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  • LUNAR AND PLANETARY EXPLORATION  (9)
  • 2020-2023
  • 1975-1979  (9)
  • 1
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    In:  Other Sources
    Publikationsdatum: 2011-08-17
    Beschreibung: He, Ne and Ar isotopes have been measured in six, and Al-26 in two diogenites. Cosmic-ray exposure ages corrected for shielding effects using Ne-22/Ne-21 ratios are generally concordant. Five diogenites have a group age of 14 Myr and three others may have a group age of 24 Myr, implying that two collisions may have produced 8 of the 9 diogenites.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geochimica et Cosmochimica Acta; 41; Jan. 197
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    facet.materialart.
    Unbekannt
    In:  Other Sources
    Publikationsdatum: 2011-08-16
    Beschreibung: Analysis of Al-26 and noble gases were conducted in a study of samples of two heavily weathered meteorites. The analyses were performed in accordance with procedures described by Cressy (1970) and by Herzog and Cressy (1974). The analytic data are presented in tables. Evidence is presented which implicates weathering as the most probable cause of the observed variation of Al-26 and the rare gas contents.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Meteoritics; 11; Mar. 31
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
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    In:  Other Sources
    Publikationsdatum: 2019-06-27
    Beschreibung: The Al-26 content of a group of stony meteorites with low levels of He-3 (implying outgassing caused by near approach to the sun) was analyzed in a test of the possible role of cosmic radiation in determining the radionuclide concentration of meteorites. The Al-26 contents of the meteorites with He-3 losses were found to be indistinguishable from the Al-26 contents of L- and H-chondrites. It is concluded that if the He-3 outgassing occurred near the sun, the flux of particles producing Al-26 must have been nearly normal, or the diffusion process must have taken place very rapidly.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geochimica et Cosmochimica Acta; 41; Oct. 197
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2019-06-27
    Beschreibung: Light curves of occultations of Europa by Io have been used to generate a crude map of albedo features on Europa. The best values currently available for the impact parameters and magnitude ratios for each event have been imposed on our model. Residuals between the observed and computed light curves are interpreted as albedo features on Europa. In order to improve the fit between the observations and the model, it became necessary to impose a general polar brightening. The effects of additional albedo features and alternate models are discussed.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus; 26; Sept
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2019-06-27
    Beschreibung: A detailed study to evaluate ground-based photographs of Mercury has been carried out. Models of the surface scattering properties have been assumed and smeared with a Gaussian function for direct comparison with center-to-limb scans along Mercury's intensity equator. Data from a range of phase angles from 31 to 92 deg have been compared with smeared models assuming a Lambert surface, a surface which obeys the Lommel-Seeliger law and one which is Minnaertian, having a variable coefficient. Within the limits of the observations a lunar Minnaert surface yields the most consistent interpretation. An objective evaluation of the resolution of the photographs is obtained in terms of Gaussian half-widths.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Icarus; 25; Aug. 197
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
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    Unbekannt
    In:  Other Sources
    Publikationsdatum: 2019-06-27
    Beschreibung: Al-26 (dpm/kg) and/or He, Ne, and Ar have been measured in samples of the Norton County meteorite from three different depths. The gas contents yield a shielding-corrected age of 75.8 + or - 5.7 million years. The ratio of atomic production rates P(Al-26)/P(Ne-21) is 0.22 + or - 0.02. He-3, Ne-21, and Al-26 increase with decreasing Ne-22/Ne-21 at nearly the same rates as they do in the smaller Keyes chondrite. Al-26 contents were measured in Bustee, Khor Temiki, Pesyanoe, and Shallowater meteorites. The ratio of observed to predicted Al-26 content correlates with Ne-22/Ne-21, and comparison with the corresponding chondrite correlation indicates that such aubrites as Malakal may have experienced an unusually high flux of cosmic rays.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 82; Aug. 10
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Publikationsdatum: 2019-06-27
    Beschreibung: Noble gases, C and S, are lost from Allende samples heated for 1 week at temperatures of 400-1000 C in a low pressure environment. In the extreme, losses of He-3 and He-4 are about 100 x while for C, S and Ne, Ar and Kr isotopes and Xe-132 these are less than or equal to 10 x. Except for He, these losses are less severe than those of Bi or Tl from samples heated in the same runs. Significant He, Ne and Ar isotopic fractionation during heating indicates preferential outgassing of specific reservoirs. Next to He, Ar-40 is the most labile of those species considered here but still less so than Bi or Tl. L-group (but not H- or LL-group) chondrites may have lost mobile elements like Tl while being outgassed after late impact-associated heating. A less likely alternative involving a collateral relation between condensation conditions and depth in a parent object may also explain the L-group trend.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Geochimica et Cosmochimica Acta; 43; Mar. 197
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2019-06-27
    Beschreibung: Mass spectroscopic analysis of neutron-irradiated targets of natural magnesium yields cross sections of 59 + or - 14, 160 + or - 8, and 11.0 + or - 3.3 mb for Ne-20, Ne-21 and Ne-22, respectively, at 14.1 MeV and of 94 + or - 8, 152 or - 12, and 13.0 + or - 2.0 mb at 14.7 Mev. Using these cross sections, calculations modeling cosmic ray interactions in stony meteoroids of radii 20 and 26 cm predict that between the surface and the center the Ne-22/Ne-21 ratio falls more than 10% while the Ne-21 production rate rises about 30%. Calculations are compared with published neon measurements for the Keyes and St. Severin meteorites.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Earth and Planetary Science Letters; 44; 2, Au; Aug. 197
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Publikationsdatum: 2019-06-27
    Beschreibung: Noble gas contents and shock effects have been studied in 21 Odessa irons from known geographic locations. Cosmogenic He-3, Ne-21, Ar-38 contents and He-3/Ne-21 ratios vary by factors of 62, 91, 68, and 1.55, respectively, while Ne-22/Ne-21 ratios are virtually constant at 1.07. The samples fall into two groups differing by a factor of 4.1 in exposure age, 1000 in source mass, or some combination of these. Three samples show significant shock effects, two of them to above 130 kbar, probably arising during terrestrial impact from the crater-forming explosion. As in Canyon Diablo plains specimens, noble gas contents do not correlate with siting or shock.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Journal of Geophysical Research; 81; July 10
    Format: text
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