Structure of two-, four-, and six-quasiparticle isomers inYb174andK-forbidden decays

Abstract

The stable nucleus Yb-174 has been studied using deep-inelastic reactions and time-correlated gamma-ray spectroscopy. New intrinsic states assigned include a 370-ns isomer at 1765 keV, which we associate with a predicted K-pi=7(-) two-quasineutron configuration. Analysis of the alignment and in-band properties of its rotational band, identified using time-correlated coincidences, allows characterization of the configuration. The properties of a newly identified rotational band built on the known 830-mu s isomer at 1518 keV support the 6(+), 2-quasineutron configuration assignment proposed previously. The 6(+) band is fed by a four-quasiparticle, K-pi=14(+) isomer at 3699 keV and several higher multiquasiparticle states, including a six-quasiparticle isomer at 6147 keV with K=(22,23). The results are discussed in terms of the states predicted on the basis of multiquasiparticle calculations. The anomalously fast K-forbidden transition strengths from the 14(+) isomer are attributed to either K mixing in the neutron configuration or to random mixing in the high-level-density region. The 7(-) isomer decays are not abnormal, whereas the very hindered E2 transition from the 6(+) isomer to the ground-state band remains unexplained.