Abstract
The background doses for the teeth of residents of Fukushima Prefecture, Japan, before the nuclear power plant accidents in Mar. 2011, were obtained by electron spin resonance (ESR) method. The doses obtained from 77 of 92 samples are less than 100 mGy while the doses of the other samples are high up to 250 mGy. The doses for buccal part of the teeth are higher than lingual part possibly due to contributions from dental X ray examination. A positive correlation was found between the ages of the donors and the obtained doses. The averaged annual ESR dose was calculated to be 0.87 mGy/y, being higher than the natural dose rate of 0.33mGy/y in this region. These doses have to be considered in actual retrospective dosimetry studies for the Fukushima nuclear power plant accidents. The statistically significant critical level for Japanese residents would be about 200 mGy for individual doses and about 100 mGy for averaged group doses for α=5 % for those with ages older than 50.
