Neutron Exposure Ages of Meteorites

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Abstract
Co60 and Ar39 were measured in a number of recently fallen meteorites. From these data the amount of shielding surrounding the samples in space was estimated. In the carbonaceous chondrite, Murray, the Co60 activity was very large compared to the Co60 activities in the other chondrites even though the Ar39 activities were almost identical. In the iron meteorites there was an inverse relationship between the Co60 and Ar39 activities; shielding material increased the Co60 activity and decreased the Ar39 activity. In the cases of Abee and Bruderheim, neutron exposure ages were obtained from the Kr80/Co80, Kr82/Co60, and Xe128/Co60 ratios because the Co60 was measured in large samples from the interior of the same fragment in which krypton, xenon, bromine, and iodine had previously been measured. The neutron exposure ages were approximately an order of magnitude larger than the spallation exposure ages. The order-of-magnitude differences in the exposure ages could be attributed to space erosion or to an ancient neutron irradiation.

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