Above 70 kVp, what percentage of X-ray photons are produced by the bremsstrahlung process?

When an X-ray tube operates above 70 kVp, the majority of X-ray photons are generated through the bremsstrahlung process, which translates to approximately 85% of the total X-ray photon production.

Bremsstrahlung, or "braking radiation," occurs when high-energy electrons are decelerated or deflected by the electric field of the nuclei of the target material (typically tungsten) within the X-ray tube. As these fast-moving electrons come close to the nuclei, they lose energy, which is then emitted as X-ray photons. The efficiency of this process increases with the energy of the incoming electrons, leading to a higher percentage of X-ray production via bremsstrahlung at higher kVp levels.

At lower kVp levels, a larger percentage of the X-rays created may come from characteristic radiation; however, as the kVp increases above 70, bremsstrahlung becomes the dominant mechanism for X-ray production. Consequently, at 70 kVp and higher, the contribution from bremsstrahlung to the overall X-ray output reaches around 85%, making this the accepted standard in X-ray physics for understanding how high-energy X-ray production predominantly occurs.