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Threshold energy problem

  1. May 5, 2010 #1
    Can someone help me out with this problem(not homework ofcourse)..

    Find the threshold energy of gamma quantum required to form
    - an electron-positron pair in the field of a stationary electron;
    - a pair of pions of opposite signs in the field of a stationary proton..

    Thank you for reading
     
  2. jcsd
  3. May 5, 2010 #2

    clem

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    Science Advisor

    Use [tex]E^2-P^2=W^2[/tex], where W= total cm energy.
    For gamma+e-->3e, this becomes [tex](k+m)^2-k^2=(3m)^2.[/tex]
     
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