# Compton effect equation

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?

Astronuc
Staff Emeritus
The Compton wavelength of a particle is given by $\lambda_C = h/mc$ 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:
opps~
thank you very much!!! :)

hang on a second...
if that has nothing to do with the compton effect, then why's it called the compton wavelength?

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.