176Lu: An unreliable s-process chronometer

A level scheme of 176Lu up to ∼1400 keV excitation energy is deduced from a gamma-gamma coincidence experiment and previously published particle transfer data. 170 gamma-ray transitions are placed between 85 levels, confirming many of the previously established levels and some of the decay scheme. A level at 835.5 keV (Jπ = 5-, t1/2 < 10 ns) decays with substantial strength to both the ground state (7-, 4.08 x 1010 yr) and the 122.9 keV isomer (1-, 3.7 hr). The presence of this level guarantees the thermal equilibration of 176Lug,m for temperatures greater than 3 x 108 K and therefore during s-process nucleosynthesis. The resulting extreme temperature sensitivity of its effective half-life rules out the use of 176Lu as an s-process chronometer. The use of 176Lu to determine s-process temperatures is discussed. 30 refs., 11 figs., 3 tabs