Nucleogenic noble gas components in the Cape York iron meteorite

Murty, S. V. S. ; Marti, K. (1987) Nucleogenic noble gas components in the Cape York iron meteorite Geochimica Et Cosmochimica Acta, 51 (1). pp. 163-172. ISSN 0016-7037

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We report data on neutron capture products of the secondary cosmic ray component, the inferred proton and neutron fluences, and the identification of double beta decay of 82Se in heavily shielded samples of the Cape York iron meteorite. One purpose of this study is to develop a new chronometer for cosmic ray exposure, based on the nuclides 129I (16 My half-life) and 129Xe from low energy cosmic ray reactions on Te. The abundance ratio of these two nuclides permits the determination of an (effective) exposure age of 93 ±16 My, which represents the first exposure age datum of Cape York. The very small concentrations of spallogenic 38Ar = 6.5 × 10-10 cm3 STP/g in the metal and troilite (per g Fe) document the heavily shielded locations of our sample. An excess of 129Xe in the troilite is shown to be entirely due to the decay of cosmic-ray-produced 129I. On the other hand, an inclusion in the troilite reveals the presence of 129Xe from extinct 129I and documents its ~4.5 Gy formation age. Mono-isotopic excess of 82Kr is identified as due to ββ-decay of 82Se with an inferred half-life of 1.0 × 1010 y. This represents the first ββ-decay product observed in a meteorite.

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Source:Copyright of this article belongs to Geological Society of America.
ID Code:23326
Deposited On:25 Nov 2010 09:16
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