Resonant heavy-ion elastic scattering from s-d shell nuclei

Angular distributions at angles 130 less than theta/sub cm/ less than 1800 were measured for 12C + 28Si, 32S, 40Ca as well as 9Be, 13C + 28Si in the energy range 20 MeV less than or equal to E/sub cm/ less than or equal to 35 MeV. Cross sections rising towards 1800 are observed for all reactions. Excitation functions for the back-angle enhancement show distinct structures, most pronounced for 12C + 28Si. Angular distributions for 12C, especially those corresponding to peaks in the excitation function show oscillations of the type vertical bar P/sub J/(cos theta) vertical bar2. The 12C back-angle enhancement decreases with target mass. Backscattering of the nonalpha nuclei 9Be and 13C is reduced by about two orders of magnitude in comparison with 12C. Similar measurements for the 28Si(12C, 16O)24Mg reaction and 16O + 24Mg elastic scattering allow comparison of reaction data with the corresponding entrance and exit channel data. Standard theoretical approaches fail to explain all the observed effects