Datsko Y. The development of methods for the precipitation deoxidation of the melt to produce single crystals of cesium iodide scintillator with improved parameters

The thesis is devoted to development of scientific and technological principles of manufacturing CsI single crystals with enhanced scintillation parameters due to deoxidization of the growth melt with the precipitation of admixtures. On the basis of potentiometric investigations the preliminary choice of cations appropriate for deoxidization of CsI melt was made. They are Mg2+, Eu2+, Be2+, Ni2+, Y3+. Mg2+ and Y3+ cations as forming the most refractory and practically insoluble in melts oxides were stated to be the most effective for the obtaining of scintillation crystals of good quality. Their use allows to decrease essentially the effective luminosity time of the fast components to 8 ns and to achieve 'Fast/Total' ratio values more than 0.8. Taking into account worse scintillation parameters of the corresponding crystals the use of other mentioned cations seems to be unsuitable. Processes of deoxidization of CsI melt using metals-getters (Ti, Ta, Zr) are investigated. It was found that the use of titanium and tantalum as forming relatively fusible oxides (~2200 K), is inappropriate because of dissolution of interaction products in the growth melt. On the contrary, action of zirconium forming refractory ZrO2 (~3000 K) permits to make deep purification of CsI melt, that leads to practically complete disappearance of the slow luminescence component in the grown crystals. Thereat "Fast/Total" values approach 0.9 and the effective luminosity time of fast components is 14 ns.