With respect to Radiation Protection, a plane source describes a source of Ionising Radiation which can physically be represented by a flat area (e.g. area of contaminated land). Sources are often represented in this way when calculations of estimates of exposures are required. In many cases, the plane source will only represent an approximation of the real source, but this is usually adequate if sufficient factors of safety are built into the model. Often the radioactivity distribution will be given as Bq per unit area (e.g. Bq/cm2)

Other useful descriptions of sources include the Point Source, the Volume Source, the Line Source, and the Immersion (cloud) Source.