Impact parameter dependence of preequilibrium particle emission

Abstract

The energy spectra and angular distributions of protons, deuterons, tritons, and alpha particles from 215 MeV ¹⁶O bombardment of Tb, Ta, and Au have been measured in coincidence with both evaporation residues and fission fragments. The evaporation residue and fission fragment triggers together with the angular momentum dependence of the evaporation residue-fission competition have enabled us to extract the impact parameter dependence of the light charged particle preequilibrium multiplicities within the fusionlike impact parameter domain. The light charged particle spectra can be parametrized as originating from a source with approximately 1/2 to 2/3 of the beam velocity and with a slope parameter of 5-7 MeV. The proton multiplicities increase with decreasing impact parameter, in agreement with a nucleon exchange transport model prediction. The ratio of the complex particle to proton multiplicities decrease with decreasing impact parameter, suggesting dynamical effects in the complex particle production mechanism.