Читать книгу Patty's Industrial Hygiene, Physical and Biological Agents - Группа авторов - Страница 17

The primordial U and Th isotopes are the progenitors of three chains of sequentially decaying radioisotopes that have several common characteristics. Each series contains a radioisotope of the gaseous element radon, and each series terminates with a stable isotope of lead. Radon gas diffuses out of the ground, and the radon daughters, which are solids under ordinary circumstances, attach themselves to atmospheric dust particles. This naturally occurring airborne radioactivity must be accounted for when using the measured radioactivity in a dust sample to compute the concentration of an airborne radiocontaminant. Although the mean concentration of these naturally occurring radioisotopes is relatively low, the actual radioactivity concentration from this source varies according to the concentrations of uranium and thorium in the ground. Areas that have uranium concentrations much higher than the average thus may be expected to have relatively high atmospheric radon concentrations.