Organization of the production of 100 tons of lead tungstate crystals for the CMS experiment at CERN

The CMS collaboration at CERN has undertaken at the end of 1994 an ambitious R&D program on Lead Tugstate scintillating crystals for its electromagnetic calorimeter. All the parameters of this crystal have been extensively studied in order to optimize its performances in the context of the Large Hadron Collider. Full size crystals (23 cm in length, up to 2.5 × 2.5 cm² in section) with the desired trapezoidal geometry can now be grown and mechanically processed with a yield in excess of 80%. A thorough investigation of the raw material preparation and of the growing conditions has led to a significant improvement in the optical transparency and in the light yield of the crystals. A detailed understanding of the light emission mechanism was 1995. A systematic analysis of the parameters influencing the structural quality of the crystals was at the origin of a considerable improvement of the radiation hardness of full size crystals. All these progress will be illustrated by results of measurements on a statistically representative number of crystals. The conditions of these improvements will be discussed in the context of the mass production of more than 80,000 crystals in a cost effective way.