ELASTIC AND INELASTIC-SCATTERING OF O-16 AND O-18 ON SI-28 AT 56 MEV INCIDENT ENERGY

Elastic and inelastic scatterings of O16 and O18 projectiles have been studied on Si28 nucleus at 56 MeV incident energy. Optical model and coupled-channel analyses have been performed in order to define the nature of the optical potential. It has turned out that the enhanced backward angle oscillations that appeared in the angular distribution for the O16 scattering are mainly due to refractive phenomena namely orbiting rather than diffractive phenomena. The potential necessary to reproduce the experimental data has to be surface transparent for O16 projectile, with a pocket in the effective potential in the grazing wave region and with a sharp diffusivity in the imaginary part in order to produce a mirror effect due to strong and abrupt volume absorption. On the other hand the potential necessary to fit the O18 scattering angular distributions is just a normal strong absorptive potential. The absence of any surface transparency in the case of O18 scattering can be attributed to the fact that many direct reaction channels are well Q matched. NUCLEAR REACTIONS Si28(O16, O16) and Si28(O18, O18), EO16, EO18=56 MeV; elastic and inelastic angular distributions measured between 5°and 71°(lab). Optical model and coupled-channel analysis. © 1979 The American Physical Society.