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A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is an atom that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferred to one of its electrons to release it as a conversion electron; or used to create and emit a new particle (alpha particle or beta particle) from the nucleus. During those processes, the radionuclide is said to undergo radioactive decay. [1] These emissions are considered ionizing radiation because they are powerful enough to liberate an electron from another atom. The radioactive decay can produce a stable nuclide or will sometimes produce a new unstable radionuclide which may undergo further decay. Radioactive decay is a random process at the level of single atoms: it is impossible to predict when one particular atom will decay. [2] [3] [4] [5] However, for a collection of atoms of a single element the decay rate, and thus the half-life (t1/2) for that collection can be calculated from their measured decay constants. The range of the half-lives of radioactive atoms have no known limits and span a time range of over 55 orders of magnitude.

Atom smallest unit of a chemical element

An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small; typical sizes are around 100 picometers.

Electron subatomic particle with negative electric charge

The electron is a subatomic particle, symbol
, whose electric charge is negative one elementary charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum (spin) of a half-integer value, expressed in units of the reduced Planck constant, ħ. As it is a fermion, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: they can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy.

Internal conversion radioactive decay process wherein an excited nucleus interacts electromagnetically with one of its electrons, causing it to be ejected from the atom

Internal conversion is a radioactive decay process wherein an excited nucleus interacts electromagnetically with one of the orbital electrons of the atom. This causes the electron to be emitted (ejected) from the atom. Thus, in an internal conversion process, a high-energy electron is emitted from the radioactive atom, but not from the nucleus. For this reason, the high-speed electrons resulting from internal conversion are not called beta particles, since the latter come from beta decay, where they are newly created in the nuclear decay process.


Radionuclides occur naturally or are artificially produced in nuclear reactors, cyclotrons, particle accelerators or radionuclide generators. There are about 730 radionuclides with half-lives longer than 60 minutes (see list of nuclides). Thirty-two of those are primordial radionuclides that were created before the earth was formed. At least another 60 radionuclides are detectable in nature, either as daughters of primordial radionuclides or as radionuclides produced through natural production on Earth by cosmic radiation. More than 2400 radionuclides have half-lives less than 60 minutes. Most of those are only produced artificially, and have very short half-lives. For comparison, there are about 253 stable nuclides. (In theory, only 146 of them are stable, and the other 107 are believed to decay (alpha decay or beta decay or double beta decay or electron capture or double electron capture))

Nuclear reactor device to initiate and control a sustained nuclear chain reaction

A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a self-sustained nuclear chain reaction. Nuclear reactors are used at nuclear power plants for electricity generation and in propulsion of ships. Heat from nuclear fission is passed to a working fluid, which in turn runs through steam turbines. These either drive a ship's propellers or turn electrical generators' shafts. Nuclear generated steam in principle can be used for industrial process heat or for district heating. Some reactors are used to produce isotopes for medical and industrial use, or for production of weapons-grade plutonium. Some are run only for research. As of early 2019, the IAEA reports there are 454 nuclear power reactors and 226 nuclear research reactors in operation around the world.

Cyclotron a type of particle accelerator

A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929-1930 at the University of California, Berkeley, and patented in 1932. A cyclotron accelerates charged particles outwards from the center along a spiral path. The particles are held to a spiral trajectory by a static magnetic field and accelerated by a rapidly varying electric field. Lawrence was awarded the 1939 Nobel prize in physics for this invention.

Particle accelerator device to propel charged particles to high speeds

A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.

All chemical elements can exist as radionuclides. Even the lightest element, hydrogen, has a well-known radionuclide, tritium. 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. gold and platinum) are too long to found)

Chemical element a species of atoms having the same number of protons in the atomic nucleus

A chemical element is a species of atom having the same number of protons in their atomic nuclei. For example, the atomic number of oxygen is 8, so the element oxygen consists of all atoms which have exactly 8 protons.

Hydrogen Chemical element with atomic number 1

Hydrogen is a chemical element with symbol H and atomic number 1. With a standard atomic weight of 1.008, hydrogen is the lightest element in the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass. Non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton and no neutrons.

Tritium isotope of hydrogen with 2 neutrons

Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons. Naturally occurring tritium is extremely rare on Earth, where trace amounts are formed by the interaction of the atmosphere with cosmic rays. It can be produced by irradiating lithium metal or lithium-bearing ceramic pebbles in a nuclear reactor. Tritium is used as a radioactive tracer, in radioluminescent light sources for watches and instruments, and, along with deuterium, as a fuel for nuclear fusion reactions with applications in energy generation and weapons. The name of this isotope is derived from Greek, Modern τρίτος (trítos), meaning 'third'.

Unplanned exposure to radionuclides generally has a harmful effect on living organisms including humans, although low levels of exposure occur naturally without harm. 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. However, radionuclides with suitable properties are used in nuclear medicine for both diagnosis and treatment. An imaging tracer made with radionuclides is called a radioactive tracer. A pharmaceutical drug made with radionuclides is called a radiopharmaceutical.

Nuclear medicine is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear medicine, in a sense, is "radiology done inside out" or "endoradiology" because it records radiation emitting from within the body rather than radiation that is generated by external sources like X-rays. In addition, nuclear medicine scans differ from radiology as the emphasis is not on imaging anatomy but the function and for such reason, it is called a physiological imaging modality. Single photon emission computed tomography (SPECT) and positron emission tomography (PET) scans are the two most common imaging modalities in nuclear medicine.

A radioactive tracer, or radioactive label, is a chemical compound in which one or more atoms have been replaced by a radionuclide so by virtue of its radioactive decay it can be used to explore the mechanism of chemical reactions by tracing the path that the radioisotope follows from reactants to products. Radiolabeling is thus the radioactive form of isotopic labeling.

Radiopharmaceutical Medicinal radiocompound

Radiopharmaceuticals, or medicinal radiocompounds, are a group of pharmaceutical drugs which have radioactivity. Radiopharmaceuticals can be used as diagnostic and therapeutic agents. Radiopharmaceuticals emit radiation themselves, which is different from contrast media which absorb or alter external electromagnetism or ultrasound. Radiopharmacology is the branch of pharmacology that specializes in these agents.



On Earth, naturally occurring radionuclides fall into three categories: primordial radionuclides, secondary radionuclides, and cosmogenic radionuclides.

Stellar nucleosynthesis is the theory explaining the creation (nucleosynthesis) of chemical elements by nuclear fusion reactions between atoms within stars. Stellar nucleosynthesis has occurred continuously since the original creation of hydrogen, helium and lithium during the Big Bang. It is a highly predictive theory that today yields excellent agreement between calculations based upon it and the observed abundances of the elements. It explains why the observed abundances of elements in the universe grow over time and why some elements and their isotopes are much more abundant than others. The theory was initially proposed by Fred Hoyle in 1946, who later refined it in 1954. Further advances were made, especially to nucleosynthesis by neutron capture of the elements heavier than iron, by Margaret Burbidge, Geoffrey Burbidge, William Alfred Fowler and Hoyle in their famous 1957 B2FH paper, which became one of the most heavily cited papers in astrophysics history.

Uranium Chemical element with atomic number 92

Uranium is a chemical element with symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weakly radioactive because all isotopes of uranium are unstable, with half-lives varying between 159,200 years and 4.5 billion years. The most common isotopes in natural uranium are uranium-238 and uranium-235. Uranium has the highest atomic weight of the primordially occurring elements. Its density is about 70% higher than that of lead, and slightly lower than that of gold or tungsten. It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite.

Thorium Chemical element with atomic number 90

Thorium is a weakly radioactive metallic chemical element with symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately hard, malleable, and has a high melting point. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state; it is quite reactive and can ignite in air when finely divided.

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. Thus polonium can be found in uranium ores at about 0.1 mg per metric ton (1 part in 1010). [7] [8] Further radionunclides may occur in nature in virtually undetectable amounts as a result of rare events such as spontaneous fission or uncommon cosmic ray interactions.

Nuclear fission

Radionuclides are produced as an unavoidable result of nuclear fission and thermonuclear explosions. The process of nuclear fission creates a wide range of fission products, most of which are radionuclides. Further radionuclides can be created from irradiation of the nuclear fuel (creating a range of actinides) and of the surrounding structures, yielding activation products. This complex mixture of radionuclides with different chemistries and radioactivity makes handling nuclear waste and dealing with nuclear fallout particularly problematic.


Artificial nuclide americium-241 emitting alpha particles inserted into a cloud chamber for visualisation Artificial nuclide americium-241 emitting alpha particles inserted into a cloud chamber for visualisation.jpg
Artificial nuclide americium-241 emitting alpha particles inserted into a cloud chamber for visualisation

Synthetic radionuclides are deliberately synthesised using nuclear reactors, particle accelerators or radionuclide generators:


Radionuclides are used in two major ways: either for their radiation alone (irradiation, nuclear batteries) or for the combination of chemical properties and their radiation (tracers, biopharmaceuticals).


The following table lists properties of selected radionuclides illustrating the range of properties and uses.

Mode of formationComments
Tritium (3H)1212.3 yβ19Cosmogeniclightest radionuclide, used in artificial nuclear fusion, also used for radioluminescence and as oceanic transient tracer. Synthesized from neutron bombardment of lithium-6 or deuterium
Beryllium-10 461,387,000 yβ556Cosmogenicused to examine soil erosion, soil formation from regolith, and the age of ice cores
Carbon-14 685,700 yβ156Cosmogenicused for radiocarbon dating
Fluorine-18 99110 minβ+, EC 633/1655Cosmogenicpositron source, synthesised for use as a medical radiotracer in PET scans.
Aluminium-26 1313717,000 yβ+, EC 4004Cosmogenicexposure dating of rocks, sediment
Chlorine-36 1719301,000 yβ, EC 709Cosmogenicexposure dating of rocks, groundwater tracer
Potassium-40 19211.24×109 yβ, EC 1330 /1505Primordialused for potassium-argon dating, source of atmospheric argon, source of radiogenic heat, largest source of natural radioactivity
Calcium-41 2021102,000 yECCosmogenicexposure dating of carbonate rocks
Cobalt-60 27335.3 yβ2824Syntheticproduces high energy gamma rays, used for radiotherapy, equipment sterilisation, food irradiation
Strontium-90 385228.8 yβ546Fission product medium-lived fission product; probably most dangerous component of nuclear fallout
Technetium-99 4356210,000 yβ294Fission productcommonest isotope of the lightest unstable element, most significant of long-lived fission products
Technetium-99m 43566 hrγ,IC141Syntheticmost commonly used medical radioisotope, used as a radioactive tracer
Iodine-129 537615,700,000 yβ194Cosmogeniclongest lived fission product; groundwater tracer
Iodine-131 53788 dβ971Fission productmost significant short term health hazard from nuclear fission, used in nuclear medicine, industrial tracer
Xenon-135 54819.1 hβ1160Fission Productstrongest known "nuclear poison" (neutron-absorber), with a major effect on nuclear reactor operation.
Caesium-137 558230.2 yβ1176Fission Productother major medium-lived fission product of concern
Gadolinium-153 6489240 dECSyntheticCalibrating nuclear equipment, bone density screening
Bismuth-209 831261.9×1019yα3137Primordiallong considered stable, decay only detected in 2003
Polonium-210 84126138 dα5307Decay ProductHighly toxic, used in poisoning of Alexander Litvinenko
Radon-222 861363.8dα5590Decay Productgas, responsible for the majority of public exposure to ionizing radiation, second most frequent cause of lung cancer
Thorium-232 901421.4×1010 yα4083Primordialbasis of thorium fuel cycle
Uranium-235 921437×108yα4679Primordial fissile, main nuclear fuel
Uranium-238 921464.5×109 yα4267PrimordialMain Uranium isotope
Plutonium-238 9414487.7 yα5593Syntheticused in radioisotope thermoelectric generators (RTGs) and radioisotope heater units as an energy source for spacecraft
Plutonium-239 9414524110 yα5245Syntheticused for most modern nuclear weapons
Americium-241 95146432 yα5486Syntheticused in household smoke detectors as an ionising agent
Californium-252 981542.64 yα/SF6217Syntheticundergoes spontaneous fission (3% of decays), making it a powerful neutron source, used as a reactor initiator and for detection devices

Key: Z = atomic number; N = neutron number; DM = decay mode; DE = decay energy; EC = electron capture

Household smoke detectors

Americium-241 container in a smoke detector. Americium-241.jpg
Americium-241 container in a smoke detector.
Americium-241 capsule as found in smoke detector. The circle of darker metal in the center is americium-241; the surrounding casing is aluminium. Americium-241 Sample from Smoke Detector.JPG
Americium-241 capsule as found in smoke detector. The circle of darker metal in the center is americium-241; the surrounding casing is aluminium.

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. It decays by emitting alpha particles and gamma radiation to become neptunium-237. Smoke detectors use a very small quantity of 241Am (about 0.29 micrograms per smoke detector) in the form of americium dioxide. 241Am is used as it emits alpha particles which ionise the air in the detector's ionization chamber. A small electric voltage is applied to the ionised air which gives rise to a small electric current. In the presence of smoke some of the ions are neutralized, thereby decreasing the current, which activates the detector's alarm. [13] [14]

Impacts on organisms

Radionuclides that find their way into the environment may cause harmful effects as radioactive contamination. They can also cause damage if they are excessively used during treatment or in other ways exposed to living beings, by radiation poisoning. Potential health damage from exposure to radionuclides depends on a number of factors, and "can damage the functions of healthy tissue/organs. Radiation exposure can produce effects ranging from skin redness and hair loss, to radiation burns and acute radiation syndrome. Prolonged exposure can lead to cells being damaged and in turn lead to cancer. Signs of cancerous cells might not show up until years, or even decades, after exposure." [15]

Summary table for classes of nuclides, "stable" and radioactive

Following is a summary table for the total list of nuclides with half-lives greater than one hour. Ninety of these 989 nuclides are theoretically stable, except to proton-decay (which has never been observed). About 253 nuclides have never been observed to decay, and are classically considered stable.

The remaining 662 radionuclides have half-lives longer than 1 hour, and are well-characterized (see list of nuclides for a complete tabulation). They include 28 nuclides with measured half-lives longer than the estimated age of the universe (13.8 billion years [16] ), and another 4 nuclides with half-lives long enough (> 100 million years) that they are radioactive primordial nuclides, and may be detected on Earth, having survived from their presence in interstellar dust since before the formation of the solar system, about 4.6 billion years ago. Another 60+ short-lived nuclides can be detected naturally as daughters of longer-lived nuclides or cosmic-ray products. The remaining known nuclides are known solely from artificial nuclear transmutation.

Numbers are not exact, and may change slightly in the future, as "stable nuclides" are observed to be radioactive with very long half-lives.

This is a summary table [17] for the 988 nuclides with half-lives longer than one hour (including those that are stable), given in list of nuclides.

Stability classNumber of nuclides Running total Notes on running total
Theoretically stable to all but proton decay 9090Includes first 40 elements. Proton decay yet to be observed.
Theoretically stable to alpha decay, beta decay, isomeric transition, and double beta decay but not spontaneous fission, which is possible for "stable" nuclides ≥ niobium-93 56146All nuclides that are possible completely stable (spontaneous fission has never been observed for nuclides with mass number < 232).
Energetically unstable to one or more known decay modes, but no decay yet seen. All considered "stable" until decay detected.107253Total of classically stable nuclides.
Radioactive primordial nuclides.33286Total primordial elements include uranium, thorium, bismuth, rubidium-87, potassium-40, tellurium-128 plus all stable nuclides.
Radioactive nonprimordial, but naturally occurring on Earth.61347 Carbon-14 (and other isotopes generated by cosmic rays) and daughters of radioactive primordial elements, such as radium, polonium, etc. 41 of these have a half life of greater than one hour.
Radioactive synthetic half-life ≥ 1.0 hour). Includes most useful radiotracers.662989These 989 nuclides are listed in the article List of nuclides.
Radioactive synthetic (half-life < 1.0 hour).>2400>3300Includes all well-characterized synthetic nuclides.

List of commercially available radionuclides

This list covers common isotopes, most of which are available in very small quantities to the general public in most countries. Others that are not publicly accessible are traded commercially in industrial, medical, and scientific fields and are subject to government regulation.

Gamma emission only

Isotope Activity Half-lifeEnergies (keV)
Barium-133 9694 TBq/kg (262 Ci/g)10.7 years81.0, 356.0
Cadmium-109 96200 TBq/kg (2600 Ci/g)453 days88.0
Cobalt-57 312280 TBq/kg (8440 Ci/g)270 days122.1
Cobalt-60 40700 TBq/kg (1100 Ci/g)5.27 years1173.2, 1332.5
Europium-152 6660 TBq/kg (180 Ci/g)13.5 years121.8, 344.3, 1408.0
Manganese-54 287120 TBq/kg (7760 Ci/g)312 days834.8
Sodium-22 237540 Tbq/kg (6240 Ci/g)2.6 years511.0, 1274.5
Zinc-65 304510 TBq/kg (8230 Ci/g)244 days511.0, 1115.5
Technetium-99m 1.95×107 TBq/kg (5.27 × 105 Ci/g)6 hours140

Beta emission only

IsotopeActivityHalf-lifeEnergies (keV)
Strontium-90 5180 TBq/kg (140 Ci/g)28.5 years546.0
Thallium-204 17057 TBq/kg (461 Ci/g)3.78 years763.4
Carbon-14 166.5 TBq/kg (4.5 Ci/g)5730 years49.5 (average)
Tritium (Hydrogen-3)357050 TBq/kg (9650 Ci/g)12.32 years5.7 (average)

Alpha emission only

IsotopeActivityHalf-lifeEnergies (keV)
Polonium-210 166500 TBq/kg (4500 Ci/g)138.376 days5304.5
Uranium-238 12580 KBq/kg (0.00000034 Ci/g)4.468 billion years4267

Multiple radiation emitters

IsotopeActivityHalf-lifeRadiation typesEnergies (keV)
Caesium-137 3256 TBq/kg (88 Ci/g)30.1 yearsGamma & betaG: 32, 661.6 B: 511.6, 1173.2
Americium-241 129.5 TBq/kg (3.5 Ci/g)432.2 yearsGamma & alphaG: 59.5, 26.3, 13.9 A: 5485, 5443

See also


  1. R.H. Petrucci, W.S. Harwood and F.G. Herring, General Chemistry (8th ed., Prentice-Hall 2002), p.1025–26
  2. "Decay and Half Life" . Retrieved 2009-12-14.
  3. Stabin, Michael G. (2007). "3". Radiation Protection and Dosimetry: An Introduction to Health Physics (Submitted manuscript). Springer. doi:10.1007/978-0-387-49983-3. ISBN   978-0387499826.
  4. Best, Lara; Rodrigues, George; Velker, Vikram (2013). "1.3". Radiation Oncology Primer and Review. Demos Medical Publishing. ISBN   978-1620700044.
  5. Loveland, W.; Morrissey, D.; Seaborg, G.T. (2006). Modern Nuclear Chemistry. Modern Nuclear Chemistry. Wiley-Interscience. p. 57. ISBN   978-0-471-11532-8.
  6. Eisenbud, Merril; Gesell, Thomas F (1997-02-25). Environmental Radioactivity: From Natural, Industrial, and Military Sources. p. 134. ISBN   9780122351549.
  7. Bagnall, K. W. (1962). "The Chemistry of Polonium". Advances in Inorganic Chemistry and Radiochemistry 4. New York: Academic Press. pp. 197–226. doi:10.1016/S0065-2792(08)60268-X. ISBN   0-12-023604-4. Retrieved June 14, 2012., p. 746
  8. Bagnall, K. W. (1962). "The Chemistry of Polonium". Advances in Inorganic Chemistry and Radiochemistry 4. New York: Academic Press., p. 198
  9. Ingvar, David H.; Lassen, Niels A. (1961). "Quantitative determination of regional cerebral blood-flow in man". The Lancet . 278 (7206): 806–807. doi:10.1016/s0140-6736(61)91092-3.
  10. Ingvar, David H.; Franzén, Göran (1974). "Distribution of cerebral activity in chronic schizophrenia". The Lancet . 304 (7895): 1484–1486. doi:10.1016/s0140-6736(74)90221-9.
  11. Lassen, Niels A.; Ingvar, David H.; Skinhøj, Erik (October 1978). "Brain Function and Blood Flow". Scientific American . 239 (4): 62–71. Bibcode:1978SciAm.239d..62L. doi:10.1038/scientificamerican1078-62.
  12. Severijns, Nathal; Beck, Marcus; Naviliat-Cuncic, Oscar (2006). "Tests of the standard electroweak model in nuclear beta decay". Reviews of Modern Physics. 78 (3): 991–1040. arXiv: nucl-ex/0605029 . Bibcode:2006RvMP...78..991S. doi:10.1103/RevModPhys.78.991.
  13. "Smoke Detectors and Americium". Archived from the original on 2010-11-12.
  14. Office of Radiation Protection – Am 241 Fact Sheet – Washington State Department of Health Archived 2011-03-18 at the Wayback Machine
  15. "Ionizing radiation, health effects and protective measures". World Health Organization. November 2012. Retrieved January 27, 2014.
  16. "Cosmic Detectives". The European Space Agency (ESA). 2013-04-02. Retrieved 2013-04-15.
  17. Table data is derived by counting members of the list; see WP:CALC. References for the list data itself are given below in the reference section in list of nuclides

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Alpha particles, also called alpha ray or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, α. The symbol for the alpha particle is α or α2+. Because they are identical to helium nuclei, they are also sometimes written as He2+
or 4
indicating a helium ion with a +2 charge. If the ion gains electrons from its environment, the alpha particle becomes a normal helium atom 4

Primordial nuclide

In geochemistry, geophysics and geonuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the interstellar medium from which the solar system was formed, and were formed in, or after, the Big Bang, by nucleosynthesis in stars and supernovae followed by mass ejection, by cosmic ray spallation, and potentially from other processes. They are the stable nuclides plus the long-lived fraction of radionuclides surviving in the primordial solar nebula through planet accretion until the present. Only 286 such nuclides are known.

Nuclear transmutation

Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. Because any element is defined by its number of protons in its atoms, i.e. in the atomic nucleus, nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus is changed.


Further reading