Preequilibrium, Statistical NuclearModel Code System for Calculation Cross Sections and Emission Spectra, Version gn9cp8.
Abstract
Version 00 GNASH provides a flexible method by which reaction and level cross sections, isomer ratios, and emission spectra (neutron, gammaray, and chargedparticle) resulting from particle and photoninduced reactions can be calculated. The September 1991 release of GNASH incorporated an additional option for calculating gammaray strength functions and transmission coefficients by including the KopeckyUhl model. In addition, improvements were made to the output routines, particularly regarding gammaray strength function information. Major improvements in the 1995 FKKGNASH release include added capabilities: to read in externally calculated preequilibrium spectrum from, e.g., FeshbachKermanKoonin theory, to do multiple preequilibrium calculations, to calculate appropriate spin distributions for nuclear states formed in preequilibrium reactions, and to do incidentphoton calculations. In the 1998 release improvements were made in the accuracy of the exciton model and other calculations, and provision was made for including energydependent renormalization of the reaction cross section and energydependent exciton model parameterization (for data evaluation purposes). The sample problems provided here are the same as those that were given in the 1998 release; however, the calculations were run using the current version of GNASH (gn9cp8). The major differences between this version and the previous one released in 1998 are as follows: 1. A seriousmore »
 Authors:
 Publication Date:
 Research Org.:
 Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
 Sponsoring Org.:
 USDOE
 OSTI Identifier:
 1271199
 Report Number(s):
 GNASHFKK; 004369WKSTN00
RSICC ID: P00535MNYCP
 DOE Contract Number:
 AC0500OR22725
 Resource Type:
 Software
 Software Revision:
 00
 Software Package Number:
 004369
 Software CPU:
 WKSTN
 Source Code Available:
 Yes
 Other Software Info:
 Owner Installation: LOS ALAMOS NATIONAL LABORATORY Contributors: Los Alamos National Laboratory, Los Alamos, New Mexico. GNASH uses HauserFeshbach theory to calculate complicated sequences of reactions and includes a preequilibrium correction for binary tertiary channels. Gammaray competition is considered in detail for every decaying compound nucleus. A multihumped fission barrier model is included for fission crosssection calculations. Three options for level densities are available. KEYWORDS: NUCLEAR MODELS; WORKSTATION; CROSS SECTION PROCESSING; ENDF
 Country of Publication:
 United States
Citation Formats
PHILLIP,, and YOUNG, G. Preequilibrium, Statistical NuclearModel Code System for Calculation Cross Sections and Emission Spectra, Version gn9cp8..
Computer software. Vers. 00. USDOE. 2 Feb. 2007.
Web.
PHILLIP,, & YOUNG, G. (2007, February 2). Preequilibrium, Statistical NuclearModel Code System for Calculation Cross Sections and Emission Spectra, Version gn9cp8. (Version 00) [Computer software].
PHILLIP,, and YOUNG, G. Preequilibrium, Statistical NuclearModel Code System for Calculation Cross Sections and Emission Spectra, Version gn9cp8..
Computer software. Version 00. February 2, 2007.
@misc{osti_1271199,
title = {Preequilibrium, Statistical NuclearModel Code System for Calculation Cross Sections and Emission Spectra, Version gn9cp8., Version 00},
author = {PHILLIP, and YOUNG, G.},
abstractNote = {Version 00 GNASH provides a flexible method by which reaction and level cross sections, isomer ratios, and emission spectra (neutron, gammaray, and chargedparticle) resulting from particle and photoninduced reactions can be calculated. The September 1991 release of GNASH incorporated an additional option for calculating gammaray strength functions and transmission coefficients by including the KopeckyUhl model. In addition, improvements were made to the output routines, particularly regarding gammaray strength function information. Major improvements in the 1995 FKKGNASH release include added capabilities: to read in externally calculated preequilibrium spectrum from, e.g., FeshbachKermanKoonin theory, to do multiple preequilibrium calculations, to calculate appropriate spin distributions for nuclear states formed in preequilibrium reactions, and to do incidentphoton calculations. In the 1998 release improvements were made in the accuracy of the exciton model and other calculations, and provision was made for including energydependent renormalization of the reaction cross section and energydependent exciton model parameterization (for data evaluation purposes). The sample problems provided here are the same as those that were given in the 1998 release; however, the calculations were run using the current version of GNASH (gn9cp8). The major differences between this version and the previous one released in 1998 are as follows: 1. A serious buffering error that affected stored state populations resulting when multiple reactions lead to the same compound nucleus is corrected. This error only affects cases with INPOPT=1, normally used for highenergy calculations. It is the reason that the present outputs for the p + Zr90 test case (described below) are significantly different from the 1998 results for the same p + Zr90 test case. 2. Minor errors were corrected in estimating preequilibrium contributions to discrete states; interpolating the spin cutoff parameter in the constant temperature region; and in combining inputted direct reaction contributions with preequilibrium contributions. In the cases we checked, these errors resulted in very small differences. 3. The present code utilizes the groundstate masses, spins, and parities from the RIPL2 database at the IAEA database in Vienna. These are included in the gsmasssp.dat file. 4. We modified the SPECTRA subroutine so that when IGAMCAS=2, primary gammaray cross sections are not included in the computed spectra. 5. An option for energydependent singleparticle state densities (GG) used in preequilibrium calculations was added. 6. Several new diagnostic print options were added. 7. Several variable dimensions were increased.},
doi = {},
year = {Fri Feb 02 00:00:00 EST 2007},
month = {Fri Feb 02 00:00:00 EST 2007},
note =
}

A new multistep HauserFeshbach code that includes corrections for preequilibrium effects is described. The code can calculate up to 60 decay reactions (cross sections and energy spectra) in one computation, and thereby provide considerable flexibility for handling processes with complicated reaction chains. Input parameter setup, problem output, and subroutine descriptions are given along with a sample problem calculation. A brief theoretical description is also included. 8 figures, 3 tables.

Equilibrium and preequilibrium models for calculation of particle emission cross sections and spectra
Improvements of equilibrium and preequilibrium models that have been applied to the evaluations of the recently released nuclear data libraries are reviewed. The improvements include energyangle correlated neutron emission in the continuum, chargedparticle and recoil spectra, widthsfluctuation correction for the continuum, preequilibrium capture, and gammaray strength functions. Their impacts on evaluated data are summarized. 
Calculation of neutron cross sections for tungsten isotopes. [Preequilibrium statistical model, 1 to 20 MeV preliminary calculations]
Neutroninduced cross sections on tungsten isotopes were calculated in the energy range between 1 and 20 MeV using preequilibriumstatistical model techniques. The success of these calculations, which form part of an effort to improve the evaluated neutron and gammaray production cross sections for tungsten appearing in ENDF/B, depends strongly on the determination of consistent input parameter sets applicable over the entire range of interest. For example, neutron optical model parameters were derived through a simultaneous analysis of total cross sections, resonance data, and angular distributions. These parameters, when used in multistep HauserFeshbach calculations, produce good agreement with varied experimental datamore » 
Measurements of (n,3n) cross sections for /sup 235/U and /sup 238/U. [4 to 22 MeV, neutron spectra, statistical preequilibrium model]
Cross sections were measured for the /sup 235/U(n,3n) reaction from 14.8 to 21 MeV, for /sup 238/U(n,2n) from 14.7 to 19 MeV, and for /sup 238/U(n,3n) from 14.7 to 22 MeV with /sup 3/H(d,n) neutrons and a large liquid scintillator tank, and (n,xn) and fission cross sections from 4 to 22 MeV were calculated for both nuclei using a statistical, preequilibrium model. Also calculated were the individual spectra of the two (n,2n) and three (n,3n) neutrons. 15 references.
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