  Date City in Fukushima Prefecture has conducted a population-wide individual
dose monitoring program after the Fukushima Daiichi Nuclear Power Plant
Accident, which provides a unique and comprehensive data set of the individual
doses of citizens. The purpose of this paper, the first in the series, is to
establish a method for estimating effective doses based on the available
ambient dose rate survey data. We thus examined the relationship between the
individual external doses and the corresponding ambient doses assessed from
airborne surveys. The results show that the individual doses were about 0.15
times the ambient doses, the coefficient of 0.15 being a factor of 4 smaller
than the value employed by the Japanese government, throughout the period of
the airborne surveys used. The method obtained in this study could aid in the
prediction of individual doses in the early phase of future radiological
accidents involving large-scale contamination.
