Compton Scattering
Together with the scattering of photons on free electrons, the photoelectric effect, and pair production, Compton scattering contributes to the attenuation of x-rays in matter. As the binding energy of electrons in atoms is low compared to that of passing near-relativistic particles, this is the relevant process in radiography. Closely related are Thompson scattering (classical treatment of photon scattering) and Rayleigh scattering (coherent scattering on atoms).
Compton Scattering, also known as incoherent scattering, occurs when the incident x-ray photon ejects a electron from an atom and an x-ray photon of lower energy is scattered from the atom. Relativistic energy and momentum are conserved in this process (demonstrated in the applet below) and the scattered x-ray photon has less energy and therefore a longer wavelength than the incident photon. Compton scattering is important for low atomic number specimens.