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The distribution of U and Pu in the St. Severin chondrite

Jones, J. H. and Burnett, D. S. (1979) The distribution of U and Pu in the St. Severin chondrite. Geochimica et Cosmochimica Acta, 43 (12). pp. 1895-1905. ISSN 0016-7037. doi:10.1016/0016-7037(79)90003-6.

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A detailed study of the U distribution of the St. Severin chondrite has been made by fission track radiography in order to clarify the interpretation of fission Xe thermal release data in terms of the mineralogical location of the fission Xe within the meteorite. This is of importance because the ^(244)Pu/^(238)U ratio for St. Severin has been widely adopted as the average solar system value. The U contents of the constituent minerals cannot account for the total rock U which, instead, appears to be primarily localized on grain boundaries. The greatest localizations of U are in olivine-poor, orthopyroxene-rich ‘clasts’. Our data coupled with those of Podosek (1970a) show that ^(244)Pu in St. Severin was also located on grain boundaries and that the bulk of Pu and U are unfractionated within this meteorite. Due to recoil, the ^(244)Pu fission Xe is found in 10 micron surface layers on major phases. Assuming that the grain boundaries (on which the Pu was located) was formed during metamorphism, the ^(244)Pu/^(238)U ratio for St. Severin applies to a time subsequent to the textural recrystallization of the meteorite. Our data support the interpretation of Podosek and our best estimate of the solar system ^(244)Pu/^(238)U is 0.015.

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Burnett, D. S.0000-0001-9521-8675
Additional Information:© 1979 Pergamon Press Ltd. Received 5 February 1979, Accepted 31 July 1979. The St. Severin samples were obtained through the co-operation of P. PELLAS J. REYNOLDS and G. J. WASSERBURG. We thank F. OBERLI and G. J. WASSERBURG for isotopic dilution measurements of our glass standards. We acknowledge profitable discussions with T. BENJAMIN and P. PELLAS and very thorough reviews by G. CROZAZ and G. LUGMAIR. We also thank Lou ANN CORDELL and BETTY ROBINKIN for their skill and patience. This research was supported by NSF grant EAR76-84402.
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Caltech Division of Geological and Planetary Science3211
Issue or Number:12
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Official Citation:J.H. Jones, D.S. Burnett, The distribution of U and Pu in the St. Severin chondrite, Geochimica et Cosmochimica Acta, Volume 43, Issue 12, December 1979, Pages 1895-1905, ISSN 0016-7037, (
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ID Code:56911
Deposited On:23 Apr 2015 19:27
Last Modified:10 Nov 2021 21:05

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