Microscopic model approach to (n,xn) pre-equilibrium reactions for medium-energy neutrons

We report on microscopic model calculations of the first step of direct pre-equilibrium (n,xn) emission in neutron interaction with Zr-90 and Pb-208 below 20 MeV. Our model is based on both an accurate description of the target excited states, provided by the self-consistent random-phase approximation (RPA) method implemented with the Gogny D1S force, and well-established in-medium two-body forces to represent the residual nucleon-nucleon interaction for the inelastic processes. Two goals have been achieved: The present microscopic approach provides a unified description of collective state excitations and the pre-equilibrium one-step process, and our reaction model reproduces the available data fairly well, without any parameter adjustment.