Fusion excitation functions with high precision have been measured for the ${}^{16}$O+${}^{76}$Ge and ${}^{18}$O+${}^{74}$Ge 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 ${}^{18}$O projectile. No obvious fusion enhancement due to the positive $Q$-value two-neutron transfer for the ${}^{18}$O+${}^{74}$Ge system is observed as compared with the reference system of ${}^{16}$O+${}^{76}$Ge. 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.

• Received 26 June 2012

DOI:https://doi.org/10.1103/PhysRevC.86.044621