27 Février 2014
February 26, 2014
A group of researchers estimates the average annual radiation exposure by residents in some areas adjoining the evacuation zones due to the Fukushima nuclear accident was on par with normal background levels.
The researchers, including Akio Koizumi, a professor of health and environmental sciences at Kyoto University’s Graduate School of Medicine, examined 459 people who lived within 20 to 50 kilometers from the crippled nuclear plant for two months from August 2012, when some residents began to temporarily enter the areas.
They found returnees to the areas targeted in the study--Kawauchi village, the Tamano district of Soma city and the Haramachi district of Minami-Soma city--were exposed up to an annual average of 2.5 millisieverts of radiation, in addition to background radiation exposure. The Japanese annual average dose from background radiation is 2.1 millisieverts.
The finding was published Feb. 25 in the online edition of the Proceedings of the National Academy of Sciences of the United States of America.
The study found that the external radiation exposure accounted for 99.5 percent of the total dosage, while the internal exposure was less than 1 percent.
The external radiation exposure was measured using personal dosimeters, while the internal exposure was determined through examination of what the test subjects ate and the measurement of atmospheric dust.
The researchers found the annual average exposure, excluding average natural doses in Fukushima Prefecture before the March 2011 nuclear accident, was 2.51 millisieverts for Tamano district residents, 1.51 millisieverts for Haramachi district residents and 0.89 millisieverts for residents of Kawauchi village.
The study estimates that residents of the Tamano district, starting from the age of 1 in 2012, will be exposed to 42.8 millisieverts by the time they turn 89, the highest of the three areas.
The study said the radiation exposure in the Tamano district would raise the risk of cancer by 0.71 percentage points for men and 1.06 percentage points for women compared with normal levels.
About 44 percent of men and 32 percent of women develop tumors in their lifetime.