Low-lying neutron f p-shell intruder states in Ne-27

The quenching of the N = 20 shell gap in neutron-rich nuclei is investigated by studying the single-particle structure of Ne-27 via neutron transfer using a Ne-26 beam. Two low-lying negative-parity intruder states have been observed, the lowest of which is identified as J(pi) = 3/2(-), confirming earlier speculations. A level identified as 7/2(-) is observed higher in energy than the 3/2(-), contrary to the ordering at beta-stability and at an energy significantly different from the predictions of previous shell-model calculations. The measured energies and deduced spectroscopic factors are well reproduced in full (0,1)-h omega 0s-0p-0d-1s-0f -1p calculations in which there is a significant ad hoc reduction (similar to 0.7 MeV) in the N = 20 shell gap.