Q.Give examples of the production of

(i) A photon produces an electron in pair production (gamma-ray to electron + positron), or ejects one in the photoelectric effect. (ii) An electron produces a photon during Bremsstrahlung / X-ray emission or during an atomic energy-level transition.

(i) Electron produced by a photon:

• Pair production: a sufficiently energetic gamma-ray photon (energy at least 1.02 MeV) passing near a heavy nucleus is converted into an electron-positron pair, so a material electron is literally created from a photon. This is the clearest example of a photon giving rise to an electron.
• (Also acceptable: the photoelectric effect, in which a photon transfers its energy to a bound electron and knocks it free.)

(ii) Photon produced by an electron:

• Bremsstrahlung (X-ray production): when a fast-moving electron strikes a metal target and is suddenly decelerated, it radiates energy as an X-ray photon. …