CdWO4 Scintillation Crystal

Cadmium tungstate (CdWO₄) is a high density, high atomic number scintillator with a relatively high light yield. The emission maximum is at 475nm and the total light output is 12 to 15 photons/keV. The light yield relative to NaI(Tl) on a bialkali PMT is 30 to 50%.

The high light output and low afterglow make it ideal for use with silicon photodiodes in detectors for medical and industrial Computed Tomography (CT) scanners. It has very good radiation resistance, and its temperature dependence is small in the 0 to 60^oC range. Its high density makes it a good choice for 300+ keV imaging for security luggage, container and vehicle scanning for security.

The intensity of the scintillation emission of CdWO₄ (irradiation with γ-rays) at room temperature (25^oC), the curve is relatively flat (-0.1%/^oC) which can be important for some applications. For further technical information, see IEEE NS, Volume 41, No. 4, August 1994.

The intensity of the scintillation emission of CdWO₄ as a function of wavelength distribution is a good match to photodiodes. CT scanners for high and low energies have been built with CdWO₄. A long decay time of 14000 nanoseconds is not a drawback for CT scanners or other systems that operate with a current-mode readout.

Furthermore, CdWO₄ has a low afterglow. This is important in preventing glare and streaking in the generated images and allows for faster processing.

The high density and stopping power make it an efficient absorber. It takes only 3mm to stop up to 150keV photons. CdWO₄ shows a very good radiation resistance: for doses of 104 Gray (106 rad) γ-rays, the optical transmission of the crystal decreases less than 15%. For β-particles, this effect is even smaller: less than 6% for 10⁵ Gray (10⁷ rad).