Tymoshenko M. Parameters optimization for process of АIВVII crystal growth from melt by continuous method

Complex investigation of growth processes of long-length (up to 300 mm) CsI(Na) and CsI(Tl) crystals up to 300 mm in diameter, and NaI(Tl) crystals up to 500 mm in diameter was realized in this work. All crystals were grown by continuous method at "ROST" type setups. Similarities in a formation mechanism of volume defects of crystalline structure were ascertained. It was demonstrated that heat exchange in growth furnace consist of three stages. Influence of melt condensate on the general heat exchange was determined. The possibility to control amount of condensate on the crystal surface by means of growth rate and change of growth atmosphere composition was shown. It allowing one to control the crystal-melt interface shape during crystal growth process. It has been found that at growth at maximal diameter ingots growth without additional temperature correction of side heater activator concentration increases with crystal length. This phenomenon is caused by increase of undermelt crystal volume due to intensification of heat transfer from crystal side surface to the periphery vessel of the crucible. A dependence between thermal lag of the "heater-crucible-crystal" system and growing crystal dimensions has been determined experimentally. A new double-circuit system of automated control above growth process, and a new algorithm of crystal diameter control with limitation of bottom heater temperature in correspondence with growth stage has been developed and introduced into industry of long-length crystal growth. Optimal growth parameters were established, allowing one to obtain single crystals for fabrication of scintillation elements with length 550 mm and improved by 25 % energy resolution (R=6,9%).