A priori pre-equilibrium decay models

Abstract

Intranuclear transition rates for a priori calculations of pre-equilibrium decay have been calculated using both the imaginary optical potential and a nucleon-nucleon scattering approach which is improved over earlier results used in the geometry dependent hybrid model. Spectra calculated using these intranuclear transition rates in several formulations of the hybrid model are compared with each other and with experimental results for the reactions 209Bi(p, p') and 54Fe(p, p') at incident proton energies of 39 and 62 MeV. Results calculated in several ways are found to be in reasonable agreement with data in view of the uncertainties of the calculation. It is shown that the initial target-projectile interaction may be treated as a direct reaction term for which it is essential to consider the geometry of the reaction with respect to the nuclear density distribution but, based on estimated nucleon mean free paths, higher order pre-equilibrium terms may be treated in a non-localized fashion. It is also shown that the relative lifetime dependences assumed in many exciton model calculations are in reasonable agreement with results from nucleon-nucleon scattering calculations at excitation energies below 25 MeV, but get progressively poorer at higher excitations.