High-Quality Lead Tungstate Crystals for PANDA Produced at CRYTUR
Lead Tungstate (PbWO4, PWO) has become presently the most commonly used scintillator material for electromagnetic calorimetry in medium and high-energy physics. There exists substantial demand for future calorimeters such as the completion of the PANDA electromagnetic compatibility (EMC) as well as various detector projects under discussion at Jefferson Lab or Brookhaven National Laboratory in the United States. Nearly, 6700 crystals are missing for the barrel section of the PANDA-EMC since the successful mass production of PWO using the Czochralski method was stopped after bankruptcy of the Bogoroditsk Technical Chemical Plant (BTCP) in Russia. Intermediate research and development efforts with the Shanghai Institute of Ceramics, Chinese Academy of Science, Shanghai, China, as an existing producer exploiting the modified Bridgman method could not reach the required quality in a consistent manner. End of 2014, the CRYTUR (Turnov, Czech Republic) has restarted the development of lead tungstate based again on the Czochralski method with impressive progress. The modified and optimized technology has already produced full size samples of PWO-II quality. This paper will present a detailed status report on a first preproduction run of 89 crystals focusing on the achieved optical performance, light yield, kinetics, and temperature dependence and radiation hardness.