Calcium molybdate is considered as a very promising scintillator material for experimental studies of rare processes. This paper reports on the production and characterization of a 40Ca100MoO4 scintillator. Using the Czochralski technique, a crystal of high optical quality with total mass 0.55 kg, 42 mm diameter (minimum) and 53 mm 1ength of the cylindrical section was produced from isotopically enriched raw materials, containing 96.1% of 100Mo and 99.964% of 40Ca. To satisfy the requirement of low intrinsic radioactivity the purity of the materials was monitored at different stages of the production process and it is shown that the concentration of 238U and 232Th in the final crystal does not exceed 0.05 ppb. The scintillation properties of 40Ca100MoO4 were measured over the 8 – 300 K temperature range and it is found that the light yield of the 40Ca100MoO4 crystal is very similar to that of the CaMoO4 reference scintillator.
Isotopically enriched materials are important for particle physics experiments searching for rare events. Motivated by this we initiated a program aiming at the development of a production technology for 40Ca100MoO4 crystals with ultra-low intrinsic radioactive background and high scintillation light yield. The level of enrichment of 100Mo and 40Ca used for crystal growth is 96.1% and 99.964% respectively. The starting materials were subjected to extensive purification that allowed reducing the concentration of natural radioactive isotopes of U and Th to below 0.05 ppb. It should be mentioned that the study of intrinsic radioactivity of this crystal were carried out when this paper was under reviewing and they will be published soon. Fig.3 Temperature dependence of long scintillation decay constant of 40Ca100MoO4 crystal. Excitation with 5.5 MeV α-particles (241Am source). Fig.4 Temperature dependence of light output of 40Ca100MoO4 and reference CaMoO4 crystals measured for excitation with 5.5 MeV α-particles (241Am source). For the first time a large (0.55 kg) 40Ca100MoO4 crystal of good optical quality was produced and characterized. The light yield of the crystal is shown to be comparable with the reference CaMoO4 scintillators throughout the wide 40Ca100MoO4 temperature range down to 8 K. These promising results as well as the availability of production capacities for enriched materials, ultra-pure raw materials and large crystals form an important capability, underpinning the application of this material in large-scale experimental searches for neutrinoless double beta decay.
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