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

Abstract

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 uncertainties 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 (<i>H*</i>(10)) and life patterns, considering a dose reduction factor to estimate the indoor <i>H*</i>(10) and a conversion factor from <i>H*</i>(10) to the effective dose. Because personal dose equivalent (<i>H</i><sub>p</sub>(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 <i>H</i><sub>p</sub>(10). The <i>H</i><sub>p</sub>(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 <i>H</i><sub>p</sub>(10); however, the estimated effective doses were lower than <i>H</i><sub>p</sub>(10) for indoor sites. A comparison with the measured indoor <i>H*</i>(10) showed that the estimated indoor <i>H*</i>(10) was not underestimated. However, the <i>H</i><sub>p</sub>(10) to <i>H*</i>(10) ratio indoors, which corresponds to the practical conversion factor from <i>H*</i>(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 <i>H</i><sub>p</sub>(10).Conclusion: The estimated effective doses correlated significantly with <i>H</i><sub>p</sub>(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.

External exposure assessment in the Fukushima accident area for governmental policy planning in Japan: part 1. Methodologies for personal dosimetry applied after the accident

“…(2022) obtained data for 148 days from 36 people by combining personal dose equivalent data and GPS location data to verify the accuracy of a simulation that considers lifestyle behavior patterns, as described in the next chapter. They discussed the differences between indoor and outdoor locations [ 21 ]. Other cases can be found where the number of subjects was small, but where actual doses were measured over a long period of time [ 22 ], or where internal exposure doses assessed by measuring radon concentrations indoors were compared with external exposure doses [ 23 ].…”

“…(2019) developed a method to calculate annual personal dose equivalents based on ambient dose rate information continuously measured by walking and driving surveys [ 9 ], location information and time spent in the area interviewed from residents, indoor and outdoor reduction factors, and conversion factors from ambient dose equivalent to effective dose. The accuracy of this method was evaluated by comparing it with information measured by personal dosimeters [ 21 ]. An example of the accuracy verification of this method obtained by the authors is shown in Fig.…”

External exposure assessment in the Fukushima accident area for governmental policy planning in Japan; Part 2. Matters to be attended for assessments of external exposure

“…As shown in equation 1 , accounting for behavioral patterns, such as place and time of stay, conversion to the effective dose allows individual exposure doses to be estimated with a certain accuracy without long-term measurements using personal dosimeters [ 15 , 16 ]. Additionally, this calculation makes it possible to predictive assessment of individual exposure dose for residents who return to the ‘specific reconstruction reproduction base area (SRR Zone)’.…”

“…GPS information refers to the location and duration of stay and is recorded using tools such as GPS loggers and smartphones [ 16 ]. Since this method records actual behavior, it can only be used for retrospective evaluation and is difficult to apply to the predictive evaluation.…”

Statistical evaluation of individual external exposure dose of outdoor worker and ambient dose rate at evacuation ordered zones after the Fukushima Daiichi Nuclear Power Station accident

“…For this reason, we use the same expression in this study. The estimation of individual external dose includes methods [7][8][9][10][11][12][13][14][15][16][17][18][19][20] based on individual external dose data and methods [21][22][23][24][25][26][27] based on ambient dose rate data. Estimation of individual external dose using individual external dose data has been conducted by the national government, local governments, researchers, and others [7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”