Actinide in Air (Rn-Progeny Rejected) Alpha Spectroscopy with Tensioned Metastable Fluid Detectors

This article discusses outcome of research for deriving a methodology and apparatus for ascertaining for the presence of ultra-trace level actinides in air from their alpha emission signatures, while remaining blind to the relatively large (1,000× higher activity) alpha emissions from Rn-progeny. Apparatus and techniques were developed to collect and characterize alpha-emitting nuclides of Rn-progeny and actinides in air on a polycarbonate 3 m pore size continuous air monitor (CAM) filter. A wet-chemistry approach was developed and validated for successfully separating the Rn-progeny alpha emitting isotopes of Po-214 and Po-218, while extracting the actinides (U, Pu, Am) in a fluid mixture that is suitable for conduct of alpha spectroscopy with a centrifugally tensioned metastable fluid detector (CTMFD). The resulting α-TMFD technology was compared against the state-of-art "Alpha-SentryTM" Continuous Air Monitor (CAM) system commonly utilized world-wide. Results indicate that the α-TMFD technology can potentially offer complementary and superior performance in multiple performance categories, and ~18× improvement in the time to detect [e.g., at 0.02 Derived Air Concentration (DAC) within ~3 h, vs ~70 h for Alpha-SentryTM] for actinides of interest while also remaining ~100% blind to ~103× higher Rn-progeny background - with the added potential for offering few keV scale energy resolution without resorting to peak shape fitting, vs ~300-400 keV for existing CAM systems.