Which interaction predominantly affects photons at low energy levels in terms of radiographic imaging?

The photoelectric effect is the dominant interaction affecting photons at low energy levels in radiographic imaging. This effect occurs when a photon has enough energy to completely remove an inner shell electron from an atom, resulting in ionization of that atom. In the context of medical imaging, this interaction is particularly significant because it directly contributes to the contrast and quality of radiographic images.

At lower photon energies, such as those used in standard X-ray radiography, the probability of the photoelectric effect occurring is much greater compared to other interactions. The absorption of these photons increases the opacity of tissues, enhancing the visibility of structures based on their density and atomic number. For instance, denser tissues like bone have a higher atomic number and thus absorb more X-rays via the photoelectric effect, appearing whiter on a radiograph, while softer tissues absorb fewer photons, appearing darker.

In contrast, Compton scattering, which involves the scattering of photons by outer shell electrons, primarily affects photons at intermediate energy levels. Pair production requires photon energies significantly higher than those typically used in radiographic imaging and occurs near dense nuclei. Radiolysis of water is a chemical process that occurs as a result of ionizing radiation and is not a direct interaction affecting radiographic imaging in the