PUBLICATION: Low-lying neutron unbound states in 12Be

Published in Physical Review C: The neutron decay of an unbound resonance in Be 12 has been measured at 1243±21 keV decay energy with a width of 634±60 keV. This state was populated with a one-proton removal reaction from a 71 MeV/u B 13 beam incident upon a beryllium target. The invariant mass reconstruction of the resonance was achieved by measuring the daughter fragment in coincidence with neutrons. Despite being above the 2 n separation energy, the state decays predominantly by the emission of one neutron to Be 11, setting an upper limit on the branching ratio for the two-neutron decay channel to Be 10 of less than 5%. From the characteristics of the population and decay of the resonance, it is concluded that this state cannot correspond to the previously observed state at 4580±5 keV.

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