Normal and anomalous K-hindered decays from four-quasiparticle isomers in Lu-176 - art. no. 031303

Two four-quasiparticle isomers, with K-pi=12(+) and (14(+)) and mean lives of 450(100) ns and 58(5) mu s, have been identified in Lu-176, at excitatio n energies of 1515 and 1588 keV, respectively. The 12(+) isomer exhibits a large number of K-forbidden decay branches, populating the rotational seque nces based on the K-pi=7(-) ground state, two K-pi= 8(+) states, and a K-pi =4(+) state from the nu{7/2(-)[514]}x pi{1/2(-)[541]} configuration. Most b ranches have decay rates that are consistent with normal K-hindrances excep t for the branch to the K-pi=4(+) band. It has an anomalously low hindrance factor, which is attributed to two-state mixing due to a near-degeneracy b etween the 12(+) isomer and the 12(+) member of this band. The implied mixi ng matrix element has a value of only 5 eV, showing explicitly that very sm all mixing matrix elements may be responsible for anomalous K-hindered deca ys.