By which process are the majority of photons in the x-ray beam created?

The majority of photons in the x-ray beam are created through Bremsstrahlung interactions. This process occurs when high-speed electrons are decelerated or deflected by the electric field of the atomic nuclei within the target material of the x-ray tube, usually made from tungsten. As these electrons lose energy during their interaction with the nuclei, they emit x-ray photons.

Bremsstrahlung, which means "braking radiation" in German, accounts for a significant portion of the x-ray production process because it can occur over a wide range of energies and is the primary mechanism for producing x-rays in most medical imaging systems. The continuous spectrum of x-ray photons generated through Bremsstrahlung allows for the imaging of varying tissue densities and anatomical structures in the body.

While other processes such as the photoelectric effect and Compton scattering do play important roles in the interaction of x-rays with matter and image formation, they do not contribute to the actual creation of the x-ray photons in the beam itself. Characteristic radiation, produced when an electron from an inner shell of the atom is knocked out and an outer shell electron fills that vacancy, also contributes but only makes up a smaller portion of the overall x-ray spectrum compared to Bremsstrahlung.