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1. $$^{222}$$Rn  emanation measurements for the XENON1T experiment

   https://doi.org/10.1140/epjc/s10052-020-08777-z  

   XENON Collaboration ; Aprile, E. ; Aalbers, J. ; Agostini, F. ; Alfonsi, M. ; Althueser, L. ; Amaro, F. D. ; Antochi, V. C. ; Angelino, E. ; Angevaare, J. R. ; et al ( April 2021 , The European Physical Journal C)

   The selection of low-radioactive construction materials is of utmost importance for the success of low-energy rare event search experiments. Besides radioactive contaminants in the bulk, the emanation of radioactive radon atoms from material surfaces attains increasing relevance in the effort to further reduce the background of such experiments. In this work, we present the$$^{222}$$${}^{222}$Rn emanation measurements performed for the XENON1T dark matter experiment. Together with the bulk impurity screening campaign, the results enabled us to select the radio-purest construction materials, targeting a$$^{222}$$${}^{222}$Rn activity concentration of$$10\,\mathrm{\,}\upmu \mathrm{Bq}/\mathrm{kg}$$$10\mu \mathrm{Bq}/\mathrm{kg}$in$$3.2\,\mathrm{t}$$$3.2t$of xenon. The knowledge of the distribution of the$$^{222}$$${}^{222}$Rn sources allowed us to selectively eliminate problematic components in the course of the experiment. The predictions from the emanation measurements were compared to data of the$$^{222}$$${}^{222}$Rn activity concentration in XENON1T. The final$$^{222}$$${}^{222}$Rn activity concentration of$$(4.5\pm 0.1)\,\mathrm{\,}\upmu \mathrm{Bq}/\mathrm{kg}$$$(4.5\pm 0.1)\mu \mathrm{Bq}/\mathrm{kg}$in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment.

    

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2. Tracing Bank Storage and Hyporheic Exchange Dynamics Using 222 Rn: Virtual and Field Tests and Comparison With Other Tracers

   https://doi.org/10.1029/2020WR028960  

   Liao, Fu ; Cardenas, M. Bayani ; Ferencz, Stephen B. ; Chen, Xiaobing ; Wang, Guangcai ( May 2021 , Water Resources Research)

   Dynamic hydrologic exchange flows in river beds and banks are important for many ecosystem functions throughout river corridors. Here we test whether the exchanges and the associated mixing between a flooding river and groundwater within the river’s bank can be effectively traced by Radon‐222 (²²²Rn), a naturally occurring, inert, radiogenic, and radioactive gas that can be analyzed and monitored in situ. The assessment was done by simulation of groundwater flow and reactive transport of²²²Rn in the bank following a single, relatively rapid (hours long) flood wave and auxiliary field observations of²²²Rn, temperature and total dissolved solids (a surrogate for any ionic conservative tracer). Results illustrate that²²²Rn is more effective than temperature and total dissolved solids in tracing dynamic hyporheic exchange.²²²Rn variations in space and time are larger than the analytical uncertainty of common measurement methods. The individual effects of aquifer hydraulic conductivity, dispersivity, river water²²²Rn concentration, and bank topography were analyzed through sensitivity analysis. Larger hydraulic conductivity and dispersivity, lower²²²Rn concentration in river water relative to groundwater, and gentler bank slopes resulted in a more prominent and traceable²²²Rn signal. The transport and residence time of exchanged water may be estimated and interpreted using reactive transport models such as those implemented here. However, such application is sensitive to fluctuations in river water²²²Rn, requiring it to be well characterized. The assessment provides guidance for using²²²Rn as a tracer for groundwater and surface water interactions in dynamic settings.

    

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3. Riverine groundwater discharge estimation in a dynamic river corridor using 222Rn

   https://doi.org/10.1002/hyp.14788  

   Liao, Fu ; Cardenas, M. Bayani ; Chen, Xiaobing ; Wang, Guangcai ( January 2023 , Hydrological Processes)

   Groundwater discharge flux into rivers (riverine groundwater discharge or RGD) is essential information for the conservation and management of aquatic ecosystems and resources. One way to estimate area‐integrated groundwater discharge into surface water bodies is to measure the concentration of a groundwater tracer within the water body. We assessed groundwater discharge using²²²Rn, a tracer common in many surface water studies, through field measurements, surface water²²²Rn mass balance model, and groundwater flow simulation, for the seldom studied but ubiquitous setting of a flooding river corridor. The investigation was conducted at the dam‐regulated Lower Colorado River (LCR) in Austin, Texas, USA. We found that²²²Rn in both the river water and groundwater in the river bank changed synchronously over a 12‐hour flood cycle. A²²²Rn mass balance model allowed for estimation of groundwater discharge into a 500‐m long reach of the LCR over the flood. The groundwater discharge ranged between negative values (indicating recharge) to 1570 m³/h; groundwater discharge from groundwater flow simulations corroborated these estimates. However, for the dynamic groundwater discharge estimated by the²²²Rn box model, assuming whether the groundwater²²²Rn endmember was constant or dynamic led to notably different results. The resultant groundwater discharge estimates are also highly sensitive to river²²²Rn values. We thus recommend that when using this approach to accurately characterize dynamic groundwater discharge, the²²²Rn in near‐stream groundwater should be monitored at the same frequency as river²²²Rn. If this is not possible, the²²²Rn method can still provide reasonable but approximate groundwater discharge given background information on surface water‐groundwater exchange time scales.

    

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4. The XENONnT dark matter experiment

   https://doi.org/10.1140/epjc/s10052-024-12982-5  

   XENON_Collaboration ; Aprile, E. ; Aalbers, J. ; Abe, K. ; Ahmed_Maouloud, S. ; Althueser, L. ; Andrieu, B. ; Angelino, E. ; Angevaare, J_R ; Antochi, V_C ; et al ( August 2024 , The European Physical Journal C)

   The multi-staged XENON program at INFN Laboratori Nazionali del Gran Sasso aims to detect dark matter with two-phase liquid xenon time projection chambers of increasing size and sensitivity. The XENONnT experiment is the latest detector in the program, planned to be an upgrade of its predecessor XENON1T. It features an active target of 5.9 tonnes of cryogenic liquid xenon (8.5 tonnes total mass in cryostat). The experiment is expected to extend the sensitivity to WIMP dark matter by more than an order of magnitude compared to XENON1T, thanks to the larger active mass and the significantly reduced background, improved by novel systems such as a radon removal plant and a neutron veto. This article describes the XENONnT experiment and its sub-systems in detail and reports on the detector performance during the first science run.

    

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5. Observation of radon mitigation in MicroBooNE by a liquid argon filtration system

   https://doi.org/10.1088/1748-0221/17/11/P11022  

   Abratenko, P. ; Anthony, J. ; Arellano, L. ; Asaadi, J. ; Ashkenazi, A. ; Balasubramanian, S. ; Baller, B. ; Barnes, C. ; Barr, G. ; Barrow, J. ; et al ( November 2022 , Journal of Instrumentation)

   Abstract The MicroBooNE liquid argon time projection chamber (LArTPC) maintains a high level of liquid argon purity through the use of a filtration system that removes electronegative contaminants in continuously-circulated liquid, recondensed boil off, and externally supplied argon gas. We use the MicroBooNE LArTPC to reconstruct MeV-scale radiological decays. Using this technique we measure the liquid argon filtration system's efficacy at removing radon. This is studied by placing a 500 kBq 222 Rn source upstream of the filters and searching for a time-dependent increase in the number of radiological decays in the LArTPC. In the context of two models for radon mitigation via a liquid argon filtration system, a slowing mechanism and a trapping mechanism, MicroBooNE data supports a radon reduction factor of greater than 97% or 99.999%, respectively. Furthermore, a radiological survey of the filters found that the copper-based filter material was the primary medium that removed the 222 Rn. This is the first observation of radon mitigation in liquid argon with a large-scale copper-based filter and could offer a radon mitigation solution for future large LArTPCs. 

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