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Homework Help: Electron/Positron Annihilation

  1. Mar 4, 2005 #1
    Well, I've been trying to figure out how to prove that when a positron and an electron annihilate and two photons are produced, the addition of their wavelengths equals

    L1+L2=Lcompton(1-cos(theta)) where theta is the angle that separates both photons.

    It's a relativity problem I guess. I keep trying E^2=Eo^2+c^2p^2 and other formulae but get no result.

    Thanks for your help
  2. jcsd
  3. Mar 4, 2005 #2
    What is L?
  4. Mar 4, 2005 #3
    I think he means lambda.
  5. Mar 4, 2005 #4


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    Who's wavelengths are u referring to...?Draw a diagram (not the Feynman diagram,it's useless) and use conservation of 4 momentum...

  6. Mar 5, 2005 #5
    Just in case the Original poster hasn't learned 4 vactor yet....

    here is another way to approach this problem:
    Use conservation of energy and momentum...
    the algebra might be a little bit messy, this is college level problem, don't expect you can finish it in 10 minutes
  7. Mar 5, 2005 #6


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    He's Feynmanfan,he SHOULD know everything about Feynman diagrams & 4momentum conservation.


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