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Xenon and iodine reveal multiple distinct exotic xenon components in Efremovka “nanodiamonds”.

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Title: Xenon and iodine reveal multiple distinct exotic xenon components in Efremovka “nanodiamonds”.
Authors: Gilmour, J.D.1 jamie.gilmour@manchester.ac.uk, Holland, G.1, Verchovsky, A.B.2, Fisenko, A.V.3, Crowther, S.A.1, Turner, G.1
Source: Geochimica et Cosmochimica Acta. Mar2016, Vol. 177, p78-93. 16p.
Subjects: Iodine, Xenon, Neutron capture, High temperatures, Pyrolysis
Abstract: We identify new xenon components in a nanodiamond-rich residue from the reduced CV3 chondrite Efremovka. We demonstrate for the first time that these, and the previously identified xenon components Xe-P3 and Xe-P6, are associated with elevated I/Xe ratios. The 129 I/ 127 I ratio associated with xenon loss from these presolar compositions during processing on planetesimals in the early solar system was (0.369 ± 0.019) × 10 −4 , a factor of 3–4 lower than the canonical value. This suggests either incorporation of iodine into carbonaceous grains before the last input of freshly synthesized 129 I to the solar system’s precursor material, or loss of noble gases during processing of planetesimals around 30 Myr after solar system formation. The xenon/iodine ratios and model closure ages were revealed by laser step pyrolysis analysis of a neutron-irradiated, coarse-grained nanodiamond separate. Three distinct low temperature compositions are identified by characteristic I/Xe ratios and 136 Xe/ 132 Xe ratios. There is some evidence of multiple compositions with distinct I/Xe ratios in the higher temperature releases associated with Xe-P6. The presence of iodine alongside Q-Xe and these components in nanodiamonds constrains the pathway by which extreme volatiles entered the solid phase and may facilitate the identification of their carriers. There is no detectable iodine contribution to the presolar Xe-HL component, which is released at intermediate temperatures; this suggests a distinct trapping process. Releases associated with the other components all include significant contributions of 128 Xe produced from iodine by neutron capture during reactor irradiation. We propose a revised model relating the origin of Xe-P3 (which exhibits an s-process deficit) through a “Q-process” to the Q component (which makes the dominant contribution to the heavy noble gas budget of primitive material). The Q-process incorporates noble gases and iodine into specific carbonaceous phases with mass dependent fractionation relative to the ambient composition. Q-Xe is dominated by the products of this “Q-process” occurring shortly before or during solar system formation. Carriers that trapped xenon by earlier Q-process events were altered, perhaps by supernova shocks, converting some Q carriers into P3 carriers. Unlike Q carriers, these carriers preserve the isotopic signature of the xenon they trapped through oxidation of samples in the laboratory. P3 carriers thus disproportionately sample xenon that was incorporated before galactic chemical evolution had produced the solar xenon signature by enriching ambient xenon with s-process material. [ABSTRACT FROM AUTHOR]
Copyright of Geochimica et Cosmochimica Acta is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Xenon and iodine reveal multiple distinct exotic xenon components in Efremovka “nanodiamonds”.
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  Data: <searchLink fieldCode="JN" term="%22Geochimica+et+Cosmochimica+Acta%22">Geochimica et Cosmochimica Acta</searchLink>. Mar2016, Vol. 177, p78-93. 16p.
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  Data: <searchLink fieldCode="DE" term="%22Iodine%22">Iodine</searchLink><br /><searchLink fieldCode="DE" term="%22Xenon%22">Xenon</searchLink><br /><searchLink fieldCode="DE" term="%22Neutron+capture%22">Neutron capture</searchLink><br /><searchLink fieldCode="DE" term="%22High+temperatures%22">High temperatures</searchLink><br /><searchLink fieldCode="DE" term="%22Pyrolysis%22">Pyrolysis</searchLink>
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  Data: We identify new xenon components in a nanodiamond-rich residue from the reduced CV3 chondrite Efremovka. We demonstrate for the first time that these, and the previously identified xenon components Xe-P3 and Xe-P6, are associated with elevated I/Xe ratios. The 129 I/ 127 I ratio associated with xenon loss from these presolar compositions during processing on planetesimals in the early solar system was (0.369 ± 0.019) × 10 −4 , a factor of 3–4 lower than the canonical value. This suggests either incorporation of iodine into carbonaceous grains before the last input of freshly synthesized 129 I to the solar system’s precursor material, or loss of noble gases during processing of planetesimals around 30 Myr after solar system formation. The xenon/iodine ratios and model closure ages were revealed by laser step pyrolysis analysis of a neutron-irradiated, coarse-grained nanodiamond separate. Three distinct low temperature compositions are identified by characteristic I/Xe ratios and 136 Xe/ 132 Xe ratios. There is some evidence of multiple compositions with distinct I/Xe ratios in the higher temperature releases associated with Xe-P6. The presence of iodine alongside Q-Xe and these components in nanodiamonds constrains the pathway by which extreme volatiles entered the solid phase and may facilitate the identification of their carriers. There is no detectable iodine contribution to the presolar Xe-HL component, which is released at intermediate temperatures; this suggests a distinct trapping process. Releases associated with the other components all include significant contributions of 128 Xe produced from iodine by neutron capture during reactor irradiation. We propose a revised model relating the origin of Xe-P3 (which exhibits an s-process deficit) through a “Q-process” to the Q component (which makes the dominant contribution to the heavy noble gas budget of primitive material). The Q-process incorporates noble gases and iodine into specific carbonaceous phases with mass dependent fractionation relative to the ambient composition. Q-Xe is dominated by the products of this “Q-process” occurring shortly before or during solar system formation. Carriers that trapped xenon by earlier Q-process events were altered, perhaps by supernova shocks, converting some Q carriers into P3 carriers. Unlike Q carriers, these carriers preserve the isotopic signature of the xenon they trapped through oxidation of samples in the laboratory. P3 carriers thus disproportionately sample xenon that was incorporated before galactic chemical evolution had produced the solar xenon signature by enriching ambient xenon with s-process material. [ABSTRACT FROM AUTHOR]
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  Data: <i>Copyright of Geochimica et Cosmochimica Acta is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1016/j.gca.2015.12.028
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      – Code: eng
        Text: English
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        PageCount: 16
        StartPage: 78
    Subjects:
      – SubjectFull: Iodine
        Type: general
      – SubjectFull: Xenon
        Type: general
      – SubjectFull: Neutron capture
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      – SubjectFull: High temperatures
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      – SubjectFull: Pyrolysis
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      – TitleFull: Xenon and iodine reveal multiple distinct exotic xenon components in Efremovka “nanodiamonds”.
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              Text: Mar2016
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