Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Compton Scattering experiment help

  1. Jun 16, 2010 #1
    1. The problem statement, all variables and given/known data
    What parts of the Compton Collision experiment can be explained using classical models and which require the "photon" model?

    Anyone can help me with this question?
  2. jcsd
  3. Jun 16, 2010 #2
    Hmm...I'm not sure what you mean. I know there are a couple of ways to treat Compton scattering. The first way involves finding the frequency (or wavelength) shift in the Compton-scattered photon. This can be done by imposing momentum and energy conservation on the system as well as the following relations for the photon:

    [tex]E = hf[/tex]
    [tex]E = pc[/tex]

    That's where you get the following equation:

    [tex]\lambda' - \lambda = \dfrac{h}{mc}(1-cos(\theta))[/tex]

    The energy-frequency relation for a photon is basically how we relate the wave and particle theories of light. The energy-momentum relation is pretty much just relativity with the understanding that the photon is a massless particle. So I guess that even here we're using "classical" and "photon" models. Depending on your definition of quantum mechanics though, even treating the photon as a particle is still "classical physics."

    Now you can also use quantum field theory to write out the Feynman diagram for Compton scattering (since it's a quantum electrodynamic process). That's how you can calculate the scattering cross-section for this process. It's pretty important for us in astrophysics, since scattering works differently in the Thompson regime (low energy) and Klein-Nishina regime (high energy). I don't know if you're supposed to worry about that though.

    You could probably work out the energy change in a photon by treating it as simple classical scattering. But to turn that into a frequency you'd need to use the "photon model."
  4. Jun 24, 2010 #3
    thx for the reply.
    Photon model means that treating it as particle, while classical model means that it was treated as wave.
  5. Jun 26, 2010 #4
    The Thompson cross section mentioned by arunma is a "classical" result, you can derive it using the Maxwell equations.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook