Angular distributions of the elastic scattering of the ${}^{6,7}\mathrm{Li}$ on ${}^{138}\mathrm{Ba}$ were measured, in the energy range $21<~E_{\mathrm{lab}}<~32$ MeV. The analysis of the data was performed via the optical model, using the Woods-Saxon potential, in order to find the energy dependence of the real and imaginary parts of the nuclear potential. The existence of a threshold anomaly for the ${}^7\mathrm{Li}$ scattering and its absence for the ${}^6\mathrm{Li}$ one was observed. It is interpreted that the breakup of ${}^6\mathrm{Li}$, with dissociation energy smaller that its first excited state, is responsible for the vanishing of the threshold anomaly.

• Received 29 October 1998

DOI:https://doi.org/10.1103/PhysRevC.59.2103