Speciation of Radioactive Soil Particles in the Fukushima Contaminated Area by IP Autoradiography and Microanalyses

Abstract

Radioactive soil particles several tens of micrometers in size were collected from litter soil in the radiation contaminated area by the Fukushima nuclear plant accident and characterized using electron and X-ray microanalyses. The radioactive particles were discriminated by autoradiography using imaging plates (IP) on which microgrids were formed by laser ablation in order to find the particles under microscopy. Fifty radioactive particles were identified and classified into three types from their morphology and chemical composition, namely: (1) aggregates of clay minerals, (2) organic matter containing clay mineral particulates, and (3) weathered biotite originating from local granite. With respect to the second type, dissolution of the organic matter did not reduce the radiation, suggesting that the radionuclides were also fixed by the clay minerals. The weathered biotite grains have a plate-like shape with well-developed cleavages inside the grains, and kaolin group minerals and goethite filling the cleavage spaces. The reduction of the radiation intensity was measured before and after the trimming of the plate edges using a focused ion beam (FIB), to examine whether radioactive cesium primarily sorbed at frayed edges. The radiation was attenuated in proportion to the volume decrease by the edge trimming, implying that radioactive cesium was sorbed uniformly in the porous weathered biotite.

Mineralogical characterization of radioactive particles from Fukushima soil using µ–XRD with synchrotron radiation

“…The methods of collection and speciation of radioactive fine particles from contaminated soil have been described by Mukai et al (2014). Besides the particles collected from soil litter in Iitate village (Mukai et al, 2014), radioactive particles were collected in a similar manner from the soil in Ohkuma town, Fukushima, Japan.…”

“…Besides the particles collected from soil litter in Iitate village (Mukai et al, 2014), radioactive particles were collected in a similar manner from the soil in Ohkuma town, Fukushima, Japan. The morphological and chemical features of the radioactive particles were characterized using a scanning electron microscope (SEM, Hitachi S-4500) with an energy-dispersive X-ray spectrometer (EDS, Kevex Sigma).…”

“…The morphological and chemical features of the radioactive particles were characterized using a scanning electron microscope (SEM, Hitachi S-4500) with an energy-dispersive X-ray spectrometer (EDS, Kevex Sigma). The particles from Ohkuma were also classified with respect to their morphology and composition as WB, OM, or AM, according to the criteria outlined by Mukai et al (2014). The Cs-137 radioactivity of each particle was estimated by IP autoradiography with a calibration curve between the intensity of several radioactive particles measured by gamma-ray spectroscopy.…”

“…Hence, to understand the state and fate of radioactive cesium in the environment at present and in the future, it is essential to determine which types of materials are sorbing radioactive cesium in Fukushima. Mukai et al (2014) investigated radioactive particles in the actual contaminated soil near the Fukushima Daiichi nuclear power plant using autoradiography with imaging plates (IPs) as well as electron microscopy. They classified the radioactive particles into three categories mainly on the basis of their morphologies and chemical compositions: weathered biotite (WB) with a plate-like morphology, aggregates of fine minerals (AM), and particles mainly consisting of organic matter (OM).…”

Imaging Techniques for Radiocesium in Soil and Plants

“…hondae, branches and leaves of Prunus percica, branches and roots of Morus alba, lichen Permotrema tinctorum, and internodes and shoots of Phyllostachys bambusoides (Sakamoto et al 2013); skeletal muscle of pig (Yamaguchi et al 2013); green onion, carrot, and lettuce (Isobe et al 2013); leaves of C. japonica, fallen leaves of Quercus serrata, and fallen leaves of Pedicularis densiflora (Tanaka et al 2013); soil particles (Mukai et al 2014); leaves of Sasa palmate, Taxus cuspidate, Quercus serrate, Trifolium spp., and Equisetum arvense (Mimura et al 2014); leaves of cabbage and spinach (Shiba et al 2013); leaves of bamboo and oak, and trunks of cedar tree and pine tree (Nakajima et al 2014); leaves of beech, pieris, and oak (Furuta 2013); soil, plant, and dust samples (Itoh (Zeissler et al 2013); leaves and ears of wheat and barley (Tanoi et al 2011;Tanoi 2013); soil, leaves of wheat, branches, leaves and fruits of peach, and rice plants ; bark of Rhus vernicifera DC. (Mori et al 2012); bamboo (Phyllostachys reticulate (Rupr.)…”