In the field of directional dark matter experiments SF₆ has emerged as an ideal target gas. A critical challenge with this gas, and with other proposed gases, is the effective removal of contaminant gases. This includes radon which produce unwanted background events, but also common pollutants such as water, oxygen and nitrogen, which can capture ionisation electrons, resulting in loss of detector gas gain over time. We present here a novel molecular sieve (MS) based gas recycling system for the simultaneous removal of both radon and common pollutants from SF₆. The apparatus has the additional benefit of minimising gas required in experiments and utilises a Vacuum Swing Adsorption (VSA) technique for continuous, long-term operation. The gas system's capabilities were tested with a 100 L low-pressure SF₆ Time Projection Chamber (TPC) detector. For the first time, we present a newly developed low-radioactive MS type 5 Å. This material was found to emanate radon at 98% less per radon captured compared to commercial counterparts, the lowest known MS emanation at the time of writing. Consequently, the radon activity in the TPC detector was reduced, with an upper limit of less than 7.2 mBq at a 95% confidence level (C.L.). Incorporation of MS types 3 Å and 4 Å to absorb common pollutants was found successfully to mitigate against gain deterioration while recycling the target gas.

中文翻译：

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用于气态暗物质和稀有事件探测器的分子筛真空变压吸附净化和氡还原系统

在定向暗物质实验领域，SF ₆已成为理想的目标气体。这种气体以及其他拟议气体的一个关键挑战是有效去除污染物气体。这包括产生不需要的背景事件的氡气，还包括水、氧气和氮气等常见污染物，它们可以捕获电离电子，导致探测器气体增益随着时间的推移而损失。我们在这里提出了一种基于分子筛 (MS) 的新型气体回收系统，用于同时去除 SF ₆中的氡气和常见污染物。该设备的另一个优点是最大限度地减少实验中所需的气体，并利用真空摇摆吸附 (VSA) 技术实现连续、长期运行。使用 100 L 低压 SF ₆时间投影室 (TPC) 检测器测试了气体系统的功能。我们首次推出新开发的 5 Å 型低放射性 MS。研究发现，与商业同类材料相比，这种材料捕获的每氡气的氡气量减少了 98%，这是撰写本文时已知的最低 MS 散发量。因此，TPC 检测器中的氡气活度降低，95% 置信水平 (CL) 下的上限低于 7.2 mBq。结合 3 Å 和 4 Å 型 MS 来吸收常见污染物已成功缓解回收目标气体时的增益恶化。