Sequential decay reactions induced by a 18 MeV 6He beam on 6Li and 7Li

The 6He + 6Li and 6He + 7Li reactions have been studied using a 18 MeV 6He radioactive beam and a highly efficient and segmented detector set-up. Triple coincidence events corresponding to the 6He + 6Li → 6He+α+d, 6He + 6Li→2α+t+n and 6He + 7Li → 6He+α+t reactions have been clearly observed. The dominant mechanism of these reactions has been found to be a sequential decay through the known cluster states in 6Li, 7Li, 8Be, 9Be and 10Be. In particular, the sequential α-decay of the 10Be state at Ex=7.54MeV has been observed although its decay energy is much smaller (130 keV) than the decay energy for neutron emission (730 keV). Furthermore, the 10Be state at Ex≈10.2MeV has been found to be strongly populated in the reactions with both used targets. Angular correlations analysis of the events corresponding to the 10.2 MeV state α-decay suggests the 4+ assignment. Both of these observations indicate a special, well-developed 6He+α cluster structure of the 10Be states involved. The structure of several low-lying 9Be states is also discussed.