The quenching of the N=8 shell gap has been under investigation for more than 40 years, yet there remains significant controversy over the extent of mixing between 0hbar&omega and 2hbar&omega configurations in 12Be. Recent neutron knockout and transfer measurements have helped quantify 2hbar&omega contributions to the ground and excited 0+ wavefunctions for the first time. The Gamow-Teller strength (B(GT)) of transitions from the ground state of 12B to the 0+ states in 12Be has been measured using the (7Li, 7Be) charge-exchange reaction in inverse knematics. Since the ground state of 12B is dominated by 0hbar&omega configurations, Gamow-Teller (&Delta L=0, &Delta S=1) transitions to the 0+ states in 12Be selectively probe the 0hbar&omega component ofthe wavefunction. The extracted B(GT) to the 0+ states in 12Be were compared with shell model calculations, performed using the cde OXBASH and employing a modified WBP interaction in the spsdpf model space. To reproduce the observed B(GT) distribution, a 0hbar&omega admixture of 25.48 ± 5.49 percent is required in the ground state of 12Be, and a 0hbar&omega admixture of 59.83 ± 4.78 percent is required in the 2.24 MeV 0+ state. These results are compared with the wavefunctions extracted from neutron knockout and transfer measurements, and the theoretical predictions of Fortune and Sherr, Barker, and Romero-Redondo et al.
Read
