Dubnium: Expectations vs. Reality...

Dubnium

Atomic research: 105

Atomic Symbol: Rf / Ku
Atomic Weight: 262
Electron Configuration: [Rn]7s²5f¹⁴6d³

Proposed Name

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 260-105 and 261-105 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 260-105 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 ,

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 261-105 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 262-105 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.