A Unified Hauser-Feshbach and Exciton Model for Calculating Double-Differential Cross Sections of Neutron-Induced Reactions Below 20 MeV

The master equation theory of precompound and compound nuclear reactions has been generalized to include the conservation of angular momentum and parity. Based on this improved semi-classical theory, the UNF code has been developed as a tool for calculating nucleon-induced reaction cross sections and double-differential cross sections at incident neutron energies below 20 MeV. It is demonstrated that the code contains the Hauser-Feshbach model and the exciton models as the limiting cases. The unified treatment of equilibrium and pre-equilibrium reaction processes includes the introduction of composite particle formation factors in calculations of pickup-type composite particle emissions. A method to calculate the double-differential cross sections for all kinds of particles is proposed based on the leading particle model.