Structure of Mg-28 studied by beta-decay spectroscopy of spin-polarized Na-28: The first step of systematic studies on neutron-rich Mg isotopes

As the first step of systematic studies on neutron-rich Mg isotopes, the structure of Mg-28 has been investigated by beta-decay spectroscopy of spin-polarized Na-28 at TRIUMF. Spin-parity assignments have been successfully performed for levels in Mg-28 by taking advantage of the anisotropic beta 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 level-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 Mg-28 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.