| Fig. 1. Gamma spectrum of 207-Bi with CWO crystal scintillator |
 |
Fig. 2. Large single crystals of CWO |
 |
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 [1]. Developed in [2] 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 [1].
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 [3] and 106Cd [4], investigation of 4th forbidden β decay of 113Cd [5], search for α decays of W isotopes [6]), 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%).
1. S.Ph.Burachas et al., Nucl. Instrum. and Meth. A
369(1996)164;
A.Sh.Georgadze et al., Instr. and Exp. Technique
39(1996)359.
2. T.Fazzini et al., Nucl. Instrum. and Meth. A 410(1998)213.
3. F.A.Danevich et al., Phys. Lett. B 344(1995)72;
Phys. Rev. C 62(2000)045501; Phys. Rev C 68(2003)035501.
4. F.A.Danevich et al., Z. Phys. A 355(1996)433.
5. F.A.Danevich et al., Phys. At. Nucl. 59(1996)1.
6. A.Sh.Georgadze et al., JETP Lett. 61(1995)882;
F.A.Danevich et al., Phys. Rev. C 67(2003)014310.
| Characteristic [units] | Value |
|
Effective atomic number Density [g/cm3] Melting point [K] Cleavage plane Hardness [Mohs] Hygroscopicity Wavelength of emission max [nm] Index of refraction Average decay time [μs] Afterglow (after 3 ms) [%] Light yield [% of NaI(Tl)] |
64 7.9 1598 <010> 4-4.5 No 470/540 2.3 12 0.1 25-40 |
| Fig. 1. Gamma spectrum of 207-Bi with CWO crystal scintillator |
|
Fig. 2. Large single crystals of CWO |
|