Yukihiko Satou

Assessment of individual radionuclide distributions from the Fukushima nuclear accident covering central-east Japan

A tremendous amount of radioactivity was discharged because of the damage to cooling systems of nuclear reactors in the Fukushima No. 1 nuclear power plant in March 2011. Fukushima and its adjacent prefectures were contaminated with fission products from the accident. Here, we show a geographical distribution of radioactive iodine, tellurium, and cesium in the surface soils of central-east Japan as determined by gamma-ray spectrometry. Especially in Fukushima prefecture, contaminated area spreads around Iitate and Naka-Dori for all the radionuclides we measured. Distributions of the radionuclides were affected by the physical state of each nuclide as well as geographical features. Considering meteorological conditions, it is concluded that the radioactive material transported on March 15 was the major contributor to contamination in Fukushima prefecture, whereas the radioactive material transported on March 21 was the major source in Ibaraki, Tochigi, Saitama, and Chiba prefectures and in Tokyo.

Vertical distribution and formation analysis of the 131I, 137Cs, 129mTe, and 110mAg from the Fukushima Dai-ichi Nuclear Power Plant in the beach soil

We have investigated vertical distributions of 110mAg, 131I, 129mTe, and 137Cs and existence in beach soil collected three months after the Great East Japan Earthquake. All the nuclides passed through tsunami deposit and original beach soil, then reached fine particle layer lying beneath them in the three months. Moreover, depth profiles of all the nuclides did not exhibit exponential decrease. Behavior of 131I, 129mTe, and 137Cs were explained with distribution coefficients (Kd) but that of 110mAg was not explained. Particulate form was observed for the 137Cs; number of the particle was proportional to the 137Cs concentration in the soil sample.

Use of a size-resolved 1-D resuspension scheme to evaluate resuspended radioactive material associated with mineral dust particles from the ground surface.

A size-resolved, one-dimensional resuspension scheme for soil particles from the ground surface is proposed to evaluate the concentration of radioactivity in the atmosphere due to the secondary emission of radioactive material. The particle size distributions of radioactive particles at a sampling point were measured and compared with the results evaluated by the scheme using four different soil textures: sand, loamy sand, sandy loam, and silty loam. For sandy loam and silty loam, the results were in good agreement with the size-resolved atmospheric radioactivity concentrations observed at a school ground in Tsushima District, Namie Town, Fukushima, which was heavily contaminated after the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. Though various assumptions were incorporated into both the scheme and evaluation conditions, this study shows that the proposed scheme can be applied to evaluate secondary emissions caused by aeolian resuspension of radioactive materials associated with mineral dust particles from the ground surface. The results underscore the importance of taking soil texture into account when evaluating the concentrations of resuspended, size-resolved atmospheric radioactivity.

Monte Carlo Evaluation of Internal Dose and Distribution Imaging Due to Insoluble Radioactive Cs-Bearing Particles of Water Deposited Inside Lungs via Pulmonary Inhalation Using PHITS Code Combined with Voxel Phantom Data

The role of this study in terms of health physics and radiation protection has been implemented to evaluate the internal dose (relative to the committed equivalent dose) and the dose distribution imaging due to gamma rays (photons) and beta particles emitted from the radioactive Cs-bearing particles in atmospheric aerosol dusts deposited in the lungs via pulmonary inhalation. The PHITS code combined with voxel phantom data (DICOM formats) of human lungs was used.We have dealt with the insoluble radioactive Cs-bearing particles of water (about ϕ 2.6 μm diameter) migrated onto any of six regions, ET1, ET2, BB, AI-bb, LNET, and LNTH, in a respiratory system until dropping into blood vessels. Source parameters were those of an adult male breathing a typical air volume outdoors; in the simulated atmosphere (such as systematically setting up a field) those particles would be released on 21:10 March 14 to 9:10 March 15, 2011 in Tukuba, Japan, as a filter sampling condition already reported by Adachi et al. In this chapter, we discuss the internal dose and the dose distribution imaging in each voxel phantom for human lung tissues corresponding to the respiratory tracts of BB and AI-bb, respectively.