NASA Astrophysics Data System (ADS)
Greedan, J. E.; Gout, Delphine; Lozano-Gorrin, A. D.; Derahkshan, Shahab; Proffen, Th.; Kim, H.-J.; Božin, E.; Billinge, S. J. L.
2009-01-01
The observation of canonical spin-glass behavior in the pyrochlore oxide Y2Mo2O7 has been a subject of considerable interest as the original structural studies were interpreted in terms of a well-ordered crystallographic model. It is widely held that the stabilization of the spin-glass state requires some level of positional disorder along with frustration. Recent reports from local probe measurements, extended x-ray-absorption fine structure (EXAFS) and Y89 NMR, have been interpreted in terms of disorder involving the Mo-Mo distances (EXAFS) and multiple Y sites (NMR). This work reports results from temperature-dependent (15-300 K) neutron diffraction (ND) and neutron pair distribution function studies which can provide from the same data set information on both the average and local structures. The principal findings are that: (1) there is no crystallographic phase transition over the temperature region studied within the resolution of the ND data; (2) the diffraction data are well fitted using a fully ordered model but with large and anisotropic displacement parameters for three of the four atomic sites; (3) the pairwise real-space correlation function G(r) shows clear evidence that the principal source of disorder is associated with the Y-O1 atom pairs rather than the Mo-Mo pairs, in disagreement with the interpretation of the EXAFS results; (4) fits to the G(r) improve significantly when anisotropic displacements for all sites are included; (5) inclusion of a split-site position parameter for O1 improves, slightly, both the G(r) fits and the Rietveld fits to the ND data; and (6) for all models the fits become worse as the temperature decreases and as the fitting range decreases. These results are qualitatively consistent with the Y89 NMR observations and perhaps recent muon-spin-relaxation studies. The issue of static versus dynamic disorder is not resolved, definitively. An estimate of the distribution of exchange constants due to the disorder is made using spin-dimer analysis and compared with the Saunders-Chalker model for the generation of spin-glass behavior from “weak” disorder on geometrically frustrated lattices.
TLD pairs, as thermal neutron detectors in neutron multisphere spectrometry
Héctor René Vega-Carrillo
2002-01-01
Pairs of thermoluminescence dosimeters, TLD600 and TLD700, have been used as a thermal neutron detector in a multisphere neutron spectrometer. The neutron spectra from a bare 252Cf and a D2O moderated 252Cf sources were measured with the spectrometer with thermoluminescence dosimeters and with a 6LiI(Eu) scintillator. With the neutron spectra the total flux, average neutron energy, dose and equivalent dose
Yields of correlated fragment pairs and neutron multiplicity in spontaneous fission of {sup 242}Pu
Veselsky, M.; Kliman, J.; Morhaccaron, M. [Institute of Physics of Slovak Academy of Sciences, Dubravska 9, 84228 Bratislava (Slovakia); Ramayya, A.V.; Kormicki, J.; Daniel, A.V. [Physics Department, Vanderbilt University, Nashville (United States)] Rasmussen, J.O. [Lawrence Berkeley National Laboratory, Berkeley (United States)] Stoyer, M.A. [Lawrence Livermore National Laboratory, Livermore (United States); Daniel, A.V.; Popeko, G.S.; Oganessian, Yu. Ts. [Joint Institute for Nuclear Research, Dubna (Russia)] Greiner, W. [Institut fur Theoretische Physik, J. W. Goethe Universitaet, Frankfurt a. M. (Germany); Aryaeinejad, R. [Idaho National Engineering Laboratory, Idaho Falls (United States)
1998-10-01
Yields of correlated fragment pairs were obtained in spontaneous fission of {sup 242}Pu. Charge, mass and neutron multiplicity distributions of fragment pairs were determined and compared to available data. The yield of cold fission without neutron emission was determined to about 10{percent} for the set of observed correlated fragment pairs. {copyright} {ital 1998 American Institute of Physics.}
Optimal Distributed All Pairs Shortest Paths
Optimal Distributed All Pairs Shortest Paths ETH Zurich Distributed Computing Group Stephan Holzer ETH Zürich Roger Wattenhofer ETH Zürich #12;Distributed network Graph G of n nodes 2 4 5 1 3 #12;Distributed network Graph G of n nodes 2 4 5 1 3 Unique IDs #12;Distributed network Graph G of n nodes 2 4 5 1
Proton-Neutron Pairing Interaction in Neutron Rich A = 132 Nuclei
Laouet, N.; Benrachi, F.; Khiter, M.; Benmicia, N.; Saifi, H. [Laboratoire de Physique Mathematique et Subatomique, Physics Departement, Montouri University, Constantine (Algeria)
2010-10-31
In infinite nuclear systems, such as neutron stars, pairing phenomena have a particular interest in the study of nuclear structure properties. Thus, pairing lies at the heart of quantum many body problems, and nuclear process connecting to nucleosynthesis. In this work, we are interested on the contribution of this aspect, for neutron rich nuclei far from stability in the vicinity of doubly magic {sup 132}Sn. The study of A = 134 isobar, which presents a proton-neutron mixing in valence space, based on the proton-neutron correlation properties. Our results, using the P{sub d} pairing gap calculations, are in a good agreement with the experimental data.
Neutrino-pair bremsstrahlung in a neutron star crust
NASA Astrophysics Data System (ADS)
Ofengeim, D. D.; Kaminker, A. D.; Yakovlev, D. G.
2014-11-01
Based on the formalism by Kaminker et al. (Astron. Astrophys., 343 (1999) 1009) we derive an analytic approximation for neutrino-pair bremsstrahlung emissivity due to scattering of electrons by atomic nuclei in a neutron star crust of any realistic composition. The emissivity is expressed through the generalized Coulomb logarithm which we fit by introducing an effective potential of electron-nucleus scattering. In addition, we study the conditions at which the neutrino bremsstrahlung in the crust is affected by strong magnetic fields. The results can be applied for modelling of many phenomena in neutron stars, such as thermal relaxation in young isolated neutron stars and in accreting neutron stars with overheated crust in soft X-ray transients.
S10 pairing for neutrons in dense neutron matter induced by a soft pion
NASA Astrophysics Data System (ADS)
Pankratov, S. S.; Baldo, M.; Saperstein, E. E.
2015-01-01
The possibility of neutron pairing in the S10 channel is studied for dense neutron matter in a vicinity of the ?0 condensation point. The S10 pairing gap ? is shown to occur in a model with a pairing force induced by the exchange of a soft neutral pionic mode. The soft pion induced potential V?(r ) is characterized by an attenuating oscillatory behavior in coordinate space, while in momentum space all S -wave matrix elements V?(p ,p') are positive. The solution of the gap equation reveals strong momentum dependence.
$^1S_0$ pairing for neutrons in dense neutron matter induced by a soft pion
S. S. Pankratov; M. Baldo; E. E. Saperstein
2015-01-19
The possibility of neutron pairing in the $^1S_0$ channel is studied for dense neutron matter in a vicinity of the $\\pi^0$ condensation point. The $^1S_0$ pairing gap $\\Delta$ is shown to occur in a model with a pairing force induced by the exchange of a soft neutral pionic mode. The soft pion induced potential $V_{\\pi}(r)$ is characterized by an attenuating oscillatory behavior in coordinate space, while in momentum space all $S$-wave matrix elements $V_{\\pi}(p,p')$ are positive. The solution of the gap equation reveals strong momentum dependence.
Pairing and shell evolution in neutron rich nuclei
M. Saha Sarkar; S. Sarkar
2012-04-23
From the experimental data on odd-even staggering of masses, we have shown that variation of pairing as a function of neutron number plays an important role in many distinctive features like occurrence of new shell closures, shell erosion, anomalous reduction of the energy of the first 2+ state and slower increase in the B(E2, 2_{+}^{1} \\rightarrow 0_{+}^{1}) in the neutron-rich even-even nuclei in different mass regions. New predictions have been made in a model independent way. Results of theoretical calculations support the phenomenological findings.
Nucleon and nucleon-pair momentum distributions in A?12 nuclei
Wiringa, Robert B. [ANL; Schiavilla, Rocco [ODU, JLAB; Pieper, Steven C. [ANL; Carlson, Joseph A. [LANL
2014-02-01
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.
Nucleon and nucleon-pair momentum distributions in A?12 nuclei
Wiringa, Robert B.; Schiavilla, Rocco; Pieper, Steven C.; Carlson, Joseph A.
2014-02-01
We report variational Monte Carlo calculations of single-nucleon momentum distributions for A?12 nuclei and nucleon-pair and nucleon-cluster momentum distributions for A?8. The wave functions have been generated for a Hamiltonian containing the Argonne ?18 two-nucleon and Urbana X three-nucleon potentials. The single-nucleon and nucleon-pair momentum distributions exhibit universal features attributable to the one-pion-exchange tensor interaction The single-nucleon distributions are broken down into proton and neutron components and spin-up and spin-down components where appropriate. The nucleon-pair momentum distributions are given separately for pp and pn pairs. The nucleon-cluster momentum distributions include dp in 3He, tp and dd in S4He, ?d inmore »6Li,?t in 7Li, and ?? in 8Be. Detailed tables are provided on-line for download.« less
The neutron star mass distribution
Kiziltan, Bülent [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kottas, Athanasios; De Yoreo, Maria [Department of Applied Mathematics and Statistics, University of California, Santa Cruz, CA 95064 (United States); Thorsett, Stephen E., E-mail: bkiziltan@cfa.harvard.edu [Department of Astronomy and Astrophysics, University of California and UCO/Lick Observatory, Santa Cruz, CA 95064 (United States)
2013-11-20
In recent years, the number of pulsars with secure mass measurements has increased to a level that allows us to probe the underlying neutron star (NS) mass distribution in detail. We critically review the radio pulsar mass measurements. For the first time, we are able to analyze a sizable population of NSs with a flexible modeling approach that can effectively accommodate a skewed underlying distribution and asymmetric measurement errors. We find that NSs that have evolved through different evolutionary paths reflect distinctive signatures through dissimilar distribution peak and mass cutoff values. NSs in double NS and NS-white dwarf (WD) systems show consistent respective peaks at 1.33 M {sub ?} and 1.55 M {sub ?}, suggesting significant mass accretion (?m ? 0.22 M {sub ?}) has occurred during the spin-up phase. The width of the mass distribution implied by double NS systems is indicative of a tight initial mass function while the inferred mass range is significantly wider for NSs that have gone through recycling. We find a mass cutoff at ?2.1 M {sub ?} for NSs with WD companions, which establishes a firm lower bound for the maximum NS mass. This rules out the majority of strange quark and soft equation of state models as viable configurations for NS matter. The lack of truncation close to the maximum mass cutoff along with the skewed nature of the inferred mass distribution both enforce the suggestion that the 2.1 M {sub ?} limit is set by evolutionary constraints rather than nuclear physics or general relativity, and the existence of rare supermassive NSs is possible.
G. Pantis; F. Simkovic; J. D. Vergados; Amand Faessler
1996-01-01
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
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
Empirical pairing gaps, shell effects, and di-neutron spatial correlation in neutron-rich nuclei
NASA Astrophysics Data System (ADS)
Changizi, S. A.; Qi, Chong; Wyss, R.
2015-08-01
The empirical pairing gaps derived from four different odd-even mass staggering formulas are compared. By performing single-j shell and multi-shell seniority model calculations as well as by using the standard HFB approach with Skyrme force we show that the simplest three-point formula ?C(3) (N) =1/2 [ B (N , Z) + B (N - 2 , Z) - 2 B (N - 1 , Z) ] can provide a good measure of the neutron pairing gap in even-N nuclei. It removes to a large extent the contribution from the nuclear mean field as well as contributions from shell structure details. It is also less contaminated by the Wigner effect for nuclei around N = Z. We also show that the strength of ?C(3) (N) can serve as a good indication of the two-particle spatial correlation in the nucleus of concern and that the weakening of ?C(3) (N) in some neutron-rich nuclei indicates that the di-neutron correlation itself is weak in these nuclei.
Pairing in exotic neutron-rich nuclei near the drip line and in the crust of neutron stars
NASA Astrophysics Data System (ADS)
Pastore, A.; Margueron, J.; Schuck, P.; Viñas, X.
2013-09-01
Exotic and drip-line nuclei as well as nuclei immersed in a low-density gas of neutrons in the inner crust of neutron stars are systematically investigated with respect to their neutron pairing properties. This is done using Skyrme density-functional and different pairing forces such as a density-dependent contact interaction and a separable form of a finite-range Gogny interaction. Hartree-Fock-Bogoliubov (HFB) and Bardeen-Cooper-Schrieffer (BCS) theories are compared. It is found that neutron pairing is reduced towards the drip line while overcast by strong shell effects. Furthermore, resonances in the continuum can have an important effect counterbalancing the tendency of reduction and leading to a persistence of pairing at the drip line. It is also shown that in these systems the difference between HFB and BCS approaches can be quantitatively large.
Spin distribution in neutron induced preequilibrium reactions
Dashdorj, D; Kawano, T; Chadwick, M; Devlin, M; Fotiades, N; Nelson, R O; Mitchell, G E; Garrett, P E; Agvaanluvsan, U; Becker, J A; Bernstein, L A; Macri, R; Younes, W
2005-10-04
The preequilibrium reaction mechanism makes an important contribution to neutron-induced reactions above E{sub n} {approx} 10 MeV. The preequilibrium process has been studied exclusively via the characteristic high energy neutrons produced at bombarding energies greater than 10 MeV. They are expanding the study of the preequilibrium reaction mechanism through {gamma}-ray spectroscopy. Cross-section measurements were made of prompt {gamma}-ray production as a function of incident neutron energy (E{sub n} = 1 to 250 MeV) on a {sup 48}Ti sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center facility. The prompt-reaction {gamma} rays were detected with the large-scale Compton-suppressed Germanium Array for Neutron Induced Excitations (GEANIE). Neutron energies were determined by the time-of-flight technique. The {gamma}-ray excitation functions were converted to partial {gamma}-ray cross sections taking into account the dead-time correction, target thickness, detector efficiency and neutron flux (monitored with an in-line fission chamber). Residual state population was predicted using the GNASH reaction code, enhanced for preequilibrium. The preequilibrium reaction spin distribution was calculated using the quantum mechanical theory of Feshback, Kerman, and Koonin (FKK). The multistep direct part of the FKK theory was calculated for a one-step process. The FKK preequilibrium spin distribution was incorporated into the GNASH calculations and the {gamma}-ray production cross sections were calculated and compared with experimental data. The difference in the partial {gamma}-ray cross sections using spin distributions with and without preequilibrium effects is significant.
Neutron dose distribution at the GSI fragment separator.
Fehrenbacher, G; Festag, J G
2004-01-01
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
Fragment Mass Distributions for Thermal-Neutron-Induced Fission of Pu239 and Pu241
F. J. Walter; H. W. Schmitt; J. H. Neiler
1964-01-01
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)
Distribution of Recoil Nucleus in Pair Production by Photons
R. Jost; J. M. Luttinger; M. Slotnick
1950-01-01
The angular and momentum distribution of the recoil nucleus in pair production by a photon is calculated covariantly by a method which utilizes the unitarity of the S matrix. The results are in disagreement with a recent experiment, particularly for small angles and high momentum transfers. The exact total cross section for pair creation is also given.
Neutrinoless Double Beta Decay within QRPA with Proton-Neutron Pairing
G. Pantis; F. Simkovic; J. D. Vergados; Amand Faessler
1996-01-01
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
Surface-enhanced pair transfer in quadrupole states of neutron-rich Sn isotopes
Masayuki Matsuo; Yasuyoshi Serizawa
2010-07-10
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 $2_1^+$ state is enhanced in the Sn isotopes with $A \\geq 132$. The transition density of the pair-addition mode has a large spatial extension in the exterior of nucleus, reaching far to $r\\sim 12-13$ 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.
Nucleon and nucleon-pair momentum distributions in A?12 nuclei
Wiringa, Robert B. [ANL; Schiavilla, Rocco [ODU, JLAB; Pieper, Steven C. [ANL; Carlson, Joseph A. [LANL
2014-02-01
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 ^{3}He, tp and dd in S^{4}He, ?d in ^{6}Li,?t in ^{7}Li, and ?? in ^{8}Be. Detailed tables are provided on-line for download.
Proton-Neutron Pairing Amplitude as a Generator Coordinate for Double-Beta Decay
Nobuo Hinohara; Jonathan Engel
2014-09-09
We treat proton-neutron pairing amplitudes, in addition to the nuclear deformation, as generator coordinates in a calculation of the neutrinoless double-beta decay of 76Ge. We work in two oscillator shells, with a Hamiltonian that includes separable terms in the quadrupole, spin-isospin, and pairing (isovector and isoscalar) channels. Our approach allows larger single-particle spaces than the shell model and includes the important physics of the proton-neutron quasiparticle random-phase approximation (QRPA) without instabilities near phase transitions. After comparing the results of a simplified calculation that neglects deformation with those of the QRPA, we present a more realistic calculation with both deformation and proton-neutron pairing amplitudes as generator coordinates. The future should see proton-neutron coordinates used together with energy-density functionals.
Proton-neutron pairing amplitude as a generator coordinate for double-? decay
NASA Astrophysics Data System (ADS)
Hinohara, Nobuo; Engel, Jonathan
2014-09-01
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.
Proton-Neutron Pairing Amplitude as a Generator Coordinate for Double-Beta Decay
Hinohara, Nobuo
2014-01-01
We treat proton-neutron pairing amplitudes, in addition to the nuclear deformation, as generator coordinates in a calculation of the neutrinoless double-beta decay of 76Ge. We work in two oscillator shells, with a Hamiltonian that includes separable terms in the quadrupole, spin-isospin, and pairing (isovector and isoscalar) channels. Our approach allows larger single-particle spaces than the shell model and includes the important physics of the proton-neutron quasiparticle random-phase approximation (QRPA) without instabilities near phase transitions. After comparing the results of a simplified calculation that neglects deformation with those of the QRPA, we briefly present a more realistic calculation with both deformation and proton-neutron pairing amplitudes as generator coordinates. The future should see proton-neutron generator coordinates used together with energy-density functionals.
Quantum-corrected pair distribution function of liquid neon
NASA Astrophysics Data System (ADS)
Barocchi, F.; Neumann, M.; Zoppi, M.
1985-06-01
By means of computer simulation we have calculated the quantum-corrected pair distribution function g(r) of liquid neon up to the term ?6 of the Wigner-Kirkwood series expansion. The agreement between calculation and the experimental data at T~=35 K of De Graaf and Mozer is now, for the first time, satisfactory.
ID-Based Distributed "Magic Ink" Signature from Pairings
Kim, Kwangjo
ID-Based Distributed "Magic Ink" Signature from Pairings Yan Xie, Fangguo Zhang, Xiaofeng Chen. For instance the perfect crime concern in e-cash system. The "magic ink" signature provides a revocable. A single signer in "magic ink" signature can easily trace the original user of the message without any
Kenichi Yoshida; Masayuki Yamagami
2008-02-16
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.
Anomalous pairing vibration in neutron-rich Sn isotopes beyond the N=82 magic number
Hirotaka Shimoyama; Masayuki Matsuo
2011-06-09
Two-neutron transfer associated with the pair correlation in superfluid neutron-rich nuclei is studied with focus on low-lying $0^+$ states in Sn isotopes beyond the N=82 magic number. We describe microscopically the two-neutron addition and removal transitions by means of the Skyrme-Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random phase approximation formulated in the coordinate space representation. It is found that the pair transfer strength for the transitions between the ground states becomes significantly large for the isotopes with $A \\ge 140$, reflecting very small neutron separation energy and long tails of the weakly bound $3p$ orbits. In $^{132-140}$Sn, a peculiar feature of the pair transfer is seen in transitions to low-lying excited $0^+$ states. They can be regarded as a novel kind of pair vibrational mode which is characterized by an anomalously long tail of the transition density extending to far outside of the nuclear surface, and a large strength comparable to that of the ground-state transitions. The presence of the weakly bound neutron orbits plays a central role for these anomalous behaviors.
Neutrinoless Double Beta Decay within QRPA with Proton-Neutron Pairing
G. Pantis; F. Simkovic; J. D. Vergados; Amand Faessler
1996-12-14
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 beta decay rates significantly, in all cases allowing for larger values of the expectation value of light neutrino masses. Using the best presently available experimental limits on the half life-time of neutrinoless double beta decay we have extracted the limits on lepton number violating parameters.
NASA Astrophysics Data System (ADS)
Kovács, Z.; Harko, T.
2011-11-01
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.
Neutron chain length distributions in subcritical systems
Nolen, S.D.; Spriggs, G.
1999-09-27
In this paper, the authors present the results of the chain-length distribution as a function of k in subcritical systems. These results were obtained from a point Monte Carlo code and a three-dimensional Monte Carlo code, MC++. Based on these results, they then attempt to explain why several of the common neutron noise techniques, such as the Rossi-{alpha} and Feynman's variance-to-mean techniques, are difficult to perform in highly subcritical systems using low-efficiency detectors.
Determination of energy distribution for photon and neutron microdosimetry
NASA Astrophysics Data System (ADS)
Todo, A. S.
This work was undertaken to provide basic physical data for use in both microdosimetry and dosimetry of high energy photons and also in the neutron radiation field. Described is the formalism to determine the initial electron energy spectra in water irradiated by photons with energies up to 1 GeV. Calculations were performed with a Monte Carlo computer code, PHOEL-3, which is also described. The code treats explicitly the production of electron-positron pairs, Compton scattering, photoelectric absorption, and the emission of Auger electrons following the occurrence of K-shell vacancies in oxygen. The tables give directly the information needed to specify the absolute single-collision kerma in water, which approximates tissue, at each photon energy. Results for continuous photon energy spectra can be obtained by using linear interpolation with the tables. The conditions under which first-collision kerma approximate absorbed dose are discussed. A formula is given for estimating bremsstrahlung energy loss, one of the principal differences between kerma and absorbed dose in practical cases. A study has been carried out, on the use of cylindrical, energy-proportional pulse-height detector for determining microdosimetric quantities, as neutron fractional dose spectra, D (L), in the function of linear energy transfer (LET). In the present study the Hurst detector was used; this device satisfies the requirement of the Bragg-Gray principle. A Monte Carlo Method was developed to obtain the D(L) spectrum from a measured pulse-height spectrum H(h), and the knowledge of the distribution of recoil-particle track lenght, P(T) in the sensitive volume of the detector. These developed programs to find P(T) and D(L) are presented. The distribution of D(L) in LET were obtained using a known distribution of P(T) and the measured H(h) spectrum fromthe Cf-2 52 neutron source. All the results are discussed and the conclusions are presented.
Z. Kovacs; K. S. Cheng; T. Harko
2010-09-30
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.
NASA Astrophysics Data System (ADS)
Ni, Dongdong; Ren, Zhongzhou
2014-12-01
The ? decays of neutron-rich Zn isotopes are investigated within the extended quasiparticle random-phase approximation, where neutron-neutron, proton-proton, and neutron-proton pairing correlations are considered in the similar manner. The Brückner G-matrix obtained with the charge-dependent Bonn nucleon-nucleon force is used for the residual particle-particle and particle-hole interactions in addition to the pairing interactions. Contributions from both allowed Gamow-Teller and first-forbidden transitions are considered, and ?-decay half-lives together with ?-delayed neutron emission probabilities are calculated. The calculated results are found to agree well with the available experimental data.
Neutron gamma mixed field measurements by means of MCP TLD600 dosimeter pair
NASA Astrophysics Data System (ADS)
Triolo, A.; Marrale, M.; Brai, M.
2007-11-01
In this paper, we compared the TL response of three types of thermoluminescence dosimeters, TLD600 ( 6LiF:Mg,Ti), TLD700 ( 7LiF:Mg,Ti) and MCP (LiF:Mg,Cu,P) after exposure to a n-? mixed field in the fluence range of radiotherapeutic applications. Since a dosimeter pair is required to discriminate the two components of the mixed field, we analyzed the ability of each dosimeter pair to provide the fluence value in the mixed field. At this aim we performed a 60Co-? calibration and a neutron calibration for all three dosimeter types. Finally, a blind test was performed in order to analyze the accuracy of each dosimeter pair and we found that in this mixed field the fluence value obtained through the TLD600-MCP pair is as accurate as the value obtained through the most common TLD600-TLD700 pair.
Sangam: a distributed pair programming plug-in for Eclipse
Chih-Wei Ho; Somik Raha; Edward F. Gehringer; Laurie Williams
2004-01-01
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
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
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
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
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)
ENERGY SPECTRUM OF INTERNAL CONVERSION PAIRS PRODUCED IN RADIATIVE THERMAL NEUTRON CAPTURE IN Gd
G. V. Danilyan; I. Ya. Korolkov
1962-01-01
An improved magnetic double-spectrometer with 4 x 10â»â¹ sec ; resolving power, oriented to 0 and 60 deg geometric angle between recorded pair ; components and equipped with scinttllation counters was used in an investigation ; of the angular distribution between electron-positron internal conversion pairs. ; The geometric scheme of the 45-mm diameter, 5- mu -thick aluminum foil exposed to
Fission meter and neutron detection using poisson distribution comparison
Rowland, Mark S; Snyderman, Neal J
2014-11-18
A neutron detector system and method for discriminating fissile material from non-fissile material wherein a digital data acquisition unit collects data at high rate, and in real-time processes large volumes of data directly into information that a first responder can use to discriminate materials. The system comprises counting neutrons from the unknown source and detecting excess grouped neutrons to identify fission in the unknown source. Comparison of the observed neutron count distribution with a Poisson distribution is performed to distinguish fissile material from non-fissile material.
Pantis, G.; Simkovic, F.; Vergados, J.D.; Faessler, A. [Theoretical Physics Section, University of Ioannina, GR 451 10, Ioannina (Greece)] [Theoretical Physics Section, University of Ioannina, GR 451 10, Ioannina (Greece); [Institute fuer Theoretische Physik der Universitaet Tuebingen, Auf der Morgenstelle 14, D-72076 Tuebingen (Germany)
1996-02-01
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 double beta decay rates significantly, in all cases allowing for larger values of the expectation value of light neutrino masses. Using the best presently available experimental limits on the half lifetime of neutrinoless double beta decay we have extracted the limits on lepton number violating parameters. {copyright} {ital 1996 The American Physical Society.}
Contributions of different neutron pairs in different approaches for neutrinoless double beta decay
Alberto Escuderos; Amand Faessler; Vadim Rodin; Fedor Simkovic
2010-06-07
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\
Quarteting and spin-aligned proton-neutron pairs in heavy N =Z nuclei
NASA Astrophysics Data System (ADS)
Sambataro, M.; Sandulescu, N.
2015-06-01
We analyze the role of maximally aligned isoscalar pairs in heavy N =Z nuclei by employing a formalism of quartets. Quartets are superpositions of two neutrons and two protons coupled to total isospin T =0 and given J . The study is focused on the contribution of spin-aligned pairs carrying the angular momentum J =9 to the structure of 96Cd and 92Pd . We show that the role played by the J =9 pairs is quite sensitive to the model space and, in particular, it decreases considerably by passing from the simple 0 g9 /2 space to the more complete 1 p1 /2,1 p3 /2,0 f5 /2,0 g9 /2 space. In the latter case the description of these nuclei in terms of only spin-aligned J =9 pairs turns out to be unsatisfactory while an important contribution, particularly in the ground state, is seen to arise from isovector J =0 and isoscalar J =1 pairs. Thus, contrary to previous studies, we find no compelling evidence of a spin-aligned pairing phase in 92Pd .
Exact Solution of the Spin-Isospin Proton-Neutron Pairing Hamiltonian
Lerma H, S.; Errea, B.; Dukelsky, J. [Instituto de Estructura de la Materia, CSIC, Serrano 123, 28006 Madrid (Spain); Satula, W. [Institute of Theoretical Physics, University of Warsaw, ul. Hoza 69, 00-681 Warsaw (Poland)
2007-07-20
The exact solution of the proton-neutron isoscalar-isovector (T=0,1) pairing Hamiltonian with nondegenerate single-particle orbits and equal pairing strengths is presented for the first time. The Hamiltonian is a particular case of a family of integrable SO(8) Richardson-Gaudin models. The exact solution of the T=0,1 pairing Hamiltonian is reduced to a problem of 4 sets of coupled nonlinear equations that determine the spectral parameters of the complete set of eigenstates. The microscopic structure of individual eigenstates is analyzed in terms of evolution of the spectral parameters in the complex plane for a system of A=80 nucleons. The spectroscopic trends of the exact solutions are discussed in terms of generalized rotations in isospace.
Global Distribution of Neutrons from Mars: Results from Mars Odyssey
W. C. Feldman; W. V. Boynton; R. L. Tokar; T. H. Prettyman; O. Gasnault; S. W. Squyres; R. C. Elphic; D. J. Lawrence; S. L. Lawson; S. Maurice; G. W. McKinney; K. R. Moore; R. C. Reedy
2002-01-01
Global distributions of thermal, epithermal, and fast neutron fluxes have been mapped during late southern summer\\/northern winter using the Mars Odyssey Neutron Spectrometer. These fluxes are selectively sensitive to the vertical and lateral spatial distributions of H and CO2 in the uppermost meter of the martian surface. Poleward of +\\/-60° latitude is terrain rich in hydrogen, probably H2O ice buried
S-pairing in neutron matter. I. Correlated Basis Function Theory
Adelchi Fabrocini; Stefano Fantoni; Alexey Yu. Illarionov; Kevin E. Schmidt
2008-05-22
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 Ref. [Nucl. Phys. A363 (1981) 383], 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 non linear 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_{14} and Argonne v_{8'}) 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.
Slow neutron distribution in a temperature gradient
Molinari, V.G.; Pollachini, L.
1985-12-01
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.
Local Density Approximation for proton-neutron pairing correlations. I. Formalism
E. Perlinska; S. G. Rohozinski; J. Dobaczewski; W. Nazarewicz
2003-10-01
In the present study we generalize the self-consistent Hartree-Fock-Bogoliubov (HFB) theory formulated in the coordinate space to the case which incorporates an arbitrary mixing between protons and neutrons in the particle-hole (p-h) and particle-particle (p-p or pairing) channels. We define the HFB density matrices, discuss their spin-isospin structure, and construct the most general energy density functional that is quadratic in local densities. The consequences of the local gauge invariance are discussed and the particular case of the Skyrme energy density functional is studied. By varying the total energy with respect to the density matrices the self-consistent one-body HFB Hamiltonian is obtained and the structure of the resulting mean fields is shown. The consequences of the time-reversal symmetry, charge invariance, and proton-neutron symmetry are summarized. The complete list of expressions required to calculate total energy is presented.
Coherence features of the spin-aligned neutron-proton pair coupling scheme
NASA Astrophysics Data System (ADS)
Qi, C.; Blomqvist, J.; Bäck, T.; Cederwall, B.; Johnson, A.; Liotta, R. J.; Wyss, R.
2012-10-01
The seniority scheme has been shown to be extremely useful for the classification of nuclear states in semi-magic nuclei. The neutron-proton (np) correlation breaks the seniority symmetry in a major way. As a result, the corresponding wave function is a mixture of many components with different seniority quantum numbers. In this paper, we show that the np interaction may favor a new kind of coupling in N=Z nuclei, i.e. the so-called isoscalar spin-aligned np pair mode. Shell model calculations reveal that the ground and low-lying yrast states of the N=Z nuclei 92Pd and 96Cd may be mainly built upon such spin-aligned np pairs, each carrying the maximum angular momentum J=9 allowed by the shell 0?g9/2 which is dominant in this nuclear region.
NASA Astrophysics Data System (ADS)
Ishikawa, Masayori; Kumada, Hiroaki; Yamamoto, Kazuyoshi; Kaneko, Junichi; Bengua, Gerard; Unesaki, Hironobu; Sakurai, Yoshinori; Tanaka, Kenichi; Kosako, Toshiso
2005-10-01
A wide range thermal neutron detector was developed based on the Scintillator with Optical Fiber (SOF) detector which has been previously used for thermal neutron monitoring during boron neutron capture therapy irradiation. With this new detector system we intended to address the issues of real-time thermal neutron flux measurement and the simultaneous measurement of a wide range of thermal neutron flux in a BNCT irradiation field which were difficult to implement with the gold wire activation method. The dynamic range of linearity of the SOF detector was expanded by using a plastic scintillator with a rapid decay time. On the other hand, the contribution of gamma rays and fast neutrons in the measured signals were compensated from those obtained by a pair of SOF detectors, one with a 6LiF neutron converter and the other without. The discrimination level for the measured signals was also optimized to further reduce the contribution of gamma rays and fast neutrons signals. A non-paralyzable system model was applied to correct for the dead-time in the detector system. A good agreement between the thermal neutron flux measured by the gold wire activation method and the paired SOF detector system was observed. However, measurements which would normally take a few days to perform with the gold wire activation method were obtained in just about 15 min using the SOF detector system. We also confirmed the dynamic range of linearity for the SOF detector system to be in the order of magnitude of 10 4.
Algorithm for systematic peak extraction from atomic pair distribution functions.
Granlund, L; Billinge, S J L; Duxbury, P M
2015-07-01
The study presents an algorithm, ParSCAPE, for model-independent extraction of peak positions and intensities from atomic pair distribution functions (PDFs). It provides a statistically motivated method for determining parsimony of extracted peak models using the information-theoretic Akaike information criterion (AIC) applied to plausible models generated within an iterative framework of clustering and chi-square fitting. All parameters the algorithm uses are in principle known or estimable from experiment, though careful judgment must be applied when estimating the PDF baseline of nanostructured materials. ParSCAPE has been implemented in the Python program SrMise. Algorithm performance is examined on synchrotron X-ray PDFs of 16 bulk crystals and two nanoparticles using AIC-based multimodeling techniques, and particularly the impact of experimental uncertainties on extracted models. It is quite resistant to misidentification of spurious peaks coming from noise and termination effects, even in the absence of a constraining structural model. Structure solution from automatically extracted peaks using the Liga algorithm is demonstrated for 14 crystals and for C60. Special attention is given to the information content of the PDF, theory and practice of the AIC, as well as the algorithm's limitations. PMID:26131896
Production, distribution and applications of californium-252 neutron sources.
Martin, R C; Knauer, J B; Balo, P A
2000-01-01
The radioisotope 252Cf is routinely encapsulated into compact, portable, intense neutron sources with a 2.6-yr half-life. A source the size of a person's little finger can emit up to 10(11) neutrons s(-1). Californium-252 is used commercially as a reliable, cost-effective neutron source for prompt gamma neutron activation analysis (PGNAA) of coal, cement and minerals, as well as for detection and identification of explosives, land mines and unexploded military ordinance. Other uses are neutron radiography, nuclear waste assays, reactor start-up sources, calibration standards and cancer therapy. The inherent safety of source encapsulations is demonstrated by 30 yr of experience and by US Bureau of Mines tests of source survivability during explosions. The production and distribution center for the US Department of Energy (DOE) Californium Program is the Radiochemical Engineering Development Center (REDC) at Oak Ridge National Laboratory (ORNL). DOE sells 252Cf to commercial reencapsulators domestically and internationally. Sealed 252Cf sources are also available for loan to agencies and subcontractors of the US government and to universities for educational, research and medical applications. The REDC has established the Californium User Facility (CUF) for Neutron Science to make its large inventory of 252Cf sources available to researchers for irradiations inside uncontaminated hot cells. Experiments at the CUF include a land mine detection system, neutron damage testing of solid-state detectors, irradiation of human cancer cells for boron neutron capture therapy experiments and irradiation of rice to induce genetic mutations. PMID:11003521
Excited-state density distributions in neutron-rich nuclei
Terasaki, J.; Engel, J. [Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599-3255 (United States) and School of Physics, Peking University, Beijing 100871 (China); Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599-3255 (United States)
2007-10-15
We calculate densities of excited states in the quasiparticle random-phase approximation (QRPA) with Skyrme interactions and volume pairing. We focus on low-energy peaks/bumps in the strength functions of a range of Ca, Ni, and Sn isotopes for J{sup {pi}}=0{sup +},1{sup -}, and 2{sup +}. We define an 'emitted-neutron number', which we then use to distinguish localized states from scattering-like states. The degree of delocalization either increases as the neutron-drip line is approached or stays high between the stability line and the drip line. In the 2{sup +} channel of Sn, however, the low-lying states, not even counting surface vibrations, are still fairly well localized on average, even at the neutron drip line.
Z. Kovacs; K. S. Cheng; T. Harko
2009-11-06
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.
Chun-Wang Ma; Xiao-Man Bai; Jiao Yu; Hui-Ling Wei
2014-09-09
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.
Mass distribution in the neutron induced fission of 232U
S. B. Manohar; P. P. Venkatesan; S. M. Deshmukh; Satya Prakash; M. V. Ramaniah
1979-01-01
Mass distribution in the neutron induced fission of 232U has been studied. The distribution though predominantly asymmetric shows the existence of a small symmetric peak. The average fission product masses for the light and heavy wing are 92.7 and 137.5 mass units, respectively. The widths of the distribution at half and one tenth maxima are 13.4 and 21.0 mass units,
Production, Distribution, and Applications of Californium-252 Neutron Sources
Balo, P.A.; Knauer, J.B.; Martin, R.C.
1999-10-03
The radioisotope {sup 252}Cf is routinely encapsulated into compact, portable, intense neutron sources with a 2.6-year half-life. A source the size of a person's little finger can emit up to 10{sup 11} neutrons/s. Californium-252 is used commercially as a reliable, cost-effective neutron source for prompt gamma neutron activation analysis (PGNAA) of coal, cement, and minerals, as well as for detection and identification of explosives, laud mines, and unexploded military ordnance. Other uses are neutron radiography, nuclear waste assays, reactor start-up sources, calibration standards, and cancer therapy. The inherent safety of source encapsulations is demonstrated by 30 years of experience and by U.S. Bureau of Mines tests of source survivability during explosions. The production and distribution center for the U. S Department of Energy (DOE) Californium Program is the Radiochemical Engineering Development Center (REDC) at Oak Ridge National Laboratory (ORNL). DOE sells The radioisotope {sup 252}Cf is routinely encapsulated into compact, portable, intense neutron sources with a 2.6- year half-life. A source the size of a person's little finger can emit up to 10 neutrons/s. Californium-252 is used commercially as a reliable, cost-effective neutron source for prompt gamma neutron activation analysis (PGNAA) of coal, cement, and minerals, as well as for detection and identification of explosives, laud mines, and unexploded military ordnance. Other uses are neutron radiography, nuclear waste assays, reactor start-up sources, calibration standards, and cancer therapy. The inherent safety of source encapsulations is demonstrated by 30 years of experience and by U.S. Bureau of Mines tests of source survivability during explosions. The production and distribution center for the U. S Department of Energy (DOE) Californium Program is the Radiochemical Engineering Development Center (REDC) at Oak Ridge National Laboratory(ORNL). DOE sells {sup 252}Cf to commercial reencapsulators domestically and internationally. Sealed {sup 252}Cf sources are also available for loan to agencies and subcontractors of the U.S. government and to universities for educational, research, and medical applications. The REDC has established the Californium User Facility (CUF) for Neutron Science to make its large inventory of {sup 252}Cf sources available to researchers for irradiations inside uncontaminated hot cells. Experiments at the CUF include a land mine detection system, neutron damage testing of solid-state detectors, irradiation of human cancer cells for boron neutron capture therapy experiments, and irradiation of rice to induce genetic mutations.
Pair distribution function study on compression of liquid gallium
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
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.
Pre-neutron emission mass distributions for low-energy neutron-induced actinide fission
Sun, Xiaojun; Wang, Ning
2012-01-01
According to the driving potential of a fissile system, we propose a phenomenological fission potential for a description of the pre-neutron emission mass distributions of neutron-induced actinide fission. Based on the nucleus-nucleus potential with the Skyrme energy-density functional, the driving potential of the fissile system is studied considering the deformations of nuclei. The energy dependence of the potential parameters is investigated based on the experimental data for the heights of the peak and valley of the mass distributions. The pre-neutron emission mass distributions for reactions 238U(n, f), 237Np(n, f), 235U(n, f), 232Th(n, f) and 239Pu(n, f) can be reasonably well reproduced. Some predictions for these reactions at unmeasured incident energies are also presented.
A. V. Afanasjev; S. E. Agbemava; D. Ray; P. Ray
2015-01-17
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.
NASA Astrophysics Data System (ADS)
Afanasjev, A. V.; Agbemava, S. E.; Ray, D.; Ring, P.
2015-01-01
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.
Non-collapsing renormalized QRPA with proton-neutron pairing for neutrinoless double beta decay
F. Simkovic; J. Schwieger; M. Veselsky; G. Pantis; Amand Faessler
1996-12-14
Using the renormalized quasiparticle random phase approximation (RQRPA), we calculate the light neutrino mass mediated mode of neutrinoless double beta decay of Ge76, Mo100, Te128 and Te130. Our results indicate that the simple quasiboson approximation is not good enough to study the neutrinoless double beta decay, because its solutions collapse for physical values of g_pp. We find that extension of the Hilbert space and inclusion of the Pauli Principle in the QRPA with proton-neutron pairing, allows us to extend our calculations beyond the point of collapse, for physical values of the nuclear force strength. As a consequence one might be able to extract more accurate values on the effective neutrino mass by using the best available experimental limits on the half-life of neutrinoless double beta decay.
THE DISTRIBUTION OF PHOSPHORUS AND GOLD IN NEUTRON IRRADIATED SILICON
Paris-Sud XI, Université de
L-257 THE DISTRIBUTION OF PHOSPHORUS AND GOLD IN NEUTRON IRRADIATED SILICON F. BÉNIÈRE and V. K contraire, est concentré à la surface. Abstract. 2014 The uniformity of phosphorus concentration produced that the phosphorus concentration is uniform throughout. Gold, on the other hand, is concentrated at the surface. LE
Characterisation of neutron fields: challenges in assessing the directional distribution.
Cauwels, Vanessa; Vanhavere, Filip; Reginatto, Marcel
2014-10-01
The SCK·CEN has carried out neutron field characterisation campaigns at several nuclear reactors. The main goal of these measurement campaigns was to evaluate the performance of different neutron personal dosemeters. To be able to evaluate the performance of neutron personal dosemeters in terms of Hp(10), knowledge of the directional distribution is indispensable. This distribution was estimated by placing several personal dosemeters on all six sides of a slab phantom. The interpretation and conversion of this information into a reliable value for Hp(10) requires great care. The data were analysed using three methods. In the first approach, a linear interpolation was performed on three perpendicular axes. In the other two approaches, an icosahedron was used to model the angle of incidence of the neutrons and a linear interpolation or a Bayesian analysis was performed. This study describes the limitations and advantages of each of these methods and provides recommendations for their use to estimate the personal dose equivalent Hp(10) for neutron dosimetry. PMID:24966340
Hyperdimensional Analysis of Amino Acid Pair Distributions in Proteins
Henriksen, Svend B.; Arnason, Omar; Söring, Jón; Petersen, Steffen B.
2011-01-01
Our manuscript presents a novel approach to protein structure analyses. We have organized an 8-dimensional data cube with protein 3D-structural information from 8706 high-resolution non-redundant protein-chains with the aim of identifying packing rules at the amino acid pair level. The cube contains information about amino acid type, solvent accessibility, spatial and sequence distance, secondary structure and sequence length. We are able to pose structural queries to the data cube using program ProPack. The response is a 1, 2 or 3D graph. Whereas the response is of a statistical nature, the user can obtain an instant list of all PDB-structures where such pair is found. The user may select a particular structure, which is displayed highlighting the pair in question. The user may pose millions of different queries and for each one he will receive the answer in a few seconds. In order to demonstrate the capabilities of the data cube as well as the programs, we have selected well known structural features, disulphide bridges and salt bridges, where we illustrate how the queries are posed, and how answers are given. Motifs involving cysteines such as disulphide bridges, zinc-fingers and iron-sulfur clusters are clearly identified and differentiated. ProPack also reveals that whereas pairs of Lys residues virtually never appear in close spatial proximity, pairs of Arg are abundant and appear at close spatial distance, contrasting the belief that electrostatic repulsion would prevent this juxtaposition and that Arg-Lys is perceived as a conservative mutation. The presented programs can find and visualize novel packing preferences in proteins structures allowing the user to unravel correlations between pairs of amino acids. The new tools allow the user to view statistical information and visualize instantly the structures that underpin the statistical information, which is far from trivial with most other SW tools for protein structure analysis. PMID:22174733
Proton-Neutron Pairing Amplitude as a Generator Coordinate for Double-Beta Decay Nobuo Hinohara1, 2
Engel, Jonathan
Proton-Neutron Pairing Amplitude as a Generator Coordinate for Double-Beta Decay Nobuo Hinohara1, 2 deformation, as generator coordinates in a calculation of the neutrinoless double-beta decay of 76 Ge. We work: 23.40.-s, 21.60.Jz, 24.10.Cn, 27.50.+e Neutrinoless double-beta (0) decay can occur only if neutrinos
Evidence for a spin-aligned neutron-proton paired phase from the level structure of (92)Pd.
Cederwall, B; Moradi, F Ghazi; Bäck, T; Johnson, A; Blomqvist, J; Clément, E; de France, G; Wadsworth, R; Andgren, K; Lagergren, K; Dijon, A; Jaworski, G; Liotta, R; Qi, C; Nyakó, B M; Nyberg, J; Palacz, M; Al-Azri, H; Algora, A; de Angelis, G; Ataç, A; Bhattacharyya, S; Brock, T; Brown, J R; Davies, P; Di Nitto, A; Dombrádi, Zs; Gadea, A; Gál, J; Hadinia, B; Johnston-Theasby, F; Joshi, P; Juhász, K; Julin, R; Jungclaus, A; Kalinka, G; Kara, S O; Khaplanov, A; Kownacki, J; La Rana, G; Lenzi, S M; Molnár, J; Moro, R; Napoli, D R; Singh, B S Nara; Persson, A; Recchia, F; Sandzelius, M; Scheurer, J-N; Sletten, G; Sohler, D; Söderström, P-A; Taylor, M J; Timár, J; Valiente-Dobón, J J; Vardaci, E; Williams, S
2011-01-01
Shell structure and magic numbers in atomic nuclei were generally explained by pioneering work that introduced a strong spin-orbit interaction to the nuclear shell model potential. However, knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers (N = Z), enhanced correlations arise between neutrons and protons (two distinct types of fermions) that occupy orbitals with the same quantum numbers. Such correlations have been predicted to favour an unusual type of nuclear superfluidity, termed isoscalar neutron-proton pairing, in addition to normal isovector pairing. Despite many experimental efforts, these predictions have not been confirmed. Here we report the experimental observation of excited states in the N = Z = 46 nucleus (92)Pd. Gamma rays emitted following the (58)Ni((36)Ar,2n)(92)Pd fusion-evaporation reaction were identified using a combination of state-of-the-art high-resolution ?-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron-proton coupling scheme, different from the previous prediction. We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling) in the ground and low-lying excited states of the heaviest N = Z nuclei. Such strong, isoscalar neutron-proton correlations would have a considerable impact on the nuclear level structure and possibly influence the dynamics of rapid proton capture in stellar nucleosynthesis. PMID:21179086
Density fluctuations and the pair distribution function V. A. Levashov
Thorpe, Michael
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
Neutron Density Distributions Observed by Proton Elastic Scattering
NASA Astrophysics Data System (ADS)
Takeda, H.; Sakaguchi, H.; Taki, T.; Yosoi, M.; Itoh, M.; Kawabata, T.; Ishikawa, T.; Uchida, M.; Tsukahara, N.; Noro, T.; Yoshimura, M.; Fujiwara, H.; Yoshida, H.; Obayashi, E.; Tamii, A.; Akimune, H.
2000-10-01
Cross sections, analyzing powers and spin rotation parameters of proton elastic scattering from 58Ni and 120Sn have been measured at intermediate energies. In order to explain the 58Ni data, it was necessary to use experimental density distributions deduced from charge distributions and to modify coupling constants and masses of ? and ? mesons. Assuming the same modification was also valid for 120Sn and using proton densities deduced from charge densities, neutron density distribution was searched so as to reproduce 120Sn data.
Modesto Montoya
2013-04-30
In this paper, the distribution of mass and kinetic energy in the cold region of the thermal neutron induced fission of U 233, U 235 and Pu 239, respectively, is interpreted in terms of nucleon pair-breaking and the Coulomb interaction energy between complementary fragments (Coulomb effect). In order to avoid the erosive consequences of neutron emission, one studies the cold fission regions, corresponding to total kinetic energy (TE) close to the maximum available energy of the reaction (Q). Contrary to expected, in cold fission is not observed high odd-even effect in mass number distribution. Nevertheless, the measured values are compatible with higher odd-even effects on proton or neutron number distribution, respectively. In addition, in cold fission, the minimal total excitation energy (X) is correlated with the Coulomb energy excess, which is defined as the difference between C (the electrostatic interaction energy between complementary fragments taken as spherical in scission configuration) and Q. These Coulomb effects increase with the asymmetry of the charge fragmentations. In sum, the experimental data on cold fission suggest that scission configurations explore all the possibilities permitted by the available energy for fission.
Partial pair distribution functions in icosahedral Al-Li-Cu quasicrystals
Boyer, Edmond
1689 Partial pair distribution functions in icosahedral Al-Li-Cu quasicrystals M. de Boissieu (1, 2 in a wealth of published papers. A bibliography of quasicrystals which chronicles the Article published online
T. Bereznai; T. D. Mac Mahon
1978-01-01
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
Global distribution of neutrons from Mars: results from Mars odyssey.
Feldman, W C; Boynton, W V; Tokar, R L; Prettyman, T H; Gasnault, O; Squyres, S W; Elphic, R C; Lawrence, D J; Lawson, S L; Maurice, S; McKinney, G W; Moore, K R; Reedy, R C
2002-07-01
Global distributions of thermal, epithermal, and fast neutron fluxes have been mapped during late southern summer/northern winter using the Mars Odyssey Neutron Spectrometer. These fluxes are selectively sensitive to the vertical and lateral spatial distributions of H and CO2 in the uppermost meter of the martian surface. Poleward of +/-60 degrees latitude is terrain rich in hydrogen, probably H2O ice buried beneath tens of centimeter-thick hydrogen-poor soil. The central portion of the north polar cap is covered by a thick CO2 layer, as is the residual south polar cap. Portions of the low to middle latitudes indicate subsurface deposits of chemically and/or physically bound H2O and/or OH. PMID:12040088
Yuan-Hao Liu; Pi-En Tsai; Hong-Ming Liu; Shiang-Huei Jiang
2010-01-01
This paper presents a way to determine the angular and spatial distributions of the thermal neutron source strength of a boron neutron capture therapy (BNCT) beam. The experiments applied 1) the indirect neutron radiography, 2) the cadmium difference method, and 3) the instrumental neutron activation analysis. The measured data were processed by the spectrum deconvolution technique to resolve into a
$(h_{11/2})^2$ alignments in neutron-rich $^{132}$Ba with negative-parity pairs
Lei, Yang
2015-01-01
The shell-model collective-pair truncation with negative-parity pairs is adopted to study the $(h_{11/2})^2$ alignment in $^{132}$Ba. The proton $(h_{11/2})^2$-alignment state is predicted as an $E\\sim$4.6MeV $\\tau\\sim 0.5\\mu$s isomer with observable E3 decay channels. The neutron $(h_{11/2})^{-2}$ alignment in the yrast band and four negative-parity bands are confirmed.
Kinematic distributions for electron pair production by muons
NASA Technical Reports Server (NTRS)
Linsker, R.
1972-01-01
Cross sections and kinematic distributions for the trident production process plus or negative muon plus charge yields plus or minus muon plus electron plus positron plus charge (with charge = dipion moment and Fe) are given for beam energies of 100 to 300 GeV at fixed (electron positron) masses from 5 to 15 GeV. This process is interesting as a test of quantum electrodynamics at high energies, and in particular as a test of the form of the photon propagator at large timelike (four-momentum) squared. For this purpose, it is desirable to impose kinematic cuts that favor those Bethe-Heitler graphs which contain a timelike photon propagator. It is found that there are substantial differences between the kinematic distributions for the full Bethe-Heitler matrix element and the distributions for the two timelike-photon graphs alone; these differences can be exploited in the selection of appropriate kinematic cuts.
S. Clough; A. Heidemann; A. H. Horsewill; M. N. J. Paley
1984-01-01
The tunnelling and torsional motions of methyl groups in lithium acetate dihydrate (CH3COOLi·2H2O) have been studied in detail by incoherent inelastic neutron scattering. The results are interpreted by a model of pairs of methyl groups performing a coupled tunnelling motion. The strength of the coupling term is estimated to be about twice as strong as the threefold hindering barrier for
Crane, Thomas W. (Los Alamos, NM)
1986-01-01
The disclosure is directed to an apparatus and method for determining the content and distribution of a thermal neutron absorbing material within an object. Neutrons having an energy higher than thermal neutrons are generated and thermalized. The thermal neutrons are detected and counted. The object is placed between the neutron generator and the neutron detector. The reduction in the neutron flux corresponds to the amount of thermal neutron absorbing material in the object. The object is advanced past the neutron generator and neutron detector to obtain neutron flux data for each segment of the object. The object may comprise a space reactor heat pipe and the thermal neutron absorbing material may comprise lithium.
Crane, T.W.
1983-12-21
The disclosure is directed to an apparatus and method for determining the content and distribution of a thermal neutron absorbing material within an object. Neutrons having an energy higher than thermal neutrons are generated and thermalized. The thermal neutrons are detected and counted. The object is placed between the neutron generator and the neutron detector. The reduction in the neutron flux corresponds to the amount of thermal neutron absorbing material in the object. The object is advanced past the neutron generator and neutron detector to obtain neutron flux data for each segment of the object. The object may comprise a space reactor heat pipe and the thermal neutron absorbing material may comprise lithium.
Greg I. Kaplan; Anatoly B. Rosenfeld; Barry J. Allen; Jeffrey A. Coderre; Hungyan B. Liu
1999-01-01
The depth distribution of the thermal neutron flux is a major factor in boron neutron capture therapy ~BNCT! in determining the efficiency of cell sterilization. In this paper the fission detector method is developed and applied to measure the in-phantom thermal neutron flux depth distribution. Advantages of the fission detector include small size, direct measurement of thermal neutron flux in
Non-coding DNA can regulate gene transcription by its base pair's distribution.
Sandler, U; Wyler, A
1998-07-01
In this paper we show that the gene transcription velocity can depend exponentially on the first moments of the base pair distribution in DNA. As the major fraction of the DNA of eucaryotes consists of non-coding sequences of base pairs and these determine the statistical characteristics of the base pair's ordering, non-coding DNA plays an important role in the functioning of the genetic apparatus. In particular, it enables a new independent mechanism for the gradual regulation of gene expression in eucaryotes. PMID:9689945
Yield, variance and spatial distribution of electron–hole pairs in CsI
Gao, Fei; Xie, YuLong; Kerisit, Sebastien N.; Campbell, Luke W.; Weber, William J.
2011-10-01
A Monte Carlo (MC) method previously developed has been applied to simulate the interaction of photons, with energies ranging from 50 eV to ~ 1 MeV, with CsI and the subsequent electron cascades. The MC model has been employed to compute nano-scale spatial distributions of electron-hole pairs and important intrinsic properties, including W, the mean energy per electron-hole pair, and the Fano factor, F. W exhibits discontinuities at the shell edges that follow the photoionization cross sections and decreases with increasing photon energy (from ~19 to 15 eV), with an asymptotic value of 15.2 eV at high energy. This decrease may contribute the initial rise in relative light yield with incident energy observed experimentally for CsI, thus suggesting that nonlinearity may be associated with intrinsic properties of the material at low energies. F is calculated to increase with increasing energy and has an asymptotic value of 0.28. A significant number of electron-hole pairs are produced through the different ionization channels of core shells and corresponding relaxation processes, which may explain why F is larger for CsI than for Si or Ge. Finally, the calculated spatial distributions show that the electron-hole pairs are primarily distributed along fast electron tracks. These spatial distributions constitute important input for large-scale simulations of electron-hole pair transport.
Leading neutron energy and p distributions in deep inelastic scattering and photoproduction at HERA
NASA Astrophysics Data System (ADS)
Chekanov, S.; Derrick, M.; Magill, S.; Miglioranzi, S.; Musgrave, B.; Nicholass, D.; Repond, J.; Yoshida, R.; Mattingly, M. C. K.; Jechow, M.; Pavel, N.; Yagües Molina, A. G.; Antonelli, S.; Antonioli, P.; Bari, G.; Basile, M.; Bellagamba, L.; Bindi, M.; Boscherini, D.; Bruni, A.; Bruni, G.; Cifarelli, L.; Cindolo, F.; Contin, A.; Corradi, M.; De Pasquale, S.; Iacobucci, G.; Margotti, A.; Nania, R.; Polini, A.; Rinaldi, L.; Sartorelli, G.; Zichichi, A.; Bartsch, D.; Brock, I.; Goers, S.; Hartmann, H.; Hilger, E.; Jakob, H.-P.; Jüngst, M.; Kind, O. M.; Paul, E.; Renner, R.; Samson, U.; Schönberg, V.; Shehzadi, R.; Wlasenko, M.; Brook, N. H.; Heath, G. P.; Morris, J. D.; Namsoo, T.; Capua, M.; Fazio, S.; Mastroberardino, A.; Schioppa, M.; Susinno, G.; Tassi, E.; Kim, J. Y.; Ma, K. J.; Ibrahim, Z. A.; Kamaluddin, B.; Wan Abdullah, W. A. T.; Ning, Y.; Ren, Z.; Sciulli, F.; Chwastowski, J.; Eskreys, A.; Figiel, J.; Galas, A.; Gil, M.; Olkiewicz, K.; Stopa, P.; Zawiejski, L.; Adamczyk, L.; Bo?d, T.; Grabowska-Bo?d, I.; Kisielewska, D.; ?ukasik, J.; Przybycie?, M.; Suszycki, L.; Kota?ski, A.; S?omi?ski, W.; Adler, V.; Behrens, U.; Bloch, I.; Blohm, C.; Bonato, A.; Borras, K.; Coppola, N.; Dossanov, A.; Fourletova, J.; Geiser, A.; Gladkov, D.; Göttlicher, P.; Gregor, I.; Haas, T.; Hain, W.; Horn, C.; Kahle, B.; Klein, U.; Kötz, U.; Kowalski, H.; Lobodzinska, E.; Löhr, B.; Mankel, R.; Melzer-Pellmann, I.-A.; Montanari, A.; Notz, D.; Nuncio-Quiroz, A. E.; Rubinsky, I.; Santamarta, R.; Schneekloth, U.; Spiridonov, A.; Stadie, H.; Szuba, D.; Szuba, J.; Theedt, T.; Wolf, G.; Wrona, K.; Youngman, C.; Zeuner, W.; Lohmann, W.; Schlenstedt, S.; Barbagli, G.; Gallo, E.; Pelfer, P. G.; Bamberger, A.; Dobur, D.; Karstens, F.; Vlasov, N. N.; Bussey, P. J.; Doyle, A. T.; Dunne, W.; Ferrando, J.; Saxon, D. H.; Skillicorn, I. O.; Gialas, I.; Gosau, T.; Holm, U.; Klanner, R.; Lohrmann, E.; Salehi, H.; Schleper, P.; Schörner-Sadenius, T.; Sztuk, J.; Wichmann, K.; Wick, K.; Foudas, C.; Fry, C.; Long, K. R.; Tapper, A. D.; Kataoka, M.; Matsumoto, T.; Nagano, K.; Tokushuku, K.; Yamada, S.; Yamazaki, Y.; Barakbaev, A. N.; Boos, E. G.; Pokrovskiy, N. S.; Zhautykov, B. O.; Son, D.; de Favereau, J.; Piotrzkowski, K.; Barreiro, F.; Glasman, C.; Jimenez, M.; Labarga, L.; del Peso, J.; Ron, E.; Soares, M.; Terrón, J.; Zambrana, M.; Corriveau, F.; Liu, C.; Walsh, R.; Zhou, C.; Tsurugai, T.; Antonov, A.; Dolgoshein, B. A.; Sosnovtsev, V.; Stifutkin, A.; Suchkov, S.; Dementiev, R. K.; Ermolov, P. F.; Gladilin, L. K.; Katkov, I. I.; Khein, L. A.; Korzhavina, I. A.; Kuzmin, V. A.; Levchenko, B. B.; Lukina, O. Yu.; Proskuryakov, A. S.; Shcheglova, L. M.; Zotkin, D. S.; Zotkin, S. A.; Abt, I.; Büttner, C.; Caldwell, A.; Kollar, D.; Schmidke, W. B.; Sutiak, J.; Grigorescu, G.; Keramidas, A.; Koffeman, E.; Kooijman, P.; Pellegrino, A.; Tiecke, H.; Vázquez, M.; Wiggers, L.; Brümmer, N.; Bylsma, B.; Durkin, L. S.; Lee, A.; Ling, T. Y.; Allfrey, P. D.; Bell, M. A.; Cooper-Sarkar, A. M.; Cottrell, A.; Devenish, R. C. E.; Foster, B.; Korcsak-Gorzo, K.; Patel, S.; Roberfroid, V.; Robertson, A.; Straub, P. B.; Uribe-Estrada, C.; Walczak, R.; Bellan, P.; Bertolin, A.; Brugnera, R.; Carlin, R.; Ciesielski, R.; Dal Corso, F.; Dusini, S.; Garfagnini, A.; Limentani, S.; Longhin, A.; Stanco, L.; Turcato, M.; Oh, B. Y.; Raval, A.; Ukleja, J.; Whitmore, J. J.; Iga, Y.; D'Agostini, G.; Marini, G.; Nigro, A.; Cole, J. E.; Hart, J. C.; Abramowicz, H.; Gabareen, A.; Ingbir, R.; Kananov, S.; Levy, A.; Kuze, M.; Hori, R.; Kagawa, S.; Okazaki, N.; Shimizu, S.; Tawara, T.; Hamatsu, R.; Kaji, H.; Kitamura, S.; Ota, O.; Ri, Y. D.; Ferrero, M. I.; Monaco, V.; Sacchi, R.; Solano, A.; Arneodo, M.; Ruspa, M.; Fourletov, S.; Martin, J. F.; Boutle, S. K.; Butterworth, J. M.; Gwenlan, C.; Jones, T. W.; Loizides, J. H.; Sutton, M. R.; Targett-Adams, C.; Wing, M.; Brzozowska, B.; Ciborowski, J.; Grzelak, G.; Kulinski, P.; ?u?niak, P.; Malka, J.; Nowak, R. J.; Pawlak, J. M.; Tymieniecka, T.; Ukleja, A.; ?arnecki, A. F.; Adamus, M.; Plucinski, P.; Eisenberg, Y.; Giller, I.; Hochman, D.; Karshon, U.; Rosin, M.; Brownson, E.; Danielson, T.; Everett, A.; Kçira, D.; Reeder, D. D.; Ryan, P.; Savin, A. A.; Smith, W. H.; Wolfe, H.; Bhadra, S.; Catterall, C. D.; Cui, Y.; Hartner, G.; Menary, S.; Noor, U.; Standage, J.; Whyte, J.; ZEUS Collaboration
2007-07-01
The production of energetic neutrons in ep collisions has been studied with the ZEUS detector at HERA. The neutron energy and pT2 distributions were measured with a forward neutron calorimeter and tracker in a 40 pb sample of inclusive deep inelastic scattering (DIS) data and a 6 pb sample of photoproduction data. The neutron yield in photoproduction is suppressed relative to DIS for the lower neutron energies and the neutrons have a steeper pT2 distribution, consistent with the expectation from absorption models. The distributions are compared to HERA measurements of leading protons. The neutron energy and transverse-momentum distributions in DIS are compared to Monte Carlo simulations and to the predictions of particle exchange models. Models of pion exchange incorporating absorption and additional secondary meson exchanges give a good description of the data.
Entangled-Pair Transmission Improvement Using Distributed Phase-Sensitive Amplification
NASA Astrophysics Data System (ADS)
Agarwal, Anjali; Dailey, James M.; Toliver, Paul; Peters, Nicholas A.
2014-10-01
We demonstrate the transmission of time-bin entangled photon pairs through a distributed optical phase-sensitive amplifier (OPSA). We utilize four-wave mixing at telecom wavelengths in a 5-km dispersion-shifted fiber OPSA operating in the low-gain limit. Measurements of two-photon interference curves show no statistically significant degradation in the fringe visibility at the output of the OPSA. In addition, coincidence counting rates are higher than direct passive transmission because of constructive interference between amplitudes of input photon pairs and those generated in the OPSA. Our results suggest that application of distributed phase-sensitive amplification to transmission of entangled photon pairs could be highly beneficial towards advancing the rate and scalability of future quantum communications systems.
NASA Astrophysics Data System (ADS)
Snyder, Douglas
2014-03-01
Feynman (Lect. on Phys., v. 3, 1965, ps. 3-7 to 3-9) maintained in his neutron scattering off a crystal experiment that which-way info can exist even if one does not perform a measurement. This interaction involves a spin flip for both the neutron and nucleus that the neutron scatters off. With the flip, the spin of the nucleus that the neutron scattered off becomes different than the spin direction of all the other nuclei in the crystal that the neutron could have scattered off. The spins of all the other nuclei are the same. It may be possible to eliminate the ww info as long as particle detections have not been made. Through spin-lattice relaxation after the neutron-nucleus interaction occurs, the spin flip of the nucleus would reverse before any detection is made. It would no longer be possible to determine which nucleus the neutron scattered off. The result is only interference in the distribution of the neutrons. This change from ww info to interference would be affected by a change in info regarding the nuclei in the crystal since there is no physical process whereby the change in the nuclei can affect the distribution of the neutrons. Altering relaxation duration relative to neutron detection time could provide a delayed choice. Another possibility would be to shut off the uniform, strong, external magnetic field B, that initially aligns all of the spins of the nuclei along the same axis, after the spin flip and before the neutron is detected. Ww info would be eliminated since the spin directions of all the nuclei would quickly become essentially random. Maintaining or turning off B could be a delayed choice.
Nuclear proton and neutron distributions in the detection of weak interacting massive particles
Co', G.; Donno, V. De [Dipartimento di Matematica e Fisica ''E. De Giorgi'', Università del Salento, via Arnesano, I-73100 Lecce (Italy); Anguiano, M.; Lallena, A.M., E-mail: gpco@le.infn.it, E-mail: viviana.de.donno@le.infn.it, E-mail: mangui@ugr.es, E-mail: lallena@ugr.es [Departamento de Física Atómica, Molecular y Nuclear, Universidad de Granada, Avda Fuentenueva s/n, E-18071 Granada (Spain)
2012-11-01
In the evaluation of weak interacting massive particles (WIMPs) detection rates, the WIMP-nucleus cross section is commonly described by using form factors extracted from charge distributions. In this work, we use different proton and neutron distributions taken from Hartree-Fock calculations. We study the effects of this choice on the total detection rates for six nuclei having different neutron excess, and taken from different regions of the nuclear chart. The use of different distributions for protons and neutrons becomes more important if isospin-dependent WIMP-nucleon interactions are considered. The need for distinct descriptions of proton and neutron densities decreases with the lowering of detection energy thresholds.
Naoki Tajima
2005-03-12
The canonical-basis HFB method provides an efficient way to describe pairing correlations involving the continuum part of the single-particle spectrum in coordinate-space representations. It can be applied to super-conducting deformed drip-line nuclei as easily as to stable or spherical nuclei. This method is applied to a simulation of the approach to the neutron drip line. It turns out that the HFB solution has a stronger pairing and a smaller deformation as the Fermi level is raised. However, such changes are smooth and finite. No divergences or discontinuities of the radius or other quantities are found in the limit of zero Fermi energy. The nuclear density continues to be localized even a little beyond the drip line.
Systematics on fission fragment mass distribution of neutron induced 235U fission
Ting-Jin Liu; Zheng-Jun Sun; Neng-Chuan Shu
2008-01-01
Based on the neutron induced fission fragment mass distribution data up to neutron energy 20 MeV measured with the double kinetic energy method (KEM) and the radio active method (RAM), the systematics of fission fragment mass distribution was investigated by using 5 Gaussian model and the systematics parameters were obtained by fitting the experimental data. With the systematics, the yields
Pairing properties of the inner crust of neutron stars at finite temperature
A. Pastore
2014-03-20
We investigate the thermal properties of the inner crust of a neutron star using the Hartree-Fock-Bogoliubov (HFB) formalism at finite temperature. We compare our results with the ones obtained solving the same equations, but within the BCS approximation. We observe that for the outermost regions of the inner crust, the two methods can show important differences, in particular when we use them to calculate the neutron specific heat of the system.
Effect of an external action on a pair distribution function in a steady state
NASA Astrophysics Data System (ADS)
Vlasenko, T. S.
2014-05-01
An external action that reduces a two-component equilibrium thermodynamic system to a nonequilibrium steady state with scalar fluxes has been studied. A system of integrodifferential equations for pair correlation functions has been obtained. These equations coincide with the second equations of the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy, but with different effective temperatures. Thus, ordinary integrodifferential equations for a pair correlation function with effective temperatures expressed in terms of the perturbed (nonequilibrium) Maxwellian momentum distribution function can be used to calculate the structural and thermodynamic properties of such a system.
Neutron Emission, Mass Distribution and Energetics in 14.5 MeV-Neutron Induced Fission of Uranium238
Hisao YAMAMOTO; Yoshiharu MORI; Yoshihisa WAKUTA; Akira KATASE; Masateru SONODA
1979-01-01
A study is performed on 14.5 MeV-neutron induced fission of U by means of three-parameter experiment in which the energies of both fragments and the time-of-flight of one fragment are measured. A mosaic-arrayed surface barrier detector of large sensitive area is used at the remote end of a flight tube. The pre- and post-neutron-emission fragment mass distributions are obtained, together
Radial Flux Distribution of Low-Energy Neutrons.
ERIC Educational Resources Information Center
Higinbotham, J.
1979-01-01
Describes an experiment designed to illustrate the basic principle involved in the process of moderation of fast neutrons by water, and the monitoring of the low-energy neutron flux using indium as a probe. (GA)
Superfluidity of Dense Neutron Matter with Spin-Triplet P-Wave Pairing in Strong Magnetic Field
Tarasov, Alexander N. [Institute for Theoretical Physics, NSC Kharkov Institute of Physics and Technology, 61108, Kharkov (Ukraine)
2006-09-07
A dense superfluid pure neutron matter with an effective Skyrme interaction, which depends on the density n of the neutrons with spin-triplet p-wave pairing similar to those of 3He-A1 and 3He-A, is studied in a strong uniform static magnetic field H in the framework of a generalized non-relativistic Fermi-liquid theory. We present an analytic solution for a set of previously derived nonlinear integral equations for the components of the order parameter and an effective magnetic field Heff. The obtained general formulas (valid for arbitrary parameterization of Skyrme forces) for the phase transition temperatures Tc1,2 of the neutron matter (from normal to a superfluid state of 3He-A1 type and then to a 3He-A type state, respectively) and the expression for Heff at T=0 are linear functions of strong magnetic field H and nonlinear functions of n. The gap equation is also solved at T=0.
D. Dambournet; K. W. Chapman; M. V. Koudriachova; P. J. Chupas; I. Belharouak; K. Amine
2011-01-01
X-ray pair distribution function (PDF) methods and first-principles calculations have been combined to probe the structure of electrochemically lithiated TiO Brookite. Traditional powder diffraction studies suggest that Brookite amorphizes upon lithium insertion, with the Bragg reflections disappearing. However, PDF analysis indicates that the TiO framework connectivity is maintained throughout lithium intercalation, with expansions along the a and b axes. The
Simple Method to Compute Pair Distribution Function from Molecular Dynamics Data
NASA Astrophysics Data System (ADS)
Uno, Toshiaki; Sogo, Kiyoshi
2015-04-01
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.
Study of nuclear dynamics of neutron-rich colliding pair at energy of vanishing flow
Sakshi Gautam
2011-07-28
We study nuclear dynamics at the energy of vanishing flow of neutron-rich systems having N/Z ratio 1.0, 1.6 and 2.0 throughout the mass range at semi central colliding geometry. In particular we study the behavior of average and maximum density with N/Z dependence of the system.
Pire, B; Szymanowski, L
2009-08-14
We describe a new way to access the chiral-odd transversity parton distribution in the proton through the photoproduction of lepton pairs. The basic ingredient is the interference of the usual Bethe-Heitler or Drell-Yan amplitudes with the amplitude of a process, where the photon couples to quarks through its chiral-odd distribution amplitude, which is normalized to the magnetic susceptibility of the QCD vacuum. A promising phenomenology of single and double spin observables emerges from the unusual features of this amplitude. PMID:19792634
W. C. Feldman; M. T. Mellon; O. Gasnault; B. Diez; R. C. Elphic; J. J. Hagerty; D. J. Lawrence; S. Maurice; T. H. Prettyman
2007-01-01
Neutron leakage currents measured using the Mars Odyssey Neutron Spectrometer are used to develop a two-layer model of the distribution of hydrogen (here parameterized as water-equivalent hydrogen, WEH) at high northern latitudes. The WEH abundance in the upper layer, Wup, was found to range between 1% and about 5%. The maximum value of the apparent thickness, D, of this upper
Improvement of dose distribution by central beam shielding in boron neutron capture therapy
NASA Astrophysics Data System (ADS)
Sakurai, Yoshinori; Ono, Koji
2007-12-01
Since boron neutron capture therapy (BNCT) with epithermal neutron beams started at the Kyoto University Reactor (KUR) in June 2002, nearly 200 BNCT treatments have been carried out. The epithermal neutron irradiation significantly improves the dose distribution, compared with the previous irradiation mainly using thermal neutrons. However, the treatable depth limit still remains. One effective technique to improve the limit is the central shield method. Simulations were performed for the incident neutron energies and the annular components of the neutron source. It was clear that thermal neutron flux distribution could be improved by decreasing the lower energy neutron component and the inner annular component of the incident beam. It was found that a central shield of 4-6 cm diameter and 10 mm thickness is effective for the 12 cm diameter irradiation field. In BNCT at KUR, the depth dose distribution can be much improved by the central shield method, resulting in a relative increase of the dose at 8 cm depth by about 30%. In addition to the depth dose distribution, the depth dose profile is also improved. As the dose rate in the central area is reduced by the additional shielding, the necessary irradiation time, however, increases by about 30% compared to normal treatment.
Billinge, Simon J L; Farrow, Christopher L
2013-11-13
We examine the equations to obtain atomic pair distribution functions (PDFs) from x-ray, neutron and electron powder diffraction data with a view to obtaining reliable and accurate PDFs from the raw data using a largely ad hoc correction process. We find that this should be possible under certain circumstances that hold, to a reasonably good approximation, in many modern experiments. We describe a variational approach that could be applied to find data correction parameters that is highly automatable and should require little in the way of user inputs yet results in quantitatively reliable PDFs, modulo unknown scale factors that are often not of scientific interest when profile fitting models are applied to the data with scale factor as a parameter. We have worked on a particular implementation of these ideas and demonstrate that it yields PDFs that are of comparable quality to those obtained with the existing x-ray data reduction program PDFgetX2. This opens the door to rapid and highly automated processing of raw data to obtain PDFs. PMID:24140913
Thorpe, Michael
Local atomic structure of semiconductor alloys using pair distribution functions Jean S. Chung of binary semiconductor crystals and pseudobinary alloys with the zinc-blende structures. The pair are presented for both crystals InAs and GaAs and alloys Ga1 xInxAs . These results can be directly compared
Pairing phenomenon in doubly odd neutron rich {sup 136}Sb nucleus
Laouet, N.; Benrachi, F. [Laboratoire de Physique Mathematique et Subatomique Mentouri University, Constantine (Algeria)
2012-06-27
Based on p-n and n-n pairing gap energies giving by K. Kaneko et al. (2003), we make modifications on the kh5082 interaction. Calculations and study of some nuclear properties for {sup 136}Sb nucleus are developed in the framework of the nuclear shell model by means of OXBASH structure code. We get the same energetic sequence as the recent experimental values of single particle energies. The effective charge values e{sub p}=1.35e and e{sub n}=0.9e, and factors given by V. I. Isakov are used to evaluate multipole electromagnetic moments.
Systematics of nucleon density distributions and neutron skin of nuclei
W. M. Seif; Hesham Mansour
2015-05-19
Proton and neutron density profiles of 760 nuclei in the mass region of A=16-304are analyzed using the Skyrme energy density for the parameter set SLy4. Simple formulae are obtained to fit the resulting radii and diffuseness data. These formulae may be useful to estimate the values of the unmeasured radii, and especially in extrapolating charge radius values for nuclei which are far from the valley of stability or to perform analytic calculations for bound and/or scattering problems. The obtained neutron and proton root-mean-square radii and the neutron skin thicknesses are in agreement with the available experimental data.
Finite Size Effects on the Real-Space Pair Distribution Function of Nanoparticles
Gilbert, Benjamin
2008-10-01
The pair distribution function (PDF) method is a powerful approach for the analysis of the structure of nanoparticles. An important approximation used in nanoparticle PDF simulations is the incorporation of a form factor describing nanoparticle size and shape. The precise effect of the form factor on the PDF is determined by both particle shape and structure if these characteristics are both anisotropic and correlated. The correct incorporation of finite size effects is important for distinguishing and quantifying the structural consequences of small particle size in nanomaterials.
Real distributed vibration sensing with high frequency response based on pulse pair
NASA Astrophysics Data System (ADS)
He, Qian; Zhu, Tao; Xiao, Xianghui; Diao, Dongmei; Huang, Wei; Bao, Xiaoyi
2014-05-01
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.
Neutron yields and angular distributions produced in antiproton annihilation at rest in uranium
Chen, B.; Armstrong, T.A.; Lewis, R.A.; Newton, R.; Smith, G.A. (Laboratory for Elementary Particle Science, Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)); Bocquet, J.P.; Malek, F. (Institut des Sciences Nucleaires de Grenoble, 53 Avenue des Martyrs, 38026 Grenoble CEDEX (France)); Nifenecker, H. (Institut des Sciences Nucleaires de Grenoble CEDEX, 53 Avenue des Martyrs, 38026 Grenoble CEDEX (France) DRFMC/LIH Centre d'Etudes Nucleaires de Grenoble, Boite Postale 85X, 38041 Grenoble CEDEX (France)); Maurel, M.; Monnand, E.; Perrin, P.; Ristori, C. (DRFMC, Centre d'Etudes Nucleaires de Grenoble, Boite Postale 85X, 38041 Grenoble CEDEX (France)); Ericsson, G.; Johansson, T.; Tibell, G. (Department of Radiation Sciences, P.O. Box 535, S-75121 Uppsala (Sweden)); Rey-Campagnolle, M. (Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse, Institut National de Physique Nucleaire et de Physique des Particules, Centr
1992-05-01
Measurements of neutron yields and their angular distributions in coincidence with fission fragments produced in antiproton annihilation at rest in a natural uranium target have been carried out Low Energy Antiproton Ring (LEAR) at CERN. A total of 16.3{plus minus}0.9 neutrons per annihilation have been found, distributed among direct knockout (27%), evaporation (21%), and fission (52%) processes. Angular distributions show that neutrons below approximately 5 MeV result entirely from moving fission fragments, and above approximately 12 MeV entirely from the excited, prescission nucleus. An estimate of the angular momentum of the excited fission fragment gives {similar to}13{h bar}. We are able to account for all baryons produced in annihilation, including neutrons from this experiment and light charged nuclei found in another LEAR experiment, to within 4.5{plus minus}2.5 of the initial 237 units in the initial state.
Neutron yields and angular distributions produced in antiproton annihilation at rest in uranium
B. Chen; T. A. Armstrong; R. A. Lewis; R. Newton; G. A. Smith; J. P. Bocquet; F. Malek; H. Nifenecker; M. Maurel; E. Monn; P. Perrin; C. Ristori; G. Ericsson; T. Johansson; G. Tibell; M. Rey-Campagnolle; S. Polikanov; T. Krogulski; J. Mougey
1992-05-01
Measurements of neutron yields and their angular distributions in coincidence with fission fragments produced in antiproton annihilation at rest in a natural uranium target have been carried out Low Energy Antiproton Ring (LEAR) at CERN. A total of 16.3±0.9 neutrons per annihilation have been found, distributed among direct knockout (27%), evaporation (21%), and fission (52%) processes. Angular distributions show that neutrons below approximately 5 MeV result entirely from moving fission fragments, and above approximately 12 MeV entirely from the excited, prescission nucleus. An estimate of the angular momentum of the excited fission fragment gives ?13?. We are able to account for all baryons produced in annihilation, including neutrons from this experiment and light charged nuclei found in another LEAR experiment, to within 4.5±2.5 of the initial 237 units in the initial state.
Conditional pair distributions in many-body systems: exact results for Poisson ensembles.
Rohrmann, René D; Zurbriggen, Ernesto
2012-05-01
We introduce a conditional pair distribution function (CPDF) which characterizes the probability density of finding an object (e.g., a particle in a fluid) to within a certain distance of each other, with each of these two having a nearest neighbor to a fixed but otherwise arbitrary distance. This function describes special four-body configurations, but also contains contributions due to the so-called mutual nearest neighbor (two-body) and shared neighbor (three-body) configurations. The CPDF is introduced to improve a Helmholtz free energy method based on space partitions. We derive exact expressions of the CPDF and various associated quantities for randomly distributed, noninteracting points at Euclidean spaces of one, two, and three dimensions. Results may be of interest in many diverse scientific fields, from fluid physics to social and biological sciences. PMID:23004705
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
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.
M. Montoya; J. Rojas; E. Saetone
2007-01-01
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
Theoretical modeling for neutron elastic scattering angular distribution in the fast energy range
Kawano, Toshihiko [Los Alamos National Laboratory
2010-12-07
One of the major issues of neutron scattering modeling in the fast energy range is the contribution of compound elastic and inelastic scattering to the total scattering process. The compound component may become large at very low energies where the angular distribution becomes 90-degree symmetric in the center-of-mass system. Together with the shape elastic component, the elastic scattering gives slightly forward-peaked angular distributions in the fast energy range. This anisotropic angular distribution gives high sensitivities to many important nuclear reactor characteristics, such as criticality and neutron shielding. In this talk we describe how the anisotropic angular distributions are calculated within the statistical model framework, including the case where strongly coupled channels exist, by combining the coupled-channels theory with the Hauser-Feshbach model. This unique capability extension will have significant advantages in understanding the neutron scattering process for deformed nuclei, like uranium or plutonium, on which advanced nuclear energy applications center.
Neutron angular distribution in a plasma focus obtained using nuclear track detectors.
Castillo-Mejía, F; Herrera, J J E; Rangel, J; Golzarri, J I; Espinosa, G
2002-01-01
The dense plasma focus (DPF) is a coaxial plasma gun in which a high-density, high-temperature plasma is obtained in a focused column for a few nanoseconds. When the filling gas is deuterium, neutrons can be obtained from fusion reactions. These are partially due to a beam of deuterons which are accelerated against the background hot plasma by large electric fields originating from plasma instabilities. Due to a beam-target effect, the angular distribution of the neutron emission is anisotropic, peaked in the forward direction along the axis of the gun. The purpose of this work is to illustrate the use of CR-39 nuclear track detectors as a diagnostic tool in the determination of the time-integrated neutron angular distribution. For the case studied in this work, neutron emission is found to have a 70% contribution from isotropic radiation and a 30% contribution from anisotropic radiation. PMID:12382811
Joydip Kundu; Sanjay Reddy
2004-05-19
We calculate the correlation functions needed to describe the linear response of superfluid matter, and go on to calculate the differential cross section for neutral-current neutrino scattering in superfluid neutron matter and in color-flavor locked quark matter (CFL). We report the first calculation of scattering rates that includes neutrino interactions with both pair-breaking excitations and low-lying collective excitations (Goldstone modes). Our results apply both above and below the critical temperature, allowing use in simulations of neutrino transport in supernovae and neutron stars.
Distribution of total radiation widths for neutron resonances of Pt isotopes
NASA Astrophysics Data System (ADS)
Koehler, P. E.; Be?vá?, F.; Krti?ka, M.
2015-05-01
High quality neutron capture and transmission data were measured on isotopically enriched 192,194,195,196Pt and natural Pt samples at ORELA. R-matrix analysis of this data revealed resonance parameters for 159, 413, 423, 258, and 11 neutron resonances for neutron energies below 5.0, 16.0, 7.5, 16.0, and 5.0 keV for 192,194,195,196,198Pt+n, respectively. Earlier analysis of data on reduced neutron widths, ?0n, showed that the distributions of ?0n for 192,194Pt deviate significantly from the Porter-Thomas distribution (PTD) predicted by random matrix theory. In this contribution we report on preliminary results of the analysis of distribution of total radiation widths, ??, in 192,194,195,196Pt+n reactions. Comparison of experimental data with predictions made within the nuclear statistical model indicates that standard models of Photon Strength Functions (PSFs) and Nuclear Level Density predict ?? distributions which are too narrow. We found that satisfactory agreement between experimental and simulated distributions can be obtained only by a strong suppression of the PSFs at low ?-ray energies and/or by violation of the usual assumption that primary transitions from neutron resonances follow the PTD. The shape of PSFs needed for reproduction of our ?? data also nicely reproduces spectra from several (n,?) experiments on the neighbor nuclide 198Au.
V. D. Simutkin; I. V. Ryzhov; G. A. Tutin; L. A. Vaishnene; J. Blomgren; S. Pomp; M. Österlund; P. Andersson; R. Bevilacqua; J. P. Meulders; R. Prieels
2009-01-01
Fragment mass distributions from neutron-induced fission of 232Th and 238U have been measured at quasi-monoenergetic neutron beam of the Louvain-la-Neuve cyclotron facility CYCLONE. The measurements have been carried out making use of a multi-section Frisch-gridded ionization chamber. The measurement technique as well as the data processing is described. Preliminary data on primary fragment mass yields are given for an incident
Wiener, M. C.; King, G. I.; White, S. H.
1991-01-01
We described in two previous papers a method for the joint refinement of the structure of fluid bilayers using neutron and x-ray diffraction data (Wiener, M. C., and S. H. White 1991a, b. Biophys. J. 59: 162-173 and 174-185). An essential part of the method is the appropriate scaling of the diffraction data. Here we describe the scaling of the neutron data and the determination of the transbilayer distribution of double bonds in liquid-crystalline (L alpha phase) phospholipid bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). The distribution was determined by neutron diffraction of oriented multilayers (66% RH) of DOPC specifically deuterated at the 9- and 10-position of both acyl chains. The double-bond distribution is described accurately by a pair of Gaussian functions each located at a position Zcc = 7.88 +/- 0.09 A from the bilayer center with 1/e-halfwidths of Acc = 4.29 +/- 0.16 A. Previously, we determined the transbilayer distribution of bromine atoms in a specifically halogenated lipid, 1-oleoyl-2-9,10-dibromostearoyl-sn-glycero-3-phosphocholine (OBPC), and showed it to be an isomorphous replacement for DOPC (Wiener, M. C., and S. H. White, 1991c. Biochemistry. In press). A comparison of the double-bond and bromine profiles indicates that the positions of the centers of the deuterated double bond and the brominated methylene Gaussian distributions are equal within experimental error and that each label undergoes similar average thermal motions with respect to the bilayer normal. The observation that the average position of a label on both acyl chains (the deuterated double bonds) is similar to the average position of a label on the 2-chain alone (the brominated methylenes) indicates that the maximum separation along the bilayer normal between the double bonds of the acyl chains is 1 A or less. The fully-resolved transbilayer water distribution, previously determined at lower resolution (Jacobs, R. E., and S. H. White. 1989. Biochemistry. 28:3421-3437), 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
Gorelik, Tatiana E; Schmidt, Martin U; Kolb, Ute; Billinge, Simon J L
2015-04-01
This paper shows that pair-distribution function (PDF) analyses can be carried out on organic and organometallic compounds from powder electron diffraction data. Different experimental setups are demonstrated, including selected area electron diffraction and nanodiffraction in transmission electron microscopy or nanodiffraction in scanning transmission electron microscopy modes. The methods were demonstrated on organometallic complexes (chlorinated and unchlorinated copper phthalocyanine) and on purely organic compounds (quinacridone). The PDF curves from powder electron diffraction data, called ePDF, are in good agreement with PDF curves determined from X-ray powder data demonstrating that the problems of obtaining kinematical scattering data and avoiding beam damage of the sample are possible to resolve. PMID:25510245
Gorelik, Tatiana E.; Billinge, Simon J. L.; Schmidt, Martin U.; Kolb, Ute
2015-04-01
This paper shows for the first time that pair-distribution function analyses can be carried out on organic and organo-metallic compounds from powder electron diffraction data. Different experimental setups are demonstrated, including selected area electron diffraction (SAED) and nanodiffraction in transmission electron microscopy (TEM) or nanodiffraction in scanning transmission electron microscopy (STEM) modes. The methods were demonstrated on organo-metallic complexes (chlorinated and unchlorinated copper-phthalocyanine) and on purely organic compounds (quinacridone). The PDF curves from powder electron diffraction data, called ePDF, are in good agreement with PDF curves determined from X-ray powder data demonstrating that the problems of obtaining kinematical scattering datamore »and avoiding beam-damage of the sample are possible to resolve.« less
X-ray pair distribution function analysis of nanostructured materials using a Mythen detector.
Haverkamp, Richard G; Wallwork, Kia S
2009-11-01
Total scattering from nanocrystalline materials recorded on the Australian Synchrotron powder diffraction beamline has been analysed to produce atomic pair distribution functions (PDFs) for structural analysis. The capability of this beamline, which uses the massively parallel Mythen II detector, has been quantified with respect to PDF structure analysis. Data were recorded to a wavevector magnitude, Q, of 20.5 A(-1), with successful PDFs obtained for counting times as short as 10 s for crystalline LaB(6) and 180 s for nanocrystalline (47 A) anatase. This paper describes the aspects of a PDF experiment that are crucial to its success, with reference to the outcomes of analysis of data collected from nanocrystalline TiO(2) and microcrystalline LaB(6) and IrO(2). PMID:19844023
Roots Revealed - Neutron imaging insight of spatial distribution, morphology, growth and function
NASA Astrophysics Data System (ADS)
Warren, J.; Bilheux, H.; Kang, M.; Voisin, S.; Cheng, C.; Horita, J.; Perfect, E.
2013-05-01
Root production, distribution and turnover are not easily measured, yet their dynamics are an essential part of understanding and modeling ecosystem response to changing environmental conditions. Root age, order, morphology and mycorrhizal associations all regulate root uptake of water and nutrients, which along with along with root distribution determines plant response to, and impact on its local environment. Our objectives were to demonstrate the ability to non-invasively monitor fine root distribution, root growth and root functionality in Zea mays L. (maize) and Panicum virgatum L. (switchgrass) seedlings using neutron imaging. Plants were propagated in aluminum chambers containing sand then placed into a high flux cold neutron beam line. Dynamics of root distribution and growth were assessed by collecting consecutive CCD radiographs through time. Root functionality was assessed by tracking individual root uptake of water (H2O) or deuterium oxide (D2O) through time. Since neutrons strongly scatter H atoms, but not D atoms, biological materials such as plants are prime candidates for neutron imaging. 2D and 3D neutron radiography readily illuminated root structure, root growth, and relative plant and soil water content. Fungal hyphae associated with the roots were also visible and appeared as dark masses since their diameter was likely several orders of magnitude less than ~100 ?m resolution of the detector. The 2D pulse-chase irrigation experiments with H2O and D2O successfully allowed observation of uptake and mass flow of water within the root system. Water flux within individual roots responded differentially to foliar illumination based on internal water potential gradients, illustrating the ability to track root functionality based on root size, order and distribution within the soil. (L) neutron image of switchgrass growing in sandy soil with 100 ?m diameter roots (R) 3D reconstruction of maize seedling following neutron tomography
Electron-pair distributions in the C=C double bond. Effects of a push-pull substitution
Marcos, E.S.; Sanz, J.F. (Univ. of Sevilla (Spain)); Karafiloglou, P. (Aristotelian Univ. of Thessaloniki (Greece))
1990-04-05
By application of a recently developed method, the populations of ionic and spin-alternant electron-pair distributions are calculated in ethylene, aminoethylene, nitroethylene, and 2-nitroethenamine, one of the simplest push-pull ethylenes. Occupation numbers, giving a measure of the existence of an ionic electron pair in one carbon atom and of a spin-alternant electron pair in the two carbon atoms of the ethylenic double bond, are investigated from ab initio MO wave functions. The effects of either an electron-donating or an electron-withdrawing group and the cooperative push-pull substitution are discussed.
A. M. Sukhovoj; V. A. Khitrov
2011-05-30
In the frameworks of hypothesis of practical constancy of the neutron resonance number in small fixed intervals of neutron energy, their most probable value was determined for nucleus mass region 230distributions. This was done under assumption that a set of the measured neutron amplitudes can correspond to one or to superposition of some normal distributions with non-zero average and dispersion differing from reduced neutron width. The main result of the analysis: the mean spacing and neutron strength function values can be determined only with unknown systematical uncertainty whose magnitude is determined by unknown precision of the Porter-Thomas hypothesis correspondence to concrete experimental sets of resonances and unknown experimental mean neutron widths.
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
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.
Directional Stand-off Detection of Fast Neutrons and Gammas Using Angular Scattering Distributions
Vanier P. e.; Dioszegi, I.; Salwen, C.; Forman, L.
2009-10-25
We have investigated the response of a DoubleScatter Neutron Spectrometer (DSNS) for sources at long distances (gr than 200 meters). We find that an alternative method for analyzing double scatter data avoids some uncertainties introduced by amplitude measurements in plastic scintillators.Time of flight is used to discriminate between gamma and neutron events, and the kinematic distributions of scattering angles are assumed to apply. Non-relativistic neutrons are most likely to scatter at 45°, while gammas with energies greater than 2 MeV are most likely to be forward scattered. The distribution of scattering angles of fission neutrons arriving from a distant point source generates a 45° cone, which can be back-projected to give the source direction. At the same time, the distribution of Compton-scattered gammas has a maximum in the forward direction, and can be made narrower by selecting events that deposit minimal energy in the first scattering event. We have further determined that the shape of spontaneous fission neutron spectra at ranges gr than 110 m is still significantly different from thecosmic ray background.
Thorpe, Michael
Uncovering the intrinsic geometry from the atomic pair distribution function of nanomaterials Ming with respect to one another. For a nanomaterial, however, the atomic pair distribution function also depends on the shape and size of the nanomaterial. A modified form of the radial distribution function is discussed
Charge distribution in the neutron at short distances
NASA Astrophysics Data System (ADS)
Abrahamyan, Sergey; E02-013 Collaboration
2014-09-01
Elastic form-factors are a fundamental property of the nucleon, and provide critical information on the nucleon's transverse spatial structure. Furthermore, by combining knowledge of the neutron electromagnetic form factors with the corresponding form factors of the proton, it is possible to gain understanding of the flavor structure of the nucleon. In this talk we present final results of the JLab experiment E02-013, comprising four measurements of the ratio of the neutron's electric and magnetic form factors, GEn /GMn , at four values of the four-momentum transfer Q2 = 1.2, 1.7, 2.5 and 3.4 GeV2. We note that the result at 1 GeV2 has not been previously reported. In E02-013, a double-polarization asymmetry was measured in the reaction 3 He --> (e-> ,e' n) p p in order to determine the ratio GEn /GMn . We present key aspects of the experimental approach that was used, as well as essential features of the data analysis such as exclusive quasi-elastic event selection, hadron charge identification and analysis of FSI effects.
H. Matsuura; T. Takaki; K. Funakoshi; Y. Nakao; K. Kudo
2000-01-01
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; K. Funakoshi; Y. Nakao
2003-01-01
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
1991-01-01
Several critical experiments were performed for a number of strong neutron absorbers periodically distributed throughout a tank filled with high-concentration fissile solution, These experiments served as a pilot study for a novel means of storing fissile solutions at a nuclear production plant handling such solutions. The configuration also approximates one commonly used method (Raschig rings) of assuring criticality safety in
Simon John Laird Billinge
1992-01-01
We have carried out a detailed Pair Distribution Function Analysis of powder diffraction data from samples of Nd_{2-x}Ce _{x}CuO _{4-y} with x = 0.165 and x = 0.2. The former is superconducting with an almost full Meissner fraction, and T_{c} = 22K. The latter is isostructural, but exhibits no superconductivity. A \\
Koji Tamura
2002-01-01
The intensity distributions of a neodymium ion beam that was extracted from laser photoionized plasma were measured by scanning a multichannel Faraday cup. The lateral width of ions at the position of the Faraday cup, which was broad without any additional electric field, was reduced by the additional concentric potential with a pair of semicylindrical electrodes set outside of the
Charge density distributions and related form factors in neutron-rich light exotic nuclei
A. N. Antonov; M. K. Gaidarov; D. N. Kadrev; P. E. Hodgson; E. Moya de Guerra
2004-01-28
Charge form factors corresponding to proton density distributions in exotic nuclei, such as $^{6,8}$He, $^{11}$Li, $^{17,19}$B and $^{14}$Be are calculated and compared. The results can be used as tests of various theoretical models for the exotic nuclei structure in possible future experiments using a colliding electron-exotic nucleus storage ring. The result of such a comparison would show the effect of the neutron halo or skin on the proton distributions in exotic nuclei.
Hietanen, A.
1971-01-01
Distribution of major and minor elements has been determined for five hornblende-biotite pairs from hornblende-biotite quartz diorite and monzotonalite and for a clinopyroxene-orthopyroxene pair from pyroxene diorite collected from the border zones and centers of zoned plutons in the northern Sierra Nevada, California. The distribution coefficients Kd [Mg/Fe] for biotite/hornblende are of the same magnitude (0.61-0.67) for both the mafic border zone and the silicic center. For comparison, KD [Mg/Fe] values for biotite/hornblende from plutonic rocks of the central Sierra Nevada and the southern California batholith were calculated from data published by others. Rocks of the oldest age group (ca. 150 m.y.) in the central Sierra Nevada have an average distribution coefficient, KD, of 0.64, close to the average KD in the study area, where K-Ar dates are 143 to 129 m.y. The intermediate age group has an average KD=0.81, and the youngest group has KD=0.77. KD [Mg/Fe] for biotite/hornblende from the southern California batholith is 0.83, close to the average of the intermediate age group in the central Sierra Nevada. The calculated difference in pressure of crystallization between rocks of the Feather River area and the southern California batholith is 1 kb; the rocks of the Feather River area being crystallized at a higher pressure. This is in good agreement with the low-pressure contact metamorphism in the south (pyroxene hornfels facies), as compared with a medium-pressure metamorphism around the northern plutons, where andalusitesillimanite-cordierite and andalusite-staurolite subfacies of the amphibolite facies indicate pressures of about 4 kb. Trace elements Cr, V, Ni, Co, Ga are distributed equally between biotite and hornblende, whereas Ba and possibly Cu are concentrated in biotite and Sr and Sc and possibly Zr in hornblende. ?? 1971 Springer-Verlag.
Properties and distribution of paired candidate stony meteorites at Meridiani Planum, Mars
NASA Astrophysics Data System (ADS)
Schröder, Christian; Herkenhoff, Kenneth E.; Farrand, William H.; Chappelow, John E.; Wang, Wei; Nittler, Larry R.; Ashley, James W.; Fleischer, Iris; Gellert, Ralf; Golombek, Matthew P.; Johnson, Jeffrey R.; Klingelhöfer, Göstar; Li, Ron; Morris, Richard V.; Squyres, Steven W.
2010-11-01
The Mars Exploration Rover Opportunity investigated four rocks, informally dubbed Barberton, Santa Catarina, Santorini, and Kasos, that are possible stony meteorites. Their chemical and mineralogical composition is similar to the howardite, eucrite, and diogenite group but with additional metal, similar to mesosiderite silicate clasts. Because of their virtually identical composition and because they appear to represent a relatively rare group of meteorites, they are probably paired. The four rocks were investigated serendipitously several kilometers apart, suggesting that Opportunity is driving across a larger population of similar rock fragments, maybe a meteorite strewn field. Small amounts of ferric Fe are a result of weathering. We did not observe evidence for fusion crusts. Four iron meteorites were found across the same area. Although mesosiderites are stony irons, a genetic link to these irons is unlikely. The stony meteorites probably fell later than the irons. The current atmosphere is sufficiently dense to land such meteorites at shallow entry angles, and it would disperse fragments over several kilometers upon atmospheric breakup. Alternatively, dispersion by spallation from an impacting meteoroid may have occurred. Santa Catarina and a large accumulation of similar rocks were found at the rim of Victoria crater. It is possible that they are associated with the impactor that created Victoria crater, but our limited knowledge about their distribution cannot exclude mere coincidence.
Calculation of the angular distribution of delay times in neutron scattering on {sup 58}Ni nuclei
Prokopets, G. A., E-mail: gaprok@uos.net.ua [National University of Kyiv-Mohyla Academy (Ukraine)
2011-05-15
Angular distributions of average delay times and time variances are calculated for resonance-neutron scattering on {sup 58}Ni nuclei at neutron energies in the range E = 600-700 keV. The effect of the energy spectrum and polarization of the beam on the scattering-process time is discussed. The angular dependence of the time law is also considered for the decay of an intermediate compound nuclear system. It is shown that the results of stationary and nonstationary calculations are in good agreement.
Mass distribution in the reactor-neutron-induced fission of thorium-232
H. N. Erten; A. R. Gruetter; H. R. Von Gunten
1981-01-01
This investigation was undertaken to improve the data on product yields in the reactor-neutron-induced fission of Â²Â³Â²Th. The mass distribution in the reactor-neutron-induced fission of Â²Â³Â²Th was studied using radiochemical techniques and direct gamma-ray measurements. Absolute fission yields of the standard nuclides â¹â¹Mo and Â¹Â³Â²Te were obtained from Â²Â³Â²Th sources irradiated in a fission counter. The yields of 36 mass
NASA Astrophysics Data System (ADS)
Flammini, D.; Pietropaolo, A.; Senesi, R.; Andreani, C.; McBride, F.; Hodgson, A.; Adams, M. A.; Lin, L.; Car, R.
2012-01-01
The spherical momentum distribution of the protons in ice is extracted from a high resolution deep inelastic neutron scattering experiment. Following a recent path integral Car-Parrinello molecular dynamics study, data were successfully interpreted in terms of an anisotropic Gaussian model, with a statistical accuracy comparable to that of the model independent scheme used previously, but providing more detailed information on the three dimensional potential energy surface experienced by the proton. A recently proposed theoretical concept is also employed to directly calculate the mean force from the experimental neutron Compton profile, and to evaluate the accuracy required to unambiguously resolve and extract the effective proton potential from the experimental data.
Mass distribution in the quasi-mono-energetic neutron-induced fission of 232Th
NASA Astrophysics Data System (ADS)
Naik, H.; Crasta, Rita; Suryanarayana, S. V.; Prajapati, P. M.; Mulik, V. K.; Shivasankar, B. S.; Jagadeesan, K. C.; Thakare, S. V.; Sharma, S. C.; Goswami, A.
2014-09-01
The cumulative yields of various fission products in 232Th(n, f) with average neutron energies of 6.35, 8.53 and 10.09 MeV have been determined using an off-line -ray spectrometric technique. The neutron beam was produced from the 7Li(p, n) reaction. From the cumulative fission yields, the mass chain yields were obtained by using charge distribution correction of medium energy. The peak-to-valley () ratio, the average value of light mass (), heavy mass () and the average number of neutrons () at the three different neutron energies of the present work and at other energies from the literature in the 232Th(n, f) reaction were obtained from the mass yield data. The present and the existing literature data in the 232Th(n, f) reaction at various excitation energies were compared with similar data in the 238U(n, f) reaction. The fine structure in the mass yield distribution was interpreted from the point of nuclear structure effect such as shell closure proximity and even-odd effect. The role of standard I and standard II asymmetric mode of fission was discussed. The different types of mass-yield distributions between 232Th(n, f) and 238U(n, f) reactions were explained from different types of the potential energy between the two fissioning systems. The role of excitation energy was also investigated.
Extraction of neutron density distributions from proton elastic scattering at intermediate energies
NASA Astrophysics Data System (ADS)
Takeda, H.; Sakaguchi, H.; Taki, T.; Yosoi, M.; Itoh, M.; Kawabata, T.; Ishikawa, T.; Uchida, M.; Tsukahara, N.; Noro, T.; Yoshimura, M.; Fujimura, H.; Yoshida, H. P.; Obayashi, E.; Tamii, A.; Akimune, H.
2002-04-01
Cross sections, analyzing powers and spin rotation parameters of proton elastic scattering from 58Ni and 120Sn have been measured at intermediate energies. In order to explain the 58Ni data, it was necessary to use experimental density distributions deduced from charge distributions and to modify coupling constants and masses of ? and ? mesons. For 120Sn, assuming the same modification and using proton densities deduced from charge densities, neutron density distribution was searched so as to reproduce 120Sn data. Effects of ? meson modifications are also discussed. .
Senftle, F.E.; Moxham, R.M.; Tanner, A.B.; Philbin, P.W.; Boynton, G.R.; Wager, R.E.
1977-01-01
To evaluate the importance of variations in the neutron energy distribution in borehole activation analysis, capture gamma-ray measurements were made in relatively dry, low-porosity gabbro of the Duluth Complex. Although sections of over a meter of solid rock were encountered in the borehole, there was significant fracturing with interstitial water leading to a substantial variation of water with depth in the borehole. The linear-correlation coefficients calculated for the peak intensities of several elements compared to the chemical core analyses were generally poor throughout the depth investigated. The data suggest and arguments are given which indicate that the variation of the thermal-to-intermediate-to-fast neutron flux density as a function of borehole depth is a serious source of error and is a major cause of the changes observed in the capture gamma-ray peak intensities. These variations in neutron energy may also cause a shift in the observed capture gamma-ray energy.
Rietveld and pair distribution function study of Hägg carbide using synchrotron X-ray diffraction.
du Plessis, Hester Esna; de Villiers, J P R; Kruger, G J; Steuwer, A; Brunelli, M
2011-03-01
Fischer-Tropsch (FT) synthesis is an important process in the manufacturing of hydrocarbons and oxygenated hydrocarbons from mixtures of carbon monoxide and hydrogen (syngas). The reduced iron catalyst reacts with carbon monoxide and hydrogen to form bulk Fe(5)C(2) Hägg carbide (?-HC) during FT synthesis. Arguably, ?-HC is the predominant catalyst phase present in the working iron catalyst. Deactivation of the working catalyst can be due to oxidation of ?-HC to iron oxide, a step-wise decarburization to cementite (?-Fe(3)C), carbon formation or sintering with accompanying loss of catalytic performance. It is therefore critical to determine the precise crystal structure of ?-HC for the understanding of the synthesis process and for comparison with the first-principles ab initio modelling. Here the results of high-resolution synchrotron X-ray powder diffraction data are reported. The atomic arrangement of ?-HC was confirmed by Rietveld refinement and subsequent real-space modelling of the pair distribution function (PDF) obtained from direct Fourier transformation. The Rietveld and PDF results of ?-HC correspond well with that of a pseudo-monoclinic phase of space group P? [a = 11.5661?(6)?Å, b = 4.5709?(1)?Å, c = 5.0611?(2)?Å, ? = 89.990?(5)°, ? = 97.753?(4)°, ? = 90.195?(4)°], where the Fe atoms are located in three distorted prismatic trigonal and one octahedral arrangement around the central C atoms. The Fe atoms are distorted from the prismatic trigonal arrangement in the monoclinic structure by the change in C atom location in the structure. PMID:21335915
The impact of fuel particle size distribution on neutron transport in stochastic media
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
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)
NASA Astrophysics Data System (ADS)
Burova, T. G.; Ten, G. N.; Anashkin, A. A.
2008-05-01
The method of quantum-mechanical calculation of the relative line intensities in the resonance Raman (RR) spectra of polyatomic molecules, which was previously applied to the analysis of the spectra of individual cyclic molecules and makes it possible to take into account the Herzberg-Teller and Duschinsky effects, as well as the frequency effect, is applied for the first time to the calculation of the spectra of a pair guanine-cytosine. Satisfactory agreement between the calculated results and the available experimental data is obtained. The particular features of the intensity distribution in the RR spectra of the guanine-cytosine pair excited by laser radiation at 266, 240, 218, and 200 nm are analyzed. The RR spectra of the guanine-cytosine pair are compared with the spectra of the individual guanine and cytosine molecules excited by the laser radiation at the same wavelengths.
Proton Recoil Energy and Angular Distribution of Neutron Radiative Beta Decay
A. N. Ivanov; R. Hollwieser; N. I. Troitskaya; M. Wellenzohn
2013-09-27
We analyse the proton recoil energy and angular distribution of the radiative beta-decay of the neutron to leading order in the large baryon mass expansion by taking into account the contributions of the proton-photon correlations. We show that the account for the proton-photon correlations does not contradict the description of the radiative corrections to the lifetime of the neutron and the proton recoil energy spectrum of the neutron beta-decay in terms of the functions (\\alpha/\\pi) g_n(E_e) and (\\alpha/\\pi) f_n(E_e), where E_e is the electron energy. In addition we find that the contributions of the proton-photon correlations in the radiative beta-decay of the neutron to the proton recoil asymmetry C are of order 10^(-4). They make the contributions of the radiative corrections to the proton recoil asymmetry C symmetric with respect to a change A_0 B_0, where A_0 and B_0 are the correlation coefficients of the neutron beta-decay.
Tanaka, Kenichi; Sakurai, Yoshinori; Endo, Satoru; Takada, Jun
2014-06-01
In order to measure the spatial distributions of neutrons and gamma rays separately using the imaging plate, the requirement for the converter to enhance specific component was investigated with the PHITS code. Consequently, enhancing fast neutrons using recoil protons from epoxy resin was not effective due to high sensitivity of the imaging plate to gamma rays. However, the converter of epoxy resin doped with (10)B was found to have potential for thermal and epithermal neutrons, and graphite for gamma rays. PMID:24485172
S. Terashima; H. Sakaguchi; H. Takeda; T. Ishikawa; M. Itoh; T. Kawabata; T. Murakami; M. Uchida; Y. Yasuda; M. Yosoi; J. Zenihiro; H. P. Yoshida; T. Noro; T. Ishida; S. Asaji; T. Yonemura
2008-02-02
Cross sections and analyzing powers for proton elastic scattering from $^{116,118,120,122,124}$Sn at 295 MeV have been measured for a momentum transfer of up to about 3.5 fm$^{-1}$ to deduce systematic changes of the neutron density distribution. We tuned the relativistic Love-Franey interaction to explain the proton elastic scattering of a nucleus whose density distribution is well known. Then, we applied this interaction to deduce the neutron density distributions of tin isotopes. The result of our analysis shows the clear systematic behavior of a gradual increase in the neutron skin thickness of tin isotopes with mass number.
M. I. Krivoruchenko
2012-07-27
The probability-generating function of the number of electron-positron pairs produced in a uniform electric field is constructed. The mean and variance of the numbers of pairs are calculated, and analytical expressions for the probability of low numbers of electron-positron pairs are given. A recursive formula is derived for evaluating the probability of any number of pairs. In electric fields of supercritical strength |eE| > \\pi m^2/ \\ln 2, where e is the electron charge, E is the electric field, and m is the electron mass, a branch-point singularity of the probability-generating function penetrates the unit circle |z| = 1, which leads to the asymptotic divergence of the cumulative probability. This divergence indicates a failure of the continuum limit approximation. In the continuum limit and for any field strength, the positive definiteness of the probability is violated in the tail of the distribution. Analyticity, convergence, and positive definiteness are restored upon the summation over discrete levels of electrons in the normalization volume. Numerical examples illustrating the field strength dependence of the asymptotic behavior of the probability distribution are presented.
Angular distribution of products of ternary nuclear fission induced by cold polarized neutrons
Bunakov, V. E., E-mail: bunakov@vb13190.spbu.edu; Kadmensky, S. G., E-mail: kadmensky@phys.vsu.ru; Kadmensky, S. S. [Voronezh State University (Russian Federation)
2008-11-15
Within quantum fission theory, angular distributions of products originating from the ternary fission of nuclei that is induced by polarized cold and thermal neutrons are investigated on the basis of a non-evaporative mechanism of third-particle emission and a consistent description of fission-channel coupling. It is shown that the inclusion of Coriolis interaction both in the region of the discrete and in the region of the continuous spectrum of states of the system undergoing fission leads to T-odd correlations in the aforementioned angular distributions. The properties of the TRI and ROT effects discovered recently, which are due to the interference between the fission amplitudes of neutron resonances, are explored. The results obtained here are compared with their counterparts from classic calculations based on the trajectory method.
NASA Astrophysics Data System (ADS)
Tarasov, A. N.
2014-03-01
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.
Abeykoon, A. M. Milinda; Hu, Hefei; Wu, Lijun; Zhu, Yimei; Billinge, Simon J. L.
2015-02-01
We explore and describe different protocols for calibrating electron pair distribution function (ePDF) measurements for quantitative studies on nano-materials. We find the most accurate approach to determine the camera-length is to use a standard calibration sample of Au nanoparticles from National Institute of Standards and Technology. Different protocols for data collection are also explored, as are possible operational errors, to find the best approaches for accurate data collection for quantitative ePDF studies.
NASA Astrophysics Data System (ADS)
Kaki, Kaori
2015-03-01
Observables of proton elastic scattering from nickel isotopes (48-82Ni) are calculated based on relativistic impulse approximation (RIA), and nuclear density distributions are provided by relativistic mean-field (RMF) calculations. Contributions of a medium effect and multiple scattering to observables are evaluated and shown to be small at incident proton energies from 200 MeV through 500 MeV so that it is confirmed to perform a model analysis based on the fundamental RIA calculation. For 58,60,62,64Ni isotopes, are considered proton distributions which are obtained by means of unfolding the charge form factor of proton from charge densities determined by the experiments of electron scattering. Through comparisons between results for the different proton densities, contributions of proton form factor to proton distributions and to elastic scattering observables at 300 MeV are discussed. It is shown that the neutron distribution is determined from the restricted observables, reaction cross-section and the first dip of differential cross-section, based on a model analysis of Woods-Saxon distribution in the case of 64Ni target at 300 MeV. Contributions of tensor density and empirical proton density are shown to obtaining the neutron distribution with the model analysis. Compared with the similar studies for 40,60Ca and 208Pb, problems of the model analysis, which arise out of errors in observables, are discussed.
3D mapping of crystallographic phase distribution using energy-selective neutron tomography.
Woracek, Robin; Penumadu, Dayakar; Kardjilov, Nikolay; Hilger, Andre; Boin, Mirko; Banhart, John; Manke, Ingo
2014-06-25
Nondestructive 3D mapping of crystallographic phases is introduced providing distribution of phase fractions within the bulk (centimeter range) of samples with micrometer-scale resolution. The novel neutron tomography based technique overcomes critical limitations of existing techniques and offers a wide range of potential applications. It is demonstrated for steel samples exhibiting phase transformation after being subjected to tensile and torsional deformation. PMID:24692200
NASA Astrophysics Data System (ADS)
Tseng, H. K.
1995-07-01
We calculated numerically in a relativistic partial-wave formulation the positron energy-angle distributions of pair production in the fields of atoms with atomic number Z=1, 6, 13, and 82 for photons of energies near threshold, k=2.001, 2.01, and 2.10mec2. Our partial-wave results show that in this low photon energy region, the atomic-electron screening effect for the positron energy-angle distributions increases as Z increases, k decreases, and the positron energy E+ decreases. The ratio of the screened to the point-Coulomb positron energy-angle cross section is almost independent of the positron angle. That is, the shape of positron energy-angle distributions is almost independent of the screening. This suggests that the screening is primarily a normalization effect. Our results also indicate that the Born approximation prediction for the shape of positron energy-angle distributions is better than its prediction for positron energy spectra of pair production. The form of the Born approximation suggests a simple way to parametrize the shape of positron energy-angle distributions.
Harris, Thomas C. (Thomas Cameron)
2006-01-01
The success of Boron Neutron Capture Therapy (BNCT) is heavily dependent on the microscopic distribution of B-10 in tissue. High Resolution Quantitative Auto-Radiography (HRQAR) is a potentially valuable analytical tool ...
Nuclear shape dependence of Gamow-Teller distributions in neutron-deficient Pb isotopes
P. Sarriguren; O. Moreno; R. Alvarez-Rodriguez; E. Moya de Guerra
2005-10-13
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.
Nuclear shape dependence of Gamow-Teller distributions in neutron-deficient Pb isotopes
Sarriguren, P.; Moreno, O.; Alvarez-Rodriguez, R.; Moya de Guerra, E. [Instituto de Estructura de la Materia, Consejo Superior de Investigaciones Cientificas, Serrano 123, E-28006 Madrid (Spain)
2005-11-01
We study Gamow-Teller strength distributions in the neutron-deficient even isotopes {sup 184-194}Pb in a search for signatures of deformation. The microscopic formalism used is based on a deformed quasiparticle random-phase approximation (QRPA) approach, which involves a self-consistent quasiparticle deformed Skyrme Hartree-Fock (HF) basis and residual spin-isospin forces in both the particle-hole and particle-particle channels. By analyzing the sensitivity of the Gamow-Teller strength distributions to the various ingredients in the formalism, we conclude that the {beta} decay of these isotopes could be a useful tool to look for fingerprints of nuclear deformation.
Limitations to presaddle neutron emission from fission-fragment charge distributions
Charity, R.J. (Department of Chemistry, Washington University, St. Louis, Missouri 63130 (United States))
1995-01-01
The effect of including mass-asymmetry dependent fission delay times into the statistical model has been investigated. The shape of the predicted charge distribution of fission fragments is found to be very sensitive to the magnitude and mass-asymmetry dependence of these delay times. Measured mass-asymmetry dependent prefission neutron multiplicities were fit with calculated presaddle values by varying the fission delay times. The resultant predictions for the charge distributions are found to have shapes inconsistent with those measured for similar mass systems indicating that measured prefission multiplicities cannot be accounted for by presaddle emission alone. Limitations to the magnitude of the presaddle component are discussed.
Giacomelli, L; Conroy, S; Gorini, G; Horton, L; Murari, A; Popovichev, S; Syme, D B
2014-02-01
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. [JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom) [JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Department of Physics, Università degli Studi di Milano-Bicocca, Milano (Italy); Conroy, S. [JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom) [JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Department of Physics and Astronomy, Uppsala University, Uppsala (Sweden); Gorini, G. [Department of Physics, Università degli Studi di Milano-Bicocca, Milano (Italy)] [Department of Physics, Università degli Studi di Milano-Bicocca, Milano (Italy); Horton, L.; Murari, A.; Popovichev, S.; Syme, D. B. [JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom)] [JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom)
2014-02-15
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.
NASA Astrophysics Data System (ADS)
Matsumoto, T.
2007-09-01
Monte Carlo simulations are performed to evaluate depth-dose distributions for possible treatment of cancers by boron neutron capture therapy (BNCT). The ICRU computational model of ADAM & EVA was used as a phantom to simulate tumors at a depth of 5 cm in central regions of the lungs, liver and pancreas. Tumors of the prostate and osteosarcoma were also centered at the depth of 4.5 and 2.5 cm in the phantom models. The epithermal neutron beam from a research reactor was the primary neutron source for the MCNP calculation of the depth-dose distributions in those cancer models. For brain tumor irradiations, the whole-body dose was also evaluated. The MCNP simulations suggested that a lethal dose of 50 Gy to the tumors can be achieved without reaching the tolerance dose of 25 Gy to normal tissue. The whole-body phantom calculations also showed that the BNCT could be applied for brain tumors without significant damage to whole-body organs.
Application of quasi-distributions for solving inverse problems of neutron and {gamma}-ray transport
Pogosbekyan, L.R.; Lysov, D.A. [Research Institute for Nuclear Power Plant Operation (VNIIAES), Moscow (Russian Federation)
1995-12-31
The considered inverse problems deal with the calculation of the unknown values of nuclear installations by means of the known (goal) functionals of neutron/{gamma}-ray distributions. The example of these problems might be the calculation of the automatic control rods position as function of neutron sensors reading, or the calculation of experimentally-corrected values of cross-sections, isotopes concentration, fuel enrichment via the measured functional. The authors have developed the new method to solve inverse problem. It finds flux density as quasi-solution of the particles conservation linear system adjointed to equalities for functionals. The method is more effective compared to the one based on the classical perturbation theory. It is suitable for vectorization and it can be used successfully in optimization codes.
The Differential cross section distribution of Drell-Yan dielectron pairs in the z boson mass region
Han, Jiyeon; /Rochester U.
2008-11-01
We report on a measurement of the rapidity distribution, d{sigma}/dy, for Z=Drell-Yan {yields} ee events produced in p{bar p} collisions at {radical}s = 1.96 TeV. The data sample consists of 2.13 fb{sup -1} corresponding to about 160,000 Z/Drell-Yan {yields} ee candidates in the Z boson mass region collected by the Collider Detector at Fermilab. The d{sigma}/dy distribution, which is measured over the full kinematic range for e{sup +}e{sup -} pairs in the invariant mass range 66 < M{sub ee} < 116 GeV/c{sup 2}, is compared with theory predictions. There is good agreement between the data and predictions of Quantum Chromodynamics in Next to Leading Order with the CTEQ6.1M Parton Distribution Functions.
Hiroki Tanaka; Yoshinori Sakurai; Minoru Suzuki; Shinichiro Masunaga; Toshinori Mitsumoto; Satoru Yajima; Hiroshi Tsutsui; Takemi Sato; Tomoyuki Asano; Genro Kashino; Yuko Kinashi; Yong Liu; Koji Ono; A. Maruhashi
2009-01-01
We have been developed an epithermal neutron source for boron neutron capture therapy(BNCT), consisting of a cyclotron accelerator that can provide a ~ 1 mA, 30 MeV proton beam, a neutron production beryllium target and the moderator that can reduce the energy of fast neutrons to an effective energy range. In order to validate the simulations, we measured the depth
NASA Astrophysics Data System (ADS)
Bucciantini, Niccolo'; Del Zanna, Luca; Pili, Antonio
Extremely magnetized neutron stars with magnetic fields as strong as ˜ 10(15-16) G, or magnetars, have received considerable attention in the last decade due to their identification as a plausible source for Soft Gamma Repeaters and Anomalous X-ray Pulsars. Moreover, this class of compact objects has been proposed as a possible engine capable of powering both Long and Short Gamma-Ray Bursts, if the rotation period in their formation stage is short enough (˜ 1 ms). Such strong fields are expected to induce substantial deformations of the star and thus to produce the emission of gravitational waves. I will present here the first fully non-linear general relativistic study of the effects of different magnetic field geometries and current's' distributions on the properties and structure of strongly magnetized neutron stars. I will show that deformations and changes in both the internal matter distribution and in global quantities like mass and radius, are not just a simple function of the magnetic field strength, but instead are strongly affected by how the magnetic field and the currents are distributed in the star. In particular I will show the different effects of peripheral vs core currents. I will also discuss mixed poloidal-toroidal configurations that are expected to be dynamically stable.
Tel, E.; Tanir, G. [Gazi University, Faculty of Art and Science, Department of Physics, Ankara (Turkey); Aydin, A. [Kirikkale University, Faculty of Art and Science, Department of Physics, Kirikkale (Turkey)
2007-03-15
The asymmetry term effects for the cross sections of (n, charged particle) and (n,2n) reactions at 14-15 MeV neutron incident energy have been investigated. The effects of pairing and odd-even nucleon numbers in new data and in the formula of Tel et al. [J. Phys. G. 29, 2169 (2003)] are discussed. We have determined three different parameters groups by the classification of nuclei into even-even, even-odd, and odd-even (n,d) reactions. In addition, since there are not enough experimental data available, we have considered two different parameters groups by the classification of nuclei into odd-A and even-A (n,t) reaction cross sections. The empirical formulas with two parameters for the evaluation of the (n,d) and (n,t) reactions cross sections are discussed in the present study.
Extraction of Neutron Density Distributions from Proton Elastic Scattering at Intermediate Energies
NASA Astrophysics Data System (ADS)
Takeda, H.; Sakaguchi, H.; Terashima, S.; Taki, T.; Yosoi, M.; Itoh, M.; Kawabata, T.; Ishikawa, T.; Uchida, M.; Tsukahara, N.; Yasuda, Y.; Noro, T.; Yoshimura, M.; Fujimura, H.; Yoshida, H. P.; Obayashi, E.; Tamii, A.; Akimune, H.
2003-04-01
Cross sections, analyzing powers and spin rotation parameters of proton elastic scattering from 58Ni and 120Sn have been measured at 200-400 MeV. Obtained data have been analyzed in the framework of relativistic impulse approximations. In order to explain the 58Ni data, it was necessary to modify NN interactions in the nuclear medium by changing coupling constants and masses of ? and ? mesons. For 120Sn, by assuming the same modification of NN interactions and by using proton densities deduced from charge densities, the neutron density distribution was searched so as to reproduce 120Sn data at 300 MeV.
Extraction of Neutron Density Distributions from Proton Elastic Scattering at Intermediate Energies
NASA Astrophysics Data System (ADS)
Takeda, H.; Sakaguchi, H.; Terashima, S.; Taki, T.; Yosoi, M.; Itoh, M.; Kawabata, T.; Ishikawa, T.; Uchida, M.; Tsukahara, N.; Yasuda, Y.; Noro, T.; Yoshimura, M.; Fujimura, H.; Yoshida, H. P.; Obayashi, E.; Tamii, A.; Akimune, H.
2003-07-01
Cross sections, analyzing powers and spin rotation parameters of proton elastic scattering from 58Ni and 120Sn have been measured at intermediate energies. Obtained data have been analyzed in the framework of relativistic impulse approximations. In order to explain the 58Ni data, it was necessary to modify NN interactions in the nuclear medium by changing coupling constants and masses of ? and ? mesons. For 120Sn, by assuming the same modification of NN interactions and by using proton densities deduced from charge densities, the neutron density distribution was searched so as to reproduce 120Sn data at 300 MeV.
NASA Astrophysics Data System (ADS)
Velyhan, A.; Krása, J.; Bienkowska, B.; Ivanova-Stanik, I. M.; Juha, L.; Karpinski, L.; Klír, D.; Králík, M.; Kravárik, J.; Kubes, P.; Paduch, M.; Scholz, M.; Tomaszewski, K.
2006-04-01
A system of moderators of DD-fusion neutrons emitted by the plasma focus device PF-1000 at IPPLM, Warsaw was employed for the use of thermoluminescent dosimeters (TLDs) as passive detectors of thermal neutrons. The diagnostics was derived from Monte Carlo calculations of responses of dosimeters located in spherical polyethylene moderators with different diameters. As time-integrating dosimeters coupled 6LiF:Mg,Cu,P (TLD-600H) and 7LiF:Mg,Cu,P (TLD-700H) detectors were applied. A difference in read-out signals between TLD-600H and TLD-700H dosimeters, which is directly proportional to the number of thermal neutron interactions, is compared with the response of silver activation detectors. The detectors used started to operate from a neutron yield of ~5×109 and present a convenient method for investigation of spatial-distribution of neutron emission.
NASA Astrophysics Data System (ADS)
Ha, Eunja; Cheoun, Myung-Ki
2015-02-01
The deformed proton-neutron quasiparticle random phase approximation (QRPA) has been developed and applied to evaluate Gamow-Teller (GT) transition strength distributions, including high-lying excited states. The data of high-lying excited states are recently available beyond one or two nucleon threshold by charge exchange reactions using hundreds of MeV projectiles. Our calculations started with single-particle states calculated using a deformed, axially symmetric Woods-Saxon potential. The neutron-neutron and proton-proton pairing correlations are explicitly taken into account at the deformed Bardeen-Cooper-Schriffer theory. Additionally, the ground state correlations and two-particle and two-hole mixing states were included in the deformed QRPA. In this work, we used a realistic two-body interaction, given by the Brueckner G-matrix based on the CD Bonn potential to reduce the ambiguity on the nucleon-nucleon interactions inside nuclei. We applied our formalism to the GT transition strengths for 76Ge, 76,82Se, and 90,92Zr, and compared the results with the available experimental data. The GT strength distributions were sensitive to the deformation parameter as well as its sign, i.e., oblate or prolate. The Ikeda sum rule, which is usually thought to be satisfied under the one-body current approximation, regardless of nucleon models, was used to test our numerical calculations and shown to be satisfied without introducing the quenching factor, if high-lying GT excited states were properly taken into account. Most of the GT strength distributions of the nuclei considered in this work have the high-lying GT excited states beyond one-nucleon threshold, which are shown to be consistent with the available experimental data.
Charge and matter distributions and form factors of light, medium and heavy neutron-rich nuclei
A. N. Antonov; D. N. Kadrev; M. K. Gaidarov; E. Moya de Guerra; P. Sarriguren; J. M. Udias; V. K. Lukyanov; E. V. Zemlyanaya; G. Z. Krumova
2005-09-09
Results of charge form factors calculations for several unstable neutron-rich isotopes of light, medium and heavy nuclei (He, Li, Ni, Kr, Sn) are presented and compared to those of stable isotopes in the same isotopic chain. For the lighter isotopes (He and Li) the proton and neutron densities are obtained within a microscopic large-scale shell-model, while for heavier ones Ni, Kr and Sn the densities are calculated in deformed self-consistent mean-field Skyrme HF+BCS method. We also compare proton densities to matter densities together with their rms radii and diffuseness parameter values. Whenever possible comparison of form factors, densities and rms radii with available experimental data is also performed. Calculations of form factors are carried out both in plane wave Born approximation (PWBA) and in distorted wave Born approximation (DWBA). These form factors are suggested as predictions for the future experiments on the electron-radioactive beam colliders where the effect of the neutron halo or skin on the proton distributions in exotic nuclei is planned to be studied and thereby the various theoretical models of exotic nuclei will be tested.
NASA Astrophysics Data System (ADS)
Harada, M.; Parker, J. D.; Sawano, T.; Kubo, H.; Tanimori, T.; Shinohara, T.; Maekawa, F.; Sakai, K.
The imaging method known as Neutron Resonance Absorption (NRA) is very suitable for nondestructive analysis of element distributions in a sample. The purposes of this study are to perform NRA test experiments using the Micro Pixel Chamber (?PIC), developed by Kyoto University and to confirm the quantitative quality of the measurements of the system. The experiment was performed at NOBORU in J-PARC. The detector was located at 14.5 m from the moderator in the experimental room. The samples, consisting of thin Cobalt, Tantalum and Molybdenum foils, were placed individually at the upstream from the detector. In the experiment, the transmission spectra with the samples and no sample were obtained. Background components were not so small in these measurements. From the neutron transport simulation, it was surmised that the origin of this background was due to scattering of neutrons in the experimental room. Therefore, the assumed background components were subtracted from the measurement data. Finally, it was found that the difference between the measurement data and the nuclear data was within about 20%. Issues remaining to be solved include how to obtain precise background data quantitatively in the case of a large absorption cross section.
M. Montoya; E. Saettone; J. Rojas
2007-01-01
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
P. Casoli; T. Ethvignot; T. Granier; R. O. Nelson; N. Fotiades; M. J. Devlin; D. M. Drake; W. Younes; P. E. Garrett; J. A. Becker
2004-01-01
Prompt gamma-ray and x-ray spectroscopy techniques are being employed to study fission induced on 238U targets by neutrons of energy from 1 MeV to 150 MeV. Data are acquired using the GEANIE high resolution gamma-ray spectrometer at the LANSCE\\/WNR unmoderated spallation neutron source. Information on the predecay yields (excitation functions and isotopic distributions) were extracted from gamma and gamma-gamma coincidence
NASA Astrophysics Data System (ADS)
Holz, Maire; Carminati, Andrea; Kuzyakov, Yakov
2015-04-01
Water and nutrients will be the major factors limiting food production in future. Plant roots employ various mechanisms to increase the access to limited soil resources. Low molecular weight organic substances released by roots into the rhizosphere increase nutrient availability by interactions with microorganisms, while mucilage improves water availability under low moisture conditions. Though composition and quality of these substances have intensively been investigated, studies on the spatial distribution and quantification of exudates in soil are scarce. Our aim was to quantify and visualize root exudates and mucilage distribution around growing roots using neutron radiography and 14C imaging depending on drought stress. Plants were grown in rhizotrons well suited for neutron radiography and 14C imaging. Plants were exposed to various soil water contents experiencing different levels of drought stress. The water content in the rhizosphere was imaged during several drying/wetting cycles by neutron radiography. The radiographs taken a few hours after irrigation showed a wet region around the root tips showing the allocation and distribution of mucilage. The increased water content in the rhizosphere of the young root segments was related to mucilage concentrations by parameterization described in Kroener et al. (2014). In parallel 14C imaging of root after 14CO2 labeling of shoots (Pausch and Kuzyakov 2011) showed distribution of rhizodeposits including mucilage. Three days after setting the water content, plants were labeled in 14CO2 atmosphere. Two days later 14C distribution in soil was imaged by placing a phosphor-imaging plate on the rhizobox. To quantify rhizodeposition, 14C activity on the image was related to the absolute 14C activity in the soil and root after destructive sampling. By comparing the amounts of mucilage (neutron radiography) with the amount of total root derived C (14C imaging), we were able to differentiate between mucilage and root exudates. We found that mucilage and 14C concentrations were higher around the young root segments. Mucilage concentration was particularly high in the most apical 3-5 cm of the roots. Drought stress increased 14C exudation relative to C fixation and led to higher mucilage concentrations around roots. However, it remains unclear, whether the lower mucilage concentration around roots grown at higher soil moisture was caused by the faster diffusion of mucilage in wet soils. Therefore, a second experiment was focused on diffusion of mucilage in soil at varying water contents. The diffusion of mucilage in soil was not very sensitive to soil water content. We conclude that mucilage release was higher for plants exposed to drought stress. In summary, the combination of neutron radiography and 14C imaging can successfully be used to visualize and to quantify the distribution of mucilage and root exudates in the rhizosphere of plants grown in soil. References Kroener, E., Zarebanadkouki, M., Kaestner, A., & Carmintati, A. (2014). Nonequilibrium water dynamics in the rhizosphere: How mucilage affects water flow in soils. Water Resources Research, 37. Pausch, J., & Kuzyakov, Y. (2011). Photoassimilate allocation and dynamics of hotspots in roots visualized by 14C phosphor imaging. Journal of Plant Nutrition and Soil Science, 174(1), 12-19.
NASA Astrophysics Data System (ADS)
Pietinen, Sami; Tenhunen, Vesa; Tukiainen, Markku
Several methods and techniques have surfaced to address the ongoing concerns of quality and productivity of software development. Among these is the Pair Programming (PP) method, which has gained a lot off attention through being an essential part of an agile software development methodology called the eXtreme Programming (XP). In this paper, we present the results of two controlled case studies that investigate the possible productivity improvement through the incorporation of PP over solo programming. The main focus is on implementation task, more specifically in programming, although PP is suitable for other tasks too. Our results show that very high level of PP use might be difficult to achieve in a very tightly scheduled software development project, but some of the benefits can be seen to come true even with proportional use of PP. In our case, PP added the additional effort of 13% over solo programming.
H. W. Schmitt; N. Feather
1964-01-01
An analysis of the fragment mass distribution for the thermal-neutron-induced ternary fission of U235 is given. Quantitative comparison of the mass-distribution data for binary and ternary fission is consistent with the influence of the closed-shell configurations in fission, although it is shown that these mass distributions of themselves are not sufficient to determine unambiguously the origin of the alpha particle.
Relation between pair potentials and radial distribution functions in liquid metals and alloys
M. Shimoji
1967-01-01
It is shown that the pairwise interactions between ions employed in the recent analysis of the radial distribution functions for liquid metals may result from perturbations due to local deviations from a uniform positively charged background of an electron gas in the Hartree description. Such a potential reveals the long-range oscillatory behaviour, as in the current established theories for the
Arshad M. Mirza; M. Adnan Sarwar; M. S. Qaisar
2003-01-01
Analytical and numerical results are presented for the slowing down of a pair of heavy test charge projectiles through a multicomponent, dust-contaminated plasma. The correlation and interference effects of two collinear and noncollinear projectiles on electrostatic potential and energy loss are studied for a Maxwellian distribution and a special class of physically reasonable size distributions. The energy loss behavior versus
Nigg, D W
1994-03-30
This article presents a survey of recent progress in the development and application of analytical methods for calculating macroscopic and microscopic radiation dose distributions for Boron Neutron Capture Therapy (BNCT). Such calculations are an essential component of in vivo BNCT research and will ultimately also be required for human BNCT treatment planning. Calculations of macroscopic absorbed dose distributions for BNCT are more complex than for photon therapy. There are several different dose components, each of which has its own characteristic spatial distribution, linear energy transfer, and relative biological effectiveness (RBE). Three-dimensional (3-D) energy-dependent radiation transport models with a detailed treatment of particle scattering are required. Geometric descriptions for such models are typically constructed directly from medical image data and both the Monte Carlo stochastic simulation method and the discrete-ordinates deterministic approach have been successfully used to perform the necessary radiation transport calculations. Microdosimetric effects can profoundly influence the therapeutic benefit that may be attainable in BNCT. These effects must be carefully taken into account in the interpretation of experimental data, especially when correlating observed in vivo radiobiological response with absorbed radiation dose. Calculations of microdosimetric parameters for BNCT are typically performed using the Monte Carlo method to generate single-event energy deposition frequency distributions for critical targets in various cell types of interest. This information is useful in the development of apparent RBE factors, or "compound factors" for the various dose components in BNCT. PMID:8175397
Optimal pair-generation rate for entanglement-based quantum key distribution
NASA Astrophysics Data System (ADS)
Holloway, Catherine; Doucette, John A.; Erven, Christopher; Bourgoin, Jean-Philippe; Jennewein, Thomas
2013-02-01
In entanglement-based quantum key distribution (QKD), the generation and detection of multiphoton modes leads to a trade-off between entanglement visibility and twofold coincidence events when maximizing the secure key rate. We produce a predictive model for the optimal twofold coincidence probability per coincidence window given the channel efficiency and detector dark count rate of a given system. This model is experimentally validated and used in simulations for QKD with satellites as well as optical fibers.
Chieng, Norman; Trnka, Hjalte; Boetker, Johan; Pikal, Michael; Rantanen, Jukka; Grohganz, Holger
2013-09-15
The purpose of this study is to investigate the use of multivariate data analysis for powder X-ray diffraction-pair-wise distribution function (PXRD-PDF) data to detect phase separation in freeze-dried binary amorphous systems. Polymer-polymer and polymer-sugar binary systems at various ratios were freeze-dried. All samples were analyzed by PXRD, transformed to PDF and analyzed by principal component analysis (PCA). These results were validated by differential scanning calorimetry (DSC) through characterization of glass transition of the maximally freeze-concentrate solute (Tg'). Analysis of PXRD-PDF data using PCA provides a more clear 'miscible' or 'phase separated' interpretation through the distribution pattern of samples on a score plot presentation compared to residual plot method. In a phase separated system, samples were found to be evenly distributed around the theoretical PDF profile. For systems that were miscible, a clear deviation of samples away from the theoretical PDF profile was observed. Moreover, PCA analysis allows simultaneous analysis of replicate samples. Comparatively, the phase behavior analysis from PXRD-PDF-PCA method was in agreement with the DSC results. Overall, the combined PXRD-PDF-PCA approach improves the clarity of the PXRD-PDF results and can be used as an alternative explorative data analytical tool in detecting phase separation in freeze-dried binary amorphous systems. PMID:23872303
Klusek-Gawenda, M. [Institute of Nuclear Physics PAN, PL-31-342 Cracow (Poland); Szczurek, A. [Institute of Nuclear Physics PAN, PL-31-342 Cracow (Poland); University of Rzeszow, PL-35-959 Rzeszow (Poland)
2010-07-15
The cross sections for exclusive muon-pair production in nucleus-nucleus collisions are calculated and several differential distributions are shown. Realistic (Fourier transform of charge density) charge form factors of nuclei are used and the corresponding results are compared with the cross sections calculated with monopole form factor often used in the literature and discussed recently in the context of higher-order QED corrections. Absorption effects are discussed and quantified. The cross sections obtained with realistic form factors are significantly smaller than those obtained with the monopole form factor. The effect is bigger for large muon rapidities and/or large muon transverse momenta. The predictions for the STAR and PHENIX collaboration measurements at RHIC as well as the ALICE and CMS collaborations at LHC are presented.
Reeder, Richard J; Michel, F Marc
2013-01-01
Total X-ray scattering and pair distribution function (PDF) analysis, using a high-energy synchrotron source, allow direct study of the short- and intermediate-range structure that distinguish amorphous, structurally disordered, and nanocrystalline biominerals. For such samples in which diffuse scatter is a significant component, care must be taken in the experimental procedures to optimize data quality and extract the useful signal necessary to calculate the PDF. General methods are described for data collection and processing, including commonly used software programs. Methods for analysis and interpretation of PDFs are presented, including direct real-space refinement and reverse Monte Carlo methods. Greater application of PDFs to amorphous and poorly crystallized biominerals will provide new insight into structure, especially over length scales that are not probed by other techniques. The rapid data collection available at synchrotron facilities also allows in situ kinetic studies of reactions involving biominerals. PMID:24188779
Rothe, R.E.
1991-01-01
Several critical experiments were performed for a number of strong neutron absorbers periodically distributed throughout a tank filled with high-concentration fissile solution, These experiments served as a pilot study for a novel means of storing fissile solutions at a nuclear production plant handling such solutions. The configuration also approximates one commonly used method (Raschig rings) of assuring criticality safety in such plants, Still, the configuration is heterogeneous, and so, easily susceptible to modeling with modern computer codes. The fissile solution was uranyl nitrate at about 363 gU/liter with the uranium enriched to 93.2% U{sup 235}. One important neutron absorber studied consisted of borosilicate glass rods, containing the same 12.5{percent} boron oxide found in Raschig rings used throughout the industry. Another consisted of rubber sheet containing 0.1 mg/mm{sup 2} boron (as B{sub 4}C) glued to thin-walled steel tubing. Cadmium sheet metal (1.6 mm thick) wrapped around steel rods formed yet another absorber; and solid polyvinyl chloride rods were also studied. Four loose powders packed into paper tubes completed the list of absorbers: cadmium oxide, anhydrous boric acid, sodium tetraborate pentahydrate, and a very inexpensive mixture of two common minerals-colmanite (calcium borate) and ulexite (sodium-calcium borate). The spacing between tubes containing each absorber was varied widely in both square and triangular patterns,
NASA Astrophysics Data System (ADS)
Zhu, Mengqiang; Farrow, Christopher L.; Post, Jeffrey E.; Livi, Kenneth J. T.; Billinge, Simon J. L.; Ginder-Vogel, Matthew; Sparks, Donald L.
2012-03-01
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), ?-MnO2, polymeric MnO2 (PolyMnO2) and a bacteriogenic Mn oxide (BioMnOx), 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 MnO6 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 MnO6 layers are estimated to be 0.936, 0.847, 0.930 and 0.935, for AcidBir, BioMnOx, ?-MnO2 and PolyMnO2, 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 PolyMnO2, ?-MnO2 and BioMnOx are at the nanometer scale, comprising one to three MnO6 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.
Effect of molecular ordering on distance distributions of flexible donor-acceptor pairs
NASA Astrophysics Data System (ADS)
Gryczynski, Ignacy; Gryczynski, Zygmunt; Wiczk, Wieslaw M.; Kusba, Jozef; Lakowicz, Joseph R.
1992-04-01
Measurements of time-resolved intramolecular energy transfer in progressively stretched poly(vinyl alcohol) films were performed. The donor (tryptophan) and acceptor (dansyl) were linked with flexible polymethylene chain. Distance distributions were recovered from frequency-domain measurements of the donor decay. In isotropic PVA (in solution) a wide range of distances were detected (Gaussian full width at half maximum of about 16 angstroms) with an average distance of 13 angstroms. The donor-acceptor distance distribution became progressively more narrow when the PVA films were stretched. Four-fold or more stretching results in a single donor-acceptor distance. The maximal measured donor-acceptor distance of 23 angstroms is in excellent agreement with the computed distance for the fully stretched conformation. The possibility of partial and/or full ordering of polymethylene chains by stretching the PVA films can also be useful in the study of other distance-dependent interactions, such as electron transfer or distance-dependent quenching.
Detection of prokaryotic promoters from the genomic distribution of hexanucleotide pairs
Jacques, Pierre-Étienne; Rodrigue, Sébastien; Gaudreau, Luc; Goulet, Jean; Brzezinski, Ryszard
2006-01-01
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
Distribution of trace elements in the human body determined by neutron activation analysis.
Yukawa, M; Amano, K; Suzuki-Yasumoto, M; Terai, M
1980-01-01
Neutron activation analysis and instrumental semiconductor gamma-ray spectrometry were used for analysis of 20 trace elements in 10 autopsied human organs and tissues (liver, kidney, cerebrum, cerebellum, heart, muscle, pancreas, spleen, lung, and aorta) from 63 Japanese persons, whose ages ranged from 15 days to 85 yr. Distributions of aluminum, bromine, magnesium, manganese, rubidium, selenium, and vanadium in human body were almost uniform. High concentrations of cadmium were found in kidney and liver samples. There was a high mercury concentration in the liver, kidney, and brain samples. Concentrations of other elements (arsenic, gold, cobalt, chromium, copper, iron, indium, antimony, selenium, titanium, and zinc) in each organ or tissue are also presented in this paper. PMID:7362268
Sumaru, K.; Matsuoka, H.; Yamaoka, H. [Department of Polymer Chemistry, Kyoto University, Kyoto 606-01 (Japan)] [Department of Polymer Chemistry, Kyoto University, Kyoto 606-01 (Japan); Wignall, G.D. [Neutron Scattering Group, Solid State Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831 (United States)] [Neutron Scattering Group, Solid State Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831 (United States)
1996-02-01
The counterion distribution around tetramethylammonium dodecyl sulfate micelles has been evaluated by small-angle neutron scattering (SANS) using the contrast variation technique. The scattering from the counterions and the hydrated shell was isolated by matching the scattering length densities of the core and aqueous medium by adjusting the H{sub 2}O-to-D{sub 2}O ratio. Thus the core component of the scattering was {open_quote}{open_quote}erased,{close_quote}{close_quote} due to zero contrast with the solvent. The counterion distribution was estimated by fitting the SANS data to a model of an isolated particle consisting of a core, shell, and counterion atmosphere, with only three adjustable parameters. For a micellar concentration of 6 vol {percent}, the aggregation number, core radius, shell thickness, and charge number were estimated as 77, 18.6 A, 4.6 A, and 44, respectively. Similar values were obtained for a concentration of 3 vol {percent}. In addition, the electrostatic potential and the dissociation equilibrium at the micellar surface were also evaluated. The estimated value of the surface potential of micelles ({minus}4.7{ital k}{ital T}) indicated the validity of using the numerical solution of nonlinear Poisson-Boltzmann equation for the calculation of the counterion distribution. {copyright} {ital 1996 The American Physical Society.}
NASA Astrophysics Data System (ADS)
Muslih, M. Refai; Sumirat, I.; Sairun; Purwanta
2008-03-01
The distribution of residual stress of SUS304 samples that were undergone TIG welding process with four different electric currents has been measured. The welding has been done in the middle part of the samples that was previously grooved by milling machine. Before they were welded the samples were annealed at 650 degree Celsius for one hour. The annealing process was done to eliminate residual stress generated by grooving process so that the residual stress within the samples was merely produced from welding process. The calculation of distribution of residual stress was carried out by measuring the strains within crystal planes of Fe(220) SUS304. Strain, Young modulus, and Poisson ratio of Fe(220) SUS304 were measured using DN1-M neutron diffractometer. Young modulus and Poisson ratio of Fe(220) SUS304 sample were measured in-situ. The result of calculations showed that distribution of residual stress of SUS304 in the vicinity of welded area is influenced both by treatments given at the samples-making process and by the electric current used during welding process.
Moran, J M; Nigg, D W; Wheeler, F J; Bauer, W F
1992-01-01
Calculations of radiation flux and dose distributions for boron neutron capture therapy (BNCT) of brain tumors are typically performed using sophisticated three-dimensional analytical models based on either a homogeneous approximation or a simplified few-region approximation to the actual highly heterogeneous geometry of the irradiation volume. Such models should be validated by comparison with calculations using detailed models in which all significant macroscopic tissue heterogeneities and geometric structures are explicitly represented as faithfully as possible. This paper describes such a validation exercise for BNCT of canine brain tumors. Geometric measurements of the canine anatomical structures of interest for this work were performed by dissecting and examining two essentially identical Labrador retriever heads. Chemical analyses of various tissue samples taken during the dissections were conducted to obtain measurements of elemental compositions for the tissues of interest. The resulting geometry and tissue composition data were then used to construct a detailed heterogeneous calculational model of the Labrador head. Calculations of three-dimensional radiation flux distributions pertinent to BNCT were performed for this model using the TORT discrete-ordinates radiation transport code. The calculations were repeated for a corresponding volume-weighted homogeneous-tissue model. Comparison of the results showed that peak neutron and photon flux magnitudes were quite similar for the two models (within 5%), but that the spatial flux profiles were shifted in the heterogeneous model such that the fluxes in some locations away from the peak differed from the corresponding fluxes in the homogeneous model by as much as 10%-20%. Differences of this magnitude can be therapeutically significant, emphasizing the need for proper validation of simplified treatment planning models. PMID:1508112
Moran, J.M.; Nigg, D.W.; Wheeler, F.J.; Bauer, W.F. (Idaho National Engineering Laboratory, EG G Idaho, Inc., P.O. Box 1625, Idaho Falls, Idaho 83415-3515 (United States))
1992-05-01
Calculations of radiation flux and dose distributions for boron neutron capture therapy (BNCT) of brain tumors are typically performed using sophisticated three-dimensional analytical models based on either a homogeneous approximation or a simplified few-region approximation to the actual highly heterogeneous geometry of the irradiation volume. Such models should be validated by comparison with calculations using detailed models in which all significant macroscopic tissue heterogeneities and geometric structures are explicitly represented as faithfully as possible. This paper describes such a validation exercise for BNCT of canine brain tumors. Geometric measurements of the canine anatomical structures of interest for this work were performed by dissecting and examining two essentially identical Labrador retriever heads. Chemical analyses of various tissue samples taken during the dissections were conducted to obtain measurements of elemental compositions for the tissues of interest. The resulting geometry and tissue composition data were then used to construct a detailed heterogeneous calculational model of the Labrador head. Calculations of three-dimensional radiation flux distributions pertinent to BNCT were performed for this model using the TORT discrete-ordinates radiation transport code. The calculations were repeated for a corresponding volume-weighted homogeneous-tissue model. Comparison of the results showed that peak neutron and photon flux magnitudes were quite similar for the two models (within 5%), but that the spatial flux profiles were shifted in the heterogeneous model such that the fluxes in some locations away from the peak differed from the corresponding fluxes in the homogeneous model by as much as 10%--20%. Differences of this magnitude can be therapeutically significant, emphasizing the need for proper validation of simplified treatment planning models.
NASA Technical Reports Server (NTRS)
Schneider, Harold
1959-01-01
This method is investigated for semi-infinite multiple-slab configurations of arbitrary width, composition, and source distribution. Isotropic scattering in the laboratory system is assumed. Isotropic scattering implies that the fraction of neutrons scattered in the i(sup th) volume element or subregion that will make their next collision in the j(sup th) volume element or subregion is the same for all collisions. These so-called "transfer probabilities" between subregions are calculated and used to obtain successive-collision densities from which the flux and transmission probabilities directly follow. For a thick slab with little or no absorption, a successive-collisions technique proves impractical because an unreasonably large number of collisions must be followed in order to obtain the flux. Here the appropriate integral equation is converted into a set of linear simultaneous algebraic equations that are solved for the average total flux in each subregion. When ordinary diffusion theory applies with satisfactory precision in a portion of the multiple-slab configuration, the problem is solved by ordinary diffusion theory, but the flux is plotted only in the region of validity. The angular distribution of neutrons entering the remaining portion is determined from the known diffusion flux and the remaining region is solved by higher order theory. Several procedures for applying the numerical method are presented and discussed. To illustrate the calculational procedure, a symmetrical slab ia vacuum is worked by the numerical, Monte Carlo, and P(sub 3) spherical harmonics methods. In addition, an unsymmetrical double-slab problem is solved by the numerical and Monte Carlo methods. The numerical approach proved faster and more accurate in these examples. Adaptation of the method to anisotropic scattering in slabs is indicated, although no example is included in this paper.
Deborah L. Nichols; Elizabeth M. Brumfiel; Hector Neff; Mary Hodge; Thomas H. Charlton; Michael D. Glascock
2002-01-01
We use instrumental neutron activation analysis (INAA) of ceramics from three centers, Cerro Portezuelo, Chalco, and Xaltocan, in the Basin of Mexico, whose occupations span the Postclassic to examine the changing role of markets and evaluate models of political economy. Our results suggest that production and distribution of Epiclassic serving wares was highly localized conforming closely to a solar market
David W. Nigg; P. D. Randolph; F. J. Wheeler
1991-01-01
The Monte Carlo stochastic simulation technique has traditionally been the only well-recognized method for computing three-dimensional radiation dose distributions in connection with boron neutron capture therapy (BNCT) research. A deterministic approach to this problem would offer some advantages over the Monte Carlo method. This paper describes an application of a deterministic method to analytically simulate BNCT treatment of a canine
J. P. Lansberg; B. Pire; K. Semenov-Tian-Shansky; L. Szymanowski
2012-12-14
Nucleon antinucleon annihilation into a near backward (or forward) produced meson and a high invariant mass lepton pair admits a factorized description in terms of antinucleon (or nucleon) distribution amplitudes and nucleon to meson (or antinucleon to meson) transition distribution amplitudes. We estimate the cross section of backward (and forward) pion and eta meson production in association with a high invariant mass lepton pair for the kinematical conditions of GSI-FAIR. The cross sections are found to be large enough to be measured with the PANDA detector. Interesting phenomenological applications of the approach are thus expected.
NASA Astrophysics Data System (ADS)
Lansberg, J. P.; Pire, B.; Semenov-Tian-Shansky, K.; Szymanowski, L.
2012-12-01
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 ?-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 P¯ANDA detector. Interesting phenomenological applications of the approach are thus expected.
Ingrand, François
-adaptatif P2PSAP Socket API (listen, connect, close, send, receive) Données partagées Retransmit Reliable pair Communications directes entre les pairs Protocole de communication auto- adaptatif , P2PSAP Expérimentations : plateforme NICTA Environnement P2Pdc Protocole auto-adaptatif P2PSAP Mode de communication
The Hydrogen Distribution of the Gale Crater: Mars Odyssey Neutron Spectrometer
NASA Astrophysics Data System (ADS)
Teodoro, L. F.; Feldman, W. C.; Elphic, R. C.; Eke, V.; Maurice, S.
2012-12-01
The Mars Science Laboratory carries the most advanced suite of scientific instruments ever sent to the surface of Mars. Its main objective is to study whether Mars has been habitable at any point of its history. Such studies include the analysis of surficial soils and rocks to understand their mineralogical and chemical make up, additionally, the distribution of hydrogen in the top ~30 cm of the surface at some locations of the Gale crater. Mars Odyssey carries a Neutron Spectrometer that has been gathering information for more than a decade. Such information maps the global hydrogen in the top few decimeters of the martian surface and is complementary to the one that will be collected by MSL. Recently, Maurice et al. (2011) has re-analyzed the MONS epithermal data and significantly lowered the statistical systematic uncertainties that plagued previous versions of the data. However, MONS counting-rate data have a FWHM of ~550 km, which is sufficiently broad to contain several Gale craters in it. In this study, we choose the PIXON numerical deconvolution technique (Pina 2001, Eke 2001). This algorithm removes the point spread function without introducing spurious features in the presence of noise. We have previously carried out a detailed study of the martian polar regions applying such a methodology to Martian epithermal neutrons near both poles (e.g. Teodoro 2010, 2011) and have been able to reach a resolution of ~45 km. In the present study, we will apply this technique to the latest MONS epithermal data at an area centered around the Gale crater.
NASA Astrophysics Data System (ADS)
Ji, Wei
The Very High Temperature Gas-Cooled Reactor (VHTR) is a promising candidate for Generation IV designs due to its inherent safety, efficiency, and its proliferation-resistant and waste minimizing fuel cycle. A number of these advantages stem from its unique fuel design, consisting of a stochastic mixture of tiny (0.78mm diameter) microspheres with multiple coatings. However, the microsphere fuel regions represent point absorbers for resonance energy neutrons, resulting in the "double heterogeneity" for particle fuel. Special care must be taken to analyze this fuel in order to predict the spatial and spectral dependence of the neutron population in a steady-state reactor configuration. The challenges are considerable and resist brute force computation: there are over 1010 microspheres in a typical reactor configuration, with no hope of identifying individual microspheres in this stochastic mixture. Moreover, when individual microspheres "deplete" (e.g., burn the fissile isotope U-235 or transmute the fertile isotope U-238 (eventually) to Pu-239), the stochastic time-dependent nature of the depletion compounds the difficulty posed by the stochastic spatial mixture of the fuel, resulting in a prohibitive computational challenge. The goal of this research is to develop a methodology to analyze particle fuel randomly distributed in the reactor, accounting for the kernel absorptions as well as the stochastic depletion of the fuel mixture. This Ph.D. dissertation will address these challenges by developing a methodology for analyzing particle fuel that will be accurate enough to properly model stochastic particle fuel in both static and time-dependent configurations and yet be efficient enough to be used for routine analyses. This effort includes creation of a new physical model, development of a simulation algorithm, and application to real reactor configurations.
Selective radiography of 10B distribution in organs using cold and thermal neutron beams.
Skvarc, Jure; Giacomelli, Marko; Yanagië, Hironobu; Kühne, Guido
2002-01-01
The investigation of boron biodistribution by neutron induced autoradiography was performed using a CR-39 etched track detector. Calibration samples, made of boronated chicken liver, and freeze-dried mouse tissue samples were irradiated both with thermal and cold neutrons. Digital images were made on the basis of track densities, with the selection of tracks due to 10B(n, alpha)7Li reaction. A comparison of results obtained both with thermal and cold neutrons demonstrated that it is possible to obtain equivalent results with both neutron sources, although the background noise due to recoil protons from the fast neutrons of the thermal neutron source is 15 % higher than that of the cold neutron source. 10B concentrations in the range of 0.5 ppm to 150 ppm were determined, with a standard deviation of 13 % and 8 % for the mouse tissue samples and calibration samples, respectively. PMID:11944078
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
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.
NASA Astrophysics Data System (ADS)
K?rösi, Ferenc; Balaskó, Márton; Sváb, Erzsébet
1999-11-01
The qualitative and semi-quantitative distributions, presumably apoplast transport patterns for the Gd, Sm and Cd were investigated in the primordial leaf tissues of the bean using dynamic neutron radiography. According to the applied 3D, 2D images and the pixel count distribution histograms of the considered gray levels, peculiar distribution patterns were postulated for the elements. Main and lateral vascular systems for Gd, the cell walls as well as intercellular spaces for Sm and the main leaf vein for Cd assumed to be the apoplast transport spaces and volumes.
Cagla Meral; C. J. Benmore; Paulo J. M. Monteiro
2011-01-01
Significant progress was achieved with the application of Rietveld method to characterize the crystalline phases in portland cement paste. However, to obtain detailed information on the amorphous or poorly crystalline phases, it is necessary to analyze the total scattering data. The pair distribution function (PDF) method has been successfully used in the study of liquids and amorphous solids. The method
NASA Astrophysics Data System (ADS)
Suzuki, H.; Kusunoki, K.; Hatanaka, Y.; Mukai, T.; Tasai, A.; Kanematsu, M.; Kabayama, K.; Harjo, S.
2014-02-01
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.
NASA Astrophysics Data System (ADS)
Billinge, Simon John Laird
1992-01-01
We have carried out a detailed Pair Distribution Function Analysis of powder diffraction data from samples of Nd_{2-x}Ce _{x}CuO _{4-y} with x = 0.165 and x = 0.2. The former is superconducting with an almost full Meissner fraction, and T_{c} = 22K. The latter is isostructural, but exhibits no superconductivity. A "real space refinement" of the PDF has been carried out to extract quantitative information about the local atomic structure of the material. Two main observations were made. The local structure is significantly different from the average crystal structure (T ^' structure) of this material. The differences are explained by displacements of oxygen. The second result was that the local structure changes with the appearance of superconductivity. This was the first observation of such a change in this material. These changes are explained by an increase in the degree of local order of the above mentioned oxygen displacements. The displacements are inhomogeneously distributed throughout the sample and interspersed with regions of undistorted crystal. We argue that this is best explained as the direct observation of the presence of polarons, or bipolarons in the structure. We speculate that the driving force that could give rise to these polarons is a strong coupling of the lattice with the O p_{z} states which lie just below the Fermi surface in the undistorted material. The effective mass of the (bi)polarons, calculated using values estimated from the experiment, was such as to give the bipolarons a condensation temperature of 17K. This is the same order of magnitude as the observed T _{c}. Thus it is plausible that the superconductivity is due to a bipolaronic condensation. The density of polarons is too small to account for all of the chemically doped carriers. Thus it appears that they form the minority of carriers. They coexist with a majority of high mobility, wide band, electronic states, of sigma character.
Dambournet, Damien; Chapman, Karena W; Koudriachova, Marina V; Chupas, Peter J; Belharouak, Ilias; Amine, Khalil
2011-07-01
X-ray pair distribution function (PDF) methods and first-principles calculations have been combined to probe the structure of electrochemically lithiated TiO(2) Brookite. Traditional powder diffraction studies suggest that Brookite amorphizes upon lithium insertion, with the Bragg reflections disappearing. However, PDF analysis indicates that the TiO(2) framework connectivity is maintained throughout lithium intercalation, with expansions along the a and b axes. The Li(+) ions within the framework are poorly observed in the X-ray PDF, which is dominated by contributions from the more strongly scattering Ti and O atoms. First-principles calculations were used to identify energetically favorable Li(+) sites within the Brookite lattice and to develop a complete structural model of the lithiated material. This model replicates the local structure and decreased intermediate range order observed in the PDF data. The analysis suggests that local structural distortions of the TiO(2) lattice accommodate lithium in five-coordinate sites. This structural model is consistent with the observed electrochemical behavior. PMID:21627151
Dambournet, D.; Chapman, K. W.; Koudriachova, M. V.; Chupas, P. J.; Belharouak, I.; Amine, K. (X-Ray Science Division); ( CSE); (Univ. Coll. London)
2011-07-04
X-ray pair distribution function (PDF) methods and first-principles calculations have been combined to probe the structure of electrochemically lithiated TiO{sub 2} Brookite. Traditional powder diffraction studies suggest that Brookite amorphizes upon lithium insertion, with the Bragg reflections disappearing. However, PDF analysis indicates that the TiO{sub 2} framework connectivity is maintained throughout lithium intercalation, with expansions along the a and b axes. The Li{sup +} ions within the framework are poorly observed in the X-ray PDF, which is dominated by contributions from the more strongly scattering Ti and O atoms. First-principles calculations were used to identify energetically favorable Li{sup +} sites within the Brookite lattice and to develop a complete structural model of the lithiated material. This model replicates the local structure and decreased intermediate range order observed in the PDF data. The analysis suggests that local structural distortions of the TiO{sub 2} lattice accommodate lithium in five-coordinate sites. This structural model is consistent with the observed electrochemical behavior.
Yang, Jian; Kunito, Takashi; Anan, Yasumi; Tanabe, Shinsuke; Miyazaki, Nobuyuki
2008-01-01
Total and subcellular renal Zn, Cu, Se, Mn, V, Hg, Cd and Ag were determined by a mother-fetus pair of Dall's porpoises (Phocoenoides dalli). All element concentrations in the maternal individual were higher than those in the fetal individual. Most of total renal elements studied were present in the cytosol of both animals. In maternal cytosol, Mn, Hg and Ag were present in high molecular weight substances (HMW); Se was in low molecular weight substances (LMW); Zn, Cu, and Cd were in metallothionein (MT), mostly; and the distribution of V in percentage among the three renal cytosolic fractions was similar. In fetal cytosol, Zn, Mn, Hg, V, Cd, and Ag were present in HMW, Cu was present in MT, mostly. In contrast, Se was observed mostly in both LMW and HMW. MT isoforms were characterized. Three obvious peaks in retention time were found in either the maternal or fetal MT. The highest elemental ion intensities were in the 7.8min peak for the mother, and in the 4.3min peak for the fetus, respectively, implying that different MT isoforms may be closely associated with elemental accumulation between maternal and fetal renal cytosols. PMID:17889254
NASA Astrophysics Data System (ADS)
Tayama, Ryuichi; Fujita, Yasuo; Tadokoro, Masahiro; Fujimaki, Hisataka; Sakae, Takeji; Terunuma, Toshiyuki
2006-08-01
For a passive scattering nozzle at the Proton Medical Research Center (PMRC), the distribution of the neutron dose equivalent in the direction transverse to the proton beam line was measured for 200 MeV protons using a tissue equivalent proportional counter REM500. The neutron dose equivalent per Gray of proton-absorbed dose at the isocenter was approximately 2.3 mSv/Gy. The neutron dose outside of the treatment field was approximately 2 mSv/Gy, at maximum and it should be reduced as low as possible according to the ALARA principle. The aperture size of the multi-leaf collimator (MLC), which is a pre-collimator for shielding unwanted protons and mounted at a position upstream from the patient bolus and collimator, was varied in order to investigate its reduction effect on the neutron dose equivalent outside of the treatment field. We confirmed that the neutron dose equivalent outside of the treatment field can be limited depending on the aperture size of the MLC. This could be considered in future treatment planning optimization and patient treatment. MCNPX calculations showed good agreement with the measurements within 10%.
Johnson, J.R.; Feldman, W.C.; Lawrence, D.J.; Maurice, S.; Swindle, T.D.; Lucey, P.G.
2002-01-01
Initial studies of neutron spectrometer data returned by Lunar Prospector concentrated on the discovery of enhanced hydrogen abundances near both lunar poles. However, the nonpolar data exhibit intriguing patterns that appear spatially correlated with surface features such as young impact craters (e.g., Tycho). Such immature crater materials may have low hydrogen contents because of their relative lack of exposure to solar wind-implanted volatiles. We tested this hypothesis by comparing epithermal* neutron counts (i.e., epithermal -0.057 ?? thermal neutrons) for Copernican-age craters classified as relatively young, intermediate, and old (as determined by previous studies of Clementine optical maturity variations). The epithermal* counts of the crater and continuous ejecta regions suggest that the youngest impact materials are relatively devoid of hydrogen in the upper 1 m of regolith. We also show that the mean hydrogen contents measured in Apollo and Luna landing site samples are only moderately well correlated to the epithermal* neutron counts at the landing sites, likely owing to the effects of rare earth elements. These results suggest that further work is required to define better how hydrogen distribution can be revealed by epithermal neutrons in order to understand more fully the nature and sources (e.g., solar wind, meteorite impacts) of volatiles in the lunar regolith.
Plans for a collaboratively developed distributed control system for the Spallation Neutron Source
W. R. DeVan; D. P. Gurd; J. Hammonds; S. A. Lewis; J. D. Smith
1999-01-01
The Spallation Neutron Source (SNS) is an accelerator-based pulsed neutron source to be built in Oak Ridge, Tennessee. The facility has five major sections-a “front end” consisting of a 65 kev H ion source followed by a 2.5 MeV RFQ; a 1 GeV linac; a storage ring; a 1 MW spallation neutron target (upgradeable to 2 MW); the conventional facilities
Measurement of energy and directional distribution of neutron fluence inside a nuclear power plant
NASA Astrophysics Data System (ADS)
Luszik-Bhadra, M.; Derdau, D.; Hallfarth, G.; Matzke, M.; Wiegel, B.; Wittstock, J.
2002-01-01
A detailed analysis of the neutron radiation field was performed at selected positions inside the Krümmel boiling water reactor. The measurements were performed with the PTB Bonner sphere spectrometer and with a newly developed directional neutron spectrometer based on silicon detectors mounted onto the surface of a 30 cm diameter polyethylene sphere. Both, angle-integrated and angle-differential spectral neutron fluences were determined in this way.
Radulovi?, Vladimir; Štancar, Žiga; Snoj, Luka; Trkov, Andrej
2014-02-01
The calculation of axial neutron flux distributions with the MCNP code at the JSI TRIGA Mark II reactor has been validated with experimental measurements of the (197)Au(n,?)(198)Au reaction rate. The calculated absolute reaction rate values, scaled according to the reactor power and corrected for the flux redistribution effect, are in good agreement with the experimental results. The effect of different cross-section libraries on the calculations has been investigated and shown to be minor. PMID:24316530
W. N. Reisdorf; J. P. Unik; L. E. Glendenin
1973-01-01
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
Vassiliki Kalogera; Chunglee Kim; Duncan R. Lorimer
2002-12-02
We present an analysis method that allows us to estimate the Galactic formation of radio pulsar populations based on their observed properties and our understanding of survey selection effects. More importantly, this method allows us to assign a statistical significance to such rate estimates and calculate the allowed ranges of values at various confidence levels. Here, we apply the method to the question of the double neutron star (NS-NS) coalescence rate using the current observed sample, and we find calculate the most likely value for the total Galactic coalescence rate to lie in the range 3-22 Myr^{-1}, for different pulsar population models. The corresponding range of expected detection rates of NS--NS inspiral are (1-9)x10^{-3} yr^{-1} for the initial LIGO, and 6-50 yr^{-1} for the advanced LIGO. Based on this newly developed statistical method, we also calculate the probability distribution for the expected number of pulsars that could be observed by the Parkes Multibeam survey, when acceleration searches will alleviate the effects of Doppler smearing due to orbital motions. We suggest that the Parkes survey will probably detect 1-2 new binary pulsars like PSRs B1913+16 and/or B1534+12.
Pair-production positron energy-angle distributions of 5m2ec and 10m2ec photons on atoms
NASA Astrophysics Data System (ADS)
Tseng, H. K.
1995-10-01
With a relativistic partial-wave method we calculated numerically the positron energy-angle distributions of pair production in the field of atoms with atomic numbers Z=1 and 92 for photons of energies k=5m2ec and 10m2ec. We have found that in this intermediate-photon-energy region, the Born approximation works fine for low-Z elements, as expected. Our partial-wave results indicate that the Born approximation prediction for the shape of positron energy-angle distributions (especially at small positron angles) is better than its prediction for positron energy spectra of pair production in this intermediate-photon-energy region. Our results also show that the shape of positron energy-angle distributions is almost independent of atomic electron screening.
Liquidlike Spatial Distribution of Magnetic Droplets Revealed by Neutron Scattering in La1-xCaxMnO3
M. Hennion; F. Moussa; G. Biotteau; J. Rodríguez-Carvajal; L. Pinsard; A. Revcolevschi
1998-01-01
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
Neutron-induced fission fragment angular distribution at CERN n TOF: The Th-232 case
Diego Tarrio; Ignacio Duran; Carlos Paradela
2012-01-01
This thesis work was done in the frame of the study of the neutron-induced fission of actinides and subactinides at the CERN n TOF facility using a fast Parallel Plate Avalanche Counters (PPACs) setup. This experimental setup provide us with an intense neutron beam with a white spectrum from thermal to 1 GeV and with an outstanding high resolution provided
Morandeau, Antoine E.; White, Claire E. (Princeton)
2015-01-01
Calcium–silicate–hydrate (C–S–H) gel is the main binder component in hydrated ordinary Portland cement (OPC) paste, and is known to play a crucial role in the carbonation of cementitious materials, especially for more sustainable alternatives containing supplementary cementitious materials. However, the exact atomic structural changes that occur during carbonation of C–S–H gel remain unknown. Here, we investigate the local atomic structural changes that occur during carbonation of a synthetic calcium–silicate–hydrate gel exposed to pure CO? vapour, using in situ X-ray total scattering measurements and subsequent pair distribution function (PDF) analysis. By analysing both the reciprocal and real-space scattering data as the C–S–H carbonation reaction progresses, all phases present during the reaction (crystalline and non-crystalline) have been identified and quantified, with the results revealing the emergence of several polymorphs of crystalline calcium carbonate (vaterite and calcite) in addition to the decalcified C–S–H gel. Furthermore, the results point toward residual calcium being present in the amorphous decalcified gel, potentially in the form of an amorphous calcium carbonate phase. As a result of the quantification process, the reaction kinetics for the evolution of the individual phases have been obtained, revealing new information on the rate of growth/dissolution for each phase associated with C–S–H gel carbonation. Moreover, the investigation reveals that the use of real space diffraction data in the form of PDFs enables more accurate determination of the phases that develop during complex reaction processes such as C–S–H gel carbonation in comparison to the conventional reciprocal space Rietveld analysis approach.
NASA Astrophysics Data System (ADS)
Schrön, Martin; Rakovec, Oldrich; Zink, Matthias; Rosolem, Rafael; Zacharias, Steffen; Oswald, Sascha; Baroni, Gabriele; Schröter, Ingmar; Wollschläger, Ute; Reinstorf, Frido; Martini, Edoardo; Samaniego, Luis
2015-04-01
Mesoscale hydrological models like mHM (Samaniego et al., 2010, WRR) are usually evaluated with observed discharge, which is a spatially integrated signal of the watershed. However, an accurate prediction of spatially distributed soil water content is of much higher value for hydrologic prediction. For hydrologic models operating at intermediate to regional scales, Cosmic-Ray Neutron Sensors provide unrivaled soil moisture data which are much more representative and of higher spatial-temporal resolution than most point-scale or remote-sensing products. We are aiming to improve soil moisture calibration and evaluation in mHM with the support of the intermediate-scale data from cosmic-ray neutrons. The relationship between soil moisture profiles in the footprint and the corresponding cosmic-ray neutron counts is non-linear and not unique. Therefore we assimilate cosmic-ray neutron data directly by employing the nested forward model COSMIC (Shuttleworth et al. 2013, HESS), which calculates neutron counts from the modeled soil moisture. In optimization mode, mHM is able to calibrate parameters of both, the hydrological system and/or the neutron prediction model itself. Sub-daily model performance is evaluated with independent measurements of soil moisture patterns from several catchment-wide TDR campaigns, time series of a Wireless Sensor Network and discharge in the small catchment "Schäfertal" (1.6 km2) in central Germany. This work is an important step towards the assimilation of continuous spatial data from mobile Cosmic Ray Sensing (Schrön et al. 2014, TERENO Conference Abstracts). The so-called TERENO:Rover delivers highly-resolved spatial patterns of water content in a whole catchment, which has a great potential to improve spatial performance of hydrological models.
Nigg, D W; Randolph, P D; Wheeler, F J
1991-01-01
The Monte Carlo stochastic simulation technique has traditionally been the only well-recognized method for computing three-dimensional radiation dose distributions in connection with boron neutron capture therapy (BNCT) research. A deterministic approach to this problem would offer some advantages over the Monte Carlo method. This paper describes an application of a deterministic method to analytically simulate BNCT treatment of a canine head phantom using the epithermal neutron beam at the Brookhaven medical research reactor (BMRR). Calculations were performed with the TORT code from Oak Ridge National Laboratory (ORNL), an implementation of the discrete ordinates, or Sn method. Calculations were from first principles and used no empirical correction factors. The phantom surface was modeled by flat facets of approximately 1 cm2. The phantom interior was homogeneous. Energy-dependent neutron and photon scalar fluxes were calculated on a 32 x 16 x 22 mesh structure with 96 discrete directions in angular phase space. The calculation took 670 min on an Apollo DN10000 workstation. The results were subsequently integrated over energy to obtain full three-dimensional dose distributions. Isodose contours and depth-dose curves were plotted for several separate dose components of interest. Phantom measurements were made by measuring neutron activation (and therefore neutron flux) as a function of depth in copper-gold alloy wires that were inserted through catheters placed in holes drilled in the phantom. Measurements agreed with calculations to within about 15%. The calculations took about an order of magnitude longer than comparable Monte Carlo calculations but provided various conveniences, as well as a useful check. PMID:1901131
NASA Astrophysics Data System (ADS)
Tropin, T. V.; Jargalan, N.; Avdeev, M. V.; Kyzyma, O. A.; Sangaa, D.; Aksenov, V. L.
2014-01-01
The aggregate growth in a C60/N-methylpyrrolidone (NMP) solution has been considered in the framework of the approach developed earlier for describing the cluster growth kinetics in fullerene polar solutions. The final cluster size distribution functions in model solutions have been estimated for two fullerene aggregation models including the influence of complex formation on the cluster growth using extrapolations of the characteristics of the cluster state and distribution parameters. Based on the obtained results, the model curves of small-angle neutron scattering have been calculated for a C60/NMP solution at various values of the model parameters.
FURTHER EVIDENCE FOR THE BIMODAL DISTRIBUTION OF NEUTRON-STAR MASSES
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
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.
Supercool Neutrons (Ultracold Neutrons)
Martin, Jeff
Supercool Neutrons (Ultracold Neutrons) Jeff Martin University of Winnipeg Skywalk 2007 Manitoba Research & Innovation Fund #12; Ultracold Neutrons What are neutrons? Why are they important? How to make lots of neutrons. Interesting properties of ultracold neutrons (UCN) Supercool
Samant, M.S.; Anand, R.P.; Choudhury, R.K.; Kapoor, S.S.; Nadkarni, D.M. [Nuclear Physics Division, Bhabha Atomic Research Centre, Bombay 400 (India)] [Nuclear Physics Division, Bhabha Atomic Research Centre, Bombay 400 (India)
1995-06-01
Measurements of prompt neutron energy spectra and angular distributions from mass and kinetic energy selected fission fragments were carried out in the thermal neutron fission of {sup 235}U. Neutron energy was determined by the time-of-flight technique and fission fragment energy and angle were measured using a back-to-back gridded ionization chamber. The measured angular distributions of neutrons emitted from fragment pairs of various mass and kinetic energy were compared with results of Monte Carlo calculations assuming neutron emission from fully accelerated fragments to determine the component of neutrons which may be emitted in the prescission stage. The calculations were carried out using as inputs the measured center-of-mass neutron energy spectra and multiplicites and assuming isotropic emission of neutrons in the center-of-mass frame of both the fission fragments, and a three source fitting of the angular distributions was done to deduce the component of prescission neutrons. The value of the prescission neutron multiplicity averaged over all fragment masses is found to be 0.25{plus_minus}0.05 (about 10% of the total neutron multiplicity). The present results have been discussed on the basis of the energy damping and time scale of the saddle to scission transition in the thermal neutron induced fission process.
Fast neutron dosimetry. Progress report, July 1, 1979-June 30, 1980
Attix, F.H.
1980-01-01
Progress is reported in: the development and testing of new gas mixtures more suitable for fast neutron dosimetry using the common A150-type Tissue-equivalent plastic ion chambers; comparison of photon doses determined with a graphite-walled proportional counter and with paired dosimeters irradiated by 14.8-MeV neutrons; a detector for the direct measurement of LET distributions from irradiation with fast neutrons; LET distributions from fast neutron irradiation of TE-plastic and graphite measured in a cylindrically symmetric geometry; progress in development of a tandem fast neutron and /sup 60/Co gamma ray source irradiation facility; an approach to the correlation of cellular response with lineal energy; calculated and measured HTO atmospheric dispersion rates within meters of a release site; application of cavity theory to fast neutrons; and fast neutron dosimetry by thermally stimulated currents in Al/sub 2/O/sub 3/. (GHT)
Milen Gateshki; Valeri Petkov; Swapan K. Pradhan; Tom Vogt
2005-01-01
The three-dimensional structure of nanocrystalline magnesium ferrite, MgFeO, prepared by ball milling, has been determined using synchrotron radiation powder diffraction and employing both Rietveld and atomic pair distribution function (PDF) analysis. The nanocrystalline ferrite exhibits a very limited structural coherence length and a high degree of structural disorder. Nevertheless, the nanoferrite possesses a very well defined local atomic ordering that
Deutsch, Maxime; Gillon, Béatrice; Claiser, Nicolas; Gillet, Jean-Michel; Lecomte, Claude; Souhassou, Mohamed
2014-01-01
Since the 1980s it has been possible to probe crystallized matter, thanks to X-ray or neutron scattering techniques, to obtain an accurate charge density or spin distribution at the atomic scale. Despite the description of the same physical quantity (electron density) and tremendous development of sources, detectors, data treatment software etc., these different techniques evolved separately with one model per experiment. However, a breakthrough was recently made by the development of a common model in order to combine information coming from all these different experiments. Here we report the first experimental determination of spin-resolved electron density obtained by a combined treatment of X-ray, neutron and polarized neutron diffraction data. These experimental spin up and spin down densities compare very well with density functional theory (DFT) calculations and also confirm a theoretical prediction made in 1985 which claims that majority spin electrons should have a more contracted distribution around the nucleus than minority spin electrons. Topological analysis of the resulting experimental spin-resolved electron density is also briefly discussed. PMID:25075338
M. W. C. Dharma-wardana; Michael S. Murillo
2007-10-15
Two-temperature, two-mass quasi-equilibrium 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 Kohn-Sham calculations and QMC are used to benchmark the procedures used in classical molecular-dynamics simulations, HNC and CHNC methods to derive electron-electron and electron-proton pair - distribution functions. Then, nonequilibrium molecular dynamics for two -temperature, two-mass plasmas are used to obtain the pair distribution. 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. Results for a mass ratio of 1:5, typical of electron-hole fluids, as well as for compressed hydrogen are presented. PACS Numbers: 52.25.Kn, 52.25Gj, 71.10.-w, 52.27.Gr, 26.30.+k
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
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.
Zenihiro, J.; Sakaguchi, H.; Murakami, T.; Yosoi, M.; Yasuda, Y.; Terashima, S.; Iwao, Y. [Department of Physics, Kyoto University, Kyoto 606-8502 (Japan); Takeda, H. [RIKEN Nishina Center for Accelerator-Based Science, Wako, Saitama 351-0198 (Japan); Itoh, M.; Yoshida, H. P.; Uchida, M. [Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047 (Japan)
2010-10-15
Cross sections and analyzing powers for polarized proton elastic scattering from {sup 58}Ni, and {sup 204,206,208}Pb were measured at intermediate energy E{sub p}=295 MeV. An effective relativistic Love-Franey interaction is tuned to reproduce {sup 58}Ni scattering data within the framework of the relativistic impulse approximation. The neutron densities of the lead isotopes are deduced using model-independent sum-of-Gaussians distributions. Their error envelopes are estimated by a new {chi}{sup 2} criterion including uncertainties associated with the reaction model. The systematic behaviors of extracted error envelopes of the neutron density distributions in {sup 204,206,208}Pb are presented. The extracted neutron and proton density distribution of {sup 208}Pb gives a neutron skin thickness of {Delta}r{sub np}=0.211{sub -0.063}{sup +0.054} fm.
NASA Astrophysics Data System (ADS)
Krutenkova, A. P.; Tsukerman, I. S.
2007-12-01
A brief nonanalytic survey of data available in the literature for parameters that characterize nuclear sizes is given, and the potentials of some methods for determining these sizes are compared. Attention is given primarily to determining nuclear sizes in experiments that study pion-nucleus interaction. For pointlike protons and neutrons, values of parameters that describe the radial dependences of their densities according to the Fermi distribution are presented in a tabular form. The method proposed previously at the Institute of Theoretical and Experimental Physics (ITEP, Moscow) for determining nuclear sizes on the basis of measuring differential cross sections for ?? + A ? ?{forw/±} + X processes in the kinematical region where the recorded interaction event occurs on a single proton (neutron) of nucleus A, the presence of the remaining nucleons manifesting itself in shadowing effects, is described, and examples of the application of this method are given.
Casoli, P. (Pierre); Ethvignot, T. (Thierry); Granier, T. (Thierry); Nelson, R. O. (Ronald O.); Fotiades, N. (Nikolaos); Devlin, M. J. (Matthew J.); Drake, D. M. (Darrell M.); Younes, W. (Walid); Garrett, P. E. (Paul E.); Becker, J. A. (John A.)
2004-01-01
Prompt gamma-ray and x-ray spectroscopy techniques are being employed to study fission induced on {sup 238}U targets by neutrons of energy from 1 MeV to 150 MeV. Data are acquired using the GEANIE high resolution gamma-ray spectrometer at the LANSCE/WNR unmoderated spallation neutron source. Information on the pre-decay yields (excitation functions and isotopic distributions) were extracted from gamma and gamma-gamma coincidence data for a wide range of nucleides. Charge yields were extracted by measuring prompt x-rays from a thin, fission-sensitive target using photovoltaic cells specially designed. The experimental results are presented and compared to model calculations.
Spin-polarized low-density neutron matter
Gezerlis, Alexandros [Department of Physics, University of Washington, Seattle, Washington 98195-1560 (United States)
2011-06-15
Low-density neutron matter is relevant to the study of neutron-rich nuclei and neutron star crusts. Unpolarized neutron matter has been studied extensively over a number of decades, while experimental guidance has recently started to emerge from the field of ultracold atomic gases. In this work, we study population-imbalanced neutron matter (possibly relevant to magnetars and to density functionals of nuclei) by applying a quantum Monte Carlo method that has proven successful in the field of cold atoms. We report on the first ab initiosimulations of superfluid low-density polarized neutron matter. For systems with small imbalances, we find a linear dependence of the energy on the polarization, the proportionality coefficient being dependent on the density. We also present results for the momentum and pair distributions of the two fermionic components.
Novel neutron focusing mirrors for compact neutron sources
Gubarev, M.V.
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. ...
M. I. Pigozzi; A. J. Solari
1997-01-01
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
Density dependence of the pairing interaction and pairing correlation in unstable nuclei
NASA Astrophysics Data System (ADS)
Changizi, S. A.; Qi, C.
2015-02-01
This work aims at a global assessment of the effect of the density dependence of the zero-range pairing interaction. Systematic Skyrme-Hartree-Fock-Bogoliubov calculations with the volume, surface, and mixed pairing forces are carried out to study the pairing gaps in even-even nuclei over the whole nuclear chart. Calculations are also done in coordinate representation for unstable semimagic even-even nuclei. The calculated pairing gaps are compared with empirical values from four different odd-even staggering formulas. Calculations with the three pairing interactions are comparable for most nuclei close to the ? -stability line. However, the surface interaction calculations predict neutron pairing gaps in neutron-rich nuclei that are significantly stronger than those given by the mixed and volume pairing. On the other hand, calculations with volume and mixed pairing forces show noticeable reduction of neutron pairing gaps in nuclei far from stability.
Charge distribution studies in the fast-neutron-induced fission of 232Th, 238U, 240Pu and 244Cm
H. Naik; R. J. Singh; R. H. Iyer
2003-01-01
Charge distribution studies for heavy-mass fission products were carried out in the fast-neutron-induced fission of 232Th, 238U, 240Pu and 244Cm using radiochemical and gamma-ray spectrometric techniques. The width parameter( sigmaZ\\/sigmaA), the most probable charge\\/mass ( ZP\\/AP), the charge polarization (DeltaZ) and the slope of charge polarization [ delta(DeltaZ)\\/deltaA'] as a function of the fragment mass (A') were deduced. The average
Charge distribution studies in the fast-neutron-induced fission of 232 Th, 238 U, 240 Pu and 244 Cm
H. Naik; R. J. Singh; R. H. Iyer
2003-01-01
: Charge distribution studies for heavy-mass fission products were carried out in the fast-neutron-induced fission of 232Th, 238U, 240Pu and 244Cm using radiochemical and gamma-ray spectrometric techniques. The width parameter( ?Z\\/?A), the most probable charge\\/mass ( Z\\u000a P\\/A\\u000a P), the charge polarization (?Z) and the slope of charge polarization [ ?(?Z)\\/?A\\u000a ?] as a function of the fragment mass (A
Ichikawa, G; Komamiya, S; Kamiya, Y; Minami, Y; Tani, M; Geltenbort, P; Yamamura, K; Nagano, M; Sanuki, T; Kawasaki, S; Hino, M; Kitaguchi, M
2014-02-21
Ultracold neutrons (UCNs) can be bound by the potential of terrestrial gravity and a reflecting mirror. The wave function of the bound state has characteristic modulations. We carried out an experiment to observe the vertical distribution of the UCNs above such a mirror at the Institut Laue-Langevin in 2011. The observed modulation is in good agreement with that prediction by quantum mechanics using the Wigner function. The spatial resolution of the detector system is estimated to be 0.7???m. This is the first observation of gravitationally bound states of UCNs with submicron spatial resolution. PMID:24579585
B. J. Patil; S. T. Chavan; S. N. Pethe; R. Krishnan; S. D. Dhole
2010-01-01
The 6MeV race track microtron based pulsed neutron source has been designed specifically for the elemental analysis of short lived activation products, where the low neutron flux requirement is desirable. Electrons impinges on a e–? target to generate bremsstrahlung radiations, which further produces neutrons by photonuclear reaction in ?–n target. The optimisation of these targets along with their spectra were
Eunja Ha; Myung-Ki Cheoun
2014-09-06
We developed the deformed proton-neutron quasiparticle random phase approximation (QRPA) and applied to the evaluation of the Gamow-Teller (GT) transition strength distributions including high-lying excited states, which data becomes recently available beyond one or two nucleon threshold by charge exchange reactions using hundreds of MeV projectiles. Our calculations started with single-particle states calculated by a deformed axially symmetric Woods-Saxon potential. Neutron-neutron and proton-proton pairing correlations are explicitly taken into account at the deformed Bardeen Cooper Schriffer theory. Ground state correlations, and two-particle and two-hole mixing states are included in the deformed QRPA. In this work, we use a realistic two-body interaction given by the Brueckner $G$-matrix based on the CD Bonn potential to reduce the ambiguity on the nucleon-nucleon interactions inside nuclei. We applied our formalism to the GT transition strengths for $^{76}$Ge, $^{76,82}$Se, and $^{90,92}\\textrm{Zr}$, and compared to available experimental data. The GT strength distributions were sensitive on the deformation parameter as well as its sign, {\\it i.e.}, oblate or prolate. The Ikeda sum rule, which is usually thought to be satisfied under the one-body current approximation irrespective of nucleon models, is used to test our numerical calculations and shown to be satisfied without introducing the quenching factor, if high-lying GT excited states are properly taken into account. Most of the GT strength distributions of the nuclei considered in this work turn out to have the high-lying GT excited states beyond one nucleon threshold, which are shown to be consistent with available experimental data.
Dai, Shi; Lin, Mengxiang; Yue, Youling; Hobbs, George; Xu, Renxin
2015-01-01
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...
Lebowitz, Joel
with a specified density F and radial distribution function g(r). In d ) 1 we give necessary and sufficient); g(r) ) g(-r) is the radial distribution function and Fg(r) is the density of particles distribution function is given by the proposed g(r)? This is the realizability problem which has a long history
C. Romano; Y. Danon; R. Block; J. Thompson; E. Blain; E. Bond
2010-01-01
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
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
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.
Karol Kolodziej; Aleksandra Slapik
2015-07-06
We complement the analysis of the anomalous top-Higgs coupling effects on the secondary lepton distributions in the associated production of the top-quark pair and Higgs boson in proton-proton collisions at the LHC of the former work by one of the present authors by taking into account the quark-antiquark production mechanism. We also present simple arguments which explain why the effects of the scalar and pseudoscalar anomalous couplings on the unpolarized cross section of the process are completely insensitive to the sign of either of them.
1962-01-01
Neutrons were deflected 90 deg with a carbon reflector onto shield ; materials of linear and borated linear polyethylene, ZrH\\/subv 1.95\\/. Inconel X, ; BeO, Be, and stainless steel (type 309). The emergent flux of various ; monoenergetic capture gamma rays was experimentally determined for several ; thicknesses of each materlal with a special 3-crystal NaI(Tl) anticoincidence ; total-absorption gamma
THE ULTRAVIOLET SPECTRAL ENERGY DISTRIBUTIONS OF QUIESCENT BLACK HOLES AND NEUTRON STARS
Hynes, R. I. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Robinson, E. L., E-mail: rih@phys.lsu.edu, E-mail: elr@astro.as.utexas.edu [Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712 (United States)
2012-04-10
We present Hubble Space Telescope/Advanced Camera for Surveys ultraviolet photometry of three quiescent black hole X-ray transients, X-ray Nova Muscae 1991 (GU Mus), GRO J0422+32 (V518 Per), and X-ray Nova Vel 1993 (MM Vel), and one neutron star system, Aql X-1. These are the first quiescent UV detections of these objects. All are detected at a much higher level than expected from their companion stars alone and are significant detections of the accretion flow. Three of the four UV excesses can be characterized by a blackbody of temperature 5000-13, 000 K, hotter than expected for the quiescent outer disk. A good fit could not be found for MM Vel. The source of the blackbody-like emission is most likely a heated region of the inner disk. Contrary to initial indications from spectroscopy, there does not appear to be a systematic difference in the UV luminosity or spectral shape between black holes and neutron star systems. However, combining our new data with earlier spectroscopy and published X-ray luminosities, there is a significant difference in the X-ray to UV flux ratios, with the neutron stars exhibiting L{sub X}/L{sub UV} about 10 times higher than the black hole systems. This is consistent with earlier comparisons based on estimating non-stellar optical light, but since both bandpasses we use are expected to be dominated by accretion light, we present a cleaner comparison. This suggests that the difference in X-ray luminosities cannot simply reflect differences in quiescent accretion rates and so the UV/X-ray ratio is a more robust discriminator between the black hole and neutron star populations than the comparison of X-ray luminosities alone.
Probing fission time scales and dynamics via GDR gamma rays and neutron angular distributions
Tye William Botting
1999-01-01
This dissertation presents a study of fission dynamics and time scales for the following reactions; 133 MeV 16O + 208Pb, 104 MeV 4He + 209Bi, 133 MeV 16O + 176Yb, and 104 MeV 4He + 188Os. Two disparate means were utilized: fission coincidence measurements of pre- and post-scission neutrons and of gamma rays. These measurements were accomplished simultaneously and analyzed
Mass distributions in monoenergetic-neutron-induced fission of 239Pu
J. E. Gindler; L. E. Glendenin; D. J. Henderson; J. W. Meadows
1983-01-01
Fission product yields for 24 masses were determined for the fission of 239Pu with essentially monoenergetic neutrons of 0.17, 1.0, 2.0, 3.4, 4.5, 6.1, and 7.9 MeV. Fission product activities were measured by Ge(Li) gamma-ray spectrometry of irradiated 239Pu targets and by chemical separation of the fission product elements followed by beta counting. Yields of near symmetric (valley) fission products
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
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.
NASA Astrophysics Data System (ADS)
Romano, C.; Danon, Y.; Block, R.; Thompson, J.; Blain, E.; Bond, E.
2010-01-01
A new method of measuring fission fragment mass and energy distributions as a function of incident neutron energy in the range from below 0.1 eV to 1 keV has been developed. The method involves placing a double-sided Frisch-gridded fission chamber in Rensselaer Polytechnic Institute’s lead slowing-down spectrometer (LSDS). The high neutron flux of the LSDS allows for the measurement of the energy-dependent, neutron-induced fission cross sections simultaneously with the mass and kinetic energy of the fission fragments of various small samples. The samples may be isotopes that are not available in large quantities (submicrograms) or with small fission cross sections (microbarns). The fission chamber consists of two anodes shielded by Frisch grids on either side of a single cathode. The sample is located in the center of the cathode and is made by depositing small amounts of actinides on very thin films. The chamber was successfully tested and calibrated using 0.41±0.04 ng of Cf252 and the resulting mass distributions were compared to those of previous work. As a proof of concept, the chamber was placed in the LSDS to measure the neutron-induced fission cross section and fragment mass and energy distributions of 25.3±0.5?g of U235. Changes in the mass distributions as a function of incident neutron energy are evident and are examined using the multimodal fission mode model.
Neutron removal cross section as a measure of neutron skin
Fang, D. Q.; Ma, Y. G.; Cai, X. Z.; Tian, W. D.; Wang, H. W. [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Post Office Box 800-204, Shanghai 201800 (China)
2010-04-15
We study the relation between neutron removal cross section (sigma{sub -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 sigma{sub -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.
Switchable radioactive neutron source device
Boyar, Robert E. (La Grange, IL); DeVolpi, Alexander (Bolingbrook, IL); Stanford, George S. (Downers Grove, IL); Rhodes, Edgar A. (Woodridge, IL)
1989-01-01
This invention is a switchable neutron generating apparatus comprised of a pair of plates, the first plate having an alpha emitter section on it and the second plate having a target material portion on it which generates neutrons when its nuclei absorb an alpha particle. In operation, the alpha portion of the first plate is aligned with the neutron portion of the second plate to produce neutrons and brought out of alignment to cease production of neutrons.
Schrewe, U J; Newhauser, W D; Brede, H J; DeLuca, P M
2000-03-01
Low-pressure proportional counters (LPPCs) with walls made from the elements C, Mg, Al, Si, Fe and Zr and from the chemical compounds A-150 plastic, AlN, Al2O3, SiO2 and ZrO2 were used to measure neutron fluence-to-kerma conversion coefficients at energies up to 66 MeV. The LPPCs served to measure the absorbed dose deposited in the gas of a cavity surrounded by the counter walls that could be converted to the absorbed dose to the wall on the basis of the Bragg-Gray cavity theory. Numerically the absorbed doses to the walls were almost equal to the corresponding kerma values of the wall materials. The neutron fluence was determined by various experimental methods based on the reference cross sections of the 1H(n, p) scattering and/or the 238U(n, f) reactions. The measurements were performed in monoenergetic neutron fields of energies of 5 MeV, 8 MeV, 15 MeV and 17 MeV and in polyenergetic neutron beams with prominent peaks of energies of 34 MeV, 44 MeV and 66 MeV. For the measurements in the polyenergetic neutron beams, significant corrections for the contributions of the non peak energy neutrons were applied. The fluence-to kerma conversion coefficients of N and O were determined using the difference technique applied with matched pairs of LPPCs made from a chemical compound and a pure element. This paper reports experimental fluence-to-kerma conversion coefficient values of eight elements and four compounds measured for seven neutron energies, and presents a comparison with data from previous measurements and theoretical predictions. The distributions of the absorbed dose as a function of the lineal energy were measured for monoenergetic neutrons or, for polyenergetic neutron fields, deduced by applying iterative unfolding procedures in order to subtract the contributions from non-peak energy neutrons. The dose distributions provide insight into the neutron interaction processes. PMID:10730963
Abazov, V.?M.; Abbott, B.; Acharya, B.?S.; Adams, M.; Adams, T.; Agnew, J.?P.; Alexeev, G.?D.; Alkhazov, G.; Alton, A.; Askew, A.; et al
2015-04-01
We present a measurement of the distribution of the variable ?*? for muon pairs with masses between 30 and 500 GeV, using the complete run II data set collected by the D0 detector at the Fermilab Tevatron proton-antiproton collider. This corresponds to an integrated luminosity of 10.4 fb?¹ at ?s=1.96 TeV. The data are corrected for detector effects and presented in bins of dimuon rapidity and mass. The variable ?*? probes the same physical effects as the Z/?* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. These are the first measurements at anymore »collider of the ?*? distributions for dilepton masses away from the Z?l?l? boson mass peak. The data are compared to QCD predictions based on the resummation of multiple soft gluons.« less
NASA Astrophysics Data System (ADS)
Abazov, V. M.; Abbott, B.; Acharya, B. S.; Adams, M.; Adams, T.; Agnew, J. P.; Alexeev, G. D.; Alkhazov, G.; Alton, A.; Askew, A.; Atkins, S.; Augsten, K.; Avila, C.; Badaud, F.; Bagby, L.; Baldin, B.; Bandurin, D. V.; Banerjee, S.; Barberis, E.; Baringer, P.; Bartlett, J. F.; Bassler, U.; Bazterra, V.; Bean, A.; Begalli, M.; Bellantoni, L.; Beri, S. B.; Bernardi, G.; Bernhard, R.; Bertram, I.; Besançon, M.; Beuselinck, R.; Bhat, P. C.; Bhatia, S.; Bhatnagar, V.; Blazey, G.; Blessing, S.; Bloom, K.; Boehnlein, A.; Boline, D.; Boos, E. E.; Borissov, G.; Borysova, M.; Brandt, A.; Brandt, O.; Brock, R.; Bross, A.; Brown, D.; Bu, X. B.; Buehler, M.; Buescher, V.; Bunichev, V.; Burdin, S.; Buszello, C. P.; Camacho-Pérez, E.; Casey, B. C. K.; Castilla-Valdez, H.; Caughron, S.; Chakrabarti, S.; Chan, K. M.; Chandra, A.; Chapon, E.; Chen, G.; Cho, S. W.; Choi, S.; Choudhary, B.; Cihangir, S.; Claes, D.; Clutter, J.; Cooke, M.; Cooper, W. E.; Corcoran, M.; Couderc, F.; Cousinou, M.-C.; Cutts, D.; Das, A.; Davies, G.; de Jong, S. J.; De La Cruz-Burelo, E.; Déliot, F.; Demina, R.; Denisov, D.; Denisov, S. P.; Desai, S.; Deterre, C.; DeVaughan, K.; Diehl, H. T.; Diesburg, M.; Ding, P. F.; Dominguez, A.; Dubey, A.; Dudko, L. V.; Duperrin, A.; Dutt, S.; Eads, M.; Edmunds, D.; Ellison, J.; Elvira, V. D.; Enari, Y.; Evans, H.; Evdokimov, V. N.; Fauré, A.; Feng, L.; Ferbel, T.; Fiedler, F.; Filthaut, F.; Fisher, W.; Fisk, H. E.; Fortner, M.; Fox, H.; Fuess, S.; Garbincius, P. H.; Garcia-Bellido, A.; García-González, J. A.; Gavrilov, V.; Geng, W.; Gerber, C. E.; Gershtein, Y.; Ginther, G.; Gogota, O.; Golovanov, G.; Grannis, P. D.; Greder, S.; Greenlee, H.; Grenier, G.; Gris, Ph.; Grivaz, J.-F.; Grohsjean, A.; Grünendahl, S.; Grünewald, M. W.; Guillemin, T.; Gutierrez, G.; Gutierrez, P.; Haley, J.; Han, L.; Harder, K.; Harel, A.; Hauptman, J. M.; Hays, J.; Head, T.; Hebbeker, T.; Hedin, D.; Hegab, H.; Heinson, A. P.; Heintz, U.; Hensel, C.; Heredia-De La Cruz, I.; Herner, K.; Hesketh, G.; Hildreth, M. D.; Hirosky, R.; Hoang, T.; Hobbs, J. D.; Hoeneisen, B.; Hogan, J.; Hohlfeld, M.; Holzbauer, J. L.; Howley, I.; Hubacek, Z.; Hynek, V.; Iashvili, I.; Ilchenko, Y.; Illingworth, R.; Ito, A. S.; Jabeen, S.; Jaffré, M.; Jayasinghe, A.; Jeong, M. S.; Jesik, R.; Jiang, P.; Johns, K.; Johnson, E.; Johnson, M.; Jonckheere, A.; Jonsson, P.; Joshi, J.; Jung, A. W.; Juste, A.; Kajfasz, E.; Karmanov, D.; Katsanos, I.; Kaur, M.; Kehoe, R.; Kermiche, S.; Khalatyan, N.; Khanov, A.; Kharchilava, A.; Kharzheev, Y. N.; Kiselevich, I.; Kohli, J. M.; Kozelov, A. V.; Kraus, J.; Kumar, A.; Kupco, A.; Kur?a, T.; Kuzmin, V. A.; Lammers, S.; Lebrun, P.; Lee, H. S.; Lee, S. W.; Lee, W. M.; Lei, X.; Lellouch, J.; Li, D.; Li, H.; Li, L.; Li, Q. Z.; Li, X.; Lim, J. K.; Lincoln, D.; Linnemann, J.; Lipaev, V. V.; Lipton, R.; Liu, H.; Liu, Y.; Lobodenko, A.; Lokajicek, M.; Lopes de Sa, R.; Luna-Garcia, R.; Lyon, A. L.; Maciel, A. K. A.; Madar, R.; Magaña-Villalba, R.; Malik, S.; Malyshev, V. L.; Mansour, J.; Martínez-Ortega, J.; McCarthy, R.; McGivern, C. L.; Meijer, M. M.; Melnitchouk, A.; Menezes, D.; Mercadante, P. G.; Merkin, M.; Meyer, A.; Meyer, J.; Miconi, F.; Mondal, N. K.; Mulhearn, M.; Nagy, E.; Narain, M.; Nayyar, R.; Neal, H. A.; Negret, J. P.; Neustroev, P.; Nguyen, H. T.; Nunnemann, T.; Orduna, J.; Osman, N.; Osta, J.; Pal, A.; Parashar, N.; Parihar, V.; Park, S. K.; Partridge, R.; Parua, N.; Patwa, A.; Penning, B.; Perfilov, M.; Peters, Y.; Petridis, K.; Petrillo, G.; Pétroff, P.; Pleier, M.-A.; Podstavkov, V. M.; Popov, A. V.; Prewitt, M.; Price, D.; Prokopenko, N.; Qian, J.; Qin, Y.; Quadt, A.; Quinn, B.; Ratoff, P. N.; Razumov, I.; Ripp-Baudot, I.; Rizatdinova, F.; Rominsky, M.; Ross, A.; Royon, C.; Rubinov, P.; Ruchti, R.; Sajot, G.; Sánchez-Hernández, A.; Sanders, M. P.; Santos, A. S.; Savage, G.; Savitskyi, M.; Sawyer, L.; Scanlon, T.; Schamberger, R. D.; Scheglov, Y.; Schellman, H.; Schwanenberger, C.; Schwienhorst, R.; Sekaric, J.; Severini, H.; Shabalina, E.; Shary, V.; Shaw, S.; Shchukin, A. A.; Simak, V.; Skubic, P.; Slattery, P.; Smirnov, D.; Snow, G. R.; Snow, J.; Snyder, S.; Söldner-Rembold, S.; Sonnenschein, L.; Soustruznik, K.; Stark, J.; Stoyanova, D. A.; Strauss, M.; Suter, L.; Svoisky, P.; Titov, M.; Tokmenin, V. V.; Tsai, Y.-T.; Tsybychev, D.; Tuchming, B.; Tully, C.; Uvarov, L.; Uvarov, S.; Uzunyan, S.; Van Kooten, R.; van Leeuwen, W. M.; Varelas, N.; Varnes, E. W.; Vasilyev, I. A.; Verkheev, A. Y.; Vertogradov, L. S.; Verzocchi, M.; Vesterinen, M.; Vilanova, D.; Vokac, P.; Wahl, H. D.; Wang, M. H. L. S.; Warchol, J.; Watts, G.; Wayne, M.; Weichert, J.; Welty-Rieger, L.; Williams, M. R. J.; Wilson, G. W.; Wobisch, M.; Wood, D. R.; Wyatt, T. R.; Xie, Y.; Yamada, R.; Yang, S.; Yasuda, T.; Yatsunenko, Y. A.; Ye, W.
2015-04-01
We present a measurement of the distribution of the variable ??* for muon pairs with masses between 30 and 500 GeV, using the complete run II data set collected by the D0 detector at the Fermilab Tevatron proton-antiproton collider. This corresponds to an integrated luminosity of 10.4 fb-1 at ?{s }=1.96 TeV . The data are corrected for detector effects and presented in bins of dimuon rapidity and mass. The variable ??* probes the same physical effects as the Z /?* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. These are the first measurements at any collider of the ??* distributions for dilepton masses away from the Z ??+?- boson mass peak. The data are compared to QCD predictions based on the resummation of multiple soft gluons.
D0 Collaboration
2015-03-04
We present a measurement of the distribution of the variable $\\phi^*_\\eta$ for muon pairs with masses between 30 and 500 GeV, using the complete Run II data set collected by the D0 detector at the Fermilab Tevatron proton-antiproton collider. This corresponds to an integrated luminosity of 10.4 fb$^{-1}$ at $\\sqrt{s}$ = 1.96 TeV. The data are corrected for detector effects and presented in bins of dimuon rapidity and mass. The variable $\\phi^*_\\eta$ probes the same physical effects as the $Z/\\gamma^*$ boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. These are the first measurements at any collider of the $\\phi^*_\\eta$ distributions for dilepton masses away from the $Z\\rightarrow \\ell^+\\ell^-$ boson mass peak. The data are compared to QCD predictions based on the resummation of multiple soft gluons.
Imaging with Scattered Neutrons
H. Ballhausen; H. Abele; R. Gaehler; M. Trapp; A. Van Overberghe
2006-10-30
We describe a novel experimental technique for neutron imaging with scattered neutrons. These scattered neutrons are of interest for condensed matter physics, because they permit to reveal the local distribution of incoherent and coherent scattering within a sample. In contrast to standard attenuation based imaging, scattered neutron imaging distinguishes between the scattering cross section and the total attenuation cross section including absorption. First successful low-noise millimeter-resolution images by scattered neutron radiography and tomography are presented.
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
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
YOSHINAGA Sho; MATSUURA Hideaki; NAKAO Yasuyuki; KUDO Kazuhiko
2006-01-01
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
Residual stress distribution in steel butt welds measured using neutron and synchrotron diffraction.
Paradowska, A. M.; Price, J. W. H.; Finlayson, T. R.; Lienert, U.; Walls, P.; Ibrahim, R.; X-Ray Science Division; Rutherford Appleton Lab.; Monash Univ.; Univ. of Melborne; ANSTO
2009-01-01
70 keV synchrotron radiation and thermal neutrons have been employed to investigate the residual stress characteristics in a fully restrained, steel, butt weld. The focus is on the values of the subsurface and through-thickness strain/stress variation in the middle of the weld. The advantages and limitations of the techniques have been addressed, in relation to the gauge volume, the stress-free reference sample and positioning. The measurement of residual stress around the weld achieved in this work significantly improves the resolution at which residual stress in welded components has been determined.
Mass distributions in monoenergetic-neutron-induced fission of 232Th
L. E. Glendenin; J. E. Gindler; I. Ahmad; D. J. Henderson; J. W. Meadows
1980-01-01
Fission product yields for 38 masses were determined for the fission of 232Th with essentially monoenergetic neutrons of 2.0, 3.0, 4.0, 5.9, 6.4, 6.9, 7.6, and 8.0 MeV. Fission product activities were measured by Ge(Li) gamma-ray spectrometry of irradiated 232Th foils and by chemical separation of the fission product elements followed by beta counting. The mass yield data for 232Th(n,
Mass distributions in monoenergetic-neutron-induced fission of Â²Â³Â²Th
L. E. Glendenin; J. E. Gindler; I. Ahmad; D. J. Henderson; J. W. Meadows
1980-01-01
Fission product yields for 38 masses were determined for the fission of Â²Â³Â²Th with essentially monoenergetic neutrons of 2.0, 3.0, 4.0, 5.9, 6.4, 6.9, 7.6, and 8.0 MeV. Fission product activities were measured by Ge(Li) ..gamma..-ray spectrometry of irradiated Â²Â³Â²Th foils and by chemical separation of the fission product elements followed by ..beta.. counting. The mass yield data for Â²Â³Â²Th(n,f
Mass distributions for monoenergetic-neutron-induced fission of 235U
L. E. Glendenin; J. E. Gindler; D. J. Henderson; J. W. Meadows
1981-01-01
Fission product yields for 37 masses were determined for the fission of 235U with essentially monoenergetic neutrons of 0.17, 0.55, 1.0, 2.0, 4.0, 5.5, 6.3, 7.1, and 8.1 MeV. Fission product activities were measured by Ge(Li) gamma-ray spectrometry of irradiated 235U targets and by chemical separation of the fission product elements followed by beta counting and\\/or gamma-ray spectrometry. The mass-yield
Mass distributions in monoenergetic-neutron-induced fission of Â²Â³â¸U
S. Nagy; K. F. Flynn; J. E. Gindler; J. W. Meadows; L. E. Glendenin
1978-01-01
Fission product yields for 44 masses were determined for the fission of Â²Â³â¸U with essentially monoenergetic neutrons of 1.5, 2.0, 3.9, 5.5, 6.9, and 7.7 MeV. Fission product activities were measured by Ge(Li) ..gamma..-ray spectrometry of irradiated Â²Â³â¸U foils and by chemical separation of the fission product elements followed by ..beta.. counting and\\/or ..gamma..-ray spectrometry. The mass-yield data for Â²Â³â¸U(n,f)
Mass distributions in monoenergetic-neutron-induced fission of 238U
S. Nagy; K. F. Flynn; J. E. Gindler; J. W. Meadows; L. E. Glendenin
1978-01-01
Fission product yields for 44 masses were determined for the fission of 238U with essentially monoenergetic neutrons of 1.5, 2.0, 3.9, 5.5, 6.9, and 7.7 MeV. Fission product activities were measured by Ge(Li) gamma-ray spectrometry of irradiated 238U foils and by chemical separation of the fission product elements followed by beta counting and\\/or gamma-ray spectrometry. The mass-yield data for 238U(n,f)
Shoulders in the very asymmetric mass distribution for reactor-neutron-induced fission of 238U
V. K. Rao; V. K. Bhargava; S. G. Marathe; S. M. Sahakundu; R. H. Iyer
1979-01-01
New experimental data have been obtained on the cumulative yields of some short-lived very asymmetric products in the reactor-neutron-induced fission of 238U. Fission yields of 73Ga(t12=4.8 h), 167Ho(t12=3.1 h), 171Er(t12=7.5 h), 173Tm(t12=8.2 h), and 179Lu(t12=4.6 h) are reported. These yields together with those reported earlier by us for other relatively longer lived products (half-lives of the order of a few
Superfluid Response and the Neutrino Emissivity of Neutron Matter
Andrew W. Steiner; Sanjay Reddy
2008-04-03
{We calculate the neutrino emissivity of superfluid neutron matter in the inner crust of neutron stars. We find that neutrino emission due to fluctuations resulting from the formation of Cooper pairs at finite temperature is highly suppressed in non-relativistic systems. This suppression of the pair breaking emissivity in a simplified model of neutron matter with interactions that conserve spin is of the order of $v_F^4$ for density fluctuations and $v_F^2$ for spin fluctuations, where $v_F$ is the Fermi velocity of neutrons. The larger suppression of density fluctuations arises because the dipole moment of the density distribution of a single component system does not vary in time. For this reason, we find that the axial current response (spin fluctuations) dominates. In more realistic models of neutron matter which include tensor interactions where the neutron spin is not conserved, neutrino radiation from bremsstrahlung reactions occurs at order $v_F^0$. Consequently, even with the suppression factors due to superfluidity, this rate dominates near $T_C$. Present calculations of the pair-breaking emissivity are incomplete because they neglect the tensor component of the nucleon-nucleon interaction.
Continuous distribution of defect states and band gap narrowing in neutron irradiated GaAs
Fleming, R. M.; Lang, D. V.; Seager, C. H.; Bielejec, E.; Patrizi, G. A.; Campbell, J. M. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1415 (United States)
2010-06-15
We find that fast neutron irradiated n- and p-GaAs diodes both show a broad feature in deep level transient spectroscopy (DLTS) previously studied primarily in n-GaAs and termed the ''U-band.'' The high temperature edge of the broad DLTS feature cuts off at the same temperature in both n- and p-GaAs suggesting that the cut off is due to the DLTS behavior expected for a continuous density of defect states that spans midgap. The band gap implied by the DLTS midgap cut off is 1.36 eV, as compared to the bulk GaAs band gap 1.52 eV. Band gap narrowing is consistent with previous measurements of lattice expansion in neutron irradiated GaAs. This leads to a model of defect cascades that are regions of narrowed band gap with defect levels that are inhomogeneously broadened. We observe, in addition, that the damage cascades are surrounded by large Coulomb barriers that prevent the complete filling of traps in the damaged regions.
Krivoglaz
1959-01-01
The background distribution near the lines or spots in Debye or Laue ; crystallograms was investigated. The scattering is induced by variability of ; atomic scattering factors and atomic radii. Formulas are derived for determining ; correlation parameters (considering the geometric deformations) according to ; experimentally distributed background intensities on Debye crystallograms. ; (R.V.J.);
NASA Astrophysics Data System (ADS)
Bræstrup, F.; Hauback, B. C.; Hansen, K. K.
2008-09-01
ZnFe2O4 has a spinel-type structure with Zn ions located mainly on tetrahedral sites and Fe ions located on octahedral sites. ZnFe2O4 was synthesized in air by a solid state reaction and characterized with X-ray diffraction, high temperature neutron diffraction, resistivity measurements and dilatometry. The distribution of cations in ZnFe2O4 was measured from 298 to 1243 K and results show that above 673 K the cations start to redistributed in the structure. ZnFe2O4 has a semi-conducting behavior at room temperature, but at temperatures above 905 K the conductivity decreases as the result of an Fe-Fe interaction between octahedral sites.
NASA Astrophysics Data System (ADS)
Nakane, Y.; Sakamoto, Y.
2001-03-01
In order to validate dose evaluation methods for radiation shielding design of accelerator facilities, absorbed dose distributions in a plastic phantom of 30×30×30 cm 3 slab were measured for 40- and 65-MeV quasi-monoenergetic neutrons with a tissue-equivalent proportional counter and a tissue-equivalent ionization chamber. The measured distributions were compared with the calculated ones from the energy deposition of charged particles and neutron energy spectra by using the Monte Carlo codes, HETC-3STEP and MORSE-CG/KFA, respectively. As a result, it was revealed that the calculation method used in the present work was applicable to absorbed dose evaluation for intermediate energy neutrons with high accuracy.
S. Katano; N. Minakawa; T. Hasebe; J. Sakuraba
2006-01-01
A new high-field superconducting magnet of the cryogen-free type has been developed. The superconducting coil of this system is directly cooled down by three 4 K-GM cryocoolers. The magnet consists of a split-pair of (Nb,Ti)3Sn inner coils and NbTi outer ones; and its outer diameter is 545mm and the height is 352mm. The gap for the beam path is 18mm
Franz-Joseph Hambsch
1987-01-01
The fluctuations in the mass and energy distribution of the fission fragments of the reaction 235 U(n,f) were investigated. The role of spin resonance in the theoretical description of the fission cross section is outlined. The measurements of the cross section as well as the problems of the spin determination in actinides are presented. The experiments in the neutron energy
Theory of neutron scattering experiments on momentum distributions in quantum fluids
Silver, R.N.
1987-01-01
In this paper, the first perturbative derivation of the final state corrections to the impulse approximation for deep inelastic neutron scattering experiments was presented. The final state broadening is found to depend on g(r) and the He-He phase shifts. The theory satisfies the f-sum rule, the ..omega../sup 2/ sum rule (''kinetic energy'') valid at high Q, and the ..omega../sup 3/ sum rule. In the structure of the theory, the self-energy terms alone would lead to quasi-Lorentzian broadening. However, these are exactly canceled by a part of the vertex terms which introduce g(r). Numerical results are presented for superfluid /sup 4/He.
Rothe, R.E.
1996-09-30
A series of 62 critical and critical approach experiments were performed to evaluate a possible novel means of storing large volumes of fissile solution in a critically safe configuration. This study is intended to increase safety and economy through use of such a system in commercial plants which handle fissionable materials in liquid form. The fissile solution`s concentration may equal or slightly exceed the minimum-critical-volume concentration; and experiments were performed for high-enriched uranium solution. Results should be generally applicable in a wide variety of plant situations. The method is called the `Poisoned Tube Tank` because strong neutron absorbers (neutron poisons) are placed inside periodically spaced stainless steel tubes which separate absorber material from solution, keeping the former free of contamination. Eight absorbers are investigated. Both square and triangular pitched lattice patterns are studied. Ancillary topics which closely model typical plant situations are also reported. They include the effect of removing small bundles of absorbers as might occur during inspections in a production plant. Not taking the tank out of service for these inspections would be an economic advantage. Another ancillary topic studies the effect of the presence of a significant volume of unpoisoned solution close to the Poisoned Tube Tank on the critical height. A summary of the experimental findings is that boron compounds were excellent absorbers, as expected. This was true for granular materials such as Gerstley Borate and Borax; but it was also true for the flexible solid composed of boron carbide and rubber, even though only thin sheets were used. Experiments with small bundles of absorbers intentionally removed reveal that quite reasonable tanks could be constructed that would allow a few tubes at a time to be removed from the tank for inspection without removing the tank from production service.
Brown, Paul S. (Paul Sherman)
1962-01-01
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, ...
Angular distribution of neutron inverse beta decay, nu¯e+p-->e++n
P. Vogel; J. F. Beacom
1999-01-01
The reaction nu¯e+p-->e++n is very important for low-energy (Enu<~60 MeV) antineutrino experiments. In this paper we calculate the positron angular distribution, which at low energies is slightly backward. We show that weak magnetism and recoil corrections have a large effect on the angular distribution, making it isotropic at about 15 MeV and slightly forward at higher energies. We also show
S. P. Tripathy; A. K. Bakshi; V. Sathian; S. M. Tripathi; H. R. Vega-Carrillo; M. Nandy; P. K. Sarkar; D. N. Sharma
2009-01-01
The neutron spectra from a Pb-covered and a bare (without Pb-cover) 241Am-Be (alpha,n) source were measured using thermoluminescent detector (TLD) pairs of 6LiF and 7LiF with high-density polyethylene (HDPE) multi-spheres of seven different diameters. A total of 8 distinct neutron response signals (including a bare mode exposure) were obtained from which the energy distribution for the entire energy range was
S. P. Tripathy; A. K. Bakshi; V. Sathian; S. M. Tripathi; H. R. Vega-carrillo; M. Nandy; P. K. Sarkar; D. N. Sharma
2009-01-01
The neutron spectra from a Pb-covered and a bare (without Pb-cover) 241Am–Be (?,n) source were measured using thermoluminescent detector (TLD) pairs of 6LiF and 7LiF with high-density polyethylene (HDPE) multi-spheres of seven different diameters. A total of 8 distinct neutron response signals (including a bare mode exposure) were obtained from which the energy distribution for the entire energy range was
Paglia, G.; Bozin, E.S.; Vengust, D.; Mihailovic, D.; Billinge, S.J.L. (Joseph Stefan Inst.); (MSU)
2010-12-03
The structure of the recently discovered systematically reproducible Mo{sub 6}S{sub y}I{sub z} nanowires has been determined from the atomic pair distribution function (PDF) analysis of powder X-ray diffraction data. This total scattering approach was required because the nanowires are not perfectly crystalline and, therefore, the structure cannot be obtained crystallographically. Several nanotube and nanowire models were fit to the PDF data. The resulting best-fit model structure consists of nanowires of Mo{sub 6} octahedra that are bridged by sulfur and terminated on the outside by iodine. This demonstrates the power of total scattering methods in accurately resolving structural issues in nanostructured materials where traditional crystallographic methods fail.
Meral, Cagla [Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720 (United States); Benmore, C.J. [X-ray Science Division, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, Illinois 60439 (United States); Monteiro, Paulo J.M., E-mail: monteiro@berkeley.edu [Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720 (United States)
2011-07-15
Significant progress was achieved with the application of Rietveld method to characterize the crystalline phases in portland cement paste. However, to obtain detailed information on the amorphous or poorly crystalline phases, it is necessary to analyze the total scattering data. The pair distribution function (PDF) method has been successfully used in the study of liquids and amorphous solids. The method takes the Sine Fourier transform of the measured structure factor over a wide momentum transfer range, providing a direct measure of the probability of finding an atom surrounding a central atom at a radial distance away. The obtained experimental characteristic distances can be also used to validate the predictions by the theoretical models, such as, molecular dynamics, ab initio simulations and density functional theory. The paper summarizes recent results of PDF analysis on silica fume, rice husk ash, fly ash, ASR gel, C-S-H and geopolymers.
Chunglee Kim; Vassiliki Kalogera; Duncan R. Lorimer; Tiffany White
2004-08-10
We consider the statistics of pulsar binaries with white dwarf companions (NS-WD). Using the statistical analysis method developed by Kim et al. (2003) we calculate the Galactic coalescence rate of NS-WD binaries due to gravitational-wave emission. We find that the most likely values for the total Galactic coalescence rate (R_tot) of NS-WD binaries lie in the range 0.2--10 per Myr depending on different assumed pulsar population models. For our reference model, we obtain R_tot=4.11_(-2.56)^(+5.25) per Myr at a 68% statistical confidence level. These rate estimates are not corrected for pulsar beaming and as such they are found to be about a factor of 20 smaller than the Galactic coalescence rate estimates for double neutron star systems. Based on our rate estimates, we calculate the gravitational-wave background due to coalescing NS-WD binaries out to extragalactic distances within the frequency band of the Laser Interferometer Space Antenna. We find the contribution from NS-WD binaries to the gravitational-wave background to be negligible.
ERIC Educational Resources Information Center
Miller, Pat
2005-01-01
Cold February weather and pancakes are a traditional pairing. Pancake Day began as a way to eat up the foods that were abstained from in Lent--traditionally meat, fat, eggs and dairy products. The best-known pancake event is The Pancake Day Race in Buckinghamshire, England, which has been run since 1445. This column describes pairs of books that…
Neutron coincidence imaging for active and passive neutron assays
Estep, R. J. (Robert J.); Brunson, G. S. (Glenn S.); Melton, S. G. (Sheila G.)
2001-01-01
Neutron multiplicity assay algorithms for {sup 240}Pu assume a point source of fission neutrons that are detected in a single detector channel. The {sup 240}Pu in real waste, however, is more likely to be distributed throughout the container in some random way. For different reasons, this leads to significant errors when using either multiplicity or simpler coincidence analyses. Reduction of these errors can be achieved using tomographic imaging. In this talk we report on our results from using neutron singles and coincidence data between tagged detector pairs to provide enhanced tomographic imaging capabilities to a crate nondestructive assay system. Only simulated passive coincidence data is examined here, although the higher signal rates from active coincidence counting hold more promise for waste management. The active coincidence approach has significantly better sensitivity than the passive and is not significantly perturbed by (alpha,n) contributions. Our study was based primarily on simulated neutron pulse trains derived from the Los Alamos SIM3D software, which were subjected to analysis using the Los Alamos CTEN-FIT and TGS-FIT software. We found significantly improved imaging capability using the coincidence and singles rate data than could be obtained using the singles rate alone.
King, Graham, E-mail: gking@lanl.gov [Lujan Neutron Scattering Center, Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545 (United States)] [Lujan Neutron Scattering Center, Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545 (United States); Ramezanipour, Farshid [Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1 (Canada)] [Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1 (Canada); Llobet, Anna [Lujan Neutron Scattering Center, Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545 (United States)] [Lujan Neutron Scattering Center, Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545 (United States); Greedan, John E. [Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1 (Canada)] [Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1 (Canada)
2013-02-15
The local structures of the oxygen deficient perovskites Sr{sub 2}FeMnO{sub 5}, Sr{sub 2}FeMnO{sub 5.5}, and Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} have been analyzed using neutron pair distribution function data. The results show that locally all three structures are more complex than implied by their average cubic structures and that the distributions of oxygen vacancies are not completely random on a local level. For both Sr{sub 2}FeMnO{sub 5+y} compounds it is found that there is no short range ordering of the Fe and Mn cations. For Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} there is evidence to suggest that the Fe/Cr distribution is not completely random and is locally ordered such that there are fewer Fe--Fe nearest neighbor pairs than in a random distribution. Reverse Monte Carlo modeling of the pair distribution function data has provided the Fe--O, Mn--O, and Cr--O bond length distributions and information on the coordination numbers of the Fe, Mn, and Cr cations. In Sr{sub 2}FeMnO{sub 5} it is found that the Fe{sup 3+} cations are most often in 4-fold coordination but there is also a large amount of Fe{sup 3+} in 5-fold coordination and a small amount in 6-fold coordination. The Mn{sup 3+} is split between 5-fold and 6-fold coordination. The Mn--O bond length distributions indicate that the Mn{sup 3+}O{sub 6} octahedra and Mn{sup 3+}O{sub 5} square pyramids are locally Jahn-Teller distorted. In Sr{sub 2}FeMnO{sub 5.5} the Fe{sup 3+} is almost entirely 5 coordinate while the Mn{sup 4+} is almost entirely 6 coordinate. The Cr{sup 3+} in Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} is almost entirely 6-fold coordinated, giving the Fe{sup 3+} an average coordination number of 4.67. In Sr{sub 2}FeMnO{sub 5} and Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} the Fe{sup 3+} and Sr{sup 2+} cations undergo local displacements which are driven by the oxygen vacancies, while the Mn{sup 3+} and Cr{sup 3+} cations remain near their positions in the average structures. In Sr{sub 2}FeMnO{sub 5.5} these cations are not significantly displaced. The local coordination geometries are used to explain previously observed but yet poorly understood magnetic properties of these materials. - Graphical abstract: The actual bond angle distributions in the cubic perovskite Sr{sub 2}FeMnO{sub 5} obtained from reverse Monte Carlo modeling of the local structure using neutron pair distribution function data. Highlights: Black-Right-Pointing-Pointer No long range ordering of oxygen vacancies, but short range order is present. Black-Right-Pointing-Pointer No short range Fe/Mn order but short range Fe/Cr order is present. Black-Right-Pointing-Pointer Fe tends to have lower coordination numbers while Mn and Cr have higher ones. Black-Right-Pointing-Pointer Local bond distances and bond angles have been determined. Black-Right-Pointing-Pointer Local structures can help explain long range magnetic ordering behavior.
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
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.
Sukhovoj, A. M., E-mail: suchovoj@nf.jinr.ru; Khitrov, V. A., E-mail: khitrov@nf.jinr.ru [Joint Institute for Nuclear Research (Russian Federation)
2013-01-15
A modified model is developed for describing the distribution of random resonance width for any nuclei. The model assumes the coexistence in a nucleus of one or several partial radiative and neutron amplitudes for respective resonance widths, these amplitudes differing in their parameters. Also, it is assumed that amplitude can be described by a Gaussian curve characterized by a nonzero mean value and a variance not equal to unity and that their most probable values can be obtained with the highest reliability from approximations of cumulative sums of respective widths. An analysis of data for 157 sets of neutron widths for 0 {<=} l {<=} 3 and for 56 sets of total radiative widths has been performed to date. The basic result of this analysis is the following: both for neutron and for total radiative widths, the experimental set of resonance width can be represented with a rather high probability in the form of a superposition of k {<=} 4 types differing in mean amplitude parameters.
The ITER radial neutron camera: An updated neutronic analysis
Fabio Moro; Luigino Petrizzi; Giorgio Brolatti; Basilio Esposito; Daniele Marocco; Rosaria Villari
2009-01-01
The radial neutron camera (RNC) will provide the spatial distribution and the total strength of the ITER neutron source (emissivity profile and fusion power) by means of collimated neutron measurements. Line-integrated neutron spectral measurements can also provide information on the ion temperature profile. The present design of the RNC consists of two collimating structures for a full coverage of the
Super Cool! Neutrons! (Ultracold Neutrons)
Martin, Jeff
Super Cool! Neutrons! (Ultracold Neutrons) Jeff Martin University of Winnipeg UM Physics Foundation for Innovation Manitoba Research & Innovation Fund #12; Ultracold Neutrons What are neutrons? Why are they important? How to make lots of neutrons. Interesting properties of ultracold neutrons
Pairing and Isospin Dependence of Chaos in Nuclei
NASA Astrophysics Data System (ADS)
Gómez, J. M. G.; Molina, R.; Retamosa, J.
2003-06-01
Shell-model energy spectra of Ca, Sc and Ti isotopes are analyzed using standard statistics such as the nearest level spacing distribution and the Dyson-Mehta ?3. For all the Ca isotopes, in the ground state region the energy level fluctuations show strong deviations from GOE predictions. When one or two neutrons are replaced by protons, Sc is closer to GOE and Ti is even more chaotic. Thus we find a clear isospin dependence in the degree of nuclear chaoticity. It is also shown that the pairing force is largely responsible for the quasiregular motion in the ground state region of Ca isotopes.
Eulerian pairs on Fibonacci words
Li, Teresa X S; Miao, Melissa Y F
2011-01-01
In their recent study of Mahonian pairs, Sagan and Savage introduced the notion of Eulerian pairs. A pair $(S,T)$ of two finite sets of words is said to be an Eulerian pair if the distribution of the descent number over $S$ equals the distribution of the excedance number over $T$. Let $\\Phi_1$ denote Foata's first fundamental transformation and $\\Psi$ denote a bijection of Han on words. We observe that $\\Phi_1$ and $\\Psi$ coincide when restricted to words on $\\{1,2\\}$. Using the inverse of $\\Phi_1$ or $\\Psi$ for words on $\\{1, 2\\}$, we obtain Eulerian pairs on Fibonacci words, where a Fibonacci word is defined to be a word on $\\{1,2\\}$ with no consecutive ones. By modifying a bijection of Steingr\\'{\\i}msson, we find another Eulerian pair on Fibonacci words.
Baldik, R.; Aytekin, H., E-mail: huseyinaytekin@gmail.co [Zonguldak Karaelmas University, Department of Physics (Turkey); Tel, E. [Gazi University, Department of Physics (Turkey)
2010-01-15
The proton and neutron densities, root-mean-square (rms) radii of proton density and neutron density, and neutron skin thickness of {sup 4-10}He, {sup 6-11}Li, and {sup 7-12}Be isotopes are calculated using Skyrme-Hartree-Fock method with SLy4, SLy5, SLy6, and SLy7 force parameters. The evaluated results are compared with experimental data. Also, the results of halo nuclei ({sup 6,8}He, {sup 11}Li, and {sup 11}Be) are compared with the results of other isotopes for selected nuclei having the same neutron configuration.
C. Kim; V. Kalogera; D. R. Lorimer
2002-10-21
Estimates of the Galactic coalescence rate (R) of close binaries with two neutron stars (NS-NS) are known to be uncertain by large factors (about two orders of magnitude) mainly due to the small number of systems detected as binary radio pulsars. We present an analysis method that allows us to estimate the Galactic NS-NS coalescence rate using the current observed sample and, importantly, to assign a statistical significance to these estimates and to calculate the allowed ranges of values at various confidence levels. The method involves the simulation of selection effects inherent in all relevant radio pulsar surveys and a Bayesian statistical analysis for the probability distribution of the rate. The most likely values for the total Galactic coalescence rate (R_peak) lie in the range 2-60 per Myr depending on different pulsar population models. For our reference model 1, where the most likely estimates of pulsar population properties are adopted, we obtain R_tot = 8_{-5}^{+9} per Myr at a 68% statistical confidence level. The corresponding range of expected detection rates of NS-NS inspiral are 3_{-2}^{+4}x10^{-3} per yr for the initial LIGO and 18_{-11}^{+21} per yr for the advanced LIGO.
Evolution of fission-fragment mass distributions in the neutron-deficient lead region
NASA Astrophysics Data System (ADS)
Ghys, L.; Andreyev, A. N.; Huyse, M.; Van Duppen, P.; Sels, S.; Andel, B.; Antalic, S.; Barzakh, A.; Capponi, L.; Cocolios, T. E.; Derkx, X.; De Witte, H.; Elseviers, J.; Fedorov, D. V.; Fedosseev, V. N.; Hessberger, F. P.; Kalaninová, Z.; Köster, U.; Lane, J. F. W.; Liberati, V.; Lynch, K. M.; Marsh, B. A.; Mitsuoka, S.; Möller, P.; Nagame, Y.; Nishio, K.; Ota, S.; Pauwels, D.; Page, R. D.; Popescu, L.; Radulov, D.; Rajabali, M. M.; Randrup, J.; Rapisarda, E.; Rothe, S.; Sandhu, K.; Seliverstov, M. D.; Sjödin, A. M.; Truesdale, V. L.; Van Beveren, C.; Van den Bergh, P.; Wakabayashi, Y.; Warda, M.
2014-10-01
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.
NASA Astrophysics Data System (ADS)
Wang, J. G.
2006-01-01
We have performed 3D computing simulations to study the magnetic field distribution of the injection chicane dipoles in the SNS accumulator ring. The simulations yield the performance characteristics of the magnets and generate the magnetic field data in three dimensional grids for further beam tracking study. Based on the simulation data, a 3D multipole expansion of the chicane dipole field, consisting of the generalized gradients and their derivatives, has been made. The harmonic and pseudoharmonic components in the expansion give much insight into the magnet physics and can fit directly into theoretical frame work of beam optics. The expansion is quasianalytical by fitting numeric data into interpolation functions. A 5th-order representation of the magnetic field is generated, and the effects of even higher-order terms on the field representation are discussed.
Kostal, M.; Juricek, V.; Rypar, V.; Svadlenkova, M. [Research Center Rez Ltd., 250 68 Husinec-Rez 130 (Czech Republic); Cvachovec, F. [Univ. of Defence, Kounicova 65, 662 10 Brno (Czech Republic)
2011-07-01
The power density distribution in a reactor has significant influence on core structures and pressure vessel mechanical resistance, as well as on the physical characteristics of nuclear fuel. This quantity also has an effect on the leakage neutron and photon field. This issue has become of increasing importance, as it touches on actual questions of the VVER nuclear power plant life time extension. This paper shows the comparison of calculated and experimentally determined pin by pin power distributions. The calculation has been performed with deterministic and Monte Carlo approaches. This quantity is accompanied by the neutron and photon flux density calculation and measurements at different points of the light water zero-power (LR-0) research reactor mock-up core, reactor built-in component (core barrel), and reactor pressure vessel and model. The effect of the different data libraries used for calculation is discussed. (authors)
Chaudhuri, Santanu; Chupas, Peter; Morgan, Benjamin J; Madden, Paul A; Grey, Clare P
2006-11-21
Cubic nanoparticles of alpha-AlF(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-)(n) ring structures were observed in addition to the 4-membered rings seen in bulk alpha-AlF(3). These 3 and 5 membered ring structures are, however, present in other metastable forms of AlF(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(2)O(3), nanoparticles of AlF(3) prepared by plasma routes and alpha- and beta-AlF(3). Broad peaks between 3.3 and 4.5 A in the PDF plots of the fluorinated Al(2)O(3) and the nanoparticles indicate a distribution of Al-F distances arising from Al and F atoms in connected AlF(6) octahedra; this is consistent with the presence of ring structures other than those found in alpha-AlF(3). PMID:17091155
A background-free direction-sensitive neutron detector
Roccaro, Alvaro
We show data from a new type of detector that can be used to determine the neutron flux, the energy distribution, and the direction of motion neutron for both fast and thermal neutrons. Many neutron detectors are plagued ...
NASA Astrophysics Data System (ADS)
Kim, Hyunjeong; Bozin, Emil; Malliakas, Christos; Kanatzidis, Mercouri; Billinge, Simon; Dabrowski, Bogdan; Gutmann, Matthias
2007-03-01
The atomic pair distribution function (PDF) analysis [1], based on total scattering approach, is used to study the CDW state, one of the fundamental broken-symmetry ground-states of metals, commonly found in complex materials. Incommensurate CDW (IC-CDW) found in 2-D tellurium square-net in CeTe3 is a simple single-q CDW driven by Fermi-surface nesting. Our recent PDF study on local distortions in CeTe3 suggests that the IC-CDW in CeTe3 at 300K consists of commensurate CDW domains separated by discommensurations, rather than being a uniform incommensurate CDW as seen crystallographically [2]. Recent PDF results of a study of the local Peierls distortions in isostructural compounds SmTe3 and HoTe3 will be presented. The PDF analysis has also been extended to probe the CDW state in K doped BaBiO3, and a report on the current state of this study will be provided. [1] T. Egami & S. J. L. Billinge, Underneath the Bragg Peaks: Structural Analysis of Complex Materials, Pergamon Press Elsevier, Oxford, England, 2003 [2] H. J. Kim et al., Phys. Rev. Lett. 96, 226401 (2006)
NASA Technical Reports Server (NTRS)
Achilles, C. N.; Bish, D. L.; Rampe, E. B.; Morris, R. V.
2015-01-01
Soils on Mars have been analyzed by the Mars Exploration Rovers (MER) and most recently by the Mars Science Laboratory (MSL) rover. Chemical analyses from a majority of soil samples suggest that there is a relatively uniform global soil composition across much of the planet. A soil site, Rocknest, was sampled by the MSL science payload including the CheMin X-ray diffractometer and the Alpha Particle X-ray Spectrometer (APXS). Che- Min X-ray diffraction (XRD) data revealed crystalline phases and a broad, elevated background, indicating the presence of amorphous or poorly ordered materials (Fig 1). Based on the chemical composition of the bulk soil measured by APXS and the composition of crystalline phases derived from unit-cell parameters determined with CheMin data, the percentages of crystalline and amorphous phases were calculated at 51% and 49%, respectively. Attempts to model the amorphous contribution to CheMin XRD patterns were made using amorphous standards and full-pattern fitting methods and show that the broad, elevated background region can be fitted by basaltic glass, allophane, and palagonite. However, the modeling shows only that these phases have scattering patterns similar to that for the soil, not that they represent unique solutions. Here, we use pair distribution function (PDF) analysis to determine the short-range order of amorphous analogs in martian soils and better constrain the amorphous material detected by CheMin.
Chen, Shuang; Sheikh, Ahmad Y; Ho, Raimundo
2014-12-01
Pharmaceutical unit operations such as milling and compaction can often generate disordered regions in crystals of active pharmaceutical ingredients (APIs). This may lead to changes in a number of important pharmaceutical properties including dissolution, stability, hygroscopicity, and so on. It is therefore important for pharmaceutical industry to evaluate the effects of pharmaceutical processing on API structural orders, and to investigate and develop analytical tools that are capable of accurately detecting and assessing subtle process-induced structural disorders in pharmaceutical crystals. In this study, nanoindentation was first used to determine the intrinsic mechanical properties including hardness and Young's modulus of two API crystals, compounds 1 and 2. These crystals of different mechanical properties were then milled and compacted under various conditions. The resulting structural disorders in these crystals were subsequently evaluated using synchrotron-based high-resolution total scattering pair distribution function (TS-PDF) analysis. Furthermore, principal component analysis was applied to the PDF data to assess the relative extents of disorders in the API crystals, which showed a good correlation with the process conditions. The study demonstrates that high-resolution TS-PDF analysis coupled with nanoindentation measurement is a valuable and effective tool for detecting and assessing process-induced subtle structural disorders in API crystals. PMID:25331822
Allan, P. K.; Chapman, K. W.; Chupas, P. J.; Hriljac, J. A.; Renouf, C. L.; Lucas, T. C. A.; Morris, R. E. (X-Ray Science Division); (Univ. of St. Andrews); (Univ. of Birmingham)
2012-01-01
Flexible metal-organic frameworks (MOFs) are materials of great current interest. A small class of MOFs show flexibility driven by reversible bonding rearrangements that lead directly to unusual properties. Cu-SIP-3 is a MOF based on the 5-sulfoisophthalate ligand, where the strong copper-carboxylate bonds ensure that the three-dimensional integrity of the structure is retained while allowing bonding changes to occur at the more weakly bonding sulfonate group leading to unusual properties such as the ultra-selective adsorption of only certain gases. While the integrity of the framework remains intact during bonding changes, crystalline order is not retained at all times during the transformations. X-Ray diffraction reveals that highly crystalline single crystals lose order during the transformation before regaining crystallinity once it is complete. Here we show how X-ray pair distribution function analysis can be used to reveal the mechanism of the transformations in Cu-SIP-3, identifying the sequence of atomic displacements that occur in the disordered phase. A similar approach reveals the underlying mechanism of Cu-SIP-3's ultra-selective gas adsorption.
Rademacher, Nadine; Bayarjargal, Lkhamsuren; Morgenroth, Wolfgang; Winkler, Björn; Ciezak-Jenkins, Jennifer; Batyrev, Iskander G; Milman, Victor
2014-09-01
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
Robert J. Elliott; John Van Der Hoek; William P. Malcolm
2005-01-01
‘Pairs Trading’ is an investment strategy used by many Hedge Funds. Consider two similar stocks which trade at some spread. If the spread widens short the high stock and buy the low stock. As the spread narrows again to some equilibrium value, a profit results. This paper provides an analytical framework for such an investment strategy. We propose a mean-reverting
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
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.
R. Baldik; H. Aytekin; E. Tel
2010-01-01
The proton and neutron densities, root-mean-square (rms) radii of proton density and neutron density, and neutron skin thickness\\u000a of 4–10He, 6–11Li, and 7–12Be isotopes are calculated using Skyrme-Hartree-Fock method with SLy4, SLy5, SLy6, and SLy7 force parameters. The evaluated\\u000a results are compared with experimental data. Also, the results of halo nuclei (6,8He, 11Li, and 11Be) are compared with the results
BNCT dose distribution in liver with epithermal D–D and D–T fusion-based neutron beams
H. Koivunoro; D. L. Bleuel; U. Nastasi; T. P. Lou; J. Reijonen; K.-N. Leung
2004-01-01
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 2H(d,n)3He (D–D) or 3H(t,n)4He (D–T) fusion reactions are being developed. Preliminary simulations of the applicability of 2.45MeV
Chapman, K. W.; Chupas, P. J.; X-Ray Science Division
2009-01-01
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.
Accelerator neutron source for boron neutron capture therapy
Wang, C.K.; Blue, T.E.; Blue, J.W.; Gahbauer, R.A.
1987-01-01
If boron neutron capture therapy (BNCT) is to be widely used to treat patients with brain tumors, then a hospital-based neutron source must be developed. Accelerator neutron sources for BNCT have been proposed as alternatives to nuclear reactor beams. The ideal neutron source for BNCT is a monoenergetic neutron beam with a neutron energy that is above thermal energies but below approx. 10 keV. The optimum neutron energy is currently being studied. The purpose of this paper is to report the results of a Monte Carlo analysis of the performance of an accelerator neutron source for the treatment of brain tumors by BNCT. The proton beam is identical. Thicknesses of moderators are identified that yield neutron energy spectra which produce within a head phantom distributions of absorbed dose approaching the distributions that would be attained with the above-mentioned ideal spectra.
Frustrated Cooper pairing and the f-wave supersolidity
Hsiang-Hsuan Hung; Wei-Cheng Lee; Congjun Wu
2010-01-01
Geometric frustration in quantum magnetism refers to that magnetic interactions on different bonds cannot be simultaneously minimized. The usual Cooper pairing systems favor the uniform distribution of the pairing phase among lattice sites without frustration. In contrast, we propose ``frustrated Cooper pairing'' in non-bipartite lattices which leads to frustrated supersolid states with non-uniform distributions of the Cooper pair phase and
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
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.
Nohtomi, Akihiro
2012-01-01
Cone-like acryl converters have been used for transforming the energy-distribution information of incident fast neutrons into the spatial-distribution information of recoil protons. The characteristics of neutron-proton conversion have been studied up to around 10MeV by using an imaging plate (IP). A notable and interesting signal enhancement due to recoil protons generated in an acrylic converter was observed on IP images for irradiation with a 252Cf source. A Monte Carlo calculation was carried out in order to understand the spatial distributions of the signal enhancement by recoil protons; these distributions promisingly involve the energy information of incident neutrons in principle. Consequently, it has been revealed that the neutron energy evaluation is surely possible by analyzing the spatial distributions of signal enhancement that is caused by recoil protons. PMID:24592683
Prompt Neutrons from Thorium Photofission
C. P. Sargent; W. Bertozzi; P. T. Demos; J. L. Matthews; W. Turchinetz
1965-01-01
We have measured the distribution in angle and velocity of the prompt neutrons from the bremsstrahlung-induced photofission of Th232 in the photon energy region near threshold. Using knowledge of the fission-fragment angular distribution, the data have been interpreted in terms of the neutron distribution relative to the fragment axis. The measurement allows a quantitative estimate of the fraction of neutrons
Young-Il Kim; Katharine Page; Andi M. Limarga; David R. Clarke; Ram Seshadri
2007-01-01
The local structures of Zn1-xMgxO alloys have been studied by Raman spectroscopy and by synchrotron x-ray pair-distribution-function (PDF) analysis. Within the solid solution range (0<=x<=0.15) of Zn1-xMgxO , the wurtzite framework is maintained with Mg homogeneously distributed throughout the wurtzite lattice. The E2high Raman line of Zn1-xMgxO displays systematic changes in response to the evolution of the crystal lattice upon
C. Kim; V. Kalogera; D. R. Lorimer
2003-01-01
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
Sharifi, Monir; Wallacher, Dirk
2012-01-01
Summary Periodic mesoporous materials of the type (R?O)3Si-R-Si(OR?)3 with benzene as an organic bridge and a crystal-like periodicity within the pore walls were functionalized with SO3H or SO3 ? groups and investigated by small-angle neutron scattering (SANS) with in situ nitrogen adsorption at 77 K. If N2 is adsorbed in the pores the SANS measurements show a complete matching of all of the diffraction signals that are caused by the long-range ordering of the mesopores in the benzene-PMO, due to the fact that the benzene-PMO walls possess a neutron scattering length density (SLD) similar to that of nitrogen in the condensed state. However, signals at higher q-values (>1 1/Å) are not affected with respect to their SANS intensity, even after complete pore filling, confirming the assumption of a crystal-like periodicity within the PMO material walls due to ?–? interactions between the organic bridges. The SLD of pristine benzene-PMO was altered by functionalizing the surface with different amounts of SO3H-groups, using the grafting method. For a low degree of functionalization (0.81 mmol SO3H·g?1) and/or an inhomogeneous distribution of the SO3H-groups, the SLD changes only negligibly, and thus, complete contrast matching is still found. However, for higher amounts of SO3H-groups (1.65 mmol SO3H·g?1) being present in the mesopores, complete matching of the neutron diffraction signals is no longer observed proving that homogeneously distributed SO3H-groups on the inner pore walls of the benzene-PMO alter the SLD in a way that it no longer fits to the SLD of the condensed N2. PMID:23016147
Sunil, C.; Nandy, Maitreyee; Sarkar, P. K. [Accelerator Radiation Safety Section, RSSD, Bhabha Atomic Research Centre, Mumbai 400085 (India); Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064 (India); H.P. Unit (RSSD, BARC), Variable Energy Cyclotron Centre, 1/AF, Bidhannagar, Kolkata 700064 (India)
2008-12-15
Energy distributions of emitted neutrons were measured for 110 MeV {sup 19}F ions incident on a thick {sup 27}Al target. Measurements were done at 0 deg., 30 deg., 60 deg., 90 deg., and 120 deg. with respect to the projectile direction employing the time-of-flight technique using a proton recoil scintillation detector. Comparison with calculated results from equilibrium nuclear reaction model codes like PACE-2 and EMPIRE 2.18 using various level-density options was carried out. It is observed that the dynamic level-density approach in EMPIRE 2.18 gives the closest approximation to the measured data. In the Fermi-gas level-density approach the best approximation of the level-density parameter is a=A/12.0, where A is the mass number of the composite system. The trend in the angular distribution of emitted neutrons is well reproduced by the projection of the angular momentum on the recoil axis as done in the PACE-2 code.
Neutron angular correlations in spontaneous and neutron-induced fission
NASA Astrophysics Data System (ADS)
Vogt, R.; Randrup, J.
2014-12-01
Background: Neutron emission is correlated in fission events because, on average, more than one neutron is emitted per fission. Measurements of these correlations, coupled with studies of more inclusive observables such as neutron multiplicity, provide sensitive information about the fission mechanism. Neutron-neutron angular correlations have been studied in both spontaneous fission of 252Cf and neutron-induced fission of 235U. These correlations, until recently incalculable in most available simulations of fission, can now be calculated in event-by-event simulations of fission. Purpose: Phenomenological studies of fission are of interest both for basic science and for practical applications. Neutron-neutron angular correlations are characteristic of the fissioning isotope and could be used in material identification. Method: We use our model of complete fission events, freya, to first study the sensitivity of two-neutron angular correlations to the model inputs and then compare to available data. We also compare our simulations to neutron-fragment angular correlations. Results: We find that the correlations calculated with freya are fairly robust with respect to the input parameters. Any strong deviations in the correlations result in poor agreement with measured inclusive neutron observables such as neutron multiplicity as a function of fragment mass and the neutron multiplicity distribution. The agreement of freya with the present set of correlation data is found to be good. Conclusions: freya can be used to reliably predict neutron-neutron angular correlations and could then be used to identify materials.
Di-neutron correlation in light neutron-rich nuclei
K. Hagino; H. Sagawa; P. Schuck
2008-12-03
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.
Saxena, A.; Kailas, S.; Karnik, A.; Kapoor, S.S. (Nuclear Physics Division, Bhabha Atomic Research Centre, Bombay 400 085 (India))
1993-01-01
Earlier calculations of fission fragment anisotropies made with the use of the standard saddle point statistical model have been corrected to include the effects of prefission neutron emission. These calculations are compared with the data reported earlier for the fissioning systems formed by projectile-target combinations of [sup 10]B, [sup 12]C, [sup 16]O, and [sup 19]F on [sup 232]Th and [sup 237]Np and [sup 9]Be on [sup 232]Th. It is seen that for these systems the conclusions reached earlier regarding the entrance channel dependence of the fission fragment anisotropy as a function of mass (charge) asymmetry are not affected by the inclusion of corrections due to prefission neutron emission.
A. Saxena; S. Kailas; A. Karnik; S. S. Kapoor
1993-01-01
Earlier calculations of fission fragment anisotropies made with the use of the standard saddle point statistical model have been corrected to include the effects of prefission neutron emission. These calculations are compared with the data reported earlier for the fissioning systems formed by projectile-target combinations of 10B, 12C, 16O, and 19F on 232Th and 237Np and 9Be on 232Th. It
V. P. Pikul; U. Yu. Jovliev; Yu. N. Koblik; A. V. Khugaev; A. I. Muminov; A. K. Nasirov; K. V. Pavliy; B. S. Yuldashev
2005-01-01
The fragment mass yields in fission of 235U induced by thermal neutrons for A = 145–160 and E\\u000a K = 50–75 MeV were measured using a mass spectrometer. The fine structure is observed at A = 153, 154 and E\\u000a K = 50–60 MeV. The obtained results were described in the framework of a model based on the dinuclear system
Gamow-Teller response in deformed even and odd neutron-rich Zr and Mo isotopes
NASA Astrophysics Data System (ADS)
Sarriguren, P.; Algora, A.; Pereira, J.
2014-03-01
?-decay properties of neutron-rich Zr and Mo isotopes are investigated within a microscopic theoretical approach based on the proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme Hartree-Fock calculations with pairing correlations. Residual separable particle-hole and particle-particle forces are also included in the formalism. The structural evolution in these isotopic chains including both even and odd isotopes is analyzed in terms of the equilibrium deformed shapes. Gamow-Teller strength distributions, ?-decay half-lives, and ?-delayed neutron-emission probabilities are studied, stressing their relevance to describe the path of the nucleosynthesis rapid neutron capture process.
Gamow-Teller response in deformed even and odd neutron-rich Zr and Mo isotopes
Sarriguren, P; Pereira, J
2014-01-01
Beta-decay properties of neutron-rich Zr and Mo isotopes are investigated within a microscopic theoretical approach based on the proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme Hartree-Fock calculations with pairing correlations. Residual separable particle-hole and particle-particle forces are also included in the formalism. The structural evolution in these isotopic chains including both even and odd isotopes is analyzed in terms of the equilibrium deformed shapes. Gamow-Teller strength distributions, beta-decay half-lives, and beta-delayed neutron-emission probabilities are studied, stressing their relevance to describe the path of the nucleosynthesis rapid neutron capture process.
Gamow-Teller response in deformed even and odd neutron-rich Zr and Mo isotopes
P. Sarriguren; A. Algora; J. Pereira
2014-03-05
Beta-decay properties of neutron-rich Zr and Mo isotopes are investigated within a microscopic theoretical approach based on the proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme Hartree-Fock calculations with pairing correlations. Residual separable particle-hole and particle-particle forces are also included in the formalism. The structural evolution in these isotopic chains including both even and odd isotopes is analyzed in terms of the equilibrium deformed shapes. Gamow-Teller strength distributions, beta-decay half-lives, and beta-delayed neutron-emission probabilities are studied, stressing their relevance to describe the path of the nucleosynthesis rapid neutron capture process.
NASA Astrophysics Data System (ADS)
Hosokawa, S.; Bérar, J.-F.; Boudet, N.; Kohara, S.; Stellhorn, J.; Pilgrim, W.-C.; Zeidler, A.; Kato, H.; Kawakita, Y.; Otomo, T.
2014-04-01
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.
Gelina neutron target optimisation.
Flaska, M; Plompen, A J M; Mondelaers, W; Lathouwers, D; van der Hagen, T H J J; van Dam, H
2005-01-01
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
Neutron degeneracy and plasma physics effects on radiative neutron captures in neutron star crust
P. S. Shternin; M. Beard; M. Wiescher; D. G. Yakovlev
2012-07-25
We consider the astrophysical reaction rates for radiative neutron capture reactions ($n,\\gamma$) in the crust of a neutron star. The presence of degenerate neutrons at high densities (mainly in the inner crust) can drastically affect the reaction rates. Standard rates assuming a Maxwell-Boltzmann distribution for neutrons can underestimate the rates by several orders of magnitude. We derive simple analytical expressions for reaction rates at a variety of conditions with account for neutron degeneracy. We also discuss the plasma effects on the outgoing radiative transition channel in neutron radiative capture reactions and show that these effects can also increase the reaction rates by a few orders of magnitude. In addition, using detailed balance, we analyze the effects of neutron degeneracy and plasma physics on reverse ($\\gamma,n$) photodisintegration. We discuss the dependence of the reaction rates on temperature and neutron chemical potential and outline the efficiency of these reactions in the neutron star crust.
Transport properties and neutrino emissivity of dense neutron-star matter with localized protons
D. A. Baiko; P. Haensel
1999-06-18
As pointed out by Kutschera and W{\\'o}jcik, very low concentration of protons combined with a specific density dependence of effective neutron-proton interaction could lead to a localization of ``proton impurities'' in neutron medium at densities exceeding four times normal nuclear matter density. We study consequences of the localization of protons for transport processes in dense neutron star cores, assuming random distribution of proton impurities. Kinetic equations, relevant for the transport of charge, heat and momentum, are solved using variational method. Localization of protons removes a T^{-2} factor from the transport coefficients, which leads, at lower temperatures, to a strong decrease of thermal conductivity, electrical conductivity and shear viscosity of neutron star matter, as compared to the standard case, where protons form a Fermi liquid. Due to the localization of protons a number of conventional neutrino emission processes (including modified URCA process) become inoperative in neutron star cores. On the other hand, the energy loss rate from neutrino-antineutrino pair bremsstrahlung due to electron and neutron scattering off (localized) protons, will have a specific T^6 dependence, which could modify the cooling of the neutron star core, as compared to the standard case. Possible astrophysical implications of the localization of protons for neutron star evolution and dynamics are discussed.
Shunsuke YONAI; Mamoru BABA; Toshiro ITOGA; Takashi NAKAMURA; Hitoshi YOKOBORI; Yoshihisa TAHARA
2007-01-01
In our previous study, the simulation of a cyclotron-based neutron field for boron neutron capture therapy (BNCT) using a (p,n) spallation source with the MCNPX code was validated through measurements of the neutron energy spectrum behind the moderator assembly and the thermal neutron distribution in an acrylic phantom using reaction rates of Au. These validations showed that the simulation generally
Conservation of Isospin in Neutron-Rich Fission Fragments
Ashok Kumar Jain; Deepika Choudhury; Bhoomika Maheshwari
2014-08-11
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.
beta-decay properties of neutron-rich Zr and Mo isotopes
Sarriguren, P. [Instituto de Estructura de la Materia, CSIC, Serrano 123, E-28006 Madrid (Spain); Pereira, J. [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48823 (United States)
2010-06-15
Gamow-Teller strength distributions, beta-decay half-lives, and beta-delayed neutron emission are investigated in neutron-rich Zr and Mo isotopes within a deformed quasiparticle random-phase approximation. The approach is based on a self-consistent Skyrme Hartree-Fock mean field with pairing correlations and residual separable particle-hole and particle-particle forces. Comparison with recent measurements of half-lives stresses the important role that nuclear deformation plays in the description of beta-decay properties in this mass region.
Beta-decay properties of Zr and Mo neutron-rich isotopes
P. Sarriguren; J. Pereira
2010-06-08
Gamow-Teller strength distributions, beta-decay half-lives, and beta-delayed neutron emission are investigated in neutron-rich Zr and Mo isotopes within a deformed quasiparticle random-phase approximation. The approach is based on a self-consistent Skyrme Hartree-Fock mean field with pairing correlations and residual separable particle-hole and particle-particle forces. Comparison with recent measurements of half-lives stresses the important role that nuclear deformation plays in the description of beta-decay properties in this mass region.
A neutron-diffraction study of tetramethylammonium chloride in aqueous solution
J. Turner; A. K. Soper; J. L. Finney
1990-01-01
Neutron diffraction with isotope substitution of nitrogen, chlorine and hydrogen nuclei is used to investigate the hydration region of both ions and the possibility of ion pairing in aqueous solutions of tetramethylammonium chloride (TMACl) at 0·5 m, 1·0 m and approximately 2·0 m concentration. The use of a maximum-entropy method to calculate the radial distribution functions is discussed. The H-H
Synthesize Neutron-Drip-Line-Nuclides with Free-Neutron Bose-Einstein Condensates Experimentally
Bao-Guo Dong
2014-09-22
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.
Momentum distributions in medium and heavy exotic nuclei
M. K. Gaidarov; G. Z. Krumova; P. Sarriguren; A. N. Antonov; M. V. Ivanov; E. Moya de Guerra
2009-11-12
We study nucleon momentum distributions of even-even isotopes of Ni, Kr, and Sn in the framework of deformed self-consistent mean-field Skyrme HF+BCS method, as well as of theoretical correlation methods based on light-front dynamics and local density approximation. The isotopic sensitivities of the calculated neutron and proton momentum distributions are investigated together with the effects of pairing and nucleon-nucleon correlations. The role of deformation on the momentum distributions in even-even Kr isotopes is discussed. For comparison, the results for the momentum distribution in nuclear matter are also presented.
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
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)
Shoulders in the very asymmetric mass distribution for reactor-neutron-induced fission of Â²Â³â¸U
V. K. Rao; V. K. Bhargava; S. G. Marathe; S. M. Sahakundu; R. H. Iyer
1979-01-01
New experimental data have been obtained on the cumulative yields of some short-lived very asymmetric products in the reactor-neutron-induced fission of Â²Â³â¸U. Fission yields of â·Â³Ga(tââ = 4.8 h), Â¹â¶â·Ho(tââ = 3.1 h), Â¹â·Â¹Er(tââ = 7.5 h), Â¹â·Â³Tm(tââ = 8.2 h), and Â¹â·â¹Lu(tââ = 4.6 h) are reported. These yields together with those reported earlier by us for other relatively
F. Bridges; C. H. Booth; T. H. Geballe; G. J. Snyder
1998-01-01
We have measured the width, sigma, of the Mn-O bond pair-distribution function in La_2\\/3Ba_1\\/3MnO_3, using the x-ray-absorption fine-structure (XAFS) technique. As found recently for the Ca substituted samples, we find that sigma^2 increases significantly near the ferromagnetic\\/metal-insulator transition temperature; in this case, the step in sigma^2 occurs above 300K. In addition we again find a simple relationship between the decrease
Neutrons for Catalysis Neutrons as
Pennycook, Steve
Neutrons for Catalysis Neutrons as Microscopic Probes in Heterogeneous Catalysis Juergen Eckert-situ reactor for neutron scattering #12;In-situ gas-loading cells are available for neutron scattering available: standard equipment to monitor catalytic reactions In-situ (or ,,semi in-situ) Neutron Scattering
Neutron Exposure Accelerator System For Biological Effect Experiments (NASBEE)
Takada, Masashi; Suda, Mitsuo; Kamada, So; Hagiwara, Takuya; Imaseki, Hitoshi; Hamano, Tsuyoshi [National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage-ku Chiba, Japan 263-8555 (Japan)
2011-06-01
The neutron exposure accelerator system for biological effect experiments (NASBEE) was developed to study biological effects of fast neutrons. We have characterized the NASBEE neutron beams with neutron energy spectrum, absorbed dose energy distributions, and space distributions. The neutron energy spectrum shows 2.3 MeV as mean energy and 3.0 MeV as kerma of tissue-equivalent-plastic (A150) weighted mean energy, and the maximum neutron energy was determined to be 9 MeV. Neutron absorbed doses occupy 82% of the NASBEE neutron beam. NASBEE has been used to learn some of the outcomes of the biological effects of fast neutrons.
NASA Astrophysics Data System (ADS)
Kuksenko, V.; Pareige, C.; Genevois, C.; Pareige, P.
2013-03-01
Segregations at some dislocations and grain boundaries in Fe-5%Cr, Fe-9%Cr and Fe-12%Cr model alloys of low purity after neutron irradiation at 300 °C up to 0.6 dpa have been analyzed with atom probe tomography. All dislocation lines and low- and high-angle grain boundaries (GBs) which have been observed were enriched with Cr, Si and P. The segregations reveal the different dislocation structures associated to different type of analysed GBs. Cr and Si atoms were found to be nonhomogenously distributed around the dislocation cores because of the non isotropic stress field induced by edge dislocation lines. Concerning GBs, precipitate free zones (PFZs) are exhibited around the planar defects which were analysed in Fe-9%Cr and Fe-12%Cr model alloys. These PFZ are size dependant with the nominal level of Cr.
Fairchild, R G; Kahl, S B; Laster, B H; Kalef-Ezra, J; Popenoe, E A
1990-08-15
A major problem remaining in the evaluation of boronated compounds for neutron capture therapy (NCT) is the need to know the intra- or extracellular microdistribution of boron. This is a consequence of the short range of the 10B(n,alpha)7Li reaction products (approximately 10 microns), such that biological efficacy is dependent upon intracellular distribution. In particular, if boron location is predominantly extracellular, a significant reduction in efficacy would be expected. The in vitro procedure described here was developed mainly to provide information regarding the intra- and extracellular location and concentration of boron. However, use of the technique also allows the measurement of compound uptake and retention (binding) and the determination of biological efficacy by the evaluation of survival curves obtained following irradiation with thermal neutrons. Comparison is made to results obtained with boric acid (H3(10)BO3) and to results calculated for various boron distributions. Concomitantly, an indication of compound toxicity can be obtained from the plating efficiency of unirradiated control cells. Currently, most investigators utilize in vivo systems for testing and evaluating boron uptake from various carrier molecules. Given the large number of boron compounds being synthesized and needing evaluation as to their usefulness for NCT, the in vitro technique described here is simple and advantageous for initial compound screening. In addition to sparing animal lives, it is both time and cost effective and utilizes much smaller quantities of test compound than are required for an in vivo assay. A boronated porphyrin (BOPP) evaluated by the above procedure shows an uptake and retention approximately 20 times that of sulfhydryl boron hydride monomer (BSH); the latter compound is currently being used clinically for NCT in Japan and is anticipated for use in clinical trials in the United States. If the advantages demonstrated by BOPP in these in vitro studies are validated in animal experiments, BOPP should be considered for clinical application. PMID:2379150
Pair Cascades and Deathlines in Offset Magnetic Dipole Fields
NASA Technical Reports Server (NTRS)
Harding, Alice; Muslimov, Alex
2010-01-01
We investigate electron-positron pair cascades in a dipole magnetic field whose axis is offset from the neutron star center. In such a field geometry, the polar cap is displaced from the neutron star symmetry axis and the field line radius of curvature is modified. Using the modified parallel electric field near the polar cap of an offset dipole, we simulate pair cascades to determine the pair deathlines and pair multiplicities as a function of the offset parameter. We find that the pair multiplicity can change dramatically with a modest offset, with a significant increase on one side of the polar cap. Lower pair deathlines allow a larger fraction of the pulsar population, that include old and millisecond pulsars, to produce cascades with high multiplicity.
Counting the number of correlated pairs in a nucleus
Vanhalst, Maarten; Cosyn, Wim; Ryckebusch, Jan [Department of Physics and Astronomy, Ghent University, Proeftuinstraat 86, B-9000 Gent (Belgium)
2011-09-15
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.
Neutron Compound Refractive Prisms - DOE SBIR Phase II Final Report
Dr. Jay Theodore Cremer, Jr
2011-06-25
The results of the research led to a pulsed electromagnetic periodic magnetic field array (PMF), which coupled with a pair of collimation slits, and a mechanical chopper slit, were able to deflect spin-up neutrons to a band of line-fused neutrons a focal plane heights that correspond to the time-varying magnetic field amplitude. The electromagnetic field PMF produced 5.4 pulses per minute in which each pulse was 50 msec in duration with a full width half maximum (FWHM) of 7.5 msec. The calculated 7.7 mm vertical height of the band of focused spin-up neutrons corresponded closely to the measured 7.5 mm height of the center line of the imaged band of neutrons. The band of deflected spin-up neutrons was 5 mm in vertical width and the bottom of the band was 5 mm above the surface of the PMF pole. The limited exposure time of 3 hours and the smaller 0.78 T magnetic field allowed focused and near focused neutrons of 1.8 Ã?Â?Ã?Â? to 2.6 Ã?Â?Ã?Â? 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 Ã?Â?Ã?Â?. 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. 313Ã?Â¢Ã?Â?Ã?Â?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.
Characterisation of neutron fields at Cernavoda NPP.
Cauwels, Vanessa; Vanhavere, Filip; Dumitrescu, Dorin; Chirosca, Alecsandru; Hager, Luke; Million, Marc; Bartz, James
2013-04-01
Near a nuclear reactor or a fuel container, mixed neutron/gamma fields are very common, necessitating routine neutron dosimetry. Accurate neutron dosimetry is complicated by the fact that the neutron effective dose is strongly dependent on the neutron energy and the direction distribution of the neutron fluence. Neutron field characterisation is indispensable if one wants to obtain a reliable estimate for the neutron dose. A measurement campaign at CANDU nuclear power plant located in Cernavoda, Romania, was set up to characterise the neutron fields in four different locations and to investigate the behaviour of different neutron personal dosemeters. This investigation intends to assist in choosing a suitable neutron dosimetry system at this nuclear power plant. PMID:22874895
Frustrated Cooper pairing and the $f$-wave supersolidity
Hsiang-hsuan Hung; Wei-Cheng Lee; Congjun Wu
2009-01-01
Geometric frustration in quantum magnetism refers to that magnetic interactions on different bonds cannot be simultaneously minimized. The usual Cooper pairing systems favor the uniform distribution of the pairing phase among lattice sites without frustration. In contrast, we propose \\
A local dynamic correlation function from inelastic neutron scattering
McQueeney, R.J.
1997-07-13
Information about local and dynamic atomic correlations can be obtained from inelastic neutron scattering measurements by Fourier transform of the Q-dependent intensity oscillations at a particular frequency. A local dynamic structure function, S(r,{omega}), is defined from the dynamic scattering function, S(Q,{omega}), such that the elastic and frequency-integrated limits correspond to the average and instantaneous pair-distribution functions, respectively. As an example, S(r,{omega}) is calculated for polycrystalline aluminum in a model where atomic motions are entirely due to harmonic phonons.
Coalescing binary neutron star systems
NASA Astrophysics Data System (ADS)
Calder, Alan C.; Swesty, F. Douglas; Wang, Edward Y. M.
2001-10-01
We present numerical studies of coalescing neutron star pairs with Newtonian hydrodynamics coupled to the 2.5 Post-Newtonian radiation reaction of Blanchet, Damour, and Schäfer [1]. Our simulations evolve the Euler equations using a modification of the ZEUS 2-D algorithm [2] and use a Fast Fourier Transformation method for solving the Poisson equation for the gravitational and radiation reaction potentials. We find that the radiation reaction produces a significant effect on a neutron star pair when compared to a purely Newtonian simulation. .
Neutron Matter from Low to High Density
Gandolfi, Stefano; Carlson, J
2015-01-01
Neutron matter is an intriguing nuclear system with multiple connections to other areas of physics. Considerable progress has been made over the last two decades in exploring the properties of pure neutron fluids. Here we begin by reviewing work done to explore the behavior of very low density neutron matter, which forms a strongly paired superfluid and is thus similar to cold Fermi atoms, though at energy scales differing by many orders of magnitude. We then increase the density, discussing work that ties the study of neutron matter with the determination of the properties of neutron-rich nuclei and neutron-star crusts. After this, we review the impact neutron matter at even higher densities has on the mass-radius relation of neutron stars, thereby making contact with astrophysical observations.
Neutron Matter from Low to High Density
Stefano Gandolfi; Alexandros Gezerlis; J. Carlson
2015-01-22
Neutron matter is an intriguing nuclear system with multiple connections to other areas of physics. Considerable progress has been made over the last two decades in exploring the properties of pure neutron fluids. Here we begin by reviewing work done to explore the behavior of very low density neutron matter, which forms a strongly paired superfluid and is thus similar to cold Fermi atoms, though at energy scales differing by many orders of magnitude. We then increase the density, discussing work that ties the study of neutron matter with the determination of the properties of neutron-rich nuclei and neutron-star crusts. After this, we review the impact neutron matter at even higher densities has on the mass-radius relation of neutron stars, thereby making contact with astrophysical observations.
Neutron energy measurements for impure plutonium samples
Rael, C. D. (Carlos D.); Menlove, Howard O.
2004-01-01
This report describes a technique used to measure the average neutron energy on impure plutonium samples. This measurement is done using the Epithermal Neutron Multiplicity Counter (ENMC). The measurement of neutron energy is done at the same time as the accountability or safeguards measurement. Neutron totals and coincidence measurements of plutonium have the problem that impurities present in sample add to the observed neutron counts because of alpha particle induced source neutrons and the related multiplication. The primary signal that is needed to measure the {sup 240}Pu effective mass is the spontaneous fission rate; however, induced fissions related to the impurities increase the observed response. In most cases, the (a,n) source neutrons have an energy distribution that is different than for spontaneous fission. Thus, the ability to measure the neutron energy distribution helps in the identification of impure plutonium samples. A description of the ENMC detector components and discussion on the average neutron energy calibration are provided.
Calculation of two-neutron multiplicity in photonuclear reactions
NASA Technical Reports Server (NTRS)
Norbury, John W.; Townsend, Lawrence W.
1989-01-01
The most important particle emission processes for electromagnetic excitations in nucleus-nucleus collisions are the ejection of single neutrons and protons and also pairs of neutrons and protons. Methods are presented for calculating two-neutron emission cross sections in photonuclear reactions. The results are in a form suitable for application to nucleus-nucleus reactions.
Neutron multiplicities in spontaneous fission and nuclear structure studies
Hamilton, J.H.; Kormicki, J.; Lu, Q. [Vanderbilt Univ., Nashville, TN (United States). Dept. of Physics and Astronomy] [and others
1993-12-31
New insights into the fission process can be gained by better quantitative knowledge of how the energy released in fission is distributed between the kinetic energy of the two fragments, the excitation energy of the two fragments and the number of neutrons emitted. Studies of prompt gamma-rays emitted in spontaneous fission (SF) with large arrays of Compton suppressed Ge detector arrays are providing new quantitative answers to longstanding questions concerning fission as well as new insights into the structure of neutron-rich nuclei. For the first time the triple gamma coincidence technique was employed in spontaneous fission studies. Studies of SF of {sup 252}Cf and {sup 242}Pu have been carried out. These {gamma}-{gamma}-{gamma} data provide powerful ways to identify uniquely gamma rays from a particular nucleus in the very complex gamma-ray spectra given off by the over 100 different nuclei produced. The emphasis of this paper is on the first quantitative measurements of the multiplicities of the neutrons emitted in SF and the energy levels populated in the fragments. Indeed, in the break up into Mo-Ba pairs, we have identified for the first time fragments associated with from zero up to ten neutrons emitted and observed the excited energy states populated in these nuclei. The zero neutron emission pairs like {sup 104}Mo- {sup 148}Ba, {sup 106}Mo- {sup 146}Ba and {sup 104}Zr- {sup 148}Ce observed in this work are particularly interesting because they represent a type of cold fission or a new mode of cluster radioactivity as proposed by Greiner, Sandulescu and co-workers. These data provide new insights into the processes of cluster radioactivity and cold fission.
Ibrahim, M A
2000-01-01
This work deals with the attenuation of fission neutrons by some hydrogeneous shield materials. The attenuated fission neutrons are described by the energy groups (fast, epithermal and thermal). The exponential decrease in the fast flux is represented by the removal cross section concept. Each of the epithermal and thermal fluxes is expressed using the diffusion equation including a pair of arbitrary constants to be determined using the corresponding boundary conditions. The solution obtained for the required arbitrary constants is then approximated in a simplified form such that it may easily replace the corresponding exact solution. The attenuation values, by which the neutron dose rate distributions are exponentially decreased through certain thicknesses are also determined for the given materials. They are compared to the corresponding experimental and theoretical data. The results obtained for the total neutron dose rate distributions in terms of a suitable range of layer thicknesses are then used to determine--for each material--an average value for the total neutron dose rate representing the exponential decrease during passage through the considered range of layer thicknesses. PMID:10670922
Pulsed neutron diffraction study on the short range structure of B 2O 3–Ag 2O glasses
Hideharu Ushida; Yasuhiko Iwadate; Takeo Hattori; Shin Nishiyama; Kazuko Fukushima; Masakatsu Misawa; Toshiharu Fukunaga
2001-01-01
The short range structure of (1?x)B2O3–xAg2O (x=0.05–0.30) glasses was investigated by time-of-flight neutron scattering experiments. Radial distribution analyses were applied to extract the structural information, but the structural parameters for each atomic pair were finally optimized in the Q-space. The bond distances of near neighbor B–O pairs were estimated at 0.138 and 0.145 nm, and the corresponding coordination numbers were
Electroweak bremsstrahlung from neutron-neutron scattering
Li Yi [College of Physics and Technology, Guangxi University, Nanning, Guangxi 530004 (China); Liou, M. K. [Department of Physics and Institute for Nuclear Theory, Brooklyn College of the City University of New York, Brooklyn, New York 11210 (United States); Schreiber, W. M. [Department of Physics, College of Staten Island of the City University of New York, Staten Island, New York 10314 (United States)
2009-09-15
Background: Nucleon-nucleon (NN) bremsstrahlung processes NN{gamma} (nn{gamma}, np{gamma}, and pp{gamma}) have been extensively investigated. Neutrino-pair bremsstrahlung processes from nucleon-nucleon scattering NN{nu}{nu} (nn{nu}{nu}, np{nu}{nu}, and pp{nu}{nu}) have recently attracted attention in studies of neutrino emission in neutron stars. The calculated NN{nu}{nu} cross sections (or emissivities) are found to be sensitive to the two-nucleon dynamical model used in the calculations. Purpose and Method: A realistic one-boson-exchange (ROBE) model for NN interactions is used to construct the electroweak bremsstrahlung amplitudes using the well-known nucleon electromagnetic and weak interaction vertices. The constructed nn{gamma} and nn{nu}{nu} amplitudes are investigated by applying them to calculate nn{gamma} and nn{nu}{nu} cross sections, respectively. Results: (i) The 190-MeV ROBE nn{gamma} cross sections agree well with those calculated using the TuTts amplitude, but they are in disagreement with those calculated using the Low amplitude. (ii) The calculated nn{nu}{nu} cross sections using the ROBE amplitude at the neutrino-pair energy {omega} = 1 MeV are in quantitative agreement with those calculated by Timmermans et al.[Phys. Rev. C 65, 064007 (2002)], who used the leading-order term of the soft neutrino-pair bremsstrahlung amplitude. Conclusions: The nn{gamma} amplitude in the ROBE approach, which obeys the soft-photon theorem, has a predictive power similar to that of the TuTts amplitude. The nn{nu}{nu} amplitude in the ROBE approach, which is consistent with the soft neutrino-pair bremsstrahlung theorem, has a predictive power similar to that of the soft neutrino-pair bremsstrahlung amplitude of Timmermans et al. in the low neutrino-pair energy region.
Convergent beam neutron crystallography
NASA Astrophysics Data System (ADS)
Gibson, Walter M.; Schultz, Arthur J.; Richardson, James W.; Carpenter, John M.; Mildner, David F. R.; Chen-Mayer, Heather H.; Miller, M. E.; Maxey, E.; Prask, Henry J.; Gnaeupel-Herold, Thomas H.; Youngman, Russell
2004-01-01
Applications of neutron diffraction for small samples (<1mm3) or small fiducial areas are limited by the available neutron flux density. Recent demonstrations of convergent beam electron and x-ray diffraction and focusing of cold (?>1 Å) neutrons suggest the possibility to use convergent beam neutron diffraction for small sample crystallography. We have carried out a systematic study of diffraction of both monoenergetic and broad bandwidth neutrons at the NIST Research Reactor and at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory. Combining convergent beams with time-of-flight Laue diffraction is particularly attractive for high efficiency small sample diffraction studies. We have studied single crystal and powder diffraction of neutrons with convergence angles as large as 15° and have observed diffracted peak intensity gains greater than 20. The convergent beam method (CBM) shows promise for crystallography on small samples of small to medium size molecules (potentially even for proteins), ultra-high pressure samples, and for mapping of strain and texture distributions in larger samples.
The Inelastic Scattering of Neutrons
Walter Hauser; Herman Feshbach
1952-01-01
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
On the pairing effects in triaxial nuclei
NASA Astrophysics Data System (ADS)
Oudih, M. R.; Fellah, M.; Allal, N. H.
2014-03-01
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.
Neutron skins and neutron stars
Piekarewicz, J. [Department of Physics, Florida State University, Tallahassee, FL 32306-4350 (United States)
2013-11-07
The neutron-skin thickness of heavy nuclei provides a fundamental link to the equation of state of neutron-rich matter, and hence to the properties of neutron stars. The Lead Radius Experiment ('PREX') at Jefferson Laboratory has recently provided the first model-independence evidence on the existence of a neutron-rich skin in {sup 208}Pb. In this contribution we examine how the increased accuracy in the determination of neutron skins expected from the commissioning of intense polarized electron beams may impact the physics of neutron stars.
A slow neutron polarimeter for the measurement of parity-odd neutron rotary power.
Snow, W M; Anderson, E; Barrón-Palos, L; Bass, C D; Bass, T D; Crawford, B E; Crawford, C; Dawkins, J M; Esposito, D; Fry, J; Gardiner, H; Gan, K; Haddock, C; Heckel, B R; Holley, A T; Horton, J C; Huffer, C; Lieffers, J; Luo, D; Maldonado-Velázquez, M; Markoff, D M; Micherdzinska, A M; Mumm, H P; Nico, J S; Sarsour, M; Santra, S; Sharapov, E I; Swanson, H E; Walbridge, S B; Zhumabekova, V
2015-05-01
We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutron optical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable of measuring a neutron rotary power of d?/dz = 1 × 10(-7) rad/m. PMID:26026552
Greene, Geoffrey L. (Los Alamos, NM)
1999-01-01
A neutron guide in which lengths of cylindrical glass tubing have rectangular glass plates properly dimensioned to allow insertion into the cylindrical glass tubing so that a sealed geometrically precise polygonal cross-section is formed in the cylindrical glass tubing. The neutron guide provides easier alignment between adjacent sections than do the neutron guides of the prior art.
MAX-PLANCK-INSTITUT Enumerating the k closest pairs
are given a set of n points in D-dimensional space, and we want to compute the closest pair, all k closest closest pairs: Consider a grid with cells of length die and distribute the points over the cells. ThenMAX-PLANCK-INSTITUT·· FUR INFORMATIK Enumerating the k closest pairs optimally Hans-Peter Lenhof
Neutron Capture Cross Sections of ^234U and ^151Sm Measured at LANSCE.
NASA Astrophysics Data System (ADS)
Rundberg, R. S.; Wilhelmy, J. B.; Miller, G. G.; Dry, D.; Palmer, P.; Fowler, M. M.; Ullmann, J. L.; Haight, R. C.; Hunt, L.
2002-04-01
The neutron capture cross section of radioactive and rare stable isotopes are needed both for the improved interpretation of historical nuclear weapons test data and the interpretation of isotopic distributions from s-process and r-process nucleosynthesis. ^151Sm is an important s-process branch point. Accurate cross sections in the energy range from 1 keV to 100 keV are needed to model the production of ^151Eu and ^153Eu by ^13C(?, n)^16O neutrons (8 keV) and ^22Ne(?, n) ^25Mg neutrons (30 keV) in asymptotic giant branch, AGB, stars. The 90 y beta decay halflife makes the ^151Eu abundance sensitive to ^22Ne burning that is believed to occur during episodes of convection lasting about 100 years. The neutron capture cross section of ^151Sm, and ^234U were measured by neutron time-of-flight on the newly constructed flight path 14 at the Lujan Center of the Los Alamos Neutron Science Center, LANSCE. The excitation functions were determined over the energy range from 1.0 eV up to 100 keV. Capture gamma rays were detected using a pair of deuterated benzene scintillators. The pulse height weighting method was applied. The results of these measurements will be presented.
Observation of Neutron Skyshine from an Accelerator Based Neutron Source
Franklyn, C. B. [Radiation Science Department, Necsa, PO Box 582, Pretoria 0001 (South Africa)
2011-12-13
A key feature of neutron based interrogation systems is the need for adequate provision of shielding around the facility. Accelerator facilities adapted for fast neutron generation are not necessarily suitably equipped to ensure complete containment of the vast quantity of neutrons generated, typically >10{sup 11} n{center_dot}s{sup -1}. Simulating the neutron leakage from a facility is not a simple exercise since the energy and directional distribution can only be approximated. Although adequate horizontal, planar shielding provision is made for a neutron generator facility, it is sometimes the case that vertical shielding is minimized, due to structural and economic constraints. It is further justified by assuming the atmosphere above a facility functions as an adequate radiation shield. It has become apparent that multiple neutron scattering within the atmosphere can result in a measurable dose of neutrons reaching ground level some distance from a facility, an effect commonly known as skyshine. This paper describes a neutron detection system developed to monitor neutrons detected several hundred metres from a neutron source due to the effect of skyshine.
I. J. van Rooyen; E. Olivier; J. H Neethlin
2014-10-01
Electron microscopy examinations of selected coated particles from the first advanced gas reactor experiment (AGR-1) at Idaho National Laboratory (INL) provided important information on fission product distribution and chemical composition. Furthermore, recent research using STEM analysis led to the discovery of Ag at SiC grain boundaries and triple junctions. As these Ag precipitates were nano-sized, high resolution transmission electron microscopy (HRTEM) examination was used to provide more information at the atomic level. This paper describes some of the first HRTEM results obtained by examining a particle from Compact 4-1-1, which was irradiated to an average burnup of 19.26% fissions per initial metal atom (FIMA), a time average, volume-averaged temperature of 1072°C; a time average, peak temperature of 1182°C and an average fast fluence of 4.13 x 1021 n/cm2. Based on gamma analysis, it is estimated that this particle may have released as much as 10% of its available Ag-110m inventory during irradiation. The HRTEM investigation focused on Ag, Pd, Cd and U due to the interest in Ag transport mechanisms and possible correlation with Pd, Ag and U previously found. Additionally, Compact 4-1-1 contains fuel particles fabricated with a different fuel carrier gas composition and lower deposition temperatures for the SiC layer relative to the Baseline fabrication conditions, which are expected to reduce the concentration of SiC defects resulting from uranium dispersion. Pd, Ag, and Cd were found to co-exist in some of the SiC grain boundaries and triple junctions whilst U was found to be present in the micron-sized precipitates as well as separately in selected areas at grain boundaries. This study confirmed the presence of Pd both at inter- and intragranular positions; in the latter case specifically at stacking faults. Small Pd nodules were observed at a distance of about 6.5 micron from the inner PyC/SiC interface.
Pair Winds in Schwarzschild Spacetime with Application to Strange Stars
A. G. Aksenov; M. Milgrom; V. V. Usov
2007-01-09
We present the results of numerical simulations of stationary, spherically outflowing, electron-positron pair winds, with total luminosities in the range 10^{34}--10^{42} ergs/s. In the concrete example described here, the wind injection source is a hot, bare, strange star, predicted to be a powerful source of pairs created by the Coulomb barrier at the quark surface. We find that photons dominate in the emerging emission, and the emerging photon spectrum is rather hard and differs substantially from the thermal spectrum expected from a neutron star with the same luminosity. This might help distinguish the putative bare strange stars from neutron stars.
SWooki: Un Wiki Smantique sur rseau Pair--Pair
Paris-Sud XI, Université de
SWooki: Un Wiki Sémantique sur réseau Pair-à-Pair Charbel Rahhal -- Hala Skaf-Molli -- Pascal Molli. Les systèmes wiki évoluent vers des wikis sémantiques ou vers des wikis pair-à-pair. Les wikis et la navigation entre les pages. Les wikis pair-à-pair offrent un support pour l'édition massive
beta-decay in neutron-deficient Hg, Pb, and Po isotopes
O. Moreno; P. Sarriguren; R. Alvarez-Rodriguez; E. Moya de Guerra
2006-04-11
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.
Jeffrey Earl Woollard
1997-01-01
In this dissertation, the development and application of in-phantom neutron field optimization parameters for use in evaluating neutron fields for Boron Neutron Capture Therapy (BNCT) is presented. These parameters are based on dose rate distributions in a head phantom and include the effects of fractionation and an energy dependent normal-tissue neutron RBE. As a step in the development of these
NASA Astrophysics Data System (ADS)
Fulde, P.
An overview is given of a number of pair-breaking interactions in superconductors. They have in common that they violate a symmetry of the pair state. In most cases pairs are formed from time reversed single-particle states, a noticeable exception being antiferromagnetic superconductors. When time reversibility is broken by an interaction acting on the electrons, the time evolution of the time-reversal operator plays an important role. Depending on whether it is nonergodic or ergodic, we deal with pair weakening or pair breaking. Numerous different interactions are analyzed and discussed. Unifying features of different pair-breaking cases are pointed out. Special attention is paid to the Zeeman effect and to scattering centers with low-energy excitations. The Kondo effect and crystalline field split rare-earth ions belong in that category. Modifications caused by strongly anisotropic pair states are pointed out. There is strong evidence that in some cases intra-atomic excitations lead to pair formation rather than pair breaking for which an explanation is provided.
Fragment-mass distributions in neutron-induced fission of Th232 and U238 at 33, 45, and 60 MeV
I. V. Ryzhov; S. G. Yavshits; G. A. Tutin; N. V. Kovalev; A. V. Saulski; N. A. Kudryashev; M. S. Onegin; L. A. Vaishnene; Yu. A. Gavrikov; O. T. Grudzevich; V. D. Simutkin; S. Pomp; J. Blomgren; M. Österlund; P. Andersson; R. Bevilacqua; J. P. Meulders; R. Prieels
2011-01-01
We have measured fission fragment-mass yields for neutron-induced fission of Th232 and U238 at energies 32.8, 45.3, and 59.9 MeV. The experiments were done at quasimonoenergetic neutron beams of the Cyclotron Research Center at Louvain-la-Neuve. To detect the fission fragments, a multisection Frisch-gridded ionization chamber was used. The measurement and data analysis techniques are discussed in detail. The obtained mass
Fragment-mass distributions in neutron-induced fission of ²³²Th and ²³U at 33, 45, and 60 MeV
I. V. Ryzhov; S. G. Yavshits; G. A. Tutin; N. V. Kovalev; A. V. Saulski; N. A. Kudryashev; M. S. Onegin; L. A. Vaishnene; Yu. A. Gavrikov; O. T. Grudzevich; V. D. Simutkin; S. Pomp; J. Blomgren; M. Oesterlund; P. Andersson; R. Bevilacqua; J. P. Meulders; R. Prieels
2011-01-01
We have measured fission fragment-mass yields for neutron-induced fission of ²³²Th and ²³U at energies 32.8, 45.3, and 59.9 MeV. The experiments were done at quasimonoenergetic neutron beams of the Cyclotron Research Center at Louvain-la-Neuve. To detect the fission fragments, a multisection Frisch-gridded ionization chamber was used. The measurement and data analysis techniques are discussed in detail. The obtained mass
NASA Astrophysics Data System (ADS)
Sarriguren, P.
2015-04-01
? -decay properties of even- and odd-A neutron-rich Ge, Se, Kr, Sr, Ru, and Pd isotopes involved in the astrophysical rapid neutron capture process are studied within a deformed proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme-Hartree-Fock calculations with pairing correlations. Residual interactions in the particle-hole and particle-particle channels are also included in the formalism. The isotopic evolution of the various nuclear equilibrium shapes and the corresponding charge radii are investigated in all the isotopic chains. The energy distributions of the Gamow-Teller strength as well as the ? -decay half-lives are discussed and compared with the available experimental information. It is shown that nuclear deformation plays a significant role in the description of the decay properties in this mass region. Reliable predictions of the strength distributions are essential to evaluate decay rates in astrophysical scenarios.
A Survey of Faint Galaxy Pairs
Carlberg; Pritchet; Infante
1994-01-31
A sample of faint, V magnitude selected, galaxy pairs, having physical separations less than approximately 20\\hkpc, is used to examine the rise in the merger rate with redshift and the statistical relations between close pairs and the field galaxy population. Redshifts have been obtained for 14 galaxies ($V \\le 22.5$) that are in close ($\\theta < 6\\arcs$) pairs, along with a comparison sample of 38 field galaxies. Two color photometry is available for about 1000 galaxies in the same fields. The average redshift of the $V\\le22.5$ field population is 0.36, statistically equal to the average redshift of 0.42 for the pairs. The similarity of the two redshift distributions, $\\Delta z\\le 0.1$, limits any differential luminosity enhancement of close pairs to less than half a magnitude. The pairs are somewhat bluer than the field and have nearly twice the average [O~II] detection rate of the field, but the differences are not statistically significant. The field population has an angular correlation at separations of $\\theta\\le$6\\arcs\\ higher than the inward extrapolation of $\\omega(\\theta)\\propto \\theta^{-0.8}$, which may be a population of ``companions'' not present at the current epoch, or, luminosity enhancement of intrinsically faint galaxies in pairs. Physical pairs comprise about 7\\% of the faint galaxies in our survey fields. The same physical separation applied to local galaxies finds only 2.6\\% in pairs. If the rise in close low relatively velocity pairs with redshift is parameterized as $(1+z)^m$, then $m=2.9\\pm0.8$. If all pairs at low velocities and $r\\le 20$\\hkpc\\ merge, then the
P. Villemoes; B. Fastrup
1962-01-01
The thermal neutron spectrum of a reactor may be approximated by a ; Maxwellian distribution with an effective neutron temperature T \\/sub n\\/. ; Experimental methods for the determination of T\\/sub n\\/ are investigated, and ; their temperature criteria are shown to be different. A numerical investigation ; of these criteria is carried out. In a given theoretical neutron spectrum
NASA Technical Reports Server (NTRS)
Cottam, J.
2007-01-01
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.
Cold neutrons trapped in external fields
S. Gandolfi; J. Carlson; Steven C. Pieper
2011-01-06
The properties of inhomogeneous neutron matter are crucial to the physics of neutron-rich nuclei and the crust of neutron stars. Advances in computational techniques now allow us to accurately determine the binding energies and densities of many neutrons interacting via realistic microscopic interactions and confined in external fields. We perform calculations for different external fields and across several shells to place important constraints on inhomogeneous neutron matter, and hence the large isospin limit of the nuclear energy density functionals that are used to predict properties of heavy nuclei and neutron star crusts. We find important differences between microscopic calculations and current density functionals; in particular the isovector gradient terms are significantly more repulsive than in traditional models, and the spin-orbit and pairing forces are comparatively weaker.
Cold Neutrons Trapped in External Fields
Gandolfi, S.; Carlson, J. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Pieper, Steven C. [Physics Division, Argonne National Laboratory, Argonne, Illinois 61801 (United States)
2011-01-07
The properties of inhomogeneous neutron matter are crucial to the physics of neutron-rich nuclei and the crust of neutron stars. Advances in computational techniques now allow us to accurately determine the binding energies and densities of many neutrons interacting via realistic microscopic interactions and confined in external fields. We perform calculations for different external fields and across several shells to place important constraints on inhomogeneous neutron matter, and hence the large isospin limit of the nuclear energy density functionals that are used to predict properties of heavy nuclei and neutron star crusts. We find important differences between microscopic calculations and current density functionals; in particular, the isovector gradient terms are significantly more repulsive than in traditional models, and the spin-orbit and pairing forces are comparatively weaker.
Stylized features of single-nucleon momentum distributions
Maarten Vanhalst; Wim Cosyn; Jan Ryckebusch
2014-09-05
[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.
Micromegas neutron beam monitor neutronics.
Stephan, Andrew C; Miller, Laurence F
2005-01-01
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
Neutron structure effects in the deuteron and one neutron halos
M. Nowakowski; N. G. Kelkar; T. Mart
2006-08-29
Although the neutron (n) does not carry a total electric charge, its charge and magnetization distributions represented in momentum space by the electromagnetic form factors, $F_1^{(n)} (q^2)$ and $F_2^{(n)} (q^2)$, lead to an electromagnetic potential of the neutron. Using this fact, we calculate the electromagnetic corrections to the binding energy, $B_d$, of the deuteron and a one neutron halo nucleus (11Be), by evaluating the neutron-proton and the neutron-charged core (10Be) potential, respectively. The correction to $B_d$ (~9 keV) is comparable to that arising due to the inclusion of the $\\Delta$-isobar component in the deuteron wave function. In the case of the more loosely bound halo nucleus, 11Be, the correction is close to about 2 keV.
NASA Astrophysics Data System (ADS)
Lattimer, James M.
2014-05-01
Neutron stars are laboratories for dense matter and gravitational physics. Observations of neutron stars from sources such as radio pulsars, low-mass X-ray binaries, X-ray bursts and thermally-emitting neutron stars are setting bounds to neutron star masses, radii, rotation rates, temperatures and ages. Mass measurements constrain the equation of state at the highest densities and set firm bounds to the highest possible density of cold matter. Radii constrain the equation of state in the vicinity of the nuclear saturation density and yield information about the density dependence of the nuclear symmetry energy. Laboratory measurements and theoretical studies of pure neutron matter are in remarkable agreement with observational bounds.
Leung, Ka-Ngo (Hercules, CA); Lou, Tak Pui (Berkeley, CA); Reijonen, Jani (Oakland, CA)
2008-03-11
A neutron tube or generator is based on a RF driven plasma ion source having a quartz or other chamber surrounded by an external RF antenna. A deuterium or mixed deuterium/tritium (or even just a tritium) plasma is generated in the chamber and D or D/T (or T) ions are extracted from the plasma. A neutron generating target is positioned so that the ion beam is incident thereon and loads the target. Incident ions cause D-D or D-T (or T-T) reactions which generate neutrons. Various embodiments differ primarily in size of the chamber and position and shape of the neutron generating target. Some neutron generators are small enough for implantation in the body. The target may be at the end of a catheter-like drift tube. The target may have a tapered or conical surface to increase target surface area.
J=0, J=J_{max} and quadrupole pairing
Larry Zamick; Daniel Hertz-Kintish
2014-07-28
We consider 2 neutrons and 2 protons in the g_{9/2} shell.Wave functions and energy levels are obtained for various interactions. The wave functions for states with total angular momentum I greater or equal to 10 are not affected by what the pairing interacton (J=0 T=1) is.Other parts of the interaction are therefore of increased importance.
Properties of Pairing Correlations in Infinite Nuclear Matter
O. Elgaroy; M. Hjorth-Jensen
1997-10-26
We discuss various properties of singlet S pairing in neutron and nuclear matter in terms of the bare nuclon-nucleon interaction. Relations to the NN phase shifts are discussed, as well as various properties of the BCS wave function and the coherence length for fermion superfluids in infinite matter.
Laser Driven Neutron Generation at the Texas Petawatt
NASA Astrophysics Data System (ADS)
Pomerantz, Ishay; McCary, Eddie; Meadows, Alexander R.; Cepeda Lestrade, Arantxa; Chester, Clay; Cortez, Jose; Dyer, Gilliss; Gaul, Erhard; Gautier, Donald C.; Hamilton, David; Jung, Daniel; Shah, Rahul; Wang, Chunhua; Fernandez, Juan C.; Ditmire, Todd; Hegelich, Manuel Bjorn
2013-10-01
We realized a bright laser-driven neutron source at the Texas Petawatt laser facility. We investigated the interplay between ion- and x-ray-driven neutron production regimes, by scanning a large range of target thicknesses, converter materials and laser parameters. We employed a large suite of electron, ion, gamma and neutron diagnostics to obtain a complete characterization of the interaction energetics. Neutron yields in excess of 109 neutrons/shot with a fairly isotropic distribution were measured.
Neutron Mössbauer effect and the cold fusion in inhomogeneous materials
H. Kozima
1994-01-01
Summary In relation with the trapped-neutron catalized model (TNCF model) to explain the Cold Fusion phenomenon, the neutron Mössbauer\\u000a effect is proposed to trap neutrons in a crystal composed of nuclei which can absorb a neutron resonantly to form an excited\\u000a state of an isotope. This mechanism of neutron trapping depends on the distribution of the protons (and\\/or deuterons) in the
Neutron measurements of the OGO-VI Spacecraft
NASA Technical Reports Server (NTRS)
Lockwood, J. A.
1973-01-01
The neutron measurements with the OGO-6 spacecraft are reported. Topics discussed include: the design and calibration of a neutron monitor for measuring the cosmic ray neutron leakages from the earth's atmosphere, determination of latitude dependence of cosmic ray leakage flux, determination of the angular distribution of neutron leakage flux as deduced by measurements of the altitude dependence, and verification of the solar modulation of the cosmic ray source for the neutron leakage.
Development of pulsed neutron uranium logging instrument.
Wang, Xin-guang; Liu, Dan; Zhang, Feng
2015-03-01
This article introduces a development of pulsed neutron uranium logging instrument. By analyzing the temporal distribution of epithermal neutrons generated from the thermal fission of (235)U, we propose a new method with a uranium-bearing index to calculate the uranium content in the formation. An instrument employing a D-T neutron generator and two epithermal neutron detectors has been developed. The logging response is studied using Monte Carlo simulation and experiments in calibration wells. The simulation and experimental results show that the uranium-bearing index is linearly correlated with the uranium content, and the porosity and thermal neutron lifetime of the formation can be acquired simultaneously. PMID:25832251
Development of pulsed neutron uranium logging instrument
NASA Astrophysics Data System (ADS)
Wang, Xin-guang; Liu, Dan; Zhang, Feng
2015-03-01
This article introduces a development of pulsed neutron uranium logging instrument. By analyzing the temporal distribution of epithermal neutrons generated from the thermal fission of 235U, we propose a new method with a uranium-bearing index to calculate the uranium content in the formation. An instrument employing a D-T neutron generator and two epithermal neutron detectors has been developed. The logging response is studied using Monte Carlo simulation and experiments in calibration wells. The simulation and experimental results show that the uranium-bearing index is linearly correlated with the uranium content, and the porosity and thermal neutron lifetime of the formation can be acquired simultaneously.
Pair Correlations and Merger Bias
Steven R. Furlanetto; Marc Kamionkowski
2005-11-21
We study analytically the possibility that mergers of haloes are more highly clustered than the general population of haloes of comparable masses. We begin by investigating predictions for merger bias within the extended Press-Schechter formalism and discuss the limitations and ambiguities of this approach. We then postulate that mergers occur whenever two objects form within a (small) fixed distance of each other. We therefore study the clustering of pairs of points for a highly biased population in the linear regime, for the overall mass distribution in the quasilinear regime, and (using the halo model of clustering) in the nonlinear regime. Biasing, quasilinear evolution, and nonlinear clustering all lead to nonzero reduced (or connected) three-point and four-point correlation functions. These higher-order correlation functions can in many cases enhance the clustering of close pairs of points relative to the clustering of individual points. If close pairs are likely to merge, then the clustering of mergers may be enhanced. We discuss implications for the observed clustering of luminous z=3 galaxies and for correlations of active galactic nuclei and galaxy clusters.
Design and Simulation of a Boron-loaded Neutron Spectrometer
Martin, Thomas
2012-10-19
The measurement of the distribution of kinetic energy carried by neutron particles is of interest to the health physics and radiation protection industry. Neutron particle spectral fluence is essential to the calculation of absorbed dose, equivalent...
Neutron-Proton Interaction: The Scattering of Neutrons by Protons
William D. Harkins; Martin D. Kamen; Henry W. Newson; David M. Gans
1936-01-01
The inadequacy of present theories of proton-neutron interaction is shown in work in which 730 proton tracks produced by collisions of fast neutrons with hydrogen nuclei have been studied and measured to determine the distribution-in-angle. The recoils have been observed in three gaseous media; hydrogen, ethylene and hydrogen sulphide, by the use of a sylphon-type Wilson chamber and two cameras
Neutronic design of the ITER radial neutron camera
L. Petrizzi; R. Barnsley; L. Bertalot; B. Esposito; H. Haskell; E. Mainardi; D. Marocco; S. Podda; C. Walker; S. Villari
2007-01-01
This paper summarizes the work, performed in the frame of various EFDA contracts during 2004–2005, on the design review and upgrade of the ITER radial neutron camera (RNC). The RNC, which should provide information on the spatial distribution and energy spectrum of the neutron emission, consists of an ex-vessel system (fan-like collimator with 12×3 lines of sights) and an in-vessel
Neutron Multiplicity Measurements With 3He Alternative: Straw Neutron Detectors
Mukhopadhyay, Sanjoy
2015-01-01
Counting neutrons emitted by special nuclear material (SNM) and differentiating them from the background neutrons of various origins is the most effective passive means of detecting SNM. Unfortunately, neutron detection, counting, and partitioning in a maritime environment are complex due to the presence of high-multiplicity spallation neutrons (commonly known as ‘‘ship effect ’’) and to the complicated nature of the neutron scattering in that environment. A prototype neutron detector was built using 10B as the converter in a special form factor called ‘‘straws’’ that would address the above problems by looking into the details of multiplicity distributions of neutrons originating from a fissioning source. This paper describes the straw neutron multiplicity counter (NMC) and assesses the performance with those of a commercially available fission meter. The prototype straw neutron detector provides a large-area, efficient, lightweight, more granular (than fission meter) neutron-responsive detection surface (to facilitate imaging) to enhance the ease of application of fission meters. Presented here are the results of preliminary investigations, modeling, and engineering considerations leading to the construction of this prototype. This design is capable of multiplicity and Feynman variance measurements. This prototype may lead to a near-term solution to the crisis that has arisen from the global scarcity of 3He by offering a viable alternative to fission meters. This paper describes the work performed during a 2-year site-directed research and development (SDRD) project that incorporated straw detectors for neutron multiplicity counting. The NMC is a two-panel detector system. We used 10B (in the form of enriched boron carbide: 10B4C) for neutron detection instead of 3He. In the first year, the project worked with a panel of straw neutron detectors, investigated its characteristics, and developed a data acquisition (DAQ) system to collect neutron multiplicity information from spontaneous fission sources using a single panel consisting of 60 straws equally distributed over three rows in high-density polyethylenemoderator. In the following year, we developed the field-programmable gate array and associated DAQ software. This SDRD effort successfully produced a prototype NMC with*33% detection efficiency compared to a commercial fission meter.
Antipodal neutron time of flight (nToF) detectors more than double their diagnostic value
NASA Astrophysics Data System (ADS)
Kilkenny, Joseph; Knauer, James; Caggiano, Joseph; Eckart, Mark; Hatarik, Robert; Munro, David; Sayre, Daniel; Spears, Brian
2014-10-01
Moments of the neutron-velocity distribution give unique insights to the quality of an inertial confinement fusion (ICF) implosion. The three, 20 m distance nToF detectors on the NIF are being augmented by adding an antipodal detector to each of them. Antipodal pairs of detectors increase the sampling of imploded DT ice but also allow an accurate measurement of the areal density of the odd modes of the compressed ice from the un-scattered yield ratio, and with the two measurements distinguishing center of mass drift velocity from the thermodynamic ion temperature. NNSA Contract Number DE-AC52-07NA27344.
Shape mixing and beta-decay properties of neutron-deficient Kr and Sr isotopes
P. Sarriguren
2009-03-31
Gamow-Teller strength distributions and beta-decay half-lives in neutron-deficient Kr and Sr isotopes are investigated within a deformed quasiparticle random phase approximation. The approach is based on a selfconsistent Skyrme Hartree-Fock mean field with pairing correlations and residual separable particle-hole and particle-particle forces. A simple two-level model is used to mix the nuclear shapes into the physical ground state. Good agreement with experiment is found with shape mixing coefficients which are consistent with those obtained phenomenologically from mixing of rotational bands.
F. Nicolleau; J. C. Vassilicos
2002-05-01
Kinematic Simulations of turbulent pair diffusion in planar turbulence with a -5/3 energy spectrum reproduce the results of the laboratory measurements of Jullien Phys. Rev. Lett. 82, 2872 (1999), in particular the stretched exponential form of the PDF of pair separations and their correlation functions. The root mean square separation is found to be strongly dependent on initial conditions for very long stretches of times. This dependence is consistent with the topological picture of turbulent pair diffusion where pairs initially close enough travel together for long stretches of time and separate violently when they meet straining regions around hyperbolic points. A new argument based on the divergence of accelerations is given to support this picture.
Superfluidity of {Lambda} hyperons in neutron stars
Wang, Y. N.; Shen, H. [Department of Physics, Nankai University, Tianjin 300071 (China)
2010-02-15
We study the {sup 1}S{sub 0} superfluidity of {Lambda} hyperons in neutron star matter and neutron stars. We use the relativistic mean field (RMF) theory to calculate the properties of neutron star matter. In the RMF approach, the meson-hyperon couplings are constrained by reasonable hyperon potentials that include the updated information from recent developments in hypernuclear physics. To examine the {sup 1}S{sub 0} pairing gap of {Lambda} hyperons, we employ several {Lambda}{Lambda} interactions based on the Nijmegen models and used in double-{Lambda} hypernuclei studies. It is found that the maximal pairing gap obtained is a few tenths of a MeV. The magnitude and the density region of the pairing gap are dependent on the {Lambda}{Lambda} interaction and the treatment of neutron star matter. We calculate neutron star properties and find that whether the {sup 1}S{sub 0} superfluidity of {Lambda} hyperons exists in the core of neutron stars mainly depends on the {Lambda}{Lambda} interaction used.
L. Fallon; A. Abramowski; F. Acero; F. Aharonian; A. G. Akhperjanian; G. Anton; U. Barres de Almeida; A. R. Bazer-Bachi; Y. Becherini; B. Behera; K. Bernlühr; A. Bochow; C. Boisson; J. Bolmont; V. Borrel; J. Brucker; F. Brun; P. Brun; R. Bühler; T. Bulik; I. Büsching; T. Boutelier; P. M. Chadwick; A. Charbonnier; R. C. G. Chaves; A. Cheesebrough; J. Conrad; L.-M. Chounet; A. C. Clapson; G. Coignet; M. Dalton; M. K. Daniel; I. D. Davids; B. Degrange; C. Deil; H. J. Dickinson; A. Djannati-Ataü W. Domainko; L. O'c. Drury; F. Dubois; G. Dubus; J. Dyks; M. Dyrda; K. Egberts; P. Eger; P. Espigat; C. Farnier; S. Fegan; F. Feinstein; M. V. Fernandes; A. Fiasson; A. Fürster; G. Fontaine; M. Füssling; S. Gabici; Y. A. Gallant; L. Gérard; D. Gerbig; B. Giebels; J. F. Glicenstein; B. Glück; P. Goret; D. Güring; D. Hampf; M. Hauser; S. Heinz; G. Heinzelmann; G. Henri; G. Hermann; J. A. Hinton; A. Hoffmann; W. Hofmann; P. Hofverberg; M. Holleran; S. Hoppe; D. Horns; A. Jacholkowska; O. C. de Jager; C. Jahn; I. Jung; K. Katarzynski; U. Katz; S. Kaufmann; M. Kerschhaggl; D. Khangulyan; B. Khálifi; D. Keogh; D. Klochkov; W. Kluzniak; T. Kneiske; Nu. Komin; K. Kosack; R. Kossakowski; G. Lamanna; J.-P. Lenain; T. Lohse; C.-C. Lu; V. Marandon; A. Marcowith; J. Masbou; D. Mau-Rin; T. J. L. McComb; M. C. Medina; J. Méhault; R. Moderski; E. Moulin; M. Naumann-Godo; M. de Naurois; D. Nedbal; D. Nekrassov; N. Nguyen; B. Nicholas; J. Niemiec; S. J. Nolan; S. Ohm; J.-F. Olive; E. de Ona Wilhelmi; B. Opitz; K. J. Orford; M. Ostrowski; M. Panter; M. Paz Arribas; G. Pedaletti; G. Pelletier; P.-O. Petrucci; S. Pita; G. Pühlhofer; M. Punch; A. Quirrenbach; B. C. Raubenheimer; M. Raue; S. M. Rayner; O. Reimer; M. Renaud; R. de Los Reyes; F. Rieger; J. Ripken; L. Rob; S. Rosier-Lees; G. Rowell; B. Rudak; C. B. Rulten; J. Ruppel; F. Ryde; V. Sahakian; A. Santangelo; R. Schlickeiser; F. M. Schück; A. Schünwald; U. Schwanke; S. Schwarzburg; S. Schwemmer; A. Shalchi; I. Sushch; M. Sikora; J. L. Skilton; H. Sol; L. Stawarz; R. Steenkamp; C. Stegmann; F. Stinzing; A. Szostek; P. H. Tam; J.-P. Tavernet; R. Terrier; O. Tibolla; M. Tluczykont; K. Valerius; C. van Eldik; G. Vasileiadis; C. Venter; L. Venter; J. P. Vialle; A. Viana; P. Vincent; M. Vivier; H. J. Vülk; F. Volpe; S. Vorobiov; S. J. Wagner; M. Ward; A. A. Zdziarski; A. Zech; H.-S. Zechlin
2010-01-01
We have conducted a search for the giant Pair Halo structures which are inevitably formed around TeV sources due to interactions of very high energy gamma-rays with the Extragalactic Background Light (EBL). The resulting electron\\/positron pairs are Compton upscattered on photons of the 2.7 K Cosmic Microwave Background Radiation to produce a second generation of gamma-rays which again interact with
Yoshiaki Tsujimoto; Yukihiro Sugiura; Makoto Ando; Daisuke Katsuse; Rikizo Ikuta; Takashi Yamamoto; Masato Koashi; Nobuyuki Imoto
2015-03-10
We experimentally demonstrated entanglement extraction scheme by using photons at the telecommunication band for optical-fiber-based quantum communications. We generated two pairs of non-degenerate polarization entangled photons at 780~nm and 1551~nm by spontaneous parametric down-conversion and distributed the two photons at 1551~nm through a collective phase damping channel which gives the same amount of random phase shift on the two photons. Through local operation and classical communication, we extracted an entangled photon pair from two phase-disturbed photon pairs. An observed fidelity of the extracted photon pair to a maximally entangled photon pair was 0.73 $\\pm$ 0.07 which clearly shows the recovery of entanglement.
Tsujimoto, Yoshiaki; Sugiura, Yukihiro; Ando, Makoto; Katsuse, Daisuke; Ikuta, Rikizo; Yamamoto, Takashi; Koashi, Masato; Imoto, Nobuyuki
2015-05-18
We experimentally demonstrated entanglement extraction scheme by using photons at the telecommunication band for optical-fiber-based quantum communications. We generated two pairs of non-degenerate polarization entangled photons at 780 nm and 1551 nm by spontaneous parametric down-conversion and distributed the two photons at 1551 nm through a collective phase damping channel which gives the same amount of random phase shift on the two photons. Through local operation and classical communication, we extracted an entangled photon pair from two phase-disturbed photon pairs. An observed fidelity of the extracted photon pair to a maximally entangled photon pair was 0.73 ± 0.07 which clearly shows the recovery of entanglement. PMID:26074602
Yields of correlated fragment pairs in spontaneous fission of {sup 252}Cf
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
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)
Thermal neutron detection system
Peurrung, Anthony J. (Richland, WA); Stromswold, David C. (West Richland, WA)
2000-01-01
According to the present invention, a system for measuring a thermal neutron emission from a neutron source, has a reflector/moderator proximate the neutron source that reflects and moderates neutrons from the neutron source. The reflector/moderator further directs thermal neutrons toward an unmoderated thermal neutron detector.
The Neutron Imaging Diagnostic at NIF
Merrill, F E; Buckles, R; Clark, D; Danly, C R; Drury, O B; Dzenitis, J M; Fatherly, V E; Fittinghoff, D N; Gallegos, R; Grim, G P; Guler, N; Loomis, E N; Lutz, S; Malone, R M; Martinson, D D; Mares, D; Morley, D J; Morgan, G L; Oertel, J A; Tregillis, I L; Volegov, P L; Weiss, P B; Wilde, C H
2012-10-01
A neutron imaging diagnostic has recently been commissioned at the National Ignition Facility (NIF). This new system is an important diagnostic tool for inertial fusion studies at the NIF for measuring the size and shape of the burning DT plasma during the ignition stage of ICF implosions. The imaging technique utilizes a pinhole neutron aperture, placed between the neutron source and a neutron detector. The detection system measures the two dimensional distribution of neutrons passing through the pinhole. This diagnostic has been designed to collect two images at two times. The long flight path for this diagnostic, 28 m, results in a chromatic separation of the neutrons, allowing the independently timed images to measure the source distribution for two neutron energies. Typically the first image measures the distribution of the 14 MeV neutrons and the second image of the 6-12 MeV neutrons. The combination of these two images has provided data on the size and shape of the burning plasma within the compressed capsule, as well as a measure of the quantity and spatial distribution of the cold fuel surrounding this core.
Skinner, Lawrie [State University of New York, Stony Brook; Benmore, Chris J [Argonne National Laboratory (ANL); Weber, Richard [Argonne National Laboratory (ANL); Santodonato, Louis J [ORNL; Tumber, Sonia [Materials Development, Inc., Evanston, IL; Neuefeind, Joerg C [ORNL; Lazareva, Lena [State University of New York, Stony Brook; Du, Jincheng [University of North Texas; Parise, John B [Stony Brook University (SUNY)
2012-01-01
We have performed neutron diffraction isotopic substitution experiments on aerodynamically levitated droplets of CaSiO3, to directly extract intermediate and local structural information on the Ca environment. The results show a substantial broadening of the Ca-O peak in the pair distribution function of the melt compared to the glass, which comprises primarily of 6- and 7-fold coordinated Ca-polyhedra. The broadening can be explained by a re-distribution of Ca-O bond lengths, especially towards longer distances in the liquid. The first order neutron difference function provides a rigorous test of recent molecular dynamics simulations and supports the model of the presence of short chains or channels of edge shared Ca-octahedra in the liquid state. It is suggested that the polymerization of Ca-polyhedra is responsible for the fragile viscosity behavior of the melt and the glass forming ability in CaSiO3.
Manglos, S.H.
1988-03-10
A neutron range spectrometer and method for determining the neutron energy spectrum of a neutron emitting source are disclosed. Neutrons from the source are colliminated along a collimation axis and a position sensitive neutron counter is disposed in the path of the collimated neutron beam. The counter determines positions along the collimation axis of interactions between the neutrons in the neutron beam and a neutron-absorbing material in the counter. From the interaction positions, a computer analyzes the data and determines the neutron energy spectrum of the neutron beam. The counter is preferably shielded and a suitable neutron-absorbing material is He-3. 1 fig.
Fabio Cardone; Giovanni Cherubini; Andrea Petrucci
2008-12-06
We report the results of neutron measurements carried out during the application of ultrasounds to a solution containing only stable elements like Iron and Chlorine, without any other radioactive source of any kind. These measurements, carried out by CR39 detectors and a Boron TriFouride electronic detector, evidenced the emission of neutron pulses. These pulses stand well above the electronic noise and the background of the laboratory where the measurements were carried out.
NASA Astrophysics Data System (ADS)
Carjan, N.; Rizea, M.
2015-07-01
The main properties of the neutrons released during the neck rupture are calculated for 236U in the frame of a dynamical scission model: the angular distribution with respect to the fission axis (on spheres of radii R = 30 and 40 fm and at time T = 4 ×10-21 s), the distribution of the average neutron energies (for durations of the neck rupture ?T = 1 and 2 ×10-22 s) and the total neutron multiplicity (for two values of the minimum neck-radius rmin = 1.6 and 1.9 fm). They are compared with measurements of prompt fission neutrons during 235U (nth , f). The experimental trends are qualitatively reproduced, i.e., the focusing of the neutrons along the fission axis, the preference of emission from the light fragment, the range, slope and average value of the neutron energy-spectrum and the average total neutron multiplicity.
Neutron spectrum and doses in a 18 MV LINAC
Hector Rene Vega-Carrillo; Berenice Hernández-Almaraz; Victor Martin Hernández-Dávila; Arturo Ortíz-Hernández
2010-01-01
Bonner sphere spectrometer with TLDs pairs has been utilized to measure the neutron spectrum 100 cm from isocenter of a 18\\u000a MV LINAC, simultaneously the ambient dose equivalent due to neutrons and photons was measured in the control room area with\\u000a neutron and gamma-ray area monitors. Measurements were carried out when the LINAC was delivering a dose of 600 MU at the
NASA Astrophysics Data System (ADS)
Yoshida, Kenichi
2013-11-01
We develop a new framework for the self-consistent deformed proton-neutron quasiparticle-random-phase approximation (pnQRPA), formulated in the Hartree-Fock-Bogoliubov (HFB) single-quasiparticle basis. The same Skyrme force is used in both the HFB and pnQRPA calculations, except in the proton-neutron particle-particle channel, where an S=1 contact force is employed. A numerical application is performed for Gamow-Teller (GT) strength distributions and ? -decay rates in the deformed neutron-rich Zr isotopes located around the path of rapid-neutron-capture-process nucleosynthesis. It is found that the GT strength distributions are fragmented due to deformation. Furthermore, we find that the momentum-dependent terms in the particle-hole residual interaction lead to a stronger collectivity of the GT giant resonance. The T=0 pairing enhances the low-lying strengths cooperatively with the T=1 pairing correlation, which shortens the ? -decay half-lives by at most an order of magnitude. The new calculation scheme reproduces well the observed isotopic dependence of the ? -decay half-lives of deformed ^{100-110}Zr isotopes.
Fayer, Michael J.; Gee, Glendon W.
2005-01-12
The neutron probe is a standard tool for measuring soil water content. This article provides an overview of the underlying theory, describes the methodology for its calibration and use, discusses example applications, and identifies the safety issues. Soil water makes land-based life possible by satisfying plant water requirements, serving as a medium for nutrient movement to plant roots and nutrient cycling, and controlling the fate and transport of contaminants in the soil environment. Therefore, a successful understanding of the dynamics of plant growth, nutrient cycling, and contaminant behavior in the soil requires knowledge of the soil water content as well as its spatial and temporal variability. After more than 50 years, neutron probes remain the most reliable tool available for field monitoring of soil water content. Neutron probes provide integrated measurements over relatively large volumes of soil and, with proper access, allow for repeated sampling of the subsurface at the same locations. The limitations of neutron probes include costly and time-consuming manual operation, lack of data automation, and costly regulatory requirements. As more non-radioactive systems for soil water monitoring are developed to provide automated profiling capabilities, neutron-probe usage will likely decrease. Until then, neutron probes will continue to be a standard for reliable measurements of field water contents in soils around the globe.
FOREWORD: Neutron metrology Neutron metrology
NASA Astrophysics Data System (ADS)
Thomas, David J.; Nolte, Ralf; Gressier, Vincent
2011-12-01
The International Committee for Weights and Measures (CIPM) has consultative committees covering various areas of metrology. The Consultative Committee for Ionizing Radiation (CCRI) differs from the others in having three sections: Section (I) deals with radiation dosimetry, Section (II) with radionuclide metrology and Section (III) with neutron metrology. In 2003 a proposal was made to publish special issues of Metrologia covering the work of the three Sections. Section (II) was the first to complete their task, and their special issue was published in 2007, volume 44(4). This was followed in 2009 by the special issue on radiation dosimetry, volume 46(2). The present issue, volume 48(6), completes the trilogy and attempts to explain neutron metrology, the youngest of the three disciplines, the neutron only having been discovered in 1932, to a wider audience and to highlight the relevance and importance of this field. When originally approached with the idea of this special issue, Section (III) immediately saw the value of a publication specifically on neutron metrology. It is a topic area where papers tend to be scattered throughout the literature in journals covering, for example, nuclear instrumentation, radiation protection or radiation measurements in general. Review articles tend to be few. People new to the field often ask for an introduction to the various topics. There are some excellent older textbooks, but these are now becoming obsolete. More experienced workers in specific areas of neutron metrology can find it difficult to know the latest position in related areas. The papers in this issue attempt, without presenting a purely historical outline, to describe the field in a sufficiently logical way to provide the novice with a clear introduction, while being sufficiently up-to-date to provide the more experienced reader with the latest scientific developments in the different topic areas. Neutron radiation fields obviously occur throughout the nuclear industry, from the initial fuel enrichment and fabrication processes right through to storage or reprocessing, and neutron metrology is clearly important in this area. Neutron fields do, however, occur in other areas, for example where neutron sources are used in oil well logging and moisture measurements. They also occur around high energy accelerators, including photon linear accelerators used for cancer therapy, and are expected to be a more serious problem around the new hadron radiation therapy facilities. Roughly 50% of the cosmic ray doses experienced by fliers at the flight altitudes of commercial aircraft are due to neutrons. Current research on fusion presents neutron metrology with a whole new range of challenges because of the very high fluences expected. One of the most significant features of neutron fields is the very wide range of possible neutron energies. In the nuclear industry, for example, neutrons occur with energies from those of thermal neutrons at a few meV to the upper end of the fission spectrum at perhaps 10 MeV. For cosmic ray dosimetry the energy range extends into the GeV region. This enormous range sets a challenge for designing measuring devices and a parallel challenge of developing measurement standards for characterizing these devices. One of the major considerations when deciding on topics for this special issue was agreeing on what not to include. Modelling, i.e. the use of radiation transport codes, is now a very important aspect of neutron measurements. These calculations are vital for shielding and for instrument design; nevertheless, the topic has only been included here where it has a direct bearing on metrology and the development of standards. Neutron spectrometry is an increasingly important technique for unravelling some of the problems of dose equivalent measurements and for plasma diagnostics in fusion research. However, this topic is at least one step removed from primary metrology and so it was felt that it should not be covered, particularly as a compendium of papers on spectrometry for radiation protection has
González, Gabriela B. (DePaul)
2012-10-23
Transparent conducting oxide (TCO) materials are implemented into a wide variety of commercial devices because they possess a unique combination of high optical transparency and high electrical conductivity. Created during the processing of the TCOs, defects within the atomic-scale structure are responsible for their desirable optical and electrical properties. Therefore, studying the defect structure is essential to a better understanding of the behavior of transparent conductors. X-ray and neutron scattering techniques are powerful tools to investigate the atomic lattice structural defects in these materials. This review paper presents some of the current developments in the study of structural defects in n-type TCOs using x-ray diffraction (XRD), neutron diffraction, extended x-ray absorption fine structure (EXAFS), pair distribution functions (PDFs), and x-ray fluorescence (XRF).
Structural analysis of a completely amorphous {sup 238}Pu-doped zircon by neutron diffraction.
Fortner, J. A.; Badyal, Y.; Price, D. C.; Hanchar, J. M.; Weber, W. J.; Materials Science Division; PNNL
1999-01-01
The structure of a completely amorphous zircon was determined by time-of-flight neutron diffraction at Argonne's Intense Pulsed Neutron Source (IPNS). The sample of metamict zircon (ZrSiO{sub 4}), initially doped to 8.85 weight percent {sup 238}Pu, had been completely amorphized by alpha-recoil damage since its synthesis in 1981 at the Pacific Northwest National Laboratory (PNNL). The measured diffraction structure factor, S(Q), indicated a completely amorphous sample, with no signs of residual zircon microcrystallinity. The pair distribution function obtained indicated that the structure was that of an oxide glass, retaining the Si-0, Zr-0, and O-O bond lengths of crystalline zircon.
Structural analysis of a completely amorphous {sup 238}Pu-doped zircon by neutron diffraction.
Fortner, J. A.
1998-12-16
The structure of a completely amorphous zircon was determined by time-of-flight neutron diffraction at Argonne's Intense Pulsed Neutron Source (IPNS). The sample of metamict zircon (ZrSiO{sub 4}),initially doped to 8.85 weight percent {sup 238}Pi, had been completely amorphized by alpha-recoil damage since its synthesis in 1981 at the Pacific Northwest National Laboratory (PNNL). The measured diffraction structure factor, S(Q), indicated a completely amorphous sample, with no signs of residual zircon microcrystallinity. The pair distribution function obtained indicated that the structure was that of an oxide glass, retaining the Si-0, Zr-0, and O-O bond lengths of crystalline zircon.
New calculations of ?-delayed neutron emission
NASA Astrophysics Data System (ADS)
Mumpower, Matthew; Kawano, Toshihiko; Moller, Peter
2014-09-01
? -delayed neutron emission probabilities (Pn-values) are important inputs for nuclear astrophysics applications. We present a new model of ?-delayed neutron emission which combines QRPA and statistical decay calculations. This approach uses microscopic nuclear structure information which starts with Gamow-Teller strength distributions in the daughter nucleus, and then follows the statistical decay until the initial available excitation energy is exhausted. Explicitly included at each neutron emission stage is ?-ray competition. One consequence of this formalism is a prediction of more neutrons on average being emitted after ?-decay for neutron-rich nuclei towards the neutron dripline. The framework presented here also enables us to extend our calculations to beta-delayed fission and pre-scission neutron emission. We discuss implications of larger Pn-values and new ?-delayed fission rates for the astrophysical r process of nucleosynthesis.
Electron Pairing Without Superconductivity
NASA Astrophysics Data System (ADS)
Levy, Jeremy; Cheng, G.; Tomczyk, M.; Lu, S.; Veazey, J. P.; Huang, M.; Irvin, P.; Ryu, S.; Lee, H.; Eom, C.-B.; Hellberg, C. S.
2015-03-01
Strontium titanate (SrTiO3) exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. We describe transport experiments with nanowire-based quantum dots localized at the interface between SrTiO3 and LaAlO3. Electrostatic gating of the quantum dot reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical magnetic field Bp 1-4 Tesla, an order of magnitude larger than the superconducting critical magnetic field. For B
Divide and conquer for the closest-pair problem revisited
Jyrki Katajainen; Markku Koppinen; Timo Leipälä; Olli Nevalainen
1989-01-01
In this paper the divide-and-conquer approach to the two-dimensional closest-pair problem is studied. A new algorithm is proposed by which a closest pair, i.e. a pair of points whose distance ? is smallest among a set of N points, is found in ?(N) expected time when the points are drawn independently from the uniform distribution in a unit square. The
Neutron generator yield measurements using a phoswich detector with the digital pulse shape analysis
NASA Astrophysics Data System (ADS)
Barzilov, Alexander; Novikov, Ivan; Womble, Phillip; Heinze, Julian
2012-03-01
The phoswich detector designed as a combination of two scintillators with dissimilar pulse shape characteristics that are optically coupled to each other and to a common photomultiplier is used for the simultaneous detection of fast and thermal neutrons. The digital signal processing of detector signals is used. The pulse shape analysis distinguishes the scintillation signals produced by photons, fast neutrons, and thermal neutrons. The phoswich was tested using the photon and neutron sources. We discuss neutron yield measurements for a pulse DT neutron generator. The spatial distribution of fast neutron flux and thermal neutron flux was evaluated for the generator in presence of neutron moderating materials.
NASA Astrophysics Data System (ADS)
Prokeš, K.; Gukasov, A.; Argyriou, D. N.; Bud'ko, S. L.; Canfield, P. C.; Kreyssig, A.; Goldman, A. I.
2011-02-01
Polarized neutron diffraction has been performed on a tetragonal Ba(Fe1-xCox)2As2, x=0.066 single crystal under an applied magnetic field of 6 T directed along the [\\overline{1}10 ] direction to determine the magnetic structure factors of various Bragg reflections. The maximum entropy reconstruction based on bulk magnetization measurements and polarized neutron diffraction data reveal a small induced magnetic moment residing on the 4d Wyckoff site that is occupied by Fe/Co atoms. No significant magnetization density has been found on the Ba and As atomic positions. The small polarizability of Fe/Co sites leads to flipping ratios very close to 1.00. Our data suggest a non-zero orbital contribution to the Fe/Co magnetic form factor in good agreement with recent theoretical and experimental studies.
Massingill, Brian Edward
2009-05-15
The objective of this research was to develop a complex MCNPX model of the human head to predict absorbed dose distributions during proton therapy of ocular tumors. Absorbed dose distributions using the complex geometry were compared to a simple...
Massingill, Brian Edward
2009-05-15
The objective of this research was to develop a complex MCNPX model of the human head to predict absorbed dose distributions during proton therapy of ocular tumors. Absorbed dose distributions using the complex geometry were compared to a simple...
NASA Astrophysics Data System (ADS)
Pickl, Peter; Dürr, Detlef
2008-08-01
We give here a rigorous proof of the well known prediction of pair creation as it arises from the Dirac equation with an external time dependent potential. Pair creation happens with probability one if the potential changes adiabatically in time and becomes overcritical, which means that an eigenvalue curve (as a function of time) bridges the gap between the negative and positive spectral continuum. The potential can be thought of as being zero at large negative and large positive times. The rigorous treatment of this effect has been lacking since the pioneering work of Beck, Steinwedel and Süßmann [1] in 1963 and Gershtein and Zeldovich [8] in 1970.
Creation of boson and fermion pairs in strong fields
S. Schmidt; A. V. Prozorkevich; S. A. Smolyansky
1998-01-01
We analyze a quantum kinetic equation describing both boson and fermion pair production. We explore the solution of the kinetic equation in its Markovian limit. The numerical study shows an enhancement (bosons) or a suppression (fermions) of the pair creation rate according to their quantum statistics. The modification of the time evolution of the distribution function is small but for
Inelastic neutron scattering: resonances and fluctuations
Frank W. K. Firk
2010-03-13
R-function theory of Thomas used in study of inelastic scattering of neutrons to a definite state. Onset of fluctuations, effects of randomness of phases of interfering amplitudes, and variations in statistical distributions of neutron widths considered in detail. Fluctuations exhibit well-defined maxima and sharp minima. For certain adjacent resonances, strong interference effects are predicted.
Precision experiments in neutron beta decay
Carroll A. Trull
2008-01-01
A free neutron will disintegrate into a proton after about fourteen and a half minutes, emitting an electron and an antineutrino. The Standard Electroweak Model epitomizes the process with a decay probability distribution function (PDF) derived by Jackson, Trieman, and Wyld. This function depends on the momenta of the daughter particles and the spin of the neutron. Each correlation between
Cold Neutrons Confined in External Fields
Stefano Gandolfi; Joe Carlson; Steven C. Pieper
2010-01-01
Advances in computational techniques and facilities now allow us to calculate the properties of N=8 to 54 neutrons with realistic interactions confined in external fields. By examining the shell structure, spin orbit, and pairing properties of these systems we can provide input to constrain nuclear density functionals, particularly their properties in the extreme isospin limit where the density functionals are
Preorganized frustrated Lewis pairs.
Bertini, Federica; Lyaskovskyy, Volodymyr; Timmer, Brian J J; de Kanter, Frans J J; Lutz, Martin; Ehlers, Andreas W; Slootweg, J Chris; Lammertsma, Koop
2012-01-11
Geminal frustrated Lewis pairs (FLPs) are expected to exhibit increased reactivity when the donor and acceptor sites are perfectly aligned. This is shown for reactions of the nonfluorinated FLP tBu(2)PCH(2)BPh(2) with H(2), CO(2), and isocyanates and supported computationally. PMID:22185581
Martin Richards
An algorithm, described by Sedgewick, finds the distance between the closest pair of n given points in a plane using a variant of mergesort. This takes O(n log n )t ime. To prove this it is necessary to show that, in the merge phase of the algorithm, no more than a constant number of distances need to be checked for
Pairing-induced speedup of nuclear spontaneous fission
Jhilam Sadhukhan; J. Dobaczewski; W. Nazarewicz; J. A. Sheikh; A. Baran
2014-10-06
Collective inertia is strongly influenced at the level crossing at which quantum system changes diabatically its microscopic configuration. Pairing correlations tend to make the large-amplitude nuclear collective motion more adiabatic by reducing the effect of those configuration changes. Competition between pairing and level crossing is thus expected to have a profound impact on spontaneous fission lifetimes. To elucidate the role of nucleonic pairing on spontaneous fission, we study the dynamic fission trajectories of $^{264}$Fm and $^{240}$Pu using the state-of-the-art self-consistent framework. We employ the superfluid nuclear density functional theory with the Skyrme energy density functional SkM$^*$ and a density-dependent pairing interaction. Along with shape variables, proton and neutron pairing correlations are taken as collective coordinates. The collective inertia tensor is calculated within the nonperturbative cranking approximation. The fission paths are obtained by using the least action principle in a four-dimensional collective space of shape and pairing coordinates. Pairing correlations are enhanced along the minimum-action fission path. For the symmetric fission of $^{264}$Fm, where the effect of triaxiality on the fission barrier is large, the geometry of fission pathway in the space of shape degrees of freedom is weakly impacted by pairing. This is not the case for $^{240}$Pu where pairing fluctuations restore the axial symmetry of the dynamic fission trajectory. The minimum-action fission path is strongly impacted by nucleonic pairing. In some cases, the dynamical coupling between shape and pairing degrees of freedom can lead to a dramatic departure from the static picture. Consequently, in the dynamical description of nuclear fission, particle-particle correlations should be considered on the same footing as those associated with shape degrees of freedom.
Pairing-induced speedup of nuclear spontaneous fission
NASA Astrophysics Data System (ADS)
Sadhukhan, Jhilam; Dobaczewski, J.; Nazarewicz, W.; Sheikh, J. A.; Baran, A.
2014-12-01
Background: Collective inertia is strongly influenced at the level crossing at which the quantum system changes its microscopic configuration diabatically. Pairing correlations tend to make the large-amplitude nuclear collective motion more adiabatic by reducing the effect of these configuration changes. Competition between pairing and level crossing is thus expected to have a profound impact on spontaneous fission lifetimes. Purpose: To elucidate the role of nucleonic pairing on spontaneous fission, we study the dynamic fission trajectories of 264Fm and 240Pu using the state-of-the-art self-consistent framework. Methods: We employ the superfluid nuclear density functional theory with the Skyrme energy density functional SkM* and a density-dependent pairing interaction. Along with shape variables, proton and neutron pairing correlations are taken as collective coordinates. The collective inertia tensor is calculated within the nonperturbative cranking approximation. The fission paths are obtained by using the least action principle in a four-dimensional collective space of shape and pairing coordinates. Results: Pairing correlations are enhanced along the minimum-action fission path. For the symmetric fission of 264Fm, where the effect of triaxiality on the fission barrier is large, the geometry of the fission pathway in the space of the shape degrees of freedom is weakly impacted by pairing. This is not the case for 240Pu, where pairing fluctuations restore the axial symmetry of the dynamic fission trajectory. Conclusions: The minimum-action fission path is strongly impacted by nucleonic pairing. In some cases, the dynamical coupling between shape and pairing degrees of freedom can lead to a dramatic departure from the static picture. Consequently, in the dynamical description of nuclear fission, particle-particle correlations should be considered on the same footing as those associated with shape degrees of freedom.
Regimes of Pulsar Pair Formation and Particle Energetics
NASA Technical Reports Server (NTRS)
Harding, Alice K.; Muslimov, Alexander G.; Zhang, Bing; White, Nicholas E. (Technical Monitor)
2002-01-01
We investigate the conditions required for the production of electron-positron pairs above a pulsar polar cap (PC) and the influence of pair production on the energetics of the primary particle acceleration. Assuming space-charge limited flow acceleration including the inertial frame-dragging effect, we allow both one-photon and two-photon pair production by either curvature radiation (CR) photons or photons resulting from inverse-Compton scattering of thermal photons from the PC by primary electrons. We find that,, while only the younger pulsars can produce pairs through CR, nearly all known radio pulsars are capable of producing pairs through non-resonant inverse-Compton scatterings. The effect of the neutron star equations of state on the pair death lines is explored. We show that pair production is facilitated in more compact stars and more a massive stars. Therefore accretion of mass by pulsars in binary systems may allow pair production in most of the millisecond purser population. We also find that two-photon pair production may be important in millisecond pursers if their surface temperatures are above approx. or equal to three million degrees K. Pursers that produce pairs through CRT wilt have their primary acceleration limited by the effect of screening of the electric field. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sup 1/2, sub rot) dependence. The acceleration voltage drop in pursers that produce pairs only through inverse-Compton emission will not be limited by electric field screening. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sub rot) dependence. Thus, older pursers will have significantly lower gamma-ray luminosity.
Modeling Within-Subject Dependencies in Ordinal Paired Comparison Data.
ERIC Educational Resources Information Center
Dillon, William R.; Bockenholt, Ulf
1997-01-01
This paper presents two probabilistic models based on the logistic and the normal distribution for the analysis of dependencies in individual paired comparison judgments such as might occur in educational research. Three applications illustrate the approach. (SLD)
Magnetic field distribution in polar cap models of gamma-ray bursters
NASA Technical Reports Server (NTRS)
Bagoly, Z.; Meszaros, P.; Matz, S. M.
1990-01-01
The high-energy spectral cutoffs are discussed as a function of angle predicted by magnetized polar cap models of gamma-ray bursters, in the presence of magnetic pair production and general relativistic effects. The effect of the photon escape beam shape on the relative probability of detection as a function of energy is calculated for a range of model parameters. These predictions are compared to the burster cutoff upper limits observed with SMM and are used to derive constraints on the detectable magnetic field strength distribution among bursters from future observations. A method for determining the intrinsic magnetic field distribution among gamma-ray bursting neutron stars is discussed.
Magnetic field distribution in polar cap models of gamma-ray bursters
Bagoly, Z.; Meszaros, P.; Matz, S.M. (Pennsylvania State Univ., University Park (USA) Eotvos Lorand Tudomanyegyetem, Budapest (Hungary) Northwestern Univ., Evanston, IL (USA))
1990-08-01
The high-energy spectral cutoffs are discussed as a function of angle predicted by magnetized polar cap models of gamma-ray bursters, in the presence of magnetic pair production and general relativistic effects. The effect of the photon escape beam shape on the relative probability of detection as a function of energy is calculated for a range of model parameters. These predictions are compared to the burster cutoff upper limits observed with SMM and are used to derive constraints on the detectable magnetic field strength distribution among bursters from future observations. A method for determining the intrinsic magnetic field distribution among gamma-ray bursting neutron stars is discussed. 19 refs.
STATISTICAL ANALYSIS OF NEUTRON EMISSION IN COLD FUSION EXPERIMENTS
M. Srinivasan; A. Shyam; S. B. Degwekar; L. V. Kulkarni
The paper discusses two techniques for studying the multiplicity spectrum of neutron emission in cold fusion experiments. In the first method the multiplicity distribution of counts in 20 ms time intervals is analysed to give information about the statistics of neutron emission in cold fusion. The results of six such experiments indicate that about 10 to 25% of the neutrons
Therapeutic potential of atmospheric neutrons Cyril Voyant1,2*
Boyer, Edmond
1 Therapeutic potential of atmospheric neutrons Cyril Voyant1,2* Ph.D., Rudy Roustit2 M by the reaction i and the nucleus j (Gy) Ls,b,t Mean free path (m) No Total number of neutron (NU) Ts) t Time variable (s) F(E) Cumulative distribution function for neutron related to energy (NU) S Surface
THE DIFFUSION COOLING OF NEUTRONS IN FINITE MODERATOR
Mark Nelkin
1958-01-01
When a pulse of fast neutrons is thermalized in a finite moderating ; medium, the asymptotic spectrum at long times is slower than an equilibrium ; Maxwellian distribution, because of preferential leakage of higherenergy neutrons. ; This phenomenon of ''diffusion cooling'' can be observed by examining the ; variation of the asymptotic neutron lifetime with the size of the moderating
Neutron rich nuclei and neutron stars
C. J. Horowitz
2013-03-01
The PREX experiment at Jefferson Laboratory measures the neutron radius of 208Pb with parity violating electron scattering in a way that is free from most strong interaction uncertainties. The 208Pb radius has important implications for neutron rich matter and the structure of neutron stars. We present first PREX results, describe future plans, and discuss a follow on measurement of the neutron radius of 48Ca. We review radio and X-ray observations of neutron star masses and radii. These constrain the equation of state (pressure versus density) of neutron rich matter. We present a new energy functional that is simultaneously fit to both nuclear and neutron star properties. In this approach, neutron star masses and radii constrain the energy of neutron matter. This avoids having to rely on model dependent microscopic calculations of neutron matter. The functional is then used to predict the location of the drip lines and the properties of very neutron rich heavy nuclei.
Neutron rich nuclei and neutron stars
Horowitz, C J
2013-01-01
The PREX experiment at Jefferson Laboratory measures the neutron radius of 208Pb with parity violating electron scattering in a way that is free from most strong interaction uncertainties. The 208Pb radius has important implications for neutron rich matter and the structure of neutron stars. We present first PREX results, describe future plans, and discuss a follow on measurement of the neutron radius of 48Ca. We review radio and X-ray observations of neutron star masses and radii. These constrain the equation of state (pressure versus density) of neutron rich matter. We present a new energy functional that is simultaneously fit to both nuclear and neutron star properties. In this approach, neutron star masses and radii constrain the energy of neutron matter. This avoids having to rely on model dependent microscopic calculations of neutron matter. The functional is then used to predict the location of the drip lines and the properties of very neutron rich heavy nuclei.
Neutron Rich Nuclei and Neutron Stars
NASA Astrophysics Data System (ADS)
Horowitz, C. J.
2014-09-01
The PREX experiment at Jefferson Laboratory measures the neutron radius of 208Pb with parity violating electron scattering in a way that is free from most strong interaction uncertainties. The 208Pb radius has important implications for neutron rich matter and the structure of neutron stars. We present first PREX results, describe future plans, and discuss a follow on measurement of the neutron radius of 48Ca. We review radio and X-ray observations of neutron star masses and radii. These constrain the equation of state (pressure versus density) of neutron rich matter. We present a new energy functional that is simultaneously fit to both nuclear and neutron star properties. In this approach, neutron star masses and radii constrain the energy of neutron matter. This avoids having to rely on model dependent microscopic calculations of neutron matter. The functional is then used to predict the location of the drip lines and the properties of very neutron rich heavy nuclei.
NASA Astrophysics Data System (ADS)
Galès, S.; Crawley, G. M.; Weber, D.; Zwieglinski, B.
1983-04-01
Valence and deep-lying neutron-hole strengths corresponding to orbits near and well below the Fermi surface have been observed in high-resolution studies of the 144, 148, 152Sm( 3He, ?) and of the 144, 148, 150, 152, 154Sm(p, d) reactions at 70 and 42 MeV bombarding energy, respectively. The explored excitation energy range was 28 MeV for the ( 3He, ?) experiment and about 12 MeV in the (p, d) study. Complete angular distributions have been measured in both cases and the data was analyzed within the framework of the distorted waves Born approximation theory of direct reactions. For the neutron closed shell target ( 144Sm), in addition to the well-known fragmentation of the 2d {5}/{2} and 1g {7}/{2} valence-hole strength, a new bump observed around 7.6 MeV excitation energy is excited in both reactions. This structure corresponds to the 1g {9}/{2} inner-hole strength in 143Sm and the analysis of the ( 3He, ?) data suggests that more than 50% of the l = 4 strength can be found between 6 and 12 MeV. When one goes to the heavier Sm isotopes, the energy spacing between valence-hole states located above and just below the N = 82 shell decreases strongly and disappears in 151Sm as a result of increasing deformation. Combining good energy resolution and detailed analysis of the two reactions, rather complete spectroscopic information is obtained for the valence-hole strength distributions. With regard to inner-hole states, the energy spectra exhibit a narrow structure whose centroid energy decreases from 4.4 to 2.9 MeV when the mass number increases from A = 147 to A = 153. The main peak displays an asymmetric shape with an extremely large high-energy tail. The 1h {11}/{2} hole strength is split into the Nilsson Orbitals. The narrow bumps are found to carry a large fraction of the l = 5 and l = 2 hole strengths in 147,149,151,152Sm isotopes. In the high-energy tail of the structures one observes overlapping and increasing spreading of the g {7}/{2}, 2d {5}/{2} and possibly 1g {9}/{2} inner-hole strengths due to the disappearance of the N = 82 shell gap between N = 83 and N = 89 neutron numbers. The experimental hole strengths distributions are compared where possible to the predictions of the quasiparticle-phonon nuclear model or to the simple Nilsson model.
Comparison of various stopping gases for 3He-based position sensitive neutron detectors
NASA Astrophysics Data System (ADS)
Doumas, A.; Smith, G. C.
2012-05-01
A range of solid state, scintillator and gas based detectors are being developed for use at the next generation of high flux neutron facilities. Since gas detectors are expected to continue to play a key role in future specific thermal neutron experiments, a comparison of the performance characteristics of prospective stopping gases is beneficial. Gas detectors typically utilize the reaction 3He(n,p)t to detect thermal neutrons; the 3He gas is used in a mixture containing a particular stopping gas in order to maintain relatively short ranges for the proton and triton pair emitted from the n-3He reaction. Common stopping gases include hydrocarbons (e.g. propane), carbon tetrafluoride, and noble gases such as argon and xenon. For this study, we utilized the Monte Carlo simulation code "Stopping and Range of Ions in Matter" to analyze the expected behavior of argon, xenon, carbon dioxide, difluoroethane and octafluoropropane as stopping gases for thermal neutron detectors. We also compare these findings to our previously analyzed performance of propane, butane and carbon tetrafluoride. A discussion of these gases includes their behavior in terms of proton and triton range, ionization distribution and straggle.
High-efficiency scintillation detector for combined of thermal and fast neutrons and gamma radiation
Chiles, Marion M. (Knoxville, TN); Mihalczo, John T. (Oak Ridge, TN); Blakeman, Edward D. (Oak Ridge, TN)
1989-01-01
A scintillation based radiation detector for the combined detection of thermal neutrons, high-energy neutrons and gamma rays in a single detecting unit. The detector consists of a pair of scintillators sandwiched together and optically coupled to the light sensitive face of a photomultiplier tube. A light tight radiation pervious housing is disposed about the scintillators and a portion of the photomultiplier tube to hold the arrangement in assembly and provides a radiation window adjacent the outer scintillator through which the radiation to be detected enters the detector. The outer scintillator is formed of a material in which scintillations are produced by thermal-neutrons and the inner scintillator is formed of a material in which scintillations are produced by high-energy neutrons and gamma rays. The light pulses produced by events detected in both scintillators are coupled to the photomultiplier tube which produces a current pulse in response to each detected event. These current pulses may be processed in a conventional manner to produce a count rate output indicative of the total detected radiation even count rate. Pulse discrimination techniques may be used to distinguish the different radiations and their energy distribution.
Chiles, M.M.; Mihalczo, J.T.; Blakeman, E.D.
1987-02-27
A scintillation based radiation detector for the combined detection of thermal neutrons, high-energy neutrons and gamma rays in a single detecting unit. The detector consists of a pair of scintillators sandwiched together and optically coupled to the light sensitive face of a photomultiplier tube. A light tight radiation pervious housing is disposed about the scintillators and a portion of the photomultiplier tube to hold the arrangement in assembly and provides a radiation window adjacent the outer scintillator through which the radiation to be detected enters the detector. The outer scintillator is formed of a material in which scintillations are produced by thermal-neutrons and the inner scintillator is formed of a material in which scintillations are produced by high-energy neutrons and gamma rays. The light pulses produced by events detected in both scintillators are coupled to the photomultiplier tube which produces a current pulse in response to each detected event. These current pulses may be processed in a conventional manner to produce a count rate output indicative of the total detected radiation event count rate. Pulse discrimination techniques may be used to distinguish the different radiations and their energy distribution.
Cristache, C I; Duliu, O G; Culicov, O A; Frontasyeva, M V; Ricman, C; Toma, M
2009-05-01
Six major (Na, Al, K, Ca, Ti, Fe) and 28 trace (Sc, Cr, V, Mn, Co, Zn, Cu, As, Br, Sr, Rb, Zr, Mo, Sn, Sb, Ba, Cs, La, Ce, Nd, Eu, Sm, Tb, Hf, Ta, W, Th and U) elements were determined by epithermal neutron activation analysis (ENAA) in nine Meridional Carpathian and Macin Mountains samples of igneous and metamorphic rocks. Correlation and principal factor analysis were used to interpret data while natural radionuclides radiometry shows a good correlation with ENAA results. PMID:19231213
Burst Oscillations: Watching Neutron Stars Spin
NASA Technical Reports Server (NTRS)
Strohmayer, Tod
2010-01-01
It is now almost 15 years since the first detection of rotationally modulated emission from X-ray bursting neutron stars, "burst oscillations," This phenomenon enables us to see neutron stars spin, as the X-ray burst flux asymmetrically lights up the surface. It has enabled a new way to probe the neutron star spin frequency distribution, as well as to elucidate the multidimensional nature of nuclear burning on neutron stars. I will review our current observational understanding of the phenomenon, with an eye toward highlighting some of the interesting remaining puzzles, of which there is no shortage.
Pair production in superstrong magnetic fields
NASA Technical Reports Server (NTRS)
Daugherty, J. K.; Harding, A. K.
1983-01-01
The production of electron-positron pairs by single photons in magnetic fields 10 to the twelth power G was investigated in detail for photon energies near threshold as well as for the asymptotic limit of high photon energy. The exact attenuation coefficient, which is derived and then evaluated numerically, is strongly influenced by the discrete energy states of the electron and positron. Near threshold, it exhibits a sawtooth pattern as a function of photon energy, and its value is significantly below that predicted by the asymptotic expression for the attenuation coefficient. The energy distributions of the created pair are computed numerically near threshold and analytic expressions are derived in the asymptotic limit. These results indicate that as field strength and photon energy increase, it becomes increasingly probable for the pair to divide the photon energy unequally. This effect, as well as the threshold behavior of the attenuation coefficient, could have important consequences for pulsar models.
Nested neutron microfocusing optics on SNAP
Ice, Gene E [ORNL; Choi, Jae-Young [Pohang Accelerator Laboratory, Pohang, Korea; Takacs, P. Z. [Brookhaven National Laboratory (BNL); Khounsary, Ali [Argonne National Laboratory (ANL); Puzyrev, Yevgeniy S [ORNL; Molaison, Jamie J [ORNL; Tulk, Christopher A [ORNL; Andersen, K H [Institut Laue-Langevin (ILL); Bigault, T [Institut Laue-Langevin (ILL)
2010-01-01
The high source intensity of the Spallation Neutron Source (SNS), together with efficient detectors and large detector solid angles, now makes possible neutron experiments with much smaller sample volumes than previously were practical. Nested Kirkpatrick-Baez supermirror optics provide a promising and efficient way to further decrease the useable neutron sample size by focusing polychromatic neutrons into microbeams. Because the optics are nondispersive, they are ideal for spallation sources and for polychromatic and wide bandpass experiments on reactor sources. Theoretical calculations indicate that nested mirrors can preserve source brilliance at the sample for small beams and for modest divergences that are appropriate for diffraction experiments. Although the flux intercepted by a sample can be similar with standard beam-guided approaches, the signal-to-background is much improved with small beams on small samples. Here we describe the design, calibration and performance of a nested neutron mirror pair for the Spallation Neutrons At Pressure (SNAP) beamline at the SNS. High-pressure neutron diffraction is but one example of a large class of neutron experiments that will benefit from spatially-resolved microdiffraction.
Computer simulation of neutron capture therapy
Olson, Arne Peter
1967-01-01
Analytical methods are developed to simulate on a large digital computer the production and use of reactor neutron beams f or boron capture therapy of brain tumors. The simulation accounts for radiation dose distributions ...
G. Badurek; H. Rauch
2000-01-01
The most essential performance parameters of the upgraded neutron interferometer instrument S18 at the ILL including the novel concept of beam polarization by birefringent permanent magnetic field prisms are presented. A spin superposition experiment is proposed to test the complementarity of which-way knowledge and fringe visibility as well as for the concept of quantum erasure.
Demographic mechanisms of inbreeding adjustment through extra-pair reproduction.
Reid, Jane M; Duthie, A Bradley; Wolak, Matthew E; Arcese, Peter
2015-07-01
One hypothesis explaining extra-pair reproduction is that socially monogamous females mate with extra-pair males to adjust the coefficient of inbreeding (f) of extra-pair offspring (EPO) relative to that of within-pair offspring (WPO) they would produce with their socially paired male. Such adjustment of offspring f requires non-random extra-pair reproduction with respect to relatedness, which is in turn often assumed to require some mechanism of explicit pre-copulatory or post-copulatory kin discrimination. We propose three demographic processes that could potentially cause mean f to differ between individual females' EPO and WPO given random extra-pair reproduction with available males without necessarily requiring explicit kin discrimination. Specifically, such a difference could arise if social pairings formed non-randomly with respect to relatedness or persisted non-randomly with respect to relatedness, or if the distribution of relatedness between females and their sets of potential mates changed during the period through which social pairings persisted. We used comprehensive pedigree and pairing data from free-living song sparrows (Melospiza melodia) to quantify these three processes and hence investigate how individual females could adjust mean offspring f through instantaneously random extra-pair reproduction. Female song sparrows tended to form social pairings with unrelated or distantly related males slightly less frequently than expected given random pairing within the defined set of available males. Furthermore, social pairings between more closely related mates tended to be more likely to persist across years than social pairings between less closely related mates. However, these effects were small and the mean relatedness between females and their sets of potential extra-pair males did not change substantially across the years through which social pairings persisted. Our framework and analyses illustrate how demographic and social structuring within populations might allow females to adjust mean f of offspring through random extra-pair reproduction without necessarily requiring explicit kin discrimination, implying that adjustment of offspring f might be an inevitable consequence of extra-pair reproduction. New theoretical and empirical studies are required to explore the general magnitude of such effects and quantify the degree to which they could facilitate or constrain long-term evolution of extra-pair reproduction. PMID:25645743
Ishikawa, Masayori; Tanaka, Kenichi; Endo, Satrou; Hoshi, Masaharu
2015-01-01
Phantom experiments to evaluate thermal neutron flux distribution were performed using the Scintillator with Optical Fiber (SOF) detector, which was developed as a thermal neutron monitor during boron neutron capture therapy (BNCT) irradiation. Compared with the gold wire activation method and Monte Carlo N-particle (MCNP) calculations, it was confirmed that the SOF detector is capable of measuring thermal neutron flux as low as 105 n/cm2/s with sufficient accuracy. The SOF detector will be useful for phantom experiments with BNCT neutron fields from low-current accelerator-based neutron sources. PMID:25589504
Ishikawa, Masayori; Tanaka, Kenichi; Endo, Satrou; Hoshi, Masaharu
2015-03-01
Phantom experiments to evaluate thermal neutron flux distribution were performed using the Scintillator with Optical Fiber (SOF) detector, which was developed as a thermal neutron monitor during boron neutron capture therapy (BNCT) irradiation. Compared with the gold wire activation method and Monte Carlo N-particle (MCNP) calculations, it was confirmed that the SOF detector is capable of measuring thermal neutron flux as low as 10(5) n/cm(2)/s with sufficient accuracy. The SOF detector will be useful for phantom experiments with BNCT neutron fields from low-current accelerator-based neutron sources. PMID:25589504
Establishing local workplace field correction factors for neutron personal dosemeters.
Vanhavere, Filip; Cauwels, Vanessa
2014-10-01
The present personal neutron dosemeters still need local correction factors to be able to provide accuracy comparable with photon dosemeters. Characterisation of the local neutron field is an indispensable part of neutron dosimetry to obtain such correction factors. It is often overlooked that besides characterisation in the neutron energy also the directional distribution of neutrons plays a crucial part in this characterisation. The authors have done such characterisation in the energy and angle for four workplace fields in Paks NPP. For this a relatively simple approximation method was used using the Nprobe for the energy distribution and measurements on the six sides of the slab phantom with personal dosemeters for the directional distribution. This allowed one to estimate a reference neutron Hp(10) rate and to compare it with the response of several neutron personal dosemeters. PMID:24962515
Methods for absorbing neutrons
Guillen, Donna P. (Idaho Falls, ID); Longhurst, Glen R. (Idaho Falls, ID); Porter, Douglas L. (Idaho Falls, ID); Parry, James R. (Idaho Falls, ID)
2012-07-24
A conduction cooled neutron absorber may include a metal matrix composite that comprises a metal having a thermal neutron cross-section of at least about 50 barns and a metal having a thermal conductivity of at least about 1 W/cmK. Apparatus for providing a neutron flux having a high fast-to-thermal neutron ratio may include a source of neutrons that produces fast neutrons and thermal neutrons. A neutron absorber positioned adjacent the neutron source absorbs at least some of the thermal neutrons so that a region adjacent the neutron absorber has a fast-to-thermal neutron ratio of at least about 15. A coolant in thermal contact with the neutron absorber removes heat from the neutron absorber.
NASA Astrophysics Data System (ADS)
Cheng, Kaijia; Cheng, Shuyu
Up to now, the pairing mechanism is regarded as the rule of thumb criterion of an acceptable theory of superconductivity. It is generally held as a taboo for any theory which is not founded on this basis. However this is not true and it misleads the direction for the theoretical research for both the high and low temperature regions and eventually delays the progress in practice. It is now the time to clear up the situation.
Teresa Cecchi
2008-01-01
The present state of ion-pair chromatography (IPC) is reviewed. Emphasis is placed on the theoretical modeling of the retention behavior of charged, zwitterionic, and neutral solutes, since the theory provides the generally good understanding of the factors affecting the separation. Although stoichiometric models were credited with the first easy-to-understand demonstration of the retention mechanism of IPC, they were thermodynamic models,
Fundamental Neutron Physics Beamline Spallation Neutron Source
Fundamental Neutron Physics Beamline at the Spallation Neutron Source Overview and Status 21 that can utilize the full cold neutron energy spectrum. The external facility will be appropriate for experiments that need ultra cold neutrons generated in superfluid Helium. · The beamlines consist of
NEUTRON ELECTRIC-DIPOLE MOMENT, ULTRACOLD NEUTRONS
NEUTRON ELECTRIC-DIPOLE MOMENT, ULTRACOLD NEUTRONS AND POLARIZED 3He R. GOLUB~and Steve K REPORTS (Review Section of Physics Letters) 237, No. 1(1994)1--62. PHYSICS REPORTS North-Holland Neutron electric-dipole moment, ultracold neutrons and polarized 3He R. Goluba and Steve K. Lamoreauxb a
Internal Pair Decay of Giant Resonances
NASA Astrophysics Data System (ADS)
Montoya, Carlos Peter
The internal pair decay of giant resonances is studied experimentally and theoretically. From the equations governing the pair decay of E0 and E1 transitions in reaction aligned nuclei the two multipoles are shown to have observables which differ significantly. The strength functions for the pair decay of giant resonances, and specifically the isoscalar and isovector giant monopole (GMR) and quadrupole (GQR) resonances, are derived. These strength functions are used with the CASCADE statistical model code to predict internal pair decay in hot nuclei. The design of a highly segmented array of plastic phoswich scintillators, tailored for the measurement of high energy pairs, is described. Electron (positron) energies of 2-30 MeV can be measured by each individual element, with a total transition energy resolution of delta E/E = 13% for a 20 MeV transition. The array covers 29% of 4pi and its efficiency is 1.6% for a 6-MeV E0 internal pair decay, and 1.1% for an 18-MeV E1 transition. The detector is shown to be capable of differentiating between E0 and E1 transitions. An event simulator is developed that successfully describes all observables. The cross section for pairs from the decay of the GDR in ^{12}C is measured to be 410 nb to the ground state and 140 nb to the first excited state. Comparison with the available gamma-cross sections yields conversion coefficients which are consistent with theoretical predictions. The pair decay of the giant dipole resonance built on high excited states is measured in ^ {110}Sn and ^{110 }Cd. The two nuclei are produced in heavy ion fusion reactions with similar temperatures and spin distributions. A CASCADE calculation for hot ^{110}Sn indicates that the GDR dominates the pair decay spectrum. The measured pair energy spectrum is fit very well by the response folded CASCADE calculation at energies above 10 MeV. The measured angular correlations are consistent with the predicted E1 dominance of the spectrum, and no evidence of the isovector GMR or GQR are found.
Neutron reflecting supermirror structure
Wood, James L. (Drayton Plains, MI)
1992-01-01
An improved neutron reflecting supermirror structure comprising a plurality of stacked sets of bilayers of neutron reflecting materials. The improved neutron reflecting supermirror structure is adapted to provide extremely good performance at high incidence angles, i.e. up to four time the critical angle of standard neutron mirror structures. The reflection of neutrons striking the supermirror structure at a high critical angle provides enhanced neutron throughput, and hence more efficient and economical use of neutron sources.
M. Friedman; A. Drobot; N. C. Wyeth
1995-01-01
A non-reactor neutron source is disclosed that allows for a pulse intense current of ions to generate neutrons that are epithermal neutrons and provide low-energy neutron energy particularly suited for Boron Neutron Capture Therapy (BNCT) treatment. The present invention provides for a neutron fluence on a tumor which can be more than 10Â¹Â² neutrons\\/cmÂ² and is generated into a time
Influence of the single-particle structure on the nuclear surface and the neutron skin
M. Warda; M. Centelles; X. Vinas; X. Roca-Maza
2014-06-05
We analyze the influence of the single-particle structure on the neutron density distribution and the neutron skin in Ca, Ni, Zr, Sn, and Pb isotopes. The nucleon density distributions are calculated in the Hartree-Fock+BCS approach with the SLy4 Skyrme force. A close correlation is found between the quantum numbers of the valence neutrons and the changes in the position and the diffuseness of the nuclear surface, which in turn affect the neutron skin thickness. Neutrons in the valence orbitals with low principal quantum number and high angular momentum mainly displace the position of the neutron surface outwards, while neutrons with high principal quantum number and low angular momentum basically increase the diffuseness of the neutron surface. The impact of the valence shell neutrons on the tail of the neutron density distribution is discussed.
Pair correlations in nuclei involved in neutrinoless double beta decay: 76Ge and 76Se
S. J. Freeman; J. P. Schiffer; A. C. C. Villari; J. A. Clark; C. Deibel; S. Gros; A. Heinz; D. Hirata; C. L. Jiang; B. P. Kay; A. Parikh; P. D. Parker; J. Qian; K. E. Rehm; X. D. Tang; V. Werner; C. Wrede
2007-03-23
Precision measurements were carried out to test the similarities between the ground states of 76Ge and 76Se. The extent to which these two nuclei can be characterized as consisting of correlated pairs of neutrons in a BCS-like ground state was studied. The pair removal (p,t) reaction was measured at the far forward angle of 3 degrees. The relative cross sections are consistent (at the 5% level) with the description of these nuclei in terms of a correlated pairing state outside the N=28 closed shells with no pairing vibrations. Data were also obtained for 74Ge and 78Se.
Hoffman, D.; Lee, D.; Ghiorso, A.; Nurmia, M.; Aleklett, K.
1980-10-01
We have measured the mass and kinetic-energy distributions for fragments from the spontaneous fission of 1.2-s /sup 246/Fm and 38-s /sup 248/Fm. The mass distributions are highly asymmetric and the average total kinetic energies of 199 +- 4 MeV and 198 +- 4 MeV, respectively, are consistent with systematics for lower Z actinides. Their properties are in contrast to those of /sup 258/Fm and /sup 259/Fm, whose spontaneous fission results in narrowly symmetric mass distributions accompanied by unusually high total kinetic energies.
Neutron Spectra in a 15 MV LINAC
NASA Astrophysics Data System (ADS)
Vega-Carrillo, H. R.; Chu, Wei-Han; Tung, Chuan-Jong; Lan, Jen-Hong
2010-12-01
Neutron spectra were calculated inside the treatment hall of a 15 MV LINAC, calculations were carried out using Monte Carlo methods. With a Bonner sphere spectrometer with pairs of thermoluminiscent dosimeters the neutron spectrum at 100 cm from the isocenter was measured and compared with the calculated spectrum. All the spectra in the treatment hall show the presence of evaporation and knock-on neutrons; also the room-return due to the hall features is shown. In the maze the large contribution are due to epithermal and thermal neutrons. A good agreement between the calculated and measured spectrum at 100 cm was noticed, from this comparison the differences are attributed to the water content in the concrete of the hall.
Neutron Spectra in a 15 MV LINAC
Vega-Carrillo, H. R. [Unidad Academica de Estudios Nucleares de la Universidad Autonoma de Zacatecas. Apdo. Postal 336, 98000 Zacatecas, Zac. (Mexico); Chu, Wei-Han [National Tsing Hua University, Hsinchu, Taiwan (China); Tung, Chuan-Jong [Chan Gung University, Taiwan (China); Lan, Jen-Hong [Chan Gung Memorial Hospital-Kaohsiung Medical Center and National Kaohsiung University, Kaohsiung, Taiwan (China)
2010-12-07
Neutron spectra were calculated inside the treatment hall of a 15 MV LINAC, calculations were carried out using Monte Carlo methods. With a Bonner sphere spectrometer with pairs of thermoluminiscent dosimeters the neutron spectrum at 100 cm from the isocenter was measured and compared with the calculated spectrum. All the spectra in the treatment hall show the presence of evaporation and knock-on neutrons; also the room-return due to the hall features is shown. In the maze the large contribution are due to epithermal and thermal neutrons. A good agreement between the calculated and measured spectrum at 100 cm was noticed, from this comparison the differences are attributed to the water content in the concrete of the hall.
Superconductivity: The persistence of pairs
NASA Astrophysics Data System (ADS)
Edelman, Alex; Littlewood, Peter
2015-06-01
Fingerprints of electron pairing in a range of temperature and magnetic field above the bulk superconducting phase transition have been found, which may be evidence for the long-sought 'preformed pairs' expected in strongly coupled or very dilute superconductors.
Evaluation of Lithium Gadolinium Borate Capture-Gated Spectrometer Neutron Efficiencies
Nabil Menaa; Marcel Villani; Stephen Croft; Robert B. McElroy; Sasha A. Philips; J. Bart Czirr
2009-01-01
Accurate determination of neutron dose equivalent requires knowledge of the neutron energy distribution. Existing neutron spectrometers, such as Bonner sphere sets, are typically bulky and require long acquisition times. Hence, a handheld or portable system that could perform area monitoring with acceptable accuracy would be of interest. Such a device will require a detector that is efficient, and possesses gamma-neutron
Earth albedo neutrons from 10 to 100 MeV.
NASA Technical Reports Server (NTRS)
Preszler, A. M.; Simnett, G. M.; White, R. S.
1972-01-01
We report the measurement of the energy and angular distributions of earth albedo neutrons from 10 to 100 MeV at 40 deg N geomagnetic latitude from a balloon at 120,000 ft, below 4.65 g/sq cm. The albedo-neutron omnidirectional energy distribution is flat to 50 MeV, then decreases with energy. The absolute neutron energy distribution is of the correct strength and shape for the albedo neutrons to be the source of the protons trapped in earth's inner radiation belt.
Special Angle Pairs Discovery Activity
NSDL National Science Digital Library
Barbara Henry
2012-04-16
This lesson uses a discovery approach to identify the special angles formed when a set of parallel lines is cut by a transversal. During this lesson students identify the angle pair and the relationship between the angles. Students use this relationship and special angle pairs to make conjectures about which angle pairs are considered special angles.
Neutron facilities managers meet
A. E. Ekkebus
2003-01-01
Managers of the six North American neutron experimental facilities (Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory, Center for Neutron Research at National Institute of Standards and Technology (NIST), Neutron Program for Materials Research of the National Research Council Canada (NRC-CNRC), High Flux Isotope Reactor (HFIR) and the Spallation Neutron Source (SNS) of Oak Ridge National Laboratory, and Los
NASA Astrophysics Data System (ADS)
Wang, Hsiu-Wen; Fanelli, Victor R.; Reiche, Helmut M.; Larson, Eric; Taylor, Mark A.; Xu, Hongwu; Zhu, Jinlong; Siewenie, Joan; Page, Katharine
2014-12-01
This contribution describes a new local structure compatible gas/liquid cell apparatus for probing disordered materials at high pressures and variable temperatures in the Neutron Powder Diffraction instrument at the Lujan Neutron Scattering Center, Los Alamos National Laboratory. The new sample environment offers choices for sample canister thickness and canister material type. Finite element modeling is utilized to establish maximum allowable working pressures of 414 MPa at 15 K and 121 MPa at 600 K. High quality atomic pair distribution function data extraction and modeling have been demonstrated for a calibration standard (Si powder) and for supercritical and subcritical CO2 measurements. The new sample environment was designed to specifically target experimental studies of the local atomic structures involved in geologic CO2 sequestration, but will be equally applicable to a wide variety of energy applications, including sorption of fluids on nano/meso-porous solids, clathrate hydrate formation, catalysis, carbon capture, and H2 and natural gas uptake/storage.
First quantized pair interactions
A. F. Bennett
2015-03-12
The parametrized Dirac wave equation for multiple particles is shown here to yield the standard cross sections for creation and annihilation of fermion pairs, while avoiding the paradoxes arising from the standard single-particle Dirac equation and hole theory. These paradoxes were originally overcome with Quantum Field Theory. The creation and annihilation operators of Quantum Field Theory are subject to causality conditions which preclude entanglement across distances greater than the order of the Compton wavelength. The parametrized first-quantized formalism requires no causality condition for fermions, and it admits fermion entanglement across all of space and time, while ensuring covariant Dyson series and ${\\mathcal TPC}$ invariance.
Prospective very young asteroid pairs
NASA Astrophysics Data System (ADS)
Galád, A.; Vokrouhlický, D.; Zizka, J.
2014-07-01
Several tens of asteroid pairs can be discerned from the background main-belt asteroids. The majority of them are thought to have formed within only the last few 10^6 yr. The youngest recognized pairs have formed more than ? 10 kyr ago. As some details of pair formation are still not understood well, the study of young pairs is of great importance. It is mainly because the conditions at the time of the pair formation could be deduced much more reliably for young pairs. For example, space weathering on the surfaces of the components, or changes in their rotational properties (in spin rates, tumbling, coordinates of rotational pole) could be negligible since the formation of young pairs. Also, possible strong perturbations by main-belt bodies on pair formation can be reliably studied only for extremely young pairs. Some pairs can quickly blend in with the background asteroids, so even the frequency of asteroid pair formation could be determined more reliably based on young pairs (though only after a statistically significant sample is at disposal). In our regular search for young pairs in the growing asteroid database, only multiopposition asteroids with very similar orbital and proper elements are investigated. Every pair component is represented by a number of clones within orbital uncertainties and drifting in semimajor axis due to the Yarkovsky effect. We found that, if the previously unrecognized pairs (87887) 2000 SS_{286} - 2002 AT_{49} and (355258) 2007 LY_{4} - 2013AF_{40} formed at the recent very close approach of their components, they could become the youngest known pairs. In both cases, the relative encounter velocities of the components were only ˜ 0.1 m s^{-1}. However, the minimum distances between some clones are too large and a few clones of the latter pair did not encounter recently (within ? 10 kyr). The age of some prospective young pairs cannot be determined reliably without improved orbital properties (e.g., the second component of a pair (320025) 2007 DT_{76} - 2007 DP_{16}). It is because some components suffered recently repeated close approaches to Ceres or other large main-belt perturbers. In general, the uncertainties in age estimation can be heavily reduced after the physical properties (e.g., sense of rotation, shape, size, binarity) of the pair components are determined.
Spectra and Neutron Dosimetry Inside a PET Cyclotron Vault Room
Vega-Carrillo, Hector Rene [Unidades Academicas: Estudios Nucleares e Ing. Electrica. Universidad Autonoma de Zacatecas, A.P. 336, 98000 Zacatecas, Zac. Mexico (Mexico); Mendez, Roberto [Universidad Europea Miguel de Cervantes, Valladolid (Spain); Iniguez, Maria Pilar [Facultad de Ciencias de la Universidad de Valladolid, Valladolid (Spain); Marti-Climent, Joseph; Penuelas, Ivan [Servicio de Medicina Nuclear, Clinica Universitaria de la Universidad de Navarra (Spain); Barquero, Raquel [Hospital Universitario Rio Hortega, Valladolid (Spain)
2006-09-08
The neutron field around a PET cyclotron was investigated during 18F radioisotope production with an 18 MeV proton beam. Pairs of thermoluminescent dosemeters, TLD600 and TLD700, were used as thermal neutron detector inside a Bonner Spheres Spectrometer to measure the neutron spectra at three different positions inside the cyclotron's vault room. Neutron spectra were also determined by Monte Carlo calculations. The hardest spectrum was observed in front of cyclotron target and the softest was noticed at the antipode of target. Neutron doses derived from the measured spectra vary between 11 and 377 mSv/{mu}A-h of proton integrated current, Doses were also measured with a single-moderator remmeter, with an active thermal neutron detector, whose response in affected by the radiation field in the vault room.
Neutron multiplication error in TRU waste measurements
Veilleux, John [Los Alamos National Laboratory; Stanfield, Sean B [CCP; Wachter, Joe [CCP; Ceo, Bob [CCP
2009-01-01
Total Measurement Uncertainty (TMU) in neutron assays of transuranic waste (TRU) are comprised of several components including counting statistics, matrix and source distribution, calibration inaccuracy, background effects, and neutron multiplication error. While a minor component for low plutonium masses, neutron multiplication error is often the major contributor to the TMU for items containing more than 140 g of weapons grade plutonium. Neutron multiplication arises when neutrons from spontaneous fission and other nuclear events induce fissions in other fissile isotopes in the waste, thereby multiplying the overall coincidence neutron response in passive neutron measurements. Since passive neutron counters cannot differentiate between spontaneous and induced fission neutrons, multiplication can lead to positive bias in the measurements. Although neutron multiplication can only result in a positive bias, it has, for the purpose of mathematical simplicity, generally been treated as an error that can lead to either a positive or negative result in the TMU. While the factors that contribute to neutron multiplication include the total mass of fissile nuclides, the presence of moderating material in the matrix, the concentration and geometry of the fissile sources, and other factors; measurement uncertainty is generally determined as a function of the fissile mass in most TMU software calculations because this is the only quantity determined by the passive neutron measurement. Neutron multiplication error has a particularly pernicious consequence for TRU waste analysis because the measured Fissile Gram Equivalent (FGE) plus twice the TMU error must be less than 200 for TRU waste packaged in 55-gal drums and less than 325 for boxed waste. For this reason, large errors due to neutron multiplication can lead to increased rejections of TRU waste containers. This report will attempt to better define the error term due to neutron multiplication and arrive at values that are more realistic and accurate. To do so, measurements of standards and waste drums were performed with High Efficiency Neutron Counters (HENC) located at Los Alamos National Laboratory (LANL). The data were analyzed for multiplication effects and new estimates of the multiplication error were computed. A concluding section will present alternatives for reducing the number of rejections of TRU waste containers due to neutron multiplication error.
Multi-element Neutron Energy Spectrometer
Sanjoy Mukhopadhyay, Richard Maurer, Ronald Wolff, Stephen Mitchell, Alexis Reed
2009-09-11
In the area of nuclear radiological emergency response and preparedness applications, interest in neutron detection stems from several factors. Unlike gamma rays, which are abundant in nature and present serious difficulties in differentiating a signal from a changing background, whose values are location specific, neutrons are rare and nearly homogenous in spatial distribution. Additionally, many special nuclear materials (SNM) emit neutrons either directly by spontaneous fission or produce neutrons indirectly through (?, n) reactions in nearby light elements. Also of importance in detection scenarios is the fact that neutrons are not easily attenuated. Typically neutron detection is done by simply counting the low energy thermal neutrons by employing pressurized helium tubes operated at high voltages. Not much emphasis is put on determining the energy of the incident neutrons. However, critical information can be obtained by analyzing the neutron energy given off from radioactive materials. In the detection of an SNM, neutron energy information from an unknown source can be of paramount importance. We have modeled, designed, and prototyped multi-element neutron energy spectrometers that contain three to five pressurized helium tubes of dimensions 2" diam. x 10" in length. Each individual helium tube has a specific amount of high density plastic neutron moderators to slow down the incident energetic neutrons to an accurately estimated energy. A typical spectrometer is a set of moderator cylinders surrounding detectors that have high efficiency for detecting thermal neutrons. The larger the moderator, the higher the energy of incident neutrons for which the detector assembly has matched detection efficiency. If all the detectors are exposed to the same radiation field and the efficiency as a function of energy (response function) of each of the detectors is known, the neutron energy spectrum can be determined from the detector count rates. Monte Carlo simulation results of response function calculations for different arrays of helium tubes with varying amount of moderators will be shown. Experimental evidence of effectiveness of a set of moderated helium tubes to measure the hardness of the incident neutrons will be demonstrated.
Semiclassical pair production rate for rotating electric fields
NASA Astrophysics Data System (ADS)
Strobel, Eckhard; Xue, She-Sheng
2015-02-01
We semiclassically investigate Schwinger pair production for pulsed rotating electric fields depending on time. To do so we solve the Dirac equation for two-component fields in a Wentzel-Kramers-Brillouin-like approximation. The result shows that for two-component fields the spin distribution of produced pairs is generally not 1 ?1 . As a result the pair creation rates of spinor and scalar QED are different even for one pair of turning points. For rotating electric fields, the pair creation rate is dominated by particles with a specific spin depending on the sense of rotation for a certain range of pulse lengths and frequencies. We present an analytical solution for the momentum spectrum of the constant rotating field. We find interference effects not only in the momentum spectrum but also in the total particle number of rotating electric fields.
The Orbit of X Per and Its Neutron Star Companion
Hugo Delgado-Marti; Alan M. Levine; Eric Pfahl; Saul A. Rappaport
2000-04-18
We have observed the Be/X-ray pulsar binary system X Per/4U 0352+30 on 61 occasions spanning an interval of 600 days with the PCA instrument on RXTE. Pulse timing analyses of the 837-s pulsations yield strong evidence for the presence of orbital Doppler delays. We confirm the Doppler delays by using measurements made with the RXTE All-Sky Monitor. We obtain an orbital period of 250 days, a projected semimajor axis of the neutron star of 454 lt-s, a mass function of 1.61 solar masses, and a modest eccentricity of 0.11. We discuss the formation of the system in the context of the standard evolutionary scenario for Be/X-ray binaries with consideration of the possibility that the birth of the neutron star was accompanied by a kick of the type often inferred from the velocity distribution of isolated radio pulsars. The orbital eccentricity just after the supernova explosion was almost certainly virtually the same as at present, because the Be star is much smaller than the orbital separation. We find that the system most likely formed from a pair of massive progenitor stars, and probably involved a quasi-stable and nearly conservative transfer of mass from the primary to the secondary. We find that the He star remnant of the primary most likely had a mass less than 6 solar masses after mass transfer. Finally, we speculate that there may be a substantial population of neutron stars formed with little or no kick.
Nuclear Equation of State and Neutron Star Cooling
Yeunhwan Lim; Chang Ho Hyun; Chang-Hwan Lee
2015-01-19
We investigate the effects of the nuclear equation of state (EoS) to the neutron star cooling. New era for nuclear EoS has begun after the discovery of $\\sim 2\\msun$ neutron stars PSR J1614$-$2230 and PSR J0348$+$0432 [1, 2]. Also recent works on the mass and radius of neutron stars from low-mass X-ray binaries [3] strongly constrain the EoS of nuclear matter. On the other hand, observations of the neutron star in Cassiopeia A (Cas A) more than 10 years confirmed the existence of nuclear superfluidity [4, 5]. Nuclear superfluidity reduces the heat capacities as well as neutrino emissivities. With nuclear superfluidity the neutrino emission processes are highly suppressed, and the existence of superfluidity makes the cooling path quite different from that of the standard cooling process. Superfluidity also allows new neutrino emission process, which is called `Pair Breaking and Formation'(PBF). PBF is a fast cooling process and can explain the fast cooling rate of neutron star in Cas A. Therefore, it is essential to add the superfluidity effect in the neutron star cooling process. In this work, we simulate neutron star cooling curves using both non-relativistic and relativistic nuclear models. The existence of too early direct Urca process shows that some of nuclear models do not fit for the cooling simulation. After this first selection process, the nuclear pairing gaps are searched using the observational neutron star's age and temperature data.
Nondestructive fissile material assay by induced fission neutron correlation
NASA Astrophysics Data System (ADS)
Hage, Walter
2005-10-01
An NDA method and interpretation model for the determination of small fissile material masses, in radioactive waste, is elaborated. The method uses a pulsed neutron source to interrogate a waste item located in the sample cavity. The sample cavity is lined with graphite to yield a long thermal neutron lifetime. For each pulse of source neutrons, the slowed down neutron population causes thermal fission in the fissile material of the sample, resulting in the emission of fast neutrons from the sample. Some of these fast neutrons escape the cavity and the cavity liner, and are slowed down in an external polyethylene moderator, designed to yield a short thermal neutron lifetime, and are subsequently detected in incorporated thermal neutron detectors. Signal groups, representing the detection of fission neutrons, are recorded in several observation intervals after the pulse of source neutrons has died away in the polyethylene moderator. Following many pulses of source neutrons, the frequency of such signal groups is accumulated. The first, second, and third factorial moment of such frequency distributions are the estimated value of signal singlets, doublets and triplets, respectively. These multiplets are expressed as function of the fissile mass, the neutron detection probability, instrumental and nuclear parameters, and a stationary neutron signal background, thus permitting an absolute determination of the fissile mass of the sample.
Neutron lifetime measured with stored ultracold neutrons
Mampe, W.; Ageron, P.; Bates, C.; Pendlebury, J. M.; Steyerl, A.
1989-08-07
The neutron lifetime has been measured by counting the neutrons remaining in a fluid-walled bottle as a function of the duration of storage. Losses of neutrons caused by the wall reflections are eliminated by varying the bottle volume-to-surface ratio. The result obtained is /tau//sub /beta//=887.6/plus minus/3 s.
Production of V 0 pairs in the hyperon experiment WA89
M. I. Adamovich; Yu. A. Alexandrov; S. P. Baranov; D. Barberis; M. Beck; C. Bérat; W. Beusch; M. Boss; S. Brons; W. Brückner; M. Buénerd; C. Busch; C. Büscher; F. Charignon; J. Chauvin; E. A. Chudakov; U. Dersch; F. Dropmann; J. Engelfried; F. Faller; A. Fournier; S. G. Gerassimov; M. Godbersen; P. Grafström; T. Haller; M. Heidrich; E. Hubbard; R. B. Hurst; K. Königsmann; I. Konorov; S. Kovalenko; N. Keller; K. Martens; P. Martin; S. Masciocchi; R. Michaels; U. Müller; H. Neeb; D. Newbold; C. Newsom; S. Paul; J. Pochodzalla; I. Potashnikova; B. Povh; Z. Ren; M. Rey-Campagnolle; G. Rosner; L. Rossi; H. Rudolph; C. Scheel; L. Schmitt; H.-W. Siebert; A. Simon; V. Smith; O. Thilmann; A. Trombini; E. Vesin; B. Volkemer; K. Vorwalter; T. Walcher; G. Wälder; R. Werding; E. Wittmann; M. V. Zavertyaev
2007-01-01
We present a comprehensive study of the inclusive production of V0V0 pairs (V0=?, ?? or KS ) by ?- and ?- of 340 GeV\\/c momentum and neutrons of 260 GeV\\/c mean momentum in copper and carbon targets. In particular, the dependence of the xF spectra on the combination of beam-particle and produced V0V0 pair is investigated and compared to predictions obtained from
Pulsars with Strong Magnetic Fields - Polar Gaps Bound Pair Creation and Nonthermal Luminosities
V. V. Usov; D. B. Melrose
1995-01-01
Modifications to polar-gap models for pulsars are discussed for the case where the surface magnetic field, $B_\\\\S$, of the neutron star is strong. For $B\\\\ga4\\\\times10^8\\\\rm\\\\,T$, the curvature $\\\\gamma$-quanta emitted tangentially to the curved force lines of the magnetic field are captured near the threshold of bound pair creation and are channelled along the magnetic field as bound electron-positron pairs (positronium).
Ruderman, M.
1984-09-01
The youngest known radiopulsar in the rapidly spinning magnetized neutron star which powers the Crab Nebula, the remnant of the historical supernova explosion of 1054 AD. Similar neutron stars are probably born at least every few hundred years, but are less frequent than Galactic supernova explosions. They are initially sources of extreme relativistic electron and/or positron winds (approx.10/sup 38/s/sup -1/ of 10/sup 12/ eV leptons) which greatly decrease as the neutron stars spin down to become mature pulsars. After several million years these neutron stars are no longer observed as radiopulsars, perhaps because of large magnetic field decay. However, a substantial fraction of the 10/sup 8/ old dead pulsars in the Galaxy are the most probable source for the isotropically distributed ..gamma..-ray burst detected several times per week at the earth. Some old neutron stars are spun-up by accretion from companions to be resurrected as rapidly spinning low magnetic field radiopulsars. 52 references, 6 figures, 3 tables.
Neutron monitoring: Past, present, future
NASA Astrophysics Data System (ADS)
Bieber, John William
2013-02-01
Ground-based detectors were instrumental in establishing the nature of cosmic rays in the early days of the field, and they continue to provide invaluable information now and for the foreseeable future. This article begins with homage to Scott Forbush and the fundamental discoveries he made with the Carnegie Institution ionization chambers in the 1930s and 1940s. Circa 1950 John Simpson invented the neutron monitor, an instrument more capable, sensitive, and stable than the ionization chamber. An early landmark of the neutron monitor era was the famous 1956 solar cosmic ray event that proved diffusion theory is essential for describing charged particle transport in space. In the modern era, the instrument of choice is an array. The days are gone when a lone neutron monitor placed anywhere on Earth can make discoveries. Now and in the future, science with neutron monitors will require coordinated arrays of detectors that enable continuous, realtime measurement of the cosmic ray directional distribution and energy spectrum. An emerging application for neutron monitors is in the field of space weather prediction and specification, especially as concerns major radiation hazard from solar particles.
Pygmy resonances and neutron skins
Piekarewicz, J. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States)
2011-03-15
In a study motivated by a recent experiment, the distribution of electric dipole strength in the neutron-rich {sup 68}Ni isotope was computed using a relativistic random-phase approximation with a set of effective interactions that - although well calibrated - predict significantly different values for the neutron-skin thickness in {sup 208}Pb. The emergence of low-energy 'pygmy' strength that exhausts about 5%-8% of the energy-weighted sum rule (EWSR) is clearly identified. In addition to the EWSR, special emphasis is placed on the dipole polarizability. In particular, our results suggest a strong correlation between the dipole polarizability of {sup 68}Ni and the neutron-skin thickness of {sup 208}Pb. Yet we find a correlation just as strong, and an even larger sensitivity, between the neutron-skin thickness of {sup 208}Pb and the fraction of the dipole polarizability exhausted by the pygmy resonance. These findings suggest that dipole polarizability may be used as a proxy for the neutron skin.
Rapid Cooling of the Neutron Star in Cassiopeia A Triggered by Neutron Superfluidity in Dense Matter
NASA Astrophysics Data System (ADS)
Page, Dany; Prakash, Madappa; Lattimer, James M.; Steiner, Andrew W.
2011-02-01
We propose that the observed cooling of the neutron star in Cassiopeia A is due to enhanced neutrino emission from the recent onset of the breaking and formation of neutron Cooper pairs in the P23 channel. We find that the critical temperature for this superfluid transition is ?0.5×109K. The observed rapidity of the cooling implies that protons were already in a superconducting state with a larger critical temperature. This is the first direct evidence that superfluidity and superconductivity occur at supranuclear densities within neutron stars. Our prediction that this cooling will continue for several decades at the present rate can be tested by continuous monitoring of this neutron star.