Novel decay modes of high-Kisomers: Tunneling in a triaxial landscape

The nucleus ${}_{}{}^{176}{}_{}{}^{}\mathrm{W}$ has been studied using the reaction ${}_{}{}^{150}{}_{}{}^{}\mathrm{Nd}$ ${(}^{30}$Si,4n), with prompt and delayed γ-γ coincidence techniques. A K=14 isomer (${\mathit{t}}_{1/2}$≊70 ns) is found to exhibit a unique decay pattern, primarily decaying to K=0 states, in contrast to all previously studied high-K isomers. Calculations have been perfomed of both Coriolis mixing and tunneling through a potential barrier in the triaxial degree of freedom to understand these unusual decays. While Coriolis mixing models do not reproduce the variations in the decay patterns in neighboring nuclei, the tunneling calculations are remarkably successful.