The attenuation that results due to the interaction between penetrating radiation and
matter is not a simple process. A single interaction event between a primary X-ray
photon and a particle of matter does not usually result in the photon changing to some
other form of energy and effectively disappearing. Several interaction events are
usually involved and the total attenuation is the sum of the attenuation due to
different types of interactions. These interactions include the photoelectric effect,
scattering, and pair production.