Cadmium tungstate
Encyclopedia
Cadmium tungstate the cadmium
salt of tungstic acid
, is a dense, chemically inert solid which is used as a scintillation crystal
to detect gamma ray
s. 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 . It is not hygroscopic.
The crystal is transparent and emits light when it is hit by gamma ray
s and x-ray
s, making it useful as a detector of ionizing radiation
. Its peak scintillation wavelength is 480 nm
(with emission range between 380-660 nm), 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). It is often used in computed tomography
. Combining the scintillator crystal with externally applied piece of boron carbide
allows construction of compact detectors of gamma rays and neutron radiation
.
Cadmium tungstate was used as a replacement of calcium tungstate in some fluoroscopes since 1940's. Very high radiopurity allows to use this scintillator as a detector of rare nuclear processes (double beta decay, other rare alpha and beta decays) in low-background applications. For example, the first indication of the natural alpha activity of tungsten (alpha decay of 180W) had been found in 2003 with CWO detectors . Due to different time of light emission for different types of ionizing particles, the alpha-beta discrimination technique has been developed for CWO scintillators.
Cadmium tungstate films can be deposited by sol-gel technology. Cadmium tungstate nanorod
s can be synthesized by a hydrothermal process.
Similar materials are calcium tungstate (scheelite
) and zinc tungstate.
It is toxic, as are all cadmium compounds.
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
salt of tungstic acid
Tungstic acid
Tungstic acid refers to hydrated forms of tungsten trioxide, WO3.The simplest form, the monohydrate, is WO3.H2O, the dihydrate WO3.2H2O is also known. The solid state structure of WO3.H2O consists of layers of octahedrally coordinated WO5 units where 4 vertices are shared. the dihydrate has the...
, is a dense, chemically inert solid which is used as a scintillation crystal
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
to detect gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s. It has density of 7.9 g
Gram
The gram is a metric system unit of mass....
/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 . It is not hygroscopic.
The crystal is transparent and emits light when it is hit by gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s and x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s, making it useful as a detector of ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
. Its peak scintillation wavelength is 480 nm
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
(with emission range between 380-660 nm), and efficiency of 13000 photons/MeV. It has a relatively high light yield, its light output is about 40% of NaI(Tl)
Sodium iodide
Sodium iodide is a white, crystalline salt with chemical formula NaI used in radiation detection, treatment of iodine deficiency, and as a reactant in the Finkelstein reaction.-Uses:Sodium iodide is commonly used to treat and prevent iodine deficiency....
, but the time of scintillation is quite long (12−15 μs). It is often used in computed tomography
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
. Combining the scintillator crystal with externally applied piece of boron carbide
Boron carbide
Boron carbide is an extremely hard boron–carbon ceramic material used in tank armor, bulletproof vests, and numerous industrial applications...
allows construction of compact detectors of gamma rays and neutron radiation
Neutron radiation
Neutron radiation is a kind of ionizing radiation which consists of free neutrons. A result of nuclear fission or nuclear fusion, it consists of the release of free neutrons from atoms, and these free neutrons react with nuclei of other atoms to form new isotopes, which, in turn, may produce...
.
Cadmium tungstate was used as a replacement of calcium tungstate in some fluoroscopes since 1940's. Very high radiopurity allows to use this scintillator as a detector of rare nuclear processes (double beta decay, other rare alpha and beta decays) in low-background applications. For example, the first indication of the natural alpha activity of tungsten (alpha decay of 180W) had been found in 2003 with CWO detectors . Due to different time of light emission for different types of ionizing particles, the alpha-beta discrimination technique has been developed for CWO scintillators.
Cadmium tungstate films can be deposited by sol-gel technology. Cadmium tungstate nanorod
Nanorod
In nanotechnology, nanorods are one morphology of nanoscale objects. Each of their dimensions range from 1–100 nm. They may be synthesized from metals or semiconducting materials. Standard aspect ratios are 3-5. Nanorods are produced by direct chemical synthesis...
s can be synthesized by a hydrothermal process.
Similar materials are calcium tungstate (scheelite
Scheelite
Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten. Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws...
) and zinc tungstate.
It is toxic, as are all cadmium compounds.