Stimulation of Radiation Damage Recovery of Lead Tungstate Scintillation Crystals Operating in a High Dose-Rate Radiation Environment

Scintillation crystals of the lead tungstate family - PWO, PWO-II - became widely used in electromagnetic calorimeters in high energy physics experiments at high-luminosity accelerator facilities. During the operation of electromagnetic calorimeters a degradation of the optical transmission of these crystals occurs due to creation of color centers. In addition to the recharge by γ-radiation of the point structure defects, which exist a priori in the crystals, additional damage occurs to the crystal matrix due to the interaction of hadrons. Thus radiation induced optical absorption can limit the energy resolution of the calorimeter. To reduce the recharge by γ-radiation we have both minimized the concentration of point structure defects during manufacture, and used light from visible to infrared to stimulate the recovery of the color centers. In this paper we show that method of stimulated recovery is also applicable to recover from degradation of the crystal's optical transmission caused by hadron interactions. The mechanisms of the damage under γ- and hadron-irradiation are discussed.