Gilmour, J. D.

Turner, G.

Verchovsky, A. B. Sasha

English

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Open Research OnlineThe Open University’s repository of research publicationsand other research outputsXenon isotopes in nanodiamonds and other presolargrainsConference or Workshop ItemHow to cite:Gilmour, J. D.; Verchovsky, A. B. Sasha and Turner, G. (2002). Xenon isotopes in nanodiamonds and otherpresolar grains. In: 65th Annual Meeting of the Meteoritical Society, 21-26 Jul 2007, Los Angeles, California, USA.For guidance on citations see FAQs.c© [not recorded]Version: [not recorded]Link(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/metsoc2002/pdf/5210.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukXENON ISOTOPES IN NANODIAMONDS AND OTHER PRESOLAR GRAINS.  J. D. Gilmour1, A. B. Verchovsky2 and G. Turner1, 1Dept of Earth Sciences, University of Manchester, Man-chester M13 9PL, UK, 2PSSRI, Open University, Milton Keynes MK7 6BT.  Introduction:  Nanodiamonds isolated from primitive meteor-ites contain isotopically ‘normal’ Xe-P3 and components enriched in heavy and light isotopes - Xe-HL, exotic Xe-P6.  Excesses of 129Xe from 129I decay are also observed [1].  We discuss these in the light of data obtained from size-separated Efremovka nanodiamond samples produced at the Vernadsky Institute, Moscow [2]. Results: Excess 129Xe is present in low temperature releases from the largest grain size separate (ED9: 1.5 - 9nm) but not in the remainder (ED2,3,4: <3 nm).  In addition, the signature of Xe-P6 is also observed only in separate ED9. 129Xe Excess: 129Xe excesses are widespread in nanodiamond separates [1].  Step-heating release patterns suggest that the site of this component is identical to that of Xe-P3, but ratios of excess 129Xe to Xe-P3 show a distinctive dependence on the extent of par-ent body processing of the host meteorite.  Nanodiamonds from meteorites less processed than reduced CV3 meteorites have similar 129Xe concentrations but decreasing concentrations of Xe-P3, greater degrees of processing have led to 129Xe loss.  These observa-tions are most readily explained if the nanodiamond 129Xe excess was present as 129I during processing, xenon loss from this site being associated with a parent body process, as for other components [3].  The data constrain the trapping of the P3 component to within 10 Ma before parent body processing unless even the most P3-rich nanodiamonds have lost >85% of their original Xe-P3. This is con-sistent with the reported initial iodine ratio for a nanodiamond-rich separate from Inman, which was similar to that of other early solar system reservoirs (129I/127I = 10-4  [4]). Xe-HL and Xe-P6   These components, hosted by nanodia-monds with distinct grain size distributions, are distinguished from each other by a variation in the extent of enrichment of the heavy isotopes and by the ratio of excess 134Xe (over solar) to excesses of 131,132,136Xe.  The relative abundance of 134Xe is sensitive to minor parameter changes in both current models of Xe-H production: neu-tron fluence in the neutron burst model [5] and precursor half life in the model of involving separation of radioactive precursors [6].  Tellurium data are more consistent with the latter [7].   However, the characteristic signature of Xe-H is not observed only in nanodiamonds.  Accumulated data from nanodiamonds [1] and SiC xenon analyses [8] require contributions from 3 nucleosyn-thetic sources - one s-process and two sources of the r-process iso-topes.  Both r-process endmembers are also observed in SiC grains, suggesting that any model dependent on the size of nanodiamonds for recoil loss of xenon isotopes trapped as radioactive precursors is incorrect.  References: [1] Huss G. R. and Lewis R. S. (1994a) Meteoritics 29, 791-810. [2] Verchovsky A. B. et al. (1998) Science, 281, 1165-1168.  [3] Huss G. R. and Lewis R. S. (1994b) Meteoritics 29, 811-829. [4] Nichols Jr. R. H. et al. (1991) Geochim. Cosmochim. Acta 55, 2921-2936. [5] Clayton D. D. (1989) Ap. J. 340, 613-619. [6] Ott U. (1996) Ap. J. 461, 344-348. [7] Richter S. et al. (1998) Na-ture 391, 261-263. [8] Lewis R. S. et al. (1994) Geochim. Cosmo-chim. Acta 58, 471-494. 65th Annual Meteoritical Society Meeting (2002) 5210.pdf

Xenon isotopes in nanodiamonds and other presolar grains

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Xenon isotopes in nanodiamonds and other presolar grains

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