Polyethylene naphthalate film as a wavelength shifter in liquid argon detectors

Abstract

Liquid argon-based scintillation detectors are important for dark matter searches and neutrino physics. Argon scintillation light is in the vacuum ultraviolet region, making it hard to be detected by conventional means. Polyethylene naphthalate (PEN), an optically transparent thermoplastic polyester commercially available as large area sheets or rolls, is proposed as an alternative wavelength shifter to the commonly-used tetraphenyl butadiene (TPB). By combining the existing literature data and spectrometer measurements relative to TPB, we conclude that the fluorescence yield and timing of both materials may be very close. The evidence collected suggests that PEN is a suitable replacement for TPB in liquid argon neutrino detectors, and is also a promising candidate for dark matter detectors. Advantages of PEN are discussed in the context of scaling-up existing technologies to the next generation of very large ktonne-scale detectors. Its simplicity has a potential to facilitate such scale-ups, revolutionizing the field.

Wavelength Shifters for Applications in Liquid Argon Detectors

“…As discussed in [31], early literature suggested a significant increase of PEN PLQY at 128 nm excitation wavelengths and 87 K, compared to room temperature and near UV excitation, leading to extrapolated values consistent with TPB in LAr detector conditions. More recent ex situ measurements were performed at room temperature relative to TPB indicate PLQY in the range of 0.3-0.6 w.r.t.…”

“…Because of its low oxygen permeability and convenient mechanical, electrical and optical properties, it is industrially mass-produced for applications in e.g., food packaging or electronics. Although it is also one of the components of the Vikuiti ESR, specular reflector commonly used in LAr detectors, and its fluorescence properties have been known for a long time [62], it was only proposed as a scintillator in 2011 [63], and then, recently, as a WLS particularly well suited for large scale LAr detectors [31].…”

Usage of PEN as self-vetoing structural material in low background experiments

“…Moreover, PEN can shift the VUV light to visible light. Thus, the VUV light produced by LAr (127 nm) or LXe (175 nm) can be shifted to about 445 nm with PEN structures with an absolute re-emission probability of about 50% [5]. On the other hand, the light attenuation length of PEN is of the order of few cm, which has a tolerable impact on the light output for structures with a size of the order of a few cm.…”

Spin coating of TPB film on acrylic substrate and measurement of its wavelength shifting efficiency

“…Light in this wavelength range would be strongly absorbed by most detector materials. Tetraphenyl butadiene (TPB) is among one of the favorite WLS options [1][2][3] in a number of neutrino and dark matter experiments using liquid argon, such as Mi-croBooNE [4], DUNE [5], DEAP-3600 [6,7], DarkSide-20k [8] and ArDM [9], which absorbs UV light and re-emit lights in visible spectrum to be easily and effectively detected by photomultipliers tubes (PMT) or Silicon Photomultipliers (SiPM). WLS is also used in Cherenkov detectors to improve light yield [10][11][12].…”