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.
Table of Radioactive Elements
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.
| Element | Most Stable Isotope | Half-life of Most Stable Isotope |
| 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 | Unknown |
| Oganesson | Og-294 | 1.8 milliseconds |
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.