Structure of two-, four-, and six-quasiparticle isomers in ¹⁷⁴Yb and K-forbidden decays

The stable nucleus ¹⁷⁴Yb has been studied using deep-inelastic reactions and time-correlated γ-ray spectroscopy. New intrinsic states assigned include a 370-ns isomer at 1765 keV, which we associate with a predicted K^π=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-μs isomer at 1518 keV support the 6⁺, 2-quasineutron configuration assignment proposed previously. The 6⁺ band is fed by a four-quasiparticle, K^π=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.