Evidence Of A ( 1 d 5 / 2 ) 2 Component To The 12 Be Ground State

Data have been obtained on exclusive single neutron knockout cross sections from 12Be to study its ground state structure. The cross sections for the production of 11Be in its ground state (1/2+) and first excited state (0.32 MeV, 1/2−) have previously been measured [1], indicating a strong (2s1/2) 2 component to the 12Be ground state. In the present experiment, performed at the GANIL laboratory, cross sections for the first (0.32 MeV, 1/2−) and second (1.78 MeV, 5/2+, unbound) excited states in 11Be were measured, which gives information on the admixture of (1p1/2) 2 and (1d5/2) 2 components in the ground state of 12Be. A fragmentation beam of 12Be of ∼10000 pps (95% pure) was incident on a carbon target at 41 MeV/u. The beam particles were tracked onto the target, and their energies were measured event-by-event. The beam-like residues were measured in a position sensitive telescope mounted at zero degrees, and neutrons were measured in the DéMoN array [1]. The 1/2− state of 11Be was identified by measuring coincident 320 keV γ-rays, using four NaI detectors. Full kinematic reconstruction of unbound states in 11Be was performed using coincident neutrons and 10Be ions. Detailed simulations were performed in order to interpret the data, and spectroscopic factors were calculated, using preliminary single particle removal cross sections calculated using a Glauber model.