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Scheme of a multi-stage distillation tower with n plates, where the less volatile component is the contaminant (green dots). The incoming flow F with the contamination concentration c F in the feeding section is enriched in the stripping section below to a contamination concentration c B in the reboiler. In the case of radon, it is trapped inside the reboiler until it decays, and therefore, no bottom product extraction is required (B = 0). In the rectifying section, above the feed, the contamination is depleted to a concentration c D in the output flow D at the top condenser. Furthermore, the liquid flows L, L and gaseous flows V , V of the related sections are shown. The factor q indicates if the feed is gaseous (q = 0) or liquid (q = 1)
Source publication
A high-flow radon removal system based on cryogenic distillation was developed and constructed to reduce radon-induced backgrounds in liquid xenon detectors for rare event searches such as XENONnT. A continuous purification of the XENONnT liquid xenon inventory of 8.4 tonnes at process flows up to 71 kg/h (200 slpm) is required to achieve a radon r...
Context in source publication
Context 1
... purified outlet. In this method, the column is separated in three parts, namely the feeding section, where the raw xenon gas is injected to the tower, the rectifying section, where the less volatile component, here the contaminant radon, is depleted and the stripping section, where the less volatile contaminant is enriched. This is depicted in Fig. 3 along with relevant xenon flows and radon concentrations for each ...
Citations
... LZ employs a charcoal chromatography radon reduction system [11] in the vapor phase for on-line purification, and achieved a 222 Rn concentration of 3.26 μBq=kg. XENONnT [12,13] achieved a significantly lower 222 Rn concentration of 0.8 μBq=kg background using an in-line cryogenic distillation column [14]. These techniques compete against continuous emanation of radon from detector materials, so the efficacy scales with the xenon circulation rate. ...
Experiments searching for weakly interacting massive particle dark matter are now detecting background events from solar neutrino-electron scattering. However, the dominant radioactive background in state-of-the-art experiments such as LZ and XENONnT is beta decays from radon contamination. In spite of careful detector material screening, radon progenitor atoms are ubiquitous and long-lived, and radon is extremely soluble in liquid xenon. We propose a change of phase and demonstrate that crystalline xenon offers more than a factor ×500 exclusion against radon ingress, compared with the liquid state. This level of radon exclusion would allow crystallized versions of existing experiments to probe spin-independent cross sections near 10−47 cm2 in roughly 11 years, as opposed to the 35 years required otherwise.
... LAr and liquid xenon (LXe) detectors sensitive to low-energy signals have reduced radon contamination by implementing rigorous detector material and outgassing assay campaigns [28][29][30][31][32][33]. These experiments have also installed specialized systems capable of removing radon directly from LXe through distillation [34], as well as from gaseous argon [30,[35][36][37] and gaseous xenon [38,39]. Using these methods, the DarkSide-50 and DEAP-3600 dark matter experiments have achieved radon levels of ≈2.1 μBq=kg [14] and 0.15 μBq=kg [40] in their bulk LAr volumes, respectively. ...
We report measurements of radon progeny in liquid argon within the MicroBooNE time projection chamber (LArTPC). The presence of specific radon daughters in MicroBooNE’s 85 metric tons of active liquid argon bulk is probed with newly developed charge-based low-energy reconstruction tools and analysis techniques to detect correlated Bi214−Po214 radioactive decays. Special datasets taken during periods of active radon doping enable new demonstrations of the calorimetric capabilities of single-phase neutrino LArTPCs for β and α particles with electron-equivalent energies ranging from 0.1 to 3.0 MeV. By applying Bi214−Po214 detection algorithms to data recorded over a 46-day period, no statistically significant presence of radioactive Bi214 is detected, and a limit on the activity is placed at <0.35 mBq/kg at the 95% confidence level. This bulk Bi214 radiopurity limit—the first ever reported for a liquid argon detector incorporating liquid-phase purification—is then further discussed in relation to the targeted upper limit of 1 mBq/kg on bulk Rn222 activity for the DUNE neutrino detector.
... An activated carbon trap [29], rigorous cleaning protocols, and strict material radio-purity selections lead to a slight improvement over trends for LZ [32], which significantly improved over LUX [33]. In addition to their own radioassay program and cleanliness [34], XENONnT employs another distillation column dedicated to radon [35]. Online distillation of the gaseous xenon has enabled XENONnT to achieve a record background of 1.7 µBq/kg in the initial science data, which was subsequently dropped below 1 µBq/kg when the radon column was incorporated into the liquid xenon purification loop. ...
... It is necessary to first reduce initial radon levels in the materials with strict screening and cleaning procedures [32,34] and limit emanation with coatings [39]. Then, emanated radon must be removed via online distillation [35] and trapping [29]. Finally, radon background events can be cut in analysis [40]. ...
... While the 222 Rn emanation of this source corresponds to about 10% of the total 222 Rn emanation of the XENONnT experiment [11], its effect is expected to become subdominant approximately one week after the end of the 220 Rn calibration. This waiting time is further reduced by the radon removal system of the XENONnT experiment [24] and will thus not appreciably impact the data-taking efficiency. For future large-scale experiments, such as DARWIN/XLZD [25,26] and nEXO [27], however, this might not necessarily be true due to their more demanding background requirements. ...
Low-background liquid xenon detectors are utilized in the investigation of rare events, including dark matter and neutrinoless double beta decay. For their calibration, gaseous ²²⁰ Rn can be used. After being introduced into the xenon, its progeny isotope ²¹² Pb induces homogeneously distributed, low-energy (<30 keV) electronic recoil interactions. We report on the characterization of such a source for use in the XENONnT experiment. It consists of four commercially available ²²⁸ Th sources with an activity of 55 kBq. These sources provide a high ²²⁰ Rn emanation rate of about 8 kBq. We find no indication for the release of the long-lived ²²⁸ Th above 1.7 mBq. Though an unexpected ²²² Rn emanation rate of about 3.6 mBq is observed, this source is still in line with the requirements for the XENONnT experiment.
... This corresponds to an order of magnitude-improvement with respect to the best experiment of the current-generation [13]. The challenging goal will be met by a combination of background mitigation methods: surface treatment/coating [14], detector design [15][16][17], active radon removal [18] as well as by using only ultra-low-emanation materials for all detector parts in direct contact with the LXe. As Rn-emanation is a surface effect, bulk measurements of the 226 Ra activity via standard gamma spectrometry can be misleading. ...
Radioactive radon atoms originating from the long-lived primordial $^{238}\mathrm{U}$ and $^{232}\mathrm{Th}$ decay chains are constantly emanated from the surfaces of most materials. The radon atoms or their radioactive daughter isotopes can significantly contribute to the background of low-background experiments, e.g., the $^{222}\mathrm{Rn}$ progeny $^{214}\mathrm{Pb}$ dominates the background of liquid xenon detectors which are currently leading the direct search for WIMP dark matter. We report on a new detector system to directly quantify the $^{222}\mathrm{Rn}$ surface emanation of materials. Using cryogenic physisorption traps, emanated radon atoms are transferred from an independent emanation vessel and concentrated inside the dedicated detection vessel, where the charged daughter isotopes, most importantly $^{214}\mathrm{Po}$ and $^{218}\mathrm{Po}$, are electrostatically collected and detected on a silicon PIN photodiode. The overall detection efficiency is $\sim 36\,\%$ for both polonium channels. The intrinsic detection vessel background was measured to be $\sim 2.4\,\mathrm{cpd}$ ($28\,\mathrm{\mu Bq}$) and $\sim 1.5\,\mathrm{cpd}$ ($17\,\mathrm{\mu Bq}$) for $^{218}\mathrm{Po}$ and $^{214}\mathrm{Po}$, respectively. The radon emanation activity of the emanation vessel was determined to be $(0.16\pm 0.03)\,\mathrm{mBq}$, resulting in a detection sensitivity of $\sim 59\,\mathrm{\mu Bq}$ (at $90\,\%$ C.L.).
... To fill the vessel housing the TPC a total of 8.5 ton liquified xenon is required which is continuously purified by a new liquid-phase purification system [10]. Together with a high flow radon distillation system [11], a careful selection of detector construction materials [12], and a specialized assembly procedure, this led to an unprecedentedly low electronic recoil (ER) background of ð15.8 AE 1.3Þ events=ton yr keV below recoil energies of 30 keV [13]. ...
We report on the first search for nuclear recoils from dark matter in the form of weakly interacting massive particles (WIMPs) with the XENONnT experiment, which is based on a two-phase time projection chamber with a sensitive liquid xenon mass of 5.9 ton. During the (1.09±0.03) ton yr exposure used for this search, the intrinsic Kr85 and Rn222 concentrations in the liquid target are reduced to unprecedentedly low levels, giving an electronic recoil background rate of (15.8±1.3) events/ton yr keV in the region of interest. A blind analysis of nuclear recoil events with energies between 3.3 and 60.5 keV finds no significant excess. This leads to a minimum upper limit on the spin-independent WIMP-nucleon cross section of 2.58×1047 cm2 for a WIMP mass of 28 GeV/c2 at 90% confidence level. Limits for spin-dependent interactions are also provided. Both the limit and the sensitivity for the full range of WIMP masses analyzed here improve on previous results obtained with the XENON1T experiment for the same exposure.
... The XENONnT detector is a dual-phase xenon time projection chamber (TPC) with an active target mass of 5.9 tonnes of liquid Xe (LXe). Detailed information regarding XENONnT detector conditions, systems, and subsystems can be found in [3,[17][18][19][20][21][22]. ...
We developed a detector signal characterization model based on a Bayesian network trained on the waveform attributes generated by a dual-phase xenon time projection chamber. By performing inference on the model, we produced a quantitative metric of signal characterization and demonstrate that this metric can be used to determine whether a detector signal is sourced from a scintillation or an ionization process. We describe the method and its performance on electronic-recoil (ER) data taken during the first science run of the XENONnT dark matter experiment. We demonstrate the first use of a Bayesian network in a waveform-based analysis of detector signals. This method resulted in a 3% increase in ER event-selection efficiency with a simultaneously effective rejection of events outside of the region of interest. The findings of this analysis are consistent with the previous analysis from XENONnT, namely a background-only fit of the ER data.
... While the 222 Rn emanation of this source corresponds to about 10% of the total 222 Rn emanation of the XENONnT experiment [11], its effect is expected to become subdominant approximately one week after the end of the 220 Rn calibration. This waiting time is further reduced by the radon removal system of the XENONnT experiment [23] and will thus not appreciably impact the data-taking efficiency. For future large-scale experiments, such as DARWIN/XLZD [24,25] and nEXO [26], however, this might not necessarily be true due to their more demanding background requirements. ...
Low-background liquid xenon detectors are utilized in the investigation of rare events, including dark matter and neutrinoless double beta decay. For their calibration, gaseous $^{220}$Rn can be used. After being introduced into the xenon, its progeny isotope $^{212}$Pb induces homogeneously distributed, low-energy ($<30$ keV) electronic recoil interactions. We report on the characterization of such a source for use in the XENONnT experiment. It consists of four commercially available $^{228}$Th sources with an activity of 55 kBq. These sources provide a high $^{220}$Rn emanation rate of about 9 kBq. We find no indication for the release of the long-lived $^{228}$Th above 1.7 mBq. Though an unexpected $^{222}$Rn emanation rate of about 3.6 mBq is observed, this source is still in line with the requirements for the XENONnT experiment.
... The XENONnT detector is a dual-phase xenon time projection chamber (TPC) with an active target mass of 5.9 tonnes of liquid Xe (LXe). Detailed information regarding XENONnT detector conditions, systems, and subsystems can be found in [3,[17][18][19][20][21][22]. ...
We developed a detector signal characterization model based on a Bayesian network trained on the waveform attributes generated by a dual-phase xenon time projection chamber. By performing inference on the model, we produced a quantitative metric of signal characterization and demonstrate that this metric can be used to determine whether a detector signal is sourced from a scintillation or an ionization process. We describe the method and its performance on electronic-recoil (ER) data taken during the first science run of the XENONnT dark matter experiment. We demonstrate the first use of a Bayesian network in a waveform-based analysis of detector signals. This method resulted in a 3% increase in ER event selection efficiency with a simultaneously effective rejection of events outside of the region of interest. The findings of this analysis are consistent with the previous analysis from XENONnT, namely a background-only fit of the ER data.
... To fill the vessel housing the TPC, a total of 8.5 t liquified xenon is required which is continuously purified by a new liquid-phase purification system [10]. Together with a high flow radon distillation system [11], a careful selection of detector construction materials [12] and a specialized assembly procedure, this led to an unprecedentedly low electronic recoil (ER) background of (15.8 ± 1.3) events/(t · y · keV) below recoil energies of 30 keV [13]. ...
We report on the first search for nuclear recoils from dark matter in the form of weakly interacting massive particles (WIMPs) with the XENONnT experiment which is based on a two-phase time projection chamber with a sensitive liquid xenon mass of $5.9$~t. During the approximately 1.1 tonne-year exposure used for this search, the intrinsic $^{85}$Kr and $^{222}$Rn concentrations in the liquid target were reduced to unprecedentedly low levels, giving an electronic recoil background rate of $(15.8\pm1.3)~\mathrm{events}/(\mathrm{t\cdot y \cdot keV})$ in the region of interest. A blind analysis of nuclear recoil events with energies between $3.3$~keV and $60.5$~keV finds no significant excess. This leads to a minimum upper limit on the spin-independent WIMP-nucleon cross section of $2.58\times 10^{-47}~\mathrm{cm}^2$ for a WIMP mass of $28~\mathrm{GeV}/c^2$ at $90\%$ confidence level. Limits for spin-dependent interactions are also provided. Both the limit and the sensitivity for the full range of WIMP masses analyzed here improve on previous results obtained with the XENON1T experiment for the same exposure.
