What type of interaction occurs when photons collide with matter causing ionization?

The correct choice is B, the photoelectric effect, which is a fundamental interaction involving the absorption of a photon by an atom. During this process, the energy of the incoming photon is transferred entirely to an inner shell electron, typically in a dense material. This energy transfer results in the electron being ejected from its atomic shell, leading to ionization of the atom.

The photoelectric effect is critical in radiation protection as it highlights how ionizing radiation can directly affect biological tissues. In materials with high atomic numbers, the likelihood of this interaction increases, leading to higher doses of radiation dose deposition in those materials.

While other options involve photon interactions with matter, they either do not lead to ionization directly (like Rayleigh scattering) or involve different mechanisms (such as Compton effect and pair production, which involve other processes and energy thresholds). Understanding the distinction between these interactions is essential for comprehending how different types of radiation affect matter and how to protect against those effects.