Evidence for rotational band structures in the N = 88 nuclide 153Tb

Abstract

Excited states in 153 65Tb 88 have been studied in the reactions 151 Eu(α, 2 n) and 153 Eu(α,4 n) using in-beam γ-ray spectroscopy. Levels of positive parity are identified up to spin 27 2 . Most of these states are interpreted as members of rotational bands characterized by the Nilsson configurations 3 2 + [411], 5 2 + [402] and 7 2 + [404]. Furthermore, a sequence of negative-parity states is observed up to spin 31 2 ( 35 2 ). The negative-parity band is remarkably well described in a Coriolis coupling calculation including all configurations of the h 11 2 Nilsson multiplet. In this calculation the moment of inertia parameter varies with collective angular momentum in the same way as in the ground-state band of 152Gd. Using the same prescription for calculating rotational energies, the irregular level spacings within the 5 2 + [402] and 7 2 + [404] bands are also well explained.