Surface effects in the exciton model of preequilibrium nuclear reactions.

Surface effects on direct particle emission in the exciton model of preequilibrium nuclear reactions are described in terms of the mean effective well depth in the region of the first target-projectile interaction. A simple parametrization for this quantity as a function of the bombarding energy is derived, and its predictive ability is demonstrated. There is no evidence for a mass dependence of the parameter values. The question of surface effects is found to be tied to the assumed energy dependence of the single particle state density. A Fermi gas model square root dependence is used in this work. Only (nucleon, nucleon) reactions are considered, but sizable effects on complex particle spectra are anticipated.