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Does quantum mechanics state that a photon is a positron and electron annhilating

  1. Mar 20, 2007 #1
    Does QM tell us that photons are actually electrons and positrons goign through a cycle of annilation and creation?
     
  2. jcsd
  3. Mar 20, 2007 #2
    can an electron and positron annhilate each other without the presence of a neutron?
     
  4. Mar 20, 2007 #3

    Integral

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    No, but an electron and a positron can annihilate to create a photon. this is not a statement about ALL photons.

    Electron positron annihilation not have to happen in the presence of a neutron.
     
  5. Mar 20, 2007 #4
    Is that to say there is a 0 probabilty of a photon going to a positron and electron?
     
  6. Mar 20, 2007 #5
    A single photon cannot spontaneously become an electron and a positron, as it would be unable to simultaneously conserve energy and momentum. For the same reason, an electron and a positron cannot annihilate into a single photon.

    However, two colliding photons (if they have sufficient energy) can form and electron and a positron; and, an electron and positron can annihilate to form two photons.
     
  7. Mar 20, 2007 #6

    Mentz114

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    According to the path integral formulation of QM, a photon has a non-zero probability of spending time as a (virtual ?) e+/e- pair.
     
  8. Mar 20, 2007 #7

    mathman

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    In addition to the 2 photon into electron-positron pair, it is possible for a single photon (of enough energy >1.22 Mev) to form a pair when in the presence of a nucleus to get the required energy and momentum balance. This reaction is quite common in nuclear reactors and in lead shielding.
     
  9. Mar 20, 2007 #8

    Mentz114

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    Mathman, with the single photon near a nucleus, does the electric field of the nucleus play a part ? Presumably a 1.22 Mev photon is a gamma-ray type .
     
  10. Mar 21, 2007 #9

    mathman

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    The electric field plays a role, since (I presume) the electromagnetic force is the only force involved. As far as the photon energy, yes it is a gamma ray. Gamma rays from nuclear reactors can be as high as 10 Mev (maybe even higher).

    P.S. Error (by me) - threshold for pair production is 1.022 Mev, not 1.22.
     
    Last edited: Mar 22, 2007
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