Importance of elastic scattering in nucleon-exotic nucleus experiments

In any experiment involving the interaction of two hadronic, many-body systems, the underlying interaction is conventionally described by an optical potential. Usually, this is of phenomenological, local, form, with real and imaginary parts each of which has parameters which are determined by fits to elastic scattering data. In order to predict observables for a wide range of targets, those data must cover a wider range of nuclei so that experiments with individual targets may be described appropriately. Further, for other experiments, obtaining the relative wave functions between the interacting systems requires the optical potential. Unfortunately, for nuclei far from the valley of stability such a global approach is inappropriate given the large differences in density at the surfaces due to halos and skins. In that case, phenomenology requires the measurements of elastic scattering data for the specific interacting systems. An alternative approach is to use microscopic formulations of the optical potential, such as the Melbourne g-folding potential. Aspects of both of these approaches for intermediate energies, given the interest in establishing facilities for exotic nuclear experiments at intermediate energies, will be discussed.