From routine sample measurements in CEA to the Oklo phenomenon

In 1972, before shipping natural uranium to the USSR for enrichment operations in ²³⁵U, the analysts at Pierrelatte plant noted a slight deficit in ²³⁵U: 0.7171 instead of 0.7202. The Direction des Productions of the CEA launched a vast campaign of analyses for the different mines exploited, at all stages of the elaboration of uranium; for this analysis campaign, the Direction des Productions relied on the analytical laboratory of the Pierrelatte plant and on the Central Analytical Laboratory of the CEA where I was in charge of analyses by mass spectrometry. (authors)