Lifetime studies of the 19-channel hybrid photodiode for the CMS hadronic calorimeter

A subset of the ∼1000 CMS hybrid photodiode tubes which passed through our quality assurance program was subjected to long term testing of their properties as a function of 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 photosensitivity and some indication of possible failure modes.