  The s-process branching at mass number A = 176 depends on the coupling
between the high-K ground state and a low-lying low-K isomer in 176Lu. This
coupling is based on electromagnetic transitions via intermediate states at
higher energies. The properties of the lowest experimentally confirmed
intermediate state at 839 keV are reviewed, and the transition rate between
low-K and high-K states under stellar conditions is calculated on the basis of
new experimental data for the 839 keV state. Properties of further candidates
for intermediate states are briefly analyzed. It is found that the coupling
between the high-K ground state and the low-K isomer in 176Lu is at least one
order of magnitude stronger than previously assumed leading to crucial
consequences for the interpretation of the 176Lu/176Hf pair as an s-process
thermometer.

Nuclear Experiment