PWO-II scintillation crystals for the PANDA electromagnetic calorimeter

The PANDA detector will be one of the major experimental installations at the future acceleration facility FAIR at GSI (Darmstadt) for hadron physics studies using a cooled antiproton beam. A new type of the lead tungstate crystals (PWO-II) was developed as the scintillation material for the electromagnetic calorimeter of the target spectrometer of PANDA, which has to provide photon detection in the energy range from 10MeV up to 10GeV with excellent energy resolution operating at high interaction rates. The new PWO-II crystals of improved quality are characterized by light yield of 17–22 photoelectron per MeV of deposited energy and radiation induced absorption coefficient at 420 nm (luminescence maximum) below 1m⁻¹ (integral dose 3krad), both determined at room temperature. The crystals were optimized with respect to light yield and radiation hardness for operation at low temperatures down to T=−25°C. The paper presents studies of the quality parameters of two pre-production lots of 120 and 600 PWO-II full size crystals comprising samples of 11 different shapes for the barrel part of the calorimeter.