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[MAG33-04] Characteristics of radiocesium-bearing microparticles and Type B particles using multiple synchrotron radiation X-ray analyses
Keywords:Radioactive particle, Cesium, X-ray analyses
Method: In this study, we collected 53 Type B particles and 13 CsMPs from road dusts, non-woven fabric cloths from Fukushima, and aerosol filters from Kanagawa Prefecture by a wet separation method. After measurement of radioactivity with a high-purity germanium semiconductor detector, scanning electron microscope and energy dispersive X-ray spectroscopy analyses were performed to confirm that separated particles were CsMPs or Type B particles. We investigated inner structure and calculated the volume and porosity of Type B particles by X-ray μ-computed tomography (CT). We determined Rb/Sr ratio by X-ray fluorescence (XRF) analysis. Redox condition of each unit was investigated by X-ray adsorption near edge structure (XANES) analysis for Uranium in particles.
Result: CT combined with XRF analysis showed the presence of many voids and iron particles in Type B particles. In addition, 137Cs concentration of CsMPs were ~10000 times higher than that of Type B particles, which suggests that Type B particles were formed by fuel melt. In contrast, CsMPs were formed by gas. Among Type B particles, spherical particles had higher 137Cs concentration than non-spherical particles. Type B particles with larger porosity had higher 137Cs radioactivity because of capturing a lot of volatile elements such as Cs and Rb within the particles. Moreover, four spherical particles had inclusions in their voids which are considered to be formed by rapid cooling of gaseous materials. XANES analysis showed the presence of U(IV) in a Type B particle, whereas U(VI) in other Type B particles and a CsMP. These results suggest that Type B particles and CsMPs are totally different in forming process and they have information of condition in Units.