What phenomenon describes the energy loss of an x-ray photon while being deflected?

The phenomenon that describes the energy loss of an x-ray photon while being deflected is Compton scattering. In this process, an x-ray photon interacts with a loosely bound outer electron of an atom. During this interaction, part of the energy of the photon is transferred to the electron, resulting in the electron being ejected from the atom and the photon being deflected at a lower energy, thereby experiencing energy loss.

This contrast with other interactions like the photoelectric effect, where the photon is completely absorbed by an electron and no deflection occurs. Pair production involves a photon transforming into a particle-antiparticle pair in the presence of a strong electric field and is significant at much higher energies, whereas Rayleigh scattering involves the low-energy scattering of x-rays without energy loss, leading to no electron ejection or energy transfer.

Thus, Compton scattering accurately fit the description of an x-ray photon's energy loss due to deflection as it engages in a collision with matter.