Blair Edwards

Position reconstruction in a dual phase xenon scintillation detector

We studied the application of statistical reconstruction algorithms, namely maximum likelihood and least squares methods, to the problem of event reconstruction in a dual phase liquid xenon detector. An iterative method was developed for in-situ reconstruction of the PMT light response functions from calibration data taken with an uncollimated γ -ray source. Using the techniques described, the performance of the ZEPLIN-III dark matter detector was studied for 122 keV γ-rays. For the inner part of the detector (R <; 100 mm) , spatial resolutions of 13 mm and 1.6 mm FWHM were measured in the horizontal plane for primary and secondary scintillation, respectively. An energy resolution of 8.1% FWHM was achieved at that energy. The possibility of using this technique for improving performance and reducing cost of scintillation cameras for medical applications is currently under study.

Tritium calibration of the LUX dark matter experiment

We present measurements of the electron-recoil (ER) response of the LUX dark matter detector based upon 170 000 highly pure and spatially uniform tritium decays. We reconstruct the tritium energy spectrum using the combined energy model and find good agreement with expectations. We report the average charge and light yields of ER events in liquid xenon at 180 and 105 V/cm and compare the results to the NEST model. We also measure the mean charge recombination fraction and its fluctuations, and we investigate the location and width of the LUX ER band. These results provide input to a reanalysis of the LUX run 3 weakly interacting massive particle search.

Quenching factor for low-energy nuclear recoils in a plastic scintillator

Plastic scintillators are widely used in industry, medicine, and scientific research, including nuclear and particle physics. Although one of their most common applications is in neutron detection, experimental data on their response to low-energy nuclear recoils are scarce. Here, the relative scintillation efficiency for neutron-induced nuclear recoils in a polystyrene-based plastic scintillator (UPS-923A) is presented, exploring recoil energies between 125 and 850 keV. Monte Carlo simulations, incorporating light collection efficiency and energy resolution effects, are used to generate neutron scattering spectra which are matched to observed distributions of scintillation signals to parameterize the energy-dependent quenching factor. At energies above 300 keV the dependence is reasonably described using the semiempirical formulation of Birks and a kB factor of (0.014±0.002) g MeV -1 cm -2 has been determined. Below that energy, the measured quenching factor falls more steeply than predicted by the Birks formalism.

Calibration of a two-phase xenon time projection chamber with a

Author(s): Boulton, EM; Bernard, E; Destefano, N; Edwards, BNV; Gai, M; Hertel, SA; Horn, M; Larsen, NA; Tennyson, BP; Wahl, C; McKinsey, DN | Abstract:

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The Mid-Infrared Instrument (MIRI) is the coldest and longest wavelength (5-28 micron) science instrument on-board the James Webb Space Telescope observatory and provides imaging, coronography and high and low resolution spectroscopy. The MIRI thermal design is driven by a requirement to cool the detectors to a temperature below 7.1 Kelvin. The MIRI Optics Module (OM) is accommodated within the JWST Integrated Science Instrument Module (ISIM) which is passively cooled to between 32 and 40 K. Thermal isolation between the OM and the ISIM is therefore required, with active cooling of the OM provided by a dedicated cryostat, the MIRI Dewar. Heat transfer to the Dewar must be minimised to achieve the five year mission life with an acceptable system mass. Stringent cleanliness levels are necessary in order to maintain the optical throughput and the performance of thermal control surfaces. The ISIM (and MIRI OM) is launched warm, therefore care must be taken during the on-orbit cooldown phase, when outgassing of water and other contaminants is anticipated from composite structures within the ISIM. Given the strong link between surface temperature and contamination levels, it is essential that the MIRI thermal and contamination control philosophies are developed concurrently.

Ar source

Weakly Interacting Massive Particles (WIMPs) are a leading candidate for dark matter and are expected to produce nuclear recoil (NR) events within liquid xenon time-projection chambers. We present a measurement of liquid xenon scintillation characteristics in the LUX dark matter detector and develop a pulse shaped based discrimination parameter to be used for particle identification. To accurately measure the scintillation characteristics, we develop a template-fitting method to reconstruct the detection time of photons. Analyzing calibration data collected during the 2013-16 LUX WIMP search, we measure a singlet-to-triplet scintillation ratio for electron recoils (ER) that is consistent with existing literature, and we make a first-ever measurement of the NR singlet-to-triplet ratio at recoil energies below 74 keV. A prompt fraction discrimination parameter exploits the difference of the photon time spectra for NR and ER events and is optimized to have the least number of ER events that occur in the 50\% NR acceptance region. When this discriminator is used in conjunction with charge-to-light discrimination on the calibration data, the signal-to-noise ratio in the NR dark matter acceptance region increases by up to a factor of two.

Thermal and contamination control of the mid-infrared instrument for JWST

PIXeY (Particle Identification in Xenon at Yale) is an R&D detector that uses xenon in gas-phase, liquid-phase, or two-phase mode. It features drift and proportional electric field regions set with 92%-transparent wire grids, highly reflective Teflon walls, and 14 high-quantum-efficiency PMTs (Hamamatsu R8778) to record both initial scintillation light (S1) and proportional scintillation light (S2) from the drifting of charge in the proportional region. It promises energy resolution and gamma/neutron discrimination that are competitive with previous systems. Recently, PIXeY has run stably for 12 weeks and the first data have been collected. Initial results are presented, along with planned design modifications that will transform PIXeY into a Compton imager. Crossed wires with 3-mm spacing will be used to record interaction locations. A preamp to read out each wire is also being designed to fulfill space and noise constraints. Finally, in order to precisely know the energy from each gamma-ray interaction, the scintillation light from each interaction must be distinguished from that due to others. Simulation is used to determine the optimal optical segmentation of the active volume using thin Teflon walls.

Liquid xenon scintillation measurements and pulse shape discrimination in the LUX dark matter detector

We present a measurement of the extraction efficiency of quasi-free electrons from the liquid into the gas phase in a two-phase xenon time-projection chamber. The measurements span a range of electric fields from 2.4 to 7.1 kV/cm in the liquid xenon, corresponding to 4.5 to 13.1 kV/cm in the gaseous xenon. Extraction efficiency continues to increase at the highest extraction fields, implying that additional charge signal may be attained in two-phase xenon detectors through careful high-voltage engineering of the gate-anode region.

Status and design of two-phase liquid-Xenon compton-imaging detector

PIXeY (Particle Identification in Xenon at Yale) is a two-phase (liquid/gas) xenon prototype time projection chamber with 3 kg active mass. PIXeY was built to optimize energy resolution and gamma/neutron discrimination, with a number of technological improvements over previous work. Parallel-wire grids, which control the drift and proportionalscintillation fields, are optimized both for light collection efficiency and field uniformity. High quantum efficiency Hamamatsu R8778 PMTs, high-reflectivity Teflon walls, and charge-light anti-correlation techniques are also incorporated. The first run of the detector has concluded, where all systems were tested both using LED calibration methods as well as using sources for calibration and spectral measurements. Ultimately our results were limited by PMT calibration issues, low light collection caused by saturation, and low drift fields constrained by high voltage hardware. The second run of the detector is currently underway with several improved components. The feedthroughs for higher voltages have improved to allow a much higher operating voltage, new PMT bases for more stable operation have been installed, and three new grids with transparencies between 92% and 97% have been added. Once the energy resolution studies have concluded, PIXeY will serve as a platform for future improvements, including multiple optical volumes and single wire readout for R&D on gamma-ray imaging.

Extraction efficiency of drifting electrons in a two-phase xenon time projection chamber

We present results from the measurement of the neutron production rate in lead by high energy cosmic-ray muons at a depth of 2850 m water equivalent (mean muon energy of 260 GeV). A tonne-scale highly segmented plastic scintillator detector was utilised to detect both the energy depositions from the traversing muons as well as the delayed radiative capture signals of the induced neutrons. Complementary Monte Carlo simulations reproduce well the distributions of muons and detected muon-induced neutrons. Absolute agreement between simulation and data is of the order of 25%. By comparing the measured and simulated neutron capture rates a neutron yield in pure lead of (5.78−0.28+0.21)×10−3 neutrons/muon/(g/cm2) has been obtained.