rutherfordium

An artificially produced radioactive element with atomic number 104 that has only been produced in trace amounts. The isotope with mass number 261 has the longest confirmed half-life (65 seconds), although isotopes with longer half-lives have been reported. cross-reference: Periodic Table.

A transuranic chemical element (symbol Rf) with an atomic number of 104

A rejected name for seaborgium

a radioactive transuranic element which has been synthesized