Experimental evaluation of ageing and fading effects over 3, 6, and 12 months for three radon concentration measurement techniques based on nuclear track detectors

Evaluation of the annual average radon concentrations in dwellings and workplaces, as required by the recent international regulations, is commonly performed using techniques based on passive devices containing nuclear track detectors and tracks read-out systems. These techniques could be affected by ageing of the detector material and fading of the tracks, whose net effect is a detector sensitivity reduction. Therefore, an experimental study was carried out in order to evaluate ageing and fading effects in typical indoor environments for three different techniques used in our laboratory: i) two devices based on CR-39 materials produced by different suppliers (i.e., Intercast Spa and Radosys Ltd) with two different fully automated image analysis systems used for trackscounting; ii) a device based on LR 115 as detector material whose tracks are counted with a spark counter. The study was designed to evaluate ageing and fading for exposure periods of 3, 6, and 12 months using AlphaGUARD active monitors as reference detectors. This study represents an extension of a previous one – limited to two of the three techniques considered in this study – aimed to evaluate ageing and fading effects for measurement period of 12 months only. The results show that ageing and fading do not significantly affect the response of the technique based on LR 115 detectors, whereas an underestimation of the actual radon exposure was found for the two techniques based on CR-39 detectors. In particular, measurements performed over a single period of 12 months have a sensitivity reduction of about 10% and 20%, for techniques based on CR-39 Intercast Spa and Radosys Ltd, respectively.