Quasi-elastic backscattering of

We have performed precision elastic backscattering measurements for the weakly bound nuclei 6,7Li on the medium and heavy mass targets 58Ni, 116,120Sn and 208Pb at sub- and near-barrier energies (E c.m. /V bar = 0.6 to 1.3). Excitation functions of elastic scattering cross-sections have been measured at ±160° and ±170° and the corresponding ratios to Rutherford scattering and relevant barrier distributions have been extracted. These measurements complement recent work on a 28Si target, for probing systematically the potential at sub- and near-barrier energies and relevant reaction mechanisms, while indicate a possible breakdown of the dispersion relation