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Homework Help: Compton effect equation

  1. Oct 11, 2005 #1
    for the following question:
    x-rays scattered by a crystal are assumed to undergo no change in wavelength. show that this assumption is reasonable by calculating the compton wavelength of a Na atom and comparing it with the typical x-ray wavelength of 0.1nm.

    my problems:
    1) why doesn't x-rays undergo any change in the first place?
    2) the question doesn't give you an angle, so won't there be 2 variables in
    the compton effect equation?
  2. jcsd
  3. Oct 11, 2005 #2


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    The Compton wavelength of a particle is given by [itex]\lambda_C = h/mc[/itex] where m is the mass of the particle. The Na atom has an atomic mass of approximately 23 amu = 23*1.66x10-27 kg.

    Compare that wavelength to the 0.1 nm.

    X-ray scatter (as opposed to Compton scattering) is the basis of X-ray diffraction which is used to measure the distance between atoms in a crystal, i.e. lattice constant.

    The problem is not asking about Compton scattering where an electron is displaced by an X-ray.

    See - http://en.wikipedia.org/wiki/X-ray_crystallography
    Last edited: Oct 11, 2005
  4. Oct 11, 2005 #3
    thank you very much!!! :)
  5. Oct 11, 2005 #4
    hang on a second...
    if that has nothing to do with the compton effect, then why's it called the compton wavelength?
  6. Oct 11, 2005 #5
    The Compton wavelength is a constant in the Compton scattering equation. By calculating it you should see that the scale of the Compton effect is small compared to the original wavelength.
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