Pre-exposure to cosmic rays of chondrules and Ca-, Al-rich inclusions

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In dating primitive Solar System materials, probably least straightforward is the determination of the time between formation of the first compositional units and their compaction. In case of the primitive meteorites (the chondrites) these compositional units are matrix, chondrules and (in the particular in case of the carbonaceous chondrites) Ca-Al-rich inclusions. If in the Early Solar System these were exposed to the cosmic radiation, they should show excesses of cosmogenic isotopes relative to the abundances produced during their exposure age (the “recent” irradiation during travel from meteorite parent body to Earth) that should be detectable. Literature data provide hints in a few cases for excesses of cosmogenic noble gas isotopes in chondrules relative to bulk material that accordingly have been interpreted as pre-irradiation of chondrules in the solar nebula. We plan to enlarge and improve the database by analysis of a large number of chondrules and corresponding bulk / matrix samples with well determined chemical composition, in particular from enstatite and CR chondrites; the availability in the literature of new production rates for chemically diverse samples will also make it possible to interpret the results more reliably than in the past. At a later stage we plan to extend these investigations to Ca-Alrich inclusions.