Rotational and intrinsic states above the K^π=25/2^-, T_1/2=25 day isomer in ¹⁷⁹Hf

Time-correlated, particle-tagged γ spectroscopy of the stable nucleus ¹⁷⁹Hf was undertaken with incomplete fusion reactions initiated by beams of ⁹Be and ⁷Li incident on targets of ¹⁷⁶Yb. Intrinsic and rotational states above the three-quasiparticle K^π=25/2^-, T_1/2=25 day isomer, ¹⁷⁹Hf^m2, are reported. The rotational band based on ¹⁷⁹Hf^m2 has g_K-g_R values that are consistent with the previously suggested ν9/2⁺ ⊗π²[7/2⁺,9/2^-] configuration assignment. A value of g_R=0.34(5) was derived for the collective g factor of ¹⁷⁹Hf^m2, which is considerably higher than that found for the 9/2⁺ ground state. The difference is consistent with a reduction of the proton pairing strength due to blocking in the K^π=25/2^- ν⊗π² configuration. A number of ν³π² five-quasiparticle configurations were identified, the highest of which is an yrast K^π =43/2⁺, T_1/2=15(5) μs isomer. It decays to an yrast K^π=39/2^- state, which in turn decays to a rotational band based on a K^π=33/2^- state. The K^π=33/2^- state decays to the rotational band associated with ¹⁷⁹Hf^m2. Semiempirical calculations reproduce the excitation energies of the three-and five-quasiparticle states above ¹⁷⁹Hf^m2 to within ∼200 keV. The calculations predict that the lowest seven-quasiparticle state will arise from a ν⁵π² configuration with K^π=47/2^-, which is just beyond the maximum spin accessible with the reactions employed here.