The sub-barrier fusion excitation function of 40Ca + 96Zr has been measured down to cross sections ≃2.4 μb, i.e. two orders of magnitude smaller than obtained in a previous experiment, where the subbarrier fusion of this system was found to be greatly enhanced with respect to 40Ca + 90Zr, and the need of coupling to transfer channels was suggested relying on coupled-channels calculations. The purpose of this work has been to investigate the behavior of 40Ca + 96Zr fusion far below the barrier, thereby disentangling the elusive interplay of effects due to inelastic couplings, transfer couplings and, possibly, the appearance of the fusion hindrance. The smooth trend of the excitation function has been found to continue, and the logarithmic slope increases very slowly. No indication of hindrance shows up, and a comparison with 40Ca + 96 is illuminating in this respect. A new CC analysis of the complete excitation function has been performed, including explicitly one- and two-nucleon Q > 0 transfer channels. Such transfer couplings bring significant cross section enhancements, even at the level of a few μb. Locating the hindrance threshold, if any, in 40Ca + 96 would require challenging measurements of cross sections in the sub-μb range

The fusion excitation function of 32 S + 48 Ca has been experimentally studied in a wide energy range, from above the Coulomb barrier down to cross sections in the sub-µb region. The measurements were done at INFN-Laboratori Nazionali di Legnaro, using the 32 S beam from the XTU Tandem accelerator. The excitation function has a smooth behavior below the barrier, and no evident hindrance character shows up in the measured energy region. The fusion barrier distribution has a peculiar shape with two distinct peaks of similar height, lower and higher than the Akyüz-Winther barrier. Coupled-channels calculations using the M3Y + repulsion potential are presented for this system and for 36 S+ 48 Ca. The results of these calculations give a good account of the data, and indicate the influence of one-and two-nucleon transfer channels with positive Q-values, which are only open for 32 S + 48 Ca.

High-energy γ rays and light charged particles from the 36Ar + 96Zr and 40Ar + 92Zr reactions at Elab = 16\ud and 15.1 MeV/nucleon, respectively, were measured in coincidence with evaporation residues by means of the\ud MEDEA multidetector array coupled to four parallel plate avalanche counters. The aim of this experiment was to\ud investigate the prompt γ radiation, emitted in the decay of the dynamical dipole mode, in the about 16 MeV/nucleon\ud energy range and to map its beam energy dependence, comparing the present results with our previous ones\ud obtained at lower energies. The studied reactions populate, through entrance channels having different charge\ud asymmetries, a compound nucleus in the region of Ce under the same conditions of excitation energy and spin.\ud Light charged particle energy spectra were used to pin down the average excitation energy and the average mass\ud of the system. By studying the γ -ray spectra of the charge symmetric reaction 40Ar + 92Zr, the statistical giant\ud dipole resonance (GDR) parameters and angular distribution were extracted, and a comparison of the linearized\ud 90◦γ -ray spectra of the two reactions revealed a 12% extra yield in the GDR energy region for the more charge\ud asymmetric system. The center-of-mass angular distribution data of this extra γ yield, compatible with a dipole\ud oscillating along the symmetry axis of the dinuclear system, support its dynamical nature. The experimental\ud findings are compared with theoretical predictions performed within a Boltzmann-Nordheim-Vlasov transport\ud model and based on a collective bremsstrahlung analysis of the entrance channel reaction dynamics.An interesting\ud sensitivity to the symmetry term of the equation of state and to in-medium effects on nucleon-nucleon (nn) cross\ud sections is finally discussed