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Katengeza, E. W.*; Ochi, Kotaro; Sanada, Yukihisa; Iimoto, Takeshi*; Yoshinaga, Shinji*
Health Physics, 121(1), p.48 - 57, 2021/07
Times Cited Count：1 Percentile：16.35(Environmental Sciences)Special reconstruction and revitalization bases were designated in Fukushima's difficult-to-return zones by the Japanese government as targets of intensive decontamination to drastically lower air dose rates and enable residents to return. A pond amidst residences of one of these bases was targeted for decontamination and this study aimed at evaluating the effect and effectiveness of the decontamination by decontamination factor, air dose rate reduction factor, and the additional annual effective dose to residents. Air dose rates were measured in-situ with KURAMMA-II while soil core samples were collected and measured for radioactivity in the laboratory by gamma spectrometry. Lower decontamination factors were observed for more deeply distributed radiocesium soil profiles whereas areas covered with gravel demonstrated the largest reduction in air dose rates. Decontamination effectively lowered the radiocesium inventory and air dose rates by 51% and 37-91% respectively. Moreover, the additional annual effective dose to the public changed from 1.7
0.79 mSv to 1.20.57 mSv because of decontamination representing a dose aversion of 29%. These findings demonstrate how decontaminating ponds in residential areas can help to further lower the external exposure.
Sasaki, Miyuki; Sanada, Yukihisa; Katengeza, E. W.*; Yamamoto, Akio*
Scientific Reports (Internet), 11, p.1857_1 - 1857_11, 2021/01
Times Cited Count：13 Percentile：67.27(Multidisciplinary Sciences)This study proposed a new method to visualize the ambient dose rate distribution using artificial neural networks from the results of airborne radiation monitoring. The method used airborne radiation monitoring conducted around Fukushima Daiichi Nuclear Power Plant by an unmanned aerial vehicle. A lot of survey data which had obtained in the past was used as training data for building a network. The reliability of the artificial neural network method was evaluated by comparison with the ground-based survey data. The dose rate map that was created by the artificial neural networks method reproduced the ground-based survey results better than traditional methods.
Sanada, Yukihisa; Yoshimura, Kazuya; Urabe, Yoshimi*; Iwai, Takeyuki*; Katengeza, E. W.*
Journal of Environmental Radioactivity, 223-224, p.106397_1 - 106397_9, 2020/11
Times Cited Count：13 Percentile：57.17(Environmental Sciences)Funaki, Hironori; Sakuma, Kazuyuki; Nakanishi, Takahiro; Yoshimura, Kazuya; Katengeza, E. W.*
Science of the Total Environment, 743, p.140668_1 - 140668_9, 2020/11
Times Cited Count：19 Percentile：67.01(Environmental Sciences)
measurements with Plastic Scintillation FibersKatengeza, E. W.*; Sanada, Yukihisa; Yoshimura, Kazuya; Ochi, Kotaro; Iimoto, Takeshi*
Environmental Science; Processes & Impacts, 22(7), p.1566 - 1576, 2020/07
Times Cited Count：9 Percentile：50.05(Chemistry, Analytical)Katengeza, E.*; Ochi, Kotaro; Sanada, Yukihisa; Iimoto, Takeshi*
no journal, ,
Katengeza, E.*; Sanada, Yukihisa; Yoshimura, Kazuya; Ochi, Kotaro; Iimoto, Takeshi*
no journal, ,
The rate of temporal change of radiocesium concentration in bottom sediments is governed not only by its physical decay but also by various ecological processes. In this study, the decreasing trend of radiocesium concentration over wide pond areas of surface sediments (up to 10 cm depth), due to ecological processes, was investigated using plastic scintillation fibers (PSF) and was quantified by the ecological half life. PSF measurements were conducted between 2013 and 2019. Their conversion factors ((Bq/kg)/cps) were obtained by comparison between detected radiation counting rate obtained by PSF and the concentration of radiocesium in sediment cores collected from coinciding positions within the same ponds. A forest catchment pond exhibited the longest ecological half life and may indicate catchment derived radiocesium input as was partly evident in the spatial temporal patterns of radiocesium concentration at this pond's inlet.
Katengeza, E.*; Sanada, Yukihisa; Ochi, Kotaro; Iimoto, Takeshi*
no journal, ,
When radiocesium (RCs) deposits in water bodies, it tends to concentrate at the waterbed due to its strong adsorption to sediments. Monitoring wide areas of so-contaminated waterbed is challenging by traditional sediment sampling. In-situ techniques that can directly measure radioactivity in the waterbed are important solutions. However, their accuracy is generally lower than that of sediment sampling. This study presents the status of research on the application of in-situ radioactivity measurement technology in the waterbed focusing on RCs monitoring in Fukushima as spearheaded by the Japan Atomic Energy Agency (JAEA).
Katengeza, E.*; Sanada, Yukihisa; Ochi, Kotaro; Iimoto, Takeshi*
no journal, ,
Katengeza, E.*; Sanada, Yukihisa; Ochi, Kotaro; Iimoto, Takeshi*
no journal, ,
The calibration factor (CF) was determined by comparing the counting rate obtained by plastic scintillation fibers (PSF) with the average radiocesium (RCs) concentration in the top 10 cm of sediment core samples in previous study. The systematic biases and measurement uncertainty of estimated RCs concentration were evaluated by comparing against the RCs concentration in sampled sediment cores averaged over depths, ranging from 5 cm to 30 cm in 5 cm increments. When the calibration depth is 10 and 15 cm, the normalized mean square and relative deviation of PSF-derived RCs concentration against RCs concentration in sampled sediment were comparable. Thus, it may be necessary to revise calibration depth in order to sustainably optimize radiocesium concentration measurements by the PSF technique.
Katengeza, E.*; Sanada, Yukihisa; Ochi, Kotaro; Iimoto, Takeshi*
no journal, ,
This study aimed at evaluating the vertical distribution of radiocesium in bottom sediment core samples from 45 ponds sampled in 2015-2019 and clarifying the impact of the vertical distribution on the efficiency of decontamination by stripping the top 10 cm of bottom sediments. The relaxation mass depths and depth of sediment containing 90% of the inventory were larger than on land indicating faster downward migration of radiocesium in ponds. This may have been caused by accumulation from the ponds' catchments where radiocesium enrichment occurred. This indicates that local behavior of radiocesium in reservoirs are more important to decontamination outcomes.
Katengeza, E.*; Sanada, Yukihisa; Ochi, Kotaro; Iimoto, Takeshi*
no journal, ,
Since 2013, plastic scintillation fiber (PSF) is calibrated from counting rate to radiocesium concentration by comparing with the average concentration of the top 10 cm of sediment core sample. The purpose of this study is to clarify influence of radiocesium depth distribution on PSF calibration factor and measurement uncertainty. The radiocesium concentration was estimated by varying the calibration depth of PSF from 5 to 30 cm at 5 cm intervals. The estimated radiocesium concentration was compared with the radiocesium concentration in the bottom sediment collected at the PSF measurement point. The normalized mean squared error values were the smallest at the calibration depth of 15-20 cm, suggesting that the measurement can be optimized by changing the calibration depth.
