ABSTRACT

Structures and distribution of constituent elements of non-spherical radioactive microparticles collected in the Fukushima Prefecture were investigated mainly using scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy of high detection efficiency. An angulated radioactive microparticle collected as an aerosol in 2015 had a chemical composition similar to that of the spherical microparticles collected in 2011 but with a different distribution of Sn and alkali ions, which may have been caused by partial dissolution of the microparticle in the field. Other non-spherical microparticles collected from the atmosphere in 2013 contained Al as a constituent of silicate glass, which was not detected in the spherical microparticles. Chromium-oxide glass containing Fe, Zn and Sn was also present, coexisting intricately with silicate glass in one of the microparticles. Finally, a microparticle collected in 2015 from plant tissue was substantially an aggregate of fine particulates composed of Cs-bearing silicate glass that did not contain either Fe or Zn, which were common in the silicate glass forming the other radioactive microparticles. These results suggest that the radioactive microparticles emitted from the Fukushima Daiichi nuclear power plant are of a considerable variety and that their structures likely change with time in the field.