Chain reactions in Oklo Uranium deposits and the fine-structure "constant"

"Two billion years before Fermi's 1942 reactor experiment, uranium deposits in West Africa, underwent sustained chain reactions. Measured isotopic distributions of neodymium provided information on neutron fluence and the amount of U235 regenerated from Pu239. The Oklo reactor was moderated by water percolating the ore. When the deposit underwent chain reactions and got heated up, the water would eventually evaporate away. Moderator lost, the reactor would shut down until rocks cooled for water to accumulate and begin a new cycle. Isotopic ratios of fission products have set upper limits to the variation of the fine structure constant with time. The phenomenology of the Oklo reactor, and the geological and astronomical constraints on the variation of fundamental "constants" will be reviewed."

References:

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