Optical model calculation of exciton decay rates

The decay rate of an exciton is calculated using the imaginary part of both the phenomenological optical potential of Becchetti and Greenlees and the microscopic potential of Jeukenne et al. The decay rate thus calculated is found to be about the same for proton- and neutron-induced reactions and weakly sensitive to mass number. Kalbach's two body matrix element, obtained from the analysis of precompound reactions using the Williams exciton model, also leads to a decay rate in agreement with the phenomenological potential estimate. However, the exciton model of Gadioli et al. is inconsistent with optical model estimates. Further, remarks are made on the concept of a mean free path in finite nuclear matter