Investigation of non-uniform radiation damage observed in the ZEUS Beam Pipe Calorimeter at HERA

The ZEUS Beam Pipe Calorimeter (BPC) is a small tungsten/scintillator sampling calorimeter. It is positioned at a distance of approximately 4 cm from the HERA beams and approximately 3 m from the interaction point. The accumulated doses measured at the front side of the BPC during the HERA runs 1995, 1996 and 1997 were 12 kGy, 11 kGy and 2.5 kGy, respectively. The radiation dose influenced the optical components of the BPC. The degradation of some of the scintillators due to radiation damage has been examined using different monitoring systems. A simulation code was developed which describes quantitatively the effects of non-uniform radiation damage. The following report describes the radiation monitoring, the effects on the scintillator material and the impact on the energy linearity of the BPC