Follow-up of the Fukushima Dai-Ichi Disaster: High Radioactivity Particles in Japanese House Dusts

The 2011 earthquake and resulting tsunami in Northeastern Japan led to damages to four of the six nuclear power units at the Fukushima Dai-Ichi Station. Radiological materials escaped from the reactor units at the power plant site via air-borne plumes of contaminated gases, aerosols and particles. Airborne dusts transport radioactive materials as isolated individual particles containing high concentrations of radioisotopes. Alpha and beta emissions related to fission wastes and dispersed fuel particles are hazardous when inhaled or ingested. Radioactively-contaminated environmental dusts can accumulate in indoor spaces, potentially causing significant radiation exposures to humans via inhalation, dermal contact, and ingestion. These heterogeneously distributed hot particles can be difficult to detect and measure, making it likewise difficult to determine radiation dose to residents of contaminated areas. NaI gamma and EDS spectrometry of hot particles found ²²⁶Ra, ¹³⁴Cs, and ¹³⁷Cs, ²⁴¹Am, and ^230Th as the most commonly detected isotopes. Autoradiographic, gamma spectral and SEM/EDS results demonstrated that hot particles were present in about 25% of dusts sampled. This quartile of the samples was both contaminated with 134Cs, an indicator contaminant for the reactor accident, and was autoradiographically positive for hot particles. SEM analysis showed that the majority of these hot particles were 10 um or less in size, meaning that they were potentially inhalable.