X-RAY

Electron guns (cathodes) for red, green, and blueElectron beamsFocusing coilsDeflection coilsAnode connectionShadow maskfor separating beams for red, green, and blue parts of the displayed imagePhosphorlayerClose-up of the phosphor layer showing red, green, and blue zones Deflection coilsElectron beamFocusing coilPhosphor layerFilament for heating the cathodeGraphite layer on the inner side of the tubeAnode connectionElectron gun (cathode)Air-tight glass body of the tubeScreenDeflection yokeControl electrode modulating the intensity of the electron beamContact pins for cathode, filament and control electrodeWire for anode high voltage Acathode ray tube(CRT) is avacuum tubecontaining one or moreelectron guns, which emitelectron beams, which are directed and controlled to display images on aphosphorescentscreen.The images may represent electricalwaveformson anoscilloscope, aframeofvideoon ananalogtelevision set(TV),digitalraster graphicson acomputer monitor, or other phenomena likeradartargets. A CRT in a TV is commonly called apicture tube. CRTs have also beenused as memory devices, in which case the screen is not intended to be visible to an observer. The termcathode raywas used to describe electron beams when they were first discovered, before it was understood that what was emitted from the cathode was a beam of electrons. A CRT works by electrically heating a tungsten coilwhich in turn heats a cathode in the rear of the CRT, causing it to emit electrons which are modulated and focused by electrodes. The electrons are steered by deflection coils or plates, and an anode accelerates them towards thephosphor-coated screen, which generates light when hit by the electrons.The entire front area of the tube is scanned repeatedly and systematically in a fixed pattern called araster. In color devices, an image is produced by controlling the intensity of each of threeelectron beams, one for each additiveprimary color(red, green, and blue).In modern CRT monitors and TVs, the beams are bent by magneticdeflection, using adeflection yoke.Electrostatic deflectionis commonly used inoscilloscopes. The tube is a glass envelope that is heavy, fragile, and long from the front screen face to its rear end. Its interior must be apartial vacuumto prevent the emitted electrons from colliding with air molecules and scattering before they hit the tube's face. Thus, the interior is evacuated to less than a millionth ofatmospheric pressure.As such, handling a CRT carries the risk of violentimplosionthat can hurl glass at great velocity. The face is typically made of thicklead glassor specialbarium-strontiumglass to be shatter-resistant and to block mostX-rayemissions. The CRT makes up most of the weight of CRT TVs and computer monitors. Since the late 2000s, CRTs have been superseded byflat-panel displaytechnologies such asliquid-crystal display(LCD),plasma display, andOLED, which are cheaper to manufacture and operate and are also significantly lighter and thinner. Flat-panel displays can also be made in very large sizes, whereas 40–45 inches (100–110 cm)was about the largest size of a CRT.