Evolution from quasivibrational to quasirotational structure in Tm155 and yrast 27/2− to 25/2− energy anomaly in the A≈150 mass region

Excited states in Tm-155 have been populated via the reaction Sm-144(O-16, p4n) Tm-155 at a beam energy of 118 MeV. The ground-state band has been extended and a new side band of the ground-state band is identified. E-GOS curves and potential energy surface calculations are employed to discuss the structure evolution of the ground-state band. The newly observed side band in Tm-155 is discussed based on the spin/energy systematics. In particular, the phenomenon of seniority inversion is proposed in Tm-155, and a systematic study of this phenomenon in the A approximate to 150 mass region is performed.