CHEMICALLY FRACTIONATED URANIUM FISSION X ENON IN MANTLE ROCKS, GASESAND TERRESTRIAL ATMOSPHERE

A new conception on the origin of isotopic composition of terrestrial atmospheric xenon has been suggested, According this conception the ex cess of Xe-129 originates from I-129 that is a product of neutron indu ced fission of U-235, but not from primordial I-129 trapped by the Ear th during its accretion. Having analyzed all published data on xenon i sopotic composition mantle rocks and gases, the obvious correlation be tween excess Xe-129 and excesses in other xenon isotopes, particularly in Xe-132 and Xe-131, has been found. The isotopic pattern of excess xenon corresponds to that of CFF-Xe, the latter being the result of ch emical fractionation of radioactive Xe precursors in beta-chains deriv ed from the fission of heavy nuclei. The experimental study of xenon r eleased from the materials of naturally occurring nuclear reactor in O klo, of Colorado type uranium deposits and of some other objects prove s that the generation of chemically fractionated fission xenon under n atural conditions is quite possible. The presence of CFF-Xe in terrest rial atmosphere removes difficulties in the interpretation of present isotopic abundances of atmospheric xenon: neither hypothetical U-Xe, n or searching of exotic mechanism of selective isotopic fractionation o f AVCC-Xe are needed any more. The performed balance calculation showe d that the generation of required amount of CFF-Xe was possible in the course of neutron induced fission of U-235 migrating into the core du ring the Earth's differentiation. In the context of proposed conceptio n those models of the Earth's degassing that based upon the origin of Xe-129 from primordial I-129 become questionable.