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1

Thermal Evolution of Isolated Neutron Stars: Pairing, Pairing, and Pairing  

SciTech Connect

The thermal evolution of young isolated neutron stars is driven by neutrino emission from matter at the highest densities reached in their inner core. As such, these objects are direct probes of the structure of matter at supranuclear density. However, pairing of the neutrino emitting baryons, or quarks, can significantly alter their emission efficiency and the predicted thermal evolution is very sensitive to assumptions about gap size(s). After a brief description of these physical processes, I compare with present observational data models of cooling neutron stars driven by slow or fast neutrino emission. Depending on the assumed size of the neutron {sup 3}P{sub 2}-{sup 3}F{sub 2} gap, a minimal model of neutron stars can accommodate all present data, with the exception of the cold pulsar J0007.0+7303 in the supernova remnant CTA 1. However, in case this gap is vanishingly small or very large, the estimated surface temperatures of more than a half of the observed young cooling neutron stars would imply the intervention of some form of enhanced neutrino emission. Unfortunately, the present uncertainty on the size of the neutron {sup 3}P{sub 2}-{sup 3}F{sub 2} gap precludes us to draw any definitive conclusion about the state of dense matter from the sole study of isolated neutron stars.

Page, Dany [Departamento de Astrofisica Teorica, Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, 04510 Mexico D.F. (Mexico)

2009-05-07

2

Extracting differential pair distribution functions using MIXSCAT  

SciTech Connect

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

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

2010-08-27

3

Neutron-proton pairs in nuclei  

E-print Network

A review is given of attempts to describe nuclear properties in terms of neutron--proton pairs that are subsequently replaced by bosons. Some of the standard approaches with low-spin pairs are recalled but the emphasis is on a recently proposed framework with pairs of neutrons and protons with aligned angular momentum. The analysis is carried out for general $j$ and applied to $N=Z$ nuclei in the $1f_{7/2}$ and $1g_{9/2}$ shells.

P. Van Isacker

2013-10-18

4

Distributed pair programming: An empirical study  

E-print Network

distributed extreme programming. In Extreme Programming and Agile Methods -distributed pair programming. In Extreme Programming and Agile Methods -distributed pair programming. In Extreme Programming and Agile Methods -

Hanks, Brian F

2004-01-01

5

Overview of neutron-proton pairing  

NASA Astrophysics Data System (ADS)

The role of neutron-proton pairing correlations on the structure of nuclei along the N=Z line is reviewed. Particular emphasis is placed on the competition between isovector (T=1) and isoscalar (T=0) pair fields. The expected properties of these systems, in terms of pairing collective motion, are assessed by different theoretical frameworks including schematic models, realistic Shell Model and mean field approaches. The results are contrasted with experimental data with the goal of establishing clear signals for the existence of neutron-proton (np) condensates. We will show that there is clear evidence for an isovector np condensate as expected from isospin invariance. However, and contrary to early expectations, a condensate of deuteron-like pairs appears quite elusive and pairing collectivity in the T=0 channel may only show in the form of a phonon. Arguments are presented for the use of direct reactions, adding or removing an np pair, as the most promising tool to provide a definite answer to this intriguing question.

Frauendorf, S.; Macchiavelli, A. O.

2014-09-01

6

A search for disorder in the spin glass double perovskites Sr2CaReO6 and Sr2MgReO6 using neutron diffraction and neutron pair distribution function analysis  

NASA Astrophysics Data System (ADS)

The geometrically frustrated, B-site ordered, S = 1/2, double perovskites Sr2CaReO6 and Sr2MgReO6, which show spin frozen magnetic ground states, have been investigated using neutron powder diffraction (ND) and neutron pair distribution function (NPDF) analysis in a search for evidence for atomic positional disorder. For both materials, data were taken above and below the spin freezing temperatures of ~ 14 K and ~ 45 K for the CaRe and MgRe phases, respectively. In both cases the fully B-site ordered model was in excellent agreement with the data, both ND and NPDF, at all temperatures studied. Thus, the structure of these materials, from the average and the local perspectives, is very well described by the fully B-site ordered model, which raises questions concerning the origin of the spin glass ground state. These results are compared with those for the spin glass pyrochlore Y2Mo2O7 and other B-site ordered double perovskites.

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

2011-04-01

7

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

PubMed

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

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

2011-04-27

8

Transverse Momentum Distributions for Heavy Quark Pairs  

E-print Network

We study the transverse momentum distribution for a $pair$ of heavy quarks produced in hadron-hadron interactions. Predictions for the large transverse momentum region are based on exact order $\\alpha_s^3$ QCD perturbation theory. For the small transverse momentum region, we use techniques for all orders resummation of leading logarithmic contributions associated with initial state soft gluon radiation. The combination provides the transverse momentum distribution of heavy quark pairs for all transverse momenta. Explicit results are presented for $b\\bar b$ pair production at the Fermilab Tevatron collider and for $c\\bar c$ pair production at fixed target energies.

Edmond L. Berger; Ruibin Meng

1993-10-22

9

Proton-neutron pairing vibrations in N =Z nuclei: Precursory soft mode of isoscalar pairing condensation  

NASA Astrophysics Data System (ADS)

L =0 proton-neutron (pn) pair-addition and pair-removal strengths in Ca40 and Ni56 are investigated by means of the pn particle-particle random-phase approximation employing a Skyrme energy-density functional. It is found that the collectivity of the lowest J?=1+ state in the adjacent odd-odd nuclei becomes stronger as the strength of the isoscalar (T =0) pairing interaction increases. The results suggest the emergence of the T =0 pn-pairing vibrational mode as a possible critical phenomenon toward the T =0 pairing condensation.

Yoshida, Kenichi

2014-09-01

10

Experimental wavelength division multiplexed photon pair distribution  

E-print Network

We have experimentally implemented the distribution of photon pairs produced by spontaneous parametric down conversion through telecom dense wavelength division multiplexing filters. Using the measured counts and coincidences between symmetric channels, we evaluate the maximum fringe visibility that can be obtained with polarization entangled photons and compare different filter technologies.

Joe Ghalbouni; Imad Agha; Robert Frey; Eleni Diamanti; Isabelle Zaquine

2012-10-03

11

Reflections on the magnetic pair distribution function.  

PubMed

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

Ratcliff, William

2014-01-01

12

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

SciTech Connect

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.

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

13

Distribution of neutron resonance widths  

E-print Network

Recent data on neutron resonance widths indicate disagreement with the Porter-Thomas distribution (PTD). I discuss the theoretical arguments for the PTD, possible theoretical modifications, and I summarize the experimantal evidence.

Weidenmueller, Hans A

2011-01-01

14

Distribution of neutron resonance widths  

E-print Network

Recent data on neutron resonance widths indicate disagreement with the Porter-Thomas distribution (PTD). I discuss the theoretical arguments for the PTD, possible theoretical modifications, and I summarize the experimantal evidence.

Hans A. Weidenmueller

2011-10-28

15

Distribution of Neutron Resonance Widths  

NASA Astrophysics Data System (ADS)

Recent data on neutron resonance widths indicate disagreement with the Porter-Thomas distribution (PTD). I discuss the theoretical arguments for the PTD, possible theoretical modifications, and I summarize the experimental evidence.

Weidenmüller, Hans A.

2013-03-01

16

Probing Neutron Pair Transfer with Borromean Isotopes of Helium  

NASA Astrophysics Data System (ADS)

Recent developments in reaccelerated beams and the associated improvement in experimental techniques have now made it possible to measure the pair and single neutron transfer reactions involving short-lived nuclei far from the valley of stability. Reactions involving Borromean nuclei, such as 6, 8He and 11Li, whose binding arises essentially from pairing correlations and can be characterized as a pure embodiment of the Cooper effect, provide an ideal laboratory towards probing features of pairing correlations in a dynamical regime different from macroscopic superconductors. Here we present an overview of experimental challenges and the progress made in the deconvolution of one- and two-neutron transfer cross sections using beams of 6, 8He, on targets with A > 50 in the vicinity of the Coulomb barrier.

Navin, A.; Lemasson, A.

2013-01-01

17

Neutrino-pair bremsstrahlung in a neutron star crust  

E-print Network

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 the neutron star crust of any realistic composition. The emissivity is expressed through 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.

Ofengeim, D D; Yakovlev, D G

2014-01-01

18

Neutrino-pair bremsstrahlung in a neutron star crust  

NASA Astrophysics Data System (ADS)

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.

Ofengeim, D. D.; Kaminker, A. D.; Yakovlev, D. G.

2014-11-01

19

Pairing and Shell Evolution in Neutron Rich Nuclei  

NASA Astrophysics Data System (ADS)

From the experimental data on odd-even staggering of masses, it has been shown that variation of pairing as a function of neutron number plays an important role in many distinctive features like occurrence of new shell closures, shell erosion, anomalous reduction of the energy of the first 2+ state and slower increase in the B(E2,21^ + -> 01^ + ) in the neutron-rich even-even nuclei in different mass regions. New predictions have been made in a model independent way.

Sarkar, Maitreyee Saha; Sarkar, Sukhendusekhar

2014-09-01

20

Exact Solution of the Isovector Proton Neutron Pairing Hamiltonian  

E-print Network

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

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

2006-01-27

21

Pair cascades in the magnetospheres of strongly magnetized neutron stars  

NASA Astrophysics Data System (ADS)

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

Medin, Zach; Lai, Dong

2010-08-01

22

Quasifree Photoproduction of Pion-Pairs of Protons and Neutrons  

NASA Astrophysics Data System (ADS)

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

Oberle, M.; Krusche, B.

2014-01-01

23

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

24

Proton-neutron pairing vibrations in N=Z nuclei: Precursory soft mode of isoscalar pairing condensation  

E-print Network

L=0 proton-neutron ($pn$) pair-addition and pair-removal strengths in $^{40}$Ca and $^{56}$Ni are investigated by means of the $pn$ particle-particle random-phase approximation employing a Skyrme energy-density functional. It is found that the collectivity of the lowest $J^\\pi = 1^+$ state in the adjacent odd-odd nuclei becomes stronger as the strength of the isoscalar (T=0) pairing interaction increases. The results suggest the emergence of the T=0 $pn$-pairing vibrational mode as a possible critical phenomenon toward the T=0 pairing condensation.

Kenichi Yoshida

2014-09-17

25

Induced Pairing Interaction in Nuclei and in Neutron Stars  

NASA Astrophysics Data System (ADS)

For an electron going from X to Y, the pole of the propagator for a free particle is p2=m2. However, making measurements at X and Y one could not tell if the electron had emitted or absorbed any number of photons. Such process, the simplest of which corresponds to emission and subsequent absorption of a photon (self-energy process) causes a shift in the position of the pole. Physically, this means that nothing is really free and that what one measures, the experimental mass, is not the ``bare mass'' but something else which includes the effect of virtual processes mentioned above. If this is true for electrons moving in vacuum it is even more true in the case of nucleons moving inside a nucleus. Bouncing inelastically off the nuclear surface, a nucleon can set it into vibrations exciting a normal mode of the system which it can reabsorb at a later time. The density of levels at the Fermi energy reflects this interweaving between fermionic and bosonic degrees of freedom and the resulting effective nucleon mass. If the vibration is reabsorbed by a second nucleon it leads to an exchange of bosons and thus to an effective interaction, e.g. in the pairing channel. Within the scenario discussed above, both quantum electrodynamics (QED) and nuclear field theory (NFT), are effective field theories. Now, while the photon is an elementary particle and the exchange of photons can be accurately parametrized in terms of the Coulomb interaction, collective surface vibrations do not exist outside the nucleus and there is no simple neither accurate parametrization of the pairing induced interaction, let alone of the 1S0 NN-potential in terms of quarks and gluons. On the other hand, NFT based on effective interactions and HFB plus QRPA, provide a remarkably detailed picture of the induced pairing interaction, with which, together with e.g. the v14 NN-potential, one is able to calculate rather accurately the pairing gap of superfluid systems, including compact objects like (the inner crust of) neutron stars. The corresponding results are likely to provide the basis of a DFT of pairing in nuclei.

Broglia, R. A.; Baroni, S.; Barranco, F.; Bortignon, P. F.; Potel, G.; Pastore, A.; Vigezzi, E.; Marini, F.

2007-04-01

26

The Neutron Star Mass Distribution  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

27

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

SciTech Connect

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

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

2007-12-15

28

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

NASA Astrophysics Data System (ADS)

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

Hinohara, Nobuo; Engel, Jonathan

2014-09-01

29

Neutron dose distribution at the GSI fragment separator.  

PubMed

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

Fehrenbacher, G; Festag, J G

2004-01-01

30

Quasiprobability Distribution Functions of Squeezed Pair Coherent States  

NASA Astrophysics Data System (ADS)

Using the entangled state representation of Wigner operator and some formulae related to the two-variable Hermite polynomials, the Wigner function of the squeezed pair coherent state (SPCS) and its two marginal distributions are derived. Based on the entangled Husimi operator introduced by Fan et al. (Phys. Lett. A 358:203, 2006) and the Weyl ordering invariance under similar transformations, we also obtain the Husimi function of the SPCS and its marginal distribution functions. The comparison between the two quasibability functions shows that, for the same amount of information included in two functions, the solving process of the Husimi function is simpler than that of the Wigner function.

Meng, Xiang-Guo; Wang, Ji-Suo; Liang, Bao-Long

2009-08-01

31

Proton-neutron pairing and alpha-type quartet condensation in nuclei  

NASA Astrophysics Data System (ADS)

Proton-neutron pairing in nuclei is commonly described by generalized BCS/HFB models. By construction, these models do not conserve the particle number and the isospin. Here we shall review an alternative approach, based on quartets instead of Cooper pairs, in which both the particle number and the isospin are exactly conserved. In this approach the ground state of N=Z nuclei is approximated by a condensate of alpha-like quartets built by two neutrons and two protons coupled to the isospin T=0. For nuclei with N > Z the ground state is taken as a superposition of a quartet condensate and a pair condensate formed by the neutrons in excess relative to the isotope with N=Z.

Sandulescu, N.; Negrea, D.; Dukelsky, J.; Johnson, C. W.

2014-09-01

32

Quasifree photoabsorption on neutron-proton pairs in 3He  

E-print Network

Three-body photodisintegration of 3He is calculated in the photon energy range 200 - 400 MeV assuming quasifree absorption on np pairs both in initial quasideuteron and singlet configurations. The model includes the normal nucleonic current, explicit meson exchange currents and the Delta(1232)-isobar excitation. The total cross section is increased by a factor of about 1.5 compared with free deuteron photodisintegration. Well below and above the Delta region also some spin observables differ significantly from the ones of free deuteron disintegration due to the more compressed wave function of the correlated np pairs in 3He compared to the deuteron. The initial singlet state causes a significant change in the analyzing power Ay. These differences could presumably be seen at the conjugate angles where two-body effects are maximized and where photoreactions could complement similar pion absorption experiments. Figures by fax or post from janiskanen@phcu.helsinki.fi

J. A. Niskanen; P. Wilhelm; H. Arenhoevel

1994-06-14

33

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

SciTech Connect

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

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

2009-12-15

34

Isovector proton-neutron pairing and Wigner energy in Hartree-Fock mean field calculations  

E-print Network

We propose a new approach for the treatment of isovector pairing in self-consistent mean field calculations which conserves exactly the isospin and the particle number in the pairing channel. The mean field is generated by a Skyrme-HF functional while the isovector pairing correlations are described in terms of quartets formed by two neutrons and two protons coupled to the total isospin T=0. In this framework we analyse the contribution of isovector pairing to the symmetry and Wigner energies. It is shown that the isovector pairing provides a good description of the Wigner energy, which is not the case for the mean field calculations in which the isovector pairing is treated by BCS-like models.

D. Negrea; N. Sandulescu

2014-04-21

35

Isovector proton-neutron pairing and Wigner energy in Hartree-Fock mean field calculations  

E-print Network

We propose a new approach for the treatment of isovector pairing in self-consistent mean field calculations which conserves exactly the isospin and the particle number in the pairing channel. The mean field is generated by a Skyrme-HF functional while the isovector pairing correlations are described in terms of quartets formed by two neutrons and two protons coupled to the total isospin T=0. In this framework we analyse the contribution of isovector pairing to the symmetry and Wigner energies. It is shown that the isovector pairing provides a good description of the Wigner energy, which is not the case for the mean field calculations in which the isovector pairing is treated by BCS-like models.

Negrea, D

2014-01-01

36

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

E-print Network

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

Kenichi Yoshida; Masayuki Yamagami

2008-02-16

37

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

NASA Astrophysics Data System (ADS)

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

Kovács, Z.; Harko, T.

2011-11-01

38

Spin-aligned neutron-proton pair mode in atomic nuclei  

SciTech Connect

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

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

2011-08-15

39

Neutron star's initial spin period distribution  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

40

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

E-print Network

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

Alberto Escuderos; Amand Faessler; Vadim Rodin; Fedor Simkovic

2010-01-20

41

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

E-print Network

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

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

2014-03-26

42

Pair distribution function study on compression of liquid gallium  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

43

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

SciTech Connect

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

Douici, M.; Allal, N. H.; Fellah, M.; Benhamouda, N.; Oudih, M. R. [Laboratoire de Physique Theorique, Faculte de Physique, USTHB BP 32 El-Alia, 16111 Bab-Ezzouar, Alger (Algeria) and Institut des Sciences et Technologie, Centre Universitaire de Khemis Miliana, Route de Theniet-El-Had, 44225 Khemis-Milia (Algeria); Laboratoire de Physique Theorique, Faculte de Physique, USTHB BP 32 El-Alia, 16111 Bab-Ezzouar, Alger (Algeria) and Centre de Recherche Nucleaire d'Alger, COMENA, BP399 Alger-Gare, Alger (Algeria); Laboratoire de Physique Theorique, Faculte de Physique, USTHB BP 32 El-Alia, 16111 Bab-Ezzouar, Alger (Algeria)

2012-10-20

44

Hyperdimensional Analysis of Amino Acid Pair Distributions in Proteins  

PubMed Central

Our manuscript presents a novel approach to protein structure analyses. We have organized an 8-dimensional data cube with protein 3D-structural information from 8706 high-resolution non-redundant protein-chains with the aim of identifying packing rules at the amino acid pair level. The cube contains information about amino acid type, solvent accessibility, spatial and sequence distance, secondary structure and sequence length. We are able to pose structural queries to the data cube using program ProPack. The response is a 1, 2 or 3D graph. Whereas the response is of a statistical nature, the user can obtain an instant list of all PDB-structures where such pair is found. The user may select a particular structure, which is displayed highlighting the pair in question. The user may pose millions of different queries and for each one he will receive the answer in a few seconds. In order to demonstrate the capabilities of the data cube as well as the programs, we have selected well known structural features, disulphide bridges and salt bridges, where we illustrate how the queries are posed, and how answers are given. Motifs involving cysteines such as disulphide bridges, zinc-fingers and iron-sulfur clusters are clearly identified and differentiated. ProPack also reveals that whereas pairs of Lys residues virtually never appear in close spatial proximity, pairs of Arg are abundant and appear at close spatial distance, contrasting the belief that electrostatic repulsion would prevent this juxtaposition and that Arg-Lys is perceived as a conservative mutation. The presented programs can find and visualize novel packing preferences in proteins structures allowing the user to unravel correlations between pairs of amino acids. The new tools allow the user to view statistical information and visualize instantly the structures that underpin the statistical information, which is far from trivial with most other SW tools for protein structure analysis. PMID:22174733

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

2011-01-01

45

Energy and Isotope Dependence of Neutron Multiplicity Distributions  

E-print Network

Fission neutron multiplicity distributions are known to be well reproduced by simple Gaussian distributions. Many previous evaluations of multiplicity distributions have adjusted the widths of Gaussian distributions to best fit the measured multiplicity distributions Pn. However, many observables do not depend on the detailed shape of Pn, but depend on the first three factorial moments of the distributions. In the present evaluation, the widths of Gaussians are adjusted to fit the measured 2nd and 3rd factorial moments. The relationships between the first three factorial moments are estimated assuming that the widths of the multiplicity distributions are independent of the initial excitation energy of the fissioning system. These simple calculations are in good agreement with experimental neutron induced fission data up to an incoming neutron energy of 10 MeV.

Lestone, J P

2014-01-01

46

Kinematic distributions for electron pair production by muons  

NASA Technical Reports Server (NTRS)

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

Linsker, R.

1972-01-01

47

Letter Performance of photon-pair quantum key distribution systems  

Microsoft Academic Search

We analyse the quantitative improvement in performance pro- vided by a novel quantum key distribution ( qkd) system that employs a correlated photon source ( cps) and a photon-number resolving detector ( pnr). Calculations suggest that given current technology, the cps\\/pnr implementation oÄ ers an improvement of several orders of magnitude in secure bit rate over previously described implementations.

Z. WALTON; A. V. SERGIENKO; M. ATATUÈ

48

Performance of photon-pair quantum key distribution systems  

Microsoft Academic Search

We analyze the quantitative improvement in performance provided by a novel quantum key distribution (QKD) system that employs a correlated photon source (CPS) and a photon-number resolving detector (PNR). Our calculations suggest that given current technology, the CPR implementation offers an improvement of several orders of magnitude in secure bit rate over previously described implementations.

Z. Walton; A. V. Sergienko; M. Atatüre; B. E. A. Saleh; M. C. Teich

2001-01-01

49

Actively switchable nondegenerate polarization-entangled photon-pair distribution in dense wave-division multiplexing  

NASA Astrophysics Data System (ADS)

We have demonstrated experimentally a nondegenerate polarization-entangled photon-pair distribution in a commercial telecom dense wave-division multiplexing device (DWDM) with eight channels. A promising point of this experiment is that an entangled photon pair is obtained via spontaneous parametric down conversion in a single type-II periodically poled KTiOPO4 crystal without postselection. Another promising advantage is that we can actively switch the distribution of the photon pair between different channel pairs in DWDM at will. There is no crosstalk between different channel pairs because of a limited emission bandwidth of the source. Maximum raw visibility of 97.88%±0.86% obtained in a Bell-type interference experiment and a Clauser-Horne-Shimony-Holt (CHSH) inequality S parameter of 2.63±0.08 calculated prove high entanglement of our source. Our work is helpful for building quantum communication networks.

Zhou, Zhi-Yuan; Jiang, Yun-Kun; Ding, Dong-Sheng; Shi, Bao-Sen; Guo, Guang-Can

2013-04-01

50

Quasi-free photoproduction of pion-pairs off protons and neutrons  

E-print Network

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

M. Oberle; B. Krusche

2014-01-29

51

ON THE MASS DISTRIBUTION AND BIRTH MASSES OF NEUTRON STARS  

SciTech Connect

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

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

2012-09-20

52

Current Density and Angular Distribution of Neutrons Emitted During Scission  

NASA Astrophysics Data System (ADS)

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

Carjan, N.; Rizea, M.

2014-04-01

53

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

PubMed

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

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

2000-01-01

54

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

PubMed

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

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

55

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

E-print Network

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

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

2014-08-24

56

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

57

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

E-print Network

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

Guang-Peng Zhang

2014-06-20

58

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

SciTech Connect

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

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

2011-01-01

59

Dynamic Pairing Effects on Low-Frequency Modes of Excitation in Deformed Mg Isotopes close to the Neutron Drip Line  

E-print Network

Low-frequency quadrupole vibrations in deformed ${}^{36,38,40}$Mg are studied by means of the deformed Quasiparticle-RPA based on the coordinate-space Hartree-Fock-Bogoliubov formalism. Strongly collective $K^{\\pi}=0^{+}$ and $2^{+}$ excitation modes (carrying 10-20 W.u.) are obtained at about 3 MeV. It is found that dynamical pairing effects play an essential role in generating these modes. It implies that the lowest $K^{\\pi}=0^{+}$ excitation modes are particularly sensitive indicators of dynamical pairing correlations in deformed nuclei near the neutron drip line.

Kenichi Yoshida; Masayuki Yamagami; Kenichi Matsuyanagi

2005-07-20

60

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

PubMed

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

Cauwels, Vanessa; Vanhavere, Filip; Reginatto, Marcel

2014-10-01

61

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

Microsoft Academic Search

The tunnelling and torsional motions of methyl groups in lithium acetate dihydrate (CH3COOLi·2H2O) have been studied in detail by incoherent inelastic neutron scattering. The results are interpreted by a model of pairs of methyl groups performing a coupled tunnelling motion. The strength of the coupling term is estimated to be about twice as strong as the threefold hindering barrier for

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

1984-01-01

62

Radical distributions in ammonium tartrate single crystals exposed to photon and neutron beams.  

PubMed

The radiation therapy carried out by means of heavy charged particles (such as carbon ions) and neutrons is rapidly becoming widespread worldwide. The success of these radiation therapies relies on the high density of energy released by these particles or by secondary particles produced after primary interaction with matter. The biological damages produced by ionising radiations in tissues and cells depend more properly on the energy released per unit pathlength, which is the linear energy transfer and which determines the radiation quality. To improve the therapy effectiveness, it is necessary to grasp the mechanisms of free radical production and distribution after irradiation with these particles when compared with the photon beams. In this work some preliminary results on the analysis of the spatial distributions of the free radicals produced after exposure of ammonium tartrate crystals to various radiation beams ((60)Co gamma photons and thermal neutrons) were reported. Electron spin resonance analyses were performed by the electron spin echo technique, which allows the determination of local spin concentrations and by double electron-electron resonance technique, which is able to measure the spatial distance distribution (range 1.5-8 nm) among pairs of radicals in solids. The results of these analyses are discussed on the basis of the different distributions of free radicals produced by the two different radiation beams used. PMID:24591730

Marrale, M; Longo, A; Barbon, A; Brustolon, M; Brai, M

2014-10-01

63

Genetic algorithm for the pair distribution function of the electron gas.  

PubMed

The pair distribution function of the electron gas is calculated using a parameterized generalization of hypernetted chain approximation with the parameters being obtained by optimizing the system energy with a genetic algorithm. The functions so obtained are compared with Monte Carlo simulations performed by other authors in its variational and di_usion versions showing a very good agreement especially with the di_usion Monte Carlo results. PMID:22179762

Vericat, Fernando; Stoico, César O; Carlevaro, C Manuel; Renzi, Danilo G

2011-12-01

64

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

SciTech Connect

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

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

2007-11-15

65

Pairing properties of the inner crust of neutron stars at finite temperature  

E-print Network

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.

A. Pastore

2014-03-20

66

Proton and Neutron Momentum Distributions in A = 3 Asymmetric Nuclei  

E-print Network

A proposal approved by the Jefferson Lab (JLab) PAC to study the proton-to-neutron momentum distribution ratio in A=3 nuclei via (e,e'p) scattering off 3He and 3H mirror nuclei. The experiment will measure the 3H(e,e'p) and 3He(e,e'p) cross-sections and cross-section ratios at Q2 = 2 and xB>1 kinematics, over a missing momentum range of 0 - 450 MeV/c. The experiment was approved in 2014 at part of the JLab Hall-A Tritium run period for a total run time of 12 days.

Hen, O; Gilad, S; Boeglin, W

2014-01-01

67

Probing the birth periods and pair production multiplicities of neutron stars through multiwavelength observations of their wind nebulae.  

NASA Astrophysics Data System (ADS)

A pulsar wind nebula (PWN) contain leptons and possibly ions injected since the birth of its parent pulsar. X-ray synchrotron emitting electrons have a relatively short lifetime and would therefore reflect only the current spindown power. The latter then partly explains the ? well-known LX vs E relationhip for pulsars and their wind nebulae. Lower energy electrons radiating synchrotron emission in the radio to unseen UV domain, having lifetimes as long as, or longer than the age of the pulsar, give us a measure of the conditions since birth. The inverse Compton counterpart of the latter can however be probed by gamma-ray telesopes such as GLAST and ground-based telescopes. Such multiwavelength observations are expected to give a measure of the birth period since the injection spectrum is expected to be proportional to the change in rotational kinetic energy of the pulsar. Radiation losses towards higher energies would however hide the effect of the birth period, in which case a time dependent transport equation with losses must be solved to calculate the multiwavelength spectrum. This allows us to set constraints on the birth periods of neutron stars. The abovementioned procdure also allows us to determine the average pair production multiplicity in neutron stars: The particle acceleration process in neutron star magnetospheres, combined with the magnetic field line structure and target photon fields produce electrons and positrons through magnetic pair production and photon-photon pair production. A self consistent calculation of the pair production multiplicity M is usually difficult, although attempts have been made in the past to assess the value of M . Gamma-ray observations of associated pulsar wind nebulae in the high energy and VHE domain, combined with multiwavelength synchrotron observations in the radio through X-ray domain, allow us to probe the total amount of leptons injected since pulsar birth, which in turn gives us a measurement of M . A reliable measurement of M should constrain models for broad band magnetospheric pulsed emission. We will apply this to the composite SNR Kes 75 of which the spectrum is known from radio to TeV ?-rays. The known pulsar braking index also makes birth period estimates more reliable.

de Jager, Ocker

68

Neutron spectral distribution from a sealed-tube neutron generator by multiple-foil activation unfolding method  

Microsoft Academic Search

The spectral distribution of 14MeV neutrons from a KAMAN sealed-tube neutron generator has been determined using threshold-energy monitor reactions in combination with the SULSA unfolding code, in which no input ‘guess spectrum’ is required except measured reaction rates of threshold monitor reactions. Result indicates that value of mean neutron energy determined in the present study compares well with the value

S. A. Jonah; K. Ibikunle

2003-01-01

69

Directional pair distribution function for diffraction line profile analysis of atomistic models  

PubMed Central

The concept of the directional pair distribution function is proposed to describe line broadening effects in powder patterns calculated from atomistic models of nano-polycrystalline microstructures. The approach provides at the same time a description of the size effect for domains of any shape and a detailed explanation of the strain effect caused by the local atomic displacement. The latter is discussed in terms of different strain types, also accounting for strain field anisotropy and grain boundary effects. The results can in addition be directly read in terms of traditional line profile analysis, such as that based on the Warren–Averbach method. PMID:23396818

Leonardi, Alberto; Leoni, Matteo; Scardi, Paolo

2013-01-01

70

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

SciTech Connect

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.

Gilbert, Benjamin

2008-10-01

71

Analysis of the Size Distributions of Fetal and Maternal Cell-Free DNA by Paired-End Sequencing  

E-print Network

Analysis of the Size Distributions of Fetal and Maternal Cell-Free DNA by Paired-End Sequencing H: Noninvasive prenatal diagnosis with cell-free DNA in maternal plasma is challenging be- cause only a small of the small quantity of cell-free DNA. METHODS: We used high-throughput paired-end se- quencing to directly

Quake, Stephen R.

72

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

73

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

SciTech Connect

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

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

2008-07-01

74

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

SciTech Connect

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

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

2012-03-15

75

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

E-print Network

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

Sakshi Gautam

2011-07-28

76

Force distribution in a randomly perturbed lattice of identical particles with $1/r^2$ pair interaction  

E-print Network

We study the statistics of the force felt by a particle in the class of spatially correlated distribution of identical point-like particles, interacting via a $1/r^2$ pair force (i.e. gravitational or Coulomb), and obtained by randomly perturbing an infinite perfect lattice. In the first part we specify the conditions under which the force on a particle is a well defined stochastic quantity. We then study the small displacements approximation, giving both the limitations of its validity, and, when it is valid, an expression for the force variance. In the second part of the paper we extend to this class of particle distributions the method introduced by Chandrasekhar to study the force probability density function in the homogeneous Poisson particle distribution. In this way we can derive an approximate expression for the probability distribution of the force over the full range of perturbations of the lattice, i.e., from very small (compared to the lattice spacing) to very large where the Poisson limit is recovered. We show in particular the qualitative change in the large-force tail of the force distribution between these two limits. Excellent accuracy of our analytic results is found on detailed comparison with results from numerical simulations. These results provide basic statistical information about the fluctuations of the interactions (i) of the masses in self-gravitating systems like those encountered in the context of cosmological N-body simulations, and (ii) of the charges in the ordered phase of the One Component Plasma.

A. Gabrielli; T. Baertschiger; M. Joyce; B. Marcos; F. Sylos Labini

2006-03-06

77

Identification of Neutron Sources by Spectral Analysis of Pulse Height Distributions  

Microsoft Academic Search

This paper proposes a neutron source identification method based on the spectral analysis of neutron pulse height distributions obtained with liquid scintillation detectors. The fact that shielded and unshielded neutron sources have clearly defined spectral components with specific locations and intensities offers the possibility of identifying the sources based on spectral features alone, without having to unfold the energy spectra.

Senada Avdic; Predrag Marinkovic; Sara A. Pozzi; Marek Flaska; Vladimir Protopopescu

2009-01-01

78

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

79

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

SciTech Connect

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.

Laouet, N.; Benrachi, F. [Laboratoire de Physique Mathematique et Subatomique Mentouri University, Constantine (Algeria)

2012-06-27

80

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

E-print Network

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 with 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 of distinct descriptions of proton and neutron densities reduces with the lowering of the detection energy thresholds.

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

2012-11-08

81

Modelling the structure factors and pair distribution functions of amorphous germanium, silicon and carbon  

NASA Astrophysics Data System (ADS)

We present the results of calculations of the static structure factor S( k) and the pair distribution function g( r) of the tetrahedral amorphous semiconductors germanium, silicon and carbon using the structural diffusion model (SDM). The results obtained with the SDM for S( k) and g( r) are of comparable quality with those obtained by the unconstrained Reverse Monte Carlo simulations and existing ab initio molecular dynamics simulations for these systems. We have found that g( r) exhibits a small peak, or shoulder, a weak remnant of the prominent third neighbour peak present in the crystalline phase of these systems. This feature has been experimentally found to be present in recently reported high energy X-ray experiments of amorphous silicon (Phys. Rev. B 60 (1999) 13520), as well as in the previous X-ray diffraction of as-evaporated amorphous germanium (Phys. Rev. B 50 (1994) 539).

Dalgiç, Seyfettin; Gonzalez, Luis Enrique; Baer, Shalom; Silbert, Moises

2002-11-01

82

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

E-print Network

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

J. F. Berger; K. Pomorski

2000-06-27

83

Radial Flux Distribution of Low-Energy Neutrons.  

ERIC Educational Resources Information Center

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

Higinbotham, J.

1979-01-01

84

Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. IX: Constraint of pairing force to $^1S_0$ neutron-matter gap  

E-print Network

In this latest of our series of Skyrme-HFB mass models, HFB-16, we introduce the new feature of requiring that the contact pairing force reproduce at each density the $^1S_0$ pairing gap of neutron matter as determined in microscopic calculations with realistic nucleon-nucleon forces. We retain the earlier constraints on the Skyrme force of reproducing the energy-density curve of neutron matter, and of having an isoscalar effective mass of $0.8M$ in symmetric infinite nuclear matter at the saturation density; we also keep the recently adopted device of dropping Coulomb exchange. Furthermore, the correction term for the spurious energy of collective motion has a form that is known to favour fission barriers that are in good agreement with experiment. Despite the extra constraints on the effective force, we have achieved a better fit to the mass data than any other mean field model, the rms error on the 2149 measured masses of nuclei with $N$ and $Z \\ge$ 8 having been reduced to 0.632 MeV; the improvement is particularly striking for the most neutron-rich nuclei. Moreover, it turns out that even with no flexibility at all remaining for the pairing force, the spectral pairing gaps that we find suggest that level densities in good agreement with experiment should be obtained. This new force is thus particularly well-suited for astrophysical applications, such as stellar nucleosynthesis and neutron-star crusts.

N. Chamel; S. Goriely; J. M. Pearson

2008-09-02

85

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

E-print Network

The origin of r-process elements remains unidentified and still puzzles us. The recent discovery of evidence for the ejection of r-process elements from a short-duration gamma-ray burst singled out neutron star mergers (NSMs) as their origin. In contrast, core-collapse supernovae are ruled out as the main origin of heavy r-process elements (A>110) by recent numerical simulations. However, the properties characterizing NSM events - their rarity and high yield of r-process elements per event - have been claimed to be incompatible with the observed stellar records on r-process elements in the Galaxy. We add to this picture with our results, which show that the observed constant [r-process/H] ratio in faint dwarf galaxies and one star unusually rich in r-process in the Sculptor galaxy agree well with this rarity of NSM events. Furthermore, we found that a large scatter in the abundance ratios of r-process elements to iron in the Galactic halo can be reproduced by a scheme that incorporates an assembly of various ...

Tsujimoto, Takuji

2014-01-01

86

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

PubMed Central

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

Weber, Anton

2013-01-01

87

Evaluation of sodium activation distribution in the PMMA water phantom after fast neutron irradiation.  

PubMed

(24)Na produced by the neutron activation of stable sodium in the body is commonly used to assess neutron doses after criticality accidents. However, the (24)Na distribution is not uniform owing to the interaction with the human body. In this study, we experimentally evaluated the (24)Na distribution in a PMMA water phantom and 60 polyethylene vials. The vials were analyzed to evaluate the sodium activation distribution in the PMMA water phantom by employing a correction factor. PMID:23548694

Ha, Wi-Ho; Park, Seyong; Yoo, Jaeryong; Yoon, Seokwon; Lee, Seung-Sook; Kim, Jong Kyung

2013-11-01

88

Approximate solution for the reactor neutron probability distribution  

Microsoft Academic Search

Several authors have studied the Kolmogorov equation for a fission-driven chain-reacting system, written in terms of the generating function G(x,y,z,t) where x, y, and z are dummy variables referring to the neutron, delayed neutron precursor, and detector-count populations, n, m, and c, respectively. Pal and Zolotukhin and Mogil'ner have shown that if delayed neutrons are neglected, the solution is approximately

L. Ruby; T. L. McSwine

1985-01-01

89

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

SciTech Connect

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

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

2008-01-01

90

X-ray Pair Distribution Function Analysis of Potassium Based Geopolymer  

SciTech Connect

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

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

2008-01-01

91

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

SciTech Connect

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

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

2008-01-01

92

Measurement of momentum distribution of lightatoms and molecules in condensed matter systems using inelastic neutron scattering  

Microsoft Academic Search

Studies of single-particle momentum distributions in light atoms and molecules are reviewed with specific emphasis on experimental measurements using the deep inelastic neutron scattering technique at eV energies. The technique has undergone a remarkable development since the mid-1980s, when intense fluxes of epithermal neutrons were made available from pulsed neutron sources. These types of measurements provide a probe of the

C. Andreani; D. Colognesi; J. Mayers; G. F. Reiter; R. Senesi

2005-01-01

93

THE DISTRIBUTION OF PHOSPHORUS AND GOLD IN NEUTRON IRRADIATED SILICON  

E-print Network

one is doping by nuclear transmutation. The second one is neutron activation of silicon and background 10l 3 upto 1016/cm3. Our activation analysis confirms the high purity if one excepts the gold = 3.5 x 1013 neutrons/cm2/s for the time t 1 = 24 hours. From the specific activity due to the emitted

Paris-Sud XI, Université de

94

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

NASA Astrophysics Data System (ADS)

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

Sakurai, Yoshinori; Ono, Koji

2007-12-01

95

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

PubMed

With the ever-increasing environmentally-driven demand for technologically advanced structural materials, geopolymer cement is fast becoming a viable alternative to traditional cements due to its proven engineering characteristics and the reduction in CO2 emitted during manufacturing (as much as 80% less CO2 emitted in manufacture, compared to ordinary Portland cement). Nevertheless, much remains unknown regarding the kinetics of reaction responsible for nanostructural evolution during the geopolymerisation process. Here, in situ X-ray total scattering measurements and pair distribution function (PDF) analysis are used to quantify the extent of reaction as a function of time for alkali-activated metakaolin/slag geopolymer binders, including the impact of various activators (alkali hydroxide/silicate) on the kinetics of the geopolymerisation reaction. Quantifying the reaction process in situ from X-ray PDF data collected during the initial ten hours can provide an estimate of the total reaction extent, but when combined with data obtained at longer times (128 days here) enables more accurate determination of the overall rate of reaction. To further assess the initial stages of the geopolymerisation reaction process, a pseudo-single step first order rate equation is fitted to the extent of reaction data, which reveals important mechanistic information regarding the role of free silica in the activators in the evolution of the binder systems. Hence, it is shown that in situ X-ray PDF analysis is an ideal experimental local structure tool to probe the reaction kinetics of complex reacting systems involving transitions between disordered/amorphous phases, of which geopolymerisation is an important example. PMID:23450172

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

2013-06-14

96

Distributions and correlations for top quark pair production and decay at the Tevatron and LHC  

NASA Astrophysics Data System (ADS)

We investigate a number of observables that are and will be instrumental in the exploration of tt¯ production and decay at the Tevatron and the LHC. For this analysis we made a computer program that incorporates besides the NLO QCD corrections to tt¯ production and decay also mixed weak-QCD corrections to the production amplitudes, and that allows for studies of correlated versus uncorrelated tt¯ events. In this paper we analyze and compute observables mostly for dileptonic tt¯ final states to next-to-leading order in the strong and weak gauge couplings (NLOW), with selection cuts. We calculate charge asymmetries of the top quark and of ?=e,? and we compare, where possible, with experimental results. We show that top-quark spin correlations affect a leptonic pair asymmetry (which has not been measured so far) by ˜7%. We determine several dileptonic angular correlations, which reflect tt¯ spin correlations, namely the beam, off-diagonal and helicity correlation, and the opening angle distribution (defined in the t, t¯ rest frames) when selection cuts are applied. Our NLOW predictions for the beam, off-diagonal, and helicity correlation for the Tevatron agree with recent measurements by the CDF and DØ experiments. In addition we make predictions for estimators of these correlations as functions of M. These estimators may prove useful for the Tevatron and also in the early rounds of LHC data-analyses, where the event numbers will not be abundant. Furthermore, we compute to NLOW in the gauge couplings two dilepton angular correlations that are defined in the laboratory frame, for correlated and uncorrelated tt¯ events at the LHC. Finally, based on our SM results, we identify several observables that allow to search for non-standard parity- and CP-violating interactions, especially with future LHC data.

Bernreuther, Werner; Si, Zong-Guo

2010-09-01

97

Non-Equilibrium Thermodynamics and Energy Distribution Function of Neutron Gas in Constant Power Reactor under Coupling of Neutrons and Medium  

Microsoft Academic Search

The thermodynamics and the energy distribution function of the neutron gas in a constant power reactor are considered, taking into account the burn-up of fuel. To separate the secular motion of neutrons owing to fuel burn-up and the microscopic fluctuations of neutrons around this motion, a long time of the order of several months is divided into m equal intervals,

Hideo Hayasaka

1983-01-01

98

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

E-print Network

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

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

2004-12-31

99

Neutron density distributions from antiprotonic 208Pb and 209Bi atoms  

E-print Network

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

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

2007-02-08

100

Characterisation of superconducting capillaries for magnetic shielding of twisted-wire pairs in a neutron electric dipole moment experiment  

NASA Astrophysics Data System (ADS)

The cryoEDM neutron electric dipole moment experiment requires a SQUID magnetometry system with pick-up loops inside a magnetically shielded volume connected to SQUID sensors by long (up to 2 m) twisted-wire pairs (TWPs). These wires run outside the main shield, and therefore must run through superconducting capillaries to screen unwanted magnetic pick-up. We show that the average measured transverse magnetic pick-up of a set of lengths of TWPs is equivalent to a loop area of 5.0×10-6 m2/m, or 14 twists per metre. From this we set the requirement that the magnetic shielding factor of the superconducting capillaries used in the cryoEDM system must be greater than 8.0×104. The shielding factor-the ratio of the signal picked-up by an unshielded TWP to that induced in a shielded TWP-was measured for a selection of superconducting capillaries made from solder wire. We conclude the transverse shielding factor of a uniform capillary is greater than 107. The measured pick-up was equal to, or less than that due to direct coupling to the SQUID sensor (measured without any TWP attached). We show that discontinuities in the capillaries substantially impair the magnetic shielding, yet if suitably repaired, this can be restored to the shielding factor of an unbroken capillary. We have constructed shielding assemblies for cryoEDM made from lengths of single core and triple core solder capillaries, joined by a shielded Pb cylinder, incorporating a heater to heat the wires above the superconducting transition as required.

Henry, S.; Pipe, M.; Cottle, A.; Clarke, C.; Divakar, U.; Lynch, A.

2014-11-01

101

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

Microsoft Academic Search

The mass and kinetic energy distribution of nuclear fragments from thermal neutron-induced fission of 235U(nth,f) have been studied using a Monte-Carlo simulation. Besides reproducing the pronounced broadening in the standard deviation of the kinetic energy at the final fragment mass number around m = 109, our simulation also produces a second broadening around m = 125. These results are in

M. Montoya; J. Rojas; E. Saetone

2007-01-01

102

Excited-State Density Distributions of Neutron-Rich Unstable Nuclei  

E-print Network

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 pi = 0+, 1-, and 2+. 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+ 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.

J. Terasaki; J. Engel

2006-08-02

103

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

PubMed

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

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

2010-09-01

104

Neutron dose distribution from 12C induced reactions on Ti and Ag using proton recoil scintillator  

Microsoft Academic Search

We measured the double differential neutron yield at 0°, 30°, 60° and 90° from 12C5+ induced reactions on thick targets of Ti and Ag at 12 MeV\\/amu at the Cyclotron at National Institute of Radiological Sciences, Inage, Japan, with 5? × 5? proton recoil scintillation detectors BC-501. The measured neutron spectra were unfolded using pulse height unfolding algorithm and energy and angular distribution

M. Nandy; P. K. Sarkar; T. Sanami; T. Shibata; M. Takada

2010-01-01

105

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

Microsoft Academic Search

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

Sami Pietinen; Vesa Tenhunen; Markku Tukiainen

2008-01-01

106

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

107

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

E-print Network

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

108

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

E-print Network

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

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

2007-06-28

109

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

SciTech Connect

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

Han, Jiyeon; /Rochester U.

2008-11-01

110

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

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

111

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

SciTech Connect

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

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

2006-12-04

112

Structural Interpretation in Composite Systems Using Powder X-ray Diffraction: Applications of Error Propagation to the Pair Distribution Function  

Microsoft Academic Search

Purpose  To develop a method for drawing statistical inferences from differences between multiple experimental pair distribution function\\u000a (PDF) transforms of powder X-ray diffraction (PXRD) data.\\u000a \\u000a \\u000a \\u000a \\u000a Methods  The appropriate treatment of initial PXRD error estimates using traditional error propagation algorithms was tested using\\u000a Monte Carlo simulations on amorphous ketoconazole. An amorphous felodipine:polyvinyl pyrrolidone:vinyl acetate (PVPva) physical\\u000a mixture was prepared to define an error

Michael D. Moore; Zhenqi Shi; Peter L. D. Wildfong

2010-01-01

113

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

NASA Technical Reports Server (NTRS)

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

Huelsman, L. P.

1972-01-01

114

The number distribution of neutrons and gammas generated in a multiplying sample  

SciTech Connect

The subject of this paper is an analytical derivation of the full probability distribution of the number of neutrons and photons generated in a sample with internal multiplication by one internal source emission event, and its comparison with Monte Carlo calculations. We derive recursive analytic expressions for the probability distributions P(n) of neutrons and photons up to values of n for which P(n) is significant, as functions of the first collision probability p of the source neutrons. The derivation was performed by using the symbolic algebra code MATHEMATICA. With the introduction of a modified factorial moment of the number of fission neutrons and photons, the resulting expressions were brought to a formally equivalent form with those for the factorial moments of the searched probability distributions. The results were compared with Monte Carlo calculations, and excellent agreement was found between the analytical results and the simulations. The results show that the probability distributions change with increasing sample mass such that the 'bulk' of the distribution changes only slightly, but a tail develops for higher n values, which is the main reason for the increase of the factorial moments with increasing sample mass. (authors)

Enqvist, A. [Dept. of Nuclear Engineering, Chalmers Univ. of Technology, SE-412 96 Goeteborg (Sweden); Pozzi, S. [Oak Ridge National Laboratory, Ms60101, PO Box 2008, Oak Ridge, TN 37831-6010 (United States); Pazsit, I. [Dept. of Nuclear Engineering, Chalmers Univ. of Technology, SE-412 96 Goeteborg (Sweden)

2006-07-01

115

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

SciTech Connect

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

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

2009-10-25

116

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

E-print Network

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

Xiaojun Sun; Chenghua Pan; Chenggang Yu; Yongxu Yang; Ning Wang

2013-11-01

117

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

NASA Astrophysics Data System (ADS)

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.

Pietinen, Sami; Tenhunen, Vesa; Tukiainen, Markku

118

The effect of temperature and control rod position on the spatial neutron flux distribution in the Syrian miniature neutron source reactor  

Microsoft Academic Search

The effect on the spatial neutron flux distribution for both of water and fuel temperature increase as well as the change in the control rod position are presented in the Syrian miniature neutron source reactor (MNSR). The cross-sections of all the reactor components at different temperatures are generated using the WIMSD4 code. These group constants are used then in the

K. Khattab; H. Omar; N. Ghazi

2006-01-01

119

In-phantom spectra and dose distributions from a high-energy neutron therapy beam  

NASA Astrophysics Data System (ADS)

In radiotherapy with external beams, healthy tissues surrounding the target volumes are inevitably irradiated. In the case of neutron therapy, the estimation of dose to the organs surrounding the target volume is particularly challenging, because of the varying contributions from primary and secondary neutrons and photons of different energies. The neutron doses to tissues surrounding the target volume at the Louvain-la-Neuve (LLN) facility were investigated in this work. At LLN, primary neutrons have a broad spectrum with a mean energy of about 30 MeV. The transport of a 10×10 cm 2 beam through a water phantom was simulated by means of the Monte Carlo code MCNPX. Distributions of energy-differential values of neutron fluence, kerma and kerma equivalent were estimated at different locations in a water phantom. The evolution of neutron dose and dose equivalent inside the phantom was deduced. Measurements of absorbed dose and of dose equivalent were then carried out in a water phantom using an ionization chamber and superheated drop detectors (SDDs). On the beam axis, the calculations agreed well with the ionization chamber data, but disagreed significantly from the SDD data due to the detector's under-response to neutrons above 20 MeV. Off the beam axis, the calculated absorbed doses were significantly lower than the ionization chamber readings, since gamma fields were not accounted for. The calculated data are doses from neutron-induced charge particles, and these agreed with the values measured by the photon-insensitive SDDs. When exposed to the degraded spectra off the beam axis, the SDD offered reliable estimates of the neutron dose equivalent.

Benck, S.; d'Errico, F.; Denis, J.-M.; Meulders, J.-P.; Nath, R.; Pitcher, E. J.

2002-01-01

120

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

NASA Astrophysics Data System (ADS)

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

Vorobyev, A. S.; Dushin, V. N.; Hambsch, F.-J.; Jakovlev, V. A.; Kalinin, V. A.; Laptev, A. B.; Petrov, B. F.; Shcherbakov, O. A.

2005-05-01

121

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

NASA Astrophysics Data System (ADS)

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

Tarasov, A. N.

2014-03-01

122

Effect of pre-equilibrium spin distribution on neutron-induced reaction cross sections  

SciTech Connect

Cross section measurements were made of prompt gamma-ray production as a function of neutron energy using the germanium array for neutron induced excitations (GEANIE) at LANSCE. Measuring the prompt reaction gamma rays as a function of incident neutron energy provides more precise understanding of the spins populated by the pre-equilibrium reaction. The effect of the spin distribution in pre-equilibrium reactions has been investigated using the GNASH reaction code. Widely used classical theories such as the exciton model usually assume that the spin distribution of the pre-equilibrium reaction is the same as the spin distribution of the compound nucleus reaction mechanism. In the present approach, the pre-equilibrium reaction spin distribution was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK). This pre-equilibrium spin distribution was incorporated into the GNASH code and the gamma-ray production cross sections were calculated and compared with experimental data. Spin distributions peak at lower spin when calculated with the FKK formulation than with the Compound Nuclear theory. The measured partial gamma-ray cross sections reflect this spin difference. Realistic treatment of the spin distribution improves the accuracy of calculations of gamma-ray production cross sections.

Dashdorj, D.; Mitchell, G. E. [North Carolina State University, Raleigh, NC and Triangle Universities Nuclear Laboratory, Durham, NC (United States); Becker, J. A.; Wu, C. Y. [Lawrence Livermore National Laboratory, Livermore, CA (United States); Chadwick, M. B.; Devlin, M.; Fotiades, N.; Kawano, T.; Nelson, R. O. [Los Alamos National Laboratory Los Alamos, NM (United States); Garrett, P. E. [University of Guelph, Guelph, Ontario (Canada); Kunieda, S. [Japan Atomic Energy Agency, Tokai (Japan)

2008-04-17

123

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

E-print Network

Structural Study of Poorly Crystalline Layered Manganese Oxides Using the Atomic Pair Distribution, such as ferryhydrite. In this study, we used PDF analysis to investigate structures of manganese oxides. Manganese

Sparks, Donald L.

124

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

E-print Network

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

Teich, Malvin C.

125

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

Microsoft Academic Search

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

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

2000-01-01

126

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

Microsoft Academic Search

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

H. Matsuura; K. Funakoshi; Y. Nakao

2003-01-01

127

Measurement of angular distribution of neutrons emitted from plasma focus using NTD  

Microsoft Academic Search

Mica detectors together with thick uranium foils were used for detection and angular distribution measurement of the neutrons emitted from the d-plasma focus (DPF). The distance between detectors and plasma pinch was 4 cm. For reason of detector protection from the thermal shock, they were covered with the mica layer of 1 mm thickness. Annealing of the detectors were measured

R. Antanasijevi?; Z. Mari?; R. Banjanac; A. Dragi?; J. Stanojevi?; D. ?or?evi?; D. Joksimovi?; V. Udovi?i?; J. Vukovi?

1999-01-01

128

Non-Equilibrium Thermodynamics and Energy Distribution Function of Neutron Gas in Constant Power Reactor under Coupling of Neutrons and Medium  

NASA Astrophysics Data System (ADS)

The thermodynamics and the energy distribution function of the neutron gas in a constant power reactor are considered, taking into account the burn-up of fuel. To separate the secular motion of neutrons owing to fuel burn-up and the microscopic fluctuations of neutrons around this motion, a long time of the order of several months is divided into m equal intervals, and the respective states corresponding to m small time intervals are treated as quasi-stationary states. The local energy distribution function of the neutron gas in the quasi-stationary state is given by a generalized Boltzmann distribution specified by the respective generalized activity coefficient for each subsystem. The effects of fuel burn-up on the respective distribution functions for successive small time intervals are taken into account through various quantities relating to reactor physics, depending upon the fuel burn-up, by successive approximation.

Hayasaka, Hideo

1983-08-01

129

Distribution of the cationic state over the chlorophyll pair of the photosystem II reaction center.  

PubMed

The reaction center chlorophylls a (Chla) of photosystem II (PSII) are composed of six Chla molecules including the special pair Chla P(D1)/P(D2) harbored by the D1/D2 heterodimer. They serve as the ultimate electron abstractors for water oxidation in the oxygen-evolving Mn(4)CaO(5) cluster. Using the PSII crystal structure analyzed at 1.9 Å resolution, the redox potentials of P(D1)/P(D2) for one-electron oxidation (E(m)) were calculated by considering all PSII subunits and the protonation pattern of all titratable residues. The E(m)(Chla) values were calculated to be 1015-1132 mV for P(D1) and 1141-1201 mV for P(D2), depending on the protonation state of the Mn(4)CaO(5) cluster. The results showed that E(m)(P(D1)) was lower than E(m)(P(D2)), favoring localization of the charge of the cationic state more on P(D1). The P(D1)(•+)/P(D2)(•+) charge ratio determined by the large-scale QM/MM calculations with the explicit PSII protein environment yielded a P(D1)(•+)/P(D2)(•+) ratio of ~80/~20, which was found to be due to the asymmetry in electrostatic characters of several conserved D1/D2 residue pairs that cause the E(m)(P(D1))/E(m)(P(D2)) difference, e.g., D1-Asn181/D2-Arg180, D1-Asn298/D2-Arg294, D1-Asp61/D2-His61, D1-Glu189/D2-Phe188, and D1-Asp170/D2-Phe169. The larger P(D1)(•+) population than P(D2)(•+) appears to be an inevitable fate of the intact PSII that possesses water oxidation activity. PMID:21805998

Saito, Keisuke; Ishida, Toyokazu; Sugiura, Miwa; Kawakami, Keisuke; Umena, Yasufumi; Kamiya, Nobuo; Shen, Jian-Ren; Ishikita, Hiroshi

2011-09-14

130

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

SciTech Connect

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

Tatarskiy, D. A., E-mail: tatarsky@ipmras.ru; Udalov, O. G.; Fraerman, A. A. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

2012-10-15

131

Measurement of the beam-helicity asymmetry $I^{\\odot}$ in the photoproduction of $?^0?^{\\pm}$-pairs off protons and off neutrons  

E-print Network

Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of mixed-charge pion pairs in the reactions $\\boldsymbol{\\gamma}p\\rightarrow n\\pi^0\\pi^+$ off free protons and $\\boldsymbol{\\gamma}d\\rightarrow (p)p\\pi^0\\pi^-$ and $\\boldsymbol{\\gamma}d\\rightarrow (n)n\\pi^0\\pi^+$ off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4 GeV. Circularly polarized photons were produced from bremsstrahlung of longitudinally polarized electrons and tagged with the Glasgow-Mainz magnetic spectrometer. The charged pions, recoil protons, recoil neutrons, and decay photons from $\\pi^0$ mesons were detected in the 4$\\pi$ electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. Using a complete kinematic reconstruction of the final state, excellent agreement was found between the results for free and quasi-free protons, suggesting that the quasi-free neutron results are also a close approximation of the free-neutron asymmetries. A comparison of the results to the predictions of the Two-Pion-MAID reaction model shows that the reaction mechanisms are still not well understood, in particular at low incident photon energies in the second nucleon-resonance region.

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

2014-03-08

132

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

133

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

E-print Network

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

Matteo Rinaldi; Sergio Scopetta

2014-06-18

134

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

NASA Astrophysics Data System (ADS)

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

Rinaldi, Matteo; Scopetta, Sergio

2014-06-01

135

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

136

Heating Distributions in the Target of the Spallation Neutron Source  

SciTech Connect

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

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

1999-11-18

137

Calculation of the angular distribution of delay times in neutron scattering on 58Ni nuclei  

NASA Astrophysics Data System (ADS)

Angular distributions of average delay times and time variances are calculated for resonance-neutron scattering on 58Ni 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.

Prokopets, G. A.

2011-05-01

138

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

139

Bright Integrated Photon-Pair Source for Practical Passive Decoy-State Quantum Key Distribution  

E-print Network

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

Stephan Krapick; Michael Stefszky; Michal Jachura; Benjamin Brecht; Malte Avenhaus; Christine Silberhorn

2014-01-28

140

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

SciTech Connect

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

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

2001-02-01

141

Detection of prokaryotic promoters from the genomic distribution of hexanucleotide pairs  

PubMed Central

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

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

2006-01-01

142

Measurement of thermal neutron fluence distribution with use of 23Na radioactivation around a medical compact cyclotron.  

PubMed

A medical compact cyclotron produces about 10(15) neutrons per day along with 100 GBq of (18)F. Therefore, it is important to establish radiation safety guidelines on residual radioactivity for routine operation, maintenance work, and decommissioning. Thus, we developed a simple method for measuring the thermal neutrons in a cyclotron room. In order to verify the feasibility of our proposed method, we measured the thermal neutron distribution around a cyclotron by using the activation of (23)Na in salt. We installed 78 salt dosimeters in the cyclotron room with a 50 cm mesh. The photopeak of (24)Na was measured, and the neutron flux distribution was estimated. Monitoring the neutron flux distribution in a cyclotron room appears to be useful for not only obtaining an accurate estimate of the distribution of induced radioactivity, but also optimizing the shield design for radiation safety in preparation for the decommissioning process. PMID:20821115

Fujibuchi, Toshioh; Yamaguchi, Ichiro; Kasahara, Tetsuharu; Iimori, Takashi; Masuda, Yoshitada; Kimura, Ken-ichi; Watanabe, Hiroshi; Isobe, Tomonori; Sakae, Takeji

2009-07-01

143

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

USGS Publications Warehouse

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

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

1977-01-01

144

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

SciTech Connect

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

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

2013-07-01

145

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

146

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

SciTech Connect

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

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

2012-03-15

147

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

SciTech Connect

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

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

2012-03-15

148

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

SciTech Connect

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

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

2010-08-04

149

Proton elastic scattering from tin isotopes at 295 MeV and systematic change of neutron density distributions  

NASA Astrophysics Data System (ADS)

Cross sections and analyzing powers for proton elastic scattering from Sn116,118,120,122,124 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.

Terashima, S.; Sakaguchi, H.; Takeda, H.; Ishikawa, T.; Itoh, M.; Kawabata, T.; Murakami, T.; Uchida, M.; Yasuda, Y.; Yosoi, M.; Zenihiro, J.; Yoshida, H. P.; Noro, T.; Ishida, T.; Asaji, S.; Yonemura, T.

2008-02-01

150

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

PubMed

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

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

2014-08-01

151

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

NASA Astrophysics Data System (ADS)

Residual stresses resulting from non homogeneous heat distribution during welding process belong to most significant factor influencing behavior of welded structures. These stresses are responsible for defect occurrence during welding and they are also responsible for crack initiation and propagation at the either static or dynamic load. The significant effect of weld metal chemical composition as well as the effect of fatigue load and local plastic deformation on residual stress distribution and fatigue life have been recognized for high strength steels welds. The changes in residual stress distribution have then positive effect on cold cracking behavior and also on fatigue properties of the welds [1-3]. Several experimental methods, both destructive and non-destructive, such as hole drilling method, X-ray diffraction, neutron diffraction and others, have been used to examine residual stress distribution in all three significant orientations in the vicinity of the welds. The present contribution summarizes the results of neutron diffraction measurements of residual stress distribution in the vicinity of single-pass high-strength-steel welds having different chemical composition as well as the influence of fatigue load and local plastic deformation. It has been observed that the chemical composition of the weld metal has a significant influence on the stress distribution around the weld. Similarly, by aplying both cyclic load or pre-stress load on the specimens, stress relaxation was observed even in the region of approximately 40 mm far from the weld toe.

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

2010-06-01

152

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

PubMed

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

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

2014-06-25

153

Electrokinetics as an alternative to neutron reflectivity for evaluation of segment density distribution in PEO brushes.  

PubMed

Unravelling details of charge, structure and molecular interactions of functional polymer coatings defines an important analytical challenge that requires the extension of current methodologies. In this article we demonstrate how streaming current measurements interpreted with combined self consistent field (SCF) and soft surface electrokinetic theories allow the evaluation of the segment distribution within poly(ethylene oxide) (PEO) brushes beyond the resolution limits of neutron reflectivity technique. PMID:25144904

Zimmermann, Ralf; Romeis, Dirk; Bihannic, Isabelle; Cohen Stuart, Martien; Sommer, Jens-Uwe; Werner, Carsten; Duval, Jérôme F L

2014-10-21

154

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

SciTech Connect

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

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

2011-03-15

155

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

156

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

SciTech Connect

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.

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

157

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

NASA Astrophysics Data System (ADS)

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

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

2008-08-01

158

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

E-print Network

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

Harris, Thomas C. (Thomas Cameron)

2006-01-01

159

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

SciTech Connect

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

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

2007-10-26

160

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

NASA Astrophysics Data System (ADS)

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

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

1999-11-01

161

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

PubMed

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

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

2014-02-01

162

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

163

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

SciTech Connect

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

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

2008-08-01

164

Fast neutron absorbed dose distributions in the energy range 0.5-80 meV--a Monte Carlo study.  

PubMed

Neutron pencil-beam absorbed dose distributions in phantoms of bone, ICRU soft tissue, muscle, adipose and the tissue substitutes water, A-150 (plastic) and PMMA (acrylic) have been calculated using the Monte Carlo code FLUKA in the energy range 0.5 to 80 MeV. For neutrons of energies < or = 20 MeV, the results were compared to those obtained using the Monte Carlo code MCNP4B. Broad-beam depth doses and lateral dose distributions were derived. Broad-beam dose distributions in various materials were compared using two kinds of scaling factor: a depth-scaling factor and a dose-scaling factor. Build-up factors due to scattered neutrons and photons were derived and the appropriate choice of phantom material for determining dose distributions in soft tissue examined. Water was found to be a good substitute for soft tissue even at neutron energies as high as 80 MeV. The relative absorbed doses due to photons ranged from 2% to 15% for neutron energies 10-80 MeV depending on phantom material and depth. For neutron energies below 10 MeV the depth dose distributions derived with MCNP4B and FLUKA differed significantly, the difference being probably due to the use of multigroup transport of low energy (< 19.6 MeV) neutrons in FLUKA. Agreement improved with increasing neutron energies up to 20 MeV. At energies > 20 MeV, MCNP4B fails to describe dose build-up at the phantom interface and penumbra at the edge of the beam because it does not transport secondary charged particles. The penumbra width, defined as the distance between the 80% and 20% iso-dose levels at 5 cm depth and for a 10 x 10 cm2 field, was between 0.9 mm and 7.2 mm for neutron energies 10-80 MeV. PMID:11049184

Söderberg, J; Carlsson, G A

2000-10-01

165

Fast neutron absorbed dose distributions in the energy range 0.5-80 MeV - a Monte Carlo study  

NASA Astrophysics Data System (ADS)

Neutron pencil-beam absorbed dose distributions in phantoms of bone, ICRU soft tissue, muscle, adipose and the tissue substitutes water, A-150 (plastic) and PMMA (acrylic) have been calculated using the Monte Carlo code FLUKA in the energy range 0.5 to 80 MeV. For neutrons of energies ?20 MeV, the results were compared to those obtained using the Monte Carlo code MCNP4B. Broad-beam depth doses and lateral dose distributions were derived. Broad-beam dose distributions in various materials were compared using two kinds of scaling factor: a depth-scaling factor and a dose-scaling factor. Build-up factors due to scattered neutrons and photons were derived and the appropriate choice of phantom material for determining dose distributions in soft tissue examined. Water was found to be a good substitute for soft tissue even at neutron energies as high as 80 MeV. The relative absorbed doses due to photons ranged from 2% to 15% for neutron energies 10-80 MeV depending on phantom material and depth. For neutron energies below 10 MeV the depth dose distributions derived with MCNP4B and FLUKA differed significantly, the difference being probably due to the use of multigroup transport of low energy (<19.6 MeV) neutrons in FLUKA. Agreement improved with increasing neutron energies up to 20 MeV. At energies >20 MeV, MCNP4B fails to describe dose build-up at the phantom interface and penumbra at the edge of the beam because it does not transport secondary charged particles. The penumbra width, defined as the distance between the 80% and 20% iso-dose levels at 5 cm depth and for a 10×10 cm2 field, was between 0.9 mm and 7.2 mm for neutron energies 10-80 MeV.

Söderberg, Jonas; Alm Carlsson, Gudrun

2000-10-01

166

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

PubMed

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

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

2013-10-01

167

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

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

168

Uncovering the intrinsic geometry from the atomic pair distribution function of nanomaterials Department of Biochemistry, Brandeis University, 415 South Street, Waltham, Massachusetts 02453, USA  

E-print Network

, USA Adam M. R. de Graff and M. F. Thorpe Department of Physics, Bateman Physical Sciences PSF 359 be obtained both experimentally and from computer-generated structure models. For bulk materials, atomic pair computer-generated structure models.2 In this paper we will focus on the radial distribution function RDF

Thorpe, Michael

169

Invariant Mass Distribution of Jet Pairs Produced in Association with a W boson in ppbar Collisions at sqrt(s) = 1.96 TeV  

E-print Network

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/c^2 mass range which is not described by current theoretical predictions within the statistical and systematic uncertainties. In this letter we report studies of the properties of this excess.

CDF Collaboration; T. Aaltonen

2011-04-04

170

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

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

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

2011-04-28

171

Charge and matter distributions and form factors of light, medium, and heavy neutron-rich nuclei  

NASA Astrophysics Data System (ADS)

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.

Antonov, A. N.; Kadrev, D. N.; Gaidarov, M. K.; Guerra, E. Moya; Sarriguren, P.; Udias, J. M.; Lukyanov, V. K.; Zemlyanaya, E. V.; Krumova, G. Z.

2005-10-01

172

The investigation of the geographical and vertical distribution of several trace elements in sea water using neutron activation analysis  

Microsoft Academic Search

Methods for the determination of 18 trace elements in sea water by neutron activation analysis have been developed. Of these elements sufficient analyses have been completed for gold, selenium, antimony, silver, cobalt and nickel to permit a discussion of their distributions in the world ocean. The distributions of gold, selenium and antimony are more uniform than those of silver, cobalt

Donald F. Schutz; Karl K. Turekian

1965-01-01

173

Pairing in bulk nuclear matter beyond BCS  

E-print Network

The influence of short-range correlations on the spectral distribution of neutrons is incorporated in the solution of the gap equation for the ${}^3P_2-{}^3F_2$ coupled channel in pure neutron matter. This effect is studied for different realistic interactions including one based on chiral perturbation theory. The gap in this channel vanishes at all relevant densities due to the treatment of these correlations. We also consider the effect of long-range correlations by including polarization terms in addition to the bare interaction which allow the neutrons to exchange density and spin fluctuations governed by the strength of Landau parameters allowed to have reasonable values consistent with the available literature. Preliminary results indicate that reasonable values of these parameters do not generate a gap in the ${}^3P_2-{}^3F_2$ coupled channel either for all three realistic interactions although the pairing interaction becomes slightly more attractive.

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

2014-06-30

174

Modeling Cold-Fuel Distributions Inferred from Elastically Scattered Neutrons in Layered Cryogenic-DT Direct-Drive Implosions  

NASA Astrophysics Data System (ADS)

High-resolution neutron spectroscopy has been used to probe the areal density of a compressed shell from a cryogenic-DT direct-drive implosion in inertial confinement fusion (ICF) experiments. The two-body kinematics of (n,T) and (n,D) elastic scattering suggest that there should be a correlation between the energy of the neutron and the region of the DT shell probed when using a single line of sight with time-of-flight (TOF) techniques. A finite-source distribution and/or asymmetric compressed-fuel distribution is expected to modify the correlation in the TOF signal significantly. Low-mode perturbation of the DT source/shell have been simulated in a transport code (MCNP) to track neutrons that elastically scatter into a TOF detector. A 3-D plot of the dense-DT-shell scatter locations of the ``detected'' neutrons show that a realistic extended-source distribution probes a much larger region of the fuel shell than a simple point-source distribution. Simulations illustrate that higher ?R implosions increase multiple scatterings that further mask the correlation between neutron energy and the sampling area of the dense shell distribution. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.

Forrest, C.; Glebov, V. Yu.; Knauer, J. P.; Sangster, T. C.; Stoeckl, C.; Anderson, K. S.; Radha, P. B.; Goncharov, V. N.; Meyehofer, D. D.; Gardner, S.; Baldwin, D.

2012-10-01

175

Fast neutron absorbed dose distributions in the energy range 0.5-80 MeV - a Monte Carlo study  

Microsoft Academic Search

Neutron pencil-beam absorbed dose distributions in phantoms of bone, ICRU soft tissue, muscle, adipose and the tissue substitutes water, A-150 (plastic) and PMMA (acrylic) have been calculated using the Monte Carlo code FLUKA in the energy range 0.5 to 80 MeV. For neutrons of energies <=20 MeV, the results were compared to those obtained using the Monte Carlo code MCNP4B.

Jonas Söderberg; Gudrun Alm Carlsson

2000-01-01

176

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

SciTech Connect

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

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

2010-09-14

177

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

Microsoft Academic Search

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

M. I. Pigozzi; A. J. Solari

1997-01-01

178

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

NASA Technical Reports Server (NTRS)

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

Schneider, Harold

1959-01-01

179

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

SciTech Connect

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

Moran, J.M.; Nigg, D.W.; Wheeler, F.J.; Bauer, W.F. (Idaho National Engineering Laboratory, EG G Idaho, Inc., P.O. Box 1625, Idaho Falls, Idaho 83415-3515 (United States))

1992-05-01

180

Pore distributions in nanocrystalline metals from small-angle neutron scattering  

SciTech Connect

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

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

1998-07-24

181

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

SciTech Connect

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

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

2008-05-12

182

Pulsar Pair Cascades in Magnetic Fields with Offset Polar Caps  

NASA Technical Reports Server (NTRS)

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

Harding, Alice K.; Muslimov, Alex G.

2012-01-01

183

Pulsar Pair Cascades in Magnetic Fields with Offset Polar Caps  

NASA Astrophysics Data System (ADS)

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

Harding, Alice K.; Muslimov, Alex G.

2011-12-01

184

Selective radiography of 10B distribution in organs using cold and thermal neutron beams.  

PubMed

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

Skvarc, Jure; Giacomelli, Marko; Yanagië, Hironobu; Kühne, Guido

2002-01-01

185

Use of Instrumental Neutron Activation Analysis to investigate the distribution of trace elements among subsamples of solid materials  

E-print Network

The results of analytical measurements performed with solid-sampling techniques are affected by the distribution of the analytes within the matrix. The effect becomes significant in case of determination of trace elements in small subsamples. In this framework we propose a measurement model based on Instrumental Neutron Activation Analysis to determine the relative variability of the amount of an analyte among subsamples of a material. The measurement uncertainty is evaluated and includes the counting statistics, the full-energy gamma peak efficiency and the spatial gradient of the neutron flux at the irradiation position. The data we obtained in a neutron activation experiment and showing the relative variability of As, Au, Ir, Sb and W among subsamples of a highly pure Rh foil are also presented.

DAgostino, Giancarlo; Giordani, Laura; Oddone, Massimo; Kipphardt, Heinrich; Richter, Silke

2013-01-01

186

Use of Instrumental Neutron Activation Analysis to investigate the distribution of trace elements among subsamples of solid materials  

NASA Astrophysics Data System (ADS)

The results of analytical measurements performed with solid-sampling techniques are affected by the distribution of the analytes within the matrix. The effect becomes significant in the case of determination of trace elements in small subsamples. In this framework we propose a measurement model based on Instrumental Neutron Activation Analysis to determine the relative variability of the amount of an analyte among subsamples of a material. The measurement uncertainty is evaluated and includes the counting statistics, the full-energy gamma peak efficiency and the spatial gradient of the neutron flux at the irradiation position. The data we obtained in a neutron activation experiment and showing the relative variability of As, Au, Ir, Sb and W among subsamples of a highly pure Rh foil are also presented.

D'Agostino, G.; Bergamaschi, L.; Giordani, L.; Oddone, M.; Kipphardt, H.; Richter, S.

2014-02-01

187

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

188

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

USGS Publications Warehouse

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

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

2002-01-01

189

Measurement of neutron dose distribution for a passive scattering nozzle at the Proton Medical Research Center (PMRC)  

NASA Astrophysics Data System (ADS)

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%.

Tayama, Ryuichi; Fujita, Yasuo; Tadokoro, Masahiro; Fujimaki, Hisataka; Sakae, Takeji; Terunuma, Toshiyuki

2006-08-01

190

Effective pairing interactions with isospin density dependence  

SciTech Connect

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

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

2008-05-15

191

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

NASA Astrophysics Data System (ADS)

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

Boggara, Mohan; Mihailescu, Ella; Krishnamoorti, Ramanan

2009-03-01

192

On the nature of the bimodal initial velocity distribution of neutron stars  

NASA Astrophysics Data System (ADS)

We propose that the bimodal nature of the kick velocity distribution of radio pulsars is connected to the dichotomy between hadronic stars (i.e. neutron stars with no quark matter content) and quark stars. Bimodality can appear due to different mechanisms of explosion which lead to the formation of two types of compact stars or due to two different sets of parameters driving a particular kick mechanism. The low velocity maximum (at ˜100 km s-1) is associated with hadronic star formation, whereas the second peak corresponds to quark stars. In the model of delayed collapse of hadronic stars to quark stars \\citep{bbd2003} quark deconfinement leads to a second energy release, and to a second kick, in addition to the kick imparted to the newly formed hadronic star during the supernova explosion. If the electromagnetic rocket mechanism can give a significant contribution to pulsar kicks, then the high velocity peak can be associated with the shorter initial spin periods of quark stars with respect to hadronic stars. We discuss these scenarios.

Bombaci, I.; Popov, S. B.

2004-09-01

193

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

194

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

E-print Network

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

Henderson, Conor, 1977-

2005-01-01

195

Role of neutron transfer on fusion barrier distributions of the Si28,30 + Sn124 systems  

NASA Astrophysics Data System (ADS)

The fusion barrier distributions for Si28,30 + Sn124 systems were extracted from quasielastic excitation function measurements at backward angles. The experimental barrier distributions were then compared with coupled-channel (CC) calculations. The fusion barrier distribution for the Si30 + Sn124 reaction was well reproduced by the CC calculations with the inclusion of projectile and target inelastic couplings and only one possible positive Q-value 2n-transfer channel coupling using the ccfull code. However, CC calculations with similar coupling schemes for inelastic excitation of target and projectile with the 4n-transfer channel corresponding to the highest positive Q value failed to reproduce the barrier distribution for the Si28 + Sn124 reaction, because it has many positive Q-value multi-neutron transfer channels. A better agreement between the experimental fusion barrier distribution for the Si28 + Sn124 system and the prediction of semiempirical CC calculations based on the Zagrebaev framework [V. I. Zagrebaev, Phys. Rev. C 67, 061601(R) (2003), 10.1103/PhysRevC.67.061601] was obtained only after considering positive Q-value multi-neutron transfer couplings. The sensitivity of the fusion barrier distribution to the hexadecapole deformation parameter ?4 of the projectile was also discussed.

Danu, L. S.; Nayak, B. K.; Mirgule, E. T.; Choudhury, R. K.; Garg, U.

2014-04-01

196

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

Microsoft Academic Search

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

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

1998-01-01

197

The probability distribution for a random match between an experimental-theoretical spectral pair in tandem mass spectrometry.  

PubMed

Proteomic techniques are fast becoming the main method for qualitative and quantitative determination of the protein content in biological systems. Despite notable advances, efficient and accurate analysis of high throughput proteomic data generated by mass spectrometers remains one of the major stumbling blocks in the protein identification problem. We present a model for the number of random matches between an experimental MS-MS spectrum and a theoretical spectrum of a peptide. The shape of the probability distribution is a function of the experimental accuracy, the number of peaks in the experimental spectrum, the length of the interval over which the peaks are distributed, and the number of theoretical spectral peaks in this interval. Based on this probability distribution, a goodness-of-fit tool can be used to yield fast and accurate scoring schemes for peptide identification through database search. In this paper, we describe one possible implementation of such a method and compare the performance of the resulting scoring function with that of SEQUEST. In terms of speed, our algorithm is roughly two orders of magnitude faster than the SEQUEST program, and its accuracy of peptide identification compares favorably to that of SEQUEST. Moreover, our algorithm does not use information related to the intensities of the peaks. PMID:15852515

Fridman, Tema; Razumovskaya, Jane; Verberkmoes, Nathan; Hurst, Greg; Protopopescu, Vladimir; Xu, Ying

2005-04-01

198

Calculation of the cluster size distribution functions and small-angle neutron scattering data for C60/N-methylpyrrolidone  

NASA Astrophysics Data System (ADS)

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.

Tropin, T. V.; Jargalan, N.; Avdeev, M. V.; Kyzyma, O. A.; Sangaa, D.; Aksenov, V. L.

2014-01-01

199

Characterization of the neutron flux distribution at the Athens Tandem Accelerator NCSR "Demokritos"  

NASA Astrophysics Data System (ADS)

Quasi-monoenergetic neutron beams, in the energy range 7-11.5 MeV, produced via the 2H(d,n) reaction, have been used at the 5.5 MV tandem T11/25 Accelerator Laboratory of NCSR "Demokritos". The flux variation of the neutron beam is monitored with a BF 3 detector, while the absolute flux is obtained with respect to reference reactions. An investigation of the energy dependence of the neutron fluence has been carried out using two independent techniques: by a liquid scintillator BC501A detector and deconvolution of its recoil energy spectra performed by means of the DIFBAS code, as well as via the multiple foil activation technique in combination with the SULSA unfolding code. The neutron facility has also been characterized by means of Monte Carlo simulations with MCNP5.

Vlastou, R.; Kokkoris, M.; Diakaki, M.; Constantinou, Ch.; Kalfas, C. A.; Kotrotsou, A.; Lagoyannis, A.; Lambrou, M.; Loizou, V.; Mara, E.; Paneta, V.; Provatas, G.; Tsinganis, A.

2011-12-01

200

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

SciTech Connect

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

Hansen, L.F.

1985-05-01

201

On Theoretical Uncertainties of the W Angular Distribution in W-Pair Production at LEP2 Energies  

E-print Network

We discuss theoretical uncertainties of the distribution in the cosine of the W polar angle projected into a measurement of the anomalous triple gauge-boson coupling \\lambda=\\lambda_{\\gamma}=\\lambda_Z at LEP2 energies for the tandem of the Monte Carlo event generators KoralW and YFSWW3 and for the Monte Carlo event generator RacoonWW. Exploiting numerical results of these programs and cross-checks with experimental fitting procedures, we estimate that the theoretical uncertainty of the value of \\lambda due to electroweak corrections, as obtained at LEP2 with the help of these programs, is ~0.005, about half of the expected experimental error for the combined LEP2 experiments (~0.010). We use certain idealized event selections; however, we argue that these results are valid for realistic LEP2 measurements.

R. Bruneliere; A. Denner; S. Dittmaier; S. Jadach; S. Jezequel; W. Placzek; M. Roth; M. Skrzypek; D. Wackeroth; B. F. L. Ward; Z. Was

2002-01-31

202

Hopf algebras, distributive (Laplace) pairings and hash products: a unified approach to tensor product decompositions of group characters  

NASA Astrophysics Data System (ADS)

We show for bicommutative graded connected Hopf algebras that a certain distributive (Laplace) subgroup of the convolution monoid of 2-cochains parameterizes certain well behaved Hopf algebra deformations. Using the Laplace group, or its Frobenius subgroup, we define higher derived hash products, and develop a general theory to study their main properties. Applying our results to the (universal) bicommutative graded connected Hopf algebra of symmetric functions, we show that classical tensor product and character decompositions, such as those for the general linear group, mixed co- and contravariant or rational characters, orthogonal and symplectic group characters, Thibon and reduced symmetric group characters, are special cases of higher derived hash products. In the appendix we discuss a relation to formal group laws.

Fauser, Bertfried; Jarvis, Peter D.; King, Ronald C.

2014-05-01

203

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

Microsoft Academic Search

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

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

1997-01-01

204

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

SciTech Connect

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.

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

205

Microlensing Neutron Stars  

E-print Network

We investigate the chances that neutron stars act as the lense in a gravitational microlensing event towards the galactic bulge or a spiral arm. The observation of neutron stars by means of gravitational microlensing would allow the estimation of neutron star masses independently of the property of being a pulsar in a binary system. We estimate the contribution of neutron stars to the optical depth and the lensing rate based on two different models of the pulsar distribution in the galaxy. Since only a small fraction of all neutron stars are pulsars, it is unlikely to find a pulsar that acts as a microlense by chance. A position comparison of known radio pulsars with observed microlensing candidates towards the galactic bulge and spiral arms shows no candidate pair, which is consistent with the theoretical expectation. To improve the probability of microlensing a pulsar, we suggest to search for gravitational microlensing events of known nearby high proper motion pulsars. The pulsar PSR J1932+1059 is a good candidate for an astrometric detection of gravitational lensing.

Dominik J. Schwarz; Dirk Seidel

2002-04-03

206

Yields of Fragment Pairs in Ternary Fission of 252Cf  

NASA Astrophysics Data System (ADS)

The yields of correlated fragment pairs in He ternary fission for Zr/Ba and Mo/Xe charge splits were obtained. Neutron multiplicity distributions for these splits was determined with =2.9(1) for both charge splits Zr/Ba and Mo/Xe. With the use of minimization method, the primary fragments' mass and excitation energy distributions were obtained, with the mean masses primary fragment 102.7/145.3 for Zr/Ba and 106.4/141.6 for Mo/Xe.

Jandel, M.; Kliman, J.; Krupa, L.; Morhá?, M.; Hamilton, J. H.; Kormicki, J.; Ramayya, A. V.; Hwang, J. K.; Luo, Y. X.; Fong, D.; Gore, P.; Ter Akopian, G. M.; Oganessian, Yu. Ts.; Rodin, A. M.; Fomichev, A. S.; Popeko, G. S.; Daniel, A. V.; Rasmussen, J. O.; Macchiavelli, A. O.; Stoyer, M. A.; Donangelo, R.; Cole, J. D.

2003-10-01

207

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

SciTech Connect

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

Tsao, Cheng-Si [Massachusetts Institute of Technology (MIT); Li, Mingda [ORNL; Zhang, Yang [ORNL; Leao, Juscelino B [ORNL; Chiang, Wei-Shan [ORNL; Chung, Tsui-Yun [Institute of Nuclear Energy Research, Taiwan; Tzeng, Yi-Ren [Institute of Nuclear Energy Research, Taiwan; Chen, Sow-hsin H [ORNL

2010-01-01

208

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

E-print Network

Neutrino-nucleus coherent elastic scattering provides a theoretically appealing way to measure the neutron part of nuclear form factors. Using an expansion of form factors into moments, we show that neutrinos from stopped pions can probe not only the second moment of the form factor (the neutron radius) but also the fourth moment. Using simple Monte Carlo techniques for argon, germanium, and xenon detectors of 3.5 tonnes, 1.5 tonnes, and 300 kg, respectively, we show that the neutron radii can be found with an uncertainty of a few percent when near a neutrino flux of $3\\times10^{7}$ neutrinos/cm$^{2}$/s. If the normalization of the neutrino flux is known independently, one can determine the moments accurately enough to discriminate among the predictions of various nuclear energy functionals.

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

2012-07-03

209

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

NASA Astrophysics Data System (ADS)

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

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

2003-09-01

210

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

SciTech Connect

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

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

2013-02-21

211

Observation of the Spatial Distribution of Gravitationally Bound Quantum States of Ultracold Neutrons and Its Derivation Using the Wigner Function  

NASA Astrophysics Data System (ADS)

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.

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

2014-02-01

212

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

NASA Astrophysics Data System (ADS)

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

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

2002-07-01

213

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

SciTech Connect

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

Attix, F.H.

1980-01-01

214

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

SciTech Connect

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

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

1993-07-01

215

Novel neutron focusing mirrors for compact neutron sources  

E-print Network

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

Gubarev, M.V.

216

Eulerian pairs on Fibonacci words  

E-print Network

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.

Li, Teresa X S; Miao, Melissa Y F

2011-01-01

217

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

SciTech Connect

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

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

1980-06-01

218

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

Microsoft Academic Search

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

M. Caamano; D. Cortina-Gil; K. Summerer; J. Benlliure; E. Casarejos; H. Geissel; G. Munzenberg; J. Pereira

2004-01-01

219

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

Microsoft Academic Search

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

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

1983-01-01

220

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

Microsoft Academic Search

The partial structure factors pertaining to DNA–DNA, DNA–polyamine, and polyamine–polyamine density correlations in DNA fragment (contour length 54 nm) solutions have been measured with small angle neutron scattering and contrast matching in water. The effect of the polyamines putrescine and spermidine on the DNA molecular structure is gauged from the limiting behavior of the DNA–DNA partial structure factor at high

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

1999-01-01

221

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

Microsoft Academic Search

The partial structure factors pertaining to DNA-DNA, DNA-polyamine, and polyamine-polyamine density correlations in DNA fragment (contour length 54 nm) solutions have been measured with small angle neutron scattering and contrast matching in water. The effect of the polyamines putrescine and spermidine on the DNA molecular structure is gauged from the limiting behavior of the DNA-DNA partial structure factor at high

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

1999-01-01

222

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

SciTech Connect

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

D. SIEBE; K. PASAMEHMETOGLU

2000-11-01

223

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

PubMed

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

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

2014-09-01

224

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

PubMed

Pharmaceutical unit operations such as milling and compaction can often generate disordered regions in crystals of active pharmaceutical ingredients (APIs). This may lead to changes in a number of important pharmaceutical properties including dissolution, stability, hygroscopicity, and so on. It is therefore important for pharmaceutical industry to evaluate the effects of pharmaceutical processing on API structural orders, and to investigate and develop analytical tools that are capable of accurately detecting and assessing subtle process-induced structural disorders in pharmaceutical crystals. In this study, nanoindentation was first used to determine the intrinsic mechanical properties including hardness and Young's modulus of two API crystals, compounds 1 and 2. These crystals of different mechanical properties were then milled and compacted under various conditions. The resulting structural disorders in these crystals were subsequently evaluated using synchrotron-based high-resolution total scattering pair distribution function (TS-PDF) analysis. Furthermore, principal component analysis was applied to the PDF data to assess the relative extents of disorders in the API crystals, which showed a good correlation with the process conditions. The study demonstrates that high-resolution TS-PDF analysis coupled with nanoindentation measurement is a valuable and effective tool for detecting and assessing process-induced subtle structural disorders in API crystals. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:3879-3890, 2014. PMID:25331822

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

2014-12-01

225

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

SciTech Connect

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

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

2008-01-01

226

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

SciTech Connect

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.

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

227

Local structures of Sr{sub 2}FeMnO{sub 5+y} (y=0, 0.5) and Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} from reverse Monte Carlo modeling of pair distribution function data and implications for magnetic order  

SciTech Connect

The local structures of the oxygen deficient perovskites Sr{sub 2}FeMnO{sub 5}, Sr{sub 2}FeMnO{sub 5.5}, and Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} have been analyzed using neutron pair distribution function data. The results show that locally all three structures are more complex than implied by their average cubic structures and that the distributions of oxygen vacancies are not completely random on a local level. For both Sr{sub 2}FeMnO{sub 5+y} compounds it is found that there is no short range ordering of the Fe and Mn cations. For Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} there is evidence to suggest that the Fe/Cr distribution is not completely random and is locally ordered such that there are fewer Fe--Fe nearest neighbor pairs than in a random distribution. Reverse Monte Carlo modeling of the pair distribution function data has provided the Fe--O, Mn--O, and Cr--O bond length distributions and information on the coordination numbers of the Fe, Mn, and Cr cations. In Sr{sub 2}FeMnO{sub 5} it is found that the Fe{sup 3+} cations are most often in 4-fold coordination but there is also a large amount of Fe{sup 3+} in 5-fold coordination and a small amount in 6-fold coordination. The Mn{sup 3+} is split between 5-fold and 6-fold coordination. The Mn--O bond length distributions indicate that the Mn{sup 3+}O{sub 6} octahedra and Mn{sup 3+}O{sub 5} square pyramids are locally Jahn-Teller distorted. In Sr{sub 2}FeMnO{sub 5.5} the Fe{sup 3+} is almost entirely 5 coordinate while the Mn{sup 4+} is almost entirely 6 coordinate. The Cr{sup 3+} in Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} is almost entirely 6-fold coordinated, giving the Fe{sup 3+} an average coordination number of 4.67. In Sr{sub 2}FeMnO{sub 5} and Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} the Fe{sup 3+} and Sr{sup 2+} cations undergo local displacements which are driven by the oxygen vacancies, while the Mn{sup 3+} and Cr{sup 3+} cations remain near their positions in the average structures. In Sr{sub 2}FeMnO{sub 5.5} these cations are not significantly displaced. The local coordination geometries are used to explain previously observed but yet poorly understood magnetic properties of these materials. - Graphical abstract: The actual bond angle distributions in the cubic perovskite Sr{sub 2}FeMnO{sub 5} obtained from reverse Monte Carlo modeling of the local structure using neutron pair distribution function data. Highlights: Black-Right-Pointing-Pointer No long range ordering of oxygen vacancies, but short range order is present. Black-Right-Pointing-Pointer No short range Fe/Mn order but short range Fe/Cr order is present. Black-Right-Pointing-Pointer Fe tends to have lower coordination numbers while Mn and Cr have higher ones. Black-Right-Pointing-Pointer Local bond distances and bond angles have been determined. Black-Right-Pointing-Pointer Local structures can help explain long range magnetic ordering behavior.

King, Graham, E-mail: gking@lanl.gov [Lujan Neutron Scattering Center, Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545 (United States)] [Lujan Neutron Scattering Center, Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545 (United States); Ramezanipour, Farshid [Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1 (Canada)] [Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1 (Canada); Llobet, Anna [Lujan Neutron Scattering Center, Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545 (United States)] [Lujan Neutron Scattering Center, Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545 (United States); Greedan, John E. [Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1 (Canada)] [Department of Chemistry and Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1 (Canada)

2013-02-15

228

Diffractive charged meson pair production  

E-print Network

We investigate the possibility to measure the nonforward gluon distribution function by means of diffractively produced \\pi^+\\pi^- and K^+K^- pairs in polarized lepton nucleon scattering. The resulting cross sections are small and are dominated by the gluonic contribution. We find relatively large spin asymmetries, both for \\pi^+\\pi^- and for K^+K^- pairs.

B. Lehmann-Dronke; M. Maul; S. Schaefer; E. Stein; A. Schäfer

1999-01-12

229

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

SciTech Connect

70 keV synchrotron radiation and thermal neutrons have been employed to investigate the residual stress characteristics in a fully restrained, steel, butt weld. The focus is on the values of the subsurface and through-thickness strain/stress variation in the middle of the weld. The advantages and limitations of the techniques have been addressed, in relation to the gauge volume, the stress-free reference sample and positioning. The measurement of residual stress around the weld achieved in this work significantly improves the resolution at which residual stress in welded components has been determined.

Paradowska, A. M.; Price, J. W. H.; Finlayson, T. R.; Lienert, U.; Walls, P.; Ibrahim, R.; X-Ray Science Division; Rutherford Appleton Lab.; Monash Univ.; Univ. of Melborne; ANSTO

2009-01-01

230

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

Microsoft Academic Search

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

YOSHINAGA Sho; MATSUURA Hideaki; NAKAO Yasuyuki; KUDO Kazuhiko

2006-01-01

231

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

PubMed

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

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

2009-07-01

232

Searching for pairing energies in phase space  

E-print Network

We obtain a representation of pairing energies in phase space, for the Lipkin-Meshkov-Glick and general boson Bardeen-Cooper-Schrieffer pairing models. This is done by means of a probability distribution of the quantum state in phase space. In fact, we prove a correspondence between the points at which this probability distribution vanishes and the pairing energies. In principle, the vanishing of this probability distribution is experimentally accessible and additionally gives a method to visualize pairing energies across the model control parameter space. This result opens new ways to experimentally approach quantum pairing systems.

M. Calixto; O. Castaños; E. Romera

2014-03-25

233

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

PubMed

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

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

2009-01-01

234

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

SciTech Connect

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

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

2010-01-01

235

Theory of neutron scattering experiments on momentum distributions in quantum fluids  

SciTech Connect

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

Silver, R.N.

1987-01-01

236

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

SciTech Connect

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

Rothe, R.E.

1996-09-30

237

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

E-print Network

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

Brown, Paul S. (Paul Sherman)

1962-01-01

238

Switchable radioactive neutron source device  

DOEpatents

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

Boyar, Robert E. (La Grange, IL); DeVolpi, Alexander (Bolingbrook, IL); Stanford, George S. (Downers Grove, IL); Rhodes, Edgar A. (Woodridge, IL)

1989-01-01

239

Switchable radioactive neutron source device  

DOEpatents

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

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

1987-11-06

240

Depth Distribution of Lithium in Oxidized Binary Al-Li Alloys Determined by Secondary Ion Mass Spectrometry and Neutron Depth Profiling  

Microsoft Academic Search

Oxidation of binary Al-Li alloys during short exposures at 530 C and long exposures at 200 C was studied with regard to the Li distribution. Secondary ion mass spectrometry (SIMS) and neutron depth profiling (NDP) were used to obtain quantitative Li depth profiles across the surface oxide layer and the underlying alloy. The underlying alloy was depleted in Li as

K. K. Soni; G. K. Lamaza; D. B. Williams; D. E. Newbury; R. G. Downing; P. K. Chi

1993-01-01

241

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

SciTech Connect

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

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

2010-01-01

242

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

NASA Astrophysics Data System (ADS)

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

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

1999-12-01

243

Time dependent discrete ordinates neutron transport using distribution iteration in XYZ geometry  

Microsoft Academic Search

The distribution iteration (DI) algorithm, developed by Wager [32] and Prins [28], for solving the Boltzmann Transport Equation (BTE) has proven, with further development, to be a robust alternative to von Neumann iteration on the scattering source, aka source iteration (SI). Previous work with DI was based on the time-independent form of the transport equation. In this research, the DI

James R. Dishaw

2007-01-01

244

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

Microsoft Academic Search

Residual stresses resulting from non homogeneous heat distribution during welding process belong to most significant factor influencing behavior of welded structures. These stresses are responsible for defect occurrence during welding and they are also responsible for crack initiation and propagation at the either static or dynamic load. The significant effect of weld metal chemical composition as well as the effect

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

2010-01-01

245

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

NASA Astrophysics Data System (ADS)

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

Davis, Timur D.

246

Paired t testsPaired t tests Paired (dependent) t-testPaired (dependent) t test  

E-print Network

Paired t testsPaired t tests #12;Paired (dependent) t-testPaired (dependent) t test · Compares test means from matched pairsCompares test means from matched pairs or two different samples from the same individualsindividuals ­ e.g., pretest & post test scores for the same group of students Ho: d = 0 d is thedifference

Wolverton, Steve

247

Pair-Starved Pulsar Magnetospheres  

E-print Network

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

Alex G. Muslimov; Alice K. Harding

2008-10-16

248

Pair-Starved Pulsar Magnetospheres  

NASA Technical Reports Server (NTRS)

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

Muslimov, Alex G.; Harding, Alice K.

2009-01-01

249

Peptide-induced asymmetric distribution of charged lipids in a vesicle bilayer revealed by small-angle neutron scattering.  

PubMed

Cellular membranes are complex mixtures of lipids, proteins, and other small molecules that provide functional, dynamic barriers between the cell and its environment, as well as between environments within the cell. The lipid composition of the membrane is highly specific and controlled in terms of both content and lipid localization. The membrane structure results from the complex interplay between the wide varieties of molecules present. Here, small-angle neutron scattering and selective deuterium labeling were used to probe the impact of the membrane-active peptides melittin and alamethicin on the structure of lipid bilayers composed of a mixture of the lipids dimyristoyl phosphatidylglycerol (DMPG) and chain-perdeuterated dimyristoyl phosphatidylcholine (DMPC). We found that both peptides enriched the outer leaflet of the bilayer with the negatively charged DMPG, creating an asymmetric distribution of lipids. The level of enrichment is peptide concentration-dependent and is stronger for melittin than it is for alamethicin. The enrichment between the inner and outer bilayer leaflets occurs at very low peptide concentrations and increases with peptide concentration, including when the peptide adopts a membrane-spanning, pore-forming state. The results suggest that these membrane-active peptides may have a secondary stressful effect on target cells at low concentrations that results from a disruption of the lipid distribution between the inner and outer leaflets of the bilayer that is independent of the formation of transmembrane pores. PMID:21751797

Qian, Shuo; Heller, William T

2011-08-18

250

Ultrafast neutron detector  

DOEpatents

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

Wang, C.L.

1985-06-19

251

Distribution of radial strain in a disc-braked railway wheel measured by neutron diffraction  

NASA Astrophysics Data System (ADS)

Three sectors of a damaged disc-braked railway wheel with a flat spot and a macro-crack parallel to the tread were investigated. Differences in the radial strain distribution between the sector containing the crack and the undamaged sector were found. At crack positions the tensile strain is higher than at comparable positions in the undamaged sector. The strain in the sector with the flat spot is lower than in the other two sectors.

Grosse, M.; Ceretti, M.; Ottlinger, P.

252

Hypernuclear Physics for Neutron Stars  

E-print Network

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

Jurgen Schaffner-Bielich

2008-01-24

253

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

SciTech Connect

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

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

2013-09-10

254

Supercool Neutrons (Ultracold Neutrons)  

E-print Network

source of ultracold neutrons #12; What are neutrons? Neutrons are a basic constituent of matter.ill.fr Spallation Neutron Source, Oak Ridge, Tennessee, www.sns.gov ReactorAccelerator #12; Temperature to make them useful (I'll show you why in a moment). #12; How we cool neutrons Step One: Cold Neutrons

Martin, Jeff

255

Isospin Dependent Pairing Interactions and BCS-BEC crossover  

SciTech Connect

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

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

2008-11-11

256

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

SciTech Connect

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

Sukhovoj, A. M., E-mail: suchovoj@nf.jinr.ru; Khitrov, V. A., E-mail: khitrov@nf.jinr.ru [Joint Institute for Nuclear Research (Russian Federation)

2013-01-15

257

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

NASA Astrophysics Data System (ADS)

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

Wang, J. G.

2006-01-01

258

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

NASA Astrophysics Data System (ADS)

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

Ghys, L.; Andreyev, A. N.; Huyse, M.; Van Duppen, P.; Sels, S.; Andel, B.; Antalic, S.; Barzakh, A.; Capponi, L.; Cocolios, T. E.; Derkx, X.; De Witte, H.; Elseviers, J.; Fedorov, D. V.; Fedosseev, V. N.; Hessberger, F. P.; 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

259

Investigation of neutron and proton distributions of He, Li, and Be isotopes using the new Skyrme-Force parameters  

SciTech Connect

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.

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

260

Peptide-induced Asymmetric Distribution of Charged Lipids in a Vesicle Bilayer Revealed by Small-Angle Neutron Scattering  

NASA Astrophysics Data System (ADS)

Cellular membranes are complex mixtures of lipids, proteins and other small molecules that provide functional, dynamic barriers between the cell and its environment, as well as between environments within the cell. The lipid composition of the membrane is highly specific and controlled in terms of both content and lipid localization. Here, small-angle neutron scattering and selective deuterium labeling were used to probe the impact of the membrane-active peptides melittin and alamethicin on the structure of lipid bilayers composed of a mixture of the lipids dimyristoyl phosphatidylglycerol (DMPG) and chain-perdeuterated dimyristoyl phosphatidylcholine (DMPC). We found that both peptides enriched the outer leaflet of the bilayer with the negatively charged DMPG, creating an asymmetric distribution of lipids. The level of enrichment is peptide concentration-dependent and is stronger for melittin than alamethicin. The enrichment between the inner and outer bilayer leaflets occurs at very low peptide concentrations, and increases with peptide concentration, including when the peptide adopts a membrane-spanning, pore-forming state.

Heller, William; Qian, Shuo

2012-02-01

261

Non-empirical pairing functional  

E-print Network

The present contribution reports the first systematic finite-nucleus calculations performed using the Energy Density Functional method and a non-empirical pairing functional derived from low-momentum interactions. As a first step, the effects of Coulomb and the three-body force are omitted while only the bare two-nucleon interaction at lowest order is considered. To cope with the finite-range and non-locality of the bare nuclear interaction, the 1S0 channel of Vlowk is mapped onto a convenient operator form. For the first time, neutron-neutron and proton-proton pairing correlations generated in finite nuclei by the direct term of the two-nucleon interaction are characterized in a systematic manner. Eventually, such predictions are compared to those obtained from empirical local functionals derived from density-dependent zero range interactions. The characteristics of the latter are analyzed in view of that comparison and a specific modification of their isovector density dependence is suggested to accommodate Coulomb effects and the isovector trend of neutron gaps at the same time.

T. Duguet; T. Lesinski

2007-11-27

262

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

SciTech Connect

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)

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

263

Time dependent discrete ordinates neutron transport using distribution iteration in XYZ geometry  

NASA Astrophysics Data System (ADS)

The distribution iteration (DI) algorithm, developed by Wager [32] and Prins [28], for solving the Boltzmann Transport Equation (BTE) has proven, with further development, to be a robust alternative to von Neumann iteration on the scattering source, aka source iteration (SI). Previous work with DI was based on the time-independent form of the transport equation. In this research, the DI algorithm was (1) Improved to provide faster, more efficient, robust convergence; (2) Extended to XYZ geometry; (3) Extended to Multigroup Energy treatment; (4) Extended to solve the time-dependent form of the Boltzmann Transport Equation. The discrete ordinates equations for approximating the BTE have been solved using SI since the discrete ordinates method was developed at Los Alamos Scientific Laboratory by 1953. However, SI is often inefficient by itself and requires an accelerator in order to produce results efficiently and reliably. The acceleration schemes that are in use in production codes are Diffusion Synthetic Acceleration (DSA) and Transport Synthetic Acceleration (TSA). DSA is ineffective for some problems, and cannot be extended to high-performance spatial quadratures. TSA is less effective than DSA and fails for some problems. Krylov acceleration has been explored in recent years, but has many parameters that require problem-dependent tuning for efficiency and effectiveness. The DI algorithm is an alternative to source iteration that, in our testing, does not require an accelerator. I developed a formal verification plan and executed it to verify the results produced by my code that implemented DI with the above features. A new, matrix albedo, boundary condition treatment was developed and implemented so that infinite-medium benchmarks could be included in the verification test suite. The DI algorithm was modified for parallel efficiency and the prior instability of the refinement sweep was corrected. The testing revealed that DI performed as well or faster than source iteration with DSA and that DI continued to work where DSA failed. Performance did degrade when the diamond-difference (without fixup) spatial quadrature was used. Because diamond-difference is a non-positive spatial quadrature, it can produce nonphysical negative fluxes, particularly in higher dimensions. I developed a new fixup scheme to accommodate the negative fluxes, but it did not improve performance in XYZ geometry when the scattering ratio was near unity. My DI algorithm successfully solves the time-dependent form of the BTE using the semi-implicit method implemented by PARTISN. The agreement between DI and PARTISN was excellent. With these improvements and tests, DI is ready for use as a general replacement for von Neumann iteration on the scattering source.

Dishaw, James R.

264

Distribution of glass transition temperature in multilayered poly(methyl methacrylate) thin film supported on a Si substrate as studied by neutron reflectivity.  

PubMed

We studied the distribution of glass transition temperature (Tg) through neutron reflectivity in a poly(methyl methacrylate) (PMMA) thin film supported on a silicon substrate with a five-layered PMMA thin film consisting of deuterated-PMMA and hydrogenated-PMMA. The depth distribution of Tg was successfully observed in the PMMA thin film. Compared to the previously reported distribution of Tg in a polystyrene thin film, the presence of a long-range interfacial effect, supposedly caused by an interaction between PMMA and the substrate, is considered to be responsible for the differences in both the distribution of Tg and the thickness dependence of Tg in both polymers. Therefore, it is expected that the thickness dependence of Tg reported for single-layered polymer thin films can, in principle, be understood from the viewpoint of the difference in the depth distribution of Tg. PMID:24125286

Inoue, Rintaro; Nakamura, Makoto; Matsui, Kazuya; Kanaya, Toshiji; Nishida, Koji; Hino, Masahiro

2013-09-01

265

A method to build an analytic model of the 10B(n,?) 7Li reaction rate space distribution for boron neutron capture therapy (BNCT)  

Microsoft Academic Search

This work provides the basis of a methodology to build a deterministic model for the spatial distribution of the 10B(n,?)7Li reaction rate in boron neutron capture therapy (BNCT), as a function of space variables, boron concentration and beam incidence angle in homogeneous isotropic environments but also in different heterogeneous environments. Building the analytic function in a simple homogeneous environment with

Josselin Morand; Raymond Moss; Sabet Hachem; Wolfgang Sauerwein

2009-01-01

266

Distributions  

NSDL National Science Digital Library

This online, interactive lesson on distributions provides examples, exercises, and applets which explore the basic types of probability distributions and the ways distributions can be defined using density functions, distribution functions, and quantile functions.

Siegrist, Kyle

2008-12-24

267

Exotic modes of excitation in deformed neutron-rich nuclei  

SciTech Connect

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

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

2011-05-06

268

Mars low-latitude neutron distribution: Possible remnant near-surface water ice and a mechanism for its recent emplacement  

Microsoft Academic Search

The Mars Odyssey Gamma-Ray Spectrometer\\/Neutron Spectrometer\\/High Energy Neutron Detector has provided measurements of near-surface hydrogen, generally interpreted as resulting from water, in the equatorial and mid-latitudes. Water abundances as great as 10% by mass are inferred. Although such high abundances could be present as adsorbed water in clays or water of hydration of magnesium salts, other measurements suggest that this

Bruce M. Jakosky; Michael T. Mellon; E. Stacy Varnesa; William C. Feldman; William V. Boynton; Robert M. Haberle

2005-01-01

269

Properties and applications of the prime detecting function: infinitude of twin primes, asymptotic law of distribution of prime pairs differing by an even number  

E-print Network

The prime detecting function (PDF) approach can be effective instrument in the investigation of numbers. The PDF is constructed by recurrence sequence - each successive prime adds a sieving factor in the form of PDF. With built-in prime sieving features and properties such as simplicity, integro-differentiability and configurable capability for a wide variety of problems, the application of PDF leads to new interesting results. As an example, in this exposition we present proofs of the infinitude of twin primes and the first Hardy-Littlewood conjecture for prime pairs (the twin prime number theorem). On this example one can see that application of PDF is especially effective in investigation of asymptotic problems in combination with the proposed method of test and probe functions.

R. M. Abrarov; S. M. Abrarov

2011-09-29

270

Development of a high-speed camera system for neutron imaging at a pulsed neutron source  

NASA Astrophysics Data System (ADS)

A neutron energy resolved imaging system with a time-of-flight technique has been newly developed and installed at Japan Proton Accelerator Research Complex (J-PARC) with the aim to investigate more preciously and rapidly a spatial distribution of several elements and crystals in various kinds of materials or substances. A high-speed video camera (CMOS, 1300 k frame/s) equipped system allows to obtain TOF images consecutively resolved into narrow energy ranges with a single pulsed neutrons while conventional CCD camera imaging system could obtain only one TOF image in an arbitral neutron energy region in the pulsed neutron energy region from 0.01 eV to a few keV. Qualities of the images obtained with the system, such as spatial resolution (defined by modulation transfer function, 0.8 line-pairs/mm at En˜0.01 eV), dependence of the brightness on the neutron energy and measurement errors (˜2%) of the system were examined experimentally and evaluated by comparison with those of conventional imaging system. The results obtained in the experiments show that the system can visualize the neutron energy resolved images within a small error even at high speed.

Segawa, M.; Kai, T.; Sakai, T.; Ooi, M.; Kureta, M.

2013-01-01

271

On the Probability Distribution of the Minimal Number of Hops Between any Pair of Nodes in a Bounded Wireless Ad-Hoc Network Subject to Fading  

Microsoft Academic Search

We investigate an ad hoc network where node locations are distributed according to a homogeneous Poisson process with intensity n. We assume that all the nodes are equipped with an identical wireless transceiver capable of op- erating satisfactorily up to a certain maximal link loss. Our link model depends on the length of the link and on random lognormal fading.

Sayandev Mukherjee; Dan Avidor

2005-01-01

272

Pair Cascades and Deathlines in Offset Magnetic Dipole Fields  

NASA Technical Reports Server (NTRS)

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

Harding, Alice; Muslimov, Alex

2010-01-01

273

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

SciTech Connect

The temperature dependence of the dynamics of mesophilic and thermophilic dihydrofolate reductase is examined using elastic incoherent neutron scattering. It is demonstrated that the distribution of atomic displacement amplitudes can be derived from the elastic scattering data by assuming a (Weibull) functional form that resembles distributions seen in molecular dynamics simulations. The thermophilic enzyme has a significantly broader distribution than its mesophilic counterpart. Furthermore, although the rate of increase with temperature of the atomic mean-square displacements extracted from the dynamic structure factor is found to be comparable for both enzymes, the amplitudes are found to be slightly larger for the thermophilic enzyme. Therefore, these results imply that the thermophilic enzyme is the more flexible of the two.

Meinhold, Lars [University of Heidelberg; Clement, David [University of Waikato, New Zealand; Tehei, M [University of Waikato, New Zealand; Daniel, R. M. [University of Waikato, New Zealand; Finney, J.L. [University College, London; Smith, Jeremy C [ORNL

2008-11-01

274

A background-free direction-sensitive neutron detector  

E-print Network

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 ...

Roccaro, Alvaro

275

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

276

Paired bondage in trees  

Microsoft Academic Search

Let G=(V,E) be a graph with ?(G)?1. A set D?V is a paired dominating set if D is dominating, and the induced subgraph ?D? contains a perfect matching. The paired domination number of G, denoted by ?p(G), is the minimum cardinality of a paired dominating set of G. The paired bondage number, denoted by bp(G), is the minimum cardinality among

Joanna Raczek

2008-01-01

277

A method to build an analytic model of the 10B(n,alpha)7Li reaction rate space distribution for boron neutron capture therapy (BNCT).  

PubMed

This work provides the basis of a methodology to build a deterministic model for the spatial distribution of the (10)B(n,alpha)(7)Li reaction rate in boron neutron capture therapy (BNCT), as a function of space variables, boron concentration and beam incidence angle in homogeneous isotropic environments but also in different heterogeneous environments. Building the analytic function in a simple homogeneous environment with numerical methods leads to a mathematical formulation of the (10)B(n,alpha)(7)Li reactions rate. PMID:19375922

Morand, Josselin; Moss, Raymond; Hachem, Sabet; Sauerwein, Wolfgang

2009-07-01

278

Odd-even mass difference and isospin dependent pairing interaction  

SciTech Connect

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

Bertulani, C. A. [Department of Physics, Texas A and M University-Commerce, Commerce, Texas 75429 (United States); Lue, H. F. [College of Science, China Agricultural University, Beijing (China); Sagawa, H. [Center for Mathematics and Physics, University of Aizu, Aizu-Wakamatsu, 965-8580 Fukushima (Japan)

2009-08-15

279

Electron-pair excitations and the molecular Coulomb continuum.  

PubMed

Electron-pair excitations in the molecular hydrogen continuum are described by quantizing rotations of the momentum plane of the electron pair about the pair's relative momentum. A heliumlike description of the molecular photodouble ionization is thus extended to higher angular momenta of the electron pair. A simple three-state superposition is found to account surprisingly well for recent observations of noncoplanar electron-pair, molecular-axis angular distributions. PMID:19659273

Feagin, J M; Colgan, J; Huetz, A; Reddish, T J

2009-07-17

280

Electron-pair excitations and the molecular Coulomb continuum  

SciTech Connect

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

Colgan, James [Los Alamos National Laboratory

2009-01-01

281

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

SciTech Connect

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

Huml, O. [Department of Nuclear Reactors, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, Prague V Holesovickach 2, 180 00, Prague 8 (Czech Republic)

2008-07-15

282

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

Microsoft Academic Search

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

Anatoly Blanovsky

1993-01-01

283

Ion pair receptors†  

PubMed Central

Compared with simple ion receptors, which are able to bind either a cation or an anion, ion pair receptors bearing both a cation and an anion recognition site offer the promise of binding ion pairs or pairs of ions strongly as the result of direct or indirect cooperative interactions between co-bound ions. This critical review focuses on the recent progress in the design of ion pair receptors and summarizes the various binding modes that have been used to accommodate ion pairs (110 references). PMID:20737073

Kim, Sung Kuk

2010-01-01

284

NEUTRON INTERACTIONS IN Fe, Pb, AND Ni  

Microsoft Academic Search

A study of the interaction of fast neutrons in iron and lead has led to ; an investigation of the energy distribution of inelastically scattered neutrons, ; gamma ray production cross sections due to inelastic neutron scattering, the ; angular distribution of intense gamma rays due to inelastic neutron scattering, ; and the production of high energy gamma rays due

N. A. Bostrom; I. L. Morgan; J. T. Prudhomme; P. L. Okhuysen

1958-01-01

285

Non-Statistical Effects in Neutron Capture  

SciTech Connect

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

Koehler, P. E.; Guber, K. H.; Harvey, J. A.; Wiarda, D. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); Bredeweg, T. A.; O'Donnell, J. M.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wouters, J. M. [Los Alamos National Laboratory, Los Alamos, NM (United States); Reifarth, R. [GSI, Planckstr. 1, 64291 Darmstadt (Germany)

2009-01-28

286

Non-Statistical Effects in Neutron Capture  

SciTech Connect

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

Koehler, Paul Edward [ORNL; Bredeweg, t a [Los Alamos National Laboratory (LANL); Guber, Klaus H [ORNL; Harvey, John A [ORNL; O'Donnell, J. M. [Los Alamos National Laboratory (LANL); Reifarth, R. [Los Alamos National Laboratory (LANL); Rundberg, R. S. [Los Alamos National Laboratory (LANL); Ullmann, J. L. [Los Alamos National Laboratory (LANL); Vieira, D. J. [Los Alamos National Laboratory (LANL); Wiarda, Dorothea [ORNL; Wouters, J. M. [Los Alamos National Laboratory (LANL)

2009-01-01

287

Network of interactions among pair-rule genes regulating paired expression during primordial segmentation of Drosophila.  

PubMed

A model of the trans-regulation of the Drosophila pair-rule segmentation gene, paired (prd), has been derived from the observed alterations in the distribution of prd transcripts during early embryogenesis in single and double pair-rule mutants. Important aspects of the model include the following features and implications: (i) The regulation of prd is subject to a regulatory hierarchy among pair-rule genes. In particular, it shows that prd is at the bottom of this hierarchy, mediating the transition from pair-rule to segment-polarity genes. The transition of the early 'pair-rule' to the 'segment-polarity' pattern of prd expression is regulated by the secondary pair-rule genes opa and odd. The model predicts the distributions of pair-rule gene products regulating prd at late syncytial blastoderm, e.g., that of opa. (ii) The initial activation of prd is independent of pair-rule genes. (iii) The regulation of prd is combinatorial and hence probably cooperative. Combination of one pair-rule gene product with different pair-rule proteins may lead to opposite regulatory effects on prd. Furthermore, we discuss a two-step conversion of the initial analogue specification of position along the anteroposterior axis into a digital code specified by combinations of active segment-polarity and homeotic genes. PMID:1982920

Baumgartner, S; Noll, M

1990-12-01

288

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

SciTech Connect

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

Surman, Rebecca [Union College; Beun, Joshua [North Carolina State University; Mclaughlin, Gail C [North Carolina State University; Hix, William Raphael [ORNL

2009-01-01

289

Neutron capture rates near A=130 that effect a global change to the r-process abundance distribution  

SciTech Connect

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

Surman, R.; Beun, J.; McLaughlin, G. C.; Hix, W. R. [Department of Physics, Union College, Schenectady, New York 12308 (United States); Department of Physics, North Carolina State University, Raleigh, North Carolina 27695-8202 (United States); Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6374 (United States)

2009-04-15

290

Matched-pair classification  

SciTech Connect

Following an analogous distinction in statistical hypothesis testing, we investigate variants of machine learning where the training set comes in matched pairs. We demonstrate that even conventional classifiers can exhibit improved performance when the input data has a matched-pair structure. Online algorithms, in particular, converge quicker when the data is presented in pairs. In some scenarios (such as the weak signal detection problem), matched pairs can be generated from independent samples, with the effect not only doubling the nominal size of the training set, but of providing the structure that leads to better learning. A family of 'dipole' algorithms is introduced that explicitly takes advantage of matched-pair structure in the input data and leads to further performance gains. Finally, we illustrate the application of matched-pair learning to chemical plume detection in hyperspectral imagery.

Theiler, James P [Los Alamos National Laboratory

2009-01-01

291

The MCLIB library: Monte Carlo simulation of neutron scattering instruments  

SciTech Connect

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

Seeger, P.A.

1995-09-01

292

Nuclear pairing models  

Microsoft Academic Search

We calculate nuclear pairing gaps for nuclei throughout the periodic system in both the BCS and Lipkin-Nogami pairing models. The energy levels required for the calculations are obtained from the folded-Yukawa single-particle model for ground-state shapes obtained in the macroscopic-microscopic approach by minimizing the total potential energy with respect to ?2 and ?4 shape degrees of freedom. For both pairing

P. Möller; J. R. Nix

1992-01-01

293

ION-PAIRING POLYMERIZATION  

Microsoft Academic Search

This account describes the development of a new type of polymerization catalysis termed ion-pairing polymerization (IPP). IPP utilizes compatible and dually active transition-metal cation–main-group anion ion pairs in which both the cation and the anion can independently catalyze the polymer chain growth in a single polymerization reaction. Furthermore, cations and anions of ion pairs can exhibit different stereoselectivity and growing

Eugene Y.-X. Chen

2009-01-01

294

Galaxy pairs in the Local Group  

NASA Astrophysics Data System (ADS)

Current models of galaxy formation predict that galaxy pairs of comparable magnitudes should become increasingly rare with decreasing luminosity. This seems at odds with the relatively high frequency of pairings among dwarf galaxies in the Local Group. We use literature data to show that ˜30 per cent of all the satellites of the Milky Way and Andromeda galaxies brighter than MV = -8 are found in likely physical pairs of comparable luminosity. Besides the previously recognized pairings of the Magellanic Clouds and of NGC 147/NGC 185, other candidate pairs include the Ursa Minor and Draco dwarf spheroidals, as well as the And I/And III satellites of M31. These pairs are much closer than expected by chance if the radial and angular distributions of satellites were uncorrelated; in addition, they have very similar line-of-sight velocities and luminosities that differ by less than three magnitudes. In contrast, the same criteria pair fewer than 4 per cent of satellites in N-body/semi-analytic models that match the radial distribution and luminosity function of Local Group satellites. If confirmed in studies of larger samples, the high frequency of dwarf galaxy pairings may provide interesting clues to the formation of faint galaxies in the current cosmological paradigm.

Fattahi, Azadeh; Navarro, Julio F.; Starkenburg, Else; Barber, Christopher R.; McConnachie, Alan W.

2013-04-01

295

Modification of the University of Washington Neutron Radiotherapy Facility for optimization of neutron capture enhanced fast-neutron therapy  

Microsoft Academic Search

A modified neutron production target assembly has been developed to provide improved performance of the proton-cyclotron-based neutron radiotherapy facility at the University of Washington for applications involving neutron capture enhanced fast-neutron therapy. The new target produces a neutron beam that yields essentially the same fast-neutron physical depth-dose distribution as is produced by the current UW clinical system, but that also

David W. Nigg; Charles A. Wemple; Ruedi Risler; John K. Hartwell; Yale D. Harker; George E. Laramore

2000-01-01

296

REGIMES OF PULSAR PAIR FORMATION AND PARTICLE ENERGETICS Alice K. Harding,1  

E-print Network

for the production of electron-positron pairs above a pulsar polar cap (PC) and the influence of pair production Compton scatterings. The effect of the neutron star equations of state on the pair death lines is explored. In polar cap (PC) models (see, e.g., Arons & Sharlemann 1979; Daugherty & Harding 1996), accelera- tion

Zhang, Bing

297

Solutions of Nuclear Pairing  

E-print Network

We give the exact solution of orbit dependent nuclear pairing problem between two non-degenerate energy levels using the Bethe ansatz technique. Our solution reduces to previously solved cases in the appropriate limits including Richardson's treatment of reduced pairing in terms of rational Gaudin algebra operators.

A. B. Balantekin; Y. Pehlivan

2007-10-21

298

Fast Neutron Resonance Radiography in a Pulsed Neutron Beam  

Microsoft Academic Search

The feasibility of performing fast neutron resonance radiography at the PTB accelerator facility is studied. A neutron beam of a broad spectral distribution is produced by a pulsed 13 MeV deuterium beam hitting a thick Be target. The potential of 3 different neutron imaging detectors with time-of flight capability are investigated. The applied methods comprise wire chambers with hydrogenous converter

V. Dangendorf; G. Laczko; C. Kersten; O. Jagutzki; U. Spillmann

2003-01-01

299

Coulombic effect and renormalization in nuclear pairing  

SciTech Connect

We investigate the effects of the Coulomb force on the nuclear pairing properties by performing the Gogny Hartree-Fock-Bogolyubov calculations for the N=20, 28, 50, 82, and 126 nuclei. The Coulomb force reduces the proton pair energy and the even-odd mass difference by about 25%, except for nuclei at and around the proton shell or subshell closure. We then propose a renormalization scheme via a reduction factor {gamma}{sub p} for the proton pairing channel. It is found that a single value {gamma}{sub p}=0.90 accounts well for the Coulombic effect for nuclei covering a wide range of the mass number and the neutron excess, including the nuclei around the shell or subshell closure.

Nakada, H.; Yamagami, M. [Department of Physics, Graduate School of Science, Chiba University, Yayoi-cho 1-33, Inage, Chiba 263-8522 (Japan); Department of Computer Science and Engineering, University of Aizu, Aizu-Wakamatsu, Fukushima 965-8580 (Japan)

2011-03-15

300

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

SciTech Connect

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

Kisohara, N. [Advanced Nuclear System Research and Development Directorate, Japan Atomic Energy Agency (Japan); Suzuki, H.; Akita, K. [Quantum Beam Science Directorate, Japan Atomic Energy Agency (Japan); Kasahara, N. [Dept. of Nuclear Engineering and Management, Univ. of Tokyo (Japan)

2012-07-01

301

Cooper Pairs in Insulators?!  

SciTech Connect

Nearly 50 years elapsed between the discovery of superconductivity and the emergence of the microscopic theory describing this zero resistance state. The explanation required a novel phase of matter in which conduction electrons joined in weakly bound pairs and condensed with other pairs into a single quantum state. Surprisingly, this Cooper pair formation has also been invoked to account for recently uncovered high-resistance or insulating phases of matter. To address this possibility, we have used nanotechnology to create an insulating system that we can probe directly for Cooper pairs. I will present the evidence that Cooper pairs exist and dominate the electrical transport in these insulators and I will discuss how these findings provide new insight into superconductor to insulator quantum phase transitions. 

James Valles

2008-07-23

302

Cooper Pairs in Insulators?!  

SciTech Connect

Nearly 50 years elapsed between the discovery of superconductivity and the emergence of the microscopic theory describing this zero resistance state. The explanation required a novel phase of matter in which conduction electrons joined in weakly bound pairs and condensed with other pairs into a single quantum state. Surprisingly, this Cooper pair formation has also been invoked to account for recently uncovered high-resistance or insulating phases of matter. To address this possibility, we have used nanotechnology to create an insulating system that we can probe directly for Cooper pairs. I will present the evidence that Cooper pairs exist and dominate the electrical transport in these insulators and I will discuss how these findings provide new insight into superconductor to insulator quantum phase transitions.

Valles, James (Brown University) [Brown University

2008-07-23

303

Cooper Pairs in Insulators?!  

ScienceCinema

Nearly 50 years elapsed between the discovery of superconductivity and the emergence of the microscopic theory describing this zero resistance state. The explanation required a novel phase of matter in which conduction electrons joined in weakly bound pairs and condensed with other pairs into a single quantum state. Surprisingly, this Cooper pair formation has also been invoked to account for recently uncovered high-resistance or insulating phases of matter. To address this possibility, we have used nanotechnology to create an insulating system that we can probe directly for Cooper pairs. I will present the evidence that Cooper pairs exist and dominate the electrical transport in these insulators and I will discuss how these findings provide new insight into superconductor to insulator quantum phase transitions. 

James Valles

2010-01-08

304

Cosmic-Ray Neutron Demography  

Microsoft Academic Search

The equilibrium spatial and energy distribution is calculated for neutrons made in the earth's atmosphere by cosmic rays. The neutron current leaking into space is found, and the density of neutron decays in the vicinity of the earth is computed for a future determination of importance as a source for the Van Allen belts. The spectrum and the leakage current

W. N. Hess; E. H. Canfield; R. E. Lingenfelter

1961-01-01

305

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

306

Anomalous Spin-Density Distribution on Oxygen and Ru in Ca1.5Sr0.5RuO4: Polarized Neutron Diffraction Study  

NASA Astrophysics Data System (ADS)

By means of polarized neutron diffraction in a magnetic field of 7.0T at 1.6K an anomalously large magnetization density is observed on the in-plane oxygen in Ca1.5Sr0.5RuO4. Field-induced moments of different ions are determined by refinement on the flipping ratios, yielding ?Ru=0.346(11)?B, ?O1=0.076(6)?B, and ?O2=0.009(6)?B. The moment on the oxygen arises from the strong hybridization between the Ru-4d and O-2p orbitals. The maximum entropy magnetization density reconstruction reveals a strongly anisotropic density at the Ru site, consistent with the distribution of the xy (t2g band) d orbitals.

Gukasov, A.; Braden, M.; Papoular, R. J.; Nakatsuji, S.; Maeno, Y.

2002-08-01

307

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

NASA Astrophysics Data System (ADS)

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

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

308

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

E-print Network

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.

P. Sarriguren; A. Algora; J. Pereira

2014-03-05

309

beta-decay properties of neutron-rich Zr and Mo isotopes  

SciTech Connect

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.

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

310

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

NASA Astrophysics Data System (ADS)

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

Shubhchintak, Chatterjee, R.

2014-07-01

311

Conservation of Isospin in Neutron-Rich Fission Fragments  

E-print Network

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

Ashok Kumar Jain; Deepika Choudhury; Bhoomika Maheshwari

2014-08-11

312

Distribution  

Microsoft Academic Search

e're closer than you think: Portland's geographic location and Oregon's transportation infra - structure offer unmatched con - nectivity and time savings to international and domestic markets. Our economic development practices combine project-ready property with efficient, high-capacity infrastructure to create today's logistics advantages. Connecting people, places and products is the core of Portland's distribution and logistics industry sec - tor.

F. Gregory; B. Boyd; R. Bridges; D. Mitchell; J. Halsell; S. Fancher; D. King; R. Fore; E. Mango; D. Berlinrut; M. Leinbach; M. Maier; M. Wetmore; H. Herring; J. Guidi; M. Coolidge; J. Heald; T. Knox; D. Bartine; R. Bailey; H. Delgado; P. Conant; J. Madura; R. Thomas; F. Merceret; G. Allen; E. Bensman; R. Dittemore; N. Feldman; C. Boykin; H. Tileston; F. Brody; L. Hagerman; S. Pearson; L. Uccellini; W. Vaughan; J. Golden; D. Johnson; J. McQueen; B. Roberts; L. Freeman; G. Jasper; B. Hagemeyer; A. McCool; X. W. Proenza; S. Glover

2006-01-01

313

Synthesize Neutron-Drip-Line-Nuclides with Free-Neutron Bose-Einstein Condensates Experimentally  

E-print Network

We first show a possible way to create a new type of matter, free-neutron Bose-Einstein condensate by the ultracold free-neutron-pair Bose-Einstein condensation and then determine the neutron drip line experimentally. The Bose-Einstein condensation of bosonic and fermionic atoms in atomic gases was performed experimentally and predicted theoretically early. Neutrons are similar to fermionic atoms. We found free neutrons could be cooled to ultracold neutrons with very low energy by other colder neutral atoms which are cooled by the laser. These neutrons form neutron pairs with spin zero, and then ultracold neutron-pairs form Bose-Einstein condensate. Our results demonstrate how these condensates can react with accelerated ion beams at different energy to synthesize very neutron-rich nuclides near, on or/and beyond the neutron drip line, to determine the neutron drip line and whether there are long-life nuclide or isomer islands beyond the neutron drip line experimentally. Otherwise, these experimental results will confirm our prediction that is in the whole interacting region or distance of nuclear force in all energy region from zero to infinite, Only repulsive nuclear force exists among identical nucleons and only among different nucleons exists attractive nuclear force.

Bao-Guo Dong

2014-09-22

314

Pairing effects on spinodal decomposition of asymmetric nuclear matter  

E-print Network

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

Stefano Burrello; Maria Colonna; Francesco Matera

2013-12-04

315

Pair Winds in Schwarzschild Spacetime with Application to Strange Stars  

E-print Network

We present the results of numerical simulations of stationary, spherically outflowing, electron-positron pair winds, with total luminosities in the range 10^{34}--10^{42} ergs/s. In the concrete example described here, the wind injection source is a hot, bare, strange star, predicted to be a powerful source of pairs created by the Coulomb barrier at the quark surface. We find that photons dominate in the emerging emission, and the emerging photon spectrum is rather hard and differs substantially from the thermal spectrum expected from a neutron star with the same luminosity. This might help distinguish the putative bare strange stars from neutron stars.

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

2007-01-09

316

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

E-print Network

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

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

2012-07-25

317

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

Microsoft Academic Search

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

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

2009-01-01

318

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

NASA Astrophysics Data System (ADS)

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

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

2008-08-01

319

Neutron spectral and angular distribution measurements for 113 and 256 MeV protons on range-thick Al and sup 238 U targets using the foil activation techniques  

SciTech Connect

Second neutron yields, energy spectra, and angular distributions have been measured at seven angles from 0 to 150{degree} for 113 and 256 MeV protons stopped in range-thick targets of aluminum and depleted uranium ({sup 238}U). Thin foil stacks of ten different materials were activated by secondary neutrons at distances of 20--30 cm from the targets. Following each irradiation, 30--40 different activation products were measured by gamma-ray spectroscopy. These activation rates were then used to adjust neutron energy spectra calculated by the HETC computer code. Activation cross sections were taken from ENDF/BV below 20 MeV, from literature values tested in Be(d,n) fields up to 50 MeV, and from proton spallation data and calculations from 50--250 MeV. Spectral adjustments were made with the STAY'SL computer code using a least-squares technique to minimize {chi}{sup 2} for a covariance matrix determined from uncertainties in the measured activities, cross sections, and calculated flux spectra. Neutron scattering effects were estimated from foil packets irradiated at different distances from the target. Proton effects were measured with (p,n) reactions. Systematic differences were found between the adjusted and calculated neutron spectra, namely, that HETC underpredicts the neutron flux at back angles by a factor of 2--3 and slightly overpredicts the flux at forward angles. 19 refs., 23 figs., 13 tabs.

Greenwood, L.R.; Intasorn, A.

1989-07-01

320

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

NASA Astrophysics Data System (ADS)

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

Rivard, Mark Joseph

321

Nuclear-matter density distribution in the neutron-rich nuclei 12,14Be from proton elastic scattering in inverse kinematics  

NASA Astrophysics Data System (ADS)

In the present work, the differential cross sections for small-angle proton elastic scattering on the 12,14Be nuclei were measured in inverse kinematics, using secondary radioactive beams with energies near 700 MeV/u produced with the fragment separator FRS at GSI. The main part of the experimental setup was the active target IKAR, which was used simultaneously as a target and a detector for the recoil protons. Auxiliary detectors for projectile tracking and isotope identification completed the setup. The measured differential cross sections were analyzed using the Glauber multiple-scattering theory. For the evaluation of the data several phenomenological nuclear-matter density parametrizations and a sum of Gaussian parametrization were used. The nuclear-matter radii and radial density distributions of the isotopes 12,14Be were deduced. Extended nuclear-matter density distributions were observed in both isotopes, and the halo structure of 14Be was confirmed. The results were also compared with microscopic few-body and fermionic molecular dynamics model calculations concerning the structure of these neutron-rich nuclei.

Ilieva, S.; Aksouh, F.; Alkhazov, G. D.; Chulkov, L.; Dobrovolsky, A. V.; Egelhof, P.; Geissel, H.; Gorska, M.; Inglessi, A.; Kanungo, R.; Khanzadeev, A. V.; Kiselev, O. A.; Korolev, G. A.; Le, X. C.; Litvinov, Yu. A.; Nociforo, C.; Seliverstov, D. M.; Sergeev, L. O.; Simon, H.; Volkov, V. A.; Vorobyov, A. A.; Weick, H.; Yatsoura, V. I.; Zhdanov, A. A.

2012-02-01

322

Magnetic Pair Creation Transparency in Pulsars  

NASA Astrophysics Data System (ADS)

The Fermi gamma-ray pulsar database now exceeds 115 sources and has defined an important part of Fermi's science legacy, providing rich information for the interpretation of young energetic pulsars and old millisecond pulsars. Among the well established population characteristics is the common occurrence of exponential turnovers in the 1-10 GeV range. These turnovers are too gradual to arise from magnetic pair creation in the strong magnetic fields of pulsar inner magnetospheres, so their energy can be used to provide lower bounds to the typical altitude of GeV band emission. We explore such constraints due to single-photon pair creation transparency below the turnover energy. We adopt a semi-analytic approach, spanning both domains when general relativistic influences are important and locales where flat spacetime photon propagation is modified by rotational aberration effects. Our work clearly demonstrates that including near-threshold physics in the pair creation rate is essential to deriving accurate attenuation lengths. The altitude bounds, typically in the range of 2-6 neutron star radii, provide key information on the emission altitude in radio quiet pulsars that do not possess double-peaked pulse profiles. For the Crab pulsar, which emits pulsed radiation up to energies of 120 GeV, we obtain a lower bound of around 15 neutron star radii to its emission altitude.

Story, Sarah; Baring, M. G.

2013-04-01

323

Magnetic structure and cation distribution in (Fe,Mn) 2 SiO 4 (olivine) by neutron diffraction  

Microsoft Academic Search

The cation distribution in the synthetic samples of olivine-type structure with composition (FexMn1-x)2SiO4 was determined at room temperature and confirms previous Mössbauer results. At low temperature an antiferromagnetic ordering is observed. The magnetic structures can be described in the crystallographic cell (i.e. k=0). They are interpreted on the basis of the irreducible representations (modes) of the symmetry groups which are

O. Ballet; H. Fuess; T. Fritzsche

1987-01-01

324

Thermal Comptonization in Mildly Relativistic Pair Plasmas  

E-print Network

We use a Monte Carlo simulation to calculate the spectra of mildly relativistic thermal plasmas in pair balance. We use the exact integral expression for the electron-positron thermal annihilation spectrum, and provide accurate expressions for the Gaunt factors of electron-ion, electron-electron, and electron-positron thermal bremsstrahlung in the transrelativistic temperature regime. The particles are assumed to be uniformly distributed throughout a sphere, and the pair opacity is self-consistently calculated from the energy and angular distribution of scattered photons. The resultant photon spectra are compared with the nonrelativistic diffusion treatment of Sunyaev and Titarchuk, the bridging formulas of Zdziarski, and the relativistic corrections proposed by Titarchuk. We calculate allowed pair-balanced states of thermal plasmas with no pair escape which include bremsstrahlung and internal soft photons. The results are presented in the spectral index/compactness plane, and can be directly compared with observations of spectra from AGNs and Galactic black hole candidates. By comparing with X-ray spectral indices of Seyfert AGNs and compactnesses inferred from X-ray variability data, we find that the allowed solutions for pair equilibrium plasma imply that the temperatures of Seyfert galaxies are $\\lesssim 300$ keV. This prediction can be tested with more sensitive gamma-ray observations of Seyfert galaxies. We find that if the X-ray variability time scale gives an accurate measure of the compactness, pair-dominated solutions are inconsistent with the data.

J. G. Skibo; C. D. Dermer; R. Ramaty; J. M. McKinley

1994-12-21

325

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

326

Neutron emission in fission of 252Cf(sf)  

NASA Astrophysics Data System (ADS)

The prompt neutron emission in spontaneous fission of 252Cf has been investigated applying digital signal electronics. The goal was to compare the results of this digital data acquisition and digital signal processing analysis to the results of the pioneering work of Budtz-Jo/rgensen and Knitter. Using a twin Frisch-grid ionization chamber for fission fragment (FF) detection and a NE213 equivalent neutron detector in total about 10 neutron coincidences have been registered. Fission fragment kinetic energy, mass and angular distribution have been investigated using a 10 bit waveform digitizer. Neutron time- of- flight and pulse shape have been measured using analogue CAMAC modules, a 1 ns TDC and a pair of 12 bit charge-to-digital-converters. The fission fragment signals have been analyzed using digital signal processing algorithms. The results are in very good agreement with literature. For the first time the dependence of the number of neutrons as a function of total kinetic energy (TKE) of the fragments does not drop at low TKE.

Zeynalov, Sh.; Hambsch, F.-J.; Oberstedt, S.; Fabry, I.

2009-10-01

327

New Insights into the Crystal and Electronic Structures of Li[subscript 1+x]V[subscript 1?x]O[subscript 2] from Solid State NMR, Pair Distribution Function Analyses, and First Principles Calculations  

SciTech Connect

Pair distribution function (PDF) analyses of synchrotron data obtained for the anode materials Li{sub 1+x}V{sub 1-x}O{sub 2} (0 {le} x {le} 0.1) have been performed to characterize the short to medium range structural ordering. The data show clear evidence for the magnetically-induced distortion of the V sublattice to form trimers, the distortion persisting at even the highest excess Li content considered of x = 0.1. At least three distinct local environments were observed for the stoichiometric material LiVO{sub 2} in {sup 6}Li nuclear magnetic resonance (NMR) spectroscopy, the environments becoming progressively more disordered as the Li content increases. A two-dimensional Li-Li correlation NMR experiment (POST-C7) was used to identify the resonances corresponding to Li within the same layers. NMR spectra were acquired as a function of the state of charge, a distinct environment for Li in Li{sub 2}VO{sub 2} being observed. The results suggest that disorder within the Li layers (in addition to the presence of Li within the V layers as proposed by Armstrong et al. Nat. Mater.2011, 10, 223-229) may aid the insertion of Li into the Li{sub 1+x}V{sub 1-x}O{sub 2} phase. The previously little-studied Li{sub 2}VO{sub 2} phase was also investigated by hybrid density functional theory (DFT) calculations, providing insights into magnetic interactions, spin-lattice coupling, and Li hyperfine parameters.

Pourpoint, Frédérique; Hua, Xiao; Middlemiss, Derek S.; Adamson, Paul; Wang, Da; Bruce, Peter G.; Grey, Clare P. (SBU); (Cambridge); (St Andrews)

2012-10-29

328

Hadronic production of massive lepton pairs  

SciTech Connect

A review is presented of recent experimental and theoretical progress in studies of the production of massive lepton pairs in hadronic collisions. I begin with the classical Drell-Yan annihilation model and its predictions. Subsequently, I discuss deviations from scaling, the status of the proofs of factorization in the parton model, higher-order terms in the perturbative QCD expansion, the discrepancy between measured and predicted yields (K factor), high-twist terms, soft gluon effects, transverse-momentum distributions, implications for weak vector boson (W/sup + -/ and Z/sup 0/) yields and production properties, nuclear A dependence effects, correlations of the lepton pair with hadrons in the final state, and angular distributions in the lepton-pair rest frame.

Berger, E.L.

1982-12-01

329

Describe Angle Pair Relationships  

NSDL National Science Digital Library

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

Neubert, Mrs.

2011-09-01

330

Pairing Music with Literature.  

ERIC Educational Resources Information Center

Matches a number of famous musical compositions with literary works that can be paired for interdisciplinary lessons. Lists musical and literary works appropriate for grades 1-12 ("Samson et Delilah" by Camille Saint-Saens and readings from the Book of Judges for grade seven). Includes a list of video resources. (MJP)

Will, Howard

1997-01-01

331

Pairing-induced speedup of nuclear spontaneous fission  

E-print Network

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 princip...

Sadhukhan, Jhilam; Nazarewicz, W; Sheikh, J A; Baran, A

2014-01-01

332

Pulsar Pair Cascades in a Distorted Magnetic Dipole Field  

E-print Network

We investigate the effect of a distorted neutron star dipole magnetic field on pulsar pair cascade multiplicity and pair death lines. Using a simple model for a distorted dipole field that produces an offset polar cap, we derive the accelerating electric field above the polar cap in space charge limited flow. We find that even a modest azimuthally asymmetric distortion can significantly increase the accelerating electric field on one side of the polar cap and, combined with a smaller field line radius of curvature, leads to larger pair multiplicity. The death line for producing pairs by curvature radiation moves downward in the P-Pdot diagram, allowing high pair multiplicities in a larger percentage of the radio pulsar population. These results could have important implications for the radio pulsar population, high energy pulsed emission and the pulsar contribution to cosmic ray positrons.

Harding, Alice K

2010-01-01

333

PULSAR PAIR CASCADES IN A DISTORTED MAGNETIC DIPOLE FIELD  

SciTech Connect

We investigate the effect of a distorted neutron star dipole magnetic field on pulsar pair cascade multiplicity and pair death lines. Using a simple model for a distorted dipole field that produces an offset polar cap (PC), we derive the accelerating electric field above the PC in space-charge-limited flow. We find that even a modest azimuthally asymmetric distortion can significantly increase the accelerating electric field on one side of the PC and, combined with a smaller field line radius of curvature, leads to larger pair multiplicity. The death line for producing pairs by curvature radiation moves downward in the P- P-dot diagram, allowing high pair multiplicities in a larger percentage of the radio pulsar population. These results could have important implications for the radio pulsar population, high energy pulsed emission, and the pulsar contribution to cosmic ray positrons.

Harding, Alice K.; Muslimov, Alex G. [Astrophysics Science Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2011-01-01

334

Pulsar Pair Cascades in a Distorted Magnetic Dipole Field  

NASA Astrophysics Data System (ADS)

We investigate the effect of a distorted neutron star dipole magnetic field on pulsar pair cascade multiplicity and pair death lines. Using a simple model for a distorted dipole field that produces an offset polar cap (PC), we derive the accelerating electric field above the PC in space-charge-limited flow. We find that even a modest azimuthally asymmetric distortion can significantly increase the accelerating electric field on one side of the PC and, combined with a smaller field line radius of curvature, leads to larger pair multiplicity. The death line for producing pairs by curvature radiation moves downward in the P-\\dot{P} diagram, allowing high pair multiplicities in a larger percentage of the radio pulsar population. These results could have important implications for the radio pulsar population, high energy pulsed emission, and the pulsar contribution to cosmic ray positrons.

Harding, Alice K.; Muslimov, Alex G.

2011-01-01

335

Pulsar Pair Cascades in a Distorted Magnetic Dipole Field  

NASA Technical Reports Server (NTRS)

We investigate the effect of a distorted neutron star dipole magnetic field on pulsar pair cascade multiplicity and pair death lines. Using a simple model for a distorted dipole field that produces an offset polar cap (PC), we derive the accelerating electric field above the PC in space-charge-limited flow. We find that even a modest azimuthally asymmetric distortion can significantly increase the accelerating electric field on one side of the PC and, combined with a smaller field line radius of curvature, leads to larger pair multiplicity. The death line for producing pairs by curvature radiation moves downward in the P-P-dot diagram, allowing high pair multiplicities in a larger percentage of the radio pulsar population. These results could have important implications for the radio pulsar population, high energy pulsed emission, and the pulsar contribution to cosmic ray positrons.

Harding, Alice K.; Muslimov, Alex G.

2010-01-01

336

Simulated workplace neutron fields  

NASA Astrophysics Data System (ADS)

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

Lacoste, V.; Taylor, G.; Röttger, S.

2011-12-01

337

Characterisation of neutron fields at Cernavoda NPP.  

PubMed

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

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

2013-04-01

338

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

PubMed

The feasibility of neutron capture therapy (NCT) using an accelerator-based neutron source of the 7Li(p,n) reaction produced by 2.5 MeV protons was investigated by comparing the neutron beam tailored by both the Hiroshima University radiological research accelerator (HIRRAC) and the heavy water neutron irradiation facility in the Kyoto University reactor (KUR-HWNIF) from the viewpoint of the contamination dose ratios of the fast neutrons and the gamma rays. These contamination ratios to the boron dose were estimated in a water phantom of 20 cm diameter and 20 cm length to simulate a human head, with experiments by the same techniques for NCT in KUR-HWNIF and/or the simulation calculations by the Monte Carlo N-particle transport code system version 4B (MCNP-4B). It was found that the 7Li(p,n) neutrons produced by 2.5 MeV protons combined with 20, 25 or 30 cm thick D20 moderators of 20 cm diameter could make irradiation fields for NCT with depth-dose characteristics similar to those from the epithermal neutron beam at the KUR-HWNIF. PMID:11686282

Tanaka, K; Kobayashi, T; Sakurai, Y; Nakagawa, Y; Endo, S; Hoshi, M

2001-10-01

339

Spiral galaxies in pairs (Keel, 1996)  

Microsoft Academic Search

Rotation curves have been obtained for 76 spiral galaxies in pairs, including a geometrically selected subset from the Karachentsev catalog and a set of Seyfert galaxies with close companions. Derived parameters of the rotation curves and the galaxies' light distributions are also presented. The rotation curves are classified broadly by shape, with special emphasis on kinematic disturbances and regions of

W. C. Keel

1997-01-01

340

Dimension Reduction for Hybrid Paired Comparison Models  

Microsoft Academic Search

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

David H. Annis

2007-01-01

341

Analysis of Paired Comparison Data Using Mx  

ERIC Educational Resources Information Center

By postulating that the random utilities associated with the choice options follow a multivariate normal distribution, Thurstonian models (Thurstone, 1927) provide a straightforward representation of paired comparison data. The use of Monte Carlo Expectation-Maximization (MCEM) algorithms and limited information approaches have been proposed to…

Tsai, Rung-Ching; Wu, Tsung-Lin

2004-01-01

342

Pairing correlations and effective mass  

SciTech Connect

We study the effect of effective mass on pairing correlations in the ground states of superfluid nuclei {sup 124}Sn and {sup 136}Sn. Various parameter sets of Skyrme interactions and relativistic Lagrangians are adopted to study pairing correlations across a wide range of effective mass. It is shown that surface-type pairing interaction gives an almost constant pairing gap as a function of the effective mass, while volume-type pairing interaction shows rather strong dependence of the pairing gap upon the effective mass. The local pair potentials of various effective interactions are also examined in relation to the effective mass.

Yoshida, Satoshi [Science Research Center, Hosei University, 2-17-1 Fujimi, Chiyoda, Tokyo 102-8160 (Japan); Sagawa, Hiroyuki [Center for Mathematical Sciences, University of Aizu Aizu-Wakamatsu, Fukushima 965-8580 (Japan)

2008-05-15

343

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

SciTech Connect

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

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

2009-01-26

344

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

PubMed

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

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

2010-02-01

345

Matter and radiation in the strong magnetic fields of neutron stars  

NASA Astrophysics Data System (ADS)

Recent observations of the radiation from highly magnetized neutron stars have provided a wealth of information on these objects, but they have also raised many new questions. We study various aspects of the surfaces and magnetospheres of neutron stars, including the cohesive properties and condensation of the stellar surface, formation of magnetosphere acceleration zones, and the initiation and propagation of electron-positron cascades through the magnetosphere. We present calculations of the electronic structure of matter in strong magnetic fields ranging from B = 10^12 G to 2 × 10^15 G, appropriate for observed magnetic neutron stars. Our calculations are based on the density functional theory. We find that condensed matter surfaces composed of hydrogen, helium, and carbon are all bound relative to individual atoms for B = 10^12 G or higher. Condensed iron surfaces, however, are only significantly bound for B [Special characters omitted.] 10^14 G. We also present Hartree-Fock calculations of the polarization-dependent photoionization cross sections of the He atom in strong magnetic fields ranging from 10^12 G to 10^14 G. We investigate several important astrophysical implications of our calculations of the cohesive property of magnetic condensed matter. We find that for sufficiently strong magnetic fields and/or low temperatures, the neutron star surface may be in a condensed state with little gas or plasma above it; such surface condensation may lead to the formation of a charge-depleted acceleration zone ("vacuum gap") in the magnetosphere above the stellar polar cap. We quantitatively determine the conditions for surface condensation and vacuum gap formation in magnetic neutron stars. We find that condensation can occur if the thermal energy kT of the neutron star surface is less than about 8% of its cohesive energy Q s , and that a vacuum gap can form if kT is less than about 4% of Qs . We study the conditions for the onset of pair cascades in the magnetospheres of neutron stars and the related pulsar death line/boundary. We also present Monte Carlo simulations of the full pair cascade from onset to completion. Our calculations generalize previous works to the superstrong field regime. We find that curvature radiation is a viable mechanism for the initiation of pair cascades, but that resonant and nonresonant inverse Compton scatterings are not. Additionally, we obtain the final photon spectra and pair energy distribution functions of the cascade and find significant differences between their nature in high-field neutron stars and in moderate-field neutron stars.

Medin, Zachary James

346

Pulsed neutron diffraction study on the short range structure of B 2O 3–Ag 2O glasses  

Microsoft Academic Search

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

Hideharu Ushida; Yasuhiko Iwadate; Takeo Hattori; Shin Nishiyama; Kazuko Fukushima; Masakatsu Misawa; Toshiharu Fukunaga

2001-01-01

347

Calculation of two-neutron multiplicity in photonuclear reactions  

NASA Technical Reports Server (NTRS)

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

Norbury, John W.; Townsend, Lawrence W.

1989-01-01

348

Neutron multiplicities in spontaneous fission and nuclear structure studies  

SciTech Connect

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

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

1993-12-31

349

Evolution of closely linked gene pairs in vertebrate genomes  

Microsoft Academic Search

The orientation of closely linked genes in mammalian genomes is not random: there are more head-to-head (h2h) gene pairs than expected. To understand the origin of this enrichment in h2h gene pairs, we have analyzed the phylogenetic distribution of gene pairs separated by less than 600 bp of intergenic DNA (gene duos). We show here that a lack of head-to-tail

Erik Franck; Tim Hulsen; Martijn A. Huynen; Wilfried W. de Jong; N. H. Lunsen; Ole Madsen

2008-01-01

350

Photon Splitting and Pair Conversion in Strong Magnetic Fields  

SciTech Connect

The magnetospheres of neutron stars provide a valuable testing ground for as-yet unverified theoretical predictions of quantum electrodynamics (QED) in strong electromagnetic fields. Exhibiting magnetic field strengths well in excess of a TeraGauss, such compact astrophysical environments permit the action of exotic mechanisms that are forbidden by symmetries in field-free regions. Foremost among these processes are single-photon pair creation, where a photon converts to an electron-positron pair, and magnetic photon splitting, where a single photon divides into two of lesser energy via the coupling to the external field. The pair conversion process is exponentially small in weak fields, and provides the leading order contribution to vacuum polarization. In contrast, photon splitting possesses no energy threshold and can operate in kinematic regimes where the lower order pair conversion is energetically forbidden. This paper outlines some of the key physical aspects of these processes, and highlights their manifestation in neutron star magnetospheres. Anticipated observational signatures include profound absorption turnovers in pulsar spectra at gamma-ray wavelengths. The shapes of these turnovers provide diagnostics on the possible action of pair creation and the geometrical locale of the photon emission region. There is real potential for the first confirmation of strong field QED with the new GLAST gamma-ray mission, recently launched by NASA in June 2008. The suppression of pair creation by photon splitting and its implications for pulsars are also discussed.

Baring, Matthew G. [Rice University, Department of Physics and Astronomy-MS 108, P. O. Box 1892, Houston, Texas 77251 (United States)

2008-10-17

351

Photon Splitting and Pair Conversion in Strong Magnetic Fields  

NASA Astrophysics Data System (ADS)

The magnetospheres of neutron stars provide a valuable testing ground for as-yet unverified theoretical predictions of quantum electrodynamics (QED) in strong electromagnetic fields. Exhibiting magnetic field strengths well in excess of a TeraGauss, such compact astrophysical environments permit the action of exotic mechanisms that are forbidden by symmetries in field-free regions. Foremost among these processes are single-photon pair creation, where a photon converts to an electron-positron pair, and magnetic photon splitting, where a single photon divides into two of lesser energy via the coupling to the external field. The pair conversion process is exponentially small in weak fields, and provides the leading order contribution to vacuum polarization. In contrast, photon splitting possesses no energy threshold and can operate in kinematic regimes where the lower order pair conversion is energetically forbidden. This paper outlines some of the key physical aspects of these processes, and highlights their manifestation in neutron star magnetospheres. Anticipated observational signatures include profound absorption turnovers in pulsar spectra at gamma-ray wavelengths. The shapes of these turnovers provide diagnostics on the possible action of pair creation and the geometrical locale of the photon emission region. There is real potential for the first confirmation of strong field QED with the new GLAST gamma-ray mission, recently launched by NASA in June 2008. The suppression of pair creation by photon splitting and its implications for pulsars are also discussed.

Baring, Matthew G.

2008-10-01

352

Photon Splitting and Pair Conversion in Strong Magnetic Fields  

E-print Network

The magnetospheres of neutron stars provide a valuable testing ground for as-yet unverified theoretical predictions of quantum electrodynamics (QED) in strong electromagnetic fields. Exhibiting magnetic field strengths well in excess of a TeraGauss, such compact astrophysical environments permit the action of exotic mechanisms that are forbidden by symmetries in field-free regions. Foremost among these processes are single-photon pair creation, where a photon converts to an electron-positron pair, and magnetic photon splitting, where a single photon divides into two of lesser energy via the coupling to the external field. The pair conversion process is exponentially small in weak fields, and provides the leading order contribution to vacuum polarization. In contrast, photon splitting possesses no energy threshold and can operate in kinematic regimes where the lower order pair conversion is energetically forbidden. This paper outlines some of the key physical aspects of these processes, and highlights their manifestation in neutron star magnetospheres. Anticipated observational signatures include profound absorption turnovers in pulsar spectra at gamma-ray wavelengths. The shapes of these turnovers provide diagnostics on the possible action of pair creation and the geometrical locale of the photon emission region. There is real potential for the first confirmation of strong field QED with the new GLAST mission, to be launched by NASA in 2008. Suppression of pair creation by photon splitting and its implications for pulsars is also discussed.

Matthew G. Baring

2008-04-05

353

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

PubMed

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

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

2011-12-01

354

Quark matter in neutron stars  

E-print Network

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

Mark G. Alford

2009-07-01

355

Agile Offsharing: Using Pair Work to Overcome Nearshoring Difficulties  

E-print Network

Agile Offsharing: Using Pair Work to Overcome Nearshoring Difficulties Lutz Prechelt Freie@inf.fu-berlin.de Abstract--A major problem in distributed development sit- uations, in particular offshoring situations work at an engineering level, such as pair programming, may be a method for solving this problem

Prechelt, Lutz

356

Paired Accelerated Frames  

E-print Network

The geometrical and quantum mechanical basis for Davies' and Unruh's acceleration temperature is traced to a type of quantum mechanical (``achronal'') spin. Its existence and definition are based on pairs of causally disjoint accelerated frames. For bosons the expected spin vector of monochromatic particles is given by the ``Planckian power'' and the ``r.m.s. thermal fluctuation'' spectra. Under spacetime translation the spin direction precesses around that ``Planckian'' vector. By exhibiting the conserved achronal spin four-current, we extend the identification of achronal spin from single quanta to multiparticle systems. Total achronal spin conservation is also shown to hold, even in the presence of quadratic interactions.

Ulrich H. Gerlach

1999-10-28

357

Pair production in superstrong magnetic fields  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

358

Rotochemical heating in millisecond pulsars with Cooper pairing  

SciTech Connect

When a rotating neutron star loses angular momentum, the reduction in the centrifugal force makes it contract. This perturbs each fluid element, raising the local pressure and originating deviations from beta equilibrium that enhance the neutrino emissivity and produce thermal energy. This mechanism is named rotochemical heating and has previously been studied for neutron stars of non-superfluid matter, finding that they reach a quasi-steady state in which the rate that the spin-down modifies the equilibrium concentrations is the same to that of the neutrino reactions restoring the equilibrium. On the other hand, the neutron star interior is believed to contain superfluid nucleons, which affect the thermal evolution of the star by suppressing the neutrino reactions and the specific heat, and opening new Cooper pairing reactions.In this work we describe the thermal effects of Cooper pairing with spatially uniform energy gaps of neutrons and protons on rotochemical heating in millisecond pulsars (MSPs) when only modified Urca reactions are allowed. We find that the chemical imbalances grow up to a value close to the energy gaps, which is higher than the one of the nonsuperfluid case. Therefore, the surface temperatures predicted with Cooper pairing are higher and explain the recent measurement of MSP J0437-4715.

Petrovich, Cristobal; Reisenegger, Andreas [Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile)

2010-08-04

359

Regimes of Pulsar Pair Formation and Particle Energetics  

E-print Network

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 massive stars. Therefore accretion of mass by pulsars in binary systems may allow pair production in most of the millisecond pulsar population. We also find that two-photon pair production may be important in millisecond pulsars if their surface temperatures are above about three million degrees K. Pulsars that produce pairs through CR will have their primary acceleration limited by the effect of screening of the electric field. In this regime, the high-energy luminosity should follow a $L_{HE} \\propto \\dot E_{rot}^{1/2}$ dependence. The acceleration voltage drop in pulsars 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 $L_{HE} \\propto \\dot E_{rot}$ dependence. Thus, older pulsars will have significantly lower gamma-ray luminosity.

Alice K. Harding; Alexander G. Muslimov; Bing Zhang

2002-05-06

360

Pairing-induced speedup of nuclear spontaneous fission  

E-print Network

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.

Jhilam Sadhukhan; J. Dobaczewski; W. Nazarewicz; J. A. Sheikh; A. Baran

2014-10-06

361

Assessment Strategies for Pair Programming  

ERIC Educational Resources Information Center

Although pair programming has proved its usefulness in teaching and learning programming skills, it is difficult to assess the individual roles and abilities of students whilst programming in pairs. (Note that within this manuscript, the term assessment refers to evaluating individual student performance.) Assessing only the outcomes of a pair…

Hahn, Jan Hendrik; Mentz, Elsa; Meyer, Lukas

2009-01-01

362

Special Angle Pairs Discovery Activity  

NSDL National Science Digital Library

This lesson uses a discovery approach to identify the special angles formed when a set of parallel lines is cut by a transversal. During this lesson students identify the angle pair and the relationship between the angles. Students use this relationship and special angle pairs to make conjectures about which angle pairs are considered special angles.

Henry, Barbara

2012-04-16

363

The Inelastic Scattering of Neutrons  

Microsoft Academic Search

The total cross section and the differential cross section for the inelastic scattering of neutrons are considered. It is assumed that the compound nucleus is sufficiently excited so that the statistical model may be applied. If the statistical model may be applied as well to the residual nucleus, it is shown that the angular distribution of the inelastically scattered neutrons

Walter Hauser; Herman Feshbach

1952-01-01

364

Space-time description of neutron spin echo spectrometry  

NASA Astrophysics Data System (ADS)

Neutron spin echo (NSE) [F. Mezei, ed., Neutron Spin Echo, Lecture Notes in Physics Vol. 128 (Springer, Berlin, 1980)] is a technique for neutron scattering in which the energy resolution can be much narrower than the spectral width of the incident beam and it allows the direct measurement of the Fourier transform of the energy transfer spectrum, i.e. the time dependence of the density-density correlation function of the scattering systems. It is normally discussed in terms of neutron Larmor precession in magnetic fields and the scattering process is described in terms of S( Q, ?) . We show how a quantum mechanical treatment of the NSE technique offers new insight into the scattering process and explains how NSE directly yields the intermediate scattering function S( Q, t) or pair distribution function G( r). In addition it gives a basic picture of the physics of ‘phonon focussing’ in NSE and reveals the link between the spin echo time ?, the resolution of the measurement and the details of the scattering process. In this paper we present three different approaches to understanding the system: (i) the usual classical Larmor precession, (ii) a semi-classical ray tracing model and (iii) a full quantum mechanical treatment. We apply these models to a spin echo spectrometer as used for various kinds of measurements.

Gähler, R.; Golub, R.; Habicht, K.; Keller, T.; Felber, J.

1996-02-01

365

The effect of turbulent kinetic energy on inferred ion temperature from neutron spectra  

NASA Astrophysics Data System (ADS)

Measuring the width of the energy spectrum of fusion-produced neutrons from deuterium (DD) or deuterium-tritium (DT) plasmas is a commonly used method for determining the ion temperature in inertial confinement fusion (ICF) implosions. In a plasma with a Maxwellian distribution of ion energies, the spread in neutron energy arises from the thermal spread in the center-of-mass velocities of reacting pairs of ions. Fluid velocities in ICF are of a similar magnitude as the center-of-mass velocities and can lead to further broadening of the neutron spectrum, leading to erroneous inference of ion temperature. Motion of the reacting plasma will affect DD and DT neutrons differently, leading to disagreement between ion temperatures inferred from the two reactions. This effect may be a contributor to observations over the past decades of ion temperatures higher than expected from simulations, ion temperatures in disagreement with observed yields, and different temperatures measured in the same implosion from DD and DT neutrons. This difference in broadening of DD and DT neutrons also provides a measure of turbulent motion in a fusion plasma.

Murphy, T. J.

2014-07-01

366

Probing the tides in interacting galaxy pairs  

NASA Technical Reports Server (NTRS)

Detailed spectroscopic and imaging observations of colliding elliptical galaxies revealed unmistakable diagnostic signatures of the tidal interactions. It is possible to compare both the distorted luminosity distributions and the disturbed internal rotation profiles with numerical simulations in order to model the strength of the tidal gravitational field acting within a given pair of galaxies. Using the best-fit numerical model, one can then measure directly the mass of a specific interacting binary system. This technique applies to individual pairs and therefore complements the classical methods of measuring the masses of galaxy pairs in well-defined statistical samples. The 'personalized' modeling of galaxy pairs also permits the derivation of each binary's orbit, spatial orientation, and interaction timescale. Similarly, one can probe the tides in less-detailed observations of disturbed galaxies in order to estimate some of the physical parameters for larger samples of interacting galaxy pairs. These parameters are useful inputs to the more universal problems of (1) the galaxy merger rate, (2) the strength and duration of the driving forces behind tidally stimulated phenomena (e.g., starbursts and maybe quasi steller objects), and (3) the identification of long-lived signatures of interaction/merger events.

Borne, Kirk D.

1990-01-01

367

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

Microsoft Academic Search

We have measured production cross sections and longitudinal momentum distri- butions of fragments from neutron-deficient 36Ar at 1.05 AGeV. The production cross-sections show excellent agreement with the predictions of the semiempirical formula EPAX. We have compared these results, involving extremely neutron de- ficient nuclei, with model calculations to extract information about the response of these models close to the driplines.

M. Caamano; D. Cortina-Gil; K. Summerer; J. Benlliure; E. Casarejos; H. Geissel; G. Munzenberg; J. Pereira

368

Relativistically expanding pair plasmas as bursting sources of cosmic gamma rays  

NASA Technical Reports Server (NTRS)

High temperature shock heating of relativistically expanding plasmas produced in neutron star binary mergers provides a model for cosmic gamma ray burst sources. This requires the fireball resulting from the merger to have a very high entropy per baryon, mechanisms for which are discussed. The energy, temporal structure and spectrum produced by the blast wave and reverse shock as the fireball is decelerated in an external medium are comparable to those observed, as is the frequency of occurrence and the characteristics of the spatial distribution of the events. Difficulties common to all cosmological gamma ray burst scenarios concern the total amount of energy ultimately appearing at gamma ray energies, the time scales, the spectrum, and the great variety of time profiles. A very general mechanism which overcomes these problems is presented. Situations where the pair plasma is created in regions which are relatively free of baryons are discussed. The effect of the interaction of the expanding fireball with the external medium is considered.

Meszaros, Peter; Rees, M. J.

1993-01-01

369

Neutron spectrometry at Strasbourg University Reactor  

Microsoft Academic Search

A neutron spectrometer incorporating two silicon surface barrier detectors and a 6LiF target has been designed, constructed and used to determine neutron energy distributions in three irradiation sites of the Strasbourg University Reactor (SUR). The spectrometer is compared with other spectrometer designs using the same detectors and target by means of the energy resolution observed for a thermalized neutron beam.

A. Seghour; J. C. Sens

1999-01-01

370

Coexistence of BCS- and BEC-Like Pair Structures in Halo Nuclei  

SciTech Connect

We investigate the spatial structure of the two-neutron wave function in the Borromean nucleus {sup 11}Li, using a three-body model of {sup 9}Li+n+n, which includes many-body correlations stemming from the Pauli principle. The behavior of the neutron pair at different densities is simulated by calculating the two-neutron wave function at several distances between the core nucleus {sup 9}Li and the center of mass of the two neutrons. With this representation, a strong concentration of the neutron pair on the nuclear surface is for the first time quantitatively established for neutron-rich nuclei. That is, the neutron pair wave function in {sup 11}Li has an oscillatory behavior at normal density, while it becomes a well-localized single peak in the dilute density region around the nuclear surface. We point out that these features qualitatively correspond to the BCS- and BEC-like structures of the pair wave function found in infinite nuclear matter.

Hagino, K. [Department of Physics, Tohoku University, Sendai 980-8578 (Japan); Sagawa, H. [Center for Mathematical Sciences, University of Aizu, Aizu-Wakamatsu, Fukushima 965-8560 (Japan); Carbonell, J. [Laboratoire de Physique Subatomique et de Cosmologie, F-38026 Grenoble Cedex (France); Schuck, P. [Institut de Physique Nucleaire, CNRS, UMR8608, Orsay F-91406 (France); Universite Paris-Sud, Orsay F-91505 (France)

2007-07-13

371

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

E-print Network

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

Y. Zhang; M. Matsuo; J. Meng

2012-09-24

372

Coexistence of BCS- and BEC-like pair structures in halo nuclei.  

PubMed

We investigate the spatial structure of the two-neutron wave function in the Borromean nucleus (11)Li, using a three-body model of (9)Li + n + n, which includes many-body correlations stemming from the Pauli principle. The behavior of the neutron pair at different densities is simulated by calculating the two-neutron wave function at several distances between the core nucleus (9)Li and the center of mass of the two neutrons. With this representation, a strong concentration of the neutron pair on the nuclear surface is for the first time quantitatively established for neutron-rich nuclei. That is, the neutron pair wave function in (11)Li has an oscillatory behavior at normal density, while it becomes a well-localized single peak in the dilute density region around the nuclear surface. We point out that these features qualitatively correspond to the BCS- and BEC-like structures of the pair wave function found in infinite nuclear matter. PMID:17678220

Hagino, K; Sagawa, H; Carbonell, J; Schuck, P

2007-07-13

373

Monoenergetic fast neutron reference fields: I. Neutron production  

NASA Astrophysics Data System (ADS)

Monoenergetic neutron reference fields are required for the investigation of the energy-dependent response and the calibration of neutron detectors and dosemeters for various applications ranging from nuclear physics and nuclear data measurements to radiation protection. In a series of two separate publications the metrological aspects of the production and the measurement of fast neutrons are reviewed. In this first part, requirements for the nuclear reaction used to produce the neutron field as well as methods for target characterization and the general layout of reference facilities are discussed. The second part will focus on the most important techniques for field characterization. This includes the determination of the neutron fluence as well as the spectral neutron distribution and the determination of the fluence of contaminating photons.

Nolte, Ralf; Thomas, David J.

2011-12-01

374

Electron-pair correlations seen by recoil-ion spectroscopy  

SciTech Connect

A fourth-order Wannier description of electron-pair escape has been extended to include non-zero total angular momentum. A key element of the description is the electron-pair center-of-mass momentum, which is fully represented by the momentum distribution of the recoiling ion. The authors have thus compared general and Wannier-theory predictions with recoil-ion measurements of electron-pair angular distributions following double-photoionization of helium. Their approach and recent experimental results down to 1 eV above threshold will be presented.

Feagin, J.M. [California State Univ., Fullerton, CA (United States); Doerner, R.; Cocke, C.L.

1996-05-01

375

Observation of Neutron Skyshine from an Accelerator Based Neutron Source  

SciTech Connect

A key feature of neutron based interrogation systems is the need for adequate provision of shielding around the facility. Accelerator facilities adapted for fast neutron generation are not necessarily suitably equipped to ensure complete containment of the vast quantity of neutrons generated, typically >10{sup 11} n{center_dot}s{sup -1}. Simulating the neutron leakage from a facility is not a simple exercise since the energy and directional distribution can only be approximated. Although adequate horizontal, planar shielding provision is made for a neutron generator facility, it is sometimes the case that vertical shielding is minimized, due to structural and economic constraints. It is further justified by assuming the atmosphere above a facility functions as an adequate radiation shield. It has become apparent that multiple neutron scattering within the atmosphere can result in a measurable dose of neutrons reaching ground level some distance from a facility, an effect commonly known as skyshine. This paper describes a neutron detection system developed to monitor neutrons detected several hundred metres from a neutron source due to the effect of skyshine.

Franklyn, C. B. [Radiation Science Department, Necsa, PO Box 582, Pretoria 0001 (South Africa)

2011-12-13

376

Observation of Neutron Skyshine from an Accelerator Based Neutron Source  

NASA Astrophysics Data System (ADS)

A key feature of neutron based interrogation systems is the need for adequate provision of shielding around the facility. Accelerator facilities adapted for fast neutron generation are not necessarily suitably equipped to ensure complete containment of the vast quantity of neutrons generated, typically >1011 n?s-1. Simulating the neutron leakage from a facility is not a simple exercise since the energy and directional distribution can only be approximated. Although adequate horizontal, planar shielding provision is made for a neutron generator facility, it is sometimes the case that vertical shielding is minimized, due to structural and economic constraints. It is further justified by assuming the atmosphere above a facility functions as an adequate radiation shield. It has become apparent that multiple neutron scattering within the atmosphere can result in a measurable dose of neutrons reaching ground level some distance from a facility, an effect commonly known as skyshine. This paper describes a neutron detection system developed to monitor neutrons detected several hundred metres from a neutron source due to the effect of skyshine.

Franklyn, C. B.

2011-12-01

377

Neutron multiplicity analysis tool  

Microsoft Academic Search

I describe the capabilities of the EXCOM (EXcel based COincidence and Multiplicity) calculation tool which is used to analyze experimental data or simulated neutron multiplicity data. The input to the program is the count-rate data (including the multiplicity distribution) for a measurement, the isotopic composition of the sample and relevant dates. The program carries out deadtime correction and background subtraction

Scott L

2010-01-01

378

Stereo Pair, Pasadena, California  

NASA Technical Reports Server (NTRS)

This stereoscopic image pair is a perspective view that shows the western part of the city of Pasadena, California, looking north toward the San Gabriel Mountains. Portions of the cities of Altadena and La Canada Flintridge are also shown. The cluster of large buildings left of center, at the base of the mountains, is the Jet Propulsion Laboratory. This image shows the power of combining data from different sources to create planning tools to study problems that affect large urban areas. In addition to the well-known earthquake hazards, Southern California is affected by a natural cycle of fire and mudflows. Data shown in this image can be used to predict both how wildfires spread over the terrain and how mudflows are channeled down the canyons.

The image was created from three datasets: the Shuttle Radar Topography Mission (SRTM) supplied the elevation, U. S. Geological Survey digital aerial photography provided the image detail, and the Landsat Thematic Mapper provided the color. The United States Geological Survey's Earth Resources Observations Systems (EROS) Data Center, Sioux Falls, South Dakota, provided the Landsat data and the aerial photography. The image can be viewed in 3-D by viewing the left image with the right eye and the right image with the left eye (cross-eyed viewing), or by downloading and printing the image pair, and viewing them with a stereoscope.

The Shuttle Radar Topography Mission (SRTM), launched on February 11, 2000, used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. The mission was designed to collect three-dimensional measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter-long (200-foot) mast, an additional C-band imaging antenna and improved tracking and navigation devices. The mission is a cooperative project between the National Aeronautics and Space Administration (NASA), the National Imagery and Mapping Agency (NIMA) and the German (DLR) and Italian (ASI)space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Earth Science Enterprise, Washington, DC.

Size: 3.4 km (2.1 miles) width x 7.0 km (4.4 miles) depth Location: 34.16 deg. North lat., 118.16 deg. West lon. Orientation: Looking North Original Data Resolution: SRTM and Landsat, 30 m; aerial photo, 3 m; no vertical exaggeration Date Acquired: February 16, 2000 (SRTM), July 3, 1985 (Landsat) Image: NASA/JPL/NIMA

2000-01-01

379

Mated Fingerprint Card Pairs 2 (MFCP2)  

National Institute of Standards and Technology Data Gateway

NIST Mated Fingerprint Card Pairs 2 (MFCP2) (PC database for purchase)   NIST Special Database 14 is being distributed for use in development and testing of automated fingerprint classification and matching systems on a set of images which approximate a natural horizontal distribution of the National Crime Information Center (NCIC) fingerprint classes. A newer version of the compression/decompression software on the CDROM can be found at the website http://www.nist.gov/itl/iad/ig/nigos.cfm as part of the NBIS package.

380

Pair production in rotating electric fields  

NASA Astrophysics Data System (ADS)

We explore Schwinger pair production in rotating time-dependent electric fields using the real-time Dirac-Heisenberg-Wigner formalism. We determine the time evolution of the Wigner function as well as asymptotic particle distributions neglecting backreactions on the electric field. Whereas qualitative features can be understood in terms of effective Keldysh parameters, the field rotation leaves characteristic imprints in the momentum distribution that can be interpreted in terms of interference and multiphoton effects. These phenomena may seed characteristic features of QED cascades created in the antinodes of a high-intensity standing wave laser field.

Blinne, Alexander; Gies, Holger

2014-04-01

381

Pairing the Volcano  

E-print Network

Isogeny volcanoes are graphs whose vertices are elliptic curves and whose edges are $\\ell$-isogenies. Algorithms allowing to travel on these graphs were developed by Kohel in his thesis (1996) and later on, by Fouquet and Morain (2001). However, up to now, no method was known, to predict, before taking a step on the volcano, the direction of this step. Hence, in Kohel's and Fouquet-Morain algorithms, many steps are taken before choosing the right direction. In particular, ascending or horizontal isogenies are usually found using a trial-and-error approach. In this paper, we propose an alternative method that efficiently finds all points $P$ of order $\\ell$ such that the subgroup generated by $P$ is the kernel of an horizontal or an ascending isogeny. In many cases, our method is faster than previous methods. This is an extended version of a paper published in the proceedings of ANTS 2010. In addition, we treat the case of 2-isogeny volcanoes and we derive from the group structure of the curve and the pairing ...

Ionica, Sorina

2011-01-01

382

Simulating neutron propagations with FLUKA, GEANT4 and MCNP  

Microsoft Academic Search

We perform simulations on neutron transport properties for neutrons with energies less than 500 MeV. The simulation packages FLUKA, GEANT4 and MCNP are used. The neutron energy distributions and attenuation lengths, which are resulted from a mono-energetic initial neutron beam traversing a given thickness of medium, are presented.

Yung-Shun Yeh; Chung-Hsiang Wang; Hong-Ming Liu; Tsung-Che Liu; Guey-Lin Lin

2007-01-01

383

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

PubMed

A model of a multi-electrode ionisation chamber, with polypropylene electrodes coated with a thin layer of B4C was created within Monte Carlo N-Particle Transport Code (MCNPX) and Fluktuierende Kaskade (FLUKA) codes. The influence of the layer thickness on neutron absorption in B4C and on the neutron spectra in the consecutive intra-electrode gas volumes has been studied using the MCNPX and FLUKA codes. The results will be used for designing the new type of the ionisation chamber. PMID:24729596

Tymi?ska, K; Maciak, M; O?ko, J; Tulik, P; Zielczy?ski, M; Gryzi?ski, M A

2014-10-01

384

Pair production and optical lasers  

E-print Network

Electron-positron pair creation in a standing wave is explored using a parameter-free quantum kinetic equation. Field strengths and frequencies corresponding to modern optical lasers induce a material polarisation of the QED vacuum, which may be characterised as a plasma of e^+ e^- quasiparticle pairs with a density of ~10^{20}cm^{-3}. The plasma vanishes almost completely when the laser field is zero, leaving a very small residual pair density, n_r, which is the true manifestation of vacuum decay. The average pair density per period is proportional to the laser intensity but independent of the frequency, \

D. B. Blaschke; A. V. Prozorkevich; C. D. Roberts; S. M. Schmidt; S. A. Smolyansky

2005-11-29

385

Neutron detector  

DOEpatents

A neutron detector has a volume of neutron moderating material and a plurality of individual neutron sensing elements dispersed at selected locations throughout the moderator, and particularly arranged so that some of the detecting elements are closer to the surface of the moderator assembly and others are more deeply embedded. The arrangement captures some thermalized neutrons that might otherwise be scattered away from a single, centrally located detector element. Different geometrical arrangements may be used while preserving its fundamental characteristics. Different types of neutron sensing elements may be used, which may operate on any of a number of physical principles to perform the function of sensing a neutron, either by a capture or a scattering reaction, and converting that reaction to a detectable signal. High detection efficiency, an ability to acquire spectral information, and directional sensitivity may be obtained.

Stephan, Andrew C. (Knoxville, TN); Jardret; Vincent D. (Powell, TN)

2011-04-05

386

Delayed beta- and gamma-ray production due to thermal-neutron fission of ²³⁹Pu: tabular and graphical spectral distributions for times after fission between 2 and 14000 sec  

Microsoft Academic Search

Fission-product decay energy-release rates were measured for thermal-neutron fission of ²³⁹Pu. Samples of mass 1 and 5 ..mu..g were irradiated for 1 to 100 s using the fast pneumatic-tube facility at the Oak Ridge Research Reactor. The resulting beta- and gamma-ray emissions were separately counted for times-after-fission between 2 and 14,000 s to yield spectral distributions N(E\\/sub ..gamma..\\/) vs E\\/sub

J. K. Dickens; T. R. England; T. A. Love; J. W. McConnell; J. F. Emergy; K. J. Northcutt; R. W. Peelle

1980-01-01

387

Pair correlations in nuclei involved in neutrinoless double beta decay: 76Ge and 76Se  

E-print Network

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.

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

2007-01-03

388

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

EPA Science Inventory

The objective of this multi-institutional research effort was to understand how radionuclides, neutron absorbers, and other waste species are incorporated into single-phase amorphous matrices and ceramics. This was to provide DOE with a methodology to develop glasses and ceramics...

389

Neutron Stars  

NASA Technical Reports Server (NTRS)

Neutron stars were discovered almost 40 years ago, and yet many of their most fundamental properties remain mysteries. There have been many attempts to measure the mass and radius of a neutron star and thereby constrain the equation of state of the dense nuclear matter at their cores. These have been complicated by unknown parameters such as the source distance and burning fractions. A clean, straightforward way to access the neutron star parameters is with high-resolution spectroscopy. I will present the results of searches for gravitationally red-shifted absorption lines from the neutron star atmosphere using XMM-Newton and Chandra.

Cottam, J.

2007-01-01

390

Neutron radiography  

SciTech Connect

Neutron radiography is becoming a well established nondestructive testing (NDT) method. The American Society for Nondestructive Testing (ASNT) has recognized the method through its recommended practice SNT-TCIA which outlines training, knowledge, and experience necessary to obtain levels of competency in the method. Certification of nondestructive testing personnel is also covered in a military standard. Technical publications in the field of NDT and nuclear technology carry articles on neutron radiography and technical meetings include papers or even entire sessions on neutron radiography. There is an on-going series of international conferences on neutron radiography. Many books are available to provide introductory and advanced material on neutron radiographic techniques and applications. Neutron radiography as a service for hire is available, similar to that offered for other NDT services. The method is being adopted to solve NDT problems in specialty areas. The objective of this report is to provide a brief survey of the current state of the art in the use of neutron radiography. The survey will include information on the technique including principles of the method, sources of neutrons, detection methodology, standards and image quality indicators, and representative applications. An extensive reference list provides additional information for those who wish to investigate further and a Glossary is included which provides definitions for terms used in Neutron Radiography.

Berger, H.; Iddings, F.

1998-08-01

391

Neutronic Design and Measured Performance of the Low Energy Neutron Source (LENS) Target Moderator Reflector Assembly  

E-print Network

The Low Energy Neutron Source (LENS) is an accelerator-based pulsed cold neutron facility under construction at the Indiana University Cyclotron Facility (IUCF). The idea behind LENS is to produce pulsed cold neutron beams starting with ~MeV neutrons from (p,n) reactions in Be which are moderated to meV energies and extracted from a small solid angle for use in neutron instruments which can operate efficiently with relatively broad (~1 msec) neutron pulse widths. Although the combination of the features and operating parameters of this source is unique at present, the neutronic design possesses several features similar to those envisioned for future neutron facilities such as long-pulsed spallation sources (LPSS) and very cold neutron (VCN) sources. We describe the underlying ideas and design details of the target/moderator/reflector system (TMR) and compare measurements of its brightness, energy spectrum, and emission time distribution under different moderator configurations with MCNP simulations. Brightness measurements using an ambient temperature water moderator agree with MCNP simulations within the 20% accuracy of the measurement. The measured neutron emission time distribution from a solid methane moderator is in agreement with simulation and the cold neutron flux is sufficient for neutron scattering studies of materials. We describe some possible modifications to the existing design which would increase the cold neutron brightness with negligible effect on the emission time distribution.

C. M. Lavelle; D. V. Baxter; A. Bogdanov; V. P. Derenchuk; H. Kaiser; M. B. Leuschner; M. A. Lone; W. Lozowski; H. Nann; B. v. Przewoski; N. Remmes; T. Rinckel; Y. Shin; W. M. Snow; P. E. Sokol

2008-03-28

392

Some Special Fourier Transform Pairs  

E-print Network

Some Special Fourier Transform Pairs 24.3 Introduction ' & $ % Prerequisites Before starting period. For a non-periodic real signal f(t) with Fourier Transform F() the corresponding result is - f2): Workbook Level 2 24.3: Some Special Fourier Transform Pairs 2 #12;Wehave F()=F{e-t u(t)}= 1 1+i , so |F()|2

Vickers, James

393

Nuclear pairing: basic phenomena revisited  

E-print Network

I review the phenomena associated with pairing in nuclear physics, most prominently the ubiquitous presence of odd-even mass differences and the properties of the excitation spectra, very different for even-even and odd-A nuclei. There are also significant dynamical effects of pairing, visible in the inertias associated with nuclear rotation and large-amplitude shape deformation.

G. F. Bertsch

2012-03-25

394

Weird Stellar Pair Puzzles Scientists  

NASA Astrophysics Data System (ADS)

Astronomers have discovered a speedy spinning pulsar in an elongated orbit around an apparent Sun-like star, a combination never seen before, and one that has them puzzled about how the strange system developed. Orbital Comparison Comparing Orbits of Pulsar and Its Companion to our Solar System. CREDIT: Bill Saxton, NRAO/AUI/NSF Click on image for full caption information and available graphics. "Our ideas about how the fastest-spinning pulsars are produced do not predict either the kind of orbit or the type of companion star this one has," said David Champion of the Australia Telescope National Facility. "We have to come up with some new scenarios to explain this weird pair," he added. Astronomers first detected the pulsar, called J1903+0327, as part of a long-term survey using the National Science Foundation's Arecibo radio telescope in Puerto Rico. They made the discovery in 2006 doing data analysis at McGill University, where Champion worked at the time. They followed up the discovery with detailed studies using the Arecibo telescope, the NSF's Robert C. Byrd Green Bank Telescope (GBT) in West Virginia, the Westerbork radio telescope in the Netherlands, and the Gemini North optical telescope in Hawaii. The pulsar, a city-sized superdense stellar corpse left over after a massive star exploded as a supernova, is spinning on its axis 465 times every second. Nearly 21,000 light-years from Earth, it is in a highly-elongated orbit that takes it around its companion star once every 95 days. An infrared image made with the Gemini North telescope in Hawaii shows a Sun-like star at the pulsar's position. If this is an orbital companion to the pulsar, it is unlike any companions of other rapidly rotating pulsars. The pulsar, a neutron star, also is unusually massive for its type. "This combination of properties is unprecedented. Not only does it require us to figure out how this system was produced, but the large mass may help us understand how matter behaves at extremely high densities," said Scott Ransom of the National Radio Astronomy Observatory. Pulsars are neutron stars whose strong magnetic fields channel lighthouse-like beams of light and radio waves that whirl around as the star spins. Typical pulsars spin a few times a second, but some, like PSR J1903+0327, are much faster, rotating hundreds of times a second. They are called millisecond pulsars. Astronomers think most millisecond pulsars are sped up by material falling onto them from a companion star. This requires the pulsar to be in a tight orbit around its companion that becomes more and more circular with time. The orbits of some millisecond pulsars are the most perfect circles in the Universe, so the elongated orbit of the new pulsar is a mystery. "What we have found is a millisecond pulsar that is in the wrong kind of orbit around what appears to be the wrong kind of star," Champion said. "Now we have to figure out how this strange system was produced." The scientists are considering three possibilities. The first, that the pulsar simply was born spinning quickly, seems unlikely to them. Another possibility, they say, is that the pulsar was formed in a tight group of stars known as a globular cluster, where it had a companion that spun it up. Later, a close encounter with another star in the cluster stripped it of its companion and flung it out of the cluster. For several reasons, including the fact that they don't see a nearby cluster from which it could have come, they don't like that explanation either. A third scenario says the pulsar may be part of a triple, not a double, star system. In this case, the pulsar's 95-day orbit is around a neutron star or white dwarf, not the Sun-like star seen in the infrared image. The Sun-like star would then be in a more-distant orbit around the pulsar and its close companion. "We've found about 50 pulsars in binary systems. We may now have found our first pulsar in a stellar triple system," Ransom said. The international research team is busy trying to get their

2008-05-01

395

J=0 T=1 Pairing Interaction Selection Rules  

E-print Network

Wave functions arising form a pairing Hamiltonian E(0) i,e, one in which the interaction is only between J=0^{+}T=1 pairs, lead to magnetic dipole and Gamow-Teller transition rates that are much larger than those from an interaction E(J_{max}) in which a proton and a neutron couple to J=2j. With realistic interactions the results are in between the 2 extremes. In the course of this study we found that certain M1 and GT matrix elements vanish with E(0) . These are connected to seniority and reduced isospin isospin selection rules. We find the surprising result that The M1 strength to the single j scissors is larger for a J=0 T=1 pairing interaction than it is for Q.Q.

Matthew Harper; Larry Zamick

2014-08-18

396

Pair1,3,4,5,6Ring Pair5Ring Pair3Ring Pair1Ring  

E-print Network

, Receptacles, 5. Telephone cable. Olympic 3080 W7 SEI RN1/4T9 8K25 R1,R5 'Holco' H8 4K02 R2,R4 SEI RN1/4T9 1K5 R3 W5 W3 W4 W5 W6 X6 X10 X11 X3 X4 X5 X7 brown red W1 W2 W4 VM Type 6 Cable Schematic (for FASTBUS bins). Pair4Tip Pair6Tip Pair4Ring Pair6Ring X8 2 X1 X2 W1 W2 1 1 2 Pair4Tip Belden 9921 AWG22 2. Wire

397

Ukraine experimental neutron source facility.  

SciTech Connect

Kharkov Institute of Physics and Technology (KIPT) of Ukraine has a plan to construct an experimental neutron source facility. The facility has been developed for producing medical isotopes, training young nuclear professionals, supporting the Ukraine nuclear industry, providing capability for performing reactor physics, material research, and basic science experiments. Argonne National Laboratory (ANL) of USA is collaborating with KIPT on developing this facility. A driven subcritical assembly utilizing the KIPT electron accelerator with a target assembly is used to generate the neutron source. The target assembly utilizes tungsten or uranium for neutron production through photonuclear reactions with 100-KW of electron beam power. The neutron source intensity, spectrum, and spatial distribution have been studied to maximize the neutron yield and satisfy different engineering requirements. The subcritical assembly is designed to obtain the highest possible neutron flux intensity with a subcriticality of 0.98. Low enrichment uranium is used for the fuel material because it enhances the neutron source performance. Safety, reliability, and environmental considerations are included in the facility conceptual design. Horizontal neutron channels are incorporated for performing basic research including cold neutron source. This paper describes the conceptual design and summarizes some of the related analyses.

Gohar, Y.; Bolshinsky, I.; Nekludov, I.; Karnaukhov, I. (Nuclear Engineering Division); (INL); (Kharkov Institute of Physics and Technology)

2008-01-01

398

Pair Production and Gamma-Ray Emission in the Outer Magnetospheres of Rapidly Spinning Young Pulsars  

NASA Technical Reports Server (NTRS)

Electron-positron pair production and acceleration in the outer magnetosphere may be crucial for a young rapidly spinning canonical pulsar to be a strong Gamma-ray emitter. Collision between curvature radiated GeV photons and soft X-ray photons seems to be the only efficient pair production mechanism. For Crib-like pulsars, the magnetic field near the light cylinder is so strong, such that the synchrotron radiation of secondary pairs will be in the needed X-ray range. However, for majority of the known Gamma-ray pulsars, surface emitted X-rays seem to work as the matches and fuels for a gamma-ray generation fireball in the outer magnetosphere. The needed X-rays could come from thermal emission of a cooling neutron star or could be the heat generated by bombardment of the polar cap by energetic particles generated in the outer magnetosphere. With detection of more Gamma-ray pulsars, it is becoming evident that the neutron star's intrisic geometry (the inclination angle between the rotation and magnetic axes) and observational geometry (the viewing angle with respect to the rotation axis) are crucial to the understanding of varieties of observational properties exhibited by these pulsars. Inclination angles for many known high energy Gamma-ray pulsars appear to be large and the distribution seems to be consistent with random orientation. However, all of them except Geminga are pre-selected from known radio pulsars. The viewing angles are thus limited to be around the respective inclination angles for beamed radio emission, which may induce strong selection effect. The viewing angles as well as the inclination angles of PSR 1509-58 and PSB 0656+14 may be small such that most of the high energy Gamma-rays produced in the outer accelerators may not reach the observer's direction. The observed Gamma-rays below 5 MeV from this pulsar may be synchrotron radiation of secondary electron-positron pairs produced outside the accelerating regions.

Ruderman, Malvin; Chen, Kaiyou

1997-01-01

399

Spin-state transitions in PrCoO3 studied with neutron powder diffraction  

NASA Astrophysics Data System (ADS)

The crystal structure of PrCoO3 has been studied with high-resolution neutron powder diffraction and pair-distribution-function analysis in the temperature range from 12-600 K. The compound has the orthorhombic (Pbnm) perovskite structure over the entire temperature range. The temperature dependence of the average Co-O bond length shows clear anomalies near 60 K and 200 K where anomalous temperature dependencies of thermal conductivity and magnetic susceptibility have been reported. The data show a constant intermediate-spin-state fraction within 60

Ren, Y.; Yan, J.-Q.; Zhou, J.-S.; Goodenough, J. B.; Jorgensen, J. D.; Short, S.; Kim, H.; Proffen, Th.; Chang, S.; McQueeney, R. J.

2011-12-01

400

Neutronic Design and Measured Performance of the Low Energy Neutron Source (LENS) Target Moderator Reflector Assembly  

E-print Network

The Low Energy Neutron Source (LENS) is an accelerator-based pulsed cold neutron facility under construction at the Indiana University Cyclotron Facility (IUCF). The idea behind LENS is to produce pulsed cold neutron beams starting with ~MeV neutrons from (p,n) reactions in Be which are moderated to meV energies and extracted from a small solid angle for use in neutron instruments which can operate efficiently with relatively broad (~1 msec) neutron pulse widths. Although the combination of the features and operating parameters of this source is unique at present, the neutronic design possesses several features similar to those envisioned for future neutron facilities such as long-pulsed spallation sources (LPSS) and very cold neutron (VCN) sources. We describe the underlying ideas and design details of the target/moderator/reflector system (TMR) and compare measurements of its brightness, energy spectrum, and emission time distribution under different moderator configurations with MCNP simulations. Brightnes...

Lavelle, C M; Bogdanov, A; Derenchuk, V P; Kaiser, H; Leuschner, M B; Lone, M A; Lozowski, W; Nann, H; Von Przewoski, B; Remmes, N; Rinckel, T; Shin, Y; Snow, W M; Sokol, P E

2008-01-01

401

Neutron stars  

NASA Astrophysics Data System (ADS)

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.

Lattimer, James M.

2014-05-01

402

Neutron tubes  

DOEpatents

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.

Leung, Ka-Ngo (Hercules, CA); Lou, Tak Pui (Berkeley, CA); Reijonen, Jani (Oakland, CA)

2008-03-11

403

Superfluidity of $?$ hyperons in neutron stars  

E-print Network

We study the $^1S_0$ superfluidity of $\\Lambda$ hyperons in neutron star matter and neutron stars. We use the relativistic mean field (RMF) theory to calculate the properties of neutron star matter. In the RMF approach, the meson-hyperon couplings are constrained by reasonable hyperon potentials that include the updated information from recent developments in hypernuclear physics. To examine the $^1S_0$ pairing gap of $\\Lambda$ hyperons, we employ several $\\Lambda\\Lambda$ interactions based on the Nijmegen models and used in double-$\\Lambda$ hypernuclei studies. It is found that the maximal pairing gap obtained is a few tenths of a MeV. The magnitude and the density region of the pairing gap are dependent on the $\\Lambda\\Lambda$ interaction and the treatment of neutron star matter. We calculate neutron star properties and find that whether the $^1S_0 $ superfluidity of $\\Lambda$ hyperons exists in the core of neutron stars mainly depends on the $\\Lambda\\Lambda$ interaction used.

Y. N. Wang; H. Shen

2010-02-01

404

Neutron measurements of the OGO-VI Spacecraft  

NASA Technical Reports Server (NTRS)

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.

Lockwood, J. A.

1973-01-01

405

Neutron Star Binaries as Central Engines of GRBs  

E-print Network

We describe the results high resolution, hydrodynamic calculations of neutron star mergers. The model makes use of a new, nuclear equation of state, accounts for multi-flavour neutrino emission and solves the equations of hydrodynamics using the smoothed particle hydrodynamics method with more than $10^6$ particles. The merger leaves behind a strongly differentially rotating central object of $\\sim 2.5$ M$_{\\odot}$ together with a distribution of hot debris material. For the most realistic case of initial neutron star spins, no sign of a collapse to a black hole can be seen. We argue that the differential rotation stabilizes the central object for $\\sim 10^2$ s and leads to superstrong magnetic fields. We find the neutrino emission from the hot debris around the freshly-formed, supermassive neutron star to be substantially lower than predicted previously. Therefore the annihilation of neutrino anti-neutrino pairs will have difficulties to power very energetic bursts ($\\gg 10^{49}$ erg).

S. Rosswog

2002-04-29

406

Schwinger pair production at finite temperature in scalar QED  

NASA Astrophysics Data System (ADS)

In scalar QED we study the Schwinger pair production from an initial ensemble of charged bosons when an electric field is turned on for a finite period together with or without a constant magnetic field. The scalar QED Hamiltonian depends on time through the electric field, which causes the initial ensemble of bosons to evolve out of equilibrium. Using the Liouville von Neumann method for the density operator and quantum states for each momentum mode, we calculate the Schwinger pair-production rate at finite temperature, which is the pair-production rate from the vacuum times a thermal factor of the Bose-Einstein distribution.

Kim, Sang Pyo; Lee, Hyun Kyu

2007-12-01

407

Schwinger Pair Production at Finite Temperature in Scalar QED  

E-print Network

In scalar QED we study the Schwinger pair production from an initial ensemble of charged bosons when an electric field is turned on for a finite period together with or without a constant magnetic field. The scalar QED Hamiltonian depends on time through the electric field, which causes the initial ensemble of bosons to evolve out of equilibrium. Using the Liouville-von Neumann method for the density operator and quantum states for each momentum mode, we calculate the Schwinger pair-production rate at finite temperature, which is the pair-production rate from the vacuum times a thermal factor of the Bose-Einstein distribution.

Kim, Sang Pyo

2007-01-01

408

Schwinger Pair Production at Finite Temperature in Scalar QED  

E-print Network

In scalar QED we study the Schwinger pair production from an initial ensemble of charged bosons when an electric field is turned on for a finite period together with or without a constant magnetic field. The scalar QED Hamiltonian depends on time through the electric field, which causes the initial ensemble of bosons to evolve out of equilibrium. Using the Liouville-von Neumann method for the density operator and quantum states for each momentum mode, we calculate the Schwinger pair-production rate at finite temperature, which is the pair-production rate from the vacuum times a thermal factor of the Bose-Einstein distribution.

Sang Pyo Kim; Hyun Kyu Lee

2007-06-15

409

Schwinger pair production at finite temperature in scalar QED  

SciTech Connect

In scalar QED we study the Schwinger pair production from an initial ensemble of charged bosons when an electric field is turned on for a finite period together with or without a constant magnetic field. The scalar QED Hamiltonian depends on time through the electric field, which causes the initial ensemble of bosons to evolve out of equilibrium. Using the Liouville-von Neumann method for the density operator and quantum states for each momentum mode, we calculate the Schwinger pair-production rate at finite temperature, which is the pair-production rate from the vacuum times a thermal factor of the Bose-Einstein distribution.

Kim, Sang Pyo; Lee, Hyun Kyu [Department of Physics, Kunsan National University, Kunsan 573-701, Korea, and Asia Pacific Center for Theoretical Physics, Pohang 790-784 (Korea, Republic of); Department of Physics and BK21 Division of Advanced Research and Education in Physics, Hanyang University, Seoul 133-792 (Korea, Republic of) and Asia Pacific Center for Theoretical Physics, Pohang 790-784 (Korea, Republic of)

2007-12-15

410

Neutrons for Catalysis Neutrons as  

E-print Network

enzymes: biomimetic catalysts rational catalyst design process development development of non-precious metal catalysts with superior performance #12;Neutrons as microscopic probes in heterogeneous catalysis catalyst structure #12;Selected items from the BES report relevant to the use of neutrons: 2. Design

Pennycook, Steve

411

Gamma-ray spectra from neutron capture on Sr  

Microsoft Academic Search

The gamma-ray spectrum following neutron capture on Sr was measured at 3 neutron energies: E\\/sub n\\/ = thermal, 2 keV, and 24 keV. Gamma rays were detected in a three-crystal Ge(Li)-NaI-NaI pair spectrometer. Gamma-ray intensities deduced from these spectra by spectral unfolding are presented.

R. E. Sullivan; J. A. Becker; M. L. Stelts

1981-01-01

412

Photon-neutron correlations and microscopic description of alpha decay  

Microsoft Academic Search

The influence of proton-neutron correlations upon the formation of alpha particles is studied within the framework of a generalized BCS approach in an axially deformed Woods-Saxon potential. The enhancement of the total alpha-decay width in the two extreme cases of large and small difference between the number of proton and neutron pairs is estimated.

D. S. Delion; A. Insolia; R. J. Liotta

1992-01-01

413

Measuring the Neutron's Mean Square Charge Radius Using Neutron Interferometry  

E-print Network

The neutron is electrically neutral, but its substructure consists of charged quarks so it may have an internal charge distribution. In fact it is known to have a negative mean square charge radius (MSCR), the second moment of the radial charge density. In other words the neutron has a positive core and negative skin. In the first Born approximation the neutron MSCR can be simply related to the neutron-electron scattering length b_ne. In the past this important quantity has been extracted from the energy dependence of the total transmission cross-section of neutrons on high-Z targets, a very difficult and complicated process. A few years ago S.A. Werner proposed a novel approach to measuring b_ne from the neutron's dynamical phase shift in a perfect crystal close to the Bragg condition. We are conducting an experiment based on this method at the NIST neutron interferometer which may lead to a five-fold improvement in precision of b_ne and hence the neutron MSCR.

F. E. Wietfeldt; M. Huber; T. C. Black; H. Kaiser; M. Arif; D. L. Jacobson; S. A. Werner

2005-09-14

414

Pair Cascades and Deathlines in Magnetic Fields with Offset Polar Caps  

NASA Technical Reports Server (NTRS)

We present results of electron-positron pair cascade simulations in a dipole magnetic field whose polar cap is offset from the dipole axis. In such a field geometry, the polar cap is displaced a small fraction of the neutron star radius from the star symmetry axis and the field line radius of curvature is modified. Using the modified parallel electric field near the offset polar cap, we simulate pair cascades to determine the pair deathlines and pair multiplicities as a function of the offset. We find that the pair multiplicity can change dr;unatically 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. The results have some important implications for pulsar particle production, high-energy emission and cosmic-ray contribution.

Harding, Alice K.; Muslimov, Alex G.

2012-01-01

415

The structure of molten CaSiO3: A neutron diffraction isotope substitution and aerodynamic levitation study.  

SciTech Connect

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.

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

416

Rotational-translational fourier imaging system requiring only one grid pair  

NASA Technical Reports Server (NTRS)

The sky contains many active sources that emit X-rays, gamma rays, and neutrons. Unfortunately hard X-rays, gamma rays, and neutrons cannot be imaged by conventional optics. This obstacle led to the development of Fourier imaging systems. In early approaches, multiple grid pairs were necessary in order to create rudimentary Fourier imaging systems. At least one set of grid pairs was required to provide multiple real components of a Fourier derived image, and another set was required to provide multiple imaginary components of the image. It has long been recognized that the expense associated with the physical production of the numerous grid pairs required for Fourier imaging was a drawback. Herein one grid pair (two grids), with accompanying rotation and translation, can be used if one grid has one more slit than the other grid, and if the detector is modified.

Campbell, Jonathan W. (Inventor)

2006-01-01

417

NEUTRON DIFFRACTION ANALYSIS OF CYTOCHROME b5 RECONSTITUTED IN DEUTERATED LIPID MULTILAYERS  

E-print Network

NEUTRON DIFFRACTION ANALYSIS OF CYTOCHROME b5 RECONSTITUTED IN DEUTERATED LIPID MULTILAYERS E. P centrosymmetric pairs of asymmetric lipid-protein bilayers. Lamellar neutron diffraction data were collected. A neutron diffraction analysis ofcytochrome b5, incorporated into ordered lipid multilayers, promised

418

Observation of forward neutrons from the break-up of the 11Li neutron halo  

NASA Astrophysics Data System (ADS)

The cross-sections and forward angular distributions of fast neutrons have been studied for the reaction ( 11Li, 9Li) at 29 MeV/u on targets of Be, Ni and Au. The cross-sections are large and arise essentially from peripheral reactions. The angular distributions of the neutrons are very narrow and indicate the existence of a neutron halo with radius of about 12 fm.

Anne, R.; Arnell, S. E.; Bimbot, R.; Emling, H.; Guillemaud-Mueller, D.; Hansen, P. G.; Johannsen, L.; Jonson, B.; Lewitowicz, M.; Mattsson, S.; Mueller, A. C.; Neugart, R.; Nyman, G.; Pougheon, F.; Richter, A.; Riisager, K.; Saint-Laurent, M. G.; Schrieder, G.; Sorlin, O.; Wilhelmsen, K.

1990-11-01

419

Particle Acceleration in Pair-Starved Pulsars  

E-print Network

We investigate the physical situation above the pulsar polar cap (PC) where the accelerating primaries (electrons) are not capable of producing sufficient numbers of electron-positron pairs at low altitudes (within 1-2 stellar radii above the PC surface) to screen the accelerating electric field, and continue accelerating up to, at least, very high altitudes nearly approaching the light cylinder. We derive an analytic solution for the parallel electric field valid at high altitudes. The solution is based on the physical condition of asymptotic vanishing of the rotationally induced transverse electric field within the magnetic flux tube. This condition constrains the asymptotic value of the effective space charge that determines the distribution of the parallel electric field within the magnetic tube. Our estimates of low- to high-altitude values of the parallel electric field imply the occurrence of a regime of primary acceleration (with the characteristic Lorentz factor up to 1-2 X 10^7) all the way from the PC to the light cylinder limited by curvature-radiation reaction. In this model the primary outflow becomes asymptotically force-free, and may turn into a relativistic wind beyond the light cylinder. Such a solution will apply to both older pulsars producing only inverse Compton scattering pairs and younger very high B pulsars (magnetars). We suggest that pulsars, which are lying below the pair death line, may be radio-quiet gamma-ray sources.

Alex G. Muslimov; Alice K. Harding

2004-08-20

420

Invariant-mass distribution of jet pairs produced in association with a $W$ boson in \\ppbar collisions at $\\sqrt{s}=1.96$ TeV using the full CDF Run II data set  

E-print Network

We report on a study of the dijet invariant-mass distribution in events with one identified lepton, a significant imbalance in the total event transverse momentum, and two jets. This distribution is sensitive to the possible production of a new particle in association with a $W$ boson, where the boson decays leptonically. We use the full data set of proton-antiproton collisions at 1.96 TeV center-of-mass energy collected by the Collider Detector at the Fermilab Tevatron and corresponding to an integrated luminosity of 8.9 fb$^{-1}$. The data are found to be consistent with standard-model expectations, and a 95$\\%$ confidence level upper limit is set on the cross section for a $W$ boson produced in association with a new particle decaying into two jets.

T. Aaltonen

2014-02-27

421

Invariant-mass distribution of jet pairs produced in association with a W boson in pp ¯ collisions at ?s =1.96 TeV using the full CDF Run II data set  

NASA Astrophysics Data System (ADS)

We report on a study of the dijet invariant-mass distribution in events with one identified lepton, a significant imbalance in the total event transverse momentum, and two jets. This distribution is sensitive to the possible production of a new particle in association with a W boson, where the boson decays leptonically. We use the full data set of proton-antiproton collisions at 1.96 TeV center-of-mass energy collected by the Collider Detector at the Fermilab Tevatron, corresponding to an integrated luminosity of 8.9 fb-1. The data are found to be consistent with standard model expectations, and a 95% confidence level upper limit is set on the production cross section of a W boson in association with a new particle decaying into two jets.

Aaltonen, T.; Amerio, S.; Amidei, D.; Anastassov, A.; Annovi, A.; Antos, J.; Apollinari, G.; Appel, J. A.; Arisawa, T.; Artikov, A.; Asaadi, J.; Ashmanskas, W.; Auerbach, B.; Aurisano, A.; Azfar, F.; Badgett, W.; Bae, T.; Barbaro-Galtieri, A.; Barnes, V. E.; Barnett, B. A.; Barria, P.; Bartos, P.; Bauce, M.; Bedeschi, F.; Behari, S.; Bellettini, G.; Bellinger, J.; Benjamin, D.; Beretvas, A.; Bhatti, A.; Bland, K. R.; Blumenfeld, B.; Bocci, A.; Bodek, A.; Bortoletto, D.; Boudreau, J.; Boveia, A.; Brigliadori, L.; Bromberg, C.; Brucken, E.; Budagov, J.; Budd, H. S.; Burkett, K.; Busetto, G.; Bussey, P.; Butti, P.; Buzatu, A.; Calamba, A.; Camarda, S.; Campanelli, M.; Canelli, F.; Carls, B.; Carlsmith, D.; Carosi, R.; Carrillo, S.; Casal, B.; Casarsa, M.; Castro, A.; Catastini, P.; Cauz, D.; Cavaliere, V.; Cavalli-Sforza, M.; Cerri, A.; Cerrito, L.; Chen, Y. C.; Chertok, M.; Chiarelli, G.; Chlachidze, G.; Cho, K.; Chokheli, D.; Clark, A.; Clarke, C.; Convery, M. E.; Conway, J.; Corbo, M.; Cordelli, M.; Cox, C. A.; Cox, D. J.; Cremonesi, M.; Cruz, D.; Cuevas, J.; Culbertson, R.; d'Ascenzo, N.; Datta, M.; de Barbaro, P.; Demortier, L.; Deninno, M.; D'Errico, M.; Devoto, F.; Di Canto, A.; Di Ruzza, B.; Dittmann, J. R.; Donati, S.; D'Onofrio, M.; Dorigo, M.; Driutti, A.; Ebina, K.; Edgar, R.; Elagin, A.; Erbacher, R.; Errede, S.; Esham, B.; Farrington, S.; Fernández Ramos, J. P.; Field, R.; Flanagan, G.; Forrest, R.; Franklin, M.; Freeman, J. C.; Frisch, H.; Funakoshi, Y.; Galloni, C.; Garfinkel, A. F.; Garosi, P.; Gerberich, H.; Gerchtein, E.; Giagu, S.; Giakoumopoulou, V.; Gibson, K.; Ginsburg, C. M.; Giokaris, N.; Giromini, P.; Giurgiu, G.; Glagolev, V.; Glenzinski, D.; Gold, M.; Goldin, D.; Golossanov, A.; Gomez, G.; Gomez-Ceballos, G.; Goncharov, M.; González López, O.; Gorelov, I.; Goshaw, A. T.; Goulianos, K.; Gramellini, E.; Grinstein, S.; Grosso-Pilcher, C.; Group, R. C.; Guimaraes da Costa, J.; Hahn, S. R.; Han, J. Y.; Happacher, F.; Hara, K.; Hare, M.; Harr, R. F.; Harrington-Taber, T.; Hatakeyama, K.; Hays, C.; Heinrich, J.; Herndon, M.; Hocker, A.; Hong, Z.; Hopkins, W.; Hou, S.; Hughes, R. E.; Husemann, U.; Hussein, M.; Huston, J.; Introzzi, G.; Iori, M.; Ivanov, A.; James, E.; Jang, D.; Jayatilaka, B.; Jeon, E. J.; Jindariani, S.; Jones, M.; Joo, K. K.; Jun, S. Y.; Junk, T. R.; Kambeitz, M.; Kamon, T.; Karchin, P. E.; Kasmi, A.; Kato, Y.; Ketchum, W.; Keung, J.; Kilminster, B.; Kim, D. H.; Kim, H. S.; Kim, J. E.; Kim, M. J.; Kim, S. H.; Kim, S. B.; Kim, Y. J.; Kim, Y. K.; Kimura, N.; Kirby, M.; Knoepfel, K.; Kondo, K.; Kong, D. J.; Konigsberg, J.; Kotwal, A. V.; Kreps, M.; Kroll, J.; Kruse, M.; Kuhr, T.; Kurata, M.; Laasanen, A. T.; Lammel, S.; Lancaster, M.; Lannon, K.; Latino, G.; Lee, H. S.; Lee, J. S.; Leo, S.; Leone, S.; Lewis, J. D.; Limosani, A.; Lipeles, E.; Lister, A.; Liu, H.; Liu, Q.; Liu, T.; Lockwitz, S.; Loginov, A.; Lucchesi, D.; Lucà, A.; Lueck, J.; Lujan, P.; Lukens, P.; Lungu, G.; Lys, J.; Lysak, R.; Madrak, R.; Maestro, P.; Malik, S.; Manca, G.; Manousakis-Katsikakis, A.; Marchese, L.; Margaroli, F.; Marino, P.; Martínez, M.; Matera, K.; Mattson, M. E.; Mazzacane, A.; Mazzanti, P.; McNulty, R.; Mehta, A.; Mehtala, P.; Mesropian, C.; Miao, T.; Mietlicki, D.; Mitra, A.; Miyake, H.; Moed, S.; Moggi, N.; Moon, C. S.; Moore, R.; Morello, M. J.; Mukherjee, A.; Muller, Th.; Murat, P.; Mussini, M.; Nachtman, J.; Nagai, Y.; Naganoma, J.; Nakano, I.; Napier, A.; Nett, J.; Neu, C.; Nigmanov, T.; Nodulman, L.; Noh, S. Y.; Norniella, O.; Oakes, L.; Oh, S. H.; Oh, Y. D.; Oksuzian, I.; Okusawa, T.; Orava, R.; Ortolan, L.; Pagliarone, C.; Palencia, E.; Palni, P.; Papadimitriou, V.; Parker, W.; Pauletta, G.; Paulini, M.; Paus, C.; Phillips, T. J.; Piacentino, G.; Pianori, E.; Pilot, J.; Pitts, K.; Plager, C.; Pondrom, L.; Poprocki, S.; Potamianos, K.; Pranko, A.; Prokoshin, F.; Ptohos, F.; Punzi, G.; Ranjan, N.; Redondo Fernández, I.; Renton, P.; Rescigno, M.; Rimondi, F.; Ristori, L.; Robson, A.; Rodriguez, T.; Rolli, S.; Ronzani, M.; Roser, R.; Rosner, J. L.; Ruffini, F.; Ruiz, A.; Russ, J.; Rusu, V.; Sakumoto, W. K.; Sakurai, Y.; Santi, L.; Sato, K.; Saveliev, V.; Savoy-Navarro, A.; Schlabach, P.; Schmidt, E. E.; Schwarz, T.; Scodellaro, L.; Scuri, F.; Seidel, S.; Seiya, Y.; Semenov, A.; Sforza, F.; Shalhout, S. Z.; Shears, T.; Shepard, P. F.; Shimojima, M.; Shochet, M.; Shreyber-Tecker, I.; Simonenko, A.; Sliwa, K.; Smith, J. R.; Snider, F. D.; Song, H.; Sorin, V.; St. Denis, R.; Stancari, M.; Stentz, D.; Strologas, J.; Sudo, Y.; Sukhanov, A.; Suslov, I.; Takemasa, K.; Takeuchi, Y.; Tang, J.; Tecchio, M.; Teng, P. K.; Thom, J.; Thomson, E.; Thukral, V.; Toback, D.; Tokar, S.; Tollefson, K.; Tomura, T.; Tonelli, D.; Torre, S.; Torretta, D.; Totaro, P.; Trovato, M.; Ukegawa, F.; Uozumi, S.; Velev, G.; Vellidis, C.

2014-05-01

422

The neutron imaging diagnostic at NIF (invited)  

SciTech Connect

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

Merrill, F. E.; Clark, D. D.; Danly, C. R.; Drury, O. B.; Fatherley, V. E.; Gallegos, R.; Grim, G. P.; Guler, N.; Loomis, E. N.; Martinson, D. D.; Mares, D.; Morley, D. J.; Morgan, G. L.; Oertel, J. A.; Tregillis, I. L.; Volegov, P. L.; Wilde, C. H.; Wilson, D. C. [Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States); Bower, D.; Dzenitis, J. M. [Livermore National Laboratory, Livermore, California 94550 (United States); and others

2012-10-15

423

The neutron imaging diagnostic at NIF (invited).  

PubMed

A neutron imaging diagnostic has recently been commissioned at the National Ignition Facility (NIF). This new system is an important diagnostic tool for inertial fusion studies at the NIF for measuring the size and shape of the burning DT plasma during the ignition stage of Inertial Confinement Fusion (ICF) implosions. The imaging technique utilizes a pinhole neutron aperture, placed between the neutron source and a neutron detector. The detection system measures the two dimensional distribution of neutrons passing through the pinhole. This diagnostic has been designed to collect two images at two times. The long flight path for this diagnostic, 28 m, results in a chromatic separation of the neutrons, allowing the independently timed images to measure the source distribution for two neutron energies. Typically the first image measures the distribution of the 14 MeV neutrons and the second image of the 6-12 MeV neutrons. The combination of these two images has provided data on the size and shape of the burning plasma within the compressed capsule, as well as a measure of the quantity and spatial distribution of the cold fuel surrounding this core. PMID:23126843

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

2012-10-01

424

The Neutron Imaging Diagnostic at NIF  

SciTech Connect

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.

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

425

Neutron range spectrometer  

DOEpatents

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.

Manglos, S.H.

1988-03-10

426

Neutrino emissivity from Goldstone boson decay in magnetized neutron matter  

NASA Astrophysics Data System (ADS)

Neutron matter at densities somewhat above nuclear densities is believed to be superfluid due to the condensation of neutron pairs in the 3P2 channel. This condensate breaks rotational symmetry spontaneously and leads to the existence of Goldstone bosons (angulons). We show that the coupling to magnetic fields mediated by the magnetic moment of the neutron makes angulons massive and capable of decaying into a neutrino-antineutrino pair. We compute the rate for this process and argue they become competitive with other cooling processes for temperatures around 107 K as long as the interior magnetic field of the star is in the B ?1015 G range or above.

Bedaque, Paulo; Sen, Srimoyee

2014-03-01

427

An accurate paired sample test for count data  

PubMed Central

Motivation: Recent technology platforms in proteomics and genomics produce count data for quantitative analysis. Previous works on statistical significance analysis for count data have mainly focused on the indepen