The maximum energy of bremsstrahlung photons that can be created during an x-ray exposure is equal to the:

• A. energy of the incident electron
• B. binding energy of the k-shell electrons
• C. binding energy of the outer shell electron
• D. tube current used for the exposure

Answer: (A)

In bremsstrahlung, a high-speed electron slows in the nucleus’s field and can transfer essentially any of its kinetic energy to a single photon. The maximum energy a bremsstrahlung photon can have is therefore equal to the incident electron’s initial kinetic energy (in an X-ray tube this is e times the tube voltage, Emax ≈ eV). This is why the maximum photon energy is determined by how much energy the electron has to give, not by the binding energies of electrons in the atom or by how many electrons are produced. The binding energies of inner or outer shells relate to characteristic X-ray emission, not to the maximum possible energy of a bremsstrahlung photon, and the tube current affects how many photons are produced, not their maximum energy.