The gas radon-222 gives off three short lived daughter products commonly designated as raa, rab, and rac. Air, within the environment whose level is to be measured, is pumped through an open face filter and screen assembly forming part of a detector holder mount. Radioactive particulate matter, consisting of radon-222 daughter products, is collected on the filter. Thereafter, beta particles generated by the radioactive decay of the daughter products impinge upon a geiger-muller tube, which detects the beta particle activity per unit time. A pulse integrating system counts the detected beta particles. Based on prior experimentally calibrated results, the total count of beta particles is converted to a working level exposure.
U.S. Pat. 4,185,199, Jan. 22, 1980; Chem. Abstr. Not Found