Evaluation of MDA instant working level meters.

The U.S. Bureau of Mines and the Mine Safety and Health Administration have evaluated, for accuracy and reliability, a commercially available Instant Working Level Meter (IWLM) used by the mining industry to measure short-lived 222Rn-progeny concentrations. Six evaluation parameters were determined experimentally. These included two alpha and two beta detector efficiencies for the short-lived 222Rn progeny and two internal conversion factors. The experimental procedure detailing the evaluation technique is described in the paper. The measuring accuracy of 13 instruments is as follows: average inherent uncertainty (at least 68% confidence interval) is +/- 18%; for counting statistics and rounding at 0.10 WL (2.1 microJ m-3), coefficients of variation range from +/- 15% at low gamma flux backgrounds to +/- 50% at gamma flux backgrounds of 0.39 microC kg-1 h-1 (1.5 mR h-1). All parameters were derived theoretically and measured experimentally. All tests were conducted at a sample flow rate of 2.5 L min-1. A sample air flow rate of 7.5 L min-1 can lower the counting statistics to more acceptable levels at 0.1 WL (2.1 microJ m-3).

Radon-222 and 222Rn progeny concentrations measured in an energy-efficient house equipped with a heat exchanger.

Radon-222 and 222Rn progeny concentrations, barometric pressure and pressure differentials between inside and outside were measured continuously in the basement of a recently constructed energy-efficient house in metropolitan Denver, CO. Although the monitoring equipment was developed primarily for underground mines, it proved to be applicable for house monitoring. Results indicate that for tightly sealed houses, forced-flow transport does not significantly contribute to the 222Rn present even when the pressure within the house is less than the outside pressure by 0.8 Pa (.006 mm Hg). Calculations of 222Rn levels using diffusion as the primary transport mechanism are in agreement with observed data. The diffusion coefficient of 222Rn in the walls and floor surrounding the basement is higher than values previously reported. Ventilation by means of a heat exchanger reduces the 222Rn levels in accordance with measured air exchange rates, regardless of the pressure differential between inside and outside.