Japan's charge at the 2nd International Nuclear Science Olympiad

Satoh, Daiki; Tsunoyama, Yuichi*; Iimoto, Takeshi*

Nihon Genshiryoku Gakkai-Shi ATOMO, 68(3), p.183 - 186, 2026/02

https://doi.org/10.3327/jaesjb.68.3_183

The 2nd International Nuclear Science Olympiad (INSO) was held in Malaysia, from July 31 to August 5, 2025. INSO is an international competition supported by the International Atomic Energy Agency (IAEA), in which pre-university students under the age of 20, selected by each participating country, compete in comprehensive nuclear science challenges. Japan participated for the first time, sending four high school students as national representatives. All four earned medals-one gold, two silver, and one bronze-and additionally received the Highest Score in Experimental Examination Award and the Outstanding Female Participant Award, both of which are granted to only one individual each across all participants. This article reports on the journey from domestic training to medal achievement, from the perspective of the expert team who accompanied the Japanese delegation as team leaders or IAEA specialists. The 2nd INSO featured both experimental and theoretical examinations, with questions spanning a wide range of disciplines including chemistry, medicine, astronomy, environmental science, materials engineering, and reactor engineering. The competition reaffirmed the broad scope of nuclear science and highlighted the need to build educational platforms and human resource networks capable of covering this interdisciplinary field to foster the next generation.

Review of articles related to the accident at the Fukushima Daiichi Nuclear Power Station published in the Japanese Journal of Health Physics; Opinion and others (Secondary Publication)

Takahara, Shogo; Iimoto, Takeshi*; Igarashi, Takayuki*; Kawabata, Masako*

Journal of Radiation Protection and Research, 50(1), p.1 - 9, 2025/03

https://doi.org/10.14407/jrpr.2023.00703

The Health Physics Society of Japan established a working group to obtain insights and findings from articles related to the 1F accident, published in the Japanese Journal of Health Physics. This study describes the review results of 47 articles classified into the field without risk communication, environmental measurement and monitoring, radiation dose measurement and assessment, radiation medicine, and radioactive waste. The reviewed articles contain various insights and issues depending on the authors' standpoints and relevant social interests. As a result, the 1F accident relevant articles offer various discussion points depending on the authors' awareness of the issues, which give an opportunity to make reconsiderations on what kind of academic system health physics or radiation protection should be on the basis of the experiences from the 1F accident. Note that this is an English translation of an article published in Japanese Journal of Health Physics.

Seasonal variations in radon and thoron exhalation rates from solid concrete interior walls observed using in situ measurements

Sakoda, Akihiro; Ishimori, Yuu; Hasan, Md. M.*; Jin, Q.*; Iimoto, Takeshi*

Atmosphere (Internet), 15(6), p.701_1 - 701_12, 2024/06

https://doi.org/10.3390/atmos15060701

Building materials such as brick and concrete are known indoor radon (Rn) and thoron (Rn) sources. Most radon and thoron exhalation studies are based on the laboratory testing of pieces and blocks of such materials. To discuss if laboratory findings can be applied to a real-world environment, we conducted intensive in-situ exhalation tests on two solid concrete interior walls of an apartment in Japan for over a year. Exhalation rates of radon () and thoron () were measured by a measurement system, mainly consisting of an accumulation chamber and dedicated monitors. The indoor air temperature () and absolute humidity () were measured in parallel, and the wall-surface temperature and water content were occasionally measured. All data obtained here were investigated to reveal environmental and material-associated factors affecting exhalation from the concrete walls. There were weak correlations between or and T or at one tested wall, and moderate correlations of and strong correlations of with or at the other wall. Our findings on were consistent with those in a previous laboratory work where a concrete sample was subject to various temperatures, although a corresponding laboratory study of could not be collected. Additionally, moderate or strong correlation between and was observed for both tested walls. The comparison of the measured data and theoretical calculations revealed a new issue on how much impact each process of the emanation and migration within concrete pore spaces has on radon and thoron exhalation. This study provides an insight into parameterizing radon and thoron source inputs in modeling the spatiotemporal dynamics of indoor radon and thoron.

Optimizing calibration factors of plastic scintillation fibers for improved accuracy of radiocesium concentration measurements in bottom sediments of agricultural ponds

Katengeza, E. W.*; Sanada, Yukihisa; Ochi, Kotaro; Iimoto, Takeshi*

Cogent Engineering (Internet), 11(1), p.2340203_1 - 2340203_9, 2024/04

https://doi.org/10.1080/23311916.2024.2340203

The uncertainty of radioactivity measurements can be influenced by the vertical distribution of the target radionuclide in the sediments. This study used 2015-2019 field measurement data from 47 ponds to evaluate the depth dependence of calibration factors of plastic scintillation fiber (PSF) and its influence on measurement uncertainty. By changing the depth of focus from 10 cm to 15-20 cm when calculating the conversion factor, the normalized mean square error of the radiocesium concentration estimated by the PSF with respect to the radiocesium concentration in core sediments sampled at the same location was found to be smaller.

Review of articles related to the accident of TEPCO's Fukushima Daiichi Nuclear Power Station published on Japanese Journal of Health Physics; Opinion and others

Takahara, Shogo; Iimoto, Takeshi*; Igarashi, Takayuki*; Kawabata, Masako*

Hoken Butsuri (Internet), 58(2), p.50 - 58, 2023/08

https://doi.org/10.5453/jhps.58.50

The Health Physics Society of Japan established a working group to obtain the insights and findings from the articles, which are related to the Fukushima Daiichi Nuclear Power Station (1F) accident, published in the Japanese Journal of Health Physics. This paper describes the results of the review on 47 articles, which are classified into the field without risk communication, environmental measurement and monitoring, radiation dose measurement and assessment, radiation medicine and radioactive waste. In the reviewed articles, there are various insights and issues depending on the standpoint of the authors and social interests in the timing those published. It is important to face these insights and issues to consider prudently "what is health physics or radiation protection?" for the future development of the Health Physics society.

Nuclear disaster prevention based on lessons learned from the Fukushima Daiichi Nuclear Power Station accident

Shimada, Kazumasa; Nagai, Haruyasu; Hashimoto, Makoto; Iimoto, Takeshi*

Nihon Genshiryoku Gakkai-Shi ATOMO, 65(5), P. 290, 2023/05

https://doi.org/10.3327/jaesjb.65.5_290

This article is part of the special feature article "What should be done from now on after the 1F accident and what should be conveyed to the next generation after the 1F accident?" of the Atomic Energy Society of Japan, which summarizes the discussions and future proposals on nuclear disaster prevention in which the members of the Health Physics and Environment Science Subcommittee have been involved. In view of the recommendations of the Accident Investigation Committee of the Atomic Energy Society of Japan and the Meteorological Society of Japan, the behavior of radioactive plumes and the prediction of residents' evacuation behavior should be studied to support decision-making on evacuation and other protective measures for residents in and outside the UPZ. Furthermore, decision-making on protective measures and practical risk communication to residents based on radiation health risks to residents and ethical aspects are newly proposed.

Validation study of ambient dose equivalent conversion coefficients for radiocaesium distributed in the ground; Lessons from the Fukushima Daiichi Nuclear Power Station accident

Ochi, Kotaro; Funaki, Hironori; Yoshimura, Kazuya; Iimoto, Takeshi*; Matsuda, Norihiro; Sanada, Yukihisa

Radiation and Environmental Biophysics, 61(1), p.147 - 159, 2022/03

https://doi.org/10.1007/s00411-022-00969-3

Activity report of the Task Group on Parameters Used in Biospheric Dose Assessment Models for Radioactive Waste Disposal

Takahashi, Tomoyuki*; Fukaya, Yukiko*; Iimoto, Takeshi*; Uni, Yasuo*; Kato, Tomoko; Sun, S.*; Takeda, Seiji; Nakai, Kunihiro*; Nakabayashi, Ryo*; Uchida, Shigeo*; et al.

Hoken Butsuri (Internet), 56(4), p.288 - 305, 2021/12

https://doi.org/10.5453/jhps.56.288

We report the results of activities related to the Task Group of Parameters Used in Biospheric Dose Assessment Models for Radioactive Waste Disposal at the Japan Health Physics Society.

The Effect and effectiveness of decontaminating a pond in a residential area of Fukushima

Katengeza, E. W.*; Ochi, Kotaro; Sanada, Yukihisa; Iimoto, Takeshi*; Yoshinaga, Shinji*

Health Physics, 121(1), p.48 - 57, 2021/07

https://doi.org/10.1097/HP.0000000000001413

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 1.70.79 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.

Development of dose estimation system integrating sediment model for recycling radiocesium-contaminated soil to coastal reclamation

Miwa, Kazuji; Takeda, Seiji; Iimoto, Takeshi*

Radiation Protection Dosimetry, 184(3-4), p.372 - 375, 2019/10

https://doi.org/10.1093/rpd/ncz128

The Ministry of the Environment has indicated the policy of recycling the contaminated soil generated by decontamination activity after the Fukushima accident. By recycling to coastal reclamation which is one of effective recycling application, dissolved radiocesium and absorbed radiocesium on soil particles will flow out to the ocean by construction, therefore evaluating radiocesium transition in ocean considering the both types of radiocesium is important for safety assessment. In this study, the radiocesium outflow during constructing and after constructing is modeled, and radiocesium transition in ocean is evaluated by Sediment model suggested in OECD/NEA. The adaptability of sediment model is confirmed by reproducing evaluation of the coastal area of Fukushima. We incorporate the sediment model to PASCLR2 code system to evaluate the doses from radiocesium in ocean.