Optical model analyses of 6,7Li+208Pb elastic scattering near the Coulomb barrier

The elastic scattering of 6Li and 7Li by 208Pb has been measured at several energies near the Coulomb barrier and analysed in terms of the optical model. Previous reports have suggested that the normalization factor, NR, for the double-folded real potential is approximately 0.6 for both isotopes at bombarding energies well above the Coulomb barrier. In this paper we show that, whereas this low value for NR persists for 6Li at energies close to the barrier, for 7Li it is somewhat greater than unity, and indicates the existence of a threshold anomaly for this porjectile. (orig.)