Which interaction does not significantly contribute to attenuation at diagnostic radiography energies?

• A. Photoelectric interaction
• B. Compton interaction
• C. Pair production
• D. Both Photoelectric and Compton

Answer: (C)

Pair production does not significantly contribute to attenuation at diagnostic radiography energies. The photons used in diagnostic imaging are typically well below 1 MeV, so there isn’t enough energy to create an electron-positron pair. The threshold for pair production is 1.022 MeV, and below that energy its probability is essentially negligible. Attenuation in this energy range is dominated by photoelectric absorption (more likely with higher atomic number materials and lower photon energies) and Compton scattering (dominant at higher diagnostic energies and depends on electron density). Once energies rise toward and above about 1 MeV, pair production becomes more relevant, but it’s not a factor in standard diagnostic imaging.