Dubnium (Hahnium)

History

In 1967 G.N. Flerov reported that a Soviet team working at the Joint Institute for Nuclear Research at Dubna may have produced a few atoms of  ²⁶⁰105 and ²⁶¹105 by bombarding ²⁴³Am with ²²Ne. The evidence was based on time-coincidence measurements of alpha 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 its chemical properties," according to a report in 1970. The Soviet group had not proposed 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, had positively identified element 105. The discovery was made by bombarding a target of ²⁴⁹Cf with a beam of 84 MeV nitrogen nuclei in the Heavy Ion Linear Accelerator (HILAC). When a ¹⁵N nuclear is absorbed by a ²⁴⁹Cf nucleus, four neutrons are emitted and a new atom of ²⁶⁰105 with a half-life of 1.6 s is formed. While the first atoms of Element 105 are said to have been detected conclusively on March 5, 1970, there is evidence that Element 105 had been formed in Berkeley experiments a year earlier by the method described.

Ghiorso and his associates have attempted to confirm Soviet findings by more sophisticated methods without success. The Berkeley Group proposed the name hahnium -- after the late German scientist Otto Hahn (1879-1968) -- and symbol Ha.  However, the International Union of Pure and Applied Chemistry panel members in 1977 recommended that element 105 be named to Dubnium (symbol Db) after the site of the Joint Institute for Nuclear Research in Russia. Unfortunately, the name hahnium will not be used again according to the rules for naming new elements. Some scientists still use the earlier name of hahnium because it had been used for about 25 years.

Isotopes

In October 1971, it was announced that two new isotopes of element 105 were synthesized with the heavy ion linear accelerator by A. Ghiorso and co-workers a Berkeley. Element ²⁶¹105 was produced both by bombarding ²⁵⁰Cf with ¹⁵N and by bombarding ²⁴⁹Bk with ¹⁶O. The isotope emits 8.93-MeV alpha particles and decays to ²⁵⁷Lr with a half-life of about 1.8 s. Element ²⁶²105 was produced by bombarding ²⁴⁹Bk with ¹⁸O. It emits 8.45 MeV alpha particles and decays to ²⁵⁸Lr with a half-life of about 40 s. Seven isotopes of element 105 (unnilpentium) are now recognized.