G. Normand

Structure of Be-12: Intruder d-wave strength at N=8

The breaking of the N=8 shell-model magic number in the 12Be ground state has been determined to include significant occupancy of the intruder d-wave orbital. This is in marked contrast with all other N=8 isotones, both more and less exotic than 12Be. The occupancies of the [FORMULA: SEE TEXT]orbital and the [FORMULA: SEE TEXT], intruder orbital were deduced from a measurement of neutron removal from a high-energy 12Be beam leading to bound and unbound states in 11Be.

B(E1) Strengths from Coulomb excitation of 11Be

The B(E1;1/2{sup +}{yields} 1/2{sup -}) strength for {sup 11}Be has been extracted from intermediate energy Coulomb excitation measurements, over a range of beam energies using a new reaction model, the extended continuum discretized coupled channels (XCDCC) method. In addition, a measurement of the excitation cross section for {sup 11}Be+{sup 208}Pb at 38.6 MeV/nucleon is reported. The B(E1) strength of 0.105(12) e{sup 2}fm{sup 2} derived from this measurement is consistent with those made previously at 60 and 64 MeV/nucleon, in contrast to an anomalously low result obtained at 43 MeV/nucleon. By coupling a multi-configuration description of the projectile structure with realistic reaction theory, the XCDCC model provides for the first time a fully quantum mechanical description of Coulomb excitation. The XCDCC calculations reveal that the excitation process involves significant contributions from nuclear, continuum, and higher-order effects. An analysis of the present and two earlier intermediate energy measurements yields a combined B(E1) strength of 0.105(7) e{sup 2}fm{sup 2}. This value is in good agreement with the value deduced independently from the lifetime of the 1/2{sup -} state in {sup 11}Be, and has a comparable precision.

Experimental evidence of a v (1d5/2)2 component to the 12Be ground state

Data have been obtained on exclusive single neutron knockout cross sections from 12Be to study its ground state structure. Preliminary cross sections for the first (0.32 MeV, 1/2−) and second (1.78 MeV, 5/2+, unbound) excited states in 11Be have been obtained, giving evidence of significant admixtures of both v (1p 1/2)2 and v (1d 5/2)2 configurations in the ground state of 12Be.

Evidence Of A (1d52)2 Component To The 12Be 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, indicating a strong (2s12)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 (1p12)2 and (1d52)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 DeMoN array. The 1/2− state of 11Be was identified by measuring coincident...