176Lu: An unreliable s-process chronometer

A level scheme of 176Lu up to ∼1400 keV excitation energy is deduced from a γ-γ coincidence experiment and previously published particle transfer data. 170 γ-ray transitions are placed between 85 levels. We identify 27 previously unknown levels and 131 previously unknown transitions in 176Lu. With this γ-ray data we place the energy of the isomer at 122.9 keV. A level at 838.5 keV (Jπ=5-, t1/2<10 ns) is found to decay with substantial strength to both the ground state (7-, 4.08x1010 yr) and the 122.9 keV isomer (1-, 3.7 hr). The presence of this level guarantees the thermal equilibrium of 176Lug,m for T≥3x108 K and therefore during s-process nucleosynthesis. The resulting 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