Quasielastic backscattering and barrier distribution for the weakly bound projectile Li 6 on Tb 159

The excitation function for quasielastic scattering of the weakly bound projectile $^{6}\mathrm{Li}$ on a $^{159}\mathrm{Tb}$ target, at large backward angle, has been measured at energies around the Coulomb barrier. The corresponding quasielastic barrier distribution has been extracted from the experimental cross sections, both including and excluding the $\ensuremath{\alpha}$ particles produced in the reaction. The quasielastic scattering cross sections, excluding the $\ensuremath{\alpha}$ particles, have been analyzed in the framework of coupled channels calculations. The centroid of the quasielastic barrier distribution, including the $\ensuremath{\alpha}$ particles, is found to shift towards higher energy relative to the centroid of the fusion barrier distribution for the system. This has been attributed to the low $\ensuremath{\alpha}$-breakup threshold of the nucleus $^{6}\mathrm{Li}$.