Date of Completion

12-18-2015

Embargo Period

6-15-2016

Keywords

Xenon, gamma-ray, energy resolution, gamma-ray spectroscopy, time projection chambers, nobel liquid dual phase detectors, liquid xenon target, recombination fluctuations

Major Advisor

Moshe Gai

Associate Advisor

Daniel McKinsey

Associate Advisor

Peter Schweitzer

Field of Study

Physics

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

PIXeY (Particle Identification in Xenon at Yale) is a two-phase (liquid/gas) xenon prototype detector with 3-kg active mass. The two-phase xenon technology has many applications that include gamma-ray imaging, neutrinoless double beta decay searches, dark matter searches, and medical imaging PET scanners. PIXeY was built to optimize energy resolution, with a number of technological improvements over previous work. Parallel-wire grids, which control the drift and proportional-scintillation fields, are optimized both for light-collection efficiency and field uniformity with optical transparencies between 92% and 97%. High voltage epoxy feedthroughs have been installed with stable operating voltages better than 5 kV on the anode and -10 kV on the cathode. High quantum efficiency Hamamatsu R8778 PMTs (photomultiplier tubes), high-reflectivity Teflon walls, and charge-light anti-correlation techniques are also incorporated.

A number of fiducial cuts and correction factors were used to optimize energy resolution. The light and charge signals were corrected by the spatial location of the event within the detector, taking into account effects such as the electron lifetime, and geometric light collection. The energy spectrum of various sources was studied by varying the cathode, anode, and PMT voltages. Optimal configurations for the drift and scintillation fields were found for energies ranging from 41.5 keV (83mKr) to 2.61 MeV (228Th), resolving the light signal and keeping the charge signal unsaturated. After quality cuts and optimization of parameters, energy resolutions of 5.4 ± 0.4 % σ/E at 42 keV, 1.81 ± 0.13 % σ/E at 350 keV, 1.71 ± 0.12 % σ/E at 511 keV, 1.16 ± 0.08 % σ/E at 662 keV, 1.01 ± 0.07 % σ/E at 1275 keV, and 0.85 ± 0.06 % σ/E at 2614 keV for 1,000 V/cm drift field were obtained. In addition, the recombination fluctuations at the source energies were studied, with the recombination fluctuations modeled as a binomial variance with an additional prefactor that is a function of the number of ion quanta, which appears to plateau at Eτ = 527±137 keV.

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