Surface and collective effects in preequilibrium reactions

Surface localization of the initial target-projectile interaction has been investigated for incident protons and neutrons at bombarding energies of 14–100 MeV within the framework of the exciton preequilibrium model. Incident neutrons, at least at energies up to around 30 MeV, show a greater amount of surface peaking than do incident protons as judged by the effective well depth available to the hole degree of freedom created. With this difference included, exciton model calculations can describe the energy spectra in all four $\mathrm{}(N,N)\mathrm{}$ reaction channels with a consistent set of model input. To aid in this study, the excitation of strong spectroscopic collective states was included in the calculations. The addition of giant resonance state excitation has a small but helpful effect. There is a need for additional data, especially for incident neutrons above 26 MeV.