Cadmium tungstate (CdWO4) is a high density, high atomic number scintillator with 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 density and stopping power of CdWO4 make it an efficient absorber, particularly for high energy X-ray. It takes only 3mm to stop up to 150keV photons.
CdWO4 high light output and low afterglow make it ideal for use with silicon photodiodes in detectors for medical and industrial CT scanners. CdWO4 has very good radiation resistance, and its temperature dependence is small in the 0 to 60oC range. Its high density makes it a good choice for 300+ keV imaging for container and vehicle scanning.
CdWO4 is non-hygroscopic and does not require a hermetic package. Crystals are typically provided in block or arrray form and is a good match to photodiodes.
Arrays with pixels as small as 0.3mm x 1mm have been provided. In other forms, round crystals range from 50mm diameter x .5mm minimum; for rectangular sizes, (depending on geometry), crystals can typically range in cross-sections as large as 130mm x 50mm or as thin as 10 microns (size dependant). Contact Saint-Gobain for specific applications and alternate sizes.
|Melting point [K]||1598|
|Thermal expansion coefficient [C-1]||10.2 x 10-6|
|Wavelength of emission max. [nm]||475|
|Lower wavelength cutoff [nm]||330|
|Refractive index @ emission max||2.2-2.3|
|Primary decay time [ns]||14000|
|Light yield [photons/keVγ]||12-15|
|Photoelectron yield [% of NaI(Tl)] (for γ-rays)||30-50|