On the possibility to detect some radioactive noble gases by Cherenkov counting of polycarbonates

Since the discovery of the high absorption ability of polycarbonates to Radon-222 about 15 years ago, this property became a basis for the development of techniques for measurement of activity concentration of radioactive noble gases (RNGs). The polycarbonates absorb and concentrate RNGs from the environment (air or water) and can be used for precise retrospective radon measurements by home stored CDs/DVDs, prospective measurements of Radon-222, Krypton-85 and Xenon-133 in air or water. The ambient activity concentration is correlated to the activity absorbed in the polycarbonate, thus measuring the absorbed activity one may estimate the ambient activity concentration to which the polycarbonate was exposed. Recently, the liquid scintillation counting of polycarbonates was proposed for measurement of the absorbed activity in the polycarbonate, leading to a sensitive technique for measurement of ambient RNG concentrations. The objective of this work is to point out that the Cherenkov counting can be used to measure the activity of some radioactive noble gases absorbed in polycarbonates. We note that, if certain RNGs are absorbed in polycarbonates, part of the beta- particles emitted in their decays may have sufficient energy to emit Cherenkov radiation in the polycarbonate. We performed dedicated experiments in which we exposed polycarbonates in Radon-222 atmosphere and then measured the emitted light. We used a liquid scintillation counter as a light detector and we obtained typical Cherenkov pulse-height spectra. Our results clearly demonstrate that there is Cherenkov radiation emitted from the exposed polycarbonates. We have obtained a very good linear response with this technique which implies that it is feasible for measurement of Radon-222 absorbed in polycarbonates. We performed calculations which show that the technique might also be applicable to measurement of Xenon-133 and Krypton-85. The proposed method offers a new concept for development of monitors for radioactive noble gases. Two designs for such monitors are proposed and discussed.