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Homework Help: Electron Undergoing Annihilation

  1. Apr 13, 2005 #1
    A 5MeV electron undergoes annihilation with a positron that is at rest, producing two photons. One of the photons travels in the direction of the incident electron. Calculate the energy of each photon.

    So the 5 MeV electron undergoes annihilation with a positron and from that 2 seperate photons are formed. The energy of both photons should equal back up to the 5 MeV correct? Also one of the photons travels back the same way the electron came but I am not clear on how to use that piece of info.
  2. jcsd
  3. Apr 13, 2005 #2


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    Don't forget to include the rest energy of the stationary particle. Is 5 MeV is the total energy or kinetic energy of the other one?

    You need to conserve both momentum (a vector) and energy (a scalar).
  4. Apr 13, 2005 #3
    Ah, right..momentum is conserved. So the particles will be a sum of the 5MeV and the rest energy of that positron.
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