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Assessment of Exposure Doses and Decontamination


What kinds of measurements and evaluations for radiation doses have been conducted until now? What are the results?

External radiation doses for residents have been estimated since just after the accident on the basis of models of air dose rates and measurements with personal dosimeters. It was evaluated that the integrated radiation doses for four months after the accident are in most cases lower than 3 mSv. Now, additional radiation doses in a year are lower than 1 mSv.

◆ Result for radiation dose estimated on the basis of personal action pattern using the system developed by the National Institute of Radiological Sciences.

Fig.1 Estimation of external radiation dose for four months after the accident

  • On the basis of the data on personal action patterns examined in health survey, radiation doses for 4 months after the accident were estimated for more than 100,000 people.
  • Radiation doses of more than 99% people were lower than 3 mSv.
  • The highest radiation dose of a person was 13 mSv.

Annual radiation dose of a person in Fukushima City in FY 2014.

Fig.2 Annual radiation dose of a person in Fukushima City in FY 2014

Additional radiation doses are evaluated by distributing personal dosimeters to many residents in the other many municipalities.

  • On the basis of the results obtained by personal dosimeters, additional radiation doses in a year were estimated excluding contribution of natural radiation.
  • Additional radiation doses for more than 95 % persons were lower than 1 mSv, and those for more than 90 % were lower than 2 mSv.

(Ishikawa, T., Yasumura, S., Ozawa, K., et al., (2015) The Fukushima Health Management Survey: estimation of external doses to residents in Fukushima Prefecture. Sci. Rep. 5: 12712. doi:10.1038/srep12712)

  • Estimation of radiation doses just after the accident using a model was also conduced by the United Nations Scientific Committee. The results are in good agreement with those measured in Fukushima Prefecture.
  • It is confirmed by annual measurements with personal dosimeters that radiation doses have decreased gradually year by year.