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Isotopic Composition of Molybdenum and Barium in Single Presolar Silicon Carbide Grains of Type A+BPresolar SiC grains fall into several groups based on C, N, and Si isotopic compositions. Approximately 93% are defined as mainstream, having 10 less than C-12/C-13 less than 100 and N-14/N-15 ranging from 50 to 20,000. A number of studies have shown that the most likely sources of mainstream grains are low mass asymptotic giant branch stars. Models of nucleosynthesis in AGB stars reproduce the s-process enhancements seen in the heavy elements in mainstream SiC grains. Among the less common grains, A+B grains, which comprise approximately 3-4% of presolar SiC, are perhaps the least well understood. Recent studies by Amari et al. show that A+B grains can be divided into at least 4 groups based on their trace element concentration patterns. Of 20 grains studied, 7 showed trace element patterns consistent with condensation from a gas of solar system composition, while the rest had varying degrees of process enhancements. Our previous measurements on 3 A+B grains showed Mo of solar isotopic composition, but Zr with a strong enhancement in 96Zr, which is an r-process isotope but can be made in an sprocess if the neutron density is high enough to bridge the unstable Zr-95 (T(sub 1/2)= 64 d). The observation of Mo with solar system isotopic composition in the same grains is puzzling however. Meyer et al. have recently shown that a neutron burst mechanism can produce a high Zr-96/Zr-94 without enhancing Mo-100, however this model leads to enhancements in Mo-95 and Mo-97 not observed in A+B grains. We report here results of Mo measurements on 7 additional A+B grains, and Ba measurements on 2 A+B grains, and compare these to the previous studies.
Document ID
Document Type
Conference Paper
Savina, M. R. (Argonne National Lab. IL, United States)
Tripa, C. E. (Chicago Univ. Chicago, IL, United States)
Pellin, M. J. (Argonne National Lab. IL, United States)
Davis, A. M. (Chicago Univ. Chicago, IL, United States)
Clayton, R. N. (Chicago Univ. Chicago, IL, United States)
Lewis, R. S. (Chicago Univ. Chicago, IL, United States)
Amari, S. (Washington Univ. Saint Louis, MO, United States)
Date Acquired
August 21, 2013
Publication Date
January 1, 2003
Publication Information
Publication: Lunar and Planetary Science XXXIV
Subject Category
Lunar and Planetary Science and Exploration
Funding Number(s)
CONTRACT_GRANT: W-31-109-eng-38
Distribution Limits
Public Use Permitted.

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IDRelationTitle20030110578Analytic PrimaryLunar and Planetary Science XXXIV
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