IMPROVEMENT OF SEVERAL PROPERTIES OF LEAD TUNGSTATE CRYSTALS WITH DIFFERENT DOPING IONS

A very good radiation resistance of lead tungstate crystals is mandato ry for their use in the high-precision electromagnetic calorimeter of the CMS experiment at LHC. Since the beginning of 1996 we have organis ed systematic investigations of the parameters influencing the radiati on hardness of this crystal. Two classes of parameters have been parti cularly studied, the first one related to the control of the stoichiom etry and structure-associated defects, the second one connected with t he suppression and the charge compensation of existing defects with di fferent kinds of doping ions. This paper reports about the second part of this study and complements a first paper where the role of the sto ichiometry was already discussed. Results of tests are given on a sign ificant statistical sample of full size crystals (23 cm) which show a considerable improvement in the optical properties and the radiation r esistance of appropriately doped crystals.