Db - Dubnium
In 1967 G.N. Flerov reported that a Soviet team working at the Joint Institute forNuclear Research at Dubna may have produced a few atoms of 260-105 and 261-105 bybombarding 243Am with 22Ne. The evidence was based on time-coincidence measurements ofalpha energies.
In 1970 Dubna scientists synthesized Element 105 and, by the end of April 1970,"had investigated all the types of decay of the new element and had determined itschemical properties," according to a report in 1970. The Soviet group had notproposed a name for 105. In late April 1970, it was announced that Ghiorso, Nurmia, Haris,K.A.Y. Eskola, and P.L. Eskola, working at the University of California at Berkeley, hadpositively identified element 105. The discovery was made by bombarding a target of 249Cfwith a beam of 84 MeV nitrogen nuclei in the Heavy Ion Linear Accelerator (HILAC). When a15N nuclear is absorbed by a 249Cf nucleus, four neutrons are emitted and a new atom of260-105 with a half-life of 1.6 s is formed. While the first atoms of Element 105 are saidto have been detected conclusively on March 5, 1970, there is evidence that Element 105had been formed in Berkeley experiments a year earlier by the method described.
Ghiorso and his associates have attempted to confirm Soviet findings by moresophisticated methods without success. The Berkeley Group proposed the name hahnium --after the late German scientist Otto Hahn (1879-1968) -- and symbol Ha. However, theInternational Union of Pure and Applied Chemistry panel members in 1977 recommended thatelement 105 be named to Dubnium (symbol Db) after the site of the Joint Institute forNuclear Research in Russia. Unfortunately, the name hahnium will not be used againaccording to the rules for naming new elements. Some scientists still use the earlier nameof hahnium because it had been used for about 25 years.