Abstract
The momentum distribution of 11Be fragments produced by the breakup of 12Be 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 11Be fragments from the one-neutron knockout Be12(p,pn) 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 0d5/2 orbital in 12Be to the transverse momentum distribution of the 11Be fragments. The single-neutron 0d5/2 spectroscopic factor deduced from the present knock-out data is 1.39(10), which is significantly larger than that deduced recently from data of 12Be breakup on a carbon target. This result provides a strong experimental evidence for the dominance of the neutron ν(0d5/2)2 configuration in the ground state of 12Be.
Highlights
The momentum distribution of 11Be fragments produced by the breakup of 12Be interacting with a proton target at 700.5 MeV/u energy has been measured at GSI Darmstadt
While the extended sizes of the halo nuclei can be accurately deduced from the measured interaction cross section [3, 4], or from the angular distribution of intermediate energy proton elastic scattering in inverse kinematics [5, 6, 7, 8, 9, 10, 11], the shell structure of the unstable neutron-rich nuclei has been studied mainly based on the analysis of momentum distributions of fragments from breakup reactions [12, 13, 14]
The observation of 12Be fragmentation followed by the γ-emission from the bound states of 11Be has shown that the 1s1/2 neutron shell is mixed with the 0p1/2 shell in the ground state of 12Be
Summary
The momentum distribution of 11Be fragments produced by the breakup of 12Be interacting with a proton target at 700.5 MeV/u energy has been measured at GSI Darmstadt. While the extended sizes of the halo nuclei can be accurately deduced from the measured interaction (or reaction) cross section [3, 4], or from the angular distribution of intermediate energy proton elastic scattering in inverse kinematics [5, 6, 7, 8, 9, 10, 11], the shell structure of the unstable neutron-rich nuclei has been studied mainly based on the analysis of momentum distributions of fragments from breakup reactions [12, 13, 14].
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