1. NAME AND TITLE
GNASH-FKK: Pre-equilibrium, Statistical Nuclear-Model Code System for
Calculation of Cross Sections and Emission Spectra, Version gn9cp0.
AUXILIARY CODE
GNXS: Analyze decay chains, retrieve cross sections and spectra, and make
various ENDF-6 formatted files from GNASH output.
DATA LIBRARY
STRUCTURE.DAT: Nuclear level energies, spins, parities, and gamma-ray branching ratios.
TRANS.COEF: Particle transmission coefficients from spherical or deformed optical model calculations.
MASS.DAT: Table of ground-state masses, spins, and parities.
2. CONTRIBUTOR
Los Alamos National Laboratory, Los Alamos, New Mexico.
3. CODING LANGUAGE AND COMPUTER
Fortran 77; Sun (P00125/SUN05/00).
4. NATURE OF PROBLEM SOLVED
GNASH provides a flexible method by which reaction and level cross sections,
isomer ratios, and emission spectra (neutron, gamma-ray, and charged-particle)
resulting from particle- and photon-induced reactions can be calculated. The
September 1991 release of GNASH incorporated an additional option for
calculating gamma-ray strength functions and transmission coefficients by
including the Kopecky-Uhl model. In addition, improvements were made to the
output routines, particularly regarding gamma-ray strength function information.
Major improvements in the 1995 FKK-GNASH release include added capabilities: to
read in externally calculated preequilibrium spectrum from, e.g.,
Feshbach-Kermin-Koonin theory, to do multiple preequilibrium calculations, to
calculate appropriate spin distributions for nuclear states formed in
preequilibrium reactions, and to do incident-photon calculations. In the 1998
release improvements were made in the accuracy of the exciton model and other
calculations, and provision was made for including energy-dependent
renormalization of the reaction cross section and energy-dependent exciton model
parameterization (for data evaluation purposes).
5. METHOD OF SOLUTION
GNASH uses Hauser-Feshbach theory to calculate complicated sequences of
reactions and includes a pre-equilibrium correction for binary tertiary
channels. Gamma-ray competition is considered in detail for every decaying
compound nucleus. A multi-humped fission barrier model is included for fission
cross-section calculations. Three options for level densities are available.
6. RESTRICTIONS OR LIMITATIONS
In its present configuration, each calculation can handle decay sequences
involving up to 38 compound nuclei and each decaying compound nucleus can emit a
maximum of 5 types of radiation (neutrons, gamma rays, protons, alphas, etc.).
Angular-momentum effects and conservation of parity are included explicitly.
Each residual nucleus in a calculation can contain up to 78 discrete levels
whereas its continuum region can be represented by up to 204 energy bins. The
incident-particle types that are permitted are neutrons, protons, deuterons,
tritons, 3He, and 4He. Angular distributions are not
calculated; i.e., isotropy is assumed in the center-of-mass (c.m.) system.
Angular distribution effects can be added in postprocessing utility codes making
use of, for example, Kalbach-Mann systematics. The above restrictions can be
easily adjusted by increasing the array dimensions in the parameter statements
in the code.
7. TYPICAL RUNNING TIME
The running times typically range from a few seconds to a few minutes per
incident energy depending upon incident particle energy, mass range of the
target, number of compound nuclei included, and the energy bin width that is
used.
8. COMPUTER HARDWARE REQUIREMENTS
GNASH was developed originally on the CDC 6600 and 7600 then on Cray. The
current release runs on Sun Sparcstations. Using GNASH for ENDF evaluations to
150 MeV, requires more than 100 MB RAM, to include all the necessary decay
chains.
9. COMPUTER SOFTWARE REQUIREMENTS
At RSICC GNASH-FKK was run on a Sun Sparcstation20 under Solaris 2.6 using
f77 Vers. 4.2. Double precision (-r8) is needed.
10. REFERENCES
a. included in documentation:
M. Chadwick, "readme.tr98" (January 1998).
P. G. Young, M. B. Chadwick, "Code Input Description, Version T2/PGYC/93GNASH/GN7SRC (Update 17)" (May 1996).
P. G. Young, E. D. Arthur, and M. B. Chadwick, "Comprehensive Nuclear Model
Calculations: Theory and Use of the GNASH Code," (to be published)(1998).
b. background information:
J. Kopecky and M. Uhl, "Test of Gamma-Ray Strength Functions in Nuclear Model Calculations," Phys. Rev. C 41, 1941 (1990).
P. G. Young, E. D. Arthur, M. B. Chadwick, "Comprehensive Nuclear Model
Calculations: Introduction to the Theory and Use of the GNASH Code," LA-12343-MS
(July 1992).
11. CONTENTS OF CODE PACKAGE
Included are the referenced documents and one 3.5-in. DS/HD (1.44 MB)
diskette containing the source code, data libraries, sample problem input and
output in a compressed tar file.
12. DATE OF ABSTRACT
March 1984, revised June 1988, March 1989, September 1991, December 1992,
January 1996, March 1998.
KEYWORDS: NUCLEAR MODELS; WORKSTATION; CROSS SECTION PROCESSING