How does fusion hindrance show up in medium-light systems? The case of Ca-48+Ca-48

The fusion excitation function of (48)Ca + (48)Ca has been measured above and well below the Coulomb barrier, thereby largely extending the energy range of a previous experiment down to very low cross sections. This system has a negative Q-value for compound nucleus formation. The fusion cross section decreases steadily below the barrier with no conspicuous change of slope below similar or equal to 300 mu b. Coupled-channels calculations using a Woods-Saxon potential indicate that a large diffuseness parameter is needed to reproduce the sub-barrier cross sections. A close analogy with the case of (36)S + (48)Ca, with Q > 0, is pointed out. The sign of the Q-value does not influence fusion cross sections down to the 300-600 nb level.