List of Radioactive Elements and Their Most Stable Isotopes

uranium periodic table
Uraniam is one of the most well known radioactive elements. JacobH / Getty Images

This is a list or table of elements that are radioactive. Keep in mind, all elements can have radioactive isotopes. If enough neutrons are added to an atom, it becomes unstable and decays. A good example of this is tritium, a radioactive isotope of hydrogen naturally present at extremely low levels. This table contains the elements that have no stable isotopes. Each element is followed by the most stable known isotope and its half-life.

Note increasing atomic number doesn't necessarily make an atom more unstable. Scientists predict there may be islands of stability in the periodic table, where superheavy transuranium elements may be more stable (although still radioactive) than some lighter elements.

This list is sorted by increasing atomic number.

Radioactive Elements

ElementMost Stable IsotopeHalf-life
of Most Stable Istope
TechnetiumTc-914.21 x 106 years
PromethiumPm-14517.4 years
PoloniumPo-209102 years
AstatineAt-2108.1 hours
RadonRn-2223.82 days
FranciumFr-22322 minutes
RadiumRa-2261600 years
ActiniumAc-22721.77 years
ThoriumTh-2297.54 x 104 years
ProtactiniumPa-2313.28 x 104 years
UraniumU-2362.34 x 107 years
NeptuniumNp-2372.14 x 106 years
PlutoniumPu-2448.00 x 107 years
AmericiumAm-2437370 years
CuriumCm-2471.56 x 107 years
BerkeliumBk-2471380 years
CaliforniumCf-251898 years
EinsteiniumEs-252471.7 days
FermiumFm-257100.5 days
MendeleviumMd-25851.5 days
NobeliumNo-25958 minutes
LawrenciumLr-2624 hours
RutherfordiumRf-26513 hours
DubniumDb-26832 hours
SeaborgiumSg-2712.4 minutes
BohriumBh-26717 seconds
HassiumHs-2699.7 seconds
MeitneriumMt-2760.72 seconds
DarmstadtiumDs-28111.1 seconds
RoentgeniumRg-28126 seconds
CoperniciumCn-28529 seconds
NihoniumNh-2840.48 seconds
FleroviumFl-2892.65 seconds
MoscoviumMc-28987 milliseconds
LivermoriumLv-29361 milliseconds
OganessonOg-2941.8 milliseconds


Where Do Radionuclides Come From?

Radioactive elements form naturally, as a result of nuclear fission, and via intentional synthesis in nuclear reactors or particle accelerators.


Natural radioisotopes may remain from nucleosynthesis in stars and supernova explosions. Typically these primordial radioisotopes have half-lives so long they are stable for all practical purposes, but when they decay they form what are called secondary radionuclides.

For example, primordial isotopes thorium-232, uranium-238, and uranium-235 can decay to form secondary radionuclides of radium and polonium. Carbon-14 is an example of a cosmogenic isotope. This radioactive element is continually formed in the atmosphere due to cosmic radiation.

Nuclear Fission

Nuclear fission from nuclear power plants and thermonuclear weapons produces radioactive isotopes called fission products. In addition, irradiation of surrounding structures and the nuclear fuel produces isotopes called activation products. A wide range of radioactive elements may result, which is part of why nuclear fallout and nuclear waste are so difficult to deal with.


The latest element on the periodic table have not been found in nature. These radioactive elements are produced in nuclear reactors and accelerators. There are different strategies used to form new elements. Sometimes elements are placed within a nuclear reactor, where the neutrons from the reaction react with the specimen to form desired products. Iridium-192 is an example of a radioisotope prepared in this manner. In other cases, particle accelerators bombard a target with energetic particles. An example of a radionuclide produced in an accelerator is fluorine-18.

Sometimes a specific isotope is prepared in order to gather its decay product. For example, molybdenum-99 is used to produce technetium-99m.

Commercially Available Radionuclides

Sometimes the longest-lived half-life of a radionuclide is not the most useful or affordable. Certain common isotopes are available even to the general public in small quantities in most countries. Others on this list are available by regulation to professionals in industry, medicine, and science:

Gamma Emitters

  • Barium-133
  • Cadmium-109
  • Cobalt-57
  • Cobalt-60
  • Europium-152
  • Manganese-54
  • Sodium-22
  • Zinc-65
  • Technetium-99m

Beta Emitters

  • Strontium-90
  • Thallium-204
  • Carbon-14
  • Tritium

Alpha Emitters

  • Polonium-210
  • Uranium-238

Multiple Radiation Emitters

  • Cesium-137
  • Americium-241

Effects of Radionuclides on Organisms

Radioactivity exists in nature, but radionuclides can cause radioactive contamination and radiation poisonin if find their way into the environment or an organism is over-exposed.

The type of potential damage depends on the type and energy of the emitted radiation. Typically, radiation exposure causes burns and cell damage. Radiation can cause cancer, but it might not appear for many years following exposure.


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  • Luig, H.; Kellerer, A. M.; Griebel, J. R. (2011). "Radionuclides, 1. Introduction". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a22_499.pub2 ISBN 978-3527306732.
  • Martin, James (2006). Physics for Radiation Protection: A Handbook. ISBN 978-3527406111.
  • Petrucci, R.H.; Harwood, W.S.; Herring, F.G. (2002). General Chemistry (8th ed.). Prentice-Hall. p.1025–26.