High-K isomers in 176W and mechanisms of K violation

An isomer, with t_1/2=35+/-10 ns and J,K^π=14,14⁺, has been observed in the nucleus ¹⁷⁶W using the reaction ¹⁵⁰Nd(³⁰Si,4n) at a beam energy of 133 MeV. The isomer exhibits an unusual pattern of decay in which the majority of the flux proceeds directly to states with <K>=0, bypassing available levels of intermediate K. This severe breakdown of normal K-selection rules in ¹⁷⁶W is compared with recent observations of K violation in neighboring nuclei, within the framework of proposed theoretical approaches. The available data on these K-violating decays seem to have a consistent explanation in models of K mixing which include large-amplitude fluctuations of the nuclear shape.