Which is the primary photon interaction that contributes to image formation in radiography?

The primary photon interaction that contributes to image formation in radiography is the photoelectric effect. In this interaction, an incoming photon is absorbed by an atom in the irradiated material, typically within the tissues being imaged. This absorption leads to the ejection of an electron from an inner shell of the atom, resulting in a vacancy that can lead to characteristic radiation or Auger electron emission. The photoelectric effect is particularly significant in radiography because it is responsible for creating contrast in images; it varies with the atomic number of the materials being imaged and with the energy of the x-ray photons.

Higher atomic number materials absorb more photons through the photoelectric effect, leading to darker areas on the radiograph, while lower atomic number materials appear lighter because fewer photons are absorbed. Consequently, the resulting image is a representation of the varying densities and compositions of the materials in the path of the x-rays.

The other interactions, while present in the context of x-ray physics, play a lesser or different role in image formation. For example, Compton scattering does contribute to image formation by scattering photons, but this process generally reduces image contrast due to the creation of background noise. Pair production primarily occurs at high photon energies and results in the formation of matter