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Development and applications of multi-step Hauser-Feshbach/pre-equilibrium model theory

Description: A recently developed model that combines compound and precompound reactions with conservation of angular momentum is discussed. This model allows a consistent description of intermediate excitations from which tertiary reaction cross sections can be calculated for transitions to the continuum as well as to the discrete residual levels with known spins and parities. Predicted neutron, proton, and alpha-particle production cross sections and emission spectra from 14-MeV neutron-induced reactions are compared favorably with angle-integrated experimental data for 12 nuclides. The model is further developed to include angular distributions of outgoing particles. The random phase approximation used for the compound stage is partially removed for the precompound stages, allowing off-diagonal terms of the collision matrix to produce both odd and even terms in the Legendre polynomial expansion for the angular distribution. Calculated double differential cross sections for the 14.6-MeV /sup 23/Na(n,n'x) reaction are compared with experimental data.
Date: January 1, 1980
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Consistent nuclear model for compound and precompound reactions with conservation of angular momentum. [14. 6 MeV]

Description: The exciton model is modified such that it automatically reduces to the usual evaporation formula after equilibrium has been reached. The result is further modified to conserve angular momentum in a form compatible with the Hauser-Feshbach formula. This approach allows a consistent description of intermediate excitations from which tertiary reaction cross sections can be calculated for transitions to discrete residual levels with known spins and parities. Level densities used for the compound component of reaction cross sections are derived from direct summation of the particle-hole state densities used for the precompound component.
Date: January 1, 1979
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Evaluation of photon production data from neutron-induced reactions

Description: The evaluation methods and procedures used for generating the photon production data in the current Evaluated Nuclear Data File (ENDF/B, Version V) are reviewed. There are 42 materials in the General Purpose File of ENDF/B-V that contain data for prompt photon production. Almost all evaluations had substantial experimental data bases, but fewer than half of them employed any of the following evaluation methods. Only a few used theoretical techniques that are sophisticated enough to ensure internal consistency with other particle production data. Comments are made on four evaluation methods: the empirical formalism of Howerton et al., the Troubetzkoy model, the multiparticle Hauser-Feshbach/precompound model, and the Yost method. Critiques are also made on three procedures used for conserving photon energies in neutron capture reactions. The presence of photon production data in the file is useful for studying energy balance, since photon production generally accounts for a large portion of the reaction energy output. Problems found in energy balance checks are discussed. 9 figures, 1 table.
Date: January 1, 1980
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Pairing correction for particle-hole state densities

Description: The pairing correction proposed by Ignatyuk and Sokolov for particle-hole state densities has been examined. It has been found that the accuracy of the correction is sufficient for practical applications only if the system is in its normal state (..delta.. = 0). In the superfluid state (..delta.. not equal to 0), a consistent pairing-Pauli correction is developed here for improved accuracy. Practical implementations of the pairing correction are given and further developments are outlined.
Date: January 1, 1983
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Pairing correction of particle-hole state densities for two kinds of Fermions

Description: Pairing corrections in particle-hole (exciton) state-density formulas used in precompound nuclear reaction theories are, strictly speaking, dependent on the nuclear excitation energy U and the exciton number n. A general formula for (U,n)-dependent pairing corrections has been derived in an earlier paper for exciton state-density formulas for one kind of Fermion. In the present paper, a similar derivation is made for two kinds of Fermions. It is shown that the constant-pairing-energy correction used in standard level-density formulas, such as U/sub 0/ in Gilbert and Cameron, is a limiting case of the present general (U,n)-dependent results.
Date: January 1, 1985
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

A simplified unified Hauser-Feshbach/Pre-Equilibrium model for calculating double differential cross sections

Description: A unified Hauser-Feshbach/Pre-Equilibrium model is extended and simplified. The extension involves the addition of correlations among states of different total quantum numbers (J and J') and the introduction of consistent level density formulas for the H-F and the P-E parts of the calculation. The simplification, aimed at reducing the computational cost, is achieved mainly by keeping only the off-diagonal terms that involve strongly correlated 2p-1h states. A correlation coefficient is introduced to fit the experimental data. The model has been incorporated into the multistep H-F model code TNG. Calculated double differential (n,xn) cross sections at 14 and 25.7 MeV for iron, niobium, and bismuth are in good agreement with experiments. In use at ORNL and JAERI, the TNG code in various stages of development has been applied with success to the evaluation of double differential (n,xn) cross sections from 1 to 20 MeV for the dominant isotopes of chromium, manganese, iron, nickel, copper, and lead. 11 refs., 2 figs.
Date: January 1, 1988
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

A re-evaluation of /sup 32/S(n,p) cross sections from threshold to 5 MeV

Description: Two evaluations of the /sup 32/S(n,p) reaction cross sections, currently being used for the Nagasaki and Hiroshima dosimetry studies, yielded results that differ significantly. These two evaluations were reviewed and both were found to be quite old and without benefit of modern theoretical guidance and recent experimental data, hence inadequate in view of its relative importance for the present application. The necessity for a re-evaluation is further enhanced by the fact that: the present data search has uncovered a relatively high-quality data set that was not known previously, a generalized Bayes-theorem code is now available for averaging the various data sets with uncertainties and generating uncertainties for the results, effects on data combination of differing energy resolution in the various measurements can now be accounted for, and the ENDF/B-VI standards for /sup 238/U(n,f) cross sections have become available for renormalizing two of the available data sets. The re-evaluation is performed to 5 MeV, the upper energy limit for the present purpose. 8 refs., 2 figs.
Date: January 1, 1989
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Experience in using the covariances of some ENDF/B-V dosimetry cross sections: proposed improvements and addition of cross-reaction covariances

Description: Recent ratio data, with carefully evaluated covariances, were combined with eleven of the ENDF/B-V dosimetry cross sections using the generalized least-squares method. The purpose was to improve these evaluated cross sections and covariances, as well as to generate values for the cross-reaction covariances. The results represent improved cross sections as well as realistic and usable covariances. The latter are necessary for meaningful intergral-differential comparisons and for spectrum unfolding.
Date: January 1, 1982
Creator: Fu, C.Y. & Hetrick, D.M.
Partner: UNT Libraries Government Documents Department

Effects of shape differences in the level densities of three formalisms of calculated cross sections

Description: Effects of shape differences in the level densities of three formalisms on calculated cross sections and particle emission spectra are described. Reactions for incident neutrons up to 20 MeV on {sup 58}Ni are chosen for illustrations. Level-density parameters for one of the formalisms are determined from the available neutron resonance data for one residual nuclide in the binary channels and from fitting the measured (n, n{prime}), (n, p), and (n, {alpha}) cross sections for the other two residual nuclides. Level-density parameters for the other two formalisms are determined such that they yield the same values as the above one at two selected energies. This procedure forces the level densities from the three formalisms used for the binary part of the calculation to be as close as possible. The remaining differences are in their energy dependences (shapes). It is shown that these shape differences alone are enough to cause the calculated cross sections and particle emission spectra to be different by up to 60%.
Date: September 1, 1995
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Combining Semi-Classical and Quantum Mechanical Methodologies for Nuclear Cross-section Calculations Between 1 Mev and 5 Gev

Description: With a goal to develop a nuclear cross-section code usable over the wide energy range of 1 MeV to 5 GeV, one option is to combine intranuclear cascade, pre-equilibrium, and Hauser-Feshbach models in existing codes. However, the first two models are semi-classical while the third one is quantum mechanical, and combining them is not straightforward because the third model requires spin and parity distributions for all excited states that cannot be supplied by either one of the first two models. Approximations to overcome this difficulty are described in this paper. Success of this combined model will allow nuclear data evaluations for a large number of materials whose cross sections are needed in a wide range of applications, including the design, operation, and future upgrades of the SNS (1 GeV proton). The incident particles may be neutrons, protons, charged pions, or photons. Though only partially completed at this time, the new model compares well with experimental radionuclide production cross sections from thresholds to 2.6 GeV for proton-induced reactions on Fe.
Date: August 15, 2001
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

TNG calculations and evaluations of photon production data for some ENDF/B-VI materials

Description: Among the new evaluations in the ENDF/B-VI general purpose files, 25 were based on calculations using TNG, a consistent Hauser-Feshbach pre-equilibrium nuclear model code. The photon production cross sections and spectra were calculated simultaneously with the particle emission cross sections and spectra, assuring energy balance for each reaction. The theories used in TNG for these calculations are summarized. Several examples of photon production data, taken from the ENDF/B-VI files, are compared with the available experimental data.
Date: December 31, 1994
Creator: Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Evaluation and testing of double differential Fe(n,n') cross sections

Description: Analyses of integral experiments that include thick (>15 cm) iron regions have shown a consistent underprediction of neutron transmission. One explanation that has been offered is that the angular distributions of the inelastically scattered neutrons in the continuum in the current ENDF/B-V iron evaluation were assumed to be isotropic. In reality, these distributions are forward peaked, especially if the incident neutron energies (E/sub n/) are a few MeV greater than the continuum Q-value. The forward peaking also increases with increasing outgoing neutron energies (E/sub n/'), giving rise to correlated energy-angle distributions. In order to understand their effects on neutron penetration through iron, we generated such correlated distributions in a special update of the ENDF/B-V Mod-3 iron evaluation and re-analyzed an iron sphere problem. 9 refs., 2 figs.
Date: January 1, 1986
Creator: Fu, C.Y. & Hetrick, D.M.
Partner: UNT Libraries Government Documents Department

Summary of ENDF/B-V evaluations for carbon, calcium, iron, copper, and lead and ENDF/B-V Revision 2 for calcium and iron

Description: This report, together with documents already published, describes the ENDF/B-V evaluations of the neutron and gamma-ray-production cross sections for carbon, calcium, iron, copper, and lead and the ENDF/B-V Revision 2 evaluations for calcium and iron.
Date: September 1, 1982
Creator: Fu, C Y
Partner: UNT Libraries Government Documents Department

Description of evaluation of /sup nat/Pb performed for ENDF/B-VI

Description: An evaluation of data for neutron induced reactions on natural lead was performed for ENDF/B-VI and is briefly reviewed. The evaluation is based on experimental data and results of model calculations which reproduce the experimental data. Evaluated data are given for neutron induced reaction cross sections, angular and energy distributions, and for gamma-ray production cross sections associated with the reactions. File 6 formats are used to represent energy-angle correlated data. Uncertainty files are included for the major cross sections. Much of the present evaluation is taken over from ENDF/B-IV and ENDF/B-V; emphasis is placed on updates for ENDF/B-VI. 14 refs., 3 figs.
Date: January 1, 1987
Creator: Larson, D.C. & Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Group structure and weighting function effects on neutron penetration through thick sodium-iron shields

Description: The effects of group structures and weighting functions on neutron penetration through a thick Na-Fe geometry are studied. The recommended broad-group (61-neutron/23-gamma-ray) and few-group (22-neutron/10-gamma-ray) structures are tailored to the sodium and iron resonances, windows, and capture gamma-ray spectra. The best weighting functions are shown to be fine-group fluxes selected from a few key locations in the geometry. These group structures and weighting functions, relative to existing group structures and conventional weighting functions, improve the accuracy of the computed 61-neutron-group Bonner ball responses by up to one hundred percent and of the computed 22-neutron-group results by up to six hundred percent.
Date: January 1, 1987
Creator: Fu, C.Y. & Ingersoll, D.T.
Partner: UNT Libraries Government Documents Department

Impact of /sup 57/Fe on neutron penetration in thick sodium-iron shields

Description: The latest release of the VITAMIN-E multigroup cross-section library contains two different versions of neutron cross sections for natural iron, one based on ENDF/B-V MOD-1, and the other on MOD-3. The isotope /sup 57/Fe has four inelastic-scattering levels below 846 keV, the energy of the first excited state in /sup 56/Fe. The importance of the new cross sections was investigated by using both VITAMIN-E versions of the iron cross sections in S/sub 8/P/sub 3/ 174 group ANISN calculations for two Na-Fe shield configurations. In neutron penetration calculations through thick steel regions, /sup 57/Fe can be 10 times more important than is indicated by its isotopic abundance in natural iron. The 14.4-keV inelastic level of /sup 57/Fe is sufficiently important that it may be worthwhile to perform a measurement of this cross section to validate the ENDF/B-V MOD-3 value, which was obtained from nuclear model calculations. Shielding analyses were done with iron cross sections predating ENDF/B-V MOD-3 should be reviewed and may need to be revised.
Date: January 1, 1985
Creator: Fu, C. Y. & Ingersoll, D. T.
Partner: UNT Libraries Government Documents Department

Neutron damage calculations in Cu, Nb, and Au to 32 MeV: application to sputtering and deuteron-breakup neutron sources

Description: Primary recoil distributions and specific damage energies have been computed for high energy deuteron-breakup neutrons in Cu, Nb, and Au. The calculations are based on theoretical neutron cross sections, and consider in particular a d-Be spectrum broadly peaked at 15 MeV with some neutrons above 30 MeV. The theoretical results are similar to corresponding calculations for monoenergetic 15-MeV neutrons and are in good agreement with range measurements of (n,2n) recoils generated by high energy d-Be neutrons in Nb and Au. The calculations are also consistent with recent d-Be neutron sputtering experiments in Nb and Au and demonstrate the usefulness of deuteron-breakup neutron sources for simulating fusion neutron effects. (auth)
Date: February 1, 1976
Creator: Roberto, J.B.; Robinson, M.T. & Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Potential improvements to ENDF/B-VI for fusion data

Description: While ENDF/B-6 is significant improvement over previous versions for fusion reactor design calculations, several areas have not received attention and may need improvement. In addition, broadening of the contents of the evaluations to contain information not easily derived at present should be considered. 11 refs.
Date: January 1, 1991
Creator: Larson, D.C. & Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Description of evaluation for /sup 50,52,53,54/Cr performed for ENDF/B-VI

Description: Isotopic evaluations for /sup 50,52,53,54/Cr performed for ENDF/B-VI are briefly reviewed. The evaluations are based on analysis of experimental data and results of model calculations which reproduce the experimental data. Evaluated data are given for neutron induced reaction cross sections, angular and energy distributions, and for gamma-ray production cross sections associated with the reactions. File 6 formats are used to represent energy-angle correlated data and recoil spectra. Uncertainty files are included for the major cross sections. Detailed evaluations are given for /sup 52,53/Cr, and results of calculations for reactions with large cross sections are used for evaluation of the minor isotopes. 27 refs., 6 figs.
Date: January 1, 1987
Creator: Larson, D.C.; Hetrick, D.M. & Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Description of evaluations for /sup 58,60,61,62,64/Ni performed for ENDF/B-VI

Description: Isotopic evaluations for /sup 58,50,61,62,64/Ni performed for ENDF/B-VI are briefly reviewed. The evaluations are based on analysis of experimental data and results of model calculations which reproduce the experimental data. Evaluated data are given for neutron induced reaction cross sections, angular and energy distributions, and for gamma-ray production cross sections associated with the reactions. File 6 formats are used to represent energy-angle correlated data and recoil spectra. Uncertainty files are included for the major cross sections. Detailed evaluations are given for /sup 58/60/Ni, and results of calculations for the major reactions are used for evaluations of the minor isotopes. 29 refs., 8 figs.
Date: January 1, 1987
Creator: Larson, D.C.; Hetrick, D.M. & Fu, C.Y.
Partner: UNT Libraries Government Documents Department

Calculated neutron-induced cross sections for /sup 63,65/Cu /sup 58,60/Ni, and /sup 52/Cr from 1 to 20 MeV and comparisons with experiments

Description: Nuclear model codes were used to compute cross sections for neutron-induced reactions on /sup 63,65/Cu, /sup 58,60/Ni, and /sup 52/Cr for incident energies from 1 to 20 MeV. The input parameters for the model codes determined through analysis of experimental data in this energy region. The models used, the input data, the resulting calculations, and comparisons with measured data are discussed. 15 refs.
Date: January 1, 1985
Creator: Hetrick, D.M.; Fu, C.Y. & Larson, D.C.
Partner: UNT Libraries Government Documents Department

HETC96/MORSE calculations of activations in KEK beam stop and room by 500-MeV protons and comparisons with experiments

Description: The 1996 version of HETC has a pre-equilibrium reaction model to bridge the gap between the existing intranuclear-cascade and evaporation models. This code was used to calculate proton-induced activations, to calculate neutron fluxes for neutron energies above 19.6 MeV, and to write the neutron source for lower energies to be transported further by MORSE. For MORSE, the HILO cross section library was used for neutron transport for all detectors. Additionally for the {sup 197}Au(n, {gamma}) detector, the BUGLE96 library was used to study the effects of the low-lying {sup 57}Fe inelastic levels and the resonance self-shielding in iron. Neutron fluxes were obtained from the track-length estimator for detectors inside the beam stop and from the boundary-crossing estimator for detectors attached to the surfaces of the concrete walls. Activation cross sections given in JAERI-Data/Code are combined with the calculated neutron fluxes to get the saturated activities induced by neutrons. C/E values are too low (0.5) for Fe(N, {chi}){sup 54}Mn, close to unity for Cu(n, {chi}){sup 58}Co, and too high (6.0) for {sup 197}Au (n, {gamma}){sup 198}Au. It is difficult to interpret the disagreements because most of the activation cross sections are also calculated and their uncertainties are not known. However, the calculated results are in good agreement with those calculated by others using different codes. Calculated results for four of the ten activations reported here have not been done previously, and among the four, {sup 197}Au(n, {gamma}) is the most bothersome because its cross section is the most well known while the calculated activations for most detector locations are in largest disagreement with experiments.
Date: May 1, 1997
Creator: Fu, C.Y. & Gabriel, T.A.
Partner: UNT Libraries Government Documents Department