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Pair Production

  1. Dec 21, 2003 #1
    I'm pretty much okay with pair production but in the eqt we have that a photo gives an electron and a positron. If we do it the other way round we have an electron and a positron giving 2 photos in order to conserve momentum. Why do we not have 2 photos of energy for pair production ir order to conserve momentum?
  2. jcsd
  3. Dec 21, 2003 #2


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    You are correct (up to a point). Pair production in a vacuum does require two photons to interact. However, when a high energy photon passes near a nucleus of an atom (the heavier the better), it can give rise to pair production alone, with the nucleus taking care of the momentum balance.
  4. Dec 22, 2003 #3
    Is that to do with the recoil momentum of the nucleus? I've heard it mentioned before so just wondering if that's what is going on here.
  5. Dec 22, 2003 #4


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    Your description is correct. It also explains why heavier nuclei are better. It is easier for them to absorb the recoil momentum.
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