Isotopes of magnesium

Magnesium (Mg) naturally occurs in three stable isotopes, ²⁴Mg, ²⁵Mg, and ²⁶Mg. There are 19 radioisotopes that have been discovered, ranging from ¹⁹Mg to ⁴⁰Mg. The longest-lived radioisotope is ²⁸Mg with a half-life of 20.915 hours. The lighter isotopes mostly decay to isotopes of sodium while the heavier isotopes decay to isotopes of aluminium. The shortest-lived is ³⁹Mg with a half-life shorter than 180 nanoseconds, or possibly ⁴⁰Mg, with a half-life longer than 170 nanoseconds (the half-life of ¹⁹Mg is unknown).

Relative atomic mass: 24.3050(6)