Lutetium thermometry for Oklo natural reactors: a new look at old data

Background: Lutetium thermometry has been used to analyze Oklo natural nuclear reactor zones but leads to widely varying and puzzling predictions for the temperatures T-0 which in turn impacts bounds on time variation of the fine structure constant alpha. Purpose: We revisit results for reactor zone RZ10 in light of new measurements of the isomer branching ratio B-g in Lu-175 neutron capture at 5 and 25 keV. Method: We recalculate predictions for T-0 as a function of B-g using realistic models of the Oklo neutron flux. Results: We find T-0 = 100 +/- 30 degrees C using a new value of B-g, in contrast to 350 < T-0 < 500 degrees C using the evaluated value at thermal energy. Conclusions: Lutetium thermometry can be applicable to analyses of Oklo reactor data, but a better measurement of B-g with thermal neutrons is needed to confirm the reliability of temperature predictions.