放射性同位体と安定同位体を組み合わせることによって，年代測定を行うことができる。本稿では，ヨウ素の同位体システム（放射性同位体129Iと安定同位体127I）を利用した年代測定について筆者がこれまでに検討してきたことを紹介する。129Iは，環境中ではごく微量にしか存在しない核種であり，その測定には，加速器質量分析を必要とする。合わせて分析手法についても解説する。
The combination of isotopes, a radio isotope and a stable isotope can be used for dating, like 14C-dating. This article discusses the possibility of dating using iodine isotope system (129I and 127I). Since 129I is a long lived radio isotope (half life=15.7 Myr), the iodine isotope system is a potential dating tool for large time scale, which had been initially proposed by Fehn (Rochester University) in Science article published in 2,000. He tried to determine the formation age of methane hydrates in Blake ridge, the United States using 129I/127I. For the dating, we should know the initial isotopic ratio and he used the value proposed by J. Moran in 1998. However, for the initial ratio, there still is under debate. This article discusses in details the conditions which make possible the dating. As an indispensable measurement method for detection of environmental 129I, Accelerator Mass Spectrometry is also explained in details, hardware configuration, physical principle, and pre-treatment of environmental samples.
Key words: iodine-129; iodine isotope system; Accelerator Mass Spectrometry (AMS); anthropogenic radio nuclides; naturally occurring radio isotopes; dating; MALT (Micro Analysis Laboratory, Tandem accelerator, The University of Tokyo)
© Japan Radioisotope Association 2024. This is an open access article distributed under the Creative Commons Attribution 4.0 International (CC BY 4.0) License (https://creativecommons.org/licenses/by/4.0/)© Japan Radioisotope Association 2024. This is an open access article distributed under the Creative Commons Attribution 4.0 International (CC BY 4.0) License (https://creativecommons.org/licenses/by/4.0/)
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