2020 年 54 巻 4 号 p. 209-217
The accident at the Fukushima Daiichi Nuclear Power Plant resulted in a substantial release of radionuclides including Iodine-131, Cesium-134, and Cesium-137 to the atmosphere, and caused significant contamination of the environment. Most parts of the eastern Japan were subjected to the radioactive contamination, especially in Fukushima Prefecture. An effective dose estimation of released 131I is important but difficult due to lack of data on the deposition of 131I. The long-lived radioiodine isotope 129I (half-life: 1.57×107 y) is one of the important radionuclides released from nuclear fuel reprocessing plants and nuclear accidents into the environment. This radionuclide has provided useful information on the behavior of radioiodines, whose half-lives are very short, in the environment. In particular, 129I has been used as a tool to reconstruct the initial distribution of 131I (half-life: 8 days) at nuclear accidents. Therefore the determination of 129I in soils in Fukushima is needed to reconstruct the distribution of 131I in the environment. In this article, I review recent studies on radioactive iodine in Fukushima.