Which electron interaction with the anode causes the x-ray beam to be polygenergetic?

• A. Characteristic
• B. Compton
• C. Pair production
• D. Bremsstrahlung

Answer: (D)

Bremsstrahlung is the braking radiation produced when fast electrons are slowed as they pass near the strong electric field of the target nucleus. Because the energy transfer to the photon can vary from almost nothing up to the electron’s entire kinetic energy, the emitted photons form a continuous spectrum with energies ranging from near zero to the maximum set by the electron's initial energy (the tube voltage).

This continuous spectrum is what makes the x-ray beam polyenergetic. In contrast, characteristic radiation comes from electrons dropping between fixed shells and produces photons with specific, discrete energies, which would add lines to the spectrum but not create a broad continuum. Compton scattering and pair production are different processes that either occur later (scattering of photons) or require much higher energies and matter interactions, and they don’t establish the primary polyenergetic bremsstrahlung spectrum produced in the anode.