<page_title> Isotopes of magnesium </page_title> <section_title> List of isotopes </section_title> <table> <cell> 28Mg <col_header> nuclide symbol </col_header> </cell> <cell> 20.915(9) h <col_header> half-life </col_header> </cell> </table>
The longest-lived isotope is ²⁸Mg, with a half-life of 20.915 hours.