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Noble gases,KrKr ages, andBe of chrondrites from China
Authors:O Eugster  Ch Shen  J Beer  M Suter  W Wlfli  W Yi  D Wang
Institution:O. Eugster, Ch. Shen, J. Beer, M. Suter, W. Wölfli, W. Yi,D. Wang
Abstract:A comprehensive study of the cosmic-ray exposure history of five ordinary chondrites from China was carried out using measurements of the noble gas isotopic abundances and10Be concentrations. The following average cosmic-ray exposure ages, based on cosmogenic21Ne and on81KrKr dating were obtained: Zhaodong (L4) — 15.7 ± 3.0 m.y., Nan Yang Pao (L6) — 48 ± 10.0 m.y., Guangrao (L6) — 16.8 ± 3.5 m.y., and Lunan (H6) — 26.7 ± 5.0 m.y. The H5 chondrite Zaoyang was exposed for only 0.90 ± 0.12 m.y. to galactic cosmic rays as calculated from the10Be activity and from the low amounts of cosmic-ray-produced noble gases. The Zhaodong chondrite contains large amounts of80Kr and82Kr produced by neutron capture of bromine. From the high slowing down density for neutrons we derive a preatmospheric mass of more than 1800 kg for this meteorite.
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