Cosmogenic K-40 in Antarctic Meteorites

概要

論文の詳細を見る
The present work extends the measurements of cosmogenic K-40 by mass spectrometry in the metal phase separated from chondrites and others, especially antarctic meteorites. Potassium-40 (t_<1/2> : 1.28×(10)^9y) is regarded as a stable nuclide rather than radioactive, in the time scale of cosmic ray exposure to chondrites. According to our current sampling, chemical and mass-spectro-metric techniques, starting from 10mg size metal samples and at a contamination level of lower than (10)^<-8>gK, we are able to measure the exposure ages as low as one million years. We determined the production rate of ^<40>K in Fe+Ni relative to the rates of ^<36>(Ar) and ^<36>(Cl), using samples separated from some mesosiderites and irons. Potassium-40 (irradiation) ages obtained in this work were compared with the ages based on the light rare gases contents. Both agreed with each other. Some samples are indicating their near-surface irradiation histories. In a few samples, Yamato-74116 and the Kirin chondrite, multi-stage irradiation histories were detected.
国立極地研究所の論文