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Pair production

  1. Sep 23, 2014 #1
    Does pair production use helium nuclei for matter creation?

    Pair production occurs when a photon (Light Particle) strikes a heavy nucleus, it disintegrates and produces a pair of an electron and a positron. Is that heavy nucleus of Helium?
  2. jcsd
  3. Sep 23, 2014 #2


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    The heavy nucleus can be anything, doesn't matter. Its just there to conserve momentum! No other point.
  4. Sep 23, 2014 #3

    Simon Bridge

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    Not normally, but it may be.
    Low energy targets for pair production from light are typically metals like aluminium or copper.

    Note: it is not usually helpful to think of the process as a collision or a disintegration.
  5. Sep 23, 2014 #4
    In principle you only need two photons for pair production. Usually, however, one photon comes from a high-energy gamma ray and the second one is a "virtual" photon from the electric field close to a nucleus. Heavier nuclei have stronger electric fields. The nucleus is not directly affected by the pair production process.
  6. Sep 23, 2014 #5


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    Thr cross section for pair production increases with atomic weight.
  7. Sep 23, 2014 #6

    Vanadium 50

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    Does it? I thought it went as Z squared.
  8. Sep 23, 2014 #7

    Simon Bridge

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    mathman did not say how it increased ;)
    @avito009: has your question been answered yet?
  9. Sep 24, 2014 #8
    The cross section should increase with the nuclear charge, Z, not its mass.
    The cross section for normal Hydrogen, Deuterium and Tritium should be the same, even though they have different atomic masses.
  10. Sep 24, 2014 #9


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    It does depend on atomic number, but I believe it is more complicated
  11. Sep 27, 2014 #10
    Actually I will tell you why I asked the question. Especially why I asked about helium.

    Pair production is one of the primary methods of forming matter in the early Universe. So 3 seconds after the Big Bang Protons and neutrons came together to form the nuclei of simple elements: hydrogen, helium and lithium. It took another 300,000 years for electrons to be captured into orbits around these nuclei to form stable atoms.

    So early on Hygrogen and Helium were created. So for pair production to happen a photon (Light Particle) should strike a heavy nucleus (Which according to me is Helium nucleus), so that it disintegrates and produces a pair of an electron and a positron.

    But after reading some more I realised this could be the wrong approach as Pair Production can happen when two high energy gamma ray photons collide and an electron-positron pair are produced (Energy is converted to mass E=MC2)
  12. Sep 27, 2014 #11
    Given enough energy you can produce particle-antiparticle pairs of almost anything, including protons and antiprotons.

    The real question is: Why was more matter produced than antimatter?
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