sēbôrˈgēəm, artificially produced radioactive chemical element; symbol Sg; at. no. 106; mass number of most stable isotope 266; m.p., b.p., sp. gr., and valence unknown. Situated in group VIb of the periodic table, it is expected to have properties similar to those of tungsten.

The discovery of element 106 took place almost simultaneously in two different laboratories. In June, 1974, a Soviet team led by G. N. Flerov at the Joint Institute for Nuclear Research at Dubna reported bombarding lead-207 and lead-208 atoms with chromium-54 ions to produce an isotope with mass number 259 and a half-life of 7 msec. In Sept., 1974, an American research team led by A. Ghiorso at the Lawrence Berkeley National Laboratory reported bombarding californium-249 atoms with oxygen-18 ions to create an isotope with mass number 263 and a half-life of 0.9 sec. Because their work was independently confirmed first, the Americans suggested the name seaborgium to honor the American chemist Glenn T. Seaborg. An international committee decided in 1992 that the Berkeley and Dubna laboratories should share credit for the discovery. The syntheses of at least six isotopes of seaborgium, with half-lives ranging from 0.4 msec (Sg-260) to 30 sec (Sg-266), have been confirmed.

In 1994 a committee of the International Union of Pure and Applied Chemistry (IUPAC), convened to resolve naming disputes for the transactinide elements, recommended that element 106 be named rutherfordium. In 1997, however, the name seaborgium for element 106 was recognized internationally.

See also synthetic elements; transuranium elements.

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