Structure of 30Mg Studied by beta-decay spectroscopy of spin-polarized 30Na -- shape coexistence in 30Mg --

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We have been studying the structure of Mg isotopes in the region of the N=20 island of inversion, to clarify the structure change as a function of the neutron number. The experiments were performed by our unique method of b-decay spectroscopy taking advantage of highly-spin-polarized radioactive nuclear beams at TRIUMF. The b-decay asymmetry in the Na-isotope decay enables unambiguous spin-parity assignments of the levels in the daughter Mg isotope, and it becomes possible to compare the experimental data and theoretical predictions on a level-by-level basis.The present work focused on the results of the b-decay of 30Na-->30Mg. From the detailed analyses, fourteen g-transitions were newly found and four new levels at 4.683, 4.694, 5.897 and 6.064~MeV were also found in 30Mg. It should be emphasized that the spins and parities of ten levels have been assigned for the first time. Five of them were firmly assigned. An evidence of shape coexistence was proposed.