Radioisotopes in radioactive dating
An imaging tracer made with radionuclides is called a radioactive tracer.A pharmaceutical drug made with radionuclides is called a radiopharmaceutical.Elements heavier than lead, and the elements technetium and promethium, exist only as radionuclides.(In theory, elements heavier than dysprosium exist only as radionuclides, but the half-life for some such elements, e.g. Unplanned exposure to radionuclides generally has a harmful effect on living organisms including humans, although low levels of exposure occur naturally without harm.It decays by emitting alpha particles and gamma radiation to become neptunium-237.Smoke detectors use a very small quantity of Am is used as it emits alpha particles which ionise the air in the detector's ionization chamber.The degree of harm will depend on the nature and extent of the radiation produced, the amount and nature of exposure (close contact, inhalation or ingestion), and the biochemical properties of the element; with increased risk of cancer the most usual consequence.
More than 2400 radionuclides have half-lives less than 60 minutes.Radionuclides are present in many homes as they are used inside the most common household smoke detectors.The radionuclide used is americium-241, which is created by bombarding plutonium with neutrons in a nuclear reactor.Many of these radionuclides exist only in trace amounts in nature, including all cosmogenic nuclides.
Secondary radionuclides will occur in proportion to their half-lives, so short-lived ones will be very rare.The radioactive decay can produce a stable nuclide or will sometimes produce a new unstable radionuclide which may undergo further decay.