Dating by radioisotopes
Other significant applications include the use of radioactive isotopes as compact sources of electrical power—e.g., plutonium-238 in spacecraft.
In such cases, the heat produced in the decay of the radioactive isotope is converted into electricity by means of thermoelectric junction circuits or related devices.
Other radioactive isotopes are produced by humans via nuclear reactions, which result in unstable combinations of neutrons and protons.
Medical applications use artificial radioisotopes that have been produced from stable isotopes bombarded with neutrons.