Temperature Dependent Emission of Acrylic Relative to Tetrapheynl Butadiene (TPB)

Abstract

After decades of astronomical observation and study, the majority of mass in the universe is known to be composed of dark matter, an unknown substance which is strictly non-luminous unlike the more familiar baryonic matter. Efforts to detect the elusive dark matter include low background particle detectors, which use the natural environment and precise technologies to try and observe interactions of a Standard Model particle with a dark matter particle. These are able to set limits on characteristics of dark matter particles based on their specific experiment. For these sensitive searches, materials that are not traditionally considered to have background contributions can produce nuisance signals. Poly(methyl methacrylate) (PMMA), or acrylic, is one such material. In other fields, acrylic is known to have low level fluorescence emissions, produced by microscopic impurities from surface handling or manufacturing additives. This work aims to characterize the magnitude of fluorescence emissions from acrylic from 300.0K to 4.0K, relative to 1,1,4,4-tetraphenyl-1,3-butadiene (TPB), a wavelength shifter commonly used in rare event detectors. Since the fluores- cence is expected to be produced by impurities, this work studies a specific batch of acrylic produced by Reynold’s Polymer Technologies (RPT) for the DEAP-3600 experiment acrylic vessel. Limits on any amount of fluorescence from the acrylic can allow the DEAP-3600 collaboration to more accurately model the overall detector response, which in turn maximizes sensitivity. The samples studied consist of one blank RPT sample with sanded sides, and an identically shaped RPT sample coated with (1.040 ± 0.052)μm of TPB on one side. They were exposed to 280.0nm UV light, which was chosen to better simulate the effect Cherenkov radiation may have on acrylic. Emissions from the blank sample were found to be (0.5 ± 0.1)% relative to the emissions from the TPB coated sample, under the same conditions, integrated over a 50.0ns window. This value was consistent with the one measured at the boiling temperature of liquid argon (87.0K). Photons from the blank sample were emitted in the lower visible regime, rising around 375.0nm, consistent for all temperatures. Each sample showed a trend of increasing emissions at decreasing temperatures.