Compton Scattering
?? = ?scattered - ?incident = (h/mc)[1-cos(?)]
Note that the maximum change in wavelength is
(for scattering from an electron)
2h/mc = 2(6.63 x 10-34 J-s) / (9.1 x 10-31 kg * 3 x 108 m/s)
which would be insignificant for visible light but NOT for x-ray and ?-ray light.