Comparison of the UNSCEAR isodose maps for annual external exposure in Fukushima with those obtained based on airborne monitoring surveys

In 2016, UNSCEAR published an attachment to its Fukushima 2015 White Paper, entitled 'Development of isodose maps representing annual external exposure in Japan as a function of time', in which the committee presented an annual additional 1 mSv effective dose ab extra isodose lines for 1, 3, 5, 10, 30, 50 years after the accident, based on the soil deposition data of radionuclides within 100 km of the Fukushima Dai-ichi Nuclear Power Plant. Meanwhile, the median of the ratio, c, between the external effective dose rates and the ambient dose equivalent rates 1 m above the ground obtained by airborne monitoring has been established to be [Formula: see text]. Here, we compare the UNSCEAR predictions with estimates based on the airborne monitoring. Although both the methods and the data used in the two approaches are different, the resultant contours show relatively good agreement. However, to improve the accuracy of long-term annual effective isodose lines, feedback from continuous measurements such as airborne monitoring is important.