Interaction of X-Rays with Matter

Röntgen’s studies in the late nineteenth and early twentieth centuries quickly established the penetrating nature of X-Rays, and the potential for medical imaging was soon realized. However, the interaction of X-Rays with matter is more complex than simply ‘passing through’. On reaching a material, some of the x-rays will be absorbed, and some scattered – if neither process occurs, the X-Rays will be transmitted through the material.

When absorption occurs, the X-Rays interact with the material at the atomic level, and can cause subsequent fluorescence – it is this X-Ray Fluorescence which forms the basis of XRF spectroscopy, and the process is discussed in more detail in the next section. In addition to the absorption/fluorescence process, the X-Rays can also be scattered from the material. This scattering can occur both with and without loss of energy, called Compton and Rayleigh scattering respectively.

The ratio of absorption/fluorescence, Compton and Rayleigh scatter and transmission depends on the sample thickness, density and composition, and the X-Ray energy.