PSR-0125 GNASH-FKK.

GNASH-FKK.

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 GNASH-FKK release include added capabilities: to read in externally calculated preequilibrium spectrum from, e.g., Feshbah-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.

GNASH uses Hauser-Feshbach theory to calculate complicated sequences of reactions and includes a preequilibrium 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.

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.

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.

AUXILIARY CODE:

• SEARCH3: Operates on the output of the GNASH-FKK code to produce ENDF/B-formatted cross section records.

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.

• J. Kopecky and M. Uhl: Test of Gamma-Ray Strength Functions in Nuclear Model Calculations
  Phys. Rev. C41, 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)

GNASH was developed originally on the CDC 6600 and 7600 then on CRAY.

The codes run on Cray computers under the UNICOS operating system. The gnash and search3 Fortran sources call routines which are Cray specific, but they can be ported to other Unix systems. Calls to filerep and qstart equate internal and external file names and may be removed. Substitutions need to be supplied for "date" and "second" which retrieve calendar data and time of day. Two "encode" statements in search3 may need to be changed.

Contributed by: Radiation Safety Information Computational Center
                Oak Ridge National Laboratory
                Oak Ridge,TN, USA
Developed by:   Los Alamos National Laboratory,
                Los Alamos, NM, USA