Insights into the mechanisms and time-scales of breakup of 6,7Li

Using a back-angle detector array covering 117° to 167°, coincidence measurements of breakup fragments at sub-barrier energies have enabled the complete characterisation of the breakup processes in the reactions of 6,7Li with 208Pb. Those breakup processes fast enough (∼10−22 s) to affect fusion are identified through the measured relative energy of the two breakup fragments. The majority of these prompt breakup events are triggered by transfer of a neutron from 6Li, and of a proton to 7Li. These mechanisms, rather than breakup following direct projectile excitation, should thus be responsible for the majority of the ∼30% suppression of complete fusion observed at above-barrier energies. Breakup characteristics thus depend both on the properties of the initial nucleus and its neighbours. Quantitative modelling of this two-step process will require development of a complete reactions model, relevant for reactions involving both α-cluster nuclei, and exotic nuclei near the neutron and proton drip-lines.