<P> As 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 . A high voltage power source, for example 30 to 150 kilovolts (kV), is connected across cathode and anode to accelerate the electrons . The X-ray spectrum depends on the anode material and the accelerating voltage . </P> <P> In many applications, the current flow (typically in the range 1 mA to 1 A) is able to be pulsed on for between about 1 ms to 1 s . This enables consistent doses of X-rays, and taking snapshots of motion . Until the late 1980s, X-ray generators were merely high - voltage, AC to DC variable power supplies . In the late 1980s a different method of control was emerging, called high speed switching . 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 . </P> <P> Electrons from the cathode collide with the anode material, usually tungsten, molybdenum or copper, and accelerate other electrons, ions and nuclei within the anode material . About 1% of the energy generated is emitted / radiated, usually perpendicular to the path of the electron beam, as X-rays . The rest of the energy is released as heat . Over time, tungsten will be deposited from the target onto the interior surface of the tube, including the glass surface . This will slowly darken the tube and was thought to degrade the quality of the X-ray beam . Vaporized tungsten condenses on the inside of the envelope over the "window" and thus acts as an additional filter and decreases the tubes ability to radiate heat . Eventually, the tungsten deposit may become sufficiently conductive that at high enough voltages, arcing occurs . The arc will jump from the cathode to the tungsten deposit, and then to the anode . This arcing causes an effect called "crazing" on the interior glass of the X-ray window . As time goes on, the tube becomes unstable even at lower voltages, and must be replaced . At this point, the tube assembly (also called the "tube head") is removed from the X-ray system, and replaced with a new tube assembly . The old tube assembly is shipped to a company that reloads it with a new X-ray tube . </P> <P> The X-ray photon - generating effect is generally called the bremsstrahlung effect, a contraction of the German bremsen for braking, and strahlung for radiation . </P>

Where is radiation produced in the xray tube