Radioactivity is the tendency of unstable nuclei to emit particles to bring it closer to stability. These particles are encountered at typically very low levels in nature. Sources for naturally occurring radioactivity include minerals containing radioactive elements, background cosmic rays, solar flux, radon gas, radioactive materials in manufacturing, nuclear medicine, and industrial operations such as nuclear power plants, nuclear laboratories, and radioactive waste handling and disposal.

Exposure to radioactive particles can be severely detrimental to humans and the ecosystem. Regulatory agencies have set concentration limits, standards and analytical testing methods to detect radioactivity in environmental matrices. Any entities that deal with radioactive substances must perform radioactivity-level determinations.