Artificial isotopes are laboratory-created forms of elements. An isotope is an element with a non-standard number of neutrons; these extra neutrons add to the atom's mass and can change the element's physical structure, but otherwise do not change the chemical properties of the element.
There are two types of isotope: stable and unstable. Both natural and artificial isotopes can be either stable or unstable. Stable isotopes are not radioactive, whereas unstable isotopes undergo radioactive decay and release nuclear radiation. Stable isotopes are more common than unstable ones in nature, so most unstable isotopes in wide-scale use are artificial.
All artificial isotopes of elements with atomic numbers of 83 or higher are radioactive. All elements heavier than barium, which has the atomic number 83, are naturally radioactive or only have one stable isotope. Elements with atomic numbers below 83 can occur as either stable or unstable isotopes.
Artificial isotopes are used in physics research, medicine and as industrial radiation sources. Within medicine, they are used as tracer compounds and to treat cancer and other diseases. Technetium-99 and iodine-131 are examples of artificial isotopes used in medicine. Technetium is used as a tracer in diagnostic tests, and iodine is used to treat thyroid cancer.