FUKUSHIMA - About 58 per cent of Fukushima Prefecture residents were likely externally exposed to radiation measuring less than 1 millisievert during the first four months of the Fukushima nuclear crisis, according to a survey released Monday by the prefectural government.
The prefectural government released its estimate of the external radiation doses of 10,468 people. The prefecture has a population of about 2 million people.
Of 9,747 people, excluding workers at the crippled Fukushima No. 1 nuclear power plant, 57.8 per cent were estimated to have been exposed to levels less than 1 millisievert - which is considered the annual limit of radiation exposure under normal circumstances--during the first four months, according to the survey.
The survey found 94.6 per cent of residents were considered to have been exposed to less than 5 millisieverts of radiation.
Only two women were estimated to have been exposed to radiation levels exceeding 20 millisieverts.
The main reason behind the two women's high exposure level is that the two stayed in the expanded evacuation zone - the area spanning five municipalities beyond a 20-kilometer radius around the power plant -for more than three months.
One of the women is thought to have been exposed to 23 millisieverts of radiation, the highest among people who did not work at the nuclear plant.
Among 1,693 people under 20 years old who were surveyed, one male was estimated to have been exposed to 18.1 millisieverts, but all others were exposed to less than 10 millisieverts.
Among workers at the nuclear plant, the highest level was 47.2 millisieverts.
"In past epidemiological examinations, obvious health effects have not been observed with cumulative doses of 100 millisieverts or less. The results of the survey show the level of radiation exposure will not likely impact residents' health," an official of the prefecture said.
A total of 431,720 people, or 21 per cent of Fukushima residents, responded to the questionnaire by the end of January.
The released results are from 10,468 out of 29,103 residents in Iitate, Namie and the Yamakiya district of Kawamata, which are designated as expanded evacuation zones, and the no-entry zone within 20 kilometers of the nuclear plant.
Residents in these areas were surveyed before residents in other areas.
Based on the survey results, the estimated external exposure levels were calculated according to time-series data on air radiation levels at various locations.
Residents were asked to recall where they stayed and what they did for the first four months of the nuclear crisis that began soon after the March 11 earthquake and tsunami.
The data was calculated using the Education, Culture, Sports, Science and Technology Ministry's monitoring survey results and the System for Prediction of Environmental Emergency Dose Information (SPEEDI), the government's computer system that simulates the dispersal of radioactive substances.