Structure of Mg Isotope Studied by $\beta$-Decay Spectroscopy of Spin-Polarized Na Isotopes

International audienceWe 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 are being performed by our unique method of beta-decay spectroscopy taking advantage of highly-spin-polarized radioactive nuclear beams at TRIUMF. The beta-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 paper reports on the results of the beta decay of Na-30 -> Mg-30. From the detailed decay scheme of Na-30, it is suggested that the Mg-30 levels at 1.788 MeV [(0(2)(+))], 3.460 MeV [(2)(+)], 4.967 MeV [1(+)], and 5.414 MeV [2(+)] have deformed shapes with intruder configurations, whereas the level at 2.466 MeV [(2(2)(+))] has different nature both from the spherical ground state and the deformed four levels. It is proposed that the 2(2)(+) level is the band-head of the predicted gamma-band