Near-barrier fusion of S32+Zr90,96: The effect of multi-neutron transfers in sub-barrier fusion reactions

Fusion excitation functions have been measured for the first time with rather good accuracy for S32+Zr90 and S32+Zr96 near and below the Coulomb barrier. The sub-barrier cross sections for S32+Zr96 are much larger than for S32+Zr90. A coupled-channels calculation considering the inelastic excitations is capable of describing sub-barrier enhancement only for S32+Zr90. The unexplained part for S32+Zr96 is found to be correlated with the positive-Q-value intermediate neutron transfers in this system. The comparison with Ca40+Zr96 suggests that couplings to the positive-Q-value neutron transfer channels may play a role in the sub-barrier fusion enhancement. Multi-neutron transfers are taken into account in Zagrebaev’s semiclassical model to explain the discrepancies of the sub-barrier fusion cross sections for S32+Zr96.