Alpha-pat-tide emission from He-6+Bi-209

In a recent experiment, we have for the first time studied near-barrier and sub-barrier fusion of the exotic "Borromean" nucleus He-6 with Bi-209 and found that the sub-barrier fusion of this system is exceptionally enhanced, implying a 20% reduction in the nominal fusion barrier. It was suggested t hat this striking effect might be due to coupling to positive Q-value neutr on transfer channels, leading to "neutron flow" and consequent neck formati on between the projectile and target. The results of a new experiment using s the radioactive nuclear beam facility at the University of Notre Dame to measure fast a-particle emission from He-6 f + Bi-209 are discussed. A exce ptionally strong transfer/breakup group was observed at near-barrier and su b-barrier energies; this is very likely to be the "doorway state" that expl ains the enhanced sub-barrier fusion.