Spallation, Fission, and Neutron Capture Anomalies in Meteoritic Krypton and Xenon

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Abstract
Measurements of the Kr and Xe concentrations and isotopic compositions in five meteorites are reported. Experimental techniques and reproducibility are discussed in detail. In the Stannern achondrite 75% of the total Kr and 30% of the total Xe are due to cosmic ray induced spallation reactions. Also Bruderheim and H - Ausson show distinct spallation components. The isotopic composition of pure spallation Kr is derived as Kr78 : Kr80 : Kr82 : Kr83 : Kr84 = 0.179 : 0.495 : 0.765 : 1.00 : 0.63 and of spallation Xe as Xe124 : Xe126 : Xe128 : Xe130 : Xe131 : Xe132 = 0.590 : 1.00 : 1.45 : 0.97 : 3.9 : 0.9. It is shown that the spallation components found were produced by the cosmic radiation late in the history of the meteorite during a period given by the radiation age. The observed Xe128/Xe124 spallation ratio rules out a substantial contribution of spallation products in the xenon of carbonaceous chondrites. The Xe fission spectrum derived by ROWE and KURODA from Pasamonte is corrected for spallation and the following composition is obtained for fission Xe : Xe131 : Xe132 : Xe134 : Xe136· = 0.22 : 1.00 : 1.02 : 1.00. In Mezö-Madaras and Abee Kr80, Kr82 and Xe128 excesses are found, due to (n.γ) reactions on Br and I. It is shown that neutrons produced by the cosmic radiation during the radiation age can account for the observed effect in Abee and the evidence so far suggests that this is also true for Mezö-Madaras.

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