Microscopic models for direct inelastic scattering and direct preequilibrium emission: nucleon induced reactions

Abstract

We have developed microscopic models for nucleon induced inelastic scattering and one-step direct preequilibrium emission. These models are based on reliable effective in-medium two-body interactions and a microscopic description of the ground and excited states of target nuclei. No arbitrary renormalization process enters our analyzes and the predictions are directly compar ed to experimental data. The nuclear structure in- formation are obtained in the Random Phase Approximation (RPA) framework with the Gogny force, which provides accurate descriptions of spherical nuclei withou t pairing. For medium energy (50-200 MeV) proton in- duced reactions, this approach gives very good predictions for direct inelastic scattering and for the first-step in direct preequilibrium emission. The one-step preequilibr ium model has also been extended to fast neutron scat- tering (10-20 MeV) for the 90 Zr target described with RPA theory, and for axially deformed nuclei with a simpler description of the excited states (i.e. particle-hole exci tations). Predictions of the reaction model reproduce well experimental data for 90 Zr. For deformed targets ( 232 Th and 238 U), our calculations underestimate the data at high emission energy. The cross section missing for both actinides may stem from the excitation of vibrational states with excitation energies lower than 5 MeV which are not described with incoherent particle-hole excitations. This defect might be cured if the target spectra are described wit hin the Quasi-particle-RPA (QRPA) theory recently implemented with the Gogny force.