Radon and Progeny Detection Using Tensioned Metastable Fluid Detectors.

Abstract

Radon and other alpha-emitting nuclides in air can be a significant risk for health hazards in the workplace and in dwellings. Radon gas in US homes causes over 21,000 deaths from lung cancer annually, according to the US Environmental Protection Agency (US EPA). Alpha-emitting radionuclides from airborne contamination in the nuclear industry also constitute a known safety and security-safeguards related issue. Purdue University, along with Sagamore Adams Laboratories LLC, have developed the tensioned metastable fluid detector (TMFD) sensor technology for general-purpose alpha-neutron-fission. For radon detection, radon gas in air is sparged through the TMFD detection fluid, after which this radon-bearing fluid is placed into a tensioned metastable state. In this metastable state, an audible-visible cavitation (alpha radiation) detection event is created and electronically recorded. Tailoring the level of tension enables spectroscopic information through energy discrimination of radon and its progeny; This is also applicable to other alpha emitting isotopes (Pu, Cm, U…). TMFDs boast high intrinsic detection efficiencies (>95%) for alpha spectroscopy while remaining blind to background beta and gamma radiation even in ~10 R h fields. The immunity to beta and gammas allows for reusability of the detection fluid through immunity to beta buildup from thoron and radon progeny. TMFD technology was used to measure the concentration of radon and radon progeny in air for concentrations from 74 Bq m to 740 Bq m. The system measures radon concentration between these levels within 24 h with an intrinsic relative error (IRE) of ± 15% according to the standards set forth by the American Association of Radon Scientists and Technicians-National Radon Proficiency Program (AARST-NRPP) Device Evaluation Program (DEP). Precision evaluation defined using the relative standard deviation set by the AARST-NRPP measured a deviation of <5%, which exceeds the requirement of <25%. Temperature effects from 10°C and 27°C were assessed and corrected for dynamically. A radon decay correction method was introduced to correct for the radon activity decrease in the detection fluid over the counting period due to the ~3.8 d half-life. Blind testing was also successfully performed* with standards from the ; within 6 h, the TMFD-based technology accurately measured the concentration of radon to within 20% of the reference standards. Non-condensing relative humidity levels up to 95% per AARST-NRPP were assessed for and were found to have no impact on radon detection. This work improves upon the previous work by splitting the calibration curve into two distinct regions and adds additional information pertaining to the effects of relative humidity on the system.