GNASH-FKK, FKK, Pre-equilibrium, Statistical Model Cross-Sections and Emission Spectra

1 - Description of program or function: 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 pre-equilibrium spectrum from, e.g., Feshbah-Kermin-Koonin theory, to do multiple pre-equilibrium calculations, to calculate appropriate spin distributions for nuclear states formed in pre-equilibrium reactions, and to do incident-photon calculations. PSR-0125/06: 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). 2 - 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. 3 - Restrictions on the complexity of the problem: 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