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  • 2015-2019
  • 1980-1984  (8)
  • 1983  (8)
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  • 2015-2019
  • 1980-1984  (8)
Year
  • 1
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    Nuclear track and compositional studies of olivines in CI and CM chondrites (1983)
    American Geophysical Union
    Details
    Publication Date: 1983-01-01
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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    PAPER CURRENT
  • 2
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    Cosmogenic neon from procompaction irradiation OF Kapoeta and Murchison (1983)
    American Geophysical Union
    Details
    Publication Date: 1983-01-01
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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    PAPER CURRENT
  • 3
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    Cosmogenic records in Antarctic meteorites (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Aliquot samples of 29 Antarctic L and H chondrites are analyzed for their nuclear track records and Mn-53 activities. The track density in the analyzed samples ranges from 10 to the 4th to approximately 6 x 10 to the 6th per sq cm. A significant finding is the observation of track-rich grains in a set of four L3 chondrites (ALHA 77215, 77216, 77217, and 77252), suspected of belonging to the same fall based on petrographic observations. An additional sample, ALHA 78105, an L6 chondrite, also has track-rich grains. Mn-53 activity is at near saturation level in approximately 65 percent of the analyzed samples, suggesting exposure ages of greater than 10 m.y. in these cases. Very few H chondrites from the 7-m.y. exposure age peak are apparently sampled among the ones investigated in this study. Approximately 6 percent and 4 percent, respectively, of the Antarctic H and L chondrites analyzed thus far for their cosmogenic records have precompaction irradiation features. A combined analysis of Mn-53 and nuclear track data makes it possible to confirm or rule out the proposed pairing of several sets of Antarctic meteorites and to estimate the preatmospheric sizes of some of these meteorites. The results suggest that most of the small Antarctic meteorites (less than 1 kg) have suffered high (greater than 95 percent) ablation mass-loss.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth and Planetary Science Letters (ISSN 0012-821X); 64; 1 Ju; July 198
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Cosmogenic neon from precompaction irradiation of Kapoeta and Murchison (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Neon from hand-picked Murchison and Kapoeta grains, selected on the basis of the presence or absence of solar flare particle tracks, was analyzed in order to delineate the precompaction history of this material. The irradiated grains showed large enrichments of cosmogenic neon relative to the unirradiated grains. Galactic cosmic ray (GCR) exposure ages for the unirradiated grains yield the nominal values reported for the recent exposure history of these meteorites. Apparent minimum precompaction galactic exposure ages of 28 m.y. and 56 m.y. would have been obtained for Murchison and Kapoeta, respectively, if the cosmogenic effects in the irradiated grains were due to GCR irradiation. Since this seems unreasonably long, the cosmogenic neon in the irradiated grains may be due to spallation by solar cosmic rays. This, however, would require a more active early sun. The isotopic composition of the cosmogenic neon in these grains suggests a harder energy spectrum than is characteristic of present solar flares. Lack of apparent solar wind effects may require some kind of shielding, such as nebular gas.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research, Supplement (ISSN 0148-0227); 88; B267-B27
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Nuclear track records in the Abee enstatite chondrite (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A determination of preatmospheric mass and a delineation of cosmic ray exposure history are made, through the study of nuclear track records in 14 samples taken from different locations of an Abee enstatite chondrite cut slab. Measured track densities in different samples range from 10,000 to 1,000,000/sq cm. Excess tracks of fissiogenic origin were found near the grain edges and across cleavage planes in eight enstatite grains out of the 300 analyzed. The track data rule out preirradiation of any of the analyzed samples with shielding of less than a few tens of cm. The isotrack density contours on the plane of the slab imply an asymmetric ablation of the Abee chondrite during its atmospheric transit. A sphere of about 30 cm radius approximates the preatmospheric shape and size of the Abee meteorite, which underwent a 70% mass loss during ablation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth and Planetary Science Letters; 62; 1, Ja; Jan. 198
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Solar flare particle fluences during solar cycles 19, 20 and 21 (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Satellite data for solar flare particle events during solar cycle 21 (up to July 1982) have been analyzed to obtain event-integrated fluxes of energetic protons and alpha particles. Thirty nine events with proton fluences (E greater than 10 MeV) greater than 10-million/sq cm occurred during 1976-1982. The average flux of protons with kinetic energy greater than 10 MeV is 65 per sq cm/s for this period. The event averaged alpha to proton ratio, in the energy interval 1-22 MeV/n, varies between 0.006 to 0.04, with an average value of about 0.02 for the whole cycle. The flux of protons (with energies greater than 10 MeV) averaged over cycle 21 is lower than those for solar-cycle 20 per sq cm/s based on satellite data, and for solar-cycle 19 378 per sq cm/s based on lunar sample data. There is no definitive correlation between solar-cycle averaged proton fluxes and sunspot numbers.
    Keywords: SOLAR PHYSICS
    Type: International Cosmic Ray Conference; Aug 22, 1983 - Sep 03, 1983; Bangalore; India
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Secular variations in solar flare proton fluxes (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Proton fluences in contemporary solar-flare events (1965-82) are analyzed to obtain values of average flux and characteristic rigidity R0 (MV). Both proton fluences F (E greater than 10MeV) and R0 (in the energy interval 10-30 MeV) values for individual events follow log-normal distribution. Comparison of contemporary average flux and R0 values with long-term averaged values, based on lunar sample data, indicate that the ancient solar-flare proton spectra were harder compared to that observed in contemporary flares. The contemporary and long-term (greater than 10,000 yr) averaged fluxes are similar, although such a comparison may not be meaningful because the contemporary averages suffer from uncertainty due to statistics of a single event. The long-term average data suggests a secular variation in solar-flare activity with enhanced proton fluxes during the last 100,000 years.
    Keywords: SOLAR PHYSICS
    Type: International Cosmic Ray Conference; Aug 22, 1983 - Sep 03, 1983; Bangalore; India
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Nuclear track and compositional studies of olivines in CI and CM chondrites (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The CI and CM chondrites, with bulk chemical compositions closely resembling solar values, are important for the study of early solar system processes. Noble gas and particle track studies have revealed that a majority of the CI and CM chondrites contain precompaction solar wind and solar flare irradiation records. A quantitative understanding of these records is important because it would allow constraints to be placed on the environment in which the irradiation occurred, and, therefore, on the mode of evolution of the CI and CM chondrites. The present investigation is concerned primarily with fossil track evidence, taking into account selected specimens of several CI and CM chondrites. In addition, the results are presented of extensive studies of the angular distributions of tracks in irradiated grains from four CM chondrites. The results provide information on the exposure geometry of the grains.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 15, 1982 - Mar 19, 1982; Houston, TX
    Format: text
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    NASA TECHNICAL REPORTS
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