Evaluation of radon adsorption efficiency values in xenon with activated carbon fibers

Abstract

The radioactive noble gas radon-222 (222Rn) produced in the uranium series is a crucial background source in many underground experiments. We have estimated the adsorption property of Rn with activated carbon fibers (ACFs) in air, argon, and xenon gas.We evaluated six ACFs, named A-7, A-10, A-15, A-20, A-25, and S-25, provided by Unitika Ltd.We measured the intrinsic radioactivity of these ACF samples, and found A-20's radioactivity of the uranium series to be < 5.5 mBq/kg with 90% confidence level. In air and Ar gas, we found thatACF A-15 has an adsorption efficiency of 1/10000 reduction at maximum before saturation of Rn adsorption, and more than 97% adsorption efficiency after the saturation. In Xe gas, we found that ACF A-20 has the best Rn adsorption ability among the tested ACFs. We also found that S-25, A-25, and A-15 have similar Rn adsorption performance.