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1

Atom Pair Distribution Functions of Liquid Water at 25{degrees}C from Neutron Diffraction.  

PubMed

The structure of liquid water is described by three atom pair distribution functions gOO(r), gOH(r), and gHH(r). These functions have now been derived from neutron diffraction data on four mixtures of light and heavy water. They will provide a crucial and sensitive test for proposed models of liquid water. PMID:17839340

Narten, A H; Thiessen, W E; Blum, L

1982-09-10

2

Atom Pair Distribution Functions of Liquid Water at 25circC from Neutron Diffraction  

NASA Astrophysics Data System (ADS)

The structure of liquid water is described by three atom pair distribution functions gOO(r), gOH(r), and gHH(r). These functions have now been derived from neutron diffraction data on four mixtures of light and heavy water. They will provide a crucial and sensitive test for proposed models of liquid water.

Narten, A. H.; Thiessen, W. E.; Blum, L.

1982-09-01

3

Atom Pair Distribution Functions of Liquid Water at 25circC from Neutron Diffraction  

Microsoft Academic Search

The structure of liquid water is described by three atom pair distribution functions gOO(r), gOH(r), and gHH(r). These functions have now been derived from neutron diffraction data on four mixtures of light and heavy water. They will provide a crucial and sensitive test for proposed models of liquid water.

A. H. Narten; W. E. Thiessen; L. Blum

1982-01-01

4

Local structure in BaTi1-xZrxO3 relaxors from neutron pair distribution function analysis  

NASA Astrophysics Data System (ADS)

The pair distribution functions (PDF) of BaTi1-xZrxO3 (BTZ) relaxors (x=0.25,0.32,0.35) , as well as those of the end members BaTiO3 and BaZrO3 , were determined at 300 K from neutron powder scattering data. In the relaxors, the PDF provides direct evidence that the Ti and Zr atoms do not occupy the equivalent octahedral sites expected from the crystallographic cubic perovskite structure. It is shown that the TiO6 and ZrO6 octahedra in BTZ relaxors are instead similar to those observed in BaTiO3 and BaZrO3 , respectively. In BaZrO3 , the Zr atoms lie at the center of regular oxygen octahedra, forming nonpolar ZrO6 units. In the tetragonal ferroelectric phase of BaTiO3 , the distribution of Ti-O distances within TiO6 octahedra is found compatible with a displacement of the Ti atoms in the [111]p direction of the pseudocubic perovskite cell. We conclude that the local polarization in BTZ relaxors is mainly due to the displacements of the Ti atoms and that moreover the Ti displacements are very similar in BTZ relaxors and in the classical ferroelectric BaTiO3 .

Laulhé, C.; Hippert, F.; Bellissent, R.; Simon, A.; Cuello, G. J.

2009-02-01

5

Pair correlations and pair transfers in neutron-rich nuclei  

SciTech Connect

Features of the neutron pair correlation characteristic to neutron-rich nuclei are discussed on the basis of the Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random phase approximations. We discuss the monopole and quadrupole pair transfer modes in neutron-rich Sn isotopes beyond the N = 82 shell closure. We investigate also how the pair correlation behaves in deformed weakly bound nuclei, and we show that the neutron pairing enhances as the binding energy of neutrons becomes small.

Matsuo, Masayuki [Department of Physics, Faculty of Science, Niigata University, Niigata 950-2181 (Japan); Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan); Shimoyama, Hirotaka; Oba, Hiroshi [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan)

2010-05-12

6

TLD pairs, as thermal neutron detectors in neutron multisphere spectrometry  

Microsoft Academic Search

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

Héctor René Vega-Carrillo

2002-01-01

7

Isovector neutron-proton pairing with particle number projected BCS  

NASA Astrophysics Data System (ADS)

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

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

2009-10-01

8

Interactive FORTRAN Program for the Evaluation of Structure Factors and Pair Distribution Functions from Neutron Diffraction Experiments.  

National Technical Information Service (NTIS)

This report describes an interactive program to evaluate neutron diffraction data using the Graphic System (GS) under MVS (TSO). Different evaluation steps may be directed by a CLIST. The present program is limited to cylindrical sample geometry. From the...

W. Abel

1985-01-01

9

A search for disorder in the spin glass double perovskites Sr(2)CaReO(6) and Sr(2)MgReO(6) using neutron diffraction and neutron pair distribution function analysis.  

PubMed

The geometrically frustrated, B-site ordered, S = 1/2, double perovskites Sr(2)CaReO(6) and Sr(2)MgReO(6), which show spin frozen magnetic ground states, have been investigated using neutron powder diffraction (ND) and neutron pair distribution function (NPDF) analysis in a search for evidence for atomic positional disorder. For both materials, data were taken above and below the spin freezing temperatures of ? 14 K and ? 45 K for the CaRe and MgRe phases, respectively. In both cases the fully B-site ordered model was in excellent agreement with the data, both ND and NPDF, at all temperatures studied. Thus, the structure of these materials, from the average and the local perspectives, is very well described by the fully B-site ordered model, which raises questions concerning the origin of the spin glass ground state. These results are compared with those for the spin glass pyrochlore Y(2)Mo(2)O(7) and other B-site ordered double perovskites. PMID:21471633

Greedan, J E; Derakhshan, Shahab; Ramezanipour, F; Siewenie, J; Proffen, Th

2011-04-27

10

Neutrino emission from triplet pairing of neutrons in neutron stars  

SciTech Connect

Neutrino emission resulting from the pair breaking and formation processes in the bulk triplet superfluid in neutron stars is investigated taking into account anomalous weak interactions. I consider the problem in the BCS approximation discarding Fermi-liquid effects. By this approach I derive self-consistent equations for anomalous vector and axial-vector vertices of weak interactions taking into account {sup 3}P{sub 2}-{sup 3}F{sub 2} mixing. Further, I simplify the problem and consider pure {sup 3}P{sub 2} pairing with m{sub j}=0, as is adopted in the minimal-cooling paradigm. As was expected because of current conservation, I have obtained a large suppression of neutrino emissivity in the vector channel. More exactly, the neutrino emission through the vector channel vanishes in the nonrelativistic limit V{sub F}=0. The axial channel is also found to be moderately suppressed. Total neutrino emissivity is suppressed by a factor of 1.9x10{sup -1} relative to original estimates using bare weak vertices.

Leinson, L. B. [Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation RAS, RU-142190 Troitsk, Moscow Region (Russian Federation)

2010-02-15

11

Effect of BCS pairing on entrainment in neutron superfluid current in neutron star crust  

NASA Astrophysics Data System (ADS)

The relative current density n of “conduction” neutrons in a neutron star crust beyond the neutron drip threshold can be expected to be related to the corresponding particle momentum covector p by a linear relation of the form n=Kp in terms of a physically well-defined mobility tensor K. This result is describable as an “entrainment” whose effect—wherever the crust lattice is isotropic—will simply be to change the ordinary neutron mass m to a “macroscopic” effective mass m such that in terms of the relevant number density n of unconfined neutrons we shall have K=(n/m)?. In a preceding work based on a independent particle treatment beyond the Wigner Seitz approximation, using Bloch type boundary conditions to obtain the distribution of energy E and associated group velocity vki=?E/??k as a function of wave vector k, it was shown that the mobility tensor would be proportional to a phase space volume integral K??dkvkivkj?{E-?}, where ? is the Fermi energy. Using the approach due to Bogoliubov, it is shown here that the effect of BCS pairing with a superfluid energy gap ? and corresponding quasiparticle energy function €=E+?F2 will just be to replace the Dirac distributional integrand by the smoother distribution in the formula K??dkvkivkj?F2/€k3. It is also shown how the pairing condensation gives rise to superfluidity in the technical sense of providing (meta) stability against resistive perturbations for a current that is not too strong (its momentum p must be small enough to give 2|pvki|<€k2/|E-?| for all modes). It is concluded that the prediction of a very large effective mass enhancement in the middle layers of the star crust will not be significantly effected by the pairing mechanism.

Carter, Brandon; Chamel, Nicolas; Haensel, Pawel

2005-09-01

12

Probing the pairing interaction through two-neutron transfer reactions  

SciTech Connect

Cross sections for (p,t) two-neutron transfer reactions are calculated in the one-step zero-range distorted-wave Born approximation for the tin isotopes {sup 124}Sn and {sup 136}Sn and for incident proton energies from 15 to 35 MeV. Microscopic quasiparticle random-phase approximation form factors are provided for the reaction calculation and phenomenological optical potentials are used in both the entrance and the exit channels. Three different surface/volume mixings of a zero-range density-dependent pairing interaction are employed in the microscopic calculations and the sensitivity of the cross sections to the different mixings is analyzed. Since absolute cross sections cannot be obtained within our model, we compare the positions of the diffraction minima and the shapes of the angular distributions. No differences are found in the position of the diffraction minima for the reaction {sup 124}Sn(p,t){sup 122}Sn. On the other side, the angular distributions obtained for the reaction {sup 136}Sn(p,t){sup 134}Sn with surface and mixed interactions differ at large angles for some values of the incident proton energy. For this reaction, we compare the ratios of the cross sections associated to the ground state and the first excited state transitions. Differences among the three different theoretical predictions are found and they are more important at the incident proton energy of 15 MeV. As a conclusion, we indicate (p,t) two-neutron transfer reactions with very neutron-rich Sn isotopes and at proton energies around 15 MeV as good experimental cases where the surface/volume mixing of the pairing interaction may be probed.

Pllumbi, E. [Dipartimento di Fisica, University of Pisa, Largo Bruno Pontecorvo 3, I-56127 Pisa (Italy); Grasso, M.; Beaumel, D.; Khan, E.; Margueron, J.; Wiele, J. van de [Institut de Physique Nucleaire, IN2P3-CNRS, Universite Paris-Sud, F-91406 Orsay Cedex (France)

2011-03-15

13

Neutron-Proton Pairing in 64Ge  

Microsoft Academic Search

Isotopes of germanium are studied in the framework of the relativistic mean-field theory with a delta-pairing type residual interaction. Both pairing channels T=1 and T=0 are included. The T=0 channel does not contribute to the pairing energy even with a large coupling strength of the delta force. It is shown that the Wigner-like term (congruence energy) may be partly reproduced

Andrzej Baran; Kamila Sieja

2005-01-01

14

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

15

Effective pair gap of weakly bound neutrons in deformed nuclei  

SciTech Connect

The dependence of effective pair gap on weakly bound neutron orbits is studied in deformed nuclei in comparison with that in spherical nuclei, solving the Hartree-Fock-Bogoliubov equation in a simplified model in coordinate space with the correct asymptotic boundary conditions. In spherical nuclei the effective pair gap of s{sub 1/2} neutrons decreases to zero in the limit that the corresponding Hartree-Fock one-particle energy approaches zero. In the same limit, the effective pair gap of {omega}{sup {pi}}=1/2{sup +} neutrons in deformed nuclei becomes very small when the wave functions of {omega}{sup {pi}}=1/2{sup +} orbits contain an appreciable amount of s{sub 1/2} components, even if a considerable amount of larger-l components remains in the wave functions. Then, the one-particle excitation spectra of deformed even-even neutron-drip-line nuclei, in which an {omega}{sup {pi}}=1/2{sup +} level is weakly bound, can start at much lower energy than twice the average pair gap in the presence of many-body pair correlation.

Hamamoto, Ikuko [Division of Mathematical Physics, Lund Institute of Technology at the University of Lund, Lund (Sweden); Niels Bohr Institute, Blegdamsvej 17, Copenhagen O, DK-2100 (Denmark)

2005-03-01

16

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

17

Probing the pairing interaction through two-neutron transfer reactions  

NASA Astrophysics Data System (ADS)

The treatment of the pairing interaction in mean-field-based models is addressed. In particular, the possibility to use pair transfers as A tool to better constrain this interaction is discussed. First, pairing inter-actions with various density dependencies (surface/volume mixing) are used in the microscopic Hartree-Fock-Bogoliubov + quasiparticle random-phase approximation model to generate the form factors to be used in reaction calculations. Cross sections for (p,t) two-neutron transfer reactions are calculated in the one-step zero-range distorted-wave Born approximation for some Tin isotopes and for incident proton energies from 15 to 35 MeV. Three different surface/volume mixings of A zero-range density-dependent pairing interaction are employed in the microscopic calculations and the sensitivity of the cross sections to the different mixings is analyzed. Differences among the three different theoretical predictions are found espacially for the nucleus 136Sn and they are more important at the incident proton energy of 15 MeV. We thus indicate (p,t) two-neutron transfer reactions with very neutron-rich Sn isotopes and at proton energies around 15 MeV as good experimental cases where the surface/volume mixing of the pairing interaction may be probed. In the second part of the manuscript, ground-state to ground-state transitions are investigated. Approximations made to estimate two-nucleon transfer probabilities in ground-state to ground-state transitions and the physical interpretation of these probabilities are discussed. Probabilities are often calculated by approximating both ground states of the initial nucleus A and of the final nucleus A±2 by the same quasiparticle vacuum. We analyze two improvements of this approach. First, the effect of using two different ground states with average numbers of particles A and A±2 is quantified. Second, by using projection techniques, the role of particle number restoration is analyzed. Our analysis shows that the improved treatment plays A role close to magicity, leading to an enhancement of the pair-transfer probability. In midshell regions, part of the error made by approximating the initial and final ground states by A single vacuum is compensated by projecting onto A good particle number. Surface effects are analyzed by using pairing interactions with A different volume/surface mixing. Finally, A simple expression of the pair-transfer probability is given in terms of occupation probabilities in the canonical basis. We show that, in the canonical basis formulation, surface effects that are visible in the transfer probability are related to the fragmentation of single-particle occupancies close to the Fermi energy. This provides A complementary interpretation with respect to the standard quasiparticle representation where surface effects are generated by the integrated radial profiles of the contributing wave functions.

Grasso, M.; Beaumel, D.; Khan, E.; Lacroix, D.; Margueron, J.; Vitturi, A.

2012-12-01

18

Quasifree Photoproduction of Pion-Pairs of Protons and Neutrons  

NASA Astrophysics Data System (ADS)

Beam-helicity asymmetries and mass-differential cross sections have been measured at the MAMI accelerator in Mainz for the photoproduction of neutral and mixed-charge pion pairs in the reactions ?p ? n?0?+ and ?p ? p?0?0 off free protons and ?d ? (p)p?0?-, ?d ? (n)p?0?0 and ?d ? (n)n?0?+, ?d ? (p)n?0?0 off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4 GeV. Circularly polarized photons were produced in bremsstrahlung processes of longitudinally polarized electrons and tagged with the Glasgow-Mainz magnetic spectrometer. The decay products (photons, protons neutrons and charged pions) were detected in the 4? electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. Using a full kinematic reconstruction of the final state, excellent agreement was found between the results for free and quasi-free protons, indicate that the quasi-free neutron results are also a close approximation of the free-neutron results. Comparison of the results to predictions of model calculations portend that especially the reaction mechanisms in the production of the mixed-charge final states are still not well understood, in particular at low incident photon energies in the second nucleon resonance region.

Oberle, M.; Krusche, B.

2014-01-01

19

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

20

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

PubMed

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

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

2013-11-13

21

The Neutron Star Mass Distribution  

NASA Astrophysics Data System (ADS)

In recent years, the number of pulsars with secure mass measurements has increased to a level that allows us to probe the underlying neutron star (NS) mass distribution in detail. We critically review the radio pulsar mass measurements. For the first time, we are able to analyze a sizable population of NSs with a flexible modeling approach that can effectively accommodate a skewed underlying distribution and asymmetric measurement errors. We find that NSs that have evolved through different evolutionary paths reflect distinctive signatures through dissimilar distribution peak and mass cutoff values. NSs in double NS and NS-white dwarf (WD) systems show consistent respective peaks at 1.33 M ? and 1.55 M ?, suggesting significant mass accretion (?m ? 0.22 M ?) has occurred during the spin-up phase. The width of the mass distribution implied by double NS systems is indicative of a tight initial mass function while the inferred mass range is significantly wider for NSs that have gone through recycling. We find a mass cutoff at ~2.1 M ? for NSs with WD companions, which establishes a firm lower bound for the maximum NS mass. This rules out the majority of strange quark and soft equation of state models as viable configurations for NS matter. The lack of truncation close to the maximum mass cutoff along with the skewed nature of the inferred mass distribution both enforce the suggestion that the 2.1 M ? limit is set by evolutionary constraints rather than nuclear physics or general relativity, and the existence of rare supermassive NSs is possible.

Kiziltan, Bülent; Kottas, Athanasios; De Yoreo, Maria; Thorsett, Stephen E.

2013-11-01

22

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

NASA Astrophysics Data System (ADS)

Background: Momentum distributions of individual nucleons and nucleon pairs reflect features of the short-range structure of nuclei and provide useful insights into various reactions on nuclei, such as (e,e'p) and (e,e'pp/pn) electrodisintegration processes or neutrino-nucleus interaction experiments. Purpose: To provide the nuclear physics community with the results (available online) of a systematic study of single-nucleon momentum distributions and nucleon-pair and nucleon-cluster momentum distributions for A ?12 nuclei. Method: The realistic Argonne v18 two-nucleon and Urbana X three-nucleon potentials are used to generate accurate variational Monte Carlo wave functions for the A ?12 nuclei; quantum Monte Carlo methods are used to calculate the momentum distributions. Results: Single-nucleon distributions are given, broken down into proton and neutron components and spin-up and spin-down components where appropriate. Nucleon-pair momentum distributions are given either in pair spin and isospin ST projection or for pp, pn, and nn pairs. Nucleon-cluster momentum distributions include dp in 3He, tp and dd in 4He, ?d in 6Li, ?t in 7Li, and ?? in 8Be. Conclusions: The momentum distributions exhibit common characteristic shapes, with tensor correlations (or lack thereof) playing a dominant role in the 1.5-3 fm-1 range, while spin-isospin correlations dominate at higher momenta.

Wiringa, R. B.; Schiavilla, R.; Pieper, Steven C.; Carlson, J.

2014-02-01

23

Enhanced cooling of neutron stars via Cooper-pairing neutrino emission  

NASA Astrophysics Data System (ADS)

We simulate cooling of superfluid neutron stars with nucleon cores where the direct Urca process is forbidden. We adopt density-dependent critical temperatures Tcp(?) and Tcn(?) of singlet-state proton and triplet-state neutron pairing in a stellar core and consider strong proton pairing (with maximum Tcpmax ? 5 × 109 K) and moderate neutron pairing (Tcnmax ˜ 6 × 108 K). When the internal stellar temperature T falls below Tcnmax, the neutrino luminosity LCP due to Cooper pairing of neutrons behaves ? T8, just as that produced by the modified Urca process (in a non-superfluid star) but is higher by about two orders of magnitude. In this case the Cooper-pairing neutrino emission acts like an enhanced cooling agent. By tuning the density dependence Tcn(?) we can explain observations of cooling isolated neutron stars in the scenario in which the direct Urca process or a similar process in kaon/pion condensed or quark matter are absent.

Gusakov, M. E.; Kaminker, A. D.; Yakovlev, D. G.; Gnedin, O. Y.

2004-09-01

24

Neutron density distributions deduced from antiprotonic atoms.  

PubMed

The differences between neutron and proton density distributions at large nuclear radii in stable nuclei were determined. Two experimental methods were applied: nuclear spectroscopy analysis of the antiproton annihilation residues one mass unit lighter than the target mass and the measurements of strong-interaction effects on antiprotonic x rays. Assuming the validity of two-parameter Fermi neutron and proton distributions at these large radii, the conclusions are that the two experiments are consistent with each other and that for neutron rich nuclei it is mostly the neutron diffuseness which increases and not the half-density radius. The obtained neutron and proton rms radii differences are in agreement with previous results. PMID:11497938

Trzci?ska, A; Jastrzébski, J; Lubi?ski, P; Hartmann, F J; Schmidt, R; von Egidy, T; K?os, B

2001-08-20

25

Pair-Distribution Functions of Composite Fermion Liquids  

Microsoft Academic Search

Pair-distribution functions g(r) of Laughlin quasielectrons (QE’s) are calculated for the fractional quantum Hall liquids at electron filling factors ? = 4\\/11 and 3\\/8. They all have a shoulder at a medium range. The intra- and inter-cluster contributions to g(r) are identified, supporting the idea of cluster formation (QE pairs at ? = 4\\/11 and QE triplets at ? =

Arkadiusz Wo´js; Daniel Wodzin´ski; John J. Quinn

2006-01-01

26

Support for Distributed Pair Programming in the Transparent Video Facetop  

Microsoft Academic Search

The Transparent Video Facetop is a novel user interface concept that supports not only single-user interactions with a PC, but also close pair collaborations, such as that found in collaborative Web browsing, remote medicine, and in distributed pair programming. We recently demonstrated the Vis-a-Vid Facetop prototype as a single-user GUI for manipulating the elements of a traditional WIMP desktop (16).

P. David Stotts; Jason Mcc. Smith; Karl Gyllstrom

2004-01-01

27

Systematic study of proton-neutron pairing correlations in the nuclear shell model  

NASA Astrophysics Data System (ADS)

A shell-model study of proton-neutron pairing in 2p1f shell nuclei using a parametrized Hamiltonian that includes deformation and spin-orbit effects as well as isoscalar and isovector pairing is reported. By working in a shell-model framework we are able to assess the role of the various modes of proton-neutron pairing in the presence of nuclear deformation without violating symmetries. Results are presented for 44Ti, 45Ti, 46Ti, 46V, and 48Cr to assess how proton-neutron pair correlations emerge under different scenarios. We also study how the presence of a one-body spin-obit interaction affects the contribution of the various pairing modes.

Lei, Y.; Pittel, S.; Sandulescu, N.; Poves, A.; Thakur, B.; Zhao, Y. M.

2011-10-01

28

Angular distributions of neutron-nucleus collisions  

SciTech Connect

We derive the total and the differential cross sections with respect to angle for neutron-induced reactions from an analytical model having a simple functional form to demonstrate the quantitative agreement with the measured cross sections. The energy dependence of the neutron-nucleus interaction cross sections are estimated successfully for energies ranging from 5 to 600 MeV. In this work, the effect of the imaginary part of the nuclear potential is treated more appropriately compared to our earlier work. The angular distributions for neutron scattering also agree reasonably well with the experimental data at forward angles.

Mukhopadhyay, Tapan; Lahiri, Joydev; Basu, D. N. [Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata 700 064 (India)

2011-06-15

29

Distributed wireless quantum communication networks with partially entangled pairs  

NASA Astrophysics Data System (ADS)

Wireless quantum communication networks transfer quantum state by teleportation. Existing research focuses on maximal entangled pairs. In this paper, we analyse the distributed wireless quantum communication networks with partially entangled pairs. A quantum routing scheme with multi-hop teleportation is proposed. With the proposed scheme, is not necessary for the quantum path to be consistent with the classical path. The quantum path and its associated classical path are established in a distributed way. Direct multi-hop teleportation is conducted on the selected path to transfer a quantum state from the source to the destination. Based on the feature of multi-hop teleportation using partially entangled pairs, if the node number of the quantum path is even, the destination node will add another teleportation at itself. We simulated the performance of distributed wireless quantum communication networks with a partially entangled state. The probability of transferring the quantum state successfully is statistically analyzed. Our work shows that multi-hop teleportation on distributed wireless quantum networks with partially entangled pairs is feasible.

Yu, Xu-Tao; Zhang, Zai-Chen; Xu, Jin

2014-01-01

30

Paired ion-chamber constants for fission gamma-neutron fields. Technical report  

Microsoft Academic Search

Paired ionization chamber constants are calculated for the 50-cm³ spherical ionization chambers used in dosimetry of the AFRRI TRIGA reactor. The calculations include the most recently available information on energy spectra for neutron and gamma radiation present in AFRRI reactor exposure rooms, as well as for kerma factors and W-values of neutrons. The constant kT, which expresses neutron sensitivity of

Ferlic

1984-01-01

31

Systematic study of proton-neutron pairing correlations in the nuclear shell model  

NASA Astrophysics Data System (ADS)

A systematic study of proton-neutron pairing in 1f - 2p shell nuclei is reported, based on a model that includes deformation, spin-orbit effects and isoscalar and isovector pairing. Selected results are presented for 44Ti, 46V and 48Cr.

Lei, Y.; Pittel, S.; Sandulescu, N.; Poves, A.; Thakur, B.; Zhao, Y. M.

2012-09-01

32

The spatial distribution of supernovae in paired and interacting galaxies  

NASA Astrophysics Data System (ADS)

In order to investigate the location of supernovae (SNe) in paired and interacting galaxies, the 54 supernovae discovered up to May 1993 in 14 Isolated Pairs of Galaxies and the 32 Interacting Systems were taken as a sample and studied. The whole sample of SNe, as well as a subsample formed of type II, and Ib SNe, whose progenitors are young massive stars, do not appear in any one particluar direction with respect to the companion. On paired and interacting galaxies, the radial distribution of type Ib and II SNe peaks more toward the galaxy centers than it does in isolated galaxies, indicating an enhanced Star Formation Rate (SFR) around the nuclei and in the inner disks. The distribution of SNIa appear similar in both samples, confirming that their progenitors are not the same as those of SNII and IB. The SN rates are related to galaxy luminosity and, as expected, the discovery of SNe is twice more frequent in the brighter galaxy of the pair than in fainter ones. We did not find any relation between the locations of SNe in parent galaxies, the total Star Formation activity and the kinematics of paired and interacting galaxies.

Petrosian, A. R.; Turatto, M.

1995-05-01

33

Crystal structure solution from experimentally determined atomic pair distribution functions  

SciTech Connect

An extension of the Liga algorithm for structure solution from atomic pair distribution functions (PDFs), to handle periodic crystal structures with multiple elements in the unit cell, is described. The procedure is performed in three separate steps. First, pair distances are extracted from the experimental PDF. In the second step the Liga algorithm is used to find unit-cell sites consistent with these pair distances. Finally, the atom species are assigned over the cell sites by minimizing the overlap of their empirical atomic radii. The procedure has been demonstrated on synchrotron X-ray PDF data from 16 test samples. The structure solution was successful for 14 samples, including cases with enlarged supercells. The algorithm success rate and the reasons for the failed cases are discussed, together with enhancements that should improve its convergence and usability.

Juhas, P.; Granlund, L.; Gujarathi, S.R.; Duxbury, P.M.; Billinge, S.J.L. (MSU); (Columbia)

2010-05-25

34

Proton-neutron pairing correlations in the nuclear shell model  

NASA Astrophysics Data System (ADS)

Systematic shell-model calculations in 2p1f shell nuclei are reported, to assess the relative importance of isoscalar and isovector pairing in the presence of nuclear deformation and spin-orbit effects. Results are presented for three N = Z nuclei, 44Ti, 46V and 48Cr.

Pittel, S.; Lei, Y.; Sandulescu, N.; Poves, A.; Thakur, B.; Zhao, Y. M.

2012-12-01

35

Single and pair neutron transfers at sub-barrier energies  

NASA Astrophysics Data System (ADS)

Multinucleon transfer cross sections in the 96Zr+40Ca system have been measured, in inverse kinematics, at bombarding energies ranging from the Coulomb barrier to ˜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+ excited states of 42Ca are discussed by employing, for the reaction mechanism, the successive approximation. It is found that the transition to the 0+ state at ˜6 MeV, whose wave function is dominated by the two neutrons in the 2p3/2 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.; Szilner, S.; Pollarolo, G.; Colò, G.; Mason, P.; Farnea, E.; Fioretto, E.; Gadea, A.; Haas, F.; Jelavi?-Malenica, D.; M?rginean, N.; Michelagnoli, C.; Montagnoli, G.; Montanari, D.; Scarlassara, F.; Soi?, N.; Stefanini, A. M.; Ur, C. A.; Valiente-Dobón, J. J.

2011-09-01

36

Neutron gamma mixed field measurements by means of MCP TLD600 dosimeter pair  

NASA Astrophysics Data System (ADS)

In this paper, we compared the TL response of three types of thermoluminescence dosimeters, TLD600 ( 6LiF:Mg,Ti), TLD700 ( 7LiF:Mg,Ti) and MCP (LiF:Mg,Cu,P) after exposure to a n-? mixed field in the fluence range of radiotherapeutic applications. Since a dosimeter pair is required to discriminate the two components of the mixed field, we analyzed the ability of each dosimeter pair to provide the fluence value in the mixed field. At this aim we performed a 60Co-? calibration and a neutron calibration for all three dosimeter types. Finally, a blind test was performed in order to analyze the accuracy of each dosimeter pair and we found that in this mixed field the fluence value obtained through the TLD600-MCP pair is as accurate as the value obtained through the most common TLD600-TLD700 pair.

Triolo, A.; Marrale, M.; Brai, M.

2007-11-01

37

Spin-aligned neutron-proton pair mode in atomic nuclei  

SciTech Connect

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

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

2011-08-15

38

Neutron star's initial spin period distribution  

NASA Astrophysics Data System (ADS)

We analyse different possibilities to explain the wide initial spin period distribution of radio pulsars presented by Noutsos et al. With a population synthesis modelling, we demonstrate that magnetic field decay can be used to interpret the difference between the recent results by Noutsos et al and those by Popov and Turolla, where a much younger population of neutron stars associated with supernova remnants with known ages has been studied. In particular, an exponential field decay with ?mag = 5 Myr can produce a `tail' in the reconstructed initial spin period distribution up to P0 > 1 s starting with a standard Gaussian with = 0.3 s and ?P = 0.15 s. Another option to explain the difference between initial spin period distributions from Noutsos et al. and Popov and Turolla - the emerging magnetic field - is also briefly discussed.

Igoshev, A. P.; Popov, S. B.

2013-06-01

39

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

40

Local structure studies of materials using pair distribution function analysis  

NASA Astrophysics Data System (ADS)

A collection of pair distribution function studies on various materials is presented in this dissertation. In each case, local structure information of interest pushes the current limits of what these studies can accomplish. The goal is to provide insight into the individual material behaviors as well as to investigate ways to expand the current limits of PDF analysis. Where possible, I provide a framework for how PDF analysis might be applied to a wider set of material phenomena. Throughout the dissertation, I discuss 0 the capabilities of the PDF method to provide information pertaining to a material's structure and properties, ii) current limitations in the conventional approach to PDF analysis, iii) possible solutions to overcome certain limitations in PDF analysis, and iv) suggestions for future work to expand and improve the capabilities PDF analysis.

Peterson, Joseph W.

41

Effect Of Weakly-Bound Neutrons On Pair-Correlation And Deformation  

SciTech Connect

The unique role of weakly-bound low-angular-momentum neutrons in the structure of neutron-drip-line nuclei is presented, studying both the many-body pair-correlation in spherical nuclei and the one-particle orbits in the deformed Woods-Saxon potential. Both the HFB equations in the former case and the Schroedinger equation in the latter are solved in coordinate space with correct asymptotic boundary conditions. Combining the results of those two cases, it is concluded, for example, that all {omega}{pi} = 1/2+ one-particle levels become practically unavailable for both deformation and many-body pair-correlation, when the HF one-particle levels approach continuum or lie in the continuum.

Hamamoto, I. [Division of Mathematical Physics, LTH, University of Lund (Sweden); Niels Bohr Institute, Blegdamsvej 17, Copenhagen O, DK 2100 (Denmark)

2005-04-05

42

Neutrino pair emission due to scattering of electrons off fluxoids in superfluid neutron star cores.  

NASA Astrophysics Data System (ADS)

We study the emission of neutrinos, resulting from the scattering of electrons off magnetic flux tubes (fluxoids) in the neutron star cores with superfluid (superconducting) protons. In the absence of proton superfluidity (T>=T_cp_), this process transforms into the well known electron synchrotron emission of neutrino pairs in a locally uniform magnetic field B, with the neutrino energy loss rate Q proportional to B^2^ T^5^. For temperatures T not much below T_cp_, the synchrotron regime (Q{prop.to}T^5^) persists and the emissivity Q can be amplified by several orders of magnitude due to the appearance of the fluxoids and associated enhancement of the field within them. For lower T, the synchrotron regime transforms into the bremsstrahlung regime (Q{prop.to}T^6^) similar to the ordinary neutrino-pair bremsstrahlung of electrons which scatter off atomic nuclei. We calculate Q numerically and represent our results through a suitable analytic fit. In addition, we estimate the emissivities of two other neutrino-production mechanisms which are usually neglected - neutrino-pair bremsstrahlung processes due to electron-proton and electron-electron collisions. We show that the electron-fluxoid and electron-electron scattering can provide the main neutrino production mechanisms in the neutron star cores with highly superfluid protons and neutrons at T<~5x10^8^K. The electron-fluxoid scattering is significant if the initial, locally uniform magnetic field B>10^13^G.

Kaminker, A. D.; Yakovlev, D. G.; Haensel, P.

1997-09-01

43

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

SciTech Connect

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

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

2011-06-15

44

Temperature effects on atomic pair distribution functions of melts.  

PubMed

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. PMID:24527926

Ding, J; Xu, M; Guan, P F; Deng, S W; Cheng, Y Q; Ma, E

2014-02-14

45

Investigation of the Neutron Angular Distribution and Neutron Yield on the APF Plasma Focus Device  

NASA Astrophysics Data System (ADS)

This paper presents an experimental study of neutron yield as well as neutron angular distribution on the APF plasma focus device. The system operates with pure deuterium gas in varying the filling pressure and working voltages of 11.5 and 13.5 kV. The maximum average of neutron yield is (2.88 ± 0.29 × 108) neutrons per shot at the pressure of 7 torr. The neutron angular distribution is measured with housing an array of seven silver activation Geiger-Muller counters at the angles of 0°, ±30°, ±60°, and ±90° in a distance of 90 cm from the anode tip. The results of neutron angular distribution suggest that the neutron production mechanism may be predominantly beam target model.

Baghdadi, R.; Amrollahi, R.; Habibi, M.; Etaati, G. R.

2011-02-01

46

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)] [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)] [Joint Institute for Power and Nuclear Research-Sosny, 99 Academician A.K. Krasin Str., Minsk 220109 (Belarus)

2013-07-01

47

Pair distribution function study on compression of liquid gallium  

NASA Astrophysics Data System (ADS)

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

Yu, T.; Ehm, L.; Chen, J.; Guo, Q.; Luo, S.; Parise, J.

2008-12-01

48

Pair distribution function study on compression of liquid gallium  

SciTech Connect

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

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

2008-01-01

49

Hyperdimensional Analysis of Amino Acid Pair Distributions in Proteins  

PubMed Central

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

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

2011-01-01

50

Quantitative structure determination of nanostructured materials using the atomic pair distribution function analysis  

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. The conventional XRD experiments probe for the presence of periodic structure which are reflected in the Bragg peaks. Local structural deviations or disorder mainly affect the diffuse scattering background. In order to have information about both long-range order and local structure disorder, a technique that takes both Bragg and diffuse scattering need to be used, such as the atomic pair distribution function (PDF) technique. This Ph.D. work introduces a PDF based methodology to quantitatively study nanostructure materials in general. The introduced methodology have been applied to a size-dependent structural study on CdSe nanoparticles (NPs). Quantitative structural information about structure, crystallinity level, core size, NP size, and inhomogeneous internal strain in the studied NPs have been obtained. This method is generally applicable to the characterization of the nano-scale solid, many of which may exhibit complex disorder and strain. The introduced methodology have been also applied on technologically important system, ultra-small CdSe NPs.

Masadeh, Ahmad Salah

51

Scalable secure multicasting with distributed key management from pairings  

Microsoft Academic Search

Multicast communication is an efficient way to send data to a group of participants and its security issue has received a great deal of attention. As members can join or leave a multicast group dynamically, to guarantee confidentiality, it has to have a dynamic key management mechanism. In this paper, we apply the pairings on elliptic curve and propose an

Shyi-Tsong Wu; Jung-Hui Chiu; Bin-Chang Chieu

2005-01-01

52

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

53

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

54

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

55

Drell-Yan massive lepton-pair's angular distributions at large QT  

NASA Astrophysics Data System (ADS)

By measuring Drell-Yan massive lepton-pair's angular distributions, we can identify the polarization of the virtual photon of invariant mass /Q which decays immediately into the lepton-pair. In terms of a modified QCD factorization formula for Drell-Yan process, which is valid even if QT>>Q, we calculate the massive lepton-pair's angular distributions at large QT. We find that the virtual photons produced at high QT are more likely to be transversely polarized. We discuss the implications of this finding to the J//? mesons' polarization measured recently at Fermilab.

Qiu, J.-W.; Rodriguez, R.; Zhang, X.-F.

2001-05-01

56

Angular Distribution of Fragments in Fission Induced by Mev Neutrons  

Microsoft Academic Search

A multiangle gas-filled counter has been used to measure the fragment angular distribution in fission induced by neutrons in the energy range 0.5<=EN<=9 Mev. The target nuclei used were: Th230, U233, U234, U235, U236, U238, Np237, and Pu239. In the cases of U233 and U235 the neutron energy range was extended to include energies between 14.8 and 23 Mev. The

J. E. Simmons; R. L. Henkel

1960-01-01

57

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

NASA Astrophysics Data System (ADS)

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

Yamagami, Masayuki

2005-01-01

58

Extracting generalized neutron parton distributions from 3He data  

NASA Astrophysics Data System (ADS)

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

Rinaldi, M.; Scopetta, S.

2013-03-01

59

Zwanzig-Mori equation for the time-dependent pair distribution function.  

PubMed

We develop a microscopic theoretical framework for the time-dependent pair distribution function starting from the Liouville equation. An exact Zwanzig-Mori equation of motion for the time-dependent pair distribution function is derived based on the projection-operator formalism. It is demonstrated that, under the Markovian approximation, our equation reduces to the so-called telegraph equation that includes the potential of mean force acting between the pair particles. With the additional approximation neglecting the inertia term, our equation takes the form of Smoluchowski's equation, which has been previously introduced with intuitive arguments and shown to satisfactorily reproduce the simulation results of the particle-pair dynamics. PMID:21599146

Chong, Song-Ho; Son, Chang-Yun; Lee, Sangyoub

2011-04-01

60

Obtaining the nuclear gluon distribution from heavy quark decays to lepton pairs in p A collisions  

Microsoft Academic Search

We have studied how lepton pairs from decays of heavy-flavoured mesons produced in pA collisions can be used to determine the modifications of the gluon distribution in the nucleus. Since heavy-quark production is dominated by the gg channel, the ratio of correlated lepton pair cross sections from DD and BB decays in pA and pp collisions directly reflects the ratio

K. J. Eskola; V. J. Kolhinen; R. Vogt

2001-01-01

61

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

62

Steric Effects in Ionic Pairing and Polyelectrolyte Interdiffusion within Multilayered Films: A Neutron Reflectometry Study  

SciTech Connect

Using a series of polycations synthesized by atom transfer radical polymerization (ATRP), we investigate the effects of the polymer charge density and hydrophobicity on salt-induced interdiffusion of polymer layers within polyelectrolyte multilayer (PEM) films. Polycations with two distinct hydrophobicities and various quaternization degrees (QPDMA and QPDEA) were derived from parent polymers of matched molecular weights poly(2-(dimethylamino)ethyl methacrylate) (PDMA) and poly(2-(diethylamino)ethyl methacrylate) (PDEA) by quaternization with either methyl or ethyl sulfate. Multilayers of these polycations with polystyrene sulfonate (PSS) were assembled in low-salt conditions, and annealed in NaCl solutions to induce layer intermixing. As revealed by neutron reflectometry (NR), polycations with lower charge density resulted in a faster decay of film structure with distance from the substrate. Interestingly, when comparing polymer mobility in QPDEA/PSS and QPDMA/PSS films, layer intermixing was faster in the case of more hydrophobic QPDEA as compared to QPDMA, because of the weaker ionic pairing (due to the presence of a bulky ethyl spacer) between QPDEA and PSS.

Xu, Li [Stevens Institute of Technology, Hoboken, New Jersey; Ankner, John Francis [ORNL; Sukhishvili, Prof. Svetlana A. [Stevens Institute of Technology, Hoboken, New Jersey

2011-01-01

63

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

64

Absorption of gamma-ray photons in a vacuum neutron star magnetosphere: I. Electron-positron pair production  

SciTech Connect

The production of electron-positron pairs in a vacuum neutron star magnetosphere is investigated for both low (compared to the Schwinger one) and high magnetic fields. The case of a strong longitudinal electric field where the produced electrons and positrons acquire a stationary Lorentz factor in a short time is considered. The source of electron-positron pairs has been calculated with allowance made for the pair production by curvature and synchrotron photons. Synchrotron photons are shown to make a major contribution to the total pair production rate in a weak magnetic field. At the same time, the contribution from bremsstrahlung photons may be neglected. The existence of a time delay due to the finiteness of the electron and positron acceleration time leads to a great reduction in the electron-positron plasma generation rate compared to the case of a zero time delay. The effective local source of electron-positron pairs has been constructed. It can be used in the hydrodynamic equations that describe the development of a cascade after the absorption of a photon from the cosmic gamma-ray background in a neutron star magnetosphere.

Istomin, Ya. N., E-mail: istomin@lpi.ru; Sob'yanin, D. N., E-mail: sobyanin@lpi.ru [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

2011-10-15

65

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

66

Scaling neutron absorbed dose distributions from one medium to another  

SciTech Connect

Central axis depth dose (CADD) and off-axis absorbed dose ratio (OAR) measurements were made in water, muscle and whole skeletal bone TE-solutions, mineral oil and glycerin with a clinical neutron therapy beam. These measurements show that, for a given neutron beam quality and field size, there is a universal CADD distribution at infinity if the depth in the phantom is expressed in terms of appropriate scaling lengths. These are essentially the kerma-weighted neutron mean free paths in the media. The method used in ICRU No. 26 to scale the CADD by the ratio of the densities is shown to give incorrect results. the OAR's measured in different media at depths proportional to the respective mean free paths were also found to be independent of the media to a good approximation. It is recommended that relative CADD and OAR measurements be performed in water because of its universality and convenience. A table of calculated scaling lengths is given for various neutron energy spectra and for various tissues and materials of practical importance in neutron dosimetry.

Awschalom, M.; Rosenberg, I.; Ten Haken, R.K.

1982-11-01

67

Measurements of neutron distribution in neutrons-gamma-rays mixed field using imaging plate for neutron capture therapy.  

PubMed

The imaging plate (IP) technique is tried to be used as a handy method to measure the spatial neutron distribution via the (157)Gd(n,gamma)(158)Gd reaction for neutron capture therapy (NCT). For this purpose, IP is set in a water phantom and irradiated in a mixed field of neutrons and gamma-rays. The Hiroshima University Radiobiological Research Accelerator is utilized for this experiment. The neutrons are moderated with 20-cm-thick D(2)O to obtain suitable neutron field for NCT. The signal for IP doped with Gd as a neutron-response enhancer is subtracted with its contribution by gamma-rays, which was estimated using IP without Gd. The gamma-ray response of Gd-doped IP to non-Gd IP is set at 1.34, the value measured for (60)Co gamma-rays, in estimating the gamma-ray contribution to Gd-doped IP signal. Then measured distribution of the (157)Gd(n,gamma)(158)Gd reaction rate agrees within 10% with the calculated value based on the method that has already been validated for its reproducibility of Au activation. However, the evaluated distribution of the (157)Gd(n,gamma)(158)Gd reaction rate is so sensitive to gamma-ray energy, e.g. the discrepancy of the (157)Gd(n,gamma)(158)Gd reaction rate between measurement and calculation becomes 30% for the photon energy change from 33keV to 1.253MeV. PMID:19726204

Tanaka, Kenichi; Endo, Satoru; Hoshi, Masaharu

2010-01-01

68

Pair Lay Distribution with Regard to Far-End Crosstalk in Symmetric Telecommunication Cable.  

National Technical Information Service (NTIS)

The selection of the pair lay distribution to achieve satisfactory far-end crosstalk (FEXT) in symmetrical telecom cables is a problem which frequently has to be faced when dealing with machinery of already existing production lines. In this paper a solut...

C. Tencer A. T. Nogueira

1982-01-01

69

Time-dependent pair distribution function: The constant acceleration approximation revisited  

NASA Astrophysics Data System (ADS)

The constant-acceleration approximation for the time-dependent pair distribution function as introduced by Bloom and Oppenheim is critically examined. The previously noted inconsistencies for the initial behaviour of the correlation functions are eliminated by a proper treatment of the short time dynamics.

Balucani, U.; Vallauri, R.

1980-03-01

70

Studies of some problems related to atomic ordering, molecular motion and pair distribution function  

NASA Astrophysics Data System (ADS)

In this thesis the results of my work on three out of four projects on which I was working during my Ph.D. under supervision of Prof. M. F. Thorpe are summarized. The first project was devoted to the study of properties of a model that was developed to reproduce the ordering of ions in layered double hydroxides. In the model two types of positive ions occupy the sites of triangular lattice. The ordering of ions is assumed to occur due to the long-range Coulomb interaction. The charge neutrality is provided by the negative background charge, which is assumed to be the same at every site of the lattice. General properties of the model in 1d and 2d were studied and the phase diagrams were obtained. The obtained results predict multiple phase separations in this system of charges that can, in particularly, affect the stability of the layered double hydroxides. Some properties of the atomic pair distribution function (PDF) were studied during my work on the second project. Traditionally PDF was used to study atomic ordering at small distances, while it was assumed that at large distances PDF is featureless. Puzzled by the observation that PDF calculated for the crystalline Ni does not decay at large distances we studied the behavior, in particularly the origin of decay, of PDF at large distances. The obtained results potentially could be used to measure the amount of imperfections in crystalline materials and to test instrumental resolution in X-ray and neutron diffraction experiments. During my work on the third project we were developing a technique that would allow accurate calculation of PDF for the flexible molecules. Since quantum mechanical calculations are complicated and computationally demanding in calculations of PDF for molecules in liquid or gaseous phases, classical methods, like molecular dynamics are usually employed. Thus, quantum mechanical effects, like zero-point atomic motion, are usually ignored. However, it is necessary to take into account the effect of atomic zero-point motion if there is a desire to extract fine structural details from the PDF. We developed a method that allows incorporation of the effect of atomic zero-point motion into the results of classical MD simulations without performing full quantum mechanical calculations. This technique could be used to correct classically calculated PDFs and thus to achieve better agreement between modeled and experimental PDFs.

Levashov, Valentin A.

71

Neutron density distribution and the halo structure of C22  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

72

Flux Distribution in Phantom for Biomedical Use of Beam-Type Thermal Neutrons  

Microsoft Academic Search

For boron neutron capture therapy, the thermal neutron beam is worth using (1)as therapeutic neutron irradiation without useless and unfavorable exposure of normal tissues around tumor and (2) for microanalysis system to measure ppm-order B concentrations in tissue and to search for the location of the metastasis of tumor. In the present study, the thermal neutron flux distribution in a

Kazuhiko AOKI; Tooru KOBAYASHI; Keiji KANDA; Itsuro KIMURA

1985-01-01

73

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

74

Enrichment history of r-process elements shaped by a merger of neutron star pairs  

NASA Astrophysics Data System (ADS)

The origin of r-process elements remains unidentified and still puzzles us. The recent discovery of evidence for the ejection of r-process elements from a short-duration ?-ray burst singled out neutron star mergers (NSMs) as their origin. In contrast, core-collapse supernovae are ruled out as the main origin of heavy r-process elements (A > 110) by recent numerical simulations. However, the properties characterizing NSM events - their rarity and high yield of r-process elements per event - have been claimed to be incompatible with the observed stellar records on r-process elements in the Galaxy. We add to this picture with our results, which show that the observed constant [r-process/H] ratio in faint dwarf galaxies and one star unusually rich in r-process in the Sculptor galaxy agree well with this rarity of NSM events. Furthermore, we found that a large scatter in the abundance ratios of r-process elements to iron in the Galactic halo can be reproduced by a scheme that incorporates an assembly of various protogalactic fragments, in each of which r-process elements supplied by NSMs pervade the whole fragment while supernovae distribute heavy elements only inside the regions swept up by the blast waves. Our results demonstrate that NSMs occurring at Galactic rate of 12-23 Myr-1 are the main site of r-process elements, and we predict the detection of gravitational waves from NSMs at a high rate with upcoming advanced detectors.

Tsujimoto, T.; Shigeyama, T.

2014-05-01

75

Ultrasound-driven preparation and pair distribution function-assisted structure solution of a copper-based layered coordination polymer.  

PubMed

Nanoparticles of a copper-based layered coordination polymer, STAM-2, have been prepared via an ultrasound mediated transformation from a layered metal-organic framework, STAM-1. The structure of the material was then solved using pair distribution function analysis to identify the structural units present and the final structural model refined against the pair distribution function data. PMID:24310447

Mohideen, M Infas; Allan, Phoebe K; Chapman, Karena W; Hriljac, Joseph A; Morris, Russell E

2014-07-21

76

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

77

Analysis of neutron multiplicity and fission fragment mass distribution within the asymmetric two-center shell model  

NASA Astrophysics Data System (ADS)

The fission fragment mass distribution followed by neutron emission is studied for the 238U(18O, f) reaction using the asymmetric two-center shell model. Within the thermodynamic approach, excitation energy carried by the compound nucleus is dissipated in the emission of a pair of neutrons in several consecutive steps. Therefore, we have considered 2-12 (in step of 2) neutron emission channels in our formalism. The mass distribution corresponding to 8-neutron emission channel compares reasonably well with the experimental data. The observed fine structure dips corresponding to shell closure ( Z = 50 and N = 82 of individual fission fragment arise mainly due to shell structure in the mass parameters. However, an exact location and magnitude of the dip at A = 124 in the mass distribution depends on how the temperature modifies masses and, also, on the precise information of pre- and post-neutron emission data. This suggests a possible importance of extending these calculations to get new insight into an understanding of the dynamical behaviour of fragment formation in the fission process.

Singh, Pardeep; Kaur, Harjeet; Malik, Sham S.

2014-04-01

78

Analysis of the Total Scattering Using the Quantitative High Pressure Pair Distribution Function: Case Studies  

NASA Astrophysics Data System (ADS)

X-ray total scattering and pair distribution function analysis have been used to investigate the structural changes in nano-crystalline mackinawite (FeS), with three distinct particle sizes, at high pressure. Nano-crystalline mackinawite undergoes an irreversible first-order phase transition at about 3 GPa from tetragonal mackinawite to orthorhombic FeS-II. The transition mechanism and the grain size effect on the transition pressure and the compressibility have been determined.

Ehm, L.; Michel, F. M.; Parise, J. B.

79

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) [Los Alamos, NM

1986-01-01

80

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

81

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

NASA Astrophysics Data System (ADS)

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

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

2008-07-01

82

Thermal expansion of a glassy alloy studied using a real-space pair distribution function  

SciTech Connect

Thermal expansion of a glassy Cu{sub 55}Hf{sub 25}Ti{sub 15}Pd{sub 5} alloy studied by using reciprocal space functions is verified using a real-space pair distribution function. The experimental results obtained by real-time diffraction during heating in a synchrotron beam and their Fourier transformation processing to derive radial distribution functions indicate that both reciprocal and real-space distribution functions give good agreement in the calculation of thermal expansion data. In addition to providing structural information, these findings indicate that the change in the average atomic nearest-neighbor distance evaluated from the variation of the position of the main broad diffraction maximum can provide good thermal expansion data for metallic glasses.

Louzguine-Luzgin, Dmitri V.; Inoue, Akihisa; Yavari, Alain R.; Vaughan, Gavin [Institute for Materials Research, Tohoku University, Aoba-Ku, Sendai 980-8577 (Japan); Institut National Polytechnique de Grenoble, Saint-Martin-d'Heres Campus, Boite Postale 75, Saint-Martin-d'Heres 38402 (France); European Syncrotron Radiation Facilities, 38042 Grenoble (France)

2006-03-20

83

Measurement of the beam-helicity asymmetry I? in the photoproduction of pairs off protons and off neutrons  

NASA Astrophysics Data System (ADS)

Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of mixed-charge pion pairs in the reactions off free protons and and off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4GeV. Circularly polarized photons were produced from bremsstrahlung of longitudinally polarized electrons and tagged with the Glasgow-Mainz magnetic spectrometer. The charged pions, recoil protons, recoil neutrons, and decay photons from mesons were detected in the electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. Using a complete kinematic reconstruction of the final state, excellent agreement was found between the results for free and quasi-free protons, suggesting that the quasi-free neutron results are also a close approximation of the free-neutron asymmetries. A comparison of the results to the predictions of the Two-Pion-MAID reaction model shows that the reaction mechanisms are still not well understood, in particular at low incident photon energies in the second nucleon-resonance region.

Oberle, M.; Ahrens, J.; Annand, J. R. M.; Arends, H. J.; Bantawa, K.; Bartolome, P. A.; Beck, R.; Bekrenev, V.; Berghäuser, H.; Braghieri, A.; Branford, D.; Briscoe, W. J.; Brudvik, J.; Cherepnya, S.; Demissie, B.; Dieterle, M.; Downie, E. J.; Drexler, P.; Fil'kov, L. V.; Fix, A.; Glazier, D. I.; Heid, E.; Hornidge, D.; Howdle, D.; Huber, G. M.; Jahn, O.; Jaegle, I.; Jude, T. C.; Käser, A.; Kashevarov, V. L.; Keshelashvili, I.; Kondratiev, R.; Korolija, M.; Kruglov, S. P.; Krusche, B.; Kulbardis, A.; Lisin, V.; Livingston, K.; MacGregor, I. J. D.; Maghrbi, Y.; Mancell, J.; Manley, D. M.; Marinides, Z.; Martinez, M.; McGeorge, J. C.; McNicoll, E.; Mekterovic, D.; Metag, V.; Micanovic, S.; Middleton, D. G.; Mushkarenkov, A.; Nefkens, B. M. K.; Nikolaev, A.; Novotny, R.; Ostrick, M.; Oussena, B.; Pedroni, P.; Pheron, F.; Polonski, A.; Prakhov, S. N.; Robinson, J.; Rosner, G.; Rostomyan, T.; Schumann, S.; Sikora, M. H.; Sober, D. I.; Starostin, A.; Supek, I.; Thiel, M.; Thomas, A.; Unverzagt, M.; Watts, D. P.; Werthmüller, D.; Witthauer, L.; Zehr, F.

2014-03-01

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

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

SciTech Connect

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

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

2012-03-15

86

Bayesian Analysis of the Mass Distribution of Neutron Stars  

NASA Astrophysics Data System (ADS)

The distribution of masses for neutron stars is analyzed using the Bayesian statistical inference, evaluating the likelihood of two a priori gaussian peaks distribution by using fifty-five measured points obtained in a variety of systems. The results strongly suggest the existence of a bimodal distribution of the masses, with the first peak around 1.35M? ± 0.06M? and a much wider second peak at 1.73M? ± 0.36M?. We compared the two gaussian's model centered at 1.35M? and 1.55M? against a "single gaussian" model with 1.50M? ± 0.11M? using 3? that provided a wide peak covering objects the full range of observed of masses. In order to compare models, BIC (Baysesian Information Criterion) can be used and a strong evidence for two distributions model against one peak model was found. The results support earlier views related to the different evolutionary histories of the members for the first two peaks, which produces a natural separation (in spite that no attempt to "label" the systems has been made). However, the recently claimed low-mass group, possibly related to O - Mg - Ne core collapse events, has a monotonically decreasing likelihood and has not been identified within this sample.

Valentim, Rodolfo; Horvath, Jorge E.; Rangel, Eraldo M.

87

Transport calculations of depth-dose distributions for gadolinium neutron capture therapy  

Microsoft Academic Search

Depth-dose distributions were calculated for thermal and epithermal neutron fluence and capture gamma ray dose rates using a two-dimensional neutron-coupled gamma-ray transport code (DOT 3.5) for gadolinium neutron capture therapy. The results show that (i) a capture gamma-ray dose rate of 10 Gy h-1 was obtained with a thermal neutron fluence rate of 1.5*109 cm-2 s-1 in a simulated tumour

T. Matsumoto

1992-01-01

88

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

SciTech Connect

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

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

2008-12-01

89

Number projected isovector neutron-proton pairing effect in odd-mass nuclei  

NASA Astrophysics Data System (ADS)

A formalism which enables one to strictly conserve the number of particles when taking into account the isovector pairing correlations is presented in the case of odd-mass nuclei. With this aim, we had to first establish the expression of the projector for such systems. Expressions of the ground state and its energy have been exhibited. The model has been numerically tested in the framework of a schematic model.

Berbiche, Amine; Fellah, Mohamed; Allal, Nassima H.

2014-03-01

90

Nuclear proton and neutron distributions in the detection of weak interacting massive particles  

NASA Astrophysics Data System (ADS)

In the evaluation of weak interacting massive particles (WIMPs) detection rates, the WIMP-nucleus cross section is commonly described by using form factors extracted from charge distributions. In this work, we use different proton and neutron distributions taken from Hartree-Fock calculations. We study the effects of this choice on the total detection rates for six nuclei having different neutron excess, and taken from different regions of the nuclear chart. The use of different distributions for protons and neutrons becomes more important if isospin-dependent WIMP-nucleon interactions are considered. The need for distinct descriptions of proton and neutron densities decreases with the lowering of detection energy thresholds.

Co', G.; De Donno, V.; Anguiano, M.; Lallena, A. M.

2012-11-01

91

Effect of differences in proton and neutron density distributions on fission barriers  

PubMed

The neutron and proton density distributions obtained in constrained Hartree-Fock-Bogolyubov calculations with the Gogny force along the fission paths of 232Th, 236U, 238U, and 240Pu are analyzed. Significant differences in the multipole deformations of neutron and proton densities are found. The effect on potential energy surfaces and on barrier heights is studied under an additional constraint by imposing similar spatial distributions to neutrons and protons, as assumed in macroscopic-microscopic models. PMID:10991151

Berger; Pomorski

2000-07-01

92

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

93

Transport calculations of depth-dose distributions for gadolinium neutron capture therapy.  

PubMed

Depth-dose distributions were calculated for thermal and epithermal neutron fluence and capture gamma ray dose rates using a two-dimensional neutron-coupled gamma-ray transport code (DOT 3.5) for gadolinium neutron capture therapy. The results show that (i) a capture gamma-ray dose rate of 10 Gy h-1 was obtained with a thermal neutron fluence rate of 1.5 x 10(9) cm-2 s-1 in a simulated tumour containing 5000 PPM gadolinium placed near the surface of a water phantom, (ii) deep-seated tumours may be treated with epithermal neutrons, and (iii) gadolinium neutron capture therapy appears to achieve comparable dose distributions to those of boron neutron capture therapy. PMID:1741420

Matsumoto, T

1992-01-01

94

Curved straight neutron guide system with uniform spatial intensity distribution  

NASA Astrophysics Data System (ADS)

The spatial intensity distribution of neutrons emerging from a curved guide is asymmetric, and straight guide sections are sometimes appended to curved guides to make the intensity distribution more nearly uniform. For idealized uniform illumination and in the perfect reflectivity approximation, the spatial-angular acceptance at the exit of the combination can be made exactly uniform for a range of long wavelengths by using a sufficiently long straight section, together with a curved guide whose outer wall coating has a critical angle slightly greater than those of the other guide walls. We refer to this as a "phase space tailoring guide" where the coatings on the inner wall and straight section are used to define the required divergence at the end of the guide. Increasing the critical angle of the outer wall of the curved section reduces the characteristic wavelength of the curved guide as well as the wavelength at which ideal uniformity can be obtained. The outer wall coating need only be of sufficiently high critical angle to fill the transmittable phase space area of the straight guide uniformly to adequately short wavelength.

Mildner, D. F. R.; Cook, J. C.

2008-07-01

95

Solvent dependence of structure, charge distribution, and absorption spectrum in the photochromic merocyanine-spiropyran pair.  

PubMed

We have studied the structures and absorption spectra of merocyanine, the photoresponsive isomer of the spiropyran (SP)-merocyanine (MC) pair, in chloroform and in water solvents using a combined hybrid QM/MM Car-Parrinello molecular dynamics (CP-QM/MM) and ZINDO approach. We report remarkable differences in the molecular structure and charge distribution of MC between the two solvents; the molecular structure of MC remains in neutral form in chloroform while it becomes charge-separated, zwitterionic, in water. The dipole moment of MC in water is about 50% larger than in chloroform, while the value for SP in water is in between, suggesting that the solvent is more influential than the conformation itself in deciding the dipole moment for the merocyanine-spiropyran pair. The calculations could reproduce the experimentally reported blue shift in the absorption spectra of MC when going from the nonpolar to the polar solvent, though the actual value of the absorption maximum is overestimated in chloroform solvent. We find that the CP-QM/MM approach is appropriate for structure modeling of solvatochromic and thermochromic molecules as this approach is able to capture the solvent and thermal-induced structural changes within the solute important for an accurate assessment of the properties. PMID:21417244

Murugan, N Arul; Chakrabarti, Swapan; Ågren, Hans

2011-04-14

96

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

PubMed

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

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

2013-10-01

97

Puzzles and promises in finding nanostructure from pair distribution function data  

NASA Astrophysics Data System (ADS)

The pair distribution function (PDF) method provides detailed information about nanostructure and efficient software is available for refining PDF data to starting structures provided by the user. Starting structures may be developed using intuition, homologous structures from the literature, or by using ab-initio theoretical structures. However, in studies of nanoparticles good starting structures are hard to identify, particularly in systems where complex surface distortions occur. Moreover, refinement from random structures typically fails, or converges to unphysical structures. We quantify this problem through a systematic study of PDF refinement using starting structures that are randomly perturbed variants of the correct structures and identify the threshold perturbations beyond which refinement fails. To alleviate the difficulties in guessing or searching over starting structures it would be ideal if good starting structures could be found directly from PDF data. We outline our progress in this direction.

Musolff, Corey; Farrow, Christopher; Duxbury, Phillip; Billinge, Simon; Juhas, Pavol

2010-03-01

98

Design of a Pair of Superconducting Solenoids for a Neutron Spin-Echo Spectrometer at the SNS  

Microsoft Academic Search

A neutron spin-echo spectrometer (NSE) of the next generation will be build for the spallation neutron source (SNS) in Oak Ridge, USA. A NSE spectrometer measures tiny velocity changes of the neutrons encoded by the neutrons spin clock at a sample while the neutron spin precesses in large magnetic fields following Bloch's equation. This instrument will be the best of

W. Walter; M. Borlein; F. Eysselein; M. Gehring; T. Kozielewski; A. Kramer; M. Monkenbusch; M. Ohl; A. Paul; B. Schrauth; C. Tiemann

2007-01-01

99

Determination of Deuteron Energy Distribution From Neutron Diagnostics in a Plasma-Focus Device  

Microsoft Academic Search

Fast neutrons from deuteron-deuteron fusion reactions were used for a study of fast deuterons in the PF-1000 plasma-focus device. The energy spectrum of neutrons was determined by the time-of-flight method using ten scintillation detectors positioned downstream, upstream, and side-on the experimental facility. Neutron energy-distribution functions enabled the determination of axial and radial components of energy of deuterons producing the fusion

Pavel Kubes; Jozef Kravarik; Daniel Klir; Karel Rezac; Martin Bohata; Marek Scholz; Marian Paduch; Krzysztof Tomaszewski; Irena Ivanova-Stanik; Leslaw Karpinski; Marek Jan Sadowski

2009-01-01

100

Two-dimensional multiplicity distributions of neutrons in a cosmic ray neutron monitor  

Microsoft Academic Search

A cosmic ray neutron monitor has been built in which 16 proportional counters (BF3) are used for the detection of thermalized evaporation neutrons. Half of the counters are parallel immediately above and the other half symmetrically under the producer. The counting rate of the monitor is 83,000 p\\/hour. The magnitude of the average multiplicity is about 1.87. The neutron multiplicities

E. Valtonen; M. Nieminen; E. Paukkunen; J. J. Torsti

1980-01-01

101

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

SciTech Connect

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

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

2009-12-15

102

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

SciTech Connect

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

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

2008-01-01

103

Pair distribution function X-ray analysis explains dissolution characteristics of felodipine melt extrusion products.  

PubMed

Solid solutions of felodipine with EUDRAGIT E and EUDRAGIT E/NE were shown to dramatically increase the dissolution rate of felodipine in biorelevant media. Of the two polymer systems, extrudates containing 5% EUDRAGIT NE showed a faster dissolution rate and less recrystallization (no precipitation within 2 h). Although differential scanning calorimetry (DSC) and conventional X-ray powder diffraction (XRPD) were able to verify the amorphous state of the drug after melt extrusion, it was not possible to differentiate the two extrudate compositions further with these methods. We then applied pair distribution function (PDF) analysis to investigate extrudates. It was possible to more closely characterize the solid state of the amorphous extrudates in terms of local structural order: PDF analysis revealed that addition of minor amounts of EUDRAGIT NE to the main component EUDRAGIT E during extrusion changed the local structure of EUDRAGIT E in a nonadditive way. We conclude that local ordering can be important to the release characteristics of extrudates, even when the components are present in the amorphous state. PMID:18752290

Nollenberger, K; Gryczke, A; Meier, Ch; Dressman, J; Schmidt, M U; Brühne, S

2009-04-01

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

Instrumental Neutron Activation Analysis in the Measurement of Trace Element Distribution at Two Coal Conversion Plants.  

National Technical Information Service (NTIS)

Instrumental neutron activation analysis was used to study the elemental concentration in the complex materials produced by the H-Coal process and the low Btu gasification process at the University of Minnesota at Duluth (UMD). Trace element distribution ...

L. M. Roseberry F. F. Dyer

1984-01-01

106

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

National Technical Information Service (NTIS)

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...

R. E. Rothe

1991-01-01

107

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

108

Point by Point model calculation of the prompt neutron multiplicity distribution P( ?) for spontaneous and neutron induced fission of actinides  

Microsoft Academic Search

The prompt neutron multiplicity distribution P(?) is a very sensitive quantity which depends on the model calculation of the multi-parametric matrix ?(A,TKE) and on the fission fragment distributions.The Point by Point model is able to give an excellent description of the existing P(?) experimental data, this fact being exemplified in the present work for the following seven fissioning systems: 235U(nth,f),

Anabella Tudora; F.-J. Hambsch

2010-01-01

109

Copy number variation distribution in six monozygotic twin pairs discordant for schizophrenia.  

PubMed

We have evaluated copy number variants (CNVs) in six monozygotic twin pairs discordant for schizophrenia. The data from Affymetrix® Human SNP 6.0 arrays™ were analyzed using Affymetrix® Genotyping Console™, Partek® Genomics Suite™, PennCNV, and Golden Helix SVS™. This yielded both program-specific and overlapping results. Only CNVs called by Affymetrix Genotyping Console, Partek Genomics Suite, and PennCNV were used in further analysis. This analysis included an assessment of calls in each of the six twin pairs towards identification of unique CNVs in affected and unaffected co-twins. Real time polymerase chain reaction (PCR) experiments confirmed one CNV loss at 7q11.21 that was found in the affected patient but not in the unaffected twin. The results identified CNVs and genes that were previously implicated in mental abnormalities in four of the six twin pairs. It included PYY (twin pairs 1 and 5), EPHA3 (twin pair 3), KIAA1211L (twin pair 4), and GPR139 (twin pair 5). They represent likely candidate genes and CNVs for the discordance of four of the six monozygotic twin pairs for this heterogeneous neurodevelopmental disorder. An explanation for these differences is ontogenetic de novo events that differentiate in the monozygotic twins during development. PMID:24556202

Castellani, Christina A; Awamleh, Zain; Melka, Melkaye G; O'Reilly, Richard L; Singh, Shiva M

2014-04-01

110

Controllability of depth dose distribution for neutron capture therapy at the Heavy Water Neutron Irradiation Facility of Kyoto University Research Reactor.  

PubMed

The updating construction of the Heavy Water Neutron Irradiation Facility of the Kyoto University Research Reactor has been performed from November 1995 to March 1996 mainly for the improvement in neutron capture therapy. On the performance, the neutron irradiation modes with the variable energy spectra from almost pure thermal to epi-thermal neutrons became available by the control of the heavy-water thickness in the spectrum shifter and by the open-and-close of the cadmium and boral thermal neutron filters. The depth distributions of thermal, epi-thermal and fast neutron fluxes were measured by activation method using gold and indium, and the depth distributions of gamma-ray absorbed dose rate were measured using thermo-luminescent dosimeter of beryllium oxide for the several irradiation modes. From these measured data, the controllability of the depth dose distribution using the spectrum shifter and the thermal neutron filters was confirmed. PMID:12408308

Sakurai, Yoshinori; Kobayashi, Tooru

2002-10-01

111

Long-range proximity effect for opposite-spin pairs in superconductor-ferromagnet heterostructures under nonequilibrium quasiparticle distribution.  

PubMed

By now it is known that in a singlet superconductor-ferromagnet (S-F) structure the superconducting correlations carried by opposite-spin pairs penetrate into the ferromagnet over a short distance of the order of magnetic coherence length. The long-range proximity effect (LRPE), taking place on the length scale of the normal metal coherence length, can only be maintained by equal-spin pairs, which can be generated by magnetic inhomogeneities in the system. In this Letter, we have predicted a new type of LRPE, which can take place in S-F heterostructures under nonequilibrium conditions. The superconducting correlations in the F region are generated by opposite-spin Cooper pairs and equal-spin pairs are not involved. The possibility for an opposite-spin pair to penetrate into the ferromagnet over a large distance is provided by creation of the proper nonequilibrium quasiparticle distribution there. This leads to a sharp increase (up to a few orders of magnitude) of the critical Josephson current through a S-F-S junction at some values of the voltage controlling the nonequilibrium distribution in the F interlayer. PMID:23003078

Bobkova, I V; Bobkov, A M

2012-05-11

112

Rietveld and pair distribution function study of Hägg carbide using synchrotron X-ray diffraction.  

PubMed

Fischer-Tropsch (FT) synthesis is an important process in the manufacturing of hydrocarbons and oxygenated hydrocarbons from mixtures of carbon monoxide and hydrogen (syngas). The reduced iron catalyst reacts with carbon monoxide and hydrogen to form bulk Fe(5)C(2) Hägg carbide (?-HC) during FT synthesis. Arguably, ?-HC is the predominant catalyst phase present in the working iron catalyst. Deactivation of the working catalyst can be due to oxidation of ?-HC to iron oxide, a step-wise decarburization to cementite (?-Fe(3)C), carbon formation or sintering with accompanying loss of catalytic performance. It is therefore critical to determine the precise crystal structure of ?-HC for the understanding of the synthesis process and for comparison with the first-principles ab initio modelling. Here the results of high-resolution synchrotron X-ray powder diffraction data are reported. The atomic arrangement of ?-HC was confirmed by Rietveld refinement and subsequent real-space modelling of the pair distribution function (PDF) obtained from direct Fourier transformation. The Rietveld and PDF results of ?-HC correspond well with that of a pseudo-monoclinic phase of space group P? [a = 11.5661?(6)?Å, b = 4.5709?(1)?Å, c = 5.0611?(2)?Å, ? = 89.990?(5)°, ? = 97.753?(4)°, ? = 90.195?(4)°], where the Fe atoms are located in three distorted prismatic trigonal and one octahedral arrangement around the central C atoms. The Fe atoms are distorted from the prismatic trigonal arrangement in the monoclinic structure by the change in C atom location in the structure. PMID:21335915

du Plessis, Hester Esna; de Villiers, J P R; Kruger, G J; Steuwer, A; Brunelli, M

2011-03-01

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

Spatial distribution of neutrons guided through a monolithic tapered lens  

Microsoft Academic Search

The cold neutron transmission through a monolithic polycapillary lens is studied by scanning a pinhole beam across the entrance cross section of the lens. The relative transmission as a function of bending radius of a tapered channel is obtained. The results are explained in terms of a reduced critical angle for total reflection for the tapered channels. A technique for

K. M. Podurets; V. A. Sharov; D. F. R. Mildner

1997-01-01

115

Angular distribution and altitude dependence of atmospheric neutrons from 10 to 100 MeV  

NASA Technical Reports Server (NTRS)

The altitude dependence of atmospheric neutrons from ground level to 5 g/sq cm of residual atmosphere at neutron energies of 10 to 100 MeV is reported. Ground level measurements were taken at Cape Girardeau, Missouri, on Sept. 18, 1972. The other measurements were made during ascent and float on launch from Palestine, Texas, on Sept. 26, 1971. The intensity of both the downward- and the upward-moving neutrons is maximum at about 100 g/sq cm of residual atmosphere. Neutron angular distributions are reported from 20 to 80 deg and from 100 to 160 deg for 10- to 100-MeV neutrons. Omnidirectional fluxes at altitudes of 5, 50, 100, and 200 g/sq cm of residual atmosphere are in good agreement with recent theoretical calculations of Armstrong et al. (1973) in the three energy intervals of 10 to 30, 30 to 50, and 50 to 100 MeV.

Preszler, A. M.; Simmett, G. M.; White, R. S.

1974-01-01

116

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

117

Measurement of angular distribution of neutron flux for the 6MeV race-track microtron based pulsed neutron source.  

PubMed

The 6MeV race track microtron based pulsed neutron source has been designed specifically for the elemental analysis of short lived activation products, where the low neutron flux requirement is desirable. Electrons impinges on a e-gamma target to generate bremsstrahlung radiations, which further produces neutrons by photonuclear reaction in gamma-n target. The optimisation of these targets along with their spectra were estimated using FLUKA code. The measurement of neutron flux was carried out by activation of vanadium at different scattering angles. Angular distribution of neutron flux indicates that the flux decreases with increase in the angle and are in good agreement with the FLUKA simulation. PMID:20447829

Patil, B J; Chavan, S T; Pethe, S N; Krishnan, R; Dhole, S D

2010-09-01

118

Comparison of flux density distributions from massive or ring-shaped isotopic neutron sources  

Microsoft Academic Search

A comparison has been made between flux density distributions from massive and ring-shaped cylindrical isotopic neutron sources.\\u000a A considerable gain in direct fast neutron flux is obtained for the latter geometry as well as a neat separation of fast and\\u000a thermal flux density maxima along the axis of the source. Applications of these favourable properties are discussed.

L. Alaerts; J. P. Op De Beeck; J. Hoste

1975-01-01

119

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

SciTech Connect

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

Nathan Isgur

1998-12-01

120

Spatial distribution of neutrons guided through a monolithic tapered lens  

SciTech Connect

The cold neutron transmission through a monolithic polycapillary lens is studied by scanning a pinhole beam across the entrance cross section of the lens. The relative transmission as a function of bending radius of a tapered channel is obtained. The results are explained in terms of a reduced critical angle for total reflection for the tapered channels. A technique for qualitative examination of monolithic lenses is proposed. {copyright} {ital 1997 American Institute of Physics.}

Podurets, K.M.; Sharov, V.A.; Mildner, D.F. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)] [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

1997-11-01

121

Quantum communication via controlled holes in the statistical distribution of excitations in a nanoresonator coupled to a Cooper pair box  

NASA Astrophysics Data System (ADS)

We propose a scheme to transmit information via the statistical distribution of excitations of a nanomechanical resonator. It employs a controllable coupling between this system and a Cooper pair box. The success probability and the fidelity are calculated and compared with those obtained in an atom-field system in different regimes. Addtionaly, the scheme can also be applied to prepare low excited Fock states.

Valverde, C.; A. T., Avelar; Baseia, B.

2012-03-01

122

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

123

NLO differential distributions of massive lepton-pair production in longitudinally polarized proton-proton collisions  

NASA Astrophysics Data System (ADS)

We present the full next-to-leading order (NLO) corrected inclusive cross section d3??/ dQ2/ dy/ dpT for massive lepton pair production in longitudinally polarized proton-proton collisions p+p?l +l -+ 'X' . Here 'X' denotes any inclusive hadronic state and Q represents the invariant mass of the lepton pair which has transverse momentum pT and rapidity y. All QCD partonic subprocesses have been included provided the lepton pair is created by a virtual photon, which is a valid approximation for Q<50 GeV. Like in unpolarized proton-proton scattering the dominant subprocess is given by q( q¯)+g?? ?+ 'X' so that massive lepton pair production provides us with an excellent method to measure the spin density of the gluon. Our calculations are carried out using the method of n-dimensional regularization by making a special choice for the ?5-matrix. Like in the case of many other prescriptions evanescent counter terms appear. They are determined by computing the NLO coefficient functions for d??/ dQ2 and the polarized cross section for Higgs production using both n-dimensional regularization and a four-dimensional regularization technique in which the ?5-matrix is uniquely defined. Our calculations reveal that the non-singlet polarized coefficient function equals the unpolarized one up to a minus sign. We give predictions for double longitudinal spin asymmetry measurements at the RHIC.

Ravindran, V.; Smith, J.; van Neerven, W. L.

2002-12-01

124

Coupled Intrinsic Connectivity Distribution Analysis: A Method for Exploratory Connectivity Analysis of Paired fMRI Data  

PubMed Central

We present a novel voxel-based connectivity approach for paired functional magnetic resonance imaging (fMRI) data collected under two different conditions labeled the Coupled Intrinsic Connectivity Distribution (coupled-ICD). Our proposed method jointly models both conditions to incorporate additional paired information into the connectivity metric. Voxel-based connectivity holds promise as a clinical tool to characterize a wide range of neurological and psychiatric diseases, and monitor their treatment. As such, examining paired connectivity data such as scans acquired pre- and post-intervention is an important application for connectivity methodologically. When presented with data from paired conditions, conventional voxel-based methods analyze each condition separately. However, summarizing each connection separately can misrepresent patterns of changes in connectivity. We show that commonly used methods can underestimate functional changes and subsequently introduce and evaluate our solution to this problem, the coupled-ICD metric, using two studies: 1) healthy controls scanned awake and under anesthesia, and 2) cocaine-dependent subjects and healthy controls scanned while being presented with relaxing or drug-related imagery cues. The coupled-ICD approach detected differences between paired conditions in similar brain regions as the conventional approaches while also revealing additional changes in regions not identified using conventional voxel-based connectivity analyses. Follow-up seed-based analyses on data independent from the voxel-based results also showed connectivity differences between conditions in regions detected by coupled-ICD. This approach of jointly analyzing paired resting-state scans provides a new and important tool with many applications for clinical and basic neuroscience research.

Scheinost, Dustin; Shen, Xilin; Finn, Emily; Sinha, Rajita; Constable, R. Todd; Papademetris, Xenophon

2014-01-01

125

Neutron radiation distribution sensor using flexible plastic scintillating fiber combined with the time-of-flight technique  

Microsoft Academic Search

As a promising neutron radiation distribution sensor, a long fiber system has been made using two silica fibers connected to both ends of the plastic scintillating fiber (PSF). Its basic properties were investigated to detect the position of neutron incidence with the time-of-flight (TOF) method. From the experimental results for the fission neutron source, the two linear relations were confirmed

E. Takada; K. Sugiyama; H. Takahashi; T. Iguchi; M. Nakazawa

1995-01-01

126

Comparisons of calculated and measured spectral distributions of neutrons from a 14MeV neutron source inside the Tokamak Fusion Test Reactor  

Microsoft Academic Search

A recent paper presented neutron spectral distributions (energy greater than or equal to 0.91 MeV) measured at various locations around the Tokamak Fusion Test Reactor (TFTR) at the Princeton Plasma Physics Laboratory. The neutron source for the series of measurements was a small deuterium-tritium generator placed at various positions in the TFTR vacuum chamber. The results of neutron transport calculations

R. T. Santoro; J. M. Barnes; R. G. Jr. Alsmiller; M. B. Emme; J. D. Drischler

1987-01-01

127

Neutron Emission and Angular Distribution in Compact Plasma Focus Devices Operating at Hundreds of Joules  

NASA Astrophysics Data System (ADS)

Measurement of anisotropy and neutron energy of the very small device PF-400J (880 nF, 30 kV, 120 kA, 400 J, 300 ns time to peak current, dI/dt~4×1011 A/s) are presented. Neutron emission with the device operating in deuterium has been obtained and the maximum total neutron yield measured is of the order of 106 per shot at 9mbar. The following diagnostics have been applied: time of flight (TOF) to estimate the neutron mean energy, and angular distribution of the neutron emission using CR-39 nuclear track detectors covered with polyethylene located at several positions (between -90° to 90°). Discharges were performed at different pressures, 5-12 mbar, with a charging voltage of 30+/-2 KV (~400J). With the results of the TOF measurements a mean neutron energy of (2.4+/-0.4) MeV was obtained. The angular measurements are compared with the total neutron yield (integral of the angular measurements). The results are consistent with an angular uniform plateau (isotropic emission) plus a shape peaked in the direction of the axis of the discharge (anisotropic emission). Isotropic components accounts for 57.5% of the accumulative emission, while the anisotropy component accounts for the remaining 42.5%. Anisotropic component appears between +50° and -50° approximately.

Silva, Patricio; Moreno, José; Pavez, Cristian; Castillo, Fermín; Herrera, Julio; Soto, Leopoldo

2006-12-01

128

Neutron Emission and Angular Distribution in Compact Plasma Focus Devices Operating at Hundreds of Joules  

SciTech Connect

Measurement of anisotropy and neutron energy of the very small device PF-400J (880 nF, 30 kV, 120 kA, 400 J, 300 ns time to peak current, dI/dt{approx}4x1011 A/s) are presented. Neutron emission with the device operating in deuterium has been obtained and the maximum total neutron yield measured is of the order of 106 per shot at 9mbar. The following diagnostics have been applied: time of flight (TOF) to estimate the neutron mean energy, and angular distribution of the neutron emission using CR-39 nuclear track detectors covered with polyethylene located at several positions (between -90 deg. to 90 deg. ). Discharges were performed at different pressures, 5-12 mbar, with a charging voltage of 30{+-}2 KV ({approx}400J). With the results of the TOF measurements a mean neutron energy of (2.4{+-}0.4) MeV was obtained. The angular measurements are compared with the total neutron yield (integral of the angular measurements). The results are consistent with an angular uniform plateau (isotropic emission) plus a shape peaked in the direction of the axis of the discharge (anisotropic emission). Isotropic components accounts for 57.5% of the accumulative emission, while the anisotropy component accounts for the remaining 42.5%. Anisotropic component appears between +50 deg. and -50 deg. approximately.

Silva, Patricio; Moreno, Jose; Soto, Leopoldo [Comision Chilena de Energia Nuclear, Casilla 188-D, Santiago (Chile); Pavez, Cristian [Comision Chilena de Energia Nuclear, Casilla 188-D, Santiago (Chile); Universidad de Concepcion, Facultad de Ciencias, Departamento de Fisica, Concepcion (Chile); Castillo, Fermin; Herrera, Julio [Universidad Nacional Autonoma de Mexico, Ciudad de Mexico (Mexico)

2006-12-04

129

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

Microsoft Academic Search

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

Sami Pietinen; Vesa Tenhunen; Markku Tukiainen

2008-01-01

130

Generalized Parton Distributions of 3He and the Neutron Orbital Structure  

NASA Astrophysics Data System (ADS)

The two leading twist, quark helicity conserving generalized parton distributions (GPDs) of 3He, accessible, for example, in coherent deeply virtual Compton scattering (DVCS), are calculated in impulse approximation (IA). Their sum, at low momentum transfer, is found to be largely dominated by the neutron contribution, so that 3He is very promising for the extraction of the neutron information. Anyway, such an extraction could be not trivial. A technique, able to take into account the nuclear effects included in the IA analysis in the extraction procedure, even at moderate values of the momentum transfer, is proposed. Coherent DVCS arises therefore as a crucial experiment to access, for the first time, the neutron GPDs and the orbital angular momentum of the partons in the neutron.

Rinaldi, M.; Scopetta, S.

2013-08-01

131

Notch Test for Radial Sensitivity on Neutron Density Distribution in 48Ca Probed by ?-Particle Elastic Scattering  

NASA Astrophysics Data System (ADS)

Notch tests are made to study the sensitive regions in the neutron density distribution in the ground state of 48Ca probed by the angular distributions of differential cross sections of ?-particle elastic scattering at 104MeV with optical model potentials calculated by using a systematic single-folding model. An improved notch scheme is proposed, which perturbs the neutron density distribution of the target nucleus locally. Results of the notch tests show that the angular distribution of differential cross sections for ? particle elastic scattering at 104MeV only probe the surface of the neutron density distribution in 48Ca.

Zhang, Xiao-Fu; Pang, Dan-Yang

2014-05-01

132

Influence of the Deviation from the Equilibrium Deuteron Distribution on the Neutron Spectra in Linear Pinch Geometries.  

National Technical Information Service (NTIS)

In order to analyse 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 mono-energetic deuteron distribution, was studied. An essential diffe...

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

1982-01-01

133

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

134

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

135

Application of the transmission probability method to the calculation of neutron flux distributions in hexagonal geometry  

Microsoft Academic Search

A transmission probability method for hexagonal geometry implemented in the program TPHEX is described briefly. This program was developed for the calculation of neutron flux distributions in hexagonal light water reactor fuel assemblies. The accuracy appears to be superior to diffusion theory, and the computation time is shorter than that of the collision probability method.

Wasastjerna

1979-01-01

136

Determining the Fission Yield Distribution for the Reactor Neutron Induced Fission of exp 241 AM.  

National Technical Information Service (NTIS)

For the reactor neutron induced fission of exp 241 Am the fission yields for a total of 35 masses were determined as against exp 235 U fission yields and compared with available data. The shape of the mass distribution curve was well defined by the measur...

W. Weinlaender H. J. Born

1972-01-01

137

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

Microsoft Academic Search

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

1991-01-01

138

Distribution of trace metal concentrations in paired cancerous and non-cancerous human stomach tissues  

PubMed Central

AIM: To assess whether trace metal concentrations (which influence metabolism as both essential and non-essential elements) are increased or decreased in cancerous tissues and to understand the precise role of these metals in carcinogenesis. METHODS: Concentrations of trace metals including Cd, Ni, Cu, Zn, Fe, Mg and Ca in both cancerous and non-cancerous stomach tissue samples were determined by atomic absorption spectrometry (AAS). Tissue samples were digested using microwave energy. Slotted tube atom trap was used to improve the sensitivity of copper and cadmium in flame AAS determinations. RESULTS: From the obtained data in this study, the concentrations of nickel, copper and iron in the cancerous human stomach were found to be significantly higher than those in the non-cancerous tissues, by using t-test for the paired samples. Furthermore, the average calcium concentrations in the cancerous stomach tissue samples were found to be significantly lower than those in the non-cancerous stomach tissue samples by using t-test. Exceedingly high Zn concentrations (207-826 mg/kg) were found in two paired stomach tissue samples from both cancerous and non-cancerous parts. CONCLUSION: In contrast to the literature data for Cu and Fe, the concentrations of copper, iron and nickel in cancerous tissue samples are higher than those in the non-cancerous samples. Furthermore, the Ca levels are lower in cancerous tissue samples than in non-cancerous tissue samples.

Yaman, Mehmet; Kaya, Gokce; Yekeler, Hayrettin

2007-01-01

139

Exact time evolution of the pair distribution function for an entangled two-electron initial state  

NASA Astrophysics Data System (ADS)

Based on the correlated ground-state wave function of an exactly solvable interacting one-dimensional two-electron model Hamiltonian we address the switch-off of confining and interparticle interactions to calculate the exact time-evolving wave function from a prescribed correlated initial state. Using this evolving wave function, the time-dependent pair probability function R(x1,x2,t)?n2(x1,x2,t)/[n(x1,t)n(x2,t)] is determined via the pair density n2(x1,x2,t) and single-particle density n(x,t). It is found that R(0,0,t=?)=R(0,0,t=0)>1, and R(x1,x2,t*)=1 at a finite t* for ??0 interparticle interaction strength in the initial two-electron model. By expanding n(x,t) in an infinite sum of closed-shell products of time-dependent normalized single-particle states and time-dependent occupation numbers Pk(?,t), the von Neumann entropy S(?,t)=-?k=0?Pk(t)lnPk(t) is calculated as well. The such-defined information entropy is zero at t*(?) and its maximum in time is S(?,t=?)=S(?,t=0).

Nagy, I.; Aldazabal, I.; Rubio, A.

2012-08-01

140

Beta strength distribution in neutron-deficient nuclei  

SciTech Connect

The results of recent studies of the Gamow-Teller {beta}-decays of nuclei in the {sup 100}Sn region are presented. Measurements performed with the use of the total absorption {gamma}-ray spectrometer and the Cluster Cube array of germanium detectors revealed qualitatively new information on the Gamow-Teller strength distribution in the decays of {sup 97}Ag and {sup 103-107}In. The shape of the measured {beta}-strength distribution and the resulting total B{sub GT} values are compared with the results of shell-model calculations.

Janas, Z.; Gierlik, M.; Karny, M.; Plochocki, A.; Szerypo, J. [Institute of Experimental Physics, University of Warsaw, PL-00681 Warsaw (Poland); Agramunt, J.; Algora, A.; Cano-Ott, D.; Gadea, A.; Rubio, B.; Tain, J. L. [Instituto de Fisica Corpuscular, C.S.I.C.-University Valencia, E-46100 Burjassot (Spain); Batist, L.; Moroz, F.; Wittmann, V. [St. Petersburg Nuclear Physics Institute, 188-350 Gatchina (Russian Federation); Brown, B. A. [NSCL, Department of Physics and Astronomy, MSU, East Lansing, Michigan 48824-1321 (United States); Collatz, R.; Grawe, H.; Gulielmetti, A.; Hellstroem, M.; Hu, Z. [Gesellschaft fuer Schwerionenforschung mbH, D-64291, Darmstadt (Germany)] (and others)

1998-12-21

141

Beta strength distribution in neutron-deficient nuclei  

SciTech Connect

The results of recent studies of the Gamow-Teller {beta}-decays of nuclei in the {sup 100}Sn region are presented. Measurements performed with the use of the total absorption {gamma}-ray spectrometer and the Cluster Cube array of germanium detectors revealed qualitatively new information on the Gamow-Teller strength distribution in the decays of {sup 97}Ag and {sup 103{endash}107}In. The shape of the measured {beta}-strength distribution and the resulting total B{sub GT} values are compared with the results of shell-model calculations. {copyright} {ital 1998 American Institute of Physics.}

Janas, Z.; Gierlik, M.; Gorska, M.; Karny, M.; Plochocki, A.; Rejmund, M.; Rykaczewski, K.; Szerypo, J. [Institute of Experimental Physics, University of Warsaw, PL-00681 Warsaw (Poland); Agramunt, J.; Algora, A.; Cano-Ott, D.; Gadea, A.; Rubio, B.; Tain, J.L. [Instituto de Fisica Corpuscular, C.S.I.C.-University Valencia, E-46100 Burjassot (Spain); Batist, L.; Moroz, F.; Wittmann, V. [St. Petersburg Nuclear Physics Institute, 188-350 Gatchina (Russia); Brown, B.A. [NSCL, Department of Physics and Astronomy, MSU, East Lansing, Michigan 48824-1321 (United States); Collatz, R.; Gorska, M.; Grawe, H.; Gulielmetti, A.; Hellstroem, M.; Hu, Z.; Kirchner, R.; Rejmund, M.; Roeckl, E.; Shibata, M. [Gesellschaft fuer Schwerionenforschung mbH, D-64291, Darmstadt (Germany); Piechaczek, A.; Woehr, A. [Instituut voor Kern- en Stralingsfysica, University of Leuven, B-3001 Leuven (Belgium); Rykaczewski, K. [Oak Ridge National Laboratory, Physics Division, PO Box 2008, Oak Ridge, Tennessee 37831 (United States)

1998-12-01

142

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

143

Combining density functional theory (DFT) and pair distribution function (PDF) analysis to solve the structure of metastable materials: the case of metakaolin.  

PubMed

Understanding the atomic structure of complex metastable (including glassy) materials is of great importance in research and industry, however, such materials resist solution by most standard techniques. Here, a novel technique combining thermodynamics and local structure is presented to solve the structure of the metastable aluminosilicate material metakaolin (calcined kaolinite) without the use of chemical constraints. The structure is elucidated by iterating between least-squares real-space refinement using neutron pair distribution function data, and geometry optimisation using density functional modelling. The resulting structural representation is both energetically feasible and in excellent agreement with experimental data. This accurate structural representation of metakaolin provides new insight into the local environment of the aluminium atoms, with evidence of the existence of tri-coordinated aluminium. By the availability of this detailed chemically feasible atomic description, without the need to artificially impose constraints during the refinement process, there exists the opportunity to tailor chemical and mechanical processes involving metakaolin and other complex metastable materials at the atomic level to obtain optimal performance at the macro-scale. PMID:20237714

White, Claire E; Provis, John L; Proffen, Thomas; Riley, Daniel P; van Deventer, Jannie S J

2010-04-01

144

Evaluation of water distribution in a small operating fuel cell using neutron color image intensifier  

NASA Astrophysics Data System (ADS)

Neutron radiography is one of the useful tools for visualizing water behavior in operating fuel cells. In order to observe the detailed information about the water distribution in membrane electrode assembly (MEA) and gas diffusion layer (GDL) in fuel cells, a high performance neutron imaging system is required. A neutron color image intensifier (NCII) is a high spatial resolution and high sensitivity neutron image detector. We have developed an imaging system using an NCII for visualizing the behavior of water in fuel cells. The pixel size of the imaging system is around 4.7 ?m in the small view field. By using this system, water distribution of a small sized fuel cell was observed continuously every 20 s at the Thermal Neutron Radiography Facility (TNRF). In the results, the water area appears from the GDL and MEA regions, and expanded to the cathode side channel with time. However, the voltage was gradually reduced with time, and steeply dropped. It is considered that the reduction and the drop of voltage were caused by a blockage of gas flow due to accumulation of water in the GDL and the gas flow channel in the cathode side.

Yasuda, R.; Nittoh, K.; Konagai, C.; Shiozawa, M.; Takenaka, N.; Asano, H.; Murakawa, H.; Sugimoto, K.; Nojima, T.; Hayashida, H.; Iikura, H.; Sakai, T.; Matsubayashi, M.

2011-09-01

145

Heating Distributions in the Target of the Spallation Neutron Source  

SciTech Connect

Detailed calculation of the heat distributions in the structural parts of the target (Hg) and the target itself were made with realistic proton profiles. Preliminary current profiles of the protons coming from the accumulator ring, calculated and parameterized by the Brookhaven National Laboratory (BNL), were used as input to the Monte Carlo code LAHET. Due to limitations of the present version of the LAHET code, the real source was approximated with a nest of elliptical rings (all with the same eccentricity). The BNL's source was then fitted according to this elliptical description considering two constraints: (1) to preserve the areas of the contours of equal intensity of the real proton current density, and (2) to keep the ellipses with the same shape. In this way the best elliptical shape to describe the source was found. Because of the gaussian nature of the real current distribution, the elliptical fit is also gaussian in the elliptical coordinate.

Charlton, L.A.; Difilippo, F.C.

1999-11-18

146

The distribution of the zeros of the Hermite-Padé polynomials for a pair of functions forming a Nikishin system  

NASA Astrophysics Data System (ADS)

The distribution of the zeros of the Hermite-Padé polynomials of the first kind for a pair of functions with an arbitrary even number of common branch points lying on the real axis is investigated under the assumption that this pair of functions forms a generalized complex Nikishin system. It is proved (Theorem 1) that the zeros have a limiting distribution, which coincides with the equilibrium measure of a certain compact set having the \\mathscr S-property in a harmonic external field. The existence problem for \\mathscr S-compact sets is solved in Theorem 2. The main idea of the proof of Theorem 1 consists in replacing a vector equilibrium problem in potential theory by a scalar problem with an external field and then using the general Gonchar-Rakhmanov method, which was worked out in the solution of the '1/9'-conjecture. The relation of the result obtained here to some results and conjectures due to Nuttall is discussed. Bibliography: 51 titles.

Rakhmanov, E. A.; Suetin, S. P.

2013-09-01

147

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

148

Modeling the momentum distributions of annihilating electron-positron pairs in solids  

Microsoft Academic Search

Measuring the Doppler broadening of the positron annihilation radiation or the angular correlation between the two annihilation gamma quanta reflects the momentum distribution of electrons seen by positrons in the material. Vacancy-type defects in solids localize positrons and the measured spectra are sensitive to the detailed chemical and geometric environments of the defects. However, the measured information is indirect and

I. Makkonen; M. Hakala; M. J. Puska

2006-01-01

149

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

150

Measurements of the neutron yield and the neutron energy distribution from the 9Be(d,n) 10B reaction on a thick Be target at an incident deuteron energy of 20.2 MeV  

Microsoft Academic Search

A fast neutron irradiation facility has been set up at the SARA cyclotron located in Grenoble. This facility provides the possibility to carry out fast neutron irradiation tests at both cryogenic and ambient temperatures. Neutrons are produced by stopping a 20.2 MeV deuteron beam in a 3 mm thick beryllium target. The angular distribution of the neutron flux and the

A. Belymam; A. Hoummada; J. Collot; P. de Saintignon; G. Mahout; B. Merkel

1998-01-01

151

Optimal pair-generation rate for entanglement-based quantum key distribution  

NASA Astrophysics Data System (ADS)

In entanglement-based quantum key distribution (QKD), the generation and detection of multiphoton modes leads to a trade-off between entanglement visibility and twofold coincidence events when maximizing the secure key rate. We produce a predictive model for the optimal twofold coincidence probability per coincidence window given the channel efficiency and detector dark count rate of a given system. This model is experimentally validated and used in simulations for QKD with satellites as well as optical fibers.

Holloway, Catherine; Doucette, John A.; Erven, Christopher; Bourgoin, Jean-Philippe; Jennewein, Thomas

2013-02-01

152

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

NASA Astrophysics Data System (ADS)

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

Enqvist, Andreas; Pázsit, Imre

2010-06-01

153

Bright integrated photon-pair source for practical passive decoy-state quantum key distribution  

NASA Astrophysics Data System (ADS)

We report on a bright, nondegenerate type-I parametric down-conversion source, which is well suited for passive decoy-state quantum key distribution. We show the photon-number-resolved analysis over a broad range of pump powers and we prove heralded higher-order n-photon states up to n =4. The inferred photon click statistics exhibit excellent agreements to the theoretical predictions. From our measurement results we conclude that our source meets the requirements to avert photon-number-splitting attacks.

Krapick, S.; Stefszky, M. S.; Jachura, M.; Brecht, B.; Avenhaus, M.; Silberhorn, C.

2014-01-01

154

Detection of prokaryotic promoters from the genomic distribution of hexanucleotide pairs  

PubMed Central

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

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

2006-01-01

155

Study of the nuclear matter distribution in neutron-rich Li isotopes  

NASA Astrophysics Data System (ADS)

The differential cross sections for small-angle proton elastic scattering on the 6,8,9,11Li nuclei at energies near 700 MeV/nucleon were measured in inverse kinematics using secondary nuclear beams at GSI Darmstadt. The hydrogen-filled ionization chamber IKAR was employed as target and recoil proton detector. For determining the nuclear matter radii and radial matter distributions, the measured cross sections have been analysed with the aid of the Glauber multiple-scattering theory. The nuclear matter distribution deduced for 11Li exhibits a very pronounced halo structure, the matter radius of 11Li being significantly larger than those of the 6,8,9Li isotopes. The data on 8,9Li are consistent with the existence of sizable neutron skins in these nuclei. The obtained data allow for a test of various theoretical model calculations of the structure of the studied neutron-rich nuclei.

Dobrovolsky, A. V.; Alkhazov, G. D.; Andronenko, M. N.; Bauchet, A.; Egelhof, P.; Fritz, S.; Geissel, H.; Gross, C.; Khanzadeev, A. V.; Korolev, G. A.; Kraus, G.; Lobodenko, A. A.; Münzenberg, G.; Mutterer, M.; Neumaier, S. R.; Schäfer, T.; Scheidenberger, C.; Seliverstov, D. M.; Timofeev, N. A.; Vorobyov, A. A.; Yatsoura, V. I.

2006-02-01

156

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

157

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

2014-06-01

158

Comparisons of calculated and measured spectral distributions of neutrons from a 14MeV neutron source inside the Tokamak Fusion Test Reactor  

Microsoft Academic Search

A recent paper presented neutron spectral distributions (energy greater than or equal to0.91 MeV) measured at various locations around the Tokamak Fusion Test Reactor (TFTR) at the Princeton Plasma Physics Laboratory. The neutron source for the series of measurements was a small D-T generator placed at various positions in the TFTR vacuum chamber. In the present paper the results of

R. T. Santoro; J. M. Barnes; R. G. Jr. Alsmiller; M. B. Emmett; J. D. Drischler

1985-01-01

159

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

PubMed

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

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

2013-09-15

160

Association constants and distribution functions for ion pairs in binary solvent mixtures: Application to a cyanine dye system  

NASA Astrophysics Data System (ADS)

The computations of the association constants Kass were performed at the microscopic level for the ion pair Cy+I- composed of the complex cyanine dye cation Cy+ coupled to the negative iodine counterion. The wide array of Kass values is arranged by a variation of the composition of the binary solvent mixtures toluene/dimethylsulfoxide with the accompanying change of the solvent polarity. The potentials of mean force (PMFs) are calculated for a set of interionic separations R in the Cy+I- by a methodology which combines the quantum-chemical techniques for the treatment of the electronic structure of the Cy+I- system with the recent dielectric continuum approach which accounts for the solvation effects. For a given solute/solvent system the probability function P(R), which describes the distribution of interionic separations, is constructed in terms of the PMFs and implemented for the evaluation of the Kass.

Odinokov, A. V.; Basilevsky, M. V.; Nikitina, E. A.

2011-10-01

161

The Analysis of the Atomic Pair Distribution Function of Pmn-Based Nanopowders by X-Ray Diffraction  

NASA Astrophysics Data System (ADS)

The three-dimensional atomic-scale structure around Mg, Nb, Ti and Zr atoms in a series ferroelectric material such as PMN, PZT, PMN-PZT and PMN-PT has been studied using X-ray diffraction (MoK?), Rietveld refinement and the atomic pair distribution function (PDF) technique. The structure and particle size of the powders was determined by X-ray diffraction and TEM observation. The studies show that the materials are disordered at nanometer length distances. The three-dimensional atomic ordering in PMN-based nanopowders may well be described by a cubic structure of the perovskite type, similar to that occurring in the bulk crystals. At the end, the analyzed data show that the sizes of ZrO6 octahedral are larger than TiO6 octahedral.

Ghasemifard, M.; Khorrami, Gh. H.

162

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

PubMed

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

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

2013-06-14

163

A widely distributed putative mammalian transcriptional regulator containing multiple paired amphipathic helices, with similarity to yeast SIN3  

SciTech Connect

The mammalian Sin3 gene (mSin3) encodes four paired amphipathic helix (PAH) motifs, three of which and an extended region beyond PAH3 share between 59 and 70% sequence similarity with the yeast transcriptional regulator, SIN3. However, mSin3/SIN3 fusion proteins were not able to substitute for the yeast molecule in complementation assays. Transcripts encoding this putative transcriptional regulator, which maps to human chromosome 15q24, were detected in multiple mouse tissues, with highest levels seen in testis, lung, and thymus. Its wide tissue distribution suggests that mSin3, like yeast SIN3, may regulate the transcription of multiple genes. 12 refs., 2 figs.

Halleck, M.S. [Pennsylvania State Univ., University Park, PA (United States)] [Pennsylvania State Univ., University Park, PA (United States); Pownall, S.; Harder, K.W. [Univ. of British Columbia, Vancouver (Canada)] [and others] [Univ. of British Columbia, Vancouver (Canada); and others

1995-03-20

164

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

SciTech Connect

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

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

2011-03-15

165

Neutron-Proton Pairing Correlation for the Rotational Motion of N = Z 72Kr, 76Sr, and 80Zr Nuclei  

NASA Astrophysics Data System (ADS)

The high-spin state properties of the neutron-proton (np) residual effective interaction are analyzed in N = Z 72Kr, 76Sr, and 80Zr nuclei. The self-consistent microscopic Hartree-Fock-Bogoliubov (HFB) equations have been solved by employing monopole corrected two-body effective interaction. A band crossing is observed in 72Kr nucleus at J = 14? state with monopole corrected "HPU1" and "HPU2" effective interactions. The VAP-HFB theory suggests that the "4p-4h" excitations by np residual interaction are the essential ingredients of the mean-field description of the occurence of backbending in 72Kr nucleus.

Roy, Prianka; Dhiman, Shashi K.

166

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

167

Cosmogenic {sup 36}Cl accumulation in unstable landforms 1. Effects of the thermal neutron distribution  

SciTech Connect

Cosmogenic nuclides produced in situ within minerals at the surface of the Earth are proving to be an effective means of assessing geomorphic histories. The use of multiple cosmogenic nuclides permits both exposure times and erosion rates to be determined. However, if two nuclides are produced only by spallation reactions, the systematic differences in their accumulation rates depend only on the differences in their production rates and half-lives. The relatively small differences that result require a high degree of analytical precision to yield useful results. In contrast to other spallogenic nuclides, {sup 36}Cl is also produced by low-energy neutron, absorption, which creates a different pattern of production as a function of depth. We have measured the thermal flux with depth in a concrete block using {sup 3}He-filled neutron detectors. The measured thermal neutron profile agrees well with predictions from a simple diffusion-based thermal neutron distribution model. Calculations of {sup 36}Cl production using the model suggest that the use of {sup 36}Cl along with a purely spallogenic nuclide to determine erosion rates and exposure times should be less sensitive to analytical error than are determinations from two purely spallogenic nuclides. 31 refs., 7 figs., 3 tabs.

Liu, B.; Phillips, F.M.; Stone, W.D. [New Mexico Tech., Socorro, NM (United States)] [New Mexico Tech., Socorro, NM (United States); Fabryka-Martin, J.T.; Fowler, M.M. [Los Alamos National Lab., NM (United States)] [Los Alamos National Lab., NM (United States)

1994-11-01

168

Mass distributions for monoenergetic-neutron-induced fission of 235U  

NASA Astrophysics Data System (ADS)

Fission product yields for 37 masses were determined for the fission of 235U with essentially monoenergetic neutrons of 0.17, 0.55, 1.0, 2.0, 4.0, 5.5, 6.3, 7.1, and 8.1 MeV. Fission product activities were measured by Ge(Li) ?-ray spectrometry of irradiated 235U targets and by chemical separation of the fission product elements followed by ? counting and/or ?-ray spectrometry. The mass-yield data show a sensitive increase of fission yields in the near symmetric mass region (valley) with increasing incident neutron energy En (peak-to-valley ratio decreasing from 590 to 13) over the range of 0.17 to 8.1 MeV with only small changes in yields in other regions of the mass distribution. Curves of valley yields as a function of En display a flat step in the region of second-chance fission (above ~6 MeV) where the excitation energy is lowered by competition with neutron evaporation prior to fission. Comparison is made with monoenergetic-neutron-induced fission of 238U. NUCLEAR REACTIONS, FISSION 235O(n,f), En=0.17, 0.55, 1.0, 2.0, 4.0, 5.5, 6.3, 7.1, and 8.1 MeV; measured mass yields.

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

1981-12-01

169

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

Microsoft Academic Search

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

N Takenaka; H Asano; T Fujii; M Matsubayashi

1998-01-01

170

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

171

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

172

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

NASA Astrophysics Data System (ADS)

Reaction cross sections (?) for 11Be and 8B on proton targets at 50A˜120AMeV have been measured to distinguish between the proton- and neutron- density distributions at the nuclear surface. The ? is connected with the nucleon density distributions by the Glauber theory. Since the nucleon-nucleon total cross sections in that energy region have a large isospin dependence, the ? on proton targets should have a large difference between the proton and neutron in the halo structure. The experimental ? on proton targets are in good agreement with the calculated ones assuming that the tail dominantly consists of a neutron for 11Be and a proton for 8B.

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

2010-03-01

173

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

174

Neutron density distributions of Pb204,206,208 deduced via proton elastic scattering at Ep=295 MeV  

NASA Astrophysics Data System (ADS)

Cross sections and analyzing powers for polarized proton elastic scattering from Ni58, and Pb204,206,208 were measured at intermediate energy Ep=295 MeV. An effective relativistic Love-Franey interaction is tuned to reproduce Ni58 scattering data within the framework of the relativistic impulse approximation. The neutron densities of the lead isotopes are deduced using model-independent sum-of-Gaussians distributions. Their error envelopes are estimated by a new ?2 criterion including uncertainties associated with the reaction model. The systematic behaviors of extracted error envelopes of the neutron density distributions in Pb204,206,208 are presented. The extracted neutron and proton density distribution of Pb208 gives a neutron skin thickness of ?rnp=0.211-0.063+0.054 fm.

Zenihiro, J.; Sakaguchi, H.; Murakami, T.; Yosoi, M.; Yasuda, Y.; Terashima, S.; Iwao, Y.; Takeda, H.; Itoh, M.; Yoshida, H. P.; Uchida, M.

2010-10-01

175

Speciation of As(III) and As(V) in water and sediment using reverse-phase ion-pair high-performance liquid chromatography-neutron activation analysis (HPLC-NAA).  

PubMed

Total As content and the As species distribution in water and sediments from the Kwabrafo stream, a major water body draining the Obuasi gold mining community in southwestern Ghana, have been investigated. Total As content was determined by instrumental neutron activation analysis (INAA). Ion-pair reverse phase high-performance liquid chromatography-neutron activation analysis (HPLC-NAA) was used for speciation of As species. Solid phase extraction with phosphate buffer was used to extract soluble As species from lyophilized sediment. The mass balance after phosphate extraction of soluble As species in sediment varied from 89 to 96 %. Compositionally appropriate reference material International Atomic Energy Agency (IAEA)-Lake Sediment (SL)-1 was used to check the validity of INAA method for total As determination. The measured values are in good agreement with the IAEA recommended value and also within the 95 % confidence interval. The accuracy of the measurement in terms of relative deviation from the IAEA recommended value was ±0.83 %. "In-house" prepared As(III) and As(V) standards were used to validate the HPLC-INAA method used for the As species determination. Total As concentration in the water samples ranged from 1.15 to 9.20 mg/L. As(III) species in water varied from 0.13 to 0.7 mg/L, while As(V) species varied from 0.79 to 3.85 mg/L. Total As content in sediment ranged from 2,134 to 3,596 mg/kg dry mass. The levels of As(III) and As(V) species in the sediment ranges from 138 to 506 mg/kg dry mass and 156 to 385 mg/kg dry mass, respectively. PMID:23494192

Tulasi, Delali; Adotey, Dennis; Affum, Andrews; Carboo, Derick; Serfor-Armah, Yaw

2013-10-01

176

Extracting the pair distribution function of liquids and liquid-vapor surfaces by grazing incidence x-ray diffraction mode  

SciTech Connect

We show that the structure factor S(q) of water can be obtained from x-ray synchrotron experiments at grazing angle of incidence (in reflection mode) by using a liquid surface diffractometer. The corrections used to obtain S(q) self-consistently are described. Applying these corrections to scans at different incident beam angles (above the critical angle) collapses the measured intensities into a single master curve, without fitting parameters, which within a scale factor yields S(q). Performing the measurements below the critical angle for total reflectivity yields the structure factor of the top most layers of the water/vapor interface. Our results indicate water restructuring at the vapor/water interface. We also introduce a new approach to extract g(r), the pair distribution function (PDF), by expressing the PDF as a linear sum of error functions whose parameters are refined by applying a nonlinear least square fit method. This approach enables a straightforward determination of the inherent uncertainties in the PDF. Implications of our results to previously measured and theoretical predictions of the PDF are also discussed.

Vaknin, D.; Bu, W.; Travesset, A. (Iowa State)

2008-08-01

177

Study of the transmembrane potential distribution of cell pairs in a microfluidic device using polymer obstacles to initiate electrofusion  

NASA Astrophysics Data System (ADS)

In this paper, we investigate the different parameters that affect the distribution of the transmembrane potential of cells brought into contact before electrofusion in a miniaturized fluidic device. In particular, we discuss the deviation of the effective transmembrane voltage compared to the one predicted by Schwan's law. The application of electric field pulses to biological cells induces a transmembrane potential which leads to cell permeabilization. Electrofusion occurs when several cells are brought into contact while they are electropermeabilized. Nevertheless, we show that in this case, the mutual presence of cells interferes on Schwan's equation. Consequently, the transmembrane voltage at the cell contacting point is drastically reduced, which is not favorable for an electrofusion in smooth conditions, as the applied voltage needs to be increased to compensate this phenomenon. We show that the introduction of polymer obstacles reverses this trend, as the high electric field region is focused on the fusion zone. To confirm the theory we developed, quantitative biological experiments are presented in which murine melanoma cells were paired and fused in both conditions (with and without obstacles).

Sihem Hamdi, Feriel; Français, Olivier; Subra, Frédéric; Wang, Wei; Woytasik, Marion; Dufour-Gergam, Elisabeth; Le Pioufle, Bruno

2013-04-01

178

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

179

Charge distribution in the reactor-neutron-induced fission of /sup 232/Th  

SciTech Connect

The independent yields of /sup 82/Br, /sup 86/Rb, /sup 96/Nb, /sup 98/Nb /sup m/, /sup 128/Sb /sup q/, and /sup 136/Cs were determined in the reactor-neutron-induced fission of /sup 232/Th using radiochemical techniques. Results: (2.3 +- 2.3) x 10/sup -4ts/% for /sup 82/Br, <3.8 x 10/sup -4ts/% for /sup 86/Rb, <4.2 x 10/sup -5ts/% for /sup 96/Nb, (2.48 +- 0.53) x 10/sup -3/ % for /sup 98/Nb /sup m/, (2.34 +- 0.37) x 10/sup -3ts/% for /sup 128/Sb /sup g/, and (1.70 +- 0.13) x 10/sup -4ts/% for /sup 136/Cs. Using the extended Zp model of Wahl with the yield data from this work and the literature the following parameters were obtained for the charge distribution in /sup 232/Th fission: Width of Gaussian dispersion sigma-bar/sub Z/ = 0.52 +- 0.01, ..delta..Z/sub P/ ( = Z/sub P/-Z/sub UCD/) = 0.45 +- 0.02. The even-odd proton and neutron enhancement factors were found to be small. These parameters and systematics of even-odd proton and neutron effects in low energy fission are discussed.

Erten, H.N.; Gruetter, A.; Roessler, E.; Von Gunten, H.R.

1982-05-01

180

Charge distribution in the reactor-neutron-induced fission of 232Th  

NASA Astrophysics Data System (ADS)

The independent yields of 82Br, 86Rb, 96Nb, 98Nbm, 128Sbg, and 136Cs were determined in the reactor-neutron-induced fission of 232Th using radiochemical techniques. Results: (2.3+/-2.3)×10-4% for 82Br, <3.8×10-4% for 86Rb, <4.2×10-5% for 96Nb, (2.48+/-0.53)×10-3% for 98Nbm, (2.34+/-0.37)×10-3% for 128Sbg, and (1.70+/-0.13) ×10-4% for 136Cs. Using the extended Zp model of Wahl with the yield data from this work and the literature the following parameters were obtained for the charge distribution in 232Th fission: width of Gaussian dispersion ?¯Z=0.52+/-0.01, ?ZP (=ZP-ZUCD)=0.45+/-0.02. The even-odd proton and neutron enhancement factors were found to be small. These parameters and systematics of even-odd proton and neutron effects in low energy fission are discussed. NUCLEAR REACTIONS, FISSION Radiochemical fission yields 232Th(n,f), calculated charge dispersion parameters, and odd-even effects.

Erten, H. N.; Grütter, A.; Rössler, E.; von Gunten, H. R.

1982-05-01

181

Angular distributions of low-energy neutrons from 390-MeV/nucleon Ne+Pb collisions  

SciTech Connect

Multiplicity-selected angular distributions of low-energy neutrons from collisions of 390 MeV/nucleon Ne+Pb are peaked forward, in contrast to relatively flat distributions of protons from Ne+U. A model that includes both Coulomb repulsion and composite-fragment formation accounts for the neutron and proton distributions, and the dependence on nucleon energy of the n/p ratio of inclusive cross sections. This comparison casts doubt on the interpretation of the suppression of forward proton emission as a signal of collective flow.

Madey, R.; Varga, J.; Fai, G.; Barghouty, A.F.; Anderson, B.D.; Baldwin, A.R.; Cecil, R.; Watson, J.W.; Westfall, G.D.

1986-10-01

182

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

PubMed

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

Cho, Hyung Min; Chu, Jhih-Wei

2009-10-01

183

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

Microsoft Academic Search

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

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

2011-01-01

184

Instrumental neutron activation analysis in the measurement of trace element distribution at two coal conversion plants  

SciTech Connect

Instrumental neutron activation analysis was used to study the elemental concentration in the complex materials produced by the H-Coal process and the low Btu gasification process at the University of Minnesota at Duluth (UMD). Trace element distribution in feed coal, ash, cyclone fines, and ESP tar were determined in the UMD gasifier. Trace element distribution in feed coal and vacuum bottoms were determined for the H-Coal liquefaction pilot plant. The results were compared. Elements measured were: Al, Sb, As, Ba, Br, Ca, Ce, Cs, Cl, Cr, Co, Eu, Ga, Hf, Fe, La, Mg, Mn, Mo, K, Rb, Sm, Sc, Se, Na, Ta, Th, Ti, W, U, V, Yb, and Zn. 11 references, 1 table (DMC)

Roseberry, L.M.; Dyer, F.F.

1984-01-01

185

Evaluation of the uncertainties in the source distribution for pressure vessel neutron fluence calculations  

SciTech Connect

The methodology used to prepare the source for neutron fluence calculation at the reactor pressure vessel is examined, and its effect on the calculated cavity dosimeter reaction rate is evaluated. Different source distributions for the Three Mile Island Unit 1 and Davis-Besse reactors and a simulated low low-leakage loading pattern are analyzed based on different levels of homogenization, different isotopic averaging approaches, contribution of {sup 238}U, use of the LEPRICON C factor formulation, and the SAILOR spectrum. Fuel isotopics can significantly affect the source distributions (through the fission spectrum), thereby leading to uncertainties of {approximately}7% in the calculated cavity dosimetry reaction rates. Higher uncertainties (>10%) are expected due to both the C factor and fission spectrum when the low low-leakage fuel designs are utilized.

Haghighat, A.; Mahgerefteh, M.; Petrovic, B.G. [Pennsylvania State Univ., University Park, PA (United States). Nuclear Engineering Dept.

1995-01-01

186

Crystallographic Characterization: 3D Mapping of Crystallographic Phase Distribution using Energy-Selective Neutron Tomography (Adv. Mater. 24/2014).  

PubMed

On page 4069, D. Penumadu and co-workers describe studies involving non-destructive 3D mapping of crystallographic phases in stainlesssteel samples. The background of the image shows a digitally altered neutron-radiograph of the phase transformed tensile and torsion samples. Photographs of the specimen and the reconstructed neutron-tomography data, revealing the crystallographic phase fraction distribution, are also shown. PMID:24946996

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

2014-06-01

187

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

NASA Astrophysics Data System (ADS)

A polymer electrolyte fuel cell (PEFC) consists of a membrane electrode assembly (MEA), gas diffusion layers (GDL), hydrogen and oxygen supply channels. At the anode, protons and electrons are generated, while at the cathode the protons and electrons combine to form water. The condensed water may affect the fuel cell performance. In order to clarify the effect of water distribution on the PEFC performance, three-dimensional water distribution in the PEFC was visualized by using a neutron radiography facility at JRR-3 in JAEA. For observing the detailed water distribution, a small sized PEFC was designed. Size of the gas channel is 1 mm width and 0.5 mm depth. Thickness of the MEA and the GDL are about 50 and 200 ?m. The electrode area is 0.35×3.5 cm 2. The PEFC was set on an automatic rotating stage, and a picture was taken every 2.25° by using a cooled CCD camera with grey scale of 16 bit. The exposure time was set at 15 s. Using the 80 pictures which correspond to 180°, a computed tomography (CT) was carried out. In order to observe water distribution with high spatial resolution, the LiF scintillator with a thickness of 50 ?m was used. From the water distributions parallel and perpendicular to the MEA, existence of water around O-ring can be confirmed. However, the detailed distribution in the PEFC is difficult to obtain from the two-dimensional pictures. On the other hand, CT pictures make possible to obtain the three-dimensional water distribution. In this study, the spatial resolution of 76.5 ?m was achieved, and existence of water in the PEFC could be confirmed.

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

2009-06-01

188

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

189

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

SciTech Connect

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

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

2007-01-01

190

Neutron Capture from ^87Sr  

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

191

Analysis of neutron flux distribution for the validation of computational methods for the optimization of research reactor utilization.  

PubMed

In order to verify and validate the computational methods for neutron flux calculation in TRIGA research reactor calculations, a series of experiments has been performed. The neutron activation method was used to verify the calculated neutron flux distribution in the TRIGA reactor. Aluminium (99.9 wt%)-Gold (0.1 wt%) foils (disks of 5mm diameter and 0.2mm thick) were irradiated in 33 locations; 6 in the core and 27 in the carrousel facility in the reflector. The experimental results were compared to the calculations performed with Monte Carlo code MCNP using detailed geometrical model of the reactor. The calculated and experimental normalized reaction rates in the core are in very good agreement for both isotopes indicating that the material and geometrical properties of the reactor core are modelled well. In conclusion one can state that our computational model describes very well the neutron flux and reaction rate distribution in the reactor core. In the reflector however, the accuracy of the epithermal and thermal neutron flux distribution and attenuation is lower, mainly due to lack of information about the material properties of the graphite reflector surrounding the core, but the differences between measurements and calculations are within 10%. Since our computational model properly describes the reactor core it can be used for calculations of reactor core parameters and for optimization of research reactor utilization. PMID:20855215

Snoj, L; Trkov, A; Ja?imovi?, R; Rogan, P; Zerovnik, G; Ravnik, M

2011-01-01

192

Determination of the magnetization distribution in Cr2O3 using spherical neutron polarimetry  

NASA Astrophysics Data System (ADS)

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

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

2002-03-01

193

The spectral energy distributions of isolated neutron stars in the resonant cyclotron scattering model  

NASA Astrophysics Data System (ADS)

The X-ray dim isolated neutron stars (XDINSs) are peculiar pulsar-like objects, characterized by their very well Planck-like spectrum. In studying their spectral energy distributions, the optical/UV excess is a long standing problem. Recently, Kaplan et al. (2011) have measured the optical/UV excess for all seven sources, which is understandable in the resonant cyclotron scattering (RCS) model previously addressed. The RCS model calculations show that the RCS process can account for the observed optical/UV excess for most sources. The flat spectrum of RX J2143.0+0654 may due to contribution from bremsstrahlung emission of the electron system in addition to the RCS process.

Tong, Hao; Xu, Renxin

2013-03-01

194

The observed neutron star mass distribution as a probe of the supernova explosion mechanism  

NASA Astrophysics Data System (ADS)

The observed distribution of neutron star (NS) masses reflects the physics of core-collapse supernova explosions and the structure of the massive stars that produce them at the end of their evolution. We present a Bayesian analysis that directly compares the NS mass distribution observed in double NS systems to theoretical models of NS formation. First, we find that models with standard binary mass ratio distributions are strongly preferred over independently picking the masses from the initial mass function, although the strength of the inference depends on whether current assumptions for identifying the remnants of the primary and secondary stars are correct. Secondly, NS formation models with no mass fallback are favoured because they reduce the dispersion in NS masses. The double NS system masses thus directly point to the mass coordinate where the supernova explosion was initiated, making them an excellent probe of the supernova explosion mechanism. If we assume no fallback and simply vary the mass coordinate separating the remnant and the supernova ejecta, we find that for solar metallicity stars the explosion most likely develops at the edge of the iron core at a specific entropy of S/NA? 2.8 kB. The primary limitations of our study are the poor knowledge of the supernova explosion mechanism and the lack of broad range of supernova model explosions of Large Magellanic Cloud to solar metallicity.

Pejcha, Ond?ej; Thompson, Todd A.; Kochanek, Christopher S.

2012-08-01

195

Internal Stress Distribution Measurement of TIG Welded SUS304 Samples Using Neutron Diffraction Technique  

NASA Astrophysics Data System (ADS)

The distribution of residual stress of SUS304 samples that were undergone TIG welding process with four different electric currents has been measured. The welding has been done in the middle part of the samples that was previously grooved by milling machine. Before they were welded the samples were annealed at 650 degree Celsius for one hour. The annealing process was done to eliminate residual stress generated by grooving process so that the residual stress within the samples was merely produced from welding process. The calculation of distribution of residual stress was carried out by measuring the strains within crystal planes of Fe(220) SUS304. Strain, Young modulus, and Poisson ratio of Fe(220) SUS304 were measured using DN1-M neutron diffractometer. Young modulus and Poisson ratio of Fe(220) SUS304 sample were measured in-situ. The result of calculations showed that distribution of residual stress of SUS304 in the vicinity of welded area is influenced both by treatments given at the samples-making process and by the electric current used during welding process.

Muslih, M. Refai; Sumirat, I.; Sairun; Purwanta

2008-03-01

196

Measurements of water distribution in through-plane direction of PEFC by using neutron radiography  

NASA Astrophysics Data System (ADS)

Fuel gas (hydrogen gas) and oxidant gas (air) are supplied to a polymer electrolyte fuel cell (PEFC). Protons pass through the electrolyte membrane, and combine with oxygen to form water in the cathode reaction site. The generated water must be supplied appropriately to the membrane for proton conduction. On the other hand, the generated water may affect the fuel cell performances because of the blocking of oxygen from reaching the cathode reaction site. Therefore, water management in the PEFC is important, and water distribution during the operation in the through-plane direction has been of wide concern. In order to obtain the water distributions in a membrane electrode assembly (MEA) and a gas diffusion layer (GDL), a borescope system was newly employed using neutron radiography. The system could obtain the water distribution in the MEA and the GDL, and pixel size of 6.5 ?m was achieved. Furthermore, the system was applied for a tilted converter system. The pixel of 1.0 ?m at an angle of 81° was achieved, and improvement of the spatial resolution was confirmed.

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

2011-09-01

197

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

198

A benchmark analysis of radiation flux distribution for Boron Neutron Capture Therapy of canine brain tumors  

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 work describes 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 tissues of interest. The resulting geometry and tissue composition data were then used to construct a detailed heterogeneous calculational model of the Labrador Retriever head. Calculations of three-dimensional radiation flux distributions pertinent to BNCT were performed for the 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 the 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.

1992-02-01

199

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

200

Neutron angular and energy distributions from 710MeV alphas stopping in water, carbon, steel, and lead, and 640MeV alphas stopping in lead  

Microsoft Academic Search

We measured neutron angular and energy distributions from 710-MeV alphas stopping in targets of water, carbon, steel, and lead for neutron energies from 3 MeV to above 300 MeV. We also measured neutron spectra from 640-MeV alphas stopping in lead. These spectra are similar to the 710-MeV spectra but are reduced in magnitude by about 20 percent. The angular distributions

R. A. Cecil; B. D. Anderson; A. R. Baldwin; R. Madey; A. Galonsky; P. Miller; L. Young; F. M. Waterman

1980-01-01

201

Neutron multiplicity distributions for 200 MeV proton-, deuteron- and 4He-induced spallation reactions in thick Pb targets  

Microsoft Academic Search

Inclusive neutron multiplicity distributions associated with 197MeV proton-, 188MeV deuteron- and 214MeV 4 He-induced spallation reactions on thick (l=2–25cm) Pb targets are presented, together with distributions associated with nuclear-reaction events. The mean neutron multiplicity per incident particle, n\\/p, which is a crucial parameter for applications on accelerator-driven neutron sources, has been obtained for various conditions. For the thickest targets used

B. Lott; F. Cnigniet; J. Galin; F. Goldenbaum; D. Hilscher; A. Liénard; A. Péghaire; Y. Périer; X. Qian

1998-01-01

202

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

Microsoft Academic Search

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

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

2002-01-01

203

Distribution of transport current in a type-II superconductor studied by small-angle neutron scattering.  

PubMed

We report small-angle neutron scattering measurements on the vortex lattice in a PbIn polycrystal in the presence of an applied current. Using the rocking curves as a probe of the distribution of current in the sample, we observe that vortex pinning is due to the surface roughness. This leads to a surface current that persists in the flux-flow region. We show the influence of surface treatments on the distribution of this current. PMID:12633451

Pautrat, A; Goupil, C; Simon, Ch; Charalambous, D; Forgan, E M; Lazard, G; Mathieu, P; Brûlet, A

2003-02-28

204

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

SciTech Connect

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

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

2010-09-14

205

Invariant Mass Distribution of Jet Pairs Produced in Association with a W Boson in pp Collisions at {radical}(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{sup -1}. The observed distribution has an excess in the 120-160 GeV/c{sup 2} 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.; Brucken, E.; Devoto, F.; Mehtala, P.; Orava, R. [Division of High Energy Physics, Department of Physics, University of Helsinki and Helsinki Institute of Physics, FIN-00014, Helsinki (Finland); Alvarez Gonzalez, B.; Casal, B.; Cuevas, J.; Gomez, G.; Palencia, E.; Rodrigo, T.; Ruiz, A.; Scodellaro, L.; Vila, I.; Vilar, R.; Vizan, J. [Instituto de Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander (Spain); Amerio, S.; Dorigo, T.; Totaro, P. [Istituto Nazionale di Fisica Nucleare, Sezione di Padova-Trento, I-35131 Padova (Italy); Amidei, D. [University of Michigan, Ann Arbor, Michigan 48109 (United States)

2011-04-29

206

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

207

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

NASA Astrophysics Data System (ADS)

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

Ji, Wei

208

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

SciTech Connect

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

Sarriguren, P. [Instituto de Estructura de la Materia, CSIC, Serrano 123, E-28006 Madrid (Spain); Gaidarov, M. K. [Instituto de Estructura de la Materia, CSIC, Serrano 123, E-28006 Madrid (Spain); Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Sofia 1784 (Bulgaria); Moya de Guerra, E. [Departamento de Fisica Atomica, Molecular y Nuclear, Facultad de Ciencias Fisicas, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Antonov, A. N. [Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Sofia 1784 (Bulgaria)

2008-05-12

209

Gamow-Teller Strength Distributions for Solar Neutrino Detectors via the (proton, Neutron) Reaction.  

NASA Astrophysics Data System (ADS)

The Gamow-Teller transition strengths, denoted B(GT)_{rm N}, of several proposed solar neutrino (nu_ {{e}-}) detectors (i.e. ^{71}{rm Ga}, ^{81}{rm Br} and ^{205}{rm Tl}) for absorptions into excited final nuclear states were previously unknown. Electron capture decay studies can provide values of B(GT)_{rm N} for nu_{{e}-} absorptions into individual states, but are often limited by short initial state lifetimes to ground or low-lying state transitions. This restriction is avoided through the use of intermediate energy (p,n) reactions. Zero degree differential cross sections for such reactions can be related to the B(GT)_ {rm N} transition strengths. High resolution neutron time-of-flight measurements using {rm E_ {p}} = 120 and 200 MeV were performed on (p,n) reactions at the Indiana University Cyclotron Facility (IUCF). At the lower energy, a four point angular distribution ( theta_{rm lab} = 0 ^circ, 2.5^circ , 5.2^circ and 9.4 ^circ) of differential cross section was obtained for ^{71}Ga by using the IUCF beam swinger. Similarly, three point angular distributions (theta_{ rm lab} = 0^circ , 5^circ and 9.8 ^circ) were obtained for ^ {81}Br and ^{205} Tl. These distributions were used to estimate and subtract non-GT components from the zero degree differential cross section spectra. Conversion of the remaining GT cross section to distributions of B(GT)_ {rm N} per excitation energy bin in the product nuclei was then accomplished through an energy dependent Fermi-to-Gamow-Teller strength ratio. For the first time, B(GT)_{rm N} distributions up to ~ 17 MeV in ^{71}Ge and ^{81}Kr, and ~ 21 MeV in ^{205}Pb have been deduced from experiment. Combining the deduced GT transition strengths with predicted standard solar model (SSM) neutrino fluxes leads to estimations of the neutrino detector capture rates. It is determined that the ^{81}Br detector is most sensitive to ^{8} B neutrinos and not those of ^{7 }Be, as previously believed. Transitions to final excited states reduces the SSM p-p neutrino sensitivity of the ^{71}Ga detector from 65% to 53% of its overall capture rate. In contrast, contributions to the overall neutrino capture rate due to allowed GT transitions for the ^{205 }Tl detector are found to be small.

Krofcheck, David

1987-09-01

210

Gadolinium neutron capture therapy  

Microsoft Academic Search

A computer study of the dose distribution for gadolinium neutron capture therapy is carried out to determine its feasibility. Gadolinium is a potential neutron capture therapy (NCT) agent that produces gamma radiation, conversion electrons, and Auger electrons. The dose distribution from neutrons, neutron-induced gammas, and the reaction products from neutron capture in gadolinium were modeled using the Los Alamos National

G. A. Jr. Miller; N. E. Hertel; B. W. Wehring; J. L. Horton

1993-01-01

211

Pairing correlations in exotic nuclei  

NASA Astrophysics Data System (ADS)

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

Sagawa, H.; Hagino, K.

2013-02-01

212

Estimation of angular distribution of neutron dose using time-of-flight for 19 F + Al system at 110 MeV  

Microsoft Academic Search

We have reported measured angular and energy distributions of neutron dose from 110MeV 19F projectiles bombarding a thick aluminum target. The measurements are carried out with BC501 liquid scintillator detector using the time-of-flight technique. We have measured neutron energy distributions at 0?, 30?, 60?, 90?, and 120? and converted them to dose distributions using the ICRP recommended fluence to ambient

Maitreyee Nandy; C. Sunil; Moumita Maiti; R. Palit; P. K. Sarkar

2007-01-01

213

Plans for a collaboratively developed distributed control system for the Spallation Neutron Source  

Microsoft Academic Search

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 ion source followed by a 2.5 MeV RFQ; a 1 GeV linac; a storage ring; a 1 MW spallation neutron target (upgradeable to 2 MW); the conventional facilities

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

1999-01-01

214

Neutron Beam Spectrometer Studies of Boron, Cadmium, and the Energy Distribution from Paraffin  

Microsoft Academic Search

A slow neutron velocity selector has been developed for use with the Columbia University cyclotron. By the method of arc modulation, neutron production is usually confined to intervals of (10-200) microseconds out of a (1000-10,000) microsecond cycle. Neutrons slowed down in paraffin are detected by BF3 proportional counters. Excellent collimation is obtained by using an extensive B4C and Cd collimating

James Rainwater; William W. Havens

1946-01-01

215

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

216

Validation of absolute axial neutron flux distribution calculations with MCNP with 197Au(n,?)198Au reaction rate distribution measurements at the JSI TRIGA Mark II reactor.  

PubMed

The calculation of axial neutron flux distributions with the MCNP code at the JSI TRIGA Mark II reactor has been validated with experimental measurements of the (197)Au(n,?)(198)Au reaction rate. The calculated absolute reaction rate values, scaled according to the reactor power and corrected for the flux redistribution effect, are in good agreement with the experimental results. The effect of different cross-section libraries on the calculations has been investigated and shown to be minor. PMID:24316530

Radulovi?, Vladimir; Štancar, Žiga; Snoj, Luka; Trkov, Andrej

2014-02-01

217

Pulsar Pair Cascades in Magnetic Fields with Offset Polar Caps  

NASA Technical Reports Server (NTRS)

Neutron star magnetic fields may have polar caps (PC) 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) approximates 10(exp -3) L(sub sd) for normal pulsars and L(sub pair) approximates 10(exp -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.

2012-01-01

218

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

219

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

220

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

221

Two-dimensional pair distribution functions from synchrotron x-ray data: Application to an Al-Cu-Co decagonal quasicrystal  

SciTech Connect

A new method is developed to study the atomic structure of layered materials by a two-dimensional atomic pair distribution function (2D-PDF) analysis. Using synchrotron x-ray scattering, this method is applied to the study of an Al[sub 65]Cu[sub 15]Co[sub 20] single decagonal quasicrystal. The obtained 2D-PDF's are in excellent agreement with those calculated from a recently proposed structure model based on decagonal cluster packing. However, additional short-range structure is found by analyzing the diffuse scattering intensity. A modification of the model is proposed to explain this short-range structure.

He, Y.; Hu, R.; Egami, T.; Poon, S.J.; Shiflet, G.J. (Department of Physics, University of Virginia, Charlottesville, Virginia 22901 (United States) Department of Materials Science and Engineering and Laboratory for Research on Structures of Materials, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6272 (United States) Department of Materials Science, University of Virginia, Charlottesville, Virginia 22901 (United States))

1993-04-19

222

Dense-medium modifications to jet-induced hadron pair distributions in Au+Au collisions at sqrt s NN=200 GeV.  

PubMed

Azimuthal correlations of jet-induced high-p(T) charged hadron pairs are studied at midrapidity in Au+Au collisions at sqrt[s(NN)]=200 GeV. The distribution of jet-associated partner hadrons (1.0

Adler, S S; Afanasiev, S; Aidala, C; Ajitanand, N N; Akiba, Y; Alexander, J; Amirikas, R; Aphecetche, L; Aronson, S H; Averbeck, R; Awes, T C; Azmoun, R; Babintsev, V; Baldisseri, A; Barish, K N; Barnes, P D; Bassalleck, B; Bathe, S; Batsouli, S; Baublis, V; Bazilevsky, A; Belikov, S; Berdnikov, Y; Bhagavatula, S; Boissevain, J G; Borel, H; Borenstein, S; Brooks, M L; Brown, D S; Bruner, N; Bucher, D; Buesching, H; Bumazhnov, V; Bunce, G; Burward-Hoy, J M; Butsyk, S; Camard, X; Chai, J-S; Chand, P; Chang, W C; Chernichenko, S; Chi, C Y; Chiba, J; Chiu, M; Choi, I J; Choi, J; Choudhury, R K; Chujo, T; Cianciolo, V; Cobigo, Y; Cole, B A; Constantin, P; d'Enterria, D; David, G; Delagrange, H; Denisov, A; Deshpande, A; Desmond, E J; Devismes, A; Dietzsch, O; Drapier, O; Drees, A; du Rietz, R; Durum, A; Dutta, D; Efremenko, Y V; El Chenawi, K; Enokizono, A; En'yo, H; Esumi, S; Ewell, L; Fields, D E; Fleuret, F; Fokin, S L; Fox, B D; Fraenkel, Z; Frantz, J E; Franz, A; Frawley, A D; Fung, S-Y; Garpman, S; Ghosh, T K; Glenn, A; Gogiberidze, G; Gonin, M; Gosset, J; Goto, Y; Granier de Cassagnac, R; Grau, N; Greene, S V; Grosse Perdekamp, M; Guryn, W; Gustafsson, H-A; Hachiya, T; Haggerty, J S; Hamagaki, H; Hansen, A G; Hartouni, E P; Harvey, M; Hayano, R; Hayashi, N; He, X; Heffner, M; Hemmick, T K; Heuser, J M; Hibino, M; Hill, J C; Holzmann, W; Homma, K; Hong, B; Hoover, A; Ichihara, T; Ikonnikov, V V; Imai, K; Isenhower, D; Ishihara, M; Issah, M; Isupov, A; Jacak, B V; Jang, W Y; Jeong, Y; Jia, J; Jinnouchi, O; Johnson, B M; Johnson, S C; Joo, K S; Jouan, D; Kametani, S; Kamihara, N; Kang, J H; Kapoor, S S; Katou, K; Kelly, S; Khachaturov, B; Khanzadeev, A; Kikuchi, J; Kim, D H; Kim, D J; Kim, D W; Kim, E; Kim, G-B; Kim, H J; Kistenev, E; Kiyomichi, A; Kiyoyama, K; Klein-Boesing, C; Kobayashi, H; Kochenda, L; Kochetkov, V; Koehler, D; Kohama, T; Kopytine, M; Kotchetkov, D; Kozlov, A; Kroon, P J; Kuberg, C H; Kurita, K; Kuroki, Y; Kweon, M J; Kwon, Y; Kyle, G S; Lacey, R; Ladygin, V; Lajoie, J G; Lebedev, A; Leckey, S; Lee, D M; Lee, S; Leitch, M J; Li, X H; Lim, H; Litvinenko, A; Liu, M X; Liu, Y; Maguire, C F; Makdisi, Y I; Malakhov, A; Manko, V I; Mao, Y; Martinez, G; Marx, M D; Masui, H; Matathias, F; Matsumoto, T; McGaughey, P L; Melnikov, E; Messer, F; Miake, Y; Milan, J; Miller, T E; Milov, A; Mioduszewski, S; Mischke, R E; Mishra, G C; Mitchell, J T; Mohanty, A K; Morrison, D P; Moss, J M; Mühlbacher, F; Mukhopadhyay, D; Muniruzzaman, M; Murata, J; Nagamiya, S; Nagle, J L; Nakamura, T; Nandi, B K; Nara, M; Newby, J; Nilsson, P; Nyanin, A S; Nystrand, J; O'Brien, E; Ogilvie, C A; Ohnishi, H; Ojha, I D; Okada, K; Ono, M; Onuchin, V; Oskarsson, A; Otterlund, I; Oyama, K; Ozawa, K; Pal, D; Palounek, A P T; Pantuev, V; Papavassiliou, V; Park, J; Parmar, A; Pate, S F; Peitzmann, T; Peng, J-C; Peresedov, V; Pinkenburg, C; Pisani, R P; Plasil, F; Purschke, M L; Purwar, A K; Rak, J; Ravinovich, I; Read, K F; Reuter, M; Reygers, K; Riabov, V; Riabov, Y; Roche, G; Romana, A; Rosati, M; Rosnet, P; Ryu, S S; Sadler, M E; Saito, N; Sakaguchi, T; Sakai, M; Sakai, S; Samsonov, V; Sanfratello, L; Santo, R; Sato, H D; Sato, S; Sawada, S; Schutz, Y; Semenov, V; Seto, R; Shaw, M R; Shea, T K; Shibata, T-A; Shigaki, K; Shiina, T; Silva, C L; Silvermyr, D; Sim, K S; Singh, C P; Singh, V; Sivertz, M; Soldatov, A; Soltz, R A; Sondheim, W E; Sorensen, S P; Sourikova, I V; Staley, F; Stankus, P W; Stenlund, E; Stepanov, M; Ster, A; Stoll, S P; Sugitate, T; Sullivan, J P; Takagui, E M; Taketani, A; Tamai, M; Tanaka, K H; Tanaka, Y; Tanida, K; Tannenbaum, M J; Tarján, P; Tepe, J D; Thomas, T L; Tojo, J; Torii, H; Towell, R S; Tserruya, I; Tsuruoka, H; Tuli, S K; Tydesjö, H; Tyurin, N; van Hecke, H W; Velkovska, J; Velkovsky, M; Veszprémi, V; Villatte, L; Vinogradov, A A; Volkov, M A; Vznuzdaev, E; Wang, X R; Watanabe, Y; White, S N; Wohn, F K; Woody, C L; Xie, W; Yang, Y; Yanovich, A; Yokkaichi, S; Young, G R; Yushmanov, I E; Zajc, W A; Zhang, C; Zhou, S; Zhou, S J; Zolin, L

2006-08-01

223

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

224

Measurement of the Pulse Height Distribution of a Lithium Glass Scintillator at Different Neutron Energies.  

National Technical Information Service (NTIS)

The shape of the pulse-height response of a lithium-glass scintillator detector to neutrons has been measured in the range of neutron energies from 33 eV to 1.170 MeV using time-of-flight techniques. The variation of the width and mean pulse height of the...

T. J. Haste

1978-01-01

225

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

Microsoft Academic Search

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

A. A. Smales; D. Mapper; K. F. Fouché

1967-01-01

226

Polarized and unpolarized {mu}-pair meson-induced Drell-Yan production and the pion distribution amplitude  

SciTech Connect

We present a detailed analysis of meson-induced massive lepton (muon) Drell-Yan production for the process {pi}{sup -}N{yields}{mu}{sup +}{mu}{sup -}X, considering both an unpolarized nucleon target and longitudinally polarized protons. Using a QCD framework, we focus on the angular distribution of {mu}{sup +}, 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}{sup +} distribution in the polarized case, relevant for the planned COMPASS experiment. QCD evolution is given particular attention in both considered cases.

Bakulev, A. P.; Stefanis, N. G.; Teryaev, O. V. [Bogoliubov Laboratory of Theoretical Physics, JINR, 141980 Dubna (Russian Federation); Institut fuer Theoretische Physik II, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Bogoliubov Laboratory of Theoretical Physics, JINR, 141980 Dubna (Russian Federation)

2007-10-01

227

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

228

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

Microsoft Academic Search

By means of polarized small-angle neutron scattering, we have resolved the long-standing challenge of determining the magnetization distribution in magnetic nanoparticles in absolute units. The reduced magnetization, localized in non-interacting nanoparticles, indicates strongly particle shape- dependent surface spin canting with a 0.3(1) and 0.5(1) nm thick surface shell of reduced magnetization found for ?9 nm nanospheres and ?8.5 nm nanocubes,

S Disch; E Wetterskog; R P Hermann; A Wiedenmann; U Vainio; G Salazar-Alvarez; L Bergström; Th Brückel

2012-01-01

229

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

230

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

SciTech Connect

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

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

2007-01-01

231

Structure determination of plagioclase (Labradorite): I. Al\\/Si distribution in an An66 (neutron diffraction): II. Superstructure of an An54 (X-ray diffraction)  

Microsoft Academic Search

The Al\\/Si distribution in a plagioclase An66 was determined using neutron diffraction. According to the results of neutron experiments and the extended theory of satellites the superstructure of an An54 was determined. The final R-value is 4.7% for all over 2540 reflections (Ra-ref.=2.8% and Re-ref.=21.4%).

M. Korekawa; W. Horst; T. Tagai; W. Joswig; H. R. Wenk

1979-01-01

232

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

233

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

PubMed

The distribution of bone calcium between morphologically identifiable cortical and trabecular bone obtained by dissection and quantitated by neutron activation analysis (NAA) is described. The skeleton of a female beagle dog was dissected into approximately 400 pieces and assayed for 49Ca produced in the University of California, Irvine TRIGA reactor. For each of the skeletal sections, we give the initial weight of the alcohol-fixed tissue, which includes cortical bone, trabecular bone, marrow, and cartilage, and a final tissue weight after the marrow and trabecular bone have been dissected away; total section and cortical section calcium weights are reported. The level of detail is represented, for example, by the vertebrae, which were divided into three parts (body, spine, and transverse processes) and by the long bones, which were divided into 10-12 parts such that characterization of the epiphysis, metaphysis, and diaphysis was accomplished. The median percentage cortical calcium values for cervical, thoracic, and lumbar vertebrae were 82%, 56%, and 66%, respectively; however, variation within these groups and among individual vertebral sections was about a factor of 2. For long bones, the median percentage cortical calcium varied from 90-100% in the midshaft to below 50% in the proximal and distal sections. The final calculated cortical tissue-to-calcium mass ratio (TCR) varied from about 4.5 for midshafts of the long bones to about 9 for thoracic vertebral bodies and indicated that the mineral fraction of cortical bone is not constant throughout the skeleton. The ratio of cortical to trabecular calcium in the skeleton was 79.6:20.4. PMID:3740463

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

1986-07-01

234

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...

235

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

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

236

Effect of adding Ar gas on the pulse height distribution of BF 3 -filled neutron detectors  

Microsoft Academic Search

Boron trifluoride (BF3) proportional counters are used as detectors for thermal neutrons. They are characterized by high neutron sensitivity and\\u000a good gamma discriminating properties. Most practical BF3 counters are filled with pure boron trifluoride gas enriched up to 96% 10B. But BF3 is not an ideal proportional counter gas. Worsening of plateau characteristics is observed with increasing radius due to

M. Padalakshmi; A. M. Shaikh

2008-01-01

237

Efiect of adding Ar gas on the pulse height distribution of BF3-fllled neutron detectors  

Microsoft Academic Search

Boron tri?uoride (BF3) proportional counters are used as detectors for ther- mal neutrons. They are characterized by high neutron sensitivity and good gamma dis- criminating properties. Most practical BF3 counters are fllled with pure boron tri?uoride gas enriched up to 96% 10B. But BF3 is not an ideal proportional counter gas. Worsening of plateau characteristics is observed with increasing radius

A M SHAIKH

238

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.

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

2014-01-01

239

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

SciTech Connect

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

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

2012-07-01

240

Neutron density distributions of {sup 204,206,208}Pb deduced via proton elastic scattering at E{sub p}=295 MeV  

SciTech Connect

Cross sections and analyzing powers for polarized proton elastic scattering from {sup 58}Ni, and {sup 204,206,208}Pb were measured at intermediate energy E{sub p}=295 MeV. An effective relativistic Love-Franey interaction is tuned to reproduce {sup 58}Ni scattering data within the framework of the relativistic impulse approximation. The neutron densities of the lead isotopes are deduced using model-independent sum-of-Gaussians distributions. Their error envelopes are estimated by a new {chi}{sup 2} criterion including uncertainties associated with the reaction model. The systematic behaviors of extracted error envelopes of the neutron density distributions in {sup 204,206,208}Pb are presented. The extracted neutron and proton density distribution of {sup 208}Pb gives a neutron skin thickness of {Delta}r{sub np}=0.211{sub -0.063}{sup +0.054} fm.

Zenihiro, J.; Sakaguchi, H.; Murakami, T.; Yosoi, M.; Yasuda, Y.; Terashima, S.; Iwao, Y. [Department of Physics, Kyoto University, Kyoto 606-8502 (Japan); Takeda, H. [RIKEN Nishina Center for Accelerator-Based Science, Wako, Saitama 351-0198 (Japan); Itoh, M.; Yoshida, H. P.; Uchida, M. [Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047 (Japan)

2010-10-15

241

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

242

Neutrino-nucleus coherent scattering as a probe of neutron density distributions  

NASA Astrophysics Data System (ADS)

Neutrino-nucleus coherent elastic scattering provides a theoretically appealing way to measure the neutron part of the associated form factor. We show, using an expansion of the form factor into moments, that neutrinos from stopped muons can probe not only the second moment of the form factor (the neutron radius) but also the fourth moment. Using simple Monte Carlo techniques for Argon, Germanium, and Xenon detectors of 25 tonnes, 10 tonnes, and 3 tonnes, respectively, we show that the neutron radii could be found with an uncertainty of a few percent. If the luminosity of the neutrino flux is known independently, it is possible to discriminate between the predictions of various Skyme models as well.

Patton, Kelly; Engel, Jon; McLaughlin, Gail

2011-10-01

243

Neutrino-nucleus coherent scattering as a probe of neutron density distributions  

NASA Astrophysics Data System (ADS)

Neutrino-nucleus coherent elastic scattering provides a theoretically appealing way to measure the neutron part of nuclear form factors. Using an expansion of form factors into moments, we show that neutrinos from stopped pions can probe not only the second moment of the form factor (the neutron radius) but also the fourth moment. Using simple Monte Carlo techniques for argon, germanium, and xenon detectors of 3.5 tonnes, 1.5 tonnes, and 300 kg, respectively, we show that the neutron radii can be found with an uncertainty of a few percent when near a neutrino flux of 3×107 neutrinos/(cm2 s). If the normalization of the neutrino flux is known independently, one can determine the moments accurately enough to discriminate among the predictions of various nuclear energy functionals.

Patton, Kelly; Engel, Jonathan; McLaughlin, Gail C.; Schunck, Nicolas

2012-08-01

244

Understanding improved electrochemical properties of NiO-doped NiF2-C composite conversion materials by X-ray absorption spectroscopy and pair distribution function analysis.  

PubMed

The conversion reactions of pure NiF2 and the NiO-doped NiF2-C composite (NiO-NiF2-C) were investigated using X-ray absorption spectroscopy (XAS) and pair distribution function (PDF) analysis. The enhanced electronic conductivity of NiO-NiF2-C is associated with a significant improvement in the reversibility of the conversion reaction compared to pure NiF2. Different evolutions of the size distributions of the Ni nanoparticles formed during discharge were observed. While a bimodal nanoparticle size distribution was maintained for NiO-NiF2-C following the 1st and 2nd discharge, for pure NiF2 only smaller nanoparticles (?14 Å) remained following the 2nd discharge. We postulate that the solid electrolyte interphase formed upon the 1st discharge at large overpotential retards the growth of metallic Ni leading to formation of smaller Ni particles during the 2nd discharge. In contrast, the NiO doping and the carbon layer covering the NiO-NiF2-C possibly facilitate the conversion process on the surface preserving the reaction kinetics upon the 2nd discharge. Based on the electronic conductivity and surface properties, the resulting size of the Ni nanoparticles is associated with the conversion kinetics and consequently the cyclability. PMID:24402565

Lee, Dae Hoe; Carroll, Kyler J; Chapman, Karena W; Borkiewicz, Olaf J; Calvin, Scott; Fullerton, Eric E; Meng, Ying Shirley

2014-02-21

245

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

SciTech Connect

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

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

2010-12-03

246

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

247

Neutron and PIMC determination of the longitudinal momentum distribution of HCP, BCC and normal liquid {sup 4}He  

SciTech Connect

Deep inelastic neutron scattering has been used to measure the neutron Compton profile (NCP) of a series of condensed {sup 4}He samples at densities from 28.8 atoms/nm{sup 3} (essentially the minimum possible density in the solid phase) up to 39.8 atoms/nm{sup 3} using a chopper spectrometer at the Argonne National Laboratory Intense Pulsed Neutron Source. At the lowest density, the NCP was measured along an isochore through the hcp, bcc, and normal liquid phases. Average atomic kinetic energies are extracted from each of the data sets and are compared to both published and new path integral Monte-Carlo (PIMC) calculations as well as other theoretical predictions. In this preliminary analysis of the data, account is taken of the effects of instrumental resolution, multiple scattering, and final-state interactions. Both our measurements and the PIMC theory show that there are only small differences in the kinetic energy and longitudinal momentum distribution of isochoric helium samples, regardless of their phase or crystal structure.

Blasdell, R.C. [Argonne National Lab., IL (United States); Ceperley, D.M.; Simmons, R.O. [Illinois Univ., Urbana, IL (United States)

1993-07-01

248

Neutron-Capture Element Distributions in Metal-Poor Stars: Examination of a New Star with New Atomic Data  

NASA Astrophysics Data System (ADS)

In a recent large-sample abundance survey of about 50 halo giant stars in the metallicity regime [Fe/H] -1.0 to -3.0, Burris et al. (2000, ApJ, in press) found that BD+17 3248 ([Fe/H] -2.0) has the largest overabundance of europium ([Eu/Fe] +1.0) and other very heavy elements. This star merits a detailed abundance scrutiny, and we present here a full new model atmosphere, equivalent width and spectrum synthesis analysis of this star. Our abundance analysis makes use of new laboratory transition probability data for three critical neutron-capture species (La II, Tb II and Dy II) to provide a more accurate confrontation of the abundance distribution with neutron-capture element predictions. An age estimate of the neutron-capture material in this star from Th II transitions will be presented, and the derived age is consistent with other radioactive thorium age results for Galactic halo stars. This work has been supported by grants from the National Science Foundation to several of the authors.

Sneden, C.; Cowan, J. J.; Beers, T. C.; Burles, S.; Fuller, G. M.; Ivans, I. I.; Lawler, J. E.

2000-12-01

249

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

NASA Astrophysics Data System (ADS)

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

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

1983-05-01

250

Spin-polarized low-density neutron matter  

SciTech Connect

Low-density neutron matter is relevant to the study of neutron-rich nuclei and neutron star crusts. Unpolarized neutron matter has been studied extensively over a number of decades, while experimental guidance has recently started to emerge from the field of ultracold atomic gases. In this work, we study population-imbalanced neutron matter (possibly relevant to magnetars and to density functionals of nuclei) by applying a quantum Monte Carlo method that has proven successful in the field of cold atoms. We report on the first ab initiosimulations of superfluid low-density polarized neutron matter. For systems with small imbalances, we find a linear dependence of the energy on the polarization, the proportionality coefficient being dependent on the density. We also present results for the momentum and pair distributions of the two fermionic components.

Gezerlis, Alexandros [Department of Physics, University of Washington, Seattle, Washington 98195-1560 (United States)

2011-06-15

251

A Non-Destructive Method for Determining the Distribution of Soil Water Content by Measuring Fast Neutron Transmission Using an NE-213 Organic Scintillator  

NASA Astrophysics Data System (ADS)

A method of measuring the water content distribution in a soil layer packed in a column, using fast neutron transmission, has been developed. The calibration curve of the water content was obtained from the rate of decrease of fast neutrons per unit of water content. An NE-213 organic scintillator (2'' in diameter × 2'' in length) and Cf-252(273 ?Ci) were used as the fast neutron detector and neutron source respectively. The distribution curve of soil water content obtained by the present method was consistent with that obtained by the destructive drying method. The NE-213 scintillator was superior to other conventional detectors (3He, BF3 counter) in measurement accuracy, spatial resolution and measurement sensitivity. The relative error and sensitivity of the present method are discussed in detail in this report.

Ohnuki, Toshihiko; Yamamoto, Tadatoshi; Wadachi, Yoshiki

1984-08-01

252

Neutron angular and energy distributions from 710-MeV alphas stopping in water, carbon, steel, and lead, and 640-MeV alphas stopping in lead  

SciTech Connect

We measured neutron angular and energy distributions from 710-MeV alphas stopping in targets of water, carbon, steel, and lead for neutron energies from 3 MeV to above 300 MeV. We also measured neutron spectra from 640-MeV alphas stopping in lead. These spectra are similar to the 710-MeV spectra but are reduced in magnitude by about 20 percent. The angular distributions are forward peaked and have a broad bump at about 120 MeV in the 0- and 6-degree spectra. The 710-MeV integrated yields above 10 MeV are about 0.5 neutron per incident alpha, independent of the target. The measured spectra from the water target are consistent with the calculations of an intranuclear-cascade model at the forward angles, but are larger than the calculations at the backward angles.

Cecil, R.A.; Anderson, B.D.; Baldwin, A.R.; Madey, R.; Galonsky, A.; Miller, P.; Young, L.; Waterman, F.M.

1980-06-01

253

Benchmark oxygen-oxygen pair-distribution function of ambient water from x-ray diffraction measurements with a wide Q-range  

SciTech Connect

Four recent x-ray diffraction measurements of ambient liquid water are reviewed here. Each of these measurements represents a significant development of the x-ray diffraction technique applied to the study of liquid water. Sources of uncertainty from statistical noise, Q-range, Compton scattering, and self-scattering are discussed. The oxygen-hydrogen contribution to the measured x-ray scattering pattern was subtracted using literature data to yield an experimental determination, with error bars, of the oxygen-oxygen pair-distribution function, g{sub OO}(r), which essentially describes the distribution of molecular centers. The extended Q-range and low statistical noise of these measurements has significantly reduced truncation effects and related errors in the g{sub OO}(r) functions obtained. From these measurements and error analysis, the position and height of the nearest neighbor maximum in g{sub OO}(r) were found to be 2.80(1) A and 2.57(5) respectively. Numerical data for the coherent differential x-ray scattering cross-section I{sub X}(Q), the oxygen-oxygen structure factor S{sub OO}(Q), and the derived g{sub OO}(r) are provided as benchmarks for calibrating force-fields for water.

Skinner, Lawrie B. [Mineral Physics Institute, Stony Brook University, Stony Brook, New York 11794-2100 (United States); X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Huang, Congcong [Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, P.O. Box 20450, Stanford, California 94309 (United States); Schlesinger, Daniel; Pettersson, Lars G. M. [Department of Physics, AlbaNova University Center, Stockholm University, S-10691 Stockholm (Sweden); Nilsson, Anders [Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, P.O. Box 20450, Stanford, California 94309 (United States); Department of Physics, AlbaNova University Center, Stockholm University, S-10691 Stockholm (Sweden); Benmore, Chris J. [X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

2013-02-21

254

Temperature effects and resonance elastic cross section influence on secondary energy distributions of scattered neutrons in the resolved resonance region  

SciTech Connect

It is customary to neglect the effect of thermal motion (Doppler effect) and resonance behavior of elastic cross section on the energy distribution of scattered neutrons in the resonance region. But as has been shown earlier for {sup 238}U, there is certain effect of replacing usual step-function by more exact expression, where {sigma}{sub s} has resonance behavior The question of interest was to check the effect of replacing step distribution by more exact one for the simplest cylindrical two-zone cell with different V{sub mod} / V{sub f}. A code has been written to solve slowing-down equation from unit source in ultra-fine energy scale with two different kernels. Energy averaged cross sections were calculated for {sup 238}U and {sup 235}U. (authors)

Kolesov, V. V.; Ukraintsev, V. F. [Obninsk Inst. of Nuclear Power Engineering, Studgorodok 1, 249040 Obninsk, Kaluga reg. (Russian Federation)

2006-07-01

255

A Non-Destructive Method for Determining the Distribution of Soil Water Content by Measuring Fast Neutron Transmission Using an NE213 Organic Scintillator  

Microsoft Academic Search

A method of measuring the water content distribution in a soil layer packed in a column, using fast neutron transmission, has been developed. The calibration curve of the water content was obtained from the rate of decrease of fast neutrons per unit of water content. An NE-213 organic scintillator (2'' in diameter × 2'' in length) and Cf-252(273 muCi) were

Toshihiko Ohnuki; Tadatoshi Yamamoto; Yoshiki Wadachi

1984-01-01

256

Neutron distributions from the deuteron bombardment of a thick beryllium target  

Microsoft Academic Search

The energy spectrum of neutrons emitted when deuterons impinge on a thick beryllium target has been measured using an NE213 scintillation detector and the time-of-flight technique. Spectra have been measured at angles of 0, 30, 45, 60, 90, 120 and 150 degrees and deuteron energies of 1.4, 1.8, 2.3 and 2.8 MeV. Results presented are angular yields and angle-integrated energy

S. Whittlestone

1977-01-01

257

The Ultraviolet Spectral Energy Distributions of Quiescent Black Holes and Neutron Stars  

NASA Astrophysics Data System (ADS)

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

Hynes, R. I.; Robinson, E. L.

2012-04-01

258

Quantitative CT-reconstruction of void fraction distributions in two-phase flow by neutron radiography  

Microsoft Academic Search

A quantitative void fraction measurement method based on the umbra method using a neutron absorber grid was applied to the void fraction measurement of two-phase flow in a rod bundle. The grid 3mm in width and 3mm in interval was made from B4C. The two-phase flow direction was vertical and the grid was placed vertically between the rod bundle and

N. Takenaka; H. Asano

2005-01-01

259

Pairing anti-halo effect  

NASA Astrophysics Data System (ADS)

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

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

2000-12-01

260

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

261

Peninsulas of the neutron stability of nuclei in the vicinity of neutron magic numbers  

SciTech Connect

On the basis of the Hartree-Fock method as implemented with Skyrme forces (Ska, SkM*, Sly4, and SkI2) and with allowance for an axial deformation and nucleon pairing in the Bardeen-Cooper-Schrieffer approximation, the properties of extremely neutron-rich even-even nuclei were calculated beyond the neutron drip line known earlier from theoretical calculations. It was shown that the chains of isotopes beyond the neutron drip line that contain N = 32, 58, 82, 126, and 184 neutrons form peninsulas of nuclei stable against the emission of one neutron and, in some cases, peninsulas of nuclei stable against the emission of two neutrons. The neutron- and proton-density distributions in nuclei forming stability peninsulas were found to be spherically symmetric. A mechanism via which the stability of nuclei might be restored beyond the neutron drip line was discussed. A comparison with the results of calculations by the Hartree-Fock-Bogolyubov method was performed for long chains of sulfur and gadolinium isotopes up to the neutron drip line.

Tarasov, V. N., E-mail: vtarasov@kipt.kharkov.ua [Kharkov Institute of Physics and Technology, National Science Center (Ukraine); Gridnev, K. A. [St. Petersburg State University, Fock Institute of Physics (Russian Federation); Greiner, W.; Gridnev, D. K. [Johann Wolfgang Goethe-Universitaet, Institut fuer Theoretische Physik (Germany); Kuprikov, V. I.; Tarasov, D. V. [Kharkov Institute of Physics and Technology, National Science Center (Ukraine); Vinas, X. [Universitat de Barcelona (Spain)

2012-01-15

262

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

263

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

264

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

265

Production cross-sections and momentum distributions of fragments from neutron-deficient 36Ar at 1.05 A GeV  

NASA Astrophysics Data System (ADS)

We have measured production cross-sections and longitudinal momentum distributions of fragments from neutron-deficient 36Ar at 1.05 A GeV. The production cross-sections show excellent agreement with the predictions of the semiempirical formula EPAX. We have compared these results, involving extremely neutron deficient nuclei, with model calculations to extract information about the response of these models close to the driplines. The longitudinal momentum distributions have also been extracted and are compared with the Goldhaber and Morrissey systematics.

Caamaño, M.; Cortina-Gil, D.; Sümmerer, K.; Benlliure, J.; Casarejos, E.; Geissel, H.; Münzenberg, G.; Pereira, J.

2004-03-01

266

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

267

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

SciTech Connect

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

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

2007-01-01

268

Experimental kerma coefficients and dose distributions of C, N, O, Mg, Al, Si, Fe, Zr, A-150 plastic, Al2O3, AlN, SiO2 and ZrO2 for neutron energies up to 66 MeV  

NASA Astrophysics Data System (ADS)

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, Al2 O3 , 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 1 H(n,p) scattering and/or the 238 U(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.

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

2000-03-01

269

Shielding data for 100 250 MeV proton accelerators: Double differential neutron distributions and attenuation in concrete  

NASA Astrophysics Data System (ADS)

Double differential distributions of neutrons produced by 100, 150, 200 and 250 MeV protons stopped in a thick iron target were simulated with the FLUKA Monte Carlo code at four emission angles: forward, 45°, transverse and 135° backwards. The attenuation in ordinary concrete of the dose equivalent due to secondary neutrons, protons, photons and electrons was calculated. Some of the resulting attenuation curves are best fitted by a double-exponential function rather than a single-exponential. The effect of various approximations introduced in the simulations is thoroughly discussed. The contribution to the total ambient dose equivalent from photons and protons is usually limited to a few percent, except in the backward direction where photons contribute more than 10% and up to 35% to the total dose for a shield thickness of 1-2 m. Source terms and attenuation lengths are given as a function of energy and emission angle, along with fit to the Monte Carlo data. An extensive comparison is made of values obtained in the present work with published experimental and computational data.

Agosteo, S.; Magistris, M.; Mereghetti, A.; Silari, M.; Zajacova, Z.

2007-12-01

270

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

271

Partial pair correlation functions of low-density supercritical water determined by neutron diffraction with the H/D isotopic substitution method.  

PubMed

Neutron diffraction measurements were carried out on H/ D isotopically substituted water in the low-density supercritical condition (T = 673 K, P = 26.3 MPa, and rho = 0.0068 molecules.A-3) in order to obtain direct information on the intermolecular partial structure functions, gHH inter(r), gOH inter(r), and gOO inter(r). In correspondence to the high-density supercritical water previously reported, the intermolecular nearest neighbor peaks in gHH inter(r), gOH inter(r), and gOO inter(r) are diffuse compared with the ambient ones. The nearest neighbor O...O distance (3.3 A) and its coordination number (2.6) were determined from the observed gOO inter(r). These results indicate that the orientational correlation between neighboring water molecules is considerably lost in low-density supercritical water. Small clusters involving a few water molecules are preferentially formed in low-density supercritical water, which is consistent with results obtained by previous IR and NMR studies. PMID:18361526

Otomo, Toshiya; Iwase, Hiroki; Kameda, Yasuo; Matubayasi, Nobuyuki; Itoh, Keiji; Ikeda, Susumu; Nakahara, Masaru

2008-04-17

272

Systematics and parameterization of continuum angular distributions for application to reactions induced by 14-MeV neutrons  

SciTech Connect

Systematics are improved for application to reactions induced by 14-MeV neutrons. On the basis of this approach, new parameters for nucleon emission reactions are derived from Legendre polynomials fit 18- 25-MeV (p,n) and 18-MeV (p,p{prime}) data. For alpha-particle emissions, separate parameterizations are performed for equilibrium and preequilibrium components: Legendre coefficients obtained from calculations are parameterized for the former and the procedure used for nucleon emissions is applied to the latter. The angular distributions calculated using the present parameters show good agreement with those for 14-MeV (n,n{prime}), (n,p), and (n,{alpha}) reactions.

Kumabe, I.; Watanabe, Y.; Hanada, M. (Kyushu Univ., Fukuoka (Japan)); Nohtomi, Y. (Japan Air System Co., Ltd., Tokyo International Airport (JP))

1990-03-01

273

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

SciTech Connect

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

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

2012-09-19

274

Asymmetric distribution of cone-shaped lipids in a highly curved bilayer revealed by a small angle neutron scattering technique.  

PubMed

We have investigated the lipid sorting in a binary small unilamellar vesicle (SUV) composed of cone-shaped (1,2-dihexanoyl-sn-glycero-3-phosphocholine: DHPC) and cylinder-shaped (1,2-dipalmitoyl-sn-glycero-3-phosphocholine: DPPC) lipids. In order to reveal the lipid sorting we adopted a contrast matching technique of small angle neutron scattering (SANS), which extracts the distribution of deuterated lipids in the bilayer quantitatively without steric modification of lipids as in fluorescence probe techniques. First the SANS profile of protonated SUVs at a film contrast condition showed that SUVs have a spherical shape with an inner radius of 190 Å and a bilayer thickness of 40 Å. The SANS profile of deuterated SUVs at a contrast matching condition showed a characteristic scattering profile, indicating an asymmetric distribution of cone-shaped lipids in the bilayer. The characteristic profile was described well by a spherical bilayer model. The fitting revealed that most DHPC molecules are localized in the outer leaflet. Thus the shape of the lipid is strongly coupled with the membrane curvature. We compared the obtained asymmetric distribution of the cone-shaped lipids in the bilayer with the theoretical prediction based on the curvature energy model. PMID:21709321

Sakuma, Y; Urakami, N; Taniguchi, T; Imai, M

2011-07-20

275

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

SciTech Connect

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

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

2010-01-01

276

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

277

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

278

Estimation of angular distribution of neutron dose using time-of-flight for 19F+Al system at 110 MeV  

NASA Astrophysics Data System (ADS)

We have reported measured angular and energy distributions of neutron dose from 110 MeV 19F projectiles bombarding a thick aluminum target. The measurements are carried out with BC501 liquid scintillator detector using the time-of-flight technique. We have measured neutron energy distributions at 0?, 30?, 60?, 90?, and 120? and converted them to dose distributions using the ICRP recommended fluence to ambient dose equivalent and absorbed dose conversion coefficients. Similar conversions to ambient dose equivalent are done for theoretically estimated distributions from the nuclear reaction model code EMPIRE-2.18. The experimental results are compared with calculated ambient dose equivalent from different empirical formulations proposed by earlier workers. Based on the comparison, we have attempted modifications of the parameters in these empirical expressions.

Nandy, Maitreyee; Sunil, C.; Maiti, Moumita; Palit, R.; Sarkar, P. K.

2007-06-01

279

Nuclear pairing: Global trends and local fluctuations  

SciTech Connect

We calculate nuclear pairing gaps for ground-state configurations for 8979 nuclei from {sup 16}O to A = 339 in the Lipkin-Nogami pairing model. The energy levels required for the calculation are obtained from the folded-Yukawa single-particular model for ground-state shapes obtained in the macroscopic-microscopic approach by minimizing the total potential energy with respect to {epsilon}{sub 2},{epsilon}{sub 4}, {epsilon}{sub 3} and {epsilon}{sub 6} shape degrees of freedom. We study the behavior of the calculated pairing gap {Delta} and the number-fluctuation constant {lambda}2 on neutron number N and proton number Z. We discuss alternative methods for comparing calculated pairing gaps to odd-even experimental mass differences and study the trends of the deviations between calculated and measured quantities versus N and Z. In particular we discuss the many non-smooth contributions to the so-called experimental pairing gap that is extracted from odd-even measured mass differences and the resulting difficulties that are present when these axe compared to calculated results. In recent years several studies have investigated whether nuclear pairing depends on neutron excess. Furthermore, any dependence on neutron excess is small compared to both the random and the correlated errors in the pairing gaps that are extracted from experimental odd-even mass differences. Therefore appropriate care is required before conclusions can be drawn from calculated and experimental quantities. We use our global calculations of nuclear pairing quantities as a basis for a discussion of what conclusions can be drawn about the accuracy of current pairing models and the behavior of nuclear pairing with neutron excess. We also suggest what new nuclear mass measurements would serve as useful tests of pairing models. To provide the most informative presentation of the trends of the quantities studied over the entire periodic chart we display several of our results in the form of color

Moeller, P.; Nix, J.R.; Vieira, D.J.

1993-12-29

280

Application of high-energy x-rays and pair-distribution-function analysis to nano-scale structural studies in catalysis.  

SciTech Connect

We investigate the structure of supported Pt catalysts using high-energy X-ray scattering coupled with Pair-Distribution-Function (PDF) analysis. Recently, experimental approaches that enable the collection of PDF data in situ have been developed with time-resolution sufficient to study the structure of Pt nano-particles as they form. The differential PDF approach is utilized which allows the atom-atom correlations involving only Pt to be selectively recovered, enabling structural investigation of the supported particles and the mechanism of their formation. In parallel to the in situ analysis, we have examined samples prepared ex situ. Data collected on the ex situ samples show that the initial deposition of Pt{sup 4+} occurs as the PtCl{sub 6}{sup 2-} species which are retained even when annealed in an oxygen atmosphere. The Pt differential PDFs of the samples reduced in hydrogen at 200 and 500 C indicated nano-crystalline face-centered-cubic (fcc) metallic Pt particles. The ex situ reduced samples also contain a weak correlations at 2.1 {angstrom}, which we assign to Pt-O interactions between the particles and the support surface. The in situ experiments, following the reduction of Pt{sup 4+} from 0 to 227 C, indicate that the initial Pt nano-particles formed are ca. 1 nm in size, and become larger and more crystalline by 200 C. The data suggest a particle growth mechanism where the initial particles that form are small (<1 nm), then agglomerate into ensembles of many small particles and lastly anneal to form larger well-ordered particles. Lastly, we discus potential future developments in operando PDF studies, and identify opportunities for synchronous application of complementary methods.

Chupas, P. J.; Chapman, K. W.; Chen, H.; Grey, C.; X-Ray Science Division; State Univ. of New York

2009-07-30

281

Co-Localized or Randomly Distributed? Pair Cross Correlation of In Vivo Grown Subgingival Biofilm Bacteria Quantified by Digital Image Analysis  

PubMed Central

The polymicrobial nature of periodontal diseases is reflected by the diversity of phylotypes detected in subgingival plaque and the finding that consortia of suspected pathogens rather than single species are associated with disease development. A number of these microorganisms have been demonstrated in vitro to interact and enhance biofilm integration, survival or even pathogenic features. To examine the in vivo relevance of these proposed interactions, we extended the spatial arrangement analysis tool of the software daime (digital image analysis in microbial ecology). This modification enabled the quantitative analysis of microbial co-localization in images of subgingival biofilm species, where the biomass was confined to fractions of the whole-image area, a situation common for medical samples. Selected representatives of the disease-associated red and orange complexes that were previously suggested to interact with each other in vitro (Tannerella forsythia with Fusobacterium nucleatum and Porphyromonas gingivalis with Prevotella intermedia) were chosen for analysis and labeled with specific fluorescent probes via fluorescence in situ hybridization. Pair cross-correlation analysis of in vivo grown biofilms revealed tight clustering of F. nucleatum/periodonticum and T. forsythia at short distances (up to 6 µm) with a pronounced peak at 1.5 µm. While these results confirmed previous in vitro observations for F. nucleatum and T. forsythia, random spatial distribution was detected between P. gingivalis and P. intermedia in the in vivo samples. In conclusion, we successfully employed spatial arrangement analysis on the single cell level in clinically relevant medical samples and demonstrated the utility of this approach for the in vivo validation of in vitro observations by analyzing statistically relevant numbers of different patients. More importantly, the culture-independent nature of this approach enables similar quantitative analyses for “as-yet-uncultured” phylotypes which cannot be characterized in vitro.

Lux, Renate; Riep, Birgit; Kikhney, Judith; Friedmann, Anton; Wolinsky, Lawrence E.; Gobel, Ulf B.; Daims, Holger; Moter, Annette

2012-01-01

282

A study on the separation and distribution of the chemical forms of 131 I produced from thermal neutron-irradiated tellurium compounds by thin-layer chromatography  

Microsoft Academic Search

The separation and distribution of the chemical forms of131I produced from thermal neutron-irradiated tellurium compounds were investigated by thin-layer chromatography using alumina\\u000a as adsorbent and water as developer as well as the effect of iodine carriers added on the distribution of different chemical\\u000a forms of131I was studied. The effects of both atmospheric oxygen and light were investigated on the oxidation

Y. Maki

1975-01-01

283

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

284

Superfluid response and the neutrino emissivity of neutron matter  

SciTech Connect

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 nonrelativistic 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{sub F}{sup 4} for density fluctuations and v{sub F}{sup 2} for spin fluctuations, where v{sub 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 that include tensor interactions where the neutron spin is not conserved, neutrino radiation from bremsstrahlung reactions occurs at order v{sub F}{sup 0}. Consequently, even with the suppression factors due to superfluidity, this rate dominates near T{sub C}. Present calculations of the pair-breaking emissivity are incomplete because they neglect the tensor component of the nucleon-nucleon interaction.

Steiner, Andrew W.; Reddy, Sanjay [Joint Institute for Nuclear Astrophysics, National Superconducting Cyclotron Laboratory Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 (United States); Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2009-01-15

285

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

SciTech Connect

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

Mishler, Jeffrey H [Los Alamos National Laboratory; Mukundan, Rangachary [Los Alamos National Laboratory; Borup, Rodney L [Los Alamos National Laboratory; Wang, Yun [UC IRVINE; Hussey, Daniel S [NIST; Jacobson, David L [NIST

2010-01-01

286

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

287

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

288

Changes in the calcium cluster distribution of ultrafiltered and diafiltered fresh skim milk as observed by Small Angle Neutron Scattering.  

PubMed

The effect of ultrafiltration and diafiltration on the distribution of the calcium phosphate clusters of the casein micelle was investigated using Small Angle Neutron Scattering (SANS). In the case of ultrafiltration, fresh skim milk was subjected to concentration using membrane filtration up to 5× its original volume, the retentate was rediluted with its corresponding serum and subsequently dialyzed against reconstituted milk powder dispersed in D2O/H2O (UF 5×(D)). In the case of diafiltered samples, the samples were concentrated adding water (diafiltration) at two different levels (DF 2·5× or DF 5×) and then redispersed with D2O/H2O. In the DF 5× case, the serum components were diluted to less than 1% of their original concentration. For analysis, all samples had the same volume fraction of dispersed casein micelles (?=0·1), which is that of the control, unprocessed skim milk. A peak in the SANS data was observed in fresh skim milk at a scattering vector, qo, of 0·034 Å-1 (directly proportional to the reciprocal characteristic length), in agreement with previous literature results. Neutron data on the ultrafiltered, UF 5×(D) and diafiltered, DF 2·5× and DF 5× milk samples showed a progressive decrease in the intensity of the peak but invariance in qo. These results, combined with the determination of soluble and insoluble calcium in the samples, suggest a progressive and irreversible removal of calcium from within the micelle during membrane filtration of milk. Using SANS it was possible to clearly show changes in the micellar calcium clusters that may not otherwise be fully determined by only measuring the amount of total and insoluble calcium in milk. PMID:21774861

Alexander, Marcela; Nieh, Mu-Ping; Ferrer, Mary Ann; Corredig, Milena

2011-08-01

289

Use of Activation Technique and MCNP Calculations for Measurement of Fast Neutron Spatial Distribution at the MJ Plasma Focus Device  

SciTech Connect

In this paper Plasma-Focus (PF) neutron emission properties have been studied using Monte Carlo calculations for neutron and photon transport. A Thermal Neutron Scaling Factor as a function of angular position of silver activation detectors placed around MJ Plasma Focus (PF-1000) device has been calculated. Detector responses calculated for 2.5 MeV neutrons and neutrons produced by Am-Be calibration source have been obtained .The results have shown the detector response dependence on the kind of calibration neutron source and on local geometrical/structural characteristics of the PF-1000 devices. Thus the proper calibration procedure ought to be performed for correct measurement of neutron yield within Plasma-Focus devices.

Bienkowska, B.; Scholz, M. [Institute of Plasma Physics and Laser Microfusion, P.O. Box 49, 00-908 Warsaw (Poland); Wincel, K.; Zareba, B. [Soltan Institute for Nuclear Studies (IPJ), 05-400 Otwock-Swierk (Poland)

2008-03-19

290

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

291

A MASS-DEPENDENT YIELD ORIGIN OF NEUTRON-CAPTURE ELEMENT ABUNDANCE DISTRIBUTIONS IN ULTRA-FAINT DWARFS  

SciTech Connect

One way to constrain the nature of the high-redshift progenitors of the Milky Way (MW) is to look at the low-metallicity stellar populations of the different Galactic components today. For example, high-resolution spectroscopy of very metal poor (VMP) stars demonstrates remarkable agreement between the distribution of [Ti/Fe] in the stellar populations of the MW halo and ultra-faint dwarf (UFD) galaxies. In contrast, for the neutron-capture (nc) abundance ratio distributions [(Sr, Ba)/Fe], the peak of the small UFD sample (6 stars) exhibits a significant under-abundance relative to the VMP stars in the larger MW halo sample ({approx}300 stars). We present a simple scenario that can simultaneously explain these similarities and differences by assuming: (1) that the MW VMP stars were predominately enriched by a prior generation of stars which possessed a higher total mass than the prior generation of stars that enriched the UFD VMP stars; and (2) a much stronger mass-dependent yield (MDY) for nc-elements than for the (known) MDY for Ti. Simple statistical tests demonstrate that conditions (1) and (2) are consistent with the observed abundance distributions, albeit without strong constraints on model parameters. A comparison of the broad constraints for these nc-MDY with those derived in the literature seems to rule out Ba production from low-mass supernovae (SNe) and affirms models that primarily generate yields from high-mass SNe. Our scenario can be confirmed by a relatively modest (factor of {approx}3-4) increase in the number of high-resolution spectra of VMP stars in UFDs.

Lee, Duane M.; Johnston, Kathryn V. [Department of Astronomy, Columbia University, New York City, NY 10027 (United States); Tumlinson, Jason [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Sen, Bodhisattva [Department of Statistics, Columbia University, New York City, NY 10027 (United States); Simon, Joshua D. [The Observatories of the Carnegie Institution of Washington, Pasadena, CA 91101 (United States)

2013-09-10

292

A Mass-dependent Yield Origin of Neutron-capture Element Abundance Distributions in Ultra-faint Dwarfs  

NASA Astrophysics Data System (ADS)

One way to constrain the nature of the high-redshift progenitors of the Milky Way (MW) is to look at the low-metallicity stellar populations of the different Galactic components today. For example, high-resolution spectroscopy of very metal poor (VMP) stars demonstrates remarkable agreement between the distribution of [Ti/Fe] in the stellar populations of the MW halo and ultra-faint dwarf (UFD) galaxies. In contrast, for the neutron-capture (nc) abundance ratio distributions [(Sr, Ba)/Fe], the peak of the small UFD sample (6 stars) exhibits a significant under-abundance relative to the VMP stars in the larger MW halo sample (~300 stars). We present a simple scenario that can simultaneously explain these similarities and differences by assuming: (1) that the MW VMP stars were predominately enriched by a prior generation of stars which possessed a higher total mass than the prior generation of stars that enriched the UFD VMP stars; and (2) a much stronger mass-dependent yield (MDY) for nc-elements than for the (known) MDY for Ti. Simple statistical tests demonstrate that conditions (1) and (2) are consistent with the observed abundance distributions, albeit without strong constraints on model parameters. A comparison of the broad constraints for these nc-MDY with those derived in the literature seems to rule out Ba production from low-mass supernovae (SNe) and affirms models that primarily generate yields from high-mass SNe. Our scenario can be confirmed by a relatively modest (factor of ~3-4) increase in the number of high-resolution spectra of VMP stars in UFDs.

Lee, Duane M.; Johnston, Kathryn V.; Tumlinson, Jason; Sen, Bodhisattva; Simon, Joshua D.

2013-09-01

293

Determination of time-dependent void fraction distribution in bubbly two-phase flow by a real-time neutron radiography technique  

SciTech Connect

Radiographic images generated by the real-time neutron radiography system (RTNR) are analyzed by customized image processing software of the determination of instantaneous void fraction distribution. The cross-sectional averaged axial void fraction profiles and the two-dimensional void fraction profiles are determined simultaneously for each image. Various flow regimes are generated to determine if the RTNR system can accurately predict the void distribution in the radial, axial, and temporal coordinates. The results show the RTNR system correctly determines the void fraction distribution for each flow regime; however, accuracy decreases with decreasing void fraction. For net water thicknesses > 1.0 cm, the accuracy decreases with increasing water thickness due to the extreme sensitivity of thermal neutron interactions with light water. Heavy water is a more suitable fluid than light water for void fraction measurements in large-diameter flow systems.

Harvel, G.D.; Chang, J.S. [McMaster Univ., Hamilton, Ontario (Canada). Dept. of Engineering Physics; Krishnan, V.S. [Atomic Energy of Canada Ltd., Mississauga, Ontario (Canada). Safety Analysis Branch

1995-01-01

294

Neutron measurements  

SciTech Connect

Methods of neutron detection and measurement are discussed. Topics include sources of neutrons, neutrons in medicine, interactions of neutrons with matter, neutron shielding, neutron measurement units, measurement methods, and neutron spectroscopy. (ACR)

McCall, R.C.

1981-01-01

295

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.

296

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

297

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

298

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

299

Magnetic field distribution of injection chicane dipoles in Spallation Neutron Source accumulator ring  

NASA Astrophysics Data System (ADS)

We have performed 3D computing simulations to study the magnetic field distribution of the injection chicane dipoles in the SNS accumulator ring. The simulations yield the performance characteristics of the magnets and generate the magnetic field data in three dimensional grids for further beam tracking study. Based on the simulation data, a 3D multipole expansion of the chicane dipole field, consisting of the generalized gradients and their derivatives, has been made. The harmonic and pseudoharmonic components in the expansion give much insight into the magnet physics and can fit directly into theoretical frame work of beam optics. The expansion is quasianalytical by fitting numeric data into interpolation functions. A 5th-order representation of the magnetic field is generated, and the effects of even higher-order terms on the field representation are discussed.

Wang, J. G.

2006-01-01

300

Energy distribution and yield of neutrons from the (p,n) reaction in thick LiF targets  

Microsoft Academic Search

The zero degree yield and the energy spectra have been investigated of neutrons being produced by protons of Ep <= 7 MeV in a thick natural LiF target, both experimentally by applying time-of-flight measurements and by a Monte Carlo simulation. While the experimental neutron energy spectra are disturbed by the neutron detector efficiency and by the finite time resolution of

F. M. Baumann; B. Brüggemann; H. Freiesleben; Th. Grodotzki; H. Chr. Hilber

1985-01-01

301

Angular distribution measurements of photo-neutron yields produced by 2.0 GeV electrons incident on thick targets.  

PubMed

A study of differential photo-neutron yields by irradiation with 2 GeV electrons has been carried out. In this extension of a previous study in which measurements were made at an angle of 90 degrees relative to incident electrons, the differential photo-neutron yield was obtained at two other angles, 48 degrees and 140 degrees, to study its angular characteristics. Photo-neutron spectra were measured using a pulsed beam time-of-flight method and a BC418 plastic scintillator. The reliable range of neutron energy measurement was 8-250 MeV. The neutron spectra were measured for 10 Xo-thick Cu, Sn, W and Pb targets. The angular distribution characteristics, together with the previous results for 90 degrees, are presented in the study. The experimental results are compared with Monte Carlo calculation results. The yields predicted by MCNPX 2.5 tend to underestimate the measured ones. The same trend holds for the comparison results using the EGS4 and PICA3 codes. PMID:16604719

Lee, Hee-Seock; Ban, Syuichi; Sanami, Toshiya; Takahashi, Kazutoshi; Sato, Tatsuhiko; Shin, Kazuo; Chung, Chinwha

2005-01-01

302

s-process studies in the light of new experimental cross sections - Distribution of neutron fluences and r-process residuals  

NASA Technical Reports Server (NTRS)

A best set of neutron-capture cross sections has been evaluated for the most important s-process isotopes. With this data base, s-process studies have been carried out using the traditional model which assumes a steady neutron flux and an exponential distribution of neutron irradiations. The calculated sigma-N curve is in excellent agreement with the empirical sigma-N-values of pure s-process nuclei. Simultaneously, good agreement is found between the difference of solar and s-process abundances and the abundances of pure r-process nuclei. The abundance pattern of the iron group elements where s-process results complement the abundances obtained from explosive nuclear burning is discussed. The results obtained from the traditional s-process model such as seed abundances, mean neutron irradiations, or neutron densities are compared to recent stellar model calculations which assume the He-burning shells of red giant stars as the site for the s-process.

Kaeppeler, F.; Beer, H.; Wisshak, K.; Clayton, D. D.; Macklin, R. L.; Ward, R. A.

1982-01-01

303

S-process studies in the light of new experimental cross sections - Distribution of neutron fluences and r-process residuals  

NASA Astrophysics Data System (ADS)

A best set of neutron-capture cross sections has been evaluated for the most important s-process isotopes. With this data base, s-process studies have been carried out using the traditional model which assumes a steady neutron flux and an exponential distribution of neutron irradiations. The calculated sigma-N curve is in excellent agreement with the empirical sigma-N-values of pure s-process nuclei. Simultaneously, good agreement is found between the difference of solar and s-process abundances and the abundances of pure r-process nuclei. The abundance pattern of the iron group elements where s-process results complement the abundances obtained from explosive nuclear burning is discussed. The results obtained from the traditional s-process model such as seed abundances, mean neutron irradiations, or neutron densities are compared to recent stellar model calculations which assume the He-burning shells of red giant stars as the site for the s-process.

Kaeppeler, F.; Beer, H.; Wisshak, K.; Clayton, D. D.; Macklin, R. L.; Ward, R. A.

1982-06-01

304

Fission dynamics for capture reactions in 58,64Ni + 208Pb systems: New results in terms of thermal energy and neutron multiplicity correlated distributions  

NASA Astrophysics Data System (ADS)

The neutron multidetector DéMoN has been used to investigate the symmetric splitting dynamics in the reactions 58,64Ni + 208Pb with excitation energies ranging from 65 to 186 MeV for the composite system. An analysis based on the new backtracing technique has been applied on the neutron data to determine the two-dimensional correlations between the parent composite system initial thermal energy ( ECNth) and the total neutron multiplicity ( ?tot), and between pre- and post-scission neutron multiplicities ( ?pre and ?post, respectively). The ?pre distribution shape indicates the possible coexistence of fast-fission and fusion-fission for the system 58Ni + 208Pb ( Ebeam = 8.86 A MeV). The analysis of the neutron multiplicities in the framework of the combined dynamical statistical model (CDSM) gives a reduced friction coefficient ? = 23 ± 1225 × 10 21s-1, above the one-body dissipation limit. The corresponding fission time is ?f = 40 ± 2046 × 10 -21s.

Donadille, L.; Liatard, E.; Benoit, B.; Hanappe, F.; Stuttgé, L.; Rudolf, G.; Kozulin, E. M.; Lazarev, Yu. A.; Désesquelles, P.; Litnevsky, L. A.; Bilwes, B.; Bruandet, J.-F.; Costa, G. J.; Dorvaux, O.; Farget, F.; Fayot, J.; Guillaume, G.; Huck, A.; Itkis, I.; Itkis, M. G.; Joki? , S.; Kondratiev, N. A.; Lecolley, F.-R.; Lecolley, J.-F.; Oganessian, Yu. Ts.; Perrin, G.; Santos, D.; Schussler, F.; Tomaš Evi? , S.; Viano, J.-B.; Vignon, B.

1999-08-01

305

Nuclear-charge distribution for A = 121 from thermal-neutron-induced fission of /sup 235/U  

SciTech Connect

The fractional cumulative yield of /sup 121/Ag and the fractional independent yields of /sup 121/Cd, /sup 121/In, and /sup 121/Sn from thermal-neutron-induced fission of /sup 235/U were determined radiochemically to be 0.12 +- 0.05, 0.61 +- 0.09, 0.24 +- 0.08, and 0.03 +- 0.04, respectively. The yield values were used to determine the nuclear-charge-distribution parameters sigma/sub Z/ = 0.55 +- 0.10 and ..delta..Z = 0.50 +- 0.05 for A = 121. The sigma/sub Z/ for A = 121 is close to sigma/sub Z/$ = 0.52 +- 0.02 for high-yield fission products, and no evidence for an even-odd Z effect was found for A = 121. The positive ..delta..Z value, which corresponds to Z/sub P/ = 48.15, is similar to those for several higher mass numbers reported previously, and it is considerably greater than the negative values predicted by the scission-point theoretical model. The use of a separation distance between nascent fragments greater than 1.4 fm, the value used in the theoretical calculations, could reduce the discrepancy and could also account for the observed enhanced independent yields of tin fission products with Z/sub P/ near 50 (A = 126--129).

Robinson, L.; Wahl, A.C.; Semkow, T.M.; Norris, A.E.

1985-04-01

306

Monte Carlo characterization of the near-field energy and angular distribution for the HENRE DT neutron generator  

Microsoft Academic Search

Rigorous physical modeling and three-dimensional neutron transport ; techniques have been used to characterize the nearfield radiation for the HENRE D-; T neutron generator. Monte Carlo transport analysis was used to calculate the ; near-field lar source configurations. The results were obtained in 66 energy ; groups ranging from thermal to 14.6 MeV and in 40 angular (solid angle) ;

ODell

1972-01-01

307

Local structure of germanium selenide glasses around the rigidity percolation threshold using atomic pair distribution function and X-ray absorption fine structure techniques  

NASA Astrophysics Data System (ADS)

A search for a structural response to a recently proposed self-organized and stress-free intermediate phase [1, 2] in semiconductor chalcogenide Ge xSe1-x glasses has been performed in this study. These glasses, according to the mean-field approach, undergo a structural phase transition from floppy to rigid network that occurs at a mean coordination number of 2.4. Based on thermodynamic and spectroscopic measurements, these glasses appear to exhibit two transitions instead of one [3]. The region between these transitions has been called the intermediate phase (IP) [3, 4]. The original theoretical work assumed that the network was generic and the connectivity random [5]. It was therefore suggested [1] that the IP phase is a region of finite width in composition where the network could self-organize in such a way that maintains a rigid but unstressed state. However, it has proved difficult to establish this result experimentally. High-resolution atomic pair distribution functions (PDF), derived from high energy synchrotron radiation, coupled with high-resolution X-ray absorption fine structure (XAFS) measurements on 18 compositions of well-prepared Ge xSe1-x glasses that span the range of the IP have been performed to elucidate aspects of rigidity percolation and the IP. These data sets are the most complete and the highest resolution data set on this system to date. Analysis of the structure functions (in reciprocal space) and the PDFs (in real space) as well as the XAFS data at both Ge and Se edges show no correlations with the IP. The network evolves smoothly without any break in slope or discontinuity that might be linked due to the IP. The results obtained in this study contradict previously published work [1, 2] that claim experimental evidence for a structural origin of the IP. The so-called first sharp diffraction peak (FSDP), which is a signature of the medium range order in these glasses, changes systematically with Ge content. It develops smoothly from a low background for low Ge-content to a well-defined, sharp peak at the stoichiometric composition (GeSe2). Its position shifts towards lower Q-values when Ge content is increased. The height of this peak reaches its maximum at the stoichiometric composition (x = 0.33), after which it starts to decrease. This is interpreted as being due to the change of the role of Ge atoms in the network. For x < 0.33, the Ge atoms work as a network former, so adding Ge results in a progressive increase in the correlations contributing to this peak. On the contrary, for x > 0.33, Ge atoms work as network modifiers. This will weaken the ordering of the correlations responsible for the FSDP and hence decrease its intensity. The basic building block in these glasses is the Ge(Se1/2) 4 tetrahedron. For low Ge content, the tetrahedra are immersed in a floppy Se-matrix. The first PDF peak is mainly due to Ge-Se correlations. Se-Se and Ge-Ge homopolar bonds were found only in the low-Ge and high-Ge regions, respectively, consistent with the chemically ordered network (CON) model, in which Ge-Se bonds are always favored over Se-Se and Ge-Ge bonds.

Shatnawi, Moneeb Taiseer

308

A fission-based, distributed, 14 MeV fusion neutron radiation source for first wall\\/blanket component testing and system development  

Microsoft Academic Search

A large-volume, distributed, pulsed, 14 MeV neutron source, which utilizes the high powered (270-GW) Power Burst Facility (PBF) at the Idaho National Engineering Laboratory, is described. The concept of utilizing existing fission test reactors to test fusion first wall\\/blanket (FW\\/B) components and systems has been adequately documented. In all previous scenarios, the normal fission spectrum (including tailoring) was shown to

P. Y. Hsu; L. G. Miller

1983-01-01

309

Familial Type 1 Diabetes Mellitus - Gender Distribution and Age at Onset of Diabetes Distinguish between Parent-Offspring and Sib-Pair Subgroups  

PubMed Central

Background Familial type 1 diabetes mellitus (T1D) comprises parent-offspring and sib-pair subgroups. Objective To compare the demographic and clinical characteristics in the two subgroups at diagnosis and evaluate the differences between index cases and second affected family members. Methods Retrieved from our institutional registry of new T1D cases for the years 1979 to 2008 were a cohort of 194 familial cases (87 parent-offspring, 107 sib-pairs) ; 133 sporadic cases matched by age, gender, and year of diagnosis were selected as controls. Extracted from their medical files were demographic data, family background, clinical and laboratory findings. Results The parent-offspring subgroup was characterized by male preponderance (p=0.009). At diagnosis parents were significantly older than their offspring (p<0.001); probands were significantly younger than their affected siblings (p=0.03). Clinical symptoms and metabolic decompensation were similar in the familial subgroups. Diabetic ketoacidosis (DKA) rate and HbA1c levels were lower in second affected family members in both parent–offspring (p=0.05 and p<0.001) and sib-pair subgroups (p<0.001, for both parameters). Consanguinity and T1D were more frequent in the extended family of familial than sporadic cases (p<0.001 and p=0.012, respectively) with no difference between the two sub-groups. Conclusions The genetic background for T1D would appear to differ not only between familial and sporadic cases but also between parent-offspring and sib-pair subgroups. Whereas differences in age of onset are attributable to both genetic and environmental factors, the less severe clinical manifestations in second affected family members may result from increased awareness or a less aggressive disease process.

Lebenthal, Yael; de Vries, Liat; Phillip, Moshe; Lazar, Liora

2009-01-01

310

Formalism for the determination of structural isotope effects with neutrons  

SciTech Connect

In general the analysis of neutron isotopic substitution experiments in terms of partial structure factors and partial pair distribution functions is based on the assumption that the structure of isotopic variants of a molecule is identical. This assumption is clearly only an approximation especially in the case of hydrogen bonding molecular liquids like liquid water and structural isotope effects have been measured with X-rays for more than 20 years. A analysis method of neutron isotope data is presented that avoids the necessity to assume structural equality and allows the determination of the isotope effect in the hydrogen-hydrogen partial structure factor of liquid water from neutron data. It is shown that a combination of X-ray and neutron scattering measurements allows in principle the determination of the isotope effects on all all partials structure factors of liquid water.

Neuefeind, Joerg C [ORNL; Benmore, Chris J [Argonne National Laboratory (ANL)

2009-01-01

311

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

2008-12-24

312

The ITER radial neutron camera: An updated neutronic analysis  

Microsoft Academic Search

The radial neutron camera (RNC) will provide the spatial distribution and the total strength of the ITER neutron source (emissivity profile and fusion power) by means of collimated neutron measurements. Line-integrated neutron spectral measurements can also provide information on the ion temperature profile. The present design of the RNC consists of two collimating structures for a full coverage of the

Fabio Moro; Luigino Petrizzi; Giorgio Brolatti; Basilio Esposito; Daniele Marocco; Rosaria Villari

2009-01-01

313

Exotic modes of excitation in deformed neutron-rich nuclei  

SciTech Connect

Low-lying dipole excitation mode in neutron-rich Mg isotopes close to the drip line is investigated in the framework of the Hartree-Fock-Bogoliubov and the quasiparticle random-phase approximation employing the Skyrme and the pairing energy-density functionals. It is found that the low-lying dipole-strength distribution splits into the K{sup {pi}} = 0{sup -} and 1{sup -} components due to the nuclear deformation. The low-lying dipole strength increases as the neutron drip-line is approached.

Yoshida, Kenichi [RIKEN Nishina Center for Accelerator-Based Science, Wako, Saitama 351-0198 (Japan)

2011-05-06

314

Use of thermoluminescent dosimeters for measurement of fast-neutron spatial-distribution at the plasma focus device PF1000  

Microsoft Academic Search

A system of moderators of DD-fusion neutrons emitted by the plasma focus device PF-1000 at IPPLM, Warsaw was employed for the use of thermoluminescent dosimeters (TLDs) as passive detectors of thermal neutrons. The diagnostics was derived from Monte Carlo calculations of responses of dosimeters located in spherical polyethylene moderators with different diameters. As time-integrating dosimeters coupled 6LiF:Mg,Cu,P (TLD-600H) and 7LiF:Mg,Cu,P

A. Velyhan; J. Krása; B. Bienkowska; I. M. Ivanova-Stanik; L. Juha; L. Karpinski; D. Klír; M. Králík; J. Kravárik; P. Kubes; M. Paduch; M. Scholz; K. Tomaszewski

2006-01-01

315

Ion pair formation in multiphoton excitation of NO(2) using linearly and circularly polarized femtosecond light pulses: kinetic energy distribution and fragment recoil anisotropy.  

PubMed

The NO(2) ion pair photodissociation dynamics leading to NO(+)(X(1)Sigma(+),v) + O(-)((2)P(3/2) or (2)P(1/2)), induced by a 1 kHz femtosecond laser with wavelengths near 400 nm, has been characterized using the coincidence vector correlation method. The ion pair production after four-photon absorption reaches more than 15% of the primary ionization. The kinetic energy release of the fragments demonstrates a significant vibrational excitation of the NO(+)(X(1)Sigma(+),v) molecular fragment. Recoil ion fragment emission is strongly aligned along the polarization axis of linearly polarized light or preferentially emitted in the plane perpendicular to the propagation axis of circularly polarized light. The formalism describing the recoil anisotropy for bound-to-bound n-photon transition inducing prompt axial recoil dissociation of a nonlinear molecule has been developed to interpret the measured anisotropies in terms of excitation pathways via near-resonant intermediate states of specific symmetries. Possible reaction pathways are discussed that are consistent with the data and supported by calculations of potential energy surfaces and transition moments. PMID:20704179

Elkharrat, C; Picard, Y J; Billaud, P; Cornaggia, C; Garzella, D; Perdrix, M; Houver, J C; Lucchese, R R; Dowek, D

2010-09-16

316

Collective excitations induced by pairing anti-halo effect  

NASA Astrophysics Data System (ADS)

We emphasize a special interplay of loosely-bound neutrons with small orbital angular momentum ? and self-consistent pairing correlations for low-lying collective vibrational excitations in neutron drip line nuclei. Change of the spatial structure in quasiparticle wave functions by self-consistent pairing correlations leads to the broad localization of two-quasiparticle states with low-? neutrons. We show that the broad localization can cause the enhancement of the low-lying collectivity. By performing HFB plus quasiparticle random phase approximation (QRPA) calculation for the first 2+ states in neutron rich Ni isotopes, the unique role of self-consistent pairing correlations is examined. Finally we make a comment on deformation effects for low-lying vibrational excitations in neutron drip line nuclei.

Yamagami, M.

2005-09-01

317

Geometrical effect on the issue of asymmetric C 1s photoelectron angular distributions detected in coincidence with the fragment ion pairs of CO+–O+ for CO2 molecules  

NASA Astrophysics Data System (ADS)

We have measured C 1s photoelectron angular distributions (PADs) in coincidence with the CO+–O+ fragment ion pairs of CO2 molecules at the photoelectron energies of 85, 120 and 150 eV. The observed left–right asymmetric PADs have been well reproduced by our theoretical model taking into account the two degenerate zero-point bending vibrations. This leads to a conclusive result on the interpretation of such PADs; although it has been believed so far that they are the molecular frame, in fact they are the recoil frame.

Tsuru, Shota; Kazama, Misato; Fujikawa, Takashi; Adachi, Jun-ichi; Yagishita, Akira

2014-04-01

318

CALIBAN: Distribution des Fluences Neutroniques et des Doses Gamma en Fonctionnement Continu (CALIBAN: Distribution of Neutron Flux and Gamma Doses in Continuous Operation).  

National Technical Information Service (NTIS)

In order to compensate for the temporary interruption of the PROSPERO reactor, it is desirable to use the CALIBAN reactor in continuous operation. As part of efforts to establish parameters for this service, a study was made of neutron flux and gamma dosa...

J. Morin J. Chevallier R. Blanc A. Mathieu C. Sester

1974-01-01

319

Gadolinium neutron capture therapy  

SciTech Connect

A computer study of the dose distribution for gadolinium neutron capture therapy is carried out to determine its feasibility. Gadolinium is a potential neutron capture therapy (NCT) agent that produces gamma radiation, conversion electrons, and Auger electrons. The dose distribution from neutrons, neutron-induced gammas, and the reaction products from neutron capture in gadolinium were modeled using the Los Alamos National Laboratory Monte Carlo neutron photon computer code. The results of these calculations are that gadolinium has promise as an NCT agent. Using two parallel opposed epithermal neutron beams for a tumor at an 8.0-cm depth with a gadolinium loading of 100[mu]g/g, the tumor to peak normal tissue dose was determined to be 1.48.

Miller, G.A. Jr. (Univ. of Austin, TX (United States). Biomedical Engineering); Hertel, N.E. (Georgia Inst. of Technology, Atlanta, GA (United States). Mechanical Engineering); Wehring, B.W. (Univ. of Texas, Austin, Tx (United States). Mechanical Engineering); Horton, J.L. (Univ. of Texas, Houston, TX (United States). M.D. Anderson Cancer Center)

1993-09-01

320

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

321

Water distributions in polystyrene-block-poly[styrene-g-poly(ethylene oxide)] block grafted copolymer system in aqueous solutions revealed by contrast variation small angle neutron scattering study  

NASA Astrophysics Data System (ADS)

We develop an experimental approach to analyze the water distribution around a core-shell micelle formed by polystyrene-block-poly[styrene-g-poly(ethylene oxide (PEO)] block copolymers in aqueous media at a fixed polymeric concentration of 10 mg/ml through contrast variation small angle neutron scattering (SANS) study. Through varying the D2O/H2O ratio, the scattering contributions from the water molecules and the micellar constituent components can be determined. Based on the commonly used core-shell model, a theoretical coherent scattering cross section incorporating the effect of water penetration is developed and used to analyze the SANS I(Q). We have successfully quantified the intramicellar water distribution and found that the overall micellar hydration level increases with the increase in the molecular weight of hydrophilic PEO side chains. Our work presents a practical experimental means for evaluating the intramacromolecular solvent distributions of general soft matter systems.

Li, Xin; Hong, Kunlun; Liu, Yun; Shew, Chwen-Yang; Liu, Emily; Herwig, Kenneth W.; Smith, Gregory S.; Zhao, Junpeng; Zhang, Guangzhao; Pispas, Stergios; Chen, Wei-Ren

2010-10-01

322

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

323

Neutron radiography as a tool for cadmium distribution measurement in Hg 1- xCd xTe single-crystals?  

NASA Astrophysics Data System (ADS)

Neutron radiography as applied to the determination of cadmium content in Hg 1- xCd xTe is described. This technique, in addition to a reasonable sensitivity and spatial resolution, allows a visual estimate of cadmium distribution. In the range 0.19 ? x ? 0.24, composition measurements with an everall uncertainty ? x less than 0.01 and spatial resolution better than 150 ?m may be performed. Capabilities of the method to study the parameters affecting the growth of crystals suitable for infrared detection are shown.

Gasparrini, G.; Mangialajo, M.; Passoni, D.; Pirovano, B.

1974-05-01

324

Presence of ? phase domains in the phonon-glass thermoelectric ?-Zn4Sb3 from atomic pair distribution function (PDF) analysis  

NASA Astrophysics Data System (ADS)

The promisingly high ZT of ?-Zn4Sb3 between 450 K and 670 K is known to be due to its exceptionally low thermal conductivity. The discovery of significant Zn interstitial disorder in ?-Zn4Sb3 provides foundation for better understanding of the origin of the glass-like thermal conductivity[1]. Furthermore, it has been reported that Zn interstitial atoms become ordered in ?-phase[2]. We report on the local structural study of ?-Zn4Sb3 using PDF technique, which has been successfully applied to solve the structures of crystallographically challenged materials[3,4]. Prominent diffuse scattering is found both in neutron and x-ray data. The PDF analysis suggests that the average ?-structure consists of locally ?-structure like domains where Zn interstitial atoms are ordered. This provides an important local structural insight into not well understood ? to ? order-disorder phase transition in Zn4Sb3 at 260 K. [1] G. J. Snyder et al. Nat. Mater. 3, 458 (2004) [2] J. Nyl'en et al. J. Am. Chem. Soc. 126, 16306 (2004) [3] T. Egami and S. J. L. Billinge, Underneath the Bragg peaks, Pergamon Press, Elsevier, Oxford, England, 2003 [4] S. J. L. Billinge and M. G. Kanatzidis, Chem. Commun., 749 (2004)

Kim, H. J.; Bozin, E. S.; Billinge, S. J. L.; Haile, S.; Snyder, G. J.

2006-03-01

325

Pair correlation of giant halo nuclei in continuum Skyrme-Hartree-Fock-Bogoliubov theory  

NASA Astrophysics Data System (ADS)

The giant halos predicted in neutron-rich Zr isotopes with A=124-138 are investigated by using the self-consistent continuum Skyrme-Hartree-Fock-Bogoliubov approach, in which the asymptotic behavior of continuum quasiparticle states is properly treated by the Green's function method. We study in detail the neutron pair correlation involved in the giant halo by analyzing the asymptotic exponential tail of the neutron pair condensate (pair density) in addition to that of the neutron particle density. The neutron quasiparticle spectra associated with these giant halo nuclei are examined. It is found that the asymptotic exponential tail of the neutron pair condensate is dominated by nonresonant continuum quasiparticle states corresponding to the scattering states with low asymptotic kinetic energy. This is in contrast to the asymptotic tail of the neutron density, whose main contributions arise from the resonant quasiparticle states corresponding to the weakly bound single-particle orbits and resonance orbits in the Hartree-Fock potential.

Zhang, Y.; Matsuo, M.; Meng, J.

2012-11-01

326

Characterization of the energy distribution of neutrons generated by 5 MeV protons on a thick beryllium target at different emission angles.  

PubMed

Neutron energy spectra at different emission angles, between 0° and 120° from the Be(p,xn) reaction generated by a beryllium thick-target bombarded with 5 MeV protons, have been measured at the Legnaro Laboratories (LNL) of the Italian National Institute for Nuclear Physics research (INFN). A new and quite compact recoil-proton spectrometer, based on a monolithic silicon telescope, coupled to a polyethylene converter, was efficiently used with respect to the traditional Time-of-Flight (TOF) technique. The measured distributions of recoil-protons were processed through an iterative unfolding algorithm in order to determine the neutron energy spectra at all the angles accounted for. The neutron energy spectrum measured at 0° resulted to be in good agreement with the only one so far available at the requested energy and measured years ago with TOF technique. Moreover, the results obtained at different emission angles resulted to be consistent with detailed past measurements performed at 4 MeV protons at the same angles by TOF techniques. PMID:21478028

Agosteo, S; Colautti, P; Esposito, J; Fazzi, A; Introini, M V; Pola, A

2011-12-01

327

Structural variations and cation distributions in Mn 3- xCo xO 4 (0 ? x ? 3) dense ceramics using neutron diffraction data  

NASA Astrophysics Data System (ADS)

Single phase ceramics of cobalt manganese oxide spinels Mn 3- xCo xO 4 were structurally characterized by neutron powder diffraction over the whole solid solution range. For x < 1.75, ceramics obtained at room temperature by conventional sintering techniques are tetragonal, while for x ? 1.75 ceramics sintered by Spark Plasma Sintering are of cubic symmetry. The unit cells, metal-metal and metal-oxygen average bonds decrease regularly with increasing cobalt content. Rietveld refinements using neutron data show that cobalt is first preferentially substituted on the tetrahedral site for x < 1, then on the octahedral site for increasing x values. Structural methods (bond valence sum computations and calculations based on Poix's work in oxide spinels) applied to our ceramics using element repartitions and [M-O] distances determined after neutron data refinements allowed us to specify the cation distributions in all phases. Mn 2+ and/or Co 2+ occupy the tetrahedral site while Mn 3+, Co 2+, Co III (cobalt in low-spin state) and Mn 4+ occupy the octahedral site. The electronic conduction mechanisms in our highly densified ceramics of pure cobalt and manganese oxide spinels are explained by the hopping of polarons between adjacent Mn 3+/Mn 4+ and Co 2+/Co III on the octahedral sites.

Bordeneuve, H.; Tenailleau, C.; Guillemet-Fritsch, S.; Smith, R.; Suard, E.; Rousset, A.

2010-03-01

328

System For The Transmutation Of Nuclear Waste Based On The Target-distributed High-intensity Neutron Sources  

Microsoft Academic Search

At the present time fuel cycle in the US based on light water reactors with use only fresh uranium fuel. The production of enriched fuel by means of fast breeder poses considerable problems in the high potential radiological risk of them. Other possible methods of obtaining large neutron fluxes are plasma and electronuclear. Until the technical problems made this methods

Anatoly Blanovsky

1993-01-01

329

Energy behaviour of neutrons generated by Witch-type distributed axi-symmetrical deuteron beams accelerated onto plane tritium targets  

PubMed

This paper is an analytical study of the spatial dependency of the d-T neutron energy in the vicinity of a homogeneous tritium-occluded plane target. Close to the target, and along the path of incidence of axially symmetric deuteron beams, the transverse density of accelerated deuterons is assumed to be governed by a law approximated by the 'Witch' function. In particular circumstances, the elementary neutron emission process in non-dispersive media can be considered to be omni-directional (due consideration being paid to collision kinetics, depending upon mass and kinetic energy of particles involved in the nuclear collision, nuclear reaction energy, etc.). Consequently, analytical expressions can be considerably simplified. By applying the classical kinetic energy and momentum conservation laws to nuclear processes, a theoretical description is obtained, taking into account the exoergic character of d-T fusion reaction. A number of expressions for energetic prediction of the fast neutron field are proposed. The associated relations, involving elementary functions, can be investigated using a desk-top computer. Computationally tractable tools are of importance in the study of diverse situations such as induced reactions and activation analysis using 14 MeV neutron generators, investigations in health-physics, radiation dose measurements, nuclear medicine, damage effects, and simulation studies. PMID:11003522

Timus; Bradley; Timus; Kalla; Srivastava

2000-10-01

330

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

331

Atom-Pair Correlations in Fe-13.5% V.  

National Technical Information Service (NTIS)

Diffuse neutron scattering data were used to determine the atom-pair correlations for Fe-13.5% V in terms of both the Warren-Cowley ASRO parameters and the Krivoglaz-Clapp-Moss pair-potentials. These agree reasonably well with those calculated by Hennion ...

J. W. Cable H. R. Child Y. Nakai

1988-01-01

332

Pulsar Pair Cascades in a Distorted Magnetic Dipole Field  

Microsoft Academic Search

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

Alice K. Harding; Alex G. Muslimov

2011-01-01

333

Pair Cascades and Deathlines in Offset Magnetic Dipole Fields  

NASA Technical Reports Server (NTRS)

We investigate electron-positron pair cascades in a dipole magnetic field whose axis is offset from the neutron star center. In such a field geometry, the polar cap is displaced from the neutron star symmetry axis and the field line radius of curvature is modified. Using the modified parallel electric field near the polar cap of an offset dipole, we simulate pair cascades to determine the pair deathlines and pair multiplicities as a function of the offset parameter. We find that the pair multiplicity can change dramatically with a modest offset, with a significant increase on one side of the polar cap. Lower pair deathlines allow a larger fraction of the pulsar population, that include old and millisecond pulsars, to produce cascades with high multiplicity.

Harding, Alice; Muslimov, Alex

2010-01-01

334

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.

Sharifi, Monir; Wallacher, Dirk

2012-01-01

335

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  

Microsoft Academic Search

Second neutron yields, energy spectra, and angular distributions have been measured at seven angles from 0 to 150° for 113 and 256 MeV protons stopped in range-thick targets of aluminum and depleted uranium (²³⁸U). 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

L. R. Greenwood; A. Intasorn

1989-01-01

336

Casimir light: photon pairs.  

PubMed Central

Expressions are developed for weak single pair emission probability and strong emission average number of pairs. The water transparency cutoff is closely realized, showing that the fundamental time scale is even shorter.

Schwinger, J

1993-01-01

337

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

338

Measurement and analysis of energy and angular distributions of thick target neutron yields from 110 MeV {sup 19}F on {sup 27}Al  

SciTech Connect

Energy distributions of emitted neutrons were measured for 110 MeV {sup 19}F ions incident on a thick {sup 27}Al target. Measurements were done at 0 deg., 30 deg., 60 deg., 90 deg., and 120 deg. with respect to the projectile direction employing the time-of-flight technique using a proton recoil scintillation detector. Comparison with calculated results from equilibrium nuclear reaction model codes like PACE-2 and EMPIRE 2.18 using various level-density options was carried out. It is observed that the dynamic level-density approach in EMPIRE 2.18 gives the closest approximation to the measured data. In the Fermi-gas level-density approach the best approximation of the level-density parameter is a=A/12.0, where A is the mass number of the composite system. The trend in the angular distribution of emitted neutrons is well reproduced by the projection of the angular momentum on the recoil axis as done in the PACE-2 code.

Sunil, C.; Nandy, Maitreyee; Sarkar, P. K. [Accelerator Radiation Safety Section, RSSD, Bhabha Atomic Research Centre, Mumbai 400085 (India); Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064 (India); H.P. Unit (RSSD, BARC), Variable Energy Cyclotron Centre, 1/AF, Bidhannagar, Kolkata 700064 (India)

2008-12-15

339

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).

Kim, Sung Kuk

2010-01-01

340

Levels of 159Gd populated in average resonance neutron capture  

NASA Astrophysics Data System (ADS)

The primary ?-rays and energy levels in 159Gd were investigated in average resonance neutron capture using tailored neutron beams at 2 keV and 24 keV and a pair spectrometer at the high flux reactor at Brookhaven. Nearly 200 levels with spin up to {5}/{2} are reported below 3 MeV. The distribution of radiative strength in this nucleus was obtained and is compared with a giant dipole resonance and single-particle strength models. The density of observed levels was determined and is described in terms of the constant temperature Fermi gas model. The neutron binding energy in 159Gd was determined to be 5943.32(12) keV.

Granja, C.; Pospíšil, S.; Telezhnikov, S. A.; Chrien, R. E.

2003-12-01

341

Detailed mapping of the local Ir{sup 4+} dimers through the metal-insulator transitions of CuIr{sub 2}S{sub 4} thiospinel by x-ray atomic pair distribution function measurements.  

SciTech Connect

The evolution of the short-range structural signature of the Ir{sup 4+} dimer state in CuIr{sub 2}S{sub 4} thiospinel has been studied across the metal-insulator phase transitions as the metallic state is induced by temperature, Cr doping, and x-ray fluence. An atomic pair distribution function (PDF) approach reveals that there are no local dimers that survive into the metallic phase when this is invoked by temperature and doping. The PDF shows Ir{sup 4+} dimers when they exist, regardless of whether or not they are long-range ordered. At 100 K, exposure to a 98 keV x-ray beam melts the long-range dimer order within a few seconds, though the local dimers remain intact. This shows that the metallic state accessed on warming and doping is qualitatively different from the state obtained under x-ray irradiation.

Bozin, E. S.; Masadeh, A. S.; Hor, Y. S.; Mitchell, J. F.; Billinge, S. J. L.; Materials Science Division; BNL; Michigan State Univ.; Univ. of Jordan; Columbia Univ.

2011-01-24

342

Detailed Mapping of the Local Ir4+ Dimers through the Metal-Insulator Transitions of CuIr2S4 Thiospinel by X-Ray Atomic Pair Distribution Function Measurements  

NASA Astrophysics Data System (ADS)

The evolution of the short-range structural signature of the Ir4+ dimer state in CuIr2S4 thiospinel has been studied across the metal-insulator phase transitions as the metallic state is induced by temperature, Cr doping, and x-ray fluence. An atomic pair distribution function (PDF) approach reveals that there are no local dimers that survive into the metallic phase when this is invoked by temperature and doping. The PDF shows Ir4+ dimers when they exist, regardless of whether or not they are long-range ordered. At 100 K, exposure to a 98 keV x-ray beam melts the long-range dimer order within a few seconds, though the local dimers remain intact. This shows that the metallic state accessed on warming and doping is qualitatively different from the state obtained under x-ray irradiation.

Božin, E. S.; Masadeh, A. S.; Hor, Y. S.; Mitchell, J. F.; Billinge, S. J. L.

2011-01-01

343

Direct Deterministic Method for Neutronics Analysis and Computation of Asymptotic Burnup Distribution in a Recirculating Pebble-Bed Reactor  

SciTech Connect

A new deterministic method has been developed for the neutronics analysis of a pebble-bed reactor (PBR). The method accounts for the flow of pebbles explicitly and couples the flow to the neutronics. The method allows modeling of once-through cycles as well as cycles in which pebbles are recirculated through the core an arbitrary number of times. This new work is distinguished from older methods by the systematically semi-analytical approach it takes. In particular, whereas older methods use the finite-difference approach (or an equivalent one) for the discretization and the solution of the burnup equation, the present work integrates the relevant differential equation analytically in discrete and complementary sub-domains of the reactor. Like some of the finite-difference codes, the new method obtains the asymptotic fuel-loading pattern directly, without modeling any intermediate loading pattern. This is a significant advantage for the design and optimization of the asymptotic fuel-loading pattern. The new method is capable of modeling directly both the once-through-then-out fuel cycle and the pebble recirculating fuel cycle. Although it currently includes a finite-difference neutronics solver, the new method has been implemented into a modular code that incorporates the framework for the future coupling to an efficient solver such as a nodal method and to modern cross section preparation capabilities. In its current state, the deterministic method presented here is capable of quick and efficient design and optimization calculations for the in-core PBR fuel cycle. The method can also be used as a practical "scoping" tool. It could, for example, be applied to determine the potential of the PBR for resisting nuclear-weapons proliferation and to optimize proliferation-resistant features. However, the purpose of this paper is to show that the method itself is viable. Refinements to the code are under way, with the objective of producing a powerful reactor physics analysis tool for PBRs.

Terry, William Knox; Gougar, Hans D; Ougouag, Abderrafi Mohammed-El-Ami

2002-07-01

344

Electron-positron pair production by ultrarelativistic electrons in a soft-photon field  

SciTech Connect

The fully differential cross section for photon-electron pair production is integrated numerically over phase space. Results for the astrophysically interesting case are obtained, in which the interaction between an ultrarelativistic electron and a soft photon results in e/sup -/-e/sup +/ pair production. The positron spectrum is a function of the energies of both the photon and the electron, as well as the angle of interaction. An isotropic distribution of photons is assumed in integration over solid angle. The energy at which the positron distribution peaks is found to be inversely proportional to the photon energy and independent of the electron energy. The positron spectrum is integrated once more over initial electron energies for a power-law energy distribution of primary electrons. The same procedure is repeated for the recoil particle; it is shown that the peak of the recoil energy distribution depends linearly on the energy of the primary electron. Finally, semi-analytical expressions are obtained for the energy losses of the primary electrons. Triplet pair production turns out to be important in the magnetospheres of hot (T approx. 10/sup 7/K), young (t less than or equal to 200 yrs) neutron stars. Interactions between thermal photons and highly relativistic electrons accelerated in the pulsar magnetosphere can initiate intense electromagnetic cascades. Finally, the possibility of a young pulsar (presumably arising from a recent supernova explosion) in the galactic center region is considered.

Mastichiadis, A.

1985-01-01

345

Di-Neutron Correlation in Light Neutron-Rich Nuclei  

NASA Astrophysics Data System (ADS)

Using a three-body model with density-dependent contact interaction, we discuss the root mean square distance between the two valence neutrons in 11Li nuclues as a function of the center of mass of the neutrons relative to the core nucleus 9Li. We show that the mean distance takes a pronounced minimum around the surface of the nucleus, indicating a strong surface di-neutron correlation. We demonstrate that the pairing correlation plays an essential role in this behavior. We also discuss the di-neutron structure in the 8He nucleus.

Hagino, K.; Sagawa, H.; Schuck, P.

346

Separation Pair Detection  

Microsoft Academic Search

A separation pair of a biconnected graph is a pair of vertices whose removal disconnects the graph. The central part of any\\u000a algorithm that finds triconnected components is an algorithm for separation pairs. Recently Miller and Ramachandran have given\\u000a a parallel algorithm that runs in O(log\\u000a 2 n) time using O(m) processors. We present a new algorithm for finding all

Donald S. Fussell; Ramakrishna Thurimella

1988-01-01

347

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

348

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

349

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

350

Distribution of decane within the unit cell of the inverted hexagonal (H sub II ) phase of lipid-water-decane systems determined by neutron diffraction  

SciTech Connect

The addition of a free alkane such as decane to lipid-water systems is known to promote the formation of a low-temperature inverted hexagonal (H{sub II}) phase. By combining neutron and X-ray diffraction data to do a Fourier reconstruction of the H{sub II} phase of dioleoylphosphatidylethanolamine (DOPE) + water + deuterated decane, it was found that the decane preferentially partitions into the interstitial regions of the H{sub II} unit cell where it should be the most effective in alleviating the hydrocarbon chain packing stress, supporting the suggestion of Kirk et al. Using the distribution of decane within the unit cell, the authors have calculated the lipid length distribution for the situations with and without added alkane. With a suitable molecular model, this lipid length distribution may eventually be used to calculate the free energy change upon the addition of alkane. Such a measurement is important for a more realistic understanding of the interactions which lead to the formation of the H{sub II} phase.

Turner, D.C.; Gruner, S.M. (Princeton Univ., NJ (United States)); Huang, J.S. (Exxon Research and Engineering Co., Annandale, NJ (United States))

1992-02-11

351

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

352

Gel dosimeters as useful dose and thermal-fluence detectors in boron neutron capture therapy  

NASA Astrophysics Data System (ADS)

The dosimetry method based on Fricke-Xylenol-Orange-infused gels in form of layers has shown noticeable potentiality for in-phantom or in-free-beam dose and thermal flux profiling and imaging in the high fluxes of thermal or epithermal neutrons utilised for boron neutron capture therapy (BNCT). Gel-dosimeters in form of layers give the possibility not only of obtaining spatial dose distributions but also of achieving measurements of each dose contribution in neutron fields. The discrimination of the various dose components is achieved by means of pixel-to-pixel manipulations of pairs of images obtained with gel-dosimeters having different isotopic composition. It is possible to place large dosimeters, detecting in such a way large dose images, because the layer geometry of dosimeters avoids sensitive variation of neutron transport due to the gel isotopic composition. Some results obtained after the last improvements of the method are reported.

Gambarini, G.; Moss, R. L.; Mariani, M.; Carrara, M.; Daquino, G. G.; Nievaart, V. A.; Valente, M.; Vanossi, E.

353

A combination of anomalous x-ray scattering and neutron diffraction for structural characterizations of Zr63Ni25Al12 metallic glass  

NASA Astrophysics Data System (ADS)

Zr63Ni25Al12 bulk metallic glass was investigated using neutron diffraction and anomalous x-ray scattering close to the Zr and Ni K edges. The experimental results were analyzed using reverse Monte Carlo modeling (RMC) to obtain partial structure factors and pair distribution functions. The obtained partial structural results were compared with RMC results when neutron diffraction data are not included in the analysis and the report of Zr60Ni25Al15 by Fukunaga et al. using high-energy x-ray and neutron total scattering data.

Hosokawa, S.; Bérar, J.-F.; Boudet, N.; Kohara, S.; Stellhorn, J.; Pilgrim, W.-C.; Zeidler, A.; Kato, H.; Kawakita, Y.; Otomo, T.

2014-04-01

354

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. 

355

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

356

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.

357

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

358

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

Microsoft Academic Search

In order to generate epithermal neutrons for boron neutron capture therapy (BNCT), we proposed the method of filtering and moderating fast neutrons, which are emitted from the reaction between a beryllium target and 30MeV protons accelerated by a cyclotron, using an optimum moderator system composed of iron, lead, aluminum, calcium fluoride, and enriched 6LiF ceramic filter. At present, the epithermal-neutron

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

2009-01-01

359

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) [Augusta, GA; Babcock, Dale F. (Wilmington, DE) [Wilmington, DE; Menegus, Robert L. (Wilmington, DE) [Wilmington, DE

1983-01-01

360

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

361

Fermionic condensation in ultracold atoms, nuclear matter and neutron stars  

NASA Astrophysics Data System (ADS)

We investigate the Bose-Einstein condensation of fermionic pairs in three different superfluid systems: ultracold and dilute atomic gases, bulk neutron matter, and neutron stars. In the case of dilute gases made of fermionic atoms the average distance between atoms is much larger than the effective radius of the inter-atomic potential. Here the condensation of fermionic pairs is analyzed as a function of the s-wave scattering length, which can be tuned in experiments by using the technique of Feshbach resonances from a small and negative value (corresponding to the Bardeen-Cooper-Schrieffer (BCS) regime of Cooper Fermi pairs) to a small and positive value (corresponding to the regime of the Bose-Einstein condensate (BEC) of molecular dimers), crossing the unitarity regime where the scattering length diverges. In the case of bulk neutron matter the s-wave scattering length of neutron-neutron potential is negative but fixed, and the condensate fraction of neutron-neutron pairs is studied as a function of the total neutron density. Our results clearly show a BCS-quasiunitary-BCS crossover by increasing the neutron density. Finally, in the case of neutron stars, where again the neutron-neutron scattering length is negative and fixed, we determine the condensate fraction as a function of the distance from the center of the neutron star, finding that the maximum condensate fraction appears in the crust of the neutron star.

Salasnich, Luca

2014-04-01

362

NEUTRON-FLUX DISTRIBUTION IN A CYLINDRICAL CELL OBTAINED BY THE Sâ APPROXIMATION TO THE TRANSPORT EQUATION. ADDENDUM  

Microsoft Academic Search

A recalculation was made with the revised boundary conditions mentioned ; in the footnote on page 5 of GA-93 for Cases 1 and 6. These conditions mean ; physically that the angular flux distribution at the cell boundary has to be ; representable at the lowest possible spherical harmonics. The detailcd numerical ; results are reproduced. (W.D.M.);

L. W. Nordheim; E. K. Bjornerud

1957-01-01

363

Characterization of the source neutrons produced by the Frascati Neutron Generator  

Microsoft Academic Search

Integral experiments with a neutron source based on the T(d,n)? reaction require a good knowledge of the source neutron distribution. The source neutrons are energy-angle distributed with an energy spread of a few mega-electronvolts and anisotropy emission of a few percent.The characterization of the 14-MeV neutron source of the Frascati Neutron Generator (FNG) has been carried out using an absolutely

M Pillon; M Angelone; M Martone; V Rado

1995-01-01

364

Subradiant Split Cooper Pairs  

NASA Astrophysics Data System (ADS)

We suggest a way to characterize the coherence of the split Cooper pairs emitted by a double-quantum-dot based Cooper pair splitter (CPS), by studying the radiative response of such a CPS inside a microwave cavity. The coherence of the split pairs manifests in a strongly nonmonotonic variation of the emitted radiation as a function of the parameters controlling the coupling of the CPS to the cavity. The idea to probe the coherence of the electronic states using the tools of cavity quantum electrodynamics could be generalized to many other nanoscale circuits.

Cottet, Audrey; Kontos, Takis; Yeyati, Alfredo Levy

2012-04-01

365

Gd isotope systematics with Skyrme and delta-pairing forces  

Microsoft Academic Search

Assuming axial symmetry of the nuclear shape and the Skyrme force SIII updated on the pairing interaction V0delta(r-->12) we performed constrained Hartree-Fock calculations of well deformed even gadolinium 64Gd isotopes with neutron numbers N=86-106. The mass spectrum, nuclear radii, neutron skin thickness, quadrupole moments (deformations), and low-spin rotational levels are calculated. In all the cases viewed the angular momentum projection

Andrzej Baran; Walter Höhenberger

1996-01-01

366

Pairing effects on spinodal decomposition of asymmetric nuclear matter  

NASA Astrophysics Data System (ADS)

We investigate the impact of pairing correlations on the behavior of unstable asymmetric nuclear matter at low temperature. We focus on the relative role of the pairing interaction, coupling nucleons of the same type (neutrons or protons), with respect to the symmetry potential, which enhances the neutron-proton attraction, along the clusterization process driven by spinodal instabilities. It is found that, especially at the transition temperature from the normal to the superfluid phase, pairing effects may induce significant variations in the isotopic content of the clusterized matter. This analysis is potentially useful for gathering information on the temperature dependence of nuclear pairing and, in general, on the properties of clusterised low-density matter, which are of interest also in the astrophysical context.

Burrello, S.; Colonna, M.; Matera, F.

2014-05-01

367

Pair Winds in Schwarzschild Spacetime with Application to Strange Stars  

NASA Astrophysics Data System (ADS)

We present the results of numerical simulations of stationary, spherically outfiowing, e± pair winds, with total luminosities in the range 1034 - 1042 ergs s-1. In the concrete example described here, the wind injection source is a hot, bare, strange star, predicted to be a powerful source of e± 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.

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

2008-09-01

368

Three-dimensional structure of nanocomposites from atomic pair distribution function analysis: study of polyaniline and (polyaniline)(0.5)V(2)O(5) x 1.0 H(2)O.  

PubMed

The three-dimensional structures of emeraldine base polyaniline (PANI) and (polyaniline)(0.5)V(2)O(5) x 1.0 H(2)O have been determined by total X-ray scattering experiments. Atomic pair distribution functions (PDF) were measured to obtain experimental observables against which structural models were tested and refined. The PDF approach is necessary because of the limited structural coherence in these nanostructured materials. Polyaniline possesses a well-defined local atomic arrangement that can be described in terms of an 84-atom orthorhombic unit cell. The nanocomposite (PANI)(0.5)V(2)O(5) x 1.0 H(2)O too is locally well ordered and may be described in terms of a small number of structure-sensible parameters. The PDF approach allows the construction of structure models of PANI and (PANI)(0.5)V(2)O(5) x 1.0 H(2)O on the basis of which important materials' properties can be explained predicted and possibly improved. PMID:15954787

Petkov, Valeri; Parvanov, Vencislav; Trikalitis, Pantelis; Malliakas, Christos; Vogt, Tom; Kanatzidis, Mercouri G

2005-06-22

369

Probing local structure in the yellow phosphor LaSr[subscript 2]AlO[subscript 5]:Ce[superscript 3+], by the maximum entropy method and pair distribution function analysis  

SciTech Connect

The compound LaSr{sub 2}AlO{sub 5} was recently introduced as a competitive Ce{sup 3+} host material for blue-pumped yellow phosphors for use in white light emitting diodes. A crucial feature of the crystal structure of LaSr{sub 2}AlO{sub 5} is that La, which is the host site for Ce{sup 3+}, is located in the 8h positions of the I4/mcm crystal structure, a site equally shared with Sr. While the average crystal structure of LaSr{sub 2}AlO{sub 5} as revealed by Rietveld analysis of laboratory and synchrotron X-ray diffraction data suggests nothing untoward, maximum entropy method analysis of the synchrotron X-ray data reveals the existence of conspicuous non-sphericity of the electron density. Pair distribution function analysis of the data suggests that despite their occupying the same crystallographic site, La and Sr possess distinct coordination environments, and the environment around La is more compact and regular than the environment suggested by the Rietveld refinement of the average structure. The absorption and emission from Ce{sup 3+} centers is controlled by the local coordination and symmetry, and the use of powerful new tools in unraveling details of these strengthens the rational search for new phosphors for solid state white lighting.

Im, Won Bin; Page, Katharine; DenBaars, Steven P.; Seshadri, Ram (UCSB); (LANL)

2011-08-04

370

Pulsar Pair Cascades in a Distorted Magnetic Dipole Field  

Microsoft Academic Search

We investigate the effect of a distorted neutron star dipole magnetic field\\u000aon pulsar pair cascade multiplicity and pair death lines. Using a simple model\\u000afor a distorted dipole field that produces an offset polar cap, we derive the\\u000aaccelerating electric field above the polar cap in space charge limited flow.\\u000aWe find that even a modest azimuthally asymmetric distortion

Alice K. Harding; Alex G. Muslimov

2010-01-01

371

Treatment of the like-particle pairing of quartets  

NASA Astrophysics Data System (ADS)

The ground state correlations induced by a general pairing Hamiltonian in a finite system of like fermions are described in terms of four-body correlated structures (quartets). These are real superpositions of the products of two pairs of particles in time-reversed states. Quartets are determined variationally through an iterative sequence of diagonalizations of the Hamiltonian in restricted model spaces and are, in principle, all distinct from one another. The ground state is represented as a product of quartets to which, depending on the number of particles (supposed to be even, in any case), an extra collective pair is added. The extra pair is also determined variationally. In the case of pairing in a spherically symmetric mean field, both the quartets and the extra pair (if any) are characterized by a total angular momentum J = 0. Realistic applications of the quartet formalism are carried out for Sn isotopes with valence neutrons in the 50-82 neutron shell. The exact ground state correlation energies, occupation numbers and pair transfer matrix elements are reproduced to a very high degree of precision. The formalism also lends itself to a straightforward and accurate description of the lowest seniority 0 and 2 excited states of the pairing Hamiltonian. A simplified representation of the ground state as a product of identical quartets is eventually discussed and found to improve considerably upon the more traditional particle-number projected BCS approach.

Sambataro, M.; Sandulescu, N.

2013-05-01

372

Neutron Compound Refractive Prisms - DOE SBIR Phase II Final Report  

SciTech Connect

The results of the research led to a pulsed electromagnetic periodic magnetic field array (PMF), which coupled with a pair of collimation slits, and a mechanical chopper slit, were able to deflect spin-up neutrons to a band of line-fused neutrons a focal plane heights that correspond to the time-varying magnetic field amplitude. The electromagnetic field PMF produced 5.4 pulses per minute in which each pulse was 50 msec in duration with a full width half maximum (FWHM) of 7.5 msec. The calculated 7.7 mm vertical height of the band of focused spin-up neutrons corresponded closely to the measured 7.5 mm height of the center line of the imaged band of neutrons. The band of deflected spin-up neutrons was 5 mm in vertical width and the bottom of the band was 5 mm above the surface of the PMF pole. The limited exposure time of 3 hours and the smaller 0.78 T magnetic field allowed focused and near focused neutrons of 1.8 ���� to 2.6 ���� neutrons, which were in the tails of the McClellan Nuclear Radiation Center Bay 4 Maxwell Boltzmann distribution of neutrons with peak flux at 1.1-1.2 ����. The electromagnetic PMF was expected to produces a 2.0 T peak magnetic field amplitude, which would be operational at a higher duty factor, rather than the as built 7.5 msec FWHM with pulse repetition frequency of 5.4 pulses per minute. The fabricated pulsed electromagnetic PMF with chopper is expected to perform well on a cold, very cold or ultra cold beam line as a spectrometer or monochromator source of spin-up polarized neutron. In fact there may be a possible use of the PMF to do ultra-cold neutron trapping, see paper by A. I. Frank1, V. G. Nosov, Quantum Effects in a One-Dimensional Magnetic Gravitational Trap for Ultracold Neutrons, JETP Letters, Vol. 79, No. 7, 2004, pp. 313�¢����315. The next step is to find a cold or very cold neutron facility, where further testing or use of the pulsed magnetic field PMF can be pursued.

Dr. Jay Theodore Cremer, Jr

2011-06-25

373

Coalescing binary neutron star systems  

NASA Astrophysics Data System (ADS)

We present numerical studies of coalescing neutron star pairs with Newtonian hydrodynamics coupled to the 2.5 Post-Newtonian radiation reaction of Blanchet, Damour, and Schäfer [1]. Our simulations evolve the Euler equations using a modification of the ZEUS 2-D algorithm [2] and use a Fast Fourier Transformation method for solving the Poisson equation for the gravitational and radiation reaction potentials. We find that the radiation reaction produces a significant effect on a neutron star pair when compared to a purely Newtonian simulation. .

Calder, Alan C.; Swesty, F. Douglas; Wang, Edward Y. M.

2001-10-01

374

Coherence length of neutron superfluids  

SciTech Connect

The coherence length of superfluid neutron matter is calculated from the microscopic BCS wave function of a Cooper pair in momentum space making use of recent nucleon-nucleon potential models and including polarization (RPA) effects. We find as our main result that the coherence length is proportional to the Fermi momentum to pairing gap ratio, in good agreement with simple estimates used in the literature, with a nearly interaction independent constant of proportionality. Our calculations can be applied to the problem of inhomogeneous superfluidity of hadronic matter in the crust of a neutron star. {copyright} {ital 1997} {ital The American Physical Society}

De Blasio, F.V.; Hjorth-Jensen, M. [NORDITA, Blegdamsvej 17, DK-2100 Copenhagen O/ (Denmark)] [NORDITA, Blegdamsvej 17, DK-2100 Copenhagen O/ (Denmark); Elgaro/y, O.; Engvik, L. [Department of Physics, University of Oslo, N-0316 Oslo (Norway)] [Department of Physics, University of Oslo, N-0316 Oslo (Norway); Lazzari, G. [European Centre for Theoretical Studies in Nuclear Physics and Related Areas, Trento (Italy)] [European Centre for Theoretical Studies in Nuclear Physics and Related Areas, Trento (Italy); Baldo, M.; Schulze, H. [Dipartimento di Fisica, Universita di Catania and I.N.F.N., Sezione di Catania, corso Italia 57, I-95129 Catania (Italy)] [Dipartimento di Fisica, Universita di Catania and I.N.F.N., Sezione di Catania, corso Italia 57, I-95129 Catania (Italy)

1997-10-01

375

Hierarchical Bayesian Analysis of Binary Matched Pairs Data  

Microsoft Academic Search

ABSTRACT Hierarchical Bayesian Analysis of Binary Matched Pairs Data The paper introduces a hierarchical Bayesian analysis of binary matched pairs data with non- informative prior distributions. Certain properties of the posterior distributions, including their propriety, are established. The Bayesian methods are implemented via Markov chain Monte Carlo integration techniques, and numerical illustrations are provided. For the logit link, the conditional

Malay Ghosh; Ming-hui Chen; Atalanta Ghosh; Alan Agresti; Eli Lilly

2000-01-01

376

Neutron Diagnostics for Pulsed Plasma Sources  

Microsoft Academic Search

Neutron detectors have been developed and applied to a variety of pulsed plasma sources with intensities ranging from 102 to 1012 neutrons\\/pulse. For yields as small as 102 neutrons, a 6Li-glass-scintillator detector is used. A rhodium-activation counter has been developed for yields greater than 106 neutrons. These detectors are used for total yield and angular distribution measurements. Neutron energies are

Frank C. Young

1975-01-01

377

Pair correlations in a bidisperse ferrofluid in an external magnetic field: theory and computer simulations  

NASA Astrophysics Data System (ADS)

The pair distribution function g( r) for a ferrofluid modeled by a bidisperse system of dipolar hard spheres is calculated. The influence of an external uniform magnetic field and polydispersity on g( r) and the related structure factor is studied. The calculation is performed by diagrammatic expansion methods within the thermodynamic perturbation theory in terms of the particle number density and the interparticle dipole-dipole interaction strength. Analytical expressions are provided for the pair distribution function to within the first order in number density and the second order in dipole-dipole interaction strength. The constructed theory is compared with the results of computer (Monte Carlo) simulations to determine the range of its validity. The scattering structure factor is determined using the Fourier transform of the pair correlation function g( r) - 1. The influence of the granulometric composition and magnetic field strength on the height and position of the first peak of the structure factor that is most amenable to an experimental study is analyzed. The data obtained can serve as a basis for interpreting the experimental small-angle neutron scattering results and determining the regularities in the behavior of the structure factor, its dependence on the fractional composition of a ferrofluid, interparticle correlations, and external magnetic field.

Nekhoroshkova, Yu. E.; Goldina, O. A.; Camp, P. J.; Elfimova, E. A.; Ivanov, A. O.

2014-03-01

378

Investigation of nuclear matter distribution of the neutron-rich He isotopes by proton elastic scattering at intermediate energies  

NASA Astrophysics Data System (ADS)

Absolute differential cross-sections for elastic p6He and p8He scattering were measured in inverse kinematics with secondary beams. In order to supplement data taken for small-angle scattering, differential cross-sections for higher momentum transfer were measured using liquid hydrogen target. Both data sets were analyzed together. They have permitted to deduce the radial shape of the nuclear matter distributions and the root-mean-square radii with the help of Glauber theory. In addition to a phenomenological analysis, used already in the previous work, a model-independent analysis with a help of a Sum-Of-Gaussians (SOG) method has been performed. The experimental p6,8He elastic scattering cross-sections have also been compared with the predictions from various theoretical nuclear models.

Kiselev, O. A.; Aksouh, F.; Bleile, A.; Bochkarev, O. V.; Chulkov, L. V.; Cortina-Gil, D.; Dobrovolsky, A. V.; Egelhof, P.; Geissel, H.; Hellström, M.; Isaev, N. B.; Komkov, B. G.; Mátos, M.; Moroz, F. V.; Münzenberg, G.; Mutterer, M.; Mylnikov, V. A.; Neumaier, S. R.; Pribora, V. N.; Seliverstov, D. M.; Sergueev, L. O.; Shrivastava, A.; Sümmerer, K.; Weick, H.; Winkler, M.; Yatsoura, V. I.

2005-09-01

379

Investigating concentration distributions of arsenic, gold and antimony in grain-size fractions of gold ore using instrumental neutron activation analysis.  

PubMed

Instrumental neutron activation analysis (INAA) has been used to quantify concentrations of arsenic (As), gold (Au) and antimony (Sb) in grain-size fractions of a gold ore. The ore, which was taken from the Ahafo project site of Newmont Ghana Gold Ltd., was fractionated into 14 grain-size fractions using state-of-the-art analytical sieve machine. The minimum sieve mesh size used was 36mum and grains >2000mum were not considered for analysis. Result of the sieving was analysed with easysieve(R) software. The<36mum subfraction was found to be the optimum, hosting bulk of all three elements. Arsenic was found to be highly concentrated in<36-100mum size fractions and erratically distributed in from 150mum fraction and above. For gold, with the exception of the subfraction <36mum which had exceptionally high concentration, the element was found to be approximately equally distributed in all the size fractions but slightly "played out" in 150-400mum size fractions. Antimony occurrence in the sample was relatively high in <36mum size fraction followed by 600, 800, 400 and 36mum size fractions in that order. Gold content in the sample was comparatively far greater than arsenic and antimony; this is indicative of level of gold mineralization in the concession where the sample ore was taken. The concentration of gold in the composite sample was in the range 564-8420ppm as compared to 14.33-186.92ppm for arsenic and 1.09-9.48ppm for antimony. Elemental concentrations were correlated with each other and with grain-size fractions and the relationships between these descriptive parameters were established. PMID:19896855

Nyarku, M; Nyarko, B J B; Serfor-Armah, Y; Osae, S

2010-02-01

380

Di-neutron correlation in monopole two-neutron transfer modes in the Sn isotope chain  

NASA Astrophysics Data System (ADS)

We study microscopic structures of monopole pair vibrational modes and associated two-neutron transfer amplitudes in neutron-rich Sn isotopes by means of the linear response formalism of the quasiparticle random phase approximation (QRPA). For this purpose we introduce a method to decompose the transfer amplitudes with respect to two-quasiparticle components of the QRPA eigenmode. It is found that pair-addition vibrational modes in neutron-rich 132-140Sn and the pair rotational modes in 142-150Sn are commonly characterized by coherent contribution of quasaiparticle states having high orbital angular momenta l?5, which suggests transfer of a spatially correlated neutron pair. The calculation also predicts a high-lying pair vibration, the giant pair vibration, emerging near the one-neutron separation energy in 110-130Sn, and we find that they have the same di-neutron characters as that of the low-lying pair vibration in 132-140Sn.

Shimoyama, Hirotaka; Matsuo, Masayuki

2013-11-01

381

Spectra from pair-equilibrium plasmas  

NASA Technical Reports Server (NTRS)

A numerical model of relativistic nonmagnetized plasma with uniform temperature and electron density distributions is considered, and spectra from plasma in pair equilibrium are studied. A range of dimensionless temperature (T) greater than about 0.2 is considered. The spectra from low pair density plasmas in pair equilibrium vary from un-Comptonized bremsstrahlung spectra at Thomson cross section tau(N) much less than one to Comptonized bremsstrahlung spectra with tau(N) over one. For high pair density plasmas the spectra are flat for T greater than about one, and have broad intensity peaks at energy roughly equal to 3T for T less than one. In the latter region the total luminosity is approximately twice the annihilation luminosity. All spectra are flat in the X-ray region, in contradiction to observed AGN spectra. For dimensionless luminosity greater than about 100, the cooling time becomes shorter than the Thomson time.

Zdziarski, A. A.

1984-01-01

382

Local Structure of La1-xSrxCoO3 determined from EXAFS and neutron PDF studies  

SciTech Connect

The combined local structure techniques, extended x-ray absorption fine structure (EXAFS) and neutron pair distribution function analysis, have been used for temperatures 4<= T<= 330 K to rule out a large Jahn-Teller (JT) distortion of the Co-O bond in La1?xSrxCoO3 for a significant fraction of Co sites (x<= 0.35), indicating few, if any, JT-active, singly occupied eg Co sites exist.

Sundaram, N.; Jiang, Y.; Anderson, I. E.; Belanger, D. P.; Booth, C. H.; Bridges, F.; Mitchell, J. F.; Proffen, Th.; Zheng, H.

2009-01-26

383

La structure des verres étudiée par diffraction des neutrons  

NASA Astrophysics Data System (ADS)

La diffraction des neutrons est une méthode largement utilisée pour déterminer la structure des matériaux amorphes et en particulier des verres. L'utilisation de la méthode de substitution isotopique permet d'extraire les fonctions de distribution de paires partielles centrées autour d'un élément choisi. Nous présentons quelques exemples récents d'études par diffraction des neutrons sur des verres qui ont permis de mieux comprendre à la fois le réseau polymérique de la matrice vitreuse et l'environnement local et à moyenne distance autour des cations. Ces études ont révélées un ordre structural s'étendant au delà des premiers voisins, jusque vers de distances d'environ 10Å. Le couplage avec d'autres méthodes expérimentales (diffraction anormale des rayons X) et des techniques de simulations (dynamique moléculaire, Monte Carlo Inverse ou RMC) sont indispensables pour affiner nos connaissances de la structure des verres.

Cormier, L.

2003-09-01

384

Neutron multiplicities in spontaneous fission and nuclear structure studies  

SciTech Connect

New insights into the fission process can be gained by better quantitative knowledge of how the energy released in fission is distributed between the kinetic energy of the two fragments, the excitation energy of the two fragments and the number of neutrons emitted. Studies of prompt gamma-rays emitted in spontaneous fission (SF) with large arrays of Compton suppressed Ge detector arrays are providing new quantitative answers to longstanding questions concerning fission as well as new insights into the structure of neutron-rich nuclei. For the first time the triple gamma coincidence technique was employed in spontaneous fission studies. Studies of SF of {sup 252}Cf and {sup 242}Pu have been carried out. These {gamma}-{gamma}-{gamma} data provide powerful ways to identify uniquely gamma rays from a particular nucleus in the very complex gamma-ray spectra given off by the over 100 different nuclei produced. The emphasis of this paper is on the first quantitative measurements of the multiplicities of the neutrons emitted in SF and the energy levels populated in the fragments. Indeed, in the break up into Mo-Ba pairs, we have identified for the first time fragments associated with from zero up to ten neutrons emitted and observed the excited energy states populated in these nuclei. The zero neutron emission pairs like {sup 104}Mo- {sup 148}Ba, {sup 106}Mo- {sup 146}Ba and {sup 104}Zr- {sup 148}Ce observed in this work are particularly interesting because they represent a type of cold fission or a new mode of cluster radioactivity as proposed by Greiner, Sandulescu and co-workers. These data provide new insights into the processes of cluster radioactivity and cold fission.

Hamilton, J.H.; Kormicki, J.; Lu, Q. [Vanderbilt Univ., Nashville, TN (United States). Dept. of Physics and Astronomy] [and others

1993-12-31

385

Pulsar Pair Cascades in a Distorted Magnetic Dipole Field  

NASA Technical Reports Server (NTRS)

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.

2010-01-01

386

Enhanced Two Nucleon Transfer Due to Pairing Correlations  

NASA Astrophysics Data System (ADS)

The role of nucleon pairing in two-nucleon transfer is reviewed. Because of the collective properties of the ground states in even-even nuclei with spin zero (due to the pairing interaction), these states are preferentially populated in pair transfer. Initially two-neutron transfer has been studied mainly with (t, p) reactions. Later a large variety of heavier projectiles have been used. The dynamical features of the heavy ion reactions allowed the use of semiclassical approaches for the description of the reactions. In these cases, the definition of the enhancements in pair transfer as observed in heavier systems, can be based on the semiclassical method (transfer probabilities). This allows a simple and transparent description of the dynamics of the pair transfer and large enhancements have been observed in heavy ion systems (e.g. Pb + Sn).

von Oertzen, Wolfram

2013-01-01

387

Neutron cross sections: Volume 2, Neutron cross section curves  

Microsoft Academic Search

Data is presented only for total (i.e., integrated) reaction cross sections (and related fission parameters) as a function of incident-neutron energy. The energy range has been limited to 0.01 eV to 200 MeV in order to exclude crystalline and magnetic effects for slow neutrons and relativistic effects for high energy neutrons. Angular distributions and partial reaction cross sections to specific

V. McLane; C. L. Dunford; P. F. Rose

1988-01-01

388

Describe Angle Pair Relationships  

NSDL National Science Digital Library

This lesson will explain the types of pairs of angles you will find in Geometry. Note taking time on page 5: Angle Information Now, let's see if you get it: Angle Relationship Quiz (fun) Ok! Now for your assignment, #8 on page 38! Class Zone Geometry Textbook ...

Neubert, Mrs.

2011-09-01

389

Dimension Reduction for Hybrid Paired Comparison Models  

Microsoft Academic Search

Rating -- and subsequently ranking -- college football teams requires making sense of sometimes conflicting pair-wise comparisons. Classical statistical techniques fall into one of two classes: win\\/loss models, which focus on binary outcomes, and point-scoring models, which consider the distribution of component scores. Annis and Craig (2005) illustrate deficiencies of both, and propose a hybrid method that considers both sources

David H. Annis

2007-01-01

390

Diametral Pairs of Linear Extensions  

Microsoft Academic Search

Given a finite poset P, we consider pairs of linear extensions of P with maximal distance, where the distance between two linear extensions L_1, L_2 is the number of pairs of elements of P appearing in different orders in L_1 and L_2. A diametral pair maximizes the distance among all pairs of linear extensions of P. Felsner and Reuter defined

Graham Brightwell; Mareike Massow

2008-01-01

391

Vertical Distribution of Shallow Water in the Distinguishable Regions at Low and High Latitudes of Mars: Neutron Data Deconvolution of HEND  

NASA Technical Reports Server (NTRS)

High Energy Neutron Detector (HEND) is the part of Gamma-Ray Spectrometer suite onboard NASA Mars Odyssey orbiter [1-4]. During 16 months of mapping stage of Odyssey mission HEND has accumulated the set of maps of neutron emission of Mars at more than seven decades of energies range from the Cadmium threshold of 0.4 eV up to 15 MeV. These maps present very large variations of neutrons at different regions of Mars and they also show quite strong changes along Martian seasons.

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

2003-01-01

392

Barrier distributions from {sup 32}S+{sup 90,96}Zr quasi-elastic scattering: Investigation of the role of neutron transfer in sub-barrier fusion reactions  

SciTech Connect

The differential cross sections of quasi-elastic scattering at backward angles were measured with high precision for {sup 32}S+{sup 90,96}Zr around the Coulomb barrier, and barrier distributions were extracted from the measured excitation functions. The experimental barrier distribution of {sup 32}S+{sup 90}Zr is well reproduced by the coupled-channels calculations including the low-lying quadruple and octupole vibrations in {sup 32}S and {sup 90}Zr. However, the model with the same coupling scheme fails to reproduce the experimental barrier distribution for {sup 32}S+{sup 96}Zr. The coupled-channels calculation including the neutron transfer channels in the system {sup 32}S+{sup 96}Zr gives an improved description of the experimental data. A comparison of the data on {sup 40}Ca+{sup 90,96}Zr shows that the two systems {sup 32}S, {sup 40}Ca+{sup 90}Zr display barrier distributions that are similar to each other, whereas the barrier distributions of {sup 32}S, {sup 40}Ca+{sup 96}Zr are both wider and flatter than the those of {sup 40}Ca+{sup 90,96}Zr. The present results strongly indicate that neutron transfer plays an important role in the fusion processes.

Yang, F.; Lin, C. J.; Wu, X. K.; Zhang, H. Q.; Zhang, C. L.; Zhou, P.; Liu, Z. H. [China Institute of Atomic Energy, P. O. Box 275, Beijing 102413 (China)

2008-01-15

393

Convergent beam neutron crystallography  

NASA Astrophysics Data System (ADS)

Applications of neutron diffraction for small samples (<1mm3) or small fiducial areas are limited by the available neutron flux density. Recent demonstrations of convergent beam electron and x-ray diffraction and focusing of cold (?>1 Å) neutrons suggest the possibility to use convergent beam neutron diffraction for small sample crystallography. We have carried out a systematic study of diffraction of both monoenergetic and broad bandwidth neutrons at the NIST Research Reactor and at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory. Combining convergent beams with time-of-flight Laue diffraction is particularly attractive for high efficiency small sample diffraction studies. We have studied single crystal and powder diffraction of neutrons with convergence angles as large as 15° and have observed diffracted peak intensity gains greater than 20. The convergent beam method (CBM) shows promise for crystallography on small samples of small to medium size molecules (potentially even for proteins), ultra-high pressure samples, and for mapping of strain and texture distributions in larger samples.

Gibson, Walter M.; Schultz, Arthur J.; Richardson, James W.; Carpenter, John M.; Mildner, David F. R.; Chen-Mayer, Heather H.; Miller, M. E.; Maxey, E.; Prask, Henry J.; Gnaeupel-Herold, Thomas H.; Youngman, Russell

2004-01-01

394

Pairs of Legs  

NSDL National Science Digital Library

In this problem students practice counting by twos as they explore the natural phenomenon that legs on creatures always come in pairs, laying the foundation for doubling and halving. A set of cards can be downloaded (pdf) and matched. The Teachers' Notes page offers suggestions for implementation, discussion questions, ideas for extension and support, an expanded set of cards (pdf), and links to related activities (Noah and Number Tracks, both cataloged separately).

2011-05-01

395

Interacting magnetic nanodisks pairs  

NASA Astrophysics Data System (ADS)

Nanodots with magnetic vortex configuration are considered as promising elements of recording media [1]. When vortices are excited from their equilibrium position and allowed to relax, they perform a motion called gyrotropic, with a characteristic frequency. When two magnetic disks are close to one another there arises a frequency splitting due to the dynamic interaction [1]. Expressions for the magnetic vortex excitation frequencies and coupling constants in a pair of coupled identical circular disks were obtained previously by Shibata et al. [2]. The goal of this work is to calculate analytically the frequency of the dynamic excitation of coupled vortices in a pair of disks with different radii, with the same thickness. We considered a magnetostatic interdot interaction using the linearized Thiele's equations of motion of the vortex core, neglecting the damping term. Through micromagnetic simulation, we have investigated the interaction of these pairs of nanodisks using a recently developed tool, the magnetic vortex echoes (MVE) [3]. An analytical model of the MVE is presented. [4pt] [1] H. Jung, et al. Sci. Rep. 59, 1-6 (2011).[0pt] [2] J. Shibata et al. Phys. Rev. B67, 224404 (2003).[0pt] [3] F.Garcia et al., Journal of Applied Physics (in press).

Sinnecker, Joao Paulo; Vigo Cotrina, Helmunt Eduardo; Novais, Erico; Garcia, Flávio; Passos Guimaraes, Alberto

2013-03-01

396

MOS neutron sensor systems and their possible applications to neutron field investigations  

NASA Astrophysics Data System (ADS)

MOS sensors combined with fissile radiators are suitable for measurements of neutron flux density and neutron fluence. Two special configurations of MOS sensor systems are described for monitoring of neutrons with a known energy spectrum and for radiation field investigations in the case of an unknown neutron spectrum. Examples are given of measuring the spatial distribution of the neutron flux density and the portion of thermal, intermediate and fast neutrons in the flux density. Advantages and limits of the MOS sensor systems to the neutron field investigation are discussed.

Streubel, G.; Reinhard, J.; Hahn, B.; Kadner, K.

1992-10-01

397

A fundamental study on hyper-thermal neutrons for neutron capture therapy.  

PubMed

The utilization of hyper-thermal neutrons, which have an energy spectrum with a Maxwellian distribution at a higher temperature than room temperature (300 K), was studied in order to improve the thermal neutron flux distribution at depth in a living body for neutron capture therapy. Simulation calculations were carried out using a Monte Carlo code 'MCNP-V3' in order to investigate the characteristics of hyper-thermal neutrons, i.e. (i) depth dependence of the neutron energy spectrum, and (ii) depth distribution of the reaction rate in a water phantom for materials with 1/v neutron absorption. It is confirmed that hyper-thermal neutron irradiation can improve the thermal neutron flux distribution in the deeper areas in a living body compared with thermal neutron irradiation. When hyper-thermal neutrons with a 3000 K Maxwellian distribution are incident on a body, the reaction rates of 1/v materials such as 14N, 10B etc are about twice that observed for incident thermal neutrons at 300 K, at a depth of 5 cm. The limit of the treatable depth for tumours having 30 ppm 10B is expected to be about 1.5 cm greater by utilizing hyper-thermal neutrons at 3000 K compared with the incidence of thermal neutrons at 300 K. PMID:15551549

Sakurai, Y; Kobayashi, T; Kanda, K

1994-12-01

398

Structure functions and pair-correlation in space plasma physics  

NASA Astrophysics Data System (ADS)

Structure functions account for the microscale interparticle distributions of second order, that is, correlation between pairs of electrons or ions. Ordinarily in space plasmas physics one considers only the first order particle distributions when discussing pitch angle distributions, velocity distributions, and similar constructs. However numerous important physical aspects are only to be found in higher order distributions. Most importantly the pair-correlation function includes the effect of particle pair interactions in contrast to collective plasma effects. This work presents Monte-Carlo simulations and measurements for the purpose of obtaining pair correlation functions for typical space plasmas around the Earth. In particular the work is based on the DWP electron correlator on the CLUSTER satellite mission.

Carozzi, T. D.; Buckley, A.; Gough, M. P.; Beloff, N.

2003-04-01

399

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

400

Fragment-mass distributions in neutron-induced fission of ²³²Th and ²³U at 33, 45, and 60 MeV  

Microsoft Academic Search

We have measured fission fragment-mass yields for neutron-induced fission of ²³²Th and ²³U at energies 32.8, 45.3, and 59.9 MeV. The experiments were done at quasimonoenergetic neutron beams of the Cyclotron Research Center at Louvain-la-Neuve. To detect the fission fragments, a multisection Frisch-gridded ionization chamber was used. The measurement and data analysis techniques are discussed in detail. The obtained mass

I. V. Ryzhov; S. G. Yavshits; G. A. Tutin; N. V. Kovalev; A. V. Saulski; N. A. Kudryashev; M. S. Onegin; L. A. Vaishnene; Yu. A. Gavrikov; O. T. Grudzevich; V. D. Simutkin; S. Pomp; J. Blomgren; M. Oesterlund; P. Andersson; R. Bevilacqua; J. P. Meulders; R. Prieels

2011-01-01

401

Fragment-mass distributions in neutron-induced fission of Th232 and U238 at 33, 45, and 60 MeV  

Microsoft Academic Search

We have measured fission fragment-mass yields for neutron-induced fission of Th232 and U238 at energies 32.8, 45.3, and 59.9 MeV. The experiments were done at quasimonoenergetic neutron beams of the Cyclotron Research Center at Louvain-la-Neuve. To detect the fission fragments, a multisection Frisch-gridded ionization chamber was used. The measurement and data analysis techniques are discussed in detail. The obtained mass

I. V. Ryzhov; S. G. Yavshits; G. A. Tutin; N. V. Kovalev; A. V. Saulski; N. A. Kudryashev; M. S. Onegin; L. A. Vaishnene; Yu. A. Gavrikov; O. T. Grudzevich; V. D. Simutkin; S. Pomp; J. Blomgren; M. Österlund; P. Andersson; R. Bevilacqua; J. P. Meulders; R. Prieels

2011-01-01

402

Results with the neutron scatter camera  

Microsoft Academic Search

We present results from recent deployments with the neutron scatter camera. We successfully detected and pinpointed a hidden 252Cf neutron source in a large ocean tanker at Alameda, CA. In a lab study we detected a 252Cf neutron source at a stand off distance of about 100 ft. We measured the integral flux, differential flux and angular distribution of cosmic

Nicholas Mascarenhas; James Brennan; Kevin Krenz; Peter Marleau; Stanley Mrowka

2008-01-01

403

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

National Technical Information Service (NTIS)

Properties of a nucleon system interacting via isovector proton-neutron pairing can be described within the so(5) generalized Richardson-Gaudin exactly-solvable model. We present results for a system of 12 nucleon pairs within the full f(sub p) + g(sub 9/...

J. Dukelsky P. Pan Isacker S. S. Dimitrova V. G. Gueroguiev

2005-01-01

404

On the Fermi and Gamow-Teller strength distributions in medium-heavy mass nuclei  

Microsoft Academic Search

An isospin-selfconsistent approach based on the Continuum-Random-Phase-Approximation (CRPA) is applied to describe the Fermi and Gamow-Teller strength distributions within a wide excitation-energy interval. To take into account nucleon pairing in open-shell nuclei, we formulate an isospin-selfconsistent version of the proton-neutron-quasiparticle-CRPA (pn-QCRPA) approach by incorporating the BCS model into the CRPA method. The isospin and configurational splittings of the Gamow-Teller giant

V. A. Rodin; M. H. Urin

2003-01-01

405

High-spin neutron excitations in neutron-deficient even-mass Pb isotopes  

NASA Astrophysics Data System (ADS)

High-spin states in 194, 196pb have been investigated using the 188Os( 12C, ?n) 194, 196Pb and the 198Hg(?, 6n) 196Pb reactions. The experiments included ?-ray excitation function, ?-? coincidence, ?-?? coincidence, ?-ray angular distribution, lifetime and conversion electron measurements. The level schemes of 194Pb and 196Pb have been extended up to states with J? = 15 - ( E = 3955 keV) and J? = 20 + ( E = 5444 keV), respectively. All levels except two new isomers which have most likely spin and parity J ? = 10 - ( 194Pb) and J ? = 11 - ( 196Pb) can be interpreted as neutron excitations. The excitation energies of levels with spin J ? 12 are well accounted for by the one-broken-pair model including 1p1h excitations. The B(E2, 12 + -10 +) values reflect the systematic trend for a pure ( i{13}/{2}) 2 configuration. Levels with spin 12 < J < 20 can be described as two-broken-pair model configurations. The excitation energies of these states can be reproduced quite well in a phenomenological approach in which two i{13}/{2} neutron holes are coupled to core excitations in the A + 2 nucleus and also by calculations performed within the two-broken-pair model. Within this framework the J? = 20 + state observed in 196Pb has a pure ( i{13}/{2}) 4 configuration. The two new isomers have most likely a proton 2p2h structure. The excitation energy of the J? = 11 - isomer in 196Pb agrees with that predicted for a deformed {1}/{2}+[404] -{29}/{2}-[514] {13}/{2}+[606] 11 - state.

Van Ruyven, J. J.; Penninga, J.; Hesselink, W. H. A.; Van Nes, P.; Allaart, K.; Hengeveld, E. J.; Verheul, H.; de Voigt, M. J. A.; Sujkowski, Z.; Blomqvist, J.

1986-02-01

406

Pairs of Pulsars in the Diagram P dot Versus P.  

National Technical Information Service (NTIS)

Pairs of pulsars (PSR) selected by Vladimirskii (1984) are distributed in 3 groups of PSR found by applying discriminant analysis to the diagram P dot vs P. Evolutive implications of the isochrone t = 1 million yr are discussed. A list of pairs was select...

M. Fracassini P. Maggi L. E. Pasinetti G. Raffaelli

1986-01-01

407

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

408

Pair production in superstrong magnetic fields  

NASA Technical Reports Server (NTRS)

The production of electron-positron pairs by single photons in magnetic fields 10 to the twelth power G was investigated in detail for photon energies near threshold as well as for the asymptotic limit of high photon energy. The exact attenuation coefficient, which is derived and then evaluated numerically, is strongly influenced by the discrete energy states of the electron and positron. Near threshold, it exhibits a sawtooth pattern as a function of photon energy, and its value is significantly below that predicted by the asymptotic expression for the attenuation coefficient. The energy distributions of the created pair are computed numerically near threshold and analytic expressions are derived in the asymptotic limit. These results indicate that as field strength and photon energy increase, it becomes increasingly probable for the pair to divide the photon energy unequally. This effect, as well as the threshold behavior of the attenuation coefficient, could have important consequences for pulsar models.

Daugherty, J. K.; Harding, A. K.

1983-01-01

409

A new probe of neutron skin thickness  

NASA Astrophysics Data System (ADS)

The correlation between neutron-to-proton yield ratio (Rnp) and neutron skin thickness (?np) in neutron-rich projectile induced reactions is investigated within the framework of the Isospin-Dependent Quantum Molecular Dynamics (IQMD) model. The density distribution of the Droplet model is embedded in the initialization of the neutron and proton densities in the present IQMD model. By adjusting the diffuseness parameter of neutron density in the Droplet model for the projectile, the relationship between the neutron skin thickness and the corresponding Rnp is obtained. The results show strong linear correlation between Rnp and ?np for neutron-rich Ca and Ni isotopes. It is suggested that Rnp may be used as an experimental observable to extract ?np for neutron-rich nuclei, which is very interesting in the study of the nuclear structure of exotic nuclei, the equation of state (EOS) of asymmetric nuclear matter and neutron-rich matter in astrophysics, etc.

Sun, Xiao-Yan; Fang, De-Qing; Ma, Yu-Gang; Cai, Xiang-Zhou; Chen, Jin-Gen; Guo, Wei; Tian, Wen-Dong; Wang, Hong-Wei; Zhang, Guo-Qiang; Zhou, Pei

2011-06-01

410

Excitation energy at scission in thermal-neutron-induced fission  

NASA Astrophysics Data System (ADS)

For the thermal-neutron-induced fission of 235U and 233U, we extract the internal excitation energy at the scission point by use of two different methods. The first method uses experimental data for 235U + nth on the neutrons and gamma rays emitted from doubly magic fission fragments, where the extra stability associated with shell closures makes the deformation energy small. Under the assumption that both fragments have equal temperatures, this yields an upper limit of 9.9 MeV for the total internal excitation energy at scission. The second method uses experimental data for 233U + nth on odd-even effects in fission-fragment mass distributions and yields an average value of 5.6 MeV for the total internal excitation energy at scission when integrated over all fission-fragment kinetic energies. In both cases the internal excitation energy at scission is significantly smaller than that predicted by the one-body-dissipation theory of Swiatecki and co-workers and is instead much closer to that predicted by ordinary two-body viscosity. NUCLEAR REACTIONS, FISSION 235U + nth, 233U + nth; extracted internal excitation energy at scission point. Neutrons and gamma rays from doubly magic fission fragments, odd-even effects in fission-fragment mass distributions, one-body dissipation, two-body viscosity, temperature-dependent BCS pairing theory.

Mantzouranis, G.; Nix, J. R.

1982-02-01

411

Relativistically expanding pair plasmas as bursting sources of cosmic gamma rays  

NASA Technical Reports Server (NTRS)

High temperature shock heating of relativistically expanding plasmas produced in neutron star binary mergers provides a model for cosmic gamma ray burst sources. This requires the fireball resulting from the merger to have a very high entropy per baryon, mechanisms for which are discussed. The energy, temporal structure and spectrum produced by the blast wave and reverse shock as the fireball is decelerated in an external medium are comparable to those observed, as is the frequency of occurrence and the characteristics of the spatial distribution of the events. Difficulties common to all cosmological gamma ray burst scenarios concern the total amount of energy ultimately appearing at gamma ray energies, the time scales, the spectrum, and the great variety of time profiles. A very general mechanism which overcomes these problems is presented. Situations where the pair plasma is created in regions which are relatively free of baryons are discussed. The effect of the interaction of the expanding fireball with the external medium is considered.

Meszaros, Peter; Rees, M. J.

1993-01-01

412

New dynamical pair breaking effect  

Microsoft Academic Search

A dynamical pair breaking effect is evidenced at very low excitation energies. For this purpose, a new set of time-dependent coupled channel equations for pair-breaking in superfluid systems are deduced from the variational principle. These equations give the probability to destroy or to create a Cooper pair under the action of some perturbations or when the mean field varies in

M. Mirea

2009-01-01

413

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.

Henry, Barbara

2012-04-16

414

Crew pairing at Air France  

Microsoft Academic Search

In the airline industry, crew schedules consist of a number of pairings. These are round trips originating and terminating at the same crew home base composed of legal work days, called duties, separated by rest periods. The purpose of the airline crew pairing problem is to generate a set of minimal cost crew pairings covering all flight legs. The set

G. Desaulniers; J. Desrosiers; Y. Dumas; S. Marc; B. Rioux; M. M. Solomon; F. Soumis

1997-01-01

415

Modeling Within-Subject Dependencies in Ordinal Paired Comparison Data.  

ERIC Educational Resources Information Center

This paper presents two probabilistic models based on the logistic and the normal distribution for the analysis of dependencies in individual paired comparison judgments such as might occur in educational research. Three applications illustrate the approach. (SLD)

Dillon, William R.; Bockenholt, Ulf

1997-01-01

416

Neutron skins and neutron stars  

NASA Astrophysics Data System (ADS)

Background: The neutron skin of a heavy nucleus as well as many neutron-star properties are highly sensitive to the poorly constrained density dependence of the symmetry energy.Purpose: To provide for the first time meaningful theoretical errors and to assess the degree of correlation between the neutron-skin thickness of 208Pb and several neutron-star properties.Methods: A proper covariance analysis based on the predictions of an accurately calibrated relativistic functional “FSUGold” is used to quantify theoretical errors and correlation coefficients.Results: We find correlation coefficients of nearly 1 (or -1) between the neutron-skin thickness of 208Pb and a host of observables of relevance to the structure, dynamics, and composition of neutron stars.Conclusions: We suggest that a follow-up Lead Radius Experiment (PREX) measurement, ideally with a 0.5% accuracy, could significantly constrain the equation of state of neutron-star matter.

Fattoyev, F. J.; Piekarewicz, J.

2012-07-01

417

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.

418

In-situ neutron scattering study of crystallization in a Zr-based bulk metallic glass  

NASA Astrophysics Data System (ADS)

Crystallization of a Zr-based bulk metallic glass (Zr50.4Cu40.6Al9) upon isothermal annealing has been investigated using in-situ neutron diffraction and the pair distribution function (PDF) method. By extracting the contribution of the crystalline phase from the total scattering, we are able to obtain the real-time structure factor and pair distribution function for the crystalline phase as well as its volume fraction. Our analysis shows that the crystallization follows the Johnson-Mehl-Avrami law with a time exponent of 4.0±0.2, indicating a three-dimensional nucleation and growth process. The analysis method established in the present study paves a new way for probing the kinetics of phase transformation for a broad range of non-crystalline materials including liquids and glasses.

Ma, D.; Stoica, A. D.; Wang, X.-L.; Lu, Z. P.; Proffen, T.

2010-06-01

419

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