²⁶Al‐production rates and ⁵³Mn/²⁶Al production rate ratios in nonantarctic chondrites and their application to bombardment histories

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The long‐lived spallogenic radionuclides 26 Al and 53 Mn were systematically studied in a large number of nonantarctic meteorites by nondestructive γ‐γ‐coincidence technique and neutron activation, respectively. From the 26 Al‐activities normalized to the main target element, silicon, an average production rate of 298±55 (dpm/kg Si equ ) was derived. Based on 15 chondrites with exposure ages ≥12×10 6 a and depth profiles of Dhurmsala and Keyes, an average production rate ratio [ 53 Mn/ 26 Al] prod × 1.48±0.15 [dpm/kg Fe / dpm/kg Si equ ] was calculated, which seems to be depth‐independent for meteorites with preatmospheric radii R<35 cm. 53 Mn/ 26 Al‐radiation ages for 29 stones with short exposure ages were determined. A comparison of our results with the respective 53 Mn‐ and 21 Ne‐exposure ages generally shows a good agreement. The cosmic ray bombardment age scale covered by this method is 1×10 6 <T rad <10×10 6 a.