Radioactive can generally describe the property of a substance (or more accurately atomic nuclei) which are unstable and spontaneously Decay (disintegrate) with the release of energy, the energy being either Electromagnetic Radiation, particulate or both. This process may occur in both naturally occurring radioactive material and man-made substances. For any given element there will be a number of Isotopes, some of which may be radioactive. The point at which a substance can be said to be radioactive requires careful interpretation of the law and may depend on particular circumstances. For example, in the UK exemption criteria is used to determine if something is considered radioactive.