Last years some experimental studies of VGF method use for alkali halide crystals were described [1]. These studies were directed to the development of an efficient industrial technique.  The most important peculiarity is the use of skull layer for prevention of the melt-crucible contacts [2]. It allows to use Pt free crucible and minimize internal stresses due to the luck of adhesion between crucible and crystal.

This time the crystallization rate for such technique was studied by the melt level control from the melting stage to the full crystallization completed. The melt level control system as used for continuous halide crystal growth [3] was installed inside skull techniques furnace and successfully controlled the melt level. The melt level change (test accuracy was about 100 micro meters) allows to justify crystallization rate for flat shaped crystal-melt interface as this is typical for VGF technology [4]. Math simulation of the convection in the melt, the melt-interface shape and finally the crystallization rate was done on the base on CGSim softare [5]. Simulations corresponds to NaI crystal and melt parameter for the experimental set-up with crystallization volume 250x180x90mm³. 

The very good correlation between modeling and experimental data related to the melt level down and proper mass crystallization growth rate is found. This methodology was successfully used for the industrial sizes NaI(Tl) scintillation crystal growth. In particular, fully authomized VGF technology was developed for skull technique/technology.

[1] V. Taranyuk, A. Gektin, I. Kisil, A. Kolesnikov,  NaI(Tl) and CsI(Tl) scintillation crystal growth by skull method, Journal of Crystal Growth  318 (2010) 820 – 822.

[2] I.I. Kisil, V.I. Taranyuk, S.V. Yaroslavkin, Growing of NaI:Tl crystal plates in garnissage, Functional Materials 15 4 (2008) 600-603.

[3] V.I. Goriletsky, V.A. Nemenov, V.G. Protsenko, A.V. Radkevich, L.G. Eidelman, J., Automated pulling of large alkali halide single crystals, Journal of Crystal Growth 52 (1981) 509-503.

[4] F.-M. Kiessling, F. Büllesfeld, N. Dropka, Ch. Frank-Rotsch, M. Müller, P. Rudolph,  Characterization of mc-Si directionally solidified in travelling magnetic fields, Journal of Crystal Growth  360 (2012) 81-86.

[5] http://www.str-soft.com/products/CGSim

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1. Optimization of bottom heater parameters at growth of large BGO crystals by conventional czochralski method
2. Optimization of bottom heater parameters at growth of large BGO crystals by conventional Czochralski method