Many-Particle and Many-Hole States in Neutron-Rich Ne Isotopes Related to Broken N=20 Shell Closure

Abstract

The low-lying level structures of $^{26}{\rm Ne}$, $^{28}{\rm Ne}$ and $^{30}{\rm Ne}$ which are related to the breaking of the N=20 shell closure have been studied by the framework of the deformed-basis antisymmetrized molecular dynamics plus generator coordinate method using Gogny D1S force. The properties of the many-particle and many-hole states are discussed as well as that of the ground band. We predict that the negative-parity states in which neutrons are promoted into $pf$-orbit from $sd$ orbit have the small excitation energy in the cases of $^{28}{\rm Ne}$ and $^{30}{\rm Ne}$ which, we regard, is a typical phenomena accompanying the breaking of N=20 shell closure. It is also found that the neutron $4p4h$ structure of $^{30}{\rm Ne}$ appears in low excitation energy which contains $\alpha + ^{16}{\rm O}$ correlations.