Science, Tech, Math › Science List of Radioactive Elements and Their Most Stable Isotopes Share Flipboard Email Print ThoughtCo / Maritsa Patrinos Science Chemistry Periodic Table Basics Chemical Laws Molecules Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Todd Helmenstine Todd Helmenstine is a science writer and illustrator who has taught physics and math at the college level. He holds bachelor's degrees in both physics and mathematics. our editorial process Todd Helmenstine Updated July 30, 2019 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 Element Most Stable Isotope Half-lifeof Most Stable Istope Technetium Tc-91 4.21 x 106 years Promethium Pm-145 17.4 years Polonium Po-209 102 years Astatine At-210 8.1 hours Radon Rn-222 3.82 days Francium Fr-223 22 minutes Radium Ra-226 1600 years Actinium Ac-227 21.77 years Thorium Th-229 7.54 x 104 years Protactinium Pa-231 3.28 x 104 years Uranium U-236 2.34 x 107 years Neptunium Np-237 2.14 x 106 years Plutonium Pu-244 8.00 x 107 years Americium Am-243 7370 years Curium Cm-247 1.56 x 107 years Berkelium Bk-247 1380 years Californium Cf-251 898 years Einsteinium Es-252 471.7 days Fermium Fm-257 100.5 days Mendelevium Md-258 51.5 days Nobelium No-259 58 minutes Lawrencium Lr-262 4 hours Rutherfordium Rf-265 13 hours Dubnium Db-268 32 hours Seaborgium Sg-271 2.4 minutes Bohrium Bh-267 17 seconds Hassium Hs-269 9.7 seconds Meitnerium Mt-276 0.72 seconds Darmstadtium Ds-281 11.1 seconds Roentgenium Rg-281 26 seconds Copernicium Cn-285 29 seconds Nihonium Nh-284 0.48 seconds Flerovium Fl-289 2.65 seconds Moscovium Mc-289 87 milliseconds Livermorium Lv-293 61 milliseconds Tennessine Unknown Oganesson Og-294 1.8 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 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. Synthetic 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-133Cadmium-109Cobalt-57Cobalt-60Europium-152Manganese-54Sodium-22Zinc-65Technetium-99m Beta Emitters Strontium-90Thallium-204Carbon-14Tritium Alpha Emitters Polonium-210Uranium-238 Multiple Radiation Emitters Cesium-137Americium-241 Effects of Radionuclides on Organisms Radioactivity exists in nature, but radionuclides can cause radioactive contamination and radiation poisoning if they 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. Sources International Atomic Energy Agency ENSDF database (2010).Loveland, W.; Morrissey, D.; Seaborg, G.T. (2006). Modern Nuclear Chemistry. Wiley-Interscience. p. 57. ISBN 978-0-471-11532-8.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. View Article Sources "Radiation Emergencies." Department of Health and Human Services Fact Sheet, Center for Disease Control, 2005. 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