Direct Reactions with Exotic Beams (DREB2016)

Single-particle structure of ¹²Be studied in quasi-free (p,pn)-reactions

13 Jul 2016, 09:40

15m

Scotiabank Theatre (St. Mary's University)

Contributed Oral/Poster Shell evolution through direct reactions

Speaker

Mr Julian Kahlbow (Institut für Kernphysik, TU Darmstadt)

Description

The neutron-rich nucleus $^{12}$Be has been studied in inverse kinematics at the R$^3$B-LAND setup at GSI. In a kinematically complete measurement, proton-induced one-neutron knockout reactions at 400$~$MeV/nulceon are used to investigate single-particle properties. The high neutron-to-proton asymmetry leads to the breakdown of the magic $N=8$ shell-closure in $^{12}$Be. The valence-neutron pair configuration of the $^{12}$Be ground-state is assumed to be a mixture of the (1$p_{1/2}$)$^2$ occupation and the (2$s_{1/2}$)$^2$ & (1$d_{5/2}$)$^2$ intruder configuration above a $^{10}$Be core.[1,2] The bound and neutron-unbound states populated in the $^{11}$Be reaction fragment are disentangled by analysing the $\gamma$-ray spectrum and the relative-energy spectrum, respectively. All three partial cross sections are determined from quasi-free scattering and coherently analysed in eikonal reaction theory by C. A. Bertulani [3]. It is shown that the (2$s_{1/2}$)$^2$ & (1$d_{5/2}$)$^2$ intruder configuration is the dominant ground-state admixture in $^{12}$Be. This work is supported by HIC for FAIR, GSI-TU Darmstadt cooperation, and the BMBF project 05P15RDFN1. [1] A. Navin *et al.*, Phys. Rev. Lett. **85**, 266 (2000). [2] S. D. Pain *et al.*, Phys. Rev. Lett. **96**, 032502 (2006). [3] T. Aumann, C. A. Bertulani, and J. Ryckebusch, Phys. Rev. C **88**, 064610 (2013).