TRANSFER AND SURFACE VIBRATION COUPLINGS IN THE FUSION OF CA-40-46,TI-48,TI-50 AT NEAR-BARRIER ENERGIES(TI)

Fusion and quasielastic excitation functions were measured for Ca-40+T i-46,Ti-48,Ti-50 at energies close to the Coulomb barrier. The interes t in these systems lies in the opposite target-mass dependence of surf ace vibration couplings and neutron-transfer couplings. The cross sect ions were measured at small energy steps and with high precision, so t hat the structure in the excitation functions (barrier distributions) could be revealed through a differentiation process. The subbarrier fu sion data show a larger enhancement with increasing target mass number , which clearly indicates the importance of transfer couplings. The ag reement between the fusion and quasielastic barrier distributions is q uite good. Simplified coupled-channel calculations were performed to r eproduce the fusion data. A very good agreement is obtained by couplin g to low lying excited states (2(+) and 3(-)) and to the most positive neutron-transfer Q value (two-neutron projectile pickup channel).