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Assessment of Exposure Doses and Decontamination

（2016）

ＱWhat were the radiation exposures just after the accident?

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Just after the accident, internal exposure by inhalation of iodine-131 (131I, half-life: 8.02 days) was important. The equivalent radiation dose in the thyroid gland of one year old babies was estimated to be at most about 30 mSv.

Table 1 Results of estimated radiation dose in thyroid gland conducted by National Institute of Radiological Sciences(90th percentile Value)

Municipality One year old baby Adult Method
Futaba Town 　30 　10 Whole body measurement
Okuma Town 　20 ＜10 Whole body measurement
Tomioka Town 　10 ＜10 Whole body measurement
Naraha Town 　10 ＜10 Whole body measurement
Hirono Town 　20 ＜10 Whole body measurement
Namie Town 　20 ＜10 Whole body and thyroid grand measurement
iidate Villege 　30 　20 Whole body and thyroid grand measurement
Kawamata Town 　10 ＜10 Whole body and thyroid grand measurement
Kawauchi Villege ＜10 ＜10 Whole body measurement
Katsurao Villege 　20 ＜10 Estimated from data in Namie Town
Iwaki City 　30 　10 Diffusion simulation, Thyroid grand measurement
Minamisouma City 　20 ＜10 Estimated from data in Namie Town
Others in Fukushima Prefecture ＜10 ＜10 Diffusion simulation

※ Thyroid equivalent radiation dose is different from effective radiation dose that is generally used for the evaluation of radiation dose.
※ To obtain effective radiation dose, thyroid equivalent radiation dose must be multiplied by 0.04.

  • Due to its short half life, it is not easy to evaluate radiation dose from 131I months after the accidet.
  • Equivalent radiation dose in the thyroid gland by 131I was estimated by integrating various information (National Institute of Radiological Sciences)
  • Equivalent radiation dose in the thyroid gland by 131I was eatimated from,
    (1) direct measurements of 131I in thyroid,
    (2) whole body measurements of cesium, and
    (3) simulation of air diffusion.
  • Equivalent radiation dose of 30 mSv in thyroid gland corresponds to effective radiation dose of 1 mSv.
  • Radiation exposure just after the accident is not fully understood. Further investigation is needed.

Related articles

Reference

  1. Kim, E. et al, Internal thyroid doses to Fukushima residents-estimation and issues remaining, Journal of Radiation Research, vol.57, suppl 1, 2016, p.i118-i126.