Development of a stochastic biokinetic method and its application to internal dose estimation for insoluble cesium-bearing particles

Spherical cesium-bearing particles were found around the Fukushima Daiichi Nuclear Power Plant after its accident. These particles are insoluble with high specific activities. If such a particle is incorporated into the body, it is expected that the radioactive cesium contained in the particle will move as a single particulate material without being distributed throughout the body. Consequently, internal doses vary depending on the pathway of the particle in the body. Therefore, general deterministic methods for dose estimation are not applicable to the intake of small number of cesium-bearing particles. In this study, a Monte Carlo method was developed to evaluate a probability density function of internal doses for inhalation of a particulate material. In addition, a biokinetic model was constructed to consider the insolubility of the particles. Probability density functions of committed equivalent and effective doses were estimated using the constructed biokinetic model with the developed omputation method. As a result, the uncertainty of the doses was very large for single particle inhalation. However, it was observed that this uncertainty decreased with increasing number of simultaneously inhaled particles. On the other hand, the consideration about the insolubility made the doses somewhat higher than those based on the general cesium model