Naoyuki Osada

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.

Evaluating radiocesium retention ability of root-mat horizon using micro-PIXE analysis

A lot of radiocesium had been deposited onto pastures and grasslands following Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. More radiocesium was accumulated in root-mat horizon than in both above ground plant bodies and mineral soils. In this study, factors causing higher radiocesium concentrations in root-mat horizon were evaluated by the addition of stable cesium solution and particle-induced X-ray emission (PIXE) analysis. Results suggest that adsorption onto root surfaces played a significant role in Cs accumulation in root-mat horizon. Furthermore, absorption of Cs was key to its long-term preservation. The adsorption of Cs by clay minerals also contributed to its retention. A slow water infiltration rate may also affect the enrichment of radiocesium in root-mat horizon. Based on these results, it is concluded that both biotic and abiotic factors contributed to the effective retention of radiocesium in root-mat horizons following the FDNPP accident.