Fusion of the 16O + 76Ge and 18O + 74Ge systems and the role of positive Q-value neutron transfers.

Fusion excitation functions with high precision have been measured for the 16O + 76Ge and 18O + 74Ge systems at energies near and below the Coulomb barrier. The barrier distributions have been extracted from the corresponding excitation functions. The coupling effect of the positive Q-value neutron transfer channel in the heavy-ion fusion reaction was examined by a comparison of the two systems. The fusion excitation functions are well reproduced by coupled-channels calculations including the 2+ and 3- vibrational states of the targets and the 2+ rotational state of 18O projectile. No obvious fusion enhancement due to the positive Q-value two-neutron transfer for the 18O + 74Ge system is observed as compared with the reference system of 16O + 76Ge. Analogous systems which are available in the literature are also discussed to realize the role of one- and/or two-neutron transfers with positive Q values in the fusion process. [ABSTRACT FROM AUTHOR]