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  • 1
    ISSN: 1090-6487
    Keywords: 75.70.Ak ; 76.80.+y
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Depth-selective conversion electron Mössbauer spectroscopy was used to study magnetic properties of the thin surface layers of the α-Fe2O3 and FeBO3 single crystals. An analysis of the experimental spectra indicates that the magnetic properties of the layers at a depth of more than ∼100 nm from the surface are similar to the properties of crystal bulk, and the corresponding spectra consist of narrow lines. The lines gradually broaden as the crystal surface is approached. The spectra of the ∼10-nm-thick surface layers consist of broad lines, indicating a wide distribution δ=2.1 T of the effective magnetic field about its mean value of 32.2(4) T. The experimental spectra were used to determine the effective magnetic fields (H eff) for the iron ions situated in the surface layers of thickness ∼100 nm. The effective fields in these layers were found to gradually decrease at room temperature (291 K) as the crystal surface was approached. The H eff values in the 2.4(9)-nm-thick surface layer of the α-Fe2O3 crystal and 4.9(9)-nm layer of FeBO3 are 0.7(2) and 1.2(3)%, respectively, smaller than for the nuclei of the ions in the bulk of these crystals.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2019-07-13
    Description: We determined radiogenic and cosmogenic noble gases in a mudstone on the floor of Gale Crater. A K-Ar age of 4.21 +/- 0.35 billion years represents a mixture of detrital and authigenic components and confirms the expected antiquity of rocks comprising the crater rim. Cosmic-ray-produced 3He, 21Ne, and 36Ar yield concordant surface exposure ages of 78 T 30 million years. Surface exposure occurred mainly in the present geomorphic setting rather than during primary erosion and transport. Our observations are consistent with mudstone deposition shortly after the Gale impact or possibly in a later event of rapid erosion and deposition. The mudstone remained buried until recent exposure by wind-driven scarp retreat. Sedimentary rocks exposed by this mechanism may thus offer the best potential for organic biomarker preservation against destruction by cosmic radiation.
    Keywords: Lunar and Planetary Science and Exploration; Geosciences (General)
    Type: GSFC-E-DAA-TN21533 , Science; 343; 6169
    Format: text
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