In-field evaluation of the impact of ageing and fading effects on annual radon concentration measurements for two different techniques

Abstract

Measurements covering a 1 year period are often used and required by legislation to assess the average radon concentration within a house or a workplace. This kind of long-term measurement-generally carried out with techniques based on nuclear track detectors-can be affected by a reduction in sensitivity due to ageing and fading of latent tracks during the exposure period, thus resulting in an underestimation of the actual average concentration. In order to evaluate in field conditions the ageing and fading effects on annual radon concentration measurements, two different studies in a large sample of rooms in dwellings (162) and in workplaces (432) were conducted using two different techniques (detector and track read-out system): (i) CR-39 plastics readout with a fully automated image analysis system, and (ii) LR 115 films with a spark-counter for track counting. Study design and data analysis aimed to evaluate both the average and the variability of ageing and fading effects in real conditions, and to reduce and separate the contribution of measurement uncertainty to the observed variability. For the CR-39 based technique, the results show that radon concentration measurements over a 12month period are on average about 16% lower than those evaluated with measurements of two consecutive 6 month periods, implying the need for a correction factor to avoid measurement bias (i.e. underestimation) due to ageing and fading effects. The observed variability of ageing and fading effects among the sampled rooms is not negligible (coefficient of variation about 18%), although a considerable fraction is attributable to measurement uncertainty, which is presumably not related to ageing and fading. For the technique based on LR 115 spark counting, ageing and fading do not significantly affect the results of radon concentration measurement.

Main results of the second AIRP international radon-in-field intercomparison for passive measurement devices

“…Also, Franci et al (2015) found that the sensitivity of CR-39 detectors (manufactured by Radosys, Ltd) continuously exposed in a reference radon chamber at room temperature over 3 and 6 months reduced by 4 and 7.5%, respectively. Recently, Venoso et al (2016) carried out a study to evaluate both the average and the variability of ageing and fading effects in real conditions, by using CR-39 (Radosys, Ltd.) and LR115 (Kodak) passive devices. In case of CR-39, radon annual average values estimated over a 12-month long period were found on average 16% lower than those estimated with two consecutive 6 months samplings.…”

“…In the second "International radon in-field intercomparison for passive measurement devices: dwellings and workplaces" the attention was focused on different issues potentially affecting the quality of radon concentration measurements in real situations. In particular, the effect of long time sampling at low and high radon levels (fading) (Caresana et al, 2010;Venoso et al, 2016) and the effect of the simultaneous presence of radon and thoron (Sumesh et al, 2013;Tokonami et al, 2008). In order to provide reliable reference values of the activity radon concentration, before the intercomparison started, particular attention was paid to metrological issues as the determination of the intrinsic background of radon active monitors, to their calibration and to the evaluation of the influence of thoron in radon active measurements.…”