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Development of global medium-energy nucleon-nucleus optical model potentials

Description: The authors report on the development of new global optical model potentials for nucleon-nucleus scattering at medium energies. Using both Schroedinger and Dirac scattering formalisms, the goal is to construct a physically realistic optical potential describing nucleon-nucleus elastic scattering observables for a projectile energy range of (perhaps) 20 meV to (perhaps) 2 GeV and a target mass range of 16 to 209, excluding regions of strong nuclear deformation. They use a phenomenological approach guided by conclusions from recent microscopic studies. The experimental database consists largely of proton-nucleus elastic differential cross sections, analyzing powers, spin-rotation functions, and total reaction cross sections, and neutron-nucleus total cross sections. They will use this database in a nonlinear least-squares adjustment of optical model parameters in both relativistic equivalent Schroedinger (including relativistic kinematics) and Dirac (second-order reduction) formalisms. Isospin will be introduced through the standard Lane model and a relativistic generalization of that model.
Date: August 1, 1997
Creator: Madland, D.G. & Sierk, A.J.
Partner: UNT Libraries Government Documents Department

Recent progress in the 3N system including three-nucleon forces

Description: A new single Faddeev equation for the inclusion of a three-nucleon force (3NF) into the three-nucleon (3N) continuum and a new partial wave decomposition of a 3NF is presented. This allows for the first time in momentum space calculations the inclusion of a 3NF in higher angular momenta. The authors present converged calculations including a 3NF up to j{sub max} = 6 for the three-nucleon bound state and j{sub max} = 3 in the 3N continuum, where j is the total nucleon-nucleon angular momentum. Several 3N Hamiltonians are generated based on modern nucleon-nucleon (NN) forces and properly adjusted 3NFs, which give the correct triton binding energy. They are used to analyze recent measurements of spin transfer coefficients in elastic nucleon-deuteron scattering. They show that scales with the triton binding energy, whereas K{sub y}{sup z{prime}z{prime}} does not.
Date: July 1, 1997
Creator: Hueber, D.; Witala, H.; Kamada, H.; Nogga, A. & Gloeckle, W.
Partner: UNT Libraries Government Documents Department

Polarization phenomena in few-body systems

Description: Recent polarization studies in N--N scattering at and below 50 MeV have provided specific and significant improvements in the phase-shift parameters. High energy investigations with both polarized proton beams and targets have shown unexpectedly large spin effects, and this provides a challenge for theoretical effort to explain these results. Experimental and theoretical work on the three-nucleon problem continues to yield new and interesting results, with the emphasis now shifting to polarization studies in the breakup reaction. On- going work on several-nucleon systems continues to provide polarization data for general analyses, nuclear structure information, or specific resonance effects. Finally, the basic interaction symmetries continue to have unique and important consequences for polarization observables. 17 figures. (auth)
Date: December 1, 1975
Creator: Conzett, H.E.
Partner: UNT Libraries Government Documents Department

The effect of the new nucleon-nucleus elastic scattering data in LAHET{trademark} Version 2.8 on neutron displacement cross section calculations

Description: The latest release of the medium-energy Monte Carlo transport code LAHET includes a new nucleon-nucleus elastic scattering treatment based on a global medium-energy phenomenological optical-model potential. Implementation of this new model in LAHET allows nuclear elastic scattering for neutrons with energies greater than 15 MeV and for protons with energies greater than 50 MeV. Previous investigations on the impact of the new elastic scattering data revealed that the addition of the proton elastic scattering channel can lead to a significant increase in the calculated damage energy under certain conditions. The authors report here results on the impact of the new elastic scattering data on calculated displacement cross sections in various elements for neutrons with energies in the range 16 to 3,160 MeV. Calculated displacement cross sections at 20 MeV in low-mass materials are in better agreement with SPECTER-calculated cross sections.
Date: October 1, 1997
Creator: Pitcher, E.J.; Ferguson, P.D.; Russell, G.J.; Prael, R.E.; Madland, D.G.; Court, J.D. et al.
Partner: UNT Libraries Government Documents Department

Adaptation of a nucleon-nucleus elastic scattering model for LAHET{trademark}

Description: The LAHET Monte Carlo code for the transport and interaction of nucleons, pions, muons, light ions, and antinucleons has been upgraded by the addition of an elastic scattering model for neutrons above 15 MeV and protons above 50 MeV. Earlier elastic scattering in LAHET has been limited to neutrons below 100 MeV, using a library of elastic optical-model cross sections generated using the Bechetti-Greenlees potential. The new methodology has been adapted from the HERMES code. However, the sampling algorithm for the center-of-mass scattering angle has been completely rewritten, and the elastic cross section data has been replaced below 400 MeV. The new method is viewed as an intermediate step in the effort to provide a library of both elastic and non-elastic cross sections from a global optical-model potential for LAHET usage.
Date: July 1, 1995
Creator: Prael, R.E. & Madland, D.G.
Partner: UNT Libraries Government Documents Department

Processing needs and constraints: neutron data processing

Description: New applications for processed data and increased accuracy requirements have generated needs for change in the Evaluated Nuclear Data Files (ENDF). Some constraints must be removed to allow this growth to take place, but other strong constraints must remain to protect existing users.
Date: January 1, 1980
Creator: MacFarlane, R.E.
Partner: UNT Libraries Government Documents Department

Evaluating fission neutron-multiplicity data

Description: The present work had its origins in the practical need to obtain P[sub [nu]] for the purpose of calculating the theoretical response of instrumentation that used a correlation technique to assay spontaneously fissioning nuclides. The assay results are proportional to the factorial moments calculated with the P[sub [nu]] distribution. Obtaining experimentally derived sets of P[sub [nu]] from many sources reported over several decades led immediately to the problem of evaluating the data: Aside from the trivial problem of sometimes not being properly normalized, the first moments ([nu]) = ([nu]) = [Sigma][nu]P[sub [nu]] were typically not in accord with the best recent evaluations, or the calibration of detector efficiency was based on obsolete values for ([nu]) for supposedly well-characterized standard'' nuclides such as [sup 252]Cf. The problem of evaluating P[sub [nu]] is unusual in that, compared to the usual situation where the quantities being evaluated are single numbers, the P[sub [nu]] are sets of numbers, that moreover, are constrained so that [Sigma]P[sub [nu]][triple bond] 1 and [Sigma][nu] P[sub [nu]] = ([nu]), where ([nu]) is usually determined more accurately from a separate experiment than it can be calculated from the experimentally derived P[sub [nu]] distribution.
Date: January 1, 1992
Creator: Zucker, M.S. & Holden, N.E.
Partner: UNT Libraries Government Documents Department

Investigations of the structure and electromagnetic interactions of few-body systems. Progress report, 1 July 1991--30 June 1994

Description: In order to make it easy for the reader to see the specific research carried out and the progress made, the following report of progress is done by topic. Each item has a format layout of Topic, Investigators, Objective, Significance, and Description of Progress, followed at the end by the relevant references. As is clear from the topics listed, the emphasis of the GW nuclear theory group has been on the structure and electromagnetic interactions of few-body nuclei. Both low- and intermediate-energy electromagnetic disintegration of these nuclei is considered, including coherent photoproduction of {pi} mesons. When the excitation energy of the target nucleus is low, the aim has been to handle the continuum part of the theoretical work numerically with no approximations, that is, by means of full three- or four-body dynamics. When structure questions are the issue, numerically accurate calculations are always carried through, limited only by the underlying two-body or three-body interactions used as input. Implicit in our work is the question of how far one can go within the traditional nuclear physics framework i.e., nucleons and mesons in a nonrelativistic setting. Our central goal is to carry through state-of-the-art few-body calculations that will serve as a means of determining at what point standard nuclear physics requires introduction of relativity and/or quark degrees of freedom in order to understand the phenomena in question. So far, the problems considered were mostly concerned with low- to medium-energy regimes where little evidence was found that requires going beyond the traditional approach.
Date: July 1, 1994
Creator: Lehman, D. R.; Haberzettl, H.; Maximon, L. C.; Parke, W. C.; Bennhold, C.; Ito, Hiroshi et al.
Partner: UNT Libraries Government Documents Department

Charge exchange probes of nuclear structure and interactions with emphasis on (p,n)

Description: New results from (p,n) studies at IUCF show that it is possible to observe Gamow-Teller (GT) strength and extract GT matrix elements from (p,n) measurements. The charge exchange reactions (/sup 6/Li,/sup 6/He) and (..pi../sup +/,..pi../sup 0/) involve different projectile quantum numbers, and the relationships of these reactions to (p,n) is discussed.
Date: January 1, 1980
Creator: Goodman, C.D.
Partner: UNT Libraries Government Documents Department

150-m measurement of 0. 880- to 100. 0-keV neutron transmissions through four samples of /sup 238/U

Description: In order to study the /sup 238/U + n total cross section, neutron transmissions through 0.076-, 0.254-, 1.080-, and 3.620-cm-thick samples of isotopically enriched /sup 238/U have been measured from 0.880 to 100.0 keV using a time-of-flight technique over a path length of 150 meters with the ORELA pulsed source and a 13-mm-thick Li-glass detector. The measurement is described in detail and both a listing and figures of the resulting transmissions are given. An absolute energy scale accurate to 2 parts in 10,000 was established.
Date: October 1, 1977
Creator: Olsen, D. K.; de Saussure, G.; Perez, R. B.; Difilippo, F. C.; Ingle, R. W. & Weaver, H.
Partner: UNT Libraries Government Documents Department

Analysis of neutron data in the resonance region via the computer code SAMMY

Description: Procedures for analysis of resonance neutron cross-section data have been implemented in a state-of-the-art computer code SAMMY, developed at the Oak Ridge Electron Linear Accelerator (ORELA) at Oak Ridge National Laboratory. A unique feature of SAMMY is the use of Bayes' equations to determine ''best'' values of parameters, which permits sequential analysis of data sets (or subsets) while giving the same results as would be given by a simultaneous analysis. Another important feature is the inclusion of data-reduction parameters in the fitting procedure. Other features of SAMMY are also described.
Date: January 1, 1985
Creator: Larson, N.M.
Partner: UNT Libraries Government Documents Department

Consistency of differential and integral thermonuclear neutronics data

Description: To increase the accuracy of the neutronics analysis of nuclear reactors, physicists and engineers have employed a variety of techniques, including the adjustment of multigroup differential data to improve consistency with integral data. Of the various adjustment strategies, a generalized least-squares procedure which adjusts the combined differential and integral data can significantly improve the accuracy of neutronics calculations compared to calculations employing only differential data. This investigation analyzes 14 MeV neutron-driven integral experiments, using a more extensively developed methodology and a newly developed computer code, to extend the domain of adjustment from the energy range of fission reactors to the energy range of fusion reactors.
Date: January 1, 1978
Creator: Reupke, W.A.
Partner: UNT Libraries Government Documents Department

Use of R-matrix methods for light element evaluations

Description: Some general aspects of parameterizing nuclear reaction data with a unitary, multichannel theory are discussed. The special case of R-matrix theory are discussed. The special case of R-matrix theory is considered, where the explicit separation of long- and short-range forces and the natural occurrence of energy pole terms afford a number of advantages in describing data for light-element reactions. Examples are given for both neutron- and charged-particle-induced reactions which illustrate multichannel R-matrix techniques, including the use of charge symmetry to relate data for mirror systems. The limitations of conventional R-matrix methods are discussed briefly.
Date: January 1, 1980
Creator: Hale, G.M.
Partner: UNT Libraries Government Documents Department

Nuclear data and related services

Description: National Nuclear Data Center (NNDC) maintains a number of data bases containing bibliographic information and evaluated as well as experimental nuclear properties. An evaluated computer file maintained by the NNDC, called the Evaluated Nuclear Structure Data File (ENSDF), contains nuclear structure information for all known nuclides. The ENSDF is the source for the journal ''Nuclear Data Sheets'' which is produced and edited by NNDC. The Evaluated Nuclear Data File (ENDF), on the other hand is designed for storage and retrieval of such evaluated nuclear data as are used in neutronic, photonic, and decay heat calculations in a large variety of applications. Some of the publications from these data bases are the Nuclear Wallet Cards, Radioactivity Handbook, and books on neutron cross sections and resonance parameters. In addition, the NNDC maintains three bibliographic files: NSR - for nuclear structure and decay data related references, CINDA - a bibliographic file for neutron induced reactions, and CPBIB - for charged particle reactions. Selected retrievals from evaluated data and bibliographic files are possible on-line or on request from NNDC. 6 refs., 1 fig.
Date: January 1, 1985
Creator: Tuli, J.K.
Partner: UNT Libraries Government Documents Department

Energy-averaged neutron cross sections of fast-reactor structural materials

Description: The status of energy-averaged cross sections of fast-reactor structural materials is outlined with emphasis on U.S. data programs in the neutron-energy range 1-10 MeV. Areas of outstanding accomplishment and significant uncertainty are noted with recommendations for future efforts. Attention is primarily given to the main constituents of stainless steel (e.g., Fe, Ni, and Cr) and, secondarily, to alternate structural materials (e.g., V, Ti, Nb, Mo, Zr). Generally, the mass regions of interest are A approximately 50 to 60 and A approximately 90 to 100. Neutron total and elastic-scattering cross sections are discussed with the implication on the non-elastic-cross sections. Cross sections governing discrete-inelastic-neutron-energy transfers are examined in detail. Cross sections for the reactions (n;p), (n;n',p), (n;..cap alpha..), (n;n',..cap alpha..) and (n;2n') are reviewed in the context of fast-reactor performance and/or diagnostics. The primary orientation of the discussion is experimental with some additional attention to the applications of theory, the problems of evaluation and the data sensitivity of representative fast-reactor systems.
Date: February 1, 1978
Creator: Smith, A.; McKnight, R. & Smith, D.
Partner: UNT Libraries Government Documents Department

Present status of laser driven fusion--fission energy systems

Description: The potential of laser fusion driven hybrids to produce fissile fuel and/or electricity has been investigated in the laser program at the Lawrence Livermore Laboratory (LLL) for several years. Our earlier studies used neutronic methods of analysis to estimate hybrid performance. The results were encouraging, but it was apparent that a more accurate assessment of the hybrid's potential would require studies which treat the engineering, environmental, and economic issues as well as the neutronic aspects. More recently, we have collaborated with Bechtel and Westinghouse Corporations in two engineering design studies of laser fusion driven hybrid power plants. With Bechtel, we have been engaged in a joint effort to design a laser fusion driven hybrid which emphasizes fissile fuel production while the primary objective of our joint effort with Westinghouse has been to design a hybrid which emphasizes power production. The hybrid designs which have resulted from these two studies are briefly described and analyzed by considering their most important operational parameters.
Date: May 1, 1978
Creator: Maniscalco, J.A. & Hansen, L.F.
Partner: UNT Libraries Government Documents Department

Analysis of the /sup 235/U neutron cross sections in the resolved resonance range

Description: Using recent high-resolution measurements of the neutron transmission of /sup 235/U and the spin-separated fission cross-section data of Moore et al., a multilevel analysis of the /sup 235/U neutron cross sections was performed up to 300 eV. The Dyson Metha ..delta../sub 3/ statistics were used to help locate small levels above 100 eV where resonances are not clearly resolved even in the best resolution measurements available. The statistical properties of the resonance parameters are discussed. 13 refs., 8 figs., 1 tab.
Date: January 1, 1989
Creator: Leal, L.C.; de Saussure, G. & Perez, R.B.
Partner: UNT Libraries Government Documents Department

Fission cross section ratios for sup 233,234,236 U relative to sup 235 U from 0. 5 to 400 MeV

Description: Neutron-induced fission cross section ratios from 0.5 to 400 MeV for samples of {sup 233, 234, 236}U relative to {sup 235}U have been measured at the WNR neutron Source at Los Alamos. The fission reaction rate was determined using a fast parallel plate ionization chamber at a 20-m flight path. Cross sections over most the energy range were also extracted using the neutron fluence determined with three different proton telescope arrangements. Those data provided the shape of the {sup 235}U(n,f) cross section relative to the hydrogen scattering cross section. That shape was then normalized to the very accurately known value for {sup 235}U(n,f) at 14.1 MeV to allow us to obtain cross section section values from the ratio data and our values for {sup 235}U(n,f). 6 refs., 1 fig.
Date: January 1, 1991
Creator: Lisowski, P.W.; Gavron, A.; Parker, W.E.; Balestrini, S.J. (Los Alamos National Lab., NM (USA)); Carlson, A.D.; Wasson, O.A. (National Inst. of Standards and Technology, Gaithersburg, MD (USA)) et al.
Partner: UNT Libraries Government Documents Department

Perspective on occupational radiation exposures at a hypothetical fusion power station

Description: If current technology were used, several major sources of potential occupational radiation exposure at fusion power stations would be quite similar to those at current light water reactor power stations. Based upon this similarity, crude estimates of doses received from various maintenance operations at fusion power reactors are made. The dose estimates reinforce the need for concurrent development of sophisticated remote maintenance devices and low-activation materials for fusion reactors. It is concluded that minimization of occupational doses can be best achieved by developing an overall maintenance strategy that combines the best features of remote techniques and low activation materials as opposed to developing one or the other exclusively.
Date: January 1, 1983
Creator: Easterly, C.E. & Cannon, J.B.
Partner: UNT Libraries Government Documents Department