Improvement of optical properties and radiation hardness of NaBi(WO4)2 Cherenkov crystals

On the basis of the data on melt evaporation while growing NaBi(WO4)2 Cherenkov crystals, the formation of nonstoichiometry and most probable types of dot defects of the crystals have been considered. The influence of melt nonstoichiometry and doping with Sc on optical transmission and radiation hardness of the crystals has been experimentally investigated. The surplus of WO3 has been established to increase optical transmission and radiation hardness and lack of Bi2O3 in the melt to reduce radiation hardness. Sc doping is shifting the absorption edge to UV region by 30–35 nm and is increasing radiation hardness of the crystals about three-fold. Analytical estimations give the increase of the number of Cherenkov photons by a factor of 1.3, which leads to an improvement of the energy resolution of a calorimeter based on NaBi(WO4)2:Sc crystals compared with undoped NaBi(WO4)2 of approximately 15%.