Improved model for secondary neutron production in nucleus-nucleus collision at intermediate energies

Abstract
In previous work an analytical knockout-ablation coalescence model capable of making quantitative predictions of the neutron spectra from high-energy nucleon-nucleus and nucleus-nucleus collision has been developed. The physics of the knockout-ablation model is similar to that in intranuclear cascade codes using Monte Carlo methods. In the first or knockout stage, the collision between two nuclei results in one or more nucleons being knocked out of the projectile and/or the target nucleus. This results in an excited nucleus (called a prefragment), which is lighter than the original species. This excited prefragment decays to the ground state by emitting one or more nucleons, composites (such as deuterons or alphas) and gammas. This is the ablation (second) stage of the reaction. Significant improvements in model predictions were made previously by incorporating important coalescence effects into the formalism. Coalescence occurs when particles with similar momenta located close together in space recombine to form heavier nuclei, such as deuterons, ³H and ³He. In this work the important effects of alpha particle coalescence are included. The improved theory is described and results for predicted neutron and light ion energy and angular spectra are presented and compared with published measurements of secondary neutron and light ion production for a variety of collision pairs.