Pair production does not occur in radiography due to energy limitations. Which interaction does not occur in standard diagnostic radiography?

Pair production does not occur in radiography due to energy limitations. Which interaction does not occur in standard diagnostic radiography?

• A. Compton
• B. Coherent
• C. Photoelectric
• D. Pair production

Answer: (D)

In diagnostic radiography, photon energies are too low for pair production. This process needs at least 1.022 MeV (two times the electron rest mass), and typical clinical X-ray beams are around 30–150 keV. Those energies simply don’t reach the threshold, so pair production doesn’t occur in standard diagnostic imaging. The interactions that do take place in this energy range include Compton scattering, which dominates and causes most of the scattered radiation; photoelectric absorption, which is important at lower energies and with higher-Z materials and contributes to image contrast; and coherent (Rayleigh) scattering, an elastic process that can occur at very low energies. Therefore, pair production is the interaction that does not occur in standard diagnostic radiography.

In diagnostic radiography, photon energies are too low for pair production. This process needs at least 1.022 MeV (two times the electron rest mass), and typical clinical X-ray beams are around 30–150 keV. Those energies simply don’t reach the threshold, so pair production doesn’t occur in standard diagnostic imaging. The interactions that do take place in this energy range include Compton scattering, which dominates and causes most of the scattered radiation; photoelectric absorption, which is important at lower energies and with higher-Z materials and contributes to image contrast; and coherent (Rayleigh) scattering, an elastic process that can occur at very low energies. Therefore, pair production is the interaction that does not occur in standard diagnostic radiography.