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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; Takahashi, Fumiaki; Sato, Kaoru
no journal, ,
Japan Atomic Energy Agency is developing a program using the latest models and data for estimation of internal dose compliant with the 2007 Recommendations of the International Commission on Radiological Protection (ICRP). Nuclear decay data, specific absorbed fraction data for adult males and females, and radiation weighting factors and tissue weighting factors have been published as the models and data compatible with the 2007 Recommendations. The program equips all the latest models and data, and can evaluate radiation weighted S coefficients. A test calculation was executed using the program for evaluation of S coefficients for self-absorption in the thyroid of adult males corresponding to the 2007 and 1990 Recommendations. The coefficient based on the 2007 and 1990 Recommendations was 1.3 
10
Sv/decay and 1.6 10 Sv/decay, respectively, and the coefficient decreased 18%. This is because correction of the mass of organs considering their blood content was executed for self-absorption cases. We will report the development status of this program, and the results of test calculations and the study.
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.
Manabe, Kentaro; Sato, Kaoru; Takahashi, Fumiaki
no journal, ,
An effective dose coefficient is defined as a committed effective dose per unit intake, and it is a basic quantity for internal dose estimation and standards for radiation protection. In this study, we built a function to calculate effective dose coefficients based on the latest models and data in accordance with the 2007 Recommendations of International Commission on Radiological Protection (ICRP) as part of development of an internal dosimetry code. The methodology for dose calculation is summarized in a publication of ICRP. However, there is no description about concrete technics for solving a system of ordinary differential equations for activity distribution in the body, for interpolating specific absorbed fractions by radiation energies, and so on. Then, the best technics were searched for reproducing the effective dose coefficients recorded in the database provided by ICRP. In the presentation, we will report the result of comparison between the dose coefficients generated by the built function and those of the database and the validity of the selected technics.
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; Sato, Kaoru; Takahashi, Fumiaki
no journal, ,
Radioactivity in the body becomes in an equilibrium level after a certain period of time from a start of chronic intakes. In order to study the influence of revisions of biokinetic models by the International Commission on Radiological Protection on internal dose estimation for chronic intakes of soluble aerosols of 
Cs, we calculated the time course of radioactivity in the whole body and effective dose rates per year using the new and old sets of biokinetic models. It was found that the radioactivity at the equilibrium state increased 13% by the revision of the clearance model in the respiratory tract and that the dose rate increased 41% at the state by the revision of the systemic model for cesium.
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; Sato, Kaoru; Takahashi, Fumiaki
no journal, ,
Japan Atomic Energy Agency (JAEA) has developed an internal dose calculation code in accordance with the 2007 Recommendations of the International Commission on Radiological Protection in a four-year project from FY 2017 to FY 2020 entrusted by the Nuclear Regulation Authority. The code has two major functions. One is a function calculating dose coefficients, which are committed effective doses per intake of radioactivity: The other is a function estimating an intake of activity based on monitoring data. The graphical user interface of the code integrates the two functions and provides easy operation. A new project has been started from FY 2021 to advance the code by implementing models and data to be published in the future, to establish a system for distribution of the code, and to promote usage of the code. We present the features and the future developments of the code.
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.
