Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Chemical compound
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. It is not hygroscopic.
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),[2] 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).[2] 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.[3][4] 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.[5] For example, the first indication of the natural alpha activity of tungsten (alpha decay of 180W) was found in 2003 with CWO detectors.[6] Due to different time of light emission for different types of ionizing particles, the alpha-beta discrimination technique has been developed for CWO scintillators.[7]
Cadmium tungstate films can be deposited by sol-gel technology. Cadmium tungstate nanorods can be synthesized by a hydrothermal process.[8]
Similar materials are calcium tungstate (scheelite) and zinc tungstate.
It is toxic, as are all cadmium compounds.
^ abcNIOSH Pocket Guide to Chemical Hazards. "#0087". National Institute for Occupational Safety and Health (NIOSH).
^ abBurachas S. F.; et al. (1996). "Large volume CdWO4 crystal scintillators". Nucl. Instrum. Methods Phys. Res. A. 369 (1): 164–168. Bibcode:1996NIMPA.369..164B. doi:10.1016/0168-9002(95)00675-3.
^Kroeger, F. A. (1948). Some Aspects of the Luminescence of Solids. Elsevier.
^Bardelli L.; et al. (2006). "Further study of CdWO4 crystal scintillators as detectors for high sensitivity 2β experiments: Scintillation properties and pulse-shape discrimination". Nucl. Instrum. Methods Phys. Res. A. 569 (3): 743–753. arXiv:nucl-ex/0608004. Bibcode:2006NIMPA.569..743B. doi:10.1016/j.nima.2006.09.094. S2CID 7311888.
^Danevich F. A.; et al. (2003). "α activity of natural tungsten isotopes". Phys. Rev. C. 67 (1): 014310. arXiv:nucl-ex/0211013. Bibcode:2003PhRvC..67a4310D. doi:10.1103/PhysRevC.67.014310. S2CID 6733875.
^Fazzini T.; et al. (1998). "Pulse-shape discrimination with CdWO4 crystal scintillators". Nucl. Instrum. Methods Phys. Res. A. 410 (2): 213–219. Bibcode:1998NIMPA.410..213F. doi:10.1016/S0168-9002(98)00179-X.
^Wang Y, Ma J, Tao J, Zhu X, Zhou J, Zhao Z, Xie L, Tian H (September 2006). "Hydrothermal synthesis and characterization of CdWO4 nanorods". Journal of the American Ceramic Society. 89 (9): 2980–2982. doi:10.1111/j.1551-2916.2006.01171.x.
Cadmiumtungstate (CdWO4 or CWO), the cadmium salt of tungstic acid, is a dense, chemically inert solid which is used as a scintillation crystal to detect...
Air Training Corps and the RAF Section of the Combined Cadet Force Cadmiumtungstate, a scintillator Cash With Order, a standard UK commercial term Chief...
polymerizes; alkaline soils cause monomeric tungstates; acidic soils cause polymeric tungstates. Sodium tungstate and lead have been studied for their effect...
"Tissue distribution of tungsten in mice following oral exposure to sodium tungstate," Chemical Research in Toxicology, vol. 24, no. 4, pp 488–493, doi:10...
different forms. Manganese, magnesium, cadmium and some nickel double molybdates exist as langbeinites. Double tungstates of the form A2B2(WO4)3 are predicted...
of decatungstate W 10O4− 32 comprises edge-sharing and corner-sharing tungstate octahedra). Heteroatoms aside from the transition metal are a defining...
exchange techniques. Terbium is used to dope calcium fluoride, calcium tungstate and strontium molybdate in solid-state devices, and as a crystal stabilizer...
intensity to be commercialized. Edison had quickly discovered that calcium tungstate screens produced brighter images. Edison, however, abandoned his research...
calcium tungstate (CaWO4) as a suitable phosphor, which quickly became the standard for X-ray intensifying film. In the 1970s, calcium tungstate was replaced...
Oligomerization, and Condensation Reactions of Vanadate(V), Molybdate(vi), and Tungstate(vi), Advances in Inorganic Chemistry, vol. 49, Academic Press, pp. 127–182...
content of beryllium to emit greenish light. Small additions of magnesium tungstate improved the blue part of the spectrum to yield an acceptable white light...
weight, and gout; it can also affect the lungs, kidneys, and liver. Sodium tungstate is a competitive inhibitor of molybdenum. Dietary tungsten reduces the...
S-type stars are recognised by detection of its emission lines. Zirconium tungstate has the unusual property of shrinking in all dimensions when heated, whereas...
18−19. ISBN 978-0-465-07265-1. Jensen, WB (2003). "The place of zinc, cadmium, and mercury in the Periodic Table". Journal of Chemical Education. 80...