Multiparticle- and particle x octupole states in 65 149 Tb84

Abstract

Yrast- and above-yrast states in149Tb were investigated in (α, 6n) and (7Li, 2n) in-beamγ-ray experiments. The yrastγ-ray cascade strongly populates three-valenceparticle states involving theh 11/2 proton and thef 7/2,h 9/2, or;i 13/2 neutron orbitals, as well as the high-spin levels formed by the couplings of the three149Tb valence particles, to the low-lying146Gd octupole phonon and to higher-lying proton particle-hole core excitations. The data give the (πh 11/2 vi 13/2)12− attraction free of octupole contributions as -631 keV. The shell model with empirical two-particle- and particle-phonon residual interactions gives an excellent quantitative description of the149Tb energy levels. It is noted that the observed highspin members of theπh 11/2 vh 9/2 v f 7/2 configuration closely resemble the lowest symmetric and mixed-symmetry representations of theS 3 permutation group.