X-ray tube

Device for the creation of x-rays.

In a vacuum, electrons are released to a cathode (filament, extraction grid) by a filament current and accelerated by a connected high voltage. When the electrons strike the cathode or target (usually tungsten), x-rays are released. These consist of the bremsspectrum and the characteristic radiation of the cathode or target material. However, the majority of the electrons’ energy is changed into heat upon collision, which is why it is important to cool the x-ray tubes.

X-ray tubes create peak energies of < 1 MeV (mega electron volts); usually, in the testing of castings, tubes with < 500keV are used. If higher energies are required, for example in the testing of components with thick walls made of iron materials, this is usually done with a linear accelerator. X-ray tubes are often categorized as standard, mini-focus and micro-focus tubes, depending on the size of their  focal spot. The focusing of the electron beam which is necessary for this is ensured with the help of electron optics in the tubes. The focal spot also determines the radiation intensity which can be created with an x-ray tube: In tubes with large focal spots, more radiation intensity can be obtained than in tubes with small focal spots.

Further references:
Computed tomography
2D computed tomography
3D computed tomography