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synthetic element | [History]
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. Their evidence was based on time-coincidence measurements
of alpha energies. More recently, it was reported that
early in 1970 Dubna scientists synthesized Dubnium and
that by the end of April 1970 “had investigated all the types
of decay of the new element and had determined its chemical
properties.” In late April 1970, it was announced that Ghiorso,
Nurmia, Harris, K. A. Y. Eskola, and P. L. Eskola, working at
the University of California at Berkeley, had positively identified
Dubnium. 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 nucleus
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.
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 at Berkeley.
Element 261105 was produced both by bombarding 250Cf with
15N and by bombarding 249Bk with 16O. The isotope emits 8.93-
MeV α 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 α particles and decays to 258Lr with a
half-life of about 40 s. Nine isotopes of Dubnium are now recognized.
Soon after the discovery the names Hahnium and
Joliotium, named after Otto Hahn and Jean-Frederic Joliot
and Mme. Joliot-Curie, were suggested as names for Element
105. The IUPAC in August 1997 finally resolved the issue,
naming Element 105 Dubnium with the symbol Db. Dubnium
is thought to have properties similar to tantalum. |
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