RSICC CODE PACKAGE PSR-535
1. NAME AND TITLE
GNASH-FKK: Pre-equilibrium, Statistical Nuclear-Model Code System for Calculation of Cross Sections and Emission Spectra, Version gn9cp8.
GNXS: Analyze decay chains, retrieve cross sections and spectra, and make various ENDF-6 formatted files from GNASH output.
GS-MASS-SP.DAT: Table of ground-state masses, spins, and parities.
Los Alamos National Laboratory, Los Alamos, New Mexico.
3. CODING LANGUAGE AND COMPUTER
Fortran 77; Sun; PC (Linux); MAC (OS X) (P00535MNYCP00)
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-Kerman-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).
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 high-energy 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 ground-state masses, spins, and parities from the RIPL-2 database at the IAEA database in Vienna. These are included in the gs-mass-sp.dat file.
4. We modified the SPECTRA subroutine so that when IGAMCAS=2, primary gamma-ray cross sections are not included in the computed spectra.
5. An option for energy-dependent single-particle state densities (GG) used in preequilibrium calculations was added.
6. Several new diagnostic print options were added.
7. Several variable dimensions were increased.
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 post processing 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 was developed on Sun Sparcstations and also runs on PC under Linux, and Apple machines under Mac OS X. 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
GNASH-FKK runs on Sun Solaris workstations and on Linux PCs. The developers also ran it on MAC under OS X with the Intel Fortran compiler v.9.1. At RSICC, this release was tested on a Sun Sparc Station20 under Solaris 2.6 using f77 Vers. 4.2. Double precision (-r8) is required with the native Sun compiler. It was also tested on a 64-bit AMD Opteron under Red Hat Enterprise Linux 4 using Intel 9.1 ifort. No compiler options were required on this Linux system.
a. included in documentation:
P. G. Young, E. D. Arthur, and M. B. Chadwick, “Comprehensive Nuclear Model Calculations: Theory and Use of the GNASH Code,” (informal report 1998).
b. background information:
P.G.Young, E.D.Arthur, M.B.Chadwick, “Comprehensive Nuclear Model Calculations: Theory and Use of the GNASH code,” (GNASH manual). Proceedings of the Workshop on Nuclear Reaction Data and Nuclear Reactors- Physics, Design and Safety – Vol. 1, ICTP, Trieste, Italy, 15 April – 17 May, 1996. Eds. Gandini and Reffo (World Scientific, Singapore, 1999), pp. 227-404. (Los Alamos report LA-UR-96-3739).
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 DVD containing the source code, data libraries, sample problem input and output in a GNU-compressed Unix tar file.
12. DATE OF ABSTRACT
KEYWORDS: NUCLEAR MODELS; WORKSTATION; CROSS SECTION PROCESSING; ENDF