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Description
SrI2:Eu2+ crystals are among the brightest discovered scintillation crystals with the light yield over 100 000 ph/MeV and the energy resolution up to 3% at 662 keV [1]. Despite many reports on SrI2:Eu growth by the Bridgman method, no significant progress has been achieved in development of large size crystal growth technologies targeted at reduction of production cost.
This report represents for the first time the Czochralski growth of SrI2:Eu crystals with diameters of up to 50 mm. Czochralski method is optimal from the point of scaling up of crystal growth technology. The development of Czochralski process for highly hygroscopic substances includes the optimized conditions of raw materials preparation and their loading into the growth chamber, as well as precise control over admixture content in the raw materials and growth atmosphere. pH of the raw material water solution is shown to be a key criterion of the raw material quality [2].
Compositions, as well as optical and scintillation parameters of SrI2:Eu crystals grown by the Bridgman and Czochralski methods are compared. The Czochralski process provides a uniform distribution of Eu2+ across the crystals within +/-5 %. The latter factor favors a high energy resolution within 3.6 -3.7 % at 662 keV obtained in detectors fabricated from different parts of Czochralski-grown crystals. Such values of the energy resolution are similar to those obtained with SrI2:Eu2+ grown by the Bridgman method both in this work, and in other laboratories. This certifies a high purity and a good quality of the Czochralski grown crystals and demonstrates a feasibility to successfully produce SrI2:Eu2+, as well as other highly-hygroscopic halide scintillation crystals by the Czochralski method. The growth of 50 mm dia. crystals in R&D scale industrial furnaces is the first step in adaptation to the large size SrI2:Eu growth at industrial equipment. Further advance will be based on the well-developed growth technology of large CsI, CsI(Na) and NaI(Tl) alkali halide crystals with the diameter of up to 500 mm by the Modified Czochralksi-Kyropoulos method [3].
The work is supported by the NATO multiyear Science for Peace Project NUKR.SFPP 984958 "New sensor materials and detectors for ionizing radiation detection"
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