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  • Other Sources  (10)
  • 1985-1989  (10)
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  • 1
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    Evolution of gas-rich meteorites: Clues from cosmogenic nuclides (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The evolution of gas-rich meteorites in general, and the setting in which the observed solar-wind, solar-flare irradiation records were imprinted in individual components of these meteorites are understood only in qualitative terms, although contrary viewpoints do exist. The regolith irradiation hypothesis, bolstered by the observations of irradiation features in lunar regolith materials, similar to those observed in gas-rich meteorites, is accepted by many workers in this field. However, a close analysis of the problem suggests that the regolith irradiation may not be the dominant mode in producing the observed precompaction irradiation features in the gas-rich meteorites.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst. Workshop on Cosmogenic Nuclides; 2 p
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  • 2
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    Precompaction irradiation effects: Particles from an early active sun? (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Two recent studies have shown that solar flare irradiated grains from Murchison and Kapoeta have excess spallogenic Ne-21 compared to unirradiated grains, indicating large precompaction particle irradiation effects. The quantity of cosmogenic neon in these grains presents serious difficulties for either galactic cosmic ray or normal solar flare sources. In the first study it was suggested that the effect might be the result of exposure to an early active sun. The more recent experiment both confirms the earlier results and provides constraints on the characteristic energy spectrum on the irradiation. The first results were obtained from Murchison olivines and Kapoeta pyroxenes by mass spectrometric analysis of sets of grains selected on the basis of the presence or absence of solar flare particle tracks. In the second work plagioclase feldspar grains from Kapoeta were studied.
    Keywords: SOLAR PHYSICS
    Type: Lunar and Planetary Inst. Workshop on Cosmogenic Nuclides; 2 p
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  • 3
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    IONS (ANURADHA): Ionization states of low energy cosmic rays (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: IONS (ANURADHA), the experimental payload designed specifically to determine the ionization states, flux, composition, energy spectra and arrival directions of low energy (10 to 100 MeV/amu) anomalous cosmic ray ions of helium to iron in near-Earth space, had a highly successful flight and operation Spacelab-3 mission. The experiment combines the accuracy of a highly sensitive CR-39 nuclear track detector with active components included in the payload to achieve the experimental objectives. Post-flight analysis of detector calibration pieces placed within the payload indicated no measurable changes in detector response due to its exposure in spacelab environment. Nuclear tracks produced by alpha-particles, oxygen group and Fe ions in low energy anomalous cosmic rays were identified. It is calculated that the main detector has recorded high quality events of about 10,000 alpha-particles and similar number of oxygen group and heavier ions of low energy cosmic rays.
    Keywords: GEOPHYSICS
    Type: NASA. Marshall Space Flight Center Spacelab 3 Mission Science Review; p 64-74
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  • 4
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    Evidence in meteorites for an active early Sun (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The amounts of neon-21 found in meteorite particles indicate that the Sun experienced a period of intense solar flare activity approximately 4.5 billion years ago.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst. 16th Lunar and Planetary Sci. Conf.; p 6-8
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  • 5
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    Irradiation records in meteorites (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The approximately 4.6 billion-year history of a meteorite will encompass at least one episode of exposure to such energetic particles as cosmic rays; measurements of such exposure allow determination of how long a meteorite existed as a meter-sized body prior to earth impact. Meteorite exposure to energetic particles before their ejection from a parent body entails that the meteorite reside in the upper several m of that parent regolith. At the periods closest to the 4.6 billion year horizon, early solar system conditions may have been characterized by much gas and dust; irradiation records from this period may prove invaluable in reconstructing its characteristics.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 6
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    Evidence for extreme Ti-50 enrichments in primitive meteorites (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The results of the first high mass resolution ion microprobe study of Ti isotopic compositions in individual refractory grains from primitive carbonaceous meteorites are reported. One hibonite from the Murray carbonaceous chondrite has a 10 percent excess of Ti-50, 25 times higher than the maximum value previously reported for bulk samples of refractory inclusions from carbonaceous chondrites. The variation of the Ti compositions between different hibonite grains, and among pyroxenes from a single Allende refractory inclusion, indicates isotopic inhomogeneities over small scale lengths in the solar nebula and emphasizes the importance of the analysis of small individual phases. This heterogeneity makes it unlikely that the isotopic anomalies were carried into the solar system in the gas phase.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 296; L17-L20
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  • 7
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    O-16 excesses in Murchison and Murray hibonites - A case against a late supernova injection origin of isotopic anomalies in O, Mg, Ca, and Ti (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Ion probe measurements of the oxygen isotopic composition of seven hibonite samples from the CM chondrites Murchison and Murray are reported. All samples show large O-16 excesses relative to terrestrial oxygen. The data for all samples plot along the carbonaceous chondrite O-16-rich mixing line and show no evidence for isotopic mass fractionation effects characteristic of FUN inclusions. These hibonites have the largest Ca-48 and Ti-50 isotopic anomalies found to date; thus there is no intrinsic relationship between anomalies of a nucleosynthetic origin and isotopic mass fractionation effects. The large O-16 excess seen in the sample with the largest measured Ca-48 and Ti-50 depletions argues against a late injection of exotic material from a nearby supernova as a source for the isotopic anomalies.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 323; L91-L95
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  • 8
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    Al-26, Pu-244, Ti-50, REE, and trace element abundances in hibonite grains from CM and CV meteorites (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Hibonites from the CM meteorites Murchison, Murray, and Cold Bokkeveld, and hibonites and Ti-rich pyroxene from the CV chondrite Allende are studied. Electron microprobe measurements of major element concentrations and track and ion probe measurements of Mg and Ti isotopic ratios, rare earth elements (REEs), and trace element abundances are analyzed. Correlations between isotopic anomalies in Ti, Al-26, Pu-244, and Mg-26(asterisk) are examined. Ti isotopic anomalies are compared with REE and trace element abundance patterns. Reasons for the lack of Al-26 in the hibonites are investigated and discussed. It is observed that there is no correlation between the Ti isotopic compositions, and the presence of Mg-26(asterisk), Pu-244, and REE and trace element patterns in individual hibonite samples. The data reveal that hibonites are not interstellar dust grains but formed on a short time scale and in localized regions of the early solar system.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 51; 329-350
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  • 9
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    Solar flare protons and alpha particles during the last three solar cycles (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: This paper presents solar-flare-associated proton and alpha-particle fluxes determined for major events from October 1972 through March 1987 (the period that represents the last part of solar cycle 20 and the whole of solar cycle 21), using data obtained by detectors on board the IMP-7 and IMP-8 satellites, along with earlier obtained data for cycle 20. It was found that the average omnidirectional flux of protons with kinetic energy above 10 MeV for cycle 21 (64/sq cm per sec) is lower than the corresponding number for cycle 20 (92/sq cm per sec) and for the cycle 19 (378/sq cm per sec). No definitive correlation was found to exist between cycle-averaged solar flare proton fluxes and peak sunspot numbers.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 7195-720
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  • 10
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    Evidence in meteorites for an active early sun (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: High-sensitivity noble gas mass-spectrometric analyses of meteorite grains having solar flare heavy ion tracks show large enrichments of spallation-produced Ne-21 and Ar-38 when compared to nonirradiated grains from the same meteorite. The enhanced spallation effects in the irradiated grains are due to irradiation by energetic protons early in the history of the solar system, before compaction of the host meteorite. They require a proton fluence (E greater than 10 MeV) of 10 to the 16th to 10 to the 18th/cu cm. These results are best explained by solar flare irradiation in the early solar system with a proton flux several orders of magnitude higher than contemporary solar flares. The Ne isotopic structure suggests a harder energy spectrum than is characteristic of contemporary flares. These observations provide direct evidence for an active early (T Tauri) sun.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 313; L31-L35
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