Anomalous xenon in zone 13 Okelobondo

Meshik, A. P.; Kehm, K.; Hohenberg, C. M.

doi:10.1016/s0016-7037(00)00334-3

Cited by 19 publications

(15 citation statements)

References 47 publications

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“…Here, Xe in the ampoule was found to be enriched in 136 Xe and 134 Xe, complimentarily to the low temperature Xe releases from the irradiated powder itself which was depleted in these isotopes. In a natural environment, CFF-Xe was reproducibly observed in minerals from the Oklo reactors in Gabon [5,6] which still remain the only occurrence of natural nuclear reactors. There were several previous observations of 131 Xe and 132 Xe enrichments, similar to those found in the Oklo ores, but they were either not reproducible [7] or tentatively attributed to neutron capture reactions on Te [8,9].…”

Section: Introductionmentioning

confidence: 93%

New evidence for chemical fractionation of radioactive xenon precursors in fission chains

2016

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Mass-spectrometric analyses of Xe released from acid-treated U ore reveal that apparent Xe fission yields significantly deviate from the normal values. The anomalous Xe structure is attributed to chemically fractionated fission (CFF), previously observed only in materials experienced neutron bursts. The least retentive CFF-Xe isotopes, 136 Xe and 134 Xe, typically escape in 2:1 proportion. Xe retained in the sample is complimentarily depleted in these isotopes. This nucleochemical process allows understanding of unexplained Xe isotopic structures in several geophysical environments, which include well gasses, ancient anorthosite, some mantle rocks, as well as terrestrial atmosphere. CFF is likely responsible for the isotopic difference in Xe in the Earth's and Martian atmospheres and it is capable of explaining the relationship between two major solar system Xe carriers: the Sun and phase-Q, found in meteorites.

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Section: Introductionmentioning

confidence: 93%

New evidence for chemical fractionation of radioactive xenon precursors in fission chains

2016

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“…In-situ isotopic analyses were applied to the noble gas elements with a laser extraction technique (Meshik, Kehm, & Hohenberg, 2000). A noble gas isotopic mass spectrometer equipped with a Q-switched Nd-YAG laser was used to measure the in-situ isotopic compositions of noble gases of individual mineral phases, because it is possible to selectively degas from minerals with a nominal spatial resolution of 10 mm.…”

Section: B In-situ Noble Gas Isotopic Analysesmentioning

confidence: 99%

“…A noble gas isotopic mass spectrometer equipped with a Q-switched Nd-YAG laser was used to measure the in-situ isotopic compositions of noble gases of individual mineral phases, because it is possible to selectively degas from minerals with a nominal spatial resolution of 10 mm. This technique was used to measure Kr and Xe isotopes of crandallite-group minerals from Reactor Zone 13 (Meshik, Kehm, & Hohenberg, 2000;Meshik, Hohenberg, & Pravdiviseva, 2004 Xe, respectively, in the minerals. On the basis of the fissiogenic Xe isotopic pattern of the Al-phosphate, the data provided evidence that Reactor Zone 13 operated in a cyclic mode in which 0.5-hr active pulses were separated by approximately 2.5-hr dormant periods, in which the self-regulatory activity was controlled by water in the reactor.…”

Section: B In-situ Noble Gas Isotopic Analysesmentioning

confidence: 99%

“…A period of approximately 2.5 hr was required to allow the steam to condense, so as to again achieve reactor criticality. The unique ability of Al phosphate to capture and retain gaseous fission products has implications for the long-term storage of radioactive waste (Meshik, Kehm, & Hohenberg, 2000).…”

Section: B In-situ Noble Gas Isotopic Analysesmentioning

confidence: 99%

“…Special precautions are needed to contain these elements. For example, it has been shown that the noble gases Xe and Kr can be absorbed on aluminous hydroxyl phosphates (Meshik, Kehm, & Hohenberg, 2000). Springer, copyright (1984), (Brookins, 1984) On the basis of studies of the characteristics of the geochemical mobility of fission products at Oklo, the main fission products have been classified by the work of Ruffenach, Hagemann, & Roth (1980); Gauthier-Lafaye, Holliger, & Blanc (1996); Hidaka & Holliger (1998) Table 12 is a compilation of this information.…”

Section: Implications Of the Oklo-bangombé Natural Reactors To Rmentioning

confidence: 99%

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The role of mass spectrometry to study the Oklo–Bangombé natural reactors

Laeter

Hidaka

2007

Mass Spectrometry Reviews

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The discovery of the existence of chain reactions at the Oklo natural reactors in Gabon, Central Africa in 1972 was a triumph for the accuracy of mass spectrometric measurements, in that a 0.5% anomaly in the (235)U/(238)U ratio of certain U ore samples indicated a depletion in (235)U. Mass spectrometric techniques thereafter played a dominant role in determining the nuclear parameters of the reactor zones themselves, and in deciphering the geochemical characteristics of various elements in the U-rich ore and in the surrounding rock strata. The variations in the isotopic composition of a large number of elements, caused by a combination of nuclear fission, neutron capture and radioactive decay, provide a powerful tool for investigating this unique geological environment. Mass spectrometry can be used to measure the present-day elemental and isotopic abundances of numerous elements, so as to decipher the past history of the reactors and examine the retentivity/mobility of these elements. Many of the fission products have a radioactive decay history that have been used to date the age and duration of the reactor zones, and to provide insight into their nuclear and geochemical behavior as a function of time. The Oklo fission reactors and their near neighbor at Bangombé, some 30 km to the south-east of Oklo, are unique in that not only did they become critical some 2 x 10(9) years ago, but also the deposits have been preserved over this period of geological time. The long-term geochemical behavior of actinides and fission products have been extensively studied by a variety of mass spectrometric techniques over the past 30 years to provide us with significant information on the mobility/retentivity of this material in a natural geological repository. The Oklo-Bangombé natural reactors are therefore geological analogs that can be evaluated in terms of possible radioactive waste containment sites. As more reactor zones were discovered, it was realized that they could be classified into two groups according to their burial depth in the Oklo mine-site. Reactor Zones 10, 13, and 16 were buried more deeply, and were therefore less weathered than the other zones. The less-weathered zones are of great importance in mobility/retentivity studies and therefore to the question of radioactive waste containment. Isotopic studies of these natural reactors are also of value in physics to examine possible variations in fundamental constants over the past 2 billion years.

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