Size distribution of radiocesium aerosols after the Fukushima accident collected at 120 km SSW of Fukushima Nuclear Power Plant

Okura, Takehisa ; Meisenberg, O.*; Feistenauer, P.*; Shinonaga, Taeko*; Tschiersch, J.*

Atmospheric radioactivity monitoring was made at Nuclear Science Research Institute, JAEA, following the Fukushima accident. Aerosol-bound radiocesium (Cs) was collected on paper filter (HE-40TA). In this study, to evaluate size distribution of the Cs, radioactive aerosols collected on HE-40TA was removed into distilled water, and then radioactive aerosols were extracted from the solution with a nebulizer and collected into a cascade impactor. The size distribution soon after the accident has one peak which is found around 0.3 m. Corresponded temporal decreasing Cs concentration, the second peak which has median of 1-2 m was developed besides ca. 0.3-m-median peak at sites around field. The size distribution collected at a site in woods has only one peak after also significant decreasing of Cs concentration. It is presumed that the coarser-median peak was attributed to resuspended radioactivity, considered on the basis of distribution of radioactive aerosols on the filters observed with autoradiography and reference articles.