- noun an evacuated tube in which a stream of high-energy electrons hits a metal target to produce X-rays
- An electron tube, usually a vacuum tube, which produces X-rays. In such a device, a beam of electrons emitted by a thermionic cathode is accelerated by an electrostatic field and directed towards the target electrode, which is usually the anode. The target electrode may be made, for instance, of tungsten or a tungsten alloy, and releases X-rays when bombarded by the electron beam, and in addition helps to dissipate the enormous heat created. The voltage across such a tube may range from a few thousand kilovolts to over a megavolt, depending on the application. Used, for instance, in X-ray spectrometers and X-ray machines.