Environmental effects on TPB wavelength-shifting coatings

Abstract

The scintillation detection systems of liquid argon time projection chambers\n(LArTPCs) require wavelength shifters to detect the 128 nm scintillation light\nproduced in liquid argon. Tetraphenyl butadiene (TPB) is a fluorescent material\nthat can shift this light to a wavelength of 425 nm, lending itself well to use\nin these detectors. We can coat the glass of photomultiplier tubes (PMTs) with\nTPB or place TPB-coated plates in front of the PMTs.\n In this paper, we investigate the degradation of a chemical TPB coating in a\nlaboratory or factory environment to assess the viability of long-term TPB film\nstorage prior to its initial installation in an LArTPC. We present evidence for\nsevere degradation due to common fluorescent lights and ambient sunlight in\nlaboratories, with potential losses at the 40% level in the first day and\neventual losses at the 80% level after a month of exposure. We determine the\ndegradation is due to wavelengths in the UV spectrum, and we demonstrate\nmitigating methods for retrofitting lab and factory environments.\n