electron gun

Examples of electron gun in the following topics:

• Cathode Ray Tube, TV and Computer Monitors, and the Oscilloscope

  • A cathode ray tube consists of a vacuum tube that contains one or more electron guns used to excite phosphors on a screen to produce images.
  • The cathode ray tube (CRT) is a vacuum tube containing one or more electron guns (a source of directed electrons) and a fluorescent screen used to view images.
  • It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images.
  • These phosphors are struck by incoming electrons from the electron gun, absorb energy, and then re-emit some or all of that energy in the form of light (this process is called phosphorescence) .
  • Cutaway rendering of a color CRT: 1) Three Electron guns (for red, green, and blue phosphor dots) 2) Electron beams 3) Focusing coils 4) Deflection coils 5) Anode connection 6) Mask for separating beams for red, green, and blue part of displayed image 7) Phosphor layer with red, green, and blue zones 8) Close-up of the phosphor-coated inner side of the screen

• de Broglie and the Wave Nature of Matter

  • It took three years for Clinton Davisson and Lester Germer to observe diffraction patterns from electrons passing a crystalline metallic target (see ).
  • The experiment included an electron gun consisting of a heated filament that released thermally excited electrons, which were then accelerated through a potential difference (giving them a certain amount of kinetic energy towards the nickel crystal).
  • To avoid collisions of the electrons with other molecules on their way towards the surface, the experiment was conducted in a vacuum chamber.
  • To measure the number of electrons that were scattered at different angles, an electron detector that could be moved on an arc path about the crystal was used.
  • The detector was designed to accept only elastically scattered electrons.

• The Atomic Bomb

  • On August 6th, 1945, a uranium gun-type fission bomb code-named "Little Boy" was detonated over the Japanese city of Hiroshima.
  • This is accomplished either by shooting one piece of sub-critical material into another, termed the "gun" method, or by compressing a sub-critical sphere of material using chemical explosives to many times its original density, called the "implosion" method.
  • The implosion method is considered more sophisticated than the gun method and only can be used if the fissile material is plutonium.
  • The immediate energy release per atom is about 180 million electron volts (Me).
  • The gun-type assembly uses a conventional explosive to compress from one side, while the implosion assembly compresses from all sides simultaneously.

• Indeterminacy and Probability Distribution Maps

  • A bullet propelled from a gun at a consistent velocity under identical conditions will always follow the same trajectory and hit the same target.
  • Based on numerous observations, the quantum state, and the wave equation for the electron, we can determine a statistical map of probable positions for the electron.
  • This is called a probability distribution map, a statistical representation of the probable locations of electrons as they exist in an atom.
  • The clouds of probability are the locations of electrons as determined by making repeated measurements—each measurement finds the electron in a definite location, with a greater chance of finding the electron in some places rather than others.
  • The uncertainty principle prevents us from knowing how the electron gets from one place to another, and so an orbit really does not exist as such.

• Nitrogen Compounds

  • The reddish and poisonous nitrogen dioxide (NO2) contains an unpaired electron and is an important component of smog.
  • Nitrogen molecules containing unpaired electrons show a tendency to dimerize (thus pairing the electrons), and are, in general, highly reactive.
  • When the mixture is ignited in an enclosed space, such as a gun-barrel or a firework, the nitrate ions oxidize the carbon and sulfur in a highly exothermic reaction, producing high-temperature gases very rapidly.
  • This can propel a bullet out of a gun or cause a firework to explode.

• Properties of Nitrogen

  • It has five electrons in its outer shell and is, therefore, trivalent in most compounds.
  • This is associated with electronic transitions in the molecule to states in which charge is not distributed evenly between nitrogen atoms.
  • In production of electronic parts such as transistors, diodes, and integrated circuits
  • Nitrogen tanks are also replacing carbon dioxide as the main power source for paintball guns.
  • Sending an electric current through nitrogen excites the electrons to higher energy levels.

• The Shielding Effect and Effective Nuclear Charge

  • Therefore, these electrons are not as strongly bound as electrons closer to the nucleus.
  • Ne has 10 electrons.
  • Thus the number of nonvalence electrons is 2 (10 total electrons - 8 valence).
  • Flourine has 9 electrons but F- has gained an electron and thus has 10.
  • Sodium has 11 electrons but the Na+ ion has lost an electron and thus has 10.

• Electronic Effects

  • Such charges are produced by removing (or adding) electrons from (or to) an object.
  • Electron deficient species, which may or may not be positively charged, are attracted to electron rich species, which may or may not be negatively charged.
  • Electrophiles: Electron deficient atoms, molecules or ions that seek electron rich reaction partners.
  • Nucleophiles: Electron rich atoms, molecules or ions that seek electron deficient reaction partners.

• General Rules for Assigning Electrons to Atomic Orbitals

  • An atom's electrons exist in discrete atomic orbitals, and the atom's electron configuration can be determined using a set of guidelines.
  • This nucleus is surrounded by electrons.
  • An atom's electron shell can accommodate 2n2 electrons, where n is the energy level.
  • An element's electron configuration is the arrangement of the electrons in the shells.
  • Electrons that occur together in an orbital are called an electron pair.

• Electron Configurations

  • The electron configuration is the distribution of electrons of an atom or molecule in atomic or molecular orbitals.
  • The electron configuration is the distribution of electrons of an atom or molecule in atomic or molecular orbitals.
  • Electron configurations describe electrons as each moving independently in an orbital, in an average field created by all other orbitals.
  • For atoms or molecules with more than one electron, the motion of electrons are correlated and such picture is no longer exact.
  • However, the electronic wave function is usually dominated by a very small number of configurations and therefore the notion of electronic configuration remains essential for multi-electron systems.