Competing phenomena: High-seniority excitations and γ-softness in ¹⁸⁴Os

The nuclear structure of the stable nucleus ¹⁸⁴₇₆ Os has been studied including five newly identified rotational bands built on 2-quasiparticle K^π = 0⁺, 6^-, 8^- couplings. The excitation energies of the proposed multi-quasiparticle excitations are in good agreement with predictions of blocked BCS calculations. The interaction responsible for the first band crossing, caused by a high-K tilted 2-neutron configuration, is calculated and a new interpretation presented for the yrast states after the interaction. A second crossing with an aligned s-β band is also reported. The yrast behaviour at high spins is dominated by a wealth of short-lived (nanoseconds and shorter) high-K levels. The low reduced hindrances for intrinsic state decays are discussed, and attributed to the triaxial shapes and fluctuations predicted by configuration-constrained potential-energy-surface calculations. Comparisons with neighbouring nuclei are made.