Structure of Mg Isotope Studied by β-Decay Spectroscopy of Spin-Polarized Na Isotopes Shape Coexistence in 30Mg

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 are being performed by our unique method of β-decay spectroscopy taking advantage of highly-spin-polarized radioactive nuclear beams at TRIUMF. The β-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 β decay of 30Na→30Mg. From the detailed decay scheme of Na, it is suggested that the Mg 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 γ-band.