The dominance of the ν ( 0 d 5 / 2 ) 2 configuration in the N =8 shell in 12Be from the breakup reaction on a proton target at intermediate energy

摘要

The momentum distribution of 11 Be fragments produced by the breakup of 12 Be interacting with a proton target at 700.5 MeV/ u energy has been measured at GSI Darmstadt. To obtain the structure information on the anomaly of the N = 8 neutron shell, the momentum distribution of 11 Be fragments from the one-neutron knockout Be 12 ( p , p n ) reaction, measured in inverse kinematics, has been analysed in the distorted wave impulse approximation (DWIA) based on a quasi-free scattering scenario. The DWIA analysis shows a surprisingly strong contribution of the neutron 0 d 5 / 2 orbital in 12 Be to the transverse momentum distribution of the 11 Be fragments. The single-neutron 0 d 5 / 2 spectroscopic factor deduced from the present knock-out data is 1.39(10), which is significantly larger than that deduced recently from data of 12 Be breakup on a carbon target. This result provides a strong experimental evidence for the dominance of the neutron ν ( 0 d 5 / 2 ) 2 configuration in the ground state of 12 Be.