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Cs activity concentration in the aquatic insect 
(Tricoptera: Stenopsychidae) in the Ota River, Fukushima, JapanIshii, Yumiko*; Miura, Hikaru*; Jo, J.*; Tsuji, Hideki*; Saito, Rie; Koarai, Kazuma; Hagiwara, Hiroki; Urushidate, Tadayuki*; Nishikiori, Tatsuhiro*; Wada, Toshihiro*; et al.
PLOS ONE (Internet), 17(5), p.e0268629_1 - e0268629_17, 2022/05
Times Cited Count：3 Percentile：40.21(Multidisciplinary Sciences)We investigated the variability in Cs activity concentration in individual aquatic insects in detritivorous caddisfly () and carnivorous dobsonfly (
) larvae from the Ota River, Fukushima. Caddisfly larvae showed sporadically higher radioactivity, whereas no such outliers were observed in dobsonfly larvae. Autoradiography and scanning electron microscopy analyses confirmed that these caddisfly larvae samples contained radiocesium-bearing microparticles (CsMPs), which are insoluble Cs-bearing silicate glass particles. CsMPs were also found in potential food sources of caddisfly larvae, such as periphyton and drifting particulate organic matter, indicating that larvae may ingest CsMPs along with food particles of similar size. Although CsMPs distribution and uptake by organisms in freshwater ecosystems is relatively unknown, our study demonstrates that CsMPs can be taken up by aquatic insects.
Manabe, Kentaro; Matsumoto, Masaki*
Journal of Nuclear Science and Technology, 56(1), p.78 - 86, 2019/01
Times Cited Count：7 Percentile：61.18(Nuclear Science & Technology)If an insoluble cesium-bearing particle is incorporated into the human body, the radioactivity will move as a single particle. In this case, it is impossible to estimate the number of disintegrations by considering the average behavior of countless nuclei. Then, a method was developed to simulate the behavior of the particle stochastically; and a biokinetic model was constructed to consider the characteristics of insoluble particles. Combination of the method and the model enables to estimate the number of disintegrations, and consequently the internal doses considering the stochastic behavior of the single cesium particle. We evaluated a probability density function of committed equivalent and effective doses and its 99th percentile value and arithmetic mean by repeating the above described procedure, and compared them to the reference values based on the existing models. As a result, the 99th percentile value of committed effective doses was 70 times the reference value when the number of incorporated particles was one, and consequently the dose level was quite low. When the exposure level is 1 mSv in committed effective dose, the uncertainty originating in the insolubility of cesium particles was negligibly small.
Manabe, Kentaro; Matsumoto, Masaki*
no journal, ,
If an insoluble particle bearing radioactive cesium is incorporated into the human body, the radioactive nuclei included in the particle will move as a single particulate material without being distributed throughout the body by dissolving to blood or tissue fluid like soluble cesium. Because commonly applied methods for estimation of the numbers of decays are designed for the average behavior of large number of nuclei, the existing methods cannot be applied for insoluble cesium particles. In this study, we developed a method simulating a stochastic movement of a single particle in the body, and constructed an improved biokinetic model for insoluble particles. This method enables to estimate the numbers of decays considering the stochastic movement of the particle, and organ absorbed doses by combining the numbers of decays and corresponding S values. Repetitive execution of this procedure makes it possible to evaluate a probability density function of exposure dose.
Manabe, Kentaro; Matsumoto, Masaki*
no journal, ,
If an insoluble cesium-bearing particle is incorporated into the body, the radioactivity in the particle will move stochastically in the state of a cluster without diffusion to the blood or tissue fluid. A deterministic method is applied to estimate internal doses for generic radioactive aerosols, but the deterministic method cannot be applicable to insoluble cesium-bearing particles. We established a stochastic method to estimate probability density functions of internal doses for intakes of insoluble particles by simulating the stochastic behavior of the particles. In this presentation, we will show the result of the probability density function of doses for particles having a typical size (diameter: 2 
m). In addition, we will describe the parameters that affect probability density functions of doses, and future issues.
Suzuki, Akihiro*; Ito, Kenichi*; Nishioka, Shunichiro; Osaka, Masahiko
no journal, ,
To simulate the formation of micron-size spherical Cs-bearing particles, vaporized Cs and Si were reacted under high temperature water-vapor atmosphere and solidified in the gas phase experimentally. With this simulation study, the possibility that the Cs-bearing particles (type A spherical particles) in the environment were formed by reaction-and-solidification process under the high temperature gas phase in RPV was confirmed.
Oishi, Yuji*; Nakamori, Fumihiro*; Muta, Hiroaki*; Kurosaki, Ken*; Yamanaka, Shinsuke*; Sakata, Takao*; Sato, Kazuhisa*; Yasuda, Hidehiro*; Osaka, Masahiko
no journal, ,
Simulant material of Cs-bearing particle was synthesized from the melted glass of which composition was selected based on the composition of the Cs-bearing particle. The relationship between the nucleation behavior of Franklinite (ZnFe
O
) and cooling speed was studied. The possibility of the formation of Franklinite phase through spinodal decomposition was also evaluated.
Nakamori, Fumihiro*; Oishi, Yuji*; Muta, Hiroaki*; Kurosaki, Ken*; Yamanaka, Shinsuke*; Osaka, Masahiko
no journal, ,
Influence of elements from Zr-rich paint on composition of Cs-bearing particle was evaluated, by investigating elution behavior of Zn, Si and so on from paint mock-up samples in water at RCIC temperature condition.
Ito, Kenichi*; Suzuki, Akihiro*; Oishi, Yuji*; Nakamori, Fumihiro*; Hikida, Shiro*; Nozaki, Kenichiro*; Honda, Takeshi*; Mizokami, Shinya
no journal, ,
The spherical cesium bearing particles (insoluble Cs particles), which were found in Fukushima and Tokyo area, are considered to be formed in RPV of Fukushima Daiichi NPS unit2 because of its composition and microstructural characteristic that needs quench from high temperature.
Manabe, Kentaro; Matsumoto, Masaki*
no journal, ,
It is expected that radioactivity included in matrix of an insoluble particle incorporated into the body will move stochastically as a single particulate material without dissolving to blood or tissue fluid. Therefore, a deterministic dosimetric method which is commonly used and is designed for the average behavior of large number of nuclei cannot be applied for estimation of uncertainty of internal doses depending on the stochastic movements of insoluble particles. The authors developed a method simulating a stochastic movement of insoluble materials inhaled into the body, and this method enables to estimate the probability density function (PDF) of internal doses from the particles. In this presentation, results and interpretation of PDFs will be reported in case of inhalation of typical insoluble cesium bearing particles. In addition, the difference will also be discussed between the pdf and a dose estimated by a commonly used method.
Manabe, Kentaro; Matsumoto, Masaki*
no journal, ,
When an insoluble cesium-bearing particle which has high specific activity is inhaled into the human body, the activity will move stochastically in the state of a sphere without dissolving in the blood or tissue fluid. We have developed a stochastic biokinetic method to evaluate the stochastic behavior of the particle in the body and estimated the probability distribution of exposure doses from a typical cesium-bearing particle whose diameter is 2 m. In this study, we analyzed particle diameter dependence of dose distribution due to inhalation of the particle with considering that the activity in a particle and the deposition probability to the regions of the respiratory tract change with the diameter. As a result, the maximal values of 99%ile values and arithmetic means were observed at 3.0 m and 3.5 m, respectively.
Manabe, Kentaro; Matsumoto, Masaki*
no journal, ,
When insoluble particles containing radiocesium, CsMP, are incorporated into the body, the radioactivity contained in CsMP does not dissolve in blood or tissue fluid, but migrates through the body in particle form. Since the kinetic behavior of CsMPs in the body is stochastic, the internal dose due to CsMPs is expected to depend on the migration path and to have uncertainty. Therefore, we developed a dose estimation method that simulates the stochastic behavior of insoluble particles such as CsMPs, and evaluated the probability distribution of the effective internal dose due to inhalation of a typical CsMP with a particle size of 2 m. As a result, the ratio of the 99th percentile value to the arithmetic mean of the effective dose distribution for the inhalation of one CsMP was found to be 19, with a very large uncertainty. However, the uncertainty decreased with the increment of the number of simultaneously inhaled CsMPs, and the arithmetic mean of the effective dose was found to be 0.12 mSv and the ratio 1.6 for 10
CsMPs inhaled at the same time.
