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Antiparticles

  • Page ID
    38397
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    An introduction to particle physics.

    Particles and Antiparticles

    The material world is complicated, yet it is also very simple and symmetric. Analogous to two kinds of charge are two kinds of particles - particle and antiparticle.

    One of the beta decay processes is the emission of positrons to reduce the nuclear positive charge. The positron is actually an antiparticle of electron, but we did not mention the antiparticle concept at that time.

    • The antiparticle concept

      Paul Dirac rearranged Einstein's equation of relative mass for a moving particle in 1928, and obtained an equation showing that the kinetic energy of certain type of particles became more negative as they move faster. He called such particles antiparticles.

      Antiparticles and their counter parts have the same rest mass, but opposite charge, and opposite magnetic moment if they possess these properties.

      Nothing is observed when energy states are empty or fully occupied.
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      An electron occupying a positive energy state and an empty state in an otherwise occupied energy state are observable. This is a pair of electron and antielectron.
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      An electron annihilates an antielectron and the excess energy is released as a pair of photons. The positive energy states become empty and the negative energy state is full after the annihilation.
    • The Discovery of Antielectrons

      While studying cosmic-ray tracks in his cloud chamber in 1932, Carl Anderson saw tracks similar to those of electrons but these particles bent in opposite direction in the presence of a magnetic field. He discovered antielectrons prescribed by Dirac, and called them positron.

    • Annihilation and Pair Production

      At the end of the positron tracts, Anderson noticed two thin tracts that can be attributed to gamma rays, generated when the positrons were annihilated when colliding with electrons.

      A year later, the creation of an electron-positron pair using high-energy photon was confirmed, and this process is called pair production.

      Today, positrons and electrons are created routinely using high-energy photons. These particles are created for particle accelerator. Electrons and positrons move in opposite directions in circular accelerators accelerated using electric and magnetic fields. When high-energy electrons and positrons collide, particles with rest mass heavier than electrons are produced.

      Simhony argued that electrons and positrons form a elecron-positron lattice, (EPOLA), which is unobservable. Absorption of 1.02 MeV liberates a pair of electron and positron. Thus, energy does not convert to particles. It is absorbed, and as a result, particles are liberated.

    Internet Resources

    Electron Positron Lattice

    Contributors


    This page titled Antiparticles is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Chung (Peter) Chieh.

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