The radioactive noble gas radon-222 ($\mathrm{^{222}Rn}$, or Rn) 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 (Air), argon (Ar), and xenon (Xe) gas. In this study, we evaluated six ACFs, named A-7, A-10, A-15, A-20, A-25, and S-25, provided from UNITIKA Ltd. We measured intrinsic radioactivity of these ACF samples, and found A-20's radioactivity of the uranium series is $<5.5$~$\mathrm{mBq/kg}$ with $90\%$ confidence level. In Air and Ar gas, we found ACF A-15 has the 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 ACF A-20 has the best Rn adsorption ability among tested ACFs. We also found S-25, A-25, and A-15 have similar Rn adsorption performance.

中文翻译：

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用活性炭纤维评价氙气中氡吸附效率值

铀系列中产生的放射性惰性气体 radon-222（$\mathrm{^{222}Rn}$，或 Rn）是许多地下实验的重要背景源。我们已经估计了 Rn 与活性炭纤维 (ACF) 在空气 (Air)、氩气 (Ar) 和氙气 (Xe) 气体中的吸附性能。在这项研究中，我们评估了 UNITIKA Ltd. 提供的六种 ACF，名为 A-7、A-10、A-15、A-20、A-25 和 S-25。我们测量了这些 ACF 样品的内在放射性，并发现 A-20 铀系列的放射性为 $<5.5$~$\mathrm{mBq/kg}$，置信度为 $90\%$。在Air和Ar气中，我们发现ACF A-15在Rn吸附饱和前吸附效率最大降低$1/10000$，饱和后吸附效率超过$97\%$。在氙气中，我们发现 ACF A-20 在测试的 ACF 中具有最好的 Rn 吸附能力。