Micro-PIXE analysis of the distribution of cesium in clay particles for environmental remediation of Fukushima

The Fukushima Daiichi nuclear power plant accident caused radioactive pollution by 131I, 134Cs and 137Cs. The surface of the ground was contaminated at a volume of 3 × 107 m3. The government has mandated that the top 5 cm of the contaminated soil be removed and stored, in this way, it is desirable to reduce its volume. Soil samples were collected from a mountain, a rice field and a vegetable field in northern Japan, and the silt was extracted from the muddy water by washing the soil. Next, the silt was sprayed with a solution of cesium carbonate (Cs2CO3). We determined the amounts of Al, Si, K and Cs in the silt particles using micro-particle-induced X-ray emission (micro-PIXE) analysis. The silt particles from a vegetable field, a rice field and a mountain were mainly formed from smectite or vermiculite, which absorbs Cs atoms. The measurements at multiple detection angles confirmed that Cs atoms were uniformly absorbed within silt particles less than 10−30 μm in diameter. This resulted that the radioactive Cs atoms were adsorbed in silt particles within 10−30 μm of the surface.