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Collisions of varying frequencys of Electromagnetic Radiation.

  1. Aug 30, 2012 #1
    When Gamma Rays collide it is possible to form various units of matter (ie proton, electron, etc). Does anything happen when photons collide that are of other frequencies other then a ricochet? If X-Rays collide with other x-rays does anything happen? Also, if anything does happen, what would the result of something along the lines of a gamma ray collision with visible light?
  2. jcsd
  3. Aug 30, 2012 #2
    DO they ricochet? And if yes, how often?

    A gamma ray of sufficient energy can produce pairs with lower energy photons - as soon as a frame of reference exists where both are over 511 keV.

    But can 2 photons undergo elastic scattering? And if yes, how does the cross-section for such scattering compare with the cross-section for pair production?
  4. Aug 30, 2012 #3


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    The cross-section for photon-photon interactions of all sorts is extremely small. There is always a frame of reference where both photons have the same energy and opposite momentum - you can consider all photon-photon interactions as "head on". If the energy is more than 2*511keV in this frame, it is possible to produce electron/positron pairs (and other particles, if the energy is high enough for them).
  5. Aug 30, 2012 #4
    If energy in a collision is over 511kev, does that mean it would be possible for many lower frequency photons (i.e visible light or radio waves) to collide at a single point and have the combined enrgy over 511kev and result in particles?
  6. Aug 31, 2012 #5
    No, the collision energy must total 1022 keV. But yes, more than 2 is possible. After all, many electron-positron annihilations result not in 2 photons (with equal energies of 511 keV and opposite directions) but in 3 photons, of differing energies and directions totalling 1022 keV. It follows that it must also be possible for 3 photons to collide resulting in a pair, if the combined energy exceeds 1022 keV (in a suitable frame).
  7. Sep 1, 2012 #6
    Thanks this has been helpful.
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