Large Volume ${\rm ZnWO}_{4}$ Crystal Scintillators With Excellent Energy Resolution and Low Background

Large volume zinc tungstate crystal scintillators with improved scintillation characteristics were produced. Energy resolution and relative light output of samples with various sizes and shapes (cylinders, rectangular, and hexagonal prisms) were investigated. The energy resolutions of ZnWO₄ scintillator modules for the 662 keV gamma line of ¹³⁷Cs were 8.5% for a 1 cm³ sample and 10.7% for the large hexagonal module of dimensions diam 40 times 40 mm. A variation of the light output by 7%, depending on direction of observation was found for the 1 cm³ cubic crystal. Afterglow, measured 20 ms after termination of irradiation, was 0.002%. The relative light output of the scintillator and the decay kinetics were studied over the temperature range 7-300 K. The level of radioactive contamination of the ZnWO₄ scintillator was determined in the Solotvina Underground Laboratory at a sensitivity of ap0.1-10 mBq/kg.