X-ray tube
![Coolidge X-ray tube, from around 1917. The heated cathode is on the left, and the anode is right. The X-rays are emitted downwards.](/Images/godic/202501/06/Coolidge_xray_tube5927.jpg")
![Simplified rotating anode tube schematic A: AnodeC: cathodeT: Anode targetW: X-ray window](/Images/godic/202501/06/Xraytubeinhousing_commons5927.png")
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![Spectrum of the X-rays emitted by an X-ray tube with a rhodium target, operated at 60 kV. The smooth, continuous curve is due to bremsstrahlung, and the spikes are characteristic K lines for rhodium atoms.](/Images/godic/202501/06/TubeSpectrum5927.jpg")
An X-ray tube is a vacuum tube that converts electrical input power into X-rays. X-ray tubes evolved from experimental Crookes tubes with which X-rays were first discovered on November 8, 1895, by the German physicist Wilhelm Conrad Röntgen. The availability of this controllable source of X-rays created the field of radiography, the imaging of partly opaque objects with penetrating radiation. In contrast to other sources of ionizing radiation, X-rays are only produced as long as the X-ray tube is energized. X-ray tubes are also used in CAT scanners, airport luggage scanners, X-ray crystallography, material and structure analysis, and for industrial inspection.