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  • LUNAR AND PLANETARY EXPLORATION  (5)
  • 1
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    Carbon-14 ages of Antarctic meteorites with accelerator and small-volume counting techniques (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: C-14 measurements were made on six Yamato and Victoria Land meteorites using tandem accelerator mass spectroscopy. The studies brought to 27 the number of Antarctic meteorites that have been examined for terrestrial aging. Details of the spectroscopic method are provided, along with the results in combinations with the data from the other 21 meteorites. It is found that the Yamato meteorites are younger than those found at Allan Hills, implying that two mechanisms may exist for the abundant Antarctic meteorites: exposure where falling due to a paucity of ice, and transport and exposure by sublimating ice.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research, Supplement (ISSN 0148-0227); 89; C329-C33
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    NASA TECHNICAL REPORTS
  • 2
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    A carbon-14 depth profile in the L5 chondrite Knyahinya (1994)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We report on a series of measurements of C-14 in samples of the L-chondrite Knyahinya, as a function of depth. The results show C-14 concentrations ranging from 37 to 58 dpm/kg. These measurements are compared to the levels of Ne-21, Be-10 and noble-gas ratios in this meteorite reported by Graf et al (1990). We also compare the C-14 data to the expected profile based on two sets of model calculations. The behavior of this radioisotope with depth is similar to that expected from the models, and good agreement with the profiles of other nuclides is also observed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics (ISSN 0026-1114); 29; 5; p. 649-651
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    NASA TECHNICAL REPORTS
  • 3
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    Carbon-14 activities in recently fallen meteorites and Antarctic meteorites (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: This paper reports C-14 measurements in meteorites using an extraction method which employs RF melting of samples as small as 0.1 g. A study of extraction of cosmic-ray-produced C-14 in samples of Bruderheim gave C-14 levels between 38 and 60 dpm/kg for samples which had been preheated in air between 250 and 700 C, with a mean value of 46.8 + or - 1.4 dpm/kg. A range of values between 35 and 59 dpm/kg was found for other falls of saturated meteorites preheated to 500 C. The preheating step is shown to be effective in removing terrestrial carbon contamination. A series of samples previously dated by Kr-81 as having ages of 120-310 kyr gave C-14 levels of between less than 0.16 and 0.37 + or - 0.10 dpm/kg. These levels are consistent with levels of in situ production by cosmic rays at the earth's surface.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 53; 2095-210
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  • 4
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    Carbon-14 terrestrial ages and weathering of 27 meteorites from the southern high plains and adjacent areas (USA) (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We report on a series of 27 C-14 terrestrial ages of meteorites from four states in the central and southwestern U.S. These results were compared to the earlier work of Boeckl (1972). Our results showed that the weathering rate for destruction of meteorites is lower than suggested by Boeckl. We estimate a 'half-life' for removal of meteorites of about 10 to 15 ka, similar to that derived for Roosevelt County meteorites. We also studied the weathering of these meteorites compared to terrestrial age. Only a weak correlation was observed, and for these meteorites the degree of weathering can only be taken as a weak indicator of terrestrial residence time. We also measured the delta-C-13 and C-14 and amount of weathering-product carbonates which show some interesting variations with the length of time the meteorites have been exposed to weathering.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Meteoritics (ISSN 0026-1114); 28; 2; p. 188-195.
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  • 5
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    Distribution of terrestrial age and petrologic type of meteorites from western Libya (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A group of 54 meteorites have been recovered from Daraj, Western Libya. After assessment of pairing of samples, using petrologic criteria, C-14 terrestrial ages were obtained on 13 samples selected from 9 different fall events. Eleven of the ages range from 3500 to 7600 years, with only two samples having ages in excess of 10,000 years. The cutoff in ages may be related to the timing of climatic changes in the Hammadah al Hamra.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 54; 2895-289
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