UV Degradation of the Optical Properties of Acrylic for Neutrino and Dark Matter Experiments

TL;DR

This study investigates how UV exposure degrades the optical transmittance of acrylic used in neutrino and dark matter detectors, affecting their performance.

Contribution

It provides experimental data on UV-induced degradation of acrylic from various manufacturers and establishes safe UV exposure limits for detector applications.

Findings

Significant degradation at 343 nm after 3 hours of sunlight exposure

Some acrylics show softer degradation peaking at 310 nm over days

Safe UV exposure time limits are proposed for indoor and outdoor environments

Abstract

UV-transmitting (UVT) acrylic is a commonly used light-propagating material in neutrino and dark matter detectors as it has low intrinsic radioactivity and exhibits low absorption in the detectors' light producing regions, from 350 nm to 500 nm. Degradation of optical transmittance in this region lowers light yields in the detector, which can affect energy reconstruction, resolution, and experimental sensitivities. We examine transmittance loss as a result of short- and long-term UV exposure for a variety of UVT acrylic samples from a number of acrylic manufacturers. Significant degradation peaking at 343 nm was observed in some UVT acrylics with as little as three hours of direct sunlight, while others exhibited softer degradation peaking at 310 nm over many days of exposure to sunlight. Based on their measured degradation results, safe time limits for indoor and outdoor UV exposure of UVT acrylic are formulated.