Abstract: Neutrinoless double beta decay (0ν2β decay) process is considered the most probable to happen on the molybdenum-100 nucleus. Thus, molybdate-based crystalline scintillators are of great interest for large-scale neutrino search projects. The extreme rarity of double beta decay (for the Mo-100 nucleus - 1028 years) imposes the strictest requirements on molybdate crystal scintillators used in projects. In addition to the general requirements for scintillators - high optical quality, luminescence intensity, light output, energy resolution, the material must also contain a minimum amount of impurities and have an ultra-low radiation background. The low-thermal-gradient modification of Czochralski technique (LTG Cz) developed at NIIC SB RAS is a unique technology for obtaining large oxide crystals of high optical quality in bulk volume. LTG Cz has significant structural differences from the conventional Czochralski technique resulting in temperature gradients being reduced by two orders of magnitude to values less than 1 deg/cm. Thus, the processes of volatilization of the melt components are suppressed, the loss of expensive isotopically enriched molybdenum-100 during growth process is prevented, the number of thermoelastic stresses and defects in growing crystal is reduced. Based on literature data, alkali metal polymolybdates M+1xMoyOz are not hygroscopic, have a higher density and molybdenum content per unit volume than already developed molybdate scintillator Li2MoO4 [1, 2]. The study of the phase diagrams of Li2O-MoO3, Na2O MoO3 and Cs2O-MoO3 showed that intermediate compounds MxMoyOz melt congruently at temperatures below 1000 °C, thus, they fit into the paradigm of LTG Cz crystal growth.

Cite: Grigorieva V.D. , Kremlev A.D. , Shlegel V.N.
Growth of polymolybdate scintillating crystals by the low-thermal-gradient Czochralski technique
8th Asian Symposium on Advanced Materials 03-07 Jul 2023