Kolesnikov A. Doping as control method above thermophysical properties of a crystal and melt during growth of scintillation materials

The thesis is devoted to investigation and development method for modification of thermophysical properties of CsI:Tl and NaI:Tl crystals and melts by their doping. Peculiarities of influence of material admixture composition on large crystals growth process stability, crystallization rate and quality of single crystal ingots, obtained by the method of pulling from the melt on seed is established. It is shown that addition of impurities into the crystal and melt, which absorb infrared radiation, allows to intensity heat transfer from crystal-melt interface due to the increase of radiant component. Here in, axial temperature gradient near the crystal-melt interface, temperature in the volume and on the melt surface increase. It is experimentally proved that СО32– and NO2– ions are the most suitable dopants. Crystal doping in the concentration range from 5·10–5 to 3·10–4 mol. % decreases the probability of parasitic crystallization on the crucible, prevents formation of flat or convex toward the crystal crystal-melt interface and gives possibility to increase the pulling rate of ingots by 30%. It is shown that dynamics of temperature change of controlling heater can serve as the criterion allowing to estimate the course of heat and mass transfer processes during crystal growth. The automated control system with high service and technical characteristic is developed and introduced into industry. The influence of technical and technological factors on accuracy of diameter control system is determined. Key words: crystal growth, doping, absorption coefficient, radiative and conductive heat transfer.