Decay properties of three 166Lu isomers and the decay of 166Hf

Abstract

Two new isomers have been identified in 166Lu with half-lives of 2.12 and 1.41 min in addition to the 2.65 min ground state. Decay properties of the 166Lu isomers and of 6.77 min 166Hf have been studied with high resolution Ge(Li) detectors, a Ge(Li)-NaI(T1) Compton-suppression device and a Si (Li) detector, mounted in an electron transport solenoid. The isotope 166Hf decays mainly to a {p[523]↑− n[523]↓}1+ level in 166Lu. The decay of this level feeds all three isomers. The 2.65, 1.41 and 2.12 min isomers are identified as {[404]↓ + n[523]↓}6−, {p[411]↓ + n[523]↓}3− and p[402]↑ −n[523]↓0− configurations. All three show allowed unhindered β-decay to excited levels in 166Yb. The 2+ up to 8+ members of the ground state band, the2+ up to 8+ members of the γ-vibrational band, several octupole levels and 20 other states are excited. The values Zγ(2) = 0.053 ± 0.004 and Zγ(0) = 0.089 ± 0.004 are found for the mixing of the γ-vibrational and the ground state bands. This indicates that the intrinsic quadrupole moment of the γ-band is a factor of 0.6 smaller than that of the ground state band. A considerable mixing with higher vibrational states is probably present. The level sequence and energy spacings of 6 odd-parity levels could be explained from a Coriolis mixing calculation of the four p[514]↑ ± p[411]↓ and p[523)↑ ± p[411]↓ bands. The 6+ and 7+ members of the p[404]↓ + p[402]↑ band were identified. Positon-γ coincidence measurements yield a Q-value of 5480 ± 160 keV for the 166Lu ground state decay.