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Cadmium tungstate - CdWO4
Properties of CdWO4 - Cadmium tungstate
General description Cadmium tungstate is a high density (7.9 g/cm3), high Z scintillator with a relatively large light yield. The emission maximum is situated in the 500 nm region and the total light yield is about 35-40% of NaI(Tl). However, since the emission of CdWO4 is at a much longer wavelength than that of NaI(Tl), the relative photoelectron yield amounts to only 25-30%. CdWO4 has two emission maxima, one at 470 nm and one at 540 nm. For y-ray irradiation, both components are excited and the emission spectrum shown in Fig.1 results. For irradiation with different types of radiation, the emission spectrum can be different. The intensity of the scintillation emission of CdWO4 as a function of the temperature is shown in Fig. 2 (irradiation with g-rays). At room temperature (300 K), the curve is very flat which can be important for some applications. The decay time of the 470 nm component is 20 µs, the 540 nm component has a 5 ms decay time. The afterglow of CdWO4 upon x-ray irradiation is very low, typically less than 0.1% after 3 ms. The material shows a very good radiation resistance: for doses of 104 Gray (106 rad) g-rays, the optical transmission of the crystal decreases less than 15%. For b-particles, this effect is even smaller: less than 6% for 105 Gray (107 rad). CdWO4 is a crystal that cleaves very easily and is therefore very susceptible to mechanical and thermal shock. Since some self-absorption of the scintillation light occurs, CdWO4 is usually not fabricated in large dimensions. Due to the high density of CdWO4, the crystal thickness to stop 150 keV photons is only 3 mm. The high stopping power and the low afterglow of CdWO4, together with the possibility to detect the scintillation light efficiently with photodiodes, make it an attractive scintillator for x-ray detection (e.g. in CT scanners).
Organic Products | Inorganic Scintillation Products | Crystal Products |
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