X-ray Sources
X-ray machines work by applying controlled voltage, current, and time to the X-ray tube, which results in a beam of X-rays. The beam is projected on matter. Some of the X-ray beam will pass through the object, while some are reflected. The resulting pattern of the radiation is then ultimately detected by a detection medium including rare earth screens (which surround photographic film), semiconductor detectors or X-ray image intensifiers.

In the typical X-ray source of less than 450 kV, X-ray photons are produced by an electron beam striking a target. The electrons that make up the beam are emitted from a heated cathode filament. The electrons are then focused and accelerated towards an angled anode target. The point where the electron beam strikes the target is called the focal spot. Most of the kinetic energy contained in the electron beam is converted to heat, but around 10% of the energy is converted into X-ray photons, the excess heat is dissipated via a heat sink. At the focal spot, X-ray photons are emitted at 180deg from the target surface,the highest intensity being around 60deg to 90deg there is a small round window in the X-ray tube directly above the angled target. This window allows the X-ray to exit the tube with little attenuation while maintaining a vacuum seal required for the X-ray tube operation.