When electrons accelerated across the X-ray tube strike the anode, they interact with the atoms of the target material through several mechanisms. Most X-ray photons are produced through Bremsstrahlung interactions, where electrons are decelerated by the electric field of atomic nuclei. Because the amount of energy lost by the electron varies from interaction to interaction, the resulting photons have a wide range of energies.

This produces the continuous portion of the X-ray spectrum, with photon energies ranging from very low values up to a maximum determined by the tube voltage. The highest possible photon energy corresponds to the situation in which an electron loses all of its kinetic energy in a single interaction. This maximum photon energy is therefore equal to the tube voltage:

E(max) = kVp

In addition to the continuous spectrum, the X-ray beam also contains characteristic radiation. These photons are produced when an incoming electron ejects an inner-shell electron from the target atom. When an outer-shell electron fills the resulting vacancy, the difference in binding energy between the shells is released as an X-ray photon. Because atomic energy levels are discrete, these photons appear as sharp peaks at specific energies within the spectrum.

For tungsten targets, the most prominent characteristic peaks occur at approximately 59 keV and 67 keV, corresponding to K-shell electron transitions.

The resulting X-ray spectrum therefore consists of a continuous Bremsstrahlung distribution with superimposed characteristic peaks, with a sharp upper limit determined by the applied tube voltage.