Roles of multi-step transfer in fusion process induced by heavy-ion reactions

In nucleus-nucleus collisions of the systems, 12C+13C and 13C+16O-12C+17O, the effects of the multi-step transfers and inelastic excitations on the fusion cross sections are investigated in the framework of the coupled-reaction-channel (CRC) method. Strong CRC effects of the multi-step processes are observed. Namely, the valence neutron in 13C or 17O plays an important role in the enhancement of the fusion. The potential barrier is effectively lowered with the formation of the covalent molecule of the configuration, 12C+n+12C or 12C+n+16O. In the analyses of the system 12C+13C, however, it is still required to introduce core-core optical potential of lower barrier height in the state of the positive total parity. This could be due to the neck formation with the nucleons contained in two core nuclei. (author)