Atoms of chemical elements may have many isotopes (different forms) with the same atomic numbers but different atomic weights / atomic mass numbers. If a nuclide is radioactive, it is sometimes referred to as a radionuclide or (when the atom in question is understood) a radioisotope.

A radionuclide is an atom with an unstable nucleus. The radionuclide undergoes radioactive decay by emitting a gamma ray(s) and/or subatomic particles. Radionuclides may occur naturally, but can also be artificially produced. Properties In chemistry and physics, an atom (Greek άτομον meaning indivisible) is the smallest possible particle of a chemical element that retains its chemical properties. ... A semi-accurate depiction of the helium atom. ... Radioactive decay is the set of various processes by which unstable atomic nuclei (nuclides) emit subatomic particles (radiation). ... This article is about electromagnetic radiation. ... Helium atom (not to scale) Showing two protons (red), two neutrons (green) and a probability cloud (gray) of two electrons (yellow). ...

Radionuclides are often referred to by chemists and biologists as radioactive isotopes or radioisotopes, and play an important part in the technologies that provide us with food, water and good health. However, they can also constitute real or perceived dangers. Isotopes are forms of an element, therefore their nuclei have the same atomic number — the number of protons in the nucleus — but different mass numbers because they contain different numbers of neutrons. ...

Origin

Naturally occurring radionuclides originate mainly from the interiors of stars. Some, such as uranium, were formed directly in stars, and are still present because their half-lives are so long that they have not yet completely decayed. Radiogenic isotopes, such as carbon-14, are present because they are formed by the decay of longer-lived elements (this is how all the helium currently available was formed: although it is not radioactive, it escapes from the Earth easily, so helium is obtained from underground reservoirs). The Pleiades star cluster A star is a massive, compact body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. ... General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Atomic mass 238. ... Half-Life is a science fiction first-person shooter computer game developed by Valve Software and published by Sierra Studios in 1998, based on a heavily-modified Quake game engine. ... Carbon-14 is the radioactive isotope of carbon discovered February 27, 1940, by Martin Kamen and Sam Ruben. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ...

Artificially produced radionuclides can be produced by nuclear reactors, particle accelerators or by radionuclide generators. Core of a small nuclear reactor used for research. ...

Radioisotopes produced with nuclear reactors exploit the high flux of neutrons present. The neutrons are used to activate elements placed within the reactor. A typical product from a nuclear reactor is thallium-201. Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ... General Name, Symbol, Number thallium, Tl, 81 Chemical series poor metals Group, Period, Block 13, 6, p Appearance silvery white Atomic mass 204. ...

Particle accelerators such as cyclotrons accelerate particles to bombard a target to produce radionuclides. Cyclotrons are used to accelerate protons at a target to produce positron emitting radioisotopes e.g. fluorine-18. A pair of Dee electrodes with loops of coolant pipes on their surface at the Lawrence Hall of Science. ... General Name, Symbol, Number fluorine, F, 9 Chemical series halogens Group, Period, Block 17, 2, p Appearance pale greenish-yellow gas Atomic mass 18. ...

Radionuclide generators contain a parent isotope that decays to produce a radioisotope. The parent is usually produced in a nuclear reactor. A typical example is the technetium-99m generator used in nuclear medicine. The parent produced in the reactor is molybdenum-99. General Name, Symbol, Number technetium, Tc, 43 Chemical series transition metals Group, Period, Block 7, 5, d Appearance silvery gray metal Atomic mass [98](0) g/mol Electron configuration [Kr] 4d5 5s2 Electrons per shell 2, 8, 18, 13, 2 Physical properties Phase solid Density (near r. ... The first technetium cow (a device for separating Tc-99m from its parent isotope, Mo-99) at Brookhaven National Laboratory. ... Nuclear medicine is a branch of medicine and medical imaging that uses unsealed radioactive substances in diagnosis and therapy. ... General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Atomic mass 95. ...

Trace radionuclides are those that occur in tiny amounts in nature either due to inherent rarity, or to half-lives that are significantly shorter than the age of the Earth. Synthetic isotopes are not naturally occurring on Earth, but they can be created by nuclear reactions. Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ... In nuclear physics, a nuclear reaction is a process in which two nuclei or nuclear particles collide, to produce different products than the initial products. ...

Uses

Radionuclides are used in two major ways: for their chemical properties and as sources of radiation. Radiation in physics is a process of emission of energy or particles. ...

Radionuclides of familiar elements such as carbon can serve as tracers because they are chemically very similar to the non-radioactive nuclides, so most chemical, biological, and ecological processes treat them in a near identical way. One can then examine the result with a radiation detector, such as a geiger counter, to determine where the provided atoms ended up. For example, one might culture plants in an environment in which the carbon dioxide contained radioactive carbon; then the parts of the plant that had laid down atmospheric carbon would be radioactive. General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... A radioactive tracer is a substance containing a radioactive isotope (radioisotope). ... Modern geiger counter. ... Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. ...

In medicine, radioisotopes are used for diagnosis, treatment, and research. Radioactive chemical tracers emitting gamma rays that can provide diagnostic information about a person's internal anatomy and the functioning of specific organs. This is used in some forms of tomography single emission computed tomography and positron emission tomography scanning. Radioisotopes are also a promising method of treatment in hemopoietic forms of tumors, while the success for treatment of a solid tumors has been limited so far. 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. Sterilization (or Sterilisation) is the elimination of all transmissible agents (such as bacteria, prions and viruses) from a surface or piece of equipment. ... Nuclear medicine is a branch of medicine and medical imaging that uses unsealed radioactive substances in diagnosis and therapy. ...

In biochemistry and genetics, radionuclides are used to label molecules and allow tracing chemical and physiological processes occurring in living organisms, such as DNA replication or amino acid transport. Biochemistry is the study of the chemistry of life, a bridge between biology and chemistry that studies how complex chemical reactions give rise to life. ... Genetics (from the Greek genno γεννώ= give birth) is the science of genes, heredity, and the variation of organisms. ... DNA replication. ... An amino acid residue is what is left of an amino acid once a molecule of water has been lost (an H+ from the nitrogenous side and an OH- from the carboxylic side) in the formation of a peptide bond. ...

In food preservation, radiation is 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. Various preserved foods Food preservation is the process of treating and handling food in such a way as to stop or greatly slow down spoilage to prevent foodborne illness while maintaining nutritional value, texture and flavor. ...

In agriculture and animal husbandry, radionuclides 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. In a draw in a mountainous region, a shepherd guides a flock of about 20 sheep amidst scrub and olive trees. ...

Industrially, and in mining, radionuclides 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. Chuquicamata, the largest open pit copper mine in the world, Chile. ...

Most household smoke detectors contain the radionuclide americium formed in nuclear reactors, saving many lives. Residential ceiling-mounted smoke detector A smoke detector or smoke alarm is an active fire protection device, subject to stringent bounding, that detects airborne smoke and issues an audible alarm, thereby alerting nearby people to the danger of fire. ... General Name, Symbol, Number americium, Am, 95 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass (243) g/mol Electron configuration [Rn] 5f7 7s2 Electrons per shell 2, 8, 18, 32, 25, 8, 2 Physical properties Phase solid Density (near r. ... Core of a small nuclear reactor used for research. ...

Environmentally, radionuclides 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. Devils Punchbowl Waterfall, New Zealand. ...

Natural radionuclides can be used in archaeology and in paleontology to measure ages. When radioactive carbon, for example, is in the atmosphere, it rapidly becomes separated from its decay products. Once it is bound up in a solid, such as wood or paper, its decay products must remain in place. So by measuring how much of these decay products has accumulated, one can estimate the time when the carbon was captured into solid form. Archaeology, archeology, or archæology (from the Greek words αρχαίος = ancient and λόγος = word/speech/discourse) is the study of human cultures through the recovery, documentation and analysis of material remains and environmental data, including architecture, artifacts, biofacts, human remains, and landscapes. ... A paleontologist carefully chips rock from a column of dinosaur vertebrae. ...

Dangers

If radionuclides are released into the environment, through accident, poor disposal, or other means, they can potentially cause harmful effects of radioactive contamination. They can also cause damage if they are excessively used during treatment or in other ways applied to living beings. This is called radiation poisoning. Radionuclides can also cause malfunction of electrical devices. The radiation warning symbol (trefoil). ... Radiation poisoning, also called radiation sickness, is a form of damage to organic tissue due to excessive exposure to ionizing radiation. ...

References

• Carlsson J et al.:Tumour therapy with radionuclides: assessment of progress and problems. Radiotherapy and Oncology, Volume 66, Issue 2, February 2003, Pages 107-117. PMID 12648782. Available online as full text.

See also

• radiometric dating
• ionizing radiation