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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
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 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.
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.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.
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