Fusion of 40Ca + 40Ca, 40Ca + 48Ca and 48Ca + 48Ca

The recent experiment on fusion of 40Ca + 40Ca is described in some detail and the results are reported. A full excitation function has been measured from well above the Coulomb barrier, down to low energies where the cross section reduces to about 20 μb. A comparison is done with the recently published data on fusion of 40Ca + 48Ca and of 48Ca + 48Ca. The trends are different, in particular as far as the logarithmic derivatives (slopes) are concerned, in the interesting energy region below the barrier. The slope for systems where 40Ca is involved, shows a characteristic behavior with a tendency to saturate in a limited energy range just below the main barrier. The slopes resume increasing at lower energies, possibly indicating the influence of nuclear structure (the strong octupole vibration of 40Ca) at such low energies, together with the clear presence of the fusion hindrance phenomenon. The results of coupled-channels calculations are presented. (authors)