ELECTRON MICROSCOPIC ANALYSIS OF RADIOCAESIUM-BEARING MICROPARTICLES IN LICHENS COLLECTED WITHIN 3 KM OF THE FUKUSHIMA DAI-ICHI NUCLEAR POWER PLANT

In order to investigate statistically the physicochemical properties of the radiocaesium-bearing microparticles (CsMPs) emitted from the Fukushima Daiichi Nuclear Power Plant, an efficient method for collecting and separating the microparticles is required. In this study we established a separation method for CsMPs from lichens using electron microscopic analysis. Lichens were first digested within hydrogen peroxide and then an automatic particle analyser system based on FE-EPMA was used for detecting CsMPs within lots of mineral-like and metalic particles quickly. The elemental composition and radiocaesium activities of the separated CsMPs were measured, and the results suggest that the digestion treatment did not influence the CsMPs characteristics. An inhomogeneous elemental distribution was found in some CsMPs by two-dimensional elemental analysis using FE-EMPA. Our methods for separation of CsMPs and analysing their elemental composition are expected to be useful for grasping the chemical composition trends of CsMPs statistically as first step before more detailed analyses such as TEM analysis.