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Ji, Y.-Y.*; Ji, W.*; Kim, K.*; Kim, M. J.*; Ochi, Kotaro; Morishita, Yuki; Sanada, Yukihisa
Radiation Physics and Chemistry, 244, p.113781_1 - 113781_12, 2026/02
Times Cited Count：0UAV-based airborne gamma-ray spectrometry enables rapid radiation mapping, but accurate estimation of ground-level ambient dose rates is difficult because of altitude attenuation, detector field-of-view effects, heterogeneous contamination, and terrain variability. We developed a practical method combining hovering-flight calibration and ground-based validation near the Fukushima Daiichi Nuclear Power Plant. Altitude correction factors were derived using a dual-exponential model and compared with tripod and backpack measurements. Results showed that heterogeneous contamination and terrain introduce systematic biases if correction factors are derived under non-uniform conditions, while calibration at uniform sites improves agreement. The proposed approach demonstrates that UAV airborne surveys can reliably estimate spatial dose-rate distributions when site-dependent corrections are applied.
Shikaze, Yoshiaki; Saito, Kimiaki; Tanimura, Naoki*; Yoshimura, Kazuya; Liu, X.; Machida, Masahiko
Radiation Protection Dosimetry, 201(15), p.1025 - 1042, 2025/09
Times Cited Count：0 Percentile：0.00(Environmental Sciences)The two-component model, comprising a fast-decay and a slow-decay component, has been widely used to approximate the decreasing trends of air dose rates in contaminated areas surrounding major nuclear accident sites. However, its adequacy is yet to be thoroughly validated. This study analyzed extensive car-borne survey data collected from 2011 to 2016 after the Fukushima Daiichi Nuclear Power Plant accident using the least absolute shrinkage and selection operator regression with a high-degree-of-freedom model. This analysis aimed to evaluate the adequacy of the two-component model and investigate the profiles of ecological half-lives. Next, future predictions of air dose rate distributions were made using a prediction model formula that incorporated the average ecological half-life profiles calculated for each land-use and initial air dose rate category. Prediction accuracy was verified through comparison with integrated map data, which merge air dose rate datasets obtained using different monitoring methods and represent the most currently reliable source. In this paper, we present the results of the analysis of the above environmental half-life profiles and the evaluation of the predictive model calculations, and discuss the reasons that led to these results.
Sato, Rina; Yoshimura, Kazuya; Sanada, Yukihisa; Mikami, Satoshi; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanaizuka, Seiichi*; Sato, Tetsuro*; Mori, Tsubasa*; Takagi, Marie*
Environment International, 194, p.109148_1 - 109148_8, 2024/12
Times Cited Count：6 Percentile：53.54(Environmental Sciences)Assessment of individual external doses from ambient dose equivalents is used for predictive and retrospective assessments where personal dosimeters are not applicable. However, it tends to contain more errors than assessment by personal dosimetry due to various parameters. Therefore, in order to accurately assess the individual dose from ambient dose equivalents, a model that estimates effective doses considering life patterns and the shielding effects by buildings and vehicles, were developed in this study. The model parameters were examined using robust datasets of environmental radiation measured in the areas affected by the Fukushima Daiichi Nuclear Power Station accident in 2020 to 2021. The accuracy of the model was validated by comparison with 106 daily personal doses measured in Fukushima Prefecture in 2020. The measured personal dose was well reproduced by the model-estimated effective dose, showing that the model can be used to assess the individual exposure dose, similar to personal dosimetry. Furthermore, this model is an effective tool for radiation protection, as it can estimate the individual dose predictively and retrospectively by using environmental radiation data.
Endo, Akira
Radiation Protection Dosimetry, 200(13), p.1266 - 1273, 2024/08
Times Cited Count：0 Percentile：0.00(Environmental Sciences)This study examines the relationship between ambient dose 
, ambient dose equivalent 
, and effective dose for external neutron irradiation over 163 operational spectra from different workplaces. The results show that provides a reasonable estimate with a controlled margin, even if overestimated, to assess effective dose compared with , which can lead to a significant overestimation or underestimation of effective dose depending on the neutron spectra. The results highlight the limitations of and the superiority of in estimating effective dose according to the requirements of the operational quantity, especially in environments with high-energy neutrons.
Endo, Akira
JAEA-Research 2024-002, 90 Pages, 2024/05
JAEA-Research-2024-002.pdf:4.22MB
This report presents a comprehensive analysis of the relationship between three quantities used for area monitoring - ambient dose equivalent , maximum dose equivalent 
, and ambient dose - and effective dose for external irradiation by photons, neutrons, electrons, positrons, protons, muons, pions, and helium ions. For the analysis, calculations were performed using PHITS (Particle and Heavy Ion Transport code System) and the ICRU sphere. The analysis result shows that and can induce large differences in the estimation of effective dose over a wide energy range for various particle types covered by ICRP Publication 116 while can conservatively estimate effective dose within the acceptable range for area monitoring. In other words, and have limitations in estimating effective dose, and using is recommended as a more appropriate quantity for the purpose. This conclusion supports the proposal of ICRU Report 95 to use for estimating effective dose in various external exposure situations. The use of ambient dose is particularly important in situations where various types of radiation are encountered, such as the use of radiation in the medical and academic fields and exposure in aviation and can meet the evolving requirements of radiation monitoring for the expansion of the field of radiological protection.
Sato, Rina; Sanada, Yukihisa; Yoshimura, Kazuya; Nakayama, Mariko*
JAEA-Review 2022-055, 42 Pages, 2023/01
JAEA-Review-2022-055.pdf:1.31MB
The evacuation order zones established after the accident at the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Station have been reorganized according to the decrease in ambient dose equivalent rates and the decontamination progress. It has been decided to decontaminate the difficult-to-return zones and lift the evacuation order depending on the evacuee's intention of returning to the areas over the course of the 2020s. In order to consider the future of individual exposure dose assessment for residents for lifting of the evacuation orders, the methods and characteristics of the assessment that have been conducted after the accident using personal dosimeter measurements and simulations were systematically reviewed. This report summarized the results of the review.
Ando, Masaki; Saito, Kimiaki
JAEA-Technology 2021-032, 66 Pages, 2022/03
JAEA-Technology-2021-032.pdf:3.84MB
Since the occurrence of the accident at the TEPCO Fukushima Daiichi Nuclear Power Station, the Japan Atomic Energy Agency (JAEA) has been conducting a series of car-borne survey over a wide area in the eastern part of Japan using the monitoring system KURAMAII. In this report, outline of the car-borne surveys are summarized and the following characteristics of the temporal changes in each prefecture and region were investigated using the measured data obtained from 2012 to 2019; 1) Average and maximum values for each prefecture for the six years from 2014 to 2019, 2) Average values for each prefecture from 2012 to 2019, 3) Average values for each evacuation order area category, regional category, and northern Soso-area municipality in Fukushima Prefecture from 2012 to 2019, and 4) Average and maximum values for each municipality in each prefecture for four times (at almost two-year intervals) of the measurement results from 2012 to 2018.
Ando, Masaki; Matsuda, Norihiro; Saito, Kimiaki
Nihon Genshiryoku Gakkai Wabun Rombunshi, 20(1), p.34 - 39, 2021/03
We measured count rates and air dose rates at 11 measurement points where the influence of the Fukushima Dai-ichi Nuclear Power Plant accident could be ignored to obtain parameters for a background equation applying to KURAMA-II loaded with the high sensitivity CsI(Tl) detector, C12137-01. It was found that the sensitivity of KURAMA-II (C12137-01) was about 10 times or more for background measurement, compared with KURAMA-II loaded with the standard type CsI(Tl) detector, C12137. A background equation for the energy range of 1400-2000 keV was determined as, y (
Sv/h)=0.062 x (cps). We evaluated background air dose rates using KURAMA-II (C12137-01) for 71 municipalities and compared them with the previous study using KURAMA-II (C12137). Evaluated background air dose rates in this study were almost equal to those in the previous study. We confirmed that the background equation evaluated in this study was applicable for the KURAMA-II (C12137-01).
Yoshimura, Kazuya; Saegusa, Jun; Sanada, Yukihisa
Scientific Reports (Internet), 10(1), p.3859_1 - 3859_9, 2020/03
Times Cited Count：20 Percentile：53.86(Multidisciplinary Sciences)Ando, Masaki; Mikami, Satoshi; Tsuda, Shuichi; Yoshida, Tadayoshi; Matsuda, Norihiro; Saito, Kimiaki
Journal of Environmental Radioactivity, 192, p.385 - 398, 2018/12
Times Cited Count：17 Percentile：40.91(Environmental Sciences)Car-borne surveys using KURAMA systems have been conducted over a wide area in eastern Japan since 2011. The measurement data collected until 2016 was analyzed, and decreasing trend of the dose rates in regions within 80 km of Fukushima Dai-ichi Nuclear Power Plant were examined. The averaged dose rates tended to decrease considerably with respect to the physical decay of radiocaesium, and the ecological half-lives of the fast and slow decay components were estimated. The decrease of the dose rate in the forest was slower than its decrease in other regions, and the decrease of the dose rate in urban area was the fastest. The decrease in the dose rates obtained via the car-borne survey was larger than that obtained on flat ground with few disturbances using survey meters approximately 1.5 y after the accident; hereafter, the decrease in the dose rates obtained via the car-borne survey was same as the latter measurement.
Ando, Masaki; Yamamoto, Hideaki*; Kanno, Takashi*; Saito, Kimiaki
Journal of Environmental Radioactivity, 190-191, p.111 - 121, 2018/10
Times Cited Count：21 Percentile：50.70(Environmental Sciences)Ambient dose equivalent rates in various environments related to human lives were measured by walk surveys using the KURAMA-II systems from 2013 to 2016 around the Fukushima Dai-ichi Nuclear Power Plant. The dose rate of the locations where the walk survey was performed decreased to about 38% of its initial value in the 42 months, which was beyond that attributable to the physical decay. The air dose rates decreased depending on the level of the evacuation areas, and the decrease was slightly larger in populated areas where humans are active. The comparison of walk survey data with car-borne survey data indicated that the air dose rate varies largely even within a 100 m square area. The dose rates measured by the walk surveys were estimated to be medial of those along roads and those of undisturbed flat ground. The air dose rates measured by the walk surveys decreased quickly compared with the air dose rate from the flat ground measurement.
Tanaka, Hiroshi; Sakoda, Akihiro; Ando, Masaki; Ishimori, Yuu
Hoken Butsuri, 51(2), p.107 - 114, 2016/06
Ambient dose rates are continuously monitored in Ningyo-toge Environmental Engineering Center, Japan Atomic Energy Agency. The present study discussed the variations in ambient dose rates, observed from April 2014 to March 2015, due to snowfall as well as rainfall. It is much snowy as one of climatic features in this area. Rain or snow was sampled for a certain period in the day of interest (17 cases in total), and then the concentration of radon progeny was measured. With the measured data, the variation in ambient dose rate was calculated considering the accumulation of the radon progeny on the ground. As a whole, this calculation was found to reasonably reproduce the time trends of observed dose rates, except for four cases. Based on the backward trajectory analysis, it was explained that the discrepancy in two cases out of the four was induced by changes of radon progeny concentration in precipitation around sampling period. It was suggested that the other two cases were caused by the run-off of rain from the ground surface.
Kikuchi, Masahiro; Ukai, Mitsuko*; Kobayashi, Yasuhiko
JAEA-Review 2014-050, JAEA Takasaki Annual Report 2013, P. 89, 2015/03
Saito, Kimiaki; Yamamoto, Hideaki
Radioisotopes, 63(11), p.519 - 530, 2014/11
This article aims to provide the basic meanings and features of the doses frequently used in the measurements and evaluations of environmental radiation due to the Fukushima Dai-ichi Nuclear Power Plant accident. The following doses are explained and compared: absorbed dose as basic physical quantity; effective dose and equivalent dose for judgment in radiation protection; and ambient dose equivalent 
(10) and individual dose equivalent 
p(10) for radiation measurements.
Nakamura, Takemi*; Tonoike, Kotaro; Miyoshi, Yoshinori
Radiation Protection Dosimetry, 110(1-4), p.483 - 486, 2004/09
Times Cited Count：2 Percentile：16.59(Environmental Sciences)Dose measurement and evaluation technique in criticality accident conditions with a thermo luminescence dosimeter (TLD) was studied at the Transient Experiment Critical Facility (TRACY) of Japan Atomic Energy Research Institute (JAERI). The tissue absorbed dose can be derived from the ambient dose equivalent given by measurement with a TLD using the conversion factor given by computation. Using this technique, the neutron dose around the SILENE reactor of the Institute for Radioprotection and Nuclear Safety (IRSN) of France was measured in the Accident Dosimetry Intercomparison Exercise (June 10-21, 2002) organized by OECD/NEA and IRSN. In this exercise, the 
dose was also measured with a TLD. In this report, measurements and evaluation results at TRACY and SILENE are presented.
Ito, Masashi; Shiraishi, Akemi; Murakami, Hiroyuki
JAERI-Tech 2001-048, 20 Pages, 2001/07
JAERI-Tech-2001-048.pdf:1.27MB
In Japan Atomic Energy Research Institute, a new type radiophotoluminescent(RPL) glass dosimeter is recently adopted replaced film badge for external personal monitoring. Some fundamental characteristics of this dosimeter, such as dose dependence linearity, energy dependence, dose evaluation accuracy against mixed irradiation condition,fading, etc.,were examined at the Facility of Radiation Standard(FRS),JAERI. The results have proved that the RPL glass dosimeter has sufficient characteristics in practical use as a personal dosimeter for all of the items examined.
Sato, Rina; Yoshimura, Kazuya; Sanada, Yukihisa; Sato, Tetsuro*; Mori, Tsubasa*; Takagi, Marie*
no journal, ,
In order to accurately estimate air dose rates of indoors with a high percentage of stay, indoor dose reduction factor was evaluated based on indoor and outdoor air dose rate measurements, taking into account air dose rates due to natural radionuclides. The measurements were conducted on wooden and concrete buildings in 2021 in municipalities with specified reconstruction and revitalization base. Indoor air dose rates were estimated from outdoor air dose rates using representative values of the evaluated indoor dose reduction factors. As a result, indoor air dose rates were estimated more accurately when the effect of natural radionuclides was taken into account, because the error indicators were smaller than those in the case without the effect of natural radionuclides.
Liu, X.; Machida, Masahiko; Saito, Kimiaki; Tanimura, Naoki*
no journal, ,
Ecological half-life has been widely used to describe the long-term decrease of ambient dose rates in addition to radioactive decay. In the present work, we introduce a new, robust, and efficient numerical method to extract space dependent ecological half-lives from car-borne survey data. Numerical results indicate complexed ecological half-life profiles, which are originated from their spatial patterns.
Honda, Fumiya*; Kinase, Sakae
no journal, ,
