Influence of neutrons on signal fluctuations for APD structures

Abstract Silicon Avalanche Photo-diodes (APDs) working in proportional were chosen as a readout device for the PbWO 4 crystals in the barrel of the CMS Electromagnetic Calorimeter (ECAL). During 10 years of operation, the CMS ECAL will be exposed to 2 × 10 13 neutrons / cm 2 under a severe radiation environment. In this study, we studied on the effect of photo-statistical fluctuations from those of neutrons by using Geant4 toolkit.