Guides
Which Elements Are Radioactive? (List and Rules)
Radioactive elements have unstable nuclei that spontaneously emit alpha, beta or gamma radiation and transform into other elements. Their distribution across the periodic table follows clear rules.
Rules of thumb
- Every element with atomic number ≥ 84 (polonium, Po) is radioactive (Po, At, Rn, Fr, Ra, Ac, Th, Pa, U, and all synthetic elements beyond 92).
- In addition, technetium Tc (43) and promethium Pm (61) have no stable isotopes despite their low atomic numbers.
- Many ordinary elements also have radioactive isotopes (e.g. ¹⁴C), but an element dominated by stable isotopes is not counted as a "radioactive element".
Common radioactive elements
| Element | Significance / use |
|---|---|
| Uranium U | nuclear fuel (²³⁵U fission) |
| Thorium Th | potential nuclear fuel |
| Radium Ra | historically in luminous paint (now obsolete) |
| Radon Rn | radioactive gas; an indoor pollutant to monitor |
| Plutonium Pu | reactors / weapons (synthetic) |
Safety note
Radioactive elements and their compounds require professional handling; school study is for understanding only. The radiation comes from unstable nuclei, tightly linked to the idea of isotopes. Browse the lanthanides/actinides in the browse view.