A bremsstrahlung photon's energy cannot exceed the energy of the incident electron.

• A. It cannot exceed the incident energy
• B. It can exceed the incident energy
• C. It is independent of incident energy
• D. It is always half the incident energy

Answer: (A)

Bremsstrahlung energy is drawn from the incident electron’s kinetic energy, so energy conservation dictates the photon cannot take more energy than the electron has to begin with. In the idealized picture where the nucleus is treated as effectively stationary and the electron can shed all its energy into the photon, the photon could approach the full incident energy. In a more realistic scenario, the nucleus recoils and steals a small amount of energy, so the maximum photon energy is slightly less than the initial electron energy, but it can never exceed it. That’s why the statement is correct: the photon energy is bounded by the incident electron energy. The other options violate energy conservation or misstate how the energy scales with the incident energy.