High precision quasi-elastic scattering excitation functions have been measured at energies well below the Coulomb barrier for the reactions of ${}^{32}\mathrm{S}$ with ${}^{208}\mathrm{Pb}$, ${}^{197}\mathrm{Au}$, ${}^{186}\mathrm{W}$, and ${}^{170}\mathrm{Er}$. 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 $a=0.72\text{−}0.82$ fm, whereas coupled-channels calculations give diffuseness parameters in the range 0.58–0.75 fm.

• Received 18 May 2007

DOI:https://doi.org/10.1103/PhysRevC.76.024612