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Particle-induced X-ray emission (PIXE) analysis of Lentinula edodes (Shiitake) mushrooms contaminated with radioactive cesium was performed to study relationships between concentrations of principal elements of shiitake mushrooms and their radioactive cesium levels. After the Fukushima nuclear disaster caused by the huge tsunami on March 11, 2011, we collected five shiitake samples in Marumori town, Miyagi Prefecture, on April 21, 2011. The mean radioactive level of the samples was 228 Bq/kg (the sum of ¹³⁴Cs and ¹³⁷Cs). The preliminary result of PIXE analysis using an internal standard method has demonstrated that shiitake mushrooms significantly collect rubidium as well as potassium. It is suggested that radioactive cesium is accumulated in shiitake just like rubidium during the course of potassium uptake.

Particle-induced X-ray emission (PIXE) analysis of Lentinula edodes mushrooms (Shiitake mushrooms) contaminated with radioactive cesium was performed to study relationships between concentrations of alkali elements in the shiitake mushroom samples and their radioactive cesium levels. The shiitake mushrooms were cultivated using radiocontaminated hard wood logs due to the nuclear power plant accident in Fukushima. The significant localization of radioactive cesium was found in the pileus region of the shiitake mushroom from autoradiographic observation. The concentrations of alkali elements in the shiitake sample were measured by PIXE analysis. The PIXE analysis has shown that the concentrations and transfer coefficients of potassium and rubidium in the pileus are much higher than the other parts of the shiitake sample as is the case of radioactive cesium. It is suggested that radioactive cesium is transferred into shiitake mushrooms in a manner similar to potassium and rubidium. The results of this work have shown the possibility to be able to use rubidium as an elemental tracer for radioactive cesium.

The spatial distributions of potassium and rubidium in Lentinula edodes mushrooms contaminated with radioactive cesium were measured using particle-induced X-ray emission (PIXE) analysis by a beam scanning technique with a submillimeter sized proton beam to study relationships in elemental concentration in the mushrooms between radioactive cesium and other alkali elements. The results of PIXE analysis were compared with the spatial distribution of radioactive cesium in the samples measured by an autoradiographic method. Radioactive cesium was not uniformly distributed and strongly concentrated in the peripheral region of pileus of the mushroom while the elemental maps evaluated from PIXE analysis showed that potassium and rubidium are highly accumulated in the same area as radioactive cesium. The present results suggest a common mechanism of the accumulation of alkali elements including radioactive cesium in Lentinula edodes mushrooms.

The concentrations of alkali elements in Japanese green tea leaves were evaluated using particle-induced X-ray emission (PIXE) analysis combined with an internal standard method to investigate the elution of radioactive cesium into green tea using potassium and rubidium. The concentrations of potassium and rubidium of used tea leaf samples were lower than those of unused samples, whereas no significant differences in the concentrations of the other elements were observed between them. In addition, we found a similarity in the relative concentrations between potassium and rubidium although the other elements showed different aspects. These results suggest that it is possible to investigate the elution of radioactive cesium into green tea using potassium and rubidium as substitutes of cesium.

The amount of contaminated soil with radioactive cesium (Cs) is more than 22 million cubic meters as a result of the Fukushima Daiichi nuclear power plant accident. In order to save the cost for keeping the soil covered, it is necessary to reduce its volume. To seek methods of efficient volume reduction, we investigated the cross-sections of contaminated soil particles using autoradiography (ARG), SEM, particle-induced X-ray emission (PIXE) analysis. The results of ARG showed that the radioactive Cs atoms were distributed on the surface of contaminated soil particle. PIXE analysis showed that K, Fe and Ti were distributed also on the surface of contaminated soil particle. Therefore, it is considered that the radioactive Cs contamination correlated with the distribution of K, Fe, and Ti. Moreover, the result suggests that it is possible to reduce the volume of contaminated soil by peeling off the radioactive Cs contaminated surface of soil.

Soil polluted by the Fukushima Daiichi nuclear power plant accident was collected and reduced in volume. We explored whether clay particles adsorbed radioactive cesium. Soil was sampled in a highly contaminated zone 16 km northwest of the power plant; soil particles 0.15–200 $\mu$m in diameter were obtained by sieving and centrifugation, and specific activity was analyzed using a high-powered Ge detector. Vermiculite contents were quantified by X-ray diffraction. For soil particles$<10\mu$m in diameter, the specific activity was constant, at about 381 kBq/kg, which is close to the 350 kBq/kg reported previously. For particles 10–200 $\mu$m in diameter, the specific activity decreased by approximately the square root of the surface/entire volume ratio. The vermiculite content was identical for all soil particles $<$2.5 $\mu$m in diameter, but decreased in particles 2.5–200 $\mu$m in diameter. Thus, the specific activity and vermiculite content were approximately proportionate. Vermiculite adhered to soil particles $<$10 $\mu$m in diameter, and radioactive cesium was uniformly distributed within the vermiculite.

We subjected ¹³⁷Cs-contaminated soil to stirring and particle classification to reduce the contaminated soil volume. ¹³⁷Cs activity as a function of particle diameter changed drastically as the weight ratio of soil/water varied; 85% of all ¹³⁷Cs was adsorbed to particles of minimum diameter after stirring. Soil argillites (smectites, vermiculites, and illites) adsorbed ¹³⁷Cs. We used X-ray diffraction (XRD) analysis to measure the soil contents; the ¹³⁷Cs distribution as a function of soil particle diameter mirrored the smectite levels revealed by the XRD peak intensities. Thus, smectic was the main absorbent of ¹³⁷Cs.