EVALUATION OF ACTIVITIES OF IMPURITY RADIONUCLIDES IN CADMIUM TUNGSTATE CRYSTALS

The content of radioactive impurities in cadmium tungstate crystals (i ncluding those enriched with Cd-116 to 83%) was evaluated by analysis of the amplitude and amplitude-time background spectra of these scinti llators. One of the (CdWO4)-Cd-116 samples contained Cs-137 With an ac tivity of 1.5 +/- 0.4 mBq/kg and Th-232 (0.017 +/- 0.005 mBq/kg); a sa mple of CdWO4 contained K-40 (3.6 +/- 2.0 mBq/kg) and Th-232 (0.015 +/ - 0.008 mBq/kg), The limiting contents of Co-60, Sr-90, Pt-190, Ra-226 , U-235, and U-238, the levels 10(-3)-10(-6) Bq/kg. A sample of (CdWO4 )-Cd-116 showed the surface localization and a considerable (more than 20-fold) violation of the equilibrium for the U-238 series. The cadmi um tungstate crystals are shown to be superior to other widely employe d scintillation detectors with respect to the content of radioactive i mpurities.