Energy dependence of the optical potential of weakly and tightly bound nuclei as projectiles on a medium-mass target

Angular distributions for the elastic scattering of the weakly bound Li-6,Li-7 + Sm-144 systems were measured with high accuracy at bombarding energies from 85% up to 170% of the Coulomb barrier. An optical model analysis was performed, and the relevant parameters of the real and imaginary parts of the optical potential were extracted. The results are compared with those previously published for the tightly bound C-12 + Sm-144 and O-16 + Sm-144 systems. The usual threshold anomaly observed in the behavior of the potential of tightly bound systems was not observed for either weakly bound system. This absence is attributed to the repulsion due to breakup coupling which cancels the attraction arising from couplings with bound channels.