With respect to Radiation Protection, a volume source describes a source of Ionising Radiation which can physically be represented by a solid area. For example a drum containing radioactive waste can be considered a volume source. Sources of ionising radiation are often represented in this way when calculations of estimates of exposures from the source are required. In many cases the volume 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. Other useful descriptions of sources include the Point Source, the Planar Source, and the Line Source.

If you have a volume source the use of the inverse square law will provide unreliable data, since this law only mathematically applies to a point source. The volume source can also self shield, especially if the radioactive material is not uniformly distributed within the volume (this is typical in radioactive waste drums).

A person undergoing a nuclear medicine procedure (such as a PET scan using radioactive F-18) will also approximate to a walking, talking volume source.