The energy of a bremsstrahlung photon is dependent on which two of the following variables?

• A. energy of the incident electron and proximity of the incident electron to the nucleus
• B. energy of the incident electron and binding energy of orbital electrons in the target atom
• C. proximity of the incident electron to the nucleus and the milliamperage selected
• D. binding energy of the orbital electrons in the target atom and the milliamperage selected

Answer: (A)

The energy of a bremsstrahlung photon comes from the kinetic energy of the incident electron as it is decelerated by the nucleus. The photon energy can range from nearly zero up to the incident electron’s energy, and it increases as the electron’s distance of closest approach to the nucleus decreases—the closer the electron passes to the nucleus, the stronger the deceleration and the higher the energy radiated. Binding energies of orbital electrons don’t set the bremsstrahlung photon energy (that’s the realm of characteristic radiation when inner shells are involved). Milliamperage only changes how many electrons hit the target, affecting intensity, not the energy of individual photons. So the two factors that determine bremsstrahlung photon energy are the incident electron energy and how close the electron comes to the nucleus.