Which interaction involves the gamma photon converting into an electron-positron pair near a nucleus?

Which interaction involves the gamma photon converting into an electron-positron pair near a nucleus?

• A. Photoelectric Effect
• B. Pair Production
• C. Compton Scatter
• D. Elastic Scatter

Answer: (B)

Pair production is the process where a high-energy gamma photon is transformed into an electron-positron pair in the presence of a nucleus. The nucleus’s electric field provides the extra momentum needed to conserve momentum, which is why this conversion happens near a nucleus rather than in empty space. The photon must have at least 1.022 MeV of energy (twice the electron rest mass) for the pair to be created, with any remaining energy appearing as kinetic energy of the electron and positron. This distinguishes it from the photoelectric effect (photon absorbed, ejecting an electron), Compton scattering (photon scatters off an electron, transferring some energy and changing direction), and elastic (coherent) scattering (photon scatters off the entire atom with negligible energy transfer).

Pair production is the process where a high-energy gamma photon is transformed into an electron-positron pair in the presence of a nucleus. The nucleus’s electric field provides the extra momentum needed to conserve momentum, which is why this conversion happens near a nucleus rather than in empty space. The photon must have at least 1.022 MeV of energy (twice the electron rest mass) for the pair to be created, with any remaining energy appearing as kinetic energy of the electron and positron. This distinguishes it from the photoelectric effect (photon absorbed, ejecting an electron), Compton scattering (photon scatters off an electron, transferring some energy and changing direction), and elastic (coherent) scattering (photon scatters off the entire atom with negligible energy transfer).