COULOMB-INDUCED AND NUCLEAR-INDUCED BREAK-UP OF HALO NUCLEI AT BOMBARDING ENERGIES AROUND THE COULOMB BARRIER

We investigate the relative importance of the Coulomb and nuclear fiel ds to induce the break-up of neutron-rich nuclei such as Li-11 at ener gies close to the Coulomb barrier. We assume that the mechanism that l eads to the separation is the excitation of a low-lying dipole mode in which the weakly-bound neutron halo performs a collective oscillation against the residual nuclear core. To this end we exploit semiclassic al prescriptions that are adequate to calculate not only the average b reak-up probabilities but also to estimate the size of fluctuations ab out the quantal expectation values. Possible outcomes are explored as a function of both bombarding energy and impact parameter. Consequence s of the couplings for elastic scattering and fusion processes are als o discussed.