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I Photonuclear reaction & Conservation of momentum

  1. Sep 27, 2017 #1
    γ+2D ----> 1H + 1n

    In this photonuclear reaction, is it possible to write the momentum balance equation as it follows,

    MHvH = Mnvn

    It somehow seems to wrong to me, since the incoming photon has a certain momentum, which is not taken account in the balance equation.

    Thank you in advance.
    Last edited: Sep 27, 2017
  2. jcsd
  3. Sep 27, 2017 #2


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    Your original "equation" is not. The momentum balance is not too clear - what particles are you referring to? The outgoing particles (n and p) have momenta which sum to the momentum of te photon, assuming D is stationary.
  4. Sep 27, 2017 #3
    I am sorry about the "+" mark between D and H. just edited it. Both incoming and outgoing particles are in motion. We should consider the momentum of the photon, should not we?
  5. Sep 27, 2017 #4


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    For typical photon energies, the photon momentum is tiny compared to the momenta of the proton and neutron.
  6. Sep 28, 2017 #5


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    If you ignore the photon momentum, the outgoing (n and p) have the same momentum,but in opposite directions.
  7. Sep 28, 2017 #6
    Thank you all for answering. I should have thought this before. I have made a rough calculation. There is around eight orders of magnitude difference between the momentum of a photon and a proton with energy of 1 MeV.
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