Contribution Oral presentation
Developing of Scintillation crystals for Calorimetry and Astroparticle Physics
Development of detector materials takes place both due to the search of new scintillation crystal, and by improvement of growing technology for already known crystals. Basically scintillation crystals are grown by traditional techniques under high temperature gradient conditions. In most cases, the temperature gradients nearly growth interface are in the range 40-200 K/cm. In such conditions thermoelastic stress and melt superheating are inevitable. In some cases, especially when it is necessary to grow large size crystals or crystals with strong anisotropy of the thermal properties and low mechanical strength, high thermal gradients lead to the destruction of crystals and that is a major obstacle to growth of high quality crystals. The melt superheating leads to volatility of charge components, disruption of stoichiometry and inhomogeneity functional properties of crystal. In the report the results of growth of top quality scintillation crystals at low temperature gradient (LTG) conditions is presented. In LTG CZ technique temperature gradients are reduced by two orders of magnitude in comparison with the conventional crystal growth techniques. The results of growing BGO crystals large size (up to 60 kg) with high radiation hardness are presented. The advantages of use LTG CZ technique for growth of isotopically enriched crystals used for rare events searches are most essential. The crystal growth for these applications generally is associated the use of very expensive raw materials (high radio purity, isotopically- enriched composition,etc.) which is available in a very limited quantity. In addition for these projects requirements to crystal quality are very high. Another essential requirement is a need to obtain the maximum possible weight of a crystal from initial charge. The ossibility of the LTG technique are demonstrated on example of successful growth of isotopically enriched crystals 106CdWO₄ and 116CdWO₄ with duty factor about 85% are presented. Growth of large sized ZnMoO₄ crystals including development of precursor's synthesis starting from Mo metal and recycling of residuals for producing isotopically enriched Zn100MoO₄ crystals for LUMINEU project are also reported.