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1

Pair correlations and pair transfers in neutron-rich nuclei  

SciTech Connect

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

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

2010-05-12

2

Extracting differential pair distribution functions using MIXSCAT  

SciTech Connect

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

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

2010-08-27

3

Pair distribution function for fluid hard spheres  

Microsoft Academic Search

The pair distribution function of a system of fluid hard spheres is calculated by means of a simple generalization of the Percus-Yevick theory. A relation between the pair distribution function and the direct correlation function which leads to self-consistent results from the pressure and compressibility equations of state and which is similar, but not identical, to a proposal of Rowlinson,

R. O. Watts; D. Henderson

1969-01-01

4

Neutrino emission from triplet pairing of neutrons in neutron stars  

SciTech Connect

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

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

2010-02-15

5

Pairing and superfluidity of nucleons in neutron stars  

E-print Network

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

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

2015-04-13

6

Development of pair distribution function analysis  

SciTech Connect

This is the final report of a 3-year LDRD project at LANL. It has become more and more evident that structural coherence in the CuO{sub 2} planes of high-{Tc} superconducting materials over some intermediate length scale (nm range) is important to superconductivity. In recent years, the pair distribution function (PDF) analysis of powder diffraction data has been developed for extracting structural information on these length scales. This project sought to expand and develop this technique, use it to analyze neutron powder diffraction data, and apply it to problems. In particular, interest is in the area of high-{Tc} superconductors, although we planned to extend the study to the closely related perovskite ferroelectric materials andother materials where the local structure affects the properties where detailed knowledge of the local and intermediate range structure is important. In addition, we planned to carry out single crystal experiments to look for diffuse scattering. This information augments the information from the PDF.

Vondreele, R.; Billinge, S.; Kwei, G.; Lawson, A.

1996-09-01

7

Neutron localization induced by the pairing field in an inhomogeneous neutron matter  

E-print Network

It is shown that in an inhomogeneous neutron matter the pairing field bounds neutrons around the Fermi level leading to the formation of localized Andreev states. In the case of the inner crust of neutron stars the localization length has been determined as a function of the nuclear density.

Piotr Magierski

2007-01-10

8

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

E-print Network

The relative current density $n^i$ 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 $p_i$ by a linear relation of the form $n^i=K^{ij}p_j$ in terms of a physically well defined mobility tensor $K^{ij}$. 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 an effective mass $m_\\star$ such that in terms of the relevant number density n of unconfined neutrons we shall have $K^{ij}=n/m_\\star\\gamma^{ij}$. In a preceding analysis based on an independent particle treatment using Bloch boundary conditions to obtain the distribution of energy $E_k$ and associated group velocity $v_k^i=\\partial E_k/\\partial\\hbar k_i$ as a function of wavenumber $k_i$, it was shown that the mobility tensor would be given by $K^{ij}\\propto\\int d^3 k v_k^i v_k^j\\delta\\{E_k-\\mu\\}$, where $\\mu$ is the Fermi energy. Using the approach due to Bogoliubov, it is shown here that the effect of BCS pairing with an energy gap \\Delta_F and corresponding quasiparticle energy function \\EE_k=\\sqrt{(E_k-\\mu)^2+\\Delta_F^2}$ will just be to replace the Dirac distributional integrand by a smoother distribution : $K^{ij}\\propto \\int d^3 k v_k^i v_k^j \\Delta_F^2 /\\EE^3_k$. 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 $p_i$ must be small enough to give $2|p_i v_k^i|<\\EE_k^2/|E_k-\\mu|$ for all modes). It is concluded that the prediction of a very large effective mass enhancement in the middle layers of the crust will not be significantly affected by the pairing mechanism.

Brandon Carter; Nicolas Chamel; Pawel Haensel

2005-08-23

9

Reflections on the magnetic pair distribution function.  

PubMed

The recent application of the total scattering method to magnetic systems is discussed. The ability to determine the magnetic pair distribution function opens the door to the study of local order in magnetic systems ranging from multiferroics to dilute magnetic semiconductors. PMID:24419165

Ratcliff, William

2014-01-01

10

Aligned neutron-proton pairs in N Z nuclei  

NASA Astrophysics Data System (ADS)

It is argued that N Z nuclei with 90 ? A ? 100 can be interpreted in terms of aligned neutron-proton pairs with angular momentum J = 2j and isospin T = 0. Based on this observation, a version of the interacting boson model is formulated in terms of isoscalar high-spin bosons. To illustrate its possible uses, the model is applied to the 21+ isomer in 94Ag.

Van Isacker, P.

2012-10-01

11

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

DOE PAGESBeta

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

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

2014-02-01

12

Quasifree Photoproduction of Pion-Pairs of Protons and Neutrons  

NASA Astrophysics Data System (ADS)

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

Oberle, M.; Krusche, B.

2014-01-01

13

Bremsstrahlung pair-production of positrons with low neutron background.  

SciTech Connect

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

Lessner, E.

1998-09-16

14

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

E-print Network

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

Andrea Meucci; Matteo Vorabbi; Carlotta Giusti; Paolo Finelli

2014-04-08

15

Neutrinoless double beta decay within the quasiparticle random-phase approximation with proton-neutron pairing  

Microsoft Academic Search

We have investigated the role of proton-neutron pairing in the context of the quasiparticle random phase approximation formalism. This way the neutrinoless double beta decay matrix elements of the experimentally interesting {ital A} = 48, 76, 82, 96, 100, 116, 128, 130, and 136 systems have been calculated. We have found that the inclusion of proton-neutron pairing influences the neutrinoless

G. Pantis; F. Simkovic; J. D. Vergados; Amand Faessler

1996-01-01

16

Neutrinoless double beta decay within the quasiparticle random-phase approximation with proton-neutron pairing  

Microsoft Academic Search

We have investigated the role of proton-neutron pairing in the context of the quasiparticle random phase approximation formalism. This way the neutrinoless double beta decay matrix elements of the experimentally interesting A = 48, 76, 82, 96, 100, 116, 128, 130, and 136 systems have been calculated. We have found that the inclusion of proton-neutron pairing influences the neutrinoless double

G. Pantis; F. Simkovic; J. D. Vergados; Amand Faessler

1996-01-01

17

On the pair correlations of nuclear fission neutrons with small relative momenta  

Microsoft Academic Search

The theoretical analysis of pair correlations of low-energy neutrons produced in nuclear fission is performed on the basis\\u000a of the general method of pair correlations of particles at small relative momenta. The analytical approach to the description\\u000a of the effect of final-state interaction on narrow pair correlations of neutrons is used. It is shown that, at small but nonzero\\u000a values

V. L. Lyuboshitz; V. V. Lyuboshitz

2008-01-01

18

Spatial structure of neutron Cooper pair in low density uniform matter  

SciTech Connect

The spatial structure of the neutron Cooper pair in superfluid low-density uniform matter is analyzed by means of BCS calculations employing a bare force and the effective Gogny interaction. It is shown that the Cooper pair exhibits a strong spatial dineutron correlation over a wide range of neutron densities {rho}/{rho}{sub 0}{approx_equal}10{sup -4}-0.5. This feature is related to the crossover behavior between the pairing of the weak coupling BCS type and the Bose-Einstein condensation of bound neutron pairs. It is also shown that the zero-range {delta} interaction can describe the spatial structure of the neutron Cooper pair if the density-dependent interaction strength and the cutoff energy are appropriately chosen. Parametrizations of the density-dependent {delta} interaction satisfying this condition are discussed.

Matsuo, Masayuki [Department of Physics, Faculty of Science, Niigata University, Niigata 950-2181 (Japan)

2006-04-15

19

Angular distributions of neutron-nucleus collisions  

SciTech Connect

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

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

2011-06-15

20

Neutron dose distribution at the GSI fragment separator.  

PubMed

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

Fehrenbacher, G; Festag, J G

2004-01-01

21

Fragment Mass Distributions for Thermal-Neutron-Induced Fission of Pu239 and Pu241  

Microsoft Academic Search

The fragment mass distributions for thermal-neutron-induced fission of Pu239 and Pu241 have been determined from correlated energy measurements of fragment pairs. These mass distributions are compared with each other and with the post-neutron-emission mass yield for Pu239 obtained from radiochemical and mass spectrometric measurements. It is shown that these comparisons are consistent with the saw-tooth character of the function nu(M)

F. J. Walter; H. W. Schmitt; J. H. Neiler

1964-01-01

22

Neutrinoless Double Beta Decay within QRPA with Proton-Neutron Pairing  

Microsoft Academic Search

We have investigated the role of proton-neutron pairing in the context of the\\u000aQuasiparticle Random Phase approximation formalism. This way the neutrinoless\\u000adouble beta decay matrix elements of the experimentally interesting A= 48, 76,\\u000a82, 96, 100, 116, 128, 130 and 136 systems have been calculated. We have found\\u000athat the inclusion of proton-neutron pairing influences the neutrinoless double\\u000abeta

G. Pantis; F. Simkovic; J. D. Vergados; Amand Faessler

1996-01-01

23

Surface-enhanced pair transfer amplitude in quadrupole states of neutron-rich Sn isotopes  

SciTech Connect

We investigate the neutron pair transfer modes associated with the low-lying quadrupole states in neutron-rich Sn isotopes by means of the quasiparticle random phase approximation based on the Skyrme-Hartree-Fock-Bogoliubov mean-field model. The transition strength of the quadrupole pair-addition mode feeding the 2{sub 1}{sup +} state is enhanced in the Sn isotopes with A{>=}132. The transition density of the pair-addition mode has a large spatial extension in the exterior of the nucleus, reaching to r{approx}12-13 fm. The quadrupole pair-addition mode reflects sensitively a possible increase of the effective pairing interaction strength in the surface and exterior regions of neutron-rich nuclei.

Matsuo, Masayuki; Serizawa, Yasuyoshi [Department of Physics, Faculty of Science and Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan)

2010-08-15

24

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

NASA Astrophysics Data System (ADS)

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

Pastore, A.

2015-01-01

25

Proton-neutron pairing amplitude as a generator coordinate for double-? decay  

NASA Astrophysics Data System (ADS)

We treat proton-neutron pairing amplitudes, in addition to the nuclear deformation, as generator coordinates in a calculation of the neutrinoless double-? decay of Ge76. We work in two oscillator shells, with a Hamiltonian that includes separable terms in the quadrupole, spin-isospin, and pairing (isovector and isoscalar) channels. Our approach allows larger single-particle spaces than the shell model and includes the important physics of the proton-neutron quasiparticle random-phase approximation (QRPA) without instabilities near phase transitions. After comparing the results of a simplified calculation that neglects deformation with those of the QRPA, we present a more realistic calculation with both deformation and proton-neutron pairing amplitudes as generator coordinates. The future should see proton-neutron coordinates used together with energy-density functionals.

Hinohara, Nobuo; Engel, Jonathan

2014-09-01

26

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

SciTech Connect

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

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

2007-12-15

27

Measurements of angular and energy distributions of prompt neutrons from thermal neutron-induced fission  

Microsoft Academic Search

The experimental setup and methodology used to measure prompt neutron angular and energy distributions from thermal neutron-induced fission are described. The neutrons are detected using two scintillation detectors, while the fission fragments are detected by multi-wire proportional detectors in conjunction with the TOF technique. To separate events corresponding to neutrons and ?-quanta, a double discrimination by the pulse shape and

A. S. Vorobyev; O. A. Shcherbakov; Yu. S. Pleva; A. M. Gagarski; G. V. Val'ski; G. A. Petrov; V. I. Petrova; T. A. Zavarukhina

2009-01-01

28

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

E-print Network

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

Hirotaka Shimoyama; Masayuki Matsuo

2011-06-09

29

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

SciTech Connect

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

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

2009-12-15

30

Low-frequency $K^?=0^{+}$ modes in deformed neutron-rich nuclei: Pairing- and $?$-vibrational modes of neutron  

E-print Network

Low-frequency $K^{\\pi}=0^{+}$ states in deformed neutron-rich nuclei are investigated by means of the quasiparticle-random-phase approximation based on the Hartree-Fock-Bogoliubov formalism in the coordinate space. We have obtained the very strongly collective $K^{\\pi}=0^{+}$ modes not only in neutron-rich Mg isotope but also in Cr and Fe isotopes in N=40 region, where the onset of nuclear deformation has been discussed. It is found that the spatially extended structure of neutron quasiparticle wave functions around the Fermi level brings about a striking enhancement of the transition strengths. It is also found that the fluctuation of the pairing field plays an important role in generating coherence among two-quasiparticle excitations of neutron.

Kenichi Yoshida; Masayuki Yamagami

2008-02-16

31

Sangam: a distributed pair programming plug-in for Eclipse  

Microsoft Academic Search

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

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

2004-01-01

32

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

NASA Astrophysics Data System (ADS)

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

Kovcs, Z.; Harko, T.

2011-11-01

33

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

E-print Network

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

Z. Kovacs; K. S. Cheng; T. Harko

2010-09-30

34

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

35

Measurements of angular and energy distributions of prompt neutrons from thermal neutron-induced fission  

NASA Astrophysics Data System (ADS)

The experimental setup and methodology used to measure prompt neutron angular and energy distributions from thermal neutron-induced fission are described. The neutrons are detected using two scintillation detectors, while the fission fragments are detected by multi-wire proportional detectors in conjunction with the TOF technique. To separate events corresponding to neutrons and ?-quanta, a double discrimination by the pulse shape and the time-of-flight is applied. Some preliminary results of an experiment performed with the 235U target are presented and briefly discussed. The yield of "scission" neutrons has been estimated in the framework of a simple evaporation model and was found not to exceed 5% of the total neutron yield. Including an assumed of anisotropy of the fission neutron angular distribution in the center-of-mass system of fission fragments into the model calculation leads to an increase in the "scission" neutron yields inferred from the data.

Vorobyev, A. S.; Shcherbakov, O. A.; Pleva, Yu. S.; Gagarski, A. M.; Val'ski, G. V.; Petrov, G. A.; Petrova, V. I.; Zavarukhina, T. A.

2009-01-01

36

Measurements of angular and energy distributions of prompt neutrons from thermal neutron-induced fission  

Microsoft Academic Search

The experimental setup and methodology used to measure prompt neutron angular and energy distributions from thermal neutron-induced fission are described. The neutrons are detected using two scintillation detectors, while the fission fragments are detected by multi-wire proportional detectors in conjunction with the TOF technique. To separate events corresponding to neutrons and gamma-quanta, a double discrimination by the pulse shape and

A. S. Vorobyev; O. A. Shcherbakov; Yu. S. Pleva; A. M. Gagarski; G. V. Val'Ski; G. A. Petrov; V. I. Petrova; T. A. Zavarukhina

2009-01-01

37

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

NASA Technical Reports Server (NTRS)

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.

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

1983-01-01

38

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

SciTech Connect

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

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

2013-07-01

39

Screening and asymptotic decay of pair distributions in asymmetric electrolytes  

NASA Astrophysics Data System (ADS)

An accurate description of the screening behavior of asymmetric binary electrolyte solutions is obtained by applying the dressed ion theory to acquire the three leading terms in the asymptotic decay of the radial pair distribution function gij(r) at large distances r. These terms give a surprisingly good representation of the distribution function for quite small r values. A minimum of two asymptotic terms are needed for representing gij(r) at moderately large r in a quite wide concentration range. The relationships between the large r asymptotic behavior of charge-charge, density-density, and charge-density correlations are investigated by means of the dressed ion distribution functions. The role that the dielectric response function of the electrolyte plays for the asymptotic behavior is illuminated and the relationship between this function and the dressed ion charge distributions is given. Ionic effective charges, effective permittivities, and decay lengths and their higher order analogues are calculated for 1:2 electrolytes using the hypernetted chain approximation.

Ulander, Johan; Kjellander, Roland

1998-12-01

40

Contributions of different neutron pairs in different approaches for neutrinoless double beta decay  

E-print Network

The methods used till now to calculate the neutrinoless double beta decay matrix elements are: the Quasiparticle Random Phase Approximation (QRPA), the Shell Model (SM), the angular momentum projected Hartee-Fock-Bogoliubov approach (HFB) and the Interacting Boson Model (IBM). The different approaches are compared specifically concerning the the angular momenta and parities of the neutron pairs, which are changed into two protons by the $0\

Alberto Escuderos; Amand Faessler; Vadim Rodin; Fedor Simkovic

2010-06-07

41

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

42

Fission meter and neutron detection using poisson distribution comparison  

DOEpatents

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

Rowland, Mark S; Snyderman, Neal J

2014-11-18

43

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

E-print Network

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

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

2014-09-24

44

S-pairing in neutron matter: I. Correlated basis function theory  

NASA Astrophysics Data System (ADS)

S-wave pairing in neutron matter is studied within an extension of correlated basis function (CBF) theory to include the strong, short range spatial correlations due to realistic nuclear forces and the pairing correlations of the Bardeen, Cooper and Schrieffer (BCS) approach. The correlation operator contains central as well as tensor components. The correlated BCS scheme of [S. Fantoni, Nucl. Phys. A 363 (1981) 381], developed for simple scalar correlations, is generalized to this more realistic case. The energy of the correlated pair condensed phase of neutron matter is evaluated at the two-body order of the cluster expansion, but considering the one-body density and the corresponding energy vertex corrections at the first order of the Power Series expansion. Based on these approximations, we have derived a system of Euler equations for the correlation factors and for the BCS amplitudes, resulting in correlated nonlinear gap equations, formally close to the standard BCS ones. These equations have been solved for the momentum independent part of several realistic potentials (Reid, Argonne v and Argonne v) to stress the role of the tensor correlations and of the many-body effects. Simple Jastrow correlations and/or the lack of the density corrections enhance the gap with respect to uncorrelated BCS, whereas it is reduced according to the strength of the tensor interaction and following the inclusion of many-body contributions.

Fabrocini, Adelchi; Fantoni, Stefano; Illarionov, Alexey Yu.; Schmidt, Kevin E.

2008-05-01

45

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

Microsoft Academic Search

Classical Non-Destructive Assay (NDA) Passive Neutron Coincidence Counting (PNCC) and Differential Die-Away (DDA) active neutron interrogation techniques [1, 2] are well suited for determining the gross matrix correction factors for homogenous mass distributions of Special Nuclear Material (SNM) within an interfering waste drum matrix. These measured passive and active matrix correction factors are crucial in quantifying the SNM mass, associated

Marcel F. Villani; Stephen Croft; Eloisa Alvarez; Colin G. Wilkins; Dave Stamp; John Fisher; Alessandro Ambrifi; Gianluca Simone; Ludovic C. Bourva

2008-01-01

46

Temperature effects on atomic pair distribution functions of melts  

SciTech Connect

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

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

2014-02-14

47

Proton-proton pair distribution in dense fluid hydrogen  

NASA Astrophysics Data System (ADS)

Recent experiments on hydrogen at very high pressures have stimulated new quantum statistical studies of this simplest Coulomb system since a transition from nonconducting to metallic behavior occurs at Mbar pressures which is forced by drastic changes of the electronic and structural properties in the molecular system with increasing density. The variation of the thermodynamic and structural properties as a function of the density and temperature can be studied within molecular dynamics and Monte Carlo simulations as well as within analytical approaches such as integral equation techniques. In the region where hydrogen molecules still dominate the physical behavior, the proton-proton pair distribution function is determined both from a modified hypernetted chain approximation which starts with effective intermolecular and interatomic potentials in the neutral system, and a wave-packet molecular dynamics simulation with the Coulomb interaction between protons and electrons as the basic interaction. Comparison of both complementary approaches gives hints for the validity region of the chemical picture as well as for the accuracy of computer simulations.

Nagel, Stefan; Redmer, Ronald; Rpke, Gerd; Knaup, Michael; Toepffer, Christian

1998-05-01

48

Slow neutron distribution in a temperature gradient  

SciTech Connect

A set of equations that describes the diffusion of thermal neutrons is obtained from the energy-dependent Boltzmann equation. These equations are analogous to the phenomenological laws of the thermodynamic theory of irreversible processes and show, for instance, that as a temperatur gradient produces a neutron current (Soret effect), a density gradient yields an energy flow (Dufour effect). The method is applied to the ''two-temperature problem'' in order to gain better insight into the thermal diffusion phenomenon. The thermal diffusion of neutrons is shown to strongly depend on the scattering law of the two media where neutrons diffuse, and it is determined that some of the conclusions previously obtained are valid only for the case of a heavy gas moderator with the scat tering cross section independent of the energy.

Molinari, V.G.; Pollachini, L.

1985-12-01

49

Pair distribution function study on compression of liquid gallium  

SciTech Connect

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

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

2008-01-01

50

ON THE MASS DISTRIBUTION AND BIRTH MASSES OF NEUTRON STARS  

SciTech Connect

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

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

2012-09-20

51

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

E-print Network

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

Z. Kovacs; K. S. Cheng; T. Harko

2009-11-06

52

Current Density and Angular Distribution of Neutrons Emitted During Scission  

NASA Astrophysics Data System (ADS)

A time-dependent approach to the angular distribution of the scission neutrons with respect to the fission axis based on a recently developed dynamical scission model is presented. It implies the numerical solution of the bi-dimensional time-dependent Schrdinger equation with time-dependent potential for the motion of a neutron inside a nucleus that undergoes fission. The time evolution is calculated from the configuration with a minimum neck radius (?i), the start of the scission process, to the configuration of two just-separated fragments (?f), the end of the scission process. The resulting neutron wave packets are then propagated further in time but with the configuration of the fissioning system frozen at ?f. The numerical solutions at a given time t are used to calculate the current density Dbarem(?,z,t), a key quantity in the angular distribution evaluation. We investigate the nucleus 236U at two mass asymmetries defined by the light fragment mass AL=70 and 96. The number of neutrons that leave a sphere of radius R=30 fm (a test is done with R=40 fm) around the fissioning nucleus in a solid angle d? and in a time interval dt, d?sc/d?, is calculated. The integration in time of this quantity from 0 to ? gives the angular distribution. In practice we could only reach Tmax=410-21 sec. At this time however the majority of the scission neutrons left the sphere. The scission neutron emission is found to take place mainly along the fission axis with a small preference for the light fragment similar with what is experimentally observed for all prompt neutrons. A ratio ?L/?H close to the experimental value (1.41) is obtained. We concluded that the distinction between scission and evaporated neutrons, based on their angular distribution, is more challenging than expected.

Carjan, N.; Rizea, M.

2014-04-01

53

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

PubMed

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

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

2000-01-01

54

Neutron density distributions of neutron-rich nuclei studied with the isobaric yield ratio difference  

NASA Astrophysics Data System (ADS)

The isobaric yield ratio difference (IBD) between two reactions of similar experimental setups is found to be sensitive to nuclear density differences between projectiles. In this article, the IBD probe is used to study the density variation in neutron-rich 48Ca . By adjusting diffuseness in the neutron density distribution, three different neutron density distributions of 48Ca are obtained. The yields of fragments in the 80 A MeV 40, 48Ca + 12C reactions are calculated by using a modified statistical abrasion-ablation model. It is found that the IBD results obtained from the prefragments are sensitive to the density distribution of the projectile, while the IBD results from the final fragments are less sensitive to the density distribution of the projectile.

Ma, Chun-Wang; Bai, Xiao-Man; Yu, Jiao; Wei, Hui-Ling

2014-09-01

55

Neutron Density Distributions of Neutron-Rich Nuclei Studied with the Isobaric Yield Ratio Difference  

E-print Network

The isobaric yield ratio difference (IBD) between two reactions of similar experimental setups is found to be sensitive to nuclear density differences between projectiles. In this article, the IBD probe is used to study the density variation in neutron-rich $^{48}$Ca. By adjusting diffuseness in the neutron density distribution, three different neutron density distributions of $^{48}$Ca are obtained. The yields of fragments in the 80$A$ MeV $^{40, 48}$Ca + $^{12}$C reactions are calculated by using a modified statistical abrasion-ablation model. It is found that the IBD results obtained from the prefragments are sensitive to the density distribution of the projectile, while the IBD results from the final fragments are less sensitive to the density distribution of the projectile.

Chun-Wang Ma; Xiao-Man Bai; Jiao Yu; Hui-Ling Wei

2014-09-09

56

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

SciTech Connect

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

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

1999-10-03

57

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

E-print Network

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

A. V. Afanasjev; S. E. Agbemava; D. Ray; P. Ray

2015-01-17

58

Neutron drip line: Single-particle degrees of freedom and pairing properties as sources of theoretical uncertainties  

NASA Astrophysics Data System (ADS)

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

Afanasjev, A. V.; Agbemava, S. E.; Ray, D.; Ring, P.

2015-01-01

59

Density fluctuations and the pair distribution function V. A. Levashov  

E-print Network

with experimental and modeling results for powdered crystalline nickel, where we find an undiminished fluctuation to neutron diffraction data on nickel. Results are shown to be similar for crystals and for a single atom in a glass. DOI: 10.1103/PhysRevB.72.024111 PACS number s : 61.12.Bt, 61.10.Eq, 63.20. e I. INTRODUCTION

Thorpe, Michael

60

A preliminary inter-centre comparison study for photon, thermal neutron and epithermal neutron responses of two pairs of ionisation chambers used for BNCT  

Microsoft Academic Search

The dual ionisation chamber technique is the recommended method for mixed field dosimetry of epithermal neutron beams. This paper presents initial data from an ongoing inter-comparison study involving two identical pairs of ionisation chambers used at the BNCT facilities of Petten, NL and of the University of Birmingham, UK. The goal of this study is to evaluate the photon, thermal

Antoaneta Roca; Yuan-Hao Liu; Cecile Wojnecki; Stuart Green; Sander Nievaart; Zamir Ghani; Ray Moss

2009-01-01

61

A preliminary inter-centre comparison study for photon, thermal neutron and epithermal neutron responses of two pairs of ionisation chambers used for BNCT.  

PubMed

The dual ionisation chamber technique is the recommended method for mixed field dosimetry of epithermal neutron beams. This paper presents initial data from an ongoing inter-comparison study involving two identical pairs of ionisation chambers used at the BNCT facilities of Petten, NL and of the University of Birmingham, UK. The goal of this study is to evaluate the photon, thermal neutron and epithermal neutron responses of both pairs of TE(TE) (Exradin T2 type) and Mg(Ar) (Exradin M2 type) ionisation chambers in similar experimental conditions. At this stage, the work has been completed for the M2 type chambers and is intended to be completed for the T2 type chambers in the near future. PMID:19376717

Roca, Antoaneta; Liu, Yuan-Hao; Wojnecki, Cecile; Green, Stuart; Nievaart, Sander; Ghani, Zamir; Moss, Ray

2009-07-01

62

Statistical Theory of Nuclear Fission and Prompt Neutron Distribution  

Microsoft Academic Search

It is shown that the statistical theory of nuclear fission is consistent with the recent experimental results of prompt neutron distribution in fission if we assume the existence of some constraint in the process of approaching equilibrium which controls the partition of excitation energy between the two fragments.

Peter Fong

1961-01-01

63

Water distribution measurement for a PEMFC through neutron radiography  

Microsoft Academic Search

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

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

2007-01-01

64

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

PubMed

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

Cauwels, Vanessa; Vanhavere, Filip; Reginatto, Marcel

2014-10-01

65

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

PubMed

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

Tanaka, Kenichi; Endo, Satoru; Hoshi, Masaharu

2010-01-01

66

Kinematic distributions for electron pair production by muons  

NASA Technical Reports Server (NTRS)

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

Linsker, R.

1972-01-01

67

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

E-print Network

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

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

2015-01-01

68

Scaling neutron absorbed dose distributions from one medium to another  

SciTech Connect

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

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

1982-11-01

69

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

SciTech Connect

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

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

2011-01-01

70

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

Microsoft Academic Search

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

T. Bereznai; T. D. Mac Mahon

1978-01-01

71

A comparison between two evaluations of neutron multiplicity distributions  

E-print Network

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

Lestone, J P

2014-01-01

72

A comparison between two evaluations of neutron multiplicity distributions  

E-print Network

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

J. P. Lestone

2014-09-18

73

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

SciTech Connect

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

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

2011-10-15

74

Pairing and continuum effects on low-frequency quadrupole vibrations in deformed Mg isotopes close to the neutron drip line  

E-print Network

Low-frequency quadrupole vibrational modes in deformed $^{36,38,40}$Mg close to the neutron drip line are studied by means of the quasiparticle-random-phase approximation based on the coordinate-space Hartree-Fock-Bogoliubov formalism. Strongly collective $K^{\\pi}=0^{+}$ and $2^{+}$ excitation modes carrying 10-20 Weisskopf units in the intrinsic isoscalar quadrupole transition strengths are obtained at about 3 MeV. There are two reasons for the enhancement of the transition strengths. First, the quasiparticle wave functions generating these modes possess spatially very extended structure. The asymptotic selection rules characterizing the $\\beta$ and $\\gamma$ vibrations in stable deformed nuclei are thus strongly violated. Second, the dynamic pairing effects act strongly to enhance the collectivity of these modes. It is suggested that the lowest $K^{\\pi}=0^{+}$ collective mode is a particularly sensitive indicator of the nature of pairing correlations in deformed nuclei close to the neutron drip line.

K. Yoshida; M. Yamagami; K. Matsuyanagi

2006-05-27

75

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

E-print Network

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

Guang-Peng Zhang

2014-06-20

76

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

Microsoft Academic Search

The tunnelling and torsional motions of methyl groups in lithium acetate dihydrate (CH3COOLi2H2O) have been studied in detail by incoherent inelastic neutron scattering. The results are interpreted by a model of pairs of methyl groups performing a coupled tunnelling motion. The strength of the coupling term is estimated to be about twice as strong as the threefold hindering barrier for

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

1984-01-01

77

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

NASA Astrophysics Data System (ADS)

The tunnelling and torsional motions of methyl groups in lithium acetate dihydrate (CH3COOLi2H2O) have been studied in detail by incoherent inelastic neutron scattering. The results are interpreted by a model of pairs of methyl groups performing a coupled tunnelling motion. The strength of the coupling term is estimated to be about twice as strong as the threefold hindering barrier for the single particle motion.

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

1984-03-01

78

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

DOEpatents

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

Crane, Thomas W. (Los Alamos, NM)

1986-01-01

79

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

DOEpatents

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

Crane, T.W.

1983-12-21

80

Entangled-Pair Transmission Improvement Using Distributed Phase-Sensitive Amplification  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

81

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

Microsoft Academic Search

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

Ahmad Salah Masadeh

2008-01-01

82

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

SciTech Connect

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

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

2008-07-01

83

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

NASA Astrophysics Data System (ADS)

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

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

2007-07-01

84

Angular distribution in the neutron-induced fission of actinides  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

85

Applicability of paired graphite and A150 plastic proportional counters to neutron- and photon-dose determinations  

SciTech Connect

A pair of miniature proportional counters, one with graphite walls and one with walls of A150 plastic, were used to separate neutron and photon dose components in a mixed field. Data were simultaneously acquired for both counters in a combined field of 14.8-MeV neutrons and /sup 60/Co photons in three overlapping dispersions. A previously acquired /sup 60/Co spectrum in the graphite counter was used to normalize a mixed field spectrum, thereby determining the photon dose. This dose normalized a photon-only spectrum in the A150-walled counter, which was then subtracted from the mixed field spectrum. Comparison of these results to ionization chamber results is discussed.

DeLuca, P.M. Jr.; Schell, M.C.; Pearson, D.W.; Attix, F.H.

1981-01-01

86

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

SciTech Connect

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.

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

2007-11-15

87

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

NASA Astrophysics Data System (ADS)

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

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

2002-04-01

88

Simple Method to Compute Pair Distribution Function from Molecular Dynamics Data  

NASA Astrophysics Data System (ADS)

A new simple method to compute the pair distribution function from molecular dynamics data is proposed, which is applied to two examples to determine the crystal structure in the solid phase. It is found that the short-range order of a two-dimensional repulsive system is a triangular lattice, and the crystal structure of a three-dimensional finite-range potential (including both repulsive and attractive parts) system is a hexagonal-close-packed lattice.

Uno, Toshiaki; Sogo, Kiyoshi

2015-04-01

89

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

NASA Technical Reports Server (NTRS)

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

Campbell, C. W.

1983-01-01

90

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

PubMed

The aim of this study was to determine the in-phantom thermal neutron distribution derived from neutron beams for intraoperative boron neutron capture therapy (IOBNCT). Gold activation wires arranged in a cylindrical water phantom with (void-in-phantom) or without (standard phantom) a cylinder styrene form placed inside were irradiated by using the epithermal beam (ENB) and the mixed thermal-epithermal beam (TNB-1) at the Japan Research Reactor No 4. With ENB, we observed a flattened distribution of thermal neutron flux and a significantly enhanced thermal flux delivery at a depth compared with the results of using TNB-1. The thermal neutron distribution derived from both the ENB and TNB-1 was significantly improved in the void-in-phantom, and a double high dose area was formed lateral to the void. The flattened distribution in the circumference of the void was observed with the combination of ENB and the void-in-phantom. The measurement data suggest that the ENB may provide a clinical advantage in the form of an enhanced and flattened dose delivery to the marginal tissue of a post-operative cavity in which a residual and/or microscopically infiltrating tumour often occurs. The combination of the epithermal neutron beam and IOBNCT will improve the clinical results of BNCT for brain tumours. PMID:12171329

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

2002-07-21

91

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

92

Radial Flux Distribution of Low-Energy Neutrons.  

ERIC Educational Resources Information Center

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

Higinbotham, J.

1979-01-01

93

The influence of pairing and nuclear structure on the thermal-neutron-induced fission of 235 U  

Microsoft Academic Search

The mass separated fission product beam provided by the mass separator Lohengrin has been used to determine the nuclear charge distribution for the thermal-neutron-induced fission of235U for all light fission products in the region 80?A?107. The measurements were performed at the most probable kinetic energy of the fission products. By using the known fission product mass yields, the independent yields

H.-G. Clerc; W. Lang; H. Wohlfarth; K.-H. Schmidt; H. Schrader; K. E. Pferdekmper; R. Jungmann

1975-01-01

94

Production, distribution and applications of californium-252 neutron sources  

Microsoft Academic Search

The radioisotope 252Cf is routinely encapsulated into compact, portable, intense neutron sources with a 2.6-yr half-life. A source the size of a persons little finger can emit up to 1011 neutrons s?1. Californium-252 is used commercially as a reliable, cost-effective neutron source for prompt gamma neutron activation analysis (PGNAA) of coal, cement and minerals, as well as for detection and

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

2000-01-01

95

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

SciTech Connect

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

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

2000-08-15

96

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

E-print Network

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

Sakshi Gautam

2011-07-28

97

Local structure of ball-milled carbons for lithium ion batteries: A pair distribution function analysis  

SciTech Connect

The local atomic structure of ball-milled carbons was investigated by radial distribution function (RDF) analysis using pulsed time-of-flight neutron diffraction. The results exhibit a gradual loss of long-range order as a function of milling time. Modeling of the elastic structure factors and of the differential correlation functions identified the structure of ball-milled carbons as finite-size graphene fragments whose size decreases continuously with milling time. The large increase in lithium reversible capacity after 20 hours of milling was correlated with the loss of interlayer correlation between graphite flakes, similar to the structure of hard carbons in the House of Cards model.

Claye, A.; Zhou, P.; Fischer, J.E.; Disma, F.; Tarascon, J.M.

1998-07-01

98

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

E-print Network

The mass and kinetic energy distribution of nuclear fragments from thermal neutron-induced fission of 235U 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.

Montoya, M; Saettone, E

2007-01-01

99

Effects of Neutron Emission on Fragment Mass and Kinetic Energy Distribution from Thermal Neutron-Induced Fission of 235U  

NASA Astrophysics Data System (ADS)

The mass and kinetic energy distribution of nuclear fragments from thermal neutron-induced fission of 235U(nth,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.

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

2007-10-01

100

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

E-print Network

The mass and kinetic energy distribution of nuclear fragments from thermal neutron-induced fission of 235U 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.

M. Montoya; J. Rojas; E. Saettone

2007-11-06

101

Distribution of Partial Neutron Widths for Nuclei Close to a Maximum of the Neutron Strength Function  

NASA Astrophysics Data System (ADS)

For nuclei near a maximum of the neutron strength function, the secular dependence on energy E of s-wave partial neutron widths differs from the canonical form E. We derive the universal form of that dependence and show that it is expected to significantly influence the analysis of neutron resonance data.

Weidenmller, Hans A.

2010-12-01

102

Structure of Nanocrystalline Ti3C2 MXene Using Atomic Pair Distribution Function  

NASA Astrophysics Data System (ADS)

The structures of nanocrystalline pristine, potassium hydroxide and sodium acetate intercalated new two-dimensional materials Ti3C2 MXenes were studied using the x-ray atomic pair distribution function technique. Pristine MXene has a hexagonal structure with a =b=3.0505(5) , c =19.86(2) (S.G. P63/mmc No. 194). Both hydroxyl and fluoride terminating species are present. The intercalation of K+ or Na+ ions expands the Ti3C2 layers perpendicular to the planes but shrinks the in-plane a and b lattice parameters.

Shi, Chenyang; Beidaghi, Majid; Naguib, Michael; Mashtalir, Olha; Gogotsi, Yury; Billinge, Simon J. L.

2014-03-01

103

Real distributed vibration sensing with high frequency response based on pulse pair  

NASA Astrophysics Data System (ADS)

In conventional phase-sensitive optical time domain reflectometry (?-OTDR), the length of sensing fiber mainly determines the repetition rate of probe light pulses, which limits the extent of detectable frequency range. Moreover, averaging method, which is adopted to enhance the location signal-to-noise-ratio (SNR), further decreases the maximum detectable frequency. This paper demonstrates a distributed vibration sensor with satisfied location SNR and extended frequency response range by using a probe pulse pair with a frequency difference. Experimental results show that this method is able to break the trade-off between the given sensing fiber length and the traditional maximum detectable frequency response of ?-OTDR system.

He, Qian; Zhu, Tao; Xiao, Xianghui; Diao, Dongmei; Huang, Wei; Bao, Xiaoyi

2014-05-01

104

High-energy neutron depth-dose distribution experiment.  

PubMed

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

Ferenci, M S; Hertel, N E

2003-01-01

105

Spatial and energy distributions of fast monoenergetic neutrons in an infinite plane slab of material  

Microsoft Academic Search

The actual neutron energy and spatial distributions in a medium arising from unidirectional normally incident monoenergetic neutrons has been theoretically calculated using statistical techniques. The present medium of interest is an infinite plane slab of material. The nutron beam is incident isotropically on one face and the differential flux at different locations along the slab's thickness has been calculated. Effects

M. A. Roomyia; L. M. Abdelwahab; Younis S. Selim

1996-01-01

106

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

NASA Astrophysics Data System (ADS)

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.

Sakurai, Yoshinori; Ono, Koji

2007-12-01

107

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

PubMed

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. PMID:18065847

Sakurai, Yoshinori; Ono, Koji

2007-12-21

108

High-axial-resolution distributed lateral displacement measurement based on differential pulse-width pair BOTDA  

NASA Astrophysics Data System (ADS)

We report for the first time to the best of our knowledge a distributed lateral displacement sensor through measuring high-spatial-resolution axial strain based on differential pulse-width pair Brillouin optical time-domain analysis. With the assumption of a sine-shape displacement caused by a small surface deformation, the relationship between the axial strain and the lateral displacement of a flat plate is established, based on which a distributed lateral displacement measurement is realized. In experiment, a periodic lateral displacement of a flat plate is constructed through a ripple spring by applying side pressure on them, and the axial strain measurement with a 2-cm spatial resolution is performed by using a differential pulse pair of 8/8.2 ns. Using two types of ripple springs, measurements of lateral displacements with periods of 30 and 32.5 mm are demonstrated with a maximum displacement of 0.43 mm and a minimum measurable displacement of ~40 ?m.

Dong, Yongkang; Bao, Xiaoyi; Chen, Liang

2011-05-01

109

Delayed neutrons as a probe of nuclear charge distribution in fission of heavy nuclei by neutrons  

E-print Network

A method of the determination of cumulative yields of delayed neutron precursors is developed. This method is based on the iterative least-square procedure applied to delayed neutron decay curves measured after irradiation of sup 2 sup 3 sup 5 U sample by thermal neutrons. Obtained cumulative yields in turns were used for deriving the values of the most probable charge in low-energy fission of the above-mentioned nucleus.

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

2001-01-01

110

Design, Manufacturing and Performance of a Pair of Superconducting Solenoids for a Neutron Spin-Echo Spectrometer at the SNS  

Microsoft Academic Search

A Neutron spin-echo (NSE) spectrometer of the next generation is under construction at the Spallation Neutron Source (SNS) in Oak Ridge, USA. A NSE spectrometer measures small velocity changes of the neutrons encoded by the neutrons spin clock at a sample while the Neutron spin precesses in large magnetic fields following Bloch's equation. This instrument will be the best of

Wolfgang Walter; Cristian Boffo; Markus Borlein; Tadeusz Kozielewski; Michael Monkenbusch; Michael Ohl; Amitesh Paul; Bernhard Schrauth; Guenther Sikler; Christoph Tiemann

2009-01-01

111

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

Microsoft Academic Search

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

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

2007-01-01

112

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

PubMed

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

Lebreton, L; Zimbal, A; Thomas, D

2007-01-01

113

Distribution of mass in thermal-neutron-induced fission of 257Fm  

Microsoft Academic Search

Fission yields were measured radiochemically for mass chains 112, 127, 132, and 140 in thermal-neutron-induced fission of 257Fm. These yields indicate a single-peaked (symmetric) mass distribution. Comparison is made with the distribution deduced from kinetic-energy measurements, and the effects of neutron emission from the fission fragments are considered. NUCLEAR REACTIONS, FISSION 257Fm(n, f), E=0.025 eV; measured radiochemical mass yields.

K. F. Flynn; J. E. Gindler; L. E. Glendenin

1975-01-01

114

Neutron density distributions from antiprotonic 208Pb and 209Bi atoms  

E-print Network

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

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

2007-02-26

115

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

SciTech Connect

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

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

2012-06-05

116

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

PubMed

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

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

2015-04-01

117

Investigation of the Negative Thermal Expansion Mechanism of Zeolite Chabazite Using the Pair Distribution Function Method  

SciTech Connect

We have used the pair distribution function (PDF) method to gain insight into the mechanism of contraction of zeolite chabazite. Using this method we followed how the interatomic distances of the local structure changed with temperature. By optimization of the structure by free energy minimization and using the Reverse Monte Carlo technique we were able to find structural models at low and at high temperatures that agreed quantitatively with our experimental PDFs. From these models we conclude that the mechanism of contraction with temperature cannot involve rocking of the tetrahedra as rigid unit modes as there are distortions of the tetrahedra with temperature (indicating internal vibrations) and also that the mechanism of contraction probably involves a mode that translates along the Si-O3-Si-O4-Si linkages inside of the D6R of zeolite chabazite.

Martinez-Inesta, Maria M.; Lobo, Raul F. (Delaware)

2008-06-18

118

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

119

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

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

120

MEASUREMENTS OF THE H(N,N) ANGULAR DISTRIBUTION OF 10MEV NEUTRON ENERGY.  

SciTech Connect

Relative measurements of the cross section for scattering of neutrons by protons have been made at 10 MeV neutron energy for center-of-mass neutron scattering angles from 60' to 180'. The measurements were made using the Ohio University Accelerator Laboratory's tandem Van de Graaff accelerator with the D(d,n) reaction as the neutron source. The data are in good agreement with predictions from the phase shift analyses of Arndt, the groups of Nijmegen and Bonn, and the ENDF/B-V evaluation. The ENDF/B-VI evaluation does not appear to have the same angular dependence as the data. KEYWORDS: hydrogen cross section, neutron cross section standard, hydrogen angular distribution standard

Boukharouba, N.; Bateman, F. B. (Fred B.); Brient, C. E.; Carlson, A. D.; Grimes, S. M.; Massey, T. N.; Haight, Robert C.; Carlson, Allan D.; Wasson, O. A.

2001-01-01

121

Effects of Neutron Emission on Fragment Mass and Kinetic Energy Distribution from Thermal Neutron-Induced Fission of 235U  

Microsoft Academic Search

The mass and kinetic energy distribution of nuclear fragments from thermal neutron-induced fission of 235U(nth,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

M. Montoya; J. Rojas; E. Saetone

2007-01-01

122

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

PubMed Central

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

Weber, Anton

2013-01-01

123

Spatial and energy distributions of fast monoenergetic neutrons in an infinite plane slab of material  

NASA Astrophysics Data System (ADS)

The actual neutron energy and spatial distributions in a medium arising from unidirectional normally incident monoenergetic neutrons has been theoretically calculated using statistical techniques. The present medium of interest is an infinite plane slab of material. The nutron beam is incident isotropically on one face and the differential flux at different locations along the slab's thickness has been calculated. Effects of inelastic scattering have been also considered. Comparison with other calculations is given.

Roomyia, M. A.; Abdelwahab, L. M.; Selim, Younis S.

1996-05-01

124

ON ANGULAR DISTRIBUTION OF NEUTRONS IN C¹³(d,n)N¹⁴ REACTION  

Microsoft Academic Search

Calculations were made of the angular distribution of neutrons in the C\\/; sup 13\\/(d,n)N¹⁴ reaction, experimentally studied by L. L. Green et al. ; (Proc. Phys. Soc. A68, 386, 1955). with incident deuterons of 0.B6 Mev and ; four-group neutron resolution (g, g, g, and g), where ; first group corresponds to the finite nucleus N¹⁴ groundstate and the rest

T. L. Abelishvili; T. G. Gachechiladze; O. M. Mdivani

1960-01-01

125

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

PubMed

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

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

2011-12-01

126

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

Microsoft Academic Search

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

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

1975-01-01

127

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

128

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

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. 28:3421-3437), was obtained from the analysis of neutron diffraction data of DOPC hydrated with a D20/H20 mixture. The water distribution is described accurately by a pair of Gaussian functions each located at a position Zw = 22.51 +/- 0.77 A from the bilayer center with 1/e-half widths of Aw = 4.63 +/- 0.48A. We present the relative absolute neutron and x-ray structure factors of DOPC at 66% RH that will be used to solve the complete structure of DOPC which will be presented in a later paper of this series. PMID:1932548

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

1991-01-01

129

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

E-print Network

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

130

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

SciTech Connect

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

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

2008-01-01

131

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

USGS Publications Warehouse

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

Hietanen, A.

1971-01-01

132

235U(n, f) Fragment mass-, kinetic energy- and angular distributions for incident neutron energies between thermal and 6 MeV  

NASA Astrophysics Data System (ADS)

Fission fragment energies and emission angles have been measured for 235U(n, f) in the neutron energy range from thermal to 6 MeV in steps of 0.5 MeV. The pre-neutron emission mass distributions were evaluated and described by a five-gaussian representation. The resulting parameters show a sudden change in their neutron energy dependence between 1.5 and 2.0 MeV, which might be due to pair breaking. From the total kinetic energy the sum of the deformations of the two fragments was evaluated. Clear proton pairing effects are visible since the even-proton fragments are less deformed than neighbouring odd-proton fragments. The present data confirm also that the TKE averaged over all fragments drops with excitation energy above 4 MeV. This behaviour is mainly due to drastic changes in overlineTKE as function of mass split. At a yield level of 10 -6 per MeV of the light fragment kinetic energy cold fragmentation was observed for light fragment masses 87 to 110. In this mass region the light fragments are prolate and have a ground state electric quadrupole moment larger than ?1 b. The angular distributions of fission fragments showed no mass dependence.

Straede, Ch.; Budtz-Jrgensen, C.; Knitter, H.-H.

1987-01-01

133

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

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

134

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

SciTech Connect

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

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

1988-09-01

135

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

SciTech Connect

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

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

2006-12-04

136

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

SciTech Connect

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

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

2009-10-25

137

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

SciTech Connect

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

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

2005-05-24

138

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

Microsoft Academic Search

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

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

2000-01-01

139

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

Microsoft Academic Search

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

H. Matsuura; K. Funakoshi; Y. Nakao

2003-01-01

140

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

141

Nuclear charge distribution of heavy fission fragments from thermal-neutron-induced fission of 235 U  

Microsoft Academic Search

Fragments from thermal-neutron induced fission of235U have been separated by a mass spectrometer with respect to their masses and kinetic energies within 1 sec. The separation principles are briefly described. For masses 130 to 139 amu the charge distributions have been determined by counting the number of beta tracks emitted from the individual mass selected fission fragments in a nuclear

Ewald Konecny; Helmut Gunther; Helmut Rsler; Gnter Siegert; Heinz Ewald

1970-01-01

142

Ion distribution in multilayers of weak polyelectrolytes: A neutron reflectometry study  

E-print Network

Ion distribution in multilayers of weak polyelectrolytes: A neutron reflectometry study Oleh M polyelectrolyte chains is the main driving force for the formation of polyelectrolyte multilayers PEMs . The al-by-layer LbL tech- nique can produce thin multilayer films with well-defined composition, thickness

Barrett, Christopher

143

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

E-print Network

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

Sparks, Donald L.

144

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

NASA Astrophysics Data System (ADS)

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

Key, Baris

145

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

Microsoft Academic Search

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, -4rρ, 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,

S. Billinge; C. L. Farrowa

2009-01-01

146

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

Microsoft Academic Search

The size-dependent structure of CdSe nanoparticles, with diameters ranging from 2to4nm , has been studied using the atomic pair distribution function (PDF) method. The core structure of the measured CdSe nanoparticles can be described in terms of the wurtzite atomic structure with extensive stacking faults. The density of faults in the nanoparticles is 50% . The diameter of the core

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

2007-01-01

147

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

Microsoft Academic Search

The size-dependent structure of CdSe nanoparticles, with diameters ranging from 2 to 4 nm, has been studied using the atomic pair distribution function (PDF) method. The core structure of the measured CdSe nanoparticles can be described in terms of the wurtzite atomic structure with extensive stacking faults. The density of faults in the nanoparticles is 50%. The diameter of the

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

2007-01-01

148

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

USGS Publications Warehouse

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

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

1977-01-01

149

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

PubMed Central

We present a novel voxel-based connectivity approach for paired functional magnetic resonance imaging (fMRI) data collected under two different conditions labeled the Coupled Intrinsic Connectivity Distribution (coupled-ICD). Our proposed method jointly models both conditions to incorporate additional paired information into the connectivity metric. Voxel-based connectivity holds promise as a clinical tool to characterize a wide range of neurological and psychiatric diseases, and monitor their treatment. As such, examining paired connectivity data such as scans acquired pre- and post-intervention is an important application for connectivity methodologically. When presented with data from paired conditions, conventional voxel-based methods analyze each condition separately. However, summarizing each connection separately can misrepresent patterns of changes in connectivity. We show that commonly used methods can underestimate functional changes and subsequently introduce and evaluate our solution to this problem, the coupled-ICD metric, using two studies: 1) healthy controls scanned awake and under anesthesia, and 2) cocaine-dependent subjects and healthy controls scanned while being presented with relaxing or drug-related imagery cues. The coupled-ICD approach detected differences between paired conditions in similar brain regions as the conventional approaches while also revealing additional changes in regions not identified using conventional voxel-based connectivity analyses. Follow-up seed-based analyses on data independent from the voxel-based results also showed connectivity differences between conditions in regions detected by coupled-ICD. This approach of jointly analyzing paired resting-state scans provides a new and important tool with many applications for clinical and basic neuroscience research. PMID:24676034

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

2014-01-01

150

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

SciTech Connect

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)

Liang, C.; Pavlou, A. T.; Ji, W. [Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180 (United States)

2013-07-01

151

Gravitational Microlensing by Neutron Stars and Radio Pulsars: Event Rates, Timescale Distributions, and Mass Measurements  

NASA Astrophysics Data System (ADS)

We investigate properties of Galactic microlensing events in which a stellar object is lensed by a neutron star. For an all-sky photometric microlensing survey, we determine the number of lensing events caused by ? {{10}5} potentially observable radio pulsars to be ? 0.2 y{{r}-1} for 1010 background stellar sources. We expect a few detectable events per year for the same number of background sources from an astrometric microlensing survey. We show that such a study could lead to precise measurements of radio pulsar masses. For instance, if a pulsar distance could be constrained through radio observations, then its mass would be determined with a precision of ? 10%. We also investigate the timescale distributions for neutron star events, finding that they are much shorter than had been previously thought. For photometric events toward the Galactic center that last ?15 days, around 7% will have a neutron star lens. This fraction drops rapidly for longer timescales. Away from the bulge region we find that neutron stars will contribute ? 40% of the events that last less than ?10 days. These results are in contrast to earlier work which found that the maximum fraction of neutron star events would occur on timescales of hundreds of days.

Dai, S.; Smith, M. C.; Lin, M. X.; Yue, Y. L.; Hobbs, G.; Xu, R. X.

2015-04-01

152

On the theory of phase transitions in dense neutron matter with generalized Skyrme interactions and anisotropic spin-triplet p-wave pairing in strong magnetic field  

NASA Astrophysics Data System (ADS)

In the framework of the generalized non-relativistic Fermi-liquid approach we study phase transitions in spatially uniform dense pure neutron matter from normal to superfluid states with a spin-triplet p-wave pairing (similar to anisotropic superfluid phases 3He-A1 and 3He-A2) in a steady and homogeneous strong magnetic field H (but |\\mu_{\\text{n}}| H\\ll E_{\\text{c}}<\\varepsilon_{\\text{F}}(n) , where \\mu_{\\text{n}} is the magnetic dipole moment of a neutron, E_{\\text{c}} is the cutoff energy and \\varepsilon_{\\text{F}}(n) is the Fermi energy in neutron matter with density of particles n). The previously derived general formulas (valid for the arbitrary parametrization of the effective Skyrme interaction in neutron matter) for phase transition (PT) temperatures T_{\\text{c}1,2}(n,H) (which are nonlinear functions of the density n and linear functions of the magnetic field H) are specified here for new generalized BSk20 and BSk21 parameterizations of the Skyrme forces (with additional terms dependent on the density n) in the interval 0.1\\cdot n_{0} < n<3.0\\cdot n_{0} , where n_{0}=0.17\\ \\text{fm}^{-3} is the nuclear density. Our main results are mathematical expressions and figures for PT temperatures in the absence of magnetic field, T_{\\text{c0,BSk20}}(n)< 0.17\\ \\text{MeV} and T_{\\text{c0,BSk21}}(n)< 0.064\\ \\text{MeV} (at E_{\\text{c}}=10\\ \\text{MeV} ), and T_{\\text{c1,2}}(n,H) in strong magnetic fields (which may approach to 10^{17}\\ \\text{G} or even more as in the liquid outer core of magnetars strongly magnetized neutron stars). These are realistic non-monotone functions with a bell-shaped density profile.

Tarasov, A. N.

2014-03-01

153

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

PubMed

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

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

2014-06-01

154

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

NASA Astrophysics Data System (ADS)

The average of fragment kinetic energy (E*) and the multiplicity of prompt neutrons (?) as a function of fragment mass (m*), as well as the fragment mass yield (Y(m*)) from thermal neutron-induced fission of 239Pu 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 ?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 (?E(A)). As a result of the simulation we obtain the dependence ?E*(m*) which presents an enhancement between m* = 92 and m* = 110, and a peak at m* = 121.

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

2010-08-01

155

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

SciTech Connect

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

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

2010-08-04

156

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

157

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

E-print Network

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

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

2014-12-17

158

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

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

159

The effect of approximations in the energy distributions of scattered neutrons on thermal reactor Doppler effects  

SciTech Connect

In calculations of resonance shielding and Doppler coefficients the effect of thermal motion on the energy distribution of scattered neutrons is neglected. Recent publications by Ouisloumen and Sanchez, and also by Kurchenkov and Laletin, have shown that secondary energy distributions are strongly perturbed by Doppler broadening in resonances. In the presence paper calculations of resonance absorption and Doppler effects are described. These show that in a thermal reactor spectrum the resonance absorption in U-238 is increased by about 1% at reactor operating temperatures and the Doppler effect is increased by about 9%, when the exact secondary energy distribution is used instead of the asymptotic distribution. The effect of a temperature distribution across the fuel pin is also calculated and it is shown that the usual definition of equivalent temperature is valid.

Bouland, O.; Kolesov, V.; Rowlands, J.L. [CEA, St-Paul-lez-Durance (France)

1994-12-31

160

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

NASA Astrophysics Data System (ADS)

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

Kaki, Kaori

2015-03-01

161

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

E-print Network

Field validation of a cosmic-ray neutron sensor using a distributed sensor network1 Trenton E scales has become critical5 for improved meteorological and hydrological prediction. The current is from a cosmic-ray neutron sensor placed at the center of10 the study area. We find the cosmic

Zreda, Marek

162

Nuclear-charge distribution near symmetry for thermal-neutron-induced fission of 235U  

Microsoft Academic Search

Available data concerning nuclear-charge distribution for thermal-neutron-induced fission of 235U have been evaluated for the region near symmetry (104<=A<=129, 42<=Z<=50). Evaluated data or averages are listed and are interpreted by the use of empirical ZP and A'P models. The parameters and functions derived for the two models are presented and are compared with each other and with the data. Both

Arthur C. Wahl

1985-01-01

163

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

Microsoft Academic Search

Within quantum fission theory, angular distributions of products originating from the ternary fission of nuclei that is induced\\u000a by polarized cold and thermal neutrons are investigated on the basis of a nonevaporative mechanism of third-particle emission\\u000a and a consistent description of fission-channel coupling. It is shown that the inclusion of Coriolis interaction both in the\\u000a region of the discrete and

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

2008-01-01

164

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

PubMed

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

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

2014-06-25

165

The NNLO soft function for the pair invariant mass distribution of boosted top quarks  

E-print Network

At high values of the pair invariant mass the differential cross section for top-quark pair production at hadron colliders factorizes into soft, hard, and fragmentation functions. In this paper we calculate the next-to-next-to-leading-order (NNLO) corrections to the soft function appearing in this factorization formula, thus providing the final piece needed to evaluate at NNLO the differential cross section in the virtual plus soft approximation in the large invariant-mass limit. Technically, this amounts to evaluating the vacuum expectation value of a soft Wilson loop operator built out of light-like Wilson lines for each of the four partons participating in the hard scattering process, with a certain constraint on the total energy of the soft radiation. Our result turns out to be surprisingly simple, because in the sum of all graphs the three and four parton contributions multiply color structures whose coefficients are governed by the non-abelian exponentiation theorem.

Andrea Ferroglia; Ben D. Pecjak; Li Lin Yang

2012-07-19

166

Measurement of the beam-helicity asymmetry I? in the photoproduction of ?0-pairs off the proton and off the neutron  

NASA Astrophysics Data System (ADS)

Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of neutral pion pairs in the reactions ??p?p?0?0 and ??d?(n)p?0?0, ??d?(p)n?0?0 off free protons and off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4 GeV. Circularly polarized photons were produced from bremsstrahlung of longitudinally polarized electrons and tagged with the Glasgow magnetic spectrometer. Decay photons from the ?0 mesons, recoil protons, and recoil neutrons were detected in the 4? covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. After kinematic reconstruction of the final state, excellent agreement was found between the results for free and quasi-free protons. This demonstrates that the free-nucleon behavior of such observables can be extracted from measurements with quasi-free nucleons, which is the only possibility for the neutron. Contrary to expectations, the measured asymmetries are very similar for reactions off protons and neutrons. The results are compared to the predictions from the Two-Pion MAID reaction model and (for the proton) also to the Bonn-Gatchina coupled channel analysis.

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

2013-04-01

167

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

SciTech Connect

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

Han, Jiyeon; /Rochester U.

2008-11-01

168

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

SciTech Connect

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

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

2011-03-15

169

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

E-print Network

We study Gamow-Teller strength distributions in the neutron-deficient even isotopes (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.

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

2005-10-13

170

Mass distributions for thermal-neutron-induced fission of 255Fm and 251Cf  

Microsoft Academic Search

Mass distributions for thermal-neutron-induced fission (n, f) of 255Fm and 251Cf have been determined radiochemically. Both mass distributions are asymmetric with a peak-to-valley ratio of about 2.6 for 255Fm and about 13 for 251Cf. Cross sections were determined to be 3200+\\/-320 b for 255Fm(n, f) and 5300+\\/-530 b for 251Cf(n, f). NUCLEAR REACTIONS, FISSION 255Fm(n, f), 251Cf(n, f), E=0.025 eV;

K. F. Flynn; J. E. Gindler; R. K. Sjoblom; L. E. Glendenin

1975-01-01

171

Ion distribution in multilayers of weak polyelectrolytes: A neutron reflectometry study  

NASA Astrophysics Data System (ADS)

Neutron reflectometry was used to determine the distribution of salt ions and water in thin poly(acrylic acid) and poly(allylamine hydrochloride) polyelectrolyte multilayers assembled with and without salt. Increasing salt concentration reverses the exclusion of water from the substrate region, eventually leading to an asymmetric segregation of water near the substrate at high salt concentration. The counterions were found to localize near the substrate in films that were either assembled with salt or were exposed to salt solutions. In addition, the capping layer of the film was found to greatly influence the counterion distribution in the multilayer.

Tanchak, Oleh M.; Yager, Kevin G.; Fritzsche, Helmut; Harroun, Thad; Katsaras, John; Barrett, Christopher J.

2008-08-01

172

Ion distribution in multilayers of weak polyelectrolytes: A neutron reflectometry study.  

PubMed

Neutron reflectometry was used to determine the distribution of salt ions and water in thin poly(acrylic acid) and poly(allylamine hydrochloride) polyelectrolyte multilayers assembled with and without salt. Increasing salt concentration reverses the exclusion of water from the substrate region, eventually leading to an asymmetric segregation of water near the substrate at high salt concentration. The counterions were found to localize near the substrate in films that were either assembled with salt or were exposed to salt solutions. In addition, the capping layer of the film was found to greatly influence the counterion distribution in the multilayer. PMID:19044847

Tanchak, Oleh M; Yager, Kevin G; Fritzsche, Helmut; Harroun, Thad; Katsaras, John; Barrett, Christopher J

2008-08-28

173

Neutron angular distribution in (?, n) reactions with linearly polarized ?-ray beam generated by laser Compton scattering  

NASA Astrophysics Data System (ADS)

In 1957, Agodi predicted that the neutron angular distribution in (?, n) reactions with a 100% linearly polarized ?-ray beam for dipole excitation should be anisotropic and universally described by the simple function of a+b?cos?(2?) at the polar angle ?=90, where ? is the azimuthal angle. However, this prediction has not been experimentally confirmed in over half a century. We have verified experimentally this angular distribution in the (?, n) reaction for 197Au, 127I, and natural Cu targets using linearly polarized laser Compton scattering ?-rays. The result suggests that the (??, n) reaction is a novel tool to study nuclear physics in the giant dipole resonance region.

Horikawa, K.; Miyamoto, S.; Mochizuki, T.; Amano, S.; Li, D.; Imasaki, K.; Izawa, Y.; Ogata, K.; Chiba, S.; Hayakawa, T.

2014-10-01

174

Calculation of the effects of electronic threshold and pulse height walk on observed neutron time-of-flight distributions  

NASA Astrophysics Data System (ADS)

Using a simple formulation of the pulse height walk a computer program has been written to calculate the expected neutron time-of-flight distribution (TOFD) corresponding to a given neutron spectrum for a certain neutron threshold. The effect of varying each instrumental parameter is studied. A fitting procedure is used to obtain the values of these parameters from the TOFD corresponding to a known neutron spectrum. The same values can then be used in the analysis of the TOFD corresponding to an unknown spectrum measured with the same instrumental settings.

Ajitanand, N. N.

1980-10-01

175

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

E-print Network

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

Harris, Thomas C. (Thomas Cameron)

2006-01-01

176

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

E-print Network

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

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

2007-09-06

177

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

SciTech Connect

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.

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

2007-10-26

178

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

Microsoft Academic Search

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

B. Cederwall; F. Ghazi Moradi; T. Bck; A. Johnson; J. Blomqvist; E. Clment; G. de France; R. Wadsworth; K. Andgren; K. Lagergren; A. Dijon; G. Jaworski; R. Liotta; C. Qi; B. M. Nyak; J. Nyberg; M. Palacz; H. Al-Azri; A. Algora; G. de Angelis; A. Ata; S. Bhattacharyya; T. Brock; J. R. Brown; P. Davies; A. di Nitto; Zs. Dombrdi; A. Gadea; J. Gl; B. Hadinia; F. Johnston-Theasby; P. Joshi; K. Juhsz; R. Julin; A. Jungclaus; G. Kalinka; S. O. Kara; A. Khaplanov; J. Kownacki; G. La Rana; S. M. Lenzi; J. Molnr; R. Moro; D. R. Napoli; B. S. Nara Singh; A. Persson; F. Recchia; M. Sandzelius; J.-N. Scheurer; G. Sletten; D. Sohler; P.-A. Sderstrm; M. J. Taylor; J. Timr; J. J. Valiente-Dobn; E. Vardaci; S. Williams

2011-01-01

179

Use of a three-layer distributed RC network to produce two pairs of complex conjugate zeros  

NASA Technical Reports Server (NTRS)

The properties of a three layer distributed RC network consisting of two layers of resistive material separated by a dielectric are described. When the three layer network is used as a three terminal element by connecting conducting terminal strips across the ends of one of the resistive layers and the center of the other resistive layer, the network may be used to produce pairs of complex conjugate transmission zeros. The location of these zeros are determined by the parameters of the network. Design charts for determining the zero positions are included as part of the report.

Huelsman, L. P.

1972-01-01

180

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

SciTech Connect

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

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

1994-11-01

181

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

NASA Astrophysics Data System (ADS)

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

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

1999-11-01

182

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

SciTech Connect

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

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

2014-02-15

183

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

PubMed

The Joint European Torus (JET, Culham, UK) is the largest tokamak in the world devoted to nuclear fusion experiments of magnetic confined Deuterium (D)/Deuterium-Tritium (DT) plasmas. Neutrons produced in these plasmas are measured using various types of neutron detectors and spectrometers. Two of these instruments on JET make use of organic liquid scintillator detectors. The neutron emission profile monitor implements 19 liquid scintillation counters to detect the 2.45 MeV neutron emission from D plasmas. A new compact neutron spectrometer is operational at JET since 2010 to measure the neutron energy spectra from both D and DT plasmas. Liquid scintillation detectors are sensitive to both neutron and gamma radiation but give light responses of different decay time such that pulse shape discrimination techniques can be applied to identify the neutron contribution of interest from the data. The most common technique consists of integrating the radiation pulse shapes within different ranges of their rising and/or trailing edges. In this article, a step forward in this type of analysis is presented. The method applies a tomographic analysis of the 3-dimensional neutron and gamma pulse shape and pulse height distribution data obtained from liquid scintillation detectors such that n/? discrimination can be improved to lower energies and additional information can be gained on neutron contributions to the gamma events and vice versa. PMID:24593359

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

2014-02-01

184

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

185

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

186

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

NASA Astrophysics Data System (ADS)

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

Matsumoto, T.

2007-09-01

187

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

SciTech Connect

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

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

2001-02-01

188

Yield, kinetic energy, pairing effect, and shell effect of light fission products for thermal-neutron fission of uranium 233  

Microsoft Academic Search

The mass spectrometer HIAWATHA in conjunction with a thin-windowed gridded ionization chamber was used to determine the yields of light fission products for thermal-neutron fission of U-233. HIAWATHA has an energy resolution of 0.3%, a mass resolution of 0.5 amu, and an atomic-number resolving power of 38. The yields were measured as a function of mass number, atomic number, and

1983-01-01

189

Short collision time approximation for neutron scattering using discrete frequency distributions  

SciTech Connect

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

Ryskamp, J.M.

1980-01-01

190

Charge distribution in the thermal neutron fission of 245Cm: Fractional cumulative yields of 135I and 140Ba  

NASA Astrophysics Data System (ADS)

Fractional cumulative yields for 135I and 140Ba have been determined in the thermal neutron induced fission of 245Cm following the respective daughter product activities. The fractional cumulative yield values obtained are 0.951+/-0.014 and 0.969+/-0.006 for 135I and 140Ba, respectively. The fractional cumulative yield value for 135I has been compared with the one reported earlier and an attempt has been made to correlate the value to the neutron to proton ratio of the fissioning nucleus. The data have been analyzed to examine the effect of shells on the width of the charge distribution. This indicates a narrower width of charge distribution for mass chain 135 and a broader width for mass chain 140 compared to normal width of the distribution. NUCLEAR REACTIONS, FISSION Thermal neutron fission of 245Cm, measured FCY, data analyzed in terms of neutron to proton ratio, odd-even effect and shell effect.

Datta, Tarun; Dange, S. P.; Manohar, S. B.; Nair, A. G. C.; Prakash, Satya; Ramaniah, M. V.

1980-04-01

191

Studies on depth-dose-distribution controls by deuteration and void formation in boron neutron capture therapy.  

PubMed

Physical studies on (i) replacement of heavy water for body water (deuteration), and (ii) formation of a void in human body (void formation) were performed as control techniques for dose distribution in a human head under neutron capture therapy. Simulation calculations were performed for a human-head-size cylindrical phantom using a two-dimensional transport calculation code for mono-energetic incidences of higher-energy epi-thermal neutrons (1.2-10 keV), lower-energy epi-thermal neutrons (3.1-23 eV) and thermal neutrons (1 meV to 0.5 eV). The deuteration was confirmed to be effective both in thermal neutron incidence and in epi-thermal neutron incidence from the viewpoints of improvement of the thermal neutron flux distribution and elimination of the secondary gamma rays. For the void formation, a void was assumed to be 4 cm in diameter and 3 cm in depth at the surface part in this study. It was confirmed that the treatable depth was improved almost 2 cm for any incident neutron energy in the case of the 10 cm irradiation field diameter. It was made clear that the improvement effect was larger in isotropic incidence than in parallel incidence, in the case that an irradiation field size was delimited fitting into a void diameter. PMID:15379019

Sakurai, Yoshinori

2004-08-01

192

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

E-print Network

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

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

2014-12-28

193

Detection of prokaryotic promoters from the genomic distribution of hexanucleotide pairs  

PubMed Central

Background In bacteria, sigma factors and other transcriptional regulatory proteins recognize DNA patterns upstream of their target genes and interact with RNA polymerase to control transcription. As a consequence of evolution, DNA sequences recognized by transcription factors are thought to be enriched in intergenic regions (IRs) and depleted from coding regions of prokaryotic genomes. Results In this work, we report that genomic distribution of transcription factors binding sites is biased towards IRs, and that this bias is conserved amongst bacterial species. We further take advantage of this observation to develop an algorithm that can efficiently identify promoter boxes by a distribution-dependent approach rather than a direct sequence comparison approach. This strategy, which can easily be combined with other methodologies, allowed the identification of promoter sequences in ten species and can be used with any annotated bacterial genome, with results that rival with current methodologies. Experimental validations of predicted promoters also support our approach. Conclusion Considering that complete genomic sequences of over 1000 bacteria will soon be available and that little transcriptional information is available for most of them, our algorithm constitutes a promising tool for the prediction of promoter sequences. Importantly, our methodology could also be adapted to identify DNA sequences recognized by other regulatory proteins. PMID:17014715

Jacques, Pierre-tienne; Rodrigue, Sbastien; Gaudreau, Luc; Goulet, Jean; Brzezinski, Ryszard

2006-01-01

194

Angular Distribution of Charge Exchange and Inelastic Neutrons in pi--p Interactions at 313 and 371 MeV  

Microsoft Academic Search

Neutron angular distributions from the charge-exchange (pi0n) and inelastic modes (pi0pi0n,pi+pi-n) of the pi--p interaction have been investigated at 313 and 371 MeV incident-pion kinetic energy. The data were obtained with an electronic counter system. Elastic and inelastic neutrons were separated in the all-neutral final states by time of flight. At both energies the charge-exchange differential cross section at the

Don L. Lind; Barry C. Barish; Richard J. Kurz; Philip M. Ogden; Victor Perez-Mendez

1965-01-01

195

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

E-print Network

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

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

2007-08-03

196

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

197

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

PubMed

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

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

2013-06-14

198

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

SciTech Connect

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

Masadeh, A. S.; Bozin, E. S.; Farrow, C. L.; Paglia, G.; Juhas, P.; Billinge, S. J. L.; Karkamkar, A.; Kanatzidis, M. G. [Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-1116 (United States); Department of Chemistry, Michigan State University, East Lansing, Michigan 48824-1116 (United States)

2007-09-15

199

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

200

Mass distribution in the quasi-mono-energetic neutron-induced fission of 238U  

NASA Astrophysics Data System (ADS)

The yields of various fission products in the 3.72, 5.42, 7.75 and 10.09 MeV quasi-mono-energetic neutron-induced fission of 238U fission have been determined using off-line ?-ray spectrometric technique. The mass-chain yields were obtained from their fission product yields using charge distribution correction. The peak-to-valley (P/V) ratio, the average value of light mass (), heavy mass () and the average number of neutrons () at four different neutron energies of present work and at other energies from literature in the 238U(n, f) were obtained from the mass yield data. The present and the existing literature data in 238U(n, f) at various energies were compared with the similar data in the 232Th(n, f). The following observations were obtained: (i) The mass yield distribution in 238U(n, f) is double humped unlike in the 232Th(n, f), where it is triple humped. (ii) The yields of fission products for A=133-134, A=138-139, and A=143-144 and their complementary products in the 238U(n, f) at four neutron energies are higher than those of other fission products as in the 232Th(n, f). The fine structure in the mass yield distribution has been explained from the point of view of standard I and standard II asymmetric mode of fission besides even-odd effect. (iii) The yields of fission products for A=133-134 are higher in the 238U(n, f) than in the 232Th(n, f), whereas it is reversed for A=143-144. This has been explained from the point of shell combination of complementary fragments. (iv) In both the 238U(n, f) and 232Th(n, f), the yields of symmetric products increase with excitation energy, which causes the decrease of peak-to-valley (P/V) ratio with excitation energy. (v) At the same excitation energy, the yields of symmetric products are lower in the 238U(n, f) than in the 232Th(n, f). This causes higher value of P/V in 238U(n, f) than in 232Th(n, f) for same excitation energy. (vi) The approach of symmetric split with excitation energy is slower in the 238U(n, f) than in the 232Th(n, f). This is due to the different type of potential energy surface for the fissioning system 233Th* than in the fissioning system 239U*.

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

2013-09-01

201

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

SciTech Connect

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

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

2012-03-15

202

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

SciTech Connect

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

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

2012-03-15

203

Calculation of the neutron source distribution in the VENUS PWR Mockup Experiment  

SciTech Connect

The VENUS PWR Mockup Experiment is an important component of the Nuclear Regulatory Commission's program goal of benchmarking reactor pressure vessel (RPV) fluence calculations in order to determine the accuracy to which RPV fluence can be computed. Of particular concern in this experiment is the accuracy of the source calculation near the core-baffle interface, which is the important region for contributing to RPV fluence. Results indicate that the calculated neutron source distribution within the VENUS core agrees with the experimental measured values with an average error of less than 3%, except at the baffle corner, where the error is about 6%. Better agreement with the measured fission distribution was obtained with a detailed space-dependent cross-section weighting procedure for thermal cross sections near the core-baffle interface region. The maximum error introduced into the predicted RPV fluence due to source errors should be on the order of 5%.

Williams, M.L.; Morakinyo, P.; Kam, F.B.K.; Leenders, L.; Minsart, G.; Fabry, A.

1984-01-01

204

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

SciTech Connect

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

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

2008-01-01

205

ON THE ANGULAR DISTRIBUTION OF NEUTRONS IN C¹³(\\/cap alpha\\/,n)O¹⁶ REACTION  

Microsoft Academic Search

The angular distribution of neutrons in C¹³( alpha ,n) were ; measured for four alpha energies, E\\/sub alpha \\/ = 2.69, 2.83, 4.42, and 4.63 ; Mev. The finite O¹⁶ nuclei are produced in their ground state. The ; character of the angular distribution changes slowly in relation to alpha ; energy. Moreover, the angular distributions have a sharply expressed

O. M. Mdivani; T. G. Gachechiladze

1959-01-01

206

Monte-Carlo simulation for fragment mass and kinetic energy distributions from neutron induced fission of 235U  

E-print Network

The mass and kinetic energy distribution of nuclear fragments from thermal neutron induced fission of 235U have been studied using a Monte-Carlo simulation. Besides reproducing the pronounced broadening on the standard deviation of the final fragment kinetic energy distribution $\\sigma_{e}(m)$ around the mass number m = 109, our simulation also produces a second broadening around m = 125, that is in agreement with the experimental data obtained by Belhafaf et al. These results are consequence of the characteristics of the neutron emission, the variation in the primary fragment mean kinetic energy and the yield as a function of the mass.

Montoya, M; Rojas, J

2007-01-01

207

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

E-print Network

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

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

2012-12-14

208

Neutron energy distribution and temporal correlations with hard x-ray emission from a hundreds of joules plasma focus device  

NASA Astrophysics Data System (ADS)

In this paper, experimental measurements of neutron energy distribution and hard x-ray emission from a 320J deuterium operated plasma focus device are presented. Temporal measurements of neutron and hard x-ray emission are studied using different arrangements of six scintillator-photomultiplier detector systems, located either radially or axially with respect to the focus symmetry axis. The axial-to-radial ratio of both total neutron yield and neutron energies indicates anisotropic emission, which is consistent with a 100?keV kinetic energy of the deuterons in the axial direction. The energy spread among different shots was ~0.5 MeV in the axial direction which is 2.5 times the spread in the radial direction. Furthermore, temporal differences on hard x-rays and neutron production over each direction are found. These differences show correlation with neutron energies. This could be related to the existence of two temporally separated neutron production times corresponding to different moments during the plasma focus discharge.

Moreno, Jos; Veloso, Felipe; Pavez, Cristian; Tarifeo-Saldivia, Ariel; Klir, Daniel; Soto, Leopoldo

2015-03-01

209

Nuclear-charge distribution near symmetry for thermal-neutron-induced fission of 235U  

NASA Astrophysics Data System (ADS)

Available data concerning nuclear-charge distribution for thermal-neutron-induced fission of 235U have been evaluated for the region near symmetry (104<=A<=129, 42<=Z<=50). Evaluated data or averages are listed and are interpreted by the use of empirical ZP and A'P models. The parameters and functions derived for the two models are presented and are compared with each other and with the data. Both models represent most data satisfactorily, and they permit the calculation of more reliable estimates of unmeasured independent-fission-product yields near symmetry than has been possible in the past. The two models show the same major trends, so the physical phenomena deduced from the trends are not model dependent. The independent yields of fission products with Z values of 50 and 42 are much larger than those of products with Z values of 43 through 49. The yields for products with Z values of 49 and 43 are larger than those of products with Z values of 44 through 48. These yield differences indicate that the stable filled, or nearly filled, 50-proton shell in the heavy fragment causes the fission probability to increase rapidly with mass number in the range from 120 to 130 between improbable symmetric and probable asymmetric fission. The lack of even-odd-proton and -neutron effects near symmetry indicates that excitation energies are higher for 236U nuclei undergoing symmetric fission than for those undergoing asymmetric fission.

Wahl, Arthur C.

1985-07-01

210

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

SciTech Connect

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

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

2005-10-15

211

Measurement and analysis of neutron flux distribution of STACY heterogeneous core by position sensitive proportional counter. Contract research  

E-print Network

We have measured neutron flux distribution around the core tank of STACY heterogeneous core by position sensitive proportional counter (PSPC) to develop the method to measure reactivity for subcritical systems. The neutron flux distribution data in the position accuracy of +-13 mm have been obtained in the range of uranium concentration of 50g/L to 210g/L both in critical and in subcritical state. The prompt neutron decay constant, alpha, was evaluated from the measurement data of pulsed neutron source experiments. We also calculated distribution of neutron flux and sup 3 He reaction rates at the location of PSPC by using continuous energy Monte Carlo code MCNP. The measurement data was compared with the calculation results. As results of comparison, calculated values agreed generally with measurement data of PSPC with Cd cover in the region above half of solution height, but the difference between calculated value and measurement data was large in the region below half of solution height. On the other hand, ...

Murazaki, M; Uno, Y

2003-01-01

212

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

Microsoft Academic Search

The fractional cumulative yield of 121Ag and the fractional independent yields of 121Cd, 121In, and 121Sn from thermal-neutron-induced fission of 235U were determined radiochemically to be 0.12+\\/-0.05, 0.61+\\/-0.09, 0.24+\\/-0.08, and 0.03+\\/-0.04, respectively. The yield values were used to determine the nuclear-charge-distribution parameters sigmaZ=0.55+\\/-0.10 and DeltaZ=0.50+\\/-0.05 for A=121. The sigmaZ for A=121 is close to sigmaZ=0.52+\\/-0.02 for high-yield fission products, and

Larry Robinson; Arthur C. Wahl; Tomasz M. Semkow; Andrew E. Norris

1985-01-01

213

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

NASA Astrophysics Data System (ADS)

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

Tong, Hao; Xu, Renxin

2013-03-01

214

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

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

215

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

SciTech Connect

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

Moran, J.M.

1992-02-01

216

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

NASA Technical Reports Server (NTRS)

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

Schneider, Harold

1959-01-01

217

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

SciTech Connect

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

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

2010-12-01

218

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

DOE PAGESBeta

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

Aaltonen, T [Helsinki Inst. of Phys.; Alvarez Gonzalez, B [Oviedo U.; Cantabria Inst. of Phys.; Amerio, S [INFN, Padua; Amidei, D [Michigan U.; Anastassov, A [Northwestern U.; Annovi, A [Frascati; Antos, J [Comenius U.; Apollinari, G [Fermilab; Appel, J A [Fermilab; Apresyan, A [Purdue U.; Arisawa, T [Waseda U.; Dubna, JINR

2011-04-28

219

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

PubMed

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

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

2004-11-01

220

Pore distributions in nanocrystalline metals from small-angle neutron scattering  

SciTech Connect

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

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

1998-07-24

221

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

NASA Astrophysics Data System (ADS)

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

Ji, Wei

222

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

NASA Astrophysics Data System (ADS)

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

Calvin, Scott

223

Atmospheric neutrons  

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

224

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

225

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

USGS Publications Warehouse

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

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

2002-01-01

226

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

227

Mass and charge distributions in the very asymmetric mass region of the neutron induced fission of 238Np  

NASA Astrophysics Data System (ADS)

The mass-separator Lohengrin was used to measure the yields of the light fission products with A=74-85 and their nuclear charge and kinetic energy distributions from the odd- Z compound nucleus 239Np? formed by double capture of thermal neutrons. The mass yield distribution reveals an influence of the fragment shell with N=50 affecting also the nuclear charge and kinetic energy distributions. An odd-even effect for protons is found in the very asymmetric mass division, increasing from 4% to 35% with increasing fission asymmetry. This is in contrast to findings in normal asymmetric fission (region of high fission yields) where no odd-even effect for protons was observed. An odd-even effect for neutrons is also found comparable in size with that for protons. The latter effect exists also in normal asymmetric fission and is at least partly attributed to prompt neutron emission from the fragments. Some information on the number of prompt neutrons emitted is also obtained. From this information and from the energy dependence of the odd-even effect for protons it is concluded that the very light fragments originate from a cold and nearly undeformed light sphere of a dumbbell scission configuration characterised by a double shell closure with 28 protons and about 50 neutrons. In contrast to the double shell closure at mass 132 ( Z=50, N?82) the two shell closures in the light sphere do not coincide at one mass but are realised at A=70 and 80, respectively. This leads to a layered structure of the light sphere of the dumbbell scission configuration.

Tsekhanovich, I.; Denschlag, H.-O.; Davi, M.; Bykmumcu, Z.; Gnnenwein, F.; Oberstedt, S.; Faust, H. R.

2001-06-01

228

Correlation between fragment mass-distribution fine structure, charge distribution and nuclear structure for thermal-neutron-induced fission of 233U and 235U  

Microsoft Academic Search

Masses corresponding to observed fine-structure peaks in the fragment mass distributions for thermal-neutron-induced fission of 233U and 235U are shown to correspond to average measured masses for even-even nuclear charge splits. Evidence is presented that the yield enhancement for even-Z fragments is not restricted just to fission events with higher-than-average total kinetic energy. The anomalously high yield of fragments with

W. N. Reisdorf; J. P. Unik; L. E. Glendenin

1973-01-01

229

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

E-print Network

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

Vassiliki Kalogera; Chunglee Kim; Duncan R. Lorimer

2002-12-02

230

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

NASA Astrophysics Data System (ADS)

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

Boggara, Mohan; Mihailescu, Ella; Krishnamoorti, Ramanan

2009-03-01

231

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

NASA Astrophysics Data System (ADS)

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

Robinson, Larry; Wahl, Arthur C.; Semkow, Tomasz M.; Norris, Andrew E.

1985-04-01

232

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

Microsoft Academic Search

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

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

1998-01-01

233

Nuclear-charge distribution near symmetry for thermal-neutron-induced fission of ²³⁵U  

Microsoft Academic Search

Available data concerning nuclear-charge distribution for thermal-neutron-induced fission of ²³⁵U have been evaluated for the region near symmetry (104< or =A< or =129, 42< or =Z< or =50). Evaluated data or averages are listed and are interpreted by the use of empirical Z\\/sub P\\/ and A\\/sub P\\/\\/sup prime\\/ models. The parameters and functions derived for the two models are presented

Arthur Wahl

1985-01-01

234

Distributions isotopiques des gaz rares dans la fission par neutrons thermiques de 235U et 233U  

Microsoft Academic Search

The independent and cumulative fussion yields of rare gas isotopes produced from the fission of 233U and 235U by thermal neutrons have been measured by means of on-line isotopic separation. Gaussian curves can be fitted to the independent yield distributions. Values of Zp-ZUCD and sigmaz have been obtained. Elemental yields can be deduced for the two fissioning systems. An estimation

R. Brissot; J. Cranon; Ch. Ristori; J. P. Bocquet; A. Moussa

1975-01-01

235

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

SciTech Connect

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

Aaltonen, T [Helsinki Inst. of Phys.; Alvarez Gonzalez, B [Oviedo U.; Cantabria Inst. of Phys.; Amerio, S [INFN, Padua; Amidei, D [Michigan U.; Anastassov, A [Northwestern U.; Annovi, A [Frascati; Antos, J [Comenius U.; Apollinari, G [Fermilab; Appel, J A [Fermilab; Apresyan, A [Purdue U.; Arisawa, T [Waseda U.; Dubna, JINR

2011-04-28

236

Neutrino emission due to Cooper pairing of protons in cooling neutron stars: Collective effects 1 This work was supported in part by Spanish Grant DGES PB97-1432, and the Russian Foundation for Fundamental Research Grant 97-02-16501, and INTAS Grant 96-0659. 1  

Microsoft Academic Search

The process of neutrino-pair radiation due to formation and breaking of Cooper pairs of protons in superconducting cores of neutron stars is considered with taking into account of the electromagnetic coupling of protons to ambient electrons. It is shown that plasma polarization strongly modifies the effective vector weak current of protons. Collective response of ambient electrons to the proton quantum

L. B. Leinson

2000-01-01

237

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

EPA Science Inventory

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

238

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

Microsoft Academic Search

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

Lars Meinhold; David Clement; Moeava Tehei; Roy Daniel; John L. Finneye; Jeremy C. Smith

2008-01-01

239

FURTHER EVIDENCE FOR THE BIMODAL DISTRIBUTION OF NEUTRON-STAR MASSES  

SciTech Connect

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

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

2010-08-10

240

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

SciTech Connect

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

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

1986-07-01

241

Extreme axial equalization and wide distribution of recombination nodules in the primitive ZW pair of Rhea americana (Aves, Ratitae)  

Microsoft Academic Search

Pachytene oocytes from the ratite bird Rhea americana were used for synaptonemal complex analysis with a surface spreading technique and phosphotungstic acid staining. The ZW bivalent is slightly smaller than the fourth autosomal bivalent and clearly shows unequal W and Z axes only in 27% of the bivalents. Most of the ZW pairs are completely adjusted and thus the W

M. I. Pigozzi; A. J. Solari

1997-01-01

242

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

SciTech Connect

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

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

2010-09-14

243

Pulsar Pair Cascades in Magnetic Fields with Offset Polar Caps  

NASA Technical Reports Server (NTRS)

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

Harding, Alice K.; Muslimov, Alex G.

2012-01-01

244

Measurements and Calculations of Neutron Scattering Angular Distributions over a Wide Mass and Energy Range  

NASA Astrophysics Data System (ADS)

Neutron elastic and inelastic differential cross sections for targets between (9)Be and (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.

Hansen, L. F.

245

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

PubMed

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

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

2011-07-01

246

Determination of the elemental distribution in a sample using neutron induced gamma-ray emission tomography  

Microsoft Academic Search

The factors that affect accurate, quantitative results to be obtained by neutron induced gamma-ray emission tomography are stated. The technique, which is a combination of neutron activation analysis with computerised gamma-ray emission tomography, would be enhanced by the use of multiple detector assemblies, in geometrical configurations, which simultaneously record the gamma-rays emitted and improve detection efficiency. Developments in the past

N. M. Spyrou; J. M. Sharaf; S. Rajeswaran; E. Mesbahi

1997-01-01

247

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

PubMed Central

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

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

2014-01-01

248

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

SciTech Connect

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

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

2005-01-01

249

Mass, charge and energy distributions in the very asymmetric fission of 249Cf induced by thermal neutrons  

NASA Astrophysics Data System (ADS)

Fission yields of fragments with mass numbers A = 69-87 and fragment kinetic energies for A = 74-87 in the very asymmetric neutron induced fission of 249Cf have been measured using the mass separator Lohengrin at the Institut Laue-Langevin in Grenoble. The chain yields observed in this very light mass region are considerably higher than predicted. An evaluation of the isotopic yields shows a strong increase of the proton odd-even effect from 7% to 17% with increasingly asymmetric fission. The neutron odd-even effect is increasing from 4% to 10%. These observations and a narrowing of the average nuclear charge distribution can be explained by a decreasing excitation energy with increasing asymmetry of the fission process.

Hentzschel, R.; Faust, H. R.; Denschlag, H. O.; Wilkins, B. D.; Gindler, J.

1994-05-01

250

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

SciTech Connect

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

Attix, F.H.

1980-01-01

251

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

252

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

PubMed

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

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

2015-03-12

253

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

SciTech Connect

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

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

1993-04-19

254

Novel neutron focusing mirrors for compact neutron sources  

E-print Network

We demonstrated neutron beam focusing and neutron imaging using axisymmetric optics, based on pairs of confocal ellipsoid and hyperboloid mirrors. Such systems, known as Wolter mirrors, are commonly used in x-ray telescopes. ...

Gubarev, M.V.

255

Effective pairing interactions with isospin density dependence  

SciTech Connect

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

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

2008-05-15

256

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

Microsoft Academic Search

The fractional cumulative yield of ¹²¹Ag and the fractional independent yields of ¹²¹Cd, ¹²¹In, and ¹²¹Sn from thermal-neutron-induced fission of ²³⁵U were determined radiochemically to be 0.12 +- 0.05, 0.61 +- 0.09, 0.24 +- 0.08, and 0.03 +- 0.04, respectively. The yield values were used to determine the nuclear-charge-distribution parameters sigma\\/sub Z\\/ = 0.55 +- 0.10 and ..delta..Z = 0.50

Larry Robinson; Arthur Wahl; Tomasz Semkow; Andrew Norris

1985-01-01

257

Gravitational microlensing of neutron stars and radio pulsars: event rates, time-scale distributions and mass measurements  

E-print Network

We investigate properties of Galactic microlensing events in which a stellar object is lensed by a neutron star. For an all-sky photometric microlensing survey, we determine the number of lensing events caused by $\\sim10^{5}$ potentially-observable radio pulsars to be $\\sim0.2\\ \\rm{yr^{-1}}$ for $10^{10}$ background stellar sources. We expect a few detectable events per year for the same number of background sources from an astrometric microlensing survey. We show that such a study could lead to precise measurements of radio pulsar masses. For instance, if a pulsar distance could be constrained through radio observations, then its mass would be determined with a precision of $\\sim10\\%$. We also investigate the time-scale distributions for neutron star events, finding that they are much shorter than had been previously thought. For photometric events towards the Galactic centre that last $\\sim15$ days, around $7\\%$ will have a neutron star lens. This fraction drops rapidly for longer time-scales. Away from the...

Dai, Shi; Lin, Mengxiang; Yue, Youling; Hobbs, George; Xu, Renxin

2015-01-01

258

Thermal-Neutron Fission of 242 mAm: Mass and Charge Distribution  

Microsoft Academic Search

35 chain yields from thermal-neutron-induced fission of 242 mAm were measured by a recoil-catcher method, using 235U fission as a standard. Fractional cumulative yields of five krypton and of six xenon nuclides were measured by an emanation method. The results are in agreement with known trends.

K. Wolfsberg; G. P. Ford

1971-01-01

259

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

260

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

NASA Astrophysics Data System (ADS)

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.

Ghorai, S. K.

1983-09-01

261

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

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. PMID:22257567

Ghassoun, J; Senhou, N

2012-04-01

262

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

SciTech Connect

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

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

2012-01-15

263

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

SciTech Connect

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

D. SIEBE; K. PASAMEHMETOGLU

2000-11-01

264

Experimental and analytical studies of the K-reactor moderator flow patterns and neutron poison distribution  

Microsoft Academic Search

Effects of buoyancy forces and transient flow conditions on injected neutron poison [Gadolinium poison solution (GPSI)] is of interest in the safety analysis of the K reactor following a loss-of-alternating-current-power transient. During this scenario, the safety and control rods are assumed to fail, with reactor shutdown accomplished by injection of GPS. In the reactor, the radial pressure drop is sufficiently

R. L. Garrett; I. K. Paik; P. F. Peterson; G. E. McCreery; M. G. McKellar; K. G. Condi

1994-01-01

265

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

266

Determination of spatial and spectral distribution of neutron flux in the Texas A and M Nuclear Science Center reactor exposure cell. Progress report 1 Jul 74-1 Jan 75  

Microsoft Academic Search

Measurements were performed at the Nuclear Science Center to determine neutron flux distribution in the exposure cell. Both spatial and spectral flux variations were determined using neutron activation detectors. Results indicate hardening effects, and that 80%-90% of the total integral flux in the cell is due to neutrons having energies greater than 10 keV, indicating an intermediate spectrum. Results also

R. F. Schumacher; J. D. Randall; K. A. Hardy; J. A. Bachman

1976-01-01

267

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

SciTech Connect

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

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

2010-01-15

268

The second law of thermodynamics and multifractal distribution functions: Bin counting, pair correlations, and the Kaplan Yorke conjecture  

NASA Astrophysics Data System (ADS)

We explore and compare numerical methods for the determination of multifractal dimensions for a doubly-thermostatted harmonic oscillator. The equations of motion are continuous and time-reversible. At equilibrium the distribution is a four-dimensional Gaussian, so that all the dimension calculations can be carried out analytically. Away from equilibrium the distribution is a surprisingly isotropic multifractal strange attractor, with the various fractal dimensionalities in the range 1 < D < 4. The attractor is relatively homogeneous, with projected two-dimensional information and correlation dimensions which are nearly independent of direction. Our data indicate that the Kaplan-Yorke conjecture (for the information dimension) fails in the full four-dimensional phase space. We also find no plausible extension of this conjecture to the projected fractal dimensions of the oscillator. The projected growth rate associated with the largest Lyapunov exponent is negative in the one-dimensional coordinate space.

Hoover, Wm. G.; Hoover, C. G.; Posch, H. A.; Codelli, J. A.

2007-03-01

269

The Probability Distribution for a Random Match Between an Experimental-Theoretical Spectral Pair in Tandem Mass Spectrometry  

SciTech Connect

Proteomic techniques are fast becoming the main method for qualitative and quantitative determination of the protein content in biological systems. Despite notable advances, efficient and accurate analysis of high throughput proteomic data generated by mass spectrometers remains one of the major stumbling blocks in the protein identification problem. We present a model for the number of random matches between an experimental MS-MS spectrum and a theoretical spectrum of a peptide. The shape of the probability distribution is a function of the experimental accuracy, the number of peaks in the experimental spectrum, the length of the interval over which the peaks are distributed, and the number of theoretical spectral peaks in this interval. Based on this probability distribution, a goodness-of-fit tool can be used to yield fast and accurate scoring schemes for peptide identification through database search. In this paper, we describe one possible implementation of such a method and compare the performance of the resulting scoring function with that of SEQUEST. In terms of speed, our algorithm is roughly two orders of magnitude faster than the SEQUEST program, and its accuracy of peptide identification compares favorably to that of SEQUEST. Moreover, our algorithm does not use information related to the intensities of the peaks.

Fridman, Tamah [ORNL; Razumovskaya, Yevgeniya [ORNL; Verberkmoes, Nathan C [ORNL; Hurst, Gregory {Greg} B [ORNL; Protopopescu, Vladimir A [ORNL; Xu, Ying [University of Georgia, Athens, GA

2005-01-01

270

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

271

Supercool Neutrons (Ultracold Neutrons)  

E-print Network

? How to make lots of neutrons. Interesting properties of ultracold neutrons (UCN) Supercool source of ultracold neutrons #12; What are neutrons? Neutrons are a basic constituent of matter. The atomic nucleus is made of neutrons and protons. property neutron proton electric charge 0 1e

Martin, Jeff

272

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

Microsoft Academic Search

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

YOSHINAGA Sho; MATSUURA Hideaki; NAKAO Yasuyuki; KUDO Kazuhiko

2006-01-01

273

Cation distribution in ZnFe 2O 4 fine particles studied by neutron powder diffraction  

NASA Astrophysics Data System (ADS)

The structures of ZnFe 2O 4 fine particles prepared by a coprecipitation method have been studied by time-of-flight neutron powder diffraction at room temperature. The occupancy of Fe 3+ ion at a tetrahedral A-site is 0.108 for sample A (crystallite size 960 ) and 0.142 for sample B (290 ), which indicates that the cation substitution increases with decreasing particle size. The large magnetization in ZnFe 2O 4 fine particles compared with bulk materials is ascribable to a strong coupling between Fe 3+ ions at A- and B- sites due to the A-B interaction.

Kamiyama, T.; Haneda, K.; Sato, T.; Ikeda, S.; Asano, H.

1992-02-01

274

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

PubMed

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

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

2009-07-01

275

Neutron removal cross section as a measure of neutron skin  

NASA Astrophysics Data System (ADS)

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

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

2010-04-01

276

Neutron removal cross section as a measure of neutron skin  

E-print Network

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

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

2010-04-20

277

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

SciTech Connect

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

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

2010-07-20

278

Switchable radioactive neutron source device  

DOEpatents

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

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

1987-11-06

279

Optimized therapeutic neutron beam for accelerator-based BNCT by analyzing the neutron angular distribution from (7)Li(p,n)(7)Be reaction.  

PubMed

Perpendicular neutrons (i.e., solid angle bin of 50-150 degrees ) among ones generated from (7)Li(p,n)(7)Be reaction were used to produce an optimized therapeutic neutron beam for accelerator-based BNCT. A new beam port assembly was also designed to shape the fast neutrons into epithermal ones and to reduce unnecessary radiation including gammas. As a result of a simulation, it is found that a tumor at a depth of 60mm from the head skin could be treated within 5 minutes, if a typical tumor is assumed to be taken about 20RBEGy for therapeutic treatment. It is, thus, expected that the neutrons emitted into the solid angle bin of 50-150 degrees from (7)Li(p,n)(7)Be reaction are very effective in producing epithermal neutron beams for BNCT. PMID:19303311

Kim, Kyung-O; Kim, Jong Kyung; Kim, Soon Young

2009-01-01

280

Pick a Pair. Pancake Pairs  

ERIC Educational Resources Information Center

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

Miller, Pat

2005-01-01

281

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

NASA Astrophysics Data System (ADS)

We measured the energy spectra and spatial distributions of the neutron beam of Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) at the Japan Proton Accelerator Research Complex/Materials and Life Science Experimental Facility (J-PARC/MLF). Our research team designed and built ANNRI to measure nuclear data with high precision. The measurements of the neutron beam were performed on three types of beams provided by ANNRI in the neutron energy range from 1.5 meV to 10 keV. The energy spectra show a typical feature of para-hydrogen moderator, and the absolute intensities almost agree with predictions based on both a simulation calculation of the Japan Spallation Neutron Source (JSNS) and a neutron transmission calculation of the beamline. The available neutron intensities at 21.5 m are 7.510 5, 1.610 4, and 1.110 5 n/cm 2/s in the energy ranges 1.5-25 meV, 0.9-1.1 eV, and 0.9-1.1 keV, respectively, under the 17.5 kW JSNS operation. The measured spatial distributions of the beams formed by three different collimators are consistent with those expected from the collimator-system design of the beamline. The beam sizes in FWHM are about 29, 14, and 11 mm for the three different beam collimators. The edges of the spatial distributions are relatively sharp, enabling us to measure the nuclear data successfully.

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

2011-01-01

282

Ultrafast neutron detector  

DOEpatents

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

Wang, C.L.

1985-06-19

283

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

NASA Astrophysics Data System (ADS)

In order to validate dose evaluation methods for radiation shielding design of accelerator facilities, absorbed dose distributions in a plastic phantom of 303030 cm 3 slab were measured for 40- and 65-MeV quasi-monoenergetic neutrons with a tissue-equivalent proportional counter and a tissue-equivalent ionization chamber. The measured distributions were compared with the calculated ones from the energy deposition of charged particles and neutron energy spectra by using the Monte Carlo codes, HETC-3STEP and MORSE-CG/KFA, respectively. As a result, it was revealed that the calculation method used in the present work was applicable to absorbed dose evaluation for intermediate energy neutrons with high accuracy.

Nakane, Y.; Sakamoto, Y.

2001-03-01

284

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

SciTech Connect

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

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

2010-01-01

285

Theory of neutron scattering experiments on momentum distributions in quantum fluids  

SciTech Connect

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

Silver, R.N.

1987-01-01

286

Measurements of the spatial and energy distribution of thermal neutrons in uranium, heavy water lattices  

E-print Network

Intracell activity distributions were measured in three natural uranium, heavy water lattices of 1. 010 inch diameter, aluminum clad rods on triangular spacings of 4. 5 inches, 5. 0 inches, and 5. 75 inches, respectively, ...

Brown, Paul S. (Paul Sherman)

1962-01-01

287

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

SciTech Connect

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

Rothe, R.E.

1996-09-30

288

Effect of ion speed distribution on the spectral shape of the 2. 5-MeV neutron line produced by DD fusion  

SciTech Connect

Ion mean energy may be determined from Doppler broadening of the 2.5-MeV neutron line in Maxwellian deuterium plasma. Since many plasmas are non-Maxwellian a Monte-Carlo simulation has been used to predict the spectral shape produced by a variety of simple speed distributions with mean energies in the range 1--100 keV. In the case of isotropic ions considered here, the results are Gaussian to high order and their width varies as the square root of the mean ion energy. However, the linewidth varies substantially among different ion speed distributions with the same mean energy. The similarity in shape of these spectra prevent the determination of the speed distribution type from detailed measurements of the neutron spectrum, unlike the situation where co-counter beams produce anisotropic ion distributions.

Slaughter, D.

1986-08-01

289

Pairing in bulk nuclear matter beyond BCS  

SciTech Connect

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.

Ding, D.; Dickhoff, W. H.; Dussan, H. [Department of Physics, Washington University, St. Louis, Missouri 63130 (United States); Witte, S. J. [Department of Physics, Washington University, St. Louis, Missouri 63130, USA and Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Rios, A. [Department of Physics, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford, Surrey GU2 7XH (United Kingdom); Polls, A. [Departament d'Estructura i Constituents de la Matria, Universitat de Barcelona, E-08028 Barcelona (Spain)

2014-10-15

290

Domain structure for an amorphous iridium-oxide water-oxidation catalyst characterized by X-ray pair distribution function analysis.  

PubMed

The domain structure of an amorphous, "blue layer" iridium-oxide water-oxidation catalyst film (BL) electrodeposited from the soluble precursor complex, [Cp*Ir(H2O)3]SO4, was characterized by X-ray pair distribution function (PDF) analysis. The results show that the experimental PDF can be fit remarkably well using a single Ir5O22 cluster extracted from the rutile lattice. The model includes distortions that indicate the presence of Ir(?-O)3Ir or distorted Ir(?-O)2Ir substructures, and hence deviations from a rutile structure. The five Ir atom cluster is suggested to represent the population-averaged distribution of metal-oxo clusters in the film. BL is found to be distinguished from other amorphous film water-oxidation catalysts because of the remarkably small domain size and homogeneity. As such, the blue layer catalyst provides a model for investigating ligand-determined metal-oxide cluster assembly and catalyst mechanism. PMID:24336574

Huang, Jier; Blakemore, James D; Fazi, Diego; Kokhan, Oleksandr; Schley, Nathan D; Crabtree, Robert H; Brudvig, Gary W; Tiede, David M

2014-02-01

291

Pairing versus quarteting coherence length  

E-print Network

We systematically analyse the coherence length in even-even nuclei. The pairing coherence length in the spin-singlet channel for the effective density dependent delta (DDD) and Gaussian interaction is estimated. We consider in our calculations bound states as well as narrow resonances. It turns out that the pairing gaps given by the DDD interaction are similar to those of the Gaussian potential if one renormalizes the radial width to the nuclear radius. The correlations induced by the pairing interaction have in all considered cases a long range character inside the nucleus and decrease towards the surface. The mean coherence length is larger than the geometrical radius for light nuclei and approaches this value for heavy nuclei. The effect of the temperature and states in continuum is investigated. Strong shell effects are evidenced, especially for protons. We generalize this concept to quartets by considering similar relations, but between proton and neutron pairs. The quartet coherence length has a similar shape, but with larger values on the nuclear surface. We evidence the important role of proton-neutron correlations by estimating the so-called alpha coherence length, which takes into account the overlap with the proton-neutron part of the $\\alpha$-particle wave function. It turns out that it does not depend on the nuclear size and has a value comparable to the free $\\alpha$-particle radius. We have shown that pairing correlations are mainly concentrated inside the nucleus, while quarteting correlations are connected to the nuclear surface.

Doru S. Delion; Virgil V. Baran

2015-01-20

292

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

NASA Astrophysics Data System (ADS)

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

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

1999-12-01

293

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

SciTech Connect

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

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

2010-01-01

294

Multi-nuclear NMR study of polytype and defect distribution in neutron irradiated silicon carbide  

NASA Astrophysics Data System (ADS)

Silicon carbide containing 92% ?-SiC has been irradiated in a material test reactor at a fast neutron fluence (>0.1 MeV) of 3.39 1021 n cm-2 at an average temperature of 796 C, and subsequently studied by 29Si and 13C MAS NMR spectroscopy. A small amount of structural alteration was measured with the ?-SiC polytypes increasing from around 8-14%. Based on the assumption that the primary dominant defect is the paramagnetic SiV- defect. The defect concentration has been measured in both the irradiated and unirradiated sample using spin lattice relaxation time (T1) data obtained via a saturation-recovery experiment and was found to increase from 4.6 1018 cm-3 to 1.5 1020 cm-3. A case is presented to show that a small residual internuclear dipolar coupling contribution (at 3.80 10-6% of its total value) towards the T1 in the unirradiated reference sample significantly modifies the relaxation time from a value based solely on the dominant nuclear defect coupling mechanism.

Brigden, C. T.; Farnan, I.; Hania, P. R.

2014-01-01

295

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

Microsoft Academic Search

The distribution of residual stress of SUS304 samples that were undergone TIG welding process with four different electric currents has been measured. The welding has been done in the middle part of the samples that was previously grooved by milling machine. Before they were welded the samples were annealed at 650 degree Celsius for one hour. The annealing process was

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

2008-01-01

296

Determination of the elemental distribution in cigarette components and smoke by instrumental neutron activation analysis  

Microsoft Academic Search

Cigarette smoking is a major source of particles released in indoor environments. A comprehensive study of the elemental distribution in cigarettes and cigarette smoke has been completed. Specifically, concentrations of thirty elements have been determined for the components of 15 types of cigarettes. Components include tobacco, ash, butts, filters, and cigarette paper. In addition, particulate matter from mainstream smoke (MS)

D. Wu; S. Landsberger; S. M. Larson

1997-01-01

297

Autoradiography of californium-252 wire neutron sources. [To determine uniformity of distribution of Cf 252  

Microsoft Academic Search

A technique for measuring the distribution of Cf 252 in a wire is discussed. An autograph was produced by placing the wire on a photographic plate sensitive to gamma radiation. The radiograph was read by a computer automated densitometer. A brief discussion of the accuracy of the technique is presented. (DDA)

B. Tiffany; K. W. MacMurdo; R. H. Gaddy

1976-01-01

298

Temperature dependence of the low frequency dynamics of myoglobin. Measurement of the vibrational frequency distribution by inelastic neutron scattering.  

PubMed Central

Inelastic neutron scattering spectra of myoglobin hydrated to 0.33 g water (D2O)/g protein have been measured in the low frequency range (1-150 cm-1) at various temperatures between 100 and 350 K. The spectra at low temperatures show a well-resolved maximum in the incoherent dynamic structure factor Sinc(q, omega) at approximately 25 cm-1 and no elastic broadening. This maximum becomes gradually less distinct above 180 K due to the increasing amplitude of quasielastic scattering which extends out to 30 cm-1. The vibrational frequency distribution derived independently at 100 and 180 K are very similar, suggesting harmonic behavior at these temperatures. This result has been used to separate the vibrational motion from the quasielastic motion at temperatures above 180 K. The form of the density of states of myoglobin is discussed in relation to that of other amorphous systems, to theoretical calculations of low frequency modes in proteins, and to previous observations by electron-spin relaxation of fractal-like spectral properties of proteins. The onset of quasielastic scattering above 180 K is indicative of a dynamic transition of the system and correlates with an anomalous increase in the atomic mean-squared displacements observed by Mssbauer spectroscopy (Parak, F., E. W. Knapp, and D. Kucheida. 1982. J. Mol. Biol. 161: 177-194.) and inelastic neutron scattering (Doster, W., S. Cusack, and W. Petry, 1989. Nature [Lond.]. 337: 754-756.) Similar behavior is observed for a hydrated powder of lysozyme suggesting that the low frequency dynamics of globular proteins have common features. PMID:2166599

Cusack, S; Doster, W

1990-01-01

299

Toward prompt gamma spectrometry for monitoring boron distributions during extra corporal treatment of liver metastases by boron neutron capture therapy: a Monte Carlo simulation study.  

PubMed

A Monte Carlo calculation was carried out for boron neutron capture therapy (BNCT) of extra corporal liver phantom. The present paper describes the basis for a subsequent clinical application of the prompt gamma spectroscopy set-up aimed at in vivo monitoring of boron distribution. MCNP code was used first to validate the homogeneity in thermal neutron field in the liver phantom and simulate the gamma ray detection system (collimator and detector) in the treatment room. The gamma ray of 478 keV emitted by boron in small specific region can be detected and a mathematical formalism was used for the tomography image reconstruction. PMID:19394243

Khelifi, R; Nievaart, V A; Bode, P; Moss, R L; Krijger, G C

2009-07-01

300

Effect of ion speed distribution on the spectral shape of the 2. 5 MeV neutron line produced by DD fusion  

SciTech Connect

Ion mean energy may be determined from Doppler broadening of the 2.5 MeV neutron line in Maxwellian deuterium plasma. Since many plasmas are non-Maxwellian a Monte Carlo simulation has been used to predict the spectral shape produced by a variety of simple speed distributions with mean energies in the range 1 to 100 keV. The results are Gaussian to high order and their width varies as the square root of the mean ion energy. However, the line width varies substantially among different ion speed distributions with the same mean energy. The similarity in shape of these spectra prevent the determination of the speed distribution type from detailed measurements of the neutron spectrum. 24 refs., 4 figs., 2 tabs.

Slaughter, D.

1986-02-01

301

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

SciTech Connect

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

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

2013-09-10

302

Odd-even systematics in neutron fission yields of 233U and 235U  

Microsoft Academic Search

An analysis of the distribution of independent yields in neutron induced fission of 233U and 235U revealed a constant enhancement of products with an even number of protons, relative to those with an odd number. This odd-even effect in the proton pairing, related to calculated \\

S. Amiel; H. Feldstein

1975-01-01

303

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

SciTech Connect

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

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

2008-06-18

304

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

PubMed

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

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

2014-09-01

305

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

PubMed

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

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

2014-12-01

306

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

SciTech Connect

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

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

2008-01-01

307

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)

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.

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

2015-01-01

308

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

NASA Astrophysics Data System (ADS)

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

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

1999-08-01

309

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

310

NEW OPTICAL/ULTRAVIOLET COUNTERPARTS AND THE SPECTRAL ENERGY DISTRIBUTIONS OF NEARBY, THERMALLY EMITTING, ISOLATED NEUTRON STARS  

SciTech Connect

We present Hubble Space Telescope optical and ultraviolet photometry for five nearby, thermally emitting neutron stars. With these measurements, all seven such objects have confirmed optical and ultraviolet counterparts. Combining our data with archival space-based photometry, we present spectral energy distributions for all sources and measure the 'optical excess': the factor by which the measured photometry exceeds that extrapolated from X-ray spectra. We find that the majority have optical and ultraviolet fluxes that are inconsistent with that expected from thermal (Rayleigh-Jeans) emission, exhibiting more flux at longer wavelengths. We also find that most objects have optical excesses between 5 and 12, but that one object (RX J2143.0+0654) exceeds the X-ray extrapolation by a factor of more than 50 at 5000 A, and that this is robust to uncertainties in the X-ray spectra and absorption. We consider explanations for this ranging from atmospheric effects, magnetospheric emission, and resonant scattering, but find that none is satisfactory.

Kaplan, D. L.; Kamble, A. [Physics Department, University of Wisconsin-Milwaukee, Milwaukee, WI 53211 (United States); Van Kerkwijk, M. H. [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); Ho, W. C. G., E-mail: kaplan@uwm.edu, E-mail: kamble@uwm.edu, E-mail: mhvk@astro.utoronto.ca, E-mail: wynnho@slac.stanford.edu [School of Mathematics, University of Southampton, Southampton, SO17 1BJ (United Kingdom)

2011-08-01

311

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

E-print Network

Estimates of the Galactic coalescence rate (R) of close binaries with two neutron stars (NS-NS) are known to be uncertain by large factors (about two orders of magnitude) mainly due to the small number of systems detected as binary radio pulsars. We present an analysis method that allows us to estimate the Galactic NS-NS coalescence rate using the current observed sample and, importantly, to assign a statistical significance to these estimates and to calculate the allowed ranges of values at various confidence levels. The method involves the simulation of selection effects inherent in all relevant radio pulsar surveys and a Bayesian statistical analysis for the probability distribution of the rate. The most likely values for the total Galactic coalescence rate (R_peak) lie in the range 2-60 per Myr depending on different pulsar population models. For our reference model 1, where the most likely estimates of pulsar population properties are adopted, we obtain R_tot = 8_{-5}^{+9} per Myr at a 68% statistical confidence level. The corresponding range of expected detection rates of NS-NS inspiral are 3_{-2}^{+4}x10^{-3} per yr for the initial LIGO and 18_{-11}^{+21} per yr for the advanced LIGO.

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

2002-10-21

312

Short range order in (Ni 65Fe 35) 77B 23 metallic glass by neutron diffraction  

NASA Astrophysics Data System (ADS)

The S(Q) structure factor of (Ni 65Fe 35) 77B 23 metallic glass was measured by time-of-flight neutron diffraction up to 24 -1 momentum transfer. The distribution of transition metal-boron and transition metal-transition metal first neighbour atom pairs is resolved in the distribution function obtained from S(Q) by Fourier transformation. The distances of these first neighbours pairs, the width of their distribution, the partial coordination numbers and the short range order parameter are given. The results on (Ni 65Fe 35) 77B 23 and on the previously studies Fe 81B 19 amorphous alloys are compared.

Svb, E.; Kro, N.; Ishmaev, S. N.; Sadikov, I. P.; Chernyshov, A. A.

1983-04-01

313

Dependence of charge collection distributions and dose on the gas type filling the ionization chamber for a p(66)Be(49) clinical neutron beam  

SciTech Connect

Measurements of central axis depth charge distributions (CADCD) in a p(66)Be(49) clinical neutron beam using A-150 TE plastic ionization chambers (IC) have shown that these distributions are dependent on the gas type filling the ICs. IC volumes from 0.1 to 8 cm/sup 3/ and nine different gases were investigated. Off axis ratios and build-up measurements do not seem to be as sensitive to gas type. The gas dosimetry constants given in the AAPM Protocol for Neutron Beam Dosimetry for air and methane based TE gases were tested for consistency in water and in TE solution filled phantoms at depths of 10 cm, when used in conjunction with an IC having 5 mm thick walls of A-150. 29 refs., 7 figs., 1 tab.

Awschalom, M.; Haken, R.K.T.

1985-01-01

314

Formalism for the determination of structural isotope effects with neutrons  

SciTech Connect

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

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

2009-01-01

315

Polarized Neutron Diffraction Study of the Magnetization Density Distribution in Rb_2CrCl_4: A Two-Dimensional Ionic Ferromagnet  

Microsoft Academic Search

The magnetization density distribution in the ionic ferromagnet Rb_2CrCl_4 has been determined by polarized neutron diffraction from a single crystal at 4.5 K. Magnetic structure factors F_M were derived from the flipping ratios R of 660 main structure reflections (189 independent) and 57 super-structure reflections with sin theta\\/lambda <=slant 0.8 circ{ A}-1 (lambda = 0.90 circ{ A}). The main structure

P. Day; P. J. Fyne; E. Hellner; M. T. Hutchings; G. Munninghoff; F. Tasset

1986-01-01

316

Measurements of mass and energy distributions of products of thermal-neutron fission of ²³⁵U in a mass separator  

Microsoft Academic Search

A mass separator has been used to measure the mass and energy distributions of products of the heavy-nucleus group from fission of ²³⁵U by thermal neutrons. Relative yields have been determined for A = 130--147 for fixed energies of the complementary light fragment E\\/sub L\\/. An increase yield is observed for A = 137 at several E\\/sub L\\/. Periodic variations

I. I. Bakhromi; A. D. Belyaev; M. S. Vakher; V. I. Kogan; A. I. Muminov; V. P. Pikul; A. M. Usmandiyarov

1982-01-01

317

Mass and charge distributions in the very asymmetric thermal neutron induced fission of the odd-Z nucleus 242mAm  

Microsoft Academic Search

Yields of light fission products (A = 68, 7084, 87, 88, 94, 96, 98, 102 and 106108), their kinetic energies and nuclear charge distributions (A = 7184, 87 and 88) in the thermal neutron induced fission of the odd-Z nucleus 242mAm(Z = 95) were measured using the mass-separator Lohengrin at the Institute Laue-Langevin in Grenoble (France). The mass yield curve

I. Tsekhanovich; H. O. Denschlag; M. Davi; Z. Bykmumcu; M. Wstheinrich; F. Gnnenwein; S. Oberstedt; H. R. Faust

1999-01-01

318

Nuclear Charge Distribution in Fission: Independent Yields of 132I, 133I, and 134I from Thermal Neutron Fission of 233U  

Microsoft Academic Search

Independent yields of 132I, 133I, and 134I have been measured from thermal-neutron-induced fission of 233U. The yields, each expressed as the ratio of iodine independent yield to iodine cumulative yield, are 0.06+\\/-0.03, 0.21+\\/-0.03, and 0.370+\\/-0.013 for 132I, 133I, and 134I, respectively. Values of Zp estimated from these yields with the assumption that charge distribution can be represented by a Gaussian

N. G. Runnalls; D. E. Troutner

1970-01-01

319

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

Microsoft Academic Search

Radiographic images generated by the real-time neutron radiography system (RTNR) are analyzed by customized image processing software of the determination of instantaneous void fraction distribution. The cross-sectional averaged axial void fraction profiles and the two-dimensional void fraction profiles are determined simultaneously for each image. Various flow regimes are generated to determine if the RTNR system can accurately predict the void

G. D. Harvel; J. S. Chang; V. S. Krishnan

1995-01-01

320

The anomalous thermal expansion of cuprites (Cu{sub 2}O and Ag{sub 2}O) : a combined high resolution pair distribution function and geometric analysis.  

SciTech Connect

The temperature-dependent local structures of cuprites (M{sub 2}O for M = Cu{sup I}, Ag{sup I}) have been probed using variable-temperature (80-500 K) high-resolution pair distribution function (PDF) analysis of X-ray scattering data measured to very high values of momentum transfer (Q{sub max} = 35 {angstrom}{sup -1}). These noble metal oxides exhibit negative thermal expansion (NTE) behavior; however, several unusual structural features and behaviors distinguish the cuprites from other NTE frameworks the structure is inverted relative to conventional NTE frameworks and Cu{sub 2}O (but not Ag{sub 2}O) shows an unusual transition from negative to positive thermal expansion behavior at higher temperature thus motivating the present in-depth analysis of the particular thermal expansion mechanisms operating here. By coupling the local structural information from the PDFs with known geometric identities of the tetrahedra that form the framework, distortions contributing to NTE have been identified and the contrasting high temperature behaviors of the two isostructural analogues have been accounted for. Specifically, we demonstrate that thermal population of low-energy vibrational modes involving the dynamic distortion of the OM{sub 4} tetrahedra, away from the regular tetrahedral geometry (through M-O-M{prime} bending), can induce a contraction of the average tetrahedral edge length (M...M{prime}) and thus contribute to the NTE effect. This mechanism operates in combination with the transverse vibrational mechanism found in conventional NTE frameworks, where increasing transverse displacement of the bridging atom (O-M-O{prime}) draws corner-bridged polyhedra closer together.

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

2009-01-01

321

Theory of hydrogen pairing in yttrium  

SciTech Connect

The energetics of hydrogen atoms interacting with yttrium have been investigated using the self-consistent cluster model and the local-density approximation. Our results provide a theoretical understanding of a range of novel phenomena observed recently in resistivity, neutron scattering, NMR, and channeling experiments. These include pairing of hydrogen at low temperatures and the pairs structural origin, the anomalous fast diffusion of hydrogen along the pairing axis compared to the bulk rate, and the lack of long-range order between the pairs in the metal matrix.

Khanna, S.N.; Liu, F.; Challa, M.; Jena, P.

1989-09-25

322

Fragment-mass distributions in neutron-induced fission of {sup 232}Th and {sup 238}U at 33, 45, and 60 MeV  

SciTech Connect

We have measured fission fragment-mass yields for neutron-induced fission of {sup 232}Th and {sup 238}U at energies 32.8, 45.3, and 59.9 MeV. The experiments were done at quasimonoenergetic neutron beams of the Cyclotron Research Center at Louvain-la-Neuve. To detect the fission fragments, a multisection Frisch-gridded ionization chamber was used. The measurement and data analysis techniques are discussed in detail. The obtained mass yields are compared to model calculations with the intermediate-energy nuclear reaction code MCFX. The MCFX code is used to calculate the fraction of fissioning nuclei after cascade, preequilibrium, and statistical reaction stages. The formation of mass distributions is considered as a result of oscillations of the mass-asymmetry degree of freedom in the potential well calculated with the temperature-dependent shell correction method. The experimental results as well as the results of the model calculations demonstrate that the probability of symmetric fission increases with incident neutron energy for both nuclei. The comparison also shows that the symmetric fission is more enhanced for thorium than for uranium with increasing neutron energy. We also compare {sup 238}U results with available experimental data; the {sup 232}Th data were measured for the first time.

Ryzhov, I. V.; Yavshits, S. G.; Tutin, G. A.; Kovalev, N. V.; Saulski, A. V.; Kudryashev, N. A.; Onegin, M. S.; Vaishnene, L. A.; Gavrikov, Yu. A.; Grudzevich, O. T.; Simutkin, V. D.; Pomp, S.; Blomgren, J.; Oesterlund, M.; Andersson, P.; Bevilacqua, R.; Meulders, J. P.; Prieels, R. [V. G. Khlopin Radium Institute, Second Murinskiy prospect 28, 194021, Saint Petersburg (Russian Federation); Petersburg Nuclear Physics Insitute, 188300, Gatchina, Leningrad district (Russian Federation); State Technical University, Studgorodok 1, 249020, Kaluga region, Obninsk (Russian Federation); Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden); Institute of Nuclear Physics, Universite Catholique de Louvain, B-1348 Louvain-la Neuve (Belgium)

2011-05-15

323

Pairing versus quarteting coherence length  

NASA Astrophysics Data System (ADS)

We systematically analyze the coherence length in even-even nuclei. The pairing coherence length in the spin-singlet channel for the effective density-dependent delta (DDD) and Gaussian interaction is estimated. We consider in our calculations bound states as well as narrow resonances. It turns out that the pairing gaps given by the DDD interaction are similar to those of the Gaussian potential if one renormalizes the radial width to the nuclear radius. The correlations induced by the pairing interaction have, in all considered cases, a long-range character inside the nucleus and a decrease towards the surface. The mean coherence length is larger than the geometrical radius for light nuclei and approaches this value for heavy nuclei. The effect of the temperature and states in the continuum is investigated. Strong shell effects are put in evidence, especially for protons. We generalize this concept to quartets by considering similar relations, but between proton and neutron pairs. The quartet coherence length has a similar shape, but with larger values on the nuclear surface. We provide evidence of the important role of proton-neutron correlations by estimating the so-called alpha coherence length, which takes into account the overlap with the proton-neutron part of the ? -particle wave function. It turns out that it does not depend on the nuclear size and has a value comparable to the free ? -particle radius. We have shown that pairing correlations are mainly concentrated inside the nucleus, while quarteting correlations are connected to the nuclear surface.

Delion, D. S.; Baran, V. V.

2015-02-01

324

Experimental investigation of the form of the energy distribution of neutrons in the spontaneous fission of 252 Cf  

Microsoft Academic Search

We measured in our work the neutron spectrum in the energy range 0.01-i0 MeV with the time-of-flightte chnique. We used anioniZation chamber with current measurements and 23~U layers as a neutron detector. The cross Section of the reaction 235U(n, f) has been studied in detail ina wide energy range and is one of the standards of nuclear physics. The chamber

M. V. Blinov; G. S. Boikov; B. A. Vitenko

1984-01-01

325

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

NASA Astrophysics Data System (ADS)

In the development of new medicinal products, poor oral bioavailability, due to the low solubilities of many active pharmaceutical ingredients (APIs), is increasingly a barrier for treatments to be administered using tablet or capsule formulations and one of the main challenges facing the pharmaceutical industry. Non-crystalline phases such as the amorphous and nanostructured states can confer increased solubility to a drug, and therefore, have recently garnered a lot of interest from pharmaceutical researchers. However, little is known about local ordering in non-crystalline pharmaceuticals due to the lack of reliable experimental probes, hindering the clinical application of these compounds. The powerful tools of crystallography begin to lose their potency for structures on the nanoscale; conventional X-ray powder diffraction (XRPD) patterns become broad and featureless in these cases and are not useful for differentiating between different local molecular packing arrangements. In this thesis, we introduce the use of high energy X-rays coupled with total scattering pair distribution function (TSPDF) and fingerprinting analysis to investigate the local structures of non-crystalline pharmaceutical compounds. The high energy X-rays allow us to experimentally collect diffuse scattering intensities, which contain information about a sample's local ordering, in addition to the Bragg scattering available in conventional XRPD experiments, while the TSPDF allows us to view the intra- and inter-molecular correlations in real space. The goal of this study was to address some fundamental problems involving fingerprinting non-crystalline APIs using TSPDF in order to lay the groundwork for the proper use of the technique by the pharmaceutical community. We achieved this by developing the methodology as well as the exploring the scientific implications. On the methodology side, we introduced PDFGetX3, a new software program for calculating TSPDFs that simplifies the procedure and reduces user interaction. We also set a baseline for the minimum X-ray energy that is needed for fingerprinting analysis, which had implications on the type of X-ray diffractometers that can be used. On the science side, we investigated the local structures of nanocrystalline and amorphous materials as well mixtures containing crystalline and amorphous phases. First, we identified a non-crystalline sample of the mood-stabilizing drug carbamazepine as a nanocrystalline version of one of its polymorphs. Next, we found that amorphous forms created by spray drying and cryomilling a proprietary compound have the same local structure. Finally, we quantified the phase fractions of polymorphic and amorphous components in a sample of the antibiotic sulfamerazine that was recrystallizing from a cryomilling-induced amorphous state.

Davis, Timur D.

2011-12-01

326

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

Microsoft Academic Search

The evolution of the short-range structural signature of the Ir4+ dimer state in CuIr2S4 thiospinel has been studied across the metal-insulator phase transitions as the metallic state is induced by temperature, Cr doping, and x-ray fluence. An atomic pair distribution function (PDF) approach reveals that there are no local dimers that survive into the metallic phase when this is invoked

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

2011-01-01

327

Pair-Starved Pulsar Magnetospheres  

NASA Technical Reports Server (NTRS)

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

Muslimov, Alex G.; Harding, Alice K.

2009-01-01

328

Synthesis, cation distribution and crystal structure of the spinel oxides MnGa xFe 1-xCrO 4 by neutron diffraction  

NASA Astrophysics Data System (ADS)

The spinel system MnGa xFe 1-xCrO 4 ( x=0.0, 0.25, 0.50, 0.75 and 1.0) was prepared by the solid state sintering method in air at 1523 K. X-ray and neutron powder diffraction measurements were performed on the samples at 295 K for structural characterization. Rietveld refinement of the neutron diffraction data revealed that all the samples of the series possessed cubic symmetry corresponding to the space group Fd3m. The distributions of the four cations Mn, Ga, Fe and Cr over the two sublattices and other crystallographic parameters were found. The lattice constant showed a decrease with increasing Ga content in the system. The magnetic structure at room temperature was found to be ferrimagnetic in the composition range x?0.50.

Zakaria, A. K. M.; Asgar, M. A.; Eriksson, S. G.; Ahmed, F. U.; Yunus, S. M.; Azad, A. K.

2006-11-01

329

Pair-distribution functions of two-temperature two-mass systems: comparison of molecular dynamics, classical-map hypernetted chain, quantum Monte Carlo, and Kohn-Sham calculations for dense hydrogen.  

PubMed

Two-temperature, two-mass quasiequilibrium plasmas may occur in electron-ion plasmas, nuclear-matter, as well as in electron-hole condensed-matter systems. Dense two-temperature hydrogen plasmas straddle the difficult partially degenerate regime of electron densities and temperatures which are important in astrophysics, in inertial-confinement fusion research, and other areas of warm dense-matter physics. Results from quantum Monte Carlo (QMC) are used to benchmark the procedures used in classical molecular-dynamics simulations and hypernetted chain (HNC) and classical-map HNC (CHNC) methods to derive electron-electron and electron-proton pair-distribution functions. Where QMC is not available, we used Kohn-Sham results as the reference calculation. Then, nonequilibrium molecular dynamics for two-temperature, two-mass plasmas are used to obtain pair distribution functions without specifying the interspecies cross temperature. Using these results, the correct HNC and CHNC procedures for the evaluation of pair-distribution functions in two-temperature two-mass two-component charged fluids are established and results for a mass ratio of 1:5, typical of electron-hole fluids, are presented. PMID:18352127

Dharma-wardana, M W C; Murillo, Michael S

2008-02-01

330

Nucleon-pair approximation to the nuclear shell model  

NASA Astrophysics Data System (ADS)

Atomic nuclei are complex systems of nucleons-protons and neutrons. Nucleons interact with each other via an attractive and short-range force. This feature of the interaction leads to a pattern of dominantly monopole and quadrupole correlations between like particles (i.e.,proton-proton and neutron-neutron correlations) in low-lying states of atomic nuclei. As a consequence, among dozens or even hundreds of possible types of nucleon pairs, very few nucleon pairs such as proton and neutron pairs with spin zero, two (in some cases spin four), and occasionally isoscalar spin-aligned proton-neutron pairs, play important roles in low-energy nuclear structure. The nucleon-pair approximation therefore provides us with an efficient truncation scheme of the full shell model configurations which are otherwise too large to handle for medium and heavy nuclei in foreseeable future. Furthermore, the nucleon-pair approximation leads to simple pictures in physics, as the dimension of nucleon-pair subspace is always small. The present paper aims at a sound review of its history, formulation, validity, applications, as well as its link to previous approaches, with the focus on the new developments in the last two decades. The applicability of the nucleon-pair approximation and numerical calculations of low-lying states for realistic atomic nuclei are demonstrated with examples. Applications of pair approximations to other problems are also discussed.

Zhao, Y. M.; Arima, A.

2014-12-01

331

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

PubMed Central

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. PMID:18310248

Meinhold, Lars; Clement, David; Tehei, Moeava; Daniel, Roy; Finney, John L.; Smith, Jeremy C.

2008-01-01

332

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

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

333

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

SciTech Connect

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

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

2008-11-01

334

Neutron tomography of the root-soil interface: water distribution around different parts of the root structure  

NASA Astrophysics Data System (ADS)

Although the importance of the root-soil interface in water uptake by plant roots has been acknowledged in many studies, there is a gap of knowledge on how water enters the roots. The main reason for this gap is the technical difficulties in resolving soil moisture dynamics in the vicinity of roots. Spatially and temporally resolved data on water flow across soil-root interface is needed to improve our understanding of mechanisms controlling water uptake by roots. We used neutron tomography to image soil water distribution around roots in-situ. We grew chick peas and lupines in sand-filled cylinders for 10 days at a water potential of -20 hPa. The samples were tomographed for 4 days over day and night and during a drying period and after rewetting. We observed that water content near the root surface was higher than in the bulk soil during the whole course of measurement for all the samples. Our hypothesis is that this increase of water content next to roots was due to the distinct water retention curve of the soil next to roots, the rhizosphere. Our hypothesis is that the rhizosphere water retention curve is caused by mucilage exuded by roots. Mucilage contains more than 90% water even at low water potentials, consequently increasing the water holding capacity of the rhizosphere. In another words, the roots modify the physical and chemical properties of their rhizosphere. The thickness of the area of increasing water, rhizosphere, varied along the root length. It ranged from slightly less than 1.5 mm in the distal part of the roots to more than 3 mm around the root tip. Also, it was slightly thicker around the main root compared to the lateral roots. As the soil water was being consumed by the roots, the extent of the rhizosphere decreased slightly, and then increased again after rewetting. We expect that the high water-holding capacity of the rhizosphere favors root water uptake, especially in dry soils. Most of the present modeling approaches neglect this effect.

Moradi, A. B.; Carminati, A.

2009-12-01

335

Non-Statistical Effects in Neutron Capture  

SciTech Connect

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

Koehler, P. E.; Guber, K. H.; Harvey, J. A.; Wiarda, D. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); Bredeweg, T. A.; O'Donnell, J. M.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wouters, J. M. [Los Alamos National Laboratory, Los Alamos, NM (United States); Reifarth, R. [GSI, Planckstr. 1, 64291 Darmstadt (Germany)

2009-01-28

336

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

337

Deuteron distribution in nuclear matter  

NASA Astrophysics Data System (ADS)

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.

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

2002-05-01

338

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

PubMed

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

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

2008-05-21

339

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

Microsoft Academic Search

Estimates of the Galactic coalescence rate (R) of close binaries with two neutron stars (NS-NS) are known to be uncertain by large factors (about 2 orders of magnitude) mainly because of the small number of systems detected as binary radio pulsars. We present an analysis method that allows us to estimate the Galactic NS-NS coalescence rate using the current observed

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

2003-01-01

340

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

Microsoft Academic Search

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

Anatoly Blanovsky

1993-01-01

341

The MCLIB library: Monte Carlo simulation of neutron scattering instruments  

SciTech Connect

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.

Seeger, P.A.

1995-09-01

342

Mass and charge distributions in the very asymmetric thermal neutron induced fission of the odd-Z nucleus 242mAm  

NASA Astrophysics Data System (ADS)

Yields of light fission products ( A = 68, 70-84, 87, 88, 94, 96, 98, 102 and 106-108), their kinetic energies and nuclear charge distributions ( A = 71-84, 87 and 88) in the thermal neutron induced fission of the odd-Z nucleus 242mAm(Z = 95) were measured using the mass-separator Lohengrin at the Institute Laue-Langevin in Grenoble (France). The mass yield curve shows a fine structure at A = 70, probably due to shell and/or odd-even effects affecting also the nuclear charge distribution. The analysis of isotopic chain yields gives evidence for a very low excitation energy of the lightest fission fragments observed. A preferential formation of fragments with even Z is found for this odd-Z compound nucleus. Calculated values for the local odd-even effect are comparable with those for the neighbouring even-Z fissile nuclides and increase from 13% to 30% with increasing asymmetry of the mass split ( AL = 84 to 68 and ZL = 35 to 28). The neutron odd-even effect shows a similar but less pronounced behaviour.

Tsekhanovich, I.; Denschlag, H. O.; Davi, M.; Bykmumcu, Z.; Wstheinrich, M.; Gnnenwein, F.; Oberstedt, S.; Faust, H. R.

1999-10-01

343

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

SciTech Connect

We determined the cation distribution and ordering of Si, Al and Fe on the tetrahedral sites of a monoclinic low-sanidine from Itrongay, Madagascar, by combined neutron- and X-ray single-crystal diffraction. The cation distribution was determined by means of a simultaneous refinement using neutron- and X-ray data, as well as by combining scattering densities obtained from separate refinements with chemical data from a microprobe experiment. The two methods give the same results and show that Fe is fully ordered on T1, whereas Al shows a high degree of disorder. Based on this and previously published temperature-dependent X-ray data, we conclude that it is preferential ordering of Fe on T1 even at high temperature, rather than a high diffusion kinetics of Fe, which causes this asymmetry in ordering behavior between Al and Fe. The preferential ordering of Fe3+ relative to Al3+ in T1 is consistent with its 25 percent larger ionic radius.

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

2005-05-02

344

Fast Neutron Resonance Radiography in a Pulsed Neutron Beam  

Microsoft Academic Search

The feasibility of performing fast neutron resonance radiography at the PTB accelerator facility is studied. A neutron beam of a broad spectral distribution is produced by a pulsed 13 MeV deuterium beam hitting a thick Be target. The potential of 3 different neutron imaging detectors with time-of flight capability are investigated. The applied methods comprise wire chambers with hydrogenous converter

V. Dangendorf; G. Laczko; C. Kersten; O. Jagutzki; U. Spillmann

2003-01-01

345

Shell model study of pairing correlations  

SciTech Connect

A systematic study of the pairing correlations as a function of temperature and angular momentum was performed in the sd-shell region using the spherical shell model approach. Pairing correlations were derived for even-even, even-odd, and odd-odd systems near N=Z and also for the asymmetric case of N=Z+4. The results indicate that the pairing content and the behavior of pair correlations is similar in even-even and odd-mass nuclei. For the odd-odd N=Z system, angular momentum I=0 state is an isospin, t=1 neutron-proton paired configuration. Further, these t=1 correlations are shown to be dramatically reduced for the asymmetric case of N=Z+4. The shell model results obtained are qualitatively explained within a simplified degenerate model.

Sheikh, J. A. [Department of Physics, University of Kashmir, Srinagar, 190 006 (India); Inter-University Accelerator Center, New Delhi, 110 067 (India); Ganai, P. A. [Department of Physics, University of Kashmir, Srinagar, 190 006 (India); Singh, R. P.; Bhowmik, R. K. [Inter-University Accelerator Center, New Delhi, 110 067 (India); Frauendorf, S. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

2008-01-15

346

Charge distribution in the thermal neutron fission of 245Cm: Fractional cumulative yields of 135I and 140Ba  

Microsoft Academic Search

Fractional cumulative yields for 135I and 140Ba have been determined in the thermal neutron induced fission of 245Cm following the respective daughter product activities. The fractional cumulative yield values obtained are 0.951+\\/-0.014 and 0.969+\\/-0.006 for 135I and 140Ba, respectively. The fractional cumulative yield value for 135I has been compared with the one reported earlier and an attempt has been made

Tarun Datta; S. P. Dange; S. B. Manohar; A. G. C. Nair; Satya Prakash; M. V. Ramaniah

1980-01-01

347

Neutron radiographs using the ionographic process  

Microsoft Academic Search

Thermal neutron radiographs have been made using ionographic techniques. With a fluence of 107 neutrons\\/cm2 at the image plane, image resolution of three line pairs per mm was demonstrated. The apparatus for these demonstration experiments is described, and alternative modes of operation are discussed. It appears possible to make ionographic neutron radiographs using a transmitted fluence of 106 neutrons\\/cm2.

P. B. Scott; S. E. Johnson; G. W. Watson; Harold Berger

1978-01-01

348

Di-neutron correlation in light neutron-rich nuclei  

E-print Network

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

K. Hagino; H. Sagawa; P. Schuck

2008-12-03

349

Characterization of a Neutron Collimator for Neutron Radiography Applications  

Microsoft Academic Search

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 flux, its spatial\\/energetic distribution, photon air KERMA and effective beam diameter. This paper shows

M. Palomba; R. Rosa

350

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

NASA Astrophysics Data System (ADS)

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

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

351

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

352

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

SciTech Connect

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)

Kisohara, N. [Advanced Nuclear System Research and Development Directorate, Japan Atomic Energy Agency (Japan); Suzuki, H.; Akita, K. [Quantum Beam Science Directorate, Japan Atomic Energy Agency (Japan); Kasahara, N. [Dept. of Nuclear Engineering and Management, Univ. of Tokyo (Japan)

2012-07-01

353

Gelina neutron target optimisation.  

PubMed

A study is being performed on the properties of the Geel Electron Linear Accelerator (GELINA), a powerful white neutron source, designed for the high-energy resolution time-of-flight measurements. The main aim of this study is to reduce the time spread of neutrons of the given energy without compromising the neutron yield. Both time spread and neutron intensity influence the experimental accuracy of high-resolution neutron cross section measurements, which are particularly important in the resonance region. The quantities of interest have been simulated with coupled electron-photon-neutron steady state and transient MCNP4C3 calculations. Following benchmarking of the code to the properties of the existing target, neutron yield, energy spectra, resolution functions, and neutron and heat spatial distributions have been determined for various alternative geometries and materials. At a fixed accelerator power, actinides deliver the highest neutron yield and a small target provides the best time resolution. The resulting high-power density requires a joint optimisation of the thermal hydraulics and neutronics properties. PMID:16381756

Flaska, M; Plompen, A J M; Mondelaers, W; Lathouwers, D; van der Hagen, T H J J; van Dam, H

2005-01-01

354

Conservation of Isospin in Neutron-Rich Fission Fragments  

E-print Network

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

Jain, Ashok Kumar; Maheshwari, Bhoomika

2014-01-01

355

Conservation of Isospin in Neutron-rich Fission Fragments  

NASA Astrophysics Data System (ADS)

On the occasion of the 75 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(n,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.

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

2014-06-01

356

Conservation of Isospin in Neutron-Rich Fission Fragments  

E-print Network

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

Ashok Kumar Jain; Deepika Choudhury; Bhoomika Maheshwari

2014-08-11

357

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

E-print Network

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

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

2012-01-01

358

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

E-print Network

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

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

2012-07-25

359

Pairings on hyperelliptic curves  

Microsoft Academic Search

We assemble and reorganize the recent work in the area of hyperelliptic pairings: We survey the research on constructing hyperelliptic curves suitable for pairing-based cryptography. We also showcase the hyperelliptic pairings proposed to date, and develop a unifying framework. We discuss the techniques used to optimize the pairing computation on hyperelliptic curves, and present many directions for further research.

Jennifer Balakrishnan; Juliana Belding; Sarah Chisholm; Kirsten Eisentraeger; Katherine E. Stange; Edlyn Teske

2009-01-01

360

Counting the number of correlated pairs in a nucleus  

SciTech Connect

We suggest that the number of correlated nucleon pairs in an arbitrary nucleus can be estimated by counting the number of proton-neutron, proton-proton, and neutron-neutron pairs residing in a relative S state. We present numerical calculations of those amounts for the nuclei {sup 4}He, {sup 9}Be, {sup 12}C, {sup 27}Al, {sup 40}Ca, {sup 48}Ca, {sup 56}Fe, {sup 63}Cu, {sup 108}Ag, and {sup 197}Au. The results are used to predict the values of the ratios of the per-nucleon electron-nucleus inelastic scattering cross section to the deuteron in the kinematic regime where correlations dominate.

Vanhalst, Maarten; Cosyn, Wim; Ryckebusch, Jan [Department of Physics and Astronomy, Ghent University, Proeftuinstraat 86, B-9000 Gent (Belgium)

2011-09-15

361

Synthesize Neutron-Drip-Line-Nuclides with Free-Neutron Bose-Einstein Condensates Experimentally  

E-print Network

We first show a possible way to create a new type of matter, free-neutron Bose-Einstein condensate by the ultracold free-neutron-pair Bose-Einstein condensation and then determine the neutron drip line experimentally. The Bose-Einstein condensation of bosonic and fermionic atoms in atomic gases was performed experimentally and predicted theoretically early. Neutrons are similar to fermionic atoms. We found free neutrons could be cooled to ultracold neutrons with very low energy by other colder neutral atoms which are cooled by the laser. These neutrons form neutron pairs with spin zero, and then ultracold neutron-pairs form Bose-Einstein condensate. Our results demonstrate how these condensates can react with accelerated ion beams at different energy to synthesize very neutron-rich nuclides near, on or/and beyond the neutron drip line, to determine the neutron drip line and whether there are long-life nuclide or isomer islands beyond the neutron drip line experimentally. Otherwise, these experimental results will confirm our prediction that is in the whole interacting region or distance of nuclear force in all energy region from zero to infinite, Only repulsive nuclear force exists among identical nucleons and only among different nucleons exists attractive nuclear force.

Bao-Guo Dong

2014-09-22

362

Neutronic reactor  

DOEpatents

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

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

1983-01-01

363

Odd-even mass difference and isospin dependent pairing interaction  

E-print Network

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

C. A. Bertulani; H. F. Lu; H. Sagawa

2009-06-15

364

Odd-even mass difference and isospin dependent pairing interaction  

SciTech Connect

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

Bertulani, C. A. [Department of Physics, Texas A and M University-Commerce, Commerce, Texas 75429 (United States); Lue, H. F. [College of Science, China Agricultural University, Beijing (China); Sagawa, H. [Center for Mathematics and Physics, University of Aizu, Aizu-Wakamatsu, 965-8580 Fukushima (Japan)

2009-08-15

365

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

NASA Astrophysics Data System (ADS)

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

Rivard, Mark Joseph

366

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

PubMed

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 () < 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

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

367

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

Microsoft Academic Search

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

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

2009-01-01

368

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

SciTech Connect

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

Greenwood, L.R.; Intasorn, A.

1989-07-01

369

Neutron Compound Refractive Prisms - DOE SBIR Phase II Final Report  

SciTech Connect

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

Dr. Jay Theodore Cremer, Jr

2011-06-25

370

Calculation of Prompt Neutron Multiplicities and Spectra for Several Actinides  

SciTech Connect

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

Hambsch, Franz-Josef; Oberstedt, Stephan [EC-JRC-Institute for Reference Materials and Measurements, Retieseweg 111, B-2440 Geel (Belgium); Tudora, Anabella; Vladuca, Gheorghita [Faculty of Physics, Bucharest University, RO-76900 Bucharest (Romania)

2005-05-24

371

Hard exclusive electroproduction of ?+?- pairs  

NASA Astrophysics Data System (ADS)

Hard exclusive electroproduction of ?+?- pairs off hydrogen and deuterium targets has been studied by the HERMES experiment at DESY. Legendre moments and of the angular distributions of ?+ mesons in the center-of-mass frame of the pair have been measured for the first time. Their dependence on the ?+?- invariant mass can be understood as being due to the interference between relative P-wave (isovector) and S-, D-wave (isoscalar) states of the two pions. The increase in magnitude of as Bjorken x increases is interpreted in the framework of generalized parton distributions as an enhancement of flavour non-singlet qqbar exchange for larger values of x, which leads to a sizable admixture of isoscalar and isovector pion pairs. In addition, the interference between P-wave and D-wave states separately for transverse and longitudinal pion pairs has been studied. The data indicate that in the f2 (1270) region at = 3 GeV2 higher-twist effects can be as large as the leading-twist longitudinal component.

Airapetian, A.; Akopov, N.; Akopov, Z.; Amarian, M.; Ammosov, V. V.; Andrus, A.; Aschenauer, E. C.; Augustyniak, W.; Avakian, R.; Avetissian, A.; Avetissian, E.; Bailey, P.; Balin, D.; Baturin, V.; Beckmann, M.; Belostotski, S.; Bernreuther, S.; Bianchi, N.; Blok, H. P.; Bttcher, H.; Borissov, A.; Borysenko, A.; Bouwhuis, M.; Brack, J.; Brll, A.; Bryzgalov, V.; Capitani, G. P.; Chen, T.; Ciullo, G.; Contalbrigo, M.; Dalpiaz, P. F.; de Leo, R.; Demey, M.; de Nardo, L.; de Sanctis, E.; Devitsin, E.; di Nezza, P.; Dren, M.; Ehrenfried, M.; Elalaoui-Moulay, A.; Elbakian, G.; Ellinghaus, F.; Elschenbroich, U.; Fabbri, R.; Fantoni, A.; Fechtchenko, A.; Felawka, L.; Frullani, S.; Gapienko, G.; Gapienko, V.; Garibaldi, F.; Garrow, K.; Garutti, E.; Gavrilov, G.; Gharibyan, V.; Graw, G.; Grebeniouk, O.; Greeniaus, L. G.; Gregor, I. M.; Griffioen, K. A.; Hafidi, K.; Hartig, M.; Hasch, D.; Heesbeen, D.; Henoch, M.; Hertenberger, R.; Hesselink, W. H. A.; Hillenbrand, A.; Hoek, M.; Holler, Y.; Hommez, B.; Iarygin, G.; Ivanilov, A.; Izotov, A.; Jackson, H. E.; Jgoun, A.; Kaiser, R.; Kinney, E.; Kisselev, A.; Kopytin, M.; Korotkov, V.; Kozlov, V.; Krauss, B.; Krivokhijine, V. G.; Lagamba, L.; Lapiks, L.; Laziev, A.; Lenisa, P.; Liebing, P.; Linden-Levy, L. A.; Lipka, K.; Lorenzon, W.; Lu, H.; Lu, J.; Lu, S.; Ma, B.-Q.; Maiheu, B.; Makins, N. C. R.; Mao, Y.; Marianski, B.; Marukyan, H.; Masoli, F.; Mexner, V.; Meyners, N.; Mikloukho, O.; Miller, C. A.; Miyachi, Y.; Muccifora, V.; Nagaitsev, A.; Nappi, E.; Naryshkin, Y.; Nass, A.; Negodaev, M.; Nowak, W.-D.; Oganessyan, K.; Ohsuga, H.; Osborne, A.; Pickert, N.; Potashov, S.; Potterveld, D. H.; Raithel, M.; Reggiani, D.; Reimer, P. E.; Reischl, A.; Reolon, A. R.; Riedl, C.; Rith, K.; Rosner, G.; Rostomyan, A.; Rubacek, L.; Rubin, J.; Ryckbosch, D.; Salomatin, Y.; Sanjiev, I.; Savin, I.; Schfer, A.; Schill, C.; Schnell, G.; Schler, K. P.; Seele, J.; Seidl, R.; Seitz, B.; Shanidze, R.; Shearer, C.; Shibata, T.-A.; Shutov, V.; Sinram, K.; Sommer, W.; Stancari, M.; Statera, M.; Steffens, E.; Steijger, J. J. M.; Stenzel, H.; Stewart, J.; Stinzing, F.; Tait, P.; Tanaka, H.; Taroian, S.; Tchuiko, B.; Terkulov, A.; Tkabladze, A.; Trzcinski, A.; Tytgat, M.; Vandenbroucke, A.; van der Nat, P.; van der Steenhoven, G.; van Haarlem, Y.; Vetterli, M. C.; Vikhrov, V.; Vincter, M. G.; Vogel, C.; Vogt, M.; Volmer, J.; Weiskopf, C.; Wendland, J.; Wilbert, J.; Ybeles Smit, G.; Ye, Y.; Ye, Z.; Yen, S.; Zihlmann, B.; Zupranski, P.; Hermes Collaboration

2004-10-01

372

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

SciTech Connect

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

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

2011-01-24

373

Detailed mapping of the local Ir4+ dimers through the metal-insulator transitions of CuIr2S4 thiospinel by X-ray atomic pair distribution function measurements.  

PubMed

The evolution of the short-range structural signature of the Ir4+ dimer state in CuIr2S4 thiospinel has been studied across the metal-insulator phase transitions as the metallic state is induced by temperature, Cr doping, and x-ray fluence. An atomic pair distribution function (PDF) approach reveals that there are no local dimers that survive into the metallic phase when this is invoked by temperature and doping. The PDF shows Ir4+ dimers when they exist, regardless of whether or not they are long-range ordered. At 100 K, exposure to a 98 keV x-ray beam melts the long-range dimer order within a few seconds, though the local dimers remain intact. This shows that the metallic state accessed on warming and doping is qualitatively different from the state obtained under x-ray irradiation. PMID:21405330

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

2011-01-28

374

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

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

375

Nuclear charge distribution of mass-separated isobars from thermal-neutron-induced fission of 235U  

Microsoft Academic Search

The nuclear charge distribution of fission products with mass numbers A = 90, 91, 94, 99, 100, 101 and 104 provided by the mass separator ``Lohengrin'' was measured. Adjacent elements in the group of the light fission products could be separated by their different energy loss in a carbon absorber. The Z-yields were found to be strongly dependent on the

H.-G. Clerc; K.-H. Schmidt; H. Wohlfarth; W. Lang; H. Schrader; K. E. Pferdekmper; R. Jungmann; M. Asghar; J. P. Bocquet; G. Siegert

1975-01-01

376

MENTORING PAIRINGS APPRENTICE  

E-print Network

MENTORING PAIRINGS APPRENTICE Undergraduate students, e-mails, and mentors. ________________________________________________________________________________ |_Name_(18)____________|@uchicago.edu_|_______________mentor(s)________________* *_ | | Padraic James

May, J. Peter

377

Contragredient supersymmetric pairs  

NASA Astrophysics Data System (ADS)

The symmetric pairs of complex semisimple Lie algebras can be characterized by commuting involutions. We present its analogue on the contragredient Lie superalgebras, so that their symmetric pairs correspond to some commuting automorphisms. As an application, we classify the symmetric pairs of the exceptional Lie superalgebras F(4) and G(3).

Chuah, Meng-Kiat

2013-09-01

378

Galaxy pairs align with Galactic filaments  

NASA Astrophysics Data System (ADS)

Context. Gravitational collapse theory and numerical simulations suggest that the velocity field within large-scale galaxy filaments is dominated by motions along the filaments. Aims: Our aim is to check whether observational data reveal any preferred orientation of galaxy pairs with respect to the underlying filaments as a result of the expectedly anisotropic velocity field. Methods: We use galaxy pairs and galaxy filaments identified from Sloan Digital Sky Survey data. For filament extraction, we use the Bisous model that is based on the marked point process technique. During the filament detection, we use the centre point of each pair instead of the positions of galaxies to avoid a built-in influence of pair orientation on the filament construction. For pairs lying within filaments (3012 cases), we calculate the angle between the line connecting the galaxies of each pair and their host filaments. To avoid redshift-space distortions, the angle is measured in the plane of the sky. Results: The alignment analysis shows that the orientation of galaxy pairs correlates strongly with their host filaments. The alignment signal is stronger for loose pairs, with at least 25% excess of aligned pairs compared to a random distribution. The alignment of galaxy pairs and filaments measured from the observational data is in good agreement with the alignment in the Millennium simulation and thus provides support to the ?CDM formalism.

Tempel, E.; Tamm, A.

2015-04-01

379

The Generalized Model for the Description of Prompt Neutrons in the Low-energy Fission  

NASA Astrophysics Data System (ADS)

The generalized model for the description of neutron emission from the spontaneous and neutron-induced fission in the energy interval up to 20 MeV is developed. For accurate calculations of nucleon composition and excitation energy of the fissioning nucleus at the scission point, the time-dependent statistical model including the pre-equilibrium neutron emission and nuclear friction effects is used. For each member of the compound nucleus ensemble at the scission point, the primary fission-fragment characteristics such as kinetic and excitation energies and yields are calculated using the scission-point fission model with nuclear shell and pairing effects, and based on the multimodal approach. The charge distribution for the primary fragment isobaric chains is considered as a result of the frozen quantal fluctuations of the isovector nuclear matter density at the finite scission neck radius. The post-scission neutron spectra are calculated as the result of the equilibrium emission from the fully accelerated fission fragments with calculated kinetic energies. The pre- scission neutron multiplicity and spectra for multi-chance fission are also calculated. The neutron and ?-ray emission during the saddle-to-scission time is also included in the consideration. This mechanism may partially explain the long standing problem of the so-called isotropic component of prompt fission neutrons.

Rubchenya, V. A.

380

Fission-fragment charge distributions in thermal-neutron induced fission of 239Pu and 235U  

Microsoft Academic Search

Fission-fragment charge distributions of heavy fragments were investigated for fragment masses 131 <= A <= 140 in the reactions 239Pu(nth, f) and 235U(nth, f). This was done by a correlated observation of beta-tracks and fission-fragment tracks in nuclear emulsions for fission fragments separated with respect to mass and kinetic energy by a recoil mass spectrograph. The average nuclear charges are

H. Gunther; G. Siegert; R. L. Ferguson; H. Ewald; E. Konecny

1972-01-01

381

On the pairing effects in triaxial nuclei  

SciTech Connect

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.

Oudih, M. R. [Laboratoire de Physique Thorique, Facult de Physique,USTHB BP 32, El Alia, 16111 Bab Ezzouar, Algiers (Algeria); Fellah, M.; Allal, N. H. [Centre de Recherche Nuclaire d'Alger, 2 Bd. Frantz Fanon, BP. 399 Alger-Gare, Algiers, Algeria and Laboratoire de Physique Thorique, Facult de Physique,USTHB BP 32, El Alia, 16111 Bab Ezzouar, Algiers (Algeria)

2014-03-05

382

Ion pair receptors  

PubMed Central

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

Kim, Sung Kuk

2010-01-01

383

Evidence of local lattice distortions in La{sub 1-x}SrMnO provided by pulsed neutron diffraction  

Microsoft Academic Search

The pulsed neutron powder diffraction study of La{sub 1-x}SrMnO reveals that the local atomic structure is significantly different from the long range structure, and these differences are important in understanding their properties. Even though the crystal structure suggests that the JahnTeller (JT) distortion disappears quickly with Sr doping, the analysis by the pair distribution function technique indicates that locally JT

D. Louca; T. Egami

1997-01-01

384

Evidence of local lattice distortions in La1 - xSrxMnO3 provided by pulsed neutron diffraction  

Microsoft Academic Search

The pulsed neutron powder diffraction study of La1?xSrxMnO3 reveals that the local atomic structure is significantly different from the long range structure, and these differences are important in understanding their properties. Even though the crystal structure suggests that the JahnTeller (JT) distortion disappears quickly with Sr doping, the analysis by the pair distribution function technique indicates that locally JT distortions

Despina Louca; T. Egami

1997-01-01

385

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.  

PubMed

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 D20 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. PMID:11686282

Tanaka, K; Kobayashi, T; Sakurai, Y; Nakagawa, Y; Endo, S; Hoshi, M

2001-10-01

386

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)

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.

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

2001-10-01

387

Calculation of two-neutron multiplicity in photonuclear reactions  

NASA Technical Reports Server (NTRS)

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

Norbury, John W.; Townsend, Lawrence W.

1990-01-01

388

Calculation of two-neutron multiplicity in photonuclear reactions  

NASA Technical Reports Server (NTRS)

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

Norbury, John W.; Townsend, Lawrence W.

1989-01-01

389

Close pairs of galaxies in deep sky surveys  

Microsoft Academic Search

A largely complete sample of 20 close pairs of faint galaxies, separated by less than 4.5 arcsec, is studied. The colors of the galaxy pairs indicate recently enhanced star formation in some systems, but generally the distribution of the colors and size of the galaxies in pairs is not significantly different from that of equally faint field galaxies. There is

Stephen E. Zepf; David C. Koo

1989-01-01

390

Neutron multiplicities in spontaneous fission and nuclear structure studies  

SciTech Connect

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

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

1993-12-31

391

Superconducting cyclotron: neutron source for therapy  

Microsoft Academic Search

A neutron source for medical therapy purposes is described. The cyclotron consists of: an iron metal housing acting as a magnetic yoke, magnetic shield, radiation shield, and vacuum vessel; a pair of superconducting coils mounted in a cavity in the housing, the coils being cooled to superconducting temperatures; an ion orbiting region defined by pairs of sectoral-shaped rf electrode structures

C. B. Bigham; H. R. Schneider

1975-01-01

392

Coulombic effect and renormalization in nuclear pairing  

SciTech Connect

We investigate the effects of the Coulomb force on the nuclear pairing properties by performing the Gogny Hartree-Fock-Bogolyubov calculations for the N=20, 28, 50, 82, and 126 nuclei. The Coulomb force reduces the proton pair energy and the even-odd mass difference by about 25%, except for nuclei at and around the proton shell or subshell closure. We then propose a renormalization scheme via a reduction factor {gamma}{sub p} for the proton pairing channel. It is found that a single value {gamma}{sub p}=0.90 accounts well for the Coulombic effect for nuclei covering a wide range of the mass number and the neutron excess, including the nuclei around the shell or subshell closure.

Nakada, H.; Yamagami, M. [Department of Physics, Graduate School of Science, Chiba University, Yayoi-cho 1-33, Inage, Chiba 263-8522 (Japan); Department of Computer Science and Engineering, University of Aizu, Aizu-Wakamatsu, Fukushima 965-8580 (Japan)

2011-03-15

393

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

PubMed

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

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

2010-02-01

394

Matched-pair classification  

SciTech Connect

Following an analogous distinction in statistical hypothesis testing, we investigate variants of machine learning where the training set comes in matched pairs. We demonstrate that even conventional classifiers can exhibit improved performance when the input data has a matched-pair structure. Online algorithms, in particular, converge quicker when the data is presented in pairs. In some scenarios (such as the weak signal detection problem), matched pairs can be generated from independent samples, with the effect not only doubling the nominal size of the training set, but of providing the structure that leads to better learning. A family of 'dipole' algorithms is introduced that explicitly takes advantage of matched-pair structure in the input data and leads to further performance gains. Finally, we illustrate the application of matched-pair learning to chemical plume detection in hyperspectral imagery.

Theiler, James P [Los Alamos National Laboratory

2009-01-01

395

Nuclear pairing: New perspectives  

Microsoft Academic Search

Nuclear pairing correlations are known to play an important role in various single-particle and collective aspects of nuclear\\u000a structure. After the first idea by A. Bohr, B. Mottelson, and D. Pines on similarity of nuclear pairing to electron superconductivity,\\u000a S.T. Belyaev gave a thorough analysis of the manifestations of pairing in complex nuclei. The current revival of interest\\u000a in nuclear

Vladimir Zelevinsky; Alexander Volya

2003-01-01

396

Nuclear Charge Distribution in Fission: Fractional Yields of Krypton and Xenon Isotopes from Thermal Neutron Fission of U233 and Pu239 and from 14MeV Neutron Fission of U235 and U238  

Microsoft Academic Search

Measurements of fractional cumulative yields of Kr89 through Kr93, Kr95, and Xe137 through Xe144 from thermal neutron fission of U233 and Pu239 and of Kr91 through Kr93 and Xe138 through Xe141 from 14-MeV neutron fission of U235 and U238 have been made. These data and other published data show that isobaric charge dispersion for fission products with mass number 140

Kurt Wolfsberg

1965-01-01

397

Mathematics of Chromosome Pairing  

PubMed Central

Analysis of frequencies of chromosome configurations in wheat-related species hybrids is extended to include cases involving homoeologous groups of size six. Further, the expected frequencies of the various configurations emanating from homologous and homoeologous pairing events have been determined for groups consisting of two and three homoeologous pairs of homologous chromosomes. Analysis of configuration frequencies of nullisomic 5B of wheat, in which both homologous and homoeologous pairing occurs, led to estimation of the relative frequencies of homologous and homoeologous pairing events as 17.9:1. In the samples analyzed, slightly less than one homoeologous exchange occurred per gamete. PMID:17249031

Driscoll, C. J.; Gordon, G. H.; Kimber, G.

1980-01-01

398

Vortex pairs on surfaces  

SciTech Connect

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

Koiller, Jair [Centro de Matematica Aplicada, FGV/RJ, Praia de Botafogo 190 Rio de Janeiro, RJ, 22250-40 (Brazil); Boatto, Stefanella [Instituto de Matematica da UFRJ, C.P. 68530, Cidade Universitaria Rio de Janeiro, RJ 21945-970 (Brazil)

2009-05-06

399

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

PubMed

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

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

2011-12-01

400

High resolution neutron diffraction study on Fe 81B 19 metallic glass  

NASA Astrophysics Data System (ADS)

The structure factor of Fe 81B 19 metallic glass was measured by the conventional and time-of-flight neutron diffraction methods in the 0.4pair distribution function obtained by Fourier transformation is resolved into subpeaks. The distances and distribution widths of the Fe-B and Fe-Fe first neighbours, the partial coordination numbers and the short range order parameter are given. The results clearly indicate preferential chemical bonding between iron and boron atoms.

Svab, E.; Kroo, N.; Ishmaev, S. N.; Sadikov, I. P.; Chernyshov, A. A.

1982-11-01

401

Structure of the mass distributions of the products of thermal-neutron fission of ²³⁵U and ²³⁹Pu for a fixed energy of the fission products  

Microsoft Academic Search

Relative mass yields of the fission products of thermal-neutron fission of ²³⁵U and ²³⁹Pu have been determined for six values of the kinetic energy E\\/sub k\\/. A fine structure is observed at A = 137 and an anomalously low yield at A = 139. Mass distributions of fission products of the heavy group are presented for a fixed value of

A. D. Belyaev; Z. S. Bikbova; V. I. Kogan; A. I. Muminov; V. P. Pikul; A. M. Usmandiyarov

1984-01-01

402

Pair Winds in Schwarzschild Spacetime with Application to Strange Stars  

E-print Network

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

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

2007-01-09

403

Pairing effects on spinodal decomposition of asymmetric nuclear matter  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

404

The Inelastic Scattering of Neutrons  

Microsoft Academic Search

The total cross section and the differential cross section for the inelastic scattering of neutrons are considered. It is assumed that the compound nucleus is sufficiently excited so that the statistical model may be applied. If the statistical model may be applied as well to the residual nucleus, it is shown that the angular distribution of the inelastically scattered neutrons

Walter Hauser; Herman Feshbach

1952-01-01

405

NIF Neutron Image Reconstruction Techniques  

NASA Astrophysics Data System (ADS)

Neutron imaging is an important diagnostic tool for inertial fusion studies at the National Ignition Facility (NIF) for measuring asymmetries in the burn region during the ignition stage of implosions. The technique for imaging of the spatial distribution of deuterium-tritium (DT) fusion neutrons utilizes an aperture - placed between the neutron source and a spatially sensitive neutron detector - which blocks the neutron flux and produces a shadow image of the neutron source at the detector. The recorded image is related to the 2D projection of the neutron source through a convolution with some, in general case spatially dependent, point spread function. The neutron source is reconstructed from the recorded image by solving a Fredholm-type integral equation of the first kind before we can estimate the shape and the size of the source. This inverse problem is notoriously ill-posed and presents certain difficulties in the context of NIF neutron imaging. Due to relatively low yield of neutrons the recorded images are expected to be noisy, so a special attention should be paid to the regularization of the equations to avoid the unacceptable amplification of the noise. We will present an overview of the developed techniques for reconstruction of source image from detector images and the results of reconstruction of the first neutron images obtained at NIF.

Volegov, Petr; Grim, Gary; Merrill, Frank; Wilson, Douglas

2011-11-01

406

Neutron skins and neutron stars  

SciTech Connect

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

Piekarewicz, J. [Department of Physics, Florida State University, Tallahassee, FL 32306-4350 (United States)

2013-11-07

407

Neutron guide  

DOEpatents

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

Greene, Geoffrey L. (Los Alamos, NM)

1999-01-01

408

Neutron Repulsion  

Microsoft Academic Search

Earth is connected gravitationally, magnetically and electrically to its heat source - a neutron star that is obscured from view by waste products in the photosphere. Neutron repulsion is like the hot filament in an incandescent light bulb. Excited neutrons are emitted from the solar core and decay into hydrogen that glows in the photosphere like a frosted light bulb.

Oliver K. Manuel

2011-01-01

409

Argonne potential and multi-neutron systems  

NASA Astrophysics Data System (ADS)

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(N8/3), 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.

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

2014-07-01

410

Argonne potential and multi-neutron systems  

SciTech Connect

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)?=??cN{sup 3}+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.

Gridnev, D. K.; Gridnev, K. A. [Saint Petersburg State University, Uljanovskaja 1, 198504 St. Petersburg (Russian Federation); Schramm, S.; Greiner, Walter [Frankfurt Institute of Advanced Studies, Ruth-Moufang Str. 1, 60438 Frankfurt (Germany)

2014-07-23

411

Cooper Pairs in Insulators?!  

ScienceCinema

Nearly 50 years elapsed between the discovery of superconductivity and the emergence of the microscopic theory describing this zero resistance state. The explanation required a novel phase of matter in which conduction electrons joined in weakly bound pairs and condensed with other pairs into a single quantum state. Surprisingly, this Cooper pair formation has also been invoked to account for recently uncovered high-resistance or insulating phases of matter. To address this possibility, we have used nanotechnology to create an insulating system that we can probe directly for Cooper pairs. I will present the evidence that Cooper pairs exist and dominate the electrical transport in these insulators and I will discuss how these findings provide new insight into superconductor to insulator quantum phase transitions.

James Valles

2010-01-08

412

Optimal Distributed All Pairs Shortest Paths  

E-print Network

nodes Diameter of this network? #12;· Spanning Tree ­ Broadcasting, Aggregation, etc · Minimum Spanning #12;· Spanning Tree ­ Broadcasting, Aggregation, etc · Minimum Spanning Tree ­ Efficient broadcasting;· Spanning Tree ­ Broadcasting, Aggregation, etc · Minimum Spanning Tree ­ Efficient broadcasting, etc

413

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

SciTech Connect

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

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

2014-07-15

414

Neutrons for Catalysis Neutrons as  

E-print Network

Neutrons for Catalysis Neutrons as Microscopic Probes in Heterogeneous Catalysis Juergen Eckert Materials Research Laboratory University of California Santa Barbara #12;Grand Challenges for Catalysis Studies: no "windows" necessary! Diffraction Study (O'Hare): in-situ hydrothermal crystallization cell

Pennycook, Steve

415

Cubic neutrons  

E-print Network

The neutron is largely spherical and incompressible in atomic nuclei. These two properties are however challenged in the extreme pressure environment of a neutron star. Our variational computation within the Cornell model of Coulomb gauge QCD shows that the neutron (and also the Delta-3/2 baryon) can adopt cubic symmetry at an energy cost of about 150 MeV. Balancing this with the free energy gained by tighter neutron packing, we expose the possible softening of the equation of state of neutron matter.

Felipe J. Llanes-Estrada; Gaspar Moreno Navarro

2011-08-09

416

Fragment velocities, energies, and masses from fast neutron induced fission of 235U  

NASA Astrophysics Data System (ADS)

We report on a complete (2E,2v) experiment for fast neutron induced fission on 235U. The energy dependence of fragment properties so far known only for thermal neutron induced fission is studied. Experimental problems as well as difficulties in data analysis are considered in detail in order to obtain clean and unbiased results. In particular, a self-consistent determination of the fragment total kinetic energy (EK,tot) was achieved by comparing the results obtained via the respective velocities and pulse heights. We find systematic discrepancies of 2 MeV if EK,tot is determined from the observed pulse heights with the calibration scheme of Schmitt et al. Therefore, refined calibration constants were deduced by comparison with accurate radiochemical mass yields. Measurements were performed at neutron energies of 0.50 and 5.55 MeV. Our results include mean values of fragment properties before and after neutron evaporation, e.g., of fragment velocities and masses, total kinetic energies, and the respective variances. We also show the distributions of fragment mass, of EK,tot, and of the variance of EK,tot. In addition, the number of prompt fission neutrons ? is given as a function of fragment mass. Our resolution of 2.1 mass units reveals fine structure not only in the fragment mass distribution but also in EK,tot(A*) and ?(A*). For the lower neutron energy of 0.50 MeV the present results compare reasonably well with similar measurements performed with thermal neutrons. Apparently the 0.5 MeV increase in saddle point excitation does not alter the results significantly. The improved accuracy of this measurement is demonstrated by comparison of our neutron emission data with direct measurements of fission neutrons. At the higher neutron energy of 5.55 MeV we observe the expected decrease of shell and pairing effects which indicates an increase in nuclear temperature. These results are in qualitative agreement with the model of Wilkins, Chasman, and Steinberg. However, a striking discrepancy exists for the number of fission neutrons, where we find that the increase in the total number of fission neutrons is totally accounted for by heavy fragments alone.

Mller, R.; Naqvi, A. A.; Kppeler, F.; Dickmann, F.

1984-03-01

417

Excitation energy at scission in thermal-neutron-induced fission  

NASA Astrophysics Data System (ADS)

For the thermal-neutron-induced fission of 235U and 233U, we extract the internal excitation energy at the scission point by use of two different methods. The first method uses experimental data for 235U + nth on the neutrons and gamma rays emitted from doubly magic fission fragments, where the extra stability associated with shell closures makes the deformation energy small. Under the assumption that both fragments have equal temperatures, this yields an upper limit of 9.9 MeV for the total internal excitation energy at scission. The second method uses experimental data for 233U + nth on odd-even effects in fission-fragment mass distributions and yields an average value of 5.6 MeV for the total internal excitation energy at scission when integrated over all fission-fragment kinetic energies. In both cases the internal excitation energy at scission is significantly smaller than that predicted by the one-body-dissipation theory of Swiatecki and co-workers and is instead much closer to that predicted by ordinary two-body viscosity. NUCLEAR REACTIONS, FISSION 235U + nth, 233U + nth; extracted internal excitation energy at scission point. Neutrons and gamma rays from doubly magic fission fragments, odd-even effects in fission-fragment mass distributions, one-body dissipation, two-body viscosity, temperature-dependent BCS pairing theory.

Mantzouranis, G.; Nix, J. R.

1982-02-01

418

Independent Yields of Krypton and Xenon Isotopes in Thermal-Neutron Fission of 235U. Observation of an Odd-Even Effect in the Element Yield Distribution  

Microsoft Academic Search

The fractional and independent fission yields of krypton isotopes (masses 87 to 94) and xenon isotopes (masses 137-143) produced in thermal-neutron fission of 235U were measured using a mass separator operating in an on-line mode with a fission source exposed to time-controlled neutron fluxes. The noble-gas isotopes were collected simultaneously at given times and each mass was measured separately. The

B. Ehrenberg; S. Amiel

1972-01-01

419

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

E-print Network

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-decay, we have identified the best candidates to look for deformation signatures in their beta-decay patterns. beta+ half-lives and total Gamow-Teller strengths B(GT+) and B(GT-) are analyzed as well.

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

2006-04-11

420

Neutron Radiography  

NASA Astrophysics Data System (ADS)

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

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

421

Thermal Comptonization in Mildly Relativistic Pair Plasmas  

E-print Network

We use a Monte Carlo simulation to calculate the spectra of mildly relativistic thermal plasmas in pair balance. We use the exact integral expression for the electron-positron thermal annihilation spectrum, and provide accurate expressions for the Gaunt factors of electron-ion, electron-electron, and electron-positron thermal bremsstrahlung in the transrelativistic temperature regime. The particles are assumed to be uniformly distributed throughout a sphere, and the pair opacity is self-consistently calculated from the energy and angular distribution of scattered photons. The resultant photon spectra are compared with the nonrelativistic diffusion treatment of Sunyaev and Titarchuk, the bridging formulas of Zdziarski, and the relativistic corrections proposed by Titarchuk. We calculate allowed pair-balanced states of thermal plasmas with no pair escape which include bremsstrahlung and internal soft photons. The results are presented in the spectral index/compactness plane, and can be directly compared with observations of spectra from AGNs and Galactic black hole candidates. By comparing with X-ray spectral indices of Seyfert AGNs and compactnesses inferred from X-ray variability data, we find that the allowed solutions for pair equilibrium plasma imply that the temperatures of Seyfert galaxies are $\\lesssim 300$ keV. This prediction can be tested with more sensitive gamma-ray observations of Seyfert galaxies. We find that if the X-ray variability time scale gives an accurate measure of the compactness, pair-dominated solutions are inconsistent with the data.

J. G. Skibo; C. D. Dermer; R. Ramaty; J. M. McKinley

1994-12-21

422

Stylized features of single-nucleon momentum distributions  

E-print Network

[Background:] Nuclear short-range correlations (SRC) typically manifest themselves in the tail parts of the single-nucleon momentum distributions. [Purpose:] To develop an approximate flexible method for computing the single-nucleon momentum distributions throughout the whole mass table, thereby including the majority of the effects of SRC. To use this method to study the mass and isospin dependence of SRC. [Method:] The low-order cluster approximation (LCA) adopted in this work, corrects mean-field models for correlations by shifting the complexity induced by the SRC from the wave functions to the operators. Due to the local character of the SRC, it is argued that the expansion of these operators can be truncated to a low order. [Results:] After inclusion of the central and tensor correlations, the LCA can generate the SRC-related features of the single-nucleon momentum distribution like the high-momentum tails. These are dominated by correlations operating on mean-field pairs with vanishing relative radial and angular-momentum quantum numbers. In asymmetric nuclei, the correlations make the average kinetic energy for the minority nucleons larger than for the majority nucleons. [Conclusions:] The LCA method explains the dominant role of proton-neutron pairs in generating the SRC and provides predictions for the ratio of the amount of correlated proton-proton to proton-neutron pairs which are in line with the observations.

Maarten Vanhalst; Wim Cosyn; Jan Ryckebusch

2014-09-05

423

Subroutines to Simulate Fission Neutrons for Monte Carlo Transport Codes  

E-print Network

Fortran subroutines have been written to simulate the production of fission neutrons from the spontaneous fission of 252Cf and 240Pu, and from the thermal neutron induced fission of 239Pu and 235U. The names of these four subroutines are getnv252, getnv240, getnv239, and getnv235, respectively. These subroutines reproduce measured first, second, and third moments of the neutron multiplicity distributions, measured neutron-fission correlation data for the spontaneous fission of 252Cf, and measured neutron-neutron correlation data for both the spontaneous fission of 252Cf and the thermal neutron induced fission of 235U. The codes presented here can be used to study the possible uses of neutron-neutron correlations in the area of transparency measurements and the uses of neutron-neutron correlations in coincidence neutron imaging.

J. P. Lestone

2014-09-17

424

Laser channeling of Bethe-Heitler pairs.  

PubMed

Electron-positron pair creation is analyzed for an arrangement involving three external fields: a high-frequency gamma photon, the Coulomb field of a nucleus, and a strong laser wave. The frequency of the incoming gamma photon is assumed to be larger than the threshold for pair production in the absence of a laser, and the peak electric field of the laser is assumed to be much weaker than Schwinger's critical field. The total number of pairs produced is found to be essentially unchanged by the laser field, while the differential cross section is drastically modified. We show that the laser can channel the angular distribution of electron-positron pairs into a narrow angular region, which also facilitates experimental observation. PMID:19113334

Ltstedt, Erik; Jentschura, Ulrich D; Keitel, Christoph H

2008-11-14

425

PULSAR PAIR CASCADES IN A DISTORTED MAGNETIC DIPOLE FIELD  

SciTech Connect

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

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

2011-01-01

426

Pulsar Pair Cascades in a Distorted Magnetic Dipole Field  

NASA Technical Reports Server (NTRS)

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

Harding, Alice K.; Muslimov, Alex G.

2010-01-01

427

Neutron detector  

DOEpatents

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

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

2011-04-05

428

? -decay properties of neutron-rich Ge, Se, Kr, Sr, Ru, and Pd isotopes from deformed quasiparticle random-phase approximation  

NASA Astrophysics Data System (ADS)

? -decay properties of even- and odd-A neutron-rich Ge, Se, Kr, Sr, Ru, and Pd isotopes involved in the astrophysical rapid neutron capture process are studied within a deformed proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme-Hartree-Fock calculations with pairing correlations. Residual interactions in the particle-hole and particle-particle channels are also included in the formalism. The isotopic evolution of the various nuclear equilibrium shapes and the corresponding charge radii are investigated in all the isotopic chains. The energy distributions of the Gamow-Teller strength as well as the ? -decay half-lives are discussed and compared with the available experimental information. It is shown that nuclear deformation plays a significant role in the description of the decay properties in this mass region. Reliable predictions of the strength distributions are essential to evaluate decay rates in astrophysical scenarios.

Sarriguren, P.

2015-04-01

429

Neutron Radiography  

Microsoft Academic Search

Neutron radiography and its related two-dimensional (2D) neutron imaging techniques have been established as invaluable nondestructive\\u000a inspection methods and quantitative measurement tools. They have been used in a wide variety of applications ranging from\\u000a inspection of aircraft engine turbine blades to study of two-phase fluid flow in operating proton exchange membrane fuel cells.\\u000a Neutron radiography is similar to X-ray radiography

A. K. Heller; J. S. Brenizer

430

Neutron Repulsion  

Microsoft Academic Search

Earth is connected gravitationally, magnetically and electrically to its heat\\u000asource - a neutron star that is obscured from view by waste products in the\\u000aphotosphere. Neutron repulsion is like the hot filament in an incandescent\\u000alight bulb. Excited neutrons are emitted from the solar core and decay into\\u000ahydrogen that glows in the photosphere like a frosted light bulb.

Oliver K. Manuel

2011-01-01

431

Neutron radiography  

SciTech Connect

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

Berger, H.; Iddings, F.

1998-08-01

432

Neutron Stars  

NASA Technical Reports Server (NTRS)

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

Cottam, J.

2007-01-01

433

Analysis of Paired Comparison Data Using Mx  

ERIC Educational Resources Information Center

By postulating that the random utilities associated with the choice options follow a multivariate normal distribution, Thurstonian models (Thurstone, 1927) provide a straightforward representation of paired comparison data. The use of Monte Carlo Expectation-Maximization (MCEM) algorithms and limited information approaches have been proposed to

Tsai, Rung-Ching; Wu, Tsung-Lin

2004-01-01

434

Di-neutron correlation and soft dipole excitation in medium mass neutron-rich nuclei near drip line  

SciTech Connect

The neutron pairing correlation and the soft dipole excitation in medium mass nuclei near the drip line are investigated from the viewpoint of the di-neutron correlation. Numerical analyses based on the coordinate-space Hartree-Fock-Bogoliubov method and the continuum quasiparticle random phase approximation are performed for even-even {sup 18-24}O,{sup 50-58}Ca, and {sup 80-86}Ni. A clear signature of the di-neutron correlation is found in the ground state; two neutrons are correlated at short relative distances < or approx. 2 fm with large probability {approx}50%. The soft dipole excitation is influenced strongly by the neutron pairing correlation, and it accompanies a large transition density for pair motion of neutrons. This behavior originates from a coherent superposition of two-quasiparticle configurations [lx(l+1)]{sub L=1} consisting of continuum states with high orbital angular momenta l reaching an order of l{approx}10. It suggests that the soft dipole excitation under the influence of neutron pairing is characterized by the motion of di-neutron in the nuclear exterior against the remaining A-2 subsystem. Sensitivity to the density dependence of the effective pair force is discussed.

Matsuo, Masayuki; Mizuyama, Kazuhito; Serizawa, Yasuyoshi [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan)

2005-06-01

435

Yields of correlated fragment pairs in spontaneous fission of {sup 252}Cf  

SciTech Connect

Independent yields of 139 individual secondary fragment pairs of five different charge splits (Z{sub L}/Z{sub H}=46/52, 44/54, 42/56, 40/58, and 38/60) have been measured by detecting the coincidences between prompt {gamma} rays emitted in the spontaneous fission of {sup 252}Cf. Nuclear charge and mass distributions of fission fragments that follow from the measured yields of individual fragment pairs are consistent with similar previously known more integral data. Another type of data extracted is the multiplicity distributions of prompt neutrons emitted in the five above charge divisions of {sup 252}Cf. About 70{percent} of the fission events where {ge}7 neutrons are evaporated from the fission fragments occur for the Mo-Ba split of {sup 252}Cf. Mass and excitation energy distributions of primary Ru-Xe, Mo-Ba, and Zr-Ce fragments were deduced from a least squares fit to the yield pattern of secondary fragment pairs. For the Ru-Xe and Zr-Ce splits, the experimental data are well fitted by assuming one fission mode with average total kinetic energy {l_angle}TKE{r_angle} values close to the value of {l_angle}TKE{r_angle} known for the {sup 252}Cf spontaneous fission. For the Mo-Ba split, a successful fit could be obtained only with the assumption that, in addition to this {open_quotes}normal{close_quotes} fission mode, a second mode with a remarkably lower value of {l_angle}TKE{r_angle} of 153 MeV contributes to this charge split. This is 36 MeV lower than for the normal mode. These data indicate that in mode two the barium nuclei are hyperdeformed (3:1 axis ratio) at scission. Mean angular momentum values of Mo-Ba fission fragments observed in pairs together with various partners have been deduced from the measured populations of different spin levels of the fragment nuclei. These angular momentum values are discussed in terms of their dependence on the primary fragment excitation energy and presence of two fission modes. (Abstract Truncated)

Ter-Akopian, G.M.; Oganessian, Y.T.; Daniel, A.V.; Popeko, G.S. [Joint Institute for Nuclear Research, Dubna 141980 (Russia)] [Joint Institute for Nuclear Research, Dubna 141980 (Russia); Ter-Akopian, G.M.; Hamilton, J.H.; Daniel, A.V.; Kormicki, J.; Ramayya, A.V.; Babu, B.R.; Lu, Q.; Butler-Moore, K.; Jones, E.F.; Deng, J.K.; Shi, D. [Department of Physics, Vanderbilt University, Nashville, Tennessee 37235 (United States)] [Department of Physics, Vanderbilt University, Nashville, Tennessee 37235 (United States); Ma, W. [Department of Physics, Mississippi State University, Mississippi State, Mississippi 39762 (United States)] [Department of Physics, Mississippi State University, Mississippi State, Mississippi 39762 (United States); Kliman, J.; Morhac, M. [Institute of Physics, Slovak Academy of Sciences, Bratislava (Slovak Republic)] [Institute of Physics, Slovak Academy of Sciences, Bratislava (Slovak Republic); Cole, J.D.; Aryaeinejad, R. [Idaho National Engineering Laboratory, Idaho Falls, Idaho 83415 (United States)] [Idaho National Engineering Laboratory, Idaho Falls, Idaho 83415 (United States); Johnson, N.R.; Lee, I.Y.; McGowan, F.K. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)] [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

1997-03-01

436

Micromegas neutron beam monitor neutronics.  

PubMed

The Micromegas is a type of ionising radiation detector that consists of a gas chamber sandwiched between two parallel plate electrodes, with the gas chamber divided by a Frisch grid into drift and amplification gaps. Investigators have applied it to a number of different applications, such as charged particle, X-ray and neutron detection. A Micromegas device has been tested as a neutron beam monitor at CERN and is expected to be used for that purpose at the Spallation Neutron Source (SNS) under construction in Oak Ridge, TN. For the Micromegas to function effectively as neutron beam monitor, it should cause minimal disruption to the neutron beam in question. Specifically, it should scatter as few neutrons as possible and avoid neutron absorption when it does not contribute to generating useful information concerning the neutron beam. Here, we present the results of Monte Carlo calculations of the effect of different types of wall materials and detector gases on neutron beams and suggest methods for minimising disruption to the beam. PMID:16381746

Stephan, Andrew C; Miller, Laurence F

2005-01-01