Cadmium tungstate

Cadmium tungstate (CdWO₄ or CWO), the cadmium salt of tungstic acid, is a dense, chemically inert solid which is used as a scintillation crystal to detect gamma rays. It has density of 7.9 g/cm³ and melting point of 1325 °C. It is toxic if inhaled or swallowed. Its crystals are transparent, colorless, with slight yellow tint. It is odorless. Its CAS number is 7790-85-4.^[2] It is not hygroscopic.

Cadmium tungstate

Names
IUPAC name Cadmium(II) tungstate
Identifiers
CAS Number	7790-85-4 Y
3D model (JSmol)	Interactive image
ChemSpider	10636623
ECHA InfoCard	100.029.297
EC Number	232-226-2
PubChem CID	3080645
UNII	ZNL5ZHP0Q7
InChI InChI=1S/Cd.4O.W/q+2;;;2*-1; Key: OUMLAYUZCYYIOD-UHFFFAOYSA-N
SMILES [O-][W](=O)(=O)[O-].[Cd+2]
Properties
Chemical formula	CdWO4
Molar mass	360.25 g·mol−1
Appearance	colorless crystals with a yellow tint
Density	7.9 g/cm3, solid
Melting point	1,325 °C (2,417 °F; 1,598 K)
Solubility in water	0.04642 g/100 mL (20 °C)
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H312, H332, H410
Precautionary statements	P261, P264, P270, P271, P273, P280, P301+P312, P302+P352, P304+P312, P304+P340, P312, P322, P330, P363, P391, P501
NIOSH (US health exposure limits):
PEL (Permissible)	[1910.1027] TWA 0.005 mg/m3 (as Cd)[1]
REL (Recommended)	Ca[1]
IDLH (Immediate danger)	Ca [9 mg/m3 (as Cd)][1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

The crystal is transparent and emits light when it is hit by gamma rays and x-rays, making it useful as a detector of ionizing radiation. Its peak scintillation wavelength is 480 nm (with emission range between 380 and 660 nm),^[3] and efficiency of 13000 photons/MeV. It has a relatively high light yield, its light output is about 40% of NaI(Tl), but the time of scintillation is quite long (12−15 μs).^[3] It is often used in computed tomography. Combining the scintillator crystal with externally applied piece of boron carbide allows^{[citation needed]} construction of compact detectors of gamma rays and neutron radiation.

Cadmium tungstate was used as a replacement of calcium tungstate in some fluoroscopes since the 1940s.^[4][5] Very high radiopurity allows use of this scintillator as a detector of rare nuclear processes (double beta decay, other rare alpha and beta decays) in low-background applications.^[6] For example, the first indication of the natural alpha activity of tungsten (alpha decay of ¹⁸⁰W) was found in 2003 with CWO detectors.^[7] Due to different time of light emission for different types of ionizing particles, the alpha-beta discrimination technique has been developed for CWO scintillators.^[8]

Cadmium tungstate films can be deposited by sol-gel technology. Cadmium tungstate nanorods can be synthesized by a hydrothermal process.^[9]

Similar materials are calcium tungstate (scheelite) and zinc tungstate.

It is toxic, as are all cadmium compounds.