Abstract
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 58Ni + 132,124Sn found that the fusion enhancement due to the influence of neutron transfer is smaller than that in 40Ca + 132,124 Sn 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 46,50Ti + 124 Sn have been measured at energies near the Coulomb barrier. Results: A comparison of the barrier distributions for 46Ti + 124Sn and 40Ca + 124Sn shows that the 40Ca + 124Sn system has a barrier strength resulting from the coupling to the very collective octupole state in 40Ca at an energy significantly lower than the uncoupled barrier. Conclusions: The large sub-barrier fusion enhancement in 40Ca induced reactions is attributed to both couplings to neutron transfer and inelastic excitation, with the octupole vibration of 40Ca playing a major role.