The differences in performance between low- and high-purity grades of briquetted SiC need to be better understood for achieving maximum benefits, as both are very complicated materials that perform ...quite differently with advantages and disadvantages relative to each other. The effect of the degree of SiC purity on melt yield has not heretofore been accurately quantified by comprehensive mass balances for all inputs and outputs, so melt yield as a function of SiC purity is an important stand-alone metric which also serves to standardize all other variables by which all other effects (performance metrics) can be accurately quantified. The complexity of the interactions between all cupola melt process variables and the resultant effects makes it very difficult to obtain meaningful measurements by which satisfactory performance assessments can be made in comparing the relative values of low- and high-purity SiC. However, this project utilized comprehensive metal, slag and stack gas analyses which were needed for comprehensive mass balances in correlating all material inputs and outputs. The results of that were the basis for accurate assessments of performance metrics in comparing the relative advantages and disadvantages of each purity grade of SiC briquettes.
Despite the rapid growth of research on neighborhood influences on children, little of this research may be useful to prevention scientists. Most studies have ignored processes by which neighborhood ...conditions influence individual outcomes. To encourage neighborhood research that can better guide the development of preventive interventions, we propose a model that focuses attention on mediating and moderating processes, is appropriate for studies interested in individual differences in outcomes, acknowledges the transactions between residents and neighborhoods, and is sensitive to how neighborhood influences may differ for children at different developmental stages. Furthermore, we argue that greater attention to several methodological issues also can make neighborhood research more useful for the next generation of prevention programs to help low‐income urban families and children cope successfully with the challenges posed by their neighborhoods.
Searches for double beta decay of Xe134 were performed with EXO-200, a single-phase liquid xenon detector designed to search for neutrinoless double beta decay of Xe136. Using an exposure of 29.6 ...kg·yr, the lower limits of T1/22νββ>8.7×1020 yr and T1/20νββ>1.1×1023 yr at 90% confidence level were derived, with corresponding half-life sensitivities of 1.2×1021 yr and 1.9×1023 yr. These limits exceed those in the literature for Xe134, improving by factors of nearly 105 and 2 for the two antineutrino and neutrinoless modes, respectively.
Searches for double beta decay of 134Xe were performed with EXO-200, a single-phase liquid xenon detector designed to search for neutrinoless double beta decay of 136Xe. Using an exposure of 29.6 kg ...· yr, the lower limits of T2νββ 1=2 > 8.7 × 1020 yr and T0νββ 1=2 > 1.1 × 1023 yr at 90% confidence level were derived, with corresponding half-life sensitivities of 1.2 × 1021 yr and 1.9 × 1023 yr. These limits exceed those in the literature for 134Xe, improving by factors of nearly 105 and 2 for the two antineutrino and neutrinoless modes, respectively.
Future tonne-scale liquefied noble gas detectors depend on efficient light detection in the VUV range. In the past years Silicon Photomultipliers (SiPMs) have emerged as a valid alternative to ...standard photomultiplier tubes or large area avalanche photodiodes. The next generation double beta decay experiment, nEXO, with a 5 tonne liquid xenon time projection chamber, will use SiPMs for detecting the \(178\,\text{nm}\) xenon scintillation light, in order to achieve an energy resolution of \(\sigma / Q_{\beta\beta} = 1\, \%\). This paper presents recent measurements of the VUV-HD generation SiPMs from Fondazione Bruno Kessler in two complementary setups. It includes measurements of the photon detection efficiency with gaseous xenon scintillation light in a vacuum setup and dark measurements in a dry nitrogen gas setup. We report improved photon detection efficiency at \(175\,\text{nm}\) compared to previous generation devices, that would meet the criteria of nEXO. Furthermore, we present the projected nEXO detector light collection and energy resolution that could be achieved by using these SiPMs.
The search for neutrinoless double beta decay probes the fundamental properties of neutrinos, including whether or not the neutrino and antineutrino are distinct. Double beta detectors are large and ...expensive, so background reduction is essential for extracting the highest sensitivity. The identification, or 'tagging', of the \(^{136}\)Ba daughter atom from double beta decay of \(^{136}\)Xe provides a technique for eliminating backgrounds in the nEXO neutrinoless double beta decay experiment. The tagging scheme studied in this work utilizes a cryogenic probe to trap the barium atom in solid xenon, where the barium atom is tagged via fluorescence imaging in the solid xenon matrix. Here we demonstrate imaging and counting of individual atoms of barium in solid xenon by scanning a focused laser across a solid xenon matrix deposited on a sapphire window. When the laser sits on an individual atom, the fluorescence persists for \(\sim\)30~s before dropping abruptly to the background level, a clear confirmation of one-atom imaging. No barium fluorescence persists following evaporation of a barium deposit to a limit of \(\leq\)0.16\%. This is the first time that single atoms have been imaged in solid noble element. It establishes the basic principle of a barium tagging technique for nEXO.
The next-generation Enriched Xenon Observatory (nEXO) is a proposed experiment to search for neutrinoless double beta (\(0\nu\beta\beta\)) decay in \(^{136}\)Xe with a target half-life sensitivity of ...approximately \(10^{28}\) years using \(5\times10^3\) kg of isotopically enriched liquid-xenon in a time projection chamber. This improvement of two orders of magnitude in sensitivity over current limits is obtained by a significant increase of the \(^{136}\)Xe mass, the monolithic and homogeneous configuration of the active medium, and the multi-parameter measurements of the interactions enabled by the time projection chamber. The detector concept and anticipated performance are presented based upon demonstrated realizable background rates.
We report on the performance of silicon photomultiplier (SiPM) light sensors operating in electric field strength up to 30 kV/cm and at a temperature of 149K, relative to their performance in the ...absence of an external electric field. The SiPM devices used in this study show stable gain, photon detection efficiency, and rates of correlated pulses, when exposed to external fields, within the estimated uncertainties. No observable physical damage to the bulk or surface of the devices was caused by the exposure.
We apply deep neural networks (DNN) to data from the EXO-200 experiment. In the studied cases, the DNN is able to reconstruct the relevant parameters - total energy and position - directly from raw ...digitized waveforms, with minimal exceptions. For the first time, the developed algorithms are evaluated on real detector calibration data. The accuracy of reconstruction either reaches or exceeds what was achieved by the conventional approaches developed by EXO-200 over the course of the experiment. Most existing DNN approaches to event reconstruction and classification in particle physics are trained on Monte Carlo simulated events. Such algorithms are inherently limited by the accuracy of the simulation. We describe a unique approach that, in an experiment such as EXO-200, allows to successfully perform certain reconstruction and analysis tasks by training the network on waveforms from experimental data, either reducing or eliminating the reliance on the Monte Carlo.
A new design for the anode of a time projection chamber, consisting of a charge-detecting "tile", is investigated for use in large scale liquid xenon detectors. The tile is produced by depositing 60 ...orthogonal metal charge-collecting strips, 3~mm wide, on a 10~\si{\cm} \(\times\) 10~\si{\cm} fused-silica wafer. These charge tiles may be employed by large detectors, such as the proposed tonne-scale nEXO experiment to search for neutrinoless double-beta decay. Modular by design, an array of tiles can cover a sizable area. The width of each strip is small compared to the size of the tile, so a Frisch grid is not required. A grid-less, tiled anode design is beneficial for an experiment such as nEXO, where a wire tensioning support structure and Frisch grid might contribute radioactive backgrounds and would have to be designed to accommodate cycling to cryogenic temperatures. The segmented anode also reduces some degeneracies in signal reconstruction that arise in large-area crossed-wire time projection chambers. A prototype tile was tested in a cell containing liquid xenon. Very good agreement is achieved between the measured ionization spectrum of a \(^{207}\)Bi source and simulations that include the microphysics of recombination in xenon and a detailed modeling of the electrostatic field of the detector. An energy resolution \(\sigma/E\)=5.5\% is observed at 570~\si{keV}, comparable to the best intrinsic ionization-only resolution reported in literature for liquid xenon at 936~V/\si{cm}.
