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.

The effect of suppression of macrophage activity on the development of experimental allergic neuritis.

The selective toxicity of silica dust for macrophages has been used to assess the role of these cells in experimental allergic neuritis (EAN). Inbred Lewis rats were inoculated with bovine dorsal roots in Freund's complete adjuvant (day 0). In two experiments, animals received 200 mg of silica dust in 1 cm3 of saline intraperitoneally (IP) at days 8 and 16. In another two experiments, animals received IP silica at days 3, 7, and 11. Control animals received 1 cm3 saline IP at corresponding times. Regular clinical assessment showed that in animals treated on days 8 and 16 there was a significant delay in the time taken to reach their maximum degree of illness. This delay was not seen in the animals treated on days 3, 7, and 11. Neither of the injection regimes reduced the final maximum severity of the disease. In three experiments recovery of the treated and control animals occurred concurrently, hence the duration of the disease was reduced in the animals treated at days 8 and 16. However, in one group of animals given silica at days 3, 7 and 11, there was a delay in the time taken to recover from the most severe phase of the disease but thereafter the treated animals improved more quickly to reach their best grade at the same time as the controls. If the silica blockade of macrophages is to be effective in delaying the onset of EAN, the timing of injections is critical.