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Bismuth and ^(208)Pb microdistributions in enstatite chondrites

Woolum, Dorothy S. and Bies-Horn, Linda and Burnett, D. S. and August, L. S. (1979) Bismuth and ^(208)Pb microdistributions in enstatite chondrites. Geochimica et Cosmochimica Acta, 43 (11). pp. 1819-1828. ISSN 0016-7037. http://resolver.caltech.edu/CaltechAUTHORS:20150423-103355055

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Abstract

Polished sections of 5 enstatite chondrites have been irradiated with 30 MeV ^4He ions to produce the alpha-radioactive nuclei ^(211)At and ^(210)Po from ^(209)Bi and ^(208)Pb, respectively. The distribution of alpha activity can be mapped, using cellulose nitrate as an alpha track detector, to give the corresponding Bi or Pb distributions in the meteorite. No strong localization of Bi or ^(208)Pb was found; relatively uniform track distributions were observed. In particular, metal or sulfide grains are not enriched in Bi or Pb (relative to bulk), which is in agreement with the predictions of nebular condensation calculations. While the track distributions appear uniform, the results of detailed, track-by-track mappings of the Bi detectors indicate that the Bi is not totally randomly distributed; the statistical fluctuations in the observed track density are different for the cases where the Bi is totally randomly distributed and where the Bi is localized in point sources. Assuming that the Bi in a given sample is localized in identical point sources which are uniformly distributed throughout the sample, the observed relative population densities of clusters (‘stars’) of small numbers of tracks (2–5) corresponds to Bi being localized, with ~90% in grains with about 10^(−16)g-Bi (~3 × 10^5 Bi atoms), and with ~10% in 4 × 10^(−14) g-Bi sources. If these are elemental Bi, as predicted theoretically, they are ~ 10^2 Å and 10^3 Å in size, respectively.


Item Type:Article
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http://dx.doi.org/10.1016/0016-7037(79)90030-9DOIArticle
http://www.sciencedirect.com/science/article/pii/0016703779900309PublisherArticle
Additional Information:© 1979 Pergamon Press Ltd. Received 4 August 1978, Accepted 18 July 1979, Available online 4 April 2003. we are indebted to R. CLARKE (U.S. National Museum) E. OLSEN (Field Museum, Chicago), and J. T. WASSON for their cooperation in providing the meteorite samples used in this study, and we thank G. MILLER, R. B. THEUS and R. 0. BONDELID of the NRL cyclotron for their support and interest in these experiments. The hospitality extended to us by the Geophysical Lab, where we do the photomicroscopy for the short Bi exposures after our irradiations, is very much appreciated. Finally, we are pleased to acknowledge the assistance of R. MASCITELLI in the analysis of the track registration and micro-migration experiments, and J. GRIFFITH in the tandem irradiations. This research was supported by NSF grant EAR73-00245 A02 and NASA grant NSG 7314.
Funders:
Funding AgencyGrant Number
NSFEAR73-00245 A02
NASANSG 7314
Record Number:CaltechAUTHORS:20150423-103355055
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20150423-103355055
Official Citation:Dorothy S. Woolum, Bies-Horn Linda, D.S. Burnett, L.S. August, Bismuth and 208Pb microdistributions in enstatite chondrites, Geochimica et Cosmochimica Acta, Volume 43, Issue 11, November 1979, Pages 1819-1828, ISSN 0016-7037, http://dx.doi.org/10.1016/0016-7037(79)90030-9. (http://www.sciencedirect.com/science/article/pii/0016703779900309)
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ID Code:56914
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:23 Apr 2015 17:55
Last Modified:23 Apr 2015 17:55

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