16O+28Si: deep or shallow potentials

It is shown that data for 16O+28Si scattering between 33 and 215 MeV can be also fitted by optical potentials with deep, energy-independent, real parts provided the surface diffuseness of the imaginary part is allowed to increase slowly and linearly with bombarding energy. Potentials of Woods-Saxon and Woods-Saxon-squared form were used, as well as double-folded potentials using realistic nucleon-nucleon interactions. Equally good fits are also obtained using the proximity potential which is repulsive for small separations of the two ions. It is concluded that, even with data as extensive as these, it is not possible to extrapolate unambiguously to the potential for small separations. (Auth.)