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EMPIRE ULTIMATE EXPANSION: RESONANCES AND COVARIANCES.

Description: The EMPIRE code system is being extended to cover the resolved and unresolved resonance region employing proven methodology used for the production of new evaluations in the recent Atlas of Neutron Resonances. Another directions of Empire expansion are uncertainties and correlations among them. These include covariances for cross sections as well as for model parameters. In this presentation we concentrate on the KALMAN method that has been applied in EMPIRE to the fast neutron range as well as to the resonance region. We also summarize role of the EMPIRE code in the ENDF/B-VII.0 development. Finally, large scale calculations and their impact on nuclear model parameters are discussed along with the exciting perspectives offered by the parallel supercomputing.
Date: April 22, 2007
Creator: HERMAN,M.; MUGHABGHAB, S.F.; OBLOZINSKY, P.; ROCHMAN, D.; PIGNI, M.T.; KAWANO, T. et al.
Partner: UNT Libraries Government Documents Department

EVALUATION OF TUNGSTEN ISOTOPES IN THE FAST NEUTRON RANGE INCLUDING CROSS-SECTION COVARIANCE ESTIMATION.

Description: New evaluations for the tungsten isotopes {sup 180,182,183,184,186}W in the neutron energy range up to 60 MeV were produced. In the resonance range only minor adjustments to the resonance parameters were made due to a lack of adequate experimental data. Evaluations in the fast energy region were based on nuclear model calculations using the EMPIRE-2.19 code. Recently derived dispersive coupled-channel optical model potentials for W and Ta isotopes were instrumental to achieve a very good description of the available microscopic cross-section database. Model covariance data were generated with the Monte Carlo technique to produce a prior estimate for the covariance matrix. Experimental data were introduced through the GANDR system. The evaluated files were tested on selected fusion neutronics benchmarks and showed marked improvement compared to other existing evaluations.
Date: April 22, 2007
Creator: CAPOTE,R.; SIN, M.; TRKOV, A.; HERMAN, M.; CARLSON, B.V. & OBLOZINSKY, P.
Partner: UNT Libraries Government Documents Department

AN OVERVIEW OF NEUTRINO MASSES AND MIXING IN SO(10) MODELS.

Description: We review in this talk various SUSY SO(10) models. Specifically, we discuss how small neutrino masses are generated in and generic predictions of different SO(10) models. A comparison of the predictions of these models for sin{sup 2} {theta}{sub 13}is given.
Date: June 5, 2003
Creator: CHEN,M. C. MAHANTHAPPA,K. T.
Partner: UNT Libraries Government Documents Department

Gamma-ray production cross sections from neutron interactions with iron.

Description: The initial purpose of this experiment was to provide a consistent data base of neutron-induced gamma-ray production cross sections over a large energy range for use in estimating elemental composition of the martian surface by observing gamma rays produced by cosmic ray interactions on the planet's surface [Bo02]. However, these data should be useful for other projects such as oil-well logging, accelerator transmutation of nuclear waste, shielding calculations, gamma-ray heating for nuclear reactors and verification of nuclear model calculations and databases. The goal of the measurements was to collect data on the strongest gamma rays from many samples of interest. Because of the available beam time this meant that many of the measurcments were rather short. Despite the short running time the large samples used and the good beam intensity resulted in very satisfactory results. The samples, chosen mainly as common constituents of rock and soil and measured in the same few week period, include: B&, BN, C, Al, Mg, Si, S, Cay Ti, Cr, Mn, and Fe. Be was also used as a neutron scatterer that only produces one gamma ray (478 keV from 7Li) with appreciable intensity. Thus Be can serve as a measure of neutron-induced backgrounds. In this first paper we present results for Fe.
Date: January 1, 2002
Creator: Nelson, R. O. (Ronald O.); Laymon, C. M. (Charles M.); Wender, S. A. (Stephen A.); Drake, D. M. (Darrell M.); Drosg, Manfred; Bobias, S. G. (S. George) et al.
Partner: UNT Libraries Government Documents Department

{sup 7}Li(p,n) NUCLEAR DATA LIBRARY FOR INCIDENT PROTON ENERGIES TO 150 MEV

Description: Researchers at Los Alamos National Laboratory are considering the possibility of using the Low Energy Demonstration Accelerator (LEDA), constructed at LANSCE for the Accelerator Production of Tritium program (APT), as a neutron source. Evaluated nuclear data are needed for the p+{sup 7}Li reaction, to predict neutron production from thin and thick lithium targets. In this report we describe evaluation methods that make use of experimental data, and nuclear model calculations, to develop an ENDF-formatted data library for incident protons with energies up to 150 MeV. The important {sup 7}Li(p,n{sub 0}) and {sup 7}Li(p,n{sub 1}) reactions are evaluated from the experimental data, with their angular distributions represented using Lengendre polynomial expansions. The decay of the remaining reaction flux is estimated from GNASH nuclear model calculations. This leads to the emission of lower-energy neutrons and other charged particles and gamma-rays from preequilibrium and compound nucleus decay processes. The evaluated ENDF-data are described in detail, and illustrated in numerous figures. We also illustrate the use of these data in a representative application by a radiation transport simulation with the code MCNPX.
Date: November 1, 2000
Creator: MASHNIK, S. & AL, ET
Partner: UNT Libraries Government Documents Department

Ternary particles with extreme N/Z ratios from neutron-induced fission

Description: The existing ternary fission models can well reproduce the yields of the most abundant light charged particles. However, these models tend to significantly overestimate the yields of ternary particles with an extreme N/Z ratio: {sup 3}He, {sup 11}Li, {sup 14}Be, etc. The experimental yields of these isotopes were investigated with the recoil separator LOHENGRIN down to a level of 10{sup {minus}10} per fission. Results from the fissioning systems {sup 233}U (n{sub th}, f), {sup 235}U(n{sub th},f), {sup 239}Pu(n{sub th},f) {sup 241}Pu(n{sub th},f) and {sup 245}Cm(n{sub th},f) are presented and the implications for the ternary fission models are discussed.
Date: May 16, 2000
Creator: Koster, U.; Faust, H.; Friedrichs, T.; Oberstedt, S.; Fioni, G.; Grob, M. et al.
Partner: UNT Libraries Government Documents Department

THE MBX CHALLENGE COMPETITION: A NEUTRON MATTER MODEL

Description: The Bertsch, non-parametric model of neutron matter is analyzed and strong indications are found that, in the infinite system limit, the ground state is a Fermi liquid with an effective mass, except for a set of measure zero.
Date: November 1, 1999
Creator: BAKER, G.
Partner: UNT Libraries Government Documents Department

Measurement of the deuteron elastic structure functions up to large momentum transfers

Description: The cross section for elastic electron-deuteron scattering was measured in JLab experiment 91-026. The deuteron elastic structure functions A(Q{sup 2}) and B(Q{sup 2}) have been extracted from this data. The final results for the ``electric'' structure function A(Q{sup 2}), in the range of 0.7 less than or equal to Q{sup 2} less than or equal to 6.0 (GeV/c){sup 2} are presented. Preliminary results for the ``magnetic'' structure function B(Q{sup 2}) are presented in the range of 0.7 less than or equal to Q{sup 2} less than or equal to 1.35 (GeV/c){sup 2}. These data are compared with theoretical predictions of both meson-nucleon and quark-gluon based models.
Date: February 1, 1999
Creator: de Jager, Kees
Partner: UNT Libraries Government Documents Department

Analysis of nucleon-induced fission cross sections of lead and bismuth at energies from 45 to 500 MeV

Description: In order to investigate the applicability of the Cascade-Exciton model (CEM) of nuclear reactions to fission cross sections and hoping to learn more about intermediate-energy fission, the authors use an extended version of the CEM, as realized in the code CEM95 to perform a detailed analysis of proton- and neutron-induced fission cross sections of {sup 209}Bi and {sup 208}Pb nuclei and of the linear momentum transfer to the fissioning nuclei in the 45--500 meV energy range.
Date: August 1, 1998
Creator: Prokofyev, A.V.; Mashnik, S.G. & Sierk, A.J.
Partner: UNT Libraries Government Documents Department

Magnetic radius of the deuteron

Description: The root-mean square radius of the deuteron magnetic moment distribution, r{sub Md}, is calculated for several realistic models of the NN-interaction. For the Paris potential the result is r{sub Md} = 2.312 {+-} 0.010 fm. The dependence of r{sub Md} on the choice of NN model, relativistic effects and meson exchange currents is investigated. The experimental value of r{sub Md} is also considered. The necessity of new precise measurements of the deuteron magnetic form factor at low values of Q{sup 2} is stressed.
Date: August 1, 1998
Creator: Afanasev, Andrei; Afanasev, V.D. & Trubnikov, S.V.
Partner: UNT Libraries Government Documents Department

Theory of neutron emission in fission

Description: A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and some examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N(E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are treated in detail for the Los Alamos model. Recent work in the calculation of the prompt fission neutron spectrum matrix N(E, E{sub n}), where E{sub n} is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of the ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches. This paper is an extension of a similar paper presented at the International Centre for Theoretical Physics in 1996.
Date: August 1998
Creator: Madland, D. G.
Partner: UNT Libraries Government Documents Department

Interaction, currents and the electromagnetic structure of light nuclei

Description: The authors discuss the traditional model of the nucleus as a system of nucleons interacting via effective interactions and currents, and present results obtained within this framework for the electromagnetic structure of the ground- and low-lying-states of A=3-6 nuclei.
Date: June 1, 1998
Creator: L.E. Marcucci, R. Schiavilla
Partner: UNT Libraries Government Documents Department

Status of effective field theory of NN scattering

Description: There exist many nucleon-nucleon potentials which reproduce phase shifts and nuclear properties with remarkable accuracy. Three fundamental features are shared by these potential models: (1) pions are important at long distances, (2) there is a source of intermediate-range attraction, and (3) there is a source of short-distance repulsion. However, in general, distinct physical mechanisms in these models account for the same feature of the nuclear force. Agreement with experiment is maintained in spite of these differences because of the large number of fit parameters. Systematic approaches to the scattering of strongly interacting particles, such as chiral perturbation theory, are based on the ideas of effective field theory (EFT). The author reviews recent progress in developing a systematic power counting scheme for scattering processes involving more than one nucleon.
Date: June 1, 1998
Creator: Beane, S.R.
Partner: UNT Libraries Government Documents Department

Baryon-baryon mixing in hypernuclei

Description: Implications of few-body hypernuclei for the understanding of the baryon-baryon interaction are examined. Octet-octet coupling effects not present in conventional, non strange nuclei are the focus. The need to identify strangeness {minus}2 hypernuclei to test model predictions is emphasized.
Date: May 1998
Creator: Gibson, B. F.
Partner: UNT Libraries Government Documents Department

Current status and features of the T-2 Nuclear Information Service

Description: This service is run by Group T-2 (Nuclear Theory and Applications) of the Theoretical Division of the Los Alamos National Laboratory, which is operated by the University of California for the US Department of Energy. The author works on nuclear modeling, nuclear data, cross sections, nuclear masses, ENDF, NJOY data processing, nuclear astrophysics, radioactivity, radiation shielding, data for medical radiotherapy, data for high-energy accelerator applications, data and codes for fission and fusion systems, and more. For an introduction to the field of nuclear data and his site, take his Guided Tour. Much of this information can also be accessed using anonymous ftp t2.lanl.gov.
Date: April 24, 1998
Creator: MacFarlane, R.E.
Partner: UNT Libraries Government Documents Department

Extended direct-semidirect mechanism and the role of multistep processes in fast-nucleon radiative capture

Description: The authors have recently developed an extension of the direct semidirect (DSD) radiative capture model to unstable final stages and have confirmed its utility in explaining the spectrum of {gamma} rays from capture of polarized 19.6 MeV protons on {sup 89}Y. It was found that the extended DSD model, supplemented by a Hauser Feshbach contribution, successfully explains the observed {gamma} spectra, angular distributions, and analyzing powers, without requiring additional mechanisms, such as precompound or multistep emission, or nucleon-nucleon bremsstrahlung. In this contribution they show that the model also successfully explains data at higher energies (34 MeV incident protons), and that there is no need for additional contributions other than Hauser-Feshbach at this energy as well.
Date: March 1, 1998
Creator: Dietrich, F.S.; Chadwick, M.B. & Kerman, A.K.
Partner: UNT Libraries Government Documents Department

Modeling (p,xn) reactions producing proton-rich nuclides for radioactive ion beam studies

Description: Over the last few years, an intense worldwide interest has grown in the use of radioactive ion beams (RIB) to study the properties of nuclei far from stability. The relatively recent technological developments that have enabled the production of high-quality radioactive beams promise to lead to a renaissance in nuclear structure and nuclear reaction physics, as well as nuclear astrophysics. Group T-2 at Los Alamos has been working with US Nuclear Reaction Data Network Radioactive Ion Beam Task Force to address RIB nuclear data needs. The current focus is nuclear data needed to guide the choice of targets for the production of various radioactive product species using the isotope-separation on line (ISOL) method; future work will include the study of RIB nuclear reaction and structure physics. Laboratories that are undertaking RIB studies with the ISOL method in the US are principally Oak Ridge National Laboratory (ORNL) and Argonne National Laboratory (ANL).
Date: March 1, 1998
Creator: Chadwick, M.B. & Young, P.G.
Partner: UNT Libraries Government Documents Department

Two-component multistep direct reactions: A microscopic approach

Description: The authors present two principal advances in multistep direct theory: (1) A two-component formulation of multistep direct reactions, where neutron and proton excitations are explicitly accounted for in the evolution of the reaction, for all orders of scattering. While this may at first seem to be a formidable task, especially for multistep processes where the many possible reaction pathways becomes large in a two-component formalism, the authors show that this is not so -- a rather simple generalization of the FKK convolution expression 1 automatically generates these pathways. Such considerations are particularly relevant when simultaneously analyzing both neutron and proton emission spectra, which is always important since these processes represent competing decay channels. (2) A new, and fully microscopic, method for calculating MSD cross sections which does not make use of particle-hole state densities but instead directly calculates cross sections for all possible particle-hole excitations (again including an exact book-keeping of the neutron/proton type of the particle and hole at all stages of the reaction) determined from a simple non-interacting shell model. This is in contrast to all previous numerical approaches which sample only a small number of such states to estimate the DWBA strength, and utilize simple analytical formulae for the partial state density, based on the equidistant spacing model. The new approach has been applied, along with theories for multistep compound, compound, and collective reactions, to analyze experimental emission spectra for a range of targets and energies. The authors show that the theory correctly accounts for double-differential nucleon spectra.
Date: March 1, 1998
Creator: Koning, A.J. & Chadwick, M.B.
Partner: UNT Libraries Government Documents Department

What invariant one-particle multiplicity distributions and two-particle correlations are telling us about relativistic heavy-ion collisions

Description: The authors have used a nine-parameter expanding source model that includes special relativity, quantum statistics, resonance decays, and freeze-out on a realistic hypersurface in spacetime to analyze in detail invariant {pi}{sup +}, K{sup +}, and K{sup {minus}} one-particle multiplicity distributions and {pi}{sup +} and {pi}{sup {minus}} two-particle correlations in nearly central collisions of Pb + Pb at p{sub lab}/A = 158 GeV/c. These studies confirm an earlier conclusion for nearly central collisions of Si + Au at p{sub lab}/A = 14.6 GeV/c that the freeze-out temperature is less than 100 meV and that both the longitudinal and transverse collective velocities -- which are anti-correlated with the temperature -- are substantial. The authors also reconciled their current results with those of previous analyses that yielded a much higher freeze-out temperature of approximately 140 meV for both Pb + Pb collisions at p{sub lab}/A = 158 GeV/c and other reactions. One type of analysis was based upon the use of a heuristic equation that neglects relativity to extrapolate slope parameters to zero particle mass. Another type of analysis utilized a thermal model in which there was an accumulation of effects from several approximations. The future should witness the arrival of much new data on invariant one-particle multiplicity distributions and two-particle correlations as functions of bombarding energy and/or size of the colliding nuclei. The proper analysis of these data in terms of a realistic model could yield accurate values for the density, temperature, collective velocity, size, and other properties of the expanding matter as it freezes out into a collection of noninteracting hadrons. A sharp discontinuity in the value of one or more of these properties could conceivably be the long-awaited signal for the formation of a quark-gluon plasma or other new physics.
Date: February 1, 1998
Creator: Nix, J.R.; Strottman, D.; Hecke, H.W. van; Schlei, B.R.; Sullivan, J.P. & Murray, M.J.
Partner: UNT Libraries Government Documents Department

QCD scales and chiral symmetry in finite nuclei

Description: The authors report on this progress in the calculation of nuclear ground-state properties using effective Lagrangians whose construction is constrained by QCD scales and chiral symmetry. Good evidence is found that QCD and chiral symmetry apply to finite nuclei.
Date: October 1, 1997
Creator: Madland, D.G.
Partner: UNT Libraries Government Documents Department

Global economics/energy/environmental (E{sup 3}) modeling of long-term nuclear energy futures

Description: A global energy, economics, environment (E{sup 3}) model has been adopted and modified with a simplified, but comprehensive and multi-regional, nuclear energy module. Using this model, consistent nuclear energy scenarios are constructed. A spectrum of future is examined at two levels in a hierarchy of scenario attributes in which drivers are either external or internal to nuclear energy. Impacts of a range of nuclear fuel-cycle scenarios are reflected back to the higher-level scenario attributes. An emphasis is placed on nuclear materials inventories (in magnitude, location, and form) and their contribution to the long-term sustainability of nuclear energy and the future competitiveness of both conventional and advanced nuclear reactors.
Date: September 1, 1997
Creator: Krakowski, R.A.; Davidson, J.W.; Bathke, C.G.; Arthur, E.D. & Wagner, R.L. Jr.
Partner: UNT Libraries Government Documents Department

{sup 7}Be(p, {gamma}){sup 8}B and the high-energy solar neutrino flux

Description: Despite thirty years of extensive experimental and theoretical work, the predicted solar neutrino flux is still in sharp disagreement with measurements. The solar neutrino measurements strongly suggest that the problem cannot be solved within the standard electroweak and astrophysical theories. Thus, the solar neutrino problem constitutes the strongest evidence for physics beyond the Standard Model. Whatever the solution of the solar neutrino problem turns out to be, it is of paramount importance that the input parameters of the underlying electroweak and solar theories rest upon solid ground. The most uncertain nuclear input parameter in standard solar models is the low-energy {sup 7}Be(p, {gamma}){sup 8}B radiative capture cross section. This reaction produces {sup 8}B in the Sun, whose {beta}{sup +} decay is the main source of the high-energy solar neutrinos. Here, the importance of the {sup 7}Be(p, {gamma}){sup 8}B reaction in predicting the high energy solar neutrino flux is discussed. The author presents a microscopic eight-body model and a potential model for the calculation of the {sup 7}Be(p, {gamma}){sup 8}B cross section.
Date: August 1, 1997
Creator: Csoto, A.
Partner: UNT Libraries Government Documents Department