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  • 1990-1994  (12)
  • 1970-1974  (4)
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Year
  • 11
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    Do meteorites contain irradiation records from exposure to an enhanced-activity sun? (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-08-14
    Description: The meteoritic evidence for a T Tauri phase in the sun's evolution is reviewed. Emphasis is given to effects recorded in meteoritic grains before final compaction of the meteorite parent body and the evidence that these precompaction irradiation effects do or do not require an active early sun. Several other effects attributed to such early activity are also reviewed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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    NASA TECHNICAL REPORTS
  • 12
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    Observations of enhanced sub-iron (Sc-Cr) to Iron abundance ratios in the low energy galactic cosmic rays in Spacelab-3 and their implications (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The Anuradha cosmic ray experiment in Spacelab-3, flown in the orbit at 350 km with an inclination of 57 deg for about six days, was used to measure the low energy galactic cosmic ray (GCR) heavy ions using a specially designed CR-39 detector module incorporating the arrival time information of the particles. The abundances of sub-iron (Sc-Cr) and iron particles in the low energy interval of 30-300 MeV/N were determined from the measurements made in four different depths of the Cr-39 detector module of 150 layers. From these studies we obtained sub-iron (Sc-Cr) to iron abundance ratios of 0.8 to 1.2 in 30-300 MeV/N energy range. It is found that these ratios are enhanced by a factor of two as compared to interplanetary ratios of about 0.5. It is shown that the enhancement of the ratio inside the earth's magnetosphere is probably due to the degree of ionization of low energy Sc to Cr and Fe ions in the galactic cosmic rays and to the rigidity filtering effects of the geomagnetic field. Further studies are needed to understand fully the phenomena and their implications.
    Keywords: SPACE RADIATION
    Type: Journal of Astrophysics and Astronomy (ISSN 0250-6335); 15; 1; p. 85-94
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    NASA TECHNICAL REPORTS
  • 13
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    Implications of the observations of partially ionised states in the low energy galactic cosmic rays (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Of the low energy (30-100 MeV/N)Fe-group nuclei of Galactic cosmic rays (GCRs) a fraction of about 20 percent of these are in partially ionized states. The origin of these particles are not known at present. From the considerations of relevant cross-sections, the following two important processes of the phenomena are given: (1) these GCR Fe-group nuclei must have captured the orbital electrons at energies of 1-5 MeV/N, while traversing matter; and (2) that these GCR ions of 1-5 MeV/N are then reaccelerated to energies of at least 30-100 MeV/N, most probably in the heliospheric boundary region. Three possible scenarios of the electron-capture processes are briefly discussed: (1) electron capture in a large molecular cloud; (2) GCR equilibrium spectra in ISM and their equilibrium charge; and (3) electron capture in the Oort's cloud.
    Keywords: SPACE RADIATION
    Type: International Cosmic Ray Conference; Aug 11, 1991 - Aug 23, 1991; Dublin
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    NASA TECHNICAL REPORTS
  • 14
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    Oxygen isotope studies of ordinary chondrites (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Several stages in the evolution of ordinary chondritic meteorites are recorded in the oxygen isotopic composition of the meteorites and their separable components (chondrules, fragments, clasts, and matrix). The whole-rock isotopic compositions reflect the iron-group of the meteorite (H, L, or LL). Isotopic uniformity of H3 to H6 and L3 to L6 are consistent with closed-system metamorphism within each parent body. LL3 chondrites differ slightly from LL4 to LL6, implying a small degree of open-system aqueous alteration and carbon reduction. On the scale of individual chondrules, the meteorites are isotopically heterogeneous, allowing recognition of the solar-nebular processes of chondrule formation. Chondrules for all classes of ordinary chondrites are derived from a common population, which was separate from the population of chondrules in carbonaceous or enstatite chondrites. Chondrules define an isotopic mixing line dominated by exchange between (O - 16)-rich and (O - 16)-poor reservoirs. The oxygen isotopic compositions of chondrites serve as 'fingerprints' for identification of genetic association with other meteorite types (achondrites and iron) and for recognition of source materials in meteoritic breccias.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 55; 2317-233
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    NASA TECHNICAL REPORTS
  • 15
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    Noble gases in the howardites Bholghati and Kapoeta (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Analyses of noble gases in whole rock samples of the howardites Bholghati and Kapoeta and grain-size separates of Kapoeta yield evidence for excesses of the Xe isotopes Xe-129 , Xe-131, Xe-132, Xe-134, and Xe-136 in a low-temperture component, similar to lunar excess fission Xe. Such a component may be able to provide chronometric information if the relative abundances of radioactive progenitors (I-129, Pu-244, and U-238) can be determined, but the isotopic spectra obtained are not sufficiently precise to do so. Eucritic clast BH-5 in Bholghati contains Xe produced in situ by the decay of Pu-244. Calculated fission Xe retention ages are 30-70 Ma after the formation of the solar system, consistent with the apparent presence of Sm-146 decay products. Both the clast and the matrix of Bholghati have K-Ar ages of about 2 Ga, suggesting a common thermal event at least that recently.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 54; 2183-219
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    NASA TECHNICAL REPORTS
  • 16
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    Cosmogenic neon from individual grains of CM meteorites - Extremely long pre-compaction exposure histories or an enhanced early particle flux (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: This paper presents the results on cosmogenic Ne extracted from individual meteoritic grains by a laser extraction system which used, at different times, two CW lasers: an Ar-ion laser and an Nd:YAG laser, with 20 and 70 W of deliverable power, respectively. Chemical etching was used to select grains exposed to solar flare VH particles. Results show that most of the grains with solar flare VH tracks (but not those which did not exhibit such tracks) contain spallation-produed Ne in significant excess of that due to the nominal cosmic-ray exposure, providing evidence for extensive energetic particle exposure during the precompaction era.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 54; 2133-214
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    NASA TECHNICAL REPORTS
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