Energy dependence of the optical potentials for the 9 Be + 208 Pb and 9 Be + 209 Bi systems at near-Coulomb-barrier energies

We analyze the energy dependence of the interacting optical potential, at near barrier energies, for two systems involving the weakly bound projectile 9 Be and the heavy 208 Pb and 209 Bi targets, by the simultaneous fit of elastic scattering angular distributions and fusion excitation functions. The approach used consists of dividing the optical potential into two parts. A short-range potential VF + iWF that is responsible for fusion, and a superficial potential VDR + iWDR for direct reactions. It is found, for both systems studied, that the fusion imaginary potential WF presents the usual threshold anomaly (TA) observed in tightly bound systems, whereas the direct reaction imaginary potential WDR shows a breakup threshold anomaly (BTA) behavior. Both potentials satisfy the dispersion relation. The direct reaction polarization potential predominates over the fusion potential and so a net overall behavior is found to follow the BTA phenomenon.