Radioactive isotopes (often referred to as radioisotopes) play an important part in the technologies that provide us with food, water and good health. Radioisotopes are unstable radioactive isotopes; that is, they are unstable atoms containing an unusual number of neutrons. Radioisotopes do occur naturally, but are also artificially produced by bombarding particular elements with neutrons (usually emitted from a nuclear reactor). Radioisotopes are said to "decay", during which they give off energy and subatomic particles.

In medicine, radioisotopes are used for diagnosis and research. Radioactive chemical tracers emit gamma rays which provides diagnostic information about a person's anatomy and the functioning of specific organs. Radiotherapy also uses radioisotopes in the treatment of some illnesses, such as cancer. More powerful gamma sources are used to sterilise syringes, and other medical equipment. About one in two people in Western countries are likely to experience the benefits of nuclear medicine in their lifetime, and gamma sterilisation of equipment is almost universal.

In food preservation, radioisotopes are used to stop the sprouting of root crops after harvesting, to kill parasites and pests, and to control the ripening of stored fruit and vegetables.

In agriculture and animal husbandry, radioisotopes also play an important role. They are used to produce high intake of crops, disease and weather resistant varieties of crops, to study how fertilisers and insecticides work, and to improve the production and health of domestic animals.

Industrially, and in mining, they are used to examine welds, to detect leaks, to study the rate of wear of metals, and for on-stream analysis of a wide range of minerals and fuels.

Most household smoke detectors use radioisotope derived from the plutonium or americium formed in nuclear reactors, saving many lives.

Environmentally, radioisotopes are used to trace and analyse pollutants, to study the movement of surface water, and to measure water runoffs from rain and snow, as well as the flow rates of streams and rivers.