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 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.
Properties | Value |
---|---|
Density [g/cm3] | 7.9 |
Melting point [K] | 1598 |
Thermal expansion coefficient [C-1] | 10.2 x 10-6 |
Cleavage plane | <010> |
Hardness (Mho) | 4-4.5 |
Hygroscopic | No |
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 |