Uncertainty of (222)Rn concentrations in the usepa radiation and indoor environments National Laboratory Exposure Chamber.

The U.S. Environmental Protection Agency (EPA) operates an environmentally controlled chamber for purposes of exposing various radon and decay product measurement equipment to known (222)Rn concentrations. Exposure durations range from 1 h to several months, and (222)Rn concentrations vary between 37 and 4,440 Bq m(-3). Radon concentrations are generated from Ra sources mounted on the chamber, but concentrations are continuously measured using equipment calibrated using (222)Rn generated from Ra laboratory standards made from a National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) and verified through an aliquot measured by the NIST. The (222)Rn concentrations that are used to calibrate the equipment in the chamber are produced from bubbling a measured volume of air through the (226)Ra laboratory standard solution. This paper describes the process to derive an average chamber concentration during the exposure period. This includes the generation of laboratory (226)Ra standards from the original NIST SRM, (222)Rn emanation into a measured volume of air and transfer to Rocky Mountain Glassworks stainless steel scintillation cells to generate individual cell calibration factors, the calibration of larger mounted flow-through scintillation cells, and the reduction of cumulative chamber scintillation cell counts over various time periods. Each step is associated with an uncertainty based on measured and estimated factors, and each step adds an additional uncertainty to the cumulative total. The methods used follow guidance in the 1993 ISO Guide to the Expression of Uncertainty in Measurement and NIST Technical Note 1297. Chamber exposures of 96 h and (222)Rn concentrations between 150 and 2,700 Bq m(-3) are associated with a combined standard uncertainty of 4.1% (1 s). Ninety-six hour (96 h) exposures of lower (222)Rn concentrations of between 150 - 370 Bq m(-3) are associated with a combined standard uncertainty of 5%. Results indicate that there are measures that can be taken to reduce the estimated uncertainty slightly. The calculations used in this analysis have been incorporated into the computer code used to track chamber concentrations and exposures so that estimated uncertainties can be associated with each exposure.

IAEA/EPA international climatic test program for integrating radon detectors. International Atomic Energy Agency/Environmental Protection Agency.

As an element of the joint IAEA-EPA International Radon Metrology Evaluation Program, a climatic test of long-term integrating radon detectors was conducted at the U.S. EPA Radiation and Indoor Environments National Laboratory. The objective of this study was to test the performance of commonly used commercially available long-term 222Rn detector systems under extreme climatological conditions using filtered polycarbonate CR-39 plastic analyzed by the manufacturer using the track-etch method, unfiltered LR-115 film analyzed by the manufacturer, and Teflon based electrets analyzed in the field by EPA using the manufacturer's equipment. The EPA environmental radon chambers were used to expose detectors to extreme cold and dry (less than 4.0 degrees C air temperature and 25% relative humidity) and hot and humid (greater than 35 degrees C air temperature and 85% relative humidity) climatic conditions. During phase I detectors were exposed to low temperatures and low humidities, and during phase II detectors were exposed to high temperatures and high humidities. Typical indoor equilibrium fractions (near 50%) and radon concentrations of about 150 Bq m(-3) were maintained for each phase, which lasted 90 d. The results indicated that the optimal detector for extreme climatic conditions is dependent on the relative importance of bias and precision. Overall, however, the filtered track-etch type detector produced the most reliable results under the extreme conditions.

Intercomparison of radon and decay product measurements in an underground mine and EPA Radon Laboratory: a study organized by the IAEA International Radon Metrology Programme. International Atomic Energy Agency.

The International Atomic Energy Agency (IAEA) in Vienna and the European Union (EU) in Bruxelles formed the "International Radon Metrology Programme" (IRMP, scientific secretary: F. Steinhäusler, University of Salzburg, Austria). The IRMP is designed to assess and foster the improvement of radon and decay product measurements that are made around the world. Within the framework of the IRMP, the U.S. Environmental Protection Agency Radiation and Indoor Environments National Laboratory (EPA) in Las Vegas, Nevada, organized jointly with the U.S. Bureau of Mines an international intercomparison exercise at a former uranium mine (Twilight Mine, Colorado) and the EPA Radon Laboratory. The main objective of this exercise was to compare radon and radon decay product instruments under both well-controlled as well as widely fluctuating exposure conditions. The laboratory exposures occurred under relatively steady radon and decay product conditions, with a moderate equilibrium ratio, while the conditions in the mine fluctuated greatly and the equilibrium ratio was low. An additional purpose of the exercise was to provide a forum for manufacturers and measurement organizations worldwide to exchange information and plan improvements in their operations and calibration programs. Altogether 19 organizations from seven countries intercomparing 32 different radon and radon decay product instruments participated in this exercise. This paper summarizes the results from the analysis of the experimental data obtained in the Bureau of Mines Twilight Mine in July of 1994, as well as the results from the EPA Radon laboratory in August of 1994.

Multi-state surveys of indoor 222Rn.

The U.S. Environmental Protection Agency provides assistance to states in conducting surveys of indoor 222Rn. Alabama, Kentucky, Tennessee, Wisconsin, and Wyoming completed statistically designed surveys during the 1986-1987 heating season. In all states, probability-based samples of 5800 houses were tested using charcoal canisters exposed for 48 h. Thus, sample results can be validly extrapolated to the target population of all owner-occupied, ground-level houses having listed telephone numbers. Estimates of population parameters (e.g., median) and their associated confidence intervals are given for each state, for geographic regions within states, and for basement and nonbasement houses. Results confirm that 222Rn concentration varies widely from one state to another and from one geographic region to another within a state; however, the same pattern of differences was not evident in basement or nonbasement houses. Short-term 222Rn readings appear to follow a log-normal distribution.