Mixing effects on K-forbidden transition rates from the 6⁺ isomers in the N = 104 isotones

The problem of the very different E2 decay rates from the two-quasineutron K^π = 6⁺ isomers in the N = 104 isotones ¹⁷²Er, ¹⁷⁴Yb, ¹⁷⁶Hf, and ¹⁷⁸W is investigated using the triaxial projected shell model with inclusion of multi-quasiparticle configurations. It is demonstrated that the highly K-forbidden transition from the 6⁺ isomer to the ground-state band is sensitive to mixing with the 6⁺ state of the γ-vibrational band. Thus the inter-band transitions, and lifetimes, depend on the relative position of the γ-band and the isomeric state in each isotone.