This will slowly darken the tube and was thought to degrade the quality of the X-ray beam. Over time, tungsten will be deposited from the target onto the interior surface of the tube, including the glass surface. The rest of the energy is released as heat. About 1% of the energy generated is emitted/radiated, usually perpendicular to the path of the electron beam, as X-rays. Įlectrons from the cathode collide with the anode material, usually tungsten, molybdenum or copper, and accelerate other electrons, ions and nuclei within the anode material. The X-ray spectrum depends on the anode material and the accelerating voltage. A high voltage power source, for example 30 to 150 kilovolts (kV), called the tube voltage, is connected across cathode and anode to accelerate the electrons. The smooth, continuous curve is due to bremsstrahlung, and the spikes are characteristic K lines for rhodium atoms.Īs with any vacuum tube, there is a cathode, which emits electrons into the vacuum and an anode to collect the electrons, thus establishing a flow of electrical current, known as the beam, through the tube. Spectrum of the X-rays emitted by an X-ray tube with a rhodium target, operated at 60 kV. This followed the electronics technology of switching power supplies (aka switch mode power supply), and allowed for more accurate control of the X-ray unit, higher quality results, and reduced X-ray exposures. In the late 1980s a different method of control was emerging, called high speed switching. Until the late 1980s, X-ray generators were merely high-voltage, AC to DC variable power supplies. It works with a very good quality vacuum (about 10 −4 Pa, or 10 −6 Torr). The Coolidge tube, also called hot cathode tube, is the most widely used. The Crookes tube was improved by William Coolidge in 1913. These first generation cold cathode or Crookes X-ray tubes were used until the 1920s. 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. 4 Hazards of X-ray production from vacuum tubes.
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