# What Are the Radioactive Elements? 1

This is a list of the radioactive elements of the periodic table. While all elements have some radioactive isotopes, these 37 elements have no stable isotopes. These elements are considered the “radioactive elements”.

The periodic table above is a visual representation of the data in the table below. It is available to download as an image or black and white PDF.

This is a list of the radioactive elements and their most stable isotopes. While many of these elements have half-lives so long they almost appear stable, the heavier elements decay almost instantly.

### Natural vs Synthetic Radioactive Elements

Not all of the elements on the periodic table occur in nature. For the most part, elements with high atomic numbers come from nuclear reactors and particle accelerators.

Some natural radioactive elements come from nucleosynthesis in stars and supernova. These primordial elements have long half-lives, so they existed before the Earth formed. Eventually, they decay into secondary radionuclides. Examples of primordial radioisotopes include thorium-232, uranium-238, and uranium-235, which decay into radium and polonium. However, some radioisotopes still form today. For example, cosmic radiation continuously produces carbon-14.

There are a few ways of synthesizing radioactive elements. One involves placing an element in reactor and allowing neutrons to react and form products. An example of a radioactive element formed this way is iridium-192. Another process strikes a target with energetic particles. For example, fluorine-18 forms in particle accelerators. Sometimes researchers make a heavier element and obtain the desired product as part of the decay scheme. For example, technetium-99m comes from the decay of molybdenum-99. A technetium cow or moly cow is a device containing molybdenum-99, which has a half-life of 66 hours. Its decay product is technetium-99m, which only lasts about 6 hours. So, transporting the molybdenum isotopes allows delivery of the useful technetium isotope.

#### Fission Products

Nuclear fission does occur naturally in uranium or plutonium ore deposits, but most fission products come from nuclear power plants, nuclear tests, thermonuclear weapons. For example, the radioactive fission products of uranium-235 include iodine, cesium, strontium, xenon, and barium isotopes.

Some common isotopes are available (in small quantities) to researchers, medical professionals, industries, and even to the general public. For the most part, these radionuclides have relatively long half-lives, ranging from a few hours to several years. Regular people generally get radioactive elements as part of element collections. Otherwise, they primarily find use as tracers. The hydrogen isotope tritium is popular for glow in the dark items.

#### Gamma Emitters

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

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

• Polonium-210
• Uranium-238

#### Emit Multiple Particles

• Cesium-137
• Americium-241

### References

• International Atomic Energy Agency ENSDF database (2010).
• Loveland, W.; Morrissey, D.; Seaborg, G.T. (2006). Modern Nuclear Chemistry. Wiley-Interscience. ISBN 978-0-471-11532-8.
• Luig, H.; Kellerer, A. M.; Griebel, J. R. (2011). “Radionuclides, 1. Introduction”. Ullmann’s Encyclopedia of Industrial Chemistry. ISBN 978-3527306732. doi:10.1002/14356007.a22_499.pub2
• 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.

## One thought on “What Are the Radioactive Elements?”

• Anne Helmenstine

Good question! The short answer is the mass of the proton and neutron is not exactly the same, so there is no number of each that produces a stable nucleus. I’ll write up the full explanation in an article.