Testing and Calibration of CDs as Radon Detectors at Highly Variable Radon Concentrations and Temperatures.

The application of the compact disk (CD) method for radon measurements at mines, caves and other workplaces needs testing under highly variable exposure conditions. We present the results from a blind comparison of CDs exposed in the Laboratory of Natural Radiation (Saelices el Chico, Spain). During the exposure the temperature varied from 6.5 to 24.9 °C (average 12.6 °C) and the (222)Rn activity concentrations varied from <10 Bq m(-3) to 147 kBq m(-3). Good correspondence was observed between the integrated (222)Rn activity concentration determined by the reference instruments in the laboratory (122,500 ± 6100 kBq h m(-3)) and that assessed by analysis of the CDs at a depth 80 µm beneath the front surface (118,000 ± 12,000 kBq h m(-3)) and at a depth of 120 µm (106,000 ± 12,000 kBq h m(-3)). The theoretical modeling of the CD response under variable temperature and radon concentration suggested that the small bias is probably due to the time variation of the calibration factor because of the time variations of the temperature.