Which interaction is responsible for the absorption of x-ray photons in the phosphor layer of CR imaging?

• A. Photoelectric
• B. Compton
• C. Characteristic
• D. Classical

Answer: (A)

The main concept here is that the absorption of diagnostic x-ray photons in the phosphor layer occurs primarily through the photoelectric effect. In a high‑Z storage phosphor like BaFBr:Eu2+, an incoming x-ray photon is most likely to be completely absorbed by an inner-shell electron, ejecting that electron and creating a trapped charge in the phosphor lattice. This energy deposition is what stores the latent image, later read out when stimulated by a laser. Compton scattering, while possible, involves only partial energy transfer to a recoil electron and does not produce the same stored energy signal. Characteristic radiation is the photons emitted as electrons fill the vacancy after a photoelectric event; it is a consequence of absorption rather than the absorption mechanism itself. Classical (low‑energy) interactions aren’t the dominant process at diagnostic energies in this material.