Why Does X-Ray Machines Require Tungstate Materials?
Tungstate is a typical self-activated luminescent material. Its luminescence spectrum is very stable, and its intrinsic luminescence spectrum is very wide and occupies most of the visible region.
The cation in the tungstate strongly affects the position of the emission band. With the increase of atomic number of the cation, the peak shift of the emission band is blue, and the bandwidth is from 250 to 300 nm.
It was not long before Roentgen discovered X-rays in 18 century, people use the penetrating power of the rays to check the internal condition of the human body or objects, and to observe or photograph the image directly by the enhancement of the ray emitting material. In 1896 found that CaWO4 can be used as phosphor, in 1906, Puppin first used CaWO4 as X-ray luminescent material. In 1916, Patterson made it a luminescent material for X-ray intensifying screen. In recent years, a great deal of research work has been done on the luminescence properties of single tungstate doped with rare earth ions, especially for doping rare earth ions.
Some scholars have found that tungstate luminous brightness increases with the purity of the compound. Tungstate can be activated by some impurities, which are doped into the tungstate lattice and then give it a special property of luminescence. There are not many kinds of impurities, almost limited to rare earth elements.
In 1948, some scholars studied the tungstate materials doped with rare earth powder. It was found that Ba, Ca, Cd and Zn tungstate showed good scintillation at room temperature, shortly thereafter, American scholars used the Vemuil method to grow CaWO4 and CdWO4 single crystals, although their light output is lower than that of halide crystals, the density is large and the afterglow is weak, in particular, CdWO4 single crystal has high absorption coefficient of X-ray, good light transmission performance and strong radiation resistance, and is soon used as X-ray fluorescence intensifying screen. With the high energy physics electronic collider accelerator, scintillation detector is widely used to explore the new scintillation crystal and its luminous characteristics once again become a hot spot.
It is worth mentioning that ZnWO4 crystal is a promising scintillator in this field. It has the advantages of high density, high light output and short attenuation time, not easy to deliquescence. It can make up for the shortcomings of traditional scintillator NaI and CsI. At present, ZnWO4 single crystals have been used as scintillation crystals, Cambridge University Cavendish Laboratory, the American Cancer Institute and the German company Siemens are used to make radiometric detector and X-CT probe.
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