²⁶Al and ¹⁰Be production in iron meteorites

We have measured by accelerator mass spectrometry the ²⁶Al contents of 20 and the ¹⁰Be contents of 14 iron meteorites. The ²⁶Al contents are typically 30% or more lower than values obtained by counting techniques; the ¹⁰Be contents are 10-15% lower. The production rates (P) of these nuclides decrease by more than a factor of two as the ⁴He ²¹Ne ratio increases with increasing shielding from 200 to 400. For the lighter shielding conditions expected in stony meteorites we estimate P₂₆(Fe) as 3-4 dpm/kg and P₁₀(Fe) as 4-5 dpm/kg. The average P₁₀ P₂₆ activity ratio is close to 1.5. Exposure ages calculated from ²¹Ne ²⁶Al ratios cannot be calibrated so as to agree with both ⁴⁰K K ages and ages based on the shorter-lived nuclides ³⁹Ar and ³⁶Cl. If agreement with the latter is forced, then the disagreement with ⁴⁰K K ages may signal a 35% increase in the cosmic-ray intensity during the last 10⁷ a.