Airborne dusts can transport radioactive materials in the form of isolated individual radioactively-hot particles containing high concentrations of radioisotopes. These airborne particles may be inhaled or ingested, becoming a source of internal radiation exposure. After the March 11, 2011, nuclear reactor accidents at Fukushima Daiichi, in northern Japan; eighty-five Japanese environmental samples and 234 US and Canadian samples were collected and analyzed by gamma spectrometry, autoradiography, scanning electron microscopy with energy dispersive X-ray analysis (SEM/EDS), and total alpha and beta counts. Social media and volunteer organizations were an important part of the sample collection effort. The combination of autoradiography and SEM/EDS allowed individual radioactively-hot particles to be isolated and analyzed. Detectable levels of 134Cs and 137Cs were found in 62 of 85 Japanese particulate matter samples. The median dust specific activity for Japanese samples was 2.5 Bq g-1 +/- 1.6 Bq g-1, while the mean dust specific activity was 71 Bq g-1 (RSD = 335 %). The mean was skewed high due to five dust samples with sharply higher specific activities. These five samples had specific activities ranging from 167 kBq g-1 to 5.2 PBq kg-1. Only four of 234 US and Canadian environmental samples had detectable levels of both 134Cs and 137Cs. Gross gamma spectroscopy of Japanese samples also detected 131I and 60Co. US and Canadian dust samples showed primarily naturally-occurring nuclides. More than 300 individual hot particles were identified in Japanese samples. The Japanese particles analyzed by SEM/EDS were found to contain cesium, americium, radium, polonium, tellurium, rubidium and other necessarily or potentially radioactive elements. No cesium-containing hot particles were found in the US, however some dust particles were found that contained uranium, thorium and plutonium. These US particles were all related to identified uranium mines or nuclear materials storage and processing sites. Some of the hot particles detected in this study could cause significant radiation exposures to individuals if inhaled. Where hot particles are present in the environment, radiation dose models must include this exposure component to remain accurate.

"Radionuclides in particulate matter associated with outdoor and indoor dusts were analyzed to determine the form and concentration of radioactive isotopes present. These radioactive isotopes, such as Strontium 90, Cesium 137, and Uranium 235, consist of, or are sorbed onto fine particulate matter, (PM). The airborne dispersion of this fine particulate matter results in the facilitated transport of these sorbed or neat radionuclides. Sources of particulate-bound radioactive contaminants include fallout from weapons testing, accumulation of radon daughters, transport of soils containing naturally-occurring radioactive material, remediation of radiologically-contaminated sites, and nuclear material processing. Radiological contaminants in PM, may exist as trace contamination in homogenous collections of particles, but may also exist heterogeneously, as a small number of high-concentration radionuclides among a larger set of uncontaminated particles. A total of 114 samples of indoor and outdoor airborne dusts were collected from a former nuclear weapons production facility near Richland, WA, the Los Alamos National Laboratory, and the Yakama Indian Nation in Wapato, WA. Los Alamos, NM was also the site of the May 2000 Cerro Grande wildfire. The wildfire created very large amounts of airborne particulate matter, including smoke and soot. The area affected by open burning included 43,000 acres. At the national laboratory, greater than 7600 acres were affected, including some areas that were radiologically- contaminated, such as a U-238 ammunition firing area. (LANL, 2007) This introduces a potential source of hot particles in dusts and other archived particulate matter, which may remain in the environment. LANL Airborne radionuclide surveillance has historically found higher uranium levels during windy periods, and saw elevated air uranium levels associated with the Cerro Grande fire. (Ibid, p. 108) Dust samples were sieved to pass a 150 micron screen and analyzed by gamma spectroscopy. Samples with higher activity were analyzed by Scanning Electron Microscopy/Energy Dispersive X-ray analysis, SEM/EDS. The results of gamma spectroscopy and individual particle counts were compared to determine the degree of radioactive heterogeneity in each sample. Radioactive heterogeneity, isotopic distribution, and particle size can be related to the source of the radioactive PM. Radiological contaminants in particulate matter, (PM), may exist as trace contamination in homogenous collections of particles, but may also exist heterogeneously, as a small number of high-concentration radionuclides among a larger set of uncontaminated particles. Residential and source area dusts were collected from locations surrounding, and potentially impacted, by operational and remedial activities at the HNR. The dust samples were analyzed, by multiple means, in order to identify those with radiologically- contaminated particles. Samples with higher activity were further analyzed by Scanning Electron Microscopy/Energy Dispersive X-ray analysis, (SEM/EDS), to determine if the radiological contamination was homogenous or heterogeneous. Two case studies were followed. The method isolated and analyzed lead and bismuth from naturally occurring radioactive material in coal fly ash. The method isolated and fingerprinted thorium, and the rare earths cerium, lanthanum, samarium, neodymium, and gadolinium in sedimentary cerium monazite minerals, nuclear waste processing dusts, and fission waste products in a WWTP effluent channel."