Speaker
Description
Activated carbon is widely used for short-term (few days) radon sampling with consequent measurement of the adsorbed activity by liquid scintillation counting or gamma-spectrometry. This is a bulk material that can hardly be coupled with external detectors acquiring signal during exposure (e. g. solid state nuclear track detectors, semiconductor or scintillation detectors). The use of activated carbon fabrics is promising in this direction [1]. They are thin and easy to handle material that can be easily coupled with various detectors, aiming at measuring low radon levels in the environment. Their use for long term measurements is hampered by the strong influence of temperature and humidity on radon adsorption. Recent innovation combined the reciprocal temperature dependences of radon diffusive permeation through polymer foils and that of adsorption ability of activated carbon fabrics in order to compensate the influence of the temperature [2] and to retard the influence of humidity. Still, the last cannot be fully eliminated, therefore it is necessary to study it. In this report we present results of experimental study of the influence of humidity on two kinds of activated carbon fabrics that are promising for use in high sensitivity radon detectors [2]. The materials were ACC-5092-10 and ACC-5092-20, both produced by Kynol Europa GmbH, Germany. In the first set of experiments the adsorption of water was studied by exposing a number of fully dehydrated specimens at 100% RH for different time and weighting them before and after exposure. It was found that the ACC-5092-10 reaches saturation at water content of about 24% (w/w) while ACC-5092-20 at about 55%. The equilibrium of ACC-5092-10 is reached within less than 24 h exposure, while for ACC-5092-20 more than one day is needed. After saturation is reached the water content is not increased any more, even the exposure continues one month or more. In the second set of experiments specimens of fabrics with different water content – from zero up to saturation level were coupled with solid state nuclear track detectors Kodak-Pathe LR-115/II and exposed to controlled radon concentration. The dependence of the adsorption ability on water content was studied by analyzing the net track density of detectors that were coupled with different specimens. With ACC-5092-20 a break point was observed at water content 18-20%, where the signal drops by more than one order of magnitude. This is well-known phenomena, when the occlusion of the pores by water happens. However, with ACC-5092-10 only monotonic decrease up to saturation level was observed without any indication for break point. Although the signal from dehydrated to saturated specimens decreases by factor of about 3, correction of the results for humidity is possible. We conclude that ACC-5092-10 fabrics can be used even for long-term exposures at different humidity levels.
[1] Sohrabi M. JINST 13, P11012 (2018)
[2] Pressyanov D. Sci. Rep. 12, 8479 (2022)
