Fusion of 40Ca + 40Ca and other Ca + Ca systems near and below the barrier

The fusion excitation function of 40Ca+40Ca has been measured from well above the Coulomb barrier, down to low energies where the cross section is as small as ≃20 μb, and the astrophysical S factor possibly reaches a maximum vs energy. The results of coupled-channels calculations using the M3Y+repulsion potential are presented. A detailed comparison is made with recently published data on the fusion of 40Ca+48Ca and of 48Ca+48Ca, including the excitation functions, their low- energy slopes and the barrier distributions. The presence of the fusion hindrance phenomenon in all cases is pointed out, as well as the influence of the strong octupole excitation in 40Ca and of nucleon transfer channels with positive Q values in 40Ca+48Ca.