As the first step of systematic studies on neutron-rich Mg isotopes, the structure of 28 Mg has been investigated by β-decay spectroscopy of spin-polarized 28 Na at TRIUMF. Spin-parity assignments have been successfully performed for levels in 28 Mg by taking advantage of the anisotropic β decay. Previous assignments for three levels were reconfirmed. New assignments were performed for four levels including a newly found 2 + level at 7.461 MeV. The experimental results were compared, on a

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... by-level basis, with the shell-model calculation in the model space restricted to the sd shell. Overall good agreement between the experimental and theoretical results indicates dominance of the normal configurations in most of the 28 Mg levels. High performance of the present method promises successful application to heavier Mg isotopes to elucidate the shell evolution in the region of the N = 20 island of inversion.