(rŭð´´ərfôr'dēəm), artificially produced radioactive chemical element; symbol Rf; at. no. 104; mass number of most stable isotope 265; m.p., b.p., and sp. gr. unknown; valence +4. It is the first transuranium element beyond the actinide series, thus being the first of the transactinide elements. Situated in Group 4 of the periodic table, it has properties similar to those of hafnium and zirconium.
In 1964 a Soviet team led by G. N. Flerov at the Joint Institute for Nuclear Research at Dubna announced the discovery of element 104. They claimed to have isolated an isotope with mass number 260 and a half-life of 0.3 sec by bombarding plutonium-242 atoms with neon-22 ions. Subsequently, they suggested that element 104 be named kurchatovium (symbol Ku) to honor Igor Kurchatov, a Soviet pioneer in nuclear physics. In 1969, an American research team led by A. Ghiorso at the Lawrence Berkeley National Laboratory announced that, while they had been unable to confirm the Dubna group's results, they had identified at least two isotopes of element 104 different from the one identified by the Soviet scientists. They bombarded californium-249 atoms with carbon-12 and carbon-13 ions to creates isotopes with mass numbers 257 (half-life of 4.8 sec), 259 (half-life of 3 sec), and possibly 258 (half-life of 13 msec). Disputing the Soviet claim of discovery, the Americans suggested the name rutherfordium to honor the British physicist Lord Ernest Rutherford. An international committee set up to resolve such disputes decided in 1992 that the Berkeley and Dubna laboratories should share credit for the discovery. The syntheses of at least 10 isotopes of rutherfordium, with half-lives ranging from 0.5 msec (Rf-254) to about 13 hr (Rf-265), 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 104 be named dubnium in recognition of the work done at the Dubna laboratory. The committee also recommended that element 106, which had been called seaborgium by the American team that discovered it, be called rutherfordium. In 1997, however, the name rutherfordium for element 104 was recognized internationally.
See also synthetic elements.