Study of the nucleus-nucleus interaction potential via 16O elastic scattering at 94 MeV/u

The elastic scattering angular distributions of 16O at 94 MeV/u on 12C, 28Si, 40Ca, 90Zr, 208Pb targets have been measured. They have been analyzed in the framework of the optical model with Woods-Saxon potentials and in the framework of the folding model. Concerning the heaviest system 16O + 208Pb, these analyses show that the real potential is well-defined only in the vicinity of the strong absorption radius, whereas for the lighter systems, it is defined in a relatively wide region (2-3 fm), which corresponds to a strong overlap of the two nuclei, especially for the systems 16O + 28Si and 16O + 12C. This difference, between the 16O + 208Pb system and the other systems originates in the appearance of the far-side contribution which manifests itself in the angular distributions by the so-called Fraunhoefer oscillations. The imaginary part of the potential is determined only in the vicinity of the strong absorption radius. The large reduction of the strong absorption radius for all the studied systems as the energy increases shows that the nuclear surface transparency is strongly enhanced at intermediate energies. The calculations performed with folding potentials allowed a study of the nuclear potential strength, in a less ambiguous way than with phenomenological potentials. In the regions where they are well-defined, the real and imaginary potentials decrease regularly when the energy goes from 10 to 100 MeV/u. This decrease disagrees with the results of microscopic calculations which predict an increase or a saturation of the nuclear potential in this energy range