Thus the French Commissariat à l'énergie atomique (CEA) began an investigation. A series of measurements of the relative abundances of the two most significant isotopes of uranium mined at Oklo showed anomalous results compared to those obtained for uranium from other mines. Further investigations into this uranium deposit discovered uranium ore with a U concentration as low as 0.44% (almost 40% below the normal value). Subsequent examination of isotopes of fission products such as neodymium and ruthenium also showed anomalies, as described in more detail below. However, the trace radioisotope U did not deviate significantly in its concentration from other natural samples. Both depleted uranium and reprocessed uranium will usually have U concentrations significantly different from the secular equilibrium of 55 ppm U relative to U. This is due to U being enriched together with U and due to it being both consumed by neutron capture and produced from U by fast neutron induced (n,2n) reactions in nuclear reactors. In Oklo any possible deviation of U concentration present at the time the reactor was active would have long since decayed away. U must have also been present in higher than usual ratios during the time the reactor was operating, but due to its half life of 2.348 × 10 years being almost two orders of magnitude shorter than the time elapsed since the reactor operated, it has decayed to roughly 1.4 × 10 its original value and thus basically nothing and below any abilities of current equipment to detect.