Study on the light output nonuniformity of $PbWO_{4}$ crystal

This paper presents measurements on the light output nonuniformity of a full size PbWO/sub 4/ crystal, which will be used in the electromagnetic calorimeter (ECAL) of the CMS detector. It makes use of a /sup 22/Na radioactive source and the coincidence method. With the help of the convolution fitting method, it is possible to make measurements of the light output nonuniformity of the crystal. The effect of depolishing one of the lateral faces of the crystal on the nonuniformity has been studied. The slope of the nonuniformity curve decreases with increasing roughness. When the roughness reaches R/sub s/=(1.49+or-0.27) mu m the nonuniformity curve meets the requirement of CMS-ECAL. (7 refs).