Dubnium

Dubnium, also called eka-tantalum, is a chemical element in the periodic table that has the symbol Db and atomic number 105. This is a highly radioactive synthetic element whose most stable isotope has a half life of 32 hours (268Db). This relatively high stability compared to the surrounding elements on the periodic table gives evidence that by manipulating the number of neutrons in a nucleus, one can alter the stabilities of such nuclei.

History
Dubnium (named after Dubna, Russia) was reportedly first synthesized in 1967 at the Joint Institute for Nuclear Research in Dubna, Russia (reportedly producing nuclide 260105 and nuclide 261105 by bombarding 243Am with 22Ne). In late April 1970 researchers led by Albert Ghiorso working at the University of California, Berkeley had positively identified element 105.

The American team synthesized the element by bombarding a target 249Cf with a beam of 84 MeV nitrogen nuclei in the Heavy Ion Linear Accelerator (a particle accelerator), which produced nuclide 260105 with a half-life of 1.6 seconds. Atoms of element 105 were detected conclusively on March 5, 1970 but there is evidence that this element had already been formed at Berkeley a year earlier using the same method.

The Berkeley scientists later tried to confirm the Soviet findings using more sophisticated methods but were not successful. They proposed that the new element should be named hahnium (symbol Ha) in honor of the late German scientist Otto Hahn. Consequently this was the name that most American and Western European scientists used.

An element naming controversy erupted over what to name this element after Russian researchers protested. The International Union of Pure and Applied Chemistry (IUPAC) thus adopted unnilpentium (, symbol Unp) as a temporary, systematic element name. However in 1997 they resolved the dispute and adopted the current name, dubnium (symbol Db), after the city that contains the Russian Joint Institute for Nuclear Research. Its former names have included hahnium, joliotium and nielsbohrium, symbol Ns.