A novel technique for the rapid identification of alpha emitters released during a radiological incident

Before the May 2003 TOPOFF II exercise in Seattle, the U.S. EPA's Laboratory in Las Vegas prepared five spiked samples to be analyzed by the Washington State Department of Health's (WSDOH) Radiation Laboratory. Two of these were simulated deposition samples prepared on packaging tape. Laboratories throughout the world are investigating rapid methods for analyzing plume-borne radioactive materials. While measuring gamma emitters in environmental samples is fairly straightforward, the potential presence of alpha emitters adds complexity. The short range of alpha particles and the high degree of energy interference between nuclides usually require chemical separations and very thin mounts for alpha spectrometry. Work published on Frisch-Grid alpha counting of transuranics in soil and the commercial development of radon-rejection for air filters indicate that alpha spectrometry can be used directly on some media with success. This suggests that plume-borne material sampled from air or freshly deposited surface layers may be counted directly by alpha spectrometry, making it possible to identify both alpha and gamma emitters and determine their relative concentrations. The long-range objective is to propose a sampling method that can be used for rapid qualitative and semi-quantitative analyses using conventional radioanalytical instruments, with minimal preparation. This paper describes experimentation with this approach during a real-time exercise. All samples were prepared by spiking with (137)Cs, (241)Am, (238)Pu, and (239)Pu and presented to the WSDOH's Radiation Laboratory for analysis during TOPOFF II. The laboratory quickly identified and determined the ratios of all four contaminants on the tape samples using sequential alpha spectrometry and gamma-ray spectroscopy without chemical separations.