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How does Compton scattering suggest photons?

  1. Jun 28, 2014 #1
    I have seen many 'photoelectric effect vs compton effect' Questions in this and other forums, but i am still not convinced. I can see how photoelectric effect points to the particle nature of light. But i don't see how compton effect as a separate experiment is needed to confirm this. The only difference i see is that in PE, the energy of the photon is completely absorbed by the e, while in CE the photon is scattered with some energy remaining. So aren't the CE and PE two particular cases of the same phenomenon? And why does one occur in bound electrons and the other in free electrons. I have also read that CE occurs in bound electrons when the energy of incident radiation is high. why doesnt the excess energy go to the KE of electron instead of getting scattered as a photon?
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  3. Jun 28, 2014 #2

    Simon Bridge

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    The description you have been presented is likely a particle description.
    Try making a wave description of Compton effect.

    You need some experiment besides PE because there is a semi-classical model that does the same thing.
    With PE, the incident photon ejects an electron - in CE the electron is not ejected.
    The energy lost by the photon does go to KE in the electron.
  4. Jun 28, 2014 #3
    I understand that. what i meant to ask was why doesnt the entire energy go to the KE of the electron to give photoelectric effect alone. in other words, why does compton effect have to occur in bound electrons?
  5. Jun 28, 2014 #4

    Simon Bridge

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    Because the label "Compton scattering" only applies to the situation where it doesn't.
    There are other processes where it does - i.e. atomic excitation, and atomic ionization.

    If you think of it as a collision, there is no reason that all the energy of the incoming particle should be transferred to the other one.
  6. Jun 28, 2014 #5


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    In general, a photon can interact either way, with certain probabilities. That is, if you send a beam of photons, each with the same energy, towards a target, some of them will undergo the photoelectric effect and some of them will undergo Compton scattering. And some of them will undergo electron-positron pair production, if the energy is high enough.

    The probabilities vary with photon energy and the target material. We usually describe them using a quantity called the "cross section." See here for example:


    and scroll down near the bottom of the page to the "Photon Interactions" section.
  7. Jun 28, 2014 #6
    Thanks. u answered my question
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