Al andBe production in iron meteorites |
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Authors: | D Aylmer V Bonanno GF Herzog H Weber J Klein R Middleton |
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Abstract: | We have measured by accelerator mass spectrometry the26Al contents of 20 and the10Be contents of 14 iron meteorites. The26Al contents are typically 30% or more lower than values obtained by counting techniques; the10Be contents are 10–15% lower. The production rates (P) of these nuclides decrease by more than a factor of two as the4He/21Ne ratio increases with increasing shielding from 200 to 400. For the lighter shielding conditions expected in stony meteorites we estimateP26(Fe) as 3–4 dpm/kg andP10(Fe) as 4–5 dpm/kg. The average P/10P26 activity ratio is close to 1.5. Exposure ages calculated from21Ne/26Al ratios cannot be calibrated so as to agree with both40KK/ ages and ages based on the shorter-lived nuclides39Ar and36Cl. If agreement with the latter is forced, then the disagreement with40KK/ ages may signal a 35% increase in the cosmic-ray intensity during the last 107 a. |
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