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Homework Help: Positronium Decay

  1. Feb 16, 2012 #1
    1. The problem statement, all variables and given/known data

    Consider positronium decay. Show the magnitude of the momentum for each gamma ray is [tex]m_0c[/tex] where [tex]m_0[/tex] is the mass of the electron.

    2. Relevant equations

    [tex] E=\sqrt{p^2c^2+m^2c^4}, p=h\nu/v [/tex]

    3. The attempt at a solution

    I'm not sure how to start this one, though I suspect the solution is elementary. Should I use conservation of energy or momentum or both? Are the above equations relevant? I come from a mathematics background, not a physics background, so problems which require "energy considerations" still confuse me.
  2. jcsd
  3. Feb 16, 2012 #2
    Here's a first attempt: we use conservation of momentum and find [tex] |p_{\text{before}}|=|p_{\text{after}}| \Rightarrow 2\gamma m_0v =2\gamma h\nu / c \Rightarrow m_0v=h\nu/c = |p_i| [/tex] for each gamma ray [tex]p_i[/tex] where the last inequality is from a previous exercise which asks us to show this for each photon. So I end up with *almost* the solution except I have v instead of c. Where did I go wrong?
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