First study of radiation hardness of lead tungstate crystals at low temperatures

The electromagnetic calorimeter of PANDA at the FAIR facility will rely on the operation of lead tungstate (PbWO4, PWO) scintillating crystals at temperatures near -25∘C to provide sufficient resolution for photons in the energy range from 8 GeV down to 10 MeV. The radiation hardness of PWO crystals was studied at the IHEP (Protvino) irradiation facility in the temperature range from +20∘C (room temperature) down to -23∘C. These studies have indicated significantly different behavior in the time evolution of the damaging processes well below room temperature. Different signal loss levels at the same dose rate but at different temperatures were observed. The effect of a deep suppression of the crystal recovery process at temperatures below 0∘C has been seen.