Examining Photomultiplier Fatigue and Recovery Following Light Exposure

Photomultiplier tubes (PMTs) are an essential component of many experiments in high energy physics. Understanding the way in which PMTs respond to and recover from various stimuli will have implications for the way in which the resulting data are processed, and can help us quantify the changes in performance over the lifetime of the tube. In this experiment we examine how the gain of PMTs changes after exposure to light under various conditions, with the goal of establishing a time constant for recovery. Working within the context of cosmic ray air shower detection at the Telescope Array Project’s fluorescence detection sites, we will use the data to quantify the effects of exposure to transient light sources such as planes, automobiles, or other unexpected sources. Initial results suggest that exposure to UV light while high voltage is active will increase gain, with an exponential decay returning back to the baseline. We have also confirmed that exposure to broad-spectrum light while there is no voltage across the tubes will not create a significant change in gain.