Relation between the gap at Z = 64 subshell and the Abrupt transition in the region N = 88 - 90

The onset of deformation in the N = 88∼90 region and the effects of the gap at Z = 64 subshell on nuclear structure are investigated with a microscopic approach of the interacting boson model. It turns out that, besides the n-p interaction, the distribution of single particle levels in the shell model space also plays a direct and important role in the rapid transition of spectrum structure. For Nd∼Dy nuclei the calculations show excellent agreement with experimental energy systematics