Unusual Threshold Anomaly in the ⁶Li+²⁰⁸Pb System

The angular distributions of elastic scattering for the ⁶Li +²⁰⁸Pb system have been measured at several energies around the Coulomb barrier. The parameters of optical potential are extracted by means of a phenomenological optical model analysis. It is found that the real and imaginal potentials show a pronounced energy dependence. The behaviour of the potential at the nearly especially sub-barrier energies in the ⁶Li+²⁰⁸Pb system is quite different from the results of some previous reports observed in other systems, such as ¹⁹F+²⁰⁸Pb and ¹⁶O+²⁰⁸Pb. This unusual threshold phenomenon indicates that breakup channel is strongly coupled with the elastic channel and has obvious effects on optical potential.