf algebras that a certain distributive (Laplace) subgroup of the convolution monoid of 2-cochains parameterizes certain well behaved Hopf algebra deformations. Using the Laplace group, or its Frobenius subgroup, we define higher derived hash products, and develop a general theory to study their main properties. Applying our results to the (universal) bicommutative graded connected Hopf algebra of symmetric functions, we show that classical tensor product and character decompositions, such as those for the general linear group, mixed co- and contravariant or rational characters, orthogonal and symplectic group characters, Thibon and reduced symmetric group characters, are special cases of higher derived hash products. In the appendix we discuss a relation to formal group laws.

Fauser, Bertfried; Jarvis, Peter D.; King, Ronald C.

2014-05-01

219

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

220

Longitudinal asymmetry and ?-ray angular distribution in neutron-radiative-capture reactions  

NASA Astrophysics Data System (ADS)

The parity-nonconserving effect was investigated in low-energy (n, ?) reactions for several nuclei with mass numbers of ~100. The longitudinal asymmetry ( AL) was measured in p-wave resonances for 139La and 81Br taking into account the possible angular dependence within the framework of the sp mixing model. AL for 139La was found to be independent of the ?-ray energy thresholds within the experimental errors. From these results the relation between a ?-ray detection experiment and a neutron-transmission experiment is discussed. AL was measured in the p-wave resonances for 81Br, 93Nb, 108Pd, 111Cd, 124Sn and 139La. The obtained nonzero values of AL are AL = (9.8 ± 0.3)%, (2.1 ± 0.1)% and -(1.3 +0.7-0.4% for 139La( Ep = 0.734 eV), 81Br( Ep = 0.88 eV) and 111Cd( Ep = 4.53 eV), respectively. A theoretical interpretation is discussed in terms of the interference between two amplitudes of the s- and p-wave incident neutrons.

Shimizu, H. M.; Adachi, T.; Ishimoto, S.; Masaike, A.; Masuda, Y.; Morimoto, K.

1993-02-01

221

Switchable radioactive neutron source device  

DOEpatents

This invention is a switchable neutron generating apparatus comprised of a pair of plates, the first plate having an alpha emitter section on it and the second plate having a target material portion on it which generates neutrons when its nuclei absorb an alpha particle. In operation, the alpha portion of the first plate is aligned with the neutron portion of the second plate to produce neutrons and brought out of alignment to cease production of neutrons.

Boyar, Robert E. (La Grange, IL); DeVolpi, Alexander (Bolingbrook, IL); Stanford, George S. (Downers Grove, IL); Rhodes, Edgar A. (Woodridge, IL)

1989-01-01

222

Switchable radioactive neutron source device  

DOEpatents

This invention is a switchable neutron generating apparatus comprised of a pair of plates, the first plate having an alpha emitter section on it and the second plate having a target material portion on it which generates neutrons when its nuclei absorb an alpha particle. In operation, the alpha portion of the first plate is aligned with the neutron portion of the second plate to produce neutrons and brought out of alignment to cease production of neutrons. 3 figs.

Stanford, G.S.; Rhodes, E.A.; Devolpi, A.; Boyar, R.E.

1987-11-06

223

MoNA and Two-Neutron Decay Analysis  

NASA Astrophysics Data System (ADS)

The Modular Neutron Array (MoNA) is a large, high-efficiency position-sensitive neutron detector array housed at the National Superconducting Cyclotron Laboratory at Michigan State University, consisting of 144 2-meter long scintillator bars with a PMT positioned at each end, designed to detect the energy and trajectory of fast neutrons emitted in the breakup of exotic neutron-rich nuclei. Because a single neutron can scatter multiple times within MoNA, (including a large presence of dark-scattering from Carbon), the experimental challenge to distinguish between single and multiple neutron decay events is significant. We've developed special data-sorting routines that selectively filter on a combination of factors such as neutron velocity and scattering angle, hit-pattern distribution, neutron-fragment opening angle, and decay energy in order to reduce the Carbon scattering background and enhance correlations between pairs of neutrons. We've applied this analysis to the 2-neutron decays of ^24O and ^13Li from data sets from previous MoNA experiments. Results will be presented.

Grovom, Amanda; Aulie, Alegra; Rogers, Warren F.

2010-11-01

224

[The depth distribution of neutron-capture events in 10B nuclei during the irradiation of a water phantom with neutrons from the channels of the BR-10 reactor].  

PubMed

The authors present the results of experimental investigations of distribution of capture events on nuclei 10B by the depth of a water phantom during its irradiation with beams T-4 and B-3 of the BR-10 reactor. A ferrous sulfate dosimeter with added boric acid was used as a detector of such events. The depth of a water phantom on which the effect of boron capture by a neutron beam is decreased 2-fold, is 1.7 cm. For the B-3 beam a curve of depth correlation of neutron capture events had a broad maximum at a depth of 4-5 cm. PMID:1890942

Kapchigashev, S P; Potetnia, V I; Khodyreva, E V; Neshina, V S

1991-01-01

225

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 30×30×30 cm 3 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

226

Superfluid Response and the Neutrino Emissivity of Neutron Matter  

E-print Network

{We calculate the neutrino emissivity of superfluid neutron matter in the inner crust of neutron stars. We find that neutrino emission due to fluctuations resulting from the formation of Cooper pairs at finite temperature is highly suppressed in non-relativistic systems. This suppression of the pair breaking emissivity in a simplified model of neutron matter with interactions that conserve spin is of the order of $v_F^4$ for density fluctuations and $v_F^2$ for spin fluctuations, where $v_F$ is the Fermi velocity of neutrons. The larger suppression of density fluctuations arises because the dipole moment of the density distribution of a single component system does not vary in time. For this reason, we find that the axial current response (spin fluctuations) dominates. In more realistic models of neutron matter which include tensor interactions where the neutron spin is not conserved, neutrino radiation from bremsstrahlung reactions occurs at order $v_F^0$. Consequently, even with the suppression factors due to superfluidity, this rate dominates near $T_C$. Present calculations of the pair-breaking emissivity are incomplete because they neglect the tensor component of the nucleon-nucleon interaction.

Andrew W. Steiner; Sanjay Reddy

2008-04-03

227

Theory of neutron scattering experiments on momentum distributions in quantum fluids  

SciTech Connect

In this paper, the first perturbative derivation of the final state corrections to the impulse approximation for deep inelastic neutron scattering experiments was presented. The final state broadening is found to depend on g(r) and the He-He phase shifts. The theory satisfies the f-sum rule, the ..omega../sup 2/ sum rule (''kinetic energy'') valid at high Q, and the ..omega../sup 3/ sum rule. In the structure of the theory, the self-energy terms alone would lead to quasi-Lorentzian broadening. However, these are exactly canceled by a part of the vertex terms which introduce g(r). Numerical results are presented for superfluid /sup 4/He.

Silver, R.N.

1987-01-01

228

Critical experiments on an enriched uranium solution system containing periodically distributed strong thermal neutron absorbers  

SciTech Connect

A series of 62 critical and critical approach experiments were performed to evaluate a possible novel means of storing large volumes of fissile solution in a critically safe configuration. This study is intended to increase safety and economy through use of such a system in commercial plants which handle fissionable materials in liquid form. The fissile solution`s concentration may equal or slightly exceed the minimum-critical-volume concentration; and experiments were performed for high-enriched uranium solution. Results should be generally applicable in a wide variety of plant situations. The method is called the `Poisoned Tube Tank` because strong neutron absorbers (neutron poisons) are placed inside periodically spaced stainless steel tubes which separate absorber material from solution, keeping the former free of contamination. Eight absorbers are investigated. Both square and triangular pitched lattice patterns are studied. Ancillary topics which closely model typical plant situations are also reported. They include the effect of removing small bundles of absorbers as might occur during inspections in a production plant. Not taking the tank out of service for these inspections would be an economic advantage. Another ancillary topic studies the effect of the presence of a significant volume of unpoisoned solution close to the Poisoned Tube Tank on the critical height. A summary of the experimental findings is that boron compounds were excellent absorbers, as expected. This was true for granular materials such as Gerstley Borate and Borax; but it was also true for the flexible solid composed of boron carbide and rubber, even though only thin sheets were used. Experiments with small bundles of absorbers intentionally removed reveal that quite reasonable tanks could be constructed that would allow a few tubes at a time to be removed from the tank for inspection without removing the tank from production service.

Rothe, R.E.

1996-09-30

229

Ultrafast neutron detector  

DOEpatents

A neutron detector of very high temporal resolution is described. It may be used to measure distributions of neutrons produced by fusion reactions that persist for times as short as about 50 picoseconds.

Wang, C.L.

1985-06-19

230

Nuclear reaction secondary particle dose distributions and dose enhancement by boron neutron capture in proton beam therapy evaluated using the LAHET code system  

Microsoft Academic Search

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

Peter Gyula Laky

1997-01-01

231

Local structures of Sr{sub 2}FeMnO{sub 5+y} (y=0, 0.5) and Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} from reverse Monte Carlo modeling of pair distribution function data and implications for magnetic order  

SciTech Connect

The local structures of the oxygen deficient perovskites Sr{sub 2}FeMnO{sub 5}, Sr{sub 2}FeMnO{sub 5.5}, and Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} 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 Sr{sub 2}FeMnO{sub 5+y} compounds it is found that there is no short range ordering of the Fe and Mn cations. For Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} 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 Sr{sub 2}FeMnO{sub 5} it is found that the Fe{sup 3+} cations are most often in 4-fold coordination but there is also a large amount of Fe{sup 3+} in 5-fold coordination and a small amount in 6-fold coordination. The Mn{sup 3+} is split between 5-fold and 6-fold coordination. The Mn--O bond length distributions indicate that the Mn{sup 3+}O{sub 6} octahedra and Mn{sup 3+}O{sub 5} square pyramids are locally Jahn-Teller distorted. In Sr{sub 2}FeMnO{sub 5.5} the Fe{sup 3+} is almost entirely 5 coordinate while the Mn{sup 4+} is almost entirely 6 coordinate. The Cr{sup 3+} in Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} is almost entirely 6-fold coordinated, giving the Fe{sup 3+} an average coordination number of 4.67. In Sr{sub 2}FeMnO{sub 5} and Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} the Fe{sup 3+} and Sr{sup 2+} cations undergo local displacements which are driven by the oxygen vacancies, while the Mn{sup 3+} and Cr{sup 3+} cations remain near their positions in the average structures. In Sr{sub 2}FeMnO{sub 5.5} 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. - Graphical abstract: The actual bond angle distributions in the cubic perovskite Sr{sub 2}FeMnO{sub 5} obtained from reverse Monte Carlo modeling of the local structure using neutron pair distribution function data. Highlights: Black-Right-Pointing-Pointer No long range ordering of oxygen vacancies, but short range order is present. Black-Right-Pointing-Pointer No short range Fe/Mn order but short range Fe/Cr order is present. Black-Right-Pointing-Pointer Fe tends to have lower coordination numbers while Mn and Cr have higher ones. Black-Right-Pointing-Pointer Local bond distances and bond angles have been determined. Black-Right-Pointing-Pointer Local structures can help explain long range magnetic ordering behavior.

King, Graham, E-mail: gking@lanl.gov [Lujan Neutron Scattering Center, Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545 (United States)] [Lujan Neutron Scattering Center, Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545 (United States); Ramezanipour, Farshid [Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1 (Canada)] [Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1 (Canada); Llobet, Anna [Lujan Neutron Scattering Center, Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545 (United States)] [Lujan Neutron Scattering Center, Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545 (United States); Greedan, John E. [Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1 (Canada)] [Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1 (Canada)

2013-02-15

232

Experimental Study of Three-Dimensional Void Fraction Distribution in Heated Tight-Lattice Rod Bundles Using Three-Dimensional Neutron Tomography  

Microsoft Academic Search

Three-dimensional (3D) void fraction distributions in a tight-lattice of heated 7- or 14-rod bundles were measured using 3D neutron tomography. The distribution was also studied parametrically from the thermal-hydraulic point of view in order to elucidate boiling phenomena in a fuel assembly of the FLWR which is being developed as an advanced BWR-type reactor. 7-rod tests were carried out to

Masatoshi Kureta

2007-01-01

233

Measurement of Water Distribution in through-plane Direction in a PEFC using a Neutron Image Intensifier  

NASA Astrophysics Data System (ADS)

Hydrogen gas and air are supplied to a polymer electrolyte fuel cell (PEFC). The air and the hydrogen form water and condensation may occur in the cathode side. The generated water may affect the fuel cell performance because of blocking the oxygen from reaching cathode reaction area. An imaging system with a neutron image intensifier (NII) was used for visualizing the water behaviour in the PEFC. The water distributions in the proton exchange membrane (PEM) and the gas diffusion layers (GDL) were measured by the imaging system. Visualization experiments were performed during the PEFC operation in order to clarify the water distributions in the experiments with different utilization. The generated water was discharged into the channel after the amount of water thickness in the GDL increased to a certain value of about 600 ?m in thickness in the through-plane direction. The discharged water formed water drops in the channel. The effects of the water drops in the channel on the fuel cell performance could be observed clearly. It was shown that the cell voltage increased when the water was evacuated.

Sugimoto, K.; Murakawa, H.; Miyata, K.; Asano, H.; Takenaka, N.; Yasuda, R.

234

Multivalent ion-DNA interaction: Neutron scattering estimates of polyamine distribution  

NASA Astrophysics Data System (ADS)

The partial structure factors pertaining to DNA-DNA, DNA-polyamine, and polyamine-polyamine density correlations in DNA fragment (contour length 54 nm) solutions have been measured with small angle neutron scattering and contrast matching in water. The effect of the polyamines putrescine and spermidine on the DNA molecular structure is gauged from the limiting behavior of the DNA-DNA partial structure factor at high values of momentum transfer. The double layer structure and the extent to which the polyamines can approach the DNA are derived from the DNA-polyamine and polyamine-polyamine partial structure factors. For this purpose, the structure factors are interpreted with the correlation functions derived from the classical Poisson-Boltzmann and the modified Poisson-Boltzmann equations and/or Monte Carlo simulation. For simple salt free DNA with tetramethylammonium or putrescine counterions, spatial fluctuations in the charge density are discussed in terms of the charge structure factor. The structural arrangement of putrescine and spermidine can be fully rationalized in terms of their valence. In the case of spermidine, it is necessary to include ionic correlation effects, but this could be accomplished by modeling the ligands as hard spheres. The polyamines have no detectable effect on the DNA molecular structure and are too large to penetrate the grooves to any significant extent. These results imply that DNA condensation in the presence of polyamines is largely governed by electrostatic interactions, rather than by the binding of the multivalent cation per se.

Zakharova, S. S.; Egelhaaf, S. U.; Bhuiyan, L. B.; Outhwaite, C. W.; Bratko, D.; van der Maarel, J. R. C.

1999-12-01

235

The Probability Distribution of Binary Pulsar Coalescence Rate Estimates. II. Neutron Star-White Dwarf Binaries  

E-print Network

We consider the statistics of pulsar binaries with white dwarf companions (NS-WD). Using the statistical analysis method developed by Kim et al. (2003) we calculate the Galactic coalescence rate of NS-WD binaries due to gravitational-wave emission. We find that the most likely values for the total Galactic coalescence rate (R_tot) of NS-WD binaries lie in the range 0.2--10 per Myr depending on different assumed pulsar population models. For our reference model, we obtain R_tot=4.11_(-2.56)^(+5.25) per Myr at a 68% statistical confidence level. These rate estimates are not corrected for pulsar beaming and as such they are found to be about a factor of 20 smaller than the Galactic coalescence rate estimates for double neutron star systems. Based on our rate estimates, we calculate the gravitational-wave background due to coalescing NS-WD binaries out to extragalactic distances within the frequency band of the Laser Interferometer Space Antenna. We find the contribution from NS-WD binaries to the gravitational-wave background to be negligible.

Chunglee Kim; Vassiliki Kalogera; Duncan R. Lorimer; Tiffany White

2004-08-10

236

PARTICLE SIZE DISTRIBUTION ANALYSIS OF THORIUM OXIDE BY NEUTRON ACTIVATION AND RI LABELING  

Microsoft Academic Search

A gravity sedimentation method similar to the Andreasen pipette method ; is used for determining the particle size distribution of thorium oxide. The ; Andreasen Pipette Method for the accumulative percentage of the particles is ; replaced with a gamma -ray counting method. The sample material was activated ; by irradiation in JRR-1 or labeled with radioactive thoriura-234 (UXâ). In

T. Takeda; I. Suzuki; K. Kimura

1960-01-01

237

Eulerian pairs on Fibonacci words  

E-print Network

In their recent study of Mahonian pairs, Sagan and Savage introduced the notion of Eulerian pairs. A pair $(S,T)$ of two finite sets of words is said to be an Eulerian pair if the distribution of the descent number over $S$ equals the distribution of the excedance number over $T$. Let $\\Phi_1$ denote Foata's first fundamental transformation and $\\Psi$ denote a bijection of Han on words. We observe that $\\Phi_1$ and $\\Psi$ coincide when restricted to words on $\\{1,2\\}$. Using the inverse of $\\Phi_1$ or $\\Psi$ for words on $\\{1, 2\\}$, we obtain Eulerian pairs on Fibonacci words, where a Fibonacci word is defined to be a word on $\\{1,2\\}$ with no consecutive ones. By modifying a bijection of Steingr\\'{\\i}msson, we find another Eulerian pair on Fibonacci words.

Li, Teresa X S; Miao, Melissa Y F

2011-01-01

238

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

2009-07-01

239

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

240

The local atomic structures of liquid CO at 3.6?GPa and polymerized CO at 0 to 30?GPa from high-pressure pair distribution function analysis.  

PubMed

The local atomic structures of liquid and polymerized CO and its decomposition products were analyzed at pressures up to 30?GPa in diamond anvil cells by X-ray diffraction, pair distribution function (PDF) analysis, single-crystal diffraction, and Raman spectroscopy. The structural models were obtained by density functional calculations. Analysis of the PDF of a liquid CO-rich phase revealed that the local structure has a pronounced short-range order. The PDFs of polymerized amorphous CO at several pressures revealed the compression of the molecular structure; covalent bond lengths did not change significantly with pressure. Experimental PDFs could be reproduced with simulations from DFT-optimized structural models. Likely structural features of polymerized CO are thus 4- to 6-membered rings (lactones, cyclic ethers, and rings decorated with carbonyl groups) and long bent chains with carbonyl groups and bridging atoms. Laser heating polymerized CO at pressures of 7 to 9?GPa and 20?GPa resulted in the formation of CO(2). PMID:25066949

Rademacher, Nadine; Bayarjargal, Lkhamsuren; Morgenroth, Wolfgang; Winkler, Björn; Ciezak-Jenkins, Jennifer; Batyrev, Iskander G; Milman, Victor

2014-09-01

241

Evaluation of effects of pharmaceutical processing on structural disorders of active pharmaceutical ingredient crystals using nanoindentation and high-resolution total scattering pair distribution function analysis.  

PubMed

Pharmaceutical unit operations such as milling and compaction can often generate disordered regions in crystals of active pharmaceutical ingredients (APIs). This may lead to changes in a number of important pharmaceutical properties including dissolution, stability, hygroscopicity, and so on. It is therefore important for pharmaceutical industry to evaluate the effects of pharmaceutical processing on API structural orders, and to investigate and develop analytical tools that are capable of accurately detecting and assessing subtle process-induced structural disorders in pharmaceutical crystals. In this study, nanoindentation was first used to determine the intrinsic mechanical properties including hardness and Young's modulus of two API crystals, compounds 1 and 2. These crystals of different mechanical properties were then milled and compacted under various conditions. The resulting structural disorders in these crystals were subsequently evaluated using synchrotron-based high-resolution total scattering pair distribution function (TS-PDF) analysis. Furthermore, principal component analysis was applied to the PDF data to assess the relative extents of disorders in the API crystals, which showed a good correlation with the process conditions. The study demonstrates that high-resolution TS-PDF analysis coupled with nanoindentation measurement is a valuable and effective tool for detecting and assessing process-induced subtle structural disorders in API crystals. PMID:25331822

Chen, Shuang; Sheikh, Ahmad Y; Ho, Raimundo

2014-12-01

242

Fundamentals of a modified model of the distribution of neutron-resonance widths and results of its application in the mass-number range of 35 {<=} A {<=} 249  

SciTech Connect

A modified model is developed for describing the distribution of random resonance width for any nuclei. The model assumes the coexistence in a nucleus of one or several partial radiative and neutron amplitudes for respective resonance widths, these amplitudes differing in their parameters. Also, it is assumed that amplitude can be described by a Gaussian curve characterized by a nonzero mean value and a variance not equal to unity and that their most probable values can be obtained with the highest reliability from approximations of cumulative sums of respective widths. An analysis of data for 157 sets of neutron widths for 0 {<=} l {<=} 3 and for 56 sets of total radiative widths has been performed to date. The basic result of this analysis is the following: both for neutron and for total radiative widths, the experimental set of resonance width can be represented with a rather high probability in the form of a superposition of k {<=} 4 types differing in mean amplitude parameters.

Sukhovoj, A. M., E-mail: suchovoj@nf.jinr.ru; Khitrov, V. A., E-mail: khitrov@nf.jinr.ru [Joint Institute for Nuclear Research (Russian Federation)

2013-01-15

243

Evolution of fission-fragment mass distributions in the neutron-deficient lead region  

NASA Astrophysics Data System (ADS)

Low-energy ?-delayed fission of At194,196 and Fr200,202 was studied in detail at the mass separator ISOLDE at CERN. The fission-fragment mass distributions of daughter nuclei Po194,196 and Rn202 indicate a triple-humped structure, marking the transition between asymmetric fission of Hg178,180 and symmetric fission in the light Ra-Rn nuclei. Comparison with the macroscopic-microscopic finite-range liquid-drop model and the self-consistent approach employing the Gogny D1S energy density functional yields discrepancies. This demonstrates once more the need for dynamical fission calculations, because for both models the potential-energy surfaces lack pronounced structures, in contrast to those for the actinide region.

Ghys, L.; Andreyev, A. N.; Huyse, M.; Van Duppen, P.; Sels, S.; Andel, B.; Antalic, S.; Barzakh, A.; Capponi, L.; Cocolios, T. E.; Derkx, X.; De Witte, H.; Elseviers, J.; Fedorov, D. V.; Fedosseev, V. N.; Hessberger, F. P.; Kalaninová, Z.; Köster, U.; Lane, J. F. W.; Liberati, V.; Lynch, K. M.; Marsh, B. A.; Mitsuoka, S.; Möller, P.; Nagame, Y.; Nishio, K.; Ota, S.; Pauwels, D.; Page, R. D.; Popescu, L.; Radulov, D.; Rajabali, M. M.; Randrup, J.; Rapisarda, E.; Rothe, S.; Sandhu, K.; Seliverstov, M. D.; Sjödin, A. M.; Truesdale, V. L.; Van Beveren, C.; Van den Bergh, P.; Wakabayashi, Y.; Warda, M.

2014-10-01

244

Supernovae in paired galaxies  

NASA Astrophysics Data System (ADS)

We investigate the influence of close neighbor galaxies on the properties of supernovae (SNe) and their host galaxies using 56 SNe located in pairs of galaxies with different levels of star formation (SF) and nuclear activity. The mean distance of type II SNe from nuclei of hosts is greater by about a factor of 2 than that of type Ibc SNe. The distributions and mean distances of SNe are consistent with previous results compiled with the larger sample. For the first time it is shown that SNe Ibc are located in pairs with significantly smaller difference of radial velocities between components than pairs containing SNe Ia and II. We consider this as a result of higher star formation rate (SFR) of these closer systems of galaxies.

Nazaryan, T. A.; Petrosian, A. R.; Hakobyan, A. A.; Adibekyan, V. Zh.; Kunth, D.; Mamon, G. A.; Turatto, M.; Aramyan, L. S.

2014-07-01

245

Study on void fraction distribution in the moderator cell of Cold Neutron Source systems in China Advanced Research Reactor  

NASA Astrophysics Data System (ADS)

A physical model is developed for analyzing and evaluating the void fraction profiles in the moderator cell of the Cold Neutron Source (CNS) of the China Advanced Research Reactor (CARR), which is now constructing in the China Institute of Atomic Energy (CIAE). The results derived from the model are compared with the related experimental data and its propriety is verified. The model is then used to explore the influence of various factors, including the diameter of boiling vapor bubbles, liquid density, liquid viscosity and the total heating power acted on the moderator cell, on the void fraction profiles in the cell. The results calculated with the present model indicate that the void fraction in the moderator cell increases linearly with heating power, and increases with the liquid viscosity, but decreases as the size of bubbles increases, and increases linearly with heating power. For the case where hydrogen is being used as a moderator, calculation results show that the void fraction in the moderator cell may be less than 30%, which is the maximum void fraction permitted from the nuclear physics point of view. The model and the calculation results will help to obtain insight of the mechanism that controls the void fraction distribution in the moderator cell, and provide theoretical supports for the moderator cell design.

Li, Liangxing; Li, Huixiong; Hu, Jinfeng; Bi, Qincheng; Chen, Tingkuan

2007-04-01

246

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

247

Searching for pairing energies in phase space  

NASA Astrophysics Data System (ADS)

We obtain a representation of pairing energies in phase space, for the Lipkin-Meshkov-Glick and boson Bardeen-Cooper-Schrieffer pairing mean-field–like Hamiltonians. This is done by means of a probability distribution of the quantum state in phase space. In fact, we prove a correspondence between the points at which this probability distribution vanishes and the pairing energies. In principle, the vanishing of this probability distribution is experimentally accessible and additionally gives a method to visualize pairing energies across the model control parameter space. This result opens new ways to experimentally approach quantum pairing systems.

Calixto, M.; Castaños, O.; Romera, E.

2014-11-01

248

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.

2011-12-01

249

A background-free direction-sensitive neutron detector  

E-print Network

We show data from a new type of detector that can be used to determine the neutron flux, the energy distribution, and the direction of motion neutron for both fast and thermal neutrons. Many neutron detectors are plagued ...

Roccaro, Alvaro

250

Pair-Starved Pulsar Magnetospheres  

NASA Technical Reports Server (NTRS)

We propose a simple analytic model for the innermost (within the light cylinder of canonical radius, approx. c/Omega) structure of open-magnetic-field lines of a rotating neutron star (NS) with relativistic outflow of charged particles (electrons/positrons) and arbitrary angle between the NS spin and magnetic axes. We present the self-consistent solution of Maxwell's equations for the magnetic field and electric current in the pair-starved regime where the density of electron-positron plasma generated above the pulsar polar cap is not sufficient to completely screen the accelerating electric field and thus establish thee E . B = 0 condition above the pair-formation front up to the very high altitudes within the light cylinder. The proposed mode1 may provide a theoretical framework for developing the refined model of the global pair-starved pulsar magnetosphere.

Muslimov, Alex G.; Harding, Alice K.

2009-01-01

251

Distributions  

NSDL National Science Digital Library

This online, interactive lesson on distributions provides examples, exercises, and applets which explore the basic types of probability distributions and the ways distributions can be defined using density functions, distribution functions, and quantile functions.

Siegrist, Kyle

252

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

253

[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

2012-01-01

254

Paired t testsPaired t tests Paired (dependent) t-testPaired (dependent) t test  

E-print Network

Paired t testsPaired t tests #12;Paired (dependent) t-testPaired (dependent) t test · Compares test means from matched pairsCompares test means from matched pairs or two different samples from the same individualsindividuals ­ e.g., pretest & post test scores for the same group of students Ho: d = 0 d is thedifference

Wolverton, Steve

255

Protein Dynamics and Stability: The Distribution of Atomic Fluctuations in Thermophilic and Mesophilic Dihydrofolate Reductase Derived Using Elastic Incoherent Neutron Scattering  

SciTech Connect

The temperature dependence of the dynamics of mesophilic and thermophilic dihydrofolate reductase is examined using elastic incoherent neutron scattering. It is demonstrated that the distribution of atomic displacement amplitudes can be derived from the elastic scattering data by assuming a (Weibull) functional form that resembles distributions seen in molecular dynamics simulations. The thermophilic enzyme has a significantly broader distribution than its mesophilic counterpart. Furthermore, although the rate of increase with temperature of the atomic mean-square displacements extracted from the dynamic structure factor is found to be comparable for both enzymes, the amplitudes are found to be slightly larger for the thermophilic enzyme. Therefore, these results imply that the thermophilic enzyme is the more flexible of the two.

Meinhold, Lars [University of Heidelberg; Clement, David [University of Waikato, New Zealand; Tehei, M [University of Waikato, New Zealand; Daniel, R. M. [University of Waikato, New Zealand; Finney, J.L. [University College, London; Smith, Jeremy C [ORNL

2008-11-01

256

Correlated Fermion Pairs in Nuclei and Ultracold Atomic Gases  

E-print Network

In atomic nuclei the momentum distribution of nucleons above the Fermi momentum (k > k_F ~ 250 MeV/c) is dominated by short range correlated neutron-proton pairs and has the same shape as that of the deuterium, i.e. it decreases as k^-4. The high momentum distribution of atoms in two spin-state ultra-cold atomic gases with strong short-range interactions between atoms with different spins, which can be described using Tan's contact, are also dominated by short range pairs of different fermions and have the same k^-4 dependence as in atomic nuclei. A single dimensionless parameter that encodes the density and interaction strength is (k_F a)^-1. Here we show that when the value of (k_F a)^-1 for the atomic system is chosen to be similar to that of atomic nuclei, the probability for finding a short range unlike-fermion pair in both systems is the same. This is remarkable because these systems differ by about 20 orders of magnitude in density. This similarity indicates another approach to nuclear systems with their complicated interactions, possibly leading to greater understanding of nuclei and astrophysical superdense nuclear objects.

O. Hen; L. B. Weinstein; E. Piasetzky; G. A. Miller; M. M. Sargsian; Y. Sagi

2014-11-23

257

Global Distribution of Shallow Water on Mars: Neutron Mapping of Summer-Time Surface by HEND/Odyssey  

NASA Technical Reports Server (NTRS)

Orbital mapping of induced neutrons and gamma-rays by Odyssey has recently successfully proven the applicability of nuclear methods for studying of the elementary composition of Martian upper-most subsurface. In particular, the suite of Gamma-Ray Spectrometer (GRS) has discovered the presence of large water-ice rich regions southward and northward on Mars. The data of neutron mapping of summer-time surface are presented below from the Russian High Energy Neutron Spectrometer (HEND), which is a part of GRS suite. These maps represent the content of water in the soil for summer season at Southern and Northern hemispheres, when the winter deposit of CO2 is absent on the surface. The seasonal evolution of CO2 coverage on Mars is the subject of the complementary paper.

Mitrofanov, I. G.; Litvak, M. L.; Kozyrev, A. S.; Sanin, A. B.; Tretyakov, V. I.; Boynton, W.; Hamara, D.; Shinohara, C.; Saunders, R. S.; Drake, D.

2003-01-01

258

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

259

Supercool Neutrons (Ultracold Neutrons)  

E-print Network

the sun does it). 2) In an atom smasher (accelerator). Insititut LaueLangevin, Grenoble, France, www. ­ The atomic nucleus is made of neutrons and protons. property neutron proton electric charge 0 1e

Martin, Jeff

260

In vivo prompt gamma neutron activation analysis for the screening of boron-10 distribution in a rabbit knee: a simulation study  

NASA Astrophysics Data System (ADS)

Boron neutron capture synovectomy (BNCS) is under development as a potential treatment modality for rheumatoid arthritis (RA). RA is characterized by the inflammation of the synovium (the membrane lining articular joints), which leads to pain and a restricted range of motion. BNCS is a two-part procedure involving the injection of a boronated compound directly into the diseased joint followed by irradiation with a low-energy neutron beam. The neutron capture reactions taking place in the synovium deliver a local, high-linear energy transfer (LET) dose aimed at destroying the inflamed synovial membrane. For successful treatment via BNCS, a boron-labeled compound exhibiting both high synovial uptake and long retention time is necessary. Currently, the in vivo uptake behavior of potentially useful boronated compounds is evaluated in the knee joints of rabbits in which arthritis has been induced. This strategy involves the sacrifice and dissection of a large number of animals. An in vivo 10B screening approach is therefore under investigation with the goal of significantly reducing the number of animals needed for compound evaluation via dissection studies. The 'in vivo prompt gamma neutron activation analysis' (IVPGNAA) approach uses a narrow neutron beam to irradiate the knee from several angular positions following the intra-articular injection of a boronated compound whose uptake characteristics are unknown. A high-purity germanium detector collects the 478 keV gamma photons produced by the 10B capture reactions. The 10B distribution in the knee is then reconstructed by solving a system of simultaneous equations using a weighted least squares algorithm. To study the practical feasibility of IVPGNAA, simulation data were generated with the Monte Carlo N-particle transport code. The boron-containing region of a rabbit knee was partitioned into 8 compartments, and the 10B prompt gamma signals were tallied from 16 angular positions. Results demonstrate that for this level of spatial resolution, an estimate of 10B distribution inside the joint can be obtained to within 10% uncertainty, under ideal conditions. Variations of the anatomic dimensions among individual rabbit knees and potential knee positioning errors will result in an uncertainty of over 20%. IVPGNAA thus provides sufficient resolution and quantification regarding the in vivo uptake characteristics of boronated pharmaceuticals to serve as a useful means of screening new compounds of potential use in BNCS.

Zhu, X.; Clackdoyle, R.; Shortkroff, S.; Yanch, J.

2008-05-01

261

In vivo prompt gamma neutron activation analysis for the screening of boron-10 distribution in a rabbit knee: a simulation study.  

PubMed

Boron neutron capture synovectomy (BNCS) is under development as a potential treatment modality for rheumatoid arthritis (RA). RA is characterized by the inflammation of the synovium (the membrane lining articular joints), which leads to pain and a restricted range of motion. BNCS is a two-part procedure involving the injection of a boronated compound directly into the diseased joint followed by irradiation with a low-energy neutron beam. The neutron capture reactions taking place in the synovium deliver a local, high-linear energy transfer (LET) dose aimed at destroying the inflamed synovial membrane. For successful treatment via BNCS, a boron-labeled compound exhibiting both high synovial uptake and long retention time is necessary. Currently, the in vivo uptake behavior of potentially useful boronated compounds is evaluated in the knee joints of rabbits in which arthritis has been induced. This strategy involves the sacrifice and dissection of a large number of animals. An in vivo (10)B screening approach is therefore under investigation with the goal of significantly reducing the number of animals needed for compound evaluation via dissection studies. The 'in vivo prompt gamma neutron activation analysis' (IVPGNAA) approach uses a narrow neutron beam to irradiate the knee from several angular positions following the intra-articular injection of a boronated compound whose uptake characteristics are unknown. A high-purity germanium detector collects the 478 keV gamma photons produced by the (10)B capture reactions. The (10)B distribution in the knee is then reconstructed by solving a system of simultaneous equations using a weighted least squares algorithm. To study the practical feasibility of IVPGNAA, simulation data were generated with the Monte Carlo N-particle transport code. The boron-containing region of a rabbit knee was partitioned into 8 compartments, and the (10)B prompt gamma signals were tallied from 16 angular positions. Results demonstrate that for this level of spatial resolution, an estimate of (10)B distribution inside the joint can be obtained to within 10% uncertainty, under ideal conditions. Variations of the anatomic dimensions among individual rabbit knees and potential knee positioning errors will result in an uncertainty of over 20%. IVPGNAA thus provides sufficient resolution and quantification regarding the in vivo uptake characteristics of boronated pharmaceuticals to serve as a useful means of screening new compounds of potential use in BNCS. PMID:18445874

Zhu, X; Clackdoyle, R; Shortkroff, S; Yanch, J

2008-05-21

262

Study on void fraction distribution in the moderator cell of Cold Neutron Source systems in China Advanced Research Reactor  

Microsoft Academic Search

A physical model is developed for analyzing and evaluating the void fraction profiles in the moderator cell of the Cold Neutron Source (CNS) of the China Advanced Research Reactor (CARR), which is now constructing in the China Institute of Atomic Energy (CIAE). The results derived from the model are compared with the related experimental data and its propriety is verified.

Liangxing Li; Huixiong Li; Jinfeng Hu; Qincheng Bi; Tingkuan Chen

2007-01-01

263

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

264

Distribution of functional groups in periodic mesoporous organosilica materials studied by small-angle neutron scattering with in situ adsorption of nitrogen  

PubMed Central

Summary Periodic mesoporous materials of the type (R?O)3Si-R-Si(OR?)3 with benzene as an organic bridge and a crystal-like periodicity within the pore walls were functionalized with SO3H or SO3 ? groups and investigated by small-angle neutron scattering (SANS) with in situ nitrogen adsorption at 77 K. If N2 is adsorbed in the pores the SANS measurements show a complete matching of all of the diffraction signals that are caused by the long-range ordering of the mesopores in the benzene-PMO, due to the fact that the benzene-PMO walls possess a neutron scattering length density (SLD) similar to that of nitrogen in the condensed state. However, signals at higher q-values (>1 1/Å) are not affected with respect to their SANS intensity, even after complete pore filling, confirming the assumption of a crystal-like periodicity within the PMO material walls due to ?–? interactions between the organic bridges. The SLD of pristine benzene-PMO was altered by functionalizing the surface with different amounts of SO3H-groups, using the grafting method. For a low degree of functionalization (0.81 mmol SO3H·g?1) and/or an inhomogeneous distribution of the SO3H-groups, the SLD changes only negligibly, and thus, complete contrast matching is still found. However, for higher amounts of SO3H-groups (1.65 mmol SO3H·g?1) being present in the mesopores, complete matching of the neutron diffraction signals is no longer observed proving that homogeneously distributed SO3H-groups on the inner pore walls of the benzene-PMO alter the SLD in a way that it no longer fits to the SLD of the condensed N2. PMID:23016147

Sharifi, Monir; Wallacher, Dirk

2012-01-01

265

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

266

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

267

Microdosimetric spectra of the THOR neutron beam for boron neutron capture therapy.  

PubMed

A primary objective of the BNCT project in Taiwan, involving THOR (Tsing Hua Open Pool Reactor), was to examine the potential treatment of hepatoma. To characterise the epithermal neutron beam in THOR, the microdosimetry distributions in lineal energy were determined using paired tissue-equivalent proportional counters with and without boron microfoils. Microdosimetry results were obtained in free-air and at various depths in a PMMA phantom near the exit of the beam port. A biological weighting function, dependent on lineal energy, was used to estimate the relative biological effectiveness of the beam. An effective RBE of 2.7 was found at several depths in the phantom. PMID:12918789

Hsu, F Y; Tung, C J; Watt, D E

2003-01-01

268

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

269

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.

Simões Júnior, F. J. R.; Alves, M. V.; Rizzato, F. B.

2005-12-01

270

Neutron resonance averaging  

SciTech Connect

The principles of resonance averaging as applied to neutron capture reactions are described. Several illustrations of resonance averaging to problems of nuclear structure and the distribution of radiative strength in nuclei are provided. 30 refs., 12 figs.

Chrien, R.E.

1986-10-01

271

Atom Probe Tomography Characterization of the Solute Distributions in a Neutron-Irradiated and Annealed Pressure Vessel Steel Weld  

SciTech Connect

A combined atom probe tomography and atom probe field ion microscopy study has been performed on a submerged arc weld irradiated to high fluence in the Heavy-Section Steel irradiation (HSSI) fifth irradiation series (Weld 73W). The composition of this weld is Fe - 0.27 at. % Cu, 1.58% Mn, 0.57% Ni, 0.34% MO, 0.27% Cr, 0.58% Si, 0.003% V, 0.45% C, 0.009% P, and 0.009% S. The material was examined after five conditions: after a typical stress relief treatment of 40 h at 607 C, after neutron irradiation to a fluence of 2 x 10{sup 23} n m{sup {minus}2} (E > 1 MeV), and after irradiation and isothermal anneals of 0.5, 1, and 168 h at 454 C. This report describes the matrix composition and the size, composition, and number density of the ultrafine copper-enriched precipitates that formed under neutron irradiation and the change in these parameters with post-irradiation annealing treatments.

Miller, M.K.

2001-01-30

272

Conservation of Isospin in Neutron-Rich Fission Fragments  

E-print Network

On the occasion of the $75^{th}$ anniversary of the fission phenomenon, we present a surprisingly simple result which highlights the important role of isospin and its conservation in neutron rich fission fragments. We have analysed the fission fragment mass distribution from two recent heavy-ion reactions $^{238}$U($^{18}$O,f) and $^{208}$Pb($^{18}$O,f) as well as a thermal neutron fission reaction $^{245}$Cm(n$^{th}$,f). We find that the conservation of the total isospin explains the overall trend in the observed relative yields of fragment masses in each fission pair partition. The isospin values involved are very large making the effect dramatic. The findings open the way for more precise calculations of fission fragment distributions in heavy nuclei and may have far reaching consequences for the drip line nuclei, HI fusion reactions, and calculation of decay heat in the fission phenomenon.

Ashok Kumar Jain; Deepika Choudhury; Bhoomika Maheshwari

2014-08-11

273

Hard Photo-disintegration of proton pairs in ^3He  

NASA Astrophysics Data System (ADS)

Hard deuteron photo-disintegration has been investigated for 20 years, as its cross sections follow the constituent counting rules and it provides insight into the interplay between hadronic and quark-gluon degrees of freedom in high-momentum transfer exclusive reactions. During the summer of 2007, at Jefferson lab, Hall A, we measured for the first time hard pp-pair disintegration in the reaction ?,3 He ->pp + n, using kinematics corresponding to a spectator neutron. The current state of the analysis and preliminary results will be shown. Clues to the underlying physics can be found in the comparison of our measurements with deuteron photo-disintegration, the energy dependence of the cross sections at 90^o c.m., and the ?n distribution.

Pomerantz, Ishay; Piasetzky, Eli; Gilman, Ronald

2008-10-01

274

Hard Photo-disintegration of proton pairs in ^3He  

NASA Astrophysics Data System (ADS)

Hard deuteron photo-disintegration has been investigated for 20 years, as its cross sections follow the constituent counting rules and it provides insight into the interplay between hadronic and quark-gluon degrees of freedom in high-momentum transfer exclusive reactions. We have now measured for the first time hard pp-pair disintegration in the reaction ?,3 He ->pp + n, using kinematics corresponding to a spectator neutron. The current state of the analysis will be shown. Clues to the underlying physics can be found in the comparison of our measurements with deuteron photo-disintegration, the energy dependence of the cross sections at 90^o c.m., and the ?n distribution.

Gilman, Ronald; Piasetzky, Eli; Pomerantz, Ishay

2008-04-01

275

Anomalous spin-density distribution on oxygen and Ru in Ca(1.5)Sr(0.5)RuO(4): polarized neutron diffraction study.  

PubMed

By means of polarized neutron diffraction in a magnetic field of 7.0 T at 1.6 K an anomalously large magnetization density is observed on the in-plane oxygen in Ca(1.5)Sr(0.5)RuO(4). Field-induced moments of different ions are determined by refinement on the flipping ratios, yielding micro(Ru)=0.346(11)micro(B), micro(O1)=0.076(6)micro(B), and micro(O2)=0.009(6)micro(B). The moment on the oxygen arises from the strong hybridization between the Ru-4d and O-2p orbitals. The maximum entropy magnetization density reconstruction reveals a strongly anisotropic density at the Ru site, consistent with the distribution of the xy (t(2g) band) d orbitals. PMID:12190496

Gukasov, A; Braden, M; Papoular, R J; Nakatsuji, S; Maeno, Y

2002-08-19

276

Neutron degeneracy and plasma physics effects on radiative neutron captures in neutron star crust  

E-print Network

We consider the astrophysical reaction rates for radiative neutron capture reactions ($n,\\gamma$) 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 ($\\gamma,n$) 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.

P. S. Shternin; M. Beard; M. Wiescher; D. G. Yakovlev

2012-07-25

277

Experimental Study of Three-Dimensional Void Fraction Distribution in Heated Tight-Lattice Rod Bundles Using Three-Dimensional Neutron Tomography  

NASA Astrophysics Data System (ADS)

Three-dimensional (3D) void fraction distributions in a tight-lattice of heated 7- or 14-rod bundles were measured using 3D neutron tomography. The distribution was also studied parametrically from the thermal-hydraulic point of view in order to elucidate boiling phenomena in a fuel assembly of the FLWR which is being developed as an advanced BWR-type reactor. 7-rod tests were carried out to obtain high void fraction data. 14-rod tests were conducted for visualization and discussion of the 3D distribution extending from the vapor generation region to the high void fraction region at one time. Experimental data were obtained under atmospheric pressure with mass velocity, heater power and inlet quality as the test parameters. It was found from the visualization of data that the void fraction at the channel center became higher than that at the periphery, high void fraction spots appeared in narrow regions at the inlet, and a so-called 'vapor chimney' was generated at the center of a subchannel.

Kureta, Masatoshi

278

Collaborative homologous pairing during C. elegans meiosis  

PubMed Central

In preparation for meiotic chromosome segregation, homologous chromosomes need to pair, synapse (i.e., assemble the synaptonemal complex, SC), and then recombine to generate a physical linkage (i.e., chiasma) between them. In many organisms meiotic pairing capacity distributed along the entire chromosome length supports presynaptic alignment. In contrast, the prevailing model for C. elegans proposes that presynaptic homologous pairing is performed solely by a master pairing-site, the pairing center (PC). In this model, the remaining chromosomal regions (the non-PC regions) are not actively involved in presynaptic pairing, and the SC assembling from the PC aligns the homologous chromosomes along non-PC regions and holds them together. Our recent work, however, demonstrates that C. elegans chromosomes establish presynaptic alignment along the entire chromosome length, suggesting that the non-PC regions are also actively involved in the presynaptic pairing process. Furthermore, we have also discovered that the chromodomain protein MRG-1 facilitates this presynaptic non-PC pairing. The phenotype of the mrg-1 mutant indicates that the PC and the non-PC collaborate in successful pairing and synapsis. Therefore, homologous pairing mechanisms in C. elegans possibly share more similarity with those in other organisms than previously thought. Here, we elaborate on these observations and discuss a hypothetical model for presynaptic pairing in C. elegans based on our novel findings. PMID:24058834

Nabeshima, Kentaro

2012-01-01

279

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

Microsoft Academic Search

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

SJ Knight; C Yau; R Clifford; AT Timbs; E Sadighi Akha; HM Dréau; A Burns; C Ciria; DG Oscier; AR Pettitt; S Dutton; CC Holmes; J Taylor; JB Cazier; A Schuh

2012-01-01

280

Model of defect reactions and the influence of clustering in pulse-neutron-irradiated Si  

SciTech Connect

Transient reactions among irradiation defects, dopants, impurities, and carriers in pulse-neutron-irradiated Si were modeled taking into account the clustering of the primal defects in recoil cascades. Continuum equations describing the diffusion, field drift, and reactions of relevant species were numerically solved for a submicrometer spherical volume, within which the starting radial distributions of defects could be varied in accord with the degree of clustering. The radial profiles corresponding to neutron irradiation were chosen through pair-correlation-function analysis of vacancy and interstitial distributions obtained from the binary-collision code MARLOWE, using a spectrum of primary recoil energies computed for a fast-burst fission reactor. Model predictions of transient behavior were compared with a variety of experimental results from irradiated bulk Si, solar cells, and bipolar-junction transistors. The influence of defect clustering during neutron bombardment was further distinguished through contrast with electron irradiation, where the primal point defects are more uniformly dispersed.

Myers, S. M.; Cooper, P. J.; Wampler, W. R. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1056 (United States)

2008-08-15

281

Neutronic reactor  

DOEpatents

A nuclear reactor includes an active portion with fissionable fuel and neutron moderating material surrounded by neutron reflecting material. A control element in the active portion includes a group of movable rods constructed of neutron-absorbing material. Each rod is movable with respect to the other rods to vary the absorption of neutrons and effect control over neutron flux.

Wende, Charles W. J. (Augusta, GA); Babcock, Dale F. (Wilmington, DE); Menegus, Robert L. (Wilmington, DE)

1983-01-01

282

Distribution and solubility of radionuclides and neutron absorbers in waste forms for disposition of plutonium ash and scraps, excess plutonium, and miscellaneous spent nuclear fuels. 1998 annual progress report  

Microsoft Academic Search

'The objective of this research is to gain a fundamental understanding of the distributions and the solubility limits for actinides Pu and U and rare earth neutron absorbers such as Gd and Hf in waste forms. This will be accomplished by systematically studying the local structural environments of these constituents in representative waste forms such as glass, ceramics, and vitreous

X. Fen; E. R. Vance; D. K. Shuh

1998-01-01

283

Measuring the Parity-Violating Neutron Spin Rotation in Helium: The Neutron Spin Rotation Experiment  

Microsoft Academic Search

We have performed a precision measurement of the parity-violating neutron spin rotation in helium due to the nucleon-nucleon weak interaction at the NIST Center for Neutron Research. The measurement employed a beam of low energy neutrons passing through a liquid helium target system located between a neutron polarizer--analyzer pair. The parity-violating spin rotation magnitude was determined from measured count asymmetries

C. D. Bass; T. D. Bass; B. E. Crawford; J. M. Dawkins; K. Gan; B. R. Heckel; J. C. Horton; C. R. Huffer; D. Luo; D. M. Markoff; A. M. Micherdzinska; H. P. Mumm; J. S. Nico; A. K. Opper; M. G. Sarsour; E. Sharapov; W. M. Snow; H. E. Swanson; S. C. Walbridge; V. Zhumabekova

2009-01-01

284

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

285

Neutron spectral and angular distribution measurements for 113 and 256 MeV protons on range-thick Al and sup 238 U targets using the foil activation techniques  

SciTech Connect

Second neutron yields, energy spectra, and angular distributions have been measured at seven angles from 0 to 150{degree} for 113 and 256 MeV protons stopped in range-thick targets of aluminum and depleted uranium ({sup 238}U). Thin foil stacks of ten different materials were activated by secondary neutrons at distances of 20--30 cm from the targets. Following each irradiation, 30--40 different activation products were measured by gamma-ray spectroscopy. These activation rates were then used to adjust neutron energy spectra calculated by the HETC computer code. Activation cross sections were taken from ENDF/BV below 20 MeV, from literature values tested in Be(d,n) fields up to 50 MeV, and from proton spallation data and calculations from 50--250 MeV. Spectral adjustments were made with the STAY'SL computer code using a least-squares technique to minimize {chi}{sup 2} for a covariance matrix determined from uncertainties in the measured activities, cross sections, and calculated flux spectra. Neutron scattering effects were estimated from foil packets irradiated at different distances from the target. Proton effects were measured with (p,n) reactions. Systematic differences were found between the adjusted and calculated neutron spectra, namely, that HETC underpredicts the neutron flux at back angles by a factor of 2--3 and slightly overpredicts the flux at forward angles. 19 refs., 23 figs., 13 tabs.

Greenwood, L.R.; Intasorn, A.

1989-07-01

286

OVERPARTITION PAIRS JEREMY LOVEJOY  

E-print Network

OVERPARTITION PAIRS JEREMY LOVEJOY Abstract. An overpartition pair is a combinatorial object Chercheuses". 1 #12;2 JEREMY LOVEJOY and Ramanujan's 11 summation [16, p.239, (II.29)], nZ (-1/a)n(azq)n (-bq

Fondements et Applications, Université Paris 7

287

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

288

Characterization of neutron radiation damage in GaAs  

NASA Astrophysics Data System (ADS)

The NJOY and MARLOWE computer codes are used to characterize neutron damage to GaAs. The fidelity of the components that affect the calculated GaAs damage is examined. The initial defect production is found to be a linear function of the damage energy. Recombination of Frenkel pairs and the distribution of vacancies introduce a nonlinearity in the residual defect population with respect to the damage energy. Consideration of the defect recombinations only provides a slight improvement in the agreement between measured and calculated damage in GaAs but does indicate the areas where more work is needed.

Griffin, P. J.; Luera, T. F.; Kelly, J. G.; Lazo, M. S.

1989-12-01

289

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

290

Ion pair receptors†  

PubMed Central

Compared with simple ion receptors, which are able to bind either a cation or an anion, ion pair receptors bearing both a cation and an anion recognition site offer the promise of binding ion pairs or pairs of ions strongly as the result of direct or indirect cooperative interactions between co-bound ions. This critical review focuses on the recent progress in the design of ion pair receptors and summarizes the various binding modes that have been used to accommodate ion pairs (110 references). PMID:20737073

Kim, Sung Kuk

2010-01-01

291

J = 0 , J =Jmax, and quadrupole pairing  

NASA Astrophysics Data System (ADS)

We consider 2 neutrons and 2 protons in the g9/2 shell. Wave functions and energy levels are obtained for various interactions. The wavefunctions for states with total angular momentum I greater than or equal to 10 are not affected by what the pairing interaction (J = 0 T = 1) is. Other parts of the interaction are therefore of increased importance. Furthermore, states with I greater than or equal to 12 are not affected by the J = 2 interaction.

Hertz-Kintish, Daniel; Zamick, Larry

2014-12-01

292

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

293

Une Plate-forme d'Emulation Lgre pour Etudier les Systmes Pair--Pair  

E-print Network

Une Plate-forme d'Emulation Légère pour Etudier les Systèmes Pair-à-Pair RECHERCHE/SYNTHESE Lucas-to-peer systems, which combines emulation (execution of the real application inside a synthetic envi- ronment) and virtualization. After describing the main features of P2PLab (distributed network emulation, lightweight

Paris-Sud XI, Université de

294

Calculation of two-neutron multiplicity in photonuclear reactions  

NASA Technical Reports Server (NTRS)

The most important particle emission processes for electromagnetic excitations in nucleus-nucleus collisions are the ejection of single neutrons and protons and also pairs of neutrons and protons. Methods are presented for calculating two-neutron emission cross sections in photonuclear reactions. The results are in a form suitable for application to nucleus-nucleus reactions.

Norbury, John W.; Townsend, Lawrence W.

1989-01-01

295

Calculation of two-neutron multiplicity in photonuclear reactions  

NASA Technical Reports Server (NTRS)

The most important particle emission processes for electromagnetic excitations in nucleus-nucleus collisions are the ejection of single neutrons and protons and also pairs of neutrons and protons. Methods are presented for calculating two-neutron emission cross sections in photonuclear reactions. The results are in a form suitable for application to nucleus-nucleus reactions.

Norbury, John W.; Townsend, Lawrence W.

1990-01-01

296

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

297

Paired watershed study design  

SciTech Connect

The purpose of the fact sheet is to describe the paired watershed approach for conducting nonpoint source (NPS) water quality studies. The basic approach requires a minimum of two watersheds - control and treatment - and two periods of study - calibration and treatment. The basis of the paired watershed approach is that there is a quantifiable relationship between paired water quality data for the two watersheds, and that this relationship is valid until a major change is made in one of the watersheds.

Clausen, J.C.; Spooner, J.

1993-09-01

298

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

299

Pair Winds in Schwarzschild Spacetime with Application to Strange Stars  

E-print Network

We present the results of numerical simulations of stationary, spherically outflowing, electron-positron pair winds, with total luminosities in the range 10^{34}--10^{42} ergs/s. In the concrete example described here, the wind injection source is a hot, bare, strange star, predicted to be a powerful source of pairs created by the Coulomb barrier at the quark surface. We find that photons dominate in the emerging emission, and the emerging photon spectrum is rather hard and differs substantially from the thermal spectrum expected from a neutron star with the same luminosity. This might help distinguish the putative bare strange stars from neutron stars.

A. G. Aksenov; M. Milgrom; V. V. Usov

2007-01-09

300

Pair Production of Heavy-Exotic-Fermions  

E-print Network

We study the production and signatures of heavy exotic fermion pairs in the framework of the vector singlet model (VSM), vector doublet model (VDM) and fermion-mirror-fermion (FMF) model. We show that the pair production cross sections are competitive with the ones for the single production of exotic fermions due to the exchange of a photon in the $s$ channel and to the vector component of the $Z$ - boson coupling to exotic fermions. We also exhibit some kinematical distributions.

Jorge Eduardo Cieza Montalvo

1998-07-01

301

Quark matter in neutron stars  

E-print Network

According to quantum chromodynamics, matter at ultra-high density and low temperature is a quark liquid, with a condensate of Cooper pairs of quarks near the Fermi surface ("color superconductivity"). This paper reviews the physics of color superconductivity, and discusses some of the proposed signatures by which we might detect quark matter in neutron stars.

Mark G. Alford

2009-09-18

302

A Survey of Faint Galaxy Pairs  

E-print Network

A sample of faint, V magnitude selected, galaxy pairs, having physical separations less than approximately 20\\hkpc, is used to examine the rise in the merger rate with redshift and the statistical relations between close pairs and the field galaxy population. Redshifts have been obtained for 14 galaxies ($V \\le 22.5$) that are in close ($\\theta < 6\\arcs$) pairs, along with a comparison sample of 38 field galaxies. Two color photometry is available for about 1000 galaxies in the same fields. The average redshift of the $V\\le22.5$ field population is 0.36, statistically equal to the average redshift of 0.42 for the pairs. The similarity of the two redshift distributions, $\\Delta z\\le 0.1$, limits any differential luminosity enhancement of close pairs to less than half a magnitude. The pairs are somewhat bluer than the field and have nearly twice the average [O~II] detection rate of the field, but the differences are not statistically significant. The field population has an angular correlation at separations of $\\theta\\le$6\\arcs\\ higher than the inward extrapolation of $\\omega(\\theta)\\propto \\theta^{-0.8}$, which may be a population of ``companions'' not present at the current epoch, or, luminosity enhancement of intrinsically faint galaxies in pairs. Physical pairs comprise about 7\\% of the faint galaxies in our survey fields. The same physical separation applied to local galaxies finds only 2.6\\% in pairs. If the rise in close low relatively velocity pairs with redshift is parameterized as $(1+z)^m$, then $m=2.9\\pm0.8$. If all pairs at low velocities and $r\\le 20$\\hkpc\\ merge, then the

Carlberg; Pritchet; Infante

1994-01-31

303

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

304

Solutions of nuclear pairing  

SciTech Connect

We give the exact solution of orbit dependent nuclear pairing problem between two nondegenerate energy levels using the Bethe ansatz technique. Our solution reduces to previously solved cases in the appropriate limits including Richardson's treatment of reduced pairing in terms of rational Gaudin algebra operators.

Balantekin, A. B.; Pehlivan, Y. [Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States)

2007-11-15

305

Investigation of the Distribution of Fission Products Silver, Palladium and Cadmium in Neutron Irradiated SIC using a Cs Corrected HRTEM  

SciTech Connect

Electron microscopy examinations of selected coated particles from the first advanced gas reactor experiment (AGR-1) at Idaho National Laboratory (INL) provided important information on fission product distribution and chemical composition. Furthermore, recent research using STEM analysis led to the discovery of Ag at SiC grain boundaries and triple junctions. As these Ag precipitates were nano-sized, high resolution transmission electron microscopy (HRTEM) examination was used to provide more information at the atomic level. This paper describes some of the first HRTEM results obtained by examining a particle from Compact 4-1-1, which was irradiated to an average burnup of 19.26% fissions per initial metal atom (FIMA), a time average, volume-averaged temperature of 1072°C; a time average, peak temperature of 1182°C and an average fast fluence of 4.13 x 1021 n/cm2. Based on gamma analysis, it is estimated that this particle may have released as much as 10% of its available Ag-110m inventory during irradiation. The HRTEM investigation focused on Ag, Pd, Cd and U due to the interest in Ag transport mechanisms and possible correlation with Pd, Ag and U previously found. Additionally, Compact 4-1-1 contains fuel particles fabricated with a different fuel carrier gas composition and lower deposition temperatures for the SiC layer relative to the Baseline fabrication conditions, which are expected to reduce the concentration of SiC defects resulting from uranium dispersion. Pd, Ag, and Cd were found to co-exist in some of the SiC grain boundaries and triple junctions whilst U was found to be present in the micron-sized precipitates as well as separately in selected areas at grain boundaries. This study confirmed the presence of Pd both at inter- and intragranular positions; in the latter case specifically at stacking faults. Small Pd nodules were observed at a distance of about 6.5 micron from the inner PyC/SiC interface.

I. J. van Rooyen; E. Olivier; J. H Neethlin

2014-10-01

306

Cooper Pairs in Insulators?!  

ScienceCinema

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. 

James Valles

2010-01-08

307

FAST NEUTRON PENETRATION THROUGH REACTOR SHIELDS  

Microsoft Academic Search

Measurements of the penetration of reactor fast neutrons as a function ; of energy have been made in a thermal shield mock-up. The investigation was ; restricted to neutrons in the 2 to 10 Mev energy region A neutron energy ; spectrometer employing a Li⁶I(Eu) scintillation crystal was used. Relative ; spectral distributions are preserted for distances up to 12

N. Hartmann; G. R. Hopkins

1959-01-01

308

The effect of turbulent kinetic energy on inferred ion temperature from neutron spectra  

SciTech Connect

Measuring the width of the energy spectrum of fusion-produced neutrons from deuterium (DD) or deuterium-tritium (DT) plasmas is a commonly used method for determining the ion temperature in inertial confinement fusion (ICF) implosions. In a plasma with a Maxwellian distribution of ion energies, the spread in neutron energy arises from the thermal spread in the center-of-mass velocities of reacting pairs of ions. Fluid velocities in ICF are of a similar magnitude as the center-of-mass velocities and can lead to further broadening of the neutron spectrum, leading to erroneous inference of ion temperature. Motion of the reacting plasma will affect DD and DT neutrons differently, leading to disagreement between ion temperatures inferred from the two reactions. This effect may be a contributor to observations over the past decades of ion temperatures higher than expected from simulations, ion temperatures in disagreement with observed yields, and different temperatures measured in the same implosion from DD and DT neutrons. This difference in broadening of DD and DT neutrons also provides a measure of turbulent motion in a fusion plasma.

Murphy, T. J., E-mail: tjmurphy@lanl.gov [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2014-07-15

309

The effect of turbulent kinetic energy on inferred ion temperature from neutron spectra  

NASA Astrophysics Data System (ADS)

Measuring the width of the energy spectrum of fusion-produced neutrons from deuterium (DD) or deuterium-tritium (DT) plasmas is a commonly used method for determining the ion temperature in inertial confinement fusion (ICF) implosions. In a plasma with a Maxwellian distribution of ion energies, the spread in neutron energy arises from the thermal spread in the center-of-mass velocities of reacting pairs of ions. Fluid velocities in ICF are of a similar magnitude as the center-of-mass velocities and can lead to further broadening of the neutron spectrum, leading to erroneous inference of ion temperature. Motion of the reacting plasma will affect DD and DT neutrons differently, leading to disagreement between ion temperatures inferred from the two reactions. This effect may be a contributor to observations over the past decades of ion temperatures higher than expected from simulations, ion temperatures in disagreement with observed yields, and different temperatures measured in the same implosion from DD and DT neutrons. This difference in broadening of DD and DT neutrons also provides a measure of turbulent motion in a fusion plasma.

Murphy, T. J.

2014-07-01

310

Neutron guide  

DOEpatents

A neutron guide in which lengths of cylindrical glass tubing have rectangular glass plates properly dimensioned to allow insertion into the cylindrical glass tubing so that a sealed geometrically precise polygonal cross-section is formed in the cylindrical glass tubing. The neutron guide provides easier alignment between adjacent sections than do the neutron guides of the prior art.

Greene, Geoffrey L. (Los Alamos, NM)

1999-01-01

311

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  

SciTech Connect

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. A standard optical video system is also used to observe the flow regime. The annulus flow channel is operated as a bubble column and measurements obtained for gas flow rates from 0.0 to 30.01/min. The flow regimes observed by all three measurement systems through image analysis shows that the two-dimensional void fraction distribution can be obtained. The X-CT system is shown to have a superior temporal resolution capable of resolving the void fraction distribution in an (r,{theta}) plane in 33.0 ms. Void fraction distribution for bubbly flow and slug flow is determined.

Harvel, G.D. [McMaster Univ., Ontario (Canada); [Combustion and Heat Transfer Lab., Takasago (Japan); Hori, K.; Kawanishi, K. [Combustion and Heat Transfer Lab., Takasago (Japan)] [and others

1995-09-01

312

Observation of Neutron Skyshine from an Accelerator Based Neutron Source  

NASA Astrophysics Data System (ADS)

A key feature of neutron based interrogation systems is the need for adequate provision of shielding around the facility. Accelerator facilities adapted for fast neutron generation are not necessarily suitably equipped to ensure complete containment of the vast quantity of neutrons generated, typically >1011 n?s-1. Simulating the neutron leakage from a facility is not a simple exercise since the energy and directional distribution can only be approximated. Although adequate horizontal, planar shielding provision is made for a neutron generator facility, it is sometimes the case that vertical shielding is minimized, due to structural and economic constraints. It is further justified by assuming the atmosphere above a facility functions as an adequate radiation shield. It has become apparent that multiple neutron scattering within the atmosphere can result in a measurable dose of neutrons reaching ground level some distance from a facility, an effect commonly known as skyshine. This paper describes a neutron detection system developed to monitor neutrons detected several hundred metres from a neutron source due to the effect of skyshine.

Franklyn, C. B.

2011-12-01

313

Observation of Neutron Skyshine from an Accelerator Based Neutron Source  

SciTech Connect

A key feature of neutron based interrogation systems is the need for adequate provision of shielding around the facility. Accelerator facilities adapted for fast neutron generation are not necessarily suitably equipped to ensure complete containment of the vast quantity of neutrons generated, typically >10{sup 11} n{center_dot}s{sup -1}. Simulating the neutron leakage from a facility is not a simple exercise since the energy and directional distribution can only be approximated. Although adequate horizontal, planar shielding provision is made for a neutron generator facility, it is sometimes the case that vertical shielding is minimized, due to structural and economic constraints. It is further justified by assuming the atmosphere above a facility functions as an adequate radiation shield. It has become apparent that multiple neutron scattering within the atmosphere can result in a measurable dose of neutrons reaching ground level some distance from a facility, an effect commonly known as skyshine. This paper describes a neutron detection system developed to monitor neutrons detected several hundred metres from a neutron source due to the effect of skyshine.

Franklyn, C. B. [Radiation Science Department, Necsa, PO Box 582, Pretoria 0001 (South Africa)

2011-12-13

314

{beta}-decay in neutron-deficient Hg, Pb, and Po isotopes  

SciTech Connect

The effect of nuclear deformation on the energy distributions of the Gamow-Teller strength is studied in neutron-deficient Hg, Pb, and Po even isotopes. The theoretical framework is based on a self-consistent deformed Skyrme Hartree-Fock mean field with pairing correlations between like nucleons in BCS approximation and residual spin-isospin interactions treated in the proton-neutron quasiparticle random-phase approximation. After a systematic study of the Gamow-Teller strength distributions in the low-excitation-energy region, relevant for {beta}{sup +} decay, we have identified the best candidates to look for deformation signatures in their {beta}{sup +}-decay patterns. {beta}{sup +} half-lives and total Gamow-Teller strengths B(GT{sup {+-}}) are analyzed as well.

Moreno, O.; Sarriguren, P.; Alvarez-Rodriguez, R. [Instituto de Estructura de la Materia, Consejo Superior de Investigaciones Cientificas, Serrano 123, E-28006 Madrid (Spain); Guerra, E. Moya de [Departamento de Fisica Atomica, Molecular y Nuclear, Facultad de Ciencias Fisicas, Universidad Complutense de Madrid, E-28040 Madrid (Spain)

2006-05-15

315

On Adiabatic Pair Creation  

Microsoft Academic Search

We give here a rigorous proof of the well known prediction of pair creation as it arises from the Dirac equation with an external\\u000a time dependent potential. Pair creation happens with probability one if the potential changes adiabatically in time and becomes\\u000a overcritical, which means that an eigenvalue curve (as a function of time) bridges the gap between the negative

Peter Pickl; Detlef Dürr

2008-01-01

316

SWooki: Un Wiki Smantique sur rseau Pair--Pair  

E-print Network

SWooki: Un Wiki Sémantique sur réseau Pair-à-Pair Charbel Rahhal -- Hala Skaf-Molli -- Pascal Molli. Les systèmes wiki évoluent vers des wikis sémantiques ou vers des wikis pair-à-pair. Les wikis et la navigation entre les pages. Les wikis pair-à-pair offrent un support pour l'édition massive

Paris-Sud XI, Université de

317

Colors of dynamically associated asteroid pairs  

NASA Astrophysics Data System (ADS)

Recent dynamical studies have identified pairs of asteroids that reside in nearly identical heliocentric orbits. Possible formation scenarios for these systems include dissociation of binary asteroids, collisional disruption of a single parent body, or spin-up and rotational fission of a rubble-pile. Aside from detailed dynamical analyses and measurement of rotational light curves, little work has been done to investigate the colors or spectra of these unusual objects. A photometric and spectroscopic survey was conducted to determine the reflectance properties of asteroid pairs. New observations were obtained for a total of 34 individual asteroids. Additional photometric measurements were retrieved from the Sloan Digital Sky Survey Moving Object Catalog. Colors or spectra for a total of 42 pair components are presented here. The main findings of this work are: (1) the components in the observed pair systems have the same colors within the uncertainties of this survey, and (2) the color distribution of asteroid pairs appears indistinguishable from that of all Main Belt asteroids. These findings support a scenario of pair formation from a common progenitor and suggest that pair formation is likely a compositionally independent process. In agreement with previous studies, this is most consistent with an origin via binary disruption and/or rotational fission.

Moskovitz, Nicholas A.

2012-09-01

318

Validity of pair approximations for nuclei in open shells  

NASA Astrophysics Data System (ADS)

We study the validity of pair approximations of the nuclear shell model (SM) for a few realistic nuclei (130-131Te and 132I here) in open shells (i.e., nuclei with both valence protons and valence neutrons). We take a phenomenological shell model Hamiltonian, which includes the single-particle energy term, monopole and quadrupole pairing interactions for like particles, and quadrupole-quadrupole interactions between all valence nucleons. We make comparisons of energy levels and B(E2) values calculated by pair approximations with those in the SM calculations. The overlaps between wave functions of the nucleon pair approximation (NPA) and those of the SM are presented explicitly for the low-lying states. Our calculated results demonstrate that the NPA is a remarkable approximation of the SM for these nuclei. The important role played by pairs with negative parity in some low-lying states is discussed.

Lei, Y.; Zhao, Y. M.; Arima, A.

2011-10-01

319

PULSAR PAIR CASCADES IN A DISTORTED MAGNETIC DIPOLE FIELD  

SciTech Connect

We investigate the effect of a distorted neutron star dipole magnetic field on pulsar pair cascade multiplicity and pair death lines. Using a simple model for a distorted dipole field that produces an offset polar cap (PC), we derive the accelerating electric field above the PC in space-charge-limited flow. We find that even a modest azimuthally asymmetric distortion can significantly increase the accelerating electric field on one side of the PC and, combined with a smaller field line radius of curvature, leads to larger pair multiplicity. The death line for producing pairs by curvature radiation moves downward in the P- P-dot diagram, allowing high pair multiplicities in a larger percentage of the radio pulsar population. These results could have important implications for the radio pulsar population, high energy pulsed emission, and the pulsar contribution to cosmic ray positrons.

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

2011-01-01

320

Neutron Radiography  

NASA Astrophysics Data System (ADS)

Neutron radiography and its related two-dimensional (2D) neutron imaging techniques have been established as invaluable nondestructive inspection methods and quantitative measurement tools. They have been used in a wide variety of applications ranging from inspection of aircraft engine turbine blades to study of two-phase fluid flow in operating proton exchange membrane fuel cells. Neutron radiography is similar to X-ray radiography in that the method produces a 2D attenuation map of neutron radiation that has penetrated the object being examined. However, the images produced differ and are often complementary due to the differences between X-ray and neutron interaction mechanisms. The uses and types of 2D neutron imaging have expanded over the past 15 years as a result of advances in imaging technology and improvements in neutron generators/sources and computers. Still, high-intensity sources such as those from reactors and spallation neutron sources, together with conventional film radiography, remain the mainstay of high-resolution, large field-of-view neutron imaging. This chapter presents a summary of the history, methods, and related variations of neutron radiography techniques.

Heller, A. K.; Brenizer, J. S.

321

Proton momentum distribution and anomalous scattering intensities in a pseudo-spherical ammonium ion: a neutron Compton scattering study of (NH(4))(2)PdCl(6) and (NH(4))(2)TeCl(6).  

PubMed

Neutron Compton scattering (NCS) measurements on ammonium hexachloropalladate and hexachlorotellurate were performed at room temperature. Proton scattering intensities and momentum distributions, as measured in the NCS experiment, have been compared with results expected from the impulse approximation (IA) for both systems. The measurement shows that scattering intensity from protons is anomalous even though their momentum distribution has a second moment that agrees very well with the ab initio calculation for an isolated pseudo-spherical NH(4)(+) ion in the ground vibrational state. Detailed data analysis shows that there is no extra (beyond the IA expected value) broadening or peak shift of proton momentum distribution due to ultra-fast kinetics of the Compton scattering process leading to anomalous scattering intensities. This is most probably due to highly symmetric local potential in the NH(4)(+). Presented results have interesting implications for further theoretical work in the field. PMID:21817329

Krzystyniak, M; Lalowicz, Z T; Chatzidimitriou-Dreismann, C A; Lerch, M

2009-02-18

322

Neutron detector  

DOEpatents

A neutron detector has a volume of neutron moderating material and a plurality of individual neutron sensing elements dispersed at selected locations throughout the moderator, and particularly arranged so that some of the detecting elements are closer to the surface of the moderator assembly and others are more deeply embedded. The arrangement captures some thermalized neutrons that might otherwise be scattered away from a single, centrally located detector element. Different geometrical arrangements may be used while preserving its fundamental characteristics. Different types of neutron sensing elements may be used, which may operate on any of a number of physical principles to perform the function of sensing a neutron, either by a capture or a scattering reaction, and converting that reaction to a detectable signal. High detection efficiency, an ability to acquire spectral information, and directional sensitivity may be obtained.

Stephan, Andrew C. (Knoxville, TN); Jardret; Vincent D. (Powell, TN)

2011-04-05

323

Cold neutrons trapped in external fields.  

SciTech Connect

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

Gandolfi, S.; Carlson, J.; Pieper, S. C. (Physics); (LANL)

2011-01-05

324

Neutron radiography  

SciTech Connect

Neutron radiography is becoming a well established nondestructive testing (NDT) method. The American Society for Nondestructive Testing (ASNT) has recognized the method through its recommended practice SNT-TCIA which outlines training, knowledge, and experience necessary to obtain levels of competency in the method. Certification of nondestructive testing personnel is also covered in a military standard. Technical publications in the field of NDT and nuclear technology carry articles on neutron radiography and technical meetings include papers or even entire sessions on neutron radiography. There is an on-going series of international conferences on neutron radiography. Many books are available to provide introductory and advanced material on neutron radiographic techniques and applications. Neutron radiography as a service for hire is available, similar to that offered for other NDT services. The method is being adopted to solve NDT problems in specialty areas. The objective of this report is to provide a brief survey of the current state of the art in the use of neutron radiography. The survey will include information on the technique including principles of the method, sources of neutrons, detection methodology, standards and image quality indicators, and representative applications. An extensive reference list provides additional information for those who wish to investigate further and a Glossary is included which provides definitions for terms used in Neutron Radiography.

Berger, H.; Iddings, F.

1998-08-01

325

Neutron Stars  

NASA Technical Reports Server (NTRS)

Neutron stars were discovered almost 40 years ago, and yet many of their most fundamental properties remain mysteries. There have been many attempts to measure the mass and radius of a neutron star and thereby constrain the equation of state of the dense nuclear matter at their cores. These have been complicated by unknown parameters such as the source distance and burning fractions. A clean, straightforward way to access the neutron star parameters is with high-resolution spectroscopy. I will present the results of searches for gravitationally red-shifted absorption lines from the neutron star atmosphere using XMM-Newton and Chandra.

Cottam, J.

2007-01-01

326

Fast Neutron Sensitivity with HPGe  

SciTech Connect

In addition to being excellent gamma-ray detectors, germanium detectors are also sensitive to fast neutrons. Incident neutrons undergo inelastic scattering {Ge(n,n?)Ge*} off germanium nuclei and the resulting excited states emit gamma rays or conversion electrons. The response of a standard 140% high-purity germanium (HPGe) detector with a bismuth germanate (BGO) anti-coincidence shield was measured for several neutron sources to characterize the ability of the HPGe detector to detect fast neutrons. For a sensitivity calculation performed using the characteristic fast neutron response peak that occurs at 692 keV, the 140% germanium detector system exhibited a sensitivity of ~175 counts / kg of WGPumetal in 1000 seconds at a source-detector distance of 1 meter with 4 in. of lead shielding between source and detector. Theoretical work also indicates that it might be possible to use the shape of the fast-neutron inelastic scattering signatures (specifically, the end-point energy of the long high energy tail of the resulting asymmetric peak) to gain additional information about the energy distribution of the incident neutron spectrum. However, the experimentally observed end-point energies appear to be almost identical for each of the fast neutron sources counted. Detailed MCNP calculations show that the neutron energy distributions impingent on the detector for these sources are very similar in this experimental configuration, due to neutron scattering in a lead shield (placed between the neutron source and HPGe detector to reduce the gamma ray flux), the BGO anti-coincidence detector, and the concrete floor.

Seifert, Allen; Hensley, Walter K.; Siciliano, Edward R.; Pitts, W. K.

2008-01-22

327

Neutron stars as cosmic neutron matter laboratories.  

NASA Astrophysics Data System (ADS)

Recent developments which have radically changed our understanding of the dynamics of neutron star superfluids and the free precession of neutron stars are summarized, and the extent to which neutron stars are cosmic neutron matter laboratories is discussed.

Pines, D.

328

Neutron beam tailoring by means of a novel pulsed spatial magnetic spin resonator  

NASA Astrophysics Data System (ADS)

Since long neutron spin resonance in an arrangement of crossed homogeneous and spatially alternating transversal magnetic fields is known to allow for wavelength-selective polarisation manipulation. Combined with a pair of highly efficient polarising supermirrors it is an elegant method to single out a specific wavelength from an initially polychromatic polarised neutron beam, based upon the fact that in its rest frame each neutron creates its individual frequency. A spin flip process can then take place only if this individual frequency equals the neutron LARMOR frequency in the homogeneous field. Here, we present the first experimental results we have obtained with a conceptually novel type of such spatial spin resonator, consisting of a series of separate modules which can be controlled independently from each other. Thus it becomes possible to vary e.g. the amplitude distribution of the spatially alternating transversal field without any geometric modification of the setup. Moreover this device fulfils the requirements for fast electronic switching of each module, which will be an important asset for the possible decoupling of the minimal neutron pulse duration and the achievable wavelength resolution. We compare the actual performance of this prototype resonator system with the theoretically expected behaviour.

Gösselsberger, C.; Abele, H.; Badurek, G.; Jericha, E.; Mach, W.; Nowak, S.; Rechberger, T.

2012-02-01

329

Isovector Pairing within the so(5) Richardson-Gaudin Exactly Solvable Model  

SciTech Connect

Properties of a nucleon system interacting via isovector proton-neutron pairing can be described within the so(5) generalized Richardson-Gaudin exactly-solvable model [1]. We present results for a system of 12 nucleon pairs within the full f{sub p} + g{sub 9/2} shell-model space. We discuss coupling constant dependence of the pair energies, total energy of the system, and the occupation numbers.

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

2005-10-10

330

FINAL REPORT. DISTRIBUTION AND SOLUBILITY OF RADIONUCLIDES AND NEUTRON ABSORBERS IN WASTE FORMS FOR DISPOSITION OF PLUTONIUM ASH AND SCRAPS, EXCESS PLUTONIUM, AND MISCELLANEOUS SPENT NUCLEAR FUELS  

EPA Science Inventory

The objective of this multi-institutional research effort was to understand how radionuclides, neutron absorbers, and other waste species are incorporated into single-phase amorphous matrices and ceramics. This was to provide DOE with a methodology to develop glasses and ceramics...

331

Hard Photodisintegration of a Proton Pair in 3He  

E-print Network

Hard photodisintegration of the deuteron has been extensively studied in order to understand the dynamics of the transition from hadronic to quark-gluon descriptions of the strong interaction. In this work, we discuss the extension of this program to hard photodisintegration of a $pp$ pair in the $^3$He nucleus. Experimental confirmation of new features predicted here for the suggested reaction would advance our understanding of hard nuclear reactions. A main prediction, in contrast with low-energy observations, is that the $pp$ breakup cross section is not much smaller than the one for $pn$ break up.In some models, the energy-dependent oscillations observed for $pp$ scattering are predicted to appear in the $\\gamma ^3{\\rm He} \\to p p + n$ reaction. Such an observation would open up a completely new field in studies of color coherence phenomena in hard nuclear reactions. We also demonstrate that, in addition to the energy dependence, the measurement of the light-cone momentum distribution of the recoil neutron provides an independent test of the underlying dynamics of hard disintegration.

S. J. Brodsky; L. Frankfurt; R. Gilman; J. R. Hiller; G. A. Miller; E. Piasetzky; M. Sargsian; M. Strikman

2003-05-23

332

Hard Photo-disintegration of proton pairs in ^3He  

NASA Astrophysics Data System (ADS)

Hard deuteron photo-disintegration has been investigated for 20 years [1], as its cross sections follow the constituent counting rules and it provides insight into the interplay between hadronic and quark-gluon degrees of freedom in high-momentum transfer exclusive reactions [2]. During the summer of 2007, we measured in Jefferson Lab Hall A [3] hard pp-pair disintegration for the first time, in the reaction ?,3 He ->pp + n, using kinematics corresponding to a spectator neutron. The current state of the analysis and preliminary results will be shown. Clues to the underlying physics can be found in the comparison of our measurements with deuteron photo-disintegration, the energy dependence of the cross sections at 90^o c.m., and the ?n distribution. References: [1] R. Gilman and F. Gross, J. Phys. G 28, R37 (2002). [2] S. J. Brodsky et al., Phys. Lett. B 578, 69 (2004). [3] http://hallaweb.jlab.org/experiment/E03-101/

Piasetzky, E.; Pomerantz, I.; Gilman, R.

2009-05-01

333

Hard photodisintegration of a proton pair in 3He  

NASA Astrophysics Data System (ADS)

Hard photodisintegration of the deuteron has been extensively studied in order to understand the dynamics of the transition from hadronic to quark-gluon descriptions of the strong interaction. In this Letter, we discuss the extension of this program to hard photodisintegration of a pp pair in the 3He nucleus. Experimental confirmation of new features predicted here for the suggested reaction would advance our understanding of hard nuclear reactions. A main prediction, in contrast with low-energy observations, is that the pp breakup cross section is not much smaller than the one for pn break up. In some models, the energy-dependent oscillations observed for pp scattering are predicted to appear in the ? 3He?pp+n reaction. Such an observation would open up a completely new field in studies of color coherence phenomena in hard nuclear reactions. We also demonstrate that, in addition to the energy dependence, the measurement of the light-cone momentum distribution of the recoil neutron provides an independent test of the underlying dynamics of hard disintegration.

Brodsky, S. J.; Frankfurt, L.; Gilman, R.; Hiller, J. R.; Miller, G. A.; Piasetzky, E.; Sargsian, M.; Strikman, M.

2004-01-01

334

Neutron crystallography  

PubMed Central

Neutron crystallography has had an important, but relatively small role in structural biology over the years. In this review of recently determined neutron structures, a theme emerges of a field currently expanding beyond its traditional boundaries, to address larger and more complex problems, with smaller samples and shorter data collection times, and employing more sophisticated structure determination and refinement methods. The origin of this transformation can be found in a number of advances including first, the development of neutron image-plates and quasi-Laue methods at nuclear reactor neutron sources and the development of time-of-flight Laue methods and electronic detectors at spallation neutron sources; second, new facilities and methods for sample perdeuteration and crystallization; third, new approaches and computational tools for structure determination. PMID:18656544

Blakeley, Matthew P; Langan, Paul; Niimura, Nobuo; Podjarny, Alberto

2008-01-01

335

Neutron tubes  

DOEpatents

A neutron tube or generator is based on a RF driven plasma ion source having a quartz or other chamber surrounded by an external RF antenna. A deuterium or mixed deuterium/tritium (or even just a tritium) plasma is generated in the chamber and D or D/T (or T) ions are extracted from the plasma. A neutron generating target is positioned so that the ion beam is incident thereon and loads the target. Incident ions cause D-D or D-T (or T-T) reactions which generate neutrons. Various embodiments differ primarily in size of the chamber and position and shape of the neutron generating target. Some neutron generators are small enough for implantation in the body. The target may be at the end of a catheter-like drift tube. The target may have a tapered or conical surface to increase target surface area.

Leung, Ka-Ngo (Hercules, CA); Lou, Tak Pui (Berkeley, CA); Reijonen, Jani (Oakland, CA)

2008-03-11

336

Jupiter Effect (Asymmetrical Production of Dilepton Pairs)  

E-print Network

Specific results of the computer simulation of dilepton production from expanding pion gas created in Pb+Pb 160 GeV/n collisions are presented. Azimuthal asymmetry of dilepton pairs in non-central collisions and interesting shape of the rapidity distribution of dilepton pairs are predicted. These results are understood on theoretical level as a consequence of momentum and space asymmetries in the initial state of pion gas without any assumption of thermalization. Implication on the production of dileptons in pre-hadronic phase of HIC is drawn.

Peter Filip

1998-02-01

337

Neutron measurements of the OGO-VI Spacecraft  

NASA Technical Reports Server (NTRS)

The neutron measurements with the OGO-6 spacecraft are reported. Topics discussed include: the design and calibration of a neutron monitor for measuring the cosmic ray neutron leakages from the earth's atmosphere, determination of latitude dependence of cosmic ray leakage flux, determination of the angular distribution of neutron leakage flux as deduced by measurements of the altitude dependence, and verification of the solar modulation of the cosmic ray source for the neutron leakage.

Lockwood, J. A.

1973-01-01

338

Electron volt neutron spectrometers  

NASA Astrophysics Data System (ADS)

The advent of pulsed neutron sources has made available intense fluxes of epithermal neutrons (500 meV ? E?100 eV ). The possibility to open new investigations on condensed matter with eV neutron scattering techniques, is related to the development of methods, concepts and devices that drive, or are inspired by, emerging studies at this energy scale. Electron volt spectrometers have undergone continuous improvements since the construction of the first prototype instruments, but in the last decade major breakthroughs have been accomplished in terms of resolution and counting statistics, leading, for example, to the direct measurement of the proton 3-D Born-Oppenheimer potential in any material, or to quantitatively probe nuclear quantum effects in hydrogen bonded systems. This paper reports on the most effective methods and concepts for energy analysis and detection, as well as devices for the optimization of electron volt spectrometers for different applications. This is set in the context of the progress made up to date in instrument development. Starting from early stages of development of the technique, particular emphasis will be given to the Vesuvio eV spectrometer at the ISIS neutron source, the first spectrometer where extensive scientific, as well as research and development programmes have been carried out. The potential offered by this type of instrumentation, from single particle excitations to momentum distribution studies, is then put in perspective into the emerging fields of eV spectroscopy applied to cultural heritages and neutron irradiation effects in electronics.

Pietropaolo, A.; Senesi, R.

2011-11-01

339

Nuclear Neutron-Proton Contact and the Photoabsorption Cross Section  

NASA Astrophysics Data System (ADS)

The nuclear neutron-proton contact is introduced, generalizing Tan's work, and evaluated from medium energy nuclear photodisintegration experiments. To this end we reformulate the quasideuteron model of nuclear photodisintegration and establish the bridge between the Levinger constant and the contact. Using experimental evaluations of Levinger's constant, we extract the value of the neutron-proton contact in finite nuclei and in symmetric nuclear matter. Assuming isospin symmetry we propose to evaluate the neutron-neutron contact through the measurement of photonuclear spin correlated neutron-proton pairs.

Weiss, Ronen; Bazak, Betzalel; Barnea, Nir

2015-01-01

340

Neutron Star Binaries as Central Engines of GRBs  

E-print Network

We describe the results high resolution, hydrodynamic calculations of neutron star mergers. The model makes use of a new, nuclear equation of state, accounts for multi-flavour neutrino emission and solves the equations of hydrodynamics using the smoothed particle hydrodynamics method with more than $10^6$ particles. The merger leaves behind a strongly differentially rotating central object of $\\sim 2.5$ M$_{\\odot}$ together with a distribution of hot debris material. For the most realistic case of initial neutron star spins, no sign of a collapse to a black hole can be seen. We argue that the differential rotation stabilizes the central object for $\\sim 10^2$ s and leads to superstrong magnetic fields. We find the neutrino emission from the hot debris around the freshly-formed, supermassive neutron star to be substantially lower than predicted previously. Therefore the annihilation of neutrino anti-neutrino pairs will have difficulties to power very energetic bursts ($\\gg 10^{49}$ erg).

S. Rosswog

2002-04-29

341

Neutron spectrometry with He-3 proportional counters  

SciTech Connect

Helium filled proportional counters are widely used in the field of neutron detection and spectrometry. In this work the response of a commercially available He-3 counter is studied experimentally and calculated with Monte Carlo for the neutron energy range from 230 keV up to about 7 MeV. The calculated response of the system is used to determine neutron yield energy distribution emitted from an extended {sup nat}U/Pb assembly irradiated with 1.6 GeV deuterons. The results are in acceptable agreement with the calculated neutron distribution with DCM-DEM code. (authors)

Manolopoulou, M.; Fragopoulou, M.; Stoulos, S.; Vagena, E. [School of Physics, Aristotle Univ. of Thessaloniki, Thessaloniki 541 24, Hellas (Greece); Westmeier, W. [Philipps-Universitaet, Marburg 35032 (Germany); Zamani, M. [School of Physics, Aristotle Univ. of Thessaloniki, Thessaloniki 541 24, Hellas (Greece)

2011-07-01

342

Measuring the neutron's mean square charge radius using neutron interferometry  

NASA Astrophysics Data System (ADS)

The neutron is electrically neutral, but its substructure consists of charged quarks so it may have an internal charge distribution. In fact it is known to have a negative mean square charge radius (MSCR), the second moment of the radial charge density. In other words the neutron has a positive core and negative skin. In the first Born approximation the neutron MSCR can be simply related to the neutron-electron scattering length bne. In the past this important quantity has been extracted from the energy dependence of the total transmission cross-section of neutrons on high-Z targets, a very difficult and complicated process. A few years ago S.A. Werner proposed a novel approach to measuring bne from the neutron's dynamical phase shift in a perfect crystal close to the Bragg condition. We are conducting an experiment based on this method at the NIST neutron interferometer which may lead to a five-fold improvement in precision of bne and hence the neutron MSCR.

Wietfeldt, F. E.; Huber, M.; Black, T. C.; Kaiser, H.; Arif, M.; Jacobson, D. L.; Werner, S. A.

2006-11-01

343

Pairing-induced speedup of nuclear spontaneous fission  

NASA Astrophysics Data System (ADS)

Background: Collective inertia is strongly influenced at the level crossing at which the quantum system changes its microscopic configuration diabatically. Pairing correlations tend to make the large-amplitude nuclear collective motion more adiabatic by reducing the effect of these configuration changes. Competition between pairing and level crossing is thus expected to have a profound impact on spontaneous fission lifetimes. Purpose: To elucidate the role of nucleonic pairing on spontaneous fission, we study the dynamic fission trajectories of 264Fm and 240Pu using the state-of-the-art self-consistent framework. Methods: We employ the superfluid nuclear density functional theory with the Skyrme energy density functional SkM* and a density-dependent pairing interaction. Along with shape variables, proton and neutron pairing correlations are taken as collective coordinates. The collective inertia tensor is calculated within the nonperturbative cranking approximation. The fission paths are obtained by using the least action principle in a four-dimensional collective space of shape and pairing coordinates. Results: Pairing correlations are enhanced along the minimum-action fission path. For the symmetric fission of 264Fm, where the effect of triaxiality on the fission barrier is large, the geometry of the fission pathway in the space of the shape degrees of freedom is weakly impacted by pairing. This is not the case for 240Pu, where pairing fluctuations restore the axial symmetry of the dynamic fission trajectory. Conclusions: The minimum-action fission path is strongly impacted by nucleonic pairing. In some cases, the dynamical coupling between shape and pairing degrees of freedom can lead to a dramatic departure from the static picture. Consequently, in the dynamical description of nuclear fission, particle-particle correlations should be considered on the same footing as those associated with shape degrees of freedom.

Sadhukhan, Jhilam; Dobaczewski, J.; Nazarewicz, W.; Sheikh, J. A.; Baran, A.

2014-12-01

344

Regimes of Pulsar Pair Formation and Particle Energetics  

NASA Technical Reports Server (NTRS)

We investigate the conditions required for the production of electron-positron pairs above a pulsar polar cap (PC) and the influence of pair production on the energetics of the primary particle acceleration. Assuming space-charge limited flow acceleration including the inertial frame-dragging effect, we allow both one-photon and two-photon pair production by either curvature radiation (CR) photons or photons resulting from inverse-Compton scattering of thermal photons from the PC by primary electrons. We find that,, while only the younger pulsars can produce pairs through CR, nearly all known radio pulsars are capable of producing pairs through non-resonant inverse-Compton scatterings. The effect of the neutron star equations of state on the pair death lines is explored. We show that pair production is facilitated in more compact stars and more a massive stars. Therefore accretion of mass by pulsars in binary systems may allow pair production in most of the millisecond purser population. We also find that two-photon pair production may be important in millisecond pursers if their surface temperatures are above approx. or equal to three million degrees K. Pursers that produce pairs through CRT wilt have their primary acceleration limited by the effect of screening of the electric field. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sup 1/2, sub rot) dependence. The acceleration voltage drop in pursers that produce pairs only through inverse-Compton emission will not be limited by electric field screening. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sub rot) dependence. Thus, older pursers will have significantly lower gamma-ray luminosity.

Harding, Alice K.; Muslimov, Alexander G.; Zhang, Bing; White, Nicholas E. (Technical Monitor)

2002-01-01

345

Ion Pairing Chromatography  

Microsoft Academic Search

The present state of ion-pair chromatography (IPC) is reviewed. Emphasis is placed on the theoretical modeling of the retention behavior of charged, zwitterionic, and neutral solutes, since the theory provides the generally good understanding of the factors affecting the separation. Although stoichiometric models were credited with the first easy-to-understand demonstration of the retention mechanism of IPC, they were thermodynamic models,

Teresa Cecchi

2008-01-01

346

The structure of molten CaSiO3: A neutron diffraction isotope substitution and aerodynamic levitation study.  

SciTech Connect

We have performed neutron diffraction isotopic substitution experiments on aerodynamically levitated droplets of CaSiO3, to directly extract intermediate and local structural information on the Ca environment. The results show a substantial broadening of the Ca-O peak in the pair distribution function of the melt compared to the glass, which comprises primarily of 6- and 7-fold coordinated Ca-polyhedra. The broadening can be explained by a re-distribution of Ca-O bond lengths, especially towards longer distances in the liquid. The first order neutron difference function provides a rigorous test of recent molecular dynamics simulations and supports the model of the presence of short chains or channels of edge shared Ca-octahedra in the liquid state. It is suggested that the polymerization of Ca-polyhedra is responsible for the fragile viscosity behavior of the melt and the glass forming ability in CaSiO3.

Skinner, Lawrie [State University of New York, Stony Brook; Benmore, Chris J [Argonne National Laboratory (ANL); Weber, Richard [Argonne National Laboratory (ANL); Santodonato, Louis J [ORNL; Tumber, Sonia [Materials Development, Inc., Evanston, IL; Neuefeind, Joerg C [ORNL; Lazareva, Lena [State University of New York, Stony Brook; Du, Jincheng [University of North Texas; Parise, John B [Stony Brook University (SUNY)

2012-01-01

347

Mapping of the thermal neutron distribution in the lead block assembly of the PS-211 experiment at CERN, using thermoluminescence and nuclear track detectors.  

PubMed

The main purpose of the TARC (Transmutation by Adiabatic Resonance Crossing) experiment (PS-211), was to demonstrate the possibility to destroy efficiently Long-Lived Fission Fragments (LLFF) in Accelerator Driven Systems (ADS). The experimental set-up which consisted of a lead block with dimensions 3.3 x 3.3 x 3 m3, was installed in a CERN Proton Synchrotron (PS) beam line. The proton beam at 2.5 GeV/c and 3.5 GeV/c, was incident in the centre of the lead block assembly producing neutrons via spallation reactions. In this study, neutron flux measurements are presented in the lead block assembly using thermoluminescence and nuclear track detectors. The results are in good agreement with Monte Carlo calculations as well as with the results of the other methods used in the framework of the TARC experiment. PMID:12382715

Savvidis, E; Eleftheriadis, C A; Kitis, G

2002-01-01

348

Magnetization distribution in the tetragonal Ba(Fe1-xCox)2As2, x=0.066 probed by polarized neutron diffraction  

NASA Astrophysics Data System (ADS)

Polarized neutron diffraction has been performed on a tetragonal Ba(Fe1-xCox)2As2, x=0.066 single crystal under an applied magnetic field of 6 T directed along the [\\overline{1}10 ] direction to determine the magnetic structure factors of various Bragg reflections. The maximum entropy reconstruction based on bulk magnetization measurements and polarized neutron diffraction data reveal a small induced magnetic moment residing on the 4d Wyckoff site that is occupied by Fe/Co atoms. No significant magnetization density has been found on the Ba and As atomic positions. The small polarizability of Fe/Co sites leads to flipping ratios very close to 1.00. Our data suggest a non-zero orbital contribution to the Fe/Co magnetic form factor in good agreement with recent theoretical and experimental studies.

Prokeš, K.; Gukasov, A.; Argyriou, D. N.; Bud'ko, S. L.; Canfield, P. C.; Kreyssig, A.; Goldman, A. I.

2011-02-01

349

Prediction of proton and neutron absorbed-dose distributions in proton beam radiation therapy using Monte Carlo n-particle transport code (MCNPX)  

E-print Network

The objective of this research was to develop a complex MCNPX model of the human head to predict absorbed dose distributions during proton therapy of ocular tumors. Absorbed dose distributions using the complex geometry were compared to a simple...

Massingill, Brian Edward

2009-05-15

350

Thermal neutron detection system  

DOEpatents

According to the present invention, a system for measuring a thermal neutron emission from a neutron source, has a reflector/moderator proximate the neutron source that reflects and moderates neutrons from the neutron source. The reflector/moderator further directs thermal neutrons toward an unmoderated thermal neutron detector.

Peurrung, Anthony J. (Richland, WA); Stromswold, David C. (West Richland, WA)

2000-01-01

351

Spin-isospin response of deformed neutron-rich nuclei in a self-consistent Skyrme energy-density-functional approach  

NASA Astrophysics Data System (ADS)

We develop a new framework for the self-consistent deformed proton-neutron quasiparticle-random-phase approximation (pnQRPA), formulated in the Hartree-Fock-Bogoliubov (HFB) single-quasiparticle basis. The same Skyrme force is used in both the HFB and pnQRPA calculations, except in the proton-neutron particle-particle channel, where an S=1 contact force is employed. A numerical application is performed for Gamow-Teller (GT) strength distributions and ? -decay rates in the deformed neutron-rich Zr isotopes located around the path of rapid-neutron-capture-process nucleosynthesis. It is found that the GT strength distributions are fragmented due to deformation. Furthermore, we find that the momentum-dependent terms in the particle-hole residual interaction lead to a stronger collectivity of the GT giant resonance. The T=0 pairing enhances the low-lying strengths cooperatively with the T=1 pairing correlation, which shortens the ? -decay half-lives by at most an order of magnitude. The new calculation scheme reproduces well the observed isotopic dependence of the ? -decay half-lives of deformed ^{100-110}Zr isotopes.

Yoshida, Kenichi

2013-11-01

352

Polymerization by classical and frustrated Lewis pairs.  

PubMed

Main-group classical and frustrated Lewis pairs (CLPs and FLPs) comprising strong Lewis acids (LAs) and strong Lewis bases (LBs) are highly active for polymerization of conjugated polar alkenes, affording typically high molecular weight polymers with relatively narrow molecular weight distributions. Especially effective systems are the Lewis pairs (LPs) consisting of the strong LA Al(C6F5)3 and strong LBs, such as achiral phosphines and chiral chelating diphosphines, N-heterocyclic carbenes, and phosphazene superbases, for polymerization of methacrylates and acrylamides as well as renewable ?-methylene-?-butyrolactones. Chain initiation involves cooperative addition of LPs to the monomer to generate zwitterionic active species, and chain propagation proceeds via a bimetallic, activated-monomer addition mechanism. Transition metal nucleophile/electrophile pairs comprising neutral metallocene bis(ester enolate)s and strong LAs E(C6F5)3 (E = Al, B) generate two drastically different polymerization systems, depending on the LA. With E = Al, catalyst activation and chain initiating events lead to dually active ion-pairs, thereby effecting ion-pairing polymerization that affords polymers with unique stereo-multiblock microstructures. With E = B, on the other hand, the FLP-induced catalyst activation generates metallacyclic cations paired with the hydridoborate anion [HB(C6F5)3](-); uniquely, such ion-pairs effect catalytic polymerization of conjugated polar alkenes by an H-shuttling mechanism, with the cation catalyzing chain growth and the anion promoting chain transfer by shuttling the hydride between the cation and anion centers through the neutral borane. PMID:23097029

Chen, Eugene Y-X

2013-01-01

353

Neutron range spectrometer  

DOEpatents

A neutron range spectrometer and method for determining the neutron energy spectrum of a neutron emitting source are disclosed. Neutrons from the source are colliminated along a collimation axis and a position sensitive neutron counter is disposed in the path of the collimated neutron beam. The counter determines positions along the collimation axis of interactions between the neutrons in the neutron beam and a neutron-absorbing material in the counter. From the interaction positions, a computer analyzes the data and determines the neutron energy spectrum of the neutron beam. The counter is preferably shielded and a suitable neutron-absorbing material is He-3. 1 fig.

Manglos, S.H.

1988-03-10

354

Magnetic moments of T=3/2 mirror pairs  

SciTech Connect

We predict values of the magnetic moments of T=3/2 proton-rich fp-shell nuclei in the mass range A=43-53, by using known values for their neutron-rich mirrors together with shell-model estimates for small quantities. We extend the analysis to those T=3/2 sd-shell mirror pairs for which both the T{sub z}=-3/2 and T{sub z}=+3/2 magnetic moments have been measured. We find that these obey the same linear relation as previously deduced for T=1/2 mirror pairs.

Perez, S. M. [Department of Physics, University of Cape Town, Private Bag, Rondebosch 7700 (South Africa); iThemba LABS, P. O. Box 722, Somerset West 7129 (South Africa); Richter, W. A. [Department of Physics, University of the Western Cape, Private Bag X17, Bellville 7535 (South Africa); Brown, B. A. [Department of Physics and Astronomy, and National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824-1321 (United States); Horoi, M. [Department of Physics, Central Michigan University, Mount Pleasant, Michigan 48859 (United States)

2010-12-15

355

J =0 ,T =1 pairing-interaction selection rules  

NASA Astrophysics Data System (ADS)

Wave functions arising from a pairing Hamiltonian E (0 ), i.e., one in which the interaction is only between J =0+,T =1 pairs, lead to magnetic dipole and Gamow-Teller (GT) transition rates that are much larger than those from an interaction E (Jmax) in which a proton and a neutron couple to J =2 j . With realistic interactions the results are between the two extremes. In the course of this study we found that certain M 1 and GT matrix elements vanish with E (0 ) . These are connected to seniority and reduced isospin selection rules. We also relate our results to the single j scissors mode.

Harper, Matthew; Zamick, Larry

2015-01-01

356

Classes of source pairs in interference and diffraction  

NASA Astrophysics Data System (ADS)

A description of interference and diffraction based on the concept of class of source pairs is presented. It is the set of pairs of sources whose contributions to the interference or diffraction patterns exhibit the same phase difference. Each class of source pairs provides a specific cosine-like modulation on the intensity distribution of the pattern, in such a way that the set provides an expansion of this intensity distribution in an orthogonal basis. From this point of view, the classes of source pairs are the effective elementary sources for those intensity distributions. The characteristics of the classes of source pairs can be accurately determined by Fourier transforming the intensity distribution of the patterns. The central value of this Fourier spectrum is related to the number of individual sources. The remain values will provide two crucial descriptors of the classes: their positions on the Fourier transform domain will be corresponding to the separation vector of the class of pairs for wavefront splitting interferometers (WSIs) and diffraction, or the time delay for amplitude splitting interferometers (ASIs), and their heights will be proportional to their populations. The concept was also applied to Fraunhofer and Fresnel diffraction, but now the classes of source pairs constitute a continuous set instead of the discrete sets in interference. However, the set of classes can also be determined by Fourier analysis.

Castaneda, Roman; Garcia-Sucerquia, Jorge

2003-10-01

357

FOREWORD: Neutron metrology Neutron metrology  

NASA Astrophysics Data System (ADS)

The International Committee for Weights and Measures (CIPM) has consultative committees covering various areas of metrology. The Consultative Committee for Ionizing Radiation (CCRI) differs from the others in having three sections: Section (I) deals with radiation dosimetry, Section (II) with radionuclide metrology and Section (III) with neutron metrology. In 2003 a proposal was made to publish special issues of Metrologia covering the work of the three Sections. Section (II) was the first to complete their task, and their special issue was published in 2007, volume 44(4). This was followed in 2009 by the special issue on radiation dosimetry, volume 46(2). The present issue, volume 48(6), completes the trilogy and attempts to explain neutron metrology, the youngest of the three disciplines, the neutron only having been discovered in 1932, to a wider audience and to highlight the relevance and importance of this field. When originally approached with the idea of this special issue, Section (III) immediately saw the value of a publication specifically on neutron metrology. It is a topic area where papers tend to be scattered throughout the literature in journals covering, for example, nuclear instrumentation, radiation protection or radiation measurements in general. Review articles tend to be few. People new to the field often ask for an introduction to the various topics. There are some excellent older textbooks, but these are now becoming obsolete. More experienced workers in specific areas of neutron metrology can find it difficult to know the latest position in related areas. The papers in this issue attempt, without presenting a purely historical outline, to describe the field in a sufficiently logical way to provide the novice with a clear introduction, while being sufficiently up-to-date to provide the more experienced reader with the latest scientific developments in the different topic areas. Neutron radiation fields obviously occur throughout the nuclear industry, from the initial fuel enrichment and fabrication processes right through to storage or reprocessing, and neutron metrology is clearly important in this area. Neutron fields do, however, occur in other areas, for example where neutron sources are used in oil well logging and moisture measurements. They also occur around high energy accelerators, including photon linear accelerators used for cancer therapy, and are expected to be a more serious problem around the new hadron radiation therapy facilities. Roughly 50% of the cosmic ray doses experienced by fliers at the flight altitudes of commercial aircraft are due to neutrons. Current research on fusion presents neutron metrology with a whole new range of challenges because of the very high fluences expected. One of the most significant features of neutron fields is the very wide range of possible neutron energies. In the nuclear industry, for example, neutrons occur with energies from those of thermal neutrons at a few meV to the upper end of the fission spectrum at perhaps 10 MeV. For cosmic ray dosimetry the energy range extends into the GeV region. This enormous range sets a challenge for designing measuring devices and a parallel challenge of developing measurement standards for characterizing these devices. One of the major considerations when deciding on topics for this special issue was agreeing on what not to include. Modelling, i.e. the use of radiation transport codes, is now a very important aspect of neutron measurements. These calculations are vital for shielding and for instrument design; nevertheless, the topic has only been included here where it has a direct bearing on metrology and the development of standards. Neutron spectrometry is an increasingly important technique for unravelling some of the problems of dose equivalent measurements and for plasma diagnostics in fusion research. However, this topic is at least one step removed from primary metrology and so it was felt that it should not be covered, particularly as a compendium of papers on spectrometry for radiation protection has

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

2011-12-01

358

Assessment Strategies for Pair Programming  

ERIC Educational Resources Information Center

Although pair programming has proved its usefulness in teaching and learning programming skills, it is difficult to assess the individual roles and abilities of students whilst programming in pairs. (Note that within this manuscript, the term assessment refers to evaluating individual student performance.) Assessing only the outcomes of a pair…

Hahn, Jan Hendrik; Mentz, Elsa; Meyer, Lukas

2009-01-01

359

Special Angle Pairs Discovery Activity  

NSDL National Science Digital Library

This lesson uses a discovery approach to identify the special angles formed when a set of parallel lines is cut by a transversal. During this lesson students identify the angle pair and the relationship between the angles. Students use this relationship and special angle pairs to make conjectures about which angle pairs are considered special angles.

Barbara Henry

2012-04-16

360

Epithermal neutron activation, radiometric, correlation and principal component analysis applied to the distribution of major and trace elements in some igneous and metamorphic rocks from Romania.  

PubMed

Six major (Na, Al, K, Ca, Ti, Fe) and 28 trace (Sc, Cr, V, Mn, Co, Zn, Cu, As, Br, Sr, Rb, Zr, Mo, Sn, Sb, Ba, Cs, La, Ce, Nd, Eu, Sm, Tb, Hf, Ta, W, Th and U) elements were determined by epithermal neutron activation analysis (ENAA) in nine Meridional Carpathian and Macin Mountains samples of igneous and metamorphic rocks. Correlation and principal factor analysis were used to interpret data while natural radionuclides radiometry shows a good correlation with ENAA results. PMID:19231213

Cristache, C I; Duliu, O G; Culicov, O A; Frontasyeva, M V; Ricman, C; Toma, M

2009-05-01

361

Searching for Pair Halos  

NASA Astrophysics Data System (ADS)

We have conducted a search for the giant Pair Halo structures which are inevitably formed around TeV sources due to interactions of very high energy gamma-rays with the Extragalactic Background Light (EBL). The resulting electron/positron pairs are Compton upscattered on photons of the 2.7 K Cosmic Microwave Background Radiation to produce a second generation of gamma-rays which again interact with the EBL; thus an electromagnetic cascade develops. If the magnetic fields on Mpc scales surrounding the central source are sufficiently strong (10-11 G or more), electrons are effectively isotropised before interacting with radiation fields. In this case an extended halo is produced around the source. Using H.E.S.S. observations of Active Galactic Nuclei, including data from PKS 2155-304, 1ES 1101-232 and 1ES 0229+200, we have completed a detailed analysis of these sources. I will present and discuss the astrophysical implications of these results.

Fallon, Lisa; Abramowski, A.; Acero, F.; Aharonian, F.; Akhperjanian, A. G.; Anton, G.; Barres de Almeida, U.; Bazer-Bachi, A. R.; Becherini, Y.; Behera, B.; Bernlühr, K.; Bochow, A.; Boisson, C.; Bolmont, J.; Borrel, V.; Brucker, J.; Brun, F.; Brun, P.; Bühler, R.; Bulik, T.; Büsching, I.; Boutelier, T.; Chadwick, P. M.; Charbonnier, A.; Chaves, R. C. G.; Cheesebrough, A.; Conrad, J.; Chounet, L.-M.; Clapson, A. C.; Coignet, G.; Dalton, M.; Daniel, M. K.; Davids, I. D.; Degrange, B.; Deil, C.; Dickinson, H. J.; Domainko, A. Djannati-Ataü W.; Drury, L. O'c.; Dubois, F.; Dubus, G.; Dyks, J.; Dyrda, M.; Egberts, K.; Eger, P.; Espigat, P.; Fallon, L.; Farnier, C.; Fegan, S.; Feinstein, F.; Fernandes, M. V.; Fiasson, A.; Fürster, A.; Fontaine, G.; Füssling, M.; Gabici, S.; Gallant, Y. A.; Gérard, L.; Gerbig, D.; Giebels, B.; Glicenstein, J. F.; Glück, B.; Goret, P.; Güring, D.; Hampf, D.; Hauser, M.; Heinz, S.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hinton, J. A.; Hoffmann, A.; Hofmann, W.; Hofverberg, P.; Holleran, M.; Hoppe, S.; Horns, D.; Jacholkowska, A.; de Jager, O. C.; Jahn, C.; Jung, I.; Katarzynski, K.; Katz, U.; Kaufmann, S.; Kerschhaggl, M.; Khangulyan, D.; Khálifi, B.; Keogh, D.; Klochkov, D.; Kluzniak, W.; Kneiske, T.; Komin, Nu.; Kosack, K.; Kossakowski, R.; Lamanna, G.; Lenain, J.-P.; Lohse, T.; Lu, C.-C.; Marandon, V.; Marcowith, A.; Masbou, J.; Mau-Rin, D.; McComb, T. J. L.; Medina, M. C.; Méhault, J.; Moderski, R.; Moulin, E.; Naumann-Godo, M.; de Naurois, M.; Nedbal, D.; Nekrassov, D.; Nguyen, N.; Nicholas, B.; Niemiec, J.; Nolan, S. J.; Ohm, S.; Olive, J.-F.; de Ona Wilhelmi, E.; Opitz, B.; Orford, K. J.; Ostrowski, M.; Panter, M.; Paz Arribas, M.; Pedaletti, G.; Pelletier, G.; Petrucci, P.-O.; Pita, S.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raubenheimer, B. C.; Raue, M.; Rayner, S. M.; Reimer, O.; Renaud, M.; de Los Reyes, R.; Rieger, F.; Ripken, J.; Rob, L.; Rosier-Lees, S.; Rowell, G.; Rudak, B.; Rulten, C. B.; Ruppel, J.; Ryde, F.; Sahakian, V.; Santangelo, A.; Schlickeiser, R.; Schück, F. M.; Schünwald, A.; Schwanke, U.; Schwarzburg, S.; Schwemmer, S.; Shalchi, A.; Sushch, I.; Sikora, M.; Skilton, J. L.; Sol, H.; Stawarz, L.; Steenkamp, R.; Stegmann, C.; Stinzing, F.; Szostek, A.; Tam, P. H.; Tavernet, J.-P.; Terrier, R.; Tibolla, O.; Tluczykont, M.; Valerius, K.; van Eldik, C.; Vasileiadis, G.; Venter, C.; Venter, L.; Vialle, J. P.; Viana, A.; Vincent, P.; Vivier, M.; Vülk, H. J.; Volpe, F.; Vorobiov, S.; Wagner, S. J.; Ward, M.; Zdziarski, A. A.; Zech, A.; Zechlin, H.-S.

362

Multiprocessor switch with selective pairing  

DOEpatents

System, method and computer program product for a multiprocessing system to offer selective pairing of processor cores for increased processing reliability. A selective pairing facility is provided that selectively connects, i.e., pairs, multiple microprocessor or processor cores to provide one highly reliable thread (or thread group). Each paired microprocessor or processor cores that provide one highly reliable thread for high-reliability connect with a system components such as a memory "nest" (or memory hierarchy), an optional system controller, and optional interrupt controller, optional I/O or peripheral devices, etc. The memory nest is attached to a selective pairing facility via a switch or a bus

Gara, Alan; Gschwind, Michael K; Salapura, Valentina

2014-03-11

363

Prospective very young asteroid pairs  

NASA Astrophysics Data System (ADS)

Several tens of asteroid pairs can be discerned from the background main-belt asteroids. The majority of them are thought to have formed within only the last few 10^6 yr. The youngest recognized pairs have formed more than ? 10 kyr ago. As some details of pair formation are still not understood well, the study of young pairs is of great importance. It is mainly because the conditions at the time of the pair formation could be deduced much more reliably for young pairs. For example, space weathering on the surfaces of the components, or changes in their rotational properties (in spin rates, tumbling, coordinates of rotational pole) could be negligible since the formation of young pairs. Also, possible strong perturbations by main-belt bodies on pair formation can be reliably studied only for extremely young pairs. Some pairs can quickly blend in with the background asteroids, so even the frequency of asteroid pair formation could be determined more reliably based on young pairs (though only after a statistically significant sample is at disposal). In our regular search for young pairs in the growing asteroid database, only multiopposition asteroids with very similar orbital and proper elements are investigated. Every pair component is represented by a number of clones within orbital uncertainties and drifting in semimajor axis due to the Yarkovsky effect. We found that, if the previously unrecognized pairs (87887) 2000 SS_{286} - 2002 AT_{49} and (355258) 2007 LY_{4} - 2013AF_{40} formed at the recent very close approach of their components, they could become the youngest known pairs. In both cases, the relative encounter velocities of the components were only ˜ 0.1 m s^{-1}. However, the minimum distances between some clones are too large and a few clones of the latter pair did not encounter recently (within ? 10 kyr). The age of some prospective young pairs cannot be determined reliably without improved orbital properties (e.g., the second component of a pair (320025) 2007 DT_{76} - 2007 DP_{16}). It is because some components suffered recently repeated close approaches to Ceres or other large main-belt perturbers. In general, the uncertainties in age estimation can be heavily reduced after the physical properties (e.g., sense of rotation, shape, size, binarity) of the pair components are determined.

Galád, A.; Vokrouhlický, D.; Zizka, J.

2014-07-01

364

Mated Fingerprint Card Pairs 2 (MFCP2)  

National Institute of Standards and Technology Data Gateway

NIST Mated Fingerprint Card Pairs 2 (MFCP2) (PC database for purchase)   NIST Special Database 14 is being distributed for use in development and testing of automated fingerprint classification and matching systems on a set of images which approximate a natural horizontal distribution of the National Crime Information Center (NCIC) fingerprint classes. A newer version of the compression/decompression software on the CDROM can be found at the website http://www.nist.gov/itl/iad/ig/nigos.cfm as part of the NBIS package.

365

DISTRIBUTION OF THE KINETIC ENERGY AMONG THE FRAGMENTS IN THE THERMAL NEUTRON-INDUCED TERNARY FISSION OF U²³⁵  

Microsoft Academic Search

Precise data are developed on linetic energy distribution among ; fragments of ternary fission. An ionization chamber equipped with a filter and ; designed for separately recording of fission fragments and long-range alpha ; particles was used. Some 17644 ternary fissions were recorded, and the fragment ; energy distributions were plotted with consideration for recording probabilities. ; The probable energies

V. I. Mostovi; T. A. Mostovaya; M. Sovinskii; Yu. S. Saltykov

1959-01-01

366

Nucleosynthesis in neutron-rich supernova ejecta  

Microsoft Academic Search

The present study is concerned with nucleosynthesis in supernova ejecta which achieve nuclear statistical equilibrium (NSE) with a characteristic neutron excess far greater than that customarily assigned to the production of the most abundant heavy elements. A model-independent approach is adopted, and NSE distributions are calculated at a typical freeze-out temperature and density for a variety of neutron excesses. Attention

D. Hartmann; S. E. Woosley; M. F. El Eid

1985-01-01

367

Inelastic neutron scattering: resonances and fluctuations  

E-print Network

R-function theory of Thomas used in study of inelastic scattering of neutrons to a definite state. Onset of fluctuations, effects of randomness of phases of interfering amplitudes, and variations in statistical distributions of neutron widths considered in detail. Fluctuations exhibit well-defined maxima and sharp minima. For certain adjacent resonances, strong interference effects are predicted.

Frank W. K. Firk

2010-03-13

368

Pair Production and Gamma-Ray Emission in the Outer Magnetospheres of Rapidly Spinning Young Pulsars  

NASA Technical Reports Server (NTRS)

Electron-positron pair production and acceleration in the outer magnetosphere may be crucial for a young rapidly spinning canonical pulsar to be a strong Gamma-ray emitter. Collision between curvature radiated GeV photons and soft X-ray photons seems to be the only efficient pair production mechanism. For Crib-like pulsars, the magnetic field near the light cylinder is so strong, such that the synchrotron radiation of secondary pairs will be in the needed X-ray range. However, for majority of the known Gamma-ray pulsars, surface emitted X-rays seem to work as the matches and fuels for a gamma-ray generation fireball in the outer magnetosphere. The needed X-rays could come from thermal emission of a cooling neutron star or could be the heat generated by bombardment of the polar cap by energetic particles generated in the outer magnetosphere. With detection of more Gamma-ray pulsars, it is becoming evident that the neutron star's intrisic geometry (the inclination angle between the rotation and magnetic axes) and observational geometry (the viewing angle with respect to the rotation axis) are crucial to the understanding of varieties of observational properties exhibited by these pulsars. Inclination angles for many known high energy Gamma-ray pulsars appear to be large and the distribution seems to be consistent with random orientation. However, all of them except Geminga are pre-selected from known radio pulsars. The viewing angles are thus limited to be around the respective inclination angles for beamed radio emission, which may induce strong selection effect. The viewing angles as well as the inclination angles of PSR 1509-58 and PSB 0656+14 may be small such that most of the high energy Gamma-rays produced in the outer accelerators may not reach the observer's direction. The observed Gamma-rays below 5 MeV from this pulsar may be synchrotron radiation of secondary electron-positron pairs produced outside the accelerating regions.

Ruderman, Malvin; Chen, Kaiyou

1997-01-01

369

High-efficiency scintillation detector for combined of thermal and fast neutrons and gamma radiation  

DOEpatents

A scintillation based radiation detector for the combined detection of thermal neutrons, high-energy neutrons and gamma rays in a single detecting unit. The detector consists of a pair of scintillators sandwiched together and optically coupled to the light sensitive face of a photomultiplier tube. A light tight radiation pervious housing is disposed about the scintillators and a portion of the photomultiplier tube to hold the arrangement in assembly and provides a radiation window adjacent the outer scintillator through which the radiation to be detected enters the detector. The outer scintillator is formed of a material in which scintillations are produced by thermal-neutrons and the inner scintillator is formed of a material in which scintillations are produced by high-energy neutrons and gamma rays. The light pulses produced by events detected in both scintillators are coupled to the photomultiplier tube which produces a current pulse in response to each detected event. These current pulses may be processed in a conventional manner to produce a count rate output indicative of the total detected radiation even count rate. Pulse discrimination techniques may be used to distinguish the different radiations and their energy distribution.

Chiles, Marion M. (Knoxville, TN); Mihalczo, John T. (Oak Ridge, TN); Blakeman, Edward D. (Oak Ridge, TN)

1989-01-01

370

Measurement of the fast neutron albedo dose for different shields  

Microsoft Academic Search

The energy distribution of neutrons reflected from iron, soil, water, and polyethylene is measured with a monocrystal scintillation spectrometer for various angles of incidence of a beam of reactor neutrons at the surface of the medium being studied. The relationship is developed between the magnitude of the neutron albedo dose and the layer thickness for iron. The experimental data from

L. A. Trykov; I. V. Goryachev; V. I. Kukhtevich

1966-01-01

371

Nested neutron microfocusing optics on SNAP  

SciTech Connect

The high source intensity of the Spallation Neutron Source (SNS), together with efficient detectors and large detector solid angles, now makes possible neutron experiments with much smaller sample volumes than previously were practical. Nested Kirkpatrick-Baez supermirror optics provide a promising and efficient way to further decrease the useable neutron sample size by focusing polychromatic neutrons into microbeams. Because the optics are nondispersive, they are ideal for spallation sources and for polychromatic and wide bandpass experiments on reactor sources. Theoretical calculations indicate that nested mirrors can preserve source brilliance at the sample for small beams and for modest divergences that are appropriate for diffraction experiments. Although the flux intercepted by a sample can be similar with standard beam-guided approaches, the signal-to-background is much improved with small beams on small samples. Here we describe the design, calibration and performance of a nested neutron mirror pair for the Spallation Neutrons At Pressure (SNAP) beamline at the SNS. High-pressure neutron diffraction is but one example of a large class of neutron experiments that will benefit from spatially-resolved microdiffraction.

Ice, Gene E [ORNL; Choi, Jae-Young [Pohang Accelerator Laboratory, Pohang, Korea; Takacs, P. Z. [Brookhaven National Laboratory (BNL); Khounsary, Ali [Argonne National Laboratory (ANL); Puzyrev, Yevgeniy S [ORNL; Molaison, Jamie J [ORNL; Tulk, Christopher A [ORNL; Andersen, K H [Institut Laue-Langevin (ILL); Bigault, T [Institut Laue-Langevin (ILL)

2010-01-01

372

One-photon pair annihilation in magnetized relativistic plasmas  

NASA Technical Reports Server (NTRS)

In supersonic magnetic fields, electron-positron pairs may annihilate into single photons producing spectral features above 1 MeV. The paper calculates the exact one-photon annihilation rate in the general case where pairs may annihilate from excited Landau states, extending the previous studies which were restricted to pairs in the ground state. Asymptotic expressions for annihilation spectra and rates in the limit of large pair quantum numbers are also derived. It is found that the rate of annihilation from excited states can exceed the rate from the ground state by orders of magnitude in fields less than about 2 x 10 to the 12th G. This allows one-photon annihilation to be competitive with the two-photon process at typical neutron star field strengths. Annihilation spectra from a Maxwellian pair plasma at transrelativistic temperatures show fine structure near threshold on a scale (h/2pi)omega sub B as the result of contributions from individual pair states, which blend into a smooth continuum at higher energies.

Harding, A. K.

1986-01-01

373

Imaging with polarized neutrons  

NASA Astrophysics Data System (ADS)

Neutrons have zero net electrical charge and can thus penetrate deeply into matter, but their intrinsic magnetic moment makes them highly sensitive to magnetic fields. These properties have been combined with radiographic (2D) and tomographic (3D) imaging methods to provide a unique technique to probe macroscopic magnetic phenomena both within and around bulk matter. Based on the spin-rotation of a polarized neutron beam as it passes through a magnetic field, this method allows the direct, real-space visualization of magnetic field distributions. It has been used to investigate the Meissner effect in a type I (Pb) and a type II (YBCO) superconductor, flux trapping in a type I (Pb) superconductor, and the electromagnetic field associated with a direct current flowing in a solenoid. The latter results have been compared to predictions calculated using the Biot-Savart law and have been found to agree well.

Dawson, Martin; Manke, Ingo; Kardjilov, Nikolay; Hilger, André; Strobl, Markus; Banhart, John

2009-04-01

374

Burst Oscillations: Watching Neutron Stars Spin  

NASA Technical Reports Server (NTRS)

It is now almost 15 years since the first detection of rotationally modulated emission from X-ray bursting neutron stars, "burst oscillations," This phenomenon enables us to see neutron stars spin, as the X-ray burst flux asymmetrically lights up the surface. It has enabled a new way to probe the neutron star spin frequency distribution, as well as to elucidate the multidimensional nature of nuclear burning on neutron stars. I will review our current observational understanding of the phenomenon, with an eye toward highlighting some of the interesting remaining puzzles, of which there is no shortage.

Strohmayer, Tod

2010-01-01

375

Computer simulation of neutron capture therapy  

E-print Network

Analytical methods are developed to simulate on a large digital computer the production and use of reactor neutron beams f or boron capture therapy of brain tumors. The simulation accounts for radiation dose distributions ...

Olson, Arne Peter

1967-01-01

376

Computer simulation of neutron capture therapy.  

E-print Network

Analytical methods are developed to simulate on a large digital computer the production and use of reactor neutron beams f or boron capture therapy of brain tumors. The simulation accounts for radiation dose distributions ...

Olson, Arne Peter

1967-01-01

377

Pair production from nuclear collisions and cosmic ray transport  

E-print Network

Modern cosmic ray transport codes, that are capable of use for a variety of applications, need to include all significant atomic, nuclear and particle reactions at a variety of energies. Lepton pair production from nucleus-nucleus collisions has not been included in transport codes to date. Using the methods of Baur, Bertulani and Baron, the present paper provides estimates of electron-positron pair production cross sections for nuclei and energies relevant to cosmic ray transport. It is shown that the cross sections are large compared to other typical processes such as single neutron removal due to strong or electromagnetic interactions. Therefore lepton pair production may need to be included in some transport code applications involving MeV electrons.

John W. Norbury

2006-12-12

378

Perfect crystal neutron interferometry and tensorial neutron tomography  

Microsoft Academic Search

Perfect crystal neutron interferometry may be applied in the tomographic study of magnetic structures in ferromagnetic solids. As a result of such investigations one can expect a complete 3D representation of the magnetisation distribution inside the sample. While the concept is comparable to absorption and phase contrast tomography, the tensorial technique involves 3D polarisation control and specific reconstruction algorithms due

E. Jericha; R. Szeywerth; H. Leeb; G. Badurek

2008-01-01

379

Local structure of lead-containing mixed-ion perovskite ferroelectrics studied using neutron total scattering analysis  

NASA Astrophysics Data System (ADS)

We report the local structures of the lead-containing mixed-ion perovskite Pb(Ni{1/3/2+}Nb{2/3/5+})O3 (PNN), Pb(Fe{1/2/3+}Nb{1/2/5+})O3 (PFN), and Pb(Zr{0.6/4+}Ti{0.4/4+})O3 (PZT) by using a neutron total scattering analysis at low temperatures. Between PNN and PFN, we found that the Pb-O pair distributions were quite similar although they exhibited cubic and monoclinic average structures, respectively. Despite the similarity of the Pb-O pair distributions, the local structures of the B-cations in these compounds were rather different from each other. In the case of PZT, the Pb-O local structure was found to be distinctively different from those of other mixed-valence compounds. These comparisons among Pb-containing mixed-ion perovskites suggest that the valence distribution of the B-cation plays a crucial role in the Pb off-center displacement. Finally, we present the temperature evolution of the Pb-O pair distribution in PNN for temperatures from 300 K to 20 K. Based on this result, we show that a relative displacement of Pb and O against each other is an important feature of the local structure of the Pb ions.

Jeong, I.-K.; Pandey, Dhananjai

2012-07-01

380

Stereo Pair, Honolulu, Oahu  

NASA Technical Reports Server (NTRS)

Honolulu, on the island of Oahu, is a large and growing urban area. This stereoscopic image pair, combining a Landsat image with topography measured by the Shuttle Radar Topography Mission (SRTM), shows how topography controls the urban pattern. This color image can be viewed in 3-D by viewing the left image with the right eye and the right image with the left eye (cross-eyed viewing), or by downloading and printing the image pair, and viewing them with a stereoscope.

Features of interest in this scene include Diamond Head (an extinct volcano near the bottom of the image), Waikiki Beach (just above Diamond Head), the Punchbowl National Cemetary (another extinct volcano, near the image center), downtown Honolulu and Honolulu harbor (image left-center), and offshore reef patterns. The slopes of the Koolau mountain range are seen in the right half of the image. Clouds commonly hang above ridges and peaks of the Hawaiian Islands, but in this synthesized stereo rendition appear draped directly on the mountains. The clouds are actually about 1000 meters (3300 feet) above sea level.

This stereoscopic image pair was generated using topographic data from the Shuttle Radar Topography Mission, combined with a Landsat 7 Thematic Mapper image collected at the same time as the SRTM flight. The topography data were used to create two differing perspectives, one for each eye. When stereoscopically merged, the result is a vertically exaggerated view of the Earth's surface in its full three dimensions. The United States Geological Survey's Earth Resources Observations Systems (EROS) Data Center, Sioux Falls, South Dakota, provided the Landsat data.

The Shuttle Radar Topography Mission (SRTM), launched on February 11, 2000, used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. The mission was designed to collect three-dimensional measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter-long (200-foot) mast, an additional C-band imaging antenna and improved tracking and navigation devices. The mission is a cooperative project between the National Aeronautics and Space Administration (NASA), the National Imagery and Mapping Agency (NIMA) and the German (DLR) and Italian (ASI)space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Earth Science Enterprise, Washington, DC.

Size: 11 by 20 kilometers (7 by 13 miles) Location: 21.3 deg. North lat., 157.9 deg. West lon. Orientation: North toward upper right Original Data Resolution: SRTM, 30 meters (99 feet); Landsat, 15 meters (50 feet) Date Acquired: SRTM, February 18, 2000; Landsat February 12, 2000 Image: NASA/JPL/NIMA

2000-01-01

381

Epithermal Neutron Source for Neutron Resonance Spectroscopy (NRS) using High Intensity, Short Pulse Lasers  

SciTech Connect

A neutron source for neutron resonance spectroscopy (NRS) has been developed using high intensity, short pulse lasers. This measurement technique will allow for robust measurements of interior ion temperature of laser-shocked materials and provide insight into equation of state (EOS) measurements. The neutron generation technique uses protons accelerated by lasers off of Cu foils to create neutrons in LiF, through (p,n) reactions with {sup 7}Li and {sup 19}F. The distribution of the incident proton beam has been diagnosed using radiochromic film (RCF). This distribution is used as the input for a (p,n) neturon prediction code which is compared to experimentally measured neutron yields. From this calculation, a total fluence of 1.8 x 10{sup 9} neutrons is infered, which is shown to be a reasonable amount for NRS temperature measurement.

Higginson, D P; McNaney, J M; Swift, D C; Bartal, T; Hey, D S; Pape, S L; Mackinnon, A; Mariscal, D; Nakamura, H; Nakanii, N; Beg, F N

2010-04-22

382

Results with the neutron scatter camera.  

SciTech Connect

We describe the design, calibration, and measurements made with the neutron scatter camera. Neutron scatter camera design allows for the determination of the direction and energy of incident neutrons by measuring the position, recoil energy, and time-of-flight (TOF) between elastic scatters in two liquid scintillator cells. The detector response and sensitive energy range (0.5-10 MeV) has been determined by detailed calibrations using a {sup 252}Cf neutron source over its field of view (FOV). We present results from several recent deployments. In a laboratory study we detected a {sup 252}Cf neutron source at a stand off distance of 30 m. A hidden neutron source was detected inside a large ocean tanker. We measured the integral flux density, differential energy distribution and angular distribution of cosmic neutron background in the fission energy range 0.5-10 MeV at Alameda, CA (sea level), Livermore, CA (174 m), Albuquerque, NM (1615 m) and Fenton Hill, NM (2630 m). The neutron backgrounds are relatively low, and non-isotropic. The camera has been ruggedized, deployed to various locations and has performed various measurements successfully. Our results show fast neutron imaging could be a useful tool for the detection of special nuclear material (SNM).

Krenz, Kevin D.; Mascarenhas, Nicholas; Brennan, James S.; Mrowka, Stanley; Marleau, Peter

2008-10-01

383

Neutronic Characterization of the Megapie Target  

E-print Network

The MEGAPIE project is one of the key experiments towards the feasibility of Accelerator Driven Systems. On-line operation and post-irradiation analysis will provide the scientific community with unique data on the behavior of a liquid spallation target under realistic irradiation conditions. A good neutronics performance of such a target is of primary importance towards an intense neutron source, where an extended liquid metal loop requires some dedicated verifications related to the delayed neutron activity of the irradiated PbBi. In this paper we report on the experimental characterization of the MEGAPIE neutronics in terms of the prompt neutron (PN) flux inside the target and the delayed neutron (DN) flux on the top of it. For the PN measurements, a complex detector, made of 8 microscopic fission chambers, has been built and installed in the central part of the target to measure the absolute neutron flux and its spatial distribution. Moreover, integral information on the neutron energy distribution as a function of the position along the beam axis could be extracted, providing integral constraints on the neutron production models implemented in transport codes such as MCNPX. For the DN measurement, we used a standard 3He counter and we acquired data during the start-up phase of the target irradiation in order to take sufficient statistics at variable beam power. Experimental results obtained on the PN flux characteristics and their comparison with MCNPX simulations are presented, together with a preliminary analysis of the DN decay time spectrum.

Stefano Panebianco; Olivier Bringer; Pavel Bokov; Sebastien Chabod; Frederic Chartier; Emmeric Dupont; Diane Dore; Xavier Ledoux; Alain Letourneau; Ludovic Oriol; Aurelien Prevost; Danas Ridikas; Jean-Christian Toussaint

2007-10-31

384

Stereo Pair, Pasadena, California  

NASA Technical Reports Server (NTRS)

This stereoscopic image pair is a perspective view that shows the western part of the city of Pasadena, California, looking north toward the San Gabriel Mountains. Portions of the cities of Altadena and La Canada Flintridge are also shown. The cluster of large buildings left of center, at the base of the mountains, is the Jet Propulsion Laboratory. This image shows the power of combining data from different sources to create planning tools to study problems that affect large urban areas. In addition to the well-known earthquake hazards, Southern California is affected by a natural cycle of fire and mudflows. Data shown in this image can be used to predict both how wildfires spread over the terrain and how mudflows are channeled down the canyons.

The image was created from three datasets: the Shuttle Radar Topography Mission (SRTM) supplied the elevation, U. S. Geological Survey digital aerial photography provided the image detail, and the Landsat Thematic Mapper provided the color. The United States Geological Survey's Earth Resources Observations Systems (EROS) Data Center, Sioux Falls, South Dakota, provided the Landsat data and the aerial photography. The image can be viewed in 3-D by viewing the left image with the right eye and the right image with the left eye (cross-eyed viewing), or by downloading and printing the image pair, and viewing them with a stereoscope.

The Shuttle Radar Topography Mission (SRTM), launched on February 11, 2000, used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. The mission was designed to collect three-dimensional measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter-long (200-foot) mast, an additional C-band imaging antenna and improved tracking and navigation devices. The mission is a cooperative project between the National Aeronautics and Space Administration (NASA), the National Imagery and Mapping Agency (NIMA) and the German (DLR) and Italian (ASI)space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Earth Science Enterprise, Washington, DC.

Size: 3.4 km (2.1 miles) width x 7.0 km (4.4 miles) depth Location: 34.16 deg. North lat., 118.16 deg. West lon. Orientation: Looking North Original Data Resolution: SRTM and Landsat, 30 m; aerial photo, 3 m; no vertical exaggeration Date Acquired: February 16, 2000 (SRTM), July 3, 1985 (Landsat) Image: NASA/JPL/NIMA

2000-01-01

385

Precision measurements of neutron-matter interactions using neutron interferometry  

NASA Astrophysics Data System (ADS)

This thesis focuses on two experiments done at the National Institute of Standards and Technology (NIST) to measure neutron scattering lengths. Both experiments used a neutron interferometer; a device that has been used to determine the scattering lengths of a variety of isotopes to better than one percent relative uncertainty. Neutron scattering lengths are important parameters in understanding both nucleon structure and nucleon-nucleon interactions from the point of view of low-energy quantum chromodynamics (QCD). The first experiment is an attempt to measure the neutron-electron scattering length bne. The neutron-electron scattering length is important because of its relationship to the internal charge distribution of the neutron. Combining the latest bne results gives the current excepted value of bne = (-1.345 +/- 0.025) 10-3 fm. However, there is a non-statistical disagreement between the individual measurements. Here we use a neutron interferometer to measure the large-dynamical phase shift, part of which is due to bne, caused when the neutron and crystal satisfy Bragg's law. This is accomplished by rotating a perfect silicon crystal in steps as small as 10-8 rad through the Bragg condition. Because of unforeseen signal losses, this experiment has not yet produced a final result but lessons learned in this work will assist future bne measurements. The second experiment is a measurement of the spin-incoherent neutron scattering length of 3He b'i. In the study of few-body nuclear physics, two and three nucleon potentials are used to describe complex nucleon interactions which cannot be directly calculated using QCD. Neutron scattering lengths of light isotopes provide crucial tests of these nucleon-nucleon potentials. The neutron interferometry and optics facility at NIST had been used previously to determine the spin-coherent scattering lengths for n-1H, n-2H, and n-3He to better than 0.2% relative uncertainty. We report a result of b' i = (-2.512 +/- 0.018) fm using a polarized 3He target and polarized neutron beam. This result combined with spin-coherent data is in good agreement with certain theoretical models describing three nucleon interactions.

Huber, Michael Garth

386

Methods for absorbing neutrons  

DOEpatents

A conduction cooled neutron absorber may include a metal matrix composite that comprises a metal having a thermal neutron cross-section of at least about 50 barns and a metal having a thermal conductivity of at least about 1 W/cmK. Apparatus for providing a neutron flux having a high fast-to-thermal neutron ratio may include a source of neutrons that produces fast neutrons and thermal neutrons. A neutron absorber positioned adjacent the neutron source absorbs at least some of the thermal neutrons so that a region adjacent the neutron absorber has a fast-to-thermal neutron ratio of at least about 15. A coolant in thermal contact with the neutron absorber removes heat from the neutron absorber.

Guillen, Donna P. (Idaho Falls, ID); Longhurst, Glen R. (Idaho Falls, ID); Porter, Douglas L. (Idaho Falls, ID); Parry, James R. (Idaho Falls, ID)

2012-07-24

387

Controversies in kidney paired donation.  

PubMed

Kidney paired donation represented 10% of living kidney donation in the United States in 2011. National registries around the world and several separate registries in the United States arrange paired donations, although with significant variations in their practices. Concerns about ethical considerations, clinical advisability, and the quantitative effectiveness of these approaches in paired donation result in these variations. For instance, although donor travel can be burdensome and might discourage paired donation, it was nearly universal until convincing analysis showed that living donor kidneys can sustain many hours of cold ischemia time without adverse consequences. Opinions also differ about whether the last donor in a chain of paired donation transplants initiated by a nondirected donor should donate immediately to someone on the deceased donor wait-list (a domino or closed chain) or should be asked to wait some length of time and donate to start another sequence of paired donations later (an open chain); some argue that asking the donor to donate later may be coercive, and others focus on balancing the probability that the waiting donor withdraws versus the number of additional transplants if the chain can be continued. Other controversies in paired donation include simultaneous versus nonsimultaneous donor operations, whether to enroll compatible pairs, and interactions with desensitization protocols. Efforts to expand public awareness of and participation in paired donation are needed to generate more transplant opportunities. PMID:22732046

Gentry, Sommer E; Montgomery, Robert A; Segev, Dorry L

2012-07-01

388

Neutron stars as cosmic neutron matter laboratories  

SciTech Connect

Recent developments which have radically changed our understanding of the dynamics of neutron star superfluids and the free precession of neutron stars are summarized, and the extent to which neutron stars are cosmic neutron matter laboratories is discussed. 17 refs., 1 tab.

Pines, D.

1986-01-01

389

Pair attribute learning: network construction using pair features  

Microsoft Academic Search

We present the pair attribute learning (PAL) algorithm for the selection of relevant inputs and network topology. Correlations on training instance pairs are used to drive network construction of a single-hidden layer MLP. Results on nine learning problems demonstrate 70% less complexity, on average, without a significant loss of accuracy

Eric K. Henderson; Tony R. Martinez

2002-01-01

390

Recent Advances in Neutron Physics  

ERIC Educational Resources Information Center

Discusses new studies in neutron physics within the last decade, such as ultracold neutrons, neutron bottles, resonance behavior, subthreshold fission, doubly radiative capture, and neutron stars. (MLH)

Feshbach, Herman; Sheldon, Eric

1977-01-01

391

Influence of the single-particle structure on the nuclear surface and the neutron skin  

E-print Network

We analyze the influence of the single-particle structure on the neutron density distribution and the neutron skin in Ca, Ni, Zr, Sn, and Pb isotopes. The nucleon density distributions are calculated in the self-consistent Hartree-Fock approach with the SLy4 Skyrme force. A close correlation is found between the quantum numbers of the valence neutrons and the changes in the position and the diffuseness of the nuclear surface, which in turn affect the neutron skin thickness. Neutrons in the valence orbitals with low principal quantum number and high angular momentum mainly displace the position of the neutron surface outwards, while neutrons with high principal quantum number and low angular momentum basically increase the diffuseness of the neutron surface. The impact of the valence shell neutrons on the tail of the neutron density distribution is discussed.

Warda, M; Vinas, X; Roca-Maza, X

2014-01-01

392

Pygmy stars: first pair.  

PubMed

The binary LP 101-15/16 having the proper motion of 1.62 seconds of arc per year has been studied with the prime-focus spectrograph of the 200-inch (508 cm) telescope. Indications are that LP 101-15/16 is the first pair of pygmy stars ever discovered. One of its components, LP 101-16, is probably a blue pygmy star which is at least four magnitudes fainter than the ordinary white dwarfs. Also, two of the Balmer lines in absorption appear to be displaced toward the red by amounts which indicate the existence of an Einstein gravitational red shift corresponding to about 1000 km sec-1. On the other hand LP 101-15 is red and shows an entirely new type of spectrum, which suggests that it may be a first representative of a type of red pygmy star which is 2.5 magnitudes fainter than the M-type dwarf stars of the main sequence. PMID:17730606

Zwicky, F

1966-07-01

393

Radical frustrated Lewis pairs.  

PubMed

While a growing body of literature describes FLP adducts of diamagnetic unsaturated substrates such as alkenes, alkynes and heterocumulenes such as carbon dioxide, capture of the diatomic radical nitric oxide (NO) by intramolecular phosphane/borane FLPs gives a new family of radical frustrated Lewis pair adducts. Capture of NO results in heterocycles with new P-N and B-N bonds featuring a spin density Umpolung of NO to give FLP-NO species that possess significant O-centered radical reactivity. Use of these radical FLP-NO species in C-H functionalization chemistry via H-atom abstraction / radical recombination sequences as well as deployment in nitroxide mediated polymerization of alkenes indicates a rich and diverse chemistry for FLP-NO species. An alternative, complementary strategy to generate radical FLPs involves the use of transition metal centers with unpaired electrons as the Lewis acid component of an FLP in conjunction with a tethered but hindered Lewis base. PMID:23468284

Warren, Timothy H; Erker, Gerhard

2013-01-01

394

Neutron reflecting supermirror structure  

DOEpatents

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

Wood, J.L.

1992-12-01

395

Neutron reflecting supermirror structure  

DOEpatents

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

Wood, James L. (Drayton Plains, MI)

1992-01-01

396

Neutron Spectra in a 15 MV LINAC  

SciTech Connect

Neutron spectra were calculated inside the treatment hall of a 15 MV LINAC, calculations were carried out using Monte Carlo methods. With a Bonner sphere spectrometer with pairs of thermoluminiscent dosimeters the neutron spectrum at 100 cm from the isocenter was measured and compared with the calculated spectrum. All the spectra in the treatment hall show the presence of evaporation and knock-on neutrons; also the room-return due to the hall features is shown. In the maze the large contribution are due to epithermal and thermal neutrons. A good agreement between the calculated and measured spectrum at 100 cm was noticed, from this comparison the differences are attributed to the water content in the concrete of the hall.

Vega-Carrillo, H. R. [Unidad Academica de Estudios Nucleares de la Universidad Autonoma de Zacatecas. Apdo. Postal 336, 98000 Zacatecas, Zac. (Mexico); Chu, Wei-Han [National Tsing Hua University, Hsinchu, Taiwan (China); Tung, Chuan-Jong [Chan Gung University, Taiwan (China); Lan, Jen-Hong [Chan Gung Memorial Hospital-Kaohsiung Medical Center and National Kaohsiung University, Kaohsiung, Taiwan (China)

2010-12-07

397

Rotational-translational fourier imaging system requiring only one grid pair  

NASA Technical Reports Server (NTRS)

The sky contains many active sources that emit X-rays, gamma rays, and neutrons. Unfortunately hard X-rays, gamma rays, and neutrons cannot be imaged by conventional optics. This obstacle led to the development of Fourier imaging systems. In early approaches, multiple grid pairs were necessary in order to create rudimentary Fourier imaging systems. At least one set of grid pairs was required to provide multiple real components of a Fourier derived image, and another set was required to provide multiple imaginary components of the image. It has long been recognized that the expense associated with the physical production of the numerous grid pairs required for Fourier imaging was a drawback. Herein one grid pair (two grids), with accompanying rotation and translation, can be used if one grid has one more slit than the other grid, and if the detector is modified.

Campbell, Jonathan W. (Inventor)

2006-01-01

398

Dual Resolution Images from Paired Fingerprint Cards  

National Institute of Standards and Technology Data Gateway

NIST Dual Resolution Images from Paired Fingerprint Cards (PC database for purchase)   NIST Special Database 30 is being distributed for use in development and testing of fingerprint compression and fingerprint matching systems. The database allows the user to develop and evaluate data compression algorithms for fingerprint images scanned at both 19.7 ppmm (500 dpi) and 39.4 ppmm (1000 dpi). The data consist of 36 ten-print paired cards with both the rolled and plain images scanned at 19.7 and 39.4 pixels per mm. A newer version of the compression/decompression software on the CDROM can be found at the website http://www.nist.gov/itl/iad/ig/nigos.cfm as part of the NBIS package.

399

Pair production as a probe of colliding beam size  

SciTech Connect

We propose the use of soft e{sup +}e{sup {minus}} pairs as a non-evasive measurement of the colliding beam size. The angular distribution of the pair particles that have different sign of charge from that of the opposing beam, provides the information about the aspect ratio of the beam. The transverse momentum of the other species in the pair, on the other hand, carries information about the horizontal dimension of the beam. Together, one can in principle measure both {sigma}{sub x} and {sigma}{sub y}.

Chen, Pisin; Irwin, J.; Spitkovsky, A.

1994-07-01

400

Secondary neutron production from thick Pb target by light particle irradiation  

Microsoft Academic Search

Neutron multiplicities from spallation neutron sources were measured by Solid State Nuclear Track Detectors. Light particles as protons, deuterons and alphas in the GeV range were used on Pb targets. For neutron thermalization the targets were covered by 6 cm paraffin moderator. Neutron multiplicity distributions were studied inside and on the moderator surface. Comparison of SSNTDs results were made for

J. C. Adloff; R. Brandt; M. Debeauvais; F. Fernandez; M. Krivopustov; B. A. Kulakov; A. Sosnin; M. Zamani

1999-01-01

401

Rotational effect of fissile nucleus in binary fission of 235U induced by cold polarized neutrons  

Microsoft Academic Search

We have found a small inclination of the symmetry axis of the prompt fission gamma-quanta angular distribution relative to the “fission axis” in binary fission of 235U induced by cold polarized neutrons using the neutron beam line V13 at Berlin Neutron Scattering Center (BENSC). The sign of the shift depends on the direction of the cold neutron beam polarization and

G. V. Danilyan; P. Granz; V. A. Krakhotin; F. Mezei; V. V. Novitsky; V. S. Pavlov; M. Russina; P. B. Shatalov; T. Wilpert

2009-01-01

402

Influence of medium modified angular distributions and mean field on the quasielastic and inelastic peaks of neutrons induced by 1.2 GeV protons on targets with 27{<=}A{<=}232  

SciTech Connect

An analysis of the quasielastic and inelastic peaks of neutrons induced by 1.2 GeV protons on targets with 27{<=}A{<=}232 is presented using the ultrarelativistic quantum molecular dynamics (UrQMD) model. Two distinct contributions of the nuclear medium are studied in the UrQMD framework, referred to as 'in-medium' and 'mean field' effects. The former only includes modifications to the NN-elastic and NN{yields}N{delta} angular distributions as well as changes to the {delta}-mass distribution. The latter incorporates the (QMD) interaction potential between nucleons. It is shown that in-medium effect produces an important role for enhancing the quasi-inelastic peak, while the mean field effect enhances the intensity of both peaks and becomes important in the quasielastic region. The introduction of both effects in the UrQMD calculations improves the intensity and location of the quasielastic and inelastic peaks. A rather smooth dependence of the integrated cross sections of the quasielastic and inelastic peaks on the mass number at both angles is also found and shown to be in qualitative agreement with the UrQMD incorporating these two effects.

Abdel-Waged, Khaled [Umm Al-Qura University, Faculty of Applied Science, Physics Department, Makkah Unit 126, P.O. Box 7047 (Saudi Arabia)

2004-07-01

403

Pressure/temperature fluid cell apparatus for the neutron powder diffractometer instrument: Probing atomic structure in situ  

NASA Astrophysics Data System (ADS)

This contribution describes a new local structure compatible gas/liquid cell apparatus for probing disordered materials at high pressures and variable temperatures in the Neutron Powder Diffraction instrument at the Lujan Neutron Scattering Center, Los Alamos National Laboratory. The new sample environment offers choices for sample canister thickness and canister material type. Finite element modeling is utilized to establish maximum allowable working pressures of 414 MPa at 15 K and 121 MPa at 600 K. High quality atomic pair distribution function data extraction and modeling have been demonstrated for a calibration standard (Si powder) and for supercritical and subcritical CO2 measurements. The new sample environment was designed to specifically target experimental studies of the local atomic structures involved in geologic CO2 sequestration, but will be equally applicable to a wide variety of energy applications, including sorption of fluids on nano/meso-porous solids, clathrate hydrate formation, catalysis, carbon capture, and H2 and natural gas uptake/storage.

Wang, Hsiu-Wen; Fanelli, Victor R.; Reiche, Helmut M.; Larson, Eric; Taylor, Mark A.; Xu, Hongwu; Zhu, Jinlong; Siewenie, Joan; Page, Katharine

2014-12-01

404

Weird Stellar Pair Puzzles Scientists  

NASA Astrophysics Data System (ADS)

Astronomers have discovered a speedy spinning pulsar in an elongated orbit around an apparent Sun-like star, a combination never seen before, and one that has them puzzled about how the strange system developed. Orbital Comparison Comparing Orbits of Pulsar and Its Companion to our Solar System. CREDIT: Bill Saxton, NRAO/AUI/NSF Click on image for full caption information and available graphics. "Our ideas about how the fastest-spinning pulsars are produced do not predict either the kind of orbit or the type of companion star this one has," said David Champion of the Australia Telescope National Facility. "We have to come up with some new scenarios to explain this weird pair," he added. Astronomers first detected the pulsar, called J1903+0327, as part of a long-term survey using the National Science Foundation's Arecibo radio telescope in Puerto Rico. They made the discovery in 2006 doing data analysis at McGill University, where Champion worked at the time. They followed up the discovery with detailed studies using the Arecibo telescope, the NSF's Robert C. Byrd Green Bank Telescope (GBT) in West Virginia, the Westerbork radio telescope in the Netherlands, and the Gemini North optical telescope in Hawaii. The pulsar, a city-sized superdense stellar corpse left over after a massive star exploded as a supernova, is spinning on its axis 465 times every second. Nearly 21,000 light-years from Earth, it is in a highly-elongated orbit that takes it around its companion star once every 95 days. An infrared image made with the Gemini North telescope in Hawaii shows a Sun-like star at the pulsar's position. If this is an orbital companion to the pulsar, it is unlike any companions of other rapidly rotating pulsars. The pulsar, a neutron star, also is unusually massive for its type. "This combination of properties is unprecedented. Not only does it require us to figure out how this system was produced, but the large mass may help us understand how matter behaves at extremely high densities," said Scott Ransom of the National Radio Astronomy Observatory. Pulsars are neutron stars whose strong magnetic fields channel lighthouse-like beams of light and radio waves that whirl around as the star spins. Typical pulsars spin a few times a second, but some, like PSR J1903+0327, are much faster, rotating hundreds of times a second. They are called millisecond pulsars. Astronomers think most millisecond pulsars are sped up by material falling onto them from a companion star. This requires the pulsar to be in a tight orbit around its companion that becomes more and more circular with time. The orbits of some millisecond pulsars are the most perfect circles in the Universe, so the elongated orbit of the new pulsar is a mystery. "What we have found is a millisecond pulsar that is in the wrong kind of orbit around what appears to be the wrong kind of star," Champion said. "Now we have to figure out how this strange system was produced." The scientists are considering three possibilities. The first, that the pulsar simply was born spinning quickly, seems unlikely to them. Another possibility, they say, is that the pulsar was formed in a tight group of stars known as a globular cluster, where it had a companion that spun it up. Later, a close encounter with another star in the cluster stripped it of its companion and flung it out of the cluster. For several reasons, including the fact that they don't see a nearby cluster from which it could have come, they don't like that explanation either. A third scenario says the pulsar may be part of a triple, not a double, star system. In this case, the pulsar's 95-day orbit is around a neutron star or white dwarf, not the Sun-like star seen in the infrared image. The Sun-like star would then be in a more-distant orbit around the pulsar and its close companion. "We've found about 50 pulsars in binary systems. We may now have found our first pulsar in a stellar triple system," Ransom said. The international research team is busy trying to get their

2008-05-01

405

Pyrochemical neutron multiplicity counter design  

SciTech Connect

Pyrochemical process materials are difficult to measure using conventional neutron counting methods because of significant self- multiplication and variable ({alpha},n) reaction rates. Multiplicity counters measure the first three moments of the neutron multiplicity distribution and thus make it possible to determine sample mass even when multiplication and ({alpha},n) rate are unknown. A new multiplicity counter suitable for inplant measurement of pyrochemical process materials has been designed using Monte Carlo simulations. The goals were to produce a counter that has high neutron detection efficiency, low die-away time, a flat spatial efficiency profile, and is insensitive to the neutron energy spectrum. Monte Carlo calculations were performed for several prototype models consisting of four rings of 71-cm active length {sup 3}He tubes in a polyethylene body. The cadmium-lined sample well is 25 cm in diameter to accommodate a wide variety of inplant sample containers. The counter can be free-standing or in-line without mechanical modification. The calculations were performed to determine the above design criteria for several configurations of tube spacing, cadmium liners, and sample height. Calculations were also performed for distributed sample sources to understand the integrated effects of variable neutron spectra on the counter. 5 refs., 8 figs., 1 tab.

Langner, D.G.; Ensslin, N.; Krick, M.S.

1990-01-01

406

Pair Production in Classical Electrodynamics  

Microsoft Academic Search

One of the most relevant features of quantum field theory is the phenomenon of pair production, the existence of which, first suggested by Dirac, was not even suspected in the older theories. On the other hand Feynman, in the spirit of his spatiotemporal approach to quantum mechanics, showed how a description of pair production could be given within classical relativistic

A. Carati

1998-01-01

407

Applications of Neutron Generators  

NASA Astrophysics Data System (ADS)

Miscellaneous applications of low-voltage neutron generators providing 3 and 14 MeV neutrons via the D-D and D-T reactions, respectively, are reviewed. New experimental methods are reported, and emerging applications in the areas of prompt and delayed neutron activation analysis, fast neutron imaging and profiling, irradiation effects, fast neutron radiobiology, and shielding design are highlighted.

Csikai, J.; Dóczi, R.

408

Directional epithermal neutron detector  

Microsoft Academic Search

A borehole tool for epithermal neutron die-away logging of subterranean formations surrounding a borehole is described which consists of: (a) a pulsed source of fast neutrons for irradiating the formations surrounding a borehole, (b) at least one neutron counter for counting epithermal neutrons returning to the borehole from the irradiated formations, (c) a neutron moderating material, (d) an outer thermal

W. W. Givens; W. R. Jr. Mills

1986-01-01

409

Neutron transport simulation (selected topics)  

NASA Astrophysics Data System (ADS)

Neutron transport simulation is usually performed for criticality, power distribution, activation, scattering, dosimetry and shielding problems, among others. During the last fifteen years, innovative technological applications have been proposed (Accelerator Driven Systems, Energy Amplifiers, Spallation Neutron Sources, etc.), involving the utilization of intermediate energies (hundreds of MeV) and high-intensity (tens of mA) proton accelerators impinging in targets of high Z elements. Additionally, the use of protons, neutrons and light ions for medical applications (hadrontherapy) impose requirements on neutron dosimetry-related quantities (such as kerma factors) for biologically relevant materials, in the energy range starting at several tens of MeV. Shielding and activation related problems associated to the operation of high-energy proton accelerators, emerging space-related applications and aircrew dosimetry-related topics are also fields of intense activity requiring as accurate as possible medium- and high-energy neutron (and other hadrons) transport simulation. These applications impose specific requirements on cross-section data for structural materials, targets, actinides and biologically relevant materials. Emerging nuclear energy systems and next generation nuclear reactors also impose requirements on accurate neutron transport calculations and on cross-section data needs for structural materials, coolants and nuclear fuel materials, aiming at improved safety and detailed thermal-hydraulics and radiation damage studies. In this review paper, the state-of-the-art in the computational tools and methodologies available to perform neutron transport simulation is presented. Proton- and neutron-induced cross-section data needs and requirements are discussed. Hot topics are pinpointed, prospective views are provided and future trends identified.

Vaz, P.

2009-10-01

410

Impact of nuclear data on fast neutron therapy  

SciTech Connect

By combining a new, all-particle Monte Carlo radiation transport code, PEREGRINE, with the Lawrence Livermore National Laboratory (LLNL) nuclear data base, we have studied the importance of various neutron reactions on dose distributions in biological materials. Monte Carlo calculations have been performed for 5--20 MeV neutron pencil beams incident on biologically relevant materials arranged in several simple geometries. Results highlight the importance of nuclear data used for calculating dose distributions resulting from fast neutron therapy.

Hartmann Siantar, C.L.; Chandler, W.P.; Rathkopf, J.A.; Resler, D.A.; Cox, L.J.; Chadwick, M.B.; White, R.M.

1994-05-12

411

Isolated neutron stars in the galaxy: from magnetars to antimagnetars  

SciTech Connect

Using the model with decaying magnetic fields it is possible to describe with one smooth (log-Gaussian) initial magnetic field distribution three types of isolated neutron stars: radiopulsar, magnetars, and cooling close-by compact objects. The same model is used here to make predictions for old accreting isolated neutron stars. It is shown that using the updated field distribution we predict a significant fraction of isolated neutron stars at the stage of accretion despite long subsonic propeller stage.

Boldin, P. A., E-mail: boldin.pavel@gmail.com [Moscow Engineering Physics Institute (State University) (Russian Federation); Popov, S. B., E-mail: polar@sai.msu.ru [Moscow State University, Sternberg Astronomical Institute (Russian Federation)

2012-07-15

412

Base pairing and base mis-pairing in nucleic acids  

NASA Technical Reports Server (NTRS)

In recent years we have learned that DNA is conformationally active. It can exist in a number of different stable conformations including both right-handed and left-handed forms. Using single crystal X-ray diffraction analysis we are able to discover not only additional conformations of the nucleic acids but also different types of hydrogen bonded base-base interactions. Although Watson-Crick base pairings are the predominant type of interaction in double helical DNA, they are not the only types. Recently, we have been able to examine mismatching of guanine-thymine base pairs in left-handed Z-DNA at atomic resolution (1A). A minimum amount of distortion of the sugar phosphate backbone is found in the G x T pairing in which the bases are held together by two hydrogen bonds in the wobble pairing interaction. Because of the high resolution of the analysis we can visualize water molecules which fill in to accommodate the other hydrogen bonding positions in the bases which are not used in the base-base interactions. Studies on other DNA oligomers have revealed that other types of non-Watson-Crick hydrogen bonding interactions can occur. In the structure of a DNA octamer with the sequence d(GCGTACGC) complexed to an antibiotic triostin A, it was found that the two central AT base pairs are held together by Hoogsteen rather than Watson-Crick base pairs. Similarly, the G x C base pairs at the ends are also Hoogsteen rather than Watson-Crick pairing. Hoogsteen base pairs make a modified helix which is distinct from the Watson-Crick double helix.

Wang, A. H. J.; Rich, A.

1986-01-01

413

Isoscalar and isovector pairing in a formalism of quartets  

NASA Astrophysics Data System (ADS)

Isoscalar (T = 0, J = 1) and isovector (T = 1, J = 0) pairing correlations in the ground state of self-conjugate nuclei are treated in terms of alpha-like quartets built by two protons and two neutrons coupled to total isospin T = 0 and total angular momentum J = 0. Quartets are constructed dynamically via an iterative variational procedure and the ground state is represented as a product of such quartets. It is shown that the quartet formalism describes accurately the ground state energies of realistic isovector plus isoscalar pairing Hamiltonians in nuclei with valence particles outside the 16O, 40Ca and 100Sn cores. Within the quartet formalism we analyze the competition between isovector and isoscalar pairing correlations and find that for nuclei with the valence nucleons above the cores 40Ca and 100Sn the isovector correlations account for the largest fraction of the total pairing correlations. This is not the case for sd-shell nuclei for which isoscalar correlations prevail. Contrary to many mean-field studies, isovector and isoscalar pairing correlations mix significantly in the quartet approach.

Sambataro, M.; Sandulescu, N.; Johnson, C. W.

2015-01-01

414

The Subtleties of Pairing and Collective Structures in Deformed Nuclei  

NASA Astrophysics Data System (ADS)

It is well known that simple monopole pairing is a pretty crude approximation. It can account for the observations that the ground states of all even-even nuclei have spin-parity 01+ and that there is a pairing gap above the ground state in deformed nuclei before particle-hole configurations can be excited. As an approximation it is best for proton and neutron mid-shell nuclei where the available single particle Nilsson wavefunctions have large overlaps. However at the beginning of regions of deformation, where high-K orbitals can be bought to the Fermi surface from a lower shell, simple monopole pairing is inadequate in describing the physics of the observed data. More recently, with a considerable increase in the quantity and quality of experimental data available, configuration dependent pairing has been used to account for the properties of low-lying first excited 02+ states in N = 88 and 90 nuclei at the onset of deformation in the rare earths. The properties of 02+ states in these and other nuclei at the start of regions of deformation and the effects of blocking of pairing leading to a decrease in the backbending critical frequencies in odd nuclei are presented.

Sharpey-Schafer, J. F.

2015-11-01

415

Frequency modulation of spin torque oscillator pairs  

NASA Astrophysics Data System (ADS)

The current controlled modulation of nanocontact based spin torque oscillator (STO) pairs is studied in both the synchronized and nonsynchronized states. The synchronized state shows a well behaved modulation and demonstrates robust mutual locking even under strong modulation. The power distribution of the modulation sidebands can be quantitatively described by assuming a single oscillator model. However, in the nonsynchronized state, the modulation sidebands are not well described by the model, indicating interactions between the two individual nanocontact STOs. These findings are promising for potential applications requiring the modulation of large synchronized STO arrays.

Pogoryelov, Ye.; Muduli, P. K.; Bonetti, S.; Iacocca, E.; Mancoff, Fred; Åkerman, Johan

2011-05-01

416

Invariant-mass distribution of jet pairs produced in association with a W boson in pp ¯ collisions at ?s =1.96 TeV using the full CDF Run II data set  

NASA Astrophysics Data System (ADS)

We report on a study of the dijet invariant-mass distribution in events with one identified lepton, a significant imbalance in the total event transverse momentum, and two jets. This distribution is sensitive to the possible production of a new particle in association with a W boson, where the boson decays leptonically. We use the full data set of proton-antiproton collisions at 1.96 TeV center-of-mass energy collected by the Collider Detector at the Fermilab Tevatron, corresponding to an integrated luminosity of 8.9 fb-1. The data are found to be consistent with standard model expectations, and a 95% confidence level upper limit is set on the production cross section of a W boson in association with a new particle decaying into two jets.

Aaltonen, T.; Amerio, S.; Amidei, D.; Anastassov, A.; Annovi, A.; Antos, J.; Apollinari, G.; Appel, J. A.; Arisawa, T.; Artikov, A.; Asaadi, J.; Ashmanskas, W.; Auerbach, B.; Aurisano, A.; Azfar, F.; Badgett, W.; Bae, T.; Barbaro-Galtieri, A.; Barnes, V. E.; Barnett, B. A.; Barria, P.; Bartos, P.; Bauce, M.; Bedeschi, F.; Behari, S.; Bellettini, G.; Bellinger, J.; Benjamin, D.; Beretvas, A.; Bhatti, A.; Bland, K. R.; Blumenfeld, B.; Bocci, A.; Bodek, A.; Bortoletto, D.; Boudreau, J.; Boveia, A.; Brigliadori, L.; Bromberg, C.; Brucken, E.; Budagov, J.; Budd, H. S.; Burkett, K.; Busetto, G.; Bussey, P.; Butti, P.; Buzatu, A.; Calamba, A.; Camarda, S.; Campanelli, M.; Canelli, F.; Carls, B.; Carlsmith, D.; Carosi, R.; Carrillo, 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.; Cho, K.; Chokheli, D.; Clark, A.; Clarke, C.; Convery, M. E.; Conway, J.; Corbo, M.; Cordelli, M.; Cox, C. A.; Cox, D. J.; Cremonesi, M.; Cruz, D.; Cuevas, J.; Culbertson, R.; d'Ascenzo, N.; Datta, M.; de Barbaro, P.; Demortier, L.; Deninno, M.; D'Errico, M.; Devoto, F.; Di Canto, A.; Di Ruzza, B.; Dittmann, J. R.; Donati, S.; D'Onofrio, M.; Dorigo, M.; Driutti, A.; Ebina, K.; Edgar, R.; Elagin, A.; Erbacher, R.; Errede, S.; Esham, B.; Farrington, S.; Fernández Ramos, J. P.; Field, R.; Flanagan, G.; Forrest, R.; Franklin, M.; Freeman, J. C.; Frisch, H.; Funakoshi, Y.; Galloni, C.; Garfinkel, A. F.; Garosi, P.; Gerberich, H.; Gerchtein, E.; Giagu, S.; Giakoumopoulou, V.; Gibson, K.; Ginsburg, C. M.; Giokaris, N.; Giromini, P.; Giurgiu, G.; Glagolev, V.; Glenzinski, D.; Gold, M.; Goldin, D.; Golossanov, A.; Gomez, G.; Gomez-Ceballos, G.; Goncharov, M.; González López, O.; Gorelov, I.; Goshaw, A. T.; Goulianos, K.; Gramellini, E.; Grinstein, S.; Grosso-Pilcher, C.; Group, R. C.; Guimaraes da Costa, J.; Hahn, S. R.; Han, J. Y.; Happacher, F.; Hara, K.; Hare, M.; Harr, R. F.; Harrington-Taber, T.; Hatakeyama, K.; Hays, C.; Heinrich, J.; Herndon, M.; Hocker, A.; Hong, Z.; Hopkins, W.; Hou, S.; Hughes, R. E.; Husemann, U.; Hussein, M.; Huston, J.; Introzzi, G.; Iori, M.; Ivanov, A.; James, E.; Jang, D.; Jayatilaka, B.; Jeon, E. J.; Jindariani, S.; Jones, M.; Joo, K. K.; Jun, S. Y.; Junk, T. R.; Kambeitz, M.; Kamon, T.; Karchin, P. E.; Kasmi, A.; Kato, Y.; Ketchum, W.; Keung, J.; Kilminster, B.; Kim, D. H.; Kim, H. S.; Kim, J. E.; Kim, M. J.; Kim, S. H.; Kim, S. B.; Kim, Y. J.; Kim, Y. K.; Kimura, N.; Kirby, M.; Knoepfel, K.; Kondo, K.; Kong, D. J.; Konigsberg, J.; Kotwal, A. V.; Kreps, M.; Kroll, J.; Kruse, M.; Kuhr, T.; Kurata, M.; Laasanen, A. T.; Lammel, S.; Lancaster, M.; Lannon, K.; Latino, G.; Lee, H. S.; Lee, J. S.; Leo, S.; Leone, S.; Lewis, J. D.; Limosani, A.; Lipeles, E.; Lister, A.; Liu, H.; Liu, Q.; Liu, T.; Lockwitz, S.; Loginov, A.; Lucchesi, D.; Lucà, A.; Lueck, J.; Lujan, P.; Lukens, P.; Lungu, G.; Lys, J.; Lysak, R.; Madrak, R.; Maestro, P.; Malik, S.; Manca, G.; Manousakis-Katsikakis, A.; Marchese, L.; Margaroli, F.; Marino, P.; Martínez, M.; Matera, K.; Mattson, M. E.; Mazzacane, A.; Mazzanti, P.; McNulty, R.; Mehta, A.; Mehtala, P.; Mesropian, C.; Miao, T.; Mietlicki, D.; Mitra, A.; Miyake, H.; Moed, S.; Moggi, N.; Moon, C. S.; Moore, R.; Morello, M. J.; Mukherjee, A.; Muller, Th.; Murat, P.; Mussini, M.; Nachtman, J.; Nagai, Y.; Naganoma, J.; Nakano, I.; Napier, A.; Nett, J.; Neu, C.; Nigmanov, T.; Nodulman, L.; Noh, S. Y.; Norniella, O.; Oakes, L.; Oh, S. H.; Oh, Y. D.; Oksuzian, I.; Okusawa, T.; Orava, R.; Ortolan, L.; Pagliarone, C.; Palencia, E.; Palni, P.; Papadimitriou, V.; Parker, W.; Pauletta, G.; Paulini, M.; Paus, C.; Phillips, T. J.; Piacentino, G.; Pianori, E.; Pilot, J.; Pitts, K.; Plager, C.; Pondrom, L.; Poprocki, S.; Potamianos, K.; Pranko, A.; Prokoshin, F.; Ptohos, F.; Punzi, G.; Ranjan, N.; Redondo Fernández, I.; Renton, P.; Rescigno, M.; Rimondi, F.; Ristori, L.; Robson, A.; Rodriguez, T.; Rolli, S.; Ronzani, M.; Roser, R.; Rosner, J. L.; Ruffini, F.; Ruiz, A.; Russ, J.; Rusu, V.; Sakumoto, W. K.; Sakurai, Y.; Santi, L.; Sato, K.; Saveliev, V.; Savoy-Navarro, A.; Schlabach, P.; Schmidt, E. E.; Schwarz, T.; Scodellaro, L.; Scuri, F.; Seidel, S.; Seiya, Y.; Semenov, A.; Sforza, F.; Shalhout, S. Z.; Shears, T.; Shepard, P. F.; Shimojima, M.; Shochet, M.; Shreyber-Tecker, I.; Simonenko, A.; Sliwa, K.; Smith, J. R.; Snider, F. D.; Song, H.; Sorin, V.; St. Denis, R.; Stancari, M.; Stentz, D.; Strologas, J.; Sudo, Y.; Sukhanov, A.; Suslov, I.; Takemasa, K.; Takeuchi, Y.; Tang, J.; Tecchio, M.; Teng, P. K.; Thom, J.; Thomson, E.; Thukral, V.; Toback, D.; Tokar, S.; Tollefson, K.; Tomura, T.; Tonelli, D.; Torre, S.; Torretta, D.; Totaro, P.; Trovato, M.; Ukegawa, F.; Uozumi, S.; Velev, G.; Vellidis, C.

2014-05-01

417

Local Crystal Structure of Antiferroelectric Bi2Mn4/3Ni2/3O6 in Commensurate and Incommensurate Phases Described by Pair Distribution Function (PDF) and Reverse Monte Carlo (RMC) Modeling  

PubMed Central

The functional properties of materials can arise from local structural features that are not well determined or described by crystallographic methods based on long-range average structural models. The room temperature (RT) structure of the Bi perovskite Bi2Mn4/3Ni2/3O6 has previously been modeled as a locally polar structure where polarization is suppressed by a long-range incommensurate antiferroelectric modulation. In this study we investigate the short-range local structure of Bi2Mn4/3Ni2/3O6, determined through reverse Monte Carlo (RMC) modeling of neutron total scattering data, and compare the results with the long-range incommensurate structure description. While the incommensurate structure has equivalent B site environments for Mn and Ni, the local structure displays a significantly Jahn–Teller distorted environment for Mn3+. The local structure displays the rock-salt-type Mn/Ni ordering of the related Bi2MnNiO6 high pressure phase, as opposed to Mn/Ni clustering observed in the long-range average incommensurate model. RMC modeling reveals short-range ferroelectric correlations between Bi3+ cations, giving rise to polar regions that are quantified for the first time as existing within a distance of approximately 12 Å. These local correlations persist in the commensurate high temperature (HT) phase, where the long-range average structure is nonpolar. The local structure thus provides information about cation ordering and B site structural flexibility that may stabilize Bi3+ on the A site of the perovskite structure and reveals the extent of the local polar regions created by this cation.

2014-01-01

418

Passive estimation of the waveguide invariant per pair of modes.  

PubMed

In many oceanic waveguides, acoustic propagation is characterized by a parameter called waveguide invariant. This property is used in many passive and active sonar applications where knowledge of the waveguide invariant value is required. The waveguide invariant is classically considered as scalar but several studies show that it is better modeled by a distribution because of its dependence on frequency and mode pairs. This paper presents a new method for estimating the waveguide invariant distribution. Using the noise radiated by a distant ship and a single hydrophone, the proposed methodology allows estimating the waveguide invariant for each pair of modes in shallow water. Performance is evaluated on simulated data. PMID:23927230

Le Gall, Yann; Bonnel, Julien

2013-08-01

419

Pairing Properties of Superheavy Nuclei  

SciTech Connect

Pairing properties of even-even superheavy N=184 isotones are studied within the Skyrme-Hartree-Fock+BCS approach. In the particle-hole channel we take the Skyrme energy density functional SLy4, while in the particle-particle channel we employ the seniority pairing force and zero-range delta-interactions with different forms of density dependence. We conclude that the calculated static fission trajectories weakly depend on the specific form of the delta-pairing interaction. We also investigate the impact of triaxiality on the inner fission barrier and find a rather strong Z dependence of the effect.

Staszczak, A. [Maria Curie-Sklodowska University; Dobaczewski, J. [Warsaw University; Nazarewicz, Witold [ORNL

2007-01-01

420

Stereo Pair: Patagonia, Argentina  

NASA Technical Reports Server (NTRS)

This view of northern Patagonia, near El Cain, Argentina shows complexly eroded volcanic terrain, with basalt mesas, sinkholes, landslide debris, playas, and relatively few integrated drainage channels. Surrounding this site (but also extending far to the east) is a broad plateau capped by basalt, the Meseta de Somuncura. Here, near the western edge of the plateau, erosion has broken through the basalt cap in a variety of ways. On the mesas, water-filled sinkholes (lower left) are most likely the result of the collapse of old lava tubes. Along the edges of the mesas (several locations) the basalt seems to be sliding away from the plateau in a series of slices. Water erosion by overland flow is also evident, particularly in canyons where vegetation blankets the drainage channels (green patterns, bottom of image). However, overland water flow does not extend very far at any location. This entire site drains to local playas, some of which are seen here (blue). While the water can reach the playas and then evaporate, what becomes of the eroded rock debris? Wind might excavate some of the finer eroded debris, but the fate of much of the missing bedrock remains mysterious.

This cross-eyed stereoscopic image pair was generated using topographic data from the Shuttle Radar Topography Mission, combined with an enhanced Landsat 7 satellite color image. The topography data are used to create two differing perspectives of a single image, one perspective for each eye. In doing so, each point in the image is shifted slightly, depending on its elevation. When stereoscopically merged, the result is a vertically exaggerated view of the Earth's surface in its full three dimensions.

Landsat satellites have provided visible light and infrared images of the Earth continuously since 1972. SRTM topographic data match the 30-meter (99-foot) spatial resolution of most Landsat images and provide a valuable complement for studying the historic and growing Landsat data archive. The Landsat 7 Thematic Mapper image used here was provided to the SRTM project by the United States Geological Survey, Earth Resources Observation Systems (EROS) Data Center,Sioux Falls, South Dakota.

Elevation data used in this image was acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on February 11,2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect three-dimensional measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter-long (200-foot) mast, installed additional C-band and X-band antennas, and improved tracking and navigation devices. The mission is a cooperative project between the National Aeronautics and Space Administration (NASA), the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense (DoD), and the German and Italian space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Earth Science Enterprise,Washington, DC.

Size: 23.9 kilometers (14.8 miles) x 15.2 kilometers (9.4 miles) Location: 42 deg. South lat., 68 deg. West lon. Orientation: North toward upper left Image Data: Landsat bands 1,4,7 in blue, green, red Date Acquired: February 19, 2000 (SRTM), January 22, 2000 (Landsat)

2000-01-01

421

Stereo Pair, Patagonia, Argentina  

NASA Technical Reports Server (NTRS)

This view of northern Patagonia, at Los Menucos, Argentina shows remnants of relatively young volcanoes built upon an eroded plain of much older and contorted volcanic, granitic, and sedimentary rocks. The large purple, brown, and green 'butterfly' pattern is a single volcano that has been deeply eroded. Large holes on the volcano's flanks indicate that they may have collapsed soon after eruption, as fluid molten rock drained out from under its cooled and solidified outer shell. At the upper left, a more recent eruption occurred and produced a small volcanic cone and a long stream of lava, which flowed down a gully. At the top of the image, volcanic intrusions permeated the older rocks resulting in a chain of small dark volcanic peaks. At the top center of the image, two halves of a tan ellipse pattern are offset from each other. This feature is an old igneous intrusion that has been split by a right-lateral fault. The apparent offset is about 6.6 kilometers (4 miles). Color, tonal, and topographic discontinuities reveal the fault trace as it extends across the image to the lower left. However, young unbroken basalt flows show that the fault has not been active recently.

This cross-eyed stereoscopic image pair was generated using topographic data from the Shuttle Radar Topography Mission, combined with an enhanced Landsat 7satellite color image. The topography data are used to create two differing perspectives of a single image, one perspective for each eye. In doing so, each point in the image is shifted slightly, depending on its elevation. When stereoscopically merged, the result is a vertically exaggerated view of the Earth's surface in its full three dimensions.

Landsat satellites have provided visible light and infrared images of the Earth continuously since 1972. SRTM topographic data match the 30-meter (99-foot) spatial resolution of most Landsat images and provide a valuable complement for studying the historic and growing Landsat data archive. The Landsat 7 Thematic mapper image used here was provided to the SRTM project by the United States Geological Survey, Earth Resources Observation Systems (EROS) Data Center,Sioux Falls, South Dakota.

Elevation data used in this image was acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on February 11,2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect three-dimensional measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter-long (200-foot) mast, installed additional C-band and X-band antennas, and improved tracking and navigation devices. The mission is a cooperative project between the National Aeronautics and Space Administration (NASA), the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense (DoD), and the German and Italian space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Earth Science Enterprise,Washington, DC.

Size: 121 kilometers (75 miles) x 83 kilometers (52 miles) Location: 41 deg. South lat., 69 deg. West lon. Orientation: North toward upper left Image Data: Landsat bands 1,4 and 7 shown in blue, green and red Date Acquired: February 19, 2000 (SRTM), January 22, 2000 (Landsat)

2000-01-01

422

Microscopic Description of Isospin Mixing Pairing Correlations in the Framework of an Algebraic Sp(4) Model  

E-print Network

We explore isospin mixing beyond that due to the Coulomb interaction in the framework of an exactly solvable microscopic sp(4) algebraic approach. Specifically, we focus on the isospin non-conserving part of the pure nuclear pairing interaction. The outcome of this study shows the significance of the pairing charge dependence and its role in mixing isospin multiplets of pairing-governed isobaric analog 0+ states in light and medium mass nuclei, especially in nuclei with equal numbers of protons and neutrons. The model reveals possible, but still extremely weak, non-analog beta-decay transitions and estimates their relative strengths within a shell closure.

K. D. Sviratcheva; A. I. Georgieva; J. P. Draayer

2007-03-22

423

Persistent contribution of unbound quasiparticles to the pair correlation in the continuum Skyrme-Hartree-Fock-Bogoliubov approach  

SciTech Connect

The neutron pair correlation in nuclei near the neutron drip-line is investigated using the self-consistent continuum Skyrme-Hartree-Fock-Bogoliubov theory formulated with the coordinate-space Green's function technique. Numerical analysis is performed for even-even N=86 isotones in the Mo-Sn region, where the 3p{sub 3/2} and 3p{sub 1/2} orbits lying near the Fermi energy are either weakly bound or unbound. The quasiparticle states originating from the l=1 orbits form resonances with large widths, which are due to the low barrier height and the strong continuum coupling caused by the pair potential. Analyzing in detail the pairing properties and roles of the quasiparticle resonances, we found that the l=1 broad quasiparticle resonances persist to feel the pair potential and contribute to the pair correlation even when their widths are comparable with the resonance energy.

Zhang, Y. [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan); Matsuo, M. [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan); Department of Physics, Faculty of Science, Niigata University, Niigata 950-2181 (Japan); School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); Meng, J. [School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); Department of Physics, University of Stellenbosch, Stellenbosch (South Africa)

2011-05-15

424

Prediction of Empirical p Values from Asymptotic p Values for Conditional Logistic Affected Relative Pair Linkage Analysis  

Microsoft Academic Search

Objective: p Values are inaccurate for model-free linkage analysis using the conditional logistic model if we assume that the LOD score is asymptotically distributed as a simple mixture of chi-square distributions. When analyzing affected relative pairs alone, permuting the allele sharing of relative pairs does not lead to a useful permutation distribution. As an alternative, we have developed regression prediction

Moumita Sinha; Yeunjoo Song; Robert C. Elston; Jane M. Olson; Katrina A. B. Goddard

2006-01-01

425

Les points-clef de la structure des noyaux exotiques posédant un fort excess de neutrons  

NASA Astrophysics Data System (ADS)

Large neutron excess poses new issues concerning the competition of deformation and pairing as well as changes in nuclear shell structure. To cite this article: I. Hamamoto, B.R. Mottelson, C. R. Physique 4 (2003).

Hamamoto, Ikuko; Mottelson, Ben R.

2003-06-01

426

Neutron optics calculations with NOP  

NASA Astrophysics Data System (ADS)

The Neutron Optics Package NOP is a collection of codes for the computation of reactor spectra, neutron reflectivity of crystals, mirrors and multilayers and other quantities as cross-sections, attenuation in materials and refractive index. These calculations rely on the use of a databse of materials cross-sections and crystal structures. NOP is freely distributed as an extension of the x-ray package XOP [M. Sanchez del Rio and R.J. Dejus, SPIE proceedings 3448, 340, 1998.], from which it inherites the user interface and code structure. The NOP package can be used for estimating the reflectivity of optical elements as crystals and multilayers. The NOP output can also be used as an input for neutron instrument ray-tracing modules.

Alianelli, Lucia; Sanchez del Rio, Manuel; Felici, Roberto

2004-10-01

427

Dynamical interactions of galaxy pairs  

NASA Technical Reports Server (NTRS)

Here the author briefly reviews the dynamics of sinking satellites and the effect of companions on elliptical galaxies. The author then discusses recent work on interacting disk systems, and finally focuses on a favorite interacting pair, NGC 5194/5195.

Athanassoula, E.

1990-01-01

428

Directional neutron detectors for use with 14 MeV neutrons :fiber scintillation methods for directional neutron detection.  

SciTech Connect

Current Joint Test Assembly (JTA) neutron monitors rely on knock-on proton type detectors that are susceptible to X-rays and low energy gamma rays. We investigated two novel plastic scintillating fiber directional neutron detector prototypes. One prototype used a fiber selected such that the fiber width was less than 2.1mm which is the range of a proton in plastic. The difference in the distribution of recoil proton energy deposited in the fiber was used to determine the incident neutron direction. The second prototype measured both the recoil proton energy and direction. The neutron direction was determined from the kinematics of single neutron-proton scatters. This report describes the development and performance of these detectors.

Sunnarborg, Duane A.; Peel, Justin D.; Mascarenhas, Nicholas; Mengesha, Wondwosen

2005-10-01

429

Generalized Cooper Pairing in Superconductors  

Microsoft Academic Search

We review Cooper pairing starting from its simplest, original 1956 version of two electrons interacting above the Fermi sea of an ideal Fermi gas (IFG). The two-electron interaction assumed extensively (if not exclusively), is the attractive two-parameter Cooper, and then BCS, model interactions. Hole Cooper pairs (CPs) and electron-hole CPs are then included along with the initial electron-CPs in terms

M. de Llano; J. F. Annett

2007-01-01

430

Effects of laser pulse shape and carrier envelope phase on pair production  

NASA Astrophysics Data System (ADS)

For different fields of supercycle and subcycle laser pulses, the effects of laser pulse shape and carrier envelope phase on pair production are investigated by solving quantum Vlasov equation. By changing the pulse width and shape, the nonlinear behaviors of momentum distribution function and number density of created electron-positron pairs are obtained. It is found that there exist the multiphoton processes and stabilization phenomenon in pair production for supercycle situation. Our study may shed a light on optimizing the form of applied laser field to enhance the created pairs number, for example, when other conditions are fixed, the flat-top super-Gaussian laser pulse has advantage on pairs production.

Abdukerim, Nuriman; Li, Zi-Liang; Xie, Bai-Song

2013-11-01

431

Distribution of manganese between coexisting biotite and hornblende in plutonic rocks  

USGS Publications Warehouse

The distribution of manganese between coexisting biotite and hornblende for 80 mineral pairs from igneous rocks of diverse provenance (including Southern California, Sierra Nevada, Boulder, and Boulder Creek batholiths and the Jemez Mountains volcanics) has been determined by neutron activation analysis. Data on the distribution ratio (Kd = Mnhornblende Mnbiotite) indicate that an equilibrium distribution of Mn is closely approached, though not completely attained, in most samples from plutonic environments. Comparison of Kd values of mineral pairs with bulk chemical composition of host rocks reveals no correlation. Because initial crystallization temperatures vary with rock composition, the lack of correlation of composition with Kd suggests that the equilibrium distribution of Mn between biotite and hornblende reflects exchange at subsolidus temperatures rather than initial crystallization temperatures. The highest Kd values are for volcanic rocks, in which rapid quenching prevents subsolidus redistribution of Mn. For sample pairs from the Southern California and Sierra Nevada batholiths there is a positive correlation of Kd with TiO2 content of biotite. Though the evidence is not compelling, Kd may also correlate with the rate of cooling and/or the presence or absence of sphene in the rock. ?? 1968.

Greenland, L.P.; Gottfried, D.; Tilling, R.I.

1968-01-01

432

Neutronic design and simulated performance of Peking University Neutron Imaging Facility (PKUNIFTY)  

NASA Astrophysics Data System (ADS)

The Peking University Neutron Imaging Facility (PKUNIFTY) is a Radio Frequency Quadruple (RFQ) accelerator based system. The fast neutrons are produced by 2 MeV deuterons bombarding beryllium target. The moderator, reflector, shielding and collimator have been optimized with Monte-Carlo simulation to improve the neutron beam quality. The neutrons are thermalized in water cylinder of ?26×26 cm 2 with a polyethylene disk in front of Be target. The size of deuteron beam spot is optimized considering both the thermal neutron distribution and the demand of target cooling. The shielding is a combination of 8 cm thick lead and 42 cm thick boron doped polyethylene. The thermal neutrons are extracted through a rectangular inner collimator and a divergent outer collimator. The thermal neutron beam axis is perpendicular to the D + beam line in order to reduce the fast neutron and the ? ray components in the imaging beam. When the neutron yield is 3×10 12 n/s and the L/ D is 50, the thermal neutron flux is 5×10 5 n/cm 2/s at the imaging plane, the Cd ratio is 1.63 and the n/? ratio is 1.6×10 10 n/cm 2/Sv.

Wen, Weiwei; Li, Hang; Zou, Yubin; Tang, Guoyo; Mo, Dawei; Lu, Yuanrong; Guo, Zuiyu

2011-09-01

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Nondestructive fissile material assay by induced fission neutron correlation  

NASA Astrophysics Data System (ADS)

An NDA method and interpretation model for the determination of small fissile material masses, in radioactive waste, is elaborated. The method uses a pulsed neutron source to interrogate a waste item located in the sample cavity. The sample cavity is lined with graphite to yield a long thermal neutron lifetime. For each pulse of source neutrons, the slowed down neutron population causes thermal fission in the fissile material of the sample, resulting in the emission of fast neutrons from the sample. Some of these fast neutrons escape the cavity and the cavity liner, and are slowed down in an external polyethylene moderator, designed to yield a short thermal neutron lifetime, and are subsequently detected in incorporated thermal neutron detectors. Signal groups, representing the detection of fission neutron