Validation of a Model for Estimating Individual External Dose Based on Ambient Dose Equivalent and Life Patterns

Background: After the Fukushima Daiichi Nuclear Power Station (FDNPS) accident, a model was developed to estimate the external exposure doses for residents who were expected to return to their homes after evacuation orders were lifted. However, the model’s accuracy and uncer-tainties in parameters used to estimate external doses have not been evaluated. Materials and Methods: The model estimates effective doses based on the integrated ambient dose equivalent ( H * (10)) and life patterns, considering a dose reduction factor to estimate the indoor H * (10) and a conversion factor from H * (10) to the effective dose. Because personal dose equivalent ( H p (10)) has been reported to agree well with the effective dose after the FDNPS accident, this study validates the model’s accuracy by comparing the estimated effective doses with H p (10). The H p (10) and life pattern data were collected for 36 adult participants who lived or worked near the FDNPS in 2019. Results and Discussion: The estimated effective doses correlated significantly with H p (10); however, the estimated effective doses were lower than H p (10) for indoor sites. A comparison with the measured indoor H * (10) showed that the estimated indoor H * (10) was not underesti-mated. However, the H p (10) to H * (10) ratio indoors, which corresponds to the practical conversion factor from H * (10) to the effective dose, was significantly larger than the same ratio outdoors, meaning that the conversion factor of 0.6 is not appropriate for indoors due to the changes in irradiation geometry and gamma spectra. This could have led to a lower effective dose than H p (10). Conclusion: The estimated effective doses correlated significantly with H p (10), demonstrating the model’s applicability for effective dose estimation. However, the lower value of the effective dose indoors could be because the conversion factor did not reflect the actual environment.