World Library  
Flag as Inappropriate
Email this Article


Article Id: WHEBN0000037245
Reproduction Date:

Title: Radionuclide  
Author: World Heritage Encyclopedia
Language: English
Subject: Background radiation, Index of radiation articles, Monoisotopic element, Carcinogen, Health physics
Collection: Isotopes, Nuclear Chemistry, Nuclear Physics, Radioactivity
Publisher: World Heritage Encyclopedia


A radionuclide or radioactive nuclide is a nuclide that is radioactive. Also referred to as a radioisotope or radioactive isotope, it is an isotope with an unstable nucleus, characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or via internal conversion. During this process, the radionuclide is said to undergo radioactive decay, resulting in the emission of gamma ray(s) and/or subatomic particles such as alpha or beta particles.[1] These emissions constitute ionizing radiation. Many radionuclides occur naturally, and others are produced artificially, for example in nuclear reactors and cyclotrons.

There are about 650 radionuclides with half-lives longer than 60 minutes (see list of nuclides). Of these, 34 are primordial radionuclides that existed before the creation of the solar system, and there are another 50 radionuclides detectable in nature as daughters of these, or produced naturally on Earth by cosmic radiation. There is a much larger number of radionuclides, more than 2400, with decay half-lives shorter than 60 minutes. Most of these are only produced artificially, and have very short half-lives. For comparison, there are about 254 stable nuclides.

All chemical elements have radionuclides. Even the lightest element, hydrogen, has a well-known radionuclide, tritium. The heaviest elements (heavier than lead) exist only as radionuclides.

Radionuclides with suitable half-lives play an important part in a number of technologies, for example ionization smoke detectors and nuclear medicine. A pharmaceutical drug made with radionuclides is called a radiopharmaceutical, and an imaging tracer made with radionuclides is called a radiotracer. Nuclear medicine makes use of these drugs and tracers for radiation therapy such as brachytherapy and imaging.

Radionuclides can also present both real and perceived dangers to health.


  • Origin 1
  • Uses 2
  • Common examples 3
    • Americium-241 3.1
      • Steps for creating americium-241 3.1.1
    • Gadolinium-153 3.2
  • Dangers 4
  • Summary table for classes of nuclides, "stable" and radioactive 5
  • List of commercially available radionuclides 6
    • Gamma emission only 6.1
    • Beta emission only 6.2
    • Alpha emission only 6.3
    • Multiple radiation emitters 6.4
  • See also 7
  • Notes 8
  • References 9
  • Further reading 10
  • External links 11


Naturally occurring radionuclides fall into three categories: primordial radionuclides, secondary radionuclides, and cosmogenic radionuclides. Primordial radionuclides, such as uranium and thorium, originate mainly from the interiors of stars and are still present as their half-lives are so long they have not yet completely decayed. Secondary radionuclides are radiogenic isotopes derived from the decay of primordial radionuclides. They have shorter half-lives than primordial radionuclides. Cosmogenic isotopes, such as carbon-14, are present because they are continually being formed in the atmosphere due to cosmic rays.[2]

Artificially produced radionuclides can be produced by nuclear reactors, particle accelerators or by radionuclide generators:

  • Radioisotopes produced with nuclear reactors exploit the high flux of neutrons present. These neutrons activate elements placed within the reactor. A typical product from a nuclear reactor is thallium-201 and iridium-192. The elements that have a large propensity to take up the neutrons in the reactor are said to have a high neutron cross-section.
  • Particle accelerators such as cyclotrons accelerate particles to bombard a target to produce radionuclides. Cyclotrons accelerate protons at a target to produce positron-emitting radionuclides, e.g., fluorine-18.
  • Radionuclide generators contain a parent radionuclide that decays to produce a radioactive daughter. 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.
  • Radionuclides are produced as an unavoidable side-effect of nuclear and thermonuclear explosions.

Trace radionuclides are those that occur in tiny amounts in nature either due to inherent rarity or due to half-lives that are significantly shorter than the age of the Earth. Synthetic isotopes are inherently not naturally occurring on Earth, but can be created by nuclear reactions.


Radionuclides are used in two major ways: for their chemical properties and as sources of radiation. Radionuclides of familiar elements such as carbon can serve as radioactive tracers because they are chemically very similar to the nonradioactive nuclides, so most chemical, biological, and ecological processes treat them in a nearly 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.

In single-photon emission computed tomography and positron emission tomography scanning and Cerenkov luminescence imaging.

Radioisotopes are also a method of treatment in hemopoietic forms of tumors; the success for treatment of solid tumors has been limited. More powerful gamma sources sterilise syringes and other medical equipment.

In DNA replication or amino acid transport.

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.

In industry, and in mining, radionuclides examine welds, to detect leaks, to study the rate of wear, erosion and corrosion of metals, and for on-stream analysis of a wide range of minerals and fuels.

In particle physics, radionuclides help discover new physics (beyond Standard Model [BSM] physics) by measuring the energy and momentum of their beta decay products.[3]

Radionuclides are also used to trace and analyze 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. Natural radionuclides are used in geology, archaeology, and paleontology to measure ages of rocks, minerals, and fossil materials.

Common examples


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.

Most household smoke detectors contain americium produced in nuclear reactors. The radioisotope used is americium-241. The element americium is created by bombarding plutonium with neutrons in a nuclear reactor. Its isotope americium-241 decays by emitting alpha particles and gamma radiation to become neptunium-237. Most common household smoke detectors use a very small quantity of 241Am (about 0.29 micrograms per smoke detector) in the form of americium dioxide. Smoke detectors use 241Am since the alpha particles it emits collide with oxygen and nitrogen particles in the air. This occurs in the detector's ionization chamber where it produces charged particles or ions. Then, these charged particles are collected by a small electric voltage that will create an electric current that will pass between two electrodes. Then, the ions that are flowing between the electrodes will be neutralized when coming in contact with smoke, thereby decreasing the electric current between the electrodes, which will activate the detector's alarm.[4][5]

Steps for creating americium-241

The plutonium-241 is formed in any nuclear reactor by neutron capture from uranium-238.

  1. 238U + n239U
  2. 239U239Np + e + ν
  3. 239Np239Pu + e + ν
  4. 239Pu + n240Pu
  5. 240Pu + n241Pu

This will decay both in the reactor and subsequently to form 241Am, which has a half-life of 432.2 years.[6][7]


The 153Gd isotope is used in X-ray fluorescence and osteoporosis screening. It is a gamma-emitter with an 8-month half-life, making it easier to use for medical purposes. In nuclear medicine, it serves to calibrate the equipment needed like single-photon emission computed tomography systems (SPECT) to make x-rays. It ensures that the machines work correctly to produce images of radioisotope distribution inside the patient. This isotope is produced in a nuclear reactor from europium or enriched gadolinium.[8] It can also detect the loss of calcium in the hip and back bones, allowing the ability to diagnose osteoporosis.[9]


Radionuclides that find their way into the environment may cause harmful effects as 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."[10]

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 905 nuclides are theoretically stable, except to proton-decay (which has never been observed). About 254 nuclides have never been observed to decay, and are classically considered stable.

The remaining 650 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[11]), and another 6 nuclides with half-lives long enough (> 80 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 ~51 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 [12] for the 905 nuclides with half-lives longer than one hour (including those that are stable), given in list of nuclides.
Stability class Number of nuclides Running total Notes on running total
Theoretically stable to all but proton decay 90 90 Includes first 40 elements. Proton decay yet to be observed.
Energetically unstable to one or more known decay modes, but no decay yet seen. Spontaneous fission possible for "stable" nuclides ≥ niobium-93; other mechanisms possible for heavier nuclides. All considered "stable" until decay detected. 164 254 Total of classically stable nuclides.
Radioactive primordial nuclides. 34 288 Total primordial elements include uranium, thorium, bismuth, rubidium-87, potassium-40 plus all stable nuclides.
Radioactive nonprimordial, but naturally occurring on Earth. ~ 51 ~ 339 Carbon-14 (and other isotopes generated by cosmic rays) and daughters of radioactive primordial elements, such as radium, polonium, etc.
Radioactive synthetic (half-life ≥ 1.0 hour). Includes most useful radiotracers. 556 905 These 905 nuclides are listed in the article List of nuclides.
Radioactive synthetic (half-life < 1.0 hour). >2400 >3300 Includes 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. For a complete list of all known isotopes for every element (minus activity data), see list of nuclides, and Isotope Lists. For a table see Table of Nuclides.

Gamma emission only

Isotope Activity Half-life Energies (keV)
Barium-133 9694 TBq/kg (262 Ci/g) 10.7 years 81.0, 356.0
Cadmium-109 96200 TBq/kg (2600 Ci/g) 453 days 88.0
Cobalt-57 312280 TBq/kg (8440 Ci/g) 270 days 122.1
Cobalt-60 40700 TBq/kg (1100 Ci/g) 5.27 years 1173.2, 1332.5
Europium-152 6660 TBq/kg (180 Ci/g) 13.5 years 121.8, 344.3, 1408.0
Manganese-54 287120 TBq/kg (7760 Ci/g) 312 days 834.8
Sodium-22 237540 Tbq/kg (6240 Ci/g) 2.6 years 511.0, 1274.5
Zinc-65 304510 TBq/kg (8230 Ci/g) 244 days 511.0, 1115.5
Technetium-99m 1.95×104 TBq/g (5.27 × 107 Ci/g) 6 hours 140

Beta emission only

Isotope Activity Half-life Energies (keV)
Strontium-90 5180 TBq/kg (140 Ci/g) 28.5 years 546.0
Thallium-204 17057 TBq/kg (461 Ci/g) 3.78 years 763.4
Carbon-14 166.5 TBq/kg (4.5 Ci/g) 5730 years 49.5 (average)
Tritium (Hydrogen-3) 357050 TBq/kg (9650 Ci/g) 12.32 years 5.7 (average)

Alpha emission only

Isotope Activity Half-life Energies (keV)
Polonium-210 166500 TBq/kg (4500 Ci/g) 138 days 5304.5
Uranium-238 12580 KBq/kg (0.00000034 Ci/g) 4.468 billion years 4267

Multiple radiation emitters

Isotope Activity Half-life Radiation types Energies (keV)
Caesium-137 3256 TBq/kg (88 Ci/g) 30.1 years Gamma & beta G: 32, 661.6 B: 511.6, 1173.2
Americium-241 129.5 TBq/kg (3.5 Ci/g) 432.2 years Gamma & alpha G: 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. ^ Eisenbud, Merril; Gesell, Thomas F (1997-02-25). Environmental Radioactivity: From Natural, Industrial, and Military Sources. p. 134.  
  3. ^ 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.  
  4. ^ Smoke Detectors and Americium
  5. ^ Office of Radiation Protection – Am 241 Fact Sheet – Washington State Department of Health
  6. ^ "Smoke Detectors: Uses of Radioactive Isotopes". Chemistry Tutorial : Radioisotopes in Smoke Detectors. AUS-e-TUTE n.d. Retrieved March 30, 2011. 
  7. ^ Reaction in a Smoke Detector
  8. ^ PNNL: Isotope Sciences Program – Gadolinium-153
  9. ^ "Gadolinium". BCIT Chemistry Resource Center. British Columbia Institute of Technology. Retrieved 30 March 2011. 
  10. ^ "Ionizing radiation, health effects and protective measures". World Health Organization. November 2012. Retrieved January 27, 2014. 
  11. ^ "Cosmic Detectives". The European Space Agency (ESA). 2013-04-02. Retrieved 2013-04-15. 
  12. ^ 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


  • Carlsson, J.; et al., E; Hietala, SO; Stigbrand, T; Tennvall, J (2003). "Tumour therapy with radionuclides: assessment of progress and problems". Radiotherapy and Oncology 66 (2): 107–117.  
  • "Radioisotopes in Industry". World Nuclear Association. 
  • Martin, James (2006). Physics for Radiation Protection: A Handbook. p. 130.  

Further reading

  • Luig, H.; Kellerer, A. M.; Griebel, J. R. (2011). "Ullmann's Encyclopedia of Industrial Chemistry".  

External links

  • EPA – Radionuclides – EPA's Radiation Protection Program: Information.
  • FDA – Radionuclides – FDA's Radiation Protection Program: Information.
  • Interactive Chart of Nuclides – A chart of all nuclides
  • National Isotope Development Center – U.S. Government source of radionuclides – production, research, development, distribution, and information
  • The Live Chart of Nuclides – IAEA
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Hawaii eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.