Consistent exciton model calculations with shell structure, pairing and isospin effects

Abstract

Shell structure effects are included in a consistent way for all stages of preequilibrium particle emission in the exciton model. Also included are pairing, isospin, and finite well depth effects. Calculations have been performed for a variety of (N,N) reactions around N=50 and Z=50 at 18 and 25 MeV incident energies. Comparisons with experimental angle-integrated energy spectra demonstrate the utility of the current methodology for including shell effects when pairing and isospin are also included. They also show that shell structure effects wash out in about D/2d mass units. The sensitivity to and interconnectedness of model input were studied, and adjusted parameter values were applied uniformly to all systems. In particular, in order to reproduce the relative yields in the inelastic and exchange channels, the effective residual interaction between like nucleons must be larger than between a neutron and a proton. This is contrary to earlier assumptions.