Isotopic dependence and channel coupling effects in the fusion of ${}^{16}\mathrm{O}{+}^{112,116}\mathrm{Sn}$ and ${}^{32}\mathrm{S}{+}^{112,116,120}\mathrm{Sn}$ at energies around the barrier

We report here measurements of fusion cross-sections for the ${}^{16}\mathrm{O}{+}^{112,116}\mathrm{Sn}$ and ${}^{32}\mathrm{S}{+}^{112,116,120}\mathrm{Sn}$ systems. The set of systems studied with widely varying ground state Q values for the transfer of neutrons is a good case to understand the influence of single and multineutron transfer on the fusion process. The evaporation residue cross-sections were measured in small energy steps covering the region around the Coulomb barrier $(\approx {0.8V}_b$ to ${1.2V}_b).\mathrm{}$ The data have been analyzed in the framework of a coupled-channels formalism using the coupled-channels code CCFULL. A comparative study of the ${}^{16}\mathrm{O}{+}^A\mathrm{Sn}$ and ${}^{32}\mathrm{S}{+}^A\mathrm{Sn}$ systems suggests that the fusion process is predominantly influenced by coupling to collective excitations with coupling to multiphonon states (of target and projectile) becoming increasingly important for heavier systems. From the present analysis an unambiguous signature of the role of coupling to neutron transfer channels could not be inferred.