The Steenkampskraal mine in the Western Cape Province in South Africa provides some interesting challenges for radiation protection practitioners in view of the high thoron values encountered in this ...mine. The mine contains high natural thorium concentrations that lead to high thoron activity concentrations, as will be shown in this paper. The influence of ventilation has been studied, and the source term has been investigated by considering the thorium content of the rocks and the thoron exhalation. The thoron activity concentrations are around 10 kBq m -3 at a monazite seam, and the thorium exhalation is consistent with these levels. The thoron concentrations can be reduced by ventilation but not eliminated. However, the thoron progeny can probably be reduced dramatically. Issues that affect the thoron levels are also discussed. Further studies are needed, but the thoron may well not be a radiation protection problem despite the high thoron concentrations.
Abstract
The nEXO neutrinoless double beta (0
νββ
) decay experiment is designed to use a time projection chamber and 5000 kg of isotopically enriched liquid xenon to search for the decay in
136
Xe. ...Progress in the detector design, paired with higher fidelity in its simulation and an advanced data analysis, based on the one used for the final results of EXO-200, produce a sensitivity prediction that exceeds the half-life of 10
28
years. Specifically, improvements have been made in the understanding of production of scintillation photons and charge as well as of their transport and reconstruction in the detector. The more detailed knowledge of the detector construction has been paired with more assays for trace radioactivity in different materials. In particular, the use of custom electroformed copper is now incorporated in the design, leading to a substantial reduction in backgrounds from the intrinsic radioactivity of detector materials. Furthermore, a number of assumptions from previous sensitivity projections have gained further support from interim work validating the nEXO experiment concept. Together these improvements and updates suggest that the nEXO experiment will reach a half-life sensitivity of 1.35 × 10
28
yr at 90% confidence level in 10 years of data taking, covering the parameter space associated with the inverted neutrino mass ordering, along with a significant portion of the parameter space for the normal ordering scenario, for almost all nuclear matrix elements. The effects of backgrounds deviating from the nominal values used for the projections are also illustrated, concluding that the nEXO design is robust against a number of imperfections of the model.
Silicon photomultipliers are regarded as a very promising technology for next-generation, cutting-edge detectors for low-background experiments in particle physics. This work presents systematic ...reflectivity studies of Silicon Photomultipliers (SiPM) and other samples in liquid xenon at vacuum ultraviolet (VUV) wavelengths. A dedicated setup at the University of Münster has been used that allows to acquire angle-resolved reflection measurements of various samples immersed in liquid xenon with 0.45° angular resolution. Four samples are investigated in this work: one Hamamatsu VUV4 SiPM, one FBK VUV-HD SiPM, one FBK wafer sample and one Large-Area Avalanche Photodiode (LA-APD) from EXO-200. The reflectivity is determined to be 25–36 % at an angle of incidence of 20° for the four samples and increases to up to 65 % at 70° for the LA-APD and the FBK samples. The Hamamatsu VUV4 SiPM shows a decline with increasing angle of incidence. The reflectivity results will be incorporated in upcoming light response simulations of the nEXO detector.
We study a possible calibration technique for the nEXOexperiment using a 127Xe electron capture source. nEXO is anext-generation search for neutrinoless double beta decay(0νββ) that will use a ...5-tonne, monolithic liquid xenontime projection chamber (TPC). The xenon, used both as source anddetection medium, will be enriched to 90% in 136Xe. Tooptimize the event reconstruction and energy resolution,calibrations are needed to map the position- and time-dependentdetector response. The 36.3 day half-life of 127Xe and itssmall Q-value compared to that of 136Xe 0νββ would allow a small activity to be maintained continuously in thedetector during normal operations without introducing additionalbackgrounds, thereby enabling in-situ calibration andmonitoring of the detector response. In this work we describe aprocess for producing the source and preliminary experimentaltests. We then use simulations to project the precision with whichsuch a source could calibrate spatial corrections to the light andcharge response of the nEXO TPC.
We study a possible calibration technique for the nEXO experiment using a $^{127}$Xe electron capture source. nEXO is a next-generation search for neutrinoless double beta decay (0νββ) that will use ...a 5-tonne, monolithic liquid xenon time projection chamber (TPC). The xenon, used both as source and detection medium, will be enriched to 90% in $^{136}$Xe. To optimize the event reconstruction and energy resolution, calibrations are needed to map the position- and time-dependent detector response. The 36.3 day half-life of $^{127}$Xe and its small Q-value compared to that of $^{136}$Xe 0νββ would allow a small activity to be maintained continuously in the detector during normal operations without introducing additional backgrounds, thereby enabling in-situ calibration and monitoring of the detector response. In this work we describe a process for producing the source and preliminary experimental tests. We then use simulations to project the precision with which such a source could calibrate spatial corrections to the light and charge response of the nEXO TPC.
We study a possible calibration technique for the nEXO experiment using a \(^{127}\)Xe electron capture source. nEXO is a next-generation search for neutrinoless double beta decay ...(\(0\nu\beta\beta\)) that will use a 5-tonne, monolithic liquid xenon time projection chamber (TPC). The xenon, used both as source and detection medium, will be enriched to 90% in \(^{136}\)Xe. To optimize the event reconstruction and energy resolution, calibrations are needed to map the position- and time-dependent detector response. The 36.3 day half-life of \(^{127}\)Xe and its small \(Q\)-value compared to that of \(^{136}\)Xe \(0\nu\beta\beta\) would allow a small activity to be maintained continuously in the detector during normal operations without introducing additional backgrounds, thereby enabling in-situ calibration and monitoring of the detector response. In this work we describe a process for producing the source and preliminary experimental tests. We then use simulations to project the precision with which such a source could calibrate spatial corrections to the light and charge response of the nEXO TPC.
Silicon photomultipliers are regarded as a very promising technology for next-generation, cutting-edge detectors for low-background experiments in particle physics. This work presents systematic ...reflectivity studies of Silicon Photomultipliers (SiPM) and other samples in liquid xenon at vacuum ultraviolet (VUV) wavelengths. A dedicated setup at the University of M\"unster has been used that allows to acquire angle-resolved reflection measurements of various samples immersed in liquid xenon with 0.45{\deg} angular resolution. Four samples are investigated in this work: one Hamamatsu VUV4 SiPM, one FBK VUV-HD SiPM, one FBK wafer sample and one Large-Area Avalanche Photodiode (LA-APD) from EXO-200. The reflectivity is determined to be 25-36% at an angle of incidence of 20{\deg} for the four samples and increases to up to 65% at 70{\deg} for the LA-APD and the FBK samples. The Hamamatsu VUV4 SiPM shows a decline with increasing angle of incidence. The reflectivity results will be incorporated in upcoming light response simulations of the nEXO detector.
The nEXO neutrinoless double beta decay experiment is designed to use a time projection chamber and 5000 kg of isotopically enriched liquid xenon to search for the decay in \(^{136}\)Xe. Progress in ...the detector design, paired with higher fidelity in its simulation and an advanced data analysis, based on the one used for the final results of EXO-200, produce a sensitivity prediction that exceeds the half-life of \(10^{28}\) years. Specifically, improvements have been made in the understanding of production of scintillation photons and charge as well as of their transport and reconstruction in the detector. The more detailed knowledge of the detector construction has been paired with more assays for trace radioactivity in different materials. In particular, the use of custom electroformed copper is now incorporated in the design, leading to a substantial reduction in backgrounds from the intrinsic radioactivity of detector materials. Furthermore, a number of assumptions from previous sensitivity projections have gained further support from interim work validating the nEXO experiment concept. Together these improvements and updates suggest that the nEXO experiment will reach a half-life sensitivity of \(1.35\times 10^{28}\) yr at 90% confidence level in 10 years of data taking, covering the parameter space associated with the inverted neutrino mass ordering, along with a significant portion of the parameter space for the normal ordering scenario, for almost all nuclear matrix elements. The effects of backgrounds deviating from the nominal values used for the projections are also illustrated, concluding that the nEXO design is robust against a number of imperfections of the model.
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