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  • 1
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    Xenon spallation systematics in Angra dos Reis (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Literature Xe data for the Angra dos Reis meteorite have been resolved into constituent spallation, fission and trapped components. The spallation Xe compositions vary over a range wider than observed in any other samples, including lunar samples. These variations are due to the mixing of spallation Xe from Ba and rare earth element targets. It is possible to infer the Ba and rare earth spallation Xe compositions. Angra dos Reis spallation Xe compositions are systematically different from those observed in lunar samples, possibly because of differences in the irradiation conditions (geometry and shielding). Thus the Angra dos Reis data appear to be superior to lunar data for predicting spallation Xe compositions in other meteorites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta; 45; Oct. 198
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Troctolite 76535 - A study in the preservation of early isotopic records (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The lunar rock considered in the present investigation is a coarse-grained troctolite granulite containing about 58(vol)% plagioclase, 37% olivine, 4% pyroxene, and less than 1% accessory phases with a texture which indicates formation as a cumulate at depths between 10 and 30 km followed by an extended period of slow cooling. A description is presented of noble gas studies of separated minerals from 76535. The quantity of fission xenon from the in situ decay of Pu-244 provides further evidence for different, mineral-specific, isotopic closure times. The presented data shows that 76535 loses its surface-correlated xenon component upon disaggregation. No other xenon component is lost. The presence of solar gases in 76535 would seem to argue in favor of the external acquisition of the parentless extinct isotope effects and consequently favor 'thermal diffusion' and 'adsorption' over local redistribution models.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 16, 1981 - Mar 20, 1981; Houston, TX
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    NASA TECHNICAL REPORTS
  • 3
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    Argon ages for lunar breccias 14064 and 15405 (1978)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 13, 1978 - Mar 17, 1978; Houston, TX
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    NASA TECHNICAL REPORTS
  • 4
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    I-129/I-127 variations among enstatite chondrites (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The iodine isotopic compositions and corresponding I-Xe ages were obtained for eight enstatite chondrites, bringing the total number of enstatite chondrites examined by the I-Xe technique to 11. Iodine isotopic compositions of these 11 chondrites indicate a well-defined hiatus correlated with the hiatus in chemical composition defining the two distinct enstatite groups: EH(4,5) and EL(6). Judging by the I-129/I-127 ratios and assuming that both the EH and EL groups originated from a reservoir with a uniform initial iodine isotopic composition, the EH(4,5) chondrites were estimated to be about 4 mln older than the El chondrites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 52; 101-111
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    NASA TECHNICAL REPORTS
  • 5
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    Fission xenon in troctolite 76535 (1980)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Xenon released in stepwise heating of troctolite 76535 shows remarkable similarity to that from the gas-rich breccias. The low temperature fractions are highly enriched in fissiogenic xenon from Pu-244. Although the quantity of fission xenon is not inconsistent with reported age data, release patterns demonstrate that this component is not due to in situ decay. However, in contrast with the gas-rich breccias, the parentless radionuclear component in 76535 is not accompanied by solar wind xenon. Mechanisms for the emplacement of this component in 76535 cannot, therefore, involve exposure on the lunar surface but most likely involve adsorption along intergranular boundaries or thermally driven redistribution. The fact that xenon released from a gas-poor igneous cumulate can mimic that from gas-rich breccias, except for the presence of solar wind xenon in the latter, suggests that direct exposure to space is not required for the incorporation of these weakly bound, surface-correlated, parentless radionuclear components in lunar samples.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Conference on the Lunar Highlands Crust; Nov 14, 1979 - Nov 16, 1979; Houston, TX
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    NASA TECHNICAL REPORTS
  • 6
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    Shock disturbance of the I-Xe system (1982)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Three separate samples of the meteorite Bjurbole were artificially shocked at pressures of 70 kb, 200 kb, and 400 kb. Analysis of xenon released in stepwise heating shows that the I-Xe system of the 400 kb sample is substantially altered by the shock loading, and it is no longer possible to infer an age or trapped xenon composition for that sample. The 200-kb and 70-kb samples display isotopic structures progressively less altered demonstrating the gradations in shock disturbance likely to be found in natural systems. Interpretations of the I-Xe and Ar-40-Ar-39 systems for several naturally shocked meteorites are also presented. New data for Arapahoe do not confirm the previously reported age and trapped xenon composition, demonstrating instead that its I-Xe structure has been strongly disturbed by shock.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 15, 1982 - Mar 19, 1982; Houston, TX
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    NASA TECHNICAL REPORTS
  • 7
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    I-Xe ages of individual Bjurbole chondrules (1982)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Initial iodine isotopic compositions have been obtained for 10 individual chondrules from the meteorite Bjurbole, with a total range in well determined values of 6.5%, which would correspond to an age difference of 1.6 m.y. These results can be interpreted as distinct formation ages, metamorphic ages, or isotopic inhomogeneities in the early solar system, and can serve to constrain models for chondrule formation. Two of the chondrules show evidence of either isotopic inhomogeneities or disturbances of their I-Xe systems.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 15, 1982 - Mar 19, 1982; Houston, TX
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    NASA TECHNICAL REPORTS
  • 8
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    Noble gas component organization in 14301 (1980)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A study is conducted of the organization of noble gases in the Apollo 14 breccia 14301, giving particular attention to xenon from the extinct radionuclides I-129 and Pu-244. An essential ingredient of this work is the intercomparison between noble gases released in single-stage melts of grain size fractions and those released in stepwise extractions. This approach resolves 'functional' noble gas components, which are organized by siting, into the specific genetic contributions on the basis of the 'activation energies' for diffusive loss. The procedure makes it possible to resolve various genetic components on the basis of the chemical and structural differences in their specific locations. Consequently, distinctions can be made among components acquired by different processes and among components which have undergone different regolith histories.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 17, 1980 - Mar 21, 1980; Houston, TX
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    NASA TECHNICAL REPORTS
  • 9
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    Excess fission xenon at Apollo 16 (1978)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Results are reported of stepwise heating analyses of Xe and Kr in four Apollo 16 low-grade breccias: 60019, 60225, 60275, and 67455. All four samples contain significant amounts of solar wind gases and at least three contain excess fission Xe. This observation indicates that the excess fission Xe effect is global rather than local, i.e., results from moon-wide redistribution of fission Xe rather than local redistribution in KREEP-rich Apollo 14 material. It is suggested that the excess fission Xe phenomenon represents a temporal variation in the amount of fission Xe available for redistribution, that it is prominent in samples from both highland sites simply because they are older than mare sites, and that samples from these sites had experienced at least some of their surface exposure at an early epoch.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 13, 1978 - Mar 17, 1978; Houston, TX
    Format: text
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    NASA TECHNICAL REPORTS
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