Variability of the Al 26 production rate in ordinary chondrites
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, Al 26 contents and depth. We report Al 26 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 Al 26 production rate accompanies the increase of Ne 22/Ne 21 towards the pre-atmospheric surface: Al obs26/Al calc26 = 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) 1/3 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 Al 26 production rates are less sensitive to depth and vanish in the limit of large shielding; the weak correlation between Ne 22/Ne 21 and Al 26 in this region rules out the use of the Ne 22/Ne 21 ratio as a basis for a shielding correction to Al 26.
- Publication:
-
Geochimica et Cosmochimica Acta
- Pub Date:
- December 1974
- DOI:
- 10.1016/0016-7037(74)90166-5
- Bibcode:
- 1974GeCoA..38.1827H
- Keywords:
-
- Aluminum 26;
- Chondrites;
- Meteoritic Composition;
- Rare Gases;
- Argon Isotopes;
- Helium Isotopes;
- Neon Isotopes;
- Vertical Distribution