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Journal Articles

Backward estimation of atmospheric release of $$^{137}$$Cs and $$^{131}$$I using total cumulative deposition in terrestrial areas following the Fukushima Daiichi Nuclear Power Plant accident

Iijima, Masashi*; Takahara, Shogo

Health Physics, 121(6), p.587 - 596, 2021/12

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident caused a significant release of radionuclides into the environment. Backward estimations of the source term are generally performed using air concentrations, but they are difficult to measure when radioactive plumes are passing through, and only spatially and temporally limited measurements are available. Therefore, a new method of backward estimation was developed based on the total cumulative deposition density that can provide sufficient measurements by combining the atmospheric transport, dispersion and deposition model calculation. Consequently, our estimations have no significant contradiction with the previous studies that were based on air concentrations and an ambient dose equivalent rate. Further considerations are needed to clarify the source term of the FDNPP accident and explore the extent of uncertainty included in backward estimations considering the difference of model and input data.

Journal Articles

Assessment of radiation doses to off-site responders in TEPCO Fukushima Daiichi Nuclear Power Station Accident

Shimada, Kazumasa; Iijima, Masashi*; Watanabe, Masatoshi*; Takahara, Shogo

Proceedings of Asian Symposium on Risk Assessment and Management 2021 (ASRAM 2021) (Internet), 17 Pages, 2021/10

The radiation doses received by the off-site responders in the Fukushima Daiichi Nuclear Power Station accident were assessed. Atmospheric dispersion simulation was conducted with the source term of the previous research to calculate the atmospheric concentration and ground surface deposition in the municipalities where off-site responders actives. The external exposure dose from cloudshine and groundshine, the internal exposure dose due to inhalation of radioactive plume and resuspended radio nuclei, and the temporal and spatial distribution within each municipality were assessed. As a result of comparing the assessed values of the external exposure dose with the measured values of the personal dosimeter, the measured values were within the assessed range. As a result of our assessment with internal dose exposure, if the exposures occurred without protective measures, the potential daily effective dose in the period between 12 and 31 March 2011 were several tens mSv per day or more in the relatively high dose area. Therefore, to keep the doses received by the responders below the reference level of 20 mSv recommended by the ICRP, it is necessary to ensure that the protective measures for internal exposures such as masks are taken, and to manage the time spent for their activity at least daily.

Journal Articles

Assessment model of radiation doses from external exposure to the public after the Fukushima Daiichi Nuclear Power Plant accident

Takahara, Shogo; Iijima, Masashi*; Watanabe, Masatoshi*

Health Physics, 118(6), p.664 - 677, 2020/06

 Times Cited Count:6 Percentile:73.86(Environmental Sciences)

Assessment model of radiation doses from external exposures was developed based on the actual measurement of individual doses and ambient dose equivalent rate inside and outside of a house in Fukushima city. The survey on behavioral pattern was also carried out under the same purpose. In addition to the actual measurement and survey by ourselves, we also took into account the latest insights from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Comparisons between the assessed results and the measured ones revealed that the time dependences of doses obtained using the developed models were in good agreement with the results of actual measurements. In addition, we were able to reproduce the distribution of doses for indoor and outdoor workers. Therefore, our probabilistic approach was validated. According to our assessment and actual measurement, no participants received 1 mSv/y or higher in Fukushima city in eight years after the FDNPP accident.

Journal Articles

Negative muonium ion production with a C12A7 electride film

Otani, Masashi*; Fukao, Yoshinori*; Futatsukawa, Kenta*; Kawamura, Naritoshi*; Matoba, Shiro*; Mibe, Tsutomu*; Miyake, Yasuhiro*; Shimomura, Koichiro*; Yamazaki, Takayuki*; Hasegawa, Kazuo; et al.

Journal of Physics; Conference Series, 1350, p.012067_1 - 012067_6, 2019/12

 Times Cited Count:1 Percentile:53.97

Negative muonium atom ($$mu^+$$e$$^-$$e$$^-$$, Mu$$^-$$) has unique features stimulating potential interesting for several scientific fields. Since its discovery in late 1980's in vacuum, it has been discussed that the production efficiency would be improved using a low-work function material. C12A7 was a well-known insulator as a constituent of alumina cement, but was recently confirmed to exhibit electric conductivity by electron doping. The C12A7 electride has relatively low-work function (2.9 eV). In this paper, the negative muonium production measurement with several materials including a C12A7 electride film will be presented. Measured production rate of the Mu$$^-$$ were 10$$^{-3}$$/s for all the Al, electride, and SUS target. Significant enhancement on electride target was not observed, thus it is presumed that the surface condition should be more carefully treated. There was no material dependence of the Mu$$^-$$ averaged energy: it was 0.2$$pm$$0.1keV.

Journal Articles

Beam commissioning of muon beamline using negative hydrogen ions generated by ultraviolet light

Nakazawa, Yuga*; Bae, S.*; Choi, H.*; Choi, S.*; Iijima, Toru*; Iinuma, Hiromi*; Kawamura, Naritoshi*; Kitamura, Ryo; Kim, B.*; Ko, H. S.*; et al.

Nuclear Instruments and Methods in Physics Research A, 937, p.164 - 167, 2019/09

 Times Cited Count:2 Percentile:27.72(Instruments & Instrumentation)

A muon linac is under development for the precise measurement of the muon anomalous magnetic moment ($$g$$-2) and electric dipole moment (EDM) with a reaccelerated thermal muon beam. An H$$^-$$ source driven by an ultraviolet light has been developed for the muon acceleration experiment. Prior to the acceleration experiment, a beamline commissioning was performed using this H$$^-$$ beam, since the accelerated muon intensity is very low. We successfully measured the magnetic rigidity, which is essential for identifying the accelerated muons. This H$$^-$$ source is capable of utilizing as a general-purpose beam source for other beamline.

JAEA Reports

External dose evaluation of emergency responder in off-site at the time of Fukushima-Dai-ichi Nuclear Power Station Accident (Contract research)

Shimada, Kazumasa; Sasaki, Toshihisa*; Iijima, Masashi*; Munakata, Masahiro

JAEA-Research 2018-012, 68 Pages, 2019/02


The external exposure dose of off-site emergency responders at Fukushima Dai-ichi Nuclear Power Station accident were evaluated in order to consider a radiation protection of emergency responders. The maximum value of individual daily dose of emergency responders whose activities details were recorded from 12th to 31th March 2011 was 650 $$mu$$Sv engaged in evacuation support in Futaba Town on 12th. Next, atmospheric concentrations and deposition of radionuclides were calculated from the source terms estimated by previous studies using atmospheric diffusion and deposit calculation codes, and air dose rates at off-site were estimated. Then, the external exposure dose was calculated for 6 emergency responders whose daily activities and personal doses were continuously recorded. Furthermore, the maximum value and the average value of the calculation external dose of emergency responders in the activity area were compared with the measurement value of the personal dosimeter of them. These results showed that the calculated value of the external exposure dose of emergency responders calculated from the maximum value of the dose rate in the active area roughly includes the measured value.

Journal Articles

A Probabilistic Approach to Assess External Doses to the Public Considering Spatial Variability of Radioactive Contamination and Interpopulation Differences in Behavior Pattern

Takahara, Shogo; Iijima, Masashi*; Yoneda, Minoru*; Shimada, Yoko*

Risk Analysis, 39(1), p.212 - 224, 2019/01


 Times Cited Count:5 Percentile:58.07(Public, Environmental & Occupational Health)

A dose assessment model was developed based on measurements and surveys of individual doses and relevant contributors in Fukushima City for four population groups: Fukushima City Office staff, Senior Citizens' Club, Contractors' Association, and AgriculturalCooperative. In addition, probabilistic assessments were performed for these population groups by considering the spatial variability of contamination and interpopulation differencesresulting from behavior patterns. As a result of comparison with the actual measurements, the assessment results for participants from the Fukushima City Office, Senior Citizens' Club and the Agricultural Cooperative agreed with the measured values. By contrast, the measurements obtained for the participants from the Contractors' Association were not reproduced well in the present study. To assess the doses to this group, further investigations of association members' work activities and the related dose reduction effects are needed.

Journal Articles

First muon acceleration using a radio-frequency accelerator

Bae, S.*; Choi, H.*; Choi, S.*; Fukao, Yoshinori*; Futatsukawa, Kenta*; Hasegawa, Kazuo; Iijima, Toru*; Iinuma, Hiromi*; Ishida, Katsuhiko*; Kawamura, Naritoshi*; et al.

Physical Review Accelerators and Beams (Internet), 21(5), p.050101_1 - 050101_6, 2018/05

 Times Cited Count:15 Percentile:82.65(Physics, Nuclear)

Muons have been accelerated by using a radio-frequency accelerator for the first time. Negative muonium atoms (Mu$$^{-}$$), which are bound states of positive muons and two electrons, are generated from through the electron capture process in an aluminum degrader. The generated Mu$$^{-}$$'s are initially electrostatically accelerated and injected into a radio-frequency quadrupole linac (RFQ). In the RFQ, the Mu$$^{-}$$'s are accelerated to 89 keV. The accelerated Mu$$^{-}$$'s are identified by momentum measurement and time of flight. This compact muon linac opens the door to various muon accelerator applications including particle physics measurements and the construction of a transmission muon microscope.

Journal Articles

Dose-reduction effects of vehicles against gamma radiation in the case of a nuclear accident

Takahara, Shogo; Watanabe, Masatoshi*; Hirouchi, Jun; Iijima, Masashi*; Munakata, Masahiro

Health Physics, 114(1), p.64 - 72, 2018/01


 Times Cited Count:2 Percentile:24.93(Environmental Sciences)

Journal Articles

Identification of penetration path and deposition distribution of radionuclides in houses by experiments and numerical model

Hirouchi, Jun; Takahara, Shogo; Iijima, Masashi; Watanabe, Masatoshi; Munakata, Masahiro

Radiation Physics and Chemistry, 140, p.127 - 131, 2017/11


 Times Cited Count:2 Percentile:22.85(Chemistry, Physical)

Journal Articles

Bioaccessibility of Fukushima-accident-derived Cs in soils and the contribution of soil ingestion to radiation doses in children

Takahara, Shogo; Ikegami, Maiko*; Yoneda, Minoru*; Kondo, Hitoshi*; Ishizaki, Azusa; Iijima, Masashi; Shimada, Yoko*; Matsui, Yasuto*

Risk Analysis, 37(7), p.1256 - 1267, 2017/07


 Times Cited Count:4 Percentile:44.84(Public, Environmental & Occupational Health)

Journal Articles

Assessment of residual doses to population after decontamination in Fukushima Prefecture

Mori, Airi; Takahara, Shogo; Ishizaki, Azusa; Iijima, Masashi; Sanada, Yukihisa; Munakata, Masahiro

Journal of Environmental Radioactivity, 166(Part 1), p.74 - 82, 2017/01

 Times Cited Count:8 Percentile:31.07(Environmental Sciences)

Large quantities of radioactive materials were released into the environment as a result of the Fukushima Daiichi Nuclear Power Station accident. Many inhabitants residing in the affected areas are now exposed to radiation in their daily lives. In an attempt to manage this radiation dose, an additional radiation dose of 1 mSv/y was adopted as a long-term dosimetric target. An activity level reading of 0.23 $$mu$$Sv/h was then determined as a guidance value to achieve the target by implementing decontamination measures. The objectives of this study are to assess the effects of decontamination based on this guidance value and to predict any possible future problems with the decontamination strategy. Using a probabilistic approach, we assessed the annual effective dose of indoor workers, outdoor workers, and pensioners in the Fukushima Prefecture. Our probabilistic model considers the variabilities in behavioral patterns and Cs-137 surface-activity levels. Five years after the initial contamination, the 95th percentiles of indoor workers and pensioners in 53 of the 59 municipalities were found to receive annual effective doses of below 1 mSv/y (0.026-0.73 mSv/y). However, for outdoor workers in 25 municipalities, the annual doses were over 1 mSv/y (1.0-35 mSv/y). Therefore, the guidance value is effective for indoor workers and pensioners; to determine whether additional countermeasures for outdoor workers should be implemented, a detailed assessment that uses more realistic assumptions is required.

JAEA Reports

Actions to protect the public in an emergency due to severe conditions at a light water reactor (Translated document)

Homma, Toshimitsu; Takahara, Shogo; Iijima, Masashi; Sato, Sohei; Kimura, Masanori; Shimada, Kazumasa

JAEA-Review 2016-013, 162 Pages, 2016/07


This is a Japanese translation of "Actions to Protect the Public in an Emergency due to Severe Conditions at a Light Water Reactor", which is published by the International Atomic Energy Agency in May 2013. The original IAEA Publication is available on the IAEA Website (

Journal Articles

Application of health effect model of NUREG/CR-4214 to the Japanese population and comparison with a latest model

Takahara, Shogo; Iijima, Masashi; Shimada, Kazumasa

Hoken Butsuri, 50(3), p.172 - 181, 2015/09

JAEA Reports

Development of deterministic approach to assess doses to the public from external exposures in the areas contaminated by the Fukushima Daiichi Nuclear Power Station Accident

Takahara, Shogo; Iijima, Masashi; Shimada, Kazumasa; Kushida, Teruo; Shiratori, Yoshitake

JAEA-Research 2014-024, 57 Pages, 2015/01


In order to assess the doses to representative person using deterministic approach, we measured radiation dose rates and surveyed on behavioral patterns in the areas contaminated by the Fukushima Daiichi Nuclear Power Station Accident. Statistical analyzes were also performed to identify the characteristics of individual doses from external exposures, as well as radiation dose rates and behavioral patterns. Radiation dose rates measured in living areas distribute with lognormal form. Behavioral patterns of the populations were different corresponding to their occupation. Time spent outdoors of indoor workers were distributed in lognormal form and those of outdoor workers had the normal distribution. Multi-regression analyses were made to explore a significant relationship between individual doses and relevant contributors. These results indicated that the significant differences were given in individual doses due to the spatial differences of radiation dose rates as well as the interindividual differences of behavioral patterns. Based on the results of analyses of relevant contributors to the external exposures, deterministic dose assessment model was developed. The validity of this model was confirmed because the assessed values were higher than those measured.

Journal Articles

Statistical characterization of radiation doses from external exposures and relevant contributors in Fukushima Prefecture

Takahara, Shogo; Abe, Tatsuya*; Iijima, Masashi; Shimada, Kazumasa; Shiratori, Yoshitake

Health Physics, 107(4), p.326 - 335, 2014/10


 Times Cited Count:8 Percentile:56.14(Environmental Sciences)

Probabilistic dose assessment is one of the useful methods to describe the information on the dose distributions in the population. To use this assessment, statistically characterized data on the pathway-relevant contributors are necessary. The objectives of the paper are to determine the statistical values and the distribution forms of the contributors to external exposures, as well as to identify the causes of the variabilities of them. To achieve the objectives, we have measured and surveyed ambient dose rate and time spent outdoors in Fukushima Prefecture. The measurements and surveys were performed with the cooperation of indoor workers, outdoor workers and pensioners. These results allowed us to determine the statistically characters of the individual doses and its contributors. In addition, these contributors had the variabilities attributed to the spatial distributions of deposited radionuclides, as well as the temporal and interpopulational differences of behavioral patterns.

Journal Articles

Probabilistic assessment of doses to the public living in areas contaminated by the Fukushima Daiichi Nuclear Power Plant accident

Takahara, Shogo; Iijima, Masashi; Shimada, Kazumasa; Kimura, Masanori; Homma, Toshimitsu

Radiation Monitoring and Dose Estimation of the Fukushima Nuclear Accident, p.197 - 214, 2014/02


The aim of this study is to provide the scientifically-based quantitative information about a range of received doses to the evacuees from the evacuation areas and the deliberate evacuation areas. To achieve the aim, we adopted a probabilistic approach. The dose assessments were performed based on the measurement data of the surface activity concentrations of $$^{137}$$Cs and the results of actual survey on behavioral patterns of the population groups living in Fukushima Prefecture. As the result of assessments, the 95th percentile of the annual effective doses received by the inhabitants evacuated from the evacuation areas were mainly in the 1-10 mSv dose band in the first year after the contamination. However, the 95th percentile of the doses received by some outdoor workers, inhabitants evacuated from the deliberate evacuation areas and highly contaminated areas were in the 10-50 mSv dose band.

JAEA Reports

Decontamination pilot projects for the environmental remediation of evacuation areas contaminated with radioactive materials discharged from the Fukushima Daiichi Nuclear Power Plant accident; Survey on individual doses to the inhabitants living in the areas contaminated by the accident (Contract research)

Takahara, Shogo; Iijima, Masashi; Kushida, Teruo; Shiratori, Yoshitake

JAEA-Research 2013-029, 36 Pages, 2013/12


In the areas contaminated by the Fukushima Daiichi Nuclear Power Plant accident, to clarify the influences of the lifestyle habits to radiation exposures for inhabitants, we performed surveys on their behavioral patterns and measurements of their individual doses due to external exposures. In addition, an assessment model was developed and the assessments of the doses were performed based on the results of the surveys and the measurements of ambient dose equivalent rates. The assessed individual doses were compared with those measured in order to confirm the validity of the model. Clear differences were found in time spent outdoors of the inhabitants of various occupations. Significant differences in individual doses were also observed between those of indoor workers and outdoor workers. In order to assess more precisely the doses of inhabitants who continue to live in the affected areas, assessments should be performed taking into account the population-specific behavioral patterns.

Journal Articles

Assessment of radiation doses to the public in areas contaminated by the Fukushima Daiichi Nuclear Power Station accident

Takahara, Shogo; Iijima, Masashi; Shimada, Kazumasa; Kimura, Masanori; Homma, Toshimitsu

Proceedings of International Symposium on Environmental monitoring and dose estimation of residents after accident of TEPCO's Fukushima Daiichi Nuclear Power Station, p.212 - 220, 2012/12

In the areas contaminated by radioactive materials due to the Fukushima Daiichi Nuclear Power Station accident, many residents are exposed to radiation through various exposure pathways. To assess the doses realistically and comprehensively, a probabilistic approach was adopted using data that reflected realistic environmental trends and lifestyle habits in Fukushima Prefecture. In the first year after the contamination, the 95th percentile of the annual effective dose received by the inhabitants evacuated from the evacuation areas and the deliberate evacuation areas was mainly in the 1-10 mSv dose band. However, the 95th percentile of the dose received by some outdoor workers and inhabitants evacuated from highly contaminated areas was in the 10-50 mSv dose band. The doses due to external exposure to deposited radionuclides were the dominant exposure pathway, and their contributions were about 90% under prevailing contamination conditions in Fukushima Prefecture. In addition, 20%-30% of the lifetime effective dose was delivered during the first year after the contamination.

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