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||Rf / Ku
In 1964, workers at the Joint Nuclear Research Institute at Dubna (U.S.S.R.) bombarded
plutonium with accelerated 113 to 115 MeV neon ions. By measuring fission tracks in a
special glass with a microscope, they detected an isotope that decays by spontaneous
fission. They suggested that this isotope, which had a half-life of 0.3 +/- 0.1 s might be
260-104, produced by the following reaction: 242Pu + 22Ne --> 104 +4n.
Element 104, the first transactinide element, is expected to have chemical properties
similar to those of hafnium. It would, for
example, form a relatively volatile compound with chlorine
The Soviet scientists have performed experiments aimed at chemical identification, and
have attempted to show that the 0.3-s activity is more volatile than that of the
relatively nonvolatile actinide trichlorides. This experiment does not fulfill the test of
chemically separating the new element from all others, but it provides important evidence
New data, reportedly issued by Soviet scientists, have reduced the half-life of the
isotope they worked with from 0.3 to 0.15 s. The Dubna scientists suggest the name kurchatovium
and symbol Ku for element 104, in honor of Igor Vasilevich Kurchatov (1903-1960),
former Head of Soviet Nuclear Research.
In 1969 Ghiorso, Nurmia, Harris, K.A.Y. Eskola, and P.L. Eskola of the University of
California at Berkeley reported that they had positively identified two, and possibly
three, isotopes of Element 104. The group indicated that, after repeated attempts, they
produced isotope 260-104 reported by the Dubna groups in 1964.
The discoveries at Berkeley were made by bombarding a target of 249Cf with 12C nuclei
of 71 MeV, and 13C nuclei of 69 MeV. The combination of 12C with 249Cf followed by instant
emission of four neutrons produced Element 257-104. This isotope has a half-life of 4 to 5
s, decaying by emitting an alpha particle into 253No, with a half-life of 105 s.
The same reaction, except with the emission of three neutrons, was thought to have
produced 258-104 with a half-life of about 1/100 s.
Element 259-104 is formed by the merging of a 13C nuclei with 249Cf, followed by
emission of three neutrons. This isotope has a half-life of 3 to 4 s, and decays by
emitting an alpha particle into 255No, which has a half-life of 185 s.
Thousands of atoms of 257-104 and 259-104 have ben detected. The Berkeley group
believes their identification of 258-104 is correct, but attaches less confidence to this
work than to their work on 257-104 and 259-104.
The claims for discovery and the naming of Element 104 are still in question. The
Berkeley group proposes for the new element the name rutherfordium (symbol Rf), in
honor of Ernest R. Rutherford, a New Zealand physicist. Meanwhile, the International Union
of Pure and Applied Physics has proposed using the neutral temporary name, unnilquadium.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.