The intruder feature of 31Mg and the coexistence of many particle and many hole states

Abstract

The low-lying level structure of ${}^{31}\mathrm{Mg}$ has been investigated by the antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM) with the Gogny D1S force. It is shown that the N=20 magic number is broken and the ground state has the pure neutron $2p3h$ configuration. The coexistence of many particle and many hole states at very low excitation energy is discussed.