M. Korzhik

Lead tungstate (PbWO4) scintillators for LHC EM calorimetry

Abstract This report describes the work carried out in order to analyse the properties of PbWO4 crystals as scintillators and to determine the perspectives of their use in calorimetry in Large Hadron Collider (LHC) experiments. The scintillation mechanism in PWO crystals is explained and the properties connected with their use as scintillators are analysed both for undoped and Nb doped crystals. The specific problems concerning the physical parameters in the case of large scale production of PWO scintillators are discussed.

Lead tungstate scintillation material

In this paper we summarize the results of a research programme on lead-tungstate (PWO) crystals performed by the CMS Collaboration at CERN, as well as by other groups who promoted the progress of the PWO scintillation crystal technology. Crystal properties, mass production technology, scintillation mechanism, origin of colouring, defects in crystal and radiation induced phenomena, light yield improvement and results of beam tests are described.

On the origin of the transmission damage in lead tungstate crystals under irradiation

The origin of the transmission damage in PWO crystals is discussed. It is shown that both electron and hole centers created on the basis of structural defects in PbWO 4 crystals contributed to the induced absorption of the crystals. The different aspects of the suppression of the recharge processes in PWO scintillation crystals are also discussed.

Improvement of several properties of lead tungstate crystals with different doping ions

Abstract A very good radiation resistance of lead tungstate crystals is mandatory for their use in the high-precision electromagnetic calorimeter of the CMS experiment at LHC. Since the beginning of 1996 we have organised systematic investigations of the parameters influencing the radiation hardness of this crystal. Two classes of parameters have been particularly studied, the first one related to the control of the stoichiometry and structure-associated defects, the second one connected with the suppression and the charge compensation of existing defects with different kinds of doping ions. This paper reports about the second part of this study and complements a first paper where the role of the stoichiometry was already discussed. Results of tests are given on a significant statistical sample of full size crystals (23 cm) which show a considerable improvement in the optical properties and the radiation resistance of appropriately doped crystals.

Improved light yield of lead tungstate scintillators

Abstract The application at medium and low energies of lead tungstate scintillators, so far optimized for the ECAL calorimeter of CMS for the future LHC, is strongly limited by their poor light yield. Suitable dopants like molybdenum and terbium can help to overcome this problem. Concepts, results, advantages and drawbacks of this approach are discussed.

Systematic study of the short-term instability of PbWO4 scintillator parameters under irradiation

The effect of irradiation on lead tungstate PbWO4 (PWO) scintillator properties has been studied at different irradiation facilities. Lead tungstate crystals, grown with the oxide content in the melt tuned to the stoichiometry of pure sheelite or sheelite-like crystal types and doped with heterovalent, trivalent and pentavalent impurities, have been studied in order to optimize their resistance to irradiation. A combination of a selective cleaning of raw materials, a tuning of the melt from crystallization to crystallization and a destruction or compensation of the point-structure defects has to be used to minimize the short-term instability of PWO parameters under irradiation.

Origin of scintillation in cerium‐doped oxide crystals

We propose here a model of the scintillation from complex oxide single crystals doped with Ce3+ ions to explain the correlation observed between scintillation light yield and intrinsic luminescence of the matrix.

A first electromagnetic calorimeter prototype of PbWO4 crystals

Abstract The main properties of PbWO4 crystals have been measured. They are of particular interest for electromagnetic calorimetry. Beam tests of 21-cells matrix prototype are reported. An energy resolution better than 1% has been achieved for electrons energies larger than 25 GeV.

Slow components and afterglow in PWO crystal scintillations

Abstract The origin of the slow component and of the afterglow in PWO scintillation is discussed. It is shown that their presence depends strongly on the growth conditions and originates from specific impurities and host point-structure defects. The influence of the scintillation kinetics parameters on the detection properties of PWO crystals is discussed.

On the Mechanism of Radiation Damage of Optical Transmission in Lead Tungstate Crystal

A model of the radiation-induced absorption and its recovery in lead tungstate crystals is proposed. This model, which describes small variations of the crystal light yield, can be used to improve the precision of electromagnetic calorimeter monitoring. In this paper we describe the transmission damage and recovery phenomena in lead tungstate crystals through the contribution of different colour centres in the radiation-induced absorption in lead tungstate crystals.