Similar investigations into the isotopic ratios of ruthenium at Oklo found a much higher Ru concentration than otherwise naturally occurring (27–30% vs. 12.7%). This anomaly could be explained by the decay of Tc to Ru. In the bar chart, the normal natural isotope signature of ruthenium is compared with that for fission product ruthenium which is the result of the fission of U with thermal neutrons. The fission ruthenium has a different isotope signature. The level of Ru in the fission product mixture is low because fission produces neutron rich isotopes which subsequently beta decay and Ru would only be produced in appreciable quantities by double beta decay of the very long-lived (half life 7.1 × 10 years) molybdenum isotope Mo. On the timescale of when the reactors were in operation, very little (about 0.17 ppb) decay to Ru will have occurred. Other pathways of Ru production like neutron capture in Ru or Tc (quickly followed by beta decay) can only have occurred during high neutron flux and thus ceased when the fission chain reaction stopped.