Level structure of the transitional odd-mass nuclei 141-149Pm

Abstract

The level structures of the five odd-mass nuclei 141-149Pm have been studied by methods of in-beam γ-ray and electron spectroscopy using (p,xn) and (3He,xn) reactions. Over twenty new levels were observed in each of the nuclei investigated. The spins of the levels range between 1/2 and 21/2. The missing isomeric h11/2 state (T1/2 = 12 ns) was observed in 147Pm. Comparisons between experimental and theoretical results have been made. Calculations for all isotopes have been performed using the quasiparticle-vibration model with an intermediate coupling. Positive-parity levels can be interpreted as members of multiplets of the last odd proton coupled to the quadrupole vibrations of the core. The cluster-vibration model has been applied to Pm isotopes, specially to 145Pm, under the assumption of the Z = 64 subshell closure. Positive-parity levels are explained very well when the cluster consists of three proton holes in the g7/2 and d5/2 shells. The results strongly support the assumption that the Z = 64 closure persists also for the Z = 61 promethium nuclei. The probable band structures of 149Pm are discussed on the basis of calculations made using an axial particle-rotor model. The results on negative-parity levels are also compared with the predictions of the triaxial particle-rotor model.