Multi-quasiparticle states and K -forbidden transitions in ¹⁸³Os

High-spin states in ¹⁸³Os have been studied using the ¹⁷⁰Er(¹⁸O,5n) reaction at a beam energy of 85 MeV. Nine rotational bands based on 1-, 3-, 5- and 7-quasiparticle excitations have been observed. Nilsson configurations are assigned for the newly observed bands using g-factors deduced from M1/E2 branching ratios within the bands. In addition, two isomers with K^π=(43/2⁺) and (43/2^-) have been identified. The K^π=(43/2⁺) isomer decays directly to the K^π=9/2⁺ ground-state band with a large difference in the K quantum number, ΔK=17. The decay rates are discussed in terms of a tunneling model where high-K (isomeric) and low-K states interact via fluctuations towards triaxial nuclear shapes.