Isotopic effects in the (n, p) reaction cross section on heavy targets and the statistical preequilibrium model

Abstract

The systematic decrease in (n,p) cross sections with increasing neutron number for isotopes in reactions induced by 14 MeV neutrons on heavy targets is explained in terms of the preequilibrium model. The relevant physical quantities responsible for this behavior are proton and neutron separation energies, similarly to (n, p) reactions on lighter nuclei, in which proton emission is governed by the compound-nucleus model. The principal transition rateλ+ in the preequilibrium exciton-model calculations should be kept constant (for a given number of excitons and constant energy) in order to obtain a good description of data. The calculations are compared with experimental (n,p) cross sections for series of Te, Xe, W, and Os isotopes.