Radiation levels remaining from the 2011 disaster at Japan's Fukushima Daiichi nuclear plant appear to be a small fraction of what previous measurements suggested, according to a recently published study that followed levels in tens of thousands of people living near the site of the accident.
Science magazine highlighted the research Monday, calling it the first study to measure individual radiation levels in locals following a major nuclear disaster. The study was published in the peer reviewed Journal of Radiological Protection in December.
Nuclear accidents are uncommon, but they can have catastrophic effects on human health and the surrounding environment. Tracking individual exposure is difficult and expensive, as every person needs to be able to measure their levels regularly. Government officials and researchers have typically relied on aircraft to fly over affected areas and gather data on ambient radiation levels.
But in the aftermath of the earthquake and tsunami that badly damaged the Fukushima plant, sending radioactive material spewing out into the environment, officials in the nearby city of Date handed out radiation-tracking "dosimeters" to the city's roughly 65,000 residents.
Analyzing the data, researchers Makoto Miyazaki, a radiologist at Fukushima Medical University, and Ryugo Hayano, a physicist at the University of Tokyo, found the participants were exposed to about one-fourth the radiation the Japanese government had previously predicted.
So why the discrepancy? The government's estimates, based on aircraft surveys, assumed people were spending about eight hours a day outdoors without shielding, when in reality they were likely spending much of the day inside buildings that shielded them from exposure.
The authors cautioned that individual results may vary, and there is no way to know if every resident wore the dosimeters as instructed. But they noted in the paper they do not think this greatly affected the results.
The team concluded its report by saying the "method obtained in this study could aid in the prediction or in the estimation of the external doses of residents in the early phase of future radiation accidents involving large-scale contamination."
The researchers did not specify what the health and environmental implications of their study might be.