Calibration of the Politrack® system based on CR39 solid-state nuclear track detectors for passive indoor radon concentration measurements

Swiss national requirements for measuring radon gas exposures demand a lower detection limit of 50 kBq h m, representing the Swiss concentration average of 70 Bq m over a 1-month period. A solid-state nuclear track detector (SSNTD) system (Politrack, Miam, Italy) has been acquired to fulfil these requirements. This work was aimed at the calibration of the Politrack system with traceability to international standards and the development of a procedure to check the stability of the system. A total of 275 SSNTDs was exposed to 11 different radon exposures in the radon chamber of the Secondary Calibration Laboratory at the Paul Scherrer Institute, Switzerland. The exposures ranged from 50 to 15000 kBq h m. For each exposure of 20 detectors, 5 SSNTDs were used to monitor possible background exposures during transport and storage. The response curve and the calibration factor of the whole system were determined using a Monte Carlo fitting procedure. A device to produce CR39 samples with a reference number of tracks using a Am source was developed for checking the long-term stability of the Politrack system. The characteristic limits for the detection of a possible system drift were determined following ISO Standard 11929.