Identification of the actual cesium-adsorbing materials in the contaminated Fukushima soil

Abstract Since the accident at the Fukushima nuclear plant in 2011, a number of studies have been carried out to clarify the adsorption state of radioactive cesium (Cs) in the contaminated soil. However, analyses of the individual radioactive particles in the actual soil are still elementary, particularly due to the extremely-low concentration of Cs. In this study, a micro-manipulator and focused ion beam (FIB) were combined with imaging plate (IP) autoradiography to explore the distribution of Cs in radioactive particles, and to identify the actual Cs-adsorbing materials. Consequently, direct observations of the radioactive sections indicated that weathered biotite and aluminous smectite adsorbed the Cs in the actual contaminated soil. In a platy-shaped weathered biotite, the radioactive Cs was distributed almost homogeneously. Moreover, the weathered biotite was inferred to have adsorbed the Cs in preference to the neighboring materials, such as the smectite and organic matter.