S. Burachas

First study of radiation hardness of lead tungstate crystals at low temperatures

The electromagnetic calorimeter of PANDA at the FAIR facility will rely on an operation of lead tungstate (PWO) scintillation crystals at temperatures near -25 deg.C to provide sufficient resolution for photons in the energy range from 8 GeV down to 10 MeV. Radiation hardness of PWO crystals was studied at the IHEP (Protvino) irradiation facility in the temperature range from room temperature down to -25 deg.C. These studies have indicated a significantly different behaviour in the time evolution of the damaging processes well below room temperature. Different signal loss levels at the same dose rate, but at different temperatures were observed. The effect of a deep suppression of the crystal recovery process at temperatures below 0 deg.C has been seen.

Influence of variable tungsten valency on optical transmittance and radiation hardness of lead tungstate (PWO) scintillation crystals

Abstract A new approach to interpret the radiation hardness of PbWO4 (PWO) scintillators is developed by revealing importance of the inclusions of tungsten oxides WO3−x with variable valency. It is demonstrated that the influence of the ionizing radiation on PWO is, in many aspects, similar to the effect of the high-temperature annealing in oxygenless ambient. In both cases, a valency change of the tungsten oxides is initiated and results in induced absorption and, consequently, in crystal coloration. In the PWO crystals doped with L2O3 (L=Y,La,Gd), the radiation hardness and the optical properties are mainly affected by inclusions of W1−yLyO3−x (0

Development of the technology for large-scale production of lead tungstate single crystals for physical experiments

The scientific principles underlying the technology for growing crystals of lead tungstate PbWO4 (PWO) with controlled properties are discussed. The developed technology is implemented at the North Crystals Company in mass production of PWO crystals with 100% reproducibility of operating parameters. This made it possible to solve the problem associated with the preparation of PWO crystals for the ALICE experiment at CERN and to produce the pilot batch of large-sized PWO crystals (diameter, 46 mm; length, 250 mm) with required characteristics for the CMS experiment at CERN. More than 10000 PWO scintillators of high optical quality for the ALICE experiment were fabricated over a short time according to the proposed technique.

Specific features of the technology for large-scale processing of lead tungstate crystals for research in the field of high-energy physics

The technology for large-scale processing of lead tungstate crystals intended for investigations in the field of high-energy physics is implemented with the use of the processing equipment at the North Crystals Company. The quality of the PWO scintillators manufactured by the company satisfies the requirements of the ALICE and CMS experiments at CERN. More than 8000 scintillators for the ALICE project and the pilot batch of scintillators for the CMS project have been fabricated.