When the Fukushima Daiichi Nuclear Power Plant disaster occurred following an earthquake in Japan in 2011, over 150,000 people from Fukushima and the surrounding areas were evacuated due to fears of radiation and contamination. The government then continued to monitor the region using airborne observations to check radiation levels.
But for the city of Date, things were a little different. Despite being just 60 kilometers 37 miles) from the nuclear power plant, when many neighboring towns were being evacuated, Date was not. So the mayor and the city's 65,000 citizens took things into their own hands, and started measuring their own radiation exposure. What their results show, surprisingly, is that the government's predictions of radiation taken from the air overestimated the levels of radiation on the ground by a factor of four. The results have been published in the Journal of Radiological Protection.
By doing the study themselves, the residents were able to give an incredibly rare insight into an individual’s radiation exposure immediately following a nuclear disaster. Obviously, most of the time, people are evacuated, and getting personal sensors to those that haven't been is both costly and difficult. That is why most governments will rely on the aerial monitoring of regions directly following nuclear disasters, which they then use to estimate the radiation at ground level, and then predict the amounts that would be experienced if people were still living there.
“We decided that we should not depend on the national government and that we had to take our own independent actions,” the mayor of Date, Shoji Nishida, said three years after the event. The city first issued personal monitoring kits that measure gamma rays, known as dosimeters, to children under the age of 16, as well as pregnant mothers.
As residents voluntarily started to help in the decontamination of the city, and more money from city funds was made available, the dosimeters were rolled out to all 65,000 people still living in Date, producing a massive data set on individual citizen’s exposure levels for the year immediately following the disaster. This has now been compared to the official government monitoring from the air, and the conclusion was not what was expected.
It seems that the real world data of exposure levels is four times lower than the projected ones derived from the flybys. This, the researchers suggest, means that extreme measures taken following the Fukushima disaster, such as removing contaminated topsoil and stripping trees of bark, may have been unnecessary. It also puts into question the standard way of monitoring radiation levels, which might need to be revised.