Development of a Hermetic Gaseous Xenon Detector for Suppressing External Radon Background

arXiv:2511.03250v1 Announce Type: new
Abstract: Radon-induced backgrounds, particularly from $^{222}$Rn and its beta-emitting progeny, present a critical challenge for next-generation liquid xenon (LXe) detectors aimed at probing dark matter down to the neutrino fog. To address this, we developed a compact hermetic gaseous xenon (GXe) detector. This device physically isolates the active volume from external radon sources by using a PTFE vessel sealed between two quartz flanges with mechanically compressed ePTFE gaskets. To quantify radon sealing performance, we implemented a dual-loop GXe circulation system and conducted a 670-hour radon-injection measurement campaign. Radon ingress into the hermetic detector was monitored using electrostatic radon detectors and photomultiplier tubes (PMTs). From these two independent measurements, the steady-state ratios of the radon concentrations inside the hermetic detector to those outside were estimated to be $ (1.1 pm 0.1) times 10^{-2} $ and $ (1.1 pm 0.2) times 10^{-2} $, corresponding to radon-leakage flows of $ (2.9 pm 0.3) times 10^{-11} $ and $ (2.6 pm 0.4) times 10^{-11} $ $ thinspace $m$^{3}$ $ thinspace $ $mathrm{s}^{-1}$, respectively. An extrapolation to a 60-tonne LXe TPC such as XLZD suggests that the radon leakage could amount to $ 1.2 times 10^{-2} $ $ thinspace $mBq, which is negligible compared to the expected natural radon emanation inside the detector, typically 3$ thinspace $mBq. These results demonstrate that flange-based mechanical sealing provides an effective solution for realizing radon-isolated inner detectors in large-scale LXe experiments.