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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+alpha+d, 6He+6Li-->2alpha+t+n, 6He+7Li-->6He+alpha+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 alpha-decay of the 10Be state at Ex= 7.54 MeV 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 approx 10.2 MeV 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 alpha-decay suggests the 4+ assignment. Both of these observations indicate a special, well-developed 6He+alpha cluster structure of the 10Be states involved. The structure of several low-lying 9Be states is also discussed.

radioactive beam; cluster states; 9Be; 10Be

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