The variation of cosmogenic Kr and Xe in a core from Estherville mesosiderite: direct evidence that the lunar131Xe anomaly is a depth effect |
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| Authors: | Wulf A Kaiser RS Rajan |
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| Institution: | Department of Physics, University of California, Berkeley, California 94720,USA |
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| Abstract: | Kr and Xe were measured by a stepwise heating technique in three samples of a drill core in the “Minnesota” fragment of the Estherville mesosiderite. The cosmogenic78Kr/83Kr decreased from the “top” sample to the “bottom” sample(“top” = 0.163 ± 0.005, “bottom” = 0.151 ± 0.005) while the cosmogenic131Xe/126Xe ratio increased(“top” = 5.58 ± 0.35, “bottom” = 6.92 ± 0.17). Cosmic-ray track studies have shown that the “top” sample was indeed closer to the preatmospheric surface than the “bottom” sample by ～ 10 cm. This is the first direct evidence, in a sample of known geometry, that the cosmogenic131Xe/126Xe ratio increases as a function of depth, and as such, confirms the hypothesis that the lunar131Xe anomaly is a bona fide depth effect due to resonance neutron capture in130Ba. |
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