Studies that expand the scope of the Prins-pinacol synthesis of carbocyclic ring systems are described. The construction of cyclopentacyclooctanones by ring-enlarging cyclopentane annulations of ...cycloheptanone precursors is broadly examined as is the synthesis of related bicyclic ketones containing larger rings. Prins-pinacol reactions of acyclic alkenyl acetals were examined to gain insight into intrinsic stereochemical control elements in ring-enlarging cyclopentane annulations. The outcome of the carbocyclic constructions described in this report are rationalized by the mechanistic analysis we developed recently to describe Prins-pinacol constructions of tetrahydrofurans.
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We present constraints on the existence of weakly interacting massive particles (WIMPs) from an 11 kg-day target exposure of the DAMIC experiment at the SNOLAB underground laboratory. The observed ...energy spectrum and spatial distribution of ionization events with electron-equivalent energies \(>\)200 eV\(_{\rm ee}\) in the DAMIC CCDs are consistent with backgrounds from natural radioactivity. An excess of ionization events is observed above the analysis threshold of 50 eV\(_{\rm ee}\). While the origin of this low-energy excess requires further investigation, our data exclude spin-independent WIMP-nucleon scattering cross sections \(\sigma_{\chi-n}\) as low as \(3\times 10^{-41}\) cm\(^2\) for WIMPs with masses \(m_{\chi}\) from 7 to 10 GeV\(c^{-2}\) . These results are the strongest constraints from a silicon target on the existence of WIMPs with $m_{\chi}$$<\(9 GeV\)c^{-2}$ and are directly relevant to any dark matter interpretation of the excess of nuclear-recoil events observed by the CDMS silicon experiment in 2013.
The Pacific Northwest National Laboratory (PNNL) is currently developing a custom software suite capable of automating many of the tasks required to accurately analyze coincident signals within gamma ...spectrometer arrays. During the course of this work, significant crosstalk was identified in the energy determination for spectra collected with a new low-background intrinsic germanium (HPGe) array at PNNL. The HPGe array is designed for high detection efficiency, ultra-low-background performance, and sensitive ?a? coincidence detection. The first half of the array, a single cryostat containing seven HPGe crystals, was recently installed into a new shallow underground laboratory facility. This update will present a brief review of the germanium array, describe the observed crosstalk, and present a straight-forward empirical correction that significantly reduces the impact of this crosstalk on the spectroscopic performance of the system.
This paper describes the generation of
Ar, via reactor irradiation of potassium carbonate, followed by quantitative analysis (length-compensated proportional counting) to yield two calibration ...standards that are respectively 50 and 3 times atmospheric background levels. Measurements were performed in Pacific Northwest National Laboratory's shallow underground counting laboratory studying the effect of gas density on beta-transport; these results are compared with simulation. The total expanded uncertainty of the specific activity for the ~50×
Ar in P10 standard is 3.6% (k=2).
Alkyl oxalates are new bench-stable alcohol-activating groups for radical generation under visible light photoredox conditions. Using these precursors, the first net redox-neutral coupling of ...tertiary and secondary alcohols with electron-deficient alkenes is achieved.
In this paper we report on the characterization of the Hamamatsu VUV4 (S/N: S13370-6152) Vacuum Ultra-Violet (VUV) sensitive Silicon Photo-Multipliers (SiPMs) as part of the development of a solution ...for the detection of liquid xenon scintillation light for the nEXO experiment. Various SiPM features, such as: dark noise, gain, correlated avalanches, direct crosstalk and Photon Detection Efficiency (PDE) were measured in a dedicated setup at TRIUMF. SiPMs were characterized in the range \(163 \text{ } \text{K} \leq \text{T}\leq 233 \text{ } \text{K}\). At an over voltage of \(3.1\pm0.2\) V and at \(\text{T}=163 \text{ }\text{K}\) we report a number of Correlated Avalanches (CAs) per pulse in the \(1 \upmu\text{s}\) interval following the trigger pulse of \(0.161\pm0.005\). At the same settings the Dark-Noise (DN) rate is \(0.137\pm0.002 \text{ Hz/mm}^{2}\). Both the number of CAs and the DN rate are within nEXO specifications. The PDE of the Hamamatsu VUV4 was measured for two different devices at \(\text{T}=233 \text{ }\text{K}\) for a mean wavelength of \(189\pm7\text{ nm}\). At \(3.6\pm0.2\) V and \(3.5\pm0.2\) V of over voltage we report a PDE of \(13.4\pm2.6\text{ }\%\) and \(11\pm2\%\), corresponding to a saturation PDE of \(14.8\pm2.8\text{ }\%\) and \(12.2\pm2.3\%\), respectively. Both values are well below the \(24\text{ }\%\) saturation PDE advertised by Hamamatsu. More generally, the second device tested at \(3.5\pm0.2\) V of over voltage is below the nEXO PDE requirement. The first one instead yields a PDE that is marginally close to meeting the nEXO specifications. This suggests that with modest improvements the Hamamatsu VUV4 MPPCs could be considered as an alternative to the FBK-LF SiPMs for the final design of the nEXO detector.
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.
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