Lifetime Studies of the 19-channel Hybrid Photodiode for the CMS Hadronic Calorimeter

Along with quality assurance of ~1000 hybrid photodiode tubes for CMS, a subset were subjected to long term testing of their properties over time. Over the course of several years, the tubes were operated under non-uniform illumination at rates up to 3.75 nW per pixel and for total integrated charges of up to 7 C at the anode. In-situ measurements of quantum efficiency and gain, coupled with periodic photocathode uniformity scans, dark current and cross talk, provide information on expected time-dependent changes in the tube photo-sensitivity and some indication of possible failure modes.