Wavelength-shifting performance of polyethylene naphthalate films in a liquid argon environment

Liquid argon is commonly used as a detector medium for neutrino physics and dark matter experiments in part due to its copious scintillation light production response excitation ionization by charged particle interactions. As appears the vacuum ultraviolet (VUV) regime difficult detect, wavelength-shifting materials are typically convert VUV visible wavelengths more easily detectable conventional means. In this work, we examine optical properties of poly(ethylene naphthalate) (PEN), recently proposed alternative tetraphenyl butadiene (TPB), most widely-used wavelength-shifter argon-based experiments. custom cryostat system with well-demonstrated geometric stability, use 128~nm various PEN-including reflective samples' light-producing capabilities, study stability PEN when immersed liquid argon. The best-performing test reflector was found produce 34% much TPB-including reference sample, widely varying levels between different reflectors. Plausible origins these variations, including differences molecular orientation, then identified using additional measurements. Unlike TPB-coated samples, PEN-coated samples did not long-timescale collection increases associated solvation or suspension material bulk