High-Kbarrier penetration inHf174: A challenge toKselection

A sensitive study of the decay of the deformation-aligned K=14, 4-μs isomer in ${}_{}{}^{174}{}_{}{}^{}\mathrm{Hf}$ has revealed a multitude of the K-forbidden branches to the ground-state rotational band and other low-K bands, in competition with the known decays to high-K bands. The isomeric transitions have consistently low hindrance factors. These anomalous findings in an axially symmetric deformed nucleus severely test our understanding of the K-selection rule. The isomeric decay to an I=12 rotation-aligned state, and its mixing with the I=12 yrast state, provide a partial explanation.