Pre-Production of PWO-II Crystals for the PANDA-EMC

Lead Tungstate (PbWO 4 , PWO) has become presently the most commonly used scintillator material for electromagnetic (EM) calorimetry in medium and high-energy physics. There exists substantial demand for future calorimeters such as the completion of the PANDA EMC [2] as well as various detector projects under discussion at Jefferson Lab or BNL in the United States. Nearly 6,700 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 R&D efforts with the Shanghai Institute of Ceramics, Chinese Academy of Science (China) as an existing producer exploiting the modified Bridgman method could not reach the required quality in a consistent manner. End of 2014 the company CRYTUR (Turnov, Czech Republic) has re-started 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 pre-production run of 89 crystals focusing on the achieved optical performance, light yield, kinetics, temperature dependence and radiation hardness.