Onset of intruder ground state in exotic Na isotopes and evolution of the shell gap

Utsuno, Yutaka   ; Otsuka, Takaharu*; Glasmacher, T.*; Mizusaki, Takahiro*; Homma, Michio*

We perform systematic calculations of nuclear moments and energy levels in neutron-rich Na isotopes with the Monte Carlo shell model by adopting a large model space consisting of the full and part of the orbits. The calculation well reproduces those observables. The result shows that the disappearance of the magic number starts already at and that the magicity completely disappears for the isotone Na. This is in sharp contrast to previous consensus that the magic number disappears at and beyond. This early onset of disappearance indicates that the shell gap considerably narrows in Na isotopes compared to stable nuclei near Ca.