Is the Compton scattering elastic or inelastic? Because the kinetic energy is conserved (in addition to the total energy conservation) so it should be elastic, but the energy of the photon is changed, so from that point of view is inelastic. I have found both definitions online, which one is correct?

  • $\begingroup$ There is some fussing of this in the talk page of wikipedia. A Solomonic answer would call it inelastic scattering underlain by an elastic collision. Don't waste any time on the terms: just try to understand the kinematics and ignore the terms. $\endgroup$ – Cosmas Zachos Mar 16 '17 at 22:30

When you are considering scattering, you are looking to what happens to the incoming particle. In Compton scattering, the incoming particle, the photon, comes out after the scattering process with less energy than it started with, and so the scattering is called inelastic; whereas, with Thomson scattering, since the energy of the photon does not change, that would be termed as elastic scattering.

It might be that the confusion arises because of the term "elastic" alternatively being used for collisions when the total kinetic energy of the interacting particles is conserved?


It is often called an inelastic process but this would result in an excitation of inner degrees of freedom of the electron. These an electron does not provide, therefore it cannot be an inelastic process.

  • 1
    $\begingroup$ Are you perhaps confusing inelastic scattering with inelastic collision, a dramatically different concept? $\endgroup$ – Cosmas Zachos Dec 12 '17 at 23:27
  • $\begingroup$ That's right.. I leave the comment anyhow so others may be aware of that. $\endgroup$ – Ben Dec 14 '17 at 22:44
  • $\begingroup$ I stumbled over this issue again and I noticed that I can't highlight the difference between collision and scattering. Both seem to be connected to the conservation of energy. So where is the difference? $\endgroup$ – Ben Oct 12 '18 at 8:55

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