Survey of radon monitoring techniques

The HASL monitor for measuring environmental levels of radon basically is a large ''two filter'' collector which has been automated. The first filter (24'' diameter in this unit) removes the daughters and any particulate radioisotopes. The air then passes through a large chamber (approximately 240 liters) which allows a portion of the radon daughters to grow in. These are collected on a filter which is located on a strip-filter transport. The system collects the daughter sample on a two inch circle on the tape, then transports it to a position under a three inch scintillation detector for counting. The next sample is collected during the counting period. Normally, the sampling period is set for one hour and is followed by a one-hour count. Sensitivity is 0.005 pCi/liter radon with approximately a 10 percent standard deviation. The unit also can be cycled on two hour, thirty minute, or fifteen minute intervals