Abstract
The low-lying level structure of the unbound neutron-rich nucleus Be has been investigated via breakup on a carbon target of secondary beams of B at 35 MeV/nucleon. The coincident detection of the beam velocity Be fragments and neutrons permitted the invariant mass of the and systems to be reconstructed. In the case of the breakup of B, a very narrow structure at threshold was observed in the channel. Analysis of the events demonstrated that this resulted from the sequential decay of the unbound Be(2) state rather than a strongly interacting -wave virtual state in Be, as had been surmised in stable beam fragmentation studies. Single-proton removal from B was found to populate a broad low-lying structure some 0.7 MeV above the neutron-decay threshold, in addition to a less prominent feature at around 2.4 MeV. Based on the selectivity of the reaction and a comparison with ( shell-model calculations, the low-lying structure is concluded to arise from closely spaced and 5/2 resonances ( and 0.85 MeV), while the broad higher-lying feature is a second 5/2 level ( MeV). Taken in conjunction with earlier studies, the results suggest that the lowest 1/2 and 1/2 levels lie relatively close together below 1 MeV.
6 More- Received 26 November 2013
- Revised 31 January 2014
DOI:https://doi.org/10.1103/PhysRevC.89.034320
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