Light exposure and temperature effects on quantum efficiency of bialkali metal photomultipier tubes

Abstract In astroparticle experiments, photomultiplier tubes are crucial for detecting Cherenkov radiation emitted by charged particles, owing to their exceptional sensitivity to low-intensity light, which is essential for studying high-energy phenomena associated with astrophysical neutrinos. However, due to their high sensitivity, PMTs are vulnerable to significant damage to their photocathode coating when exposed to intense light and/or high temperatures. Although this scenario is rare under controlled conditions, it can become relevant in experiments with prolonged exposure to sunlight and elevated temperatures. This study presents an analysis of the damage threshold and recovery time of photomultipliers with bialkali metal coatings. The investigation involved measuring the quantum efficiency of the PMTs before and after exposure to a xenon lamp for varying durations, simulating sunlight exposure over several days. Additionally, quantum efficiency was assessed before and after the PMTs were subjected to thermal stress, providing an evaluation of their performance under different thermal conditions.