Abstract
The neutron-unbound isotope Be-13 has been studied in several
experiments using different reactions, different projectile energies,
and different experimental setups. There is, however, no real consensus
in the interpretation of the data, in particular concerning the
structure of the low-lying excited states. Gathering new experimental
information, which may reveal the Be-13 structure, is a challenge,
particularly in light of its bridging role between Be-12, where the N =
8 neutron shell breaks down, and the Borromean halo nucleus Be-14. The
purpose of the present study is to investigate the role of bound excited
states in the reaction product Be-12 after proton knockout from B-14, by
measuring coincidences between Be-12, neutrons, and gamma rays
originating from de-excitation of states fed by neutron decay of Be-13.
The Be-13 isotopes were produced in proton knockout from a 400
MeV/nucleon B-14 beam impinging on a CH2 target. The Be-12-n
relative-energy spectrum d sigma/dE(fn) was obtained from coincidences
between Be-12(g.s.) and a neutron, and also as threefold coincidences by
adding gamma rays, from the de-excitation of excited states in Be-12.
Neutron decay from the first 5/2(+) state in Be-13 to the 2(+) state in
Be-12 at 2.11 MeV is confirmed. An energy independence of the
proton-knockout mechanism is found from a comparison with data taken
with a 35 MeV/nucleon B-14 beam. A low-lying p-wave resonance in
Be-13(1/2(-)) is confirmed by comparing proton- and neutron-knockout
data from B-14 and Be-14.
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