@article{oai:nipr.repo.nii.ac.jp:00001099,
 author = {Nitoh, Osamu and Honda, Masatake and Imamura, Mineo},
 journal = {Memoirs of National Institute of Polar Research. Special issue},
 month = {Dec},
 note = {P(論文), 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.},
 pages = {189--201},
 title = {Cosmogenic K-40 in Antarctic Meteorites},
 volume = {17},
 year = {1980}
}