Assessment of Internal Exposure Doses in Fukushima by a Whole Body Counter Within One Month after the Nuclear Power Plant Accident

Abstract

Information on early internal radiation doses in Fukushima after the nuclear power plant accident on March 11, 2011, is quite limited due to initial organizational difficulties, high background radiation and contamination of radiation measuring devices. In Nagasaki, approximately 1,200 km away from Fukushima, the internal radioactivity in evacuees and short-term visitors to Fukushima has been measured by a whole body counter (WBC) since March 15, 2011. A horizontal bed-type scanning WBC equipped with two NaI(Tl) scintillation detectors was used for 173 people who stayed in the Fukushima prefecture between March 11 and April 10, 2011. The average length of stay was 4.8 days. The internal radioactivity was converted to an estimated amount of intake according to the scenario of acute inhalation, and then the committed effective dose and the thyroid dose were evaluated. (131)I, (134)Cs and (137)Cs were detected in more than 30% of examined individuals. In subjects who stayed in Fukushima from March 12 to March 18, the detection rate was approximately 50% higher for each radionuclide and 44% higher for all three nuclides. The maximum committed effective dose and thyroid equivalent dose were 1 mSv and 20 mSv, respectively. Although the number of subjects and settlements in the study are limited, the results suggest that the internal radiation exposure in Fukushima due to the intake of radioactive materials shortly after the accident will probably not result in any deterministic or stochastic health effects.

Measurements of Individual Radiation Doses in Residents Living Around the Fukushima Nuclear Power Plant

“…At Nagasaki University, Nagasaki Prefecture, Matsuda et al measured internal radioactivity by WBC in evacuees and short-term visitors to Fukushima within one month after the accident, and reported that 131 I, 134 Cs and 137 Cs were detected in more than 30% of examined individuals, at maximum committed doses and thyroid equivalent doses of 1 and 20 mSv, respectively (24).…”

The Fukushima Daiichi Accident

“…Given the importance of intakes of 131 I through both inhalation and ingestion in the first month following the accident, this made judgements on internal exposure difficult. However, it was possible to detect 131 I in measurements of evacuees and short term visitors to Fukushima Prefecture carried out at Nagasaki University [213]. The highest estimated thyroid absorbed dose was 20 mGy (i.e.…”

Radiation Exposure and Thyroid Cancer Risk After the Fukushima Nuclear Power Plant Accident in Comparison with the Chernobyl Accident

“…Yet, according to the report by Hirosaki University (23) , equivalent dose for the thyroid might have reached 10 mSv in the infants who stayed within the range of 20 km at the time of the accident; undoubtedly it is necessary to observe these individuals for a long period of time. Direct measurement of internal exposure in the very early period after the accident suggests quite a low possibility of any stochastic health effect (24) . WHO released the estimates of exposure doses around Fukushima in May 2012.…”