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Main Factors Determining Radiation Levels in Forests Elucidated By Simulations
—Results Show Radiation from Radioactive Cesium within the Top 5 cm of Soil Made the Majority Contribution to Radiation Levels in Forests since 2017—

Forests account for about 70% of the land in Fukushima Prefecture. For this reason, changes in radiation levels in forests over time are a matter of concern not only for forestry workers and those who live close to forests, but also for residents of Fukushima Prefecture as a whole.

The radiation levels depend on the amount and locations where radioactive cesium released from the nuclear disaster at Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Station are present within forests.

The Japan Atomic Energy Agency cooperated with the Forest Research and Management Organization and the University of Tsukuba to construct detailed models of radioactive cesium distributions in forests using observation results from these organizations, and to perform simulations of radiation levels.

The results confirmed that since 2017, the majority of radiation levels in forests are attributable to radioactive cesium within the top 5 cm of forest soil. Future changes in radiation levels will therefore be determined mainly by the migration characteristics of this radioactive cesium.

The constructed radiation simulation models will enable us to predict the kinds of changes that various forest management options will exert on radiation levels in forests. We will move forward and conduct further research with the models with the aim of finding realistic and effective proposals for reducing radiation levels in forests.

Schematic diagram showing the contributions of gamma rays from radioactive 134Cs and 137Cs present in different locations in forest to the radiation dose rate.
The simulations calculated the contributions to the radiation dose rate from radioactive cesium present within tree crowns, trunks, the forest litter, and soil layers. The results cover from 2011 to 2017, and they capture the changes that occurred over this period.

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