Radioactivity and Air Dose Rate
（2017）
ＱAir dose rates at flat locations without soil disturbance have decreased faster than expected by the half-life. Where did the radioactive cesium move to?
ＡRadioactive cesium gradually moves deeper into soil over time. When cesium moves downwards, air dose rates above the ground lower due to the shielding effect of the soil.
Fig.1 Time-dependence of depth where 90% of cesium is located(L90%)
Most cesium stays within the top 5 cm of the ground.
Fig.2 Time-dependence of air dose rates
Reduction of air dose rates at flat locations can be explained by the shielding effect of the soil.
(These figures were made by JAEA based on results obtained in work for the Nuclear Regulatory Agency in 2014.)