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  • 1
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    Ni isotopic compositions in Allende and other meteorites (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A new technique for high-precision isotopic analyses of Ni is applied to terrestrial samples, Allende inclusions, and materials from other meteorites. It is noted that most of the Allende inclusions analyzed here were previously reported to contain isotopically anomalous Ti. In contrast, the Ni isotopic abundances are found to be indistinguishable from normal within presently obtainable precision, with only one possible exception. The latter inclusion has been shown by others to contain a significantly fractionated magnesium isotopic pattern of 9 parts per thousand/amu. A normal Ni isotopic pattern has also been observed for the chromite/carbon fraction of an Allende acid residue, which is known to have heavy noble gases of highly anomalous isotopic composition. All other meteoritic samples analyzed reveal normal isotopic compositions of Ni; no evidence for effects from now extinct Fe-60 could be detected. Despite ubiquitous isotopic anomalies in Ti from normal Allende inclusions there is no signature of isotopic variations in Ni from the same samples.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth and Planetary Science Letters (ISSN 0012-821X); 63; 2 Ma; May 1983
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    NASA TECHNICAL REPORTS
  • 2
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    Ca isotope variations in Allende (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Ca-isotope measurements of Allende Ca-Al-rich inclusions (CAIs), together with those on an apatite-enriched fraction from Orgueil, indicate the existence of widespread excesses on the neutron-rich isotope Ca-48. Isotopic anomalies are noted in 7 out of 11 CAIs analyzed. This abundance of isotopic excesses places Ca alongside Ti and O, although no clear correlation has yet been found between Ca-48 and Ti-50, which are thought to be coproduced by neutron-rich nucleosynthetic processes within stars. It is suggested that the higher volatility of Ca, by comparison with Ti compounds, led to a variable dilution with isotopically normal Ca in vaporization and recondensation processes in stellar envelopes, the interstellar medium, and/or the solar nebula.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 48; 2651-265
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    NASA TECHNICAL REPORTS
  • 3
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    Barium isotopes in Allende meteorite - Evidence against an extinct superheavy element (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Carbon and chromite fractions from the Allende meteorite that contain isotopically anomalous xenon-131 to xenon-136 (carbonaceous chondrite fission or CCF xenon) at up to 5 x 10 to the 11th atoms per gram show no detectable isotopic anomalies in barium-130 to barium-138. This rules out the possibility that the CCF xenon was formed by in situ fission of an extinct superheavy element. Apparently the CCF xenon and its carbonaceous carrier are relics from stellar nucleosynthesis.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 222; 1013-101
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  • 4
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    Samarium-146 in the early solar system - Evidence from neodymiun in the Allende meteorite (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A carbon-chromite fraction from the Allende C3V chondrite shows strikingly large isotopic enrichments of neodymium-142 (0.47 percent) and neodymium-143 (36 percent). Both apparently formed by alpha decay of samarium-146 and samarium-147 (half-lives 1.03 x 10 to the 8th and 1.06 x 10 to the 11th years), but the isotopic enrichment was greatly magnified by recoil of residual nuclei into a carbon film surounding the samarium-bearing grains. These data provide an improved estimate of the original abundance of extinct samarium-146 in the early solar system, Sm-146/Sm-144 = (4.5 + or - 0.5) x 10 to the -3rd, higher than predicted by some models of p-process nucleosynthesis. It may be possible to use this isotopic pair as a chronometer of the early solar system.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 222; 1015-101
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