Interplay of charge clustering and weak binding in reactions of Li8

Abstract

In collisions of light, stable, weakly bound nuclides, complete fusion (capture of all of the projectile charge) has been found to be suppressed by $\ensuremath{\sim}30%$ at above-barrier energies. This is thought to be related to their low thresholds for breakup into charged clusters. The observation of fusion suppression in the neutron-rich radioactive nucleus $^{8}\mathrm{Li}$ is therefore puzzling: the lowest breakup threshold yields $^{7}\mathrm{Li}+n$ which cannot contribute to fusion suppression because $^{7}\mathrm{Li}$ retains all the projectile charge. In this work, the full characteristics of $^{8}\mathrm{Li}$ breakup in reactions with $^{209}\mathrm{Bi}$ are presented, including, for the first time, coincidence measurements of breakup into charged clusters. Correlations of cluster fragments show that most breakup occurs too slowly to significantly suppress fusion. However, a large cross section for unaccompanied $\ensuremath{\alpha}$ particles was found, suggesting that charge clustering, facilitating partial charge capture, rather than weak binding is the crucial factor in fusion suppression, which may therefore persist in exotic nuclides.