Isotopic ratio of radioactive iodine (129I/131I) released from Fukushima Daiichi NPP accident

Copyright © 2012 by The Geochemical Society of Japan. In the 1990s, many studies reported an increase in thyroid cancer in children due to the release of 131I during the Chernobyl accident in 1986 (Prisyazhniuk et al., 1991; Kazakov et al., 1992). The activity of 131I around an accident site needs to be known to evaluate precisely the health impact. However, 131I can hardly be detected after several years owing to its short half-life. The measurement of the activity of 137Cs (half-life: 30.1 y) is not completely suitable for the estimation of the 131I level because the two isotopes behave differently in the environment due to different chemical property (Hou et al., 2003). On the other hand, 129I (half-life: 1.57 × 107 yrs) is the optimum proxy for 131I because the two isotopes are of the same element and move identically after release during an accident. Moreover, 129I hardly decays and is considered to remain much longer in the environment than other proxies. Although the detection of 129I was complex and time-consuming when employing the radiochemical neutron activation analysis (RNAA) method, it became much easier to detect and with higher reliability following the development of the 129I detection system employing accelerator mass spectrometry (AMS). Several attempts were made to reconstruct the 131I level from the measureIsotopic ratio of radioactive iodine (129I/131I) released from Fukushima Daiichi NPP accident

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