Environmental Effects on TPB Wavelength-Shifting Coatings

TL;DR

This study examines how environmental factors, especially UV light, cause significant degradation of TPB wavelength-shifting coatings used in liquid argon detectors, and proposes mitigation strategies for long-term storage.

Contribution

It provides the first detailed analysis of environmental degradation effects on TPB coatings and offers practical mitigation methods for preserving their effectiveness.

Findings

Severe degradation of TPB coatings occurs under fluorescent and sunlight exposure.

UV wavelengths are primarily responsible for the degradation.

Mitigation strategies can significantly reduce coating loss during storage.

Abstract

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