An instrument for the measurement of long-term average radon levels

Air containing radon is allowed to diffuse through porous foam walls into an enclosure of defined volume. The foam traps daughter products present in the air. Within the enclosure short-lived daughter products which are produced carrying a positive charge are concentrated on to a small foil by electrostatic collection. A thermoluminescent detector (CaF2:Dy) located directly behind the foil records the daughter product alpha activity. The monitor is intended to measure the average radon concentration over periods of a week or longer. An average concentration of radon of 0.04 pCi/ltr gives an output equal to that produced by a natural gamma radiation background of 2 mR per week. (author)