Abstract
Some publications indicate that poly(methyl methacrylate) (PMMA) and polytetrafluoroethylene (PTFE) exhibit low levels of photoluminesence (fluorescence and/or phosphorescence) when irradiated with photons in the ultraviolet (UV) to visible range. PMMA (also known as acrylic) and PTFE are commonly used to contain the liquid argon (LAr) or xenon (LXe) target material in rare-event search experiments. LAr and LXe scintillate in the vacuum UV region, and the PMMA and PTFE can be directly illuminated by these photons. Photoluminescence from support materials could cause unexpected signals in these detectors. We investigate photoluminesence in the 400 nm to 550 nm region in response to excitation with UV light between 130 and 250 nm at levels relevant to rare-event search experiments. Measurements are done at room temperature and the signal intensity is time-integrated over several minutes. We tested PMMA and PTFE samples from the batches used in the DEAP-3600 and LUX experiments and observed no photoluminescence signal. We put limits on the efficiency of the plastics to shift UV photons to a wavelengths region of 400 nm–550 nm at 0.05%–0.35% relative to the wavelength shifting efficiency of tetraphenyl-butadiene.
Highlights
The scintillation and/or ionisation signal of liquid noble gases, liquid argon and liquid xenon, is commonly used in particle detectors looking for rare events [1,2,3,4,5,6,7,8]
Shown are the measurements of PTFE and Reynolds Polymer Technologies (RPT) acrylic done under the same conditions
If PTFE or acrylic display photoluminescence in the visible regime when excited by VUV light, the light yield is below the sensitivity of the spectrometer
Summary
The scintillation and/or ionisation signal of liquid noble gases, liquid argon and liquid xenon, is commonly used in particle detectors looking for rare events [1,2,3,4,5,6,7,8]. Some materials not usually considered as sources of photons in such detectors might emit light when excited by UV photons This photoluminescence is classified as either fluorescence or phosphorescence depending on the types of the excited states (singlet and triplet), which result in different lifetimes [11]. Shown is the transmittance of the RPT acrylic used in DEAP, and the response of the PMTs used in DEAP and LUX (Figure 2b) Another source of UV photons in DEAP is Cherenkov light, which can be created inside acrylic by fast electrons from the decay of radioactive contaminants. As an estimate of the lowest level of photoluminescence still relevant for rare-event search experiments using LAr, TPB, and acrylic, we consider the wavelength shifting efficiency (WLSE) PMMA would need to produce events in the energy region of interest for dark matter search, approxi-. The wavelength shifting efficiency of TPB as a function of film thickness has
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