A low-background scintillation spectrometer based on CdWO4 crystals of large volume (100-200 cm3) with improved energy resolution has been developed as a result of advances in crystal growth technology, optimization of light collection and design of a special electronic unit for amplification and shaping of CdWO4 signals . Developed in  pulse-shape discrimination method based on the optimal digital filter gives the possibility to clearly discriminate between γ rays (electrons) and α particles. The energy resolution of crystals with volume 80-150 cm3 is equal 10-12% for 662 keV γ rays. A value of 7-8%, which is comparable to that of NaI(Tl), has been obtained with small samples (10-20 cm3). The purity of CdWO4 crystals is very high; limits on internal contamination are equal (in μBq/kg):
<8 for 232Th,
<13 for 226Ra,
<4000 for 40K,
<300 for 137Cs and
<3000 for 90Sr .
The unique spectrometers based on CdWO4 crystals of large volume were developed for experiments in basic researches (search for forbidden in the Standard Model double β decay of 116Cd  and 106Cd , investigation of 4th forbidden β decay of 113Cd , search for α decays of W isotopes ), as well as for environmental control, well lodging and measurements of radioactive contamination in various samples. Sensitivity for the detection in 1 kg sample of standard earth is equal 1.2×10-12 Ci/kg for 40K and 2×10-13 Ci/kg for 208Tl (for a measuring time 24 h and with a statistical accuracy 30%).
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Effective atomic number
Melting point [K]
Wavelength of emission max [nm]
Index of refraction
Average decay time [μs]
Afterglow (after 3 ms) [%]
Light yield [% of NaI(Tl)]
|Fig. 1. Gamma spectrum of 207-Bi with CWO crystal scintillator|
Fig. 2. Large single crystals of CWO