Fusion of calcium isotopes and of other medium mass systems

Heavy-ion fusion below the barrier displays interesting, and sometimes unexpected, features. Several different facets of the fusion hindrance phenomenon have been evidenced in the last few years. Very recent data on super(40,48)Ca + super(40,48)Ca are presented and discussed in this paper. In all cases a hindrance of fusion far below the barrier has been observed. Coupled-channel effects (producing barrier distributions) influence the threshold energy for hindrance. The excitation functions of the two symmetric systems are similar, while the case of super(40)Ca + super(48)Ca is quite different both above and below the barrier, possibly due to couplings to transfer channels with positive Q-values. Other systems in the same mass region show different trends that have to be related to the nuclear structure of the colliding nuclei. Investigating the behavior of lighter systems will be interesting also from the astrophysical point of view.