Field validation study of the MDA Instant Working Level Meter in a high gamma background mine environment

Accurate and reproducible radon daughter measurements are essential to protect workers in the mining industry and assure compliance with federal regulations. The precision and accuracy of the MDA Model 811 Instant Working Level Meter (IWLM) has been questioned when it is used in a high gamma environment of an underground uranium mine due to the increased statistical uncertainty associated with the background radiations. Comparative side by side sampling at a single underground mine station exhibiting a 3.0 mR/h "gamma background" was conducted utilizing the IWLM, the Kusnetz and the Tsivoglou methods. A total of fifty sets of samples were taken, with half using an unshielded IWLM and the other half using a lead shield to reduce the effect of the high gamma background radiation. IWLM, Kusnetz and "baseline" Tsivoglou measurements were then analyzed. A significantly large error was associated with the IWLM in both the shielded and unshielded data groups.