Scintillators and photoconductors

Detecting X-rays requires the use of special materials. The list of possible materials is impressive, while those actually used in radiology, CT or nuclear medicine are less so, but still substantial. All detect X-ray photons using the same three-phase process:

1. X-ray photon absorption, where the dominant physical mechanism is the photoelectric effect. At the point of absorption – the material collides with an atom, – emitting a fluorescent X-ray photon and a high-energy electron (photoelectron). Only the electron is useful for reading the detected X-ray photon, the fluorescence X-ray photon constituting a spurious signal, unless it is reabsorbed sufficiently close to the point where it was emitted (figure