Radon Monitoring: Uranium Mill Field Experience with a Passive Detector

Year-around radon monitoring of preoperational and operational mill sites located in regions in which extreme low temperatures occur (-40° C) dictates that the radon detector be a passive instrument, having (1) no moving parts; (2) batteries that are not required to deliver power; (3) no electronics; (4) noncritical periods for data collection; and (5) construction that allows retrieval of key components by personnel in cold weather dress. Complex electronic circuitry, power line sources, data reduction, etc., should be in a conveniently located base station. A number of passive radon monitors (PRMs), based on the designs of A. C. George and A. J. Breslin, and G. Cowper and M. R. Davenport have been built, characterized, and tested. A lower limit of detection, as described in the HASL Procedures Manual, has been obtained, which is less than 0.03 pCi/1-week. The active volume of the detector is nine litres and the TLD chips may be read out on any commercially available instrument. Stability, reproducibility, and sensitivity of the instrument reading are described.