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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

    SciTech Connect

    Fry-Petit, A. M. E-mail: afry@fullerton.edu; Sheckelton, J. P.; McQueen, T. M. E-mail: afry@fullerton.edu; Rebola, A. F.; Fennie, C. J.; Mourigal, M.; Valentine, M.; Drichko, N.

    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, LiZn{sub 2}Mo{sub 3}O{sub 8}, this approach allows direct assignment of the constrained rotational mode of Mo{sub 3}O{sub 13} clusters and internal modes of MoO{sub 6} 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.

  3. 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.

  4. Extracting differential pair distribution functions using MIXSCAT

    SciTech Connect

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

    2010-08-27

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

  5. Pair correlations in neutron-rich nuclei

    SciTech Connect

    Esbensen, H.

    1995-08-01

    We started a program to study the ground-state properties of heavy, neutron-rich nuclei using the Hartree-Fock-Bogolyubov (HFB) approximation. This appears at present to be the most realistic approach for heavy nuclei that contain many loosely bound valence neutrons. The two-neutron density obtained in this approach can be decomposed into two components, one associated with the mean field and one associated with the pairing field. The latter has a structure that is quite similar to the pair-density obtained by diagonalizing the Hamiltonian for a two-neutron halo, which was studied earlier. This allows comparison of the HFB solutions against numerically exact solutions for two-neutron halos. This work is in progress. We intend to apply the HFB method to predict the ground-state properties of heavier, more neutron-rich nuclei that may be produced at future radioactive beam facilities.

  6. Pair fireball precursors of neutron star mergers

    NASA Astrophysics Data System (ADS)

    Metzger, Brian D.; Zivancev, Charles

    2016-10-01

    If at least one neutron star (NS) is magnetized in a binary NS merger, then the orbital motion of the conducting companion during the final inspiral induces a strong voltage and current along the magnetic field lines connecting the NSs. If a modest fraction η of the extracted electromagnetic power extracted accelerates relativistic particles, the resulting gamma-ray emission a compact volume will result in the formation of an electron-positron pair fireball. Applying a steady-state pair wind model, we quantify the detectability of the precursor fireball with gamma-ray satellites. For η ˜ 1 the gamma-ray detection horizon of Dmax ≈ 10(Bd/1014 G)3/4 Mpc is much closer than the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO)/Virgo horizon of 200 Mpc, unless the NS surface magnetic field strength is very large, B_d ≲ 10^{15} G. Given the quasi-isotropic nature of the emission, mergers with weaker NS fields could contribute a nearby population of short gamma-ray bursts. Power not dissipated close to the binary is carried to infinity along the open field lines by a large-scale Poynting flux. Reconnection within this outflow, well outside of the pair photosphere, provides a potential site for non-thermal emission, such as a coherent millisecond radio burst.

  7. Pair distribution function and structure factor of spherical particles

    SciTech Connect

    Howell, Rafael C.; Proffen, Thomas; Conradson, Steven D.

    2006-03-01

    The availability of neutron spallation-source instruments that provide total scattering powder diffraction has led to an increased application of real-space structure analysis using the pair distribution function. Currently, the analytical treatment of finite size effects within pair distribution refinement procedures is limited. To that end, an envelope function is derived which transforms the pair distribution function of an infinite solid into that of a spherical particle with the same crystal structure. Distributions of particle sizes are then considered, and the associated envelope function is used to predict the particle size distribution of an experimental sample of gold nanoparticles from its pair distribution function alone. Finally, complementing the wealth of existing diffraction analysis, the peak broadening for the structure factor of spherical particles, expressed as a convolution derived from the envelope functions, is calculated exactly for all particle size distributions considered, and peak maxima, offsets, and asymmetries are discussed.

  8. 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 β stability than do previous parameterizations.

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

    NASA Astrophysics Data System (ADS)

    Carter, Brandon; Chamel, Nicolas; Haensel, Pawel

    2005-09-01

    The relative current density n of “conduction” neutrons in a neutron star crust beyond the neutron drip threshold can be expected to be related to the corresponding particle momentum covector p by a linear relation of the form n=Kp in terms of a physically well-defined mobility tensor K. This result is describable as an “entrainment” whose effect—wherever the crust lattice is isotropic—will simply be to change the ordinary neutron mass m to a “macroscopic” effective mass m such that in terms of the relevant number density n of unconfined neutrons we shall have K=(n/m)γ. In a preceding work based on a independent particle treatment beyond the Wigner Seitz approximation, using Bloch type boundary conditions to obtain the distribution of energy E and associated group velocity vki=∂E/∂ℏk as a function of wave vector k, it was shown that the mobility tensor would be proportional to a phase space volume integral K∝∫dkvkivkjδ{E-μ}, where μ is the Fermi energy. Using the approach due to Bogoliubov, it is shown here that the effect of BCS pairing with a superfluid energy gap Δ and corresponding quasiparticle energy function €=E+ΔF2 will just be to replace the Dirac distributional integrand by the smoother distribution in the formula K∝∫dkvkivkjΔF2/€k3. It is also shown how the pairing condensation gives rise to superfluidity in the technical sense of providing (meta) stability against resistive perturbations for a current that is not too strong (its momentum p must be small enough to give 2|pvki|<€k2/|E-μ| for all modes). It is concluded that the prediction of a very large effective mass enhancement in the middle layers of the star crust will not be significantly effected by the pairing mechanism.

  10. Pairing gap in the inner crust of neutron stars

    SciTech Connect

    Esbensen, H.; Broglia, R.A.; Vigezzi, E.; Barranco, F.

    1995-08-01

    The pairing gap in the inner crust of a neutron star can be strongly affected by the presence of heavy nuclei. The effect is commonly estimated in a semiclassical description, using the local density approximation. It was found that the nuclear specific heat can become comparable to the electronic specific heat at certain densities and temperatures. The quantitative result depends critically upon the magnitude of the pairing gap. We therefore decided to assess the validity of the semiclassical approach. This is done by solving the quantal BCS pairing gap equation for neutrons that are confined to the Wigner-Seitz cell that surrounds a heavy nucleus. We performed calculations that are based on the Gogny pairing force. They are feasible for realistic densities of neutrons and heavy nuclei that are expected to be found in the inner crust of neutron stars. The results will be compared to the semiclassical predictions. This work is in progress.

  11. New magic nuclei and neutron-proton pairing

    SciTech Connect

    Boboshin, I. N.

    2008-07-15

    Special features of new magic nuclei and their connection with the shell structure are considered. The mechanism of neutron-proton pairing is proposed as a basis for the formation of new magic nuclei. A law of nucleon pairing is introduced. Spin-parity values are explained for a number of odd-odd nuclei.

  12. Photoproduction of π0-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 π0π0 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- → Δ(1232)3/2+π 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}→ Nσ decay for the proton, while the reaction is dominated by a sequential decay via a Δπ intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled-channel analysis.

  13. 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.

  14. 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.

  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. 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 ρB = 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.

  17. Exact Solution of the Isovector Proton Neutron Pairing Hamiltonian

    SciTech Connect

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

    2005-12-02

    The complete exact solution of the T = 1 neutron-proton pairing Hamiltonian is presented in the context of the SO(5) Richardson-Gaudin model with non-degenerate single-particle levels and including isospin-symmetry breaking terms. The power of the method is illustrated with a numerical calculation for {sup 64}Ge for a pf + g{sub 9/2} model space which is out of reach of modern shell-model codes.

  18. Neutron angular distribution in plutonium-240 spontaneous fission

    NASA Astrophysics Data System (ADS)

    Marcath, Matthew J.; Shin, Tony H.; Clarke, Shaun D.; Peerani, Paolo; Pozzi, Sara A.

    2016-09-01

    Nuclear safeguards applications require accurate fission models that exhibit prompt neutron anisotropy. In the laboratory reference frame, an anisotropic neutron angular distribution is observed because prompt fission neutrons carry momentum from fully accelerated fission fragments. A liquid organic scintillation detector array was used with pulse shape discrimination techniques to produce neutron-neutron cross-correlation time distributions and angular distributions from spontaneous fission in a 252Cf, a 0.84 g 240Pueff metal, and a 1.63 g 240Pueff metal sample. The effect of cross-talk, estimated with MCNPX-PoliMi simulations, is removed from neutron-neutron coincidences as a function of the angle between detector pairs. Fewer coincidences were observed at detector angles near 90°, relative to higher and lower detector angles. As light output threshold increases, the observed anisotropy increases due to spectral effects arising from fission fragment momentum transfer to emitted neutrons. Stronger anisotropy was observed in Cf-252 spontaneous fission prompt neutrons than in Pu-240 neutrons.

  19. Pair cascades in the magnetospheres of strongly magnetized neutron stars

    NASA Astrophysics Data System (ADS)

    Medin, Zach; Lai, Dong

    2010-08-01

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

  20. Spectral unfolding of fast neutron energy distributions

    NASA Astrophysics Data System (ADS)

    Mosby, Michelle; Jackman, Kevin; Engle, Jonathan

    2015-10-01

    The characterization of the energy distribution of a neutron flux is difficult in experiments with constrained geometry where techniques such as time of flight cannot be used to resolve the distribution. The measurement of neutron fluxes in reactors, which often present similar challenges, has been accomplished using radioactivation foils as an indirect probe. Spectral unfolding codes use statistical methods to adjust MCNP predictions of neutron energy distributions using quantified radioactive residuals produced in these foils. We have applied a modification of this established neutron flux characterization technique to experimentally characterize the neutron flux in the critical assemblies at the Nevada National Security Site (NNSS) and the spallation neutron flux at the Isotope Production Facility (IPF) at Los Alamos National Laboratory (LANL). Results of the unfolding procedure are presented and compared with a priori MCNP predictions, and the implications for measurements using the neutron fluxes at these facilities are discussed.

  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 (Δm ≈ 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. Neutron density distribution and neutron skin thickness of Pb208

    NASA Astrophysics Data System (ADS)

    Meucci, Andrea; Vorabbi, Matteo; Giusti, Carlotta; Finelli, Paolo

    2014-08-01

    We present and discuss numerical predictions for the neutron density distribution of Pb208 using various nonrelativistic and relativistic mean-field models for the nuclear structure. Our results are compared with the very recent pion photoproduction data from Mainz. The parity-violating asymmetry parameter for elastic electron scattering at the kinematics of the PREX experiment at JLab and the neutron skin thickness are compared with the available data. We consider also the dependence between the neutron skin and the parameters of the expansion of the symmetry energy.

  3. Calculated angular distributions of energetic atmospheric neutrons

    NASA Technical Reports Server (NTRS)

    Merker, M.

    1975-01-01

    Calculated angular distributions of atmospheric leakage neutron fluxes from 19 MeV to 1 GeV are presented. Comparisons with the balloon measurements of Preszler et al. and Kanbach et al. are made and show substantial agreement, strengthening the belief in the importance of the CRAND (cosmic-ray albedo-neutron decay) contribution to the high-energy protons in the earth's inner radiation belt. The calculation is presented as a means for investigating features of atmospheric flux distributions.

  4. Spin distribution in neutron induced preequilibrium reactions

    SciTech Connect

    Dashdorj, D; Kawano, T; Chadwick, M; Devlin, M; Fotiades, N; Nelson, R O; Mitchell, G E; Garrett, P E; Agvaanluvsan, U; Becker, J A; Bernstein, L A; Macri, R; Younes, W

    2005-10-04

    The preequilibrium reaction mechanism makes an important contribution to neutron-induced reactions above E{sub n} {approx} 10 MeV. The preequilibrium process has been studied exclusively via the characteristic high energy neutrons produced at bombarding energies greater than 10 MeV. They are expanding the study of the preequilibrium reaction mechanism through {gamma}-ray spectroscopy. Cross-section measurements were made of prompt {gamma}-ray production as a function of incident neutron energy (E{sub n} = 1 to 250 MeV) on a {sup 48}Ti sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center facility. The prompt-reaction {gamma} rays were detected with the large-scale Compton-suppressed Germanium Array for Neutron Induced Excitations (GEANIE). Neutron energies were determined by the time-of-flight technique. The {gamma}-ray excitation functions were converted to partial {gamma}-ray cross sections taking into account the dead-time correction, target thickness, detector efficiency and neutron flux (monitored with an in-line fission chamber). Residual state population was predicted using the GNASH reaction code, enhanced for preequilibrium. The preequilibrium reaction spin distribution was calculated using the quantum mechanical theory of Feshback, Kerman, and Koonin (FKK). The multistep direct part of the FKK theory was calculated for a one-step process. The FKK preequilibrium spin distribution was incorporated into the GNASH calculations and the {gamma}-ray production cross sections were calculated and compared with experimental data. The difference in the partial {gamma}-ray cross sections using spin distributions with and without preequilibrium effects is significant.

  5. Local distribution of old neutron stars

    NASA Technical Reports Server (NTRS)

    Frei, Szolt; Huang, Xiaolan; Paczynski, Bohdan

    1992-01-01

    The local distribution of old disk neutron stars is approximated with a 1D model, in which the steady state distribution in the direction perpendicular to the Galactic plane is calculated, assuming a variety of the initial radio pulsar positions and velocities, and various Galactic potentials. It is found that the local distribution of old neutron stars is dominated by those that were born with very low velocities. The high-velocity neutron stars spend most of their lifetime far in the Galactic halo and do not contribute much to the local density. Therefore, the rms velocity at birth is not a good indicator of the scale height of the old population. The most likely half-density scale height for the old disk neutron stars is approximately 350 pc, the same as for the old disk G, K, and M stars. If gamma-ray bursts originate on old disk neutron stars, then 350 pc should also be the scale height for the bursters.

  6. Urca Cooling Pairs in the Neutron Star Ocean and Their Effect on Superbursts

    NASA Astrophysics Data System (ADS)

    Deibel, Alex; Meisel, Zach; Schatz, Hendrik; Brown, Edward F.; Cumming, Andrew

    2016-11-01

    An accretion outburst onto a neutron star deposits hydrogen-rich and/or helium-rich material into the neutron star’s envelope. Thermonuclear burning of accreted material robustly produces Urca pairs—pairs of nuclei that undergo cycles of {e}--capture and {β }--decay. The strong T 5 dependence of the Urca cooling neutrino luminosity means that Urca pairs in the neutron star interior potentially remove heat from accretion-driven nuclear reactions. In this study, we identify Urca pairs in the neutron star’s ocean—a plasma of ions and electrons overlaying the neutron star crust—and demonstrate that Urca cooling occurs at all depths in the ocean. We find that Urca pairs in the ocean and crust lower the ocean’s steady-state temperature during an accretion outburst and that unstable carbon ignition, which is thought to trigger superbursts, occurs deeper than it would otherwise. Cooling superburst light curves, however, are only marginally impacted by cooling from Urca pairs because the superburst peak radiative luminosity {L}{peak} is always much greater than the Urca pair neutrino luminosity {L}ν in the hot post-superburst ocean.

  7. Equation of state of low-density neutron matter, and the {sup 1}S{sub 0} pairing gap

    SciTech Connect

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

    2009-10-15

    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{<=}k{sub F}{<=}1.0 fm{sup -1}. Neutron matter in this regime is superfluid because of the strong and attractive interaction in the {sup 1}S{sub 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 {sup 1}S{sub 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.

  8. Pairing in high-density neutron matter including short- and long-range correlations

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    Pairing gaps in neutron matter need to be computed in a wide range of densities to address open questions in neutron-star phenomenology. Traditionally, the Bardeen-Cooper-Schrieffer approach has been used to compute gaps from bare nucleon-nucleon interactions. Here we incorporate the influence of short- and long-range correlations in the pairing gaps. Short-range correlations are treated, including the appropriate fragmentation of single-particle states, and substantially suppress the gaps. Long-range correlations dress the pairing interaction via density and spin modes and provide a relatively small correction. We use different interactions, some with three-body forces, as a starting point to control for any systematic effects. Results are relevant for neutron-star cooling scenarios, in particular in view of the recent observational data on Cassiopeia A.

  9. Nucleon and nucleon-pair momentum distributions in A≤12 nuclei

    DOE PAGES

    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 ν18 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, αd inmore » 6Li,αt in 7Li, and αα in 8Be. Detailed tables are provided on-line for download.« less

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

    SciTech Connect

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

    2015-10-15

    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.

  11. Multi-user distribution of polarization entangled photon pairs

    SciTech Connect

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

    2015-10-14

    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.

  12. Neutron chain length distributions in subcritical systems

    SciTech Connect

    Nolen, S.D.; Spriggs, G.

    1999-09-27

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

  13. Study on the impact of pair production interaction on D-T controllable neutron density logging.

    PubMed

    Yu, Huawei; Zhang, Li; Hou, Boran

    2016-05-01

    This paper considers the effect of pair production on the precision of D-T controllable neutron source density logging. Firstly, the principle of the traditional density logging and pulsed neutron density logging are analyzed and then gamma ray cross sections as a function of energy for various minerals are compared. In addition, the advantageous areas of Compton scattering and pair production interactions on high-energy gamma ray pulse height spectrum and the errors of a controllable source density measurement are studied using a Monte Carlo simulation method. The results indicate that density logging mainly utilizes the Compton scattering of gamma rays, while the attenuation of neutron induced gamma rays and the precision of neutron gamma density measurements are affected by pair production interactions, particularly in the gamma rays with energy higher than 2MeV. By selecting 0.2-2MeV energy range and performing proper lithology correction, the effect of pair production can be eliminated effectively and the density measurement error can be rendered close to the precision of chemical source density logging. PMID:26945102

  14. Study on the impact of pair production interaction on D-T controllable neutron density logging.

    PubMed

    Yu, Huawei; Zhang, Li; Hou, Boran

    2016-05-01

    This paper considers the effect of pair production on the precision of D-T controllable neutron source density logging. Firstly, the principle of the traditional density logging and pulsed neutron density logging are analyzed and then gamma ray cross sections as a function of energy for various minerals are compared. In addition, the advantageous areas of Compton scattering and pair production interactions on high-energy gamma ray pulse height spectrum and the errors of a controllable source density measurement are studied using a Monte Carlo simulation method. The results indicate that density logging mainly utilizes the Compton scattering of gamma rays, while the attenuation of neutron induced gamma rays and the precision of neutron gamma density measurements are affected by pair production interactions, particularly in the gamma rays with energy higher than 2MeV. By selecting 0.2-2MeV energy range and performing proper lithology correction, the effect of pair production can be eliminated effectively and the density measurement error can be rendered close to the precision of chemical source density logging.

  15. Distributed wireless quantum communication networks with partially entangled pairs

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  16. Local Atomic Structure of Semiconductor Alloys Using Pair Distribution Function Analysis

    SciTech Connect

    Billinge, S.J.L.; Thorpe, M.F.

    2002-06-24

    We have been taking advantage of recent experimental developments, which involve utilizing diffraction data from x-rays or neutrons out to very large wave-vectors, to obtain a detailed structural characterization of semiconductor alloys. This approach allows an accurate Pair Distribution Function (PDF) to be obtained to 20A and beyond and reveals the local structure of the alloy directly. These data can be modeled explicitly to learn about local correlations and short-range order in materials. We are combining theory, modeling and experiments to study a range of materials from semiconductors to thermoelectrics and proton conductors.

  17. Spatial Distribution of Pair Production Over the Pulsar Polar Cap

    NASA Astrophysics Data System (ADS)

    Belyaev, Mikhail A.; Parfrey, Kyle

    2016-10-01

    Using an analytic, axisymmetric approach that includes general relativity, coupled to a condition for pair production deduced from simulations, we derive general results about the spatial distribution of pair-producing field lines over the pulsar polar cap. In particular, we show that pair production on magnetic field lines operates over only a fraction of the polar cap for an aligned rotator for general magnetic field configurations, assuming the magnetic field varies spatially on a scale that is larger than the size of the polar cap. We compare our result to force-free simulations of a pulsar with a dipole surface field and find excellent agreement. Our work has implications for first-principles simulations of pulsar magnetospheres and for explaining observations of pulsed radio and high-energy emission.

  18. Distance distributions of photogenerated charge pairs in organic photovoltaic cells.

    PubMed

    Barker, Alex J; Chen, Kai; Hodgkiss, Justin M

    2014-08-27

    Strong Coulomb interactions in organic photovoltaic cells dictate that charges must separate over relatively long distances in order to circumvent geminate recombination and produce photocurrent. In this article, we measure the distance distributions of thermalized charge pairs by accessing a regime at low temperature where charge pairs are frozen out following the primary charge separation step and recombine monomolecularly via tunneling. The exponential attenuation of tunneling rate with distance provides a sensitive probe of the distance distribution of primary charge pairs, reminiscent of electron transfer studies in proteins. By fitting recombination dynamics to distributions of recombination rates, we identified populations of charge-transfer states and well-separated charge pairs. For the wide range of materials we studied, the yield of separated charges in the tunneling regime is strongly correlated with the yield of free charges measured via their intensity-dependent bimolecular recombination dynamics at room temperature. We therefore conclude that populations of free charges are established via long-range charge separation within the thermalization time scale, thus invoking early branching between free and bound charges across an energetic barrier. Subject to assumed values of the electron tunneling attenuation constant, we estimate critical charge separation distances of ∼3-4 nm in all materials. In some blends, large fullerene crystals can enhance charge separation yields; however, the important role of the polymers is also highlighted in blends that achieved significant charge separation with minimal fullerene concentration. We expect that our approach of isolating the intrinsic properties of primary charge pairs will be of considerable value in guiding new material development and testing the validity of proposed mechanisms for long-range charge separation.

  19. Isoscalar-isovector proton-neutron pairing and quartet condensation in N =Z nuclei

    NASA Astrophysics Data System (ADS)

    Sambataro, M.; Sandulescu, N.

    2016-05-01

    We show that the correlations generated in the ground state of N =Z nuclei by the isovector and isoscalar pairing forces can be treated with high precision as a condensate of alpha-like quartets. To treat these correlations, the quartet condensation model (QCM) is extended to the treatment of spherically symmetric isovector (T =1 ,J =0 ) and isoscalar (T =0 ,J =1 ) pairing forces. Within the QCM, we discuss the competition between T =1 and T =0 pairing correlations in the case of a two-level model and for N =Z nuclei with nucleons moving in the open shells above 16O,40Ca, and 100Sn. We show that, in N =Z systems, isovector and isoscalar proton-neutron pairing correlations always coexist.

  20. Pair production and annihilation in strong magnetic fields. [of neutron stars and pulsars

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

    Electromagnetic phenomena occurring in the presence of strong magnetic fields are currently of great interest in high-energy astrophysics. In particular, the process of pair production by single photons in the presence of fields of order 10 to the 12th power Gauss is of importance in cascade models of pulsar gamma ray emission, and may also become significant in theories of other radiation phenomena whose sources may be neutron stars (e.g., gamma ray bursts). In addition to pair production, the inverse process of pair annihilation is greatly affected by the presence of superstrong magnetic fields. The most significant departures from annihilation processes in free space are a reduction in the total rate for annihilation into two photons, a broadening of the familiar 511-keV line for annihilation at rest, and the possibility for annihilation into a single photon which dominates the two-photon annihilation for B (10 to 13th power Gauss) The physics of these pair conversion processes, which is reviewed briefly, can become quite complex in the teragauss regime, and can involve calculations which are technically difficult to incorporate into models of emission mechanisms in neutron star magnetospheres. However, theoretical work, especially the case of pair annihilation, also suggests potential techniques for more direct measurements of field strengths near the stellar surface.

  1. Emission of neutron-proton and proton-proton pairs in neutrino scattering

    NASA Astrophysics Data System (ADS)

    Ruiz Simo, I.; Amaro, J. E.; Barbaro, M. B.; De Pace, A.; Caballero, J. A.; Megias, G. D.; Donnelly, T. W.

    2016-11-01

    We use a recently developed model of relativistic meson-exchange currents to compute the neutron-proton and proton-proton yields in (νμ ,μ-) scattering from 12C in the 2p-2h channel. We compute the response functions and cross sections with the relativistic Fermi gas model for different kinematics from intermediate to high momentum transfers. We find a large contribution of neutron-proton configurations in the initial state, as compared to proton-proton pairs. In the case of charge-changing neutrino scattering the 2p-2h cross section of proton-proton emission (i.e., np in the initial state) is much larger than for neutron-proton emission (i.e., two neutrons in the initial state) by a (ω , q)-dependent factor. The different emission probabilities of distinct species of nucleon pairs are produced in our model only by meson-exchange currents, mainly by the Δ isobar current. We also analyze other effects including exchange contributions and the effect of the axial and vector currents.

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

    SciTech Connect

    Talamo, A.; Gohar, Y.; Sadovich, S.; Kiyavitskaya, H.; Bournos, V.; Fokov, Y.; Routkovskaya, C.

    2013-07-01

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

  3. 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.

  4. 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.

  5. Pair neutron transfer in 60Ni+116Sn probed via γ -particle coincidences

    NASA Astrophysics Data System (ADS)

    Montanari, D.; Corradi, L.; Szilner, S.; Pollarolo, G.; Goasduff, A.; Mijatović, T.; Bazzacco, D.; Birkenbach, B.; Bracco, A.; Charles, L.; Courtin, S.; Désesquelles, P.; Fioretto, E.; Gadea, A.; Görgen, A.; Gottardo, A.; Grebosz, J.; Haas, F.; Hess, H.; Jelavić Malenica, D.; Jungclaus, A.; Karolak, M.; Leoni, S.; Maj, A.; Menegazzo, R.; Mengoni, D.; Michelagnoli, C.; Montagnoli, G.; Napoli, D. R.; Pullia, A.; Recchia, F.; Reiter, P.; Rosso, D.; Salsac, M. D.; Scarlassara, F.; Söderström, P.-A.; Soić, N.; Stefanini, A. M.; Stezowski, O.; Theisen, Ch.; Ur, C. A.; Valiente-Dobón, J. J.; Varga Pajtler, M.

    2016-05-01

    We performed a γ -particle coincidence experiment for the 60Ni + 116Sn system to investigate whether the population of the two-neutron pickup channel leading to 62Ni is mainly concentrated in the ground-state transition, as has been found in a previous work [D. Montanari et al., Phys. Rev. Lett. 113, 052501 (2014), 10.1103/PhysRevLett.113.052501]. The experiment has been performed by employing the PRISMA magnetic spectrometer coupled to the Advanced Gamma Tracking Array (AGATA) demonstrator. The strength distribution of excited states corresponding to the inelastic, one- and two-neutron transfer channels has been extracted. We found that in the two-neutron transfer channel the strength to excited states corresponds to a fraction (less than 24%) of the total, consistent with the previously obtained results that the 2 n channel is dominated by the ground-state to ground-state transition.

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

    SciTech Connect

    Leinson, L. B.

    2010-12-15

    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.

  7. 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.

  8. 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.

  9. Total Scattering and Pair Distribution Function Analysis in Modelling Disorder in PZN

    SciTech Connect

    Whitfield, Ross E.; Goossens, Darren J; Welberry, T. R.

    2016-01-01

    The ability of the pair distribution function (PDF) analysis of total scattering (TS) from a powder to determine the local ordering in ferroelectric PZN (PbZn1/3Nb2/3O3) has been explored by comparison with a model established using single-crystal diffuse scattering (SCDS). While X-ray PDF analysis is discussed, the focus is on neutron diffraction results because of the greater extent of the data and the sensitivity of the neutron to oxygen atoms, the behaviour of which is important in PZN. The PDF was shown to be sensitive to many effects not apparent in the average crystal structure, including variations in the B-site—O separation distances and the fact that (110) Pb2+ displacements are most likely. A qualitative comparison between SCDS and the PDF shows that some features apparent in SCDS were not apparent in the PDF. These tended to pertain to short-range correlations in the structure, rather than to interatomic separations. For example, in SCDS the short-range alternation of the B-site cations was quite apparent in diffuse scattering at (½ ½ ½), whereas it was not apparent in the PDF.

  10. Total Scattering and Pair Distribution Function Analysis in Modelling Disorder in PZN

    DOE PAGES

    Whitfield, Ross E.; Goossens, Darren J; Welberry, T. R.

    2016-01-01

    The ability of the pair distribution function (PDF) analysis of total scattering (TS) from a powder to determine the local ordering in ferroelectric PZN (PbZn1/3Nb2/3O3) has been explored by comparison with a model established using single-crystal diffuse scattering (SCDS). While X-ray PDF analysis is discussed, the focus is on neutron diffraction results because of the greater extent of the data and the sensitivity of the neutron to oxygen atoms, the behaviour of which is important in PZN. The PDF was shown to be sensitive to many effects not apparent in the average crystal structure, including variations in the B-site—O separationmore » distances and the fact that (110) Pb2+ displacements are most likely. A qualitative comparison between SCDS and the PDF shows that some features apparent in SCDS were not apparent in the PDF. These tended to pertain to short-range correlations in the structure, rather than to interatomic separations. For example, in SCDS the short-range alternation of the B-site cations was quite apparent in diffuse scattering at (½ ½ ½), whereas it was not apparent in the PDF.« less

  11. 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

  12. Temperature effects on atomic pair distribution functions of melts

    SciTech Connect

    Ding, J. Ma, E.; Xu, M.; Guan, P. F.; Deng, S. W.; 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. Calculating Formulas of Coefficient and Mean Neutron Exposure in the Exponential Expression of Neutron Exposure Distribution

    NASA Astrophysics Data System (ADS)

    Zhang, F. H.; Zhou, G. D.; Ma, K.; Ma, W. J.; Cui, W. Y.; Zhang, B.

    2015-11-01

    Present studies have shown that, in the main stages of the development and evolution of asymptotic giant branch (AGB) star s-process models, the distributions of neutron exposures in the nucleosynthesis regions can all be expressed by an exponential function ({ρ_{AGB}}(τ) = C/{τ_0}exp ( - τ/{τ_0})) in the effective range of values. However, the specific expressions of the proportional coefficient C and the mean neutron exposure ({τ_0}) in the formula for different models are not completely determined in the related literatures. Through dissecting the basic solving method of the exponential distribution of neutron exposures, and systematically combing the solution procedure of exposure distribution for different stellar models, the general calculating formulas as well as their auxiliary equations for calculating C and ({τ_0}) are reduced. Given the discrete distribution of neutron exposures ({P_k}), i.e. the mass ratio of the materials which have exposed to neutrons for (k) ((k = 0, 1, 2 \\cdots )) times when reaching the final distribution with respect to the materials of the He intershell, (C = - {P_1}/ln R), and ({τ_0} = - Δ τ /ln R) can be obtained. Here, (R) expresses the probability that the materials can successively experience neutron irradiation for two times in the He intershell. For the convective nucleosynthesis model (including the Ulrich model and the ({}^{13}{C})-pocket convective burning model), (R) is just the overlap factor r, namely the mass ratio of the materials which can undergo two successive thermal pulses in the He intershell. And for the (^{13}{C})-pocket radiative burning model, (R = sumlimits_{k = 1}^∞ {{P_k}} ). This set of formulas practically give the corresponding relationship between C or ({τ_0}) and the model parameters. The results of this study effectively solve the problem of analytically calculating the distribution of neutron exposures in the low-mass AGB star s-process nucleosynthesis model of (^{13}{C

  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

  15. Calculating fusion neutron energy spectra from arbitrary reactant distributions

    NASA Astrophysics Data System (ADS)

    Eriksson, J.; Conroy, S.; Andersson Sundén, E.; Hellesen, C.

    2016-02-01

    The Directional Relativistic Spectrum Simulator (DRESS) code can perform Monte-Carlo calculations of reaction product spectra from arbitrary reactant distributions, using fully relativistic kinematics. The code is set up to calculate energy spectra from neutrons and alpha particles produced in the D(d, n)3He and T(d, n)4He fusion reactions, but any two-body reaction can be simulated by including the corresponding cross section. The code has been thoroughly tested. The kinematics calculations have been benchmarked against the kinematics module of the ROOT Data Analysis Framework. Calculated neutron energy spectra have been validated against tabulated fusion reactivities and against an exact analytical expression for the thermonuclear fusion neutron spectrum, with good agreement. The DRESS code will be used as the core of a detailed synthetic diagnostic framework for neutron measurements at the JET and MAST tokamaks.

  16. Pair distribution function study on compression of liquid gallium

    SciTech Connect

    Luo, Shengnian; Yu, Tony; Chen, Jiuhua; Ehm, Lars; Guo, Quanzhong; Parise, John

    2008-01-01

    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 {angstrom}. Liquid gallium structure has been studied by x-ray absorption (Di Cicco & Filipponi, 1993; Wei et al., 2000; Comez et al., 2001), x-ray diffraction studies (Waseda & Suzuki, 1972), and molecular dynamics simulation (Tsay, 1993; Hui et al., 2002). These previous reports have focused on the 1st nearest neighbor structure, which tells us little about the atomic arrangement outside the first shell in non- crystalline materials. This study focuses on the structure of liquid gallium and the atomic structure change due to compression. The PDF results show that the observed atomic distance of the first nearest neighbor at 2.78 {angstrom} (first G(r) peak and its shoulder at the higher Q position) is consistent with previous studies by x-ray absorption (2.76 {angstrom}, Comez et al., 2001). We have also observed that the first nearest neighbor peak position did not change with pressure increasing, while the farther peaks positions in the intermediate distance range decreased with pressure increasing. This leads to a conclusion of the possible existence of 'locally rigid units' in the liquid. With the addition of reverse Monte Carlo modeling, we have observed that the coordination number in the local rigit unit increases with pressure. The bulk modulus of liquid gallium derived from the volume compression curve at ambient temperature (300K) is 12.1(6) GPa.

  17. Particle-number conservation in quasiparticle representation in the isovector neutron-proton pairing case

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Until now, the Sharp-Bardeen-Cooper-Schrieffer (SBCS) particle-number projection method, in the isovector neutron-proton pairing case, has been developed in the particle representation. However, this formalism is sometimes complicated and cumbersome. In this work, the formalism is developed in the quasiparticle representation. An expression of the projected ground state wave function is proposed. Expressions of the energy as well as the expectation values of the total particle-number operator and its square are deduced. It is shown that these expressions are formally similar to their homologues in the pairing between like-particles case. They are easier to handle than the ones obtained using the particle representation and are more adapted to numerical calculations. The method is then numerically tested within the schematic one-level model, which allows comparisons with exact results, as well as in the case of even-even nuclei within the Woods-Saxon model. In each case, it is shown that the particle-number fluctuations that are inherent to the BCS method are completely eliminated by the projection. In the framework of the one-level model, the values of the projected energy are clearly closer to the exact values than the BCS ones. In realistic cases, the relative discrepancies between projected and unprojected values of the energy are small. However, the absolute deviations may reach several MeV.

  18. 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 γ-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

  19. Distribution of thermal neutron flux around a PET cyclotron.

    PubMed

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

    2011-05-01

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

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

    PubMed

    Tanaka, Kenichi; Endo, Satoru; Hoshi, Masaharu

    2010-01-01

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

  1. 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.

  2. 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.

  3. 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.

  4. Neutron monitor generated data distributions in quantum variational Monte Carlo

    NASA Astrophysics Data System (ADS)

    Kussainov, A. S.; Pya, N.

    2016-08-01

    We have assessed the potential applications of the neutron monitor hardware as random number generator for normal and uniform distributions. The data tables from the acquisition channels with no extreme changes in the signal level were chosen as the retrospective model. The stochastic component was extracted by fitting the raw data with splines and then subtracting the fit. Scaling the extracted data to zero mean and variance of one is sufficient to obtain a stable standard normal random variate. Distributions under consideration pass all available normality tests. Inverse transform sampling is suggested to use as a source of the uniform random numbers. Variational Monte Carlo method for quantum harmonic oscillator was used to test the quality of our random numbers. If the data delivery rate is of importance and the conventional one minute resolution neutron count is insufficient, we could always settle for an efficient seed generator to feed into the faster algorithmic random number generator or create a buffer.

  5. 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.

  6. Neutron and weak-charge distributions of the 48Ca nucleus

    DOE PAGES

    Hagen, Gaute; Forssen, Christian; Nazarewicz, Witold; Papenbrock, Thomas F.; Bacca, S.; Barnea, Nir; Carlsson, Boris; Drischler, Christian; Hebeler, Kai; Hjorth-Jensen, M.; et al

    2015-11-02

    What is the size of the atomic nucleus? This deceivably simple question is difficult to answer. Although 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 48Ca. We show that the neutron skin (difference between the radii of the neutron and proton distributions)more » is significantly smaller than previously thought. We also make predictions for the electric dipole polarizability and the weak form factor; both quantities that are at present targeted by precision measurements. Here, based on ab initio results for 48Ca, we provide a constraint on the size of a neutron star.« less

  7. 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.

  8. Distributed Pair Programming Using Collaboration Scripts: An Educational System and Initial Results

    ERIC Educational Resources Information Center

    Tsompanoudi, Despina; Satratzemi, Maya; Xinogalos, Stelios

    2015-01-01

    Since pair programming appeared in the literature as an effective method of teaching computer programming, many systems were developed to cover the application of pair programming over distance. Today's systems serve personal, professional and educational purposes allowing distributed teams to work together on the same programming project. The…

  9. 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.

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

    DOEpatents

    Crane, Thomas W.

    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.

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

    NASA Astrophysics Data System (ADS)

    Sakurai, Yoshinori; Kobayashi, Tooru

    2001-01-01

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

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

    PubMed

    Sakurai, Y; Kobayashi, T

    2001-01-01

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

  13. Validation of the MCNP computational model for neutron flux distribution with the neutron activation analysis measurement

    NASA Astrophysics Data System (ADS)

    Tiyapun, K.; Chimtin, M.; Munsorn, S.; Somchit, S.

    2015-05-01

    The objective of this work is to demonstrate the method for validating the predication of the calculation methods for neutron flux distribution in the irradiation tubes of TRIGA research reactor (TRR-1/M1) using the MCNP computer code model. The reaction rate using in the experiment includes 27Al(n, α)24Na and 197Au(n, γ)198Au reactions. Aluminium (99.9 wt%) and gold (0.1 wt%) foils and the gold foils covered with cadmium were irradiated in 9 locations in the core referred to as CT, C8, C12, F3, F12, F22, F29, G5, and G33. The experimental results were compared to the calculations performed using MCNP which consisted of the detailed geometrical model of the reactor core. The results from the experimental and calculated normalized reaction rates in the reactor core are in good agreement for both reactions showing that the material and geometrical properties of the reactor core are modelled very well. The results indicated that the difference between the experimental measurements and the calculation of the reactor core using the MCNP geometrical model was below 10%. In conclusion the MCNP computational model which was used to calculate the neutron flux and reaction rate distribution in the reactor core can be used for others reactor core parameters including neutron spectra calculation, dose rate calculation, power peaking factors calculation and optimization of research reactor utilization in the future with the confidence in the accuracy and reliability of the calculation.

  14. 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.

  15. Resolving the structure of Ti3C2Tx MXenes through multilevel structural modeling of the atomic pair distribution function

    DOE PAGES

    Wesolowski, David J.; Wang, Hsiu -Wen; Page, Katharine L.; Naguib, Michael; Gogotsi, Yury

    2015-12-08

    MXenes are a recently discovered family of two-dimensional (2D) early transition metal carbides and carbonitrides, which have already shown many attractive properties and a great promise in energy storage and many other applications. However, a complex surface chemistry and small coherence length has been an obstacle in some applications of MXenes, also limiting accuracy of predictions of their properties. In this study, we describe and benchmark a novel way of modeling layered materials with real interfaces (diverse surface functional groups and stacking order between the adjacent monolayers) against experimental data. The structures of three kinds of Ti3C2Tx MXenes (T standsmore » for surface terminating species, including O, OH, and F) produced under different synthesis conditions were resolved for the first time using atomic pair distribution function obtained by high-quality neutron total scattering. The true nature of the material can be easily captured with the sensitivity of neutron scattering to the surface species of interest and the detailed third-generation structure model we present. The modeling approach leads to new understanding of MXene structural properties and can replace the currently used idealized models in predictions of a variety of physical, chemical and functional properties of Ti3C2-based MXenes. Furthermore, the developed models can be employed to guide the design of new MXene materials with selected surface termination and controlled contact angle, catalytic, optical, electrochemical and other properties. We suggest that the multi-level structural modeling should form the basis for a generalized methodology on modeling diffraction and pair distribution function data for 2D and layered materials.« less

  16. 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)

  17. 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.

  18. 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

  19. The mean hydration of carbohydrates as studied by normalized two-dimensional radial pair distributions.

    PubMed

    Andersson, C; Engelsen, S B

    1999-04-01

    The hydration of carbohydrates plays a key role in many biological processes. Molecular dynamics simulations provide an effective tool for investigating the hydration of complex solutes such as carbohydrates. In this article we devise an algorithm for the calculation of two-dimensional radial pair distributions describing the probability of finding a water molecule in a site defined by two reference atoms. The normalized 2D radial pair distribution is proposed as an effective tool for investigating and comparing localized or ordered water sites around flexible molecules such as carbohydrates when analyzing molecular dynamics simulations and the utility of 2D radial pair distributions is demonstrated using sucrose as an example. In this relatively simple structure, 2D radial pair distributions were able to characterize and quantify the importance of two unique interresidue hydration sites in which a water molecule is forming a bridge between the glycopyranosyl and fructofuranosyl residues. The approach is proposed to be a valuable tool for comparing and understanding the hydration of flexible biomolecules such as carbohydrates. PMID:10680115

  20. Distribution of 1-alkyl-3-methylimidazolium ions and their ion pairs between dichloromethane and water.

    PubMed

    Katsuta, Shoichi; Yamaguchi, Naoko; Ogawa, Ryuji; Kudo, Yoshihiro; Takeda, Yasuyuki

    2008-10-01

    The distribution behavior of the salts of a series of 1-alkyl-3-methylimidazolium cations (RMeIm(+); R = butyl, hexyl, and octyl) with tetrafluoroborate (BF(4)(-)), hexafluorophosphate (PF(6)(-)), bis(trifluoromethanesulfonyl)amide (NTf(2)(-)), and 2,4,6-trinitrophenolate (Pic(-)) anions has been investigated in a dichloromethane-water system at 25 degrees C. The distribution constants (K(D)) of the ion pairs and the transfer activity coefficients ((o)gamma(w)) of the single ions were determined. For the ion pairs with a given anion, the log K(D) value increases linearly with the number of methylene groups (N(CH2)) in the cation, which can be explained by using the regular solution theory. A similar relationship was observed between log (o)gamma(w) and N(CH2) for the free RMeIm(+) ions, and the result was discussed by decomposing the transfer activity coefficient into the Born-type electrostatic contribution and the non-electrostatic one. For the free anions and their ion pairs with a given cation, the (o)gamma(w) and K(D) values increase with increasing molar volume of the anion: i.e., BF(4)(-) < PF(6)(-) < Pic(-) < NTf(2)(-). The features of the RMeIm(+) salts in the liquid-liquid distribution and the ion-pair formation in water are also discussed by comparing the present results with those of tetraalkylammonium salts previously reported.

  1. Calculating Formulae of Proportion Factor and Mean Neutron Exposure in the Exponential Expression of Neutron Exposure Distribution

    NASA Astrophysics Data System (ADS)

    Feng-Hua, Zhang; Gui-De, Zhou; Kun, Ma; Wen-Juan, Ma; Wen-Yuan, Cui; Bo, Zhang

    2016-07-01

    Previous studies have shown that, for the three main stages of the development and evolution of asymptotic giant branch (AGB) star s-process models, the neutron exposure distribution (DNE) in the nucleosynthesis region can always be considered as an exponential function, i.e., ρAGB(τ) = C/τ0 exp(-τ/τ0) in an effective range of the neutron exposure values. However, the specific expressions of the proportion factor C and the mean neutron exposure τ0 in the exponential distribution function for different models are not completely determined in the related literature. Through dissecting the basic method to obtain the exponential DNE, and systematically analyzing the solution procedures of neutron exposure distribution functions in different stellar models, the general formulae, as well as their auxiliary equations, for calculating C and τ0 are derived. Given the discrete neutron exposure distribution Pk, the relationships of C and τ0 with the model parameters can be determined. The result of this study has effectively solved the problem to analytically calculate the DNE in the current low-mass AGB star s-process nucleosynthesis model of 13C-pocket radiative burning.

  2. Equation of State of Superfluid Neutron Matter and the Calculation of the {sup 1}S{sub 0} Pairing Gap

    SciTech Connect

    Gandolfi, S.; Illarionov, A. Yu.; Schmidt, K. E.

    2008-09-26

    We present a quantum Monte Carlo study of the zero-temperature equation of state of neutron matter and the computation of the {sup 1}S{sub 0} pairing gap in the low-density regime with {rho}<0.04 fm{sup -3}. The system is described by a nonrelativistic nuclear Hamiltonian including both two- and three-nucleon interactions of the Argonne and Urbana type. This model interaction provides very accurate results in the calculation of the binding energy of light nuclei. A suppression of the gap with respect to the pure BCS theory is found, but sensibly weaker than in other works that attempt to include polarization effects in an approximate way.

  3. Theoretical study on neutron distribution of 208Pb by parity-violating electron scattering

    NASA Astrophysics Data System (ADS)

    Liu, Jian; Zhang, Cun; Ren, Zhong-Zhou; Xu, Chang

    2016-03-01

    The precise determination of neutron distribution has important implications for both nuclear structure and nuclear astrophysics. The purpose of this paper is to study the characteristics of neutron distribution of 208Pb by parity-violating electron scattering (PVS). Parity-violating asymmetries of 208Pb with different types of neutron skins are systematically calculated and compared with the experimental data of PREx. The results indicate that the PVS experiments are very sensitive to the nuclear neutron distributions. From further PVS measurements, detailed information on nuclear neutron distributions can be extracted. Supported by the National Natural Science Foundation of China (11505292, 11175085, 11235001, 11447226), by the Shandong Provincial Natural Science Foundation, China (BS2014SF007), by the Fundamental Research Funds for the Central Universities (15CX02072A, 15CX02070A, 15CX05026A, 13CX10022A, 14CX02157A).

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

  5. Uncovering the intrinsic geometry from the atomic pair distribution function of nanomaterials

    NASA Astrophysics Data System (ADS)

    Lei, Ming; de Graff, Adam M. R.; Thorpe, M. F.; Wells, Stephen A.; Sartbaeva, Asel

    2009-07-01

    Atomic pair distribution functions are useful because they have an easy intuitive interpretation and can be obtained both experimentally and from computer-generated structure models. For bulk materials, atomic pair distribution functions are solely determined by the intrinsic atomic geometry, i.e., how atoms are positioned with respect to one another. For a nanomaterial, however, the atomic pair distribution function also depends on the shape and size of the nanomaterial. A modified form of the radial distribution function is discussed that decouples shape and size effects from intrinsic effects so that nanomaterials of any shape and size, sharing a common atomic geometry, map onto a universal curve, by using a form factor. Mapping onto this universal curve allows differences in the intrinsic atomic geometry of nanomaterials of various shapes and sizes to be directly compared. This approach is demonstrated on nanoscale amorphous and crystalline silica models. It is shown how form factors can be computed for arbitrary shapes and this is illustrated for tetrahedral nanoparticles of vitreous silica.

  6. Neutron and weak-charge distributions of the 48Ca nucleus

    SciTech Connect

    Hagen, Gaute; Forssen, Christian; Nazarewicz, Witold; Papenbrock, Thomas F.; Bacca, S.; Barnea, Nir; Carlsson, Boris; Drischler, Christian; Hebeler, Kai; Hjorth-Jensen, M.; Miorelli, Mirko; Orlandini, Giuseppina; Schwenk, Achim; Simonis, Johannes; Jansen, Gustav R.; Ekstrom, A.; Wendt, K. A.

    2015-11-02

    What is the size of the atomic nucleus? This deceivably simple question is difficult to answer. Although 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 48Ca. We show that the neutron skin (difference between the radii of the 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 that are at present targeted by precision measurements. Here, based on ab initio results for 48Ca, we provide a constraint on the size of a neutron star.

  7. 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.

  8. Improvement of dose distribution by central beam shielding in boron neutron capture therapy

    NASA Astrophysics Data System (ADS)

    Sakurai, Yoshinori; Ono, Koji

    2007-12-01

    Since boron neutron capture therapy (BNCT) with epithermal neutron beams started at the Kyoto University Reactor (KUR) in June 2002, nearly 200 BNCT treatments have been carried out. The epithermal neutron irradiation significantly improves the dose distribution, compared with the previous irradiation mainly using thermal neutrons. However, the treatable depth limit still remains. One effective technique to improve the limit is the central shield method. Simulations were performed for the incident neutron energies and the annular components of the neutron source. It was clear that thermal neutron flux distribution could be improved by decreasing the lower energy neutron component and the inner annular component of the incident beam. It was found that a central shield of 4-6 cm diameter and 10 mm thickness is effective for the 12 cm diameter irradiation field. In BNCT at KUR, the depth dose distribution can be much improved by the central shield method, resulting in a relative increase of the dose at 8 cm depth by about 30%. In addition to the depth dose distribution, the depth dose profile is also improved. As the dose rate in the central area is reduced by the additional shielding, the necessary irradiation time, however, increases by about 30% compared to normal treatment.

  9. In-phantom neutron dose distribution for bladder cancer cases treated with high-energy photons

    NASA Astrophysics Data System (ADS)

    Khaled, N. E.; Attalla, E. M.; Ammar, H.; Khalil, W.

    2011-06-01

    This work presents an estimation of the neutron dose distribution for common bladder cancer cases treated with high-energy photons of 15 MV therapy accelerators. Neutron doses were measured in an Alderson phantom, using TLD 700 and 600 thermoluminescence dosimeters, resembling bladder cancer cases treated with high-energy photons from 15 MV LINAC and having a treatment plan using the four-field pelvic box technique. Thermal neutron dose distribution in the target area and the surrounding tissue was estimated. The sensitivity of all detectors for both gamma and neutrons was estimated and used for correction of the TL reading. TLD detectors were irradiated with a Co60 gamma standard source and thermal neutrons at the irradiation facility of the National Institute for Standards (NIS). The TL to dose conversion factor was estimated in terms of both Co60 neutron equivalent dose and thermal neutron dose. The dose distribution of photo-neutrons throughout each target was estimated and presented in three-dimensional charts and isodose curves. The distribution was found to be non-isotropic through the target. It varied from a minimum of 0.23 mSv/h to a maximum of 2.07 mSv/h at 6 cm off-axis. The mean neutron dose equivalent was found to be 0.63 mSv/h, which agrees with other published literature. The estimated average neutron equivalent to the bladder per administered therapeutic dose was found to be 0.39 mSv Gy-1, which is also in good agreement with published literature. As a consequence of a complete therapeutic treatment of 50 Gy high-energy photons at 15 MV, the total thermal neutron equivalent dose to the abdomen was found to be about 0.012 Sv.

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

    PubMed

    Sakurai, Yoshinori; Kobayashi, Tooru

    2002-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  12. Measurement of Vertical Temperature Distribution Using a Single Pair of Loudspeaker and Microphone with Acoustic Reflection

    NASA Astrophysics Data System (ADS)

    Saito, Ikumi; Mizutani, Koichi; Wakatsuki, Naoto; Kawabe, Satoshi

    2009-07-01

    It is important to maintain an adequate indoor temperature for comfortable working conditions, improvement of the rate of production of farm goods grown in greenhouses, and for saving energy. Thus, it is necessary to measure the temperature distribution to realize efficient air-conditioning systems. However, we have to use many conventional instruments to measure the temperature distribution. We proposed a measurement system for vertical temperature distribution using a single pair of loudspeaker (SP) and microphone (MIC), and acoustic reflectors. This system consists of SP, MIC, and multiple acoustic reflectors, and it can be used to determine the temperature distribution from the mean temperature of the area bounded by two reflectors. In experiments, the vertical temperature distribution was measured using five sound probes in a large facility every 20 s for 24 h. From the results of this experiment, it was verified that this system can be used to measure the vertical temperature distribution from the mean temperature of each area bounded by two reflectors. This system could be used to measure the change in the temperature distribution over time. We constructed a simple system to measure the vertical temperature distribution.

  13. Verification of Anderson Superexchange in MnO via Magnetic Pair Distribution Function Analysis and ab initio Theory.

    PubMed

    Frandsen, Benjamin A; Brunelli, Michela; Page, Katharine; Uemura, Yasutomo J; Staunton, Julie B; Billinge, Simon J L

    2016-05-13

    We present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ∼1  nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory. PMID:27232042

  14. Verification of Anderson Superexchange in MnO via Magnetic Pair Distribution Function Analysis and ab initio Theory

    NASA Astrophysics Data System (ADS)

    Frandsen, Benjamin A.; Brunelli, Michela; Page, Katharine; Uemura, Yasutomo J.; Staunton, Julie B.; Billinge, Simon J. L.

    2016-05-01

    We present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ˜1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory.

  15. Investigating short-range magnetism in strongly correlated materials via magnetic pair distribution function analysis and ab initio theory

    NASA Astrophysics Data System (ADS)

    Frandsen, Benjamin; Page, Katharine; Brunelli, Michela; Staunton, Julie; Billinge, Simon

    Short-range magnetic correlations are known to exist in a variety of strongly correlated electron systems, but our understanding of the role they play is challenged by the difficulty of experimentally probing such correlations. Magnetic pair distribution function (mPDF) analysis is a newly developed neutron total scattering method that can reveal short-range magnetic correlations directly in real space, and may therefore help ameliorate this difficulty. We present temperature-dependent mPDF measurements of the short-range magnetic correlations in the paramagnetic phase of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. We observe significant correlations on a ~1 nm length scale that differ substantially from the low-temperature long-range-ordered spin arrangement. With no free parameters, ab initio calculations using the self-interaction-corrected local spin density approximation of density functional theory quantitatively reproduce the magnetic correlations to a high degree of accuracy. These results yield valuable insight into the magnetic exchange in MnO and showcase the utility of the mPDF technique for studying magnetic properties of strongly correlated electron systems.

  16. Verification of Anderson superexchange in MnO via magnetic pair distribution function analysis and ab initio theory

    DOE PAGES

    Benjamin A. Frandsen; Brunelli, Michela; Page, Katharine; Uemura, Yasutomo J.; Staunton, Julie B.; Billinge, Simon J. L.

    2016-05-11

    Here, we present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ~1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominatedmore » by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. Furthermore, the Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory.« less

  17. Electron and thermal neutron lateral distribution functions in EAS at high altitude

    NASA Astrophysics Data System (ADS)

    Shchegolev, O. B.; Alekseenko, V. V.; Cai, Z. Y.; Cao, Z.; Cui, S. W.; Gromushkin, D. M.; Guo, X. W.; He, H. H.; Liu, Y.; Ma, X.; Stenkin, Yu V.; Stepanov, V. I.; Zhao, J.

    2016-05-01

    EAS array of novel type have been constructed on the base of ARGO-YBJ experiment (Tibet, China). It consists of the four specially designed scintillator en-detectors capable to measure two main EAS components: hadrons through thermal neutrons (n) and electrons (e). The results of simulation for these arrays using CORSIKA and GEANT4 codes are presented. Simulated thermal neutron and electron lateral distributions are compared with experimental data. Obtained distributions are compared with those obtained by other arrays.

  18. Lepton distributions from the decay of wino pairs at e/sup +/e/sup -/ colliders

    SciTech Connect

    Schimert, T.; Burgess, C.; Tata, X.

    1984-07-01

    We have computed, in detail, the energy and angular distribution of the leptons (l) produced by the decay of winos (W-tilde) via the reaction e/sup +/e/sup -/ ..-->.. W-tilde/sup +/ + W-tilde/sup -/ ..-->.. l/sup +/nu..gamma..-tilde + l/sup -/anti nu..gamma..-tilde within the framework of a supergravity electroweak model. We have also computed the backgrounds to this reaction from the production and subsequent decays of tau/sup +/tau/sup -/ pairs or pairs of new sequential heavy leptons. We conclude that it is possible to distinguish the wino from an ordinary heavy lepton and, moreover, that winos lighter than the W-boson would be clearly identifiable at LEP energies. 22 refs., 3 figs.

  19. Results on the neutron energy distribution measurements at the RECH-1 Chilean nuclear reactor

    NASA Astrophysics Data System (ADS)

    Aguilera, P.; Molina, F.; Romero-Barrientos, J.

    2016-07-01

    Neutron activations experiments has been perform at the RECH-1 Chilean Nuclear Reactor to measure its neutron flux energy distribution. Samples of pure elements was activated to obtain the saturation activities for each reaction. Using - ray spectroscopy we identify and measure the activity of the reaction product nuclei, obtaining the saturation activities of 20 reactions. GEANT4 and MCNP was used to compute the self shielding factor to correct the cross section for each element. With the Expectation-Maximization algorithm (EM) we were able to unfold the neutron flux energy distribution at dry tube position, near the RECH-1 core. In this work, we present the unfolding results using the EM algorithm.

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

    SciTech Connect

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

    2006-03-20

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

  1. 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.

  2. 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.

  3. 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.

  4. d sigma/dy Distribution of Drell-Yan Dielectron Pairs

    SciTech Connect

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

    2007-11-01

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

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

    SciTech Connect

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

    2012-05-01

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

  6. Angular distribution of positrons in coherent pair production in deformed crystals.

    PubMed

    Parazian, V V

    2009-05-01

    We investigate the angular distribution of positrons in the coherent process electron-positron pair creation process by high-energy photons in a periodically deformed single crystal with a complex base. The formula for the corresponding differential cross section is derived for an arbitrary deformation field. The case is considered in detail when the photon enters into the crystal at small angles with respect to a crystallographic axis. The results of the numerical calculations are presented for SiO(2) and diamond single crystals and Moliere parameterization of the screened atomic potentials in the case of the deformation field generated by an acoustic wave of S-type.

  7. Computation of pair distribution functions and three-dimensional densities with a reduced variance principle

    NASA Astrophysics Data System (ADS)

    Borgis, Daniel; Assaraf, Roland; Rotenberg, Benjamin; Vuilleumier, Rodolphe

    2013-12-01

    No fancy statistical objects here, we go back to the computation of one of the most basic and fundamental quantities in the statistical mechanics of fluids, namely the pair distribution functions. Those functions are usually computed in molecular simulations by using histogram techniques. We show here that they can be estimated using a global information on the instantaneous forces acting on the particles, and that this leads to a reduced variance compared to the standard histogram estimators. The technique is extended successfully to the computation of three-dimensional solvent densities around tagged molecular solutes, quantities that are noisy and very long to converge, using histograms.

  8. 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.

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

    SciTech Connect

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

    2012-03-15

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

  10. SU-E-T-594: Out-Of-Field Neutron and Gamma Dose Estimated Using TLD-600/700 Pairs in the Wobbling Proton Therapy System

    SciTech Connect

    Chen, Y; Lin, Y; Tsai, H

    2015-06-15

    Purpose: Secondary fast neutrons and gamma rays are mainly produced due to the interaction of the primary proton beam with the beam delivery nozzle. These secondary radiation dose to patients and radiation workers are unwanted. The purpose of this study is to estimate the neutron and gamma dose equivalent out of the treatment volume during the wobbling proton therapy system. Methods: Two types of thermoluminescent (TL) dosimeters, TLD-600 ({sup 6}LiF: Mg, Ti) and TLD-700 ({sup 7}LiF: Mg, Ti) were used in this study. They were calibrated in the standard neutron and gamma sources at National Standards Laboratory. Annealing procedure is 400°C for 1 hour, 100°C for 2 hours and spontaneously cooling down to the room temperature in a programmable oven. Two-peak method (a kind of glow curve analysis technique) was used to evaluate the TL response corresponding to the neutron and gamma dose. The TLD pairs were placed outside the treatment field at the neutron-gamma mixed field with 190-MeV proton beam produced by the wobbling system through the polyethylene plate phantom. The results of TLD measurement were compared to the Monte Carlo simulation. Results: The initial experiment results of calculated dose equivalents are 0.63, 0.38, 0.21 and 0.13 mSv per Gy outside the field at the distance of 50, 100, 150 and 200 cm. Conclusion: The TLD-600 and TLD-700 pairs are convenient to estimate neutron and gamma dosimetry during proton therapy. However, an accurate and suitable glow curve analysis technique is necessary. During the wobbling system proton therapy, our results showed that the neutron and gamma doses outside the treatment field are noticeable. This study was supported by the grants from the Chang Gung Memorial Hospital (CMRPD1C0682)

  11. Conditional pair distributions in many-body systems: exact results for Poisson ensembles.

    PubMed

    Rohrmann, René D; Zurbriggen, Ernesto

    2012-05-01

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

  12. Measurement device-independent quantum key distribution with heralded pair coherent state

    NASA Astrophysics Data System (ADS)

    Chen, Dong; Shang-Hong, Zhao; Lei, Shi

    2016-10-01

    The original measurement device-independent quantum key distribution is reviewed, and a modified protocol using heralded pair coherent state (HPCS) is proposed to overcome the quantum bit error rate associated with the dark count rate of the detectors in long-distance quantum key distribution. Our simulation indicates that the secure transmission distance can be improved evidently with HPCS owing to the lower probability of vacuum events when compared with weak coherent source scenario, while the secure key rate can be increased with HPCS due to the higher probability of single-photon events when compared with heralded single-photon source scenario. Furthermore, we apply the finite key analysis to the decoy state MDI-QKD with HPCS and obtain a practical key rate.

  13. Measurement device-independent quantum key distribution with heralded pair coherent state

    NASA Astrophysics Data System (ADS)

    Chen, Dong; Shang-Hong, Zhao; Lei, Shi

    2016-07-01

    The original measurement device-independent quantum key distribution is reviewed, and a modified protocol using heralded pair coherent state (HPCS) is proposed to overcome the quantum bit error rate associated with the dark count rate of the detectors in long-distance quantum key distribution. Our simulation indicates that the secure transmission distance can be improved evidently with HPCS owing to the lower probability of vacuum events when compared with weak coherent source scenario, while the secure key rate can be increased with HPCS due to the higher probability of single-photon events when compared with heralded single-photon source scenario. Furthermore, we apply the finite key analysis to the decoy state MDI-QKD with HPCS and obtain a practical key rate.

  14. 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.

  15. 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.

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

    PubMed

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

    2006-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-07-01

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

  18. Distributed data processing and analysis environment for neutron scattering experiments at CSNS

    NASA Astrophysics Data System (ADS)

    Tian, H. L.; Zhang, J. R.; Yan, L. L.; Tang, M.; Hu, L.; Zhao, D. X.; Qiu, Y. X.; Zhang, H. Y.; Zhuang, J.; Du, R.

    2016-10-01

    China Spallation Neutron Source (CSNS) is the first high-performance pulsed neutron source in China, which will meet the increasing fundamental research and technique applications demands domestically and overseas. A new distributed data processing and analysis environment has been developed, which has generic functionalities for neutron scattering experiments. The environment consists of three parts, an object-oriented data processing framework adopting a data centered architecture, a communication and data caching system based on the C/S paradigm, and data analysis and visualization software providing the 2D/3D experimental data display. This environment will be widely applied in CSNS for live data processing.

  19. Cross Section Sensitivity and Uncertainty Analysis Including Secondary Neutron Energy and Angular Distributions.

    1991-03-12

    Version 00 SUSD calculates sensitivity coefficients for one- and two-dimensional transport problems. Variance and standard deviation of detector responses or design parameters can be obtained using cross-section covariance matrices. In neutron transport problems, this code can perform sensitivity-uncertainty analysis for secondary angular distribution (SAD) or secondary energy distribution (SED).

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

    NASA Astrophysics Data System (ADS)

    Koehler, P. E.; Bečvář, F.; Krtička, 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, Γ0n, showed that the distributions of Γ0n 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, Γγ, 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 Γγ 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 γ-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 Γγ data also nicely reproduces spectra from several (n,γ) experiments on the neighbor nuclide 198Au.

  1. 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 μm 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 μm diameter roots (R) 3D reconstruction of maize seedling following neutron tomography

  2. 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.

  3. The total scattering atomic pair distribution function: New methodology for nanostructure analysis

    NASA Astrophysics Data System (ADS)

    Masadeh, Ahmad

    The conventional xray diffration (XRD) methods probe for the presence of long-range order (periodic structure) which are reflected in the Bragg peaks. Local structural deviations or disorder mainly affect the diffuse scattering intensity. In order to obtain structural information about both long-range order and local structure disorder, a technique that takes in account both Bragg and diffuse scattering need to be employed, such as the atomic pair distribution function (PDF) technique. This work introduces a PDF based methodology to quantitatively investigate nanostructure materials in general. The introduced methodology can be applied to extract quantitatively structural information about structure, crystallinity level, core/shell size, nanoparticle size, and inhomogeneous internal strain in the measured nanoparticles. This method is generally applicable to the characterization of the nano-scale solid, many of which may exhibit complex disorder and strain

  4. Organic-modified and biological silica studied by synchrotron x-ray pair distribution function measurements

    NASA Astrophysics Data System (ADS)

    Dimasi, Elaine; Jeffryes, Clayton; Rorrer, Gregory; Belton, David; Perry, Carole

    2007-03-01

    Biomineralization is a process by which living organisms create composite organic/mineral tissues which have hierarchical structures on micron and submicron scales. Fine control over mineral phase and morphology make biomineralization an important inspiration for materials science. It is often not appreciated that even amorphous minerals such as silica can exhibit hierarchical structure and special properties. One difficulty is that the molecular structures of amorphous phases can be hard to elucidate. We are exploring the use of pair distribution function measurements from synchrotron x-ray scattering to study silica structures, comparing both synthetic organic-modifed silicas and germanium-containing biosilica from diatoms. The raw scattering patterns show clear differences. We will discuss how these data can be scrutinized to determine what differences may be created at the molecular level by different silicification processes.

  5. 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.

  6. 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

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

    DOE PAGES

    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

  8. Novel trends in pair distribution function approaches on bulk systems with nanoscale heterogeneities

    DOE PAGES

    Emil S. Bozin; Billinge, Simon J. L.

    2016-07-29

    Novel materials for high performance applications increasingly exhibit structural order on the nanometer length scale; a domain where crystallography, the basis of Rietveld refinement, fails [1]. In such instances the total scattering approach, which treats Bragg and diffuse scattering on an equal basis, is a powerful approach. In recent years, the analysis of the total scattering data became an invaluable tool and the gold standard for studying nanocrystalline, nanoporous, and disordered crystalline materials. The data may be analyzed in reciprocal space directly, or Fourier transformed to the real-space atomic pair distribution function (PDF) and this intuitive function examined for localmore » structural information. Here we give a number of illustrative examples, for convenience picked from our own work, of recent developments and applications of total scattering and PDF analysis to novel complex materials. There are many other wonderful examples from the work of others.« less

  9. Measurement of the angular distribution of neutron-proton scattering at 10 MeV

    SciTech Connect

    Haight, R.C.; Bateman, F.B.; Grimes, S.M.; Brient, C.E.; Massey, T.N.; Wasson, O.A.; Carlson, A.D.; Zhou, H.

    1995-12-31

    The relative angular distribution of neutrons scattered from protons was measured at an incident neutron energy of 10 MeV at the Ohio University Accelerator Laboratory. An array of 11 detector telescopes at laboratory angles of 0 to 60 degrees was used to detect recoil protons from neutron interactions with a CH{sub 2} (polypropylene) target. Data for 7 of these telescopes were obtained with one set of electronics and are presented here. These data, from 108 to 180 degrees for the center-of-mass scattering angles, have a small slope which agrees better with angular distributions predicted by the Arndt phase shifts than with the ENDF/B-VI angular distribution.

  10. Neutron distribution and induced activity inside a Linac treatment room.

    PubMed

    Juste, B; Miró, R; Verdú, G; Díez, S; Campayo, J M

    2015-01-01

    Induced radioactivity and photoneutron contamination inside a radiation therapy bunker of a medical linear accelerator (Linac) is investigated in this work. The Linac studied is an Elekta Precise electron accelerator which maximum treatment photon energy is 15 MeV. This energy exceeds the photonuclear reaction threshold (around 7 MeV for high atomic number metals). The Monte Carlo code MCNP6 has been used for quantifying the neutron contamination inside the treatment room for different gantry rotation configuration. Walls activation processes have also been simulated. The approach described in this paper is useful to prevent the overexposure of patients and medical staff. PMID:26737878

  11. Structure of a fluid dioleoylphosphatidylcholine bilayer determined by joint refinement of x-ray and neutron diffraction data. I. Scaling of neutron data and the distributions of double bonds and water.

    PubMed Central

    Wiener, M. C.; King, G. I.; White, S. H.

    1991-01-01

    We described in two previous papers a method for the joint refinement of the structure of fluid bilayers using neutron and x-ray diffraction data (Wiener, M. C., and S. H. White 1991a, b. Biophys. J. 59: 162-173 and 174-185). An essential part of the method is the appropriate scaling of the diffraction data. Here we describe the scaling of the neutron data and the determination of the transbilayer distribution of double bonds in liquid-crystalline (L alpha phase) phospholipid bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). The distribution was determined by neutron diffraction of oriented multilayers (66% RH) of DOPC specifically deuterated at the 9- and 10-position of both acyl chains. The double-bond distribution is described accurately by a pair of Gaussian functions each located at a position Zcc = 7.88 +/- 0.09 A from the bilayer center with 1/e-halfwidths of Acc = 4.29 +/- 0.16 A. Previously, we determined the transbilayer distribution of bromine atoms in a specifically halogenated lipid, 1-oleoyl-2-9,10-dibromostearoyl-sn-glycero-3-phosphocholine (OBPC), and showed it to be an isomorphous replacement for DOPC (Wiener, M. C., and S. H. White, 1991c. Biochemistry. In press). A comparison of the double-bond and bromine profiles indicates that the positions of the centers of the deuterated double bond and the brominated methylene Gaussian distributions are equal within experimental error and that each label undergoes similar average thermal motions with respect to the bilayer normal. The observation that the average position of a label on both acyl chains (the deuterated double bonds) is similar to the average position of a label on the 2-chain alone (the brominated methylenes) indicates that the maximum separation along the bilayer normal between the double bonds of the acyl chains is 1 A or less. The fully-resolved transbilayer water distribution, previously determined at lower resolution (Jacobs, R. E., and S. H. White. 1989. Biochemistry. 28

  12. 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.

  13. 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

  14. Transmission Probability Code System for Calculating Neutron Flux Distributions in Hexagonal Geometry.

    1991-01-25

    Version 00 TPHEX calculates the multigroup neutron flux distribution in an assembly of hexagonal cells using a transmission probability (interface current) method. It is primarily intended for calculations on hexagonal LWR fuel assemblies but can be used for other purposes subject to the qualifications mentioned in Restrictions/Limitations.

  15. Total scattering and pair distribution function analysis in modelling disorder in PZN (PbZn1/3Nb2/3O3).

    PubMed

    Whitfield, Ross E; Goossens, Darren J; Welberry, T Richard

    2016-01-01

    The ability of the pair distribution function (PDF) analysis of total scattering (TS) from a powder to determine the local ordering in ferroelectric PZN (PbZn1/3Nb2/3O3) has been explored by comparison with a model established using single-crystal diffuse scattering (SCDS). While X-ray PDF analysis is discussed, the focus is on neutron diffraction results because of the greater extent of the data and the sensitivity of the neutron to oxygen atoms, the behaviour of which is important in PZN. The PDF was shown to be sensitive to many effects not apparent in the average crystal structure, including variations in the B-site-O separation distances and the fact that 〈110〉 Pb(2+) displacements are most likely. A qualitative comparison between SCDS and the PDF shows that some features apparent in SCDS were not apparent in the PDF. These tended to pertain to short-range correlations in the structure, rather than to interatomic separations. For example, in SCDS the short-range alternation of the B-site cations was quite apparent in diffuse scattering at (½ ½ ½), whereas it was not apparent in the PDF. PMID:26870378

  16. Total scattering and pair distribution function analysis in modelling disorder in PZN (PbZn1/3Nb2/3O3)

    PubMed Central

    Whitfield, Ross E.; Goossens, Darren J.; Welberry, T. Richard

    2016-01-01

    The ability of the pair distribution function (PDF) analysis of total scattering (TS) from a powder to determine the local ordering in ferroelectric PZN (PbZn1/3Nb2/3O3) has been explored by comparison with a model established using single-crystal diffuse scattering (SCDS). While X-ray PDF analysis is discussed, the focus is on neutron diffraction results because of the greater extent of the data and the sensitivity of the neutron to oxygen atoms, the behaviour of which is important in PZN. The PDF was shown to be sensitive to many effects not apparent in the average crystal structure, including variations in the B-site—O separation distances and the fact that 〈110〉 Pb2+ displacements are most likely. A qualitative comparison between SCDS and the PDF shows that some features apparent in SCDS were not apparent in the PDF. These tended to pertain to short-range correlations in the structure, rather than to interatomic separations. For example, in SCDS the short-range alternation of the B-site cations was quite apparent in diffuse scattering at (½ ½ ½), whereas it was not apparent in the PDF. PMID:26870378

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

    SciTech Connect

    Tatarskiy, D. A. Udalov, O. G.; Fraerman, A. A.

    2012-10-15

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

  18. 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 (β 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

  19. Atomic Structure of a Cesium Aluminosilicate Geopolymer: A Pair Distribution Function Study

    SciTech Connect

    Bell, J.; Sarin, P; Provis, J; Haggerty, R; Driemeyer, P; Chupas, P; van Deventer, J; Kriven, W

    2008-01-01

    The atomic pair distribution function (PDF) method was used to study the structure of cesium aluminosilicate geopolymer. The geopolymer was prepared by reacting metakaolin with cesium silicate solution followed by curing at 50C for 24 h in a sealed container. Heating of Cs-geopolymer above 1000C resulted in formation of crystalline pollucite (CsAlSi{sub 2}O{sub 6}). PDF refinement of the pollucite phase formed displayed an excellent fit over the 10-30 {angstrom} range when compared with a cubic pollucite model. A poorer fit was attained from 1-10 {angstrom} due to an additional amorphous phase present in the heated geopolymer. On the basis of PDF analysis, unheated Cs-geopolymer displayed structural ordering similar to pollucite up to a length scale of 9 {angstrom}, despite some differences. Our results suggest that hydrated Cs{sup +} ions were an integral part of the Cs-geopolymer structure and that most of the water present was not associated with Al-OH or Si-OH bonds.

  20. X-ray Pair Distribution Function Analysis of Potassium Based Geopolymer

    SciTech Connect

    Bell, J.; Sarin, P; Driemeyer, P; Haggerty, R; Chupas, P; Kriven, W

    2008-01-01

    The atomic structure of geopolymers is often described as amorphous with a local structure that is equivalent to that of crystalline zeolites. However, this structural relationship has never been quantified beyond a first-nearest-neighbor bonding environment. In this study, the short to medium range (1 nm) structural order of metakaolin-based KAlSi{sub 2}O{sub 6}{center_dot}5.5H{sub 2}O geopolymer was quantified and compared to zeolitic tetragonal leucite (KAlSi2O6) using the X-ray atomic pair distribution function technique. Unheated KAlSi{sub 2}O{sub 6}{center_dot}5.5H{sub 2}O was found to be structurally similar to leucite out to a length of 8 {angstrom}, but had increased medium range disorder over the 4.5 {angstrom} < r < 8 {angstrom} range. On heating to >300 C, changes in the short to medium range structure were observed due to dehydration and removal of chemically bound water. Crystallization of leucite occurred in samples heated beyond 1050 C. Refinements of a leucite model against the PDF data for geopolymer heated to 1100 C for 24 h yielded a good fit.

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

    PubMed

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

    2009-04-01

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

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

    SciTech Connect

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

    2016-01-01

    In this study, 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 (β 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.

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

    DOE PAGES

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

    2016-01-01

    In this study, 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 bemore » 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 (β 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.« less

  4. Synthesis and structural characterisation using Rietveld and pair distribution function analysis of layered mixed titaniumzirconium phosphates

    SciTech Connect

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

    2010-07-24

    Crystalline metal (IV) phosphates with variable zirconium-to-titanium molar ratios of general formula (Ti1-xZrx)(HPO4)2 • H2O have been prepared by precipitation of soluble salts of the metals with phosphoric acid and heating the amorphous solids in 12 M H3PO4 in an autoclave. The new materials are structurally characterised by Rietveld analysis of synchrotron X-ray powder diffraction data and pair distribution function (PDF) analysis of high energy synchrotron X-ray total scattering data. A broad range of zirconium-titanium phosphate solid solutions were formed showing isomorphous substitution of titanium by zirconium in the α-titanium phosphate lattice and vice versa for titanium substitution into the α-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.

  5. 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.

  6. 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 (β 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.

  7. 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.

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

    PubMed

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

    2012-01-14

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

  9. Measurement of energy and direction distribution of neutron and photon fluences in workplace fields.

    PubMed

    Luszik-Bhadra, M; Reginatto, M; Lacoste, V

    2004-01-01

    Within the EU Project EVIDOS, a spectrometer with 24 silicon detectors mounted on the surface of a polyethylene sphere is used for the determination of the energy and direction distribution of neutrons and photons. It has been characterized with respect to neutron radiation with energies from thermal up to 15 MeV and to photon radiation with energies from 65 keV to 6 MeV. The first measurements described here were performed in the simulated workplace field, CANEL, at Cadarache, with the purpose of checking the instrument and the unfolding procedures.

  10. Nucleon-nucleon momentum-correlation function as a probe of the density distribution of valence neutrons in neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Cao, X. G.; Cai, X. Z.; Ma, Y. G.; Fang, D. Q.; Zhang, G. Q.; Guo, W.; Chen, J. G.; Wang, J. S.

    2012-10-01

    Proton-neutron, neutron-neutron, and proton-proton momentum-correlation functions (Cpn,Cnn, and Cpp) are systematically investigated for 15C and other C-isotope-induced collisions at different entrance channel conditions within the framework of the isospin-dependent quantum-molecular-dynamics model complemented by the correlation after burner (crab) computation code. 15C is a prime exotic nucleus candidate due to the weakly bound valence neutron coupling with closed-neutron-shell nucleus 14C. To study density dependence of the correlation function by removing the isospin effect, the initialized 15C projectiles are sampled from two kinds of density distribution from the relativistic mean-field (RMF) model in which the valence neutron of 15C is populated in both 1d5/2 and 2s1/2 states, respectively. The results show that the density distributions of the valence neutron significantly influence the nucleon-nucleon momentum-correlation function at large impact parameters and high incident energies. The extended density distribution of the valence neutron largely weakens the strength of the correlation function. The size of the emission source is extracted by fitting the correlation function by using the Gaussian source method. The emission source size as well as the size of the final-state phase space are larger for projectile samplings from more extended density distributions of the valence neutron, which corresponds to the 2s1/2 state in the RMF model. Therefore, the nucleon-nucleon momentum-correlation function can be considered as a potentially valuable tool to diagnose exotic nuclear structures, such as the skin and halo.

  11. Energy dependence of nuclear charge distribution in neutron induced fission of Z-even nuclei

    NASA Astrophysics Data System (ADS)

    Roshchenko, V. A.; Piksaikin, V. M.; Isaev, S. G.; Goverdovski, A. A.

    2006-07-01

    For the first time the distribution of nuclear charge of fission products with mass numbers 87, 88, 89, 91, 93, 94, 95, 137, 138, 139, and 140 and their complementary products have been studied for neutron induced fission of U235 and Pu239 in the energy range from thermal up to 1.2 MeV. The energy dependences of the cumulative yields of Br87, Br88, Br89, Br91, Kr93, Rb94, Rb95, I137, I138, I139, and I140 have been obtained by delayed neutron measurements. The most probable charge ZP(A)in the appropriate isobaric β-decay chains was estimated. The results were analyzed in terms of the deviation ΔZP(A') of the most probable charge of isobaric β-decay chains from the unchanged charge distribution before prompt neutron emission (nuclear charge polarization) and they are compared with experimental data of other authors and with predictions from Nethaway's ZP-formula and Wahl's ZP-model. We show that the nuclear charge polarization of primary fission fragments <ΔZP(A')> before prompt neutron evaporation decreases as the excitation energy of the compound nucleus increases. This decrease is more pronounced for fission of U235. The energy dependencies of ΔZP(A') and ΔZP(ZP) obtained in the present work show an attenuation of the odd-even effects in the charge distribution as the excitation energy of the compound nucleus increases.

  12. 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.

  13. 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.

  14. 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.

  15. Structural dynamics and activity of nanocatalysts inside fuel cells by in operando atomic pair distribution studies

    NASA Astrophysics Data System (ADS)

    Petkov, Valeri; Prasai, Binay; Shan, Shiyao; Ren, Yang; Wu, Jinfang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian

    2016-05-01

    Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE-XRD) we tracked the evolution of the atomic structure and activity of noble metal-transition metal (NM-TM) nanocatalysts for ORR as they function at the cathode of a fully operational proton exchange membrane fuel cell (PEMFC). Experimental HE-XRD data were analysed in terms of atomic pair distribution functions (PDFs) and compared to the current output of the PEMFC, which was also recorded during the experiments. The comparison revealed that under actual operating conditions, NM-TM nanocatalysts can undergo structural changes that differ significantly in both length-scale and dynamics and so can suffer losses in their ORR activity that differ significantly in both character and magnitude. Therefore we argue that strategies for reducing ORR activity losses should implement steps for achieving control not only over the length but also over the time-scale of the structural changes of NM-TM NPs that indeed occur during PEMFC operation. Moreover, we demonstrate how such a control can be achieved and thereby the performance of PEMFCs improved considerably. Last but not least, we argue that the unique capabilities of in operando HE-XRD coupled to atomic PDF analysis to characterize active nanocatalysts inside operating fuel cells both in a time-resolved manner and with atomic level resolution, i.e. in 4D, can serve well the ongoing search for nanocatalysts that deliver more with less platinum.Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE

  16. 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.

  17. Structural dynamics and activity of nanocatalysts inside fuel cells by in operando atomic pair distribution studies.

    PubMed

    Petkov, Valeri; Prasai, Binay; Shan, Shiyao; Ren, Yang; Wu, Jinfang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian

    2016-05-19

    Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE-XRD) we tracked the evolution of the atomic structure and activity of noble metal-transition metal (NM-TM) nanocatalysts for ORR as they function at the cathode of a fully operational proton exchange membrane fuel cell (PEMFC). Experimental HE-XRD data were analysed in terms of atomic pair distribution functions (PDFs) and compared to the current output of the PEMFC, which was also recorded during the experiments. The comparison revealed that under actual operating conditions, NM-TM nanocatalysts can undergo structural changes that differ significantly in both length-scale and dynamics and so can suffer losses in their ORR activity that differ significantly in both character and magnitude. Therefore we argue that strategies for reducing ORR activity losses should implement steps for achieving control not only over the length but also over the time-scale of the structural changes of NM-TM NPs that indeed occur during PEMFC operation. Moreover, we demonstrate how such a control can be achieved and thereby the performance of PEMFCs improved considerably. Last but not least, we argue that the unique capabilities of in operando HE-XRD coupled to atomic PDF analysis to characterize active nanocatalysts inside operating fuel cells both in a time-resolved manner and with atomic level resolution, i.e. in 4D, can serve well the ongoing search for nanocatalysts that deliver more with less platinum. PMID:27160891

  18. 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

  19. Structural dynamics and activity of nanocatalysts inside fuel cells by in operando atomic pair distribution studies.

    PubMed

    Petkov, Valeri; Prasai, Binay; Shan, Shiyao; Ren, Yang; Wu, Jinfang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian

    2016-05-19

    Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE-XRD) we tracked the evolution of the atomic structure and activity of noble metal-transition metal (NM-TM) nanocatalysts for ORR as they function at the cathode of a fully operational proton exchange membrane fuel cell (PEMFC). Experimental HE-XRD data were analysed in terms of atomic pair distribution functions (PDFs) and compared to the current output of the PEMFC, which was also recorded during the experiments. The comparison revealed that under actual operating conditions, NM-TM nanocatalysts can undergo structural changes that differ significantly in both length-scale and dynamics and so can suffer losses in their ORR activity that differ significantly in both character and magnitude. Therefore we argue that strategies for reducing ORR activity losses should implement steps for achieving control not only over the length but also over the time-scale of the structural changes of NM-TM NPs that indeed occur during PEMFC operation. Moreover, we demonstrate how such a control can be achieved and thereby the performance of PEMFCs improved considerably. Last but not least, we argue that the unique capabilities of in operando HE-XRD coupled to atomic PDF analysis to characterize active nanocatalysts inside operating fuel cells both in a time-resolved manner and with atomic level resolution, i.e. in 4D, can serve well the ongoing search for nanocatalysts that deliver more with less platinum.

  20. 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.

  1. An Antiproton Ion Collider (AIC) for Measuring Neutron and Proton Distributions in Stable and Radioactive Nuclei

    SciTech Connect

    Kienle, Paul

    2005-10-19

    An antiproton-ion collider is proposed to independently determine mean square radii for protons and neutrons in stable and short lived nuclei by means of antiproton absorption at medium energies. The experiment makes use of the electron ion collider complex (ELISE) of the GSI FAIR project with appropriate modifications of the electron ring to store, cool and collide antiprotons of 30 MeV energy with 740A MeV energy ions.The total absorption cross-section of antiprotons by the stored ions will be measured by detecting their loss by means of the Schottky noise spectroscopy method. Cross sections for the absorption on protons and neutrons, respectively, will be studied by detection of residual nuclei with A-1 either by the Schottky method or by analysing them in recoil detectors after the first dipole stage of the NESR following the interaction zone. With a measurement of the A-1 fragment momentum distribution, one can test the momentum wave functions of the annihilated neutron and proton, respectively. Furthermore by changing the incident ion energy the tails of neutron and proton distribution can be measured.The absorption cross section is at asymptotic energies in leading order proportional to the mean square radius of the nucleus. Predicted cross sections and luminosities show that the method is applicable to nuclei with production rates of about 105 s-1 or lower, depending on the lifetime of the ions in the NESR, and for half-lives down to 1 second.

  2. 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.

  3. The impact of fuel particle size distribution on neutron transport in stochastic media

    SciTech Connect

    Liang, C.; Pavlou, A. T.; Ji, W.

    2013-07-01

    This paper presents a study of the particle size distribution impact on neutron transport in three-dimensional stochastic media. An eigenvalue problem is simulated in a cylindrical container consisting of fissile fuel particles with five different size distributions: constant, uniform, power, exponential and Gaussian. We construct 15 cases by altering the fissile particle volume packing fraction and its optical thickness, but keeping the mean chord length of the spherical fuel particle the same at different size distributions. The tallied effective multiplication factor (k{sub eff}) and flux distribution along axial and radial directions are compared between different size distributions. At low packing fraction and low optical thickness, the size distribution has a significant impact on radiation transport in stochastic media, which can cause as high as {approx}270 pcm difference in k{sub eff} value and {approx}2.6% relative error difference in peak flux. As the packing fraction and optical thickness increase, the impact gradually dissipates. (authors)

  4. Analysis of the size, shape, and spatial distribution of microinclusions by neutron-activation autoradiography

    SciTech Connect

    Flitsiyan, E.S.; Romanovskii, A.V.; Gurvich, L.G.; Kist, A.A.

    1987-02-01

    The local concentration and spatial distribution of some elements in minerals, rocks, and ores can be determined by means of neutron-activation autoradiography. The local element concentration is measured in this method by placing an activated section of the rock to be analyzed, together with an irradiated standard, against a photographic emulsion which acts as a radiation detector. The photographic density of the exposed emulsion varies as a function of the tested element content in the part of the sample next to the detector. In order to assess the value of neutron-activation autoradiography in the analysis of element distribution, we considered the main factors affecting the production of selective autoradiographs, viz., resolution, detection limit, and optimal irradiation conditions, holding time, and exposure.

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

    SciTech Connect

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

    2008-11-15

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

  6. Mean square displacement evaluation by elastic neutron scattering self-distribution function.

    PubMed

    Magazù, Salvatore; Maisano, Giacomo; Migliardo, Federica; Benedetto, Antonio

    2008-06-01

    In the present work an operational recipe for the mean square displacement (MSD) determination, highlighting the connection between elastic incoherent neutron scattering (EINS) intensity profiles and the associated self-distribution function, is presented. The determination of the thermal behavior of the total MSD and of its partial contributions is tested on EINS data collected by the backscattering spectrometer IN13 (ILL, Grenoble) on a model system such as PolyEthylene Glycol with a mean molecular weight of 400 Dalton (PEG 400).

  7. Pore size distribution of shaley rock by small angle neutron scattering

    NASA Astrophysics Data System (ADS)

    Hall, P. L.; Mildner, D. F. R.; Borst, R. L.

    1983-08-01

    Information concerning pore microstructure of shaly rocks is of considerable relevance to petroleum exploration and production. Pore sizes and distributions within shaly samples have been determined by small angle neutron scattering. The data are indicative of a considerable spread of pore dimension, showing inhomogeneities with a range from 20 Å and greater. The cumulative pore volumes are compared with those derived from mercury intrusion porosimetry and nitrogen adsorption and desorption isotherms.

  8. Pore size distribution of shaly rock by small angle neutron scattering

    SciTech Connect

    Hall, P.L.; Mildner, D.F.R.; Borst, R.L.

    1983-08-01

    Information concerning pore microstructure of shaly rocks is of considerable relevance to petroleum exploration and production. Pore sizes and distributions within shaly samples have been determined by small angle neutron scattering. The data are indicative of a considerable spread of pore dimension, showing inhomogeneities with a range from 20 A and greater. The cumulative pore volumes are compared with those derived from mercury intrusion porosimetry and nitrogen adsorption and desorption isotherms.

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

    SciTech Connect

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

    2011-03-15

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

  10. Pair distribution function analysis of La(Fe{sub 1−x}Ru{sub x})AsO compounds

    SciTech Connect

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

    2014-12-15

    The local structures of La(Fe{sub 1−x}Ru{sub x})AsO (0.00≤x≤0.80) compounds were investigated by means of pair distribution function analysis at room temperature; as a result, no phase separation or clustering takes place. Local distortions are no longer correlated beyond ∼15 Å for both pure and substituted samples, indicating that the presence of Ru atoms does not determine a notable variation in the length scale of the local distortion. Different types of short range correlation between Fe and Ru atoms do not produce significant changes in the pair distribution function. - Graphical abstract: Fe–As and Ru–As bond length distributions as obtained by pair distribution function analysis of La(Fe{sub 0.70}Ru{sub 0.30})AsO; As atoms (purple spheres) undergo a random shifting around their crystallographic positions (red spheres: Fe/Ru atoms). - Highlights: • No phase separation or clustering takes place in La(Fe{sub 1−x}Ru{sub x})AsO solid solutions. • Local distortions are no longer correlated beyond ∼15 Å. • Ru displays a tendency towards local enrichment in the transition metal sublattice.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2002-01-01

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

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

    SciTech Connect

    Giacomelli, L.; Conroy, S.; Gorini, G.; Horton, L.; Murari, A.; Popovichev, S.; Syme, D. B.

    2014-02-15

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

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

    SciTech Connect

    Liu, B.; Phillips, F.M.; Stone, W.D.; Fabryka-Martin, J.T.; Fowler, M.M.

    1994-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1999-11-01

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

  16. Neutron distribution, electric dipole polarizability and weak form factor of 48Ca from chiral effective field theory

    NASA Astrophysics Data System (ADS)

    Wendt, Kyle

    2016-03-01

    How large is the 48Ca nucleus? While the electric charge distribution of this nucleus was accurately measured decades ago, both experimental and ab initio descriptions of the neutron distribution are deficient. We address this question using ab initio calculations of the electric charge, neutron, and weak distributions of 48Ca based on chiral effective field theory. Historically, chiral effective field theory calculations of systems larger than 4 nucleons have been plagued by strong systematic errors which result in theoretical descriptions that are too dense and over bound. We address these errors using a novel approach that permits us to accurately reproduce binding energy and charge radius of 48Ca, and to constrain electroweak observables such as the neutron radius, electric dipole polarizability, and the weak form factor. For a full list of contributors to this work, please see ``Neutron and weak-charge distributions of the 48Ca nucleus,'' Nature Physics (2015) doi:10.1038/nphys3529.

  17. Nuclear shape dependence of Gamow-Teller distributions in neutron-deficient Pb isotopes

    SciTech Connect

    Sarriguren, P.; Moreno, O.; Alvarez-Rodriguez, R.; Moya de Guerra, E.

    2005-11-01

    We study Gamow-Teller strength distributions in the neutron-deficient even isotopes {sup 184-194}Pb in a search for signatures of deformation. The microscopic formalism used is based on a deformed quasiparticle random-phase approximation (QRPA) approach, which involves a self-consistent quasiparticle deformed Skyrme Hartree-Fock (HF) basis and residual spin-isospin forces in both the particle-hole and particle-particle channels. By analyzing the sensitivity of the Gamow-Teller strength distributions to the various ingredients in the formalism, we conclude that the {beta} decay of these isotopes could be a useful tool to look for fingerprints of nuclear deformation.

  18. Development of monitoring method of spatial neutron distribution in neutrons-gamma rays mixed field using imaging plate for NCT--depression of the field.

    PubMed

    Tanaka, Kenichi; Endo, Satoru; Hoshi, Masaharu; Takada, Jun

    2011-12-01

    The degree of depression in the neutron field caused by neutron absorption in the materials of an imaging plate (IP) was investigated using MCNP-4C. Consequently, the IP doped with Gd, which reproduced the distribution of (157)Gd(n,γ)(158)Gd reaction rate in the previous study, depresses the relative distribution by about 50%. The depression for the IP in which Gd is replaced with similar amount of B atoms was estimated to be about 10%. The signal intensity for this IP is estimated to be at a similar level with that for Gd-doped IP.

  19. Relationship Between the Atomic Pair Distribution Function and Small-Angle Scattering: Implications for Modeling of Nanoparticles

    SciTech Connect

    Billinge, S.; Farrowa, C.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, -4{pi}r{rho}{sub 0}, 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.

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

    DOE PAGES

    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.

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

    NASA Astrophysics Data System (ADS)

    Roy, Prianka; Dhiman, Shashi K.

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

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    Matsumoto, T.

    2007-09-01

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

  4. Influence of ionic liquid film thickness on ion pair distributions and orientations at graphene and vacuum interfaces.

    PubMed

    Wang, Yong-Lei; Laaksonen, Aatto; Lu, Zhong-Yuan

    2013-08-28

    Microscopic structures, orientational preferences together with mass, number and electron density distributions of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) ionic liquid (IL) have been studied on a neutral hydrophobic graphene surface, and at the IL-vacuum interface using atomistic Molecular Dynamics simulations. At the IL-graphene interface, distinct mass, number and electron density distributions are observed oscillating into the bulk region with several compact structural layers. The imidazolium ring of [BMIM] cations lies preferentially flat on the graphene surface, with its methyl and butyl side chains elongated along the graphene surface. At the IL-vacuum interface, however, the distributions of [BMIM][PF6] ion pairs are strongly influenced by the thickness of IL film. With the increase of IL film thickness, the orientations of [BMIM] cations at the IL-vacuum interface change gradually from dominant flat distributions along the graphene surface to orientations where the imidazolium rings are either parallel or perpendicular to the IL-vacuum interface with tilted angles. The outmost layers are populated with alkyl groups and imparted with distinct hydrophobic character. The calculated radial distribution functions suggest that ionic structures of [BMIM][PF6] ion pairs in IL-graphene and IL-vacuum interfacial regions are significantly different from each other and also from that in bulk regions.

  5. Two and three-dimensional quantitative neutron imaging of the water distribution during ponded infiltration

    NASA Astrophysics Data System (ADS)

    Sacha, Jan; Snehota, Michal; Jelinkova, Vladimira

    2016-04-01

    Information on spatial and temporal water and air distribution in a soil sample during hydrological processes is important for evaluating current and developing new water transport models. Modern imaging techniques such as neutron imaging (NI) allow relatively short acquisition times and high resolution of images. At the same time, the appropriate data processing has to be applied to obtain results free of bias and artifacts. In this study a ponded infiltration experiments were conducted on two soil samples packed into the quartz glass columns of inner diameter of 29 and 34 mm, respectively. First sample was prepared by packing of fine and coarse fractions of sand and the second sample was packed using coarse sand and disks of fine porous ceramic. Ponded infiltration experiments conducted on both samples were monitored by neutron radiography to produce two dimensional (2D) projection images during the transient phase of infiltration. During the steady state flow stage of experiments neutron tomography was utilized to obtain three-dimensional (3D) information on gradual water redistribution. The acquired radiographic images were normalized for background noise and spatial inhomogeneity of the detector, fluctuations of the neutron flux in time and for spatial inhomogeneity of the neutron beam. The radiograms of dry sample were subtracted from all subsequent radiograms to determine water thickness in the 2D projection images. All projections were corrected for beam hardening and neutron scattering by empirical method of Kang et al. (2013). Parameters of the correction method uses were identified by two different approaches. The first approach was based on fitting the NI derived water thickness representing the water filled region in the layer of water above the sample surface to actual water thickness. In the second approach the NI derived volume of water in the entire sample in given time was fitted to corresponding gravimetrically determined amount of water in the

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

    NASA Astrophysics Data System (ADS)

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

    2006-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

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

    PubMed

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

    2010-04-01

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

  9. Measurements of Correlated Pair Momentum Distributions in {sup 3}He(e,e{prime}pp)n with CLAS

    SciTech Connect

    Rustam Niyazov

    2003-05-01

    We have measured the {sup 3}He(e,e{prime}pp)n reaction at 2.2 and 4.4 GeV over a wide kinematic range. The kinetic energy distribution for ''fast'' nucleons (p > 250 MeV/c) peaks where two nucleons each have 20% or less and the third or ''leading'' nucleon carries most of the transferred energy. These fast nucleon pairs (both pp and pn) are back-to-back and carry very little momentum along {rvec q}, indicating that they are spectators. Experimental and theoretical evidence indicates that we have measured NN correlations in {sup 3}He(e,e{prime}pp)n by striking the third nucleon and detecting the spectator correlated pair.

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

    NASA Astrophysics Data System (ADS)

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

    1982-05-01

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

  11. Biomolecular motion characterization by a self-distribution-function procedure in elastic incoherent neutron scattering

    NASA Astrophysics Data System (ADS)

    Magazù, Salvatore; Maisano, Giacomo; Migliardo, Federica; Benedetto, Antonio

    2009-04-01

    In the present paper we first focus on the role of the instrumental resolution in elastic incoherent neutron scattering (EINS) where the connection between the self-distribution function (SDF) and the measured EINS intensity profile is highlighted. Second we show how the SDF procedure, previously introduced, allows both the total and the partial mean-square displacement evaluations through the total and the partial SDFs. Finally, we compare the SDF and the Gaussian procedures, by applying the two approaches to EINS data collected, by the IN13 backscattering spectrometer (Institute Laue-Langevin, Grenoble), on aqueous mixtures of two homologous disaccharides, i.e., sucrose and trehalose, and on myoglobin.

  12. Gamow-Teller strength distributions for neutron-rich nitrogen, oxygen and fluorine isotopes

    NASA Astrophysics Data System (ADS)

    Zhang, Yu-Mei

    2016-08-01

    Gamow-Teller transition properties for neutron-rich nitrogen, oxygen and fluorine isotopes are studied in integrated energy. The structures of these nuclei are described by means of nuclear shell model with the WBT interaction in the p-sd shell space. Calculations of the Gamow-Teller strength distribution reproduce the experimental data reasonably in the low-energy region. For the dripline nucleus 24O, a super Gamow-Teller transition to a single state at excitation energy of 14.72 MeV in 24F is predicted. β-decay half-lives for these nuclei are calculated and compared with the available experimental data.

  13. 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.

  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. DShaper: An approach for handling missing low-Q data in pair distribution function analysis of nanostructured systems

    DOE PAGES

    Olds, Daniel; Wang, Hsiu -Wen; Page, Katharine

    2015-01-01

    This study discusses the potential problems and currently available solutions in modeling powder-diffraction-based pair distribution function (PDF) data from systems where morphological feature information content includes distances in the nanometre length scale, such as finite nanoparticles, nanoporous networks and nanoscale precipitates in bulk materials. The implications of an experimental finite minimumQvalue are reviewed by simulation, which also demonstrates the advantages of combining PDF data with small-angle scattering data. A simple Fortran90 code, DShaper, is introduced, which may be incorporated into PDF data fitting routines in order to approximate the so-called `shape function' for any atomistic model.

  16. 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.

  17. 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

  18. Water distribution in a sorption enhanced methanation reactor by time resolved neutron imaging.

    PubMed

    Borgschulte, A; Delmelle, R; Duarte, R B; Heel, A; Boillat, P; Lehmann, E

    2016-06-29

    Water adsorption enhanced catalysis has been recently shown to greatly increase the conversion yield of CO2 methanation. However, the joint catalysis and adsorption process requires new reactor concepts. We measured the spatial water distribution in a model fixed bed reactor using time resolved neutron imaging. Due to the high neutron attenuation coefficient of hydrogen, the absorbed water in the sorption catalyst gives a high contrast allowing us to follow its formation and map its distribution. At the same time, the product gas was analysed by FTIR-gas analysis. The measurements provided crucial insights into the future design of sorption reactors: during the sorption enhanced reaction, a reaction front runs through the reactor. Once the extension of the reaction front reaches the exhaust, the conversion rate of sorption enhanced methanation decreases. The existence of a reaction front running through the reactor is prerequisite for a high conversion rate. We give a simple model of the experimental results, in particular the conditions, under which a reaction front is established. In particular the latter effect must be taken into account for the dimensions of a large scale reactor. PMID:26791100

  19. Water distribution in a sorption enhanced methanation reactor by time resolved neutron imaging.

    PubMed

    Borgschulte, A; Delmelle, R; Duarte, R B; Heel, A; Boillat, P; Lehmann, E

    2016-06-29

    Water adsorption enhanced catalysis has been recently shown to greatly increase the conversion yield of CO2 methanation. However, the joint catalysis and adsorption process requires new reactor concepts. We measured the spatial water distribution in a model fixed bed reactor using time resolved neutron imaging. Due to the high neutron attenuation coefficient of hydrogen, the absorbed water in the sorption catalyst gives a high contrast allowing us to follow its formation and map its distribution. At the same time, the product gas was analysed by FTIR-gas analysis. The measurements provided crucial insights into the future design of sorption reactors: during the sorption enhanced reaction, a reaction front runs through the reactor. Once the extension of the reaction front reaches the exhaust, the conversion rate of sorption enhanced methanation decreases. The existence of a reaction front running through the reactor is prerequisite for a high conversion rate. We give a simple model of the experimental results, in particular the conditions, under which a reaction front is established. In particular the latter effect must be taken into account for the dimensions of a large scale reactor.

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

    SciTech Connect

    Herrera, J.J.E.; Castillo, F.; Gamboa, I.; Rangel, R.; Espinosa, G.; Golzarri, J. I.

    2006-01-05

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

  1. Energy dependence of mass, charge, isotopic, and energy distributions in neutron-induced fission of 235U and 239Pu

    NASA Astrophysics Data System (ADS)

    Pasca, H.; Andreev, A. V.; Adamian, G. G.; Antonenko, N. V.; Kim, Y.

    2016-05-01

    The mass, charge, isotopic, and kinetic-energy distributions of fission fragments are studied within an improved scission-point statistical model in the reactions 235U+n and 239Pu+n at different energies of the incident neutron. The charge and mass distributions of the electromagnetic- and neutron-induced fission of 214,218Ra, 230,232,238U are also shown. The available experimental data are well reproduced and the energy-dependencies of the observable characteristics of fission are predicted for future experiments.

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

    NASA Astrophysics Data System (ADS)

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

    2009-06-01

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

  3. 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.

  4. Analysis of prompt fission neutrons in 235U(nth,f) and fission fragment distributions for the thermal neutron induced fission of 234U

    NASA Astrophysics Data System (ADS)

    Al-Adili, A.; Tarrío, D.; Hambsch, F.-J.; Göök, A.; Jansson, K.; Solders, A.; Rakopoulos, V.; Gustafsson, C.; Lantz, M.; Mattera, A.; Oberstedt, S.; Prokofiev, A. V.; Vidali, M.; Österlund, M.; Pomp, S.

    2016-06-01

    This paper presents the ongoing analysis of two fission experiments. Both projects are part of the collaboration between the nuclear reactions group at Uppsala and the JRC-IRMM. The first experiment deals with the prompt fission neutron multiplicity in the thermal neutron induced fission of 235U(n,f). The second, on the fission fragment properties in the thermal fission of 234U(n,f). The prompt fission neutron multiplicity has been measured at the JRC-IRMM using two liquid scintillators in coincidence with an ionization chamber. The first experimental campaign focused on 235U(nth,f) whereas a second experimental campaign is foreseen later for the same reaction at 5.5 MeV. The goal is to investigate how the so-called sawtooth shape changes as a function of fragment mass and excitation energy. Some harsh experimental conditions were experienced due to the large radiation background. The solution to this will be discussed along with preliminary results. In addition, the analysis of thermal neutron induced fission of 234U(n,f) will be discussed. Currently analysis of data is ongoing, originally taken at the ILL reactor. The experiment is of particular interest since no measurement exist of the mass and energy distributions for this system at thermal energies. One main problem encountered during analysis was the huge background of 235U(nth,f). Despite the negligible isotopic traces in the sample, the cross section difference is enormous. Solution to this parasitic background will be highlighted.

  5. 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.

  6. 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.

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

    SciTech Connect

    Moran, J.M.; Nigg, D.W.; Wheeler, F.J.; Bauer, W.F. )

    1992-05-01

    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 paper describes such a validation exercise for BNCT of canine brain tumors. Geometric measurements of the canine anatomical structures of interest for this work were performed by dissecting and examining two essentially identical Labrador retriever heads. Chemical analyses of various tissue samples taken during the dissections were conducted to obtain measurements of elemental compositions for the tissues of interest. The resulting geometry and tissue composition data were then used to construct a detailed heterogeneous calculational model of the Labrador head. Calculations of three-dimensional radiation flux distributions pertinent to BNCT were performed for this model using the TORT discrete-ordinates radiation transport code. The calculations were repeated for a corresponding volume-weighted homogeneous-tissue model. Comparison of the results showed that peak neutron and photon flux magnitudes were quite similar for the two models (within 5%), but that the spatial flux profiles were shifted in the heterogeneous model such that the fluxes in some locations away from the peak differed from the corresponding fluxes in the homogeneous model by as much as 10%--20%. Differences of this magnitude can be therapeutically significant, emphasizing the need for proper validation of simplified treatment planning models.

  8. 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.

  9. Sensitivity of Parity-Violating A(, e')A Scattering and Atomic Parity Nonconservation to Neutron Distributions in Nuclei

    NASA Astrophysics Data System (ADS)

    Pollock, S. J.; Welliver, M. C.

    2000-01-01

    Parity-violating electron scattering (PVES) could provide a unique means to determine spatial neutron distributions and their moments in heavy nuclei. Knowledge of the neutron distribution is of fundamental interest for nuclear structure models, and the first moment is of special interest for atomic parity experiments. We have examined what could be learned from a hypothetical measurement of the parity-violating asymmetry in elastic electron scattering on barium and lead nuclei (both spin-0 and N≠Z). We find that a single measurement of this quantity could determine the rms neutron radius to within a couple of percent, to be compared with the 5-10% existing uncertainties. We also compute the quantitative connection to atomic parity nonconservation, and the resulting limits on possible low energy Standard Model tests which could be achieved.

  10. Fully self-consistent calculations of momentum distributions of annihilating electron-positron pairs in SiC

    NASA Astrophysics Data System (ADS)

    Wiktor, Julia; Jomard, Gérald; Torrent, Marc; Barthe, Marie-France; Bertolus, Marjorie

    2016-05-01

    We performed calculations of momentum distributions of annihilating electron-positron pairs in various fully relaxed vacancy defects in SiC. We used self-consistent two-component density functional theory schemes to find the electronic and positronic densities and wave functions in the considered systems. Using the one-dimensional momentum distributions (Doppler-broadened annihilation radiation line shapes) we calculated the line-shape parameters S and W . We emphasize the effect of the experimental resolution and the choice of the integration ranges for the S and W parameters on the distributions of the points corresponding to different defects in the S (W ) plot. We performed calculation for two polytypes of SiC, 3 C , and 6 H and showed that for silicon vacancies and clusters containing this defect there were no significant differences between the Doppler spectra. The results of the Doppler spectra calculations were compared with experimental data obtained for n -type 6 H -SiC samples irradiated with 4-MeV Au ions. We observed a good general agreement between the measured and calculated points.

  11. Elucidating the domain structure of the cobalt oxide water splitting catalyst by X-ray pair distribution function analysis.

    PubMed

    Du, Pingwu; Kokhan, Oleksandr; Chapman, Karena W; Chupas, Peter J; Tiede, David M

    2012-07-11

    Pair distribution function (PDF) analysis was applied for structural characterization of the cobalt oxide water-splitting catalyst films using high energy X-ray scattering. The catalyst was found to be composed of domains consistent with a cobalt dioxide lattice sheet structure, possibly containing a Co(4)O(4) cubane-type "defect". The analysis identifies the film to consist of domains composed of 13-14 cobalt atoms with distorted coordination geometries that can be modeled by alteration in terminal oxygen atom positions at the domain edge. Phosphate is seen as a disordered component in the films. This work establishes an approach that can be applied to study the structure of in situ cobalt oxide water-splitting film under functional catalytic conditions.

  12. Effect of nonuniform hole-content distribution within the interlayer pair-tunneling mechanism of layered HTSC

    NASA Astrophysics Data System (ADS)

    Angilella, Giuseppe G. N.; Pucci, Renato

    1999-04-01

    The interlayer pair-tunneling (ILPT) mechanism for high- Tc superconductivity predicts the dependence of the (optimal) critical temperature Tc on the number of layers n within a homologous series of layered cuprate oxides. We generalize the mean-field procedure employed to evaluate Tc within an extended in-plane Hubbard model in the presence of ILPT, developed for a bilayer complex ( n=2), to the case of n=3,4 inequivalent superconducting layers. As a function of doping, we show how a nonuniform hole-content distribution among different layers affects Tc. In particular, depending on doping, the onset of superconductivity may be ruled by inner or outer layers. The latter result may be related to recent experimental data of Tc as a function of pressure in Tl- and Bi-based layered superconductors.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

  15. DShaper: An approach for handling missing low-Q data in pair distribution function analysis of nanostructured systems

    SciTech Connect

    Olds, Daniel; Wang, Hsiu -Wen; Page, Katharine L.

    2015-09-04

    In this work we discuss the potential problems and currently available solutions in modeling powder-diffraction based pair-distribution function (PDF) data from systems where morphological feature information content includes distances in the nanometer length scale, such as finite nanoparticles, nanoporous networks, and nanoscale precipitates in bulk materials. The implications of an experimental finite minimum Q-value are addressed by simulation, which also demonstrates the advantages of combining PDF data with small angle scattering data (SAS). In addition, we introduce a simple Fortran90 code, DShaper, which may be incorporated into PDF data fitting routines in order to approximate the so-called shape-function for any atomistic model.

  16. DShaper: An approach for handling missing low-Q data in pair distribution function analysis of nanostructured systems

    DOE PAGES

    Olds, Daniel; Wang, Hsiu -Wen; Page, Katharine L.

    2015-09-04

    In this work we discuss the potential problems and currently available solutions in modeling powder-diffraction based pair-distribution function (PDF) data from systems where morphological feature information content includes distances in the nanometer length scale, such as finite nanoparticles, nanoporous networks, and nanoscale precipitates in bulk materials. The implications of an experimental finite minimum Q-value are addressed by simulation, which also demonstrates the advantages of combining PDF data with small angle scattering data (SAS). In addition, we introduce a simple Fortran90 code, DShaper, which may be incorporated into PDF data fitting routines in order to approximate the so-called shape-function for anymore » atomistic model.« less

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

    SciTech Connect

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

    2012-03-15

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

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

    SciTech Connect

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

    2012-03-15

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

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

    NASA Astrophysics Data System (ADS)

    Zhang, F. H.; Zhou, G. D.; Cui, W. Y.; Zhang, B.

    2013-01-01

    An investigation on the distribution of neutron exposuresin the low-mass asymptotic giant branch (AGB) stars is presented, according to the s-process nucleosynthesis model with the (^{12}C(α,n)^{16}O) reaction occurring under radiative conditions in the interpulse phases. The model parameters, such as the fractional overlap of two successive convective thermal pulses (r), the mass fraction of (^{13}C) pocket in the He intershell (q), and the mass of the effective (^{13}C) in the (^{13}C) pocket, vary with pulse number. Considering these factors, the calculating method for the distribution of neutron exposures in the He intershell is presented. This method has the characteristics of simplicity and universality. Using this method, the exposure distributions of the stellar model for a star with a mass of (3 {M_⊙}) and solar metallicity are calculated. The results suggest that, with the reasonable assumption that the (^{13}C) pocket has a uniform composition, the final exposure distribution can still be approximated by an exponential law. For a stellar model with a fixed initial mass and metallicity, there is a definite relation between the mean neutron exposure ({τ_0}), and the neutron exposure (Δτ) for per interpulse. That is ({τ_0} = 0.434λ({q_{1,}}{q_2} … {q_{{m_{max}} + 1}},{r_{1,}}{r_2} … {r_{{m_{max}} + 1}})Δτ), where ({m_{max}}) is the total number of thermal pulses with the third dredge-up episode, and the proportional coefficient (λ({q_{1,}}{q_2} … {q_{{m_{max}} + 1}},{r_{1,}}{r_2} … {r_{{m_{max}} + 1}})) can be determined through an exponential curve fitting to the final exposure distribution. This new formula quantitatively unifies the classical model with the stellar model in terms of the distribution of neutron exposures, and makes the classical model continue to offer guidance and constraints to the s-process numerical calculations in stellar models.

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

    PubMed

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

    2011-05-01

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

  1. Resolving the structure of Ti3C2Tx MXenes through multilevel structural modeling of the atomic pair distribution function

    SciTech Connect

    Wesolowski, David J.; Wang, Hsiu -Wen; Page, Katharine L.; Naguib, Michael; Gogotsi, Yury

    2015-12-08

    MXenes are a recently discovered family of two-dimensional (2D) early transition metal carbides and carbonitrides, which have already shown many attractive properties and a great promise in energy storage and many other applications. However, a complex surface chemistry and small coherence length has been an obstacle in some applications of MXenes, also limiting accuracy of predictions of their properties. In this study, we describe and benchmark a novel way of modeling layered materials with real interfaces (diverse surface functional groups and stacking order between the adjacent monolayers) against experimental data. The structures of three kinds of Ti3C2Tx MXenes (T stands for surface terminating species, including O, OH, and F) produced under different synthesis conditions were resolved for the first time using atomic pair distribution function obtained by high-quality neutron total scattering. The true nature of the material can be easily captured with the sensitivity of neutron scattering to the surface species of interest and the detailed third-generation structure model we present. The modeling approach leads to new understanding of MXene structural properties and can replace the currently used idealized models in predictions of a variety of physical, chemical and functional properties of Ti3C2-based MXenes. Furthermore, the developed models can be employed to guide the design of new MXene materials with selected surface termination and controlled contact angle, catalytic, optical, electrochemical and other properties. We suggest that the multi-level structural modeling should form the basis for a generalized methodology on modeling diffraction and pair distribution function data for 2D and layered materials.

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

    NASA Astrophysics Data System (ADS)

    Ji, Wei

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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Effect of the Temperature of the Moderator on the Velocity Distribution of Neutrons with Numerical Calculations for H as Moderator

    DOE R&D Accomplishments Database

    Wigner, E. P.; Wilkins, J. E. Jr.

    1944-09-14

    In this paper we set up an integral equation governing the energy distribution of neutrons that are being slowed down uniformly throughout the entire space by a uniformly distributed moderator whose atoms are in motion with a Maxwellian distribution of velocities. The effects of chemical binding and crystal reflection are ignored. When the moderator is hydrogen, the integral equation is reduced to a differential equation and solved by numerical methods. In this manner we obtain a refinement of the dv/v{sup 2} law. (auth)

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

    NASA Astrophysics Data System (ADS)

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

    2009-10-01

    The halo and skin structures at the nuclear surface have attracted much interest for their exotic nature. By utilizing the isospin asymmetry of nucleon-nucleon total cross sections in the intermediate energy region, in principle, the proton- and neutron-density distributions can be determined independently. To demonstrate this isospin asymmetric effect, we have studied σR for the neutron-halo nucleus ^11 Be and the proton-halo nucleus ^8B on proton targets. We measured σR for ^11Be and ^8B on C and proton targets by the transmission method in the intermidiate energy region using HIMAC heavy ion synchrotron at NIRS. The present result for ^11Be is consistent with that the tail of ^11Be density consists of a neutron. On the other hand, the experimental result for ^8B is in agreement with the calculation with a proton tail in ^8B. Thus, the proton and neutron density distributions at the nuclear surface can be distinguished successfully by the σR on C and proton targets.

  10. Effects of the neutral gas density distribution in a DPF neutron yield

    SciTech Connect

    Milanese, M.; Moroso, R.; Pouzo, J.

    1996-12-31

    The dense plasma gives an average neutron yield Y = 2 {times} 10{sup 8} when it is operated using D{sub 2} at an homogeneous pressure p = 1.5 mb in the discharge chamber, in this p-static operation, the frequency of good shots (Y > 10{sup 7}) is f {approx} 50%. In this work the authors show the results on Y and f when PACO is operated in gas-puff way with two different modalities: (1) A gas cloud is injected into the vacuum, from a set of holes distributed in a diameter of the inner electrode near the Pyrex insulator. The gas is introduced from the back of the hollow inner electrode by means of a fast valve. The cloud expands in the interelectrode space, and reaches the extreme of the coaxial cavity in some hundreds of microseconds from the valve aperture instant. In this way of operation the value of Y remains similar to the p-static operation, but the frequency f is improved up to f {approx} 80%. (2) With a relative low value of p in the discharge chamber a jet of high density D{sub 2} is injected along the axis from the inner electrode just in the focus zone. The jet is produced with a nozzle designed in order to obtain subsonic velocity, and the gas is injected through the same fast valve. In this jet operation mode the PACO performance was improved, reaching f {approx} 70% and Y {approx} 10{sup 9}.

  11. 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.

  12. 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.

  13. Method of pair exchange of fuel assemblies and its use in optimizing the energy distribution of water-cooled/water-moderated reactors

    SciTech Connect

    Simonov, V.D.; Pavlov, V.I.; Perminov, A.A.; Pechikin, V.A.; Filimonov, P.E.; Yuskov, A.M.

    1987-03-01

    The authors review various computer codes for determining the power distribution and optimizing the fueling procedure for water cooled and moderated reactors and assess their relative efficiencies in terms of computation time required. The algorithms take into account reactivity coefficients and neutron diffusion theory. A sensitivity analysis of the codes is given and steps are outlined for implementation of the codes for various reactor core configurations.

  14. Conditional pair distribution functions for ideal fluids. (Spanish Title: Funciones de distribución de pares condicionales para fluidos ideales)

    NASA Astrophysics Data System (ADS)

    Zurbriggen, E.; Rohrmann, R. D.

    The description of the microscopical spatial structure of a gas in equilibrium can be enriched by using the so-called space partition method. This thermo-statistical formalism makes use of a novel kind of conditional pair distribution function denoted g_{vv'}. The aim of the present work is to continue the analysis of the function g_{vv'} for gases composed of independent, randomly distributed particles.

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

    DOE PAGES

    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.

  16. 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.

  17. 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.

    2015-04-21

    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 CO₂ 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.

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

    SciTech Connect

    Hansen, L.F.

    1985-05-01

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

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

    PubMed

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

    2011-07-01

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

  20. Elastic incoherent neutron scattering on systems of biophysical interest: mean square displacement evaluation from self-distribution function.

    PubMed

    Magazù, Salvatore; Maisano, Giacomo; Migliardo, Federica; Benedetto, Antonio

    2008-07-31

    In the present work an operational recipe for the mean square displacement (MSD) determination, highlighting the connection between the self-distribution function and average statistical values, is presented. The determination of the MSD and of its contributions associated with different mechanisms, together with their thermal behavior, is performed by evaluating the self-distribution function derived by elastic incoherent neutron scattering (EINS). The approach is tested on EINS data collected by the backscattering spectrometer IN13 (ILL, Grenoble, France) on two model systems such as dry myoglobin in trehalose and poly(ethylene glycol) with mean molecular weight M(w) = 400 (PEG 400).

  1. Fission Fragment Mass Distributions and Total Kinetic Energy Release of 235-Uranium and 238-Uranium in Neutron-Induced Fission at Intermediate and Fast Neutron Energies

    SciTech Connect

    Duke, Dana Lynn

    2015-11-12

    This Ph.D. dissertation describes a measurement of the change in mass distributions and average total kinetic energy (TKE) release with increasing incident neutron energy for fission of 235U and 238U. Although fission was discovered over seventy-five years ago, open questions remain about the physics of the fission process. The energy of the incident neutron, En, changes the division of energy release in the resulting fission fragments, however, the details of energy partitioning remain ambiguous because the nucleus is a many-body quantum system. Creating a full theoretical model is difficult and experimental data to validate existing models are lacking. Additional fission measurements will lead to higher-quality models of the fission process, therefore improving applications such as the development of next-generation nuclear reactors and defense. This work also paves the way for precision experiments such as the Time Projection Chamber (TPC) for fission cross section measurements and the Spectrometer for Ion Determination in Fission (SPIDER) for precision mass yields.

  2. Distance distributions recovered from steady-state fluorescence measurements on thirteen donor-acceptor pairs with different Förster distances.

    PubMed

    Wiczk, W; Eis, P S; Fishman, M N; Johnson, M L; Lakowicz, J R

    1991-12-01

    The end-to-end distance distribution of a flexible molecule was recovered from steady-state fluorescence energy transfer measurements using the method suggested by Cantor and Pechukas (Proc. Natl. Acad. Sci. USA 68, 2099-2101, 1971). In this method, the Förster distance (R 0) is varied by attaching different donor-acceptor (D-A) pairs to the flexible linker of interest. Distance distributions are then recovered from energy transfer efficiency measurements on the set of D-A pairs with differentR 0 values. Thirteen D-A pair compounds were synthesized withR 0 values ranging from 6 to 32 Å. Each compound contained a tryptamine donor linked by an alkyl chain (∼10 carbons) to 1 of 13 acceptors. Using these compounds, we have experimentally confirmed the Cantor and Pechukas method for recovering distance distributions. The measured transfer efficiencies, as a function ofR 0, were fit to the transfer efficiencies predicted for both Gaussian and skewed Gaussian distance distributions. The data support the existence of a skewed Gaussian distribution, and we believe that this is the first experimental observation of an asymmetric distribution for a flexible molecule using fluorescence resonance energy transfer measurements. Finally, the experimentally recovered distance distribution was found to be in good agreement with the distribution predicted from the rotational isomeric state model of Flory (Statistical Mechanics of Chain Molecules, John Wiley & Sons, New York, 1969, Chaps. 1, 3, and 5) but not with the predicted distribution for a freely rotating or freely jointed chain. PMID:24243077

  3. 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.

  4. 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

  5. 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.

  6. Pixel pitch and particle energy influence on the dark current distribution of neutron irradiated CMOS image sensors.

    PubMed

    Belloir, Jean-Marc; Goiffon, Vincent; Virmontois, Cédric; Raine, Mélanie; Paillet, Philippe; Duhamel, Olivier; Gaillardin, Marc; Molina, Romain; Magnan, Pierre; Gilard, Olivier

    2016-02-22

    The dark current produced by neutron irradiation in CMOS Image Sensors (CIS) is investigated. Several CIS with different photodiode types and pixel pitches are irradiated with various neutron energies and fluences to study the influence of each of these optical detector and irradiation parameters on the dark current distribution. An empirical model is tested on the experimental data and validated on all the irradiated optical imagers. This model is able to describe all the presented dark current distributions with no parameter variation for neutron energies of 14 MeV or higher, regardless of the optical detector and irradiation characteristics. For energies below 1 MeV, it is shown that a single parameter has to be adjusted because of the lower mean damage energy per nuclear interaction. This model and these conclusions can be transposed to any silicon based solid-state optical imagers such as CIS or Charged Coupled Devices (CCD). This work can also be used when designing an optical imager instrument, to anticipate the dark current increase or to choose a mitigation technique.

  7. Neutron star radii, universal relations, and the role of prior distributions

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    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 M_{⊙} neutron stars to be larger than 10km, 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.

  8. Neutron star radii, universal relations, and the role of prior distributions

    DOE PAGES

    Steiner, Andrew W.; Lattimer, James M.; Brown, Edward F.

    2016-02-02

    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. Inmore » 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 solar mass neutron stars to 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. Furthermore, we also demonstrate the existence of a correlation between the neutron star binding energy and the moment of inertia.« less

  9. Atmospheric neutrons

    NASA Technical Reports Server (NTRS)

    Preszler, A. M.; Moon, S.; White, R. S.

    1976-01-01

    Additional calibrations of the University of California double-scatter neutron detector and additional analysis corrections lead to slightly changed neutron fluxes. The theoretical angular distributions of Merker (1975) are in general agreement with the reported experimental fluxes but do not give the peaks for vertical upward and downward moving neutrons. The theoretical neutron escape current is in agreement with the experimental values from 10 to 100 MeV. The experimental fluxes obtained agree with those of Kanbach et al. (1974) in the overlap region from 70 to 100 MeV.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

    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 , Phys. Rev. Lett. 76, 3132 (1996)]—eliminates the twin-image problem for single-wavelength data.

  12. Uniform acceptor distribution in neutron-transmutation-doped far-infrared p-Ge lasers

    NASA Astrophysics Data System (ADS)

    Nelson, E. W.; Dolguikh, M. V.; Flitsiyan, E. S.; Muravjov, A. V.; Peale, R. E.; Kleckley, S. H.; Vernetson, W. G.; Tsipin, V. Z.

    2003-09-01

    A neutron transmutation doped (NTD) far-infrared p-Ge laser crystal and a melt-grown p-Ge laser are analyzed and compared. Though the doping level in the NTD active crystal is twice lower than optimal, the laser performance is comparable to that produced from high-quality melt-grown crystals because of superior dopant uniformity. Compensation was examined by comparing results of neutron activation analysis with majority carrier concentration. Study of impurity breakdown electric field reveals better crystal quality in NTD. The current saturation behavior confirms the expected higher doping uniformity over melt grown laser rods.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2002-07-01

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

  15. 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  μm. This is the first observation of gravitationally bound states of UCNs with submicron spatial resolution.

  16. 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.

  17. Local structure and lattice dynamics study of low dimensional materials using atomic pair distribution function and high energy resolution inelastic x-ray scattering

    NASA Astrophysics Data System (ADS)

    Shi, Chenyang

    Structure and dynamics lie at the heart of the materials science. A detailed knowledge of both subjects would be foundational in understanding the materials' properties and predicting their potential applications. However, the task becomes increasingly dicult as the particle size is reduced to the nanometer scale. For nanostructured materials their laboratory x-ray scattering patterns are overlapped and broadened, making structure determination impossible. Atomic pair distribution function technique based on either synchrotron x-ray or neutron scattering data is known as the tool of choice for probing local structures. However, to solve the "structure problem" in low-dimensional materials with PDF is still challenging. For example for 2D materials of interest in this thesis the crystallographic modeling approach often yields unphysical thermal factors along stacking direction where new chemical intuitions about their actual structures and new modeling methodology/program are needed. Beyond this, lattice dynamical investigations on nanosized particles are extremely dicult. Laboratory tools such as Raman and infra-red only probe phonons at Brillouin zone center. Although in literature there are a great number of theoretical studies of their vibrational properties based on either empirical force elds or density functional theory, various approximations made in theories make the theoretical predictions less reliable. Also, there lacks the direct experiment result to validate the theory against. In this thesis, we studied the structure and dynamics of a wide variety of technologically relevant low-dimensional materials through synchrotron based x-ray PDF and high energy resolution inelastic x-ray scattering (HERIX) techniques. By collecting PDF data and employing advanced modeling program such as DiPy-CMI, we successfully determined the atomic structures of (i) emerging Ti3C2, Nb4C3 MXenes (transition metal carbides and/or nitrides) that are promising for energy storage

  18. Determination of neutron flux distribution by using ANISN, a one-dimensional discrete S sub n ordinates transport code with anisotropic scattering

    NASA Technical Reports Server (NTRS)

    Ghorai, S. K.

    1983-01-01

    The purpose of this project was to use a one-dimensional discrete coordinates transport code called ANISN in order to determine the energy-angle-spatial distribution of neutrons in a 6-feet cube rock box which houses a D-T neutron generator at its center. The project was two-fold. The first phase of the project involved adaptation of the ANISN code written for an IBM 360/75/91 computer to the UNIVAC system at JSC. The second phase of the project was to use the code with proper geometry, source function and rock material composition in order to determine the neutron flux distribution around the rock box when a 14.1 MeV neutron generator placed at its center is activated.

  19. The evaluation of neutron and gamma ray dose equivalent distributions in patients and the effectiveness of shield materials for high energy photons radiotherapy facilities.

    PubMed

    Ghassoun, J; Senhou, N

    2012-04-01

    In this study, the MCNP5 code was used to model radiotherapy room of a medical linear accelerator operating at 18 MV and to evaluate the neutron and the secondary gamma ray fluences, the energy spectra and the dose equivalent distributions inside a liquid tissue-equivalent (TE) phantom. The obtained results were compared with measured data published in the literature. Moreover, the shielding effects of various neutron material shields on the radiotherapy room wall were also investigated. Our simulation results showed that paraffin wax containing boron carbide presents enough effectiveness to reduce both neutron and secondary gamma ray doses.

  20. The Vertical Distribution of Buried Volatiles at the Moon revealed by Thermal and Epithermal Neutron Fluxes from LEND Observations

    NASA Astrophysics Data System (ADS)

    Chin, G.; Sagdeev, R.; Su, J. J.; Murray, J.; Livengood, T. A.

    2015-12-01

    Determining the quantity and vertical distribution of volatile species on and below the surface of planetary bodies is vital to understand the primordial chemical inventory and subsequent evolution of planets. Volatiles may provide resources to support future human exploration. This is particularly true for the Moon, which is well observed by many methods from ground-based, lunar orbit, and in situ, and is an accessible destination or way station for human exploration. We present Geant4 models of relative fluxes of Fast, Epithermal, and Thermal neutron emission generated in a planetary regolith by galactic cosmic rays to reveal the first 1-2 meters vertical structure of embedded hydrogen or water. Varying ratios of Thermal versus Epithermal, low-energy-Epithermal versus high-energy-Epithermal, and Thermal versus Fast neutron emissions are diagnostics of the depth in which hydrogen/water layers are buried within the top 1-2 meters of the regolith. In addition, we apply model calculations to Lunar Exploration Neutron Detector (LEND) thermal and epithermal data, acquired on the Lunar Reconnaissance Orbiter (LRO), in specific regions of the Moon to retrieve the vertical distribution of buried ice from the remote sensing information. GEANT4 is a set of particle physics transport simulation codes that exploits object-oriented software methods to deliver a comprehensive and flexible toolkit that is modular and extensible, based on a free open-source development model. GEANT4 has become a standard tool to simulate applications as diverse as particle telescope and detector response, space radiation shielding and optimization, total ionizing dose in spacecraft components, and biological effects of radiation.

  1. 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.

  2. Local Structure of Proton-Conducting Lanthanum Tungstate La28-xW4+xO54+δ: a Combined Density Functional Theory and Pair Distribution Function Study

    SciTech Connect

    Kalland, Liv-Elisif; Magrasó, Anna; Mancini, Alessandro; Tealdi, Cristina; Malavasi, Lorenzo

    2013-10-02

    Lanthanum tungstate (La28–xW4+xO54+δ) is a good proton conductor and exhibits a complex fluorite-type structure. To gain further understanding of the short-range order in the structure we correlate the optimized configurations obtained by density functional theory (DFT) with the experimental atomic pair distribution function analysis (PDF) of time-of-flight neutron and synchrotron X-ray data, collected at room temperature. The local atomic arrangements cannot be described by means of any average symmetric structure. Tungsten forms WO6 octahedra in alternating directions, La1 is mainly 8-fold coordinated in relatively symmetric cubes, and La2 is coordinated with 6 or 7 oxygens in heavily distorted cubes. Both DFT and PDF confirm that the excess tungsten (x) is incorporated in La2 (1/4, 1/4, 1/4) sites in the La27W5O55.5 composition. This additional tungsten can be considered as a donor self-dopant in the material and has implications to the conducting properties and the defect structure.

  3. A new gamma-ray diagnostic for energetic ion distributions - The Compton tail on the neutron capture line

    NASA Technical Reports Server (NTRS)

    Vestrand, W. Thomas

    1990-01-01

    This paper presents a new radiation diagnostic for assaying the energy spectrum and the angular distribution of energetic ions incident on thick hydrogen-rich thermal targets. This diagnostic compares the number of emergent photons in the narrow neutron capture line at 2.223 MeV to the number of Compton scattered photons that form a low-energy tail on the line. It is shown that the relative strength of the tail can be used as a measure of the hardness of the incident ion-energy spectrum. Application of this diagnostic to solar flare conditions is the main thrust of the work presented here. It is examined how the strength of the Compton tail varies with flare viewing angle and the angular distribution of the flare-accelerated particles. Application to compact X-ray binary systems is also briefly discussed.

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

    SciTech Connect

    Pikul, V.P.; Koblik, Yu.N.; Khugaev, A.V.; Yuldashev, B.S.; Jovliev, U.Yu.; Muminov, A.I.; Pavliy, K.V.; Nasirov, A.K.

    2005-02-01

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

  5. Neutron-proton bremsstrahlung as a possible probe of high-momentum component in nucleon momentum distribution

    NASA Astrophysics Data System (ADS)

    Xue, Hui; Xu, Chang; Yong, Gao-Chan; Ren, Zhongzhou

    2016-04-01

    Neutron-proton bremsstrahlung in intermediate energy nucleus-nucleus collisions is proposed as a possible probe to study the high-momentum component in nucleon momentum distribution of finite nucleus. Based on the Boltzmann-Uehling-Uhlenbeck (BUU) transport model, the effects of high-momentum component on the production of bremsstrahlung photons in the reaction of 12C+12 C collisions at different incident beam energies are studied. It is found that the high-momentum component increases the high-energy bremsstrahlung photon production remarkably. Furthermore, the ratio of photon production at different incident beam energies is suggested as a potential observable to probe the high-momentum component in nucleon momentum distribution of finite nucleus.

  6. Switchable radioactive neutron source device

    DOEpatents

    Boyar, Robert E.; DeVolpi, Alexander; Stanford, George S.; Rhodes, Edgar A.

    1989-01-01

    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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Proton Distribution Radii of C-1912 Illuminate Features of Neutron Halos

    NASA Astrophysics Data System (ADS)

    Kanungo, R.; Horiuchi, W.; Hagen, G.; Jansen, G. R.; Navratil, P.; Ameil, F.; Atkinson, J.; Ayyad, Y.; Cortina-Gil, D.; Dillmann, I.; Estradé, A.; Evdokimov, A.; Farinon, F.; Geissel, H.; Guastalla, G.; Janik, R.; Kimura, M.; Knöbel, R.; Kurcewicz, J.; Litvinov, Yu. A.; Marta, M.; Mostazo, M.; Mukha, I.; Nociforo, C.; Ong, H. J.; Pietri, S.; Prochazka, A.; Scheidenberger, C.; Sitar, B.; Strmen, P.; Suzuki, Y.; Takechi, M.; Tanaka, J.; Tanihata, I.; Terashima, S.; Vargas, J.; Weick, H.; Winfield, J. S.

    2016-09-01

    Proton radii of 12-19C densities derived from first accurate charge changing cross section measurements at 900 A MeV with a carbon target are reported. A thick neutron surface evolves from ˜0.5 fm in 15C to ˜1 fm in 19. The halo radius in 19/SUP>C is found to be 6.4 ±0.7 fm as large as 11Li. Ab initio calculations based on chiral nucleon-nucleon and three-nucleon forces reproduce the radii well.

  13. Proton Distribution Radii of 12-19C Illuminate Features of Neutron Halos

    DOE PAGES

    Kanungo, R.; Horiuchi, W.; Hagen, Gaute; Jansen, Gustav R.; Navratil, Petr; Ameil, F.; Atkinson, J.; Ayyad, Y.; Cortina-Gil, D.; Dillmann, I.; et al

    2016-09-02

    We report proton radii of 12-19C densities derived from first accurate charge changing cross section measurements at 900A MeV with a carbon target. A thick neutron surface evolves from ~0.5 fm in 15C to ~1 fm in 19C. Also, the halo radius in 19C is found to be 6.4±0.7 fm as large as 11Li. Ab initio calculations based on chiral nucleon-nucleon and three-nucleon forces reproduce the radii well.

  14. Proton Distribution Radii of ^{12-19}C Illuminate Features of Neutron Halos.

    PubMed

    Kanungo, R; Horiuchi, W; Hagen, G; Jansen, G R; Navratil, P; Ameil, F; Atkinson, J; Ayyad, Y; Cortina-Gil, D; Dillmann, I; Estradé, A; Evdokimov, A; Farinon, F; Geissel, H; Guastalla, G; Janik, R; Kimura, M; Knöbel, R; Kurcewicz, J; Litvinov, Yu A; Marta, M; Mostazo, M; Mukha, I; Nociforo, C; Ong, H J; Pietri, S; Prochazka, A; Scheidenberger, C; Sitar, B; Strmen, P; Suzuki, Y; Takechi, M; Tanaka, J; Tanihata, I; Terashima, S; Vargas, J; Weick, H; Winfield, J S

    2016-09-01

    Proton radii of ^{12-19}C densities derived from first accurate charge changing cross section measurements at 900A  MeV with a carbon target are reported. A thick neutron surface evolves from ∼0.5  fm in ^{15}C to ∼1  fm in ^{19}C. The halo radius in ^{19}C is found to be 6.4±0.7  fm as large as ^{11}Li. Ab initio calculations based on chiral nucleon-nucleon and three-nucleon forces reproduce the radii well. PMID:27636470

  15. Proton Distribution Radii of 12-19C Illuminate Features of Neutron Halos

    NASA Astrophysics Data System (ADS)

    Kanungo, R.; Horiuchi, W.; Hagen, G.; Jansen, G. R.; Navratil, P.; Ameil, F.; Atkinson, J.; Ayyad, Y.; Cortina-Gil, D.; Dillmann, I.; Estradé, A.; Evdokimov, A.; Farinon, F.; Geissel, H.; Guastalla, G.; Janik, R.; Kimura, M.; Knöbel, R.; Kurcewicz, J.; Litvinov, Yu. A.; Marta, M.; Mostazo, M.; Mukha, I.; Nociforo, C.; Ong, H. J.; Pietri, S.; Prochazka, A.; Scheidenberger, C.; Sitar, B.; Strmen, P.; Suzuki, Y.; Takechi, M.; Tanaka, J.; Tanihata, I.; Terashima, S.; Vargas, J.; Weick, H.; Winfield, J. S.

    2016-09-01

    Proton radii of 12-19C densities derived from first accurate charge changing cross section measurements at 900 A MeV with a carbon target are reported. A thick neutron surface evolves from ˜0.5 fm in 15C to ˜1 fm in 19. The halo radius in 19;C is found to be 6.4 ±0.7 fm as large as 11Li. Ab initio calculations based on chiral nucleon-nucleon and three-nucleon forces reproduce the radii well.

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

    NASA Astrophysics Data System (ADS)

    Taulbee, Timothy D.

    The goal of this research was to determine whether neutron dose reconstruction could be improved through re-analysis of historic NTA films worn by workers in the 1950 through the 1970s. To improve neutron dose reconstruction, the underlying neutron energy spectra is critical in determining the organ dose due to energy dependence of the dose conversion factor as well as the application of radiation weighting factors used in epidemiology and probability of causation calculations. Monte Carlo models of proton-recoil track length distributions were developed and benchmarked against measurement data for both NTA and Ilford films. These models, when applied to several NTA film dosimeter configurations, demonstrated that proton-recoil track length distributions change based upon incident neutron energy. The neutron energy spectra changes that result from the general work environment such as source term and shielding can subsequently be modeled to predict the response of the NTA film dosimeter. An Automatic NTA Film Analyzer has been designed and developed to determine if the difference in proton-recoil track length distributions predicted by the Monte Carlo models could be measured and whether these differences could be correlated to the incident neutron energy spectra. The design required the development of a 2D-3D hybrid track recognition algorithm for a three dimensional analysis of the NTA film in order to accurately determine the proton-recoil track length for subsequent neutron energy determination. NTA films exposed to a plutonium fluoride (PuF4) and polonium boron (PoB) calibration sources were measured and compared. The proton-recoil track lengths were used to reconstruct the incident neutron energy spectra demonstrating the functionality of the analyzer and that reconstruction of the neutron energy spectra from NTA films is feasible. These measurements were compared to the Monte Carlo models and confirmed the applicability of using models to determine the NTA

  17. Low-Altitude Neutron Measurements at Mercury: New Insights into Volatile Distributions

    NASA Astrophysics Data System (ADS)

    Peplowski, P. N.; Lawrence, D. J.; Goldsten, J. O.; Nittler, L. R.; Solomon, S. C.

    2014-12-01

    MESSENGER's low-altitude observing campaign provides an improvement by an order of magnitude in the spatial resolution of neutron measurements compared with previously reported analyses. Those prior measurements revealed the presence of distinct geochemical terranes on Mercury's surface at the ~1000-km spatial scale. The low-altitude data, in particular measurements acquired below 60 km, provide a spatial resolution of <100 km, facilitating an investigation of the chemical properties of smaller areas of interest. Specific targets include individual polar deposits, fresh impact craters, low-reflectance material, pyroclastic deposits, isolated small expanses of smooth and intercrater plains, and areas with unusual color properties or composition indicated by imaging or other elemental remote sensing observations. Because neutron measurements are particularly sensitive to volatile elements, such as H, Na, and Cl, the low-altitude data provide new insights into volatile transport processes on Mercury, including the sequestration of water ice and other frozen volatile compounds in permanently shadowed craters and volatile-driven volcanism.

  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. 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.

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

    PubMed

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

    2006-08-01

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

  1. Pair distribution function analysis: The role of structural degrees of freedom in the high-pressure insulator to metal transition of VO2

    NASA Astrophysics Data System (ADS)

    Baldini, M.; Postorino, P.; Malavasi, L.; Marini, C.; Chapman, K. W.; Mao, Ho-kwang

    2016-06-01

    The evolution of the local structure of VO2 was investigated across the pressure-induced insulator to metal transition (IMT) by means of pair distribution function measurements. The pressure behavior of the V-V and V-O bond lengths have been determined. The data demonstrated that the pressure-driven IMT is not activated by the suppression of the Peierls-type distortion. A clear octahedra symmetrization is observed in the metallic phase, suggesting a link between structural degree of freedom and the metallization process.

  2. 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

    NASA Astrophysics Data System (ADS)

    Kołodziej, Karol; Słapik, Aleksandra

    2015-10-01

    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.

  3. Neutron Capture from 87Sr

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

    The neutron-capture resonances of the reaction 87Sr(n , γ)88Sr are significant to nuclear astrophysics to estimate the neutron density during the s process, whose path is split by the branching nucleus 85Kr, and for a possible use of the 87Rb-87Sr chronometric pair to measure the age of our Galaxy. In addition, the γ rays of the product nucleus 88Sr are of importance to nuclear structure and the study of the pygmy resonance observed earlier in (γ ,γ') measurements. We report results from a neutron-capture experiment on 87Sr carried out with the 4 π BaF2 array, DANCE, at LANL. Spin values of neutron resonances have been deduced using the multiplicity and angular distributions of the cascade γ rays following the neutron capture. Work supported by the US Department of Energy under grants DE-FG02-97ER41033, DE-FG02-97ER41042, DE-FG02-97ER41041, and DE-FG52-06NA26155.

  4. Rapidly rotating neutron star progenitors

    NASA Astrophysics Data System (ADS)

    Postnov, K. A.; Kuranov, A. G.; Kolesnikov, D. A.; Popov, S. B.; Porayko, N. K.

    2016-08-01

    Rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. It was demonstrated by Imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. In the present paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. We applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. We have used the BSE population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core-envelope coupling, characterized by the coupling time, τc. The validity of this approach is checked by direct MESA calculations of the evolution of a rotating 15 M⊙ star. From comparison of the calculated spin distribution of young neutron stars with the observed one, reported by Popov and Turolla, we infer the value τc ≃ 5 × 105 years. We show that merging of stellar cores in common envelopes can lead to collapses with dynamically unstable proto-neutron stars, with their formation rate being ˜0.1 - 1% of the total core collapses, depending on the common envelope efficiency.

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

    PubMed

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

    1991-01-01

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

  6. Lepton distributions from the decay of wino and scalar-lepton pairs at electron-positron colliders and heavy-mass power-counting theorem and decoupling

    SciTech Connect

    Not Available

    1985-01-01

    The author computed in detail the energy and angular distributions of leptons from the decay of wino and scalar lepton pairs produced in e/sup +/e/sup -/ collisions within the framework of a supergravity electroweak model. The author has also computed backgrounds to these reactions coming from the production and subsequent decays of tau pairs or pairs of sequential heavy leptons. The author concludes that it is possible to distinguish the wino from an ordinary heavy lepton and, moreover, the wino and the scalar lepton (if light enough) would clearly by identifiable at CERN LEP energies. In the second part of this work the author establishes a heavy-mass power-counting theorem which provides a prescription for extracting the low-energy heavy-mass dependence from an arbitrary Feynman diagram rendered finite within the momentum subtraction scheme. Furthermore, in the absence of heavy-mass dependent vertices the author obtain as a consequence of this power-counting theorem a simple proof of the Appelquist-Carazzone decoupling theorem valid for theories with unbroken internal symmetry.

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

    NASA Astrophysics Data System (ADS)

    Wöllert, Anton; Bauke, Heiko; Keitel, Christoph H.

    2016-09-01

    Ultra strong electromagnetic fields can lead to 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 description of the fermionic 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.

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

    PubMed Central

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

    2015-01-01

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

  9. 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.

  10. 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.

  11. Effect of head phantom size on 10B and 1H[n,gamma]2H dose distributions for a broad field accelerator epithermal neutron source for BNCT.

    PubMed

    Gupta, N; Niemkiewicz, J; Blue, T E; Gahbauer, R; Qu, T X

    1993-01-01

    The effect of head phantom size on the 10B and 1H[n,gamma]2H dose distributions for a broad epithermal neutron radiation field generated by an accelerator-based epithermal neutron source for boron neutron capture therapy (BNCT) have been studied. Also two techniques for calculating the absorbed gamma dose from a measured gamma-ray source distribution are compared: a Monte Carlo technique, which is well accepted in the BNCT community, and a Point Kernel technique. The count-rate distribution in the central plane of three rectangular parallelopiped head water phantoms irradiated with an epithermal neutron field was measured with a boron trifluoride (BF3) detector. This epithermal neutron field was produced at the Ohio State University Van de Graaff Accelerator Facility. The 10B absorbed dose and the gamma-ray source have the same distribution in the head phantom as the BF3 count-rate distribution. The absorbed gamma dose from the measured source distribution was calculated using MCNP, a Monte Carlo code, and QAD-CGGP, a Point Kernel code. The most pronounced effect of phantom size on 10B absorbed dose was on the dose rate at the depth of maximum dose, dmax. An increase in dose rate at dmax was observed with a decrease in phantom size, the dose rate in the smallest phantom being larger by a factor of 1.4 than the dose rate in the largest phantom. Also, dmax for the phantoms shifted deeper with a decrease in phantom dimensions. The shift between the largest and the smallest phantoms was 6 mm. Finally, the smaller phantoms had lower entrance 10B dose as a percent of the dose at dmax, or better skin sparing. Our calculations for the gamma dose show that a Point Kernel technique can be used to calculate the dose distribution as accurately as a Monte Carlo technique, in much shorter computation times.

  12. 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...

  13. Electromagnetic heavy-lepton pair production in relativistic heavy-ion collisions

    NASA Astrophysics Data System (ADS)

    Şengül, M. Y.; Güçlü, M. C.; Mercan, Ö.; Karakuş, N. G.

    2016-08-01

    We calculate the cross sections of electromagnetic productions of muon- and tauon-pair productions from the ultra-relativistic heavy ion collisions. Since the Compton wavelengths of muon and tauon are comparable to the radius of the colliding ions, nuclear form factors play important roles for calculating the cross sections. Recent measurement (Abrahamyan et al., Phys Rev Lett 108:112502, 2012) indicates that the neutrons are differently distributed from the protons; therefore this affects the cross section of the heavy-lepton pair production. In order to see the effects of the neutron distributions in the nucleus, we used analytical expression of the Fourier transforms of the Wood-Saxon distribution. Cross section calculations show that the Wood-Saxon distribution function is more sensitive to the parameter R compared to the parameter a.

  14. Angular distribution of 4.43-MeV γ-rays produced in inelastic scattering of 14.1-MeV neutrons by 12C nuclei

    NASA Astrophysics Data System (ADS)

    Bystritsky, V. M.; Grozdanov, D. N.; Zontikov, A. O.; Kopach, Yu. N.; Rogov, Yu. N.; Ruskov, I. N.; Sadovsky, A. B.; Skoy, V. R.; Barmakov, Yu. N.; Bogolyubov, E. P.; Ryzhkov, V. I.; Yurkov, D. I.

    2016-07-01

    The work is devoted to measuring the angular distribution of 4.43-MeV γ-rays produced in inelastic scattering of 14.1-MeV neutrons by 12C nuclei. A portable ING-27 neutron generator (designed and fabricated at VNIIA, Moscow) with a built-in 64-pixel silicon α-detector was used as a source of tagged neutrons. The γ-rays of characteristic nuclear radiation from 12C were detected with a spectrometric system that consisted of 22 γ-detectors based on NaI(Tl) crystals arranged around the carbon target. The measured angular distribution of 4.43-MeV γ-rays is analyzed and compared with the results of other published experimental works.

  15. 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…

  16. Dipolar magnets and glasses: Neutron-scattering, dynamical, and calorimetric studies of randomly distributed Ising spins

    SciTech Connect

    Reich, D.H.; Ellman, B.; Yang, J.; Rosenbaum, T.F. . James Franck Institute University of Chicago, Chicago, IL . Department of Physics); Aeppli, G. ); Belanger, D.P. )

    1990-09-01

    We have measured the magnetic correlations, susceptibility, specific heat, and thermal relaxation in the dipolar-coupled Ising system LiHo{sub {ital x}}Y{sub 1{minus}{ital x}}F{sub 4}. The material is ferromagnetic for spin concentrations at least as low as {ital x}=0.46, with a Curie temperature obeying mean-field scaling relative to that of pure LiHoF{sub 4}. In contrast, an {ital x}=0.167 sample behaves as a spin glass above its transition temperature, while an {ital x}=0.045 crystal shows very different glassy properties characterized by decreasing barriers to relaxation and nonexponential thermal relaxation as {ital T}{r arrow}0. We find the properties of the {ital x}=0.045 system to be consistent with a single low-degeneracy ground state with a large gap for excitations. The {ital x}=0.167 sample, however, supports a complex ground state with no appreciable gap, in accordance with prevailing theories of spin glasses. The underlying causes of such disparate behavior are discussed in terms of random clusters as probed by neutron studies of the {ital x}=0.167 sample.

  17. 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.

  18. A unified description of the electrochemical, charge distribution, and spectroscopic properties of the special-pair radical cation in bacterial photosynthesis.

    PubMed

    Reimers, Jeffrey R; Hush, Noel S

    2004-04-01

    We apply our four-state 70-vibration vibronic-coupling model for the properties of the photosynthetic special-pair radical cation to: (1) interpret the observed correlations between the midpoint potential and the distribution of spin density between the two bacteriochlorophylls for 30 mutants of Rhodobacter sphaeroides, (2) interpret the observed average intervalence hole-transfer absorption energies as a function of spin density for six mutants, and (3) simulate the recently obtained intervalence electroabsorption Stark spectrum of the wild-type reaction center. While three new parameters describing the location of the sites of mutation with respect to the special pair are required to describe the midpoint-potential data, a priori predictions are made for the transition energies and the Stark spectrum. In general, excellent predictions are made of the observed quantities, with deviations being typically of the order of twice the experimental uncertainties. A unified description of many chemical and spectroscopic properties of the bacterial reaction center is thus provided. Central to the analysis is the assumption that the perturbations made to the reaction center, either via mutations of protein residues or by application of an external electric field, act only to independently modify the oxidation potentials of the two halves of the special pair and hence the redox asymmetry E0. While this appears to be a good approximation, clear evidence is presented that effects of mutation can be more extensive than what is allowed for. A thorough set of analytical equations describing the observed properties is obtained using the Born-Oppenheimer adiabatic approximation. These equations are generally appropriate for intervalence charge-transfer problems and include, for the first time, full treatment of both symmetric and antisymmetric vibrational motions. The limits of validity of the adiabatic approach to the full nonadiabatic problem are obtained.

  19. 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 μm 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.

  20. 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

  1. Manifestation of Negative Compressibility in Low-Density Electron Liquids: Anomaly in the Ion-Pair Distribution Function in Supercritical Fluid Rb

    NASA Astrophysics Data System (ADS)

    Takada, Yasutami

    2006-03-01

    It is a well-known fact that the electronic compressibility κ diverges in the 3D electron gas as the density parameter rs approaches 5.25. A recent investigation clarifies that this divergence is due to the excitonic effect in the electron-hole pair excitation, in particular, to its zero-energy excitation [1]. For rs>5.25, κ becomes negative, leading to the negative static dielectric function ɛ(q,0) for at least small q owing to the compressibility sum rule. Then we can expect that two positive test charges do not repel but attract to each other in such a system. Keeping this situation in mind, we have calculated the ion-pair distribution function g(R) in the expanded Rb liquid metal by using the Monte Carlo method and found interesting features in g(R) characteristic to the negative ɛ(q,0) [2]. Such features have been observed by the recent measurement of g(R) in the supercritical fluid Rb metal with continuously increasing rs from 5.25 [3]. This confirms the situation of κ<0 in the low-density 3D electron gas for the first time. [1] YT, J. Superconductivity 18, No.3 (2005). [2] H. Maebashi and YT, to be submitted. [3] K. Matsuda and K. Tamura, private communication.

  2. 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.

  3. Distribution of paired immunoglobulin-like receptor B in the nervous system related to regeneration difficulties after unilateral lumbar spinal cord injury

    PubMed Central

    Peng, Wan-shu; Qi, Chao; Zhang, Hong; Gao, Mei-ling; Wang, Hong; Ren, Fei; Li, Xia-qing

    2015-01-01

    Paired immunoglobulin-like receptor B (PirB) is a functional receptor of myelin-associated inhibitors for axonal regeneration and synaptic plasticity in the central nervous system, and thus suppresses nerve regeneration. The regulatory effect of PirB on injured nerves has received a lot of attention. To better understand nerve regeneration inability after spinal cord injury, this study aimed to investigate the distribution of PirB (via immunofluorescence) in the central nervous system and peripheral nervous system 10 days after injury. Immunoreactivity for PirB increased in the dorsal root ganglia, sciatic nerves, and spinal cord segments. In the dorsal root ganglia and sciatic nerves, PirB was mainly distributed along neuronal and axonal membranes. PirB was found to exhibit a diffuse, intricate distribution in the dorsal and ventral regions. Immunoreactivity for PirB was enhanced in some cortical neurons located in the bilateral precentral gyri. Overall, the findings suggest a pattern of PirB immunoreactivity in the nervous system after unilateral spinal transection injury, and also indicate that PirB may suppress repair after injury. PMID:26330840

  4. The determination of pair-distance distribution by double electron-electron resonance: regularization by the length of distance discretization with Monte Carlo calculations

    NASA Astrophysics Data System (ADS)

    Dzuba, Sergei A.

    2016-08-01

    Pulsed double electron-electron resonance technique (DEER, or PELDOR) is applied to study conformations and aggregation of peptides, proteins, nucleic acids, and other macromolecules. For a pair of spin labels, experimental data allows for the determination of their distance distribution function, P(r). P(r) is derived as a solution of a first-kind Fredholm integral equation, which is an ill-posed problem. Here, we suggest regularization by increasing the distance discretization length to its upper limit where numerical integration still provides agreement with experiment. This upper limit is found to be well above the lower limit for which the solution instability appears because of the ill-posed nature of the problem. For solving the integral equation, Monte Carlo trials of P(r) functions are employed; this method has an obvious advantage of the fulfillment of the non-negativity constraint for P(r). The regularization by the increasing of distance discretization length for the case of overlapping broad and narrow distributions may be employed selectively, with this length being different for different distance ranges. The approach is checked for model distance distributions and for experimental data taken from literature for doubly spin-labeled DNA and peptide antibiotics.

  5. A QCD calculation of the transverse momentum distribution of Drell-Yan pairs including soft emission and non-abelian effects

    NASA Astrophysics Data System (ADS)

    Odorico, R.

    1982-05-01

    The well-known Parisi and Petronzio LLA result for the QCD transverse momentum distribution of Drell-Yan pairs at pT≪ Q takes into account the non-singlet contribution only and totally neglects non-abelian effects due to the singlet contribution. The latter becomes substantial and sometimes dominant at pp and overlinepp collider energies, and thus any comparison with data from these machines will require computation of its effects. We present a QCD Monte Carlo procedure which allows one to calculate the transverse momentum distribution with both non-singlet and singlet contributions included. At the same time it computes the evolution of parton density functions and the correlations between transverse and longitudinal distributions. Phase-space effects are duly taken into account. It is found that, at collider energies, the singlet contribution completely alters QCD predictions for dimuon transverse momenta giving at times < pT> ˜ 4 times larger than the non-singlet contribution. Quantitative results are presented and a comparison with existing data is made, showing satisfactory agreement with the experimentally observed behaviours.

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

    SciTech Connect

    Lin, He; Božin, E.S.; Billinge, S.J.L.; Androulakis, J.; Malliakas, C.D.; Lin, C.H.; Kanatzidis, M.G.

    2009-08-13

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

  7. Asymptotic behavior of joint distributions of characteristics of a pair of randomly chosen individuals in discrete-time Fisher-Wright models with mutations and drift.

    PubMed

    Bobrowski, Adam; Kimmel, Marek

    2004-12-01

    This is a continuation of the series of articles (C.R. Rao, D.N. Shanbhag (Eds.), Handbook of Statistics 19: Stochastic Processes: Theory and Methods, Elsevier Science, Amsterdam, 2001 (Chapter 8); Math. Biosci. 175 (2002) 83; Math. Meth. Appl. Sci. 26 (2003) 1587; Adv. Appl. Probab. 36 (2004) 57) devoted to a study of the interplay between two of the main forces of population genetics, mutations and drift, in the Fisher-Wright model. We provide discrete-time versions of theorems describing asymptotic behavior of joint distributions of characteristics of a pair of individuals in this model; their continuous-time counterparts were presented in the previous papers. Furthermore, we show that imbalance index, introduced in Kimmel et al. (Genetics 148 (1998) 1921) and King et al. (Mol. Biol. Evol. 17(12) (2000) 1895) in the context of continuous-time models, may also be used in discrete-time models to detect past population growth. PMID:15560913

  8. 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.

  9. DShaper: An approach for handling missing low-Q data in pair distribution function analysis of nanostructured systems

    SciTech Connect

    Olds, Daniel; Wang, Hsiu -Wen; Page, Katharine

    2015-01-01

    This study discusses the potential problems and currently available solutions in modeling powder-diffraction-based pair distribution function (PDF) data from systems where morphological feature information content includes distances in the nanometre length scale, such as finite nanoparticles, nanoporous networks and nanoscale precipitates in bulk materials. The implications of an experimental finite minimumQvalue are reviewed by simulation, which also demonstrates the advantages of combining PDF data with small-angle scattering data. A simple Fortran90 code, DShaper, is introduced, which may be incorporated into PDF data fitting routines in order to approximate the so-called `shape function' for any atomistic model.

  10. An application of CCD read-out technique to neutron distribution measurement using the self-activation method with a CsI scintillator plate

    NASA Astrophysics Data System (ADS)

    Nohtomi, Akihiro; Kurihara, Ryosuke; Kinoshita, Hiroyuki; Honda, Soichiro; Tokunaga, Masaaki; Uno, Heita; Shinsho, Kiyomitsu; Wakabayashi, Genichiro; Koba, Yusuke; Fukunaga, Junichi; Umezu, Yoshiyuki; Nakamura, Yasuhiko; Ohga, Saiji

    2016-10-01

    In our previous paper, the self-activation of an NaI scintillator had been successfully utilized for detecting photo-neutrons around a high-energy X-ray radiotherapy machine; individual optical pulses from the self-activated scintillator are read-out by photo sensors such as a photomultiplier tube (PMT). In the present work, preliminary observations have been performed in order to apply a direct CCD read-out technique to the self-activation method with a CsI scintillator plate using a Pu-Be source and a 10-MV linac. In conclusion, it has been revealed that the CCD read-out technique is applicable to neutron measurement around a high-energy X-ray radiotherapy machine with the self-activation of a CsI plate. Such application may provide a possibility of novel method for simple neutron dose-distribution measurement.

  11. 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.

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

    SciTech Connect

    Sukhovoj, A. M. Khitrov, V. A.

    2013-01-15

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

  13. 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.

  14. FAST NEUTRON SPECTROMETER USING SPACED SEMICONDUCTORS FOR MEASURING TOTAL ENERGY OF NEUTRONS CAPTURED

    DOEpatents

    Love, T.A.; Murray, R.B.

    1964-04-14

    A fast neutron spectrometer was designed, which utilizes a pair of opposed detectors having a layer of /sup 6/LiF between to produce alpha and T pair for each neutron captured to provide signals, which, when combined, constitute a measure of neutron energy. (AEC)

  15. Breaking of Cooper pairs in 108Pd

    NASA Astrophysics Data System (ADS)

    Rahmatinejad, A.; Kakavand, T.; Razavi, R.

    2016-04-01

    In this paper, breaking of Cooper pairs in 108Pd is investigated within the canonical ensemble framework and the BCS model. Our results show an evidence of two phase transitions, which are related to neutron and proton systems. Also, with consideration of pairing interaction, the role of neutron and proton systems in entropy, spin cutoff parameter and as a result in the moment of inertia are investigated. The results show minor role for the proton system at low temperatures and approximately equal roles for both neutron and proton systems after the critical temperature. Good agreement was observed between obtained results and the experimental data.

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

    SciTech Connect

    Wang, Jian-Guang

    2006-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Wang, J. G.

    2006-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-04-01

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

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

    SciTech Connect

    Suzuki, Minoru . E-mail: msuzuki@rri.kyoto-u.ac.jp; Sakurai, Yoshinori; Masunaga, Shinichiro; Kinashi, Yuko; Nagata, Kenji; Maruhashi, Akira; Ono, Koji

    2006-12-01

    Purpose: To investigate the feasibility of boron neutron capture therapy (BNCT) for malignant pleural mesothelioma (MPM) from a viewpoint of dose distribution analysis using Simulation Environment for Radiotherapy Applications (SERA), a currently available BNCT treatment planning system. Methods and Materials: The BNCT treatment plans were constructed for 3 patients with MPM using the SERA system, with 2 opposed anterior-posterior beams. The {sup 1}B concentrations in the tumor and normal lung in this study were assumed to be 84 and 24 ppm, respectively, and were derived from data observed in clinical trials. The maximum, mean, and minimum doses to the tumors and the normal lung were assessed for each plan. The doses delivered to 5% and 95% of the tumor volume, D{sub 05} and D{sub 95}, were adopted as the representative dose for the maximum and minimum dose, respectively. Results: When the D{sub 05} to the normal ipsilateral lung was 5 Gy-Eq, the D{sub 95} and mean doses delivered to the normal lung were 2.2-3.6 and 3.5-4.2 Gy-Eq, respectively. The mean doses delivered to the tumors were 22.4-27.2 Gy-Eq. The D{sub 05} and D{sub 95} doses to the tumors were 9.6-15.0 and 31.5-39.5 Gy-Eq, respectively. Conclusions: From a viewpoint of the dose-distribution analysis, BNCT has the possibility to be a promising treatment for MPM patients who are inoperable because of age and other medical illnesses.

  20. A Tale of Two Narrow-line Regions: Ionization, Kinematics, and Spectral Energy Distributions for a Local Pair of Merging Obscured Active Galaxies

    NASA Astrophysics Data System (ADS)

    Hainline, Kevin N.; Hickox, Ryan C.; Chen, Chien-Ting; Carroll, Christopher M.; Jones, Mackenzie L.; Zervos, Alexandros S.; Goulding, Andrew D.

    2016-05-01

    We explore the gas ionization and kinematics, as well as the optical-IR spectral energy distributions for UGC 11185, a nearby pair of merging galaxies hosting obscured active galactic nuclei (AGNs), also known as SDSS J181611.72+423941.6 and J181609.37+423923.0 (J1816NE and J1816SW, z ≈ 0.04). Due to the wide separation between these interacting galaxies (˜23 kpc), observations of these objects provide a rare glimpse of the concurrent growth of supermassive black holes at an early merger stage. We use BPT line diagnostics to show that the full extent of the narrow-line emission in both galaxies is photoionized by an AGN, and confirm the existence of a 10 kpc-scale ionization cone in J1816NE, while in J1816SW the AGN narrow-line region is much more compact (1–2 kpc) and relatively undisturbed. Our observations also reveal the presence of ionized gas that nearly spans the entire distance between the galaxies, which is likely in a merger-induced tidal stream. In addition, we carry out a spectral analysis of the X-ray emission using data from XMM-Newton. These galaxies represent a useful pair to explore how the [O iii] luminosity of an AGN is dependent on the size of the region used to explore the extended emission. Given the growing evidence for AGN “flickering” over short timescales, we speculate that the appearances and impacts of these AGNs may change multiple times over the course of the galaxy merger, which is especially important given that these objects are likely the progenitors of the types of systems commonly classified as “dual AGNs.”

  1. Energy Distributions of Neutrons Scattered from Graphite, Light and Heavy Water, Ice, Zirconium Hydride, Lithium Hydride, Sodium Hydride and Ammonium Chloride by the Beryllium Detector Method

    DOE R&D Accomplishments Database

    Woods, A. D. B.; Brockhouse, Bertram N.; Sakamoto, M.; Sinclair, R. N.

    1960-09-12

    Energy distributions of neutrons scattered from various moderators and from several hydrogenous substances were measured at energy transfers of 0.02 to 0.24 ev. Results from experiments on graphite, light and heavy water, ice, ZrH, LiH, NaH, and NH4Cl are included. It is noted that the results are of a preliminary character; however, they are probably the most accurate measurements of high-energy transfers yet made. (J.R.D.)

  2. Calculations of Compound Nucleus Spin-Parity Distributions Populated via the (p,t) Reaction in Support of Surrogate Neutron Capture Measurements

    NASA Astrophysics Data System (ADS)

    Benstead, J.; Tostevin, J. A.; Escher, J. E.; Burke, J. T.; Hughes, R. O.; Ota, S.; Casperson, R. J.; Thompson, I. J.

    2016-06-01

    The surrogate reaction method may be used to determine the cross section for neutron induced reactions not accessible through standard experimental techniques. This is achieved by creating the same compound nucleus as would be expected in the desired reaction, but through a different incident channel, generally a direct transfer reaction. So far, the surrogate technique has been applied with reasonable success to determine the fission cross section for a number of actinides, but has been less successful when applied to other reactions, e.g. neutron capture, due to a `spin-parity mismatch'. This mismatch, between the spin and parity distributions of the excited levels of the compound nucleus populated in the desired and surrogate channels, leads to differing decay probabilities and hence reduces the validity of using the surrogate method to infer the cross section in the desired channel. A greater theoretical understanding of the expected distribution of levels excited in both the desired and surrogate channels is therefore required in order to attempt to address this mismatch and allow the method to be utilised with greater confidence. Two neutron transfer reactions, e.g. (p,t), which allow the technique to be utilised for isotopes further removed from the line of stability, are the subject of this study. Results are presented for the calculated distribution of compound nucleus states populated in 90Zr, via the 90Zr(p,t)90Zr reaction, and are compared against measured data at an incident proton energy of 28.56 MeV.

  3. Exotic modes of excitation in deformed neutron-rich nuclei

    SciTech Connect

    Yoshida, Kenichi

    2011-05-06

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

  4. Pair distribution function analysis and solid state NMR studies of silicon electrodes for lithium ion batteries: understanding the (de)lithiation mechanisms.

    PubMed

    Key, Baris; Morcrette, Mathieu; Tarascon, Jean-Marie; Grey, Clare P

    2011-01-26

    Lithium ion batteries (LIBs) containing silicon negative electrodes have been the subject of much recent investigation, because of the extremely large gravimetric and volumetric capacities of silicon. 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 in these systems with electrochemical performance. We apply a combination of local structure probes, ex situ (7)Li 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. For example, 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.

  5. High-energy X-ray focusing and applications to pair distribution function investigation of Pt and Au nanoparticles at high pressures.

    PubMed

    Hong, Xinguo; Ehm, Lars; Zhong, Zhong; Ghose, Sanjit; Duffy, Thomas S; Weidner, Donald J

    2016-01-01

    We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K-B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10-15 μm) has been achieved at energies of 66 and 81 keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression, and relaxation behavior of samples in the DAC can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71 GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. The coupling of sagittally bent Laue crystals with K-B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source.

  6. High-energy X-ray focusing and applications to pair distribution function investigation of Pt and Au nanoparticles at high pressures

    PubMed Central

    Hong, Xinguo; Ehm, Lars; Zhong, Zhong; Ghose, Sanjit; Duffy, Thomas S.; Weidner, Donald J.

    2016-01-01

    We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K–B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10–15 μm) has been achieved at energies of 66 and 81 keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression, and relaxation behavior of samples in the DAC can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71 GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. The coupling of sagittally bent Laue crystals with K–B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source. PMID:26902122

  7. 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.

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

    PubMed

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

    2014-12-01

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

  9. High-energy X-ray focusing and applications to pair distribution function investigation of Pt and Au nanoparticles at high pressures

    NASA Astrophysics Data System (ADS)

    Hong, Xinguo; Ehm, Lars; Zhong, Zhong; Ghose, Sanjit; Duffy, Thomas S.; Weidner, Donald J.

    2016-02-01

    We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K-B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10-15 μm) has been achieved at energies of 66 and 81 keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression, and relaxation behavior of samples in the DAC can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71 GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. The coupling of sagittally bent Laue crystals with K-B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source.

  10. High-energy X-ray focusing and applications to pair distribution function investigation of Pt and Au nanoparticles at high pressures.

    PubMed

    Hong, Xinguo; Ehm, Lars; Zhong, Zhong; Ghose, Sanjit; Duffy, Thomas S; Weidner, Donald J

    2016-01-01

    We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K-B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10-15 μm) has been achieved at energies of 66 and 81 keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression, and relaxation behavior of samples in the DAC can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71 GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. The coupling of sagittally bent Laue crystals with K-B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source. PMID:26902122

  11. High-energy X-ray focusing and applications to pair distribution function investigation of Pt and Au nanoparticles at high pressures

    DOE PAGES

    Hong, Xinguo; Ehm, Lars; Zhong, Zhong; Ghose, Sanjit; Duffy, Thomas S.; Weidner, Donald J.

    2016-02-23

    We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K–B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10–15 μm) has been achieved at energies of 66 and 81keV. PDF data for nanocrystalline platinum (n-Pt) were collected at 12.5 GPa with a single 5 s X-ray exposure, showing that the in-situ compression, decompression, and relaxation behavior of samples in the DACmore » can be investigated with this technique. PDFs of n-Pt and nano Au (n-Au) under quasi-hydrostatic loading to as high as 71GPa indicate the existence of substantial reduction of grain or domain size for Pt and Au nanoparticles at pressures below 10 GPa. In conclusion, the coupling of sagittally bent Laue crystals with K–B mirrors provides a useful means to focus high-energy synchrotron X-rays from a bending magnet or wiggler source.« less

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

    SciTech Connect

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

    2008-06-18

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

  13. Angular distributions and anisotropy of the fission fragments from neutron-induced fission of 233U and 209Bi in intermediate energy range 1-200 MeV

    NASA Astrophysics Data System (ADS)

    Vorobyev, A. S.; Gagarski, A. M.; Shcherbakov, O. A.; Vaishnene, L. A.; Barabanov, A. L.

    2016-09-01

    New results of the neutron-induced fission experiments carried out at the neutron time-of-flight spectrometer GNEIS of the PNPI are given. Angular distributions of fission fragments from the neutron-induced fission of 233U and 209Bi nuclei have been measured in the energy range 1-200 MeV using position sensitive multiwire proportional counters as fission fragment detector. The recent improvements of the measurement and data processing procedures are described. The data on anisotropy of fission fragments deduced from the measured angular distributions are presented in comparison with the experimental data of other authors.

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

    PubMed

    Radulović, Vladimir; Štancar, Žiga; Snoj, Luka; Trkov, Andrej

    2014-02-01

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

  15. Tracking Sodium-Antimonide Phase Transformations in Sodium-Ion Anodes: Insights from Operando Pair Distribution Function Analysis and Solid-State NMR Spectroscopy.

    PubMed

    Allan, Phoebe K; Griffin, John M; Darwiche, Ali; Borkiewicz, Olaf J; Wiaderek, Kamila M; Chapman, Karena W; Morris, Andrew J; Chupas, Peter J; Monconduit, Laure; Grey, Clare P

    2016-02-24

    Operando pair distribution function (PDF) analysis and ex situ (23)Na magic-angle spinning solid-state nuclear magnetic resonance (MAS ssNMR) spectroscopy are used to gain insight into the alloying mechanism of high-capacity antimony anodes for sodium-ion batteries. Subtraction of the PDF of crystalline NaxSb phases from the total PDF, an approach constrained by chemical phase information gained from (23)Na ssNMR in reference to relevant model compounds, identifies two previously uncharacterized intermediate species formed electrochemically; a-Na(3-x)Sb (x ≈ 0.4-0.5), a structure locally similar to crystalline Na3Sb (c-Na3Sb) but with significant numbers of sodium vacancies and a limited correlation length, and a-Na(1.7)Sb, a highly amorphous structure featuring some Sb-Sb bonding. The first sodiation breaks down the crystalline antimony to form first a-Na(3-x)Sb and, finally, crystalline Na3Sb. Desodiation results in the formation of an electrode formed of a composite of crystalline and amorphous antimony networks. We link the different reactivity of these networks to a series of sequential sodiation reactions manifesting as a cascade of processes observed in the electrochemical profile of subsequent cycles. The amorphous network reacts at higher voltages reforming a-Na(1.7)Sb, then a-Na(3-x)Sb, whereas lower potentials are required for the sodiation of crystalline antimony, which reacts to form a-Na(3-x)Sb without the formation of a-Na(1.7)Sb. a-Na(3-x)Sb is converted to crystalline Na3Sb at the end of the second discharge. We find no evidence of formation of NaSb. Variable temperature (23)Na NMR experiments reveal significant sodium mobility within c-Na3Sb; this is a possible contributing factor to the excellent rate performance of Sb anodes.

  16. 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.

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

    SciTech Connect

    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 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 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.

  18. 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.

  19. 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

  20. Oxyanion Induced Variations in Domain Structure for Amorphous Cobalt Oxide Oxygen Evolving Catalysts, Resolved by X-ray Pair Distribution Function Analysis

    SciTech Connect

    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. Finally, 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.

  1. Oxyanion Induced Variations in Domain Structure for Amorphous Cobalt Oxide Oxygen Evolving Catalysts, Resolved by X-ray Pair Distribution Function Analysis

    DOE PAGES

    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 sizemore » 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. Finally, 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.« less

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

    DOE PAGES

    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

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

    SciTech Connect

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

    2009-07-30

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

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  5. Point-by-Point model calculation of the prompt neutron multiplicity distribution ν (A ) for 238U(n ,f ) at incident neutron energies ranging from 1 MeV to 80 MeV

    NASA Astrophysics Data System (ADS)

    Tudora, A.; Hambsch, F.-J.; Tobosaru, V.

    2016-10-01

    Prompt neutron multiplicity distributions ν(A ) are generally required for prompt emission correction of double energy (2 E ) measurements of fission fragments in order to determine pre-neutron fragment properties. The lack of experimental ν(A ) data especially at higher incident neutron energy imposes the use of prompt emission models to predict ν(A ). At incident neutron energies (En ) where multiple fission chances are involved, the Point-by-Point (PbP) model of prompt emission is able to provide the individual ν(A ) of the compound nuclei of the main and secondary nucleus chains that are undergoing fission at a given En . The total ν(A ) are obtained by averaging these individual ν(A ) over the fission chance probabilities (expressed as total and partial fission cross-section ratios). An indirect validation of the total ν(A ) results is proposed. At high En (above 70 MeV) the PbP results of individual ν(A ) of the first few nuclei of the main and secondary nucleus chains exhibit an almost linear increase. This shape is explained by the damping of shell effects entering the superfluid expression of the level-density parameters. They tend to approach the asymptotic values for a great part of the fragments. This fact leads to a smooth and almost linear increase of fragment excitation energy with the fragment mass number that is reflected in a smooth and almost linear behavior of individual ν(A ). The comparison of the present results with those of the GEF code reveals different shapes of ν(A ) as well as different total average neutron multiplicity as a function of the En . At high En the PbP calculations definitely reflect the influence of the almost linear shape of individual ν(A ) of the first few nuclei of the U and Pa chains. The differences between the total ν(A ) obtained by averaging the PbP results of individual ν(A ) over fission cross-section ratios of different evaluations are insignificant.

  6. Non-Statistical Effects in Neutron Capture

    NASA Astrophysics Data System (ADS)

    Koehler, P. E.; Bredeweg, T. A.; Guber, K. H.; Harvey, J. A.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wiarda, D.; 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 (Γn0) 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 Γn0 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,α) measurements had revealed that the α 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 γ-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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

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

    PubMed

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

    2011-12-01

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

  14. 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

  15. 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

  16. Tracking Sodium-Antimonide Phase Transformations in Sodium-Ion Anodes: Insights from Operando Pair Distribution Function Analysis and Solid-State NMR Spectroscopy.

    PubMed

    Allan, Phoebe K; Griffin, John M; Darwiche, Ali; Borkiewicz, Olaf J; Wiaderek, Kamila M; Chapman, Karena W; Morris, Andrew J; Chupas, Peter J; Monconduit, Laure; Grey, Clare P

    2016-02-24

    Operando pair distribution function (PDF) analysis and ex situ (23)Na magic-angle spinning solid-state nuclear magnetic resonance (MAS ssNMR) spectroscopy are used to gain insight into the alloying mechanism of high-capacity antimony anodes for sodium-ion batteries. Subtraction of the PDF of crystalline NaxSb phases from the total PDF, an approach constrained by chemical phase information gained from (23)Na ssNMR in reference to relevant model compounds, identifies two previously uncharacterized intermediate species formed electrochemically; a-Na(3-x)Sb (x ≈ 0.4-0.5), a structure locally similar to crystalline Na3Sb (c-Na3Sb) but with significant numbers of sodium vacancies and a limited correlation length, and a-Na(1.7)Sb, a highly amorphous structure featuring some Sb-Sb bonding. The first sodiation breaks down the crystalline antimony to form first a-Na(3-x)Sb and, finally, crystalline Na3Sb. Desodiation results in the formation of an electrode formed of a composite of crystalline and amorphous antimony networks. We link the different reactivity of these networks to a series of sequential sodiation reactions manifesting as a cascade of processes observed in the electrochemical profile of subsequent cycles. The amorphous network reacts at higher voltages reforming a-Na(1.7)Sb, then a-Na(3-x)Sb, whereas lower potentials are required for the sodiation of crystalline antimony, which reacts to form a-Na(3-x)Sb without the formation of a-Na(1.7)Sb. a-Na(3-x)Sb is converted to crystalline Na3Sb at the end of the second discharge. We find no evidence of formation of NaSb. Variable temperature (23)Na NMR experiments reveal significant sodium mobility within c-Na3Sb; this is a possible contributing factor to the excellent rate performance of Sb anodes. PMID:26824406

  17. Tracking Sodium-Antimonide Phase Transformations in Sodium-Ion Anodes: Insights from Operando Pair Distribution Function Analysis and Solid-State NMR Spectroscopy

    PubMed Central

    2016-01-01

    Operando pair distribution function (PDF) analysis and ex situ 23Na magic-angle spinning solid-state nuclear magnetic resonance (MAS ssNMR) spectroscopy are used to gain insight into the alloying mechanism of high-capacity antimony anodes for sodium-ion batteries. Subtraction of the PDF of crystalline NaxSb phases from the total PDF, an approach constrained by chemical phase information gained from 23Na ssNMR in reference to relevant model compounds, identifies two previously uncharacterized intermediate species formed electrochemically; a-Na3–xSb (x ≈ 0.4–0.5), a structure locally similar to crystalline Na3Sb (c-Na3Sb) but with significant numbers of sodium vacancies and a limited correlation length, and a-Na1.7Sb, a highly amorphous structure featuring some Sb–Sb bonding. The first sodiation breaks down the crystalline antimony to form first a-Na3–xSb and, finally, crystalline Na3Sb. Desodiation results in the formation of an electrode formed of a composite of crystalline and amorphous antimony networks. We link the different reactivity of these networks to a series of sequential sodiation reactions manifesting as a cascade of processes observed in the electrochemical profile of subsequent cycles. The amorphous network reacts at higher voltages reforming a-Na1.7Sb, then a-Na3–xSb, whereas lower potentials are required for the sodiation of crystalline antimony, which reacts to form a-Na3–xSb without the formation of a-Na1.7Sb. a-Na3–xSb is converted to crystalline Na3Sb at the end of the second discharge. We find no evidence of formation of NaSb. Variable temperature 23Na NMR experiments reveal significant sodium mobility within c-Na3Sb; this is a possible contributing factor to the excellent rate performance of Sb anodes. PMID:26824406

  18. Pairing Learners in Pair Work Activity

    ERIC Educational Resources Information Center

    Storch, Neomy; Aldosari, Ali

    2013-01-01

    Although pair work is advocated by major theories of second language (L2) learning and research findings suggest that pair work facilitates L2 learning, what is unclear is how to best pair students in L2 classes of mixed L2 proficiency. This study investigated the nature of pair work in an English as a Foreign Language (EFL) class in a college in…

  19. 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.

  20. A bounding estimate of neutron dose based on measured photon dose around single pass reactors at the Hanford site.

    PubMed

    Taulbee, Timothy D; Glover, Samuel E; Macievic, Gregory V; Hunacek, Mickey; Smith, Cheryl; DeBord, Gary W; Morris, Donald; Fix, Jack

    2010-07-01

    Neutron and photon radiation survey records have been used to evaluate and develop a neutron to photon (NP) ratio to reconstruct neutron doses to workers around Hanford's single pass reactors that operated from 1945 to 1972. A total of 5,773 paired neutron and photon measurements extracted from 57 boxes of survey records were used in the development of the NP ratio. The development of the NP ratio enables the use of the recorded dose from an individual's photon dosimeter badge to be used to estimate the unmonitored neutron dose. The Pearson rank correlation between the neutron and photon measurements was 0.71. The NP ratio best fit a lognormal distribution with a geometric mean (GM) of 0.8, a geometric standard deviation (GSD) of 2.95, and the upper 95 th % of this distribution was 4.75. An estimate of the neutron dose based on this NP ratio is considered bounding due to evidence that up to 70% of the total photon exposure received by workers around the single pass reactors occurs during shutdown maintenance and refueling activities when there is no significant neutron exposure. Thus when this NP ratio is applied to the total measured photon dose from an individual film badge dosimeter, the resulting neutron dose is considered bounded.

  1. NEUTRON DENSITY CONTROL IN A NEUTRONIC REACTOR

    DOEpatents

    Young, G.J.

    1959-06-30

    The method and means for controlling the neutron density in a nuclear reactor is described. It describes the method and means for flattening the neutron density distribution curve across the reactor by spacing the absorbing control members to varying depths in the central region closer to the center than to the periphery of the active portion of the reactor to provide a smaller neutron reproduction ratio in the region wherein the members are inserted, than in the remainder of the reactor thereby increasing the over-all potential power output.

  2. Neutron resonance averaging

    SciTech Connect

    Chrien, R.E.

    1986-10-01

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

  3. Experimental determination of moisture distributions in fired clay brick using a 252Cf source: a neutron transmission study.

    PubMed

    El Abd, A; Abdel-Monem, A M; Kansouh, W A

    2013-04-01

    A neutron transmission method was proposed to study liquid transport in porous media. It was applied to study water penetration into two kinds of fired clay bricks. The results showed that the diffusion processes in the investigated samples are different. Water diffusivities and capillary absorption coefficients characterizing both the flow process and the brick samples were determined and compared. The proposed method is simple, accurate and reliable in studying water diffusion in porous media, in real time.

  4. Neutron Capture Rates near A=130 which Effect a Global Change to the r-Process Abundance Distribution

    SciTech Connect

    Surman, Rebecca; Beun, Joshua; Mclaughlin, Gail C; Hix, William Raphael

    2009-01-01

    We investigate the impact of neutron capture rates near the A=130 peak on the r-process abundance pattern. We show that these capture rates can alter the abundances of individual nuclear species, not only in the region of A=130 peak but also throughout the abundance pattern. We discuss in general the nonequilibrium processes that produce these abundance changes and determine which capture rates have the most significant impact.

  5. 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.

  6. Chem-Prep PZT 95/5 for Neutron Generator Applications: Particle Size Distribution Comparison of Development and Production-Scale Powders

    SciTech Connect

    SIPOLA, DIANA L.; VOIGT, JAMES A.; LOCKWOOD, STEVEN J.; RODMAN-GONZALES, EMILY D.

    2002-07-01

    The Materials Chemistry Department 1846 has developed a lab-scale chem-prep process for the synthesis of PNZT 95/5, a ferroelectric material that is used in neutron generator power supplies. This process (Sandia Process, or SP) has been successfully transferred to and scaled by Department 14192 (Ceramics and Glass Department), (Transferred Sandia Process, or TSP), to meet the future supply needs of Sandia for its neutron generator production responsibilities. In going from the development-size SP batch (1.6 kg/batch) to the production-scale TSP powder batch size (10 kg/batch), it was important that it be determined if the scaling process caused any ''performance-critical'' changes in the PNZT 95/5 being produced. One area where a difference was found was in the particle size distributions of the calcined PNZT powders. Documented in this SAND report are the results of an experimental study to determine the origin of the differences in the particle size distribution of the SP and TSP powders.

  7. 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.

  8. On the origin of the distribution of potential barriers for methyl group dynamics in glassy polymers: Neutron scattering and MD-simulations

    SciTech Connect

    Alvarez, F.; Alegria, A.; Colmenero, J.; Nicholson, T. M.; Davies, G. R.

    1999-06-15

    We have carried out molecular dynamics simulations of methyl group torsional librations in glassy polyisoprene at 150 K using the Insight and Discover programs from MSI and the Polymer Consortium Force Field. The model system used was built using the MSI Amorphous Cell Builder. During the dynamics runs, the position and velocity of the atoms as well as the dihedral angle of each of the methyl groups were recorded at 10 fs intervals. The results obtained support the threefold approximation for the single particle methyl group potential. The density of states for methyl group torsional librations, calculated from the time evolution of the dihedral angles, agrees quite well with neutron scattering results and shows a broad feature reflecting a broad distribution of potentials barriers. Performing similar simulations, but under 'phantom-chain' conditions, we conclude that the width of this distribution is mainly controlled by the non-bonded interactions.

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

    NASA Astrophysics Data System (ADS)

    Shatnawi, Moneeb Taiseer

    A search for a structural response to a recently proposed self-organized and stress-free intermediate phase [1, 2] in semiconductor chalcogenide Ge xSe1-x glasses has been performed in this study. These glasses, according to the mean-field approach, undergo a structural phase transition from floppy to rigid network that occurs at a mean coordination number of 2.4. Based on thermodynamic and spectroscopic measurements, these glasses appear to exhibit two transitions instead of one [3]. The region between these transitions has been called the intermediate phase (IP) [3, 4]. The original theoretical work assumed that the network was generic and the connectivity random [5]. It was therefore suggested [1] that the IP phase is a region of finite width in composition where the network could self-organize in such a way that maintains a rigid but unstressed state. However, it has proved difficult to establish this result experimentally. High-resolution atomic pair distribution functions (PDF), derived from high energy synchrotron radiation, coupled with high-resolution X-ray absorption fine structure (XAFS) measurements on 18 compositions of well-prepared Ge xSe1-x glasses that span the range of the IP have been performed to elucidate aspects of rigidity percolation and the IP. These data sets are the most complete and the highest resolution data set on this system to date. Analysis of the structure functions (in reciprocal space) and the PDFs (in real space) as well as the XAFS data at both Ge and Se edges show no correlations with the IP. The network evolves smoothly without any break in slope or discontinuity that might be linked due to the IP. The results obtained in this study contradict previously published work [1, 2] that claim experimental evidence for a structural origin of the IP. The so-called first sharp diffraction peak (FSDP), which is a signature of the medium range order in these glasses, changes systematically with Ge content. It develops smoothly from a

  10. Measurement of the transverse momentum and $$\\phi ^*_{\\eta }$$ distributions of Drell–Yan lepton pairs in proton–proton collisions at $$\\sqrt{s}=8$$ TeV with the ATLAS detector

    DOE PAGES

    Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Aben, R.; Abolins, M.; AbouZeid, O. S.; Abramowicz, H.; Abreu, H.; Abreu, R.; et al

    2016-05-23

    Distributions of transverse momentum pTℓℓ and the related angular variablemore » $$\\phi ^*_{\\eta }$$ of Drell-Yan lepton pairs are measured in 20.3 fb–1 of proton-proton collisions at √s=8 TeV with the ATLAS detector at the LHC. Measurements in electron-pair and muon-pair final states are corrected for detector effects and combined. Compared to previous measurements in protonΓÇôproton collisions at √s=7 TeV these new measurements benefit from a larger data sample and improved control of systematic uncertainties. Measurements are performed in bins of lepton-pair mass above, around and below the Z -boson mass peak. The data are compared to predictions from perturbative and resummed QCD calculations. For values of $$\\phi ^*_{\\eta }$$<1 the predictions from the Monte Carlo generator ResBos are generally consistent with the data within the theoretical uncertainties. However, at larger values of $$\\phi ^*_{\\eta }$$ this is not the case. Monte Carlo generators based on the parton-shower approach are unable to describe the data over the full range of pTℓℓ while the fixed-order prediction of Dynnlo falls below the data at high values of pTℓℓ. Here, ResBos and the parton-shower Monte Carlo generators provide a much better description of the evolution of the $$\\phi ^*_{\\eta }$$ and pTℓℓ distributions as a function of lepton-pair mass and rapidity than the basic shape of the data.« less

  11. Measurement of the transverse momentum and φ ^*_{η } distributions of Drell-Yan lepton pairs in proton-proton collisions at √{s}=8 TeV with the ATLAS detector

    NASA Astrophysics Data System (ADS)

    Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Aben, R.; Abolins, M.; AbouZeid, O. S.; Abramowicz, H.; Abreu, H.; Abreu, R.; Abulaiti, Y.; Acharya, B. S.; Adamczyk, L.; Adams, D. L.; Adelman, J.; Adomeit, S.; Adye, T.; Affolder, A. A.; Agatonovic-Jovin, T.; Agricola, J.; Aguilar-Saavedra, J. A.; Ahlen, S. P.; Ahmadov, F.; Aielli, G.; Akerstedt, H.; Åkesson, T. P. A.; Akimov, A. V.; Alberghi, G. L.; Albert, J.; Albrand, S.; Alconada Verzini, M. J.; Aleksa, M.; Aleksandrov, I. N.; Alexa, C.; Alexander, G.; Alexopoulos, T.; Alhroob, M.; Alimonti, G.; Alio, L.; Alison, J.; Alkire, S. P.; Allbrooke, B. M. M.; Allport, P. P.; Aloisio, A.; Alonso, A.; Alonso, F.; Alpigiani, C.; Altheimer, A.; Alvarez Gonzalez, B.; Álvarez Piqueras, D.; Alviggi, M. G.; Amadio, B. T.; Amako, K.; Amaral Coutinho, Y.; Amelung, C.; Amidei, D.; Amor Dos Santos, S. P.; Amorim, A.; Amoroso, S.; Amram, N.; Amundsen, G.; Anastopoulos, C.; Ancu, L. S.; Andari, N.; Andeen, T.; Anders, C. F.; Anders, G.; Anders, J. K.; Anderson, K. J.; Andreazza, A.; Andrei, V.; Angelidakis, S.; Angelozzi, I.; Anger, P.; Angerami, A.; Anghinolfi, F.; Anisenkov, A. V.; Anjos, N.; Annovi, A.; Antonelli, M.; Antonov, A.; Antos, J.; Anulli, F.; Aoki, M.; Aperio Bella, L.; Arabidze, G.; Arai, Y.; Araque, J. P.; Arce, A. T. H.; Arduh, F. A.; Arguin, J.-F.; Argyropoulos, S.; Arik, M.; Armbruster, A. J.; Arnaez, O.; Arnold, H.; Arratia, M.; Arslan, O.; Artamonov, A.; Artoni, G.; Artz, S.; Asai, S.; Asbah, N.; Ashkenazi, A.; Åsman, B.; Asquith, L.; Assamagan, K.; Astalos, R.; Atkinson, M.; Atlay, N. B.; Augsten, K.; Aurousseau, M.; Avolio, G.; Axen, B.; Ayoub, M. K.; Azuelos, G.; Baak, M. A.; Baas, A. E.; Baca, M. J.; Bacci, C.; Bachacou, H.; Bachas, K.; Backes, M.; Backhaus, M.; Bagiacchi, P.; Bagnaia, P.; Bai, Y.; Bain, T.; Baines, J. T.; Baker, O. K.; Baldin, E. M.; Balek, P.; Balestri, T.; Balli, F.; Balunas, W. K.; Banas, E.; Banerjee, Sw.; Bannoura, A. A. E.; Barak, L.; Barberio, E. 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B.; Simak, V.; Simard, O.; Simic, Lj.; Simion, S.; Simioni, E.; Simmons, B.; Simon, D.; Simon, M.; Sinervo, P.; Sinev, N. B.; Sioli, M.; Siragusa, G.; Sisakyan, A. N.; Sivoklokov, S. Yu.; Sjölin, J.; Sjursen, T. B.; Skinner, M. B.; Skottowe, H. P.; Skubic, P.; Slater, M.; Slavicek, T.; Slawinska, M.; Sliwa, K.; Smakhtin, V.; Smart, B. H.; Smestad, L.; Smirnov, S. Yu.; Smirnov, Y.; Smirnova, L. N.; Smirnova, O.; Smith, M. N. K.; Smith, R. W.; Smizanska, M.; Smolek, K.; Snesarev, A. A.; Snidero, G.; Snyder, S.; Sobie, R.; Socher, F.; Soffer, A.; Soh, D. A.; Sokhrannyi, G.; Solans, C. A.; Solar, M.; Solc, J.; Soldatov, E. Yu.; Soldevila, U.; Solodkov, A. A.; Soloshenko, A.; Solovyanov, O. V.; Solovyev, V.; Sommer, P.; Song, H. Y.; Soni, N.; Sood, A.; Sopczak, A.; Sopko, B.; Sopko, V.; Sorin, V.; Sosa, D.; Sosebee, M.; Sotiropoulou, C. L.; Soualah, R.; Soukharev, A. M.; South, D.; Sowden, B. C.; Spagnolo, S.; Spalla, M.; Spangenberg, M.; Spanò, F.; Spearman, W. R.; Sperlich, D.; Spettel, F.; Spighi, R.; Spigo, G.; Spiller, L. A.; Spousta, M.; St. Denis, R. D.; Stabile, A.; Staerz, S.; Stahlman, J.; Stamen, R.; Stamm, S.; Stanecka, E.; Stanek, R. W.; Stanescu, C.; Stanescu-Bellu, M.; Stanitzki, M. M.; Stapnes, S.; Starchenko, E. A.; Stark, J.; Staroba, P.; Starovoitov, P.; Staszewski, R.; Steinberg, P.; Stelzer, B.; Stelzer, H. J.; Stelzer-Chilton, O.; Stenzel, H.; Stewart, G. A.; Stillings, J. A.; Stockton, M. C.; Stoebe, M.; Stoicea, G.; Stolte, P.; Stonjek, S.; Stradling, A. R.; Straessner, A.; Stramaglia, M. E.; Strandberg, J.; Strandberg, S.; Strandlie, A.; Strauss, E.; Strauss, M.; Strizenec, P.; Ströhmer, R.; Strom, D. M.; Stroynowski, R.; Strubig, A.; Stucci, S. A.; Stugu, B.; Styles, N. A.; Su, D.; Su, J.; Subramaniam, R.; Succurro, A.; Suchek, S.; Sugaya, Y.; Suk, M.; Sulin, V. V.; Sultansoy, S.; Sumida, T.; Sun, S.; Sun, X.; Sundermann, J. E.; Suruliz, K.; Susinno, G.; Sutton, M. R.; Suzuki, S.; Svatos, M.; Swiatlowski, M.; Sykora, I.; Sykora, T.; Ta, D.; Taccini, C.; Tackmann, K.; Taenzer, J.; Taffard, A.; Tafirout, R.; Taiblum, N.; Takai, H.; Takashima, R.; Takeda, H.; Takeshita, T.; Takubo, Y.; Talby, M.; Talyshev, A. A.; Tam, J. Y. C.; Tan, K. G.; Tanaka, J.; Tanaka, R.; Tanaka, S.; Tannenwald, B. B.; Tapia Araya, S.; Tapprogge, S.; Tarem, S.; Tarrade, F.; Tartarelli, G. F.; Tas, P.; Tasevsky, M.; Tashiro, T.; Tassi, E.; Tavares Delgado, A.; Tayalati, Y.; Taylor, A. C.; Taylor, F. E.; Taylor, G. N.; Taylor, P. T. E.; Taylor, W.; Teischinger, F. A.; Teixeira-Dias, P.; Temming, K. K.; Temple, D.; Ten Kate, H.; Teng, P. K.; Teoh, J. J.; Tepel, F.; Terada, S.; Terashi, K.; Terron, J.; Terzo, S.; Testa, M.; Teuscher, R. J.; Theveneaux-Pelzer, T.; Thomas, J. P.; Thomas-Wilsker, J.; Thompson, E. N.; Thompson, P. D.; Thompson, R. J.; Thompson, A. S.; Thomsen, L. A.; Thomson, E.; Thomson, M.; Thun, R. P.; Tibbetts, M. J.; Ticse Torres, R. E.; Tikhomirov, V. O.; Tikhonov, Yu. A.; Timoshenko, S.; Tiouchichine, E.; Tipton, P.; Tisserant, S.; Todome, K.; Todorov, T.; Todorova-Nova, S.; Tojo, J.; Tokár, S.; Tokushuku, K.; Tollefson, K.; Tolley, E.; Tomlinson, L.; Tomoto, M.; Tompkins, L.; Toms, K.; Torrence, E.; Torres, H.; Torró Pastor, E.; Toth, J.; Touchard, F.; Tovey, D. R.; Trefzger, T.; Tremblet, L.; Tricoli, A.; Trigger, I. M.; Trincaz-Duvoid, S.; Tripiana, M. F.; Trischuk, W.; Trocmé, B.; Troncon, C.; Trottier-McDonald, M.; Trovatelli, M.; Truong, L.; Trzebinski, M.; Trzupek, A.; Tsarouchas, C.; Tseng, J. C.-L.; Tsiareshka, P. V.; Tsionou, D.; Tsipolitis, G.; Tsirintanis, N.; Tsiskaridze, S.; Tsiskaridze, V.; Tskhadadze, E. G.; Tsui, K. M.; Tsukerman, I. I.; Tsulaia, V.; Tsuno, S.; Tsybychev, D.; Tudorache, A.; Tudorache, V.; Tuna, A. N.; Tupputi, S. A.; Turchikhin, S.; Turecek, D.; Turra, R.; Turvey, A. J.; Tuts, P. M.; Tykhonov, A.; Tylmad, M.; Tyndel, M.; Ueda, I.; Ueno, R.; Ughetto, M.; Ukegawa, F.; Unal, G.; Undrus, A.; Unel, G.; Ungaro, F. C.; Unno, Y.; Unverdorben, C.; Urban, J.; Urquijo, P.; Urrejola, P.; Usai, G.; Usanova, A.; Vacavant, L.; Vacek, V.; Vachon, B.; Valderanis, C.; Valencic, N.; Valentinetti, S.; Valero, A.; Valery, L.; Valkar, S.; Vallecorsa, S.; Valls Ferrer, J. A.; Van Den Wollenberg, W.; Van Der Deijl, P. C.; van der Geer, R.; van der Graaf, H.; van Eldik, N.; van Gemmeren, P.; Van Nieuwkoop, J.; van Vulpen, I.; van Woerden, M. C.; Vanadia, M.; Vandelli, W.; Vanguri, R.; Vaniachine, A.; Vannucci, F.; Vardanyan, G.; Vari, R.; Varnes, E. W.; Varol, T.; Varouchas, D.; Vartapetian, A.; Varvell, K. E.; Vazeille, F.; Vazquez Schroeder, T.; Veatch, J.; Veloce, L. M.; Veloso, F.; Velz, T.; Veneziano, S.; Ventura, A.; Ventura, D.; Venturi, M.; Venturi, N.; Venturini, A.; Vercesi, V.; Verducci, M.; Verkerke, W.; Vermeulen, J. C.; Vest, A.; Vetterli, M. C.; Viazlo, O.; Vichou, I.; Vickey, T.; Vickey Boeriu, O. E.; Viehhauser, G. H. A.; Viel, S.; Vigne, R.; Villa, M.; Villaplana Perez, M.; Vilucchi, E.; Vincter, M. G.; Vinogradov, V. B.; Vivarelli, I.; Vlachos, S.; Vladoiu, D.; Vlasak, M.; Vogel, M.; Vokac, P.; Volpi, G.; Volpi, M.; von der Schmitt, H.; von Radziewski, H.; von Toerne, E.; Vorobel, V.; Vorobev, K.; Vos, M.; Voss, R.; Vossebeld, J. H.; Vranjes, N.; Vranjes Milosavljevic, M.; Vrba, V.; Vreeswijk, M.; Vuillermet, R.; Vukotic, I.; Vykydal, Z.; Wagner, P.; Wagner, W.; Wahlberg, H.; Wahrmund, S.; Wakabayashi, J.; Walder, J.; Walker, R.; Walkowiak, W.; Wang, C.; Wang, F.; Wang, H.; Wang, H.; Wang, J.; Wang, J.; Wang, K.; Wang, R.; Wang, S. M.; Wang, T.; Wang, T.; Wang, X.; Wanotayaroj, C.; Warburton, A.; Ward, C. P.; Wardrope, D. R.; Washbrook, A.; Wasicki, C.; Watkins, P. M.; Watson, A. T.; Watson, I. J.; Watson, M. F.; Watts, G.; Watts, S.; Waugh, B. M.; Webb, S.; Weber, M. S.; Weber, S. W.; Webster, J. S.; Weidberg, A. R.; Weinert, B.; Weingarten, J.; Weiser, C.; Weits, H.; Wells, P. S.; Wenaus, T.; Wengler, T.; Wenig, S.; Wermes, N.; Werner, M.; Werner, P.; Wessels, M.; Wetter, J.; Whalen, K.; Wharton, A. M.; White, A.; White, M. J.; White, R.; White, S.; Whiteson, D.; Wickens, F. J.; Wiedenmann, W.; Wielers, M.; Wienemann, P.; Wiglesworth, C.; Wiik-Fuchs, L. A. M.; Wildauer, A.; Wilkens, H. G.; Williams, H. H.; Williams, S.; Willis, C.; Willocq, S.; Wilson, A.; Wilson, J. A.; Wingerter-Seez, I.; Winklmeier, F.; Winter, B. T.; Wittgen, M.; Wittkowski, J.; Wollstadt, S. J.; Wolter, M. W.; Wolters, H.; Wosiek, B. K.; Wotschack, J.; Woudstra, M. J.; Wozniak, K. W.; Wu, M.; Wu, M.; Wu, S. L.; Wu, X.; Wu, Y.; Wyatt, T. R.; Wynne, B. M.; Xella, S.; Xu, D.; Xu, L.; Yabsley, B.; Yacoob, S.; Yakabe, R.; Yamada, M.; Yamaguchi, D.; Yamaguchi, Y.; Yamamoto, A.; Yamamoto, S.; Yamanaka, T.; Yamauchi, K.; Yamazaki, Y.; Yan, Z.; Yang, H.; Yang, H.; Yang, Y.; Yao, W.-M.; Yap, Y. C.; Yasu, Y.; Yatsenko, E.; Yau Wong, K. H.; Ye, J.; Ye, S.; Yeletskikh, I.; Yen, A. L.; Yildirim, E.; Yorita, K.; Yoshida, R.; Yoshihara, K.; Young, C.; Young, C. J. S.; Youssef, S.; Yu, D. R.; Yu, J.; Yu, J. M.; Yu, J.; Yuan, L.; Yuen, S. P. Y.; Yurkewicz, A.; Yusuff, I.; Zabinski, B.; Zaidan, R.; Zaitsev, A. M.; Zalieckas, J.; Zaman, A.; Zambito, S.; Zanello, L.; Zanzi, D.; Zeitnitz, C.; Zeman, M.; Zemla, A.; Zeng, J. C.; Zeng, Q.; Zengel, K.; Zenin, O.; Ženiš, T.; Zerwas, D.; Zhang, D.; Zhang, F.; Zhang, G.; Zhang, H.; Zhang, J.; Zhang, L.; Zhang, R.; Zhang, X.; Zhang, Z.; Zhao, X.; Zhao, Y.; Zhao, Z.; Zhemchugov, A.; Zhong, J.; Zhou, B.; Zhou, C.; Zhou, L.; Zhou, L.; Zhou, M.; Zhou, N.; Zhu, C. G.; Zhu, H.; Zhu, J.; Zhu, Y.; Zhuang, X.; Zhukov, K.; Zibell, A.; Zieminska, D.; Zimine, N. I.; Zimmermann, C.; Zimmermann, S.; Zinonos, Z.; Zinser, M.; Ziolkowski, M.; Živković, L.; Zobernig, G.; Zoccoli, A.; zur Nedden, M.; Zurzolo, G.; Zwalinski, L.

    2016-05-01

    Distributions of transverse momentum p_T^{ℓ ℓ } and the related angular variable φ ^*_η of DrellΓÇôYan lepton pairs are measured in 20.3┬áfb^{-1} of protonΓÇôproton collisions at √{s}=8┬áTeV with the ATLAS detector at the LHC. Measurements in electron-pair and muon-pair final states are corrected for detector effects and combined. Compared to previous measurements in protonΓÇôproton collisions at √{s}=7┬áTeV, these new measurements benefit from a larger data sample and improved control of systematic uncertainties. Measurements are performed in bins of lepton-pair mass above, around and below the Z-boson mass peak. The data are compared to predictions from perturbative and resummed QCD calculations. For values of φ ^*_η < 1 the predictions from the Monte Carlo generator ResBos are generally consistent with the data within the theoretical uncertainties. However, at larger values of φ ^*_η this is not the case. Monte Carlo generators based on the parton-shower approach are unable to describe the data over the full range of p_T^{ℓ ℓ } while the fixed-order prediction of Dynnlo falls below the data at high values of p_T^{ℓ ℓ }. ResBos and the parton-shower Monte Carlo generators provide a much better description of the evolution of the φ ^*_η and p_T^{ℓ ℓ } distributions as a function of lepton-pair mass and rapidity than the basic shape of the data.

  12. 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

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

    SciTech Connect

    Miller, M.K.

    2001-01-30

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

  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 (μSR) 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 μSR 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 (μ 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 μ SR result suggested that the higher Tg near the Si substrate is due to the strong orientation of phenyl rings.

  16. 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 (μSR) 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 μSR result suggested that the higher Tg near the Si substrate is due to the strong orientation of phenyl rings.

  17. 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

  18. 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.

  19. 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.

  20. 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)

  1. Characterisation of Cr, Si and P distribution at dislocations and grain-boundaries in neutron irradiated Fe-Cr model alloys of low purity

    NASA Astrophysics Data System (ADS)

    Kuksenko, V.; Pareige, C.; Genevois, C.; Pareige, P.

    2013-03-01

    Segregations at some dislocations and grain boundaries in Fe-5%Cr, Fe-9%Cr and Fe-12%Cr model alloys of low purity after neutron irradiation at 300 °C up to 0.6 dpa have been analyzed with atom probe tomography. All dislocation lines and low- and high-angle grain boundaries (GBs) which have been observed were enriched with Cr, Si and P. The segregations reveal the different dislocation structures associated to different type of analysed GBs. Cr and Si atoms were found to be nonhomogenously distributed around the dislocation cores because of the non isotropic stress field induced by edge dislocation lines. Concerning GBs, precipitate free zones (PFZs) are exhibited around the planar defects which were analysed in Fe-9%Cr and Fe-12%Cr model alloys. These PFZ are size dependant with the nominal level of Cr.

  2. Comparison of NSTX FIDA, Charge Exchange, and Neutron Fluxes with Calculated Signals Based on CQL3D-FOW Distribution Functions

    NASA Astrophysics Data System (ADS)

    Harvey, R. W.; Petrov, Yu. V.; Kinsey, J. E.; Liu, D.; Heidbrink, W. W.; Taylor, G.; Bonoli, P. T.

    2014-10-01

    Ion distribution function calculations with CQL3D have been substantially advanced through implementation of guiding-center-orbit-based Fokker-Planck Coefficients. The resulting finite-orbit-width (FOW) calculations are carried out with a fast CQL3D-Hybrid-FOW option, and in a slower but neoclassically complete (except no Er yet) CQL3D-FOW option. Good comparison between time-dependent Fast Ion Diagnostic FIDA, NPA, and neutron signals resulting from neutral beaminjection(NBI) and high harmonic fast wave (HHFW) power injected into the NSTX spherical tokamak have been simulated with the CQL3D-Hybrid-FOW, using only the FOW effects on QL diffusion, and particle losses, direct and CX. Comparisons are also made with recent CQL3D-FOW results, as well as between the original FIDA calculation code and a recent fortran version. Supported by USDOE Grants SC0006614, ER54744, and ER44649.

  3. A structural investigation of the alkali metal site distribution within bioactive glass using neutron diffraction and multinuclear solid state NMR.

    PubMed

    Martin, Richard A; Twyman, Helen L; Rees, Gregory J; Smith, Jodie M; Barney, Emma R; Smith, Mark E; Hanna, John V; Newport, Robert J

    2012-09-21

    The atomic-scale structure of Bioglass and the effect of substituting lithium for sodium within these glasses have been investigated using neutron diffraction and solid state magic angle spinning (MAS) NMR. Applying an effective isomorphic substitution difference function to the neutron diffraction data has enabled the Na-O and Li-O nearest-neighbour correlations to be isolated from the overlapping Ca-O, O-(P)-O and O-(Si)-O correlations. These results reveal that Na and Li behave in a similar manner within the glassy matrix and do not disrupt the short range order of the network former. Residual differences are attributed solely to the variation in ionic radius between the two species. Successful simplification of the 2 < r (Å) < 3 region via the difference method has enabled all the nearest neighbour correlations to be deconvolved. The diffraction data provides the first direct experimental evidence of split Na-O nearest-neighbour correlations in these melt quench bioactive glasses, and an analogous splitting of the Li-O correlations. The observed correlations are attributed to the metal ions bonded either to bridging or to non-bridging oxygen atoms. (23)Na triple quantum MAS (3QMAS) NMR data corroborates the split Na-O correlations. The structural sites present will be intimately related to the release properties of the glass system in physiological fluids such as plasma and saliva, and hence to the bioactivity of the material. Detailed structural knowledge is therefore a prerequisite for optimizing material design. PMID:22868255

  4. Conservation of Isospin in Neutron-rich Fission Fragments

    SciTech Connect

    Jain, A.K.; Choudhury, D.; Maheshwari, B.

    2014-06-15

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

  5. Conservation of Isospin in Neutron-rich Fission Fragments

    NASA Astrophysics Data System (ADS)

    Jain, A. K.; Choudhury, D.; Maheshwari, B.

    2014-06-01

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

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

    SciTech Connect

    Cremer, Jr, Jay Theodore

    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.

  7. Deuteron distribution in nuclear matter

    NASA Astrophysics Data System (ADS)

    Benhar, O.; Fabrocini, A.; Fantoni, S.; Illarionov, A. Yu.; Lykasov, G. I.

    2002-05-01

    We analyze the properties of deuteron-like structures in infinite, correlated nuclear matter, described by a realistic hamiltonian containing the Urbana v14 two-nucleon and the Urbana TNI many-body potentials. The distribution of neutron-proton pairs, carrying the deuteron quantum numbers, is obtained as a function of the total momentum by computing the overlap between the nuclear matter in its ground state and the deuteron wave functions in correlated basis functions theory. We study the differences between the S- and D-wave components of the deuteron and those of the deuteron-like pair in the nuclear medium. The total number of deuteron type pairs is computed and compared with the predictions of Levinger's quasideuteron model. The resulting Levinger's factor in nuclear matter at equilibrium density is 11.63. We use the local density approximation to estimate the Levinger's factor for heavy nuclei, obtaining results which are consistent with the available experimental data from photoreactions.

  8. 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.

  9. The distribution of genome shared identical by descent for a pair of full sibs by means of the continuous time Markov chain

    NASA Astrophysics Data System (ADS)

    Julie, Hongki; Pasaribu, Udjianna S.; Pancoro, Adi

    2015-12-01

    This paper will allow Markov Chain's application in genome shared identical by descent by two individual at full sibs model. The full sibs model was a continuous time Markov Chain with three state. In the full sibs model, we look for the cumulative distribution function of the number of sub segment which have 2 IBD haplotypes from a segment of the chromosome which the length is t Morgan and the cumulative distribution function of the number of sub segment which have at least 1 IBD haplotypes from a segment of the chromosome which the length is t Morgan. This cumulative distribution function will be developed by the moment generating function.

  10. Di-Neutron Clustering and Deuteron-like Tensor Correlation in Nuclear Structure Focusing on 11Li

    NASA Astrophysics Data System (ADS)

    Ikeda, Kiyomi; Myo, Takayuki; Kato, Kiyoshi; Toki, Hiroshi

    11Li is a Borromean nucleus, where two out of three objects as 9Li + n and two neutrons independently do not form bound systems. Two neutrons should form a di-neutron cluster in the nuclear field generated by the 9Li core nucleus. We treat di-neutron clustering by solving the two neutron relative wave function precisely by using the bare nucleon-nucleon interaction so that the spatial clustering structure is obtained quantitatively within the whole 11Li nucleus. This di-neutron clustering is an essential dynamics to form the halo structure by making a compact di-neutron cluster, which distributes loosely around the 9Li core. This concept of di-neutron clustering should be clearly distinguished from the BCS pairing correlation, where no consideration of spatial clustering is made. The di-neutron clustering is a new concept and is a general phenomenon in neutron skin and neutron halo nuclei. This quantitative description of di-neutron clustering has made it necessary to consider another important deuteron-like tensor correlation, which is caused by strong tensor interaction in the nucleon-nucleon interaction. The tensor interaction originates from pion exchange and known to provide large attraction to form the 4He nucleus. The unique feature of the tensor correlation is to make highly correlated deuteron-like excitation, which interferes with shell model like structure in a unique way. This dynamical effect removes the magic number effect and makes easy the participation of the s-wave neutrons. Hence, there are pairing and deuteron-like tensor correlations in addition to the mean field structure in 9Li. The combined system of two additional neutrons with the correlated 9Li provides the halo phenomenon, in which the di-neutron clustering develops with the help of large s-wave component caused by the deuteron-like tensor correlation. These two effects, the di-neutron clustering and the deuteron-like tensor correlation, are quite new and essential to provide the halo

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

    SciTech Connect

    Myers, S. M.; Cooper, P. J.; Wampler, W. R.

    2008-08-15

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

  12. Powered Tate Pairing Computation

    NASA Astrophysics Data System (ADS)

    Kang, Bo Gyeong; Park, Je Hong

    In this letter, we provide a simple proof of bilinearity for the eta pairing. Based on it, we show an efficient method to compute the powered Tate pairing as well. Although efficiency of our method is equivalent to that of the Tate pairing on the eta pairing approach, but ours is more general in principle.

  13. Double binding energy differences: Mean-field or pairing effect?

    NASA Astrophysics Data System (ADS)

    Qi, Chong

    2012-10-01

    In this Letter we present a systematic analysis on the average interaction between the last protons and neutrons in atomic nuclei, which can be extracted from the double differences of nuclear binding energies. The empirical average proton-neutron interaction Vpn thus derived from experimental data can be described in a very simple form as the interplay of the nuclear mean field and the pairing interaction. It is found that the smooth behavior as well as the local fluctuations of the Vpn in even-even nuclei with N ≠ Z are dominated by the contribution from the proton-neutron monopole interactions. A strong additional contribution from the isoscalar monopole interaction and isovector proton-neutron pairing interaction is seen in the Vpn for even-even N = Z nuclei and for the adjacent odd-A nuclei with one neutron or proton being subtracted.

  14. Procedure of calculation of the spatial distribution of temperatures and heat fluxes in the steam generator of a nuclear power installation with an RBEC fast-neutron reactor

    NASA Astrophysics Data System (ADS)

    Frolov, A. A.; Sedov, A. A.

    2016-08-01

    A method for combined 3D/1D-modeling of thermohydraulics of a once-through steam generator (SG) based on the joint analysis of three-dimensional thermo- and hydrodynamics of a single-phase heating coolant in the intertube space and one-dimensional thermohydraulics of steam-generating channels (tubes) with the use of well-known friction and heat-transfer correlations under various boiling conditions is discussed. This method allows one to determine the spatial distribution of temperatures and heat fluxes of heat-exchange surfaces of SGs with a single-phase heating coolant in the intertube space and with steam generation within tubes. The method was applied in the analytical investigation of typical operation of a once-through SG of a nuclear power installation with an RBEC fast-neutron heavy-metal reactor that is being designed by Kurchatov Institute in collaboration with OKB GIDROPRESS and Leipunsky Institute of Physics and Power Engineering. Flow pattern and temperature fields were obtained for the heavy-metal heating coolant in the intertube space. Nonuniformities of heating of the steam-water coolant in different heat-exchange tubes and nonuniformities in the distribution of heat fluxes at SG heat-exchange surfaces were revealed.

  15. Dose distributions in a human head phantom for neutron capture therapy using moderated neutrons from the 2.5 MeV proton-7Li reaction or from fission of 235U

    NASA Astrophysics Data System (ADS)

    Tanaka, Kenichi; Kobayashi, Tooru; Sakurai, Yoshinori; Nakagawa, Yoshinobu; Endo, Satoru; Hoshi, Masaharu

    2001-10-01

    The feasibility of neutron capture therapy (NCT) using an accelerator-based neutron source of the 7Li(p,n) reaction produced by 2.5 MeV protons was investigated by comparing the neutron beam tailored by both the Hiroshima University radiological research accelerator (HIRRAC) and the heavy water neutron irradiation facility in the Kyoto University reactor (KUR-HWNIF) from the viewpoint of the contamination dose ratios of the fast neutrons and the gamma rays. These contamination ratios to the boron dose were estimated in a water phantom of 20 cm diameter and 20 cm length to simulate a human head, with experiments by the same techniques for NCT in KUR-HWNIF and/or the simulation calculations by the Monte Carlo N-particle transport code system version 4B (MCNP-4B). It was found that the 7Li(p,n) neutrons produced by 2.5 MeV protons combined with 20, 25 or 30 cm thick D2O moderators of 20 cm diameter could make irradiation fields for NCT with depth-dose characteristics similar to those from the epithermal neutron beam at the KUR-HWNIF.

  16. Neutron guide

    DOEpatents

    Greene, Geoffrey L.

    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.

  17. Neutron dosimetry

    DOEpatents

    Quinby, Thomas C.

    1976-07-27

    A method of measuring neutron radiation within a nuclear reactor is provided. A sintered oxide wire is disposed within the reactor and exposed to neutron radiation. The induced radioactivity is measured to provide an indication of the neutron energy and flux within the reactor.

  18. 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.

  19. 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 λ, 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 λ 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.

  20. 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 dϕ/dz = 1 × 10(-7) rad/m. PMID:26026552

  1. 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 dϕ/dz = 1 × 10{sup −7} rad/m.

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

    NASA Astrophysics Data System (ADS)

    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 dϕ/dz = 1 × 10-7 rad/m.

  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. Argonne potential and multi-neutron systems

    SciTech Connect

    Gridnev, D. K.; Gridnev, K. A.; Schramm, S.; Greiner, Walter

    2009-01-01

    Recently it was proved that the neutron matter interacting through Argonne V18 pair-potential plus modern variants of Urbana or Illinois three-body forces is unstable. For the energy of N neutrons E(N), which interact through these forces one has E(N) = −cN³⁺+O(N{sup 8/3}), where c > 0 is a constant. This means that: (i) the energy per particle and neutron density diverge rapidly for large neutron numbers; (ii) bound states of N neutrons exist for N large enough. The neutron matter collapse is possible due to the form of the repulsive core in three-body forces, which vanishes when three nucleons occupy the same site in space. The obtained results partly change the paradigm, in which the stability of neutron stars is attained through the Pauli principle; the strong repulsive core in the nucleon interactions is by no means less important.

  5. Neutron multiplicities in spontaneous fission and nuclear structure studies

    SciTech Connect

    Hamilton, J.H.; Kormicki, J.; Lu, Q.

    1993-12-31

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

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

    PubMed

    Sakurai, Y; Kobayashi, T; Kanda, K

    1994-12-01

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

  7. 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.

  8. 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.

  9. Neutron detector

    DOEpatents

    Stephan, Andrew C.; Jardret; Vincent D.

    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.

  10. Neutron detector

    SciTech Connect

    Stephan, Andrew C; Jardret, Vincent D

    2009-04-07

    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.

  11. Photoproduction of η π pairs off nucleons and deuterons

    NASA Astrophysics Data System (ADS)

    Käser, A.; Müller, F.; Ahrens, J.; Annand, J. R. M.; Arends, H. J.; Bantawa, K.; Bartolome, P. A.; Beck, R.; Braghieri, A.; Briscoe, W. J.; Cherepnya, S.; Costanza, S.; Dieterle, M.; Downie, E. J.; Drexler, P.; Fil'kov, L. V.; Fix, A.; Garni, S.; Glazier, D. I.; Hamilton, D.; Hornidge, D.; Howdle, D.; Huber, G. M.; Jaegle, I.; Jude, T. C.; 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.; Oberle, M.; 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.; Starostin, A.; Strub, Th.; Supek, I.; Thiel, M.; Thomas, A.; Unverzagt, M.; Walford, N. K.; Watts, D. P.; Werthmüller, D.; Witthauer, L.

    2016-09-01

    Quasi-free photoproduction of πη-pairs has been investigated from threshold up to incident photon energies of 1.4 GeV, respectively up to photon-nucleon invariant masses up to 1.9 GeV. Total cross sections, angular distributions, invariant-mass distributions of the πη and meson-nucleon pairs, and beam-helicity asymmetries have been measured for the reactions γ p→ pπ0η, γ n→ nπ0η , γ p→ nπ+η , and γ n→ pπ-η from nucleons bound inside the deuteron. For the γ p initial-state data for free protons have also been analyzed. Finally, the total cross sections for quasi-free production of π0η pairs from nucleons bound in 3 He nuclei have been investigated in view of final state interaction (FSI) effects. The experiments were performed at the tagged photon beam facility of the Mainz MAMI accelerator using an almost 4 π covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The shapes of all differential cross section data and the asymmetries are very similar for protons and neutrons and agree with the conjecture that the reactions are dominated by the sequential Δ^{star}3/2-→ ηΔ(1232) →πη N decay chain, mainly with Δ(1700)3/2- and Δ(1940)3/2- . The ratios of the magnitude of the total cross sections also agree with this assumption. However, the absolute magnitudes of the cross sections are reduced by FSI effects with respect to free proton data.

  12. Electron-pair excitations and the molecular Coulomb continuum

    SciTech Connect

    Colgan, James

    2009-01-01

    Electron-pair excitations in the molecular hydrogen continuum are described by quantizing rotations of the momentum plane of the electron pair about by the pair's relative momentum. A helium-like description of the molecular pi.Joto double ionization is thus extended to higher angular momenta of the electron pair. A simple three-state superposition is found to account surprisingly well for recent observations of noncoplanar electron-pair, molecular-axis angular distributions.

  13. 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.

  14. 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.

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

    SciTech Connect

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

    2009-01-26

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

  16. Hard Photodisintegration of a Proton Pair

    DOE PAGES

    Pomerantz, Ishay; Bubis, Nathaniel; Allada, Kalyan; Beck, Arie; Beck, Sara; Berman, Barry L.; Boeglin, Werner U.; Camsonne, Alexandre; Canan, Mustafa; Chirapatpimol, Khem; et al

    2010-01-08

    We present the first study of high energy photodisintegration of proton-pairs through the gamma + 3He -> p+p+n channel. Photon energies from 0.8 to 4.7 GeV were used in kinematics corresponding to a proton pair with high relative momentum and a neutron nearly at rest. An s^{-11} scaling of the cross section was observed, as predicted by the constituent counting rule. The onset of the scaling is at a higher energy and the cross section is significantly lower then for pn pair photodisintegration. For photon energies below the scaling region, the scaled cross section was found to present a strongmore » energy-dependent structure not observed in deuteron photodisintegration.« less

  17. 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.

  18. Experimental extraction of an entangled photon pair from two identically decohered pairs.

    PubMed

    Yamamoto, Takashi; Koashi, Masato; Ozdemir, Sahin Kaya; Imoto, Nobuyuki

    2003-01-23

    Entanglement is considered to be one of the most important resources in quantum information processing schemes, including teleportation, dense coding and entanglement-based quantum key distribution. Because entanglement cannot be generated by classical communication between distant parties, distribution of entangled particles between them is necessary. During the distribution process, entanglement between the particles is degraded by the decoherence and dissipation processes that result from unavoidable coupling with the environment. Entanglement distillation and concentration schemes are therefore needed to extract pairs with a higher degree of entanglement from these less-entangled pairs; this is accomplished using local operations and classical communication. Here we report an experimental demonstration of extraction of a polarization-entangled photon pair from two decohered photon pairs. Two polarization-entangled photon pairs are generated by spontaneous parametric down-conversion and then distributed through a channel that induces identical phase fluctuations to both pairs; this ensures that no entanglement is available as long as each pair is manipulated individually. Then, through collective local operations and classical communication we extract from the two decohered pairs a photon pair that is observed to be polarization-entangled.

  19. 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.

  20. Improvement effect on the depth-dose distribution by CSF drainage and air infusion of a tumour-removed cavity in boron neutron capture therapy for malignant brain tumours.

    PubMed

    Sakurai, Yoshinori; Ono, Koji; Miyatake, Shin-Ichi; Maruhashi, Akira

    2006-03-01

    Boron neutron capture therapy (BNCT) without craniotomy for malignant brain tumours was started using an epi-thermal neutron beam at the Kyoto University Reactor in June 2002. We have tried some techniques to overcome the treatable-depth limit in BNCT. One of the effective techniques is void formation utilizing a tumour-removed cavity. The tumorous part is removed by craniotomy about 1 week before a BNCT treatment in our protocol. Just before the BNCT irradiation, the cerebro-spinal fluid (CSF) in the tumour-removed cavity is drained out, air is infused to the cavity and then the void is made. This void improves the neutron penetration, and the thermal neutron flux at depth increases. The phantom experiments and survey simulations modelling the CSF drainage and air infusion of the tumour-removed cavity were performed for the size and shape of the void. The advantage of the CSF drainage and air infusion is confirmed for the improvement in the depth-dose distribution. From the parametric surveys, it was confirmed that the cavity volume had good correlation with the improvement effect, and the larger effect was expected as the cavity volume was larger.

  1. 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.

  2. 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.

  3. Neutronic reactor

    DOEpatents

    Wende, Charles W. J.

    1976-08-17

    A safety rod for a nuclear reactor has an inner end portion having a gamma absorption coefficient and neutron capture cross section approximately equal to those of the adjacent shield, a central portion containing materials of high neutron capture cross section and an outer end portion having a gamma absorption coefficient at least equal to that of the adjacent shield.

  4. NEUTRONIC REACTOR

    DOEpatents

    Fermi, E.; Zinn, W.H.; Anderson, H.L.

    1958-09-16

    Means are presenied for increasing the reproduction ratio of a gaphite- moderated neutronic reactor by diminishing the neutron loss due to absorption or capture by gaseous impurities within the reactor. This means comprised of a fluid-tight casing or envelope completely enclosing the reactor and provided with a valve through which the casing, and thereby the reactor, may be evacuated of atmospheric air.

  5. Vortex pairs on surfaces

    SciTech Connect

    Koiller, Jair

    2009-05-06

    A pair of infinitesimally close opposite vortices moving on a curved surface moves along a geodesic, according to a conjecture by Kimura. We outline a proof. Numerical simulations are presented for a pair of opposite vortices at a close but nonzero distance on a surface of revolution, the catenoid. We conjecture that the vortex pair system on a triaxial ellipsoid is a KAM perturbation of Jacobi's geodesic problem. We outline some preliminary calculations required for this study. Finding the surfaces for which the vortex pair system is integrable is in order.

  6. Pairing Beyond BCS

    NASA Astrophysics Data System (ADS)

    Volya, Alexander; Zelevinsky, Vladimir

    2013-01-01

    We concentrate on the specifics of the nuclear pairing problem from the standpoint of the BCS approach. We consider the properties of nuclear pairing which usually are not discussed in standard texts: how good is the BCS theory in nuclear context compared to the exact large-scale diagonalization, whether it can be improved by the particle number conservation, how to mark the phase transition regions in a mesoscopic system like a nucleus, how may effective many-body forces influence the formation and structure of the pairing condensate, what effect the decay instability has on the paired nuclear structure, etc.

  7. Neutron tubes

    DOEpatents

    Leung, Ka-Ngo; Lou, Tak Pui; Reijonen, Jani

    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.

  8. Neutron source

    DOEpatents

    Cason, J.L. Jr.; Shaw, C.B.

    1975-10-21

    A neutron source which is particularly useful for neutron radiography consists of a vessel containing a moderating media of relatively low moderating ratio, a flux trap including a moderating media of relatively high moderating ratio at the center of the vessel, a shell of depleted uranium dioxide surrounding the moderating media of relatively high moderating ratio, a plurality of guide tubes each containing a movable source of neutrons surrounding the flux trap, a neutron shield surrounding one part of each guide tube, and at least one collimator extending from the flux trap to the exterior of the neutron source. The shell of depleted uranium dioxide has a window provided with depleted uranium dioxide shutters for each collimator. Reflectors are provided above and below the flux trap and on the guide tubes away from the flux trap.

  9. Fast Neutron Sensitivity with HPGe

    SciTech Connect

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

    2008-01-22

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

  10. Evolution of local structures in polycrystalline Zn1−xMgxO (0<=x<=0.15) studied by Raman spectroscopy and synchrotron x-ray pair-distribution-function analysis

    SciTech Connect

    Kim, Young-Il; Page, Katharine; Limarga, Andi M.; Clarke, David R.; Seshadri, Ram

    2008-09-18

    The local structures of Zn{sub 1-x}Mg{sub x}O alloys have been studied by Raman spectroscopy and by synchrotron x-ray pair-distribution-function (PDF) analysis. Within the solid solution range (0 {le} x {le} 0.15) of Zn{sub 1-x}Mg{sub x}O, the wurtzite framework is maintained with Mg homogeneously distributed throughout the wurtzite lattice. The E{sub 2}{sup high} Raman line of Zn{sub 1-x}Mg{sub x}O displays systematic changes in response to the evolution of the crystal lattice upon the Mg substitution. The redshift and broadening of the E{sub 2}{sup high} mode are explained by the expansion of hexagonal ab dimensions and compositional disorder of Zn/Mg, respectively. Synchrotron x-ray PDF analyses of Zn{sub 1-x}Mg{sub x}O reveal that the Mg atoms have a slightly reduced wurtzite parameter u and more regular tetrahedral bond distances than the Zn atoms. For both Zn and Mg, the internal tetrahedral geometries are independent of the alloy composition.

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

    DOE PAGES

    Abazov, Victor Mukhamedovich

    2015-04-06

    We present a measurement of the distribution of the variable φ*η 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 φ*η probes the same physical effects as the Z/γ* 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 φ*η distributions for dilepton masses away from the Z → ℓ+ℓ– boson mass peak. As a result, the data are compared to QCD predictions based on the resummation of multiple soft gluons.« less

  12. Measurement of the φ*η 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 φ*η 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 φ*η probes the same physical effects as the Z/γ* 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 φ*η distributions for dilepton masses away from the Z → ℓ+ boson mass peak. As a result, the data are compared to QCD predictions based on the resummation of multiple soft gluons.

  13. 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.

  14. Neutron Transport Characteristics of a Nuclear Reactor Based Dynamic Neutron Imaging System

    SciTech Connect

    Khaial, Anas M.; Harvel, Glenn D.; Chang, Jen-Shih

    2006-07-01

    An advanced dynamic neutron imaging system has been constructed in the McMaster Nuclear Reactor (MNR) for nondestructive testing and multi-phase flow studies in energy and environmental applications. A high quality neutron beam is required with a thermal neutron flux greater than 5.0 x 10{sup 6} n/cm{sup 2}-s and a collimation ratio of 120 at image plane to promote high-speed neutron imaging up to 2000 frames per second. Neutron source strength and neutron transport have been experimentally and numerically investigated. Neutron source strength at the beam tube entrance was evaluated experimentally by measuring the thermal and fast neutron fluxes, and simple analytical neutron transport calculations were performed based upon these measured neutron fluxes to predict facility components in accordance with high-speed dynamic neutron imaging and operation safety requirements. Monte-Carlo simulations (using MCNP-4B code) with multiple neutron energy groups have also been used to validate neutron beam parameters and to ensure shielding capabilities of facility shutter and cave walls. Neutron flux distributions at the image plane and the neutron beam characteristics were experimentally measured by irradiating a two-dimensional array of Copper foils and using a real-time neutron radiography system. The neutron image characteristics -- such as neutron flux, image size, beam quality -- measured experimentally and predicted numerically for beam tube, beam shutter and radiography cave are compared and discussed in detail in this paper. The experimental results show that thermal neutron flux at image plane is nearly uniform over an imaging area of 20.0-cm diameter and its magnitude ranges from 8.0 x 10{sup 6} - 1.0 x 10{sup 7} n/cm{sup 2}-sec while the neutron-to-gamma ratio is 6.0 x 10{sup 5} n/cm{sup 2}-{mu}Sv. (authors)

  15. 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.

  16. Cooper Pairs in Insulators?!

    SciTech Connect

    James Valles

    2008-07-23

    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. 

  17. Critical Schwinger Pair Production.

    PubMed

    Gies, Holger; Torgrimsson, Greger

    2016-03-01

    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 Berezinskii-Kosterlitz-Thouless-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. PMID:26991162

  18. Cooper Pairs in Insulators?!

    ScienceCinema

    James Valles

    2016-07-12

    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. 

  19. "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.

  20. Cross-sectional void fraction distribution measurements in a vertical annulus two-phase flow by high speed X-ray computed tomography and real-time neutron radiography techniques

    SciTech Connect

    Harvel, G.D. |; Hori, K.; Kawanishi, K.

    1995-09-01

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

  1. 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 λan/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.

  2. NEUTRON SOURCE

    DOEpatents

    Bernander, N.K. et al.

    1960-10-18

    An apparatus is described for producing neutrons through target bombardment with deuterons. Deuterium gas is ionized by electron bombardment and the deuteron ions are accelerated through a magnetic field to collimate them into a continuous high intensity beam. The ion beam is directed against a deuteron pervious metal target of substantially the same nnaterial throughout to embed the deuterous therein and react them to produce neutrons. A large quantity of neutrons is produced in this manner due to the increased energy and quantity of ions bombarding the target.

  3. Development of fast neutron pinhole camera using nuclear emulsion for neutron emission profile measurement in KSTAR

    NASA Astrophysics Data System (ADS)

    Izumi, Y.; Tomita, H.; Nakayama, Y.; Hayashi, S.; Morishima, K.; Isobe, M.; Cheon, M. S.; Ogawa, K.; Nishitani, T.; Naka, T.; Nakano, T.; Nakamura, M.; Iguchi, T.

    2016-11-01

    We have developed a compact fast neutron camera based on a stack of nuclear emulsion plates and a pinhole collimator. The camera was installed at J-port of Korea superconducting tokamak advanced research at National Fusion Research Institute, Republic of Korea. Fast neutron images agreed better with calculated ones based on Monte Carlo neutron simulation using the uniform distribution of Deuterium-Deuterium (DD) neutron source in a torus of 40 cm radius.

  4. Neutron collimator for neutron radiography applications at tangential port of the TRIGA RC-1 reactor

    NASA Astrophysics Data System (ADS)

    Rosa, R.; Andreoli, F.; Mattoni, M.; Palomba, M.

    2009-06-01

    At the ENEA TRIGA research reactor (Casaccia Research Center, Rome) a new neutron collimator has been designed and installed at the neutron tangential channel. This collimator, that is part of a neutron/X-ray facility for NDT analysis, was experimentally characterized and optimized in terms of thermal neutron fluence rate, spatial/energetic distribution, photon air KERMA and effective beam diameter. This paper shows the methodologies and the results of the experimental analysis that were carried out.

  5. Thermal neutron detection system

    DOEpatents

    Peurrung, Anthony J.; Stromswold, David C.

    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.

  6. 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.

  7. Neutron multiplicity ,easurements With 3He alternative: Straw neutron detectors

    DOE PAGES

    Mukhopadhyay, Sanjoy; Wolff, Ronald S.; Meade, John A.; Detweiler, Ryan; Maurer, Richard J.; Mitchell, Stephen E.; Guss, Paul P.; Lacy, Jeffrey L.; Sun, Liang; Athanasiades, Athanasios

    2015-01-27

    Counting neutrons emitted by special nuclear material (SNM) and differentiating them from the background neutrons of various origins is the most effective passive means of detecting SNM. Unfortunately, neutron detection, counting, and partitioning in a maritime environment are complex due to the presence of high-multiplicity spallation neutrons (commonly known as “ship effect”) and to the complicated nature of the neutron scattering in that environment. In this study, a prototype neutron detector was built using 10B as the converter in a special form factor called “straws” that would address the above problems by looking into the details of multiplicity distributions ofmore » neutrons originating from a fissioning source. This paper describes the straw neutron multiplicity counter (NMC) and assesses the performance with those of a commercially available fission meter. The prototype straw neutron detector provides a large-area, efficient, lightweight, more granular (than fission meter) neutron-responsive detection surface (to facilitate imaging) to enhance the ease of application of fission meters. Presented here are the results of preliminary investigations, modeling, and engineering considerations leading to the construction of this prototype. This design is capable of multiplicity and Feynman variance measurements. This prototype may lead to a near-term solution to the crisis that has arisen from the global scarcity of 3He by offering a viable alternative to fission meters. This paper describes the work performed during a 2-year site-directed research and development (SDRD) project that incorporated straw detectors for neutron multiplicity counting. The NMC is a two-panel detector system. We used 10B (in the form of enriched boron carbide: 10B4C) for neutron detection instead of 3He. In the first year, the project worked with a panel of straw neutron detectors, investigated its characteristics, and developed a data acquisition (DAQ) system to collect

  8. 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

  9. Electron pairing without superconductivity

    NASA Astrophysics Data System (ADS)

    Levy, Jeremy

    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. Support from AFOSR, ONR, ARO, NSF, DOE and NSSEFF is gratefully acknowledged.

  10. A number-projected model with generalized pairing interaction in application to rotating nuclei

    SciTech Connect

    Satula, W. |||; Wyss, R.

    1996-12-31

    A cranked mean-field model that takes into account both T=1 and T=0 pairing interactions is presented. The like-particle pairing interaction is described by means of a standard seniority force. The neutron-proton channel includes simultaneously correlations among particles moving in time reversed orbits (T=1) and identical orbits (T=0). The coupling between different pairing channels and nuclear rotation is taken into account selfconsistently. Approximate number-projection is included by means of the Lipkin-Nogami method. The transitions between different pairing phases are discussed as a function of neutron/proton excess, T{sub z}, and rotational frequency, {Dirac_h}{omega}.

  11. Slow neutron leakage spectra from spallation neutron sources

    SciTech Connect

    Das, S G; Carpenter, J M; Prael, R E

    1980-02-01

    An efficient technique is described for Monte Carlo simulation of neutron beam spectra from target-moderator-reflector assemblies typical of pulsed spallation neutron sources. The technique involves the scoring of the transport-theoretical probability that a neutron will emerge from the moderator surface in the direction of interest, at each collision. An angle-biasing probability is also introduced which further enhances efficiency in simple problems. These modifications were introduced into the VIM low energy neutron transport code, representing the spatial and energy distributions of the source neutrons approximately as those of evaporation neutrons generated through the spallation process by protons of various energies. The intensity of slow neutrons leaking from various reflected moderators was studied for various neutron source arrangements. These include computations relating to early measurements on a mockup-assembly, a brief survey of moderator materials and sizes, and a survey of the effects of varying source and moderator configurations with a practical, liquid metal cooled uranium source Wing and slab, i.e., tangential and radial moderator arrangements, and Be vs CH/sub 2/ reflectors are compared. Results are also presented for several complicated geometries which more closely represent realistic arrangements for a practical source, and for a subcritical fission multiplier such as might be driven by an electron linac. An adaptation of the code was developed to enable time dependent calculations, and investigated the effects of the reflector, decoupling and void liner materials on the pulse shape.

  12. Neutron measurements of the OGO-VI Spacecraft

    NASA Technical Reports Server (NTRS)

    Lockwood, J. A.

    1973-01-01

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

  13. NEUTRONIC REACTOR

    DOEpatents

    Wade, E.J.

    1958-09-16

    This patent relates to a reflector means for a neutronic reactor. A reflector comprised of a plurality of vertically movable beryllium control members is provided surrounding the sides of the reactor core. An absorber of fast neutrons comprised of natural uramum surrounds the reflector. An absorber of slow neutrons surrounds the absorber of fast neutrons and is formed of a plurality of beryllium blocks having natural uranium members distributcd therethrough. in addition, a movable body is positioned directly below the core and is comprised of a beryllium reflector and an absorbing member attached to the botiom thereof, the absorbing member containing a substance selected from the goup consisting of natural urantum and Th/sup 232/.

  14. NEUTRONIC REACTOR

    DOEpatents

    Fraas, A.P.; Mills, C.B.

    1961-11-21

    A neutronic reactor in which neutron moderation is achieved primarily in its reflector is described. The reactor structure consists of a cylindrical central "island" of moderator and a spherical moderating reflector spaced therefrom, thereby providing an annular space. An essentially unmoderated liquid fuel is continuously passed through the annular space and undergoes fission while contained therein. The reactor, because of its small size, is particularly adapted for propulsion uses, including the propulsion of aircraft. (AEC)

  15. NEUTRON SOURCES

    DOEpatents

    Richmond, J.L.; Wells, C.E.

    1963-01-15

    A neutron source is obtained without employing any separate beryllia receptacle, as was formerly required. The new method is safer and faster, and affords a source with both improved yield and symmetry of neutron emission. A Be container is used to hold and react with Pu. This container has a thin isolating layer that does not obstruct the desired Pu--Be reaction and obviates procedures previously employed to disassemble and remove a beryllia receptacle. (AEC)

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

    SciTech Connect

    Moreno, O.; Sarriguren, P.; Alvarez-Rodriguez, R.; Guerra, E. Moya de

    2006-05-15

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

  17. Study on the influence of the B4C layer thickness on the neutron flux and energy distribution shape in multi-electrode ionisation chamber.

    PubMed

    Tymińska, K; Maciak, M; Ośko, J; Tulik, P; Zielczyński, M; Gryziński, 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.

  18. Study on the influence of the B4C layer thickness on the neutron flux and energy distribution shape in multi-electrode ionisation chamber.

    PubMed

    Tymińska, K; Maciak, M; Ośko, J; Tulik, P; Zielczyński, M; Gryziński, 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

  19. Measurement of lineal-energy distributions for neutrons of 8 keV to 65 MeV by using a tissue-equivalent proportional counter.

    PubMed

    Nunomiya, T; Kim, E; Kurosaw, T; Taniguchi, S; Nakamura, T; Nakane, Y; Sakamoto, Y; Tanaka, S

    2002-01-01

    The lineal-energy spectra for monoenergetic and quasi-monoenergetic neutrons of 8 keV to 65 MeV were obtained using a tissue-equivalent proportional counter (TEPC). The frequency-mean lineal energy, the dose-average lineal energy and mean quality factor were estimated from the measured data. The neutron absorbed doses obtained with this TEPC were compared with the kerma coefticient for A-150 plastic defined by ICRP 26 and the mean quality factors were compared with the data of ICRP 74. respectively. These comparisons indicated good agreement between them. PMID:12212902

  20. NEUTRONIC REACTOR

    DOEpatents

    Wigner, E.P.

    1958-04-22

    A nuclear reactor for isotope production is described. This reactor is designed to provide a maximum thermal neutron flux in a region adjacent to the periphery of the reactor rather than in the center of the reactor. The core of the reactor is generally centrally located with respect tn a surrounding first reflector, constructed of beryllium. The beryllium reflector is surrounded by a second reflector, constructed of graphite, which, in tune, is surrounded by a conventional thermal shield. Water is circulated through the core and the reflector and functions both as a moderator and a coolant. In order to produce a greatsr maximum thermal neutron flux adjacent to the periphery of the reactor rather than in the core, the reactor is designed so tbat the ratio of neutron scattering cross section to neutron absorption cross section averaged over all of the materials in the reflector is approximately twice the ratio of neutron scattering cross section to neutron absorption cross section averaged over all of the material of the core of the reactor.

  1. 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

  2. Unraveling the Hydrogenation of TiO 2 and Graphene Oxide/TiO 2 Composites in Real Time by in Situ Synchrotron X-ray Powder Diffraction and Pair Distribution Function Analysis

    DOE PAGES

    Nguyen-Phan, Thuy-Duong; Liu, Zongyuan; Luo, Si; Gamalski, Andrew D.; Vovchok, Dimitry; Xu, Wenqian; Stach, Eric A.; Polyansky, Dmitry E.; Fujita, Etsuko; Rodriguez, José A.; et al

    2016-02-18

    The functionalization of graphene oxide (GO) and graphene by TiO2 and other metal oxides has attracted considerable attention due to numerous promising applications in catalysis, energy conversion, and storage. We propose hydrogenation of this class of materials as a promising way to tune catalytic properties by altering the structural and chemical transformations that occur upon H incorporation. We also investigate the structural changes that occur during the hydrogenation process using in situ powder X-ray diffraction and pair distribution function analysis of GO–TiO2 and TiO2 under H2 reduction. Sequential Rietveld refinement was employed to gain insight into the evolution of crystalmore » growth of TiO2 nanoparticles in the presence of two-dimensional (2D) GO nanosheets. GO sheets not only significantly retarded the nucleation and growth of rutile impurities, stabilizing the anatase structure, but was also partially reduced to hydrogenated graphene by the introduction of atomic hydrogen into the honeycomb lattice. We discuss the hydrogenation processes and the resulting composite structure that occurs during the incorporation of atomic H and the dynamic structural transformations that leads to a highly active photocatalyst.« less

  3. 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.

  4. 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

  5. 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.

  6. Adaptive Pairing Reversible Watermarking.

    PubMed

    Dragoi, Ioan-Catalin; Coltuc, Dinu

    2016-05-01

    This letter revisits the pairwise reversible watermarking scheme of Ou et al., 2013. An adaptive pixel pairing that considers only pixels with similar prediction errors is introduced. This adaptive approach provides an increased number of pixel pairs where both pixels are embedded and decreases the number of shifted pixels. The adaptive pairwise reversible watermarking outperforms the state-of-the-art low embedding bit-rate schemes proposed so far.

  7. Resonantly paired fermionic superfluids

    NASA Astrophysics Data System (ADS)

    Gurarie, V.; Radzihovsky, L.

    2007-01-01

    We present a theory of a degenerate atomic Fermi gas, interacting through a narrow Feshbach resonance, whose position and therefore strength can be tuned experimentally, as demonstrated recently in ultracold trapped atomic gases. The distinguishing feature of the theory is that its accuracy is controlled by a dimensionless parameter proportional to the ratio of the width of the resonance to Fermi energy. The theory is therefore quantitatively accurate for a narrow Feshbach resonance. In the case of a narrow s-wave resonance, our analysis leads to a quantitative description of the crossover between a weakly paired BCS superconductor of overlapping Cooper pairs and a strongly paired molecular Bose-Einstein condensate of diatomic molecules. In the case of pairing via a p-wave resonance, that we show is always narrow for a sufficiently low density, we predict a detuning-temperature phase diagram, that in the course of a BCS-BEC crossover can exhibit a host of thermodynamically distinct phases separated by quantum and classical phase transitions. For an intermediate strength of the dipolar anisotropy, the system exhibits a px + i py paired superfluidity that undergoes a topological phase transition between a weakly coupled gapless ground state at large positive detuning and a strongly paired fully gapped molecular superfluid for a negative detuning. In two dimensions the former state is characterized by a Pfaffian ground state exhibiting topological order and non-Abelian vortex excitations familiar from fractional quantum Hall systems.

  8. Cooper Pair Insulators

    NASA Astrophysics Data System (ADS)

    Valles, James

    One of the recent advances in the field of the Superconductor to Insulator Transition (SIT) has been the discovery and characterization of the Cooper Pair Insulator phase. This bosonic insulator, which consists of localized Cooper pairs, exhibits activated transport and a giant magneto-resistance peak. These features differ markedly from the weakly localized transport that emerges as pairs break at a ``fermionic'' SIT. I will describe how our experiments on films nano-patterned with a nearly triangular array of holes have enabled us to 1) distinguish bosonic insulators from fermionic insulators, 2) show that Cooper pairs, rather than quasi-particles dominate the transport in the Cooper Pair insulator phase, 3) demonstrate that very weak, sub nano-meter thickness inhomogeneities control whether a bosonic or fermionic insulator forms at an SIT and 4) reveal that Cooper pairs disintegrate rather than becoming more tightly bound deep in the localized phase. We have also developed a method, using a magnetic field, to tune flux disorder reversibly in these films. I will present our latest results on the influence of magnetic flux disorder and random gauge fields on phenomena near bosonic SITs. This work was performed in collaboration with M. D. Stewart, Jr., Hung Q. Nguyen, Shawna M. Hollen, Jimmy Joy, Xue Zhang, Gustavo Fernandez, Jeffrey Shainline and Jimmy Xu. It was supported by NSF Grants DMR 1307290 and DMR-0907357.

  9. 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)

  10. Gamma/neutron competition above the neutron separation energy in delayed neutron emitters

    NASA Astrophysics Data System (ADS)

    Valencia, E.; Algora, A.; Tain, J. L.; Rice, S.; Agramunt, J.; Zakari-Issoufou, A.-A.; Äystö, J.; Bowry, M.; Bui, V. M.; Caballero-Folch, R.; Cano-Ott, D.; Eloma, V.; Eronen, T.; Estevez, E.; Farrelly, G. F.; Fallot, M.; Garcia, A.; Gelletly, W.; Gomez-Hornillos, M. B.; Gorlychev, V.; Hakala, J.; Jokinen, A.; Jordan, M. D.; Kankainen, A.; Kondev, F. G.; Martinez, T.; Mendoza, E.; Molina, F.; Moore, I.; Perez, A.; Podolyak, Zs.; Penttilä, H.; Porta, A.; Regan, P. H.; Rissanen, J.; Rubio, B.; Weber, C.

    2014-03-01

    To study the β-decay properties of some well known delayed neutron emitters an experiment was performed in 2009 at the IGISOL facility (University of Jyväskylä in Finland) using Total Absorption γ-ray Spectroscopy (TAGS) technique. The aim of these measurements is to obtain the full β-strength distribution below the neutron separation energy (Sn) and the γ/neutron competition above. This information is a key parameter in nuclear technology applications as well as in nuclear astrophysics and nuclear structure. Preliminary results of the analysis show a significant γ-branching ratio above Sn.

  11. Neutron stars and black holes

    NASA Technical Reports Server (NTRS)

    Lamb, F. K.

    1991-01-01

    The radiation of neutron stars is powered by accretion, rotation, or internal heat; accreting black holes are thought to be the central engines of AGNs and of a handful of binary X-ray sources in the Galaxy. The evolution of a neutron star depends on the coupling between the rotating neutron and proton fluids in the interior, and between these fluids and the crust; it also depends on the magnetic and thermal properties of the star. Significant progress has been made in recent years in the understanding of radial and disk accretion by black holes. Radiation from pair plasmas may make an important contribution to the X- and gamma-ray spectra of AGNs and black holes in binary systems.

  12. β -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

    β -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 β -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.

  13. The neutron imaging diagnostic at NIF (invited).

    PubMed

    Merrill, F E; Bower, D; Buckles, R; Clark, D D; Danly, C R; Drury, O B; Dzenitis, J M; Fatherley, V E; Fittinghoff, D N; Gallegos, R; Grim, G P; Guler, N; Loomis, E N; Lutz, S; Malone, R M; Martinson, D D; Mares, D; Morley, D J; Morgan, G L; Oertel, J A; Tregillis, I L; Volegov, P L; Weiss, P B; Wilde, C H; Wilson, D C

    2012-10-01

    A neutron imaging diagnostic has recently been commissioned at the National Ignition Facility (NIF). This new system is an important diagnostic tool for inertial fusion studies at the NIF for measuring the size and shape of the burning DT plasma during the ignition stage of Inertial Confinement Fusion (ICF) implosions. The imaging technique utilizes a pinhole neutron aperture, placed between the neutron source and a neutron detector. The detection system measures the two dimensional distribution of neutrons passing through the pinhole. This diagnostic has been designed to collect two images at two times. The long flight path for this diagnostic, 28 m, results in a chromatic separation of the neutrons, allowing the independently timed images to measure the source distribution for two neutron energies. Typically the first image measures the distribution of the 14 MeV neutrons and the second image of the 6-12 MeV neutrons. The combination of these two images has provided data on the size and shape of the burning plasma within the compressed capsule, as well as a measure of the quantity and spatial distribution of the cold fuel surrounding this core.

  14. Magnetic Fluctuations in Pair-Density-Wave Superconductors.

    PubMed

    Christensen, Morten H; Jacobsen, Henrik; Maier, Thomas A; Andersen, Brian M

    2016-04-22

    Pair-density-wave superconductivity constitutes a novel electronic condensate proposed to be realized in certain unconventional superconductors. Establishing its potential existence is important for our fundamental understanding of superconductivity in correlated materials. Here we compute the dynamical magnetic susceptibility in the presence of a pair-density-wave ordered state and study its fingerprints on the spin-wave spectrum including the neutron resonance. In contrast to the standard case of d-wave superconductivity, we show that the pair-density-wave phase exhibits neither a spin gap nor a magnetic resonance peak, in agreement with a recent neutron scattering experiment on underdoped La_{1.905}Ba_{0.095}CuO_{4} [Z. Xu et al., Phys. Rev. Lett. 113, 177002 (2014)]. PMID:27152819

  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. 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.

  17. Outer crust of nonaccreting cold neutron stars

    SciTech Connect

    Ruester, Stefan B.; Hempel, Matthias; Schaffner-Bielich, Juergen

    2006-03-15

    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.

  18. Neutron dosimetry in boron neutron capture therapy

    SciTech Connect

    Fairchild, R.G.; Miola, U.J.; Ettinger, K.V.

    1981-01-01

    The recent development of various borated compounds and the utilization of one of these (Na/sub 2/B/sub 12/H/sub 11/SH) to treat brain tumors in clinical studies in Japan has renewed interest in neutron capture therapy. In these procedures thermal neutrons interact with /sup 10/B in boron containing cells through the /sup 10/B(n,..cap alpha..)/sup 7/Li reaction producing charged particles with a maximum range of approx. 10..mu..m in tissue. Borated analogs of chlorpromazine, porphyrin, thiouracil and deoxyuridine promise improved tumor uptake and blood clearance. The therapy beam from the Medical Research Reactor in Brookhaven contains neutrons from a modified and filtered fission spectrum and dosimetric consequences of the use of the above mentioned compounds in conjunction with thermal and epithermal fluxes are discussed in the paper. One of the important problems of radiation dosimetry in capture therapy is determination of the flux profile and, hence, the dose profile in the brain. This has been achieved by constructing a brain phantom made of TE plastic. The lyoluminescence technique provides a convenient way of monitoring the neutron flux distributions; the detectors for this purpose utilize /sup 6/Li and /sup 10/B compounds. Such compounds have been synthesized specially for the purpose of dosimetry of thermal and epithermal beams. In addition, standard lyoluminescent phosphors, like glutamine, could be used to determine the collisional component of the dose as well as the contribution of the /sup 14/N(n,p)/sup 14/C reaction. Measurements of thermal flux were compared with calculations and with measurements done with activation foils.

  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. NEUTRONIC REACTOR

    DOEpatents

    Hurwitz, H. Jr.; Brooks, H.; Mannal, C.; Payne, J.H.; Luebke, E.A.

    1959-03-24

    A reactor of the heterogeneous, liquid cooled type is described. This reactor is comprised of a central region of a plurality of vertically disposed elongated tubes surrounded by a region of moderator material. The central region is comprised of a central core surrounded by a reflector region which is surrounded by a fast neutron absorber region, which in turn is surrounded by a slow neutron absorber region. Liquid sodium is used as the primary coolant and circulates through the core which contains the fuel elements. Control of the reactor is accomplished by varying the ability of the reflector region to reflect neutrons back into the core of the reactor. For this purpose the reflector is comprised of moderator and control elements having varying effects on reactivity, the control elements being arranged and actuated by groups to give regulation, shim, and safety control.

  1. Neutron multiplicity analysis tool

    SciTech Connect

    Stewart, Scott L

    2010-01-01

    I describe the capabilities of the EXCOM (EXcel based COincidence and Multiplicity) calculation tool which is used to analyze experimental data or simulated neutron multiplicity data. The input to the program is the count-rate data (including the multiplicity distribution) for a measurement, the isotopic composition of the sample and relevant dates. The program carries out deadtime correction and background subtraction and then performs a number of analyses. These are: passive calibration curve, known alpha and multiplicity analysis. The latter is done with both the point model and with the weighted point model. In the current application EXCOM carries out the rapid analysis of Monte Carlo calculated quantities and allows the user to determine the magnitude of sample perturbations that lead to systematic errors. Neutron multiplicity counting is an assay method used in the analysis of plutonium for safeguards applications. It is widely used in nuclear material accountancy by international (IAEA) and national inspectors. The method uses the measurement of the correlations in a pulse train to extract information on the spontaneous fission rate in the presence of neutrons from ({alpha},n) reactions and induced fission. The measurement is relatively simple to perform and gives results very quickly ({le} 1 hour). By contrast, destructive analysis techniques are extremely costly and time consuming (several days). By improving the achievable accuracy of neutron multiplicity counting, a nondestructive analysis technique, it could be possible to reduce the use of destructive analysis measurements required in safeguards applications. The accuracy of a neutron multiplicity measurement can be affected by a number of variables such as density, isotopic composition, chemical composition and moisture in the material. In order to determine the magnitude of these effects on the measured plutonium mass a calculational tool, EXCOM, has been produced using VBA within Excel. This

  2. NEUTRONIC REACTOR

    DOEpatents

    Fermi, E.; Szilard, L.

    1957-09-24

    Reactors of the type employing plates of natural uranium in a moderator are discussed wherein the plates are um-formly disposed in parallel relationship to each other thereby separating the moderator material into distinct and individual layers. Each plate has an uninterrupted sunface area substantially equal to the cross-sectional area of the active portion of the reactor, the particular size of the plates and the volume ratio of moderator to uranium required to sustain a chain reaction being determinable from the known purity of these materials and other characteristics such as the predictable neutron losses due to the formation of radioactive elements of extremely high neutron capture cross section.

  3. NEUTRONIC REACTOR

    DOEpatents

    Wigner, E.P.; Weinberg, A.W.; Young, G.J.

    1958-04-15

    A nuclear reactor which uses uranium in the form of elongated tubes as fuel elements and liquid as a coolant is described. Elongated tubular uranium bodies are vertically disposed in an efficient neutron slowing agent, such as graphite, for example, to form a lattice structure which is disposed between upper and lower coolant tanks. Fluid coolant tubes extend through the uranium bodies and communicate with the upper and lower tanks and serve to convey the coolant through the uranium body. The reactor is also provided with means for circulating the cooling fluid through the coolant tanks and coolant tubes, suitable neutron and gnmma ray shields, and control means.

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

    PubMed

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

    2002-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-02-01

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

  6. 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.

  7. Colors of dynamically associated asteroid pairs

    NASA Astrophysics Data System (ADS)

    Moskovitz, Nicholas A.

    2012-09-01

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

  8. Prompt neutron multiplicity measurements with portable detectors

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Sanjoy; Wolff, Ronald; Maurer, Richard; Mitchell, Stephen; Smith, Ethan X.; Guss, Paul; Lacy, Jeffrey L.; Sun, L.; Athanasiades, A.

    2011-09-01

    Mobile detection of kilogram quantities of special nuclear materials (SNM) during maritime transportation is a challenging problem for the U.S. Department of Homeland Security. Counting neutrons emitted by the SNM and partitioning them from background neutrons of multiple origins is the most effective passive means of detecting the SNM. Unfortunately, neutron detection, counting, and partitioning in a maritime environment is complex due to the presence of spallation neutrons (commonly known as "ship effect") and to the complicated nature of the neutron scattering in that environment. This work studied the possibilities of building a prototype neutron detector using boron- 10 (10B) as the converter in a novel form factor called "straws" that would address the above problem by examining multiplicity distributions of neutrons originating from a fissioning source. Currently, commercially manufactured fission meters (FM) are available that separate cosmic neutrons from non-cosmic neutrons and quantitatively determine the strength of a fissioning source; however, these FMs use 3He, which is becoming increasingly difficult to procure; also the size and weight of a commercial FM is not conducive to manual neutron detection operations in a maritime environment. The current project may provide a near-term solution to the crisis that has arisen from the global scarcity of 3He by offering a viable alternative to the FM. The prototype detector provides a large-area, efficient, lightweight, more granular neutron responsive detection surface (to facilitate imaging) to ease the application of the new FMs.

  9. Two neutron correlations in photo-fission

    NASA Astrophysics Data System (ADS)

    Dale, D. S.; Kosinov, O.; Forest, T.; Burggraf, J.; Stave, S.; Warren, G.; Starovoitova, V.

    2016-09-01

    A large body of experimental work has established the strong kinematical correlation between fission fragments and fission neutrons. Here, we report on the progress of investigations of the potential for strong two neutron correlations arising from the nearly back-to-back nature of the two fission fragments that emit these neutrons in the photo-fission process. In initial measurements, a pulsed electron linear accelerator was used to generate bremsstrahlung photons that impinged upon an actinide target, and the energy and opening angle distributions of coincident neutrons were measured using a large acceptance neutron detector array. A planned comprehensive set of measurements of two neutron correlations in the photo-fission of actinides is expected to shed light on several fundamental aspects of the fission process including the multiplicity distributions associated with the light and heavy fission fragments, the nuclear temperatures of the fission fragments, and the mass distribution of the fission fragments as a function of energy released. In addition to these measurements providing important nuclear data, the unique kinematics of fission and the resulting two neutron correlations have the potential to be the basis for a new tool to detect fissionable materials. A key technical challenge of this program arises from the need to perform coincidence measurements with a low duty factor, pulsed electron accelerator. This has motivated the construction of a large acceptance neutron detector array, and the development of data analysis techniques to directly measure uncorrelated two neutron backgrounds.

  10. Quantum phase transitional patterns in the SD-pair shell model

    SciTech Connect

    Luo Yanan; Meng Xiangfei; Zhang Yu; Pan Feng; Draayer, Jerry P.

    2009-07-15

    Patterns of shape-phase transition in the proton-neutron coupled systems are studied within the SD-pair shell model. The results show that some transitional patterns in the SD-pair shell model are similar to the U(5)-SU(3) and U(5)-SO(6) transitions with signatures of the critical point symmetry of the interacting boson model.

  11. Neutronic reactor

    DOEpatents

    Carleton, John T.

    1977-01-25

    A graphite-moderated nuclear reactor includes channels between blocks of graphite and also includes spacer blocks between adjacent channeled blocks with an axis of extension normal to that of the axis of elongation of the channeled blocks to minimize changes in the physical properties of the graphite as a result of prolonged neutron bombardment.

  12. NEUTRONIC REACTORS

    DOEpatents

    Anderson, H.L.

    1958-10-01

    The design of control rods for nuclear reactors are described. In this design the control rod consists essentially of an elongated member constructed in part of a neutron absorbing material and having tube means extending therethrough for conducting a liquid to cool the rod when in use.

  13. NEUTRONIC REACTOR

    DOEpatents

    Wigner, E.P.

    1960-09-27

    A unit assembly is described for a neutronic reactor comprising a tube and plurality of spaced parallel sandwiches in the tube extending lengthwise thereof, each sandwich including a middle plate having a central opening for plutonium and other openings for fertile material at opposite ends of the plate.

  14. Methods for absorbing neutrons

    DOEpatents

    Guillen, Donna P.; Longhurst, Glen R.; Porter, Douglas L.; Parry, James R.

    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.

  15. 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)

  16. Hadronic production of massive lepton pairs

    SciTech Connect

    Berger, E.L.

    1982-12-01

    A review is presented of recent experimental and theoretical progress in studies of the production of massive lepton pairs in hadronic collisions. I begin with the classical Drell-Yan annihilation model and its predictions. Subsequently, I discuss deviations from scaling, the status of the proofs of factorization in the parton model, higher-order terms in the perturbative QCD expansion, the discrepancy between measured and predicted yields (K factor), high-twist terms, soft gluon effects, transverse-momentum distributions, implications for weak vector boson (W/sup + -/ and Z/sup 0/) yields and production properties, nuclear A dependence effects, correlations of the lepton pair with hadrons in the final state, and angular distributions in the lepton-pair rest frame.

  17. 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.

  18. Neutron reflecting supermirror structure

    DOEpatents

    Wood, James L.

    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.

  19. Extracting an entangled photon pair from collectively decohered pairs at a telecommunication wavelength.

    PubMed

    Tsujimoto, Yoshiaki; Sugiura, Yukihiro; Ando, Makoto; Katsuse, Daisuke; Ikuta, Rikizo; Yamamoto, Takashi; Koashi, Masato; Imoto, Nobuyuki

    2015-05-18

    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 ± 0.07 which clearly shows the recovery of entanglement.

  20. Imaging with polarized neutrons

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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