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

The fusion excitation function of 48Ca + 48Ca 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
. 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 36S + 48Ca, with
, is pointed out. The sign of the Q-value does not influence fusion cross sections down to the 300–600 nb level.