A laser ablation ion source (LAS) is a powerful tool by which diverse species of ions can be produced for mass spectrometer calibration or surface study applications. It is necessary to frequently ...shift the laser position on the target to selectively ablate materials in a controlled manner, and to mitigate degradation of the target surface caused by ablation. An alternative to mounting the target onto a rotation wheel or x − y translation stage, is to shift the laser spot position with a final reflection from a motorized kinematic mirror mount. Such a system has been developed, assembled and characterized with a two axis motorized mirror and various metal targets. In the system presented here, ions are ablated from the target surface and guided by a 90° quadrupole bender to a Faraday cup where the ion current is measured. Spatially resolved scans of the target are produced by actuating the mirror motors, thus moving the laser spot across the target, and performing synchronous measurements of the ion current to construct 2D images of a target surface which can be up to 50 mm in diameter. The spatial resolution of the system has been measured by scanning the interfaces between metals such as steel and niobium, where it was demonstrated that the LAS can selectively ablate an area of diameter ≈50 μm. This work informs the development of subsequent LAS systems, that are intended to serve as multi-element ion sources for commercial and custom-built time-of-flight mass spectrometers, or to selectively study surface specific regions of samples.
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•Motorized mirror mounts are used to selectively ablate materials in a fixed target.•The LAS can produce 2D target scans by measuring ion current in a rasterized grid.•The quadrupole spacing allows for a scanning range of up to 50 mm.•Different target materials can be selected with a spatial resolution of 50 μm.•The transport efficiency across the target surface was measured as 2.2 (7)%.
Abstract
The nEXO neutrinoless double beta (0νββ) decay experiment is designed to use a time projection chamber and 5000 kg of isotopically enriched liquid xenon to search for the decay in 136Xe. ...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 1028 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 × 1028 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.
nEXO is a proposed experiment that will search for neutrinoless double-beta decay (0νββ) in 5-tonnes of liquid xenon (LXe), isotopically enriched in 136Xe . A technique called Ba-tagging is being ...developed as a potential future upgrade for nEXO to detect the 136Xe double-beta decay daughter isotope, 136Ba . An efficient Ba-tagging technique has the potential to boost nEXO’s 0νββ sensitivity by essentially suppressing non-double-beta decay background events. A conceptual approach for the extraction from the detector volume, trapping, and identification of a single Ba ion from 5 tonnes of LXe is presented, along with initial results from the commissioning of one of its subsystems, a quadrupole mass filter.
Large-scale low-background detectors are increasingly used in rare-event searches as experimental collaborations push for enhanced sensitivity. However, building such detectors, in practice, creates ...an abundance of radioassay data especially during the conceptual phase of an experiment when hundreds of materials are screened for radiopurity. A tool is needed to manage and make use of the radioassay screening data to quantitatively assess detector design options. We have developed a Materials Database Application for the nEXO experiment to serve this purpose. This paper describes this database application, explains how it functions, and discusses how it streamlines the design of the experiment.
nEXO is a proposed tonne-scale neutrinoless double beta decay (0νββ) experiment using liquid 136Xe (LXe) in a Time Projection Chamber (TPC) to read out ionization and scintillation signals. Between ...the field cage and the LXe vessel, a layer of LXe (“skin” LXe) is present, where no ionization signal is collected. Only scintillation photons are detected, owing to the lack of optical barrier around the field cage. In this work, we show that the light originating in the skin LXe region can be used to improve background discrimination by 5% over previous published estimates. This improvement comes from two elements. First, a fraction of the γ-ray background is removed by identifying light from interactions with an energy deposition in the skin LXe. Second, background from 222Rn dissolved in the skin LXe can be efficiently rejected by tagging the α decay in the 214Bi-214Po chain in the skin LXe.
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 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 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.
Abstract
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
νββ
) 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
νββ
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.
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