Microanalysis of Particle-Based Uranium, Thorium, and Plutonium in Nuclear Workers’ House Dust

摘要

Scanning electron microscopy and energy dispersive X-ray analysis (SEM/EDS), a technique not routinely used to detect radiation, was used to identify radioactive particulate matter in house and environmental dust. The study focused on elements that are necessarily radioactive, including thorium, plutonium, americium, and uranium. Seventy-nine dust and 31 soil and sediment samples were collected from the Hanford Nuclear Reservation, Los Alamos National Laboratory, the former Rocky Flats Plant in Colorado, and from homes of workers or abutters of these nuclear facilities. Dusts containing percent levels of uranium, plutonium, americium, and both mineral and metallic thorium were detected outside of radiation-controlled areas. These radioactive dusts are a potential source of internal radiation exposure to nuclear site workers, or to their families via secondary contamination. Uranium and thorium-containing particles were fingerprinted as either natural minerals or processed industrial particles, based on elemental composition of the microparticles. Activities of individual uranium-, thorium-, or plutonium-bearing dust particles varied by five orders of magnitude, ranging from 0.005 mBq (millibecquerel) to 2,270 mBq. Hanford workplace dusts also had up to 564 ± 24 Bq/kg of~(137)Cs. SEM/EDS techniques reliably detected environmental radioactivity in samples that had barely detectable results by gamma spectrometry. The technique was able to definitively show that thorium, plutonium, and uranium from nuclear facilities could be found in general population settings outside of radiation protection zones.