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

An isomer, with t1/2=35±10 ns and J,Kπ=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 left-angle K right-angle=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. copyright 1996 The American Physical Society