Variability of the Al<sup>26</sup> production rate in ordinary chondrites期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

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Variability of the Al²⁶ production rate in ordinary chondrites

Authors:	Gregory F Herzog Philip J Cressy

Institution:	Department of Chemistry, Douglass College, Rutgers—the State University of New Jersey, New Brunswick, N.J. 08903, U.S.A.;Planetology Branch, Laboratory for Space Physics, Goddard Space Flight Center, Greenbelt, Maryland 20771, U.S.A.

Abstract:	15 ordinary chondrites for which unusually high spallogenic $Ne^{22} Ne^{21}$ or $He^{3} Ne^{21}$ ratios had been reported and one meteorite with marked shock characteristics were selected in order to investigate the relations between $Ne^{22} Ne^{21}$ ratios, Al²⁶ contents and depth. We report Al²⁶ and K contents of 13 samples from 11 of these and-noble gas contents of 30 samples from all of these stones.A decrease in the Al²⁶ production rate accompanies the increase of $Ne^{22} Ne^{21}$ towards the pre-atmospheric surface: $Al_{obs}^{26} Al_{calc}^{26} = 3.2?2.0 Ne^{22} Ne^{21}$ for $1.08 ≤ Ne^{22} Ne^{21} ≤ 1.2$ . Large deviations from this relationship may indicate that a meteorite experienced an abnormal flux of cosmic rays.For $Ne^{2} Ne^{21} > 1.2$ this trend continues but the data scatter more, probably because of the steadily increasing influence of pre-atmospheric size. $Ne^{22} Ne^{21}$ ratios increase most rapidly in the outermost few centimeters according both to a plot of $Ne^{22} Ne^{21}$ vs (recovered mass)^$13$ and to track studies. The increase seems to derive from the enhanced importance of nuclear reactions on Si. $Ne^{22} Ne^{21} < 1.08$ defines a region where the Al²⁶ production rates are less sensitive to depth and vanish in the limit of large shielding; the weak correlation between $Ne^{22} Ne^{21}$ and Al²⁶ in this region rules out the use of the $Ne^{22} Ne^{21}$ ratio as a basis for a shielding correction to Al²⁶.

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