Compton Scattering

The fact the electromagnetic radiation consists of quantized photons was firmly established in 1923 when Compton showed that x-rays scatter off electrons. If a photon is to be considered a particle, it must obey the same kinematic equations that govern scattering between two object. When an x ray scatters of an electron at rest, the x-ray must lose energy and the electron must gain energy. Thus the frequency of the x-ray is decreased and the wavelength is increased. The relation the incident wavelength and the scattered wavelength is given by

\[ \rm \mathbf{ \Delta \lambda = \lambda' - \lambda = \frac{h}{m_{0} c} \cdot (1 - cos \theta)} \]

where m_o is the mass of an electron. When $\theta$ = 180°, the x-ray collides with the electron and bounces back in the opposite direction. This situation corresponds to the largest energy loss possible for a given energy x-ray.