Structure of 33Mg sheds new light on the N=20 island of inversion

The first reaction spectroscopy on the ground state structure of 33Mg through the measurement of the longitudinal momentum distribution from the one-neutron removal reaction using a C target at 898A MeV is reported. The experiment was performed at the FRS, GSI. The distribution has a relatively narrow width (150±3 MeV/c (FWHM)) and the one-neutron removal cross-section is 74±4 mb. An increased contribution from the 2p3/2 orbital is required to explain the observation showing its lowering compared to existing model predictions. This provides new information regarding the configuration of 33Mg and the island of inversion.