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Sample records for neutron pair distribution

  1. Direct assignment of molecular vibrations via normal mode analysis of the neutron dynamic pair distribution function technique

    NASA Astrophysics Data System (ADS)

    Fry-Petit, A. M.; Rebola, A. F.; Mourigal, M.; Valentine, M.; Drichko, N.; Sheckelton, J. P.; Fennie, C. J.; McQueen, T. M.

    2015-09-01

    For over a century, vibrational spectroscopy has enhanced the study of materials. Yet, assignment of particular molecular motions to vibrational excitations has relied on indirect methods. Here, we demonstrate that applying group theoretical methods to the dynamic pair distribution function analysis of neutron scattering data provides direct access to the individual atomic displacements responsible for these excitations. Applied to the molecule-based frustrated magnet with a potential magnetic valence-bond state, LiZn2Mo3O8, this approach allows direct assignment of the constrained rotational mode of Mo3O13 clusters and internal modes of MoO6 polyhedra. We anticipate that coupling this well known data analysis technique with dynamic pair distribution function analysis will have broad application in connecting structural dynamics to physical properties in a wide range of molecular and solid state systems.

  2. Direct assignment of molecular vibrations via normal mode analysis of the neutron dynamic pair distribution function technique.

    PubMed

    Fry-Petit, A M; Rebola, A F; Mourigal, M; Valentine, M; Drichko, N; Sheckelton, J P; Fennie, C J; McQueen, T M

    2015-09-28

    For over a century, vibrational spectroscopy has enhanced the study of materials. Yet, assignment of particular molecular motions to vibrational excitations has relied on indirect methods. Here, we demonstrate that applying group theoretical methods to the dynamic pair distribution function analysis of neutron scattering data provides direct access to the individual atomic displacements responsible for these excitations. Applied to the molecule-based frustrated magnet with a potential magnetic valence-bond state, LiZn2Mo3O8, this approach allows direct assignment of the constrained rotational mode of Mo3O13 clusters and internal modes of MoO6 polyhedra. We anticipate that coupling this well known data analysis technique with dynamic pair distribution function analysis will have broad application in connecting structural dynamics to physical properties in a wide range of molecular and solid state systems. PMID:26429001

  3. Pair correlation and pair collectivity in neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Matsuo, M.; Shimoyama, H.; Ootaki, Y.

    2012-10-01

    We describe the neutron Cooper pair, the pair vibrational states and the associated two-neutron transfer strength by applying the Skyrme-Hartree-Fock-Bogoliubov mean-field model and the quasiparticle random phase approximation to neutron-rich Sn isotopes. The wave function of the Cooper pair exhibits a strong spatial correlation favoring short relative distances smaller than a few fm, in contrast to the case of the single-j Cooper pair. The model also predicts an anomalous pair vibration in neutron-rich isotopes beyond the N = 82 magic number, which originates from the weak binding of the last neutrons.

  4. Neutron-Proton pairing revisited

    E-print Network

    W. A. Friedman; G. F. Bertsch

    2007-03-15

    We reexamine neutron-proton pairing as a phenomenon that should be explanable in a microscopic theory of nuclear binding energies. Empirically, there is an increased separation energy when both neutron and proton numbers are even or if they are both odd. The enhancement is present at some level in nearly all nuclei: the separation energy difference has the opposite sign in less than 1% of the cases in which sufficient data exist. We discuss the possible origin of the effect in the context of density functional theory (DFT) and its extensions. Neutron-proton pairing from the Hartree-Fock-Bogoliubov theory does not seem promising to explain the effect. We demonstrate that much of the increased binding in the odd-odd system might be understood as a recoupling energy. This suggests that the DFT should be extended by angular momentum projection to describe the effect.

  5. Triplet Pairing in Neutron Matter

    E-print Network

    V. V. Khodel; V. A. Khodel; J. W. Clark

    2000-01-05

    The separation method developed earlier by us [Nucl. Phys. {\\bf A598} 390 (1996)] to calculate and analyze solutions of the BCS gap equation for $^1$S$_0$ pairing is extended and applied to $^3$P$_2$--$^3$F$_2$ pairing in pure neutron matter. The pairing matrix elements are written as a separable part plus a remainder that vanishes when either momentum variable is on the Fermi surface. This decomposition effects a separation of the problem of determining the dependence of the gap components in a spin-angle representation on the magnitude of the momentum (described by a set of functions independent of magnetic quantum number) from the problem of determining the dependence of the gap on angle or magnetic projection. The former problem is solved through a set of nonsingular, quasilinear integral equations, providing inputs for solution of the latter problem through a coupled system of algebraic equations for a set of numerical coefficients. An incisive criterion is given for finding the upper critical density for closure of the triplet gap. The separation method and its development for triplet pairing exploit the existence of a small parameter, given by a gap-amplitude measure divided by the Fermi energy. The revised BCS equations admit analysis revealing universal properties of the full set of solutions for $^3$P$_2$ pairing in the absence of tensor coupling, referring especially to the energy degeneracy and energetic order of these solutions. The angle-average approximation introduced by Baldo et al. is illuminated in terms of the separation-transformed BCS problem and the small parameter expansion...

  6. 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

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

    2011-04-27

    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

  7. New model of the average neutron and proton pairing gaps

    NASA Astrophysics Data System (ADS)

    Madland, David G.; Nix, J. Rayford

    1988-01-01

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

  8. Proton-neutron pairing in N=Z nuclei: quartetting versus pair condensation

    E-print Network

    N. Sandulescu; D. Negrea; D. Gambacurta

    2015-07-15

    The isoscalar proton-neutron pairing and isovector pairing, including both isovector proton-neutron pairing and like-particle pairing, are treated in a formalism which conserves exactly the particle number and the isospin. The formalism is designed for self-conjugate (N=Z) systems of nucleons moving in axially deformed mean fields and interacting through the most general isovector and isoscalar pairing interactions. The ground state of these systems is described by a superposition of two types of condensates, i.e., condensates of isovector quartets, built by two isovector pairs coupled to the total isospin T=0, and condensates of isoscalar proton-neutron pairs. The comparison with the exact solutions of realistic isovector-isoscalar pairing Hamiltonians shows that this ansatz for the ground state is able to describe with high precision the pairing correlation energies. It is also shown that, at variance with the majority of Hartree-Fock-Bogoliubov calculations, in the present formalism the isovector and isoscalar pairing correlations coexist for any pairing interactions. The competition between the isovector and isoscalar proton-neutron pairing correlations is studied for N=Z nuclei with the valence nucleons moving in the $sd$ and $pf$ shells and in the major shell above $^{100}$Sn. We find that in these nuclei the isovector pairing prevail over the isoscalar pairing, especially for heavier nuclei. However, the isoscalar proton-neutron correlations are significant in all nuclei and they always coexist with the isovector pairing correlations.

  9. Proton-neutron pairing in N = Z nuclei: Quartetting versus pair condensation

    NASA Astrophysics Data System (ADS)

    Sandulescu, N.; Negrea, D.; Gambacurta, D.

    2015-12-01

    The isoscalar proton-neutron pairing and isovector pairing, including both isovector proton-neutron pairing and like-particle pairing, are treated in a formalism which conserves exactly the particle number and the isospin. The formalism is designed for self-conjugate (N = Z) systems of nucleons moving in axially deformed mean fields and interacting through the most general isovector and isoscalar pairing interactions. The ground state of these systems is described by a superposition of two types of condensates, i.e., condensates of isovector quartets, built by two isovector pairs coupled to the total isospin T = 0, and condensates of isoscalar proton-neutron pairs. The comparison with the exact solutions of realistic isovector-isoscalar pairing Hamiltonians shows that this ansatz for the ground state is able to describe with high precision the pairing correlation energies. It is also shown that, at variance with the majority of Hartree-Fock-Bogoliubov calculations, in the present formalism the isovector and isoscalar pairing correlations coexist for any pairing interactions. The competition between the isovector and isoscalar proton-neutron pairing correlations is studied for N = Z nuclei with the valence nucleons moving in the sd and pf shells and in the major shell above 100Sn. We find that in these nuclei the isovector pairing prevail over the isoscalar pairing, especially for heavier nuclei.

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

    SciTech Connect

    Chasman, R. R.; Van Isacker, P.; Physics; Grand Accelerateur National d'Ions Lourds

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Chasman, R. R.; Van Isacker, P.

    2010-02-01

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

  12. Pairing and superfluidity of nucleons in neutron stars

    E-print Network

    A. Gezerlis; C. J. Pethick; A. Schwenk

    2015-04-13

    We survey the current status of understanding of pairing and superfluidity of neutrons and protons in neutron stars from a theoretical perspective, with emphasis on basic physical properties. During the past two decades, the blossoming of the field of ultracold atomic gases and the development of quantum Monte Carlo methods for solving the many-body problem have been two important sources of inspiration, and we shall describe how these have given insight into neutron pairing gaps. The equilibrium properties and collective oscillations of the inner crust of neutron stars, where neutrons paired in a $^1$S$_0$ state coexist with a lattice of neutron-rich nuclei, are also described. While pairing gaps are well understood at densities less than one tenth of the nuclear saturation density, significant uncertainties exist at higher densities due to the complicated nature of nucleon-nucleon interactions, the difficulty of solving the many-body problem under these conditions, and the increasing importance of many-nucleon interactions. We also touch more briefly on the subject of pairing of neutrons in other angular momentum states, specifically the $^3$P$_2$ state, as well as pairing of protons.

  13. Photoproduction of ?0-pairs off protons and off neutrons

    NASA Astrophysics Data System (ADS)

    Dieterle, M.; 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.; Costanza, S.; Demissie, B.; Downie, E. J.; Drexler, P.; Fil'kov, L. V.; Fix, A.; Garni, S.; Glazier, D. I.; Hamilton, D.; Heid, E.; Hornidge, D.; Howdle, D.; Huber, G. M.; Jahn, O.; Jude, T. C.; Käser, A.; Kashevarov, V. L.; Keshelashvili, I.; Kondratiev, R.; Korolija, M.; Krusche, B.; Lisin, V.; Livingston, K.; MacGregor, I. J. D.; Maghrbi, Y.; Mancell, J.; Manley, D. M.; Marinides, Z.; McGeorge, J. C.; McNicoll, E.; Mekterovic, D.; Metag, V.; Micanovic, S.; Middleton, D. G.; Mushkarenkov, A.; Nikolaev, A.; Novotny, R.; Ostrick, M.; Otte, P.; Oussena, B.; Pedroni, P.; Pheron, F.; Polonski, A.; Prakhov, S.; Robinson, J.; Rostomyan, T.; Schumann, S.; Sikora, M. H.; Sober, D. I.; Starostin, A.; Strub, Th.; Supek, I.; Thiel, M.; Thomas, A.; Unverzagt, M.; Walford, N. K.; Watts, D. P.; Werthmüller, D.; Witthauer, L.

    2015-11-01

    Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of ?0?0 pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections (angular distributions and invariant-mass distributions) for free and quasi-free protons are almost identical in shape, but differ in absolute magnitude up to 15%. Thus, moderate final-state interaction effects are present. The data for quasi-free neutrons are similar to the proton data in the second resonance region (final-state invariant masses up to ? 1550 MeV), where both reactions are dominated by the N(1520)3/2- ? ?(1232)3/2+? decay. At higher energies, angular and invariant-mass distributions are different. A simple analysis of the shapes of the invariant-mass distributions in the third resonance region is consistent with strong contributions of an N^{star}? N? decay for the proton, while the reaction is dominated by a sequential decay via a ?? intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled-channel analysis.

  14. Proton-Neutron Pairing Interaction in Neutron Rich A = 132 Nuclei

    SciTech Connect

    Laouet, N.; Benrachi, F.; Khiter, M.; Benmicia, N.; Saifi, H.

    2010-10-31

    In infinite nuclear systems, such as neutron stars, pairing phenomena have a particular interest in the study of nuclear structure properties. Thus, pairing lies at the heart of quantum many body problems, and nuclear process connecting to nucleosynthesis. In this work, we are interested on the contribution of this aspect, for neutron rich nuclei far from stability in the vicinity of doubly magic {sup 132}Sn. The study of A = 134 isobar, which presents a proton-neutron mixing in valence space, based on the proton-neutron correlation properties. Our results, using the P{sub d} pairing gap calculations, are in a good agreement with the experimental data.

  15. A pair distribution function analysis of zeolite beta

    SciTech Connect

    Martinez-Inesta, M.M.; Peral, I.; Proffen, T.; Lobo, R.F.

    2010-07-20

    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.

  16. Neutron-proton pairing correlations in odd mass systems

    SciTech Connect

    Fellah, M. Allal, N. H.; Oudih, M. R.

    2015-03-30

    An expression of the ground-state which describes odd mass systems within the BCS approach in the isovector neutron-proton pairing case is proposed using the blocked level technique. The gap equations as well as the energy expression are then derived. It is shown that they exactly generalize the expressions obtained in the pairing between like-particles case. The various gap parameters and the energy are then numerically studied as a function of the pairing-strength within the schematic one-level model.

  17. Quantum Key Distribution with Qubit Pairs

    E-print Network

    Mohd Asad Siddiqui; Tabish Qureshi

    2014-07-17

    We propose a new Quantum Key Distribution method in which Alice sends pairs of qubits to Bob, each in one of four possible states. Bob uses one qubit to generate a secure key and the other to generate an auxiliary key. For each pair he randomly decides which qubit to use for which key. The auxiliary key has to be added to Bob's secure key in order to match Alice's secure key. This scheme provides an additional layer of security over the standard BB84 protocol.

  18. Singlet pairing gaps of neutrons and protons in hyperonic neutron stars

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    The 1S0 nucleonic superfluids are investigated within the relativistic mean-field model and Bardeen-Cooper-Schrieffer theory in hyperonic neutron stars. The 1S0 pairing gaps of neutrons and protons are calculated based on the Reid soft-core interaction as the nucleon-nucleon interaction. In particular, we have studied the influence of degrees of freedom for hyperons on the 1S0 nucleonic pairing gap in neutron star matter. It is found that the appearance of hyperons has little impact on the baryonic density range and the size of the 1S0 neutronic pairing gap; the 1S0 protonic pairing gap also decreases slightly in this region where ?B = 0.0–0.393 fm?3. However, if baryonic density becomes greater than 0.393 fm?3, the 1S0 protonic pairing gap obviously increases. In addition, the possible range for a protonic superfluid is obviously enlarged due to the presence of hyperons. In our results, the hyperons change the 1S0 protonic pairing gap, which must change the cooling properties of neutron stars. Supported by the National Natural Science Foundation of China.

  19. Paired ion chamber constants for fission gamma-neutron fields

    NASA Astrophysics Data System (ADS)

    Ferlic, K. P.

    1984-12-01

    Paired ionization chamber constants are calculated for the 50 cc 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 the 50 cc tissue equivalent (TE) ion chamber filled with TE gas, ranged from 0.92 to 0.96 among the 18 different neutron spectra for which calculations were done. The constant kU, which expresses neutron sensitivity of the 50 cc graphite ion chamber filled with CO2, ranged from 0.07 to 0.11 among the same spectra. The constant hT, which expresses gamma sensitivity of the TE/TE ion chamber, was taken to be unity for all spectra. The constant hU, which expresses gamma sensitivity of the C/CO2 ion chamber, was 0.99 + or - 0.01(range) for all spectra. These calculations will serve as the basis for future dosimetry with the 50 cc ion chambers at the AFRRI TRIGA reactor.

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

    DOE PAGESBeta

    Wiringa, Robert B.; Schiavilla, Rocco; Pieper, Steven C.; Carlson, Joseph A.

    2014-02-10

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

  1. The neutron star mass distribution

    SciTech Connect

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

    2013-11-20

    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 {sub ?} and 1.55 M {sub ?}, suggesting significant mass accretion (?m ? 0.22 M {sub ?}) 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 {sub ?} 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 {sub ?} limit is set by evolutionary constraints rather than nuclear physics or general relativity, and the existence of rare supermassive NSs is possible.

  2. Equation of state of low--density neutron matter and the $^1S_0$ pairing gap

    E-print Network

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

    2009-07-09

    We report results of the equation of state of neutron matter in the low--density regime, where the Fermi wave vector ranges from $0.4 fm^{-1} \\leq k_F \\leq 1.0 fm^{-1}$. Neutron matter in this regime is superfluid because of the strong and attractive interaction in the $^1S_0$ channel. The properties of this superfluid matter are calculated starting from a realistic Hamiltonian that contains modern two-- and three--body interactions. The ground state energy and the $^1S_0$ superfluid energy gap are calculated using the Auxiliary Field Diffusion Monte Carlo method. We study the structure of the ground state by looking at pair distribution functions as well as the Cooper-pair wave function used in the calculations.

  3. Exploring local disorder in fast oxygen ion conductors by atomic pair distribution function analysis

    NASA Astrophysics Data System (ADS)

    Brunelli, Michela; Ceretti, Monica

    2015-10-01

    A preliminary structural investigation of local disorder in fully oxidized La2NiO4+? was performed by Pair Distribution Function (PDF) analyses of X-ray and neutron powder diffraction data. X-ray diffraction data were recorded in-situ on warming from room temperature up to 450 ?C.

  4. Empirical pairing gaps, shell effects, and di-neutron spatial correlation in neutron-rich nuclei

    E-print Network

    S. A. Changizi; Chong Qi; R. Wyss

    2015-08-08

    The empirical pairing gaps derived from four different odd-even mass staggering formulas are compared. By performing single-$j$ shell and multi-shell seniority model calculations as well as by using the standard HFB approach with Skyrme force we show that the simplest three-point formula $\\Delta_C^ {(3)}(N)=\\frac{1}{2}\\left[B(N,Z)+B(N-2,Z)-2B(N-1,Z)\\right]$ can provide a good measure of the neutron pairing gap in even-$N$ nuclei. It removes to a large extent the contribution from the nuclear mean field as well as contributions from shell structure details. It is also less contaminated by the Wigner effect for nuclei around $N=Z$. We also show that the strength of $\\Delta^ {(3)}_C(N)$ can serve as a good indication of the two-particle spatial correlation in the nucleus of concern and that the weakening of $\\Delta^ {(3)}_C(N)$ in some neutron-rich nuclei indicates that the di-neutron correlation itself is weak in these nuclei.

  5. Empirical pairing gaps, shell effects, and di-neutron spatial correlation in neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Changizi, S. A.; Qi, Chong; Wyss, R.

    2015-08-01

    The empirical pairing gaps derived from four different odd-even mass staggering formulas are compared. By performing single-j shell and multi-shell seniority model calculations as well as by using the standard HFB approach with Skyrme force we show that the simplest three-point formula ?C(3) (N) =1/2 [ B (N, Z) + B (N - 2, Z) - 2 B (N - 1, Z) ] can provide a good measure of the neutron pairing gap in even-N nuclei. It removes to a large extent the contribution from the nuclear mean field as well as contributions from shell structure details. It is also less contaminated by the Wigner effect for nuclei around N = Z. We also show that the strength of ?C(3) (N) can serve as a good indication of the two-particle spatial correlation in the nucleus of concern and that the weakening of ?C(3) (N) in some neutron-rich nuclei indicates that the di-neutron correlation itself is weak in these nuclei.

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  7. Pairing in exotic neutron rich nuclei around the drip line and in the crust of neutron stars

    E-print Network

    A. Pastore; J. Margueron; P. Schuck; X. Viñas

    2013-03-22

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

  8. Competition of isoscalar and isovector proton-neutron pairing in nuclei

    E-print Network

    G. Martinez-Pinedo; K. Langanke; P. Vogel

    1998-11-17

    We use shell model techniques in the complete pf shell to study pair correlations in nuclei. Particular attention is paid to the competition of isoscalar and isovector proton-neutron pairing modes which is investigated in the odd-odd N=Z nucleus 46V and in the chain of even Fe-isotopes. We confirm the dominance of isovector pairing in the ground states. An inspection of the level density and pair correlation strength in 46V, however, shows the increasing relative importance of isoscalar correlations with increasing excitation energy. In the Fe-isotopes we find the expected strong dependence of the isovector pairing strength on the neutron excess, while the dominant J=1 isoscalar pair correlations scale much more gently with neutron number. We demonstrate that the isoscalar pair correlations depend strongly on the spin-orbit splitting.

  9. Plasma effects in neutrino-pair emission due to Cooper pairing of protons in superconducting neutron stars

    E-print Network

    L. B. Leinson

    2002-11-12

    The neutrino emission due to formation and breaking of Cooper pairs of protons in superconducting cores of neutron stars is considered with taking into account the electromagnetic coupling of protons to ambient electrons. Our calculation shows that the contribution of the vector weak current to the $\

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

    SciTech Connect

    Wiringa, Robert B.; Schiavilla, Rocco; Pieper, Steven C.; Carlson, Joseph A.

    2014-02-10

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

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

    NASA Astrophysics Data System (ADS)

    Pastore, A.

    2015-01-01

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

  12. Multi-user distribution of polarization entangled photon pairs

    E-print Network

    J. Trapateau; J. Ghalbouni; A. Orieux; E. Diamanti; I. Zaquine

    2015-10-22

    We experimentally demonstrate multi-user distribution of polarization entanglement using commercial tele- com wavelength division demultiplexers. The entangled photon pairs are generated from a broadband source based on spontaneous parametric down conversion in a periodically poled lithium niobate crystal using a double path setup employing a Michelson interferometer and active phase stabilisation. We test and compare demultiplexers based on various technologies and analyze the effect of their characteristics, such as losses and polarization dependence, on the quality of the distributed entanglement for three channel pairs of each demultiplexer. In all cases, we obtain a Bell inequality violation, whose value depends on the demultiplexer features. This demonstrates that entanglement can be distributed to at least three user pairs of a network from a single source. Additionally, we verify for the best demultiplexer that the violation is maintained when the pairs are distributed over a total channel attenuation corresponding to 20 km of optical fiber. These tech- niques are therefore suitable for resource-efficient practical implementations of entanglement-based quantum key distribution and other quantum communication network applications.

  13. Multi-user distribution of polarization entangled photon pairs

    NASA Astrophysics Data System (ADS)

    Trapateau, J.; Ghalbouni, J.; Orieux, A.; Diamanti, E.; Zaquine, I.

    2015-10-01

    We experimentally demonstrate multi-user distribution of polarization entanglement using commercial telecom wavelength division demultiplexers. The entangled photon pairs are generated from a broadband source based on spontaneous parametric down conversion in a periodically poled lithium niobate crystal using a double path setup employing a Michelson interferometer and active phase stabilisation. We test and compare demultiplexers based on various technologies and analyze the effect of their characteristics, such as losses and polarization dependence, on the quality of the distributed entanglement for three channel pairs of each demultiplexer. In all cases, we obtain a Bell inequality violation, whose value depends on the demultiplexer features. This demonstrates that entanglement can be distributed to at least three user pairs of a network from a single source. Additionally, we verify for the best demultiplexer that the violation is maintained when the pairs are distributed over a total channel attenuation corresponding to 20 km of optical fiber. These techniques are therefore suitable for resource-efficient practical implementations of entanglement-based quantum key distribution and other quantum communication network applications.

  14. NEUTRON STARS: PROBES FOR HIGH DENSITY BARYON PAIRING

    E-print Network

    Dany PAGE

    1995-01-19

    We consider, in general terms, the early thermal evolution of an isolated neutron star, i.e., during the first $10^5$ years after the supernova explosion when the cooling is driven by neutrino emission from the core. It is shown that, if fast neutrino emission is occuring, the surface temperature is actually determined by the critical temperature $T_c$ at which the core baryons become superfluid, and almost nothing else. In particular, the dependence on the actual neutrino emission process is very weak. In other terms, fast neutrino cooling neutron stars are thermometers for the highest $T_c$ superfluid (superconductor) in the Universe. The observational data are briefly presented.

  15. ID-Based Distributed "Magic Ink" Signature from Pairings

    E-print Network

    Kim, Kwangjo

    ID-Based Distributed "Magic Ink" Signature from Pairings Yan Xie, Fangguo Zhang, Xiaofeng Chen. For instance the perfect crime concern in e-cash system. The "magic ink" signature provides a revocable. A single signer in "magic ink" signature can easily trace the original user of the message without any

  16. Anomalous pairing vibration in neutron-rich Sn isotopes beyond the N=82 magic number

    E-print Network

    Hirotaka Shimoyama; Masayuki Matsuo

    2011-06-09

    Two-neutron transfer associated with the pair correlation in superfluid neutron-rich nuclei is studied with focus on low-lying $0^+$ states in Sn isotopes beyond the N=82 magic number. We describe microscopically the two-neutron addition and removal transitions by means of the Skyrme-Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random phase approximation formulated in the coordinate space representation. It is found that the pair transfer strength for the transitions between the ground states becomes significantly large for the isotopes with $A \\ge 140$, reflecting very small neutron separation energy and long tails of the weakly bound $3p$ orbits. In $^{132-140}$Sn, a peculiar feature of the pair transfer is seen in transitions to low-lying excited $0^+$ states. They can be regarded as a novel kind of pair vibrational mode which is characterized by an anomalously long tail of the transition density extending to far outside of the nuclear surface, and a large strength comparable to that of the ground-state transitions. The presence of the weakly bound neutron orbits plays a central role for these anomalous behaviors.

  17. Proton-neutron pairing and alpha-type condensation in nuclei

    NASA Astrophysics Data System (ADS)

    Sandulescu, N.; Negrea, D.; Gambacurta, D.

    2015-10-01

    We summarize a recent work (N. Sandulescu et al, arXiv:1507.04144) on isoscalar and isovector proton-neutron pairing treated in a formalism which conserves exactly the particle number and the isospin. The formalism is designed for self-conjugate (N=Z) systems of nucleons moving in an axially deformed mean field and interacting through the most general isovector and isoscalar pairing interactions. The ground state of these systems is described by a superposition of two types of condensates, i.e., condensates of isovector quartets, built by two isovector pairs coupled to the total isospin T=0, and condensates of isoscalar proton-neutron pairs. The comparison with the exact solutions of realistic isovector-isoscalar pairing Hamiltonians shows that this formalism is able to describe accurately the pairing correlations energies. It is also shown that, contrary to the majority of HFB calculations, in the present formalism the isovector and isoscalar pairing correlations coexist together for any pairing interactions.

  18. Proton-neutron quadrupole interactions: an effective contribution to the pairing field

    E-print Network

    R. Fossion; C. De Coster; J. E. Garcia-Ramos; K. Heyde

    2002-01-22

    We point out that the proton-neutron energy contribution, for low multipoles (in particular for the quadrupole component), effectively renormalizes the strength of the pairing interaction acting amongst identical nucleons filling up a single-j or a set of degenerate many-j shells. We carry out the calculation in lowest-order perturbation theory. We perform a study of this correction in various mass regions. These results may have implications for the use of pairing theory in medium-heavy nuclei and for the study of pairing energy corrections to the liquid drop model when studying nuclear masses.

  19. Brueckner G -matrix approach for neutron-proton pairing correlations in the deformed BCS approach

    NASA Astrophysics Data System (ADS)

    Ha, Eunja; Cheoun, Myung-Ki; Šimkovic, F.

    2015-10-01

    Ground states of even-even Ge isotopes with mass number A =64 -76 have been studied in the deformed Bardeen-Cooper-Schrieffer (BCS) theory by taking neutron-proton (n p ) pairing correlations as well as neutron-neutron (n n ) and proton-proton (p p ) pairing correlations. The n p pairing has two different modes J =0 ,T =1 (isotriplet) and J =1 ,T =0 (isosinglet). In this work, the Brueckner G matrix, based on the CD-Bonn potential, has been exploited to reduce the ambiguity regarding nucleon-nucleon interactions inside nuclei compared to the results by a simple schematic phenomenological force. We found that the G matrix plays important roles to obtain reasonable descriptions of even-even nuclei compared to the schematic force. The n p pairing strength has been shown to have a clear correlation with quadrupole deformation parameter ?2 for the isotopes, and affects the smearing of the Fermi surfaces of not only N =Z nuclei but also N ?Z nuclei. In particular, the coexistence of the like particle (n n and p p ) and the n p pairing modes was found to become more salient by the G -matrix approach than by the schematic force approach.

  20. Neutron spectra and angular distributions of concrete-moderated neutron calibration fields at JAERI.

    PubMed

    Yoshizawa, M; Tanimura, Y; Saegusa, J; Nemoto, H; Yoshida, M

    2004-01-01

    The Facility of Radiation Standards of Japan Atomic Energy Research Institute has been equipped with concrete-moderated neutron calibration fields as simulated workplace neutron fields. The fields use an 241Am-Be neutron source placed in the narrow space surrounded by concrete bricks, walls and floor. The neutron spectra and the neutron fluence rates of the fields were measured with the Bonner multi-sphere spectrometer system (BMS), spherical recoil-proton proportional counters, and a liquid scintillation counter (NE-213). The results were compared with each other. The reference values of H*(10) were determined from the results of BMS. The angular distributions of neutron fluence were calculated using MCNP-4B2 to obtain the reference values of Hp(10). The calculated results show that the scattered neutrons have a wide range of incident angles. The reference Hp(10) values considered the angular distribution were found to be 10-18% smaller than those without consideration. PMID:15353626

  1. Fission meter and neutron detection using poisson distribution comparison

    SciTech Connect

    Rowland, Mark S; Snyderman, Neal J

    2014-11-18

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

  2. On the Mass Distribution and Birth Masses of Neutron Stars

    E-print Network

    Feryal Ozel; Dimitrios Psaltis; Ramesh Narayan; Antonio Santos Villarreal

    2012-09-07

    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_solar and a dispersion of 0.24 M_solar. 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_solar but with a dispersion of only 0.05 M_solar. 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_solar and a dispersion of 0.2 M_solar, consistent with the expectation that they have experienced extended mass accretion episodes. The fact that only a very small fraction of recycled neutron stars in the inferred distribution have masses that exceed ~2 M_solar suggests that only a few of these neutron stars cross the mass threshold to form low mass black holes.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  4. [Distributive pairing of chromosomes and aneuploidy in man].

    PubMed

    Kovaleva, N V

    1992-10-01

    The up-to-date state of human cytogenetics allows to turn back to hypothesis of distributive pairing as a strongly fruitful for resolving a number of problems concerning etiology of chromosome aneuploidy. Distributive pairing could account for such phenomena as: 1. Prevalence of nondisjunction (ND) in the first meiosis, compared with the second; 2. Excess of males among children with the Down syndrome; 3. Recurrent cases of aneuploidy, including aneusomies for different chromosomes; 4. Appearance of individuals with double aneusomies; 5. High recurrent risk for young parents; 6. Increased chance of ND for chromosomes not involved in rearrangement in carriers of balanced translocations; 7. Increased frequency of ND of autosomes in individuals with quantitative and structural sex chromosome anomalies; 8. The role of heterochromatic regions in ND; 9. Increased frequency of spontaneous abortions in couples having children with chromosome anomalies and in persons with unusual heterochromatic variants. The hypothesis could predict: 1. Essential contribution of errors in gonial cells to the origin of aneuploidy; 2. Important role of the factors influencing the prophase; 3. The possibility of offering forecast for sex chromosome anomalies rate on the basis of trisomy 21 rate, due to the fact that both autosomal and gonosomal aneuploidies have to be induced by the same factors. PMID:1468642

  5. Particle-number fluctuations and neutron-proton pairing effects on proton and neutron radii of even-even N Almost-Equal-To Z nuclei

    SciTech Connect

    Douici, M.; Allal, N. H.; Fellah, M.; Benhamouda, N.; Oudih, M. R.

    2012-10-20

    The particle-number fluctuation effect on the root-mean-square (rms) proton and neutron radii of even-even N Almost-Equal-To Z nuclei is studied in the isovector neutron-proton (np) pairing case using an exact particle-number projection method and the Woods-Saxon model.

  6. Quarteting and spin-aligned proton-neutron pairs in heavy N =Z nuclei

    NASA Astrophysics Data System (ADS)

    Sambataro, M.; Sandulescu, N.

    2015-06-01

    We analyze the role of maximally aligned isoscalar pairs in heavy N =Z nuclei by employing a formalism of quartets. Quartets are superpositions of two neutrons and two protons coupled to total isospin T =0 and given J . The study is focused on the contribution of spin-aligned pairs carrying the angular momentum J =9 to the structure of 96Cd and 92Pd . We show that the role played by the J =9 pairs is quite sensitive to the model space and, in particular, it decreases considerably by passing from the simple 0 g9 /2 space to the more complete 1 p1 /2,1 p3 /2,0 f5 /2,0 g9 /2 space. In the latter case the description of these nuclei in terms of only spin-aligned J =9 pairs turns out to be unsatisfactory while an important contribution, particularly in the ground state, is seen to arise from isovector J =0 and isoscalar J =1 pairs. Thus, contrary to previous studies, we find no compelling evidence of a spin-aligned pairing phase in 92Pd .

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

    SciTech Connect

    Zerguine, S.; Van Isacker, P.

    2011-06-15

    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.

  8. ON THE MASS DISTRIBUTION AND BIRTH MASSES OF NEUTRON STARS

    SciTech Connect

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

    2012-09-20

    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.

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

    E-print Network

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

  10. Current Density and Angular Distribution of Neutrons Emitted During Scission

    NASA Astrophysics Data System (ADS)

    Carjan, N.; Rizea, M.

    2014-04-01

    A time-dependent approach to the angular distribution of the scission neutrons with respect to the fission axis based on a recently developed dynamical scission model is presented. It implies the numerical solution of the bi-dimensional time-dependent Schrödinger equation with time-dependent potential for the motion of a neutron inside a nucleus that undergoes fission. The time evolution is calculated from the configuration with a minimum neck radius (?i), the start of the scission process, to the configuration of two just-separated fragments (?f), the end of the scission process. The resulting neutron wave packets are then propagated further in time but with the configuration of the fissioning system frozen at ?f. The numerical solutions at a given time t are used to calculate the current density Dbarem(?,z,t), a key quantity in the angular distribution evaluation. We investigate the nucleus 236U at two mass asymmetries defined by the light fragment mass AL=70 and 96. The number of neutrons that leave a sphere of radius R=30 fm (a test is done with R=40 fm) around the fissioning nucleus in a solid angle d? and in a time interval dt, d?sc/d?, is calculated. The integration in time of this quantity from 0 to ? gives the angular distribution. In practice we could only reach Tmax=4×10-21 sec. At this time however the majority of the scission neutrons left the sphere. The scission neutron emission is found to take place mainly along the fission axis with a small preference for the light fragment similar with what is experimentally observed for all prompt neutrons. A ratio ?L/?H close to the experimental value (1.41) is obtained. We concluded that the distinction between scission and evaporated neutrons, based on their angular distribution, is more challenging than expected.

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

    PubMed

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

    2000-01-01

    The radioisotope 252Cf is routinely encapsulated into compact, portable, intense neutron sources with a 2.6-yr half-life. A source the size of a person's little finger can emit up to 10(11) neutrons s(-1). Californium-252 is used commercially as a reliable, cost-effective neutron source for prompt gamma neutron activation analysis (PGNAA) of coal, cement and minerals, as well as for detection and identification of explosives, land mines and unexploded military ordinance. Other uses are neutron radiography, nuclear waste assays, reactor start-up sources, calibration standards and cancer therapy. The inherent safety of source encapsulations is demonstrated by 30 yr of experience and by US Bureau of Mines tests of source survivability during explosions. The production and distribution center for the US Department of Energy (DOE) Californium Program is the Radiochemical Engineering Development Center (REDC) at Oak Ridge National Laboratory (ORNL). DOE sells 252Cf to commercial reencapsulators domestically and internationally. Sealed 252Cf sources are also available for loan to agencies and subcontractors of the US government and to universities for educational, research and medical applications. The REDC has established the Californium User Facility (CUF) for Neutron Science to make its large inventory of 252Cf sources available to researchers for irradiations inside uncontaminated hot cells. Experiments at the CUF include a land mine detection system, neutron damage testing of solid-state detectors, irradiation of human cancer cells for boron neutron capture therapy experiments and irradiation of rice to induce genetic mutations. PMID:11003521

  12. Temperature effects on atomic pair distribution functions of melts

    SciTech Connect

    Ding, J. Ma, E.; Xu, M.; Guan, P. F.; Beijing Computational Science Research Center, Beijing 100086 ; Deng, S. W.; Department of Chemistry, East China University of Science and Technology, Shanghai 200237 ; Cheng, Y. Q.

    2014-02-14

    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.

  13. Algorithm for systematic peak extraction from atomic pair distribution functions.

    PubMed

    Granlund, L; Billinge, S J L; Duxbury, P M

    2015-07-01

    The study presents an algorithm, ParSCAPE, for model-independent extraction of peak positions and intensities from atomic pair distribution functions (PDFs). It provides a statistically motivated method for determining parsimony of extracted peak models using the information-theoretic Akaike information criterion (AIC) applied to plausible models generated within an iterative framework of clustering and chi-square fitting. All parameters the algorithm uses are in principle known or estimable from experiment, though careful judgment must be applied when estimating the PDF baseline of nanostructured materials. ParSCAPE has been implemented in the Python program SrMise. Algorithm performance is examined on synchrotron X-ray PDFs of 16 bulk crystals and two nanoparticles using AIC-based multimodeling techniques, and particularly the impact of experimental uncertainties on extracted models. It is quite resistant to misidentification of spurious peaks coming from noise and termination effects, even in the absence of a constraining structural model. Structure solution from automatically extracted peaks using the Liga algorithm is demonstrated for 14 crystals and for C60. Special attention is given to the information content of the PDF, theory and practice of the AIC, as well as the algorithm's limitations. PMID:26131896

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

    SciTech Connect

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

    1999-10-03

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

  15. Superfluid phases of triplet pairing and neutrino emission from neutron stars

    NASA Astrophysics Data System (ADS)

    Leinson, L. B.

    2010-12-01

    Neutrino energy losses through neutral weak currents in the triplet-spin superfluid neutron liquid are studied for the case of condensate involving several magnetic quantum numbers. Low-energy excitations of the multicomponent condensate in the timelike domain of the energy and momentum are analyzed. Along with the well-known excitations in the form of broken Cooper pairs, the theoretical analysis predicts the existence of collective waves of spin density in the one-component condensate at very low energy. Because of a rather small excitation energy of spin waves, their decay leads to a substantial neutrino emission at the lowest temperatures when all other mechanisms of neutrino energy loss are killed by a superfluidity. Neutrino energy losses caused by the pair recombination and spin-wave decays are examined in all of the multicomponent phases that might represent the ground state of the condensate, according to modern theories, and for the case when a phase transition occurs in the condensate at some temperature. Our estimate predicts a sharp increase in the neutrino energy losses followed by a decrease, along with a decrease in the temperature that takes place more rapidly than it would without the phase transition. We demonstrate the important role of the neutrino radiation caused by the decay of spin waves in the cooling of neutron stars.

  16. Pre-neutron emission mass distributions for low-energy neutron-induced actinide fission

    E-print Network

    Xiaojun Sun; Chenggang Yu; Ning Wang

    2012-01-15

    According to the driving potential of a fissile system, we propose a phenomenological fission potential for a description of the pre-neutron emission mass distributions of neutron-induced actinide fission. Based on the nucleus-nucleus potential with the Skyrme energy-density functional, the driving potential of the fissile system is studied considering the deformations of nuclei. The energy dependence of the potential parameters is investigated based on the experimental data for the heights of the peak and valley of the mass distributions. The pre-neutron emission mass distributions for reactions 238U(n, f), 237Np(n, f), 235U(n, f), 232Th(n, f) and 239Pu(n, f) can be reasonably well reproduced. Some predictions for these reactions at unmeasured incident energies are also presented.

  17. Pre-neutron emission mass distributions for low-energy neutron-induced actinide fission

    E-print Network

    Sun, Xiaojun; Wang, Ning

    2012-01-01

    According to the driving potential of a fissile system, we propose a phenomenological fission potential for a description of the pre-neutron emission mass distributions of neutron-induced actinide fission. Based on the nucleus-nucleus potential with the Skyrme energy-density functional, the driving potential of the fissile system is studied considering the deformations of nuclei. The energy dependence of the potential parameters is investigated based on the experimental data for the heights of the peak and valley of the mass distributions. The pre-neutron emission mass distributions for reactions 238U(n, f), 237Np(n, f), 235U(n, f), 232Th(n, f) and 239Pu(n, f) can be reasonably well reproduced. Some predictions for these reactions at unmeasured incident energies are also presented.

  18. Pair distribution function study on compression of liquid gallium

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    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.

  19. Dose distribution of neutron beam and chromosome analysis

    SciTech Connect

    Matsubara, S.; Kuwabara, Y.; Horiuchi, J.; Suzuki, S.; Ito, A.

    1988-03-01

    Chromosome analysis using peripheral lymphocytes is a sensitive and reliable indicator of the biological effect of radiation at low radiation doses. In the present study, using this chromosome aberration analysis, we tried to investigate the radiation dose distribution within and around the radiation field of a 6 MeV neutron beam. The efficient induction of dicentrics and rings at the irradiation of neutrons compared to those of gamma or X rays especially in a lower dose range, results in a dominant linear component in the linear quadratic model in the dose response relation of a chromosome aberration formation. A marked increase of RBE (relative biological effectiveness) in a lower dose range of neutrons was demonstrated. The radiation doses of the neutron beam as a function of depth, estimated from the yields of dicentrics and rings in a water phantom revealed a fairly good agreement with doses that were physically obtained. The radiation portal margin of the neutron beam was demonstrated to be not as sharp due to a wide penumbra. This wide penumbra and high RBE value, especially at lower dose range of the neutron beam may contribute to the induction of secondary malignancies in the normal tissue surrounding the tumor mass.

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

    PubMed

    Cauwels, Vanessa; Vanhavere, Filip; Reginatto, Marcel

    2014-10-01

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

  1. Scaling neutron absorbed dose distributions from one medium to another

    SciTech Connect

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

    1982-11-01

    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.

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

    PubMed

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

    2011-01-01

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

  3. Neutron Tomography Using Mobile Neutron Generators for Assessment of Void Distributions in Thermal Hydraulic Test Loops

    NASA Astrophysics Data System (ADS)

    Andersson, P.; Bjelkenstedt, T.; Sundén, E. Andersson; Sjöstrand, H.; Jacobsson-Svärd, S.

    Detailed knowledge of the lateral distribution of steam (void) and water in a nuclear fuel assembly is of great value for nuclear reactor operators and fuel manufacturers, with consequences for both reactor safety and economy of operation. Therefore, nuclear relevant two-phase flows are being studied at dedicated thermal-hydraulic test loop, using two-phase flow systems ranging from simplified geometries such as heated circular pipes to full scale mock-ups of nuclear fuel assemblies. Neutron tomography (NT) has been suggested for assessment of the lateral distribution of steam and water in such test loops, motivated by a good ability of neutrons to penetrate the metallic structures of metal pipes and nuclear fuel rod mock-ups, as compared to e.g. conventional X-rays, while the liquid water simultaneously gives comparatively good contrast. However, these stationary test loops require the measurement setup to be mobile, which is often not the case for NT setups. Here, it is acknowledged that fast neutrons of 14 MeV from mobile neutron generators constitute a viable option for a mobile NT system. We present details of the development of neutron tomography for this purpose at the division of Applied Nuclear Physics at Uppsala University. Our concept contains a portable neutron generator, exploiting the fusion reaction of deuterium and tritium, and a detector with plastic scintillator elements designed to achieveadequate spatial and energy resolution, all mounted in a light-weight frame without collimators or bulky moderation to allow for a mobile instrument that can be moved about the stationary thermal hydraulic test sections. The detector system stores event-to-event pulse-height information to allow for discrimination based on the energy deposition in the scintillator elements.

  4. A comparison between two evaluations of neutron multiplicity distributions

    E-print Network

    Lestone, J P

    2014-01-01

    Within MCNP6, users can use multiplicity distributions for spontaneous and neutron-induced fission from an evaluation performed by Lestone (LA-UR-05-0288). This evaluation assumes the multiplicity distributions are Gaussian and adjusts the standard deviations to reproduce measured 2nd and 3rd factorial moments. In MCNPX, users have the option of using multiplicity distributions for spontaneous fission using an evaluation of the available experimental data by Santi and Miller (LA-UR-07-6229). The spontaneous fission multiplicity distributions and corresponding factorial moments from these two evaluations are compared in the present paper. The differences are minor or within experimental errors for all but the spontaneous fission of 238Pu. The 238Pu evaluations are based on data obtained in 1956. We recommend that the 238Pu multiplicity distribution be re-measured. Given the good agreement between the two evaluations, the choice of evaluation will make little difference for the modeling of spontaneous fission. ...

  5. A comparison between two evaluations of neutron multiplicity distributions

    E-print Network

    J. P. Lestone

    2014-09-18

    Within MCNP6, users can use multiplicity distributions for spontaneous and neutron-induced fission from an evaluation performed by Lestone (LA-UR-05-0288). This evaluation assumes the multiplicity distributions are Gaussian and adjusts the standard deviations to reproduce measured 2nd and 3rd factorial moments. In MCNPX, users have the option of using multiplicity distributions for spontaneous fission using an evaluation of the available experimental data by Santi and Miller (LA-UR-07-6229). The spontaneous fission multiplicity distributions and corresponding factorial moments from these two evaluations are compared in the present paper. The differences are minor or within experimental errors for all but the spontaneous fission of 238Pu. The 238Pu evaluations are based on data obtained in 1956. We recommend that the 238Pu multiplicity distribution be re-measured. Given the good agreement between the two evaluations, the choice of evaluation will make little difference for the modeling of spontaneous fission. However, we suggest that the evaluation in LA-UR-05-0288 be adopted as the MCNP default because it also includes recommended distributions for neutron induced fission.

  6. On the angular and energy distribution of solar neutrons generated in P-P reactions

    NASA Technical Reports Server (NTRS)

    Efimov, Y. E.; Kocharov, G. E.

    1985-01-01

    The problem of high energy neutron generation in P-P reactions in the solar atmosphere is reconsidered. It is shown that the angular distribution of emitted neutrons is anisotropic and the energy spectrum of neutrons depends on the angle of neutron emission.

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

    SciTech Connect

    Xu, Li; Ankner, John Francis; Sukhishvili, Prof. Svetlana A.

    2011-01-01

    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.

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

    SciTech Connect

    Istomin, Ya. N. Sob'yanin, D. N.

    2011-10-15

    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.

  9. Kinematic distributions for electron pair production by muons

    NASA Technical Reports Server (NTRS)

    Linsker, R.

    1972-01-01

    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.

  10. $(h_{11/2})^2$ alignments in neutron-rich $^{132}$Ba with negative-parity pairs

    E-print Network

    Yang Lei; Zhengyu Xu

    2015-07-24

    The shell-model collective-pair truncation with negative-parity pairs is adopted to study the $(h_{11/2})^2$ alignment in $^{132}$Ba. The proton $(h_{11/2})^2$-alignment state is predicted as an $E\\sim4.6$ MeV and $\\tau\\sim 0.5~\\mu$s isomer with relatively strong E3 decay channels. The oblately deformed neutron $(h_{11/2})^{-2}$ alignment in the yrast band and four negative-parity bands are confirmed, even although two of these negative-parity bands favor the prolate deformation, which directly manifests the $\\gamma$ unstability of $^{132}$Ba.

  11. $(h_{11/2})^2$ alignments in neutron-rich $^{132}$Ba with negative-parity pairs

    E-print Network

    Lei, Yang

    2015-01-01

    The shell-model collective-pair truncation with negative-parity pairs is adopted to study the $(h_{11/2})^2$ alignment in $^{132}$Ba. The proton $(h_{11/2})^2$-alignment state is predicted as an $E\\sim$4.6MeV $\\tau\\sim 0.5\\mu$s isomer with observable E3 decay channels. The neutron $(h_{11/2})^{-2}$ alignment in the yrast band and four negative-parity bands are confirmed.

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

    DOEpatents

    Crane, T.W.

    1983-12-21

    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.

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

    DOEpatents

    Crane, Thomas W. (Los Alamos, NM)

    1986-01-01

    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.

  14. Measuring Hydrogen Distributions in Iron and Steel Using Neutrons

    NASA Astrophysics Data System (ADS)

    Griesche, A.; Dabah, E.; Kannengiesser, T.; Hilger, A.; Kardjilov, N.; Manke, I.; Schillinger, B.

    Neutron tomography has been applied to investigate the mechanism of hydrogen assisted cracking in technical iron and supermartensitic steel. Rectangular technical iron block samples showed blistering due to intense hydrogen charging and the tomographic method revealed in situ the spatial distribution of hydrogen and cracks. Hydrogen accumulated in a small region around cracks and the cracks are filled with hydrogen gas. Cracks close to the surface contained no hydrogen. Hydrogenous tensile test samples of supermartensitic steel were pulled until rupture and showed hydrogen accumulations at the notch base and in the plastically deformed region around the fracture surface.

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

    NASA Astrophysics Data System (ADS)

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

    2007-07-01

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

  16. Angular distribution in the neutron-induced fission of actinides

    NASA Astrophysics Data System (ADS)

    Leong, L. S.; Tassan-Got, L.; Tarrio, D.; Audouin, L.; Paradela, C.; Duran, I.; Le Naour, C.; Altstadt, S.; Andrzejewsky, J.; Barbagallo, M.; Bécares, V.; Be?vá?, F.; Belloni, F.; Berthoumieux, E.; Billowes, J.; Boccone, V.; Bosnar, D.; Brugger, M.; Calvino, F.; Calviani, M.; Cano-Ott, D.; Carrapiço, C.; Cerutti, F.; Chiaveri, E.; Chin, M.; Colonna, N.; Cortés, G.; Cortés-Giraldo, M. A.; Diakaki, M.; Domingo-Pardo, C.; Dressler, R.; Dzysiuk, N.; Eleftheriadis, C.; Ferrari, A.; Fraval, K.; Ganesan, S.; García, A. R.; Giubrone, G.; Gómez-Hornillos, M. B.; Gonçalves, I. F.; González-Romero; Griesmayer, E.; Guerrero, C.; Gunsing, F.; Gurusamy, P.; Jenkins, D. G.; Jericha, E.; Kadi, E.; Käppeler, F.; Karadimos, D.; Kivel, N.; Koehler, P.; Kokkoris, M.; Korschinek, G.; Kroll, J.; Krti?ka, M.; Langer, C.; Lederer, C.; Leeb, H.; Losito, R.; Manousos, A.; Marganiec, J.; Massimi, C.; Martínez, T.; Mastinu, P. F.; Mastromarco, M.; Meaze, M.; Mengon, A.; Mendoza, E.; Milazzo, P. M.; Mingrone, T.; Mirea, M.; Mondelaers, W.; Pavlik, A.; Perkowski, J.; Pignatari, M.; Plompen, A.; Praena, J.; Quesada, J. M.; Rauscher, T.; Reifhart, R.; Riego, A.; Roman, F.; Rubbia, C.; Sarmento, R.; Schillebeeckx, P.; Schmidt, S.; Schumann, D.; Taín, J. L.; Tagliente, G.; Tsinganis, A.; Valenta, S.; Vannini, G.; Variale, V.; Vaz, P.; Ventura, A.; Versaci, R.; Vermeulen, M. J.; Vlachoudis, V.; Vlastou, V.; Wallner, A.; Ware, T.; Weigand, M.; Weiß, C.; Wright, T.; Z?gec

    2013-12-01

    Above 1 MeV of incident neutron energy the fission fragment angular distribution (FFAD) has generally a strong anisotropic behavior due to the combination of the incident orbital momentum and the intrinsic spin of the fissioning nucleus. This effect has to be taken into account for the efficiency estimation of devices used for fission cross section measurements. In addition it bears information on the spin deposition mechanism and on the structure of transitional states. We designed and constructed a detection device, based on Parallel Plate Avalanche Counters (PPAC), for measuring the fission fragment angular distributions of several isotopes, in particular 232Th. The measurement has been performed at n_TOF at CERN taking advantage of the very broad energy spectrum of the neutron beam. Fission events were recognized by back to back detection in coincidence in two position-sensitive detectors surrounding the targets. The detection efficiency, depending mostly on the stopping of fission fragments in backings and electrodes, has been computed with a Geant4 simulation and validated by the comparison to the measured case of 235U below 3 keV where the emission is isotropic. In the case of 232Th, the result is in good agreement with previous data below 10 MeV, with a good reproduction of the structures associated to vibrational states and the opening of second chance fission. In the 14 MeV region our data are much more accurate than previous ones which are broadly scattered.

  17. Nuclear pairing: Surface or bulk?

    SciTech Connect

    Sandulescu, N.; Schuck, P.; Vinas, X.

    2005-05-01

    We analyze how the spatial localization properties of pairing correlations are changing in a major neutron shell of heavy nuclei. It is shown that the radial distribution of the pairing density depends strongly on whether the chemical potential is close to a low or a high angular momentum level and has little sensitivity to whether the pairing force acts at the surface or in the bulk. The pairing density averaged over one major shell is, however, rather flat, exhibiting little dependence on the pairing force. Hartree-Fock-Bogoliubov calculations for the isotopic chain {sup 100-132}Sn are presented for demonstration purposes.

  18. Magnetic structure determination from the magnetic pair distribution function (mPDF): ground state of MnO.

    PubMed

    Frandsen, Benjamin A; Billinge, Simon J L

    2015-05-01

    An experimental determination of the magnetic pair distribution function (mPDF) defined in an earlier paper [Frandsen et al. (2014). Acta Cryst. A70, 3-11] is presented for the first time. The mPDF was determined from neutron powder diffraction data from a reactor and a neutron time-of-flight total scattering source on a powder sample of the antiferromagnetic oxide MnO. A description of the data treatment that allowed the measured mPDF to be extracted and then modelled is provided and utilized to investigate the low-temperature structure of MnO. Atomic and magnetic co-refinements support the scenario of a locally monoclinic ground-state atomic structure, despite the average structure being rhombohedral, with the mPDF analysis successfully recovering the known antiferromagnetic spin configuration. The total scattering data suggest a preference for the spin axis to lie along the pseudocubic [10{\\overline 1}] direction. Finally, r-dependent PDF refinements indicate that the local monoclinic structure tends toward the average rhombohedral R{\\overline 3}m symmetry over a length scale of approximately 100?Å. PMID:25921501

  19. Entangled-Pair Transmission Improvement Using Distributed Phase-Sensitive Amplification

    NASA Astrophysics Data System (ADS)

    Agarwal, Anjali; Dailey, James M.; Toliver, Paul; Peters, Nicholas A.

    2014-10-01

    We demonstrate the transmission of time-bin entangled photon pairs through a distributed optical phase-sensitive amplifier (OPSA). We utilize four-wave mixing at telecom wavelengths in a 5-km dispersion-shifted fiber OPSA operating in the low-gain limit. Measurements of two-photon interference curves show no statistically significant degradation in the fringe visibility at the output of the OPSA. In addition, coincidence counting rates are higher than direct passive transmission because of constructive interference between amplitudes of input photon pairs and those generated in the OPSA. Our results suggest that application of distributed phase-sensitive amplification to transmission of entangled photon pairs could be highly beneficial towards advancing the rate and scalability of future quantum communications systems.

  20. Three-Dimensional Structure of Nanocomposites from Atomic Pair Distribution Function Analysis: Study of Polyaniline and

    E-print Network

    Trikalitis, Pantelis N.

    Three-Dimensional Structure of Nanocomposites from Atomic Pair Distribution Function Analysis of an 84-atom orthorhombic unit cell. The nanocomposite (PANI)0.5V2O5,1.0H2O too is locally well ordered polymeric nanocomposites have attracted much attention because of their unique and novel properties

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

    SciTech Connect

    Co', G.; Donno, V. De; Anguiano, M.; Lallena, A.M. E-mail: viviana.de.donno@le.infn.it E-mail: lallena@ugr.es

    2012-11-01

    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.

  2. Effects of Neutron Spatial Distributions on Atomic Parity Nonconservation in Cesium

    E-print Network

    S. J. Pollock; M. C. Welliver

    1999-11-20

    We have examined modifications to the nuclear weak charge due to small differences between the spatial distributions of neutrons and protons in the Cs nucleus. We derive approximate formulae to estimate the value and uncertainty of this modification based only on nuclear rms neutron and proton radii. Present uncertainties in neutron distributions in Cs are difficult to quantify, but we conclude that they should not be neglected when using atomic parity nonconservation experiments as a means to test the Standard Model.

  3. Log N --Log S distribution as a new test for cooling curves of neutron stars

    E-print Network

    Popov, Sergei

    Log N -- Log S distribution as a new test for cooling curves of neutron stars S.B. Popov # , H as an independent approach to test the physics governing the star cooling. Theoretical LogN­LogS distributions different cooling scenar­ ios and found that comparison with the observed LogN­LogS of isolated neutron

  4. Radial Flux Distribution of Low-Energy Neutrons.

    ERIC Educational Resources Information Center

    Higinbotham, J.

    1979-01-01

    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)

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

    SciTech Connect

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

    2007-11-15

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

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

    SciTech Connect

    Verbeke, Jerome M.; Chen, Allen S.; Vujic, Jasmina L.; Leung, Ka-Ngo

    2000-08-15

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

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

    NASA Astrophysics Data System (ADS)

    Qiu, Xiangyun

    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.

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

    PubMed

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

    2015-12-01

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

  9. Nucleon direct Urca processes and singlet pairing gap of proton in hyperonic neutron star

    E-print Network

    Yan Xu; Cheng Zhi Liu; Cun Bo Fan; Xiao Jun Zhang; Tmurbagan Bao; Ming Feng Zhu; Hong Yan Wang

    2015-11-17

    A detailed description of the nucleon direct Urca processes related to the neutron star cooling is given and how they are affected by the degrees of freedom of hyperons and hyperon direct Urca processes are presented. These results indicate that the appearance of hyperons can sharply suppress the neutrino emissivity of the nucleon direct Urca processes. However, the contribution of the hyperon direct Urca processes within the certain density (mass) range makes the total neutrino emissivity (luminosity) even exceed the corresponding value of the nucleon direct Urca processes in npe$\\mu$ matter. Furthermore, when we only consider the nucleon direct Urca processes with the $^{1}S_{0}$ proton superfluidity in neutron star cooling, for example, it is hard to differentiate the theoretical cooling curves of 1.95$M_{\\odot}$ for nphe$\\mu$ matter from 2.03$M_{\\odot}$ for npe$\\mu$ matter in GM1 model. It is also difficult to rule out hyperons at the points of intersection for the two theoretical cooling curves of 2.0$M_{\\odot}$ neutron star for npe$\\mu$ and nphe$\\mu$ matter in TM1 model.These results could be used to help prove appearing hyperons in PSR J1614-2230 and J0348+0432 from neutron star cooling perspective.

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

    E-print Network

    Sakshi Gautam

    2011-07-28

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

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

    NASA Astrophysics Data System (ADS)

    Louzguine-Luzgin, Dmitri V.; Inoue, Akihisa; Yavari, Alain R.; Vaughan, Gavin

    2006-03-01

    Thermal expansion of a glassy Cu55Hf25Ti15Pd5 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.

  12. Systematics of nucleon density distributions and neutron skin of nuclei

    E-print Network

    W. M. Seif; Hesham Mansour

    2015-05-19

    Proton and neutron density profiles of 760 nuclei in the mass region of A=16-304are analyzed using the Skyrme energy density for the parameter set SLy4. Simple formulae are obtained to fit the resulting radii and diffuseness data. These formulae may be useful to estimate the values of the unmeasured radii, and especially in extrapolating charge radius values for nuclei which are far from the valley of stability or to perform analytic calculations for bound and/or scattering problems. The obtained neutron and proton root-mean-square radii and the neutron skin thicknesses are in agreement with the available experimental data.

  13. Systematics of nucleon density distributions and neutron skin of nuclei

    E-print Network

    Seif, W M

    2015-01-01

    Proton and neutron density profiles of 760 nuclei in the mass region of A=16-304are analyzed using the Skyrme energy density for the parameter set SLy4. Simple formulae are obtained to fit the resulting radii and diffuseness data. These formulae may be useful to estimate the values of the unmeasured radii, and especially in extrapolating charge radius values for nuclei which are far from the valley of stability or to perform analytic calculations for bound and/or scattering problems. The obtained neutron and proton root-mean-square radii and the neutron skin thicknesses are in agreement with the available experimental data.

  14. Neutron density distributions from antiprotonic 208Pb and 209Bi atoms

    E-print Network

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

    2007-02-26

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

  15. Effects of differences between neutron and proton density distributions on ? -decay half-lives

    NASA Astrophysics Data System (ADS)

    Ni, Dongdong; Ren, Zhongzhou

    2015-11-01

    The neutron skin of heavy nuclei is one of the hot topics in contemporary nuclear physics. In this article, effects of differences between neutron and proton density distributions on ? decay are investigated. ? -decay calculations are performed within the generalized density-dependent cluster model, where the ? -core potential is determined in the double-folding model using the neutron and proton density distributions of daughter nuclei. The proton and neutron density distributions, assumed to be of two-parameter Fermi form, are constrained by the experimental nuclear charge radii as well as the neutron skin thickness of heavy nuclei. The resulting distribution of daughter nuclei results in an improved ? -core potential which is important for ? -decay calculations. It is found that the neutron skin thickness plays an important role in reducing the calculated ? -decay half-lives, implying a smaller ? preformation factor. The calculations with neutron skin thickness show good agreement with the available experimental data for even-even nuclei including the known heaviest nuclei.

  16. The Mass-Radius-Eccentricity Distribution of Near-Resonant Transiting Exoplanet Pairs Detected by Kepler

    NASA Astrophysics Data System (ADS)

    Shabram, Megan; Jontof-Hutter, Daniel; Ford, Eric B.

    2015-12-01

    We characterize the mass-radius-eccentricity distribution of transiting planets near first-order mean motion resonances using Transit Timing Variation (TTV) observations from NASA's Kepler mission. Kepler's precise measurements of transit times (Mazeh et al. 2014; Rowe et al. 2015) constrain the planet-star mass ratio, eccentricity and pericenter directions for hundreds of planets. Strongly-interacting planetary systems allow TTVs to provide precise measurements of masses and orbital eccentricities separately (e.g., Kepler-36, Carter et al. 2012). In addition to these precisely characterized planetary systems, there are several systems harboring at least two planets near a mean motion resonance (MMR) for which TTVs provide a joint constraint on planet masses, eccentricities and pericenter directions (Hadden et al. 2015). Unfortunately, a near degeneracy between these parameters leads to a posterior probability density with highly correlated uncertainties. Nevertheless, the population encodes valuable information about the distribution of planet masses, orbital eccentricities and the planet mass-radius relationship. We characterize the distribution of masses and eccentricities for near-resonant transiting planets by combining a hierarchical Bayesian model with an analytic model for the TTV signatures of near-resonant planet pairs (Lithwick & Wu 2012). By developing a rigorous statistical framework for analyzing the TTV signatures of a population of planetary systems, we significantly improve upon previous analyses. For example, our analysis includes transit timing measurements of near-resonant transiting planet pairs regardless of whether there is a significant detection of TTVs, thereby avoiding biases due to only including TTV detections.

  17. Measurement and simulation of neutron beam fluence energy distributions at the neutron time-of-flight facility of iThemba Labs.

    PubMed

    Herbert, M S

    2014-10-01

    A NE213 proton recoil detector using the time-of-flight technique was used to measure neutron beam fluence energy distributions at the neutron time-of-flight facility of iThemba Labs. A comparison was performed between neutron beam fluence energy distributions calculated by the Monte Carlo code MCNPX and that measured for neutron beams of energies up to ?64 MeV for the calibration of detectors. The results obtained showed good agreement between the calculated and measured distributions. PMID:24667277

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

    SciTech Connect

    Gilbert, Benjamin

    2008-10-01

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

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

    SciTech Connect

    Laouet, N.; Benrachi, F.

    2012-06-27

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

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

    PubMed Central

    Zapata, Carlos; Núñez, Concepción; Velasco, Teresa

    2002-01-01

    The within-chromosome distribution of gametic disequilibrium (GD) between protein loci, and the underlying evolutionary factors of this distribution, are still largely unknown. Here, we report a detailed study of GD between a large number of protein loci (15) spanning 87% of the total length of the third chromosome of Drosophila melanogaster in a large sample of haplotypes (600) drawn from a single natural population. We used a sign-based GD estimation method recently developed for multiallelic systems, which considerably increases both the statistical power and the accuracy of estimation of the intensity of GD. We found that strong GD between pairs of protein loci was widespread throughout the chromosome. In total, 22% of both the pairs of alleles and pairs of loci were in significant GD, with mean intensities (as measured by D' coefficients) of 0.43 and 0.31, respectively. In addition, strong GD often occurs between loci that are far apart. By way of illustration, 32% of the allele pairs in significant GD occurred within pairs of loci separated by effective frequencies of recombination (EFRs) of 15-20 cM, the mean D' value being 0.49. These observations are in sharp contrast with previous studies showing that GD between protein loci is rarely found in natural populations of outcrossing species, even between very closely linked loci. Interestingly, we found that most instances of significant interallelic GD (68%) involved functionally related protein loci. Specifically, GD was markedly more frequent between protein loci related by the functions of hormonal control, molybdenum control, antioxidant defense system, and reproduction than between loci without known functional relationship, which is indicative of epistatic selection. Furthermore, long-distance GD between functionally related loci (mean EFR 9 cM) suggests that epistatic interactions must be very strong along the chromosome. This evidence is hardly compatible with the neutral theory and has far-reaching implications for understanding the multilocus architecture of the functional genome. Our findings also suggest that GD may be a useful tool for discovering networks of functionally interacting proteins. PMID:12196399

  1. Systematics of nucleon density distributions and neutron skin of nuclei

    NASA Astrophysics Data System (ADS)

    Seif, W. M.; Mansour, Hesham

    2015-10-01

    Proton and neutron density profiles of 760 nuclei in the mass region of A = 16?304 are analyzed using the Skyrme energy density for the parameter set SLy4. Simple formulae are obtained to fit the resulting radii and diffuseness data. These formulae are useful to estimate the values of the unmeasured radii and especially in extrapolating charge radii values for nuclei which are far from the valley of stability. Also, it provides an easy way to formulate the density profile for nuclear applications and to perform analytic calculations for bound and/or scattering problems. The obtained neutron and proton root-mean-square (rms) radii and the neutron skin thicknesses are in agreement with the available experimental data and previous Hartree-Fock (HF) calculations.

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

    SciTech Connect

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

    1994-12-31

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

  3. Imaging study of vibrational predissociation of the HCl-acetylene dimer: pair-correlated distributions.

    PubMed

    Li, Guosheng; Parr, Jessica; Fedorov, Igor; Reisler, Hanna

    2006-07-01

    The state-to-state predissociation dynamics of the HCl-acetylene dimer were studied following excitation in the asymmetric C-H (asym-CH) stretch and the HCl stretch. Velocity map imaging (VMI) and resonance enhanced multiphoton ionization (REMPI) were used to determine pair-correlated product energy distributions. Different vibrational predissociation mechanisms were observed for the two excited vibrational levels. Following excitation in the of the asym-CH stretch fundamental, HCl fragments in upsilon = 0 and j = 4-7 were observed and no HCl in upsilon = 1 was detected. The fragments' center-of-mass (c.m.) translational energy distributions were derived from images of HCl (j = 4-7), and were converted to rotational state distributions of the acetylene co-fragment by assuming that acetylene is generated with one quantum of C-C stretch (nu(2)) excitation. The acetylene pair-correlated rotational state distributions agree with the predictions of the statistical phase space theory, restricted to acetylene fragments in 1nu(2). It is concluded that the predissociation mechanism is dominated by the initial coupling of the asym-CH vibration to a combination of C-C stretch and bending modes in the acetylene moiety. Vibrational energy redistribution (IVR) between acetylene bending and the intermolecular dimer modes leads to predissociation that preserves the C-C stretch excitation in the acetylene product while distributing the rest of the available energy statistically. The predissociation mechanism following excitation in the Q band of the dimer's HCl stretch fundamental was quite different. HCl (upsilon = 0) rotational states up to j = 8 were observed. The rovibrational state distributions in the acetylene co-fragment derived from HCl (j = 6-8) images were non-statistical with one or two quanta in acetylene bending vibrational excitation. From the observation that all the HCl(j) translational energy distributions were similar, it is proposed that there exists a constraint on conversion of linear to angular momentum during predissociation. A dimer dissociation energy of D(0) = 700 +/- 10 cm(-1) was derived. PMID:16880903

  4. Effects of deformation on the coexistence between neutron-proton and particle-like pairing in N =Z medium-mass nuclei

    NASA Astrophysics Data System (ADS)

    Gambacurta, Danilo; Lacroix, Denis

    2015-01-01

    A model combining self-consistent mean-field and shell-model techniques is used to study the competition between particle-like and proton-neutron pairing correlations in f p -shell even-even self-conjugate nuclei. Results obtained using constant two-body pairing interactions as well as more sophisticated interactions are presented and discussed. The standard BCS calculations are systematically compared with more refined approaches including correlation effects beyond the independent quasiparticle approach. The competition between proton-neutron correlations in the isoscalar and isovector channels is also analyzed, as well as their dependence on the deformation properties. Besides the expected role of the spin-orbit interaction and particle number conservation, it is shown that deformation leads to a reduction of the pairing correlations. This reduction originates from the change of the single-particle spectrum and from a quenching of the residual pairing matrix elements. The competition between isoscalar and isovector pairing in the deuteron transfer is finally addressed. Although a strong dependence the isovector pairing correlations with respect to nuclear deformation is observed, they always dominate over the isoscalar ones.

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

    SciTech Connect

    Das, Tanmoy; Balatsky, Alexander V.; Zhang, Chenglin; Li, Haifeng; Su, Yiki; Nethertom, Tucker; Redding, Caleb; Carr, Scott; Schneidewind, Astrid; Faulhaber, Enrico; Li, Shiliang; Yao, Daoxin; Bruckel, Thomas; Dai, Pengchen; Sobolev, Oleg

    2012-06-05

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

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

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    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.

  7. Dependence of the statistical distribution of reduced neutron widths on the quantum number K

    SciTech Connect

    Masterov, V.S.; Rabotnov, N.S.

    1984-02-01

    The assumption of a random distribution of the quantum number K in states corresponding to neutron resonances in odd nuclei is analyzed in detail; the resulting expression for the reaction amplitude is used to study the distribution of reduced neutron widths. The distribution obtained has a relative dispersion ((GAMMA/sup 0//sub n/)/sup 2/)-(Gamma-bar/sup 0//sub n/)/sup 2/)/(Gamma-bar/sup 0//sub n/)/sup 2/approx. =2.7.5. The observed dispersions are on the average smaller almost by a factor of two, which may point to appreciable correlation of the partial (with respect to K) amplitudes.

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

    PubMed

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

    2002-01-01

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

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

    SciTech Connect

    Verbeke, Jerome M.

    1999-12-14

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

  10. Distribution of total radiation widths for neutron resonances of Pt isotopes

    NASA Astrophysics Data System (ADS)

    Koehler, P. E.; Be?vá?, F.; Krti?ka, M.

    2015-05-01

    High quality neutron capture and transmission data were measured on isotopically enriched 192,194,195,196Pt and natural Pt samples at ORELA. R-matrix analysis of this data revealed resonance parameters for 159, 413, 423, 258, and 11 neutron resonances for neutron energies below 5.0, 16.0, 7.5, 16.0, and 5.0 keV for 192,194,195,196,198Pt+n, respectively. Earlier analysis of data on reduced neutron widths, ?0n, showed that the distributions of ?0n for 192,194Pt deviate significantly from the Porter-Thomas distribution (PTD) predicted by random matrix theory. In this contribution we report on preliminary results of the analysis of distribution of total radiation widths, ??, in 192,194,195,196Pt+n reactions. Comparison of experimental data with predictions made within the nuclear statistical model indicates that standard models of Photon Strength Functions (PSFs) and Nuclear Level Density predict ?? distributions which are too narrow. We found that satisfactory agreement between experimental and simulated distributions can be obtained only by a strong suppression of the PSFs at low ?-ray energies and/or by violation of the usual assumption that primary transitions from neutron resonances follow the PTD. The shape of PSFs needed for reproduction of our ?? data also nicely reproduces spectra from several (n,?) experiments on the neighbor nuclide 198Au.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

    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

  13. An analytical derivation of the full probability distribution was demonstrated for the number of neutrons and gamma photons

    E-print Network

    Pázsit, Imre

    for the number of neutrons and gamma photons generated in a fissile sample with internal multiplication. The for with the expressions for factorial moments of the total number of neutrons and photons generated in the sample The number distribution of neutrons and photons generated in a finite sample with internal multiplication has

  14. On the distribution of 1550-nm photon pairs efficiently generated using a periodically poled lithium niobate waveguide

    E-print Network

    Shigehiko Mori; Jonas Soderholm; Naoto Namekata; Shuichiro Inoue

    2005-09-27

    We report on the generation of photon pairs in the 1550-nm band suitable for long-distance fiber-optic quantum key distribution. The photon pairs were generated in a periodically poled lithium niobate waveguide with a high conversion-efficiency. Using a pulsed semiconductor laser with a pulse rate of 800 kHz and a maximum average pump power of 50 muW, we obtained a coincidence rate of 600 s^-1. Our measurements are in agreement with a Poissonian photon-pair distribution, as is expected from a comparison of the coherence time of the pump and of the detected photons. An average of 0.9 photon pairs per pulse was obtained.

  15. Total-scattering pair-distribution function of organic material from powder electron diffraction data.

    PubMed

    Gorelik, Tatiana E; Schmidt, Martin U; Kolb, Ute; Billinge, Simon J L

    2015-04-01

    This paper shows that pair-distribution function (PDF) analyses can be carried out on organic and organometallic compounds from powder electron diffraction data. Different experimental setups are demonstrated, including selected area electron diffraction and nanodiffraction in transmission electron microscopy or nanodiffraction in scanning transmission electron microscopy modes. The methods were demonstrated on organometallic complexes (chlorinated and unchlorinated copper phthalocyanine) and on purely organic compounds (quinacridone). The PDF curves from powder electron diffraction data, called ePDF, are in good agreement with PDF curves determined from X-ray powder data demonstrating that the problems of obtaining kinematical scattering data and avoiding beam damage of the sample are possible to resolve. PMID:25510245

  16. Total-scattering pair-distribution function of organic material from powder electron diffraction data

    DOE PAGESBeta

    Gorelik, Tatiana E.; Billinge, Simon J. L.; Schmidt, Martin U.; Kolb, Ute

    2015-04-01

    This paper shows for the first time that pair-distribution function analyses can be carried out on organic and organo-metallic compounds from powder electron diffraction data. Different experimental setups are demonstrated, including selected area electron diffraction (SAED) and nanodiffraction in transmission electron microscopy (TEM) or nanodiffraction in scanning transmission electron microscopy (STEM) modes. The methods were demonstrated on organo-metallic complexes (chlorinated and unchlorinated copper-phthalocyanine) and on purely organic compounds (quinacridone). The PDF curves from powder electron diffraction data, called ePDF, are in good agreement with PDF curves determined from X-ray powder data demonstrating that the problems of obtaining kinematical scattering datamore »and avoiding beam-damage of the sample are possible to resolve.« less

  17. Quantitative high-pressure pair distribution function analysis of nanocrystalline gold

    NASA Astrophysics Data System (ADS)

    Martin, C. David; Antao, Sytle M.; Chupas, Peter J.; Lee, Peter L.; Shastri, Sarvjit D.; Parise, John B.

    2005-02-01

    Using a diamond anvil cell with high-energy monochromatic x rays, we have studied the total scattering of nanocrystalline gold to 20Å-1 at pressures up to 10GPa in a hydrostatic alcohol pressure-medium. Through direct Fourier transformation of the structure function [S(Q)], pair distribution functions (PDFs) [G(r)] are calculated without Kaplow-type iterative corrections. Quantitative high-pressure PDF (QHP-PDF) analysis is performed via full-profile least-squares modeling and confirmed through comparison of Rietveld analysis of Bragg diffraction. The quality of the high pressure PDFs obtained demonstrates the integrity of our technique and suggests the feasibility of future QHP-PDF studies of liquids, disordered solids, and materials at phase transition under pressure.

  18. Total-scattering pair-distribution function of organic material from powder electron diffraction data

    SciTech Connect

    Gorelik, Tatiana E.; Billinge, Simon J. L.; Schmidt, Martin U.; Kolb, Ute

    2015-04-01

    This paper shows for the first time that pair-distribution function analyses can be carried out on organic and organo-metallic compounds from powder electron diffraction data. Different experimental setups are demonstrated, including selected area electron diffraction (SAED) and nanodiffraction in transmission electron microscopy (TEM) or nanodiffraction in scanning transmission electron microscopy (STEM) modes. The methods were demonstrated on organo-metallic complexes (chlorinated and unchlorinated copper-phthalocyanine) and on purely organic compounds (quinacridone). The PDF curves from powder electron diffraction data, called ePDF, are in good agreement with PDF curves determined from X-ray powder data demonstrating that the problems of obtaining kinematical scattering data and avoiding beam-damage of the sample are possible to resolve.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-11-01

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

  1. No influence of a N =126 neutron-shell closure in fission-fragment mass distributions

    NASA Astrophysics Data System (ADS)

    Chaudhuri, A.; Ghosh, T. K.; Banerjee, K.; Bhattacharya, S.; Sadhukhan, Jhilam; Kundu, S.; Bhattacharya, C.; Meena, J. K.; Mukherjee, G.; Saha, A. K.; Asgar, Md. A.; Dey, A.; Manna, S.; Pandey, R.; Rana, T. K.; Roy, P.; Roy, T.; Srivastava, V.; Bhattacharya, P.; Biswas, D. C.; Joshi, B. N.; Mahata, K.; Shrivastava, A.; Vind, R. P.; Pal, S.; Behera, B. R.; Singh, Varinderjit

    2015-10-01

    Mass distributions of the fragments in the fission of 206Po and the N =126 neutron shell closed nucleus 210Po have been measured. No significant deviation of mass distributions has been found between 206Po and 210Po, indicating the absence of shell correction at the saddle point in both the nuclei, contrary to the reported angular anisotropy and prescission neutron multiplicity results. This result provides benchmark data to test the new fission dynamical models to study the effect of shell correction on the potential energy surface at saddle point.

  2. Pre-neutron-emission mass distributions for reaction $^{232}$Th(n, f) up to 60 MeV

    E-print Network

    Sun, Xiaojun; Yu, Chenggang; Yang, Yongxu; Wang, Ning

    2013-01-01

    The pre-neutron-emission mass distributions for reaction $^{232}$Th(n, f) up to 60 MeV are systematically studied with an empirical fission potential model. The energy dependences of the peaks and valleys of the pre-neutron-emission mass distributions are described by the exponential expressions based on the newly measured data. The energy dependence of evaporation neutrons before scission, which plays a crucial role for the reasonable description of the mass distribution, is also considered. Both the double-humped and triple-humped shape of the measured pre-neutron-emission mass distributions for reaction $^{232}$Th(n, f) are reasonably well reproduced at incident energies up to 60 MeV. The mass distributions at unmeasured energies and the critical energies at which the humped pre-neutron-emission mass distributions are transformed into each other are also predicted.

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

    SciTech Connect

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

    2009-10-25

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

  4. Fragment Angular Distributions in Neutron-Induced Fission of w235U and 239Pu using a Time Projection Chamber

    NASA Astrophysics Data System (ADS)

    Kleinrath, Verena

    2014-09-01

    Fission fragment angular distributions can lend insights into fission barrier shapes and level densities at the scission point, both important for fission theory development. Fragment emission anisotropies are also valuable for precision cross section ratio measurements, if the distributions are different for the two isotopes used in the ratio. Available angular data is sparse for 235U and even more so for 239Pu, especially at neutron energies above 5 MeV. The Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) time projection chamber, which enables precise tracking of charged particles, can be used to study angular distributions and emission anisotropies of fission fragments in neutron-induced fission. Analysis of in-beam data collected at the Los Alamos Neutron Science Center with a 239Pu/235U target will provide angular distributions as a function of incident neutron energy for these isotopes. Preliminary angular distributions for 235U and 239Pu using the NIFFTE time projection chamber will be presented. Fission fragment angular distributions can lend insights into fission barrier shapes and level densities at the scission point, both important for fission theory development. Fragment emission anisotropies are also valuable for precision cross section ratio measurements, if the distributions are different for the two isotopes used in the ratio. Available angular data is sparse for 235U and even more so for 239Pu, especially at neutron energies above 5 MeV. The Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) time projection chamber, which enables precise tracking of charged particles, can be used to study angular distributions and emission anisotropies of fission fragments in neutron-induced fission. Analysis of in-beam data collected at the Los Alamos Neutron Science Center with a 239Pu/235U target will provide angular distributions as a function of incident neutron energy for these isotopes. Preliminary angular distributions for 235U and 239Pu using the NIFFTE time projection chamber will be presented. Neutron Induced Fission Fragment Tracking Experiment.

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

    PubMed Central

    Weber, Anton

    2013-01-01

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

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

    SciTech Connect

    Parfenova, Y.; Leclercq-Willain, Ch.

    2005-08-01

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

  7. Neutron damage in distributed Bragg reflectors and microcavity lasers. Master`s thesis

    SciTech Connect

    Suriano, M.A.

    1995-12-01

    Distributed Bragg Reflectors (DBRs) grown on a gallium-arsenide substrate for a solid state mirror and a vertical cavity surface emitting laser (VCSEL) were subjected to a neutron fluence to determine the sensitivity of the DBRs. The samples were irradiated at Ohio State University`s 500 kW research reactor. Relative and absolute reflectance measurements were taken before and after each irradiation over a spectral band of 530-880 nm. Relative reflectance measurements showed that the irradiation did not cause any spectral shift over seven decades of neutron fluences. The reflectivity of the DBRs decreased from their initial measurements after being irradiated. The reflectance decrease was correlated to the incident neutron fluence to determine a Messenger Spratt type of equation to predict the DBRs response. A radiation damage constant for the VCSEL and DBR mirror were determined to be 3.83x10(exp13) NEUTRONS/CM2 and 2.19x10(exp13)NEUTRONS/CM2 respectively utilizing a 1 MeV equivalent (Si) neutron fluence.

  8. Coherent deeply virtual Compton scattering off 3He and neutron generalized parton distributions

    E-print Network

    Matteo Rinaldi; Sergio Scopetta

    2014-06-18

    It has been recently proposed to study coherent deeply virtual Compton scattering (DVCS) off 3He nuclei to access neutron generalized parton distributions (GPDs). In particular, it has been shown that, in Impulse Approximation (IA) and at low momentum transfer, the sum of the quark helicity conserving GPDs of 3He, H and E, is dominated by the neutron contribution. This peculiar result makes the 3He target very promising to access the neutron information. We present here the IA calculation of the spin dependent GPD tilde-H of 3He. Also for this quantity the neutron contribution is found to be the dominant one, at low momentum transfer. The known forward limit of the IA calculation of tilde-H, yielding the polarized parton distributions of 3He, is correctly recovered. The extraction of the neutron information could be anyway non trivial, so that a procedure, able to take into account the nuclear effects encoded in the IA analysis, is proposed. These calculations, essential for the evaluation of the coherent DVCS cross section asymmetries, which depend on the GPDs H, E and tilde-H, represent a crucial step for planning possible experiments at Jefferson Lab.

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

    NASA Astrophysics Data System (ADS)

    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

    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.

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

    SciTech Connect

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

    2008-01-01

    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.

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

    SciTech Connect

    Farrow, Christopher L.; Shaw, Margaret; Kim, Hyunjeong; Juhás, Pavol; Billinge, Simon J.L.

    2011-12-07

    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.

  12. Towards solution and refinement of organic crystal structures by fitting to the atomic pair distribution function.

    PubMed

    Prill, Dragica; Juhás, Pavol; Billinge, Simon J L; Schmidt, Martin U

    2016-01-01

    A method towards the solution and refinement of organic crystal structures by fitting to the atomic pair distribution function (PDF) is developed. Approximate lattice parameters and molecular geometry must be given as input. The molecule is generally treated as a rigid body. The positions and orientations of the molecules inside the unit cell are optimized starting from random values. The PDF is obtained from carefully measured X-ray powder diffraction data. The method resembles `real-space' methods for structure solution from powder data, but works with PDF data instead of the diffraction pattern itself. As such it may be used in situations where the organic compounds are not long-range-ordered, are poorly crystalline, or nanocrystalline. The procedure was applied to solve and refine the crystal structures of quinacridone (? phase), naphthalene and allopurinol. In the case of allopurinol it was even possible to successfully solve and refine the structure in P1 with four independent molecules. As an example of a flexible molecule, the crystal structure of paracetamol was refined using restraints for bond lengths, bond angles and selected torsion angles. In all cases, the resulting structures are in excellent agreement with structures from single-crystal data. PMID:26697868

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

    USGS Publications Warehouse

    Hietanen, A.

    1971-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

  15. Sensitivity of Leakage from Iron Spheres to the Angular Distribution of Secondary Neutrons

    NASA Astrophysics Data System (ADS)

    Perel, Reuven L.

    2003-06-01

    We have recently developed and implemented a Monte Carlo method for the calculation of sensitivities to the angular distribution of secondary neutrons. In the current work, a sensitivity analysis of iron spheres experiments is presented, using this novel method. The experiments were performed at NRI, Rez, Czech Republic, at NIST, Gaithersburg (both with a 252Cf source), and at LLNL, Livermore (with a 14 MeV source). Sensitivities of the responses to the angular distribution of neutrons scattered elastically or inelastically to selected levels were calculated and reported. It was found that in leakage experiments the sensitivities to angular distributions are of similar magnitude as the sensitivities to the corresponding cross sections. The sensitivity to the first Legendre moment has usually the opposite sign of the sensitivity to the corresponding cross section. Lack of covariance data in cross section libraries could seriously impede realistic estimation of nuclear-data-induced calculated uncertainties when analyzing experimental results.

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

    USGS Publications Warehouse

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

    1977-01-01

    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.

  17. Experimental Free-Space Distribution of Entangled Photon Pairs over a Noisy Ground Atmosphere of 13km

    E-print Network

    Cheng-Zhi Peng; Tao Yang; Xiao-Hui Bao; Jun-Zhang; Xian-Min Jin; Fa-Yong Feng; Bin Yang; Jian Yang; Juan Yin; Qiang Zhang; Nan Li; Bao-Li Tian; Jian-Wei Pan

    2004-12-31

    We report free-space distribution of entangled photon pairs over a noisy ground atmosphere of 13km. It is shown that the desired entanglement can still survive after the two entangled photons have passed through the noisy ground atmosphere. This is confirmed by observing a space-like separated violation of Bell inequality of $2.45 \\pm 0.09$. On this basis, we exploit the distributed entangled photon source to demonstrate the BB84 quantum cryptography scheme. The distribution distance of entangled photon pairs achieved in the experiment is for the first time well beyond the effective thickness of the aerosphere, hence presenting a significant step towards satellite-based global quantum communication.

  18. Broadband source of telecom-band polarization-entangled photon-pairs for wavelength-multiplexed entanglement distribution.

    PubMed

    Lim, Han Chuen; Yoshizawa, Akio; Tsuchida, Hidemi; Kikuchi, Kazuro

    2008-09-29

    Studies on telecom-band entangled photon-pair sources for entanglement distribution have so far focused on their narrowband operations. Fiber-based sources are seriously limited by spontaneous Raman scattering while sources based on quasi-phase-matched crystals or waveguides are usually narrowband because of long device lengths and/or operations far from degeneracy. An entanglement distributor would have to multiplex many such narrowband sources before entanglement distribution to fully utilize the available fiber transmission bandwidth. In this work, we demonstrate a broadband source of polarization-entangled photon-pairs suitable for wavelength-multiplexed entanglement distribution over optical fiber. We show that our source is potentially capable of simultaneously supporting up to forty-four independent wavelength channels. PMID:18825244

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

    SciTech Connect

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

    1999-03-29

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

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

    PubMed

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

    2013-06-14

    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

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

    PubMed

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

    2014-06-01

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

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

    SciTech Connect

    Montoya, M.; Rojas, J.; Lobato, I.

    2010-08-04

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

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

    E-print Network

    Sparks, Donald L.

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

  4. Pre-neutron-emission mass distributions for reaction $^{238}$U(n, f) up to 60 MeV

    E-print Network

    Xiaojun Sun; Chenggang Yu; Ning Wang; Yongxu Yang

    2013-10-11

    The pre-neutron-emission mass distributions for reaction $^{238}$U(n, f) up to 60 MeV are systematically studied with an empirical fission potential model. The energy dependence of the peaks and valleys of the pre-neutron-emission mass distributions is described by an exponential form based on the newly measured data. The energy dependence of evaporation neutrons before scission is also considered, which plays a crucial role for the reasonable description of the mass distributions. The measured data for the pre-neutron-emission mass distributions for reaction $^{238}$U(n, f) are reasonably well reproduced up to 60 MeV. The mass distributions at unmeasured energies are also predicted with this approach.

  5. Pre-neutron-emission mass distributions for reaction $^{238}$U(n, f) up to 60 MeV

    E-print Network

    Sun, Xiaojun; Wang, Ning; Yang, Yongxu

    2013-01-01

    The pre-neutron-emission mass distributions for reaction $^{238}$U(n, f) up to 60 MeV are systematically studied with an empirical fission potential model. The energy dependence of the peaks and valleys of the pre-neutron-emission mass distributions is described by an exponential form based on the newly measured data. The energy dependence of evaporation neutrons before scission is also considered, which plays a crucial role for the reasonable description of the mass distributions. The measured data for the pre-neutron-emission mass distributions for reaction $^{238}$U(n, f) are reasonably well reproduced up to 60 MeV. The mass distributions at unmeasured energies are also predicted with this approach.

  6. Investigating Neutron-Proton Pairing in sd-Shell Nuclei via (p,3He) and (3He,p) Transfer Reactions

    NASA Astrophysics Data System (ADS)

    Ayyad, Y.; Lee, J.; Tamii, A.; Aoi, N.; Fujita, H.; Fujita, Y.; Ganioglu, E.; Hatanaka, K.; Hashimoto, T.; Ito, T.; Kawabata, T.; Kadoya, T.; Lay, J. A.; Li, Z.; Liu, H.; Macchiavelli, A. O.; Matsubara, H.; Miki, K.; Ong, H. J.; Potel, G.; Susoy, G.; Watanabe, H. D.; Yokota, N.; Zenihiro, J.

    In this work we have investigated neutron-proton pairing in self-conjugate nuclei in the 2s-1d shell by means of np transfer reactions. In particular, we aim to shed light on the existence of the isoscalar np pairing. The experiment was conducted at Grand Raiden high-resolution spectrometer (Research Center for Nuclear Physics, Osaka - Japan) by using 3He and proton beams to perform systematic measurements of (p,3He) pick-up and (3He,p) stripping reactions. We have obtained the absolute differential cross sections for a wide range of angles and the ratio of cross sections populating to the lowest J? = 0+, 1+ states in the odd-odd N = Z nuclei. Preliminary experimental results are reported.

  7. The role of currents distribution in general relativistic equilibria of magnetized neutron stars

    E-print Network

    N. Bucciantini; A. G. Pili; L. Del Zanna

    2014-12-17

    Magnetic fields play a critical role in the phenomenology of neutron stars. There is virtually no observable aspect which is not governed by them. Despite this, only recently efforts have been done to model magnetic fields in the correct general relativistic regime, characteristic of these compact objects. In this work we present, for the first time a comprehensive and detailed parameter study, in general relativity, of the role that the current distribution, and the related magnetic field structure, have in determining the precise structure of neutron stars. In particular, we show how the presence of localized currents can modify the field strength at the stellar surface, and we look for general trends, both in terms of energetic properties, and magnetic field configurations. Here we verify that, among other things, for a large class of different current distributions the resulting magnetic configurations are always dominated by the poloidal component of the current.

  8. Planetesimal Scattering and its Implications for the Period-Ratio Distribution of Kepler Planet Pairs

    NASA Astrophysics Data System (ADS)

    Chatterjee, Sourav; Krantzler, Seth O.; Ford, Eric B.; Tasker, Elizabeth; Rasio, Fred

    2015-12-01

    Period ratios of most adjacent planet pairs in Kepler's multiplanet systems seem random. However, there is a clear excess and dearth of systems just exterior and interior to major mean motion resonances, respectively. We show that dynamical interactions between initially resonant planet pairs and planetesimals in a planetesimal disk can naturally produce the observed asymmetric abundances in period ratios of near-resonant pairs for a wide variety of planet and planetesimal disk properties (Chatterjee & Ford 2015). We further extend this study to include planet pairs initially not in resonance. We will present our key results from this large suite of simulations. We will also discuss implications of planetesimal scattering for the observable properties of these planets including their TTV signal and mass-radius properties as a result of planetesimal accretion.

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

    NASA Astrophysics Data System (ADS)

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

    2010-06-01

    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.

  10. Neutron density distributions analyzed in terms of relativistic impulse approximation for nickel isotopes

    NASA Astrophysics Data System (ADS)

    Kaki, Kaori

    2015-03-01

    Observables of proton elastic scattering from nickel isotopes (48-82Ni) are calculated based on relativistic impulse approximation (RIA), and nuclear density distributions are provided by relativistic mean-field (RMF) calculations. Contributions of a medium effect and multiple scattering to observables are evaluated and shown to be small at incident proton energies from 200 MeV through 500 MeV so that it is confirmed to perform a model analysis based on the fundamental RIA calculation. For 58,60,62,64Ni isotopes, are considered proton distributions which are obtained by means of unfolding the charge form factor of proton from charge densities determined by the experiments of electron scattering. Through comparisons between results for the different proton densities, contributions of proton form factor to proton distributions and to elastic scattering observables at 300 MeV are discussed. It is shown that the neutron distribution is determined from the restricted observables, reaction cross-section and the first dip of differential cross-section, based on a model analysis of Woods-Saxon distribution in the case of 64Ni target at 300 MeV. Contributions of tensor density and empirical proton density are shown to obtaining the neutron distribution with the model analysis. Compared with the similar studies for 40,60Ca and 208Pb, problems of the model analysis, which arise out of errors in observables, are discussed.

  11. The probability distribution of the number of electron-positron pairs produced in a uniform electric field

    E-print Network

    M. I. Krivoruchenko

    2012-07-27

    The probability-generating function of the number of electron-positron pairs produced in a uniform electric field is constructed. The mean and variance of the numbers of pairs are calculated, and analytical expressions for the probability of low numbers of electron-positron pairs are given. A recursive formula is derived for evaluating the probability of any number of pairs. In electric fields of supercritical strength |eE| > \\pi m^2/ \\ln 2, where e is the electron charge, E is the electric field, and m is the electron mass, a branch-point singularity of the probability-generating function penetrates the unit circle |z| = 1, which leads to the asymptotic divergence of the cumulative probability. This divergence indicates a failure of the continuum limit approximation. In the continuum limit and for any field strength, the positive definiteness of the probability is violated in the tail of the distribution. Analyticity, convergence, and positive definiteness are restored upon the summation over discrete levels of electrons in the normalization volume. Numerical examples illustrating the field strength dependence of the asymptotic behavior of the probability distribution are presented.

  12. 3D mapping of crystallographic phase distribution using energy-selective neutron tomography.

    PubMed

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

    2014-06-25

    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

  13. Relationship between the atomic pair distribution function and small-angle scattering: implications for modeling of nanoparticles.

    PubMed

    Farrow, Christopher L; Billinge, Simon J L

    2009-05-01

    The relationship between the equations used in the atomic pair distribution function (PDF) method and those commonly used in small-angle-scattering (SAS) analyses is explicitly shown. The origin of the sloping baseline, -4pirrho0, in PDFs of bulk materials is identified as originating from the SAS intensity that is neglected in PDF measurements. The nonlinear baseline in nanoparticles has the same origin, and contains information about the shape and size of the nanoparticles. PMID:19349667

  14. Calibration and data collection protocols for reliable lattice parameter values in electron pair distribution function (ePDF) studies

    DOE PAGESBeta

    Abeykoon, A. M. Milinda; Hu, Hefei; Wu, Lijun; Zhu, Yimei; Billinge, Simon J. L.

    2015-02-01

    We explore and describe different protocols for calibrating electron pair distribution function (ePDF) measurements for quantitative studies on nano-materials. We find the most accurate approach to determine the camera-length is to use a standard calibration sample of Au nanoparticles from National Institute of Standards and Technology. Different protocols for data collection are also explored, as are possible operational errors, to find the best approaches for accurate data collection for quantitative ePDF studies.

  15. Effects of Neutron Emission on Fragment Mass and Kinetic Energy Distribution from Thermal Neutron-Induced Fission of {sup 235}U

    SciTech Connect

    Montoya, M.; Rojas, J.; Saetone, E.

    2007-10-26

    The mass and kinetic energy distribution of nuclear fragments from thermal neutron-induced fission of {sup 235}U(n{sub th},f) have been studied using a Monte-Carlo simulation. Besides reproducing the pronounced broadening in the standard deviation of the kinetic energy at the final fragment mass number around m = 109, our simulation also produces a second broadening around m = 125. These results are in good agreement with the experimental data obtained by Belhafaf et al. and other results on yield of mass. We conclude that the obtained results are a consequence of the characteristics of the neutron emission, the sharp variation in the primary fragment kinetic energy and mass yield curves. We show that because neutron emission is hazardous to make any conclusion on primary quantities distribution of fragments from experimental results on final quantities distributions.

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

    NASA Astrophysics Data System (ADS)

    Key, Baris

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

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

    E-print Network

    Harris, Thomas C. (Thomas Cameron)

    2006-01-01

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

  18. Distribution of Plagioclase-Rich Materials in the Lunar Highlands as Inferred from Lunar Prospector Thermal Neutron Measurements

    NASA Astrophysics Data System (ADS)

    Peplowski, P. N.; Beck, A. W.; Lawrence, D. J.

    2015-10-01

    We calibrate Lunar Prospector neutron data in terms of bulk composition, and infer the distribution of plagioclase in the feldspathic highlands terrane. Results are consistent with locations of PAN, and support complex crustal formation processes.

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

    NASA Astrophysics Data System (ADS)

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

    2009-09-01

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

  20. The Angular Distribution of Neutrons Scattered from Deuterium below 2 MeV

    NASA Astrophysics Data System (ADS)

    Nankov, N.; Plompen, A. J. M.; Kopecky, S.; Kozier, K. S.; Roubtsov, D.; Rao, R.; Beyer, R.; Grosse, E.; Hannaske, R.; Junghans, A. R.; Massarczyk, R.; Schwengner, R.; Yakorev, D.; Wagner, A.; Stanoiu, M.; Canton, L.; Nolte, R.; Röttger, S.; Beyer, J.; Svenne, J.

    2014-05-01

    Neutron elastic scattering measurements were carried out at the nELBE neutron time-of-flight facility at a 6 m flight path. Energies below 2 MeV were studied using a setup consisting of eight 6Li-glass detectors placed at nominal angles of 15? and 165? with respect to the incident neutron beam. A deuterated polyethylene sample with 99.999% enrichment in deuterium was used. These angles were chosen since an earlier study showed that the ratio of the differential cross section at these angles is the most sensitive to differences in evaluated files and model calculations. Accurate 165?/15? angle ratios were obtained. Above 1 MeV these are somewhat larger than given by ENDF/B-VII. Simultaneously the early day experiments using a proportional counter to infer angular distributions from deuterium recoil pulse height distributions are being studied through a new experiment with such a device at the Physikalisch-Technische Bundesanstalt (PTB). At 500 keV this experiment favors ENDF/B-VII over JENDL-4.0, while at lower energies agreement with the data is similar.

  1. The Spin Dependent Momentum Distribution of the Neutron and the Proton in HELIUM-3.

    NASA Astrophysics Data System (ADS)

    Lee, Kevin Kar

    A polarized ^3He internal gas target which delivered 50% polarized atoms at a flow rate of 1 times 10^ {17} atoms/sec was developed. This target was used in the experiment CE-25 to measure the analyzing powers and spin correlations parameters for the ^3{buildrel{-->} over{rm He}}(vec rm p,2p) and ^3{buildrel {-->}over{rm He }}(vec rm p,pn) quasielastic scatterings using the Cooler ring at IUCF at beam energies 197, 300, and 414 MeV. The target was demonstrated to have little or no depolarization in the storage cell in the elastic asymmetries measurement at 45 MeV. Analysis of the 197 MeV data is presented in this doctoral thesis. At sufficiently high momentum transfer we find ^3{buildrel{-->} over{He}}(vec p,pn) spin observables are in good agreement with free p-n scattering observables, and therefore that polarized ^3He can serve as a good polarized neutron target. We extract in PWIA the spin-dependent momentum distribution of the neutron and proton out to 300 MeV/c. The measured neutron (proton) distribution is in good (fair) agreement with a Faddeev calculation. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253 -1690.).

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

    E-print Network

    Nittler, Larry R.

    Branch Road NW, Washington D. C. 20015, USA 7 Mars Space Flight Facility, School of Earth and Space Department of Physics, University of Guelph, Guelph, Ontario, N1G 2W1, Canada 10 Jet Propulsion Laboratory to represent a relatively rare group of meteorites, they are probably paired. The four rocks were investigated

  3. Short collision time approximation for neutron scattering using discrete frequency distributions

    SciTech Connect

    Ryskamp, J.M.

    1980-01-01

    A completely general form for computing any scattering cross section based on the incoherent approximation without extending f(..omega..) to negative frequencies and without integrating over the complex plane is presented. A simple derivation of the short collision time approximation for discrete frequency distributions is also given. The approximation works well for large incident neutron energies when the duration of a collision is short compared with the natural periods of atomic motion. Single-differential scattering cross sections for light water as computed with the free proton and Nelkin scattering models at 561/sup 0/K, and the short collision time approximation with T/sub eff/ = 1468/sup 0/K, are shown for an incident neutron energy of 1.0 eV. 1 figure. (RWR)

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

    SciTech Connect

    Han, Jiyeon; /Rochester U.

    2008-11-01

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

  5. Performance of photon-pair quantum key distribution Z. WALTON,y A. V. SERGIENKO,yz M. ATATU RE,z

    E-print Network

    Teich, Malvin C.

    Letter Performance of photon-pair quantum key distribution systems Z. WALTON,y A. V. SERGIENKO,yz M in performance pro- vided by a novel quantum key distribution (qkd) system that employs a correlated photon in the ®eld of experimental quantum key distribution (qkd) since the ®rst proof-of-principle in 1992 [1

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

    SciTech Connect

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

    2001-02-01

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

  7. Kinetic Equation for Two-Particle Distribution Function in Boltzmann Gas Mixtures and Equation of Motion for Quasiparticle Pairs

    NASA Astrophysics Data System (ADS)

    Saveliev, V. L.

    2011-05-01

    Pair collisions is the main interaction process in the Boltzmann gas dynamics. By making use of exactly the same physical assumptions as was used by Ludwig Boltzmann we write the kinetic equation for two-particle distribution function of molecules in the gas mixtures. Instead of the collision integral, there are the linear scattering operator and the chaos projector in the right part of this equation. Because the scattering operator is more simple then Boltzmann collision integral this equation opens new opportunities for mathematical description of the Boltzmann gas dynamics.

  8. Distribution of root exudates and mucilage in the rhizosphere: combining 14C imaging with neutron radiography

    NASA Astrophysics Data System (ADS)

    Holz, Maire; Carminati, Andrea; Kuzyakov, Yakov

    2015-04-01

    Water and nutrients will be the major factors limiting food production in future. Plant roots employ various mechanisms to increase the access to limited soil resources. Low molecular weight organic substances released by roots into the rhizosphere increase nutrient availability by interactions with microorganisms, while mucilage improves water availability under low moisture conditions. Though composition and quality of these substances have intensively been investigated, studies on the spatial distribution and quantification of exudates in soil are scarce. Our aim was to quantify and visualize root exudates and mucilage distribution around growing roots using neutron radiography and 14C imaging depending on drought stress. Plants were grown in rhizotrons well suited for neutron radiography and 14C imaging. Plants were exposed to various soil water contents experiencing different levels of drought stress. The water content in the rhizosphere was imaged during several drying/wetting cycles by neutron radiography. The radiographs taken a few hours after irrigation showed a wet region around the root tips showing the allocation and distribution of mucilage. The increased water content in the rhizosphere of the young root segments was related to mucilage concentrations by parameterization described in Kroener et al. (2014). In parallel 14C imaging of root after 14CO2 labeling of shoots (Pausch and Kuzyakov 2011) showed distribution of rhizodeposits including mucilage. Three days after setting the water content, plants were labeled in 14CO2 atmosphere. Two days later 14C distribution in soil was imaged by placing a phosphor-imaging plate on the rhizobox. To quantify rhizodeposition, 14C activity on the image was related to the absolute 14C activity in the soil and root after destructive sampling. By comparing the amounts of mucilage (neutron radiography) with the amount of total root derived C (14C imaging), we were able to differentiate between mucilage and root exudates. We found that mucilage and 14C concentrations were higher around the young root segments. Mucilage concentration was particularly high in the most apical 3-5 cm of the roots. Drought stress increased 14C exudation relative to C fixation and led to higher mucilage concentrations around roots. However, it remains unclear, whether the lower mucilage concentration around roots grown at higher soil moisture was caused by the faster diffusion of mucilage in wet soils. Therefore, a second experiment was focused on diffusion of mucilage in soil at varying water contents. The diffusion of mucilage in soil was not very sensitive to soil water content. We conclude that mucilage release was higher for plants exposed to drought stress. In summary, the combination of neutron radiography and 14C imaging can successfully be used to visualize and to quantify the distribution of mucilage and root exudates in the rhizosphere of plants grown in soil. References Kroener, E., Zarebanadkouki, M., Kaestner, A., & Carmintati, A. (2014). Nonequilibrium water dynamics in the rhizosphere: How mucilage affects water flow in soils. Water Resources Research, 37. Pausch, J., & Kuzyakov, Y. (2011). Photoassimilate allocation and dynamics of hotspots in roots visualized by 14C phosphor imaging. Journal of Plant Nutrition and Soil Science, 174(1), 12-19.

  9. Measurement of spatial distribution of neutrons and gamma rays for BNCT using multi-imaging plate system.

    PubMed

    Tanaka, Kenichi; Sakurai, Yoshinori; Tanaka, Hiroki; Kajimoto, Tsuyoshi; Takata, Takushi; Takada, Jun; Endo, Satoru

    2015-12-01

    Quality assurance of the spatial distributions of neutrons and gamma rays was tried using imaging plates (IPs) and converters to enhance the beam components in the epithermal neutron mode of the Kyoto University Reactor. The converters used were 4mm thick epoxy resin with B4C at 6.85 weight-percent (wt%) (10)B for epithermal neutrons, and 3mm thick carbon for gamma rays. Results suggested that the IP signal does not need a sensitivity correction regardless of the incident radiation that produces it. PMID:26278346

  10. Hyperfine anomaly in Be isotopes and the neutron spatial distribution: A three-cluster model for {sup 9}Be

    SciTech Connect

    Parfenova, Y.L.; Leclercq-Willain, Ch.

    2005-11-01

    The study of the hyperfine (hfs) anomaly in neutron rich nuclei can give a very specific and unique way to study the neutron distribution and the clustering structure. We study the sensitivity of the hfs anomaly to the clustering effects in the {sup 9}Be isotope using two different nuclear wave functions obtained in the three-cluster ({alpha}+{alpha}+n) model. The results are compared to those obtained for {sup 9,11}Be in a two-body core+neutron model to examine whether the hfs anomaly is sensitive to a halo structure in {sup 11}Be.

  11. Systematic for parity distribution in nuclear level density near neutron separation energies

    NASA Astrophysics Data System (ADS)

    Singhal, S. K.; Agrawal, H. M.

    2011-03-01

    The correct form of nuclear level density function ?(U,J,?) is required to calculate nuclear cross-sections needed for various applications ranging from reactor designing, nuclear astrophysics, etc., to transmutation of nuclear waste. The asymmetrical statistical distribution of parity of nuclear levels at low energies poses an intriguing problem leading to larger uncertainties in the calculated values of cross-sections. On the basis of high resolution data available on individual resonance parameters (E,J,?) for s- and p-wave neutrons, mass and energy dependence formulae for the parity distribution in the nuclear level density have been proposed which supports the fact of equipartition of parities at high excitation energies.

  12. Proton-neutron pairing correlations in the self-conjugate nucleus (38)K probed via a direct measurement of the isomer shift.

    PubMed

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

    2014-08-01

    A marked difference in the nuclear charge radius was observed between the I^{?}=3^{+} ground state and the I^{?}=0^{+} isomer of ^{38}K and is qualitatively explained using an intuitive picture of proton-neutron pairing. In a high-precision measurement of the isomer shift using bunched-beam collinear laser spectroscopy at CERN-ISOLDE, a change in the mean-square charge radius of ?r_{c}^{2}?(^{38}K^{m})-?r_{c}^{2}?(^{38}K^{g})=0.100(6)??fm^{2} was obtained. This is an order of magnitude more accurate than the result of a previous indirect measurement from which it was concluded that both long-lived states in ^{38}K have similar charge radii. Our observation leads to a substantially different understanding since the difference in charge radius is, moreover, opposite in sign to previously reported theoretical predictions. It is demonstrated that the observed isomer shift can be reproduced by large-scale shell-model calculations including proton and neutron excitations across the N,Z=20 shell gaps, confirming the significance of cross-shell correlations in the region of ^{40}Ca. PMID:25126913

  13. Nuclear Instruments and Methods in Physics Research A 566 (2006) 598608 The number distribution of neutrons and gamma photons generated in a

    E-print Network

    Pázsit, Imre

    2006-01-01

    of neutrons and gamma photons generated in a multiplying sample Andreas Enqvista,Ã, Imre Pa´ zsita , Sara is an analytical derivation of the full probability distribution of the number of neutrons and photons generated. With the introduction of a modified factorial moment of the number of neutrons and gamma photons generated in fission

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

    NASA Astrophysics Data System (ADS)

    Pietinen, Sami; Tenhunen, Vesa; Tukiainen, Markku

    Several methods and techniques have surfaced to address the ongoing concerns of quality and productivity of software development. Among these is the Pair Programming (PP) method, which has gained a lot off attention through being an essential part of an agile software development methodology called the eXtreme Programming (XP). In this paper, we present the results of two controlled case studies that investigate the possible productivity improvement through the incorporation of PP over solo programming. The main focus is on implementation task, more specifically in programming, although PP is suitable for other tasks too. Our results show that very high level of PP use might be difficult to achieve in a very tightly scheduled software development project, but some of the benefits can be seen to come true even with proportional use of PP. In our case, PP added the additional effort of 13% over solo programming.

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

    E-print Network

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

    2015-07-11

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

  16. 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

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

    2013-10-01

    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

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

    SciTech Connect

    Asano, Yoshihiro; Sugita, Takeshi; Hirose, Hideyuki; Suzaki, Takenori

    2005-10-15

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

  18. Investigation of surface structures by powder diffraction : a differential pair distribution function study on arsenate sorption on ferrihydrite.

    SciTech Connect

    Harrington, R.; Hausner, D. B.; Bhandari, N.; Strongin, D. R.; Chapman, K. W.; Chupas, P. J.; Middlemiss, D. S.; Grey, C. P.; Parise, J. B.; X-Ray Science Division; Stony Brook Univ.; Temple Univ.

    2010-01-01

    Differential pair distribution function (d-PDF) analysis of high energy powder X-ray diffraction data was carried out on 2-line ferrihydrite nanoparticles with arsenate oxyanions adsorbed on the surface to investigate the binding mechanism. In this analysis, a PDF of ferrihydrite is subtracted from a PDF of ferrihydrite with arsenate sorbed on the surface, leaving only correlations from within the surface layer and between the surface and the particle. As-O and As-Fe correlations were observed at 1.68 and 3.29 {angstrom}, respectively, in good agreement with previously published EXAFS data, confirming a bidentate binuclear binding mechanism. Further peaks are observed in the d-PDF which are not present in EXAFS, corresponding to correlations between As and O in the particle and As-2nd Fe.

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

    SciTech Connect

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

    2011-02-24

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

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

    PubMed

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

    2013-06-14

    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

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

    E-print Network

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

    2007-08-03

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-09-01

    Crystalline metal (IV) phosphates with variable zirconium-to-titanium molar ratios of general formula (Ti 1- xZr x)(HPO 4) 2·H 2O have been prepared by precipitation of soluble salts of the metals with phosphoric acid and heating the amorphous solids in 12 M H 3PO 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 ?-titanium phosphate lattice and vice versa for titanium substitution into the ?-zirconium phosphate lattice. In both cases the solubility is partial with the coexistence of two substituted phases observed in samples with nominal compositions between the solubility limits.

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

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

    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.

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

    SciTech Connect

    Moran, J.M.

    1992-02-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Schneider, Harold

    1959-01-01

    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.

  7. Accessing baryon to meson transition distribution amplitudes in meson production in association with a high invariant mass lepton pair at GSI-FAIR with PANDA

    E-print Network

    J. P. Lansberg; B. Pire; K. Semenov-Tian-Shansky; L. Szymanowski

    2012-12-14

    Nucleon antinucleon annihilation into a near backward (or forward) produced meson and a high invariant mass lepton pair admits a factorized description in terms of antinucleon (or nucleon) distribution amplitudes and nucleon to meson (or antinucleon to meson) transition distribution amplitudes. We estimate the cross section of backward (and forward) pion and eta meson production in association with a high invariant mass lepton pair for the kinematical conditions of GSI-FAIR. The cross sections are found to be large enough to be measured with the PANDA detector. Interesting phenomenological applications of the approach are thus expected.

  8. Pore distributions in nanocrystalline metals from small-angle neutron scattering

    SciTech Connect

    Sanders, P.G.; Weertman, J.R.; Eastman, J.A.

    1998-07-24

    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.

  9. Preliminary analysis of the distribution of water in human hair by small-angle neutron scattering.

    PubMed

    Kamath, Yash; Murthy, N Sanjeeva; Ramaprasad, Ram

    2014-01-01

    Diffusion and distribution of water in hair can reveal the internal structure of hair that determines the penetration of various products used to treat hair. The distribution of water into different morphological components in unmodified hair, cuticle-free hair, and hair saturated with oil at various levels of humidity was examined using small-angle neutron scattering (SANS) by substituting water with deuterium oxide (D(2)O). Infrared spectroscopy was used to follow hydrogen-deuterium exchange. Water present in hair gives basically two types of responses in SANS: (i) interference patterns, and (ii) central diffuse scattering (CDS) around the beam stop. The amount of water in the matrix between the intermediate filaments that gives rise to interference patterns remained essentially constant over the 50-98% humidity range without swelling this region of the fiber extensively. This observation suggests that a significant fraction of water in the hair, which contributes to the CDS, is likely located in a different morphological region of hair that is more like pores in a fibrous structure, which leads to significant additional swelling of the fiber. Comparison of the scattering of hair treated with oil shows that soybean oil, which diffuses less into hair, allows more water into hair than coconut oil. These preliminary results illustrate the utility of SANS for evaluating and understanding the diffusion of deuterated liquids into different morphological structures in hair. PMID:24602821

  10. Atmospheric neutrons

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

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

  11. What Can We Learn from a Detailed Study of the Temperature Dependence of ?, the Width of the Pair Distribution Function?

    NASA Astrophysics Data System (ADS)

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

    2007-02-01

    In many systems there is a significant coupling between the local structure and other properties of the system such as magnetism, electrical and thermal transport, metal/insulator transitions etc. In such materials, a detailed temperature-dependent study of the width of the Pair Distribution Function (PDF), ?, can separate different contributions and provide a connection between the observed macroscopic observations and the underlying atomic interactions that produce them. The usual model for simple systems is that the T-dependence of ?2 is described by an Einstein or Correlated Debye model, with one characteristic temperature for the system; in such models ?2(T) increases smoothly with T and has a slowly increasing slope. However that is not always the case: in structures with large unit cells containing several types of atoms, some atoms in the crystal can have a low Einstein temperature while others have a very high correlated Debye temperature as observed in a number of thermoelectric systems (skutterudites and clathrates). In others systems such as the negative thermal expansion material ZrW2O8, the same atom cam be involved in both low and high temperature Einstein modes. Vibrations of atoms (or molecular unit) described by a low Einstein temperature often control/determine the lattice properties. In other systems there are deviations from the T-dependence expected for either the Einstein or correlated Debye models — such as a small increase in ?2 at low temperatures for the Ru-Ru pair in PrRu4Sb12 which has a metal/insulator transition near 60K, or a very sharp step in ?2(T) observed in the bilayer colossal magnetoresistance system La2-2xSr1+2xMn2O7 at the ferromagnetic transition. We discuss broadening of the PDF in more complex systems, show some simulations and then present several recent examples.

  12. Scattering influences in quantitative fission neutron radiography for the in situ analysis of hydrogen distribution in metal hydrides

    NASA Astrophysics Data System (ADS)

    Börries, S.; Metz, O.; Pranzas, P. K.; Bücherl, T.; Söllradl, S.; Dornheim, M.; Klassen, T.; Schreyer, A.

    2015-10-01

    In situ neutron radiography allows for the time-resolved study of hydrogen distribution in metal hydrides. However, for a precise quantitative investigation of a time-dependent hydrogen content within a host material, an exact knowledge of the corresponding attenuation coefficient is necessary. Additionally, the effect of scattering has to be considered as it is known to violate Beer's law, which is used to determine the amount of hydrogen from a measured intensity distribution. Within this study, we used a metal hydride inside two different hydrogen storage tanks as host systems, consisting of steel and aluminum. The neutron beam attenuation by hydrogen was investigated in these two different setups during the hydrogen absorption process. A linear correlation to the amount of absorbed hydrogen was found, allowing for a readily quantitative investigation. Further, an analysis of scattering contributions on the measured intensity distributions was performed and is described in detail.

  13. Thick target double differential neutron energy distribution from 12C+ 27Al at 115 MeV

    NASA Astrophysics Data System (ADS)

    Suman, V.; Sunil, C.; Nair, Soumya; Paul, S.; Biju, K.; Sahoo, G. S.; Sarkar, P. K.

    2015-11-01

    Neutron yield from 115 MeV 12C projectiles bombarding a thick 27Al target has been measured using the time of flight technique. Nuclear reaction model code PACE and the FLUKA Monte Carlo code are used to calculate the yield and the results are compared with the experimental data. The energy for maximum neutron emission in experimental measurement and reaction code output has a slight disagreement in the extreme forward emission angle but in all other angles it has a close match. The slope of the distribution in general shows good match between the experimental and the reaction code results as well as FLUKA calculations. The maximum energy of the emitted neutrons is observed to decrease with the increasing emission angles.

  14. Investigations on average and local structures of Li(Li1/6Mn1/2Ni1/6Co1/6)O2 by the pair distribution function and the density functional theory

    NASA Astrophysics Data System (ADS)

    Idemoto, Yasushi; Akatsuka, Kazumasa; Kitamura, Naoto

    2015-12-01

    We synthesize Li(Li1/6Mn1/2Ni1/6Co1/6)O2 with a coprecipitation method, and study the electrochemical properties and the atomic configuration by means of galvanostatic charge-discharge test, neutron total scatterings, and the density functional theory calculation. From the average-structure analysis using the Bragg profile, that is, the Rietveld analysis, it is found that the sample has the Li2MnO3-type layered structure (space group; C2/m) and Ni and Co exist at both the two sites (4g and 2b sites) in the transition-metal layer. The DFT calculation indicates that there is a local atomic ordering denoted as LiMn6 in the transition-metal layer in the same way as Li2MnO3. Moreover, such a local structure can explain a reduced pair distribution function, G(r), derived from neutron total scatterings. Detailed investigation on the G(r) also suggests a local distortion along the c axis perpendicular to the layer.

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

    USGS Publications Warehouse

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

    2002-01-01

    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.

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

    DOE PAGESBeta

    Aaltonen, T

    2011-04-28

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

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

    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.

  18. Investigation of the experimental effects on the quality of the rapid acquisition pair distribution function (RA-PDF) data

    NASA Astrophysics Data System (ADS)

    Masadeh, Ahmad S.

    2013-03-01

    Series of experiments have been carried out to investigate the quality of the recently developed rapid acquisition atomic pair distribution function (RA-PDF) method, which combines the uses of high energy X-rays and an image plate area detector. Image plate data for simple elements (C, Mg, Al, Si, Ni, Cu, Zn, Ag, and Pb) have been analyzed, using (RA-PDF) technique. The affect of undiscriminated Compton and fluorescence is investigated for a wide range of materials with atomic Z numbers ranging from 6(Carbon) and 82 (Pb). We find the RA-PDF method is capable of obtaining high quality PDFs where quantitatively reliable structure information can be extracted. We would also like to acknowledge Dr. Simon Billinge group at NSLS and The University of Jordan for the support.This work was supported in part by (NSF) grant DMR-0304391.Use of the APS is supported by the U.S. DOE, Contract No. W-31-109-Eng-38.

  19. Three-dimensional Structure of Nanoparticles from High-energy X-ray Diffraction and Atomic Pair Distribution Function Analysis

    NASA Astrophysics Data System (ADS)

    Petkov, Valeri

    2006-03-01

    Knowledge of the atomic-scale structure is an important prerequisite to understand and predict the properties of materials. In the case of crystals it is obtained from the positions and intensities of the Bragg peaks in the diffraction patterns. However, materials constructed at the nanoscale lack the translational symmetry and long-range order of perfect crystals. The diffraction patterns of such materials show only a few Bragg peaks, if any, and a pronounced diffuse component. This poses a real challenge to the usual techniques for structure characterization. The challenge can be met by employing the so-called atomic Pair Distribution Function (PDF) technique and high energy x-ray diffraction. This non-traditional experimental approach takes into account both Bragg and diffuse scattering and yields the atomic structure in terms of a small set of parameters such as a unit cell and atomic coordinates. The basics of the technique will be introduced and its potential demonstrated with results from recent structural studies gold, ZrO2 and GaN nanoparticles.

  20. Neutron to proton mass difference, parton distribution functions and baryon resonances from dynamics on the Lie group u(3)

    E-print Network

    Ole L. Trinhammer

    2012-06-25

    We present a hamiltonian structure on the Lie group u(3) to describe the baryon spectrum. The ground state is identified with the proton. From this single fit we calculate approximately the relative neutron to proton mass shift to within half a percentage of the experimental value. From the same fit we calculate the nucleon and delta resonance spectrum with correct grouping and no missing resonances. For specific spin eigenfunctions we calculate the delta to nucleon mass ratio to within one percent. Finally we derive parton distribution functions that compare well with those for the proton valence quarks. The distributions are generated by projecting the proton state to space via the exterior derivative on u(3). We predict scarce neutral flavour singlets which should be visible in neutron diffraction dissociation experiments or in invariant mass spectra of protons and negative pions in B-decays and in photoproduction on neutrons. The presence of such singlet states distinguishes experimentally the present model from the standard model as does the prediction of the neutron to proton mass splitting. Conceptually the Hamiltonian may describe an effective phenomenology or more radically describe interior dynamics implying quarks and gluons as projections from u(3) which we then call allospace.

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

    NASA Astrophysics Data System (ADS)

    Boggara, Mohan; Mihailescu, Ella; Krishnamoorti, Ramanan

    2009-03-01

    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.

  2. The Probability Distribution of the Double Neutron Star Coalescence Rate and Predictions for More Detections

    E-print Network

    Vassiliki Kalogera; Chunglee Kim; Duncan R. Lorimer

    2002-12-02

    We present an analysis method that allows us to estimate the Galactic formation of radio pulsar populations based on their observed properties and our understanding of survey selection effects. More importantly, this method allows us to assign a statistical significance to such rate estimates and calculate the allowed ranges of values at various confidence levels. Here, we apply the method to the question of the double neutron star (NS-NS) coalescence rate using the current observed sample, and we find calculate the most likely value for the total Galactic coalescence rate to lie in the range 3-22 Myr^{-1}, for different pulsar population models. The corresponding range of expected detection rates of NS--NS inspiral are (1-9)x10^{-3} yr^{-1} for the initial LIGO, and 6-50 yr^{-1} for the advanced LIGO. Based on this newly developed statistical method, we also calculate the probability distribution for the expected number of pulsars that could be observed by the Parkes Multibeam survey, when acceleration searches will alleviate the effects of Doppler smearing due to orbital motions. We suggest that the Parkes survey will probably detect 1-2 new binary pulsars like PSRs B1913+16 and/or B1534+12.

  3. The Use of Neutron Analysis Techniques for Detecting The Concentration And Distribution of Chloride Ions in Archaeological Iron

    PubMed Central

    Watkinson, D; Rimmer, M; Kasztovszky, Z; Kis, Z; Maróti, B; Szentmiklósi, L

    2014-01-01

    Chloride (Cl) ions diffuse into iron objects during burial and drive corrosion after excavation. Located under corrosion layers, Cl is inaccessible to many analytical techniques. Neutron analysis offers non-destructive avenues for determining Cl content and distribution in objects. A pilot study used prompt gamma activation analysis (PGAA) and prompt gamma activation imaging (PGAI) to analyse the bulk concentration and longitudinal distribution of Cl in archaeological iron objects. This correlated with the object corrosion rate measured by oxygen consumption, and compared well with Cl measurement using a specific ion meter. High-Cl areas were linked with visible damage to the corrosion layers and attack of the iron core. Neutron techniques have significant advantages in the analysis of archaeological metals, including penetration depth and low detection limits. PMID:26028670

  4. FURTHER EVIDENCE FOR THE BIMODAL DISTRIBUTION OF NEUTRON-STAR MASSES

    E-print Network

    Schwab, J.

    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 ...

  5. Assimilation of Cosmic-Ray Neutron Data to Improve Soil Moisture in the Distributed Hydrological Model mHM

    NASA Astrophysics Data System (ADS)

    Schrön, Martin; Rakovec, Oldrich; Zink, Matthias; Rosolem, Rafael; Zacharias, Steffen; Oswald, Sascha; Baroni, Gabriele; Schröter, Ingmar; Wollschläger, Ute; Reinstorf, Frido; Martini, Edoardo; Samaniego, Luis

    2015-04-01

    Mesoscale hydrological models like mHM (Samaniego et al., 2010, WRR) are usually evaluated with observed discharge, which is a spatially integrated signal of the watershed. However, an accurate prediction of spatially distributed soil water content is of much higher value for hydrologic prediction. For hydrologic models operating at intermediate to regional scales, Cosmic-Ray Neutron Sensors provide unrivaled soil moisture data which are much more representative and of higher spatial-temporal resolution than most point-scale or remote-sensing products. We are aiming to improve soil moisture calibration and evaluation in mHM with the support of the intermediate-scale data from cosmic-ray neutrons. The relationship between soil moisture profiles in the footprint and the corresponding cosmic-ray neutron counts is non-linear and not unique. Therefore we assimilate cosmic-ray neutron data directly by employing the nested forward model COSMIC (Shuttleworth et al. 2013, HESS), which calculates neutron counts from the modeled soil moisture. In optimization mode, mHM is able to calibrate parameters of both, the hydrological system and/or the neutron prediction model itself. Sub-daily model performance is evaluated with independent measurements of soil moisture patterns from several catchment-wide TDR campaigns, time series of a Wireless Sensor Network and discharge in the small catchment "Schäfertal" (1.6 km2) in central Germany. This work is an important step towards the assimilation of continuous spatial data from mobile Cosmic Ray Sensing (Schrön et al. 2014, TERENO Conference Abstracts). The so-called TERENO:Rover delivers highly-resolved spatial patterns of water content in a whole catchment, which has a great potential to improve spatial performance of hydrological models.

  6. 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...

  7. In situ X-ray pair distribution function analysis of accelerated carbonation of a synthetic calcium-?silicate?-hydrate gel

    SciTech Connect

    Morandeau, Antoine E.; White, Claire E.

    2015-01-01

    Calcium–silicate–hydrate (C–S–H) gel is the main binder component in hydrated ordinary Portland cement (OPC) paste, and is known to play a crucial role in the carbonation of cementitious materials, especially for more sustainable alternatives containing supplementary cementitious materials. However, the exact atomic structural changes that occur during carbonation of C–S–H gel remain unknown. Here, we investigate the local atomic structural changes that occur during carbonation of a synthetic calcium–silicate–hydrate gel exposed to pure CO? vapour, using in situ X-ray total scattering measurements and subsequent pair distribution function (PDF) analysis. By analysing both the reciprocal and real-space scattering data as the C–S–H carbonation reaction progresses, all phases present during the reaction (crystalline and non-crystalline) have been identified and quantified, with the results revealing the emergence of several polymorphs of crystalline calcium carbonate (vaterite and calcite) in addition to the decalcified C–S–H gel. Furthermore, the results point toward residual calcium being present in the amorphous decalcified gel, potentially in the form of an amorphous calcium carbonate phase. As a result of the quantification process, the reaction kinetics for the evolution of the individual phases have been obtained, revealing new information on the rate of growth/dissolution for each phase associated with C–S–H gel carbonation. Moreover, the investigation reveals that the use of real space diffraction data in the form of PDFs enables more accurate determination of the phases that develop during complex reaction processes such as C–S–H gel carbonation in comparison to the conventional reciprocal space Rietveld analysis approach.

  8. FURTHER EVIDENCE FOR THE BIMODAL DISTRIBUTION OF NEUTRON-STAR MASSES

    SciTech Connect

    Schwab, J.; Rappaport, S.; Podsiadlowski, Ph. E-mail: jschwab@mit.ed E-mail: podsi@astro.ox.ac.u

    2010-08-10

    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.

  9. Pairing forces in nuclei

    SciTech Connect

    Chasman, R.R.

    1996-12-31

    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.

  10. Dosimetry for Neutrons from 0.25 to 15 MeV by the Measurement of Linear Energy Transfer Distributions for Secondary Charged Particles in CR-39 Plastic

    NASA Astrophysics Data System (ADS)

    Tawara, Hiroko; Eda, Kazuyoshi; Sanami, Toshiya; Sasaki, Shinichi; Takahashi, Kazutoshi; Sonkawade, Rajendra; Nagamatsu, Aiko; Kitajo, Keiichi; Kumagai, Hidenori; Doke, Tadayoshi

    2008-03-01

    In the radiation fields of high energy accelerator facilities, high-altitude aircraft and space flights, high-energy neutron dosimetry of ˜20 MeV or more is a significant issue for radiological protection. We studied the feasibility of experimental measurements of linear energy transfer (LET) distributions for secondary charged particles induced by fast neutrons using CR-39 plastic nuclear track detectors. In order to investigate a method of analyzing the CR-39 detectors that is appropriate for fast neutron dosimetry, two-layer CR-39 stacks were exposed to monochromatic neutrons (0.25, 0.55, 5, and 15 MeV) at the Fast Neutron Laboratory of Tohoku University in Japan. We also conducted Monte Carlo calculations to estimate the detection efficiency of the CR-39 detector for recoil protons. The CR-39 detectors treated by single-step chemical etching were used to obtain LET distributions for LET > 10 keV/µm-water. The results indicated that measurements of short-range particles are very important for obtaining the correct LET distributions. Using the measured LET distributions, we calculated neutron sensitivities, absorbed doses and dose equivalents based on the ICRP 60 Q-L relation and averaged quality factors. The dose equivalents were compared with the neutron fluence-to-dose equivalent conversion factors given by ICRP 74 and the averaged quality factors were compared with weighting factors given by ICRP 60 and ICRP 92.

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

    PubMed Central

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

    2014-01-01

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

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

    SciTech Connect

    Jia Ying; Bao Jingdong

    2007-03-15

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

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

    SciTech Connect

    Sur, B.; Anghel, V.N.P.; Rogge, R.B.; Katsaras, J.

    2005-01-01

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

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

    SciTech Connect

    Pantelias, M.; Volmert, B.; Caruso, S.; Zvoncek, P.; Bitterli, B.; Neukaeter, E.; Nissen, W.; Ledergerber, G.; Vielma, R.

    2012-07-01

    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)

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

    SciTech Connect

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

    2010-10-15

    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.

  16. The study of noncrystalline material under high pressure using high energy x-ray pair distribution function combined with synchrotron x-ray microtomography techniques

    NASA Astrophysics Data System (ADS)

    Li, Liangliang; Li, Renfeng; Wang, Luhong; Liu, Haozhe

    2015-08-01

    For non-crystalline samples, such as amorphous materials and melts, due to their lack of periodicity, scattering patterns from amorphous and liquid phases are very broad. Thus, the pair distribution function (PDF) and X-ray microtomography are important methods to investigate structural change for non-crystalline samples under high pressure conditions. Here we present experimental results on liquid gallium using microtomography and Yb-based metallic glass using PDF under high pressure.

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

    SciTech Connect

    Attix, F.H.

    1980-01-01

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

  18. Neutron Star Radii, Universal Relations, and the Role of Prior Distributions

    E-print Network

    A. W. Steiner; J. M. Lattimer; E. F. Brown

    2015-10-26

    We investigate constraints on neutron star structure arising from the assumptions that neutron stars have crusts, that recent calculations of pure neutron matter limit the equation of state of neutron star matter near the nuclear saturation density, that the high-density equation of state is limited by causality and the largest high-accuracy neutron star mass measurement, and that general relativity is the correct theory of gravity. We explore the role of prior assumptions by considering two classes of equation of state models. In a first, the intermediate- and high-density behavior of the equation of state is parameterized by piecewise polytropes. In the second class, the high-density behavior of the equation of state is parameterized by piecewise continuous line segments. The smallest density at which high-density matter appears is varied in order to allow for strong phase transitions above the nuclear saturation density. We critically examine correlations among the pressure of matter, radii, maximum masses, the binding energy, the moment of inertia, and the tidal deformability, paying special attention to the sensitivity of these correlations to prior assumptions about the equation of state. It is possible to constrain the radii of $1.4~\\mathrm{M}_{\\odot}$ neutron stars to a be larger than 10 km, even without consideration of additional astrophysical observations, for example, those from photospheric radius expansion bursts or quiescent low-mass X-ray binaries. We are able to improve the accuracy of known correlations between the moment of inertia and compactness as well as the binding energy and compactness. We also demonstrate the existence of a correlation between the neutron star binding energy and the moment of inertia.

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

    SciTech Connect

    Aaltonen, T

    2011-04-28

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

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

    SciTech Connect

    Tsao, Cheng-Si; Li, Mingda; Zhang, Yang; Leao, Juscelino B; Chiang, Wei-Shan; Chung, Tsui-Yun; Tzeng, Yi-Ren; Chen, Sow-hsin H

    2010-01-01

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

  1. Pulsar Pair Cascades in Magnetic Fields with Offset Polar Caps

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Muslimov, Alex G.

    2012-01-01

    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.

  2. Brightness constraint for cooling models of young neutron stars

    E-print Network

    Hovik Grigorian

    2006-06-21

    We study the systematics of neutron star cooling curves with three representative masses from the most populated interval of the estimated mass distribution for compact objects. The cooling simulations are made in the framework of the nuclear medium cooling (NMC) scenario using different combinations of possible nucleon-nucleon pairing gaps. Possible heating or enhanced cooling mechanisms in the crust are not considered. We define a constraint on the highest possible temperatures for a given age of young neutron stars and show that this limits the freedom of modeling pairing gaps and crust properties.

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

    PubMed

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

    2014-02-21

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

  4. Spatial distribution of cell–cell and cell–ECM adhesions regulates force balance while main­taining E-cadherin molecular tension in cell pairs

    PubMed Central

    Sim, Joo Yong; Moeller, Jens; Hart, Kevin C.; Ramallo, Diego; Vogel, Viola; Dunn, Alex R.; Nelson, W. James; Pruitt, Beth L.

    2015-01-01

    Mechanical linkage between cell–cell and cell–extracellular matrix (ECM) adhesions regulates cell shape changes during embryonic development and tissue homoeostasis. We examined how the force balance between cell–cell and cell–ECM adhesions changes with cell spread area and aspect ratio in pairs of MDCK cells. We used ECM micropatterning to drive different cytoskeleton strain energy states and cell-generated traction forces and used a Förster resonance energy transfer tension biosensor to ask whether changes in forces across cell–cell junctions correlated with E-cadherin molecular tension. We found that continuous peripheral ECM adhesions resulted in increased cell–cell and cell–ECM forces with increasing spread area. In contrast, confining ECM adhesions to the distal ends of cell–cell pairs resulted in shorter junction lengths and constant cell–cell forces. Of interest, each cell within a cell pair generated higher strain energies than isolated single cells of the same spread area. Surprisingly, E-cadherin molecular tension remained constant regardless of changes in cell–cell forces and was evenly distributed along cell–cell junctions independent of cell spread area and total traction forces. Taken together, our results showed that cell pairs maintained constant E-cadherin molecular tension and regulated total forces relative to cell spread area and shape but independently of total focal adhesion area. PMID:25971797

  5. Spatial distribution of cell-cell and cell-ECM adhesions regulates force balance while main-taining E-cadherin molecular tension in cell pairs.

    PubMed

    Sim, Joo Yong; Moeller, Jens; Hart, Kevin C; Ramallo, Diego; Vogel, Viola; Dunn, Alex R; Nelson, W James; Pruitt, Beth L

    2015-07-01

    Mechanical linkage between cell-cell and cell-extracellular matrix (ECM) adhesions regulates cell shape changes during embryonic development and tissue homoeostasis. We examined how the force balance between cell-cell and cell-ECM adhesions changes with cell spread area and aspect ratio in pairs of MDCK cells. We used ECM micropatterning to drive different cytoskeleton strain energy states and cell-generated traction forces and used a Förster resonance energy transfer tension biosensor to ask whether changes in forces across cell-cell junctions correlated with E-cadherin molecular tension. We found that continuous peripheral ECM adhesions resulted in increased cell-cell and cell-ECM forces with increasing spread area. In contrast, confining ECM adhesions to the distal ends of cell-cell pairs resulted in shorter junction lengths and constant cell-cell forces. Of interest, each cell within a cell pair generated higher strain energies than isolated single cells of the same spread area. Surprisingly, E-cadherin molecular tension remained constant regardless of changes in cell-cell forces and was evenly distributed along cell-cell junctions independent of cell spread area and total traction forces. Taken together, our results showed that cell pairs maintained constant E-cadherin molecular tension and regulated total forces relative to cell spread area and shape but independently of total focal adhesion area. PMID:25971797

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

    SciTech Connect

    Biswas, Anindya; Das, Tapan Kumar; Chakrabarti, Barnali

    2010-09-14

    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.

  7. Momentum distributions of {sup 9}Li fragments from the breakup of {sup 11}Li and the neutron halo

    SciTech Connect

    Orr, N.A.; Anantaraman, N.; Austin, S.M.; Bertulani, C.A.; Hanold, K.; Kelley, J.H.; Kryger, R.A.; Morrissey, D.J.; Sherrill, B.M.; Souliotis, G.A.; Steiner, M.; Thoennessen, M.; Winfield, J.S.; Winger, J.A.; Young, B.M.

    1995-06-01

    The inclusive parallel momentum distributions of {sup 9}Li fragments from the breakup of a secondary {sup 11}Li beam have been measured at 66 MeV/nucleon over a wide range of targets ({sup 9}Be to {sup 238}U). The measurements were performed using a zero-degree fragment separator as an energy-loss spectrometer operating in a dispersion matched mode. Earlier measurements have been extended here to the case of breakup by {sup 238}U where a distribution with a width of FWHM=38.1{plus_minus}1.9 MeV/{ital c} was observed. Together with a remeasurement of breakup on {sup 93}Nb (FWHM)=42.8{plus_minus}2.6 MeV/({ital c}) a weak dependence of distribution width on target nucleus was observed. A discussion of the nature of the momentum distributions and relationship to the structure of the halo is presented in the light of recent calculations. It is concluded that the {sup 9}Li fragment parallel momentum distributions are relatively insensitive to the reaction and reflect the extended neutron distribution of the halo.

  8. Density dependence of the pairing interaction and pairing correlation in unstable nuclei

    E-print Network

    S. A. Changizi; Chong Qi

    2015-08-08

    This work aims at a global assessment of the effect of the density dependence of the zero-range pairing interaction. Systematic Skyrme-Hartree-Fock-Bogoliubov calculations with the volume, surface and mixed pairing forces are carried out to study the pairing gaps in even-even nuclei over the whole nuclear chart. Calculations are also done in coordinate representation for unstable semi-magic even-even nuclei. The calculated pairing gaps are compared with empirical values from four different odd-even staggering formulae. Calculations with the three pairing interactions are comparable for most nuclei close to $\\beta$-stability line. However, the surface interaction calculations predict neutron pairing gaps in neutron-rich nuclei that are significantly stronger than those given by the mixed and volume pairing. On the other hand, calculations with volume and mixed pairing forces show noticeable reduction of neutron pairing gaps in nuclei far from the stability.

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

    SciTech Connect

    Tarasov, V. N.; Gridnev, K. A.; Greiner, W.; Gridnev, D. K.; Kuprikov, V. I.; Tarasov, D. V.; Vinas, X.

    2012-01-15

    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.

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

    SciTech Connect

    D. SIEBE; K. PASAMEHMETOGLU

    2000-11-01

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

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

    SciTech Connect

    Romano, C.; Danon, Y.; Block, R.; Thompson, J.; Blain, E.; Bond, E.

    2010-01-15

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

  12. Study of the reaction products of SF6 and C in the laser heated diamond anvil cell by pair distribution function analysis and micro-Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Rademacher, N.; Bayarjargal, L.; Morgenroth, W.; Bauer, J. D.; Milman, V.; Winkler, B.

    2015-05-01

    The decomposition of SF6 in the presence of glassy carbon was induced in laser heated diamond anvil cells at 10-11 GPa and 2000-2500 K. The reaction products were characterised by synchrotron X-ray diffraction, including high pressure pair distribution function analysis, and micro-Raman spectroscopy combined with atomistic model calculations. The decomposition leads to elemental amorphous helical sulfur and crystalline CF4-III. Two different sulfur phases, namely helical S? and crystalline ?-S8, were observed after recovering the laser heated samples of different experiments at ambient conditions.

  13. Probing the top-Higgs coupling through the secondary lepton distributions in the associated production of the top-quark pair and Higgs boson at the LHC

    E-print Network

    Karol Kolodziej; Aleksandra Slapik

    2015-09-04

    We complement the analysis of the anomalous top-Higgs coupling effects on the secondary lepton distributions in the associated production of the top-quark pair and Higgs boson in proton-proton collisions at the LHC of the former work by one of the present authors by taking into account the quark-antiquark production mechanism. We also present simple arguments which explain why the effects of the scalar and pseudoscalar anomalous couplings on the unpolarized cross section of the process are completely insensitive to the sign of either of them.

  14. Atomic-scale structure of nancrystalline CeO{sub 2}-ZrO{sub 2} oxides by total x-ray diffraction and pair distribution function analysis.

    SciTech Connect

    Gateshki, M.; Niederberger, M.; Deshpande, A. S.; Ren, Y.; Petkov, V.; Central Michigan Univ.; Colloid Univ.

    2007-01-01

    Total x-ray diffraction and atomic pair distribution function analysis have been used to determine the atomic ordering in nanocrystalline ({approx}1.5 nm in size) CeO{sub 2}-ZrO{sub 2} prepared by a sol-gel route. Experimental data show that the oxides are a structurally and chemically inhomogeneous mixture of nanoscale domains with cubic-type and monoclinic-type atomic ordering, predominantly occupied by Ce and Zr atomic species, respectively. The study is another demonstration of the great potential of non-traditional crystallography in studying the structure of nanocrystalline materials.

  15. Detection and characterization of nanoparticles in suspension at low concentrations using the X-ray total scattering pair distribution function technique.

    PubMed

    Terban, Maxwell W; Johnson, Matthew; Di Michiel, Marco; Billinge, Simon J L

    2015-03-12

    Difference atomic pair distribution function methods have been applied to detect and characterize nanoparticles suspended in a solvent at very dilute concentrations. We specifically consider nanoparticles of a pharmaceutical compound in aqueous solution using X-ray PDF methods, a challenging case due to the low atomic number of the nanoparticle species. The nanoparticles were unambiguously detected at the level of 0.25 wt%. Even at these low concentrations the signals were highly reproducible, allowing for reliable detection and quantitative analysis of the nanoparticle structure. PMID:25732228

  16. Neutron removal cross section as a measure of neutron skin

    E-print Network

    D. Q. Fang; Y. G. Ma; X. Z. Cai; W. D. Tian; H. W. Wang

    2010-04-20

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

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

    SciTech Connect

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

    2012-12-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  19. Switchable radioactive neutron source device

    DOEpatents

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

    1987-11-06

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

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

    NASA Astrophysics Data System (ADS)

    Paradowska, A M; Price, J W H; Finlayson, T R; Lienert, U; Walls, P; Ibrahim, R

    2009-03-01

    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.

  1. Measurement of the ? ? * distribution of muon pairs with masses between 30 and 500 GeV in 10.4 fb - 1 of p p ¯ collisions

    DOE PAGESBeta

    Abazov, V.?M.; Abbott, B.; Acharya, B.?S.; Adams, M.; Adams, T.; Agnew, J.?P.; Alexeev, G.?D.; Alkhazov, G.; Alton, A.; Askew, A.; et al

    2015-04-06

    We present a measurement of the distribution of the variable ?*? for muon pairs with masses between 30 and 500 GeV, using the complete run II data set collected by the D0 detector at the Fermilab Tevatron proton-antiproton collider. This corresponds to an integrated luminosity of 10.4 fb?¹ at ?s=1.96 TeV. The data are corrected for detector effects and presented in bins of dimuon rapidity and mass. The variable ?*? probes the same physical effects as the Z/?* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. These are the first measurements at anymore »collider of the ?*? distributions for dilepton masses away from the Z?l?l? boson mass peak. The data are compared to QCD predictions based on the resummation of multiple soft gluons.« less

  2. Measurement of the ??* distribution of muon pairs with masses between 30 and 500 GeV in 10.4 fb-1 of p p ¯ collisions

    NASA Astrophysics Data System (ADS)

    Abazov, V. M.; Abbott, B.; Acharya, B. S.; Adams, M.; Adams, T.; Agnew, J. P.; Alexeev, G. D.; Alkhazov, G.; Alton, A.; Askew, A.; Atkins, S.; Augsten, K.; Avila, C.; Badaud, F.; Bagby, L.; Baldin, B.; Bandurin, D. V.; Banerjee, S.; Barberis, E.; Baringer, P.; Bartlett, J. F.; Bassler, U.; Bazterra, V.; Bean, A.; Begalli, M.; Bellantoni, L.; Beri, S. B.; Bernardi, G.; Bernhard, R.; Bertram, I.; Besançon, M.; Beuselinck, R.; Bhat, P. C.; Bhatia, S.; Bhatnagar, V.; Blazey, G.; Blessing, S.; Bloom, K.; Boehnlein, A.; Boline, D.; Boos, E. E.; Borissov, G.; Borysova, M.; Brandt, A.; Brandt, O.; Brock, R.; Bross, A.; Brown, D.; Bu, X. B.; Buehler, M.; Buescher, V.; Bunichev, V.; Burdin, S.; Buszello, C. P.; Camacho-Pérez, E.; Casey, B. C. K.; Castilla-Valdez, H.; Caughron, S.; Chakrabarti, S.; Chan, K. M.; Chandra, A.; Chapon, E.; Chen, G.; Cho, S. W.; Choi, S.; Choudhary, B.; Cihangir, S.; Claes, D.; Clutter, J.; Cooke, M.; Cooper, W. E.; Corcoran, M.; Couderc, F.; Cousinou, M.-C.; Cutts, D.; Das, A.; Davies, G.; de Jong, S. J.; De La Cruz-Burelo, E.; Déliot, F.; Demina, R.; Denisov, D.; Denisov, S. P.; Desai, S.; Deterre, C.; DeVaughan, K.; Diehl, H. T.; Diesburg, M.; Ding, P. F.; Dominguez, A.; Dubey, A.; Dudko, L. V.; Duperrin, A.; Dutt, S.; Eads, M.; Edmunds, D.; Ellison, J.; Elvira, V. D.; Enari, Y.; Evans, H.; Evdokimov, V. N.; Fauré, A.; Feng, L.; Ferbel, T.; Fiedler, F.; Filthaut, F.; Fisher, W.; Fisk, H. E.; Fortner, M.; Fox, H.; Fuess, S.; Garbincius, P. H.; Garcia-Bellido, A.; García-González, J. A.; Gavrilov, V.; Geng, W.; Gerber, C. E.; Gershtein, Y.; Ginther, G.; Gogota, O.; Golovanov, G.; Grannis, P. D.; Greder, S.; Greenlee, H.; Grenier, G.; Gris, Ph.; Grivaz, J.-F.; Grohsjean, A.; Grünendahl, S.; Grünewald, M. W.; Guillemin, T.; Gutierrez, G.; Gutierrez, P.; Haley, J.; Han, L.; Harder, K.; Harel, A.; Hauptman, J. M.; Hays, J.; Head, T.; Hebbeker, T.; Hedin, D.; Hegab, H.; Heinson, A. P.; Heintz, U.; Hensel, C.; Heredia-De La Cruz, I.; Herner, K.; Hesketh, G.; Hildreth, M. D.; Hirosky, R.; Hoang, T.; Hobbs, J. D.; Hoeneisen, B.; Hogan, J.; Hohlfeld, M.; Holzbauer, J. L.; Howley, I.; Hubacek, Z.; Hynek, V.; Iashvili, I.; Ilchenko, Y.; Illingworth, R.; Ito, A. S.; Jabeen, S.; Jaffré, M.; Jayasinghe, A.; Jeong, M. S.; Jesik, R.; Jiang, P.; Johns, K.; Johnson, E.; Johnson, M.; Jonckheere, A.; Jonsson, P.; Joshi, J.; Jung, A. W.; Juste, A.; Kajfasz, E.; Karmanov, D.; Katsanos, I.; Kaur, M.; Kehoe, R.; Kermiche, S.; Khalatyan, N.; Khanov, A.; Kharchilava, A.; Kharzheev, Y. N.; Kiselevich, I.; Kohli, J. M.; Kozelov, A. V.; Kraus, J.; Kumar, A.; Kupco, A.; Kur?a, T.; Kuzmin, V. A.; Lammers, S.; Lebrun, P.; Lee, H. S.; Lee, S. W.; Lee, W. M.; Lei, X.; Lellouch, J.; Li, D.; Li, H.; Li, L.; Li, Q. Z.; Li, X.; Lim, J. K.; Lincoln, D.; Linnemann, J.; Lipaev, V. V.; Lipton, R.; Liu, H.; Liu, Y.; Lobodenko, A.; Lokajicek, M.; Lopes de Sa, R.; Luna-Garcia, R.; Lyon, A. L.; Maciel, A. K. A.; Madar, R.; Magaña-Villalba, R.; Malik, S.; Malyshev, V. L.; Mansour, J.; Martínez-Ortega, J.; McCarthy, R.; McGivern, C. L.; Meijer, M. M.; Melnitchouk, A.; Menezes, D.; Mercadante, P. G.; Merkin, M.; Meyer, A.; Meyer, J.; Miconi, F.; Mondal, N. K.; Mulhearn, M.; Nagy, E.; Narain, M.; Nayyar, R.; Neal, H. A.; Negret, J. P.; Neustroev, P.; Nguyen, H. T.; Nunnemann, T.; Orduna, J.; Osman, N.; Osta, J.; Pal, A.; Parashar, N.; Parihar, V.; Park, S. K.; Partridge, R.; Parua, N.; Patwa, A.; Penning, B.; Perfilov, M.; Peters, Y.; Petridis, K.; Petrillo, G.; Pétroff, P.; Pleier, M.-A.; Podstavkov, V. M.; Popov, A. V.; Prewitt, M.; Price, D.; Prokopenko, N.; Qian, J.; Qin, Y.; Quadt, A.; Quinn, B.; Ratoff, P. N.; Razumov, I.; Ripp-Baudot, I.; Rizatdinova, F.; Rominsky, M.; Ross, A.; Royon, C.; Rubinov, P.; Ruchti, R.; Sajot, G.; Sánchez-Hernández, A.; Sanders, M. P.; Santos, A. S.; Savage, G.; Savitskyi, M.; Sawyer, L.; Scanlon, T.; Schamberger, R. D.; Scheglov, Y.; Schellman, H.; Schwanenberger, C.; Schwienhorst, R.; Sekaric, J.; Severini, H.; Shabalina, E.; Shary, V.; Shaw, S.; Shchukin, A. A.; Simak, V.; Skubic, P.; Slattery, P.; Smirnov, D.; Snow, G. R.; Snow, J.; Snyder, S.; Söldner-Rembold, S.; Sonnenschein, L.; Soustruznik, K.; Stark, J.; Stoyanova, D. A.; Strauss, M.; Suter, L.; Svoisky, P.; Titov, M.; Tokmenin, V. V.; Tsai, Y.-T.; Tsybychev, D.; Tuchming, B.; Tully, C.; Uvarov, L.; Uvarov, S.; Uzunyan, S.; Van Kooten, R.; van Leeuwen, W. M.; Varelas, N.; Varnes, E. W.; Vasilyev, I. A.; Verkheev, A. Y.; Vertogradov, L. S.; Verzocchi, M.; Vesterinen, M.; Vilanova, D.; Vokac, P.; Wahl, H. D.; Wang, M. H. L. S.; Warchol, J.; Watts, G.; Wayne, M.; Weichert, J.; Welty-Rieger, L.; Williams, M. R. J.; Wilson, G. W.; Wobisch, M.; Wood, D. R.; Wyatt, T. R.; Xie, Y.; Yamada, R.; Yang, S.; Yasuda, T.; Yatsunenko, Y. A.; Ye, W.

    2015-04-01

    We present a measurement of the distribution of the variable ??* for muon pairs with masses between 30 and 500 GeV, using the complete run II data set collected by the D0 detector at the Fermilab Tevatron proton-antiproton collider. This corresponds to an integrated luminosity of 10.4 fb-1 at ?{s }=1.96 TeV . The data are corrected for detector effects and presented in bins of dimuon rapidity and mass. The variable ??* probes the same physical effects as the Z /?* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. These are the first measurements at any collider of the ??* distributions for dilepton masses away from the Z ??+?- boson mass peak. The data are compared to QCD predictions based on the resummation of multiple soft gluons.

  3. Measurement of the ?*? distribution of muon pairs with masses between 30 and 500 GeV in 10.4 fb-1 of pp¯ collisions

    DOE PAGESBeta

    Abazov, Victor Mukhamedovich

    2015-04-06

    We present a measurement of the distribution of the variable ?*? for muon pairs with masses between 30 and 500 GeV, using the complete run II data set collected by the D0 detector at the Fermilab Tevatron proton-antiproton collider. This corresponds to an integrated luminosity of 10.4 fb–1 at ?s = 1.96 TeV. The data are corrected for detector effects and presented in bins of dimuon rapidity and mass. The variable ?*? probes the same physical effects as the Z/?* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. These are the first measurementsmore »at any collider of the ?*? distributions for dilepton masses away from the Z ? ?+?– boson mass peak. As a result, the data are compared to QCD predictions based on the resummation of multiple soft gluons.« less

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    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.

  5. Imaging with Scattered Neutrons

    E-print Network

    H. Ballhausen; H. Abele; R. Gaehler; M. Trapp; A. Van Overberghe

    2006-10-30

    We describe a novel experimental technique for neutron imaging with scattered neutrons. These scattered neutrons are of interest for condensed matter physics, because they permit to reveal the local distribution of incoherent and coherent scattering within a sample. In contrast to standard attenuation based imaging, scattered neutron imaging distinguishes between the scattering cross section and the total attenuation cross section including absorption. First successful low-noise millimeter-resolution images by scattered neutron radiography and tomography are presented.

  6. Ultrafast neutron detector

    DOEpatents

    Wang, C.L.

    1985-06-19

    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.

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

    NASA Astrophysics Data System (ADS)

    Nakane, Y.; Sakamoto, Y.

    2001-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  9. Theory of neutron scattering experiments on momentum distributions in quantum fluids

    SciTech Connect

    Silver, R.N.

    1987-01-01

    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.

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

    SciTech Connect

    Mishler, Jeffrey H; Mukundan, Rangachary; Borup, Rodney L; Wang, Eunkyoung Y; Jacobson, David L

    2010-01-01

    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.

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

    SciTech Connect

    Rothe, R.E.

    1996-09-30

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-06-01

    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.

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

    E-print Network

    Henderson, Conor, 1977-

    2005-01-01

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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  15. Hypernuclear Physics for Neutron Stars

    E-print Network

    Jurgen Schaffner-Bielich

    2008-01-24

    The role of hypernuclear physics for the physics of neutron stars is delineated. Hypernuclear potentials in dense matter control the hyperon composition of dense neutron star matter. The three-body interactions of nucleons and hyperons determine the stiffness of the neutron star equation of state and thereby the maximum neutron star mass. Two-body hyperon-nucleon and hyperon-hyperon interactions give rise to hyperon pairing which exponentially suppresses cooling of neutron stars via the direct hyperon URCA processes. Non-mesonic weak reactions with hyperons in dense neutron star matter govern the gravitational wave emissions due to the r-mode instability of rotating neutron stars.

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

    NASA Astrophysics Data System (ADS)

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

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

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

    E-print Network

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

    2004-08-10

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

  18. Driven neutron star collapse: Type~I critical phenomena and the initial black hole mass distribution

    E-print Network

    Noble, Scott C

    2015-01-01

    We study the general relativistic collapse of neutron star (NS) models in spherical symmetry. Our initially stable models are driven to collapse by the addition of one of two things: an initially in-going velocity profile, or a shell of minimally coupled, massless scalar field that falls onto the star. Tolman-Oppenheimer-Volkoff (TOV) solutions with an initially isentropic, gamma-law equation of state serve as our NS models. The initial values of the velocity profile's amplitude and the star's central density span a parameter space which we have surveyed extensively and which we find provides a rich picture of the possible end states of NS collapse. This parameter space survey elucidates the boundary between Type I and Type II critical behavior in perfect fluids which coincides, on the subcritical side, with the boundary between dispersed and bound end states. For our particular model, initial velocity amplitudes greater than 0.3c are needed to probe the regime where arbitrarily small black holes can form. In...

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

    SciTech Connect

    Mishler, Jeffrey H; Mukundan, Rangachary; Borup, Rodney L; Wang, Yun; Hussey, Daniel S; Jacobson, David L

    2010-01-01

    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.

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

    SciTech Connect

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

    2010-07-20

    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.

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

    SciTech Connect

    Meral, Cagla; Benmore, C.J.; Monteiro, Paulo J.M.

    2011-07-15

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

  2. Beyond the Horizon Distance: LIGO-Virgo can Boost Gravitational-Wave Detection Rates by Exploiting the Mass Distribution of Neutron Stars.

    PubMed

    Bartos, I; Márka, S

    2015-12-01

    The masses of neutron stars in neutron star binaries are observed to fall in a narrow mass range around ?1.33M_{?}. We explore the advantage of focusing on this region of the parameter space in gravitational-wave searches. We find that an all-sky (externally triggered) search with an optimally reduced template bank is expected to detect 14% (61%) more binary mergers than without the reduction. A reduced template bank can also represent significant improvement in technical cost. We also develop a more detailed search method using binary mass distribution, and find a sensitivity increase similar to that due to the reduced template bank. PMID:26684105

  3. Beyond the Horizon Distance: LIGO-Virgo can Boost Gravitational-Wave Detection Rates by Exploiting the Mass Distribution of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Bartos, I.; Márka, S.

    2015-12-01

    The masses of neutron stars in neutron star binaries are observed to fall in a narrow mass range around ˜1.33 M?. We explore the advantage of focusing on this region of the parameter space in gravitational-wave searches. We find that an all-sky (externally triggered) search with an optimally reduced template bank is expected to detect 14% (61%) more binary mergers than without the reduction. A reduced template bank can also represent significant improvement in technical cost. We also develop a more detailed search method using binary mass distribution, and find a sensitivity increase similar to that due to the reduced template bank.

  4. Monte Carlo modelling of distributions of the d-d and d-t reaction products in a dedicated measuring chamber at the fast neutron generator

    NASA Astrophysics Data System (ADS)

    Wi?cek, U.; Dankowski, J.

    2015-04-01

    A fast neutron generator with a tritium target can be used to generate d-d and d-t reaction products corresponding to thermonuclear reactions in tokamaks or stellarators. In this way, convenient laboratory conditions for tests of spectrometric detectors - prior to their installation at the big fusion devices - can be achieved. Distributions of the alpha particles, protons, deuterons, and tritons generated by the fast neutron generator operating at the Institute of Nuclear Physics PAN in Cracow, Poland, were calculated by means of the Monte Carlo (MC) codes. Results of this MC modelling are presented.

  5. Monitoring the distribution of prompt gamma rays in boron neutron capture therapy using a multiple-scattering Compton camera: A Monte Carlo simulation study

    NASA Astrophysics Data System (ADS)

    Lee, Taewoong; Lee, Hyounggun; Lee, Wonho

    2015-10-01

    This study evaluated the use of Compton imaging technology to monitor prompt gamma rays emitted by 10B in boron neutron capture therapy (BNCT) applied to a computerized human phantom. The Monte Carlo method, including particle-tracking techniques, was used for simulation. The distribution of prompt gamma rays emitted by the phantom during irradiation with neutron beams is closely associated with the distribution of the boron in the phantom. Maximum likelihood expectation maximization (MLEM) method was applied to the information obtained from the detected prompt gamma rays to reconstruct the distribution of the tumor including the boron uptake regions (BURs). The reconstructed Compton images of the prompt gamma rays were combined with the cross-sectional images of the human phantom. Quantitative analysis of the intensity curves showed that all combined images matched the predetermined conditions of the simulation. The tumors including the BURs were distinguishable if they were more than 2 cm apart.

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

    SciTech Connect

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

    2013-09-10

    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.

  7. Neutron angular distributions from the core break-up reactions of the {sup 11}Be and {sup 11}Li halo nuclei

    SciTech Connect

    Grevy, S.; Axelsson, L.; Jonson, B.; Nilsson, T.; Nyman, G.; Smedberg, M.; Angelique, J. C.; Orr, N.; Anne, R.; Lewitowicz, M.; Saint-Laurent, M. G.; Guillemaud-Mueller, D.; Mueller, A. C.; Pougheon, F.; Sorlin, O.; Hansen, P. G.; Hornshoj, P.; Riisager, K.

    1998-12-21

    The halo nuclei {sup 11}Be and {sup 11}Li have been studied through core break-up reactions, where the halo neutrons are detected in anti-coincidence with the core of the halo nucleus. In this particular channel, the halo neutrons are not expected to participate in the reaction and should therefore show the same properties as when situated inside the halo nucleus. The widths of the halo neutron momentum distributions have been extracted in coincidence with He fragments, {gamma}=32{+-}4 MeV/c, and Li fragments, {gamma}=42{+-}4 MeV/c for {sup 11}Be and with He fragments, {gamma}=42{+-}6 MeV/c for {sup 11}Li. An experimental value of the shadow effect for {sup 11}Be when breaking up to Li and He fragments has been obtained to be 0.63. A simple theoretical calculation to reproduce this value is given.

  8. Pairing in bulk nuclear matter beyond BCS

    SciTech Connect

    Ding, D.; Dickhoff, W. H.; Dussan, H.; Witte, S. J.; Rios, A.; Polls, A.

    2014-10-15

    The influence of short-range correlations on the spectral distribution of neutrons is incorporated in the solution of the gap equation for the {sup 3}P{sub 2}?{sup 3}F{sub 2} coupled channel in pure neutron matter. This effect is studied for different realistic interactions including one based on chiral perturbation theory. The gap in this channel vanishes at all relevant densities due to the treatment of these correlations. We also consider the effect of long-range correlations by including polarization terms in addition to the bare interaction which allow the neutrons to exchange density and spin fluctuations governed by the strength of Landau parameters allowed to have reasonable values consistent with the available literature. Preliminary results indicate that reasonable values of these parameters do not generate a gap in the {sup 3}P{sub 2}?{sup 3}F{sub 2} coupled channel either for all three realistic interactions although the pairing interaction becomes slightly more attractive.

  9. Pick a Pair. Pancake Pairs

    ERIC Educational Resources Information Center

    Miller, Pat

    2005-01-01

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

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

    SciTech Connect

    Skinner, Lawrie B.; Huang, Congcong; Schlesinger, Daniel; Pettersson, Lars G. M.; Nilsson, Anders; Benmore, Chris J.

    2013-02-21

    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.

  11. Distribution of Residence Time of Water around DNA Base Pairs: Governing Factors and the Origin of Heterogeneity.

    PubMed

    Saha, Debasis; Supekar, Shreyas; Mukherjee, Arnab

    2015-08-27

    Water dynamics in the solvation shell around biomolecules plays a vital role in their stability, function, and recognition processes. Although extensively studied through various experimental and computational methods, dynamical time scales of water near DNA is highly debated. The residence time of water is one such dynamical quantity that has been probed rarely around DNA using computational methods. Moreover, the effect of local DNA sequence variation in water residence time has also not been addressed. Using 20 DNA systems with different sequences, we capture here the mean residence time (MRT) of water molecules around 360 different sites in the major and minor grooves of DNA. Thus, we show that a distribution of time scales exists even for a regular structure of DNA, reflecting the effect of chemistry, topography, and other factors governing dynamics of water. We used the stable state picture (SSP) formalism to calculate MRT that avoids the effect of transient recrossing. Results obtained from simulations agree well with experiments done on a few specific systems at a similar temperature. Most importantly, we find that although the groove width and depth influence water time scale, MRT of water is always longer in the middle of the DNA, in agreement with NMR experiments. We propose a simple kinetic model of water escape from DNA where water molecules move along the DNA and perpendicular to it in both the first and second solvation shell before it escapes to bulk. We show that this simple kinetic model captures both the time scale and the position dependence of MRT of water around DNA. This study thus portrays the origin and a measure of heterogeneity in water dynamics around DNA and provides a fresh perspective in the ongoing debate on water dynamical time scales around DNA. PMID:25993473

  12. The Probability Distribution of Binary Pulsar Coalescence Rates. I. Double Neutron Star Systems in the Galactic Field

    E-print Network

    C. Kim; V. Kalogera; D. R. Lorimer

    2002-10-21

    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 two orders of magnitude) mainly due to 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 sample and, importantly, to assign a statistical significance to these estimates and to calculate the allowed ranges of values at various confidence levels. The method involves the simulation of selection effects inherent in all relevant radio pulsar surveys and a Bayesian statistical analysis for the probability distribution of the rate. The most likely values for the total Galactic coalescence rate (R_peak) lie in the range 2-60 per Myr depending on different pulsar population models. For our reference model 1, where the most likely estimates of pulsar population properties are adopted, we obtain R_tot = 8_{-5}^{+9} per Myr at a 68% statistical confidence level. The corresponding range of expected detection rates of NS-NS inspiral are 3_{-2}^{+4}x10^{-3} per yr for the initial LIGO and 18_{-11}^{+21} per yr for the advanced LIGO.

  13. On Cooper Pairing in Finite Fermi Systems

    E-print Network

    A. V. Avdeenkov; S. P. Kamerdzhiev

    2001-11-27

    In order to analyse the role of the quasiparticle-phonon interaction in the origin of nuclear gap, we applied an approach which is similar to the Eliashberg theory for usual superconductors. We obtained that the averaged contribution of the quasiparticle-phonon mechanism to the observed value of the pairing gap for $^{120}$Sn is 26% and the BCS-type mechanism gives 74% . Thus, pairing is of a mixed nature at least in semi-magic nuclei -- it is due to the quasiparticle-phonon and BCS mechanisms, the first one being mainly a surface mechanism and the second one mainly a volume mechanism. The calculations of the strength distribution for the odd-mass nuclei $^{119}Sn$ and $^{121}Sn$ have shown that the quasiparticle-phonon mechanism mainly improves the description of the observed spectroscopic factors in these nuclei. For the case of nuclei with pairing in both proton and neutron systems it is necessary to go beyond the Eliashberg-Migdal approximations and include the vertex correction graphs in addition to the rainbow ones. The estimations for spectroscopic factors performed within a three-level model have shown that the contribution of the vertex correction graphs was rather noticeable.

  14. The power distribution and neutron fluence measurements and calculations in the VVER-1000 Mock-Up on the LR-0 research reactor

    SciTech Connect

    Kostal, M.; Juricek, V.; Rypar, V.; Svadlenkova, M.; Cvachovec, F.

    2011-07-01

    The power density distribution in a reactor has significant influence on core structures and pressure vessel mechanical resistance, as well as on the physical characteristics of nuclear fuel. This quantity also has an effect on the leakage neutron and photon field. This issue has become of increasing importance, as it touches on actual questions of the VVER nuclear power plant life time extension. This paper shows the comparison of calculated and experimentally determined pin by pin power distributions. The calculation has been performed with deterministic and Monte Carlo approaches. This quantity is accompanied by the neutron and photon flux density calculation and measurements at different points of the light water zero-power (LR-0) research reactor mock-up core, reactor built-in component (core barrel), and reactor pressure vessel and model. The effect of the different data libraries used for calculation is discussed. (authors)

  15. Pairing correlations and transitions in nuclear systems

    E-print Network

    A. Belic; D. J. Dean; M. Hjorth-Jensen

    2003-09-29

    We discuss several pairing-related phenomena in nuclear systems, ranging from superfluidity in neutron stars to the gradual breaking of pairs in finite nuclei. We describe recent experimental evidence that points to a relation between pairing and phase transitions (or transformations) in finite nuclear systems. A simple pairing interaction model is used in order to study and classify an eventual pairing phase transition in finite fermionic systems such as nuclei. We show that systems with as few as 10-16 fermions can exhibit clear features reminiscent of a phase transition.

  16. Pairing and Isospin Dependence of Chaos in Nuclei

    NASA Astrophysics Data System (ADS)

    Gómez, J. M. G.; Molina, R.; Retamosa, J.

    2003-06-01

    Shell-model energy spectra of Ca, Sc and Ti isotopes are analyzed using standard statistics such as the nearest level spacing distribution and the Dyson-Mehta ?3. For all the Ca isotopes, in the ground state region the energy level fluctuations show strong deviations from GOE predictions. When one or two neutrons are replaced by protons, Sc is closer to GOE and Ti is even more chaotic. Thus we find a clear isospin dependence in the degree of nuclear chaoticity. It is also shown that the pairing force is largely responsible for the quasiregular motion in the ground state region of Ca isotopes.

  17. Structural characterization of Green River oil-shale at high-pressure using pair distribution function analysis and small angle x-ray scattering.

    SciTech Connect

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

    2008-01-01

    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 (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 30.7%). Indeed the features in the PDF beyond 6 {angstrom}, were similarly well fit by a single phase model of the highest symmetry, highly crystalline quartz component.

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

    SciTech Connect

    Allan, P. K.; Chapman, K. W.; Chupas, P. J.; Hriljac, J. A.; Renouf, C. L.; Lucas, T. C. A.; Morris, R. E.

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Key, Baris

    2012-02-01

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

  20. Characterization of the ferromagnetic phase of La_1-xCa_xMnO3 using the atomic pair distribution function

    NASA Astrophysics Data System (ADS)

    Proffen, Thomas; Billinge, Simon; Petkov, Valeri

    2000-03-01

    Colossal magnetoresistant manganites are subject of ongoing theoretical as well as experimental studies. We have used the analysis of the atomic pair distribution function (PDF) of high energy X-ray diffraction to distinguish the charge localization and delocalization of La_1-xCa_xMnO3 (x=0.12, 0.25, 0.33). The indicator for charge localization is the Jahn-Teller Mn-O long bond, that can be observed in the PDF. We find that the ferromagnetic (FM) phase is only homogeneous at low temperatures and high dopings above x ? 0.3. As the doping is decreased or the temperature increased towards the metal-to-insulator phase transition, but still well within the FM region of the phase diagram, the sample becomes inhomogeneous with coexisting localized JT distorted regions and delocalized Zener state regions. The inhomogeneities are microscopic and there is no evidence of phase separation in the diffraction pattern as is observed in low-Tc materials such as Pr_1-xCa_xMnO_3.

  1. Atomic ordering in nanostructural V_2O_5.nH_2O observed by the atomic pair distribution function technique

    NASA Astrophysics Data System (ADS)

    Bozin, Emil S.; Petkov, Valeri; J. L. Billinge, Simon; Trikalitis, Pantelis; Kanatzidis, Mercouri G.

    2002-03-01

    The three dimensional structure of highly disordered but crystalline V_2O_5.nH_2O has been determined by the atomic pair distribution function (PDF) technique using x-ray powder diffraction data. Measurements were carried out at the beamline X7A of the National Synchrotron Light Source at the Brookhaven National Laboratory. Versatile properties of this xerogel inspired research for potential applications such as chemical sensors, electrochemical and fast switching devices, high energy density lithium ion bateries and host materials. PDF technique shows that at the atomic scale the structure of the xerogel can be well described as an assembly of almost perfect bi-layers of VO5 units, with water molecules residing between the bi-layers. The bi-layers are stacked along the z-axis of a monoclinic unit cell (space group C2/m) with parameters a=11.722(3)Åb=3.570(3)Åc=11.520(3)Åand ?=88.65 with stacking sequence showing signature of turbostratic disorder.

  2. Amorphous Analogs of Martian Global Soil: Pair Distribution Function Analyses and Implications for Scattering Models of Chemin X-ray Diffraction Data

    NASA Technical Reports Server (NTRS)

    Achilles, C. N.; Bish, D. L.; Rampe, E. B.; Morris, R. V.

    2015-01-01

    Soils on Mars have been analyzed by the Mars Exploration Rovers (MER) and most recently by the Mars Science Laboratory (MSL) rover. Chemical analyses from a majority of soil samples suggest that there is a relatively uniform global soil composition across much of the planet. A soil site, Rocknest, was sampled by the MSL science payload including the CheMin X-ray diffractometer and the Alpha Particle X-ray Spectrometer (APXS). Che- Min X-ray diffraction (XRD) data revealed crystalline phases and a broad, elevated background, indicating the presence of amorphous or poorly ordered materials (Fig 1). Based on the chemical composition of the bulk soil measured by APXS and the composition of crystalline phases derived from unit-cell parameters determined with CheMin data, the percentages of crystalline and amorphous phases were calculated at 51% and 49%, respectively. Attempts to model the amorphous contribution to CheMin XRD patterns were made using amorphous standards and full-pattern fitting methods and show that the broad, elevated background region can be fitted by basaltic glass, allophane, and palagonite. However, the modeling shows only that these phases have scattering patterns similar to that for the soil, not that they represent unique solutions. Here, we use pair distribution function (PDF) analysis to determine the short-range order of amorphous analogs in martian soils and better constrain the amorphous material detected by CheMin.

  3. A background-free direction-sensitive neutron detector

    E-print Network

    Roccaro, Alvaro

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

  4. Supernovae in paired galaxies

    E-print Network

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

    2013-01-01

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

  5. Multi-pair states in electron-positron pair creation

    E-print Network

    Anton Wöllert; Heiko Bauke; Christoph H. Keitel

    2015-11-24

    Ultra strong electromagnetic fields can lead to a breakdown of the vacuum and the spontaneous creation of single or multiple electron-positron pairs. A quantum field theoretical treatment of the pair creation process combined with numerical methods provides a complete description of the quantum field state, from which all observables of the multiple electron-positron pairs can be inferred. This allows to study the complex multi-particle dynamics of electron-positron pair creation in-depth, including multi-pair statistics as well as momentum distributions and spin. To illustrate the potential benefit of this approach, it is applied to the intermediate regime of pair creation between nonperturbative Schwinger pair creation and perturbative multiphoton pair creation where the creation of multi-pair states becomes nonnegligible but cascades do not yet set in. Furthermore, it is demonstrated how spin and helicity of the created electrons and positrons are affected by the polarization of the counterpropagating laser fields, which induce the creation of electron-positron pairs.

  6. Demonstration of thin film pair distribution function analysis (tfPDF) for the study of local structure in amorphous and crystalline thin films

    PubMed Central

    Jensen, Kirsten M. Ø.; Blichfeld, Anders B.; Bauers, Sage R.; Wood, Suzannah R.; Dooryhée, Eric; Johnson, David C.; Iversen, Bo B.; Billinge, Simon J. L.

    2015-01-01

    By means of normal-incidence, high-flux and high-energy X-rays, total scattering data for pair distribution function (PDF) analysis have been obtained from thin films (tf), suitable for local structure analysis. By using amorphous substrates as support for the films, the standard Rapid Acquisition PDF setup can be applied and the scattering signal from the film can be isolated from the total scattering data through subtraction of an independently measured background signal. No angular corrections to the data are needed, as would be the case for grazing incidence measurements. The ‘tfPDF’ method is illustrated through studies of as-deposited (i.e. amorphous) and crystalline FeSb3 films, where the local structure analysis gives insight into the stabilization of the metastable skutterudite FeSb3 phase. The films were prepared by depositing ultra-thin alternating layers of Fe and Sb, which interdiffuse and after annealing crystallize to form the FeSb3 structure. The tfPDF data show that the amorphous precursor phase consists of corner-sharing FeSb6 octahedra with motifs highly resembling the local structure in crystalline FeSb3. Analysis of the amorphous structure allows the prediction of whether the final crystalline product will form the FeSb3 phase with or without excess Sb present. The study thus illustrates how analysis of the local structure in amorphous precursor films can help to understand crystallization processes of metastable phases and opens for a range of new local structure studies of thin films. PMID:26306190

  7. Oxyanion induced variations in domain structure for amorphous cobalt oxide oxygen evolving catalysts, resolved by X-ray pair distribution function analysis.

    PubMed

    Kwon, Gihan; Kokhan, Oleksandr; Han, Ali; Chapman, Karena W; Chupas, Peter J; Du, Pingwu; Tiede, David M

    2015-12-01

    Amorphous thin film oxygen evolving catalysts, OECs, of first-row transition metals show promise to serve as self-assembling photoanode materials in solar-driven, photoelectrochemical `artificial leaf' devices. This report demonstrates the ability to use high-energy X-ray scattering and atomic pair distribution function analysis, PDF, to resolve structure in amorphous metal oxide catalyst films. The analysis is applied here to resolve domain structure differences induced by oxyanion substitution during the electrochemical assembly of amorphous cobalt oxide catalyst films, Co-OEC. PDF patterns for Co-OEC films formed using phosphate, Pi, methylphosphate, MPi, and borate, Bi, electrolyte buffers show that the resulting domains vary in size following the sequence Pi < MPi < Bi. The increases in domain size for CoMPi and CoBi were found to be correlated with increases in the contributions from bilayer and trilayer stacked domains having structures intermediate between those of the LiCoOO and CoO(OH) mineral forms. The lattice structures and offset stacking of adjacent layers in the partially stacked CoMPi and CoBi domains were best matched to those in the LiCoOO layered structure. The results demonstrate the ability of PDF analysis to elucidate features of domain size, structure, defect content and mesoscale organization for amorphous metal oxide catalysts that are not readily accessed by other X-ray techniques. PDF structure analysis is shown to provide a way to characterize domain structures in different forms of amorphous oxide catalysts, and hence provide an opportunity to investigate correlations between domain structure and catalytic activity. PMID:26634728

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

    PubMed Central

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

    2012-01-01

    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. PMID:22655057

  9. Oxyanion induced variations in domain structure for amorphous cobalt oxide oxygen evolving catalysts, resolved by X-ray pair distribution function analysis

    PubMed Central

    Kwon, Gihan; Kokhan, Oleksandr; Han, Ali; Chapman, Karena W.; Chupas, Peter J.; Du, Pingwu; Tiede, David M.

    2015-01-01

    Amorphous thin film oxygen evolving catalysts, OECs, of first-row transition metals show promise to serve as self-assembling photoanode materials in solar-driven, photoelectrochemical ‘artificial leaf’ devices. This report demonstrates the ability to use high-energy X-ray scattering and atomic pair distribution function analysis, PDF, to resolve structure in amorphous metal oxide catalyst films. The analysis is applied here to resolve domain structure differences induced by oxyanion substitution during the electrochemical assembly of amorphous cobalt oxide catalyst films, Co-OEC. PDF patterns for Co-OEC films formed using phosphate, Pi, methylphosphate, MPi, and borate, Bi, electrolyte buffers show that the resulting domains vary in size following the sequence Pi < MPi < Bi. The increases in domain size for CoMPi and CoBi were found to be correlated with increases in the contributions from bilayer and trilayer stacked domains having structures intermediate between those of the LiCoOO and CoO(OH) mineral forms. The lattice structures and offset stacking of adjacent layers in the partially stacked CoMPi and CoBi domains were best matched to those in the LiCoOO layered structure. The results demonstrate the ability of PDF analysis to elucidate features of domain size, structure, defect content and mesoscale organization for amorphous metal oxide catalysts that are not readily accessed by other X-ray techniques. PDF structure analysis is shown to provide a way to characterize domain structures in different forms of amorphous oxide catalysts, and hence provide an opportunity to investigate correlations between domain structure and catalytic activity. PMID:26634728

  10. Demonstration of thin film pair distribution function analysis (tfPDF) for the study of local structure in amorphous and crystalline thin films.

    PubMed

    Jensen, Kirsten M Ø; Blichfeld, Anders B; Bauers, Sage R; Wood, Suzannah R; Dooryhée, Eric; Johnson, David C; Iversen, Bo B; Billinge, Simon J L

    2015-09-01

    By means of normal-incidence, high-flux and high-energy X-rays, total scattering data for pair distribution function (PDF) analysis have been obtained from thin films (tf), suitable for local structure analysis. By using amorphous substrates as support for the films, the standard Rapid Acquisition PDF setup can be applied and the scattering signal from the film can be isolated from the total scattering data through subtraction of an independently measured background signal. No angular corrections to the data are needed, as would be the case for grazing incidence measurements. The 'tfPDF' method is illustrated through studies of as-deposited (i.e. amorphous) and crystalline FeSb3 films, where the local structure analysis gives insight into the stabilization of the metastable skutterudite FeSb3 phase. The films were prepared by depositing ultra-thin alternating layers of Fe and Sb, which interdiffuse and after annealing crystallize to form the FeSb3 structure. The tfPDF data show that the amorphous precursor phase consists of corner-sharing FeSb6 octahedra with motifs highly resembling the local structure in crystalline FeSb3. Analysis of the amorphous structure allows the prediction of whether the final crystalline product will form the FeSb3 phase with or without excess Sb present. The study thus illustrates how analysis of the local structure in amorphous precursor films can help to understand crystallization processes of metastable phases and opens for a range of new local structure studies of thin films. PMID:26306190

  11. Demonstration of thin film pair distribution function analysis (tfPDF) for the study of local structure in amorphous and crystalline thin films

    DOE PAGESBeta

    Jensen, K. M.Ø.; Blichfeld, A. B.; Bauers, S. R.; Wood, S. R.; Dooryhee, E.; Johnson, D. C.; Iversen, B. B.; Billinge, S.

    2015-07-05

    By means of normal incidence, high flux and high energy x-rays, we have obtained total scattering data for Pair Distribution Function (PDF) analysis from thin films (tf), suitable for local structure analysis. By using amorphous substrates as support for the films, the standard Rapid Acquisition PDF setup can be applied and the scattering signal from the film can be isolated from the total scattering data through subtraction of an independently measured background signal. No angular corrections to the data are needed, as would be the case for grazing incidence measurements. We illustrate the ‘tfPDF’ method through studies of as depositedmore »(i.e. amorphous) and crystalline FeSb3 films, where the local structure analysis gives insight into the stabilization of the metastable skutterudite FeSb3 phase. The films were prepared by depositing ultra-thin alternating layers of Fe and Sb, which interdiffuse and after annealing crystallize to form the FeSb3 structure. The tfPDF data show that the amorphous precursor phase consists of corner-sharing FeSb6 octahedra with motifs highly resembling the local structure in crystalline FeSb3. Analysis of the amorphous structure allows predicting whether the final crystalline product will form the FeSb3 phase with or without excess Sb present. The study thus illustrates how analysis of the local structure in amorphous precursor films can help to understand crystallization processes of metastable phases and opens for a range of new local structure studies of thin films.« less

  12. 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)

    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

    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.

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

    SciTech Connect

    Meinhold, Lars; Clement, David; Tehei, M; Daniel, R. M.; Finney, J.L.; Smith, Jeremy C

    2008-11-01

    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.

  14. Direction distribution of ambient neutron dose equivalent from 20 MeV protons incident on thick Be and Cu targets.

    PubMed

    Sunil, C; Shanbhag, A A; Nandy, M; Maiti, M; Bandyopadhyay, T; Sarkar, P K

    2009-09-01

    Ambient neutron dose equivalent from 20 MeV protons incident on thick Be and Cu targets are measured at 0 degrees, 30 degrees, 60 degrees and 90 degrees with respect to the beam direction using a conventional dose equivalent meter. The neutron spectra calculated using nuclear reaction model codes ALICE, PRECO and earlier reported empirical expressions are converted to the ambient dose equivalent using the ICRP fluence-to-dose conversion coefficients and are compared with the measured values. The experimental energy spectra reported in the literature for 19.08 MeV protons incident on a thick Be target are also converted to ambient neutron dose equivalent and are compared with the present experimental results. It is observed that the values estimated from the neutron spectra obtained from the nuclear reaction codes are unable to predict the measured values. The results obtained from the reported experimental energy spectra compare well with the results obtained here. An empirical relation that was used to calculate the directional dependence of the measured neutron dose equivalent from heavy ion-induced reactions is used in this study to check its effectiveness for proton-induced reactions. PMID:19700498

  15. Accelerator neutron source for boron neutron capture therapy

    SciTech Connect

    Wang, C.K.; Blue, T.E.; Blue, J.W.; Gahbauer, R.A.

    1987-01-01

    If boron neutron capture therapy (BNCT) is to be widely used to treat patients with brain tumors, then a hospital-based neutron source must be developed. Accelerator neutron sources for BNCT have been proposed as alternatives to nuclear reactor beams. The ideal neutron source for BNCT is a monoenergetic neutron beam with a neutron energy that is above thermal energies but below approx. 10 keV. The optimum neutron energy is currently being studied. The purpose of this paper is to report the results of a Monte Carlo analysis of the performance of an accelerator neutron source for the treatment of brain tumors by BNCT. The proton beam is identical. Thicknesses of moderators are identified that yield neutron energy spectra which produce within a head phantom distributions of absorbed dose approaching the distributions that would be attained with the above-mentioned ideal spectra.

  16. Superfluidity in the Core of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Page, Dany

    2013-04-01

    The year (1958) after the publication of the BCS theory, Bohr, Mottelson & Pines showed that nuclei should also contain superfluid neutrons and superconducting protons. In 1959, A. Migdal proposed that neutron superfluidity should also occur in the interior of neutron stars. Pairing in nuclei forms Cooper pairs with zero spin, but the relevant component of the nuclear interaction becomes repulsive at densities larger than the nuclear matter density. It has been proposed that neutron-neutron interaction in the spin-triplet state, and L=1 orbital angular momentum, that is known to be attractive from laboratory experiments, may result in a new form of neutron superfluidity in the neutron star interior. I will review our present understanding of the structure of neutron stars and describe how superfluidity strongly affects their thermal evolution. I will show how a ``Minimal Model'' that excludes the presence of ``exotic'' matter (Bose condensates, quarks, etc.) is compatible with most observations of the surface temperatures of young isolated neutron stars in the case this neutron superfluid exists. Compared to the case of isotropic spin-zero Cooper pairs, the formation of anisotropic spin-one Cooper pairs results in a strong neutrino emission that leads to an enhanced cooling of neutron stars after the onset of the pairing phase transition and allows the Minimal Cooling scenario to be compatible with most observations. In the case the pairing critical temperature Tc is less than about 6 x10^8 K, the resulting rapid cooling of the neutron star may be observable. It was recently reported that 10 years of Chandra observations of the 333 year young neutron star in the Cassiopeia A supernova remnant revealed that its temperature has dropped by about 5%. This result indicates that neutrons in this star are presently becoming superfluid and, if confirmed, provides us with the first direct observational evidence for neutron superfluidity at supra-nuclear densities.

  17. Non-Statistical Effects in Neutron Capture

    SciTech Connect

    Koehler, P. E.; Guber, K. H.; Harvey, J. A.; Wiarda, D.; Bredeweg, T. A.; O'Donnell, J. M.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wouters, J. M.; Reifarth, R.

    2009-01-28

    There have been many reports of non-statistical effects in neutron-capture measurements. However, reports of deviations of reduced-neutron-width ({gamma}{sub n}{sup 0}) distributions from the expected Porter-Thomas (PT) shape largely have been ignored. Most of these deviations have been reported for odd-A nuclides. Because reliable spin (J) assignments have been absent for most resonances for such nuclides, it is possible that reported deviations from PT might be due to incorrect J assignments. We recently developed a new method for measuring spins of neutron resonances by using the DANCE detector at the Los Alamos Neutron Science Center (LANSCE). Measurements made with a {sup 147}Sm sample allowed us to determine spins of almost all known resonances below 1 keV. Furthermore, analysis of these data revealed that the {gamma}{sub n}{sup 0} distribution was in good agreement with PT for resonances below 350 eV, but in disagreement with PT for resonances between 350 and 700 eV. Our previous (n,{alpha}) measurements had revealed that the {alpha} strength function also changes abruptly at this energy. There currently is no known explanation for these two non-statistical effects. Recently, we have developed another new method for determining the spins of neutron resonances. To implement this technique required a small change (to record pulse-height information for coincidence events) to a much simpler apparatus: A pair of C{sub 6}D{sub 6}{gamma}-ray detectors which we have employed for many years to measure neutron-capture cross sections at the Oak Ridge Electron Linear Accelerator (ORELA). Measurements with a {sup 95}Mo sample revealed that not only does the method work very well for determining spins, but it also makes possible parity assignments. Taken together, these new techniques at LANSCE and ORELA could be very useful for further elucidation of non-statistical effects.

  18. Non-Statistical Effects in Neutron Capture

    SciTech Connect

    Koehler, Paul Edward; Bredeweg, t a; Guber, Klaus H; Harvey, John A; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wiarda, Dorothea; Wouters, J. M.

    2009-01-01

    There have been many reports of non-statistical effects in neutron-capture measurements. However, reports of deviations of reduced-neutron-width ({Gamma}n{sup 0}) distributions from the expected Porter-Thomas (PT) shape largely have been ignored. Most of these deviations have been reported for odd-A nuclides. Because reliable spin (J) assignments have been absent for most resonances for such nuclides, it is possible that reported deviations from PT might be due to incorrect J assignments. We recently developed a new method for measuring spins of neutron resonances by using the DANCE detector at the Los Alamos Neutron Science Center (LANSCE). Measurements made with a 147Sm sample allowed us to determine spins of almost all known resonances below 1 keV. Furthermore, analysis of these data revealed that the {Gamma}n{sup 0} distribution was in good agreement with PT for resonances below 350 eV, but in disagreement with PT for resonances between 350 and 700 eV. Our previous (n,{alpha}) measurements had revealed that the {alpha} strength function also changes abruptly at this energy. There currently is no known explanation for these two non-statistical effects. Recently, we have developed another new method for determining the spins of neutron resonances. To implement this technique required a small change (to record pulse-height information for coincidence events) to a much simpler apparatus: A pair of C6D6 ?-ray detectors which we have employed for many years to measure neutron-capture cross sections at the Oak Ridge Electron Linear Accelerator (ORELA). Measurements with a 95Mo sample revealed that not only does the method work very well for determining spins, but it also makes possible parity assignments. Taken together, these new techniques at LANSCE and ORELA could be very useful for further elucidation of non-statistical effects.

  19. Isospin Dependent Pairing Interactions and BCS-BEC crossover

    SciTech Connect

    Sagawa, H.; Margueron, J.; Hagino, K.

    2008-11-11

    We propose new types of density dependent contact pairing interaction which reproduce the pairing gaps in symmetric and neutron matters obtained by a microscopic treatment based on the realistic nucleon-nucleon interaction. The BCS-BEC crossover of neutrons pairs in symmetric and asymmetric nuclear matters is studied by using these contact interactions. It is shown that the bare and screened pairing interactions lead to different features of the BCS-BEC crossover in symmetric nuclear matter. We perform Hartree-Fock-Bogoliubov (HFB) calculations for semi-magic Calcium, Nickel, Tin and Lead isotopes and N = 20, 28, 50 and 82 isotones using these density-dependent pairing interactions. Our calculations well account for the experimental data for the neutron number dependence of binding energy, two neutrons separation energy, and odd-even mass staggering of these isotopes. Especially the interaction IS+IV Bare without the medium polarization effect gives satisfactory results for all the isotopes.

  20. Determination of neutron flux density distribution in the core with LEU fuel IRT-4M at the training reactor VR-1

    SciTech Connect

    Huml, O.

    2008-07-15

    The objective of this work was to determine the neutron flux density distribution in various places of the training reactor VR-1 Sparrow. This experiment was performed on the new core design C1, composed of the new low-enriched uranium fuel cells IRT-4M (19.7 %). This fuel replaced the old high-enriched uranium fuel IRT-3M (36 %) within the framework of the RERTR Program in September 2005. The measurement used the neutron activation analysis method with gold wires. The principle of this method consists in neutron capture in a nucleus of the material forming the activation detector. This capture can change the nucleus in a radioisotope, whose activity can be measured. The absorption cross-section values were evaluated by MCNP computer code. The gold wires were irradiated in seven different positions in the core C1. All irradiations were performed at reactor power level 1E8 (1 kW{sub therm}). The activity of segments of irradiated wires was measured by special automatic device called 'Drat' (Wire in English). (author)

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

    NASA Astrophysics Data System (ADS)

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

    2008-05-01

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

  2. Fingerprinting analysis of non-crystalline pharmaceutical compounds using high energy X-rays and the total scattering pair distribution function

    NASA Astrophysics Data System (ADS)

    Davis, Timur D.

    2011-12-01

    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.

  3. Pair-Starved Pulsar Magnetospheres

    NASA Technical Reports Server (NTRS)

    Muslimov, Alex G.; Harding, Alice K.

    2009-01-01

    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.

  4. Integrability and exact spectrum of a pairing model for nucleons

    E-print Network

    J. Links; H. -Q. Zhou; M. D. Gould; R. H. McKenzie

    2001-10-31

    A pairing model for nucleons, introduced by Richardson in 1966, which describes proton-neutron pairing as well as proton-proton and neutron-neutron pairing, is re-examined in the context of the Quantum Inverse Scattering Method. Specifically, this shows that the model is integrable by enabling the explicit construction of the conserved operators. We determine the eigenvalues of these operators in terms of the Bethe ansatz, which in turn leads to an expression for the energy eigenvalues of the Hamiltonian.

  5. The MCLIB library: Monte Carlo simulation of neutron scattering instruments

    SciTech Connect

    Seeger, P.A.

    1995-09-01

    Monte Carlo is a method to integrate over a large number of variables. Random numbers are used to select a value for each variable, and the integrand is evaluated. The process is repeated a large number of times and the resulting values are averaged. For a neutron transport problem, first select a neutron from the source distribution, and project it through the instrument using either deterministic or probabilistic algorithms to describe its interaction whenever it hits something, and then (if it hits the detector) tally it in a histogram representing where and when it was detected. This is intended to simulate the process of running an actual experiment (but it is much slower). This report describes the philosophy and structure of MCLIB, a Fortran library of Monte Carlo subroutines which has been developed for design of neutron scattering instruments. A pair of programs (LQDGEOM and MC{_}RUN) which use the library are shown as an example.

  6. The heat capacity of the neutron star inner crust within an extended NSE model

    E-print Network

    Burrello, S; Aymard, F; Colonna, M; Raduta, Ad R

    2015-01-01

    Superfluidity in the crust is a key ingredient for the cooling properties of proto-neutron stars. Present theoretical calculations employ the quasi-particle mean-field Hartree-Fock-Bogoliubov theory with temperature dependent occupation numbers for the quasi-particle states. Finite temperature stellar matter is characterized by a whole distribution of different nuclear species. We want to assess the importance of this distribution on the calculation of heat capacity in the inner crust. Following a recent work, the Wigner-Seitz cell is mapped into a model with cluster degrees of freedom. The finite temperature distribution is then given by a statistical collection of Wigner-Seitz cells. We additionally introduce pairing correlations in the local density BCS approximation both in the homogeneous unbound neutron component, and in the interface region between clusters and neutrons. The heat capacity is calculated in the different baryonic density conditions corresponding to the inner crust, and in a temperature r...

  7. Vortex structure of neutron stars with triplet neutron superfluidity

    NASA Astrophysics Data System (ADS)

    Shahabasyan, K. M.; Shahabasyan, M. K.

    2011-09-01

    The vortex structure of the "npe" phase of neutron stars with a 3P2 superfluid neutron condensate of Cooper pairs is discussed. It is shown that, as the star rotates, superfluid neutron vortex filaments described by a unitary ordering parameter develop in the "npe" phase. The entrainment of superconducting protons by the rotating superfluid neutrons is examined. The entrainment effect leads to the appearance of clusters of proton vortices around each neutron vortex and generates a magnetic field on the order of 1012 G. 3P2 neutron vortex filaments combine with quark semi-superfluid vortex filaments at the boundary of the "npe" and "CFL" phases. At the boundary of the "Aen" and "npe" phases, they combine with 1S0 neutron vortex filaments. In this way, a unified vortex structure is formed. The existence of this structure and its collective elastic oscillations explain the observed oscillations in the angular rotation velocity of pulsars.

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

    PubMed Central

    Sharifi, Monir; Wallacher, Dirk

    2012-01-01

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

  9. Cation distribution in a Fe-bearing K-feldspar from Itrongay,Madagascar. A combined neutron- and X-ray single crystal diffractionstudy

    SciTech Connect

    Ackermann, Sonia; Kunz, Martin; Armbruster, Thomas; Schefer,Jurg; Hanni, Henry

    2005-05-02

    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.

  10. Transverse momentum distribution and left-right asymmetry of Drell-Yan pairs in single-spin hadron-hadron collisions

    SciTech Connect

    Boros, C.; Meng Ta-chung

    1995-07-01

    This Brief Report is an addendum to a previous Letter. The usefulness of measuring Drell-Yan pairs in single-spin hadron-hadron collisions is discussed in more detail and the following points are explicitly shown. (i) In the central rapidity region, the average transverse momentum and the left-right asymmetry of the produced Drell-Yan pairs should not only be nonvanishing, but also be much larger than those of the produced mesons. (ii) The effect of QCD corrections on the proposed model do not change the qualitative features of the results published in the Letter.

  11. Neutron angular correlations in spontaneous and neutron-induced fission

    NASA Astrophysics Data System (ADS)

    Vogt, R.; Randrup, J.

    2014-12-01

    Background: Neutron emission is correlated in fission events because, on average, more than one neutron is emitted per fission. Measurements of these correlations, coupled with studies of more inclusive observables such as neutron multiplicity, provide sensitive information about the fission mechanism. Neutron-neutron angular correlations have been studied in both spontaneous fission of 252Cf and neutron-induced fission of 235U. These correlations, until recently incalculable in most available simulations of fission, can now be calculated in event-by-event simulations of fission. Purpose: Phenomenological studies of fission are of interest both for basic science and for practical applications. Neutron-neutron angular correlations are characteristic of the fissioning isotope and could be used in material identification. Method: We use our model of complete fission events, freya, to first study the sensitivity of two-neutron angular correlations to the model inputs and then compare to available data. We also compare our simulations to neutron-fragment angular correlations. Results: We find that the correlations calculated with freya are fairly robust with respect to the input parameters. Any strong deviations in the correlations result in poor agreement with measured inclusive neutron observables such as neutron multiplicity as a function of fragment mass and the neutron multiplicity distribution. The agreement of freya with the present set of correlation data is found to be good. Conclusions: freya can be used to reliably predict neutron-neutron angular correlations and could then be used to identify materials.

  12. Quantum Entanglement of Neutrino Pairs

    E-print Network

    Junli Li; Cong-Feng Qiao

    2014-02-19

    It is practically shown that a pair of neutrinos from tau decay can form a flavor entangled state. With this kind of state we show that the locality constrains imposed by Bell inequality are violated by the quantum mechanics, and an experimental test of this effect is feasible within the earth's length scale. Theoretically, the quantum entanglement of neutrino pairs can be employed to the use of long distance cryptography distribution in a protocol similar to the BB84.

  13. Supercool Neutrons (Ultracold Neutrons)

    E-print Network

    Martin, Jeff

    . ("BigBang Nucleosynthesis") Important for many reactions going on in our sun, and in nuclear reactors later) #12; How to make lots of neutrons: Liberate them from nuclei! 1) In a nuclear reactor (how the neutrons have no charge, they interact mainly via the strong nuclear force with materials, giving a new

  14. Distribution of glass transition temperatures Tg in polystyrene thin films as revealed by low-energy muon spin relaxation: A comparison with neutron reflectivity results.

    PubMed

    Kanaya, Toshiji; Ogawa, Hiroki; Kishimoto, Mizuki; Inoue, Rintaro; Suter, Andreas; Prokscha, Thomas

    2015-08-01

    In a previous paper [Phys. Rev. E 83, 021801 (2011)] we performed neutron reflectivity (NR) measurements on a five-layer polystyrene (PS) thin film consisting of alternatively stacked deuterated polystyrene (dPS) and hydrogenated polystyrene (hPS) layers (dPS/hPS/dPS/hPS/dPS, ?100 nm thick) on a Si substrate to reveal the distribution of Tg along the depth direction. Information on the Tg distribution is very useful to understand the interesting but unusual properties of polymer thin films. However, one problem that we have to clarify is if there are effects of deuterium labeling on Tg or not. To tackle the problem we performed low-energy muon spin relaxation (?SR) measurements on the above-mentioned deuterium-labeled five-layer PS thin film as well as dPS and hPS single-layer thin films ?100 nm thick as a function of muon implantation energy. It was found that the deuterium labeling had no significant effects on the Tg distribution, guaranteeing that we can safely discuss the unusual thin film properties based on the Tg distribution revealed by NR on the deuterium-labeled thin films. In addition, the ?SR result suggested that the higher Tg near the Si substrate is due to the strong orientation of phenyl rings. PMID:26382423

  15. Distribution of glass transition temperatures Tg in polystyrene thin films as revealed by low-energy muon spin relaxation: A comparison with neutron reflectivity results

    NASA Astrophysics Data System (ADS)

    Kanaya, Toshiji; Ogawa, Hiroki; Kishimoto, Mizuki; Inoue, Rintaro; Suter, Andreas; Prokscha, Thomas

    2015-08-01

    In a previous paper [Phys. Rev. E 83, 021801 (2011), 10.1103/PhysRevE.83.021801] we performed neutron reflectivity (NR) measurements on a five-layer polystyrene (PS) thin film consisting of alternatively stacked deuterated polystyrene (dPS) and hydrogenated polystyrene (hPS) layers (dPS/hPS/dPS/hPS/dPS, ˜100 nm thick) on a Si substrate to reveal the distribution of Tg along the depth direction. Information on the Tg distribution is very useful to understand the interesting but unusual properties of polymer thin films. However, one problem that we have to clarify is if there are effects of deuterium labeling on Tg or not. To tackle the problem we performed low-energy muon spin relaxation (? SR ) measurements on the above-mentioned deuterium-labeled five-layer PS thin film as well as dPS and hPS single-layer thin films ˜100 nm thick as a function of muon implantation energy. It was found that the deuterium labeling had no significant effects on the Tg distribution, guaranteeing that we can safely discuss the unusual thin film properties based on the Tg distribution revealed by NR on the deuterium-labeled thin films. In addition, the ? SR result suggested that the higher Tg near the Si substrate is due to the strong orientation of phenyl rings.

  16. Structure of a fluid dioleoylphosphatidylcholine bilayer determined by joint refinement of x-ray and neutron diffraction data. II. Distribution and packing of terminal methyl groups.

    PubMed Central

    Wiener, M C; White, S H

    1992-01-01

    We continue in this paper the presentation of theoretical and experimental methods for the joint refinement of neutron and x-ray lamellar diffraction data for the analysis of fluid (L alpha phase) bilayer structure (Wiener, M. C., and S. H. White. 1991 a, b, c. Biophys. J. 59:162-173 and 174-185; Biochemistry. 30:6997-7008; Wiener, M. C., G. I. King, and S. H. White. Biophys. J. 60: 568-576). We show how to obtain the distribution and packing of the terminal methyls in the interior of a fluid dioleoylphosphatidylcholine bilayer (66% RH) by combining x-ray and neutron scattering-length transbilayer profiles with no a priori assumptions about the functional form of the distribution. We find that the methyls can be represented by a Gaussian function with 1/e-halfwidth of 2.95 +/- 0.28 A situated at the bilayer center. There is substantial mixing of the methyls and methylenes in the bilayer center. The Gaussian representation of the methyl distribution is narrower and has a different shape than predicted by several simulations of fluid bilayers (Gruen, D. W. R., and E. H. B. de Lacey. 1984. Surfactants in Solution, Vol. 1. Plenum Publishing Corp., New York. 279-306; de Loof, H., et al. 1991. Biochemistry. 30:2099-2133) but this may be due to the smaller area/lipid of our experiments and the presence of the double-bonds. Determination of the absolute specific volume of DOPC and an analysis of bulk alkane volumetric data over a range of hydrostatic pressures lead to estimates of methylene and methyl volumes at the bilayer center of 27 +/- 1 A3 and 57.2 +/- 3.6 A3, respectively. This result provides direct confirmation of the common assumption that the molecular packing of methyl and methylene groups in bilayers is the same as in bulk liquid alkanes. Images FIGURE 2 PMID:1547330

  17. Gamow-Teller response in deformed even and odd neutron-rich Zr and Mo isotopes

    NASA Astrophysics Data System (ADS)

    Sarriguren, P.; Algora, A.; Pereira, J.

    2014-03-01

    ?-decay properties of neutron-rich Zr and Mo isotopes are investigated within a microscopic theoretical approach based on the proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme Hartree-Fock calculations with pairing correlations. Residual separable particle-hole and particle-particle forces are also included in the formalism. The structural evolution in these isotopic chains including both even and odd isotopes is analyzed in terms of the equilibrium deformed shapes. Gamow-Teller strength distributions, ?-decay half-lives, and ?-delayed neutron-emission probabilities are studied, stressing their relevance to describe the path of the nucleosynthesis rapid neutron capture process.

  18. Gamow-Teller response in deformed even and odd neutron-rich Zr and Mo isotopes

    E-print Network

    Sarriguren, P; Pereira, J

    2014-01-01

    Beta-decay properties of neutron-rich Zr and Mo isotopes are investigated within a microscopic theoretical approach based on the proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme Hartree-Fock calculations with pairing correlations. Residual separable particle-hole and particle-particle forces are also included in the formalism. The structural evolution in these isotopic chains including both even and odd isotopes is analyzed in terms of the equilibrium deformed shapes. Gamow-Teller strength distributions, beta-decay half-lives, and beta-delayed neutron-emission probabilities are studied, stressing their relevance to describe the path of the nucleosynthesis rapid neutron capture process.

  19. Properties of neutron stars with hyperons in the relativistic mean field theory

    NASA Astrophysics Data System (ADS)

    Ma, Z. X.; Dai, Z. G.; Lu, T.

    2001-02-01

    We study the equation of state (EOS) of the dense matter in the core of neutron stars with hyperons included and the star structure based on the Zimanyi & Moszkowski (ZM) model in the relativistic mean-field theory with a set of recent satisfactory parameters. The relation between hyperon abundances and baryon number densities is calculated and the distribution of baryons in the core of a typical neutron star of 1.4 M_sun is presented. Our results satisfy the requirements from observations of the mass of binary radio pulsars, and the ratio, I_c/I_tot, of the crustal momentum of inertia to the total one. The actual surface thermal radiation detected seems to indicate that baryons in the core of neutron stars should pair to form a superfluid phase, if hyperons appear in the core of neutron stars.

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

    E-print Network

    Shternin, P S; Wiescher, M; Yakovlev, D G; 10.1103/PhysRevC.86.015808

    2012-01-01

    We consider the astrophysical reaction rates for radiative neutron capture reactions ($n,\\gamma$) in the crust of a neutron star. The presence of degenerate neutrons at high densities (mainly in the inner crust) can drastically affect the reaction rates. Standard rates assuming a Maxwell-Boltzmann distribution for neutrons can underestimate the rates by several orders of magnitude. We derive simple analytical expressions for reaction rates at a variety of conditions with account for neutron degeneracy. We also discuss the plasma effects on the outgoing radiative transition channel in neutron radiative capture reactions and show that these effects can also increase the reaction rates by a few orders of magnitude. In addition, using detailed balance, we analyze the effects of neutron degeneracy and plasma physics on reverse ($\\gamma,n$) photodisintegration. We discuss the dependence of the reaction rates on temperature and neutron chemical potential and outline the efficiency of these reactions in the neutron s...

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

    E-print Network

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

    2012-07-25

    We consider the astrophysical reaction rates for radiative neutron capture reactions ($n,\\gamma$) in the crust of a neutron star. The presence of degenerate neutrons at high densities (mainly in the inner crust) can drastically affect the reaction rates. Standard rates assuming a Maxwell-Boltzmann distribution for neutrons can underestimate the rates by several orders of magnitude. We derive simple analytical expressions for reaction rates at a variety of conditions with account for neutron degeneracy. We also discuss the plasma effects on the outgoing radiative transition channel in neutron radiative capture reactions and show that these effects can also increase the reaction rates by a few orders of magnitude. In addition, using detailed balance, we analyze the effects of neutron degeneracy and plasma physics on reverse ($\\gamma,n$) photodisintegration. We discuss the dependence of the reaction rates on temperature and neutron chemical potential and outline the efficiency of these reactions in the neutron star crust.

  2. Solid Targets for Neutron Spallation Sources

    E-print Network

    McDonald, Kirk

    targets produce higher neutron fluxes than liquid metal targets · Neutron flux ~ neutron production is less than 30%, solid tungsten targets will generate equal or greater neutron flux than liquid metal · Liquid metal targets distribute the decay heat within the total liquid metal volume, typically ~100x

  3. Evaluation on double-wall-tube residual stress distribution of sodium-heated steam generator by neutron diffraction and numerical analysis

    SciTech Connect

    Kisohara, N.; Suzuki, H.; Akita, K.; Kasahara, N.

    2012-07-01

    A double-wall-tube is nominated for the steam generator heat transfer tube of future sodium fast reactors (SFRs) in Japan, to decrease the possibility of sodium/water reaction. The double-wall-tube consists of an inner tube and an outer tube, and they are mechanically contacted to keep the heat transfer of the interface between the inner and outer tubes by their residual stress. During long term SG operation, the contact stress at the interface gradually falls down due to stress relaxation. This phenomenon might increase the thermal resistance of the interface and degrade the tube heat transfer performance. The contact stress relaxation can be predicted by numerical analysis, and the analysis requires the data of the initial residual stress distributions in the tubes. However, unclear initial residual stress distributions prevent precious relaxation evaluation. In order to resolve this issue, a neutron diffraction method was employed to reveal the tri-axial (radius, hoop and longitudinal) initial residual stress distributions in the double-wall-tube. Strain gauges also were used to evaluate the contact stress. The measurement results were analyzed using a JAEA's structural computer code to determine the initial residual stress distributions. Based on the stress distributions, the structural computer code has predicted the transition of the relaxation and the decrease of the contact stress. The radial and longitudinal temperature distributions in the tubes were input to the structural analysis model. Since the radial thermal expansion difference between the inner (colder) and outer (hotter) tube reduces the contact stress and the tube inside steam pressure contributes to increasing it, the analytical model also took these effects into consideration. It has been conduced that the inner and outer tubes are contacted with sufficient stresses during the plant life time, and that effective heat transfer degradation dose not occur in the double-wall-tube SG. (authors)

  4. Momentum distributions in medium and heavy exotic nuclei

    E-print Network

    M. K. Gaidarov; G. Z. Krumova; P. Sarriguren; A. N. Antonov; M. V. Ivanov; E. Moya de Guerra

    2009-11-12

    We study nucleon momentum distributions of even-even isotopes of Ni, Kr, and Sn in the framework of deformed self-consistent mean-field Skyrme HF+BCS method, as well as of theoretical correlation methods based on light-front dynamics and local density approximation. The isotopic sensitivities of the calculated neutron and proton momentum distributions are investigated together with the effects of pairing and nucleon-nucleon correlations. The role of deformation on the momentum distributions in even-even Kr isotopes is discussed. For comparison, the results for the momentum distribution in nuclear matter are also presented.

  5. TU-F-BRE-07: In Vivo Neutron Detection in Patients Undergoing Stereotactic Ablative Radiotherapy (SABR) for Primary Kidney Cancer Using 6Li and 7Li Enriched TLD Pairs

    SciTech Connect

    Lonski, P; Kron, T; Franich, R; Keehan, S; Siva, S; Taylor, M

    2014-06-15

    Purpose: Stereotactic ablative radiotherapy (SABR) for primary kidney cancer often involves the use of high-energy photons combined with a large number of monitor units. While important for risk assessment, the additional neutron dose to untargeted healthy tissue is not accounted for in treatment planning. This work aims to detect out-of-field neutrons in vivo for patients undergoing SABR with high-energy (>10 MV) photons and provides preliminary estimates of neutron effective dose. Methods: 3 variations of high-sensitivity LiF:Mg,Cu,P thermoluminescent dosimeter (TLD) material, each with varying {sup 6}Li / {sup 7}Li concentrations, were used in custom-made Perspex holders for in vivo measurements. The variation in cross section for thermal neutrons between Li isotopes was exploited to distinguish neutron from photon signal. Measurements were made out-of-field for 7 patients, each undergoing 3D-conformal SABR treatment for primary kidney cancer on a Varian 21iX linear accelerator. Results: In vivo measurements show increased signal for the {sup 6}Li enriched material for patients treated with 18 MV photons. Measurements on one SABR patient treated using only 6 MV showed no difference between the 3 TLD materials. The out-of-field photon signal decreased exponentially with distance from the treatment field. The neutron signal, taken as the difference between {sup 6}Li enriched and {sup 7}Li enriched TLD response, remains almost constant up to 50 cm from the beam central axis. Estimates of neutron effective dose from preliminary TLD calibration suggest between 10 and 30 mSv per 1000 MU delivered at 18 MV for the 7 patients. Conclusion: TLD was proven to be a useful tool for the purpose of in vivo neutron detection at out-of-field locations. Further work is required to understand the relationship between TL signal and neutron dose. Dose estimates based on preliminary TLD calibration in a neutron beam suggest the additional neutron dose was <30 mSv per 1000 MU at 18 MV.

  6. Neutron dosimetry, moderated energy spectrum, and neutron capture therapy for californium-252 medical sources

    NASA Astrophysics Data System (ADS)

    Rivard, Mark Joseph

    Examination of neutron dosimetry for 252Cf has been conducted using calculative and experimental means. Monte Carlo N-Particle (MCNP) transport code was used in a distributed computing environment as a parallel virtual machine (PVM) to determine the absorbed neutron dose and neutron energy spectrum from 252Cf in a variety of clinically relevant materials. Herein, a Maxwellian spectrum was used to model the 252Cf neutron emissions within these materials. 252Cf mixed-field dosimetry of Applicator Tube (AT) type sources was measured using 1.0 and 0.05 cm3 tissue-equivalent ion chambers and a miniature GM counter. A dosimetry protocol was formulated similar that of ICRU 45. The 252Cf AT neutron dosimetry was determined in the cylindrical coordinate system formalism recommended by the AAPM Task Group 43. These results demonstrated the overwhelming dependence of dosimetry on the source geometry factor as there was no significant neutron attenuation within the source or encapsulation. Gold foils and TLDs were used to measure the thermal flux in the vicinity of 252Cf AT sources to compare with the results calculated using MCNP. As the fast neutron energy spectrum did not markedly changed at increasing distances from the AT source, neutron dosimetry results obtained with paired ion chambers using fixed sensitivity factors agreed well with MCNP results and those in the literature. Calculations of moderated 252Cf neutron energy spectrum with various loadings of 10B and 157Gd were performed, in addition to analysis of neutron capture therapy dosimetry with these isotopes. Radiological concerns such as personnel exposure and shielding of 252Cf emissions were examined. Feasibility of a high specific-activity 252Cf HDR source was investigated through radiochemical and metallurgical studies using stand-ins such as Tb, Gd and 249Cf. Issues such as capsule burst strength due to helium production for a variety of proposed HDR sources were addressed. A recommended 252Cf source strength of at least 1mg was necessary for fabrication of a 252Cf HDR source.

  7. Neutron Matter from Low to High Density

    NASA Astrophysics Data System (ADS)

    Gandolfi, Stefano; Gezerlis, Alexandros; Carlson, J.

    2015-10-01

    Neutron matter is an intriguing nuclear system with multiple connections to condensed matter and astrophysics. Considerable progress has been made over the past 20 years in exploring the properties of pure neutron fluids. We begin by reviewing research exploring the behavior of very low density neutron matter, which forms a strongly paired superfluid and is thus similar to cold Fermi atoms, although at energy scales that differ by many orders of magnitude. We then review the behavior of higher-density neutron matter, discussing research that ties the study of neutron matter to the determination of the properties of neutron-rich nuclei and neutron star crusts. Finally, we review the impact that neutron matter at even higher densities has on the mass–radius relation of neutron stars, thereby making contact with astrophysical observations.

  8. Fermionic condensation in ultracold atoms, nuclear matter and neutron stars

    E-print Network

    Luca Salasnich

    2013-08-05

    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.

  9. Breakdown of the N =8 magic number near the neutron drip line from parallel momentum distribution analyses

    NASA Astrophysics Data System (ADS)

    Shubhchintak, Chatterjee, R.

    2014-07-01

    By using two theoretical models (the postform finite range distorted wave Born approximation and the adiabatic model) we calculate the parallel momentum distribution of the charged core in the Coulomb breakup of Be isotopes on a heavy target at 100 MeV/nucleon. We show that the full width at half maxima of the parallel momentum distribution can be used to study the breakdown of the N =8 magic number away from the valley of stability.

  10. VOLUME 85, NUMBER 1 P H Y S I C A L R E V I E W L E T T E R S 3 JULY 2000 Effect of Differences in Proton and Neutron Density Distributions on Fission Barriers

    E-print Network

    Pomorski, Krzysztof

    in Proton and Neutron Density Distributions on Fission Barriers J. F. Berger Commissariat à l along the fission paths of 232 Th, 236 U, 238 U, and 240 Pu are analyzed. Significant differences paths to fission are, and to what extent fission barriers depend on such differences. This study

  11. Heat capacity of the neutron star inner crust within an extended nuclear statistical equilibrium model

    NASA Astrophysics Data System (ADS)

    Burrello, S.; Gulminelli, F.; Aymard, F.; Colonna, M.; Raduta, Ad. R.

    2015-11-01

    Background: Superfluidity in the crust is a key ingredient for the cooling properties of proto-neutron stars. Present theoretical calculations employ the quasiparticle mean-field Hartree-Fock-Bogoliubov theory with temperature-dependent occupation numbers for the quasiparticle states. Purpose: Finite temperature stellar matter is characterized by a whole distribution of different nuclear species. We want to assess the importance of this distribution on the calculation of heat capacity in the inner crust. Method: Following a recent work, the Wigner-Seitz cell is mapped into a model with cluster degrees of freedom. The finite temperature distribution is then given by a statistical collection of Wigner-Seitz cells. We additionally introduce pairing correlations in the local density BCS approximation both in the homogeneous unbound neutron component, and in the interface region between clusters and neutrons. Results: The heat capacity is calculated in the different baryonic density conditions corresponding to the inner crust, and in a temperature range varying from 100 KeV to 2 MeV. We show that accounting for the cluster distribution has a small effect at intermediate densities, but it considerably affects the heat capacity both close to the outer crust and close to the core. We additionally show that it is very important to consider the temperature evolution of the proton fraction for a quantitatively reliable estimation of the heat capacity. Conclusions: We present the first modelization of stellar matter containing at the same time a statistical distribution of clusters at finite temperature, and pairing correlations in the unbound neutron component. The effect of the nuclear distribution on the superfluid properties can be easily added in future calculations of the neutron star cooling curves. A strong influence of resonance population on the heat capacity at high temperature is observed, which deserves to be further studied within more microscopic calculations.

  12. 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

    Greenwood, L.R.; Intasorn, A.

    1989-07-01

    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.

  13. Pairing Nambu-Goldstone modes within nuclear density functional theory

    E-print Network

    Hinohara, Nobuo

    2016-01-01

    We show that the Nambu-Goldstone formalism of the broken gauge symmetry in the presence of the $T=1$ pairing condensate offers a quantitative description of the binding energy differences of open-shell superfluid nuclei. We conclude that the pairing rotational moments of inertia are excellent pairing indicators, which are free from ambiguities attributed to odd-mass systems. We offer a new, unified interpretation of the binding-energy differences traditionally viewed in the shell model picture as signatures of the valence nucleon properties. We present the first systematic analysis of the off-diagonal pairing rotational moments of inertia, and demonstrate the mixing of the neutron and proton pairing rotational modes in the ground states of even-even nuclei. Finally, we discuss the importance of mass measurements of neutron-rich nuclei for constraining the pairing energy density functional.

  14. Pair Cascades and Deathlines in Offset Magnetic Dipole Fields

    NASA Technical Reports Server (NTRS)

    Harding, Alice; Muslimov, Alex

    2010-01-01

    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.

  15. Measurement of the $\\phi^*_\\eta$ distribution of muon pairs with masses between 30 and 500 GeV in 10.4 fb$^{-1}$ of $p\\bar{p}$ collisions

    DOE PAGESBeta

    Abazov, Victor Mukhamedovich

    2015-04-06

    We present a measurement of the distribution of the variable ?*? for muon pairs with masses between 30 and 500 GeV, using the complete run II data set collected by the D0 detector at the Fermilab Tevatron proton-antiproton collider. This corresponds to an integrated luminosity of 10.4 fb–1 at ?s = 1.96 TeV. The data are corrected for detector effects and presented in bins of dimuon rapidity and mass. The variable ?*? probes the same physical effects as the Z/?* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. These are the first measurementsmore »at any collider of the ?*? distributions for dilepton masses away from the Z ? ?+?– boson mass peak. As a result, the data are compared to QCD predictions based on the resummation of multiple soft gluons.« less

  16. Measurement of the ?*? distribution of muon pairs with masses between 30 and 500 GeV in 10.4 fb-1 of pp¯ collisions

    SciTech Connect

    Abazov, Victor Mukhamedovich

    2015-04-06

    We present a measurement of the distribution of the variable ?*? for muon pairs with masses between 30 and 500 GeV, using the complete run II data set collected by the D0 detector at the Fermilab Tevatron proton-antiproton collider. This corresponds to an integrated luminosity of 10.4 fb–1 at ?s = 1.96 TeV. The data are corrected for detector effects and presented in bins of dimuon rapidity and mass. The variable ?*? probes the same physical effects as the Z/?* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. These are the first measurements at any collider of the ?*? distributions for dilepton masses away from the Z ? ?+? boson mass peak. As a result, the data are compared to QCD predictions based on the resummation of multiple soft gluons.

  17. Measurement of the secondary neutron dose distribution from the LET spectrum of recoils using the CR-39 plastic nuclear track detector in 10 MV X-ray medical radiation fields

    NASA Astrophysics Data System (ADS)

    Fujibuchi, Toshioh; Kodaira, Satoshi; Sawaguchi, Fumiya; Abe, Yasuyuki; Obara, Satoshi; Yamaguchi, Masae; Kawashima, Hajime; Kitamura, Hisashi; Kurano, Mieko; Uchihori, Yukio; Yasuda, Nakahiro; Koguchi, Yasuhiro; Nakajima, Masaru; Kitamura, Nozomi; Sato, Tomoharu

    2015-04-01

    We measured the recoil charged particles from secondary neutrons produced by the photonuclear reaction in a water phantom from a 10-MV photon beam from medical linacs. The absorbed dose and the dose equivalent were evaluated from the linear energy transfer (LET) spectrum of recoils using the CR-39 plastic nuclear track detector (PNTD) based on well-established methods in the field of space radiation dosimetry. The contributions and spatial distributions of these in the phantom on nominal photon exposures were verified as the secondary neutron dose and neutron dose equivalent. The neutron dose equivalent normalized to the photon-absorbed dose was 0.261 mSv/100 MU at source to chamber distance 90 cm. The dose equivalent at the surface gave the highest value, and was attenuated to less than 10% at 5 cm from the surface. The dose contribution of the high LET component of ?100 keV/?m increased with the depth in water, resulting in an increase of the quality factor. The CR-39 PNTD is a powerful tool that can be used to systematically measure secondary neutron dose distributions in a water phantom from an in-field to out-of-field high-intensity photon beam.

  18. Neutron Compound Refractive Prisms - DOE SBIR Phase II Final Report

    SciTech Connect

    Dr. Jay Theodore Cremer, Jr

    2011-06-25

    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.

  19. Simulated workplace neutron fields

    NASA Astrophysics Data System (ADS)

    Lacoste, V.; Taylor, G.; Röttger, S.

    2011-12-01

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

  20. Calculation of Prompt Neutron Multiplicities and Spectra for Several Actinides

    SciTech Connect

    Hambsch, Franz-Josef; Oberstedt, Stephan; Tudora, Anabella; Vladuca, Gheorghita

    2005-05-24

    The prompt fission neutron multiplicity and spectra of actinides are nuclear data of crucial importance. Based on experimental fission yield and total kinetic energy data, new calculations for the prompt neutron multiplicity and spectra for 238U(n,f), 237Np(n,f) in the incident neutron energy range up to the second chance fission threshold, for 238U(n,f), up to 50 MeV, and for 252Cf(SF) have been performed.For the first time the multi-modality of the fission process was taken into account up to the second fission chance (about 6 MeV). Additionally, for some isotopes a more realistic fission fragment residual temperature distribution as well as an anisotropy of the prompt neutron emission led to improved agreement between the calculation and experimental results. Also, the range of fission fragment pairs entering in the multiplicity and spectrum model was extended over the entire experimental fission-fragment mass range. This led to an improved version of the Los Alamos (LA) model and especially to an improved determination of the input model parameters. In addition the LA model is extended towards higher incident neutron energy, where the fission of compound nuclei formed by charged particle emission occurs.

  1. Characterisation of neutron fields at Cernavoda NPP.

    PubMed

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

    2013-04-01

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

  2. Odd-even mass difference and isospin dependent pairing interaction

    SciTech Connect

    Bertulani, C. A.; Lue, H. F.; Sagawa, H.

    2009-08-15

    The neutron and proton odd-even mass differences are studied with Hartree-Fock + BCS (HF+BCS) calculations with Skyrme interactions and an isospin dependent contact pairing interaction, which is recently derived from a microscopic nucleon-nucleon interaction. To this end, we perform HF+BCS calculations for even and odd semi-magic tin and lead isotopes together with even and odd Z isotones with N=50 and 82. The filling approximation is applied to the last unoccupied particle in odd nuclei. Comparisons with the experimental data show a clear manifestation of the isospin dependent pairing correlations in both proton and neutron pairing gaps.

  3. Characterization of neutron radiation damage in GaAs

    SciTech Connect

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

    1989-12-01

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

  4. Characterization of neutron radiation damage in GaAs

    NASA Astrophysics Data System (ADS)

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

    1989-12-01

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

  5. Characterization of neutron radiation damage in GaAs

    SciTech Connect

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

    1989-01-01

    The NJOY and MARLOWE computer codes are used to characterize neutron damage to GaAs. The fidelity of the components that affect the calculated GaAs damage is examined. The initial defect production is found to be a linear function of the damage energy. Recombination of Frenkel pairs and the distribution of vacancies introduces a non-linearity in the residual defect population with respect to the damage energy. Consideration of the defect recombinations only provides a slight improvement in the agreement between measured and calculated damage in GaAs but does indicate the areas where more work is needed. 35 refs., 9 figs., 3 tabs.

  6. Conventional BCS, unconventional BCS, and non-BCS hidden dineutron phases in neutron matter

    NASA Astrophysics Data System (ADS)

    Khodel, V. A.; Clark, J. W.; Shaginyan, V. R.; Zverev, M. V.

    2014-09-01

    The nature of pairing correlations in neutron matter is re-examined. Working within the conventional approximation in which the nn pairing interaction is provided by a realistic bare nn potential fitted to scattering data, it is demonstrated that the standard BCS theory fails in regions of neutron number density, where the pairing constant ?, depending crucially on density, has a non-BCS negative sign. We are led to propose a non-BCS scenario for pairing phenomena in neutron matter that involves the formation of a hidden dineutron state. In low-density neutron matter, where the pairing constant has the standard BCS sign, two phases organized by pairing correlations are possible and compete energetically: a conventional BCS phase and a dineutron phase. In dense neutron matter, where ? changes sign, only the dineutron phase survives and exists until the critical density for termination of pairing correlations is reached at approximately twice the neutron density in heavy atomic nuclei.

  7. Neutron Matter from Low to High Density

    E-print Network

    Stefano Gandolfi; Alexandros Gezerlis; J. Carlson

    2015-01-22

    Neutron matter is an intriguing nuclear system with multiple connections to other areas of physics. Considerable progress has been made over the last two decades in exploring the properties of pure neutron fluids. Here we begin by reviewing work done to explore the behavior of very low density neutron matter, which forms a strongly paired superfluid and is thus similar to cold Fermi atoms, though at energy scales differing by many orders of magnitude. We then increase the density, discussing work that ties the study of neutron matter with the determination of the properties of neutron-rich nuclei and neutron-star crusts. After this, we review the impact neutron matter at even higher densities has on the mass-radius relation of neutron stars, thereby making contact with astrophysical observations.

  8. Adiabatic Pair Creation in Heavy Ion and Laser Fields

    E-print Network

    Peter Pickl; Detlef Duerr

    2007-06-20

    The planned generation of lasers and heavy ion colliders renews the hope to see electron-positron pair creation in strong classical fields (so called spontaneous pair creation). This adiabatic relativistic effect has however not been described in a unified manner. We discuss here the theory of adiabatic pair creation yielding the momentum distribution of scattered pairs in overcritical fields. Our conclusion about the possibility of adiabatic pair creation is different from earlier predictions for laser fields.

  9. Calculation of two-neutron multiplicity in photonuclear reactions

    NASA Technical Reports Server (NTRS)

    Norbury, John W.; Townsend, Lawrence W.

    1990-01-01

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

  10. Calculation of two-neutron multiplicity in photonuclear reactions

    NASA Technical Reports Server (NTRS)

    Norbury, John W.; Townsend, Lawrence W.

    1989-01-01

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

  11. Electroweak bremsstrahlung from neutron-neutron scattering

    SciTech Connect

    Li Yi; Liou, M. K.; Schreiber, W. M.

    2009-09-15

    Background: Nucleon-nucleon (NN) bremsstrahlung processes NN{gamma} (nn{gamma}, np{gamma}, and pp{gamma}) have been extensively investigated. Neutrino-pair bremsstrahlung processes from nucleon-nucleon scattering NN{nu}{nu} (nn{nu}{nu}, np{nu}{nu}, and pp{nu}{nu}) have recently attracted attention in studies of neutrino emission in neutron stars. The calculated NN{nu}{nu} cross sections (or emissivities) are found to be sensitive to the two-nucleon dynamical model used in the calculations. Purpose and Method: A realistic one-boson-exchange (ROBE) model for NN interactions is used to construct the electroweak bremsstrahlung amplitudes using the well-known nucleon electromagnetic and weak interaction vertices. The constructed nn{gamma} and nn{nu}{nu} amplitudes are investigated by applying them to calculate nn{gamma} and nn{nu}{nu} cross sections, respectively. Results: (i) The 190-MeV ROBE nn{gamma} cross sections agree well with those calculated using the TuTts amplitude, but they are in disagreement with those calculated using the Low amplitude. (ii) The calculated nn{nu}{nu} cross sections using the ROBE amplitude at the neutrino-pair energy {omega} = 1 MeV are in quantitative agreement with those calculated by Timmermans et al.[Phys. Rev. C 65, 064007 (2002)], who used the leading-order term of the soft neutrino-pair bremsstrahlung amplitude. Conclusions: The nn{gamma} amplitude in the ROBE approach, which obeys the soft-photon theorem, has a predictive power similar to that of the TuTts amplitude. The nn{nu}{nu} amplitude in the ROBE approach, which is consistent with the soft neutrino-pair bremsstrahlung theorem, has a predictive power similar to that of the soft neutrino-pair bremsstrahlung amplitude of Timmermans et al. in the low neutrino-pair energy region.

  12. Neutron skins and neutron stars

    SciTech Connect

    Piekarewicz, J.

    2013-11-07

    The neutron-skin thickness of heavy nuclei provides a fundamental link to the equation of state of neutron-rich matter, and hence to the properties of neutron stars. The Lead Radius Experiment ('PREX') at Jefferson Laboratory has recently provided the first model-independence evidence on the existence of a neutron-rich skin in {sup 208}Pb. In this contribution we examine how the increased accuracy in the determination of neutron skins expected from the commissioning of intense polarized electron beams may impact the physics of neutron stars.

  13. A Complete Sample of Galaxy Pairs

    NASA Astrophysics Data System (ADS)

    Nordgren, T. E.; Chengalur, J. N.; Salpeter, E. E.; Terzian, Y.

    1996-12-01

    HI velocities have been obtained for 132 galaxy pairs chosen from the CfA and SSRS galaxy redshift catalogs. The 21cm HI observations have accuracies of +/- 5 km/s. Selection criteria, including a maximum projected separation of 1.5 Mpc, a maximum velocity difference of 250 km/s and a maximum number density of surrounding galaxies were applied to the catalogs and the observed sample is complete. No consideration has been given in the selection of these pairs towards tidal morphology or similarity in size or magnitude between pair members. We find evidence for bound galaxy pairs with projected separations as great as a megaparsec and are able to gauge the effects of various isolation requirements on the tidal morphology of close galaxy pairs and the distribution of velocity differences. We find no indication of galaxy pair redshift quantization.

  14. Performance evaluation of the source description of the THOR BNCT epithermal neutron beam.

    PubMed

    Liu, Yuan-Hao; Tsai, Pi-En; Yu, Hui-Ting; Lin, Yi-Chun; Huang, Yu-Shiang; Huang, Chun-Kai; Liu, Yen-Wan Hsueh; Liu, Hong-Ming; Jiang, Shiang-Huei

    2011-12-01

    This paper aims to evaluate the performance of the source description of the THOR BNCT beam via different measurement techniques in different phantoms. The measurement included (1) the absolute reaction rate measurement of a set of triple activation foils, (2) the neutron and gamma-ray dose rates measured using the paired ionization chamber method, and (3) the relative reaction rate distributions obtained using the indirect neutron radiography. Three source descriptions, THOR-Y09, surface source file RSSA, and THOR-50C, were tested. The comparison results concluded that THOR-Y09 is a well-tested source description not only for neutron components, but also for gamma-ray component. PMID:21570855

  15. Quark matter in neutron stars

    E-print Network

    Mark G. Alford

    2009-09-18

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

  16. Distribution of vortices in Nb/Al multilayers studied by spin-polarized neutron reflectivity and magnetization

    NASA Astrophysics Data System (ADS)

    Han, S.-W.; Farmer, J.; Miceli, P. F.; Felcher, G.; Goyette, R.; Kiehne, G. T.; Ketterson, J. B.

    2003-08-01

    We present SPNR and DC magnetization studies of non-uniformly distributed vortices in Nb/Al multilayers for fields applied near-parallel to the film surface. Peaks are observed in the M- H curves that are shown to correspond to vortex row-transitions and the field values of the transitions agree well with free energy calculations. An additional peak is observed at an applied field smaller than the first row-transition field and this is shown to arise from the lower critical field parallel to the surface. Demagnetization effects are discussed. SPNR measurements performed at low field give the London penetration length and measurements in the mixed state are consistent with a single row of vortices residing in the film center, but with positional fluctuations amounting to 1/4 of the film thickness. It is also shown that cycling the applied field leads to a surface-induced reorientation of the vortex magnetic field, which points perpendicular to the surface in zero field.

  17. A slow neutron polarimeter for the measurement of parity-odd neutron rotary power

    SciTech Connect

    Snow, W. M.; Anderson, E.; Bass, T. D.; Dawkins, J. M.; Fry, J.; Haddock, C.; Horton, J. C.; Luo, D.; Micherdzinska, A. M.; Walbridge, S. B.; Barrón-Palos, L.; Maldonado-Velázquez, M.; Bass, C. D.; Crawford, B. E.; Crawford, C.; Esposito, D.; Gardiner, H.; Gan, K.; Heckel, B. R.; Swanson, H. E. [University of Washington and others

    2015-05-15

    We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutron optical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable of measuring a neutron rotary power of d?/dz = 1 × 10{sup ?7} rad/m.

  18. A slow neutron polarimeter for the measurement of parity-odd neutron rotary power.

    PubMed

    Snow, W M; Anderson, E; Barrón-Palos, L; Bass, C D; Bass, T D; Crawford, B E; Crawford, C; Dawkins, J M; Esposito, D; Fry, J; Gardiner, H; Gan, K; Haddock, C; Heckel, B R; Holley, A T; Horton, J C; Huffer, C; Lieffers, J; Luo, D; Maldonado-Velázquez, M; Markoff, D M; Micherdzinska, A M; Mumm, H P; Nico, J S; Sarsour, M; Santra, S; Sharapov, E I; Swanson, H E; Walbridge, S B; Zhumabekova, V

    2015-05-01

    We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutron optical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable of measuring a neutron rotary power of d?/dz = 1 × 10(-7) rad/m. PMID:26026552

  19. Superfluid properties of the inner crust of neutron stars

    NASA Astrophysics Data System (ADS)

    Pastore, Alessandro; Baroni, Simone; Losa, Cristina

    2011-12-01

    We investigated the superfluid properties of the inner crust of neutron stars, solving the Hartree-Fock-Bogoliubov equations in spherical Wigner-Seitz cells. Using realistic two-body interactions in the pairing channel, we studied in detail the Cooper-pair and the pairing-field spatial properties, together with the effect of the proton clusters on the neutron pairing gap. Calculations with effective pairing interactions are also presented, showing significant discrepancies with the results obtained with realistic pairing forces. At variance with recent studies on finite nuclei, the neutron coherence length is found to depend on the strength of the pairing interaction, even inside the nucleus. We also show that the spherical Wigner-Seitz approximation breaks down in the innermost regions of the inner crust, already at baryonic densities ?b?8×10+13 g/cm3.

  20. Neutron guide

    DOEpatents

    Greene, Geoffrey L. (Los Alamos, NM)

    1999-01-01

    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.

  1. A number projected model with generalized pairing interaction

    E-print Network

    W. Satula; R. Wyss

    2000-04-17

    A mean-field model with a generalized pairing interaction that accounts for neutron-proton pairing is presented. Both the BCS as well as number-projected solutions of the model are presented. For the latter case the Lipkin-Nogami projection technique was extended to encompass the case of non-separable proton-neutron systems. The influence of the projection on various pairing phases is discussed. In particular, it is shown that number-projection allows for mixing of different pairing phases but, simultanously, acts destructively on the proton-neutron correlations. The basic implications of proton-neutron pairing correlations on nuclear masses are discussed. It is shown that these correlations may provide a natural microscopic explanation of the Wigner energy lacking in mean-field models. A possible phase transition from isovector to isoscalar pairing condensate at high angular momenta is also discussed. In particular predictions for the dynamical moments of inertia for the superdeformed band in $^{88}$Ru are given.

  2. Spontaneous Pair Creation Revisited

    E-print Network

    P. Pickl; D. Duerr

    2006-02-17

    Recently the so called Spontaneous Pair Creation of electron positron pairs in a strong external field has been rigorously established. We give here the heuristic core of the proof, since the results differ from those given in earlier works.

  3. On the pairing effects in triaxial nuclei

    SciTech Connect

    Oudih, M. R.; Fellah, M.; Allal, N. H.

    2014-03-05

    Triaxial deformation effect on the pairing correlations is studied in the framework of the Skyrme Hartree-Fock-Bogoliubov theory. Quantities such as binding energy, gap parameter and particle-number fluctuation are considered in neutron-rich Mo isotopes. The results are compared with those of axially symmetric calculation and with available experimental data. The role played by the particle-number projection is outlined.

  4. Contragredient supersymmetric pairs

    NASA Astrophysics Data System (ADS)

    Chuah, Meng-Kiat

    2013-09-01

    The symmetric pairs of complex semisimple Lie algebras can be characterized by commuting involutions. We present its analogue on the contragredient Lie superalgebras, so that their symmetric pairs correspond to some commuting automorphisms. As an application, we classify the symmetric pairs of the exceptional Lie superalgebras F(4) and G(3).

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

    SciTech Connect

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

    2014-10-01

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

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

    SciTech Connect

    Murphy, T. J.

    2014-07-15

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

  7. Observation of Neutron Skyshine from an Accelerator Based Neutron Source

    NASA Astrophysics Data System (ADS)

    Franklyn, C. B.

    2011-12-01

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

  8. Observation of Neutron Skyshine from an Accelerator Based Neutron Source

    SciTech Connect

    Franklyn, C. B.

    2011-12-13

    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.

  9. Ion pair receptors†

    PubMed Central

    Kim, Sung Kuk

    2010-01-01

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

  10. 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)

    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

    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.

  11. Neutron Radiography

    NASA Astrophysics Data System (ADS)

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

    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.

  12. "Influence Method" applied to measure a moderated neutron flux

    NASA Astrophysics Data System (ADS)

    Rios, I. J.; Mayer, R. E.

    2016-01-01

    The "Influence Method" is conceived for the absolute determination of a nuclear particle flux in the absence of known detector efficiency. This method exploits the influence of the presence of one detector, in the count rate of another detector when they are placed one behind the other and define statistical estimators for the absolute number of incident particles and for the efficiency. The method and its detailed mathematical description were recently published (Rios and Mayer, 2015 [1]). In this article we apply it to the measurement of the moderated neutron flux produced by an 241AmBe neutron source surrounded by a light water sphere, employing a pair of 3He detectors. For this purpose, the method is extended for its application where particles arriving at the detector obey a Poisson distribution and also, for the case when efficiency is not constant over the energy spectrum of interest. Experimental distributions and derived parameters are compared with theoretical predictions of the method and implications concerning the potential application to the absolute calibration of neutron sources are considered.

  13. Antipodal hotspot pairs on the earth

    NASA Technical Reports Server (NTRS)

    Rampino, Michael R.; Caldeira, Ken

    1992-01-01

    The results of statistical analyses performed on three published hotspot distributions suggest that significantly more hotspots occur as nearly antipodal pairs than is anticipated from a random distribution, or from their association with geoid highs and divergent plate margins. The observed number of antipodal hotspot pairs depends on the maximum allowable deviation from exact antipodality. At a maximum deviation of not greater than 700 km, 26 to 37 percent of hotspots form antipodal pairs in the published lists examined here, significantly more than would be expected from the general hotspot distribution. Two possible mechanisms that might create such a distribution include: (1) symmetry in the generation of mantle plumes, and (2) melting related to antipodal focusing of seismic energy from large-body impacts.

  14. Isospin-dependent pairing interaction from nuclear matter calculations

    NASA Astrophysics Data System (ADS)

    Zhang, S. S.; Cao, L. G.; Lombardo, U.; Zhao, E. G.; Zhou, S. G.

    2010-04-01

    The isospin dependence of the effective pairing interaction is discussed on the basis of the Bardeen, Cooper, and Schrieffer theory of superfluid asymmetric nuclear matter. It is shown that the energy gap, calculated within the mean field approximation in the range from symmetric nuclear matter to pure neutron matter, is not linearly dependent on the symmetry parameter owing to the nonlinear structure of the gap equation. Moreover, the construction of a zero-range effective pairing interaction compatible with the neutron and proton gaps in homogeneous matter is investigated, along with some recent proposals of isospin dependence tested on the nuclear data table.

  15. Pair Winds in Schwarzschild Spacetime with Application to Strange Stars

    E-print Network

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

    2007-01-09

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

  16. Isospin-dependent pairing interaction from nuclear matter calculations

    SciTech Connect

    Zhang, S. S.; Cao, L. G.; Lombardo, U.; Zhao, E. G.; Zhou, S. G.

    2010-04-15

    The isospin dependence of the effective pairing interaction is discussed on the basis of the Bardeen, Cooper, and Schrieffer theory of superfluid asymmetric nuclear matter. It is shown that the energy gap, calculated within the mean field approximation in the range from symmetric nuclear matter to pure neutron matter, is not linearly dependent on the symmetry parameter owing to the nonlinear structure of the gap equation. Moreover, the construction of a zero-range effective pairing interaction compatible with the neutron and proton gaps in homogeneous matter is investigated, along with some recent proposals of isospin dependence tested on the nuclear data table.

  17. Probing mixed-spin pairing in heavy nuclei

    E-print Network

    Bulthuis, Brendan

    2015-01-01

    The nature of the nuclear pairing condensate is an active topic of investigation, especially as regards its neutron-proton versus identical-particle character, which manifests as the difference between spin-singlet and spin-triplet pairing. In this work, we probe the recently proposed mixed-spin pairing condensates, using a phenomenological Hamiltonian and Hartree-Fock-Bogoliubov theory along with the gradient method. In addition to improving the solution of the many-body problem, we have calculated a series of physical quantities and examined the robustness of the mixed-spin pairing state as the input Hamiltonian is modified. Overall, we find that even though the mixed-spin correlation energy is suppressed in comparison to earlier work, the new pairing behavior persists. We also discuss the possibility of directly probing the mixed-spin pairing phase.

  18. Probing mixed-spin pairing in heavy nuclei

    E-print Network

    Brendan Bulthuis; Alexandros Gezerlis

    2015-09-14

    The nature of the nuclear pairing condensate is an active topic of investigation, especially as regards its neutron-proton versus identical-particle character, which manifests as the difference between spin-singlet and spin-triplet pairing. In this work, we probe the recently proposed mixed-spin pairing condensates, using a phenomenological Hamiltonian and Hartree-Fock-Bogoliubov theory along with the gradient method. In addition to improving the solution of the many-body problem, we have calculated a series of physical quantities and examined the robustness of the mixed-spin pairing state as the input Hamiltonian is modified. Overall, we find that even though the mixed-spin correlation energy is suppressed in comparison to earlier work, the new pairing behavior persists. We also discuss the possibility of directly probing the mixed-spin pairing phase.

  19. Neutron detector

    DOEpatents

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

    2011-04-05

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

  20. Centromere Associations in Meiotic Chromosome Pairing.

    PubMed

    Da Ines, Olivier; White, Charles I

    2015-11-23

    Production of gametes of halved ploidy for sexual reproduction requires a specialized cell division called meiosis. The fusion of two gametes restores the original ploidy in the new generation, and meiosis thus stabilizes ploidy across generations. To ensure balanced distribution of chromosomes, pairs of homologous chromosomes (homologs) must recognize each other and pair in the first meiotic division. Recombination plays a key role in this in most studied species, but it is not the only actor and particular chromosomal regions are known to facilitate the meiotic pairing of homologs. In this review, we focus on the roles of centromeres and in particular on the clustering and pairwise associations of nonhomologous centromeres that precede stable pairing between homologs. Although details vary from species to species, it is becoming increasingly clear that these associations play active roles in the meiotic chromosome pairing process, analogous to those of the telomere bouquet. PMID:26421510

  1. Matched-pair classification

    SciTech Connect

    Theiler, James P

    2009-01-01

    Following an analogous distinction in statistical hypothesis testing, we investigate variants of machine learning where the training set comes in matched pairs. We demonstrate that even conventional classifiers can exhibit improved performance when the input data has a matched-pair structure. Online algorithms, in particular, converge quicker when the data is presented in pairs. In some scenarios (such as the weak signal detection problem), matched pairs can be generated from independent samples, with the effect not only doubling the nominal size of the training set, but of providing the structure that leads to better learning. A family of 'dipole' algorithms is introduced that explicitly takes advantage of matched-pair structure in the input data and leads to further performance gains. Finally, we illustrate the application of matched-pair learning to chemical plume detection in hyperspectral imagery.

  2. Pairing effects in low density domain of nuclear matter

    E-print Network

    A. A. Isayev; S. I. Bastrukov; J. Yang

    2004-12-26

    Using equations, governing np pairing correlations in S=1, T=0 pairing channel (PRC 63 (2001) 021304(R)), it is shown that at low densities equations for the energy gap in the spectrum of quasiparticles and chemical potentials of protons and neutrons allow solutions with negative chemical potential. This corresponds to appearance of Bose--Einstein condensate (BEC) of deuterons in low density region of nuclear matter.

  3. Monitoring the hydrogen distribution in poly(2,5-benzimidazole)-based (ABPBI) membranes in operating high-temperature polymer electrolyte fuel cells by using H-D contrast neutron imaging

    NASA Astrophysics Data System (ADS)

    Arlt, Tobias; Lüke, Wiebke; Kardjilov, Nikolay; Banhart, John; Lehnert, Werner; Manke, Ingo

    2015-12-01

    Neutron imaging in combination with the deuterium contrast method was used to analyze the hydrogen distribution and exchange processes in a high-temperature polymer electrolyte fuel cell in-operando. While operating the cell at steady state conditions at 200 mA cm-2 and ?an/ca = 2/2, changeovers of the anode feed gases between hydrogen (H2) and deuterium were analyzed by neutron radiography. Proton-deuterium exchange times and progresses were studied in-operando. The exchange of protons by deuterons proceeds much faster (approx. 108-138 s) than the exchange of deuterons by protons (approx. 144-174 s), whereby the exchange takes place first near the gas inlet while a delayed onset was observed near the outlet. We can explain this effect by the different diffusion coefficients and atomic masses of deuterium and hydrogen and the operating conditions of the cell.

  4. Paired watershed study design

    SciTech Connect

    Clausen, J.C.; Spooner, J.

    1993-09-01

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

  5. Charge, neutron, and weak size of the atomic nucleus

    E-print Network

    G. Hagen; A. Ekström; C. Forssén; G. R. Jansen; W. Nazarewicz; T. Papenbrock; K. A. Wendt; S. Bacca; N. Barnea; B. Carlsson; C. Drischler; K. Hebeler; M. Hjorth-Jensen; M. Miorelli; G. Orlandini; A. Schwenk; J. Simonis

    2015-09-23

    What is the size of the atomic nucleus? This deceivably simple question is difficult to answer. While the electric charge distributions in atomic nuclei were measured accurately already half a century ago, our knowledge of the distribution of neutrons is still deficient. In addition to constraining the size of atomic nuclei, the neutron distribution also impacts the number of nuclei that can exist and the size of neutron stars. We present an ab initio calculation of the neutron distribution of the neutron-rich nucleus $^{48}$Ca. We show that the neutron skin (difference between radii of neutron and proton distributions) is significantly smaller than previously thought. We also make predictions for the electric dipole polarizability and the weak form factor; both quantities are currently targeted by precision measurements. Based on ab initio results for $^{48}$Ca, we provide a constraint on the size of a neutron star.

  6. In-situ neutron scattering study of crystallization in a Zr-based bulk metallic glass

    SciTech Connect

    Ma, Dong; Stoica, Alexandru Dan; Wang, Xun-Li; Lu, Zhao Ping; Proffen, Thomas E

    2010-01-01

    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 separating the crystalline peaks from the scattering of the amorphous phase, 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 an exponent of 4.0?.3, indicating a three-dimensional nucleation and growth process distinctly different from conventional phase transformations in crystalline alloys. 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.

  7. ? -decay properties of neutron-rich Ge, Se, Kr, Sr, Ru, and Pd isotopes from deformed quasiparticle random-phase approximation

    NASA Astrophysics Data System (ADS)

    Sarriguren, P.

    2015-04-01

    ? -decay properties of even- and odd-A neutron-rich Ge, Se, Kr, Sr, Ru, and Pd isotopes involved in the astrophysical rapid neutron capture process are studied within a deformed proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme-Hartree-Fock calculations with pairing correlations. Residual interactions in the particle-hole and particle-particle channels are also included in the formalism. The isotopic evolution of the various nuclear equilibrium shapes and the corresponding charge radii are investigated in all the isotopic chains. The energy distributions of the Gamow-Teller strength as well as the ? -decay half-lives are discussed and compared with the available experimental information. It is shown that nuclear deformation plays a significant role in the description of the decay properties in this mass region. Reliable predictions of the strength distributions are essential to evaluate decay rates in astrophysical scenarios.

  8. Compact ion chamber based neutron detector

    DOEpatents

    Derzon, Mark S.; Galambos, Paul C.; Renzi, Ronald F.

    2015-10-27

    A directional neutron detector has an ion chamber formed in a dielectric material; a signal electrode and a ground electrode formed in the ion chamber; a neutron absorbing material filling the ion chamber; readout circuitry which is electrically coupled to the signal and ground electrodes; and a signal processor electrically coupled to the readout circuitry. The ion chamber has a pair of substantially planar electrode surfaces. The chamber pressure of the neutron absorbing material is selected such that the reaction particle ion trail length for neutrons absorbed by the neutron absorbing material is equal to or less than the distance between the electrode surfaces. The signal processor is adapted to determine a path angle for each absorbed neutron based on the rise time of the corresponding pulse in a time-varying detector signal.

  9. Compact ion chamber based neutron detector

    DOEpatents

    Derzon, Mark S; Galambos, Paul C; Renzi, Ronald F

    2015-11-05

    A directional neutron detector has an ion chamber formed in a dielectric material; a signal electrode and a ground electrode formed in the ion chamber; a neutron absorbing material filling the ion chamber; readout circuitry which is electrically coupled to the signal and ground electrodes; and a signal processor electrically coupled to the readout circuitry. The ion chamber has a pair of substantially planar electrode surfaces. The chamber pressure of the neutron absorbing material is selected such that the reaction particle ion trail length for neutrons absorbed by the neutron absorbing material is equal to or less than the distance between the electrode surfaces. The signal processor is adapted to determine a path angle for each absorbed neutron based on the rise time of the corresponding pulse in a time-varying detector signal.

  10. Cold neutrons trapped in external fields.

    PubMed

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

    2011-01-01

    The properties of inhomogeneous neutron matter are crucial to the physics of neutron-rich nuclei and the crust of neutron stars. Advances in computational techniques now allow us to accurately determine the binding energies and densities of many neutrons interacting via realistic microscopic interactions and confined in external fields. We perform calculations for different external fields and across several shells to place important constraints on inhomogeneous neutron matter, and hence the large isospin limit of the nuclear energy density functionals that are used to predict properties of heavy nuclei and neutron star crusts. We find important differences between microscopic calculations and current density functionals; in particular, the isovector gradient terms are significantly more repulsive than in traditional models, and the spin-orbit and pairing forces are comparatively weaker. PMID:21231734

  11. LOW TEMPERATURE PHYSICS The effect of neutron and gamma radiation on

    E-print Network

    McDonald, Kirk

    LOW TEMPERATURE PHYSICS The effect of neutron and gamma radiation on magnet components Michael, iterlaminar shear strength, fatigue behavior ­ Gas evolution · Conclusions #12;LOW TEMPERATURE PHYSICS Fission;LOW TEMPERATURE PHYSICS Neutron Energy Distribution Intense Pulsed Neutron Source, Argonne National

  12. Element-specific structure of materials with intrinsic disorder by high-energy resonant x-ray diffraction and differential atomic pair-distribution functions: A study of PtPd nanosized catalysts

    NASA Astrophysics Data System (ADS)

    Petkov, V.; Shastri, S. D.

    2010-04-01

    We demonstrate how high-energy resonant x-ray diffraction (XRD) and differential atomic-pair-distribution function (PDF) analysis can be used to characterize the atomic ordering in materials of limited structural coherence with both excellent spatial resolution and element specificity. First we prove that this experimental approach is feasible by probing the K -absorption edge of Au(˜81keV) atoms in chemically ordered and disordered bulk Cu3Au alloys. The resulting Au-differential PDFs show very clearly the different ways Au atoms are known to occupy the sites of otherwise identical cubic lattices of those materials. Next we apply it to a more complex material: PtPd alloy and core-shell nanosized (˜2-4nm) particles by probing the K -absorption edge of Pt(˜78keV) . The resulting Pt-differential atomic PDFs reveal how exactly the atomic ordering of catalytically active Pt atoms is affected by the nanoparticles’ design, thus providing a firm structural basis for understanding their properties. The work is a step forward in expanding the limits of applicability of nontraditional XRD to the rapidly growing field of materials of unusual structural complexity.

  13. Unified description of astrophysical properties of neutron stars independent of the equation of state

    NASA Astrophysics Data System (ADS)

    Pappas, George

    2015-12-01

    In recent years, a lot of work was done that has revealed some very interesting properties of neutron stars. One can relate the first few multipole moments of a neutron star, or quantities that can be derived from them, with relations that are independent of the equation of state (EoS). This is a very significant result that has great implications for the description of neutron stars and in particular for the description of the spacetime around them. Additionally, it was recently shown that there is a four-parameter analytic spacetime, known as the two-soliton spacetime, which can accurately capture the properties of the geometry around neutron stars. This allows for the possibility of describing in a unified formalism the astrophysically relevant properties of the spacetime around a neutron star independently of the particulars of the EoS for the matter of the star. More precisely, the description of these astrophysical properties is done using an EoS omniscient spacetime that can describe the exterior of any neutron star. In the present work, we investigate properties such as the location of the innermost stable circular orbit RISCO (or the surface of the star when the latter overcomes the former), the various frequencies of perturbed circular equatorial geodesics, the efficiency of an accretion disc, its temperature distribution, and other properties associated with the emitted radiation from the disc, in a way that holds for all possible choices of a realistic EoS for the neutron star. Furthermore, we provide proof of principle that if one were to measure the right combinations of pairs of these properties, with the additional knowledge of the mass of the neutron star, one could determine the EoS of the star.

  14. Neutron tubes

    DOEpatents

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

    2008-03-11

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

  15. Neutron gamma fraction imaging: Detection, location and identification of neutron sources

    NASA Astrophysics Data System (ADS)

    Gamage, K. A. A.; Taylor, G. C.

    2015-07-01

    In this paper imaging of neutron sources and identification and separation of a neutron source from another neutron source is described. The system is based upon organic liquid scintillator detector, tungsten collimator, bespoke fast digitiser and adjustable equatorial mount. Three environments have been investigated with this setup corresponding to an AmBe neutron source, a 252Cf neutron source and both sources together separated in space. In each case, events are detected, digitised, discriminated and radiation images plotted corresponding to the area investigated. The visualised neutron count distributions clearly locate the neutron source and, relative gamma to neutron (or neutron to gamma) fraction images aid in discriminating AmBe sources from 252Cf source. The measurements were performed in the low scatter facility of the National Physical Laboratory, Teddington, UK.

  16. Detectors for time-of-flight fast-neutron radiography 1. Neutron-counting gas detector

    NASA Astrophysics Data System (ADS)

    Dangendorf, V.; Laczko, G.; Reginatto, M.; Vartsky, D.; Goldberg, M.; Mor, I.; Breskin, A.; Chechik, R.

    2005-04-01

    One of our two methods for fast-neutron imaging with spectrometric capability is presented here. It is a neutron-counting technique based on a hydrogenous neutron converter coupled to Gaseous Electron Multipliers (GEM). The principles of the detection techniques and the optimization of the converter, electron amplification and the readout are described. Evaluation of the properties is derived from a experiment in a pulsed neutron beam of spectral distribution between 2 and 10 MeV.

  17. Critical Schwinger pair production

    E-print Network

    Gies, Holger

    2015-01-01

    We investigate Schwinger pair production in spatially inhomogeneous electric backgrounds. A critical point for the onset of pair production can be approached by fields that marginally provide sufficient electrostatic energy for an off-shell long-range electron-positron fluctuation to become a real pair. Close to this critical point, we observe features of universality which are analogous to continuous phase transitions in critical phenomena with the pair-production rate serving as an order parameter: electric backgrounds can be subdivided into universality classes and the onset of pair production exhibits characteristic scaling laws. An appropriate design of the electric background field can interpolate between power-law scaling, essential BKT-type scaling and a power-law scaling with log corrections. The corresponding critical exponents only depend on the large-scale features of the electric background, whereas the microscopic details of the background play the role of irrelevant perturbations not affecting ...

  18. Critical Schwinger pair production

    E-print Network

    Holger Gies; Greger Torgrimsson

    2015-07-28

    We investigate Schwinger pair production in spatially inhomogeneous electric backgrounds. A critical point for the onset of pair production can be approached by fields that marginally provide sufficient electrostatic energy for an off-shell long-range electron-positron fluctuation to become a real pair. Close to this critical point, we observe features of universality which are analogous to continuous phase transitions in critical phenomena with the pair-production rate serving as an order parameter: electric backgrounds can be subdivided into universality classes and the onset of pair production exhibits characteristic scaling laws. An appropriate design of the electric background field can interpolate between power-law scaling, essential BKT-type scaling and a power-law scaling with log corrections. The corresponding critical exponents only depend on the large-scale features of the electric background, whereas the microscopic details of the background play the role of irrelevant perturbations not affecting criticality.

  19. Cooper Pairs in Insulators?!

    ScienceCinema

    James Valles

    2010-01-08

    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. 

  20. Dynamics of Binary Galaxies. I. Wide Pairs

    NASA Astrophysics Data System (ADS)

    Chengalur, Jayaram N.; Salpeter, E. E.; Terzian, Yervant

    1993-12-01

    We analyze pairs of galaxies selected from the CfA magnitude limited and SSRS diameter-limited redshift catalogs. The pairs are chosen only from regions of low galaxy density and have projected separations of up to 1.0 Mpc. This is almost an order of magnitude larger than the typical projected separations of samples of binary galaxies used in earlier studies. Accurate H I velocities for these pairs were obtained at both Arecibo and Parkes Observatories, and we tabulate these new velocities along with total H I flux and other quantities of interest. The velocity measurements are very homogeneous, and we estimate the typical internal error in the measured systemic velocity to be under 5 km s-1. The velocity difference distribution f(?V) for our sample of isolated wide pairs of galaxies decreases monotonically with increasing velocity difference A V. In particular, we do not find a peak near 70 km s-1 as seen in earlier, more compact samples. This tends to confirm the suggestion of Schneider & Salpeter (1992) that the nonmonotonicity of earlier samples of binary galaxies is a consequence of a selection bias. The distribution of ?V for galaxy pairs in low-density regions is found to have two components, a peak around zero and a tail extending to larger velocity differences. The tail of the ?V distribution has a strong dependence on the degree of isolation. As the stringency of the isolation criterion is increased, pairs are preferentially lost from the tail of the distribution. The width of the peak around zero, on the other hand, has little dependence on the isolation criterion. For our sample of isolated pairs of galaxies, the median of the velocity differences is ˜30 km s-1. The velocity difference of the galaxy pairs decreases with increasing projected separation. The characteristic 30 km s 1 velocity difference for our isolated sample is less than half the typical 70 km s-1 velocity difference found in previous studies using relatively compact pairs. We thus confirm the suggestion of Charlton & Salpeter (1991) that there exist physically associated galaxy pairs even at separations as large as 1.0 Mpc. Unlike earlier samples of binary galaxies, the crossing time rp/?V for our pairs is comparable to the Hubble time, so unique mass derivations are not possible. We nonetheless compute the dynamical mass of the galaxies as given by a variety of estimators, to get values of up to a few times 1012 Msun. This is consistent with both dynamical mass estimates for the Local Group, and also the recent mass estimates of spiral galaxies from the dynamics of faint satellites by Zaritsky et al. (1993).

  1. Study on the influence of the B4C layer thickness on the neutron flux and energy distribution shape in multi-electrode ionisation chamber.

    PubMed

    Tymi?ska, K; Maciak, M; O?ko, J; Tulik, P; Zielczy?ski, M; Gryzi?ski, M A

    2014-10-01

    A model of a multi-electrode ionisation chamber, with polypropylene electrodes coated with a thin layer of B4C was created within Monte Carlo N-Particle Transport Code (MCNPX) and Fluktuierende Kaskade (FLUKA) codes. The influence of the layer thickness on neutron absorption in B4C and on the neutron spectra in the consecutive intra-electrode gas volumes has been studied using the MCNPX and FLUKA codes. The results will be used for designing the new type of the ionisation chamber. PMID:24729596

  2. Development of pulsed neutron uranium logging instrument

    SciTech Connect

    Wang, Xin-guang; Liu, Dan; Zhang, Feng

    2015-03-15

    This article introduces a development of pulsed neutron uranium logging instrument. By analyzing the temporal distribution of epithermal neutrons generated from the thermal fission of {sup 235}U, we propose a new method with a uranium-bearing index to calculate the uranium content in the formation. An instrument employing a D-T neutron generator and two epithermal neutron detectors has been developed. The logging response is studied using Monte Carlo simulation and experiments in calibration wells. The simulation and experimental results show that the uranium-bearing index is linearly correlated with the uranium content, and the porosity and thermal neutron lifetime of the formation can be acquired simultaneously.

  3. Pair contact process with diffusion of pairs

    NASA Astrophysics Data System (ADS)

    Santos, F. L.; Dickman, Ronald; Fulco, U. L.

    2011-03-01

    The pair contact process (PCP) is a nonequilibrium stochastic model which, like the basic contact process (CP), exhibits a phase transition to an absorbing state. The two models belong to the directed percolation (DP) universality class, despite the fact that the PCP possesses infinitely many absorbing configurations whereas the CP has but one. The critical behavior of the PCP with hopping by particles (PCPD) is as yet unclear. Here we study a version of the PCP in which nearest-neighbor particle pairs can hop but individual particles cannot. Using quasistationary simulations for three values of the diffusion probability (D = 0.1, 0.5 and 0.9), we find convincing evidence of DP-like critical behavior.

  4. Design and Simulation of a Boron-loaded Neutron Spectrometer 

    E-print Network

    Martin, Thomas

    2012-10-19

    The measurement of the distribution of kinetic energy carried by neutron particles is of interest to the health physics and radiation protection industry. Neutron particle spectral fluence is essential to the calculation of absorbed dose, equivalent...

  5. Optimization of neutron source

    SciTech Connect

    Hooper, E.B.

    1993-11-09

    I consider here the optimization of the two component neutron source, allowing beam species and energy to vary. A simple model is developed, based on the earlier publications, that permits the optimum to be obtained simply. The two component plasma, with one species of hot ion (D{sup +} or T{sup +}) and the complementary species of cold ion, is easy to analyze in the case of a spatially uniform cold plasma, as to good approximation the total number of hot ions is important but not their spatial distribution. Consequently, the optimization can ignore spatial effects. The problem of a plasma with both types of hot ions and cold ions is rather more difficult, as the neutron production by hot-hot interactions is sensitive to their spatial distributions. Consequently, consideration of this problem will be delayed to a future memorandum. The basic model is that used in the published articles on the two-component, beam-plasma mirror source. I integrate the Fokker-Planck equation analytically, obtaining good agreement with previous numerical results. This simplifies the optimization, by providing a functional form for the neutron production. The primary result is expressed in terms of the power efficiency: watts of neutrons/watts of primary power. The latter includes the positive ion neutralization efficiency. At 150 keV, the present model obtains an efficiency of 0.66%, compared with 0.53% of the earlier calculation.

  6. The heat capacity of the neutron star inner crust within an extended NSE model

    E-print Network

    S. Burrello; F. Gulminelli; F. Aymard; M. Colonna; Ad. R. Raduta

    2015-11-01

    Superfluidity in the crust is a key ingredient for the cooling properties of proto-neutron stars. Present theoretical calculations employ the quasi-particle mean-field Hartree-Fock-Bogoliubov theory with temperature dependent occupation numbers for the quasi-particle states. Finite temperature stellar matter is characterized by a whole distribution of different nuclear species. We want to assess the importance of this distribution on the calculation of heat capacity in the inner crust. Following a recent work, the Wigner-Seitz cell is mapped into a model with cluster degrees of freedom. The finite temperature distribution is then given by a statistical collection of Wigner-Seitz cells. We additionally introduce pairing correlations in the local density BCS approximation both in the homogeneous unbound neutron component, and in the interface region between clusters and neutrons. The heat capacity is calculated in the different baryonic density conditions corresponding to the inner crust, and in a temperature range varying from 100 KeV to 2 MeV. We show that accounting for the cluster distribution has a small effect at intermediate densities, but it considerably affects the heat capacity both close to the outer crust and close to the core. We additionally show that it is very important to consider the temperature evolution of the proton fraction for a quantitatively reliable estimation of the heat capacity.

  7. Properties of Pairing Correlations in Infinite Nuclear Matter

    E-print Network

    O. Elgaroy; M. Hjorth-Jensen

    1997-10-26

    We discuss various properties of singlet S pairing in neutron and nuclear matter in terms of the bare nuclon-nucleon interaction. Relations to the NN phase shifts are discussed, as well as various properties of the BCS wave function and the coherence length for fermion superfluids in infinite matter.

  8. J=0, J=J_{max} and quadrupole pairing

    E-print Network

    Zamick, Larry

    2014-01-01

    We consider 2 neutrons and 2 protons in the g_{9/2} shell.Wave functions and energy levels are obtained for various interactions. The wave functions for states with total angular momentum I greater or equal to 10 are not affected by what the pairing interacton (J=0 T=1) is.Other parts of the interaction are therefore of increased importance.

  9. Electron pairing without superconductivity

    NASA Astrophysics Data System (ADS)

    Cheng, Guanglei; Tomczyk, Michelle; Lu, Shicheng; Veazey, Joshua P.; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Lee, Hyungwoo; Eom, Chang-Beom; Hellberg, C. Stephen; Levy, Jeremy

    2015-05-01

    Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity.

  10. Electron pairing without superconductivity.

    PubMed

    Cheng, Guanglei; Tomczyk, Michelle; Lu, Shicheng; Veazey, Joshua P; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Lee, Hyungwoo; Eom, Chang-Beom; Hellberg, C Stephen; Levy, Jeremy

    2015-05-14

    Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances-paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity. PMID:25971511

  11. Ion Pair-? Interactions.

    PubMed

    Fujisawa, Kaori; Humbert-Droz, Marie; Letrun, Romain; Vauthey, Eric; Wesolowski, Tomasz A; Sakai, Naomi; Matile, Stefan

    2015-09-01

    We report that anion-? and cation-? interactions can occur on the same aromatic surface. Interactions of this type are referred to as ion pair-? interactions. Their existence, nature, and significance are elaborated in the context of spectral tuning, ion binding in solution, and activation of cell-penetrating peptides. The origin of spectral tuning by ion pair-? interactions is unraveled with energy-minimized excited-state structures: The solvent- and pH-independent red shift of absorption and emission of push-pull fluorophores originates from antiparallel ion pair-? attraction to their polarized excited state. In contrast, the complementary parallel ion pair-? repulsion is spectroscopically irrelevant, in part because of charge neutralization by intriguing proton and electron transfers on excited push-pull surfaces. With time-resolved fluorescence measurements, very important differences between antiparallel and parallel ion pair-? interactions are identified and quantitatively dissected from interference by aggregation and ion pair dissociation. Contributions from hydrogen bonding, proton transfer, ?-? interactions, chromophore twisting, ion pairing, and self-assembly are systematically addressed and eliminated by concise structural modifications. Ion-exchange studies in solution, activation of cell-penetrating peptides in vesicles, and computational analysis all imply that the situation in the ground state is complementary to spectral tuning in the excited state; i.e., parallel rather than antiparallel ion pair-? interactions are preferred, despite repulsion from the push-pull dipole. The overall quite complete picture of ion pair-? interactions provided by these remarkably coherent yet complex results is expected to attract attention throughout the multiple disciplines of chemistry involved. PMID:26291550

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

    EPA Science Inventory

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

  13. Neutron spectrometry with He-3 proportional counters

    SciTech Connect

    Manolopoulou, M.; Fragopoulou, M.; Stoulos, S.; Vagena, E.; Westmeier, W.; Zamani, M.

    2011-07-01

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

  14. Nuclear neutron-proton contact and the photoabsorption cross section.

    PubMed

    Weiss, Ronen; Bazak, Betzalel; Barnea, Nir

    2015-01-01

    The nuclear neutron-proton contact is introduced, generalizing Tan's work, and evaluated from medium energy nuclear photodisintegration experiments. To this end we reformulate the quasideuteron model of nuclear photodisintegration and establish the bridge between the Levinger constant and the contact. Using experimental evaluations of Levinger's constant, we extract the value of the neutron-proton contact in finite nuclei and in symmetric nuclear matter. Assuming isospin symmetry we propose to evaluate the neutron-neutron contact through the measurement of photonuclear spin correlated neutron-proton pairs. PMID:25615461

  15. Pulsar Pair Cascades in a Distorted Magnetic Dipole Field

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Muslimov, Alex G.

    2010-01-01

    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.

  16. Superfluidity of $?$ hyperons in neutron stars

    E-print Network

    Y. N. Wang; H. Shen

    2010-02-01

    We study the $^1S_0$ superfluidity of $\\Lambda$ hyperons in neutron star matter and neutron stars. We use the relativistic mean field (RMF) theory to calculate the properties of neutron star matter. In the RMF approach, the meson-hyperon couplings are constrained by reasonable hyperon potentials that include the updated information from recent developments in hypernuclear physics. To examine the $^1S_0$ pairing gap of $\\Lambda$ hyperons, we employ several $\\Lambda\\Lambda$ interactions based on the Nijmegen models and used in double-$\\Lambda$ hypernuclei studies. It is found that the maximal pairing gap obtained is a few tenths of a MeV. The magnitude and the density region of the pairing gap are dependent on the $\\Lambda\\Lambda$ interaction and the treatment of neutron star matter. We calculate neutron star properties and find that whether the $^1S_0 $ superfluidity of $\\Lambda$ hyperons exists in the core of neutron stars mainly depends on the $\\Lambda\\Lambda$ interaction used.

  17. Thermal neutron detection system

    DOEpatents

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

    2000-01-01

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

  18. Neutron Star Binaries as Central Engines of GRBs

    E-print Network

    S. Rosswog

    2002-04-29

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

  19. New Insights into the Crystal and Electronic Structures of Li[subscript 1+x]V[subscript 1?x]O[subscript 2] from Solid State NMR, Pair Distribution Function Analyses, and First Principles Calculations

    SciTech Connect

    Pourpoint, Frédérique; Hua, Xiao; Middlemiss, Derek S.; Adamson, Paul; Wang, Da; Bruce, Peter G.; Grey, Clare P.

    2012-10-29

    Pair distribution function (PDF) analyses of synchrotron data obtained for the anode materials Li{sub 1+x}V{sub 1-x}O{sub 2} (0 {le} x {le} 0.1) have been performed to characterize the short to medium range structural ordering. The data show clear evidence for the magnetically-induced distortion of the V sublattice to form trimers, the distortion persisting at even the highest excess Li content considered of x = 0.1. At least three distinct local environments were observed for the stoichiometric material LiVO{sub 2} in {sup 6}Li nuclear magnetic resonance (NMR) spectroscopy, the environments becoming progressively more disordered as the Li content increases. A two-dimensional Li-Li correlation NMR experiment (POST-C7) was used to identify the resonances corresponding to Li within the same layers. NMR spectra were acquired as a function of the state of charge, a distinct environment for Li in Li{sub 2}VO{sub 2} being observed. The results suggest that disorder within the Li layers (in addition to the presence of Li within the V layers as proposed by Armstrong et al. Nat. Mater.2011, 10, 223-229) may aid the insertion of Li into the Li{sub 1+x}V{sub 1-x}O{sub 2} phase. The previously little-studied Li{sub 2}VO{sub 2} phase was also investigated by hybrid density functional theory (DFT) calculations, providing insights into magnetic interactions, spin-lattice coupling, and Li hyperfine parameters.

  20. Paired Straight Hearth Furnace

    SciTech Connect

    2009-04-01

    This factsheet describes a research project whose goals are to design, develop, and evaluate the scalability and commercial feasibility of the PSH Paired Straight Hearth Furnace alternative ironmaking process.

  1. Neutron reflectivity

    NASA Astrophysics Data System (ADS)

    Cousin, Fabrice; Menelle, Alain

    2015-10-01

    The specular neutron reflectivity is a technique enabling the measurement of neutron scattering length density profile perpendicular to the plane of a surface or an interface, and thereby the profile of chemical composition. The characteristic sizes that are probed range from around 5 Å up 5000 Å. It is a scattering technique that averages information on the entire surface and it is therefore not possible to obtain information within the plane of the interface. The specific properties of neutrons (possibility of tuning the contrast by isotopic substitution, sensitivity to magnetism, negligible absorption, low energy of the incident neutrons) makes it particularly interesting in the fields of soft matter, biophysics and magnetic thin films. This course is a basic introduction to the technique and does not address the magnetic reflectivity. It is composed of three parts describing respectively its principle and its formalism, the experimental aspects of the method (spectrometers, samples) and two examples related to the materials for energy.

  2. Capillary rise dynamics of liquid hydrocarbons in mesoporous silica as explored by gravimetry, optical and neutron imaging: Nano-rheology and determination of pore size distributions from the shape of imbibition fronts

    E-print Network

    Simon Gruener; Helen E. Hermes; Burkhard Schillinger; Stefan U. Egelhaaf; Patrick Huber

    2015-11-27

    We present gravimetrical, optical, and neutron imaging measurements of the capillarity-driven infiltration of mesoporous silica glass by hydrocarbons. Square-root-of-time Lucas-Washburn invasion kinetics are found for linear alkanes from n-decane (C10) to n-hexacontane (C60) and for squalane, a branched alkane, in porous Vycor with 6.5 nm or 10 nm pore diameter, respectively. Humidity-dependent experiments allow us to study the influence on the imbibition kinetics of water layers adsorbed on the pore walls. Except for the longest molecule studied, C60, the invasion kinetics can be described by bulk fluidity and bulk capillarity, provided we assume a sticking, pore-wall adsorbed boundary layer, i.e. a monolayer of water covered by a monolayer of flat-laying hydrocarbons. For C60, however, an enhanced imbibition speed compared to the value expected in the bulk is found. This suggests the onset of velocity slippage at the silica walls or a reduced shear viscosity due to the transition towards a polymer-like flow in confined geometries. Both, light scattering and neutron imaging indicate a pronounced roughening of the imbibition fronts. Their overall shape and width can be resolved by neutron imaging. The fronts can be described by a superposition of independent wetting fronts moving with pore size-dependent square-root-of-time laws and weighted according to the pore size distributions obtained from nitrogen gas sorption isotherms. This finding indicates that the shape of the imbibition front in a porous medium, such as Vycor glass, with interconnected, elongated pores, is solely determined by independent movements of liquid menisci. These are dictated by the Laplace pressure and hydraulic permeability variations and thus the pore size variation at the invasion front. Our results suggest that pore size distributions can be derived from the broadening of imbibition fronts.

  3. Neutron range spectrometer

    DOEpatents

    Manglos, S.H.

    1988-03-10

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

  4. Extracting an entangled photon pair from collectively decohered pairs at a telecommunication wavelength

    E-print Network

    Yoshiaki Tsujimoto; Yukihiro Sugiura; Makoto Ando; Daisuke Katsuse; Rikizo Ikuta; Takashi Yamamoto; Masato Koashi; Nobuyuki Imoto

    2015-03-10

    We experimentally demonstrated entanglement extraction scheme by using photons at the telecommunication band for optical-fiber-based quantum communications. We generated two pairs of non-degenerate polarization entangled photons at 780~nm and 1551~nm by spontaneous parametric down-conversion and distributed the two photons at 1551~nm through a collective phase damping channel which gives the same amount of random phase shift on the two photons. Through local operation and classical communication, we extracted an entangled photon pair from two phase-disturbed photon pairs. An observed fidelity of the extracted photon pair to a maximally entangled photon pair was 0.73 $\\pm$ 0.07 which clearly shows the recovery of entanglement.

  5. Prompt neutron fission spectrum mean energies for the fissile nuclides and /sup 252/Cf

    SciTech Connect

    Holden, N.E.

    1985-01-01

    The international standard for a neutron spectrum is that produced from the spontaneous fission of /sup 252/Cf, while the thermal neutron induced fission neutron spectra for the four fissile nuclides, /sup 233/U, /sup 235/U, /sup 239/Pu, and /sup 241/Pu are of interest from the standpoint of nuclear reactors. The average neutron energies of these spectra are tabulated. The individual measurements are recorded with the neutron energy range measured, the method of detection as well as the average neutron energy for each author. Also tabulated are the measurements of the ratio of mean energies for pairs of fission neutron spectra. 75 refs., 9 tabs. (LEW)

  6. FOREWORD: Neutron metrology Neutron metrology

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  7. Stylized features of single-nucleon momentum distributions

    E-print Network

    Jan Ryckebusch; Maarten Vanhalst; Wim Cosyn

    2015-08-12

    Nuclear short-range correlations (SRC) typically manifest themselves in the tail parts of the single-nucleon momentum distributions. We propose an approximate practical method for computing those SRC contributions to the high-momentum parts. The framework adopted in this work is applicable throughout the nuclear mass table and corrects mean-field models for central, spin-isospin and tensor correlations by shifting the complexity induced by the SRC from the wave functions to the operators. It is argued that the expansion of these modified operators can be truncated to a low order. The proposed model can generate the SRC-related high-momentum tail of the single-nucleon momentum distribution. These are dominated by correlation operators acting on mean-field pairs with vanishing relative radial and angular-momentum quantum numbers. The proposed method explains the dominant role of proton-neutron pairs in generating the SRC and accounts for the magnitude and mass dependence of SRC as probed in inclusive electron scattering. It also provides predictions for the ratio of the amount of correlated proton-proton to proton-neutron pairs which are in line with the observations. In asymmetric nuclei, the correlations make the average kinetic energy for the minority nucleons larger than for the majority nucleons.

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

    SciTech Connect

    Skinner, Lawrie; Benmore, Chris J; Weber, Richard; Santodonato, Louis J; Tumber, Sonia; Neuefeind, Joerg C; Lazareva, Lena; Du, Jincheng; Parise, John B

    2012-01-01

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

  9. Outer crust of nonaccreting cold neutron stars

    NASA Astrophysics Data System (ADS)

    Rüster, Stefan B.; Hempel, Matthias; Schaffner-Bielich, Jürgen

    2006-03-01

    The properties of the outer crust of nonaccreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables, updating in particular the classic work of Baym, Pethick, and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 are used and a thorough comparison of many modern theoretical nuclear models, both relativistic and nonrelativistic, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared to check their differences concerning the neutron drip line, magic neutron numbers, the equation of state, and the sequence of neutron-rich nuclei up to the drip line in the outer crust of nonaccreting cold neutron stars.

  10. Analysis of Paired Comparison Data Using Mx

    ERIC Educational Resources Information Center

    Tsai, Rung-Ching; Wu, Tsung-Lin

    2004-01-01

    By postulating that the random utilities associated with the choice options follow a multivariate normal distribution, Thurstonian models (Thurstone, 1927) provide a straightforward representation of paired comparison data. The use of Monte Carlo Expectation-Maximization (MCEM) algorithms and limited information approaches have been proposed to…

  11. Photon Splitting and Pair Conversion in Strong Magnetic Fields

    E-print Network

    Matthew G. Baring

    2008-04-05

    The magnetospheres of neutron stars provide a valuable testing ground for as-yet unverified theoretical predictions of quantum electrodynamics (QED) in strong electromagnetic fields. Exhibiting magnetic field strengths well in excess of a TeraGauss, such compact astrophysical environments permit the action of exotic mechanisms that are forbidden by symmetries in field-free regions. Foremost among these processes are single-photon pair creation, where a photon converts to an electron-positron pair, and magnetic photon splitting, where a single photon divides into two of lesser energy via the coupling to the external field. The pair conversion process is exponentially small in weak fields, and provides the leading order contribution to vacuum polarization. In contrast, photon splitting possesses no energy threshold and can operate in kinematic regimes where the lower order pair conversion is energetically forbidden. This paper outlines some of the key physical aspects of these processes, and highlights their manifestation in neutron star magnetospheres. Anticipated observational signatures include profound absorption turnovers in pulsar spectra at gamma-ray wavelengths. The shapes of these turnovers provide diagnostics on the possible action of pair creation and the geometrical locale of the photon emission region. There is real potential for the first confirmation of strong field QED with the new GLAST mission, to be launched by NASA in 2008. Suppression of pair creation by photon splitting and its implications for pulsars is also discussed.

  12. Photon Splitting and Pair Conversion in Strong Magnetic Fields

    SciTech Connect

    Baring, Matthew G.

    2008-10-17

    The magnetospheres of neutron stars provide a valuable testing ground for as-yet unverified theoretical predictions of quantum electrodynamics (QED) in strong electromagnetic fields. Exhibiting magnetic field strengths well in excess of a TeraGauss, such compact astrophysical environments permit the action of exotic mechanisms that are forbidden by symmetries in field-free regions. Foremost among these processes are single-photon pair creation, where a photon converts to an electron-positron pair, and magnetic photon splitting, where a single photon divides into two of lesser energy via the coupling to the external field. The pair conversion process is exponentially small in weak fields, and provides the leading order contribution to vacuum polarization. In contrast, photon splitting possesses no energy threshold and can operate in kinematic regimes where the lower order pair conversion is energetically forbidden. This paper outlines some of the key physical aspects of these processes, and highlights their manifestation in neutron star magnetospheres. Anticipated observational signatures include profound absorption turnovers in pulsar spectra at gamma-ray wavelengths. The shapes of these turnovers provide diagnostics on the possible action of pair creation and the geometrical locale of the photon emission region. There is real potential for the first confirmation of strong field QED with the new GLAST gamma-ray mission, recently launched by NASA in June 2008. The suppression of pair creation by photon splitting and its implications for pulsars are also discussed.

  13. Electron Pairing Without Superconductivity

    NASA Astrophysics Data System (ADS)

    Levy, Jeremy; Cheng, G.; Tomczyk, M.; Lu, S.; Veazey, J. P.; Huang, M.; Irvin, P.; Ryu, S.; Lee, H.; Eom, C.-B.; Hellberg, C. S.

    2015-03-01

    Strontium titanate (SrTiO3) exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. We describe transport experiments with nanowire-based quantum dots localized at the interface between SrTiO3 and LaAlO3. Electrostatic gating of the quantum dot reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical magnetic field Bp 1-4 Tesla, an order of magnitude larger than the superconducting critical magnetic field. For B Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as T = 900 mK, far above the superconducting transition temperature (Tc 300 mK). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by an attractive-U Hubbard model that describes real-space electron pairing as a precursor to superconductivity. This work was supported by ARO MURI W911NF-08-1-0317 (J.L.), AFOSR MURI FA9550-10-1-0524 (C.-B.E., J.L.) and FA9550-12-1-0342 (C.-B.E.), and grants from the National Science Foundation DMR-1104191 (J.L.), DMR.

  14. Kidney paired donation.

    PubMed

    Wallis, C Bradley; Samy, Kannan P; Roth, Alvin E; Rees, Michael A

    2011-07-01

    Kidney paired donation (KPD) was first suggested in 1986, but it was not until 2000 when the first paired donation transplant was performed in the USA. In the past decade, KPD has become the fastest growing source of transplantable kidneys, overcoming the barrier faced by living donors deemed incompatible with their intended recipients. This review provides a basic overview of the concepts and challenges faced by KPD as we prepare for a national pilot program with the United Network for Organ Sharing. Several different algorithms have been creatively implemented in the USA and elsewhere to transplant paired donors, each method uniquely contributing to the success of KPD. As the paired donor pool grows, the problem of determining allocation strategies that maximize equity and utility will become increasingly important as the transplant community seeks to balance quality and quantity in choosing the best matches. Financing for paired donation is a major issue, as philanthropy alone cannot support the emerging national system. We also discuss the advent of altruistic or non-directed donors in KPD, and the important role of chains in addition to exchanges. This review is designed to provide insight into the challenges that face the emerging national KPD system in the USA, now 5 years into its development. PMID:21454351

  15. Neutron Repulsion

    E-print Network

    Oliver K. Manuel

    2011-02-08

    Earth is connected gravitationally, magnetically and electrically to its heat source - a neutron star that is obscured from view by waste products in the photosphere. Neutron repulsion is like the hot filament in an incandescent light bulb. Excited neutrons are emitted from the solar core and decay into hydrogen that glows in the photosphere like a frosted light bulb. Neutron repulsion was recognized in nuclear rest mass data in 2000 as the overlooked source of energy, the keystone of an arch that locked together these puzzling space-age observations: 1.) Excess 136Xe accompanied primordial helium in the stellar debris that formed the solar system (Fig. 1); 2.) The Sun formed on the supernova core (Fig. 2); 3.) Waste products from the core pass through an iron-rich mantle, selectively carrying lighter elements and lighter isotopes of each element into the photosphere (Figs. 3-4); and 4.) Neutron repulsion powers the Sun and sustains life (Figs. 5-7). Together these findings offer a framework for understanding how: a.) The Sun generates and releases neutrinos, energy and solar-wind hydrogen and helium; b.) An inhabitable planet formed and life evolved around an ordinary-looking star; c.) Continuous climate change - induced by cyclic changes in gravitational interactions of the Sun's energetic core with planets - has favored survival by adaptation.

  16. Neutron diagnostics at the Wendelstein 7-X stellarator

    NASA Astrophysics Data System (ADS)

    Schneider, W.; Wiegel, B.; Grünauer, F.; Burhenn, R.; Koch, S.; Schuhmacher, H.; Zimbal, A.

    2012-03-01

    The stellarator W7-X, presently under construction at the Institute for Plasma Physics in Greifswald, will be equipped with a set of neutron monitors in order to study the time behaviour of neutron emission generated during D-D plasma operation and neutral beam heating with Deuterium. Each of these neutron monitors consists of several neutron detector tubes inserted in a dedicated moderator. The neutron monitors at W7-X are designed to monitor neutron yields with a time resolution of 5 ms and with a statistical uncertainty of better than 15%. One of the monitors is located in the centre above the stellarator. The other five monitors are distributed around the torus. A prerequisite for the determination of the absolute neutron source strength produced by D(d,n)3He fusion reactions in the plasma is an in-situ calibration with a neutron source of known source strength. During such a calibration procedure, the neutron source will be moved along the torus axis and the count rates of the different neutron monitors will be measured. In a first benchmark experiment, an 241AmBe neutron source was moved along the torus axis within one module of the stellarator and the neutron signals were measured by a De Pangher Long Counter outside of the cryostat chamber as a function of the neutron source position. These measurements have been compared with predictions of Monte Carlo calculations (MCNP) of the neutron propagation from the location of the neutron source to the long counter. The concept of neutron monitors will be reported together with results from the benchmark experiment and results from MCNP calculations. The neutron monitor system is the first part of several neutron diagnostic systems such as neutron activation system, neutron profile camera planned for future neutron analysis. A short survey of these neutron diagnostic tools of W7-X will be given.

  17. Dark matter, mergers, and morphology: clues from galaxy pairs

    NASA Astrophysics Data System (ADS)

    Charlton, Jane C.; Salpeter, Edwin E.

    1991-04-01

    We have examined the distributions of radial velocity differences ?v and projected separations rp of pairs in low density regions of the CfA and SSRS redshift catalogs. Bound pairs exist even at relatively large projected separations (up to 1 Mpc), indicating large amounts of dark matter around galaxies. The distribution of rp for bound pairs is flat, with significant numbers of pairs at projected separations less than 50 kpc. Pairs at small separations merge rapidly, but the distribution is replenished by those originally at larger separation that are being drawn toward merger by dynamical friction. As a result of this merger/replenishment process, at least 20% of galaxies in low density regions are the product of a merger; thus it seems that nearly all ellipicals and S0's in these regions are created in this way.

  18. Determination of solar flare accelerated ion angular distributions from SMM gamma ray and neutron measurements and determination of the He-3/H ratio in the solar photosphere from SMM gamma ray measurements

    NASA Technical Reports Server (NTRS)

    Lingenfelter, Richard E.

    1989-01-01

    Comparisons of Solar Maximum Mission (SMM) observations of gamma-ray line and neutron emission with theoretical calculation of their expected production by flare accelerated ion interactions in the solar atmosphere have led to significant advances in the understanding of solar flare particle acceleration and interaction, as well as the flare process itself. These comparisons have enabled the determination of, not only the total number and energy spectrum of accelerated ions trapped at the sun, but also the ion angular distribution as they interact in the solar atmosphere. The Monte Carlo program was modified to include in the calculations of ion trajectories the effects of both mirroring in converging magnetic fields and of pitch angle scattering. Comparing the results of these calculations with the SMM observations, not only the angular distribution of the interacting ions can be determined, but also the initial angular distribution of the ions at acceleration. The reliable determination of the solar photospheric He-3 abundance is of great importance for understanding nucleosynthesis in the early universe and its implications for cosmology, as well as for the study of the evolution of the sun. It is also essential for the determinations of the spectrum and total number of flare accelerated ions from the SMM/GRS gamma-ray line measurements. Systematic Monte Carlo calculations of the time dependence were made as a function of the He-3 abundance and other variables. A new series of calculations were compared for the time-dependent flux of 2.223 MeV neutron capture line emission and the ratio of the time-integrated flux in the 2.223 MeV line to that in the 4.1 to 6.4 MeV nuclear deexcitation band.

  19. Neutron therapy of cancer

    NASA Technical Reports Server (NTRS)

    Frigerio, N. A.; Nellans, H. N.; Shaw, M. J.

    1969-01-01

    Reports relate applications of neutrons to the problem of cancer therapy. The biochemical and biophysical aspects of fast-neutron therapy, neutron-capture and neutron-conversion therapy with intermediate-range neutrons are presented. Also included is a computer program for neutron-gamma radiobiology.

  20. Rotochemical heating in millisecond pulsars with Cooper pairing

    NASA Astrophysics Data System (ADS)

    Petrovich, Cristóbal; Reisenegger, Andreas

    2010-08-01

    When a rotating neutron star loses angular momentum, the reduction in the centrifugal force makes it contract. This perturbs each fluid element, raising the local pressure and originating deviations from beta equilibrium that enhance the neutrino emissivity and produce thermal energy. This mechanism is named rotochemical heating and has previously been studied for neutron stars of non-superfluid matter, finding that they reach a quasi-steady state in which the rate that the spin-down modifies the equilibrium concentrations is the same to that of the neutrino reactions restoring the equilibrium. On the other hand, the neutron star interior is believed to contain superfluid nucleons, which affect the thermal evolution of the star by suppressing the neutrino reactions and the specific heat, and opening new Cooper pairing reactions. In this work we describe the thermal effects of Cooper pairing with spatially uniform energy gaps of neutrons and protons on rotochemical heating in millisecond pulsars (MSPs) when only modified Urca reactions are allowed. We find that the chemical imbalances grow up to a value close to the energy gaps, which is higher than the one of the nonsuperfluid case. Therefore, the surface temperatures predicted with Cooper pairing are higher and explain the recent measurement of MSP J0437-4715.

  1. Neutron flux mapping inside a cubic and a head PMMA phantom using indirect neutron radiography.

    PubMed

    Tsai, Pi-En; Liu, Yuan-Hao; Huang, Chun-Kai; Liu, Hong-Ming; Jiang, Shiang-Huei

    2009-07-01

    This study aims to measure the two-dimensional (2D) neutron spatial distribution inside a cubic and a head PMMA phantom for the purpose of further comparison with the treatment planning. The measurements were made by using the indirect neutron radiography (INR), which utilized a thin copper foil and the imaging plate. The developed image provides satisfactory spatial resolution and very low statistical error (< 1%). As to the time cost, the whole procedure normally takes less than 3 h. The result shows that the indirect neutron radiography can be a quick and reliable method to provide a 2D neutron spatial distribution inside a phantom. PMID:19394242

  2. Mass distributions of 22.0 MeV neutron-induced fission of sup 2 sup 3 sup 8 U

    E-print Network

    LiuYongHui; Cui An Zhi; Feng Jing; Guo Jing Ru; Li Ze; Qi Bu Jia; Ruan Xi Chao; Sun Hong Qing; Tang Hong Qing; Yang Yi; Zhang Sheng Dong; Zhou Zu Ying

    2001-01-01

    Chain yields of 32 chains were determined for the fission of sup 2 sup 3 sup 8 U induced by 22.0 MeV mono-energetic neutrons for the first time. Fission product activities were measured by HPGe gamma ray spectrometry without chemical separation. Absolute fission rate was monitored with a double fission chamber. The efficiency of the fission chamber was checked by determination of sup 1 sup 9 sup 8 Au activity from sup 1 sup 9 sup 7 Au(n, gamma) sup 1 sup 9 sup 8 Au reaction

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

    PubMed

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

    2009-05-01

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

  4. Data from the Versatile Array of Neutron Detectors at Low Energy (VANDLE) will impact modeling of processes occurring in neutron-rich

    E-print Network

    Data from the Versatile Array of Neutron Detectors at Low Energy (VANDLE) will impact modeling of processes occurring in neutron-rich environments ·The energies of beta-delayed neutrons emitted from 25 strong feeding to high-lying states that emit high energy neutrons while others have broad distributions

  5. Jupiter Effect (Asymmetrical Production of Dilepton Pairs)

    E-print Network

    Peter Filip

    1998-02-01

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

  6. Neutron rich nuclei and neutron stars

    E-print Network

    C. J. Horowitz

    2013-03-01

    The PREX experiment at Jefferson Laboratory measures the neutron radius of 208Pb with parity violating electron scattering in a way that is free from most strong interaction uncertainties. The 208Pb radius has important implications for neutron rich matter and the structure of neutron stars. We present first PREX results, describe future plans, and discuss a follow on measurement of the neutron radius of 48Ca. We review radio and X-ray observations of neutron star masses and radii. These constrain the equation of state (pressure versus density) of neutron rich matter. We present a new energy functional that is simultaneously fit to both nuclear and neutron star properties. In this approach, neutron star masses and radii constrain the energy of neutron matter. This avoids having to rely on model dependent microscopic calculations of neutron matter. The functional is then used to predict the location of the drip lines and the properties of very neutron rich heavy nuclei.

  7. Measurements of the neutron spectra from the 7Li(p,n) accelerator based neutron source: Position and angular dependences

    NASA Astrophysics Data System (ADS)

    Matysiak, W.; Prestwich, W. V.; Byun, S. H.

    2012-11-01

    Thick target 7Li(p,n) neutron spectra were measured using a 3He ion chamber in the proton energy range of 1.95 to 2.30 MeV. The fast neutron spectra were collected for various distances from the lithium target as well as for various neutron emission angles. By unfolding the 3He raw data with the iterative van Cittert algorithm, the neutron fluence spectra were obtained. The 3He measured neutron spectra were compared with both analytically computed and Monte Carlo simulated spectra to account for neutron scatterings in the lithium target assembly and in the experimental area. To verify the accuracy of the neutron dose computation, the fast neutron kerma was obtained for each neutron spectrum using the fluence to kerma conversion coefficients and was compared with the measured neutron dose using tissue-equivalent proportional counters. In the position dependence investigation at the 0° emission angle, the analytically computed neutron kerma overestimates the experimental kerma by a factor of two mainly due to neutron moderation. The corresponding neutron kerma from the 3He measured spectra were in agreement with the neutron doses measured using tissue-equivalent proportional counters within 20% for lower proton energies, but the discrepancy increased to ˜50% for higher proton energies. In the angular distribution investigation, a notable discrepancy between measured and computed neutron spectra were observed due to the neutron scattering effects in the target assembly and experimental room.

  8. Regimes of Pulsar Pair Formation and Particle Energetics

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  9. Pairing-induced speedup of nuclear spontaneous fission

    DOE PAGESBeta

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

    2014-12-22

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

  10. Pairing-induced speedup of nuclear spontaneous fission

    SciTech Connect

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

    2014-12-22

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

  11. Burst Oscillations: Watching Neutron Stars Spin

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2010-01-01

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

  12. Structure of the vacuum states in the presence of isovector and isoscalar pairing correlations

    E-print Network

    Bes, D R; Maqueda, E E; Scoccola, N N

    2000-01-01

    The long standing problem of proton-neutron pairing and, in particular, the limitations imposed on the solutions by the available symmetries, is revisited. We look for solutions with non-vanishing expectation values of the proton, the neutron and the isoscalar gaps. For an equal number of protons and neutrons we find two solutions where the absolute values of proton and neutrons gaps are equal but have the same or opposite sign. The behavior and structure of these solutions differ for spin saturated (single l-shell) and spin unsaturared systems (single j-shell). In the former case the BCS results are checked against an exact calculation.

  13. Computer simulation of neutron capture therapy

    E-print Network

    Olson, Arne Peter

    1967-01-01

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

  14. Computer simulation of neutron capture therapy.

    E-print Network

    Olson, Arne Peter

    1967-01-01

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

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

    DOEpatents

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

    1989-01-01

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

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

    DOEpatents

    Chiles, M.M.; Mihalczo, J.T.; Blakeman, E.D.

    1987-02-27

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

  17. Methods for absorbing neutrons

    DOEpatents

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

    2012-07-24

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

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

    SciTech Connect

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

    2010-04-22

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

  19. Results with the neutron scatter camera.

    SciTech Connect

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

    2008-10-01

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

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

    PubMed

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

    2015-03-01

    Phantom experiments to evaluate thermal neutron flux distribution were performed using the Scintillator with Optical Fiber (SOF) detector, which was developed as a thermal neutron monitor during boron neutron capture therapy (BNCT) irradiation. Compared with the gold wire activation method and Monte Carlo N-particle (MCNP) calculations, it was confirmed that the SOF detector is capable of measuring thermal neutron flux as low as 10(5) n/cm(2)/s with sufficient accuracy. The SOF detector will be useful for phantom experiments with BNCT neutron fields from low-current accelerator-based neutron sources. PMID:25589504

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

    PubMed Central

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

    2015-01-01

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

  2. Wide Separation Quasars: Pairs or Lenses?

    NASA Astrophysics Data System (ADS)

    Green, Paul

    1999-09-01

    We propose to image the wide (7'') separation quasar pair Q2345+007 to determine whether it is a binary quasar or a gravitational lens and to probe the nature of the lensing matter. With nearly identical optical spectra and identical redshifts, this quasar pair remains the most intriguing example of an observed configuration requiring the presence of massive, concentrated dark matter acting as a gravitational lens. If the quasar pair Q2345+007 proves consistent with a lens in X-rays, we expect to constrain, detect, or characterize the most compelling ``dark cluster'' candidate known. If not, our observation will lend credence to the binary interpretation, showing Q2345+007 to be a bizarre case of virtually identical spectral energy distributions in quasars separated by about 3Mpc.

  3. Recent Advances in Neutron Physics

    ERIC Educational Resources Information Center

    Feshbach, Herman; Sheldon, Eric

    1977-01-01

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

  4. Neutron reflecting supermirror structure

    DOEpatents

    Wood, J.L.

    1992-12-01

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

  5. Neutron reflecting supermirror structure

    DOEpatents

    Wood, James L. (Drayton Plains, MI)

    1992-01-01

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

  6. Development of Energy-Selective Neutron Imaging

    NASA Astrophysics Data System (ADS)

    Kiyanagi, Yoshiaki; Sato, Hirotaka; Shiota, Yoshinori; Kamiyma, Takashi; Iwase, Kenji; Uno, Shoji

    A neutron transmission image gives different features depending on neutron energy. Therefore, energy-selective imaging has become increasingly popular for obtaining comprehensive information. Neutron imaging using a pulsed neutron source can offer energy-selective imaging much more easily than a reactor neutron source, since it can use the time-of-flight method for energy analysis. Furthermore, by analyzing a transmission spectrum we can obtain physical quantities such as crystallographic information, elemental information, temperature, magnetic field, and so on. Such a spectrum analysis method, namely spectroscopic imaging performed at a pulsed neutron source, is a useful method for the material analysis and inspection of industrial products. Here, the principle of the method is explained and recent results are presented for a quenched iron rod, a hydrogen storage material, and elemental distributions in stainless steel.

  7. Small inorganic scintillators as neutron detectors

    SciTech Connect

    Bartle, C.M.; Haight, R.C.

    1998-12-01

    Small organic scintillators that exhibit pulse shape differences (PSD) in response to charged particles have been investigated as possible neutron detectors in the energy range from 1 to 200 MeV. Neutrons in this energy range can induce reactions such as (n,p) and (n,alpha) in these scintillators, and the cross sections for these reactions vary with energy. Pulse-height and PSD distributions were measured as a function of neutron energy for small crystals of NaI(Tl) and CsI(Tl) at the LANSCE-WNR pulsed spallation neutron source. PSD information indicating the relative numbers of protons and alphas produced can give information about the neutron spectrum in fast-neutron radiation fields such as those encountered in space exploration.

  8. Gravitational Redshift of Deformed Neutron Stars

    NASA Astrophysics Data System (ADS)

    Romero, Alexis; Zubairi, Omair; Weber, Fridolin

    2015-04-01

    Non-rotating neutron stars are generally treated in theoretical studies as perfect spheres. Such a treatment, however, may not be correct if strong magnetic fields are present and/or the pressure of the matter in the cores of neutron stars is non-isotropic, leading to neutron stars which are deformed. In this work, we investigate the impact of deformation on the gravitational redshift of neutron stars in the framework of general relativity. Using a parameterized metric to model non-spherical mass distributions, we derive an expression for the gravitational redshift in terms of the mass, radius, and deformity of a neutron star. Numerical solutions for the redshifts of sequences of deformed neutron stars are presented and observational implications are pointed out. This research is funded by the NIH through the Maximizing Access to Research Careers (MARC), under Grant Number: 5T34GM008303-25 and through the National Science Foundation under grant PHY-1411708.

  9. SWCN characterization by neutron diffraction

    NASA Astrophysics Data System (ADS)

    Giannasi, A.; Celli, M.; Sauvajol, J. L.; Zoppi, M.; Bowron, D. T.

    2004-07-01

    Single-wall carbon nanotube structure has been investigated by neutron diffraction using the SANDALS time of flight diffractometer (at R.A.L.). The Q range of the detector allows for the determination of single the tube diameter, diameter distribution, and mean number of tubes in the bundle. Results are compared to theoretical predictions.

  10. Cold neutron energy dependent production of ultracold neutrons in solid deuterium.

    PubMed

    Atchison, F; Blau, B; Bodek, K; van den Brandt, B; Bry?, T; Daum, M; Fierlinger, P; Frei, A; Geltenbort, P; Hautle, P; Henneck, R; Heule, S; Holley, A; Kasprzak, M; Kirch, K; Knecht, A; Konter, J A; Ku?niak, M; Liu, C-Y; Morris, C L; Pichlmaier, A; Plonka, C; Pokotilovski, Y; Saunders, A; Shin, Y; Tortorella, D; Wohlmuther, M; Young, A R; Zejma, J; Zsigmond, G

    2007-12-31

    A measurement of the production of ultracold neutrons from velocity-selected cold neutrons on gaseous and solid deuterium targets is reported. The expected energy dependence for two-particle collisions with well defined neutron and Maxwell-Boltzmann distributed molecular velocities is found for the gas target. The solid target data agree in shape with the phonon density-of-states curve and provide strong evidence for the phonon model including multiphonon excitations. PMID:18233572

  11. Cold Neutron Energy Dependent Production of Ultracold Neutrons in Solid Deuterium

    SciTech Connect

    Atchison, F.; Blau, B.; Brandt, B. van den; Brys, T.; Daum, M.; Fierlinger, P.; Hautle, P.; Henneck, R.; Heule, S.; Kasprzak, M.; Kirch, K.; Knecht, A.; Konter, J. A.; Pichlmaier, A.; Wohlmuther, M.; Zsigmond, G.; Bodek, K.; Kuzniak, M.; Zejma, J.; Frei, A.

    2007-12-31

    A measurement of the production of ultracold neutrons from velocity-selected cold neutrons on gaseous and solid deuterium targets is reported. The expected energy dependence for two-particle collisions with well defined neutron and Maxwell-Boltzmann distributed molecular velocities is found for the gas target. The solid target data agree in shape with the phonon density-of-states curve and provide strong evidence for the phonon model including multiphonon excitations.

  12. Demographic mechanisms of inbreeding adjustment through extra-pair reproduction

    PubMed Central

    Reid, Jane M; Duthie, A Bradley; Wolak, Matthew E; Arcese, Peter; van de Pol, Martijn

    2015-01-01

    One hypothesis explaining extra-pair reproduction is that socially monogamous females mate with extra-pair males to adjust the coefficient of inbreeding (f) of extra-pair offspring (EPO) relative to that of within-pair offspring (WPO) they would produce with their socially paired male. Such adjustment of offspring f requires non-random extra-pair reproduction with respect to relatedness, which is in turn often assumed to require some mechanism of explicit pre-copulatory or post-copulatory kin discrimination. We propose three demographic processes that could potentially cause mean f to differ between individual females’ EPO and WPO given random extra-pair reproduction with available males without necessarily requiring explicit kin discrimination. Specifically, such a difference could arise if social pairings formed non-randomly with respect to relatedness or persisted non-randomly with respect to relatedness, or if the distribution of relatedness between females and their sets of potential mates changed during the period through which social pairings persisted. We used comprehensive pedigree and pairing data from free-living song sparrows (Melospiza melodia) to quantify these three processes and hence investigate how individual females could adjust mean offspring f through instantaneously random extra-pair reproduction. Female song sparrows tended to form social pairings with unrelated or distantly related males slightly less frequently than expected given random pairing within the defined set of available males. Furthermore, social pairings between more closely related mates tended to be more likely to persist across years than social pairings between less closely related mates. However, these effects were small and the mean relatedness between females and their sets of potential extra-pair males did not change substantially across the years through which social pairings persisted. Our framework and analyses illustrate how demographic and social structuring within populations might allow females to adjust mean f of offspring through random extra-pair reproduction without necessarily requiring explicit kin discrimination, implying that adjustment of offspring f might be an inevitable consequence of extra-pair reproduction. New theoretical and empirical studies are required to explore the general magnitude of such effects and quantify the degree to which they could facilitate or constrain long-term evolution of extra-pair reproduction. PMID:25645743

  13. "Frustrated Lewis pair" hydrogenations.

    PubMed

    Stephan, Douglas W

    2012-08-14

    This perspective article discusses developments of metal-free hydrogenation catalysts derived from "frustrated Lewis pair" (FLP) systems. The range of catalysts uncovered and the applications to reductions of imines, aziridines, enamines, silyl enol ethers, diimines, metallocene derivatives and nitrogen-based heterocycles are described. In addition, FLP aromatic reduction of aniline derivatives to the cyclohexylamine analogs is discussed. The potential applications of these metal-free reductions are considered. PMID:22505184

  14. Adiabatic Pair Creation

    E-print Network

    Peter Pickl; Detlef Duerr

    2007-06-20

    We give here the proof that pair creation in a time dependent potentials is possible. It happens with probability one if the potential changes adiabatically in time and becomes overcritical, that is when an eigenvalue enters the upper spectral continuum. The potential may be assumed to be zero at large negative and positive times. The rigorous treatment of this effect has been lacking since the pioneering work of Beck, Steinwedel and Suessmann in 1963 and Gershtein and Zeldovich in 1970.

  15. Neutron Spectra in a 15 MV LINAC

    SciTech Connect

    Vega-Carrillo, H. R.; Chu, Wei-Han; Tung, Chuan-Jong; Lan, Jen-Hong

    2010-12-07

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

  16. Competition Between T=0 and T=1 Pairing in Proton-Rich Nuclei

    E-print Network

    W. Satu?a; R. Wyss

    1996-08-19

    A cranked mean-field model with two-body T=1 and T=0 pairing interactions is presented. Approximate projection onto good particle-number is enforced via an extended Lipkin-Nogami scheme. Our calculations suggest the simultaneous presence of both T=0 and T=1 pairing modes in N=Z nuclei. The transitions between different pairing phases are discussed as a function of neutron/proton excess, T$_z$, and rotational frequency, $\\hbar\\omega$. The additional binding energy due to the T=0 $np$-pairing correlations, is suggested as a possible microscopic explanation of the Wigner energy term in even-even nuclei.

  17. Temperature-dependent isovector pairing gap equations using a path integral approach

    SciTech Connect

    Fellah, M.; Allal, N. H.; Belabbas, M.; Oudih, M. R.; Benhamouda, N.

    2007-10-15

    Temperature-dependent isovector neutron-proton (np) pairing gap equations have been established by means of the path integral approach. These equations generalize the BCS ones for the pairing between like particles at finite temperature. The method has been numerically tested using the one-level model. It has been shown that the gap parameter {delta}{sub np} has a behavior analogous to that of {delta}{sub nn} and {delta}{sub pp} as a function of the temperature: one notes the presence of a critical temperature. Moreover, it has been shown that the isovector pairing effects remain beyond the critical temperature that corresponds to the pairing between like particles.

  18. Neutron transport simulation (selected topics)

    NASA Astrophysics Data System (ADS)

    Vaz, P.

    2009-10-01

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

  19. J=0,J=J{sub max}, and quadrupole pairing

    SciTech Connect

    Hertz-Kintish, Daniel; Zamick, Larry

    2014-12-15

    We consider 2 neutrons and 2 protons in the g{sub 9/2} shell. Wave functions and energy levels are obtained for various interactions. The wavefunctions for states with total angular momentum I greater than or equal to 10 are not affected by what the pairing interaction (J=0T=1) is. Other parts of the interaction are therefore of increased importance. Furthermore, states with I greater than or equal to 12 are not affected by the J=2 interaction.

  20. Evaluation of sup 252 Cf prompt fission neutron data from 0 to 20 MeV by Watt spectrum fit

    SciTech Connect

    Frohner, F.H. )

    1990-11-01

    This paper reports that recent measurements define the prompt fission neutron spectrum of {sup 252}Cf from 25 keV to 20 MeV with sufficient accuracy to show that the standard representation by a Maxwell spectrum with the temperature parameter T{sub M} = 1.42 MeV is not adequate. The next simplest macroscopic representation, a Watt spectrum with the two parameters T{sub W} = 1.18 MeV and E{sub W} = 0.36 MeV, fits the recent data surprisingly well, at least as well as the best currently available microscopic models of fission neutron emission. The resulting chi-square does not indicate any need for a more sophisticated description, nor is the fit improved by refinements such as superposition of two Watt distributions (for a representative fragment pair), or relativistic corrections.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  2. Structure of molten CaSiO3: neutron diffraction isotope substitution with aerodynamic levitation and molecular dynamics study.

    PubMed

    Skinner, L B; Benmore, C J; Weber, J K R; Tumber, S; Lazareva, L; Neuefeind, J; Santodonato, L; Du, J; Parise, J B

    2012-11-15

    We have performed neutron diffraction isotopic substitution experiments on aerodynamically levitated droplets of CaSiO(3), to directly extract intermediate and local structural information on the Ca environment. The results show a substantial broadening of the first Ca-O peak in the pair distribution function of the melt compared to the glass, which comprises primarily of 6- and 7-fold coordinated Ca-polyhedra. The broadening can be explained by a redistribution of Ca-O bond lengths, especially toward longer distances in the liquid. The first order neutron difference function provides a test of recent molecular dynamics simulations and supports the MD model which contains short chains or channels of edge shared Ca-octahedra in the liquid state. It is suggested that the polymerization of Ca-polyhedra is responsible for the fragile viscosity behavior of the melt and the glass forming ability in CaSiO(3). PMID:23106223

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

    NASA Technical Reports Server (NTRS)

    Ruderman, Malvin; Chen, Kaiyou

    1997-01-01

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

  4. Assessment Strategies for Pair Programming

    ERIC Educational Resources Information Center

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

    2009-01-01

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

  5. Mated Fingerprint Card Pairs 2 (MFCP2)

    National Institute of Standards and Technology Data Gateway

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

  6. High energy neutron radiography

    SciTech Connect

    Gavron, A.; Morley, K.; Morris, C.; Seestrom, S.; Ullmann, J.; Yates, G.; Zumbro, J.

    1996-06-01

    High-energy spallation neutron sources are now being considered in the US and elsewhere as a replacement for neutron beams produced by reactors. High-energy and high intensity neutron beams, produced by unmoderated spallation sources, open potential new vistas of neutron radiography. The authors discuss the basic advantages and disadvantages of high-energy neutron radiography, and consider some experimental results obtained at the Weapons Neutron Research (WNR) facility at Los Alamos.

  7. Spectra and Neutron Dosimetry Inside a PET Cyclotron Vault Room

    SciTech Connect

    Vega-Carrillo, Hector Rene; Mendez, Roberto; Iniguez, Maria Pilar; Marti-Climent, Joseph; Penuelas, Ivan; Barquero, Raquel

    2006-09-08

    The neutron field around a PET cyclotron was investigated during 18F radioisotope production with an 18 MeV proton beam. Pairs of thermoluminescent dosemeters, TLD600 and TLD700, were used as thermal neutron detector inside a Bonner Spheres Spectrometer to measure the neutron spectra at three different positions inside the cyclotron's vault room. Neutron spectra were also determined by Monte Carlo calculations. The hardest spectrum was observed in front of cyclotron target and the softest was noticed at the antipode of target. Neutron doses derived from the measured spectra vary between 11 and 377 mSv/{mu}A-h of proton integrated current, Doses were also measured with a single-moderator remmeter, with an active thermal neutron detector, whose response in affected by the radiation field in the vault room.

  8. Multiprocessor switch with selective pairing

    DOEpatents

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

    2014-03-11

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

  9. Prospective very young asteroid pairs

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  10. Pair production, Comptonization and dynamics in astrophysical plasmas

    NASA Astrophysics Data System (ADS)

    Guilbert, P. W.; Stepney, S.

    1985-02-01

    Electron-positron pair production is an important cooling mechanism for plasmas at mildly relativistic temperatures. A thorough understanding of the process is necessary to explain the hard X-ray spectra of AGNs and gamma-ray bursters. An investigation is presented of thermal plasmas with temperatures kT approximately equal to m(e)sq c and optical depths of about 1-5, including pair processes, Comptonization and bremsstrahlung. Results are presented for equilibrium and impulsively heated models. It is found that, in the former case, the observed spectrum is featureless, but in the latter case it can show a broad, flat annihilation feature. The non-thermal pair production in plasmas confined by strong magnetic fields, such as those thought to exist at the surface of neutron stars, is discussed. It is shown that two photon pair production cannot give an annihilation feature, but that magnetic pair production (gamma B to positron-electron) can give a significant annihilation line. Finally, consideration is given to simple dynamical systems and the effect of expansion on the spectrum of a gas in which pair production is important. Adiabatic cooling steepens the flat spectral feature to omega to the -3rd in the thermal case, and in the nonthermal case the spectrum has a flat component with a turnover at about 2 MeV.

  11. Neutron multiplication error in TRU waste measurements

    SciTech Connect

    Veilleux, John; Stanfield, Sean B; Wachter, Joe; Ceo, Bob

    2009-01-01

    Total Measurement Uncertainty (TMU) in neutron assays of transuranic waste (TRU) are comprised of several components including counting statistics, matrix and source distribution, calibration inaccuracy, background effects, and neutron multiplication error. While a minor component for low plutonium masses, neutron multiplication error is often the major contributor to the TMU for items containing more than 140 g of weapons grade plutonium. Neutron multiplication arises when neutrons from spontaneous fission and other nuclear events induce fissions in other fissile isotopes in the waste, thereby multiplying the overall coincidence neutron response in passive neutron measurements. Since passive neutron counters cannot differentiate between spontaneous and induced fission neutrons, multiplication can lead to positive bias in the measurements. Although neutron multiplication can only result in a positive bias, it has, for the purpose of mathematical simplicity, generally been treated as an error that can lead to either a positive or negative result in the TMU. While the factors that contribute to neutron multiplication include the total mass of fissile nuclides, the presence of moderating material in the matrix, the concentration and geometry of the fissile sources, and other factors; measurement uncertainty is generally determined as a function of the fissile mass in most TMU software calculations because this is the only quantity determined by the passive neutron measurement. Neutron multiplication error has a particularly pernicious consequence for TRU waste analysis because the measured Fissile Gram Equivalent (FGE) plus twice the TMU error must be less than 200 for TRU waste packaged in 55-gal drums and less than 325 for boxed waste. For this reason, large errors due to neutron multiplication can lead to increased rejections of TRU waste containers. This report will attempt to better define the error term due to neutron multiplication and arrive at values that are more realistic and accurate. To do so, measurements of standards and waste drums were performed with High Efficiency Neutron Counters (HENC) located at Los Alamos National Laboratory (LANL). The data were analyzed for multiplication effects and new estimates of the multiplication error were computed. A concluding section will present alternatives for reducing the number of rejections of TRU waste containers due to neutron multiplication error.

  12. J=0 T=1 Pairing Interaction Selection Rules

    E-print Network

    Matthew Harper; Larry Zamick

    2015-05-10

    Wave functions arising form a pairing Hamiltonian E(0) i,e, one in which the interaction is only between J=0^{+}T=1 pairs, lead to magnetic dipole and Gamow-Teller transition rates that are much larger than those from an interaction E(J_{max}) in which a proton and a neutron couple to J=2j. With realistic interactions the results are in between the 2 extremes. In the course of this study we found that certain M1 and GT matrix elements vanish with E(0) . These are connected to seniority and reduced isospin isospin selection rules. We find the surprising result that The M1 strength to the single j scissors is larger for a J=0 T=1 pairing interaction than it is for Q.Q.

  13. Mixed-spin pairing condensates in heavy nuclei.

    PubMed

    Gezerlis, Alexandros; Bertsch, G F; Luo, Y L

    2011-06-24

    We show that the Bogoliubov-de Gennes equations for nuclear ground-state wave functions support solutions in which the condensate has a mixture of spin-singlet and spin-triplet pairing. We find that such mixed-spin condensates do not occur when there are equal numbers of neutrons and protons, but only when there is an isospin imbalance. Using a phenomenological Hamiltonian, we predict that such nuclei may occur in the physical region within the proton dripline. We also solve the Bogoliubov-de Gennes equations with variable constraints on the spin-singlet and spin-triplet pairing amplitudes. For nuclei that exhibit this new pairing behavior, the resulting energy surface can be rather soft, suggesting that there may be low-lying excitations associated with the spin mixing. PMID:21770636

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

    SciTech Connect

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

    2005-10-01

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

  15. Utilization of the intense pulsed neutron source (IPNS) at Argonne National Laboratory for neutron activation analysis

    SciTech Connect

    Heinrich, R.R.; Greenwood, L.R.; Popek, R.J.; Schulke, A.W. Jr.

    1983-01-01

    The Intense Pulsed Neutron Source (IPNS) neutron scattering facility (NSF) has been investigated for its applicability to neutron activation analysis. A polyethylene insert has been added to the vertical hole VT3 which enhances the thermal neutron flux by a factor of two. The neutron spectral distribution at this position has been measured by the multiple-foil technique which utilized 28 activation reactions and the STAYSL computer code. The validity of this spectral measurement was tested by two irradiations of National Bureau of Standards SRM-1571 (orchard leaves), SRM-1575 (pine needles), and SRM-1645 (river sediment). The average thermal neutron flux for these irradiations normalized to 10 ..mu..amp proton beam is 4.0 x 10/sup 11/ n/cm/sup 2/-s. Concentrations of nine trace elements in each of these SRMs have been determined by gamma-ray spectrometry. Agreement of measured values to certified values is demonstrated to be within experiment error.

  16. Pair Dispersion in Turbulence: The Subdominant Role of Scaling

    NASA Astrophysics Data System (ADS)

    Rast, Mark Peter; Pinton, Jean-François

    2011-11-01

    The mixing properties of turbulent flows are, at first order, related to the dynamics of separation of particle pairs. Scaling laws for the evolution in time of the mean distance between particle pairs ?r2?(t) have been proposed since the pioneering work of Richardson. We analyze a model which shares some features with 3D experimental and numerical turbulence, and suggest that pure scaling laws are only subdominant. The dynamics is dominated by a very wide distribution of “delay times” td, the duration for which particle pairs remain together before their separation increases significantly. The delay time distribution is exponential for small separations and evolves towards a flat distribution at large separations. The observed ?r2?(t) behavior is best understood as an average over separations that individually follow the Richardson-Obukhov scaling, r2?t3, but each only after a fluctuating time delay td, where td is distributed uniformly.

  17. Prompt fission neutron spectra and average prompt neutron multiplicities

    SciTech Connect

    Madland, D.G.; Nix, J.R.

    1983-01-01

    We present a new method for calculating the prompt fission neutron spectrum N(E) and average prompt neutron multiplicity anti nu/sub p/ as functions of the fissioning nucleus and its excitation energy. The method is based on standard nuclear evaporation theory and takes into account (1) the motion of the fission fragments, (2) the distribution of fission-fragment residual nuclear temperature, (3) the energy dependence of the cross section sigma/sub c/ for the inverse process of compound-nucleus formation, and (4) the possibility of multiple-chance fission. We use a triangular distribution in residual nuclear temperature based on the Fermi-gas model. This leads to closed expressions for N(E) and anti nu/sub p/ when sigma/sub c/ is assumed constant and readily computed quadratures when the energy dependence of sigma/sub c/ is determined from an optical model. Neutron spectra and average multiplicities calculated with an energy-dependent cross section agree well with experimental data for the neutron-induced fission of /sup 235/U and the spontaneous fission of /sup 252/Cf. For the latter case, there are some significant inconsistencies between the experimental spectra that need to be resolved. 29 references.

  18. The Orbit of X Per and Its Neutron Star Companion

    E-print Network

    Hugo Delgado-Marti; Alan M. Levine; Eric Pfahl; Saul A. Rappaport

    2000-04-18

    We have observed the Be/X-ray pulsar binary system X Per/4U 0352+30 on 61 occasions spanning an interval of 600 days with the PCA instrument on RXTE. Pulse timing analyses of the 837-s pulsations yield strong evidence for the presence of orbital Doppler delays. We confirm the Doppler delays by using measurements made with the RXTE All-Sky Monitor. We obtain an orbital period of 250 days, a projected semimajor axis of the neutron star of 454 lt-s, a mass function of 1.61 solar masses, and a modest eccentricity of 0.11. We discuss the formation of the system in the context of the standard evolutionary scenario for Be/X-ray binaries with consideration of the possibility that the birth of the neutron star was accompanied by a kick of the type often inferred from the velocity distribution of isolated radio pulsars. The orbital eccentricity just after the supernova explosion was almost certainly virtually the same as at present, because the Be star is much smaller than the orbital separation. We find that the system most likely formed from a pair of massive progenitor stars, and probably involved a quasi-stable and nearly conservative transfer of mass from the primary to the secondary. We find that the He star remnant of the primary most likely had a mass less than 6 solar masses after mass transfer. Finally, we speculate that there may be a substantial population of neutron stars formed with little or no kick.

  19. Old and new neutron stars

    SciTech Connect

    Ruderman, M.

    1984-09-01

    The youngest known radiopulsar in the rapidly spinning magnetized neutron star which powers the Crab Nebula, the remnant of the historical supernova explosion of 1054 AD. Similar neutron stars are probably born at least every few hundred years, but are less frequent than Galactic supernova explosions. They are initially sources of extreme relativistic electron and/or positron winds (approx.10/sup 38/s/sup -1/ of 10/sup 12/ eV leptons) which greatly decrease as the neutron stars spin down to become mature pulsars. After several million years these neutron stars are no longer observed as radiopulsars, perhaps because of large magnetic field decay. However, a substantial fraction of the 10/sup 8/ old dead pulsars in the Galaxy are the most probable source for the isotropically distributed ..gamma..-ray burst detected several times per week at the earth. Some old neutron stars are spun-up by accretion from companions to be resurrected as rapidly spinning low magnetic field radiopulsars. 52 references, 6 figures, 3 tables.

  20. Scattering model approximations for neutron thermalization problems

    SciTech Connect

    Ritenour, R.L.; Rydin, R.A.; Mulder, R.U. )

    1990-12-01

    In this paper a variety of scattering model approximations are devised and evaluated. One such scattering model, designated the balanced single collision thermalization (BSCT) approximation, has proven to be very effective. It assumes that neutrons attain a thermalized distribution with only a single collision within the moderating material, independent of incident energy. This approximation leads to separability of the incident and outscattering energies and to significant simplification of the neutron scattering kernel for thermalization problems. The BSCT approximation is particularly useful in thermalization problems involving cold neutron sources, for which it yields flux predictions to within a few percent of exact solutions of theoretical problems. The BSCT approximation also predicts cold neutron fractions to within 10% of measured values for a cold neutron thermalization experiment done at Argonne National Laboratory.