Study of transfer reactions induced by a 16C beam

Abstract

Recent experiments have evidenced the existence of new nuclear shell gaps at N=14 and N=16 in neutron-rich oxygen isotopes associated with the vanishing of the N=20 shell gap. However, in the neutron-rich carbon isotopes, the extent to which these gaps persist is unclear. In an effort to answer this question we have attempted to probe the low-lying level structure of 17C using the (d,p) transfer reaction to locate the single-particle orbitals involved in the formation of the N=14 and N=16 shell gaps. The experiment was carried out at the GANIL facility. A 16C beam at 17.2 AMeV produced by fragmentation was used to bombard a CD2 target. The light ejectiles were detected using the TIARA silicon strip array while a Si-Si-CsI telescope was placed at zero degrees to identify beam-like residues. In addition, four HPGe-EXOGAM clover detectors were used to measure the gamma-rays arising from 17C bound excited states. The measured angular distributions confirm the spin and parity assignments of 3/2+, 1/2+ and 5/2+ for the ground and the first and second excited states located at 217 keV and 335 keV respectively. The spectroscopic factors deduced for these excited states indicate a large single particle strength, in agreement with shell model calculations. With a strong l = 0 valence neutron component and a low separation energy, the first excited state of 17C appears as a good one-neutron halo candidate.