A vacuum electronic device which produces x-rays by using high-speed electrons to hit a metal target. The X-ray tube can be divided into two types: inflatable tube and vacuum tube according to the way of producing electrons.
An inflatable X-ray tube is an early X-ray tube. In 1895, W. C. Roentgen discovered X-rays during the Crookes tube experiment. The Crookes tube is the first gas-filled X-ray tube. After the tube is connected with high pressure, the gas is ionized in the tube, and electrons are escaping from the cathode under the positive ion bombardment, and the X-rays are produced by accelerating the impact of the target surface. The gas-filled X-ray tube has little power, short life and difficult control. In 1913, W. D. Kuligi invented the vacuum X-ray tube. Tube Vacuum degree not less than 10-4 kpa. The yin is extremely straight hot spiral tungsten wire, and the metal target inlaid by the anode of the copper block. The target material and the electron beam energy are selected according to the use of the pipe. In some uses, it also uses silver, palladium, rhodium, molybdenum, copper, nickel, cobalt, iron, chromium and other materials. The cathode operating temperature is about 2000K, and the electrons emitted from tens of thousands of to hundreds of thousands of volts are accelerated to impact the target surface. The cathode is surrounded by a metal shroud with a front-end slot. The potential of the metal cover is equal to or below the cathode, forcing the electron to focus on a narrow area on the target to form a focal spot. X-rays radiate from the focal spot to each direction and output through the window of the tube wall. The window is generally made of beryllium, aluminum or light glass, which absorbs very little of the X-rays, and is best for beryllium films.