Nucleon-pair shell model: Effect of non-collective pairs for odd 123−129Sn

In this paper, odd-mass isotopic chain of [Formula: see text]Sn has been studied within the framework of nucleon-pair shell model (NPSM) with the noncollective pair originating from the alignment of two neutrons in the [Formula: see text]h11/2 orbit included. It was found that NPSM can reproduce the properties of the yrast bands satisfactorily, it is crucial to include the noncollective pair in the NPSM. The band structure can be explained as the backbending or the phase transition from vibrational limit to the rotational limit. The mechanism of the yrast band can be explained as band crossing between the ground state band and the S band constructed from the neutron alignment in the [Formula: see text]h11/2 orbit. Our results also suggest that the mechanism of the band structure of those four Sn isotopes can also be interpreted as the competition and transition between collective and noncollective phase.