Investigating the evolution of the nuclear magic numbers via single-neutron transfer populating 26Na

Abstract

The changing shell structure close to the N = 20 shell gap has been explored by studying one-neutron transfer on 26Na in inverse kinematics. The experiment employed a 5MeV per nucleon beam of 25Na, incident on a 0.5mgcm-2 (CD2)n target, produced by the ISAC-II facility at TRIUMF, in Vancouver. A compact, highly-segmented silicon array, SHARC was positioned close to the target for the detection of the ejected protons. Coincident y rays, from the de-excitation of the 26Na recoil nucleus, were detected in the fully-suppressed γ- ray array, TIGRESS. Through the use of P γ: and p γ γ -gating, states in 26Na populated close in excitation energy were able to be resolved, and the proton angular distributions extracted. The proton angular distributions have been analysed for seven states directly populated by (d,p) in 26Na; and compared to theoretical cross-sections generated using TWOFNR. These states, amongst others, were compared to shell model calculations and to the N = 15 isotone 28 Al in order to tentatively assign spin and parity. Different interactions were em- ployed and compared to the experimental data, including USD, USD-A and USD-B calcu- . lations. The experimental data were also compared to SDPF-M Monte-Carlo Shell Model predictions, as well as WBP shell model calculations, in which the single-particle energies of the pf-shell were artificially lowered by 0.7 and 1.0MeV. A new level scheme with spin and parity assignments for states, including the negative parity states from f7/2 transfer, has been determined. It has been found that the gap observed between the f7/2 and SI/2 shells is approximately right, based on the shell model predictions with a 0.7MeV reduction in the shell gap. The gap between the sd- and pf-shells is found to be reduced by 1. 2 MeV, indicating the closure of the N = 20 shell gap for nuclei far from stability.EThOS - Electronic Theses Online ServiceGBUnited Kingdo