A SEMICLASSICAL THEORY OF MULTISTEP NUCLEAR-REACTION PROCESSES

The master equation theory of precompound and compound nuclear reactions has been generalized with inclusion of the conservation of angular momentum and parity. This improved semiclassical theory has been extended for application as an evaluation tool of the calculations of nucleon induced reaction cross sections and double differential cross sections. For structural materials at incident neutron energies below 20 MeV, it is demonstrated that the constructed model contains the Hauser-Feshbach, Weisskopf-Ewing as well as the exciton models as limiting cases. The unified treatment of pre-equilibrium processes includes a number of interesting features, such as the exciton state densities with the exact Pauli exclusion correction which are renormalized to the back-shifted Fermi-gas formula, the introduction of formation factors of composite particle in calculations of pick-up type composite particle emission and the double differential cross sections (DDCS) for all kinds of particles in terms of the leading particle model.