The effects of neutron irradiation on multi-pixel hybrid photodiode tubes

The effects of neutron irradiation on a multi-pixel hybrid photodiode tube (HPD) were studied. The HPD underwent an integrated fluence of 1013neutronscm2 from a 252Cf source. Increased leakage currents were observed during this irradiation, consistent with that observed from bare silicon detectors. The HPD was observed to be fully operational, with acceptable leakage currents, at the fluences expected during the lifetime of the CMS experiment. After the full dosage, small intrapixel inhomogeneities were observed in the HPDʹs response. The origins of these inhomogeneities and methods to mitigate the radiation damage were investigated.