title: Record of cycling operation of the natural nuclear reactor in the Oklo/Okelobondo area in Gabon.
abstract: Using selective laser extraction technique combined with sensitive ion-counting mass spectrometry, we have analyzed the isotopic structure of fission noble gases in U-free La-Ce-Sr-Ca aluminous hydroxy phosphate associated with the 2 billion yr old Oklo natural nuclear reactor. In addition to elevated abundances of fission-produced Zr, Ce, and Sr, we discovered high (up to 0.03 cm(3) STP/g) concentrations of fission Xe and Kr, the largest ever observed in any natural material. The specific isotopic structure of xenon in this mineral defines a cycling operation for the reactor with 30-min active pulses separated by 2.5 h dormant periods. Thus, nature not only created conditions for self-sustained nuclear chain reactions, but also provided clues on how to retain nuclear wastes, including fission Xe and Kr, and prevent uncontrolled runaway chain reaction.
authors.affiliation: Physics Department, Washington University, St. Louis, MO 63130, USA.
authors.forename: A P
authors.initials: AP
authors.lastname: Meshik
authors.forename: C M
authors.initials: CM
authors.lastname: Hohenberg
authors.forename: O V
authors.initials: OV
authors.lastname: Pravdivtseva