<page_title> Isotopes of fermium </page_title> <section_title> List of isotopes </section_title> <table> <cell> 257Fm <col_header> nuclide symbol </col_header> <col_header> excitation energy </col_header> </cell> <cell> 100.5(2) d <col_header> half-life </col_header> </cell> </table>
The isotope is ²⁵⁷Fm, with a half-life of 100.5 days.