LU-176 - AN UNRELIABLE S-PROCESS CHRONOMETER

A level scheme of Lu-176 up to approximately 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. We identify 27 previously unknown levels and 131 previously unknown transitions in Lu-176. With this gamma-ray data we place the energy of the isomer at 122.9 keV. A level at 838.5 keV (J-pi = 5-, t1/2 < 10 ns) is found to decay with substantial strength to both the ground state (7-, 4.08 x 10(10) yr) and the 122.9 keV isomer (1-, 3.7 hr). The presence of this level guarantees the thermal equilibrium of Lu-176g,m for T greater-than-or-equal-to 3 x 10(8) K and therefore during s-process nucleosynthesis. The resulting temperature sensitivity of its effective half-life rules out the use of Lu-176 as an s-process chronometer. The use of Lu-176 to determine s-process temperatures is discussed.