Examining the role of transfer coupling in sub-barrier fusion of Ti 46,50 + Sn 124

Background: The presence of neutron transfer channels with positive Q values can enhance sub-barrier fusion cross sections. Recent measurements of the fusion excitation functions for Ni58+Sn132,124 found that the fusion enhancement due to the influence of neutron transfer is smaller than that in Ca40+Sn132,124 although the Q values for multineutron transfer are comparable. Purpose: To investigate the differences observed between the fusion of Sn + Ni and Sn + Ca. Methods: Fusion excitation functions for Ti46,50+Sn124 have been measured at energies near the Coulomb barrier. Results: A comparison of the barrier distributions for Ti46+Sn124 and Ca40+Sn124 shows that the Ca40+Sn124 system has a barrier strength resulting from the coupling to the very collective octupole state in Ca40 at an energy significantly lower than the uncoupled barrier. Conclusions: The large sub-barrier fusion enhancement in Ca40 induced reactions is attributed to both couplings to neutron transfer and inelastic excitation, with the octupole vibration of Ca40 playing a major role.