Which interaction occurs at megavoltage energy levels and involves creation of new particles?

Which interaction occurs at megavoltage energy levels and involves creation of new particles?

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

Answer: (D)

High-energy photons can transform into matter when they pass through the strong electric field near a nucleus. This creates a particle–antiparticle pair, specifically an electron and a positron, so new particles appear. The process turns on only when the photon energy exceeds 1.022 MeV (twice the electron rest mass), and in megavoltage ranges its likelihood increases, especially in high-Z materials. Other interactions at lower energies—like the photoelectric effect, Compton scattering, or elastic (coherent) scattering—don’t produce new particles; they involve absorption or scattering of the photon or ejection of an existing electron. Thus, the interaction that occurs at megavoltage energies and involves creation of new particles is pair production.

High-energy photons can transform into matter when they pass through the strong electric field near a nucleus. This creates a particle–antiparticle pair, specifically an electron and a positron, so new particles appear. The process turns on only when the photon energy exceeds 1.022 MeV (twice the electron rest mass), and in megavoltage ranges its likelihood increases, especially in high-Z materials. Other interactions at lower energies—like the photoelectric effect, Compton scattering, or elastic (coherent) scattering—don’t produce new particles; they involve absorption or scattering of the photon or ejection of an existing electron. Thus, the interaction that occurs at megavoltage energies and involves creation of new particles is pair production.