Atomic Number: 105
Atomic Mass: 262.0 amu (atomic mass units)
Melting Point: Unknown
Boiling Point: Unknown
Number of Protons: 105
Number of Electrons: 105
Number of Neutrons: 157
Classification: Transition Metal
Crystal Structure: Unknown
Density @ 293 K: Unknown
Dubnium is a radioactive man made super-heavy element. The first claim to have produced atoms of element 105 were was made in1967 by the a team of Russian scientists under Georgy Nikolayevich Flerov based at the Joint Institute for Nuclear Research in Dubna, Russia. They measured alpha energies resulting from the bombardment of americium-243 atoms with neon-22 ions. From these measurements they concluded that atoms of two isotopes of element 105 had been formed 105-260 and 105-261. At this point the team did not give the element a name.
In April 1970 two substantive claims to the element were made. One was from the original Russian team and the other by a team under Albert Ghiorso from the University of California at Berkeley. The American team bombarded atoms of californium-249 with nitrogen-15 ions to produce 105-260. The American team proposed the name Hahnium with the symbol after the German scientist Otto Hahn with the symbol Ha.
The team from Berkeley was also able to produce the element from collisions between berkelium- 249 and ions of nitrogen-16. However they were not able repeat the results obtained by the Russians despite using more sophisticated equipment and so disputed their claim.
As there was a dispute between the two groups as to who had made the original substantive discovery of element 105 the International Union for Pure and Applied Chemistry (IUPAC) gave the element a temporary name using their nomenclature system for new elements. So for a while element 105 became known as unnilpentium (un-nil-pent meaning 1-0-5) with the symbol Unp. IUPAC also suggested the name juliotium with the symbol Jl. The Russian team suggested the name nielsbohrium with the symbol Ns. Eventually with the names hahnium, juliotium and nielsbohrium all rejected the name dubnium was officially given to element 105 after the Russian town of Dubna. This naming ceremony was carried out at the Geneva conference of IUPAC in 1997. The credit for the discovery being given jointly to both teams the dispute is now deemed closed.
For an element with such a story behind its name not much else is known. It has eleven known isotopes all of which are unstable. The most stable isotope is dubnium-268 which has a half life of about 16 hours. Very few atoms of dubnium have been produced and the only atoms of the element are likely to found in a detection chamber within laboratories specializing in research into the super-heavy elements.