seaborgium

Synthesized radioactive element of the transactinide series, atomic number 106, relative atomic mass 263. It was first synthesized in 1974 in the USA and given the temporary name unnilhexium. The discovery was not confirmed until 1993. It was officially named in 1997 after US nuclear chemist Glenn Seaborg.

The University of California, Berkeley, bombarded californium with oxygen nuclei to get isotope 263; the Joint Institute for Nuclear Research, Dubna, Russia, bombarded lead with chromium nuclei to obtain isotopes 259 and 260.