I-131 (Eastern Part of Fukushima Prefecture)

In the soil survey conducted by the national government in June 2011, three months after the accident, analysis of I-131 was conducted for soil samples collected within the 100-km zone of Tokyo Electric Power Company (TEPCO)'s Fukushima Daiichi NPS. While a band of areas showing high deposition amounts of cesium extended to the northwest of the NPS, areas showing high I-131 deposition amounts extended to the south of the NPS as well. I-131 and Cs-137 were thus deposited at different ratios in different areas because the ratio between I-131 and Cs-137 in radioactive plumes differed depending on the time when they were discharged. There is also the possibility that the ratio of I-131 against Cs-137 was relatively larger in plumes that flowed down to the south or that deposition was not even and a larger amount of Cs-137 was deposited in the north due to rainfall, resulting in increased concentrations of Cs-137 in soil in the north.

• Included in this reference material on March 31, 2013
• Updated on February 28, 2018