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Title: Anomalous xenon in zone 13 Okelobondo

Abstract

In situ laser extraction techniques were applied for the study of heavy noble gases in a polished section of Zone 13 from the natural nuclear reactor in Okelobondo. Three main mineral phases were identified in this polished section using SEM-EDX. The Xe and Kr isotopic structures were determined by multiple measurements in each of these phases. Twenty-four isotopic analyses of the gases extracted from two different U-rich phases revealed nearly normal fission spectra. All 9 analyses of a U-free phase, consisting mainly of alumophosphates, demonstrated an unusual isotopic composition ({sup 136}Xe/{sup 134}Xe/{sup 132}Xe/{sup 131}Xe/{sup 130}Xe{sup 129}Xe/{sup 128}Xe = 1/1.25/1.73/0.89/0.0045/0.274/0) with concentrations ranging up to 10{sup {minus}2} cm{sup 3} STP/g. This is the highest Xe concentration ever measured in a natural material. Kr was also anomalous, although to a lesser extent. These results confirm the presence of Chemical Fractionation of Fission Xe (CFF-Xe) in the Okelobondo alumophosphates. CFF-Xe is a decay product of intermediate fission fragments that have migrated out of the U-rich host phases into adjacent U-free minerals. The CFF-Xe spectra in the alumophosphates are also accompanied by {sup 130}Xe excesses, which are attributed to neutron capture on fissiogenic {sup 129}I that apparently migrated out of the nearby U-rich minerals.more » The {sup 130}Xe/{sup 129}Xe ratio allows one to estimate the thermal equivalent neutron dose of 1.1 x 10{sup 21} n/cm{sup 2}. The presence of an unknown fission component remarkably similar in composition to CFF-Xe can be inferred from the atmospheric and terrestrial data. This leads one to the hypothesis that the CFF process has operated on a global scale on the Earth.« less

Authors:
; ;
Publication Date:
Research Org.:
Washington Univ., St. Louis, MO (US)
OSTI Identifier:
20062616
Resource Type:
Journal Article
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 64; Journal Issue: 9; Other Information: PBD: May 2000; Journal ID: ISSN 0016-7037
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; NATURAL URANIUM REACTORS; XENON; RADIOECOLOGICAL CONCENTRATION; KRYPTON; ISOTOPE RATIO; AFRICA

Citation Formats

Meshik, A.P., Kehm, K., and Hohenberg, C.M. Anomalous xenon in zone 13 Okelobondo. United States: N. p., 2000. Web. doi:10.1016/S0016-7037(00)00334-3.
Meshik, A.P., Kehm, K., & Hohenberg, C.M. Anomalous xenon in zone 13 Okelobondo. United States. doi:10.1016/S0016-7037(00)00334-3.
Meshik, A.P., Kehm, K., and Hohenberg, C.M. Mon . "Anomalous xenon in zone 13 Okelobondo". United States. doi:10.1016/S0016-7037(00)00334-3.
@article{osti_20062616,
title = {Anomalous xenon in zone 13 Okelobondo},
author = {Meshik, A.P. and Kehm, K. and Hohenberg, C.M.},
abstractNote = {In situ laser extraction techniques were applied for the study of heavy noble gases in a polished section of Zone 13 from the natural nuclear reactor in Okelobondo. Three main mineral phases were identified in this polished section using SEM-EDX. The Xe and Kr isotopic structures were determined by multiple measurements in each of these phases. Twenty-four isotopic analyses of the gases extracted from two different U-rich phases revealed nearly normal fission spectra. All 9 analyses of a U-free phase, consisting mainly of alumophosphates, demonstrated an unusual isotopic composition ({sup 136}Xe/{sup 134}Xe/{sup 132}Xe/{sup 131}Xe/{sup 130}Xe{sup 129}Xe/{sup 128}Xe = 1/1.25/1.73/0.89/0.0045/0.274/0) with concentrations ranging up to 10{sup {minus}2} cm{sup 3} STP/g. This is the highest Xe concentration ever measured in a natural material. Kr was also anomalous, although to a lesser extent. These results confirm the presence of Chemical Fractionation of Fission Xe (CFF-Xe) in the Okelobondo alumophosphates. CFF-Xe is a decay product of intermediate fission fragments that have migrated out of the U-rich host phases into adjacent U-free minerals. The CFF-Xe spectra in the alumophosphates are also accompanied by {sup 130}Xe excesses, which are attributed to neutron capture on fissiogenic {sup 129}I that apparently migrated out of the nearby U-rich minerals. The {sup 130}Xe/{sup 129}Xe ratio allows one to estimate the thermal equivalent neutron dose of 1.1 x 10{sup 21} n/cm{sup 2}. The presence of an unknown fission component remarkably similar in composition to CFF-Xe can be inferred from the atmospheric and terrestrial data. This leads one to the hypothesis that the CFF process has operated on a global scale on the Earth.},
doi = {10.1016/S0016-7037(00)00334-3},
journal = {Geochimica et Cosmochimica Acta},
issn = {0016-7037},
number = 9,
volume = 64,
place = {United States},
year = {2000},
month = {5}
}