X-ray Tube Development
Inflatable X-ray tube is an early X-ray tube. In 1895, W.C. Roentgen discovered X-rays during a Croix tube experiment. Crookes tube is the earliest inflatable X-ray tube. After the tube is connected to high pressure, the gas in the tube is ionized. Under positive ion bombardment, the electrons escape from the cathode and collide with the target surface to generate X-ray after acceleration. Inflatable X-ray tube power, short life, difficult to control, has rarely been applied. In 1913, W. D. Coolidge invented a vacuum X-ray tube. Tube vacuum of not less than 10-4 Pa. The cathode is a direct thermal helical tungsten wire, and the anode is a metal target embedded in the copper end face. According to the purpose of the tube to choose the target and electron beam energy, commonly used tungsten as a target. In some uses, but also silver, palladium, rhodium, molybdenum, copper, nickel, cobalt, iron, chromium and other materials. The working temperature of the cathode is about 2000K, and the emitted electrons hit the target surface after being accelerated by tens of thousands to hundreds of thousands of volts. The cathode is surrounded by a front-end slotted metal cover. The potential of the metal cap is equal to or lower than that of the cathode, forcing the electrons to focus on a narrow area on the target surface, forming a focal spot. X-ray radiation from the focal spot in all directions, through the window on the tube wall output. Windows are generally made of beryllium, aluminum or light-weight glass that absorbs very little X-rays, with beryllium being the best.
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