Systematic study of the nuclear potential through high precision back-angle quasi-elastic scattering measurements

High precision quasi-elastic scattering excitation functions have been measured at energies well below the Coulomb barrier for the reactions of S-32 with Pb-208, Au-197, W-186, and Er-170. Single-channel and coupled-channels calculations have been performed to extract the diffuseness parameter of the nuclear potential. For the reactions involving near-spherical targets, both theoretical analyses give the same diffuseness parameter. On the other hand, for deformed systems, couplings are important even at deep sub-barrier energies. In general, the effect of couplings is to reduce the diffuseness parameter value extracted from a single-channel potential. Single-channel fits to quasi-elastic scattering data result in a=0.72-0.82 fm, whereas coupled-channels calculations give diffuseness parameters in the range 0.58-0.75 fm.