Dubna group

In 1969 Ghiorso, Nurmia, Harris, K.A.Y. Eskola, and P.E. 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 first (inconclusive) work bearing on the synthesis of element 104 was published by the Dubna group in 1964. However, the crucial Dubna evidence (1969-70) for the production of element 104 by bombardment of 94PU with loNe came after the development of a sophisticated method for rapid in situ chlorination of the product atoms followed by their gas-chromatographic separation on an atom-by-atom basis. This was a heroic enterprise which combined cyclotron nuclear physics and chemical separations. As we have seen, the actinide series of elements ends with 103 Lr. The next element should be in Group 4 of the transition elements, i.e. a heavier congenor of Ti, Zr and Hf. As such it would be expected to have a chloride... 

The Lawrence Berkeley Laboratory and other groups were unable to confirm the spontaneous-fission reaction of Ku-260, so the Dubna groups discovery was disputed. The Berkeley equipment was unable to accelerate neon ions to the speeds required to produce Ku-260, and thus they tried a different reaction in a new automated rapid chemistry apparatus that identified and confirmed new isotopes of heavy metals. The procedure involved bombarding the element californium-239 with a mixture of the isotopes carbon-12 and carbon-13 ions, as follows ... 

Contemporaneously with the Berkeley experiments, Zvara et al. (1969, 1970), working at Dubna, produced 3.2 + 0.8 s 259104 by the Pu/ Ne, 5n) reaction. The chloride of this spontaneously fissioning activity was shown using gas chromatography to be slightly less volatile than Hf, but more volatile than the actinides. An international group of reviewers (Barber et al., 1992) has determined that the Berkeley and Dubna groups should share the credit for the discovery of element... 

Element 105 was reported by the Berkeley group in 1970 and the Dubna group in 1971. The Berkeley team used... 

The first report concerning the discovery of element 104 (rutherfordium) came from Dubna (Flerov et al., 1964). By irradiation of " Pu with Ne a radionuchde exhibiting a spontaneous fission half-life of 0.3 s was found and attributed to 104. Because only few atoms were obtained, the details of the report were rather inaccurate. Further investigations of the Dubna group revealed that two isotopes of element 104 were formed... 

Two names were proposed for element 104, kurtchatovium (in honour of the Russian physicist Kurtchatov) by the Dubna group and rutherfordium (in honour of Rutherford) by the Berkeley group. The Dubna group (Flerov et al., 1968) was also the first to announce the discovery of element 105 (dubnium) by bombardment of 243 Am with 22]Sfe However, the assignment of the mass numbers 260 or 261 was not possible unambiguously. In Berkeley, element 105 was produced by the reactions (Ghiorso et al., 1970) ... 

Again, two names were proposed, nielsbohrium (in honour of Niels Bohr) by the Dubna group and hahnium (in honour of Otto Hahn) by the Berkeley group. 

Credit for discovery of a transfermium element is extremely complicated. In most cases, no more than a handful of atoms is produced in an atom smasher. For example, the Dubna group first claimed to have found element 104 in 1964, but many scientists doubted this report. Five years later, American scientists also reported making element 104. This time, the evidence was better. 

The Dubna group also discussed the kinetics of reactions in gases to look for the fundamental reasons which might cause deviations in behavior of a tracer with the decreasing number or, better, concentration of its species. Only one inherent reason could be seen a deviation may happen when two entities practically cannot... 

This type of reaction was used at Berkeley also for production of element 106, while the Dubna group utilized a reaction involving a lighter target element and a heavier projectile ... 

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 (a tetrachloride). 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 for evaluation. New data, reportedly issued by Soviet scientists, have reduced the half-hfe 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), late Head of Soviet Nuclear Research. The Dubna Group also has proposed the name for Element 104. In 1969, Ghiorso, Nurmia, Harris, K. A. Y. Eskola, and P. L. Eskolaof the University of California... 

The situation was clarified in 1965 when the Dubna group carried out the nuclear reaction Am( 0, 5re) 103 giving rise to the isotope with a mass number of 256 and determined its parameters. They coincided with those reported by the Berklev scientists for the product of the nuclear reaction Cf( B, 4k) 103 three years later. This is why the discovery date of 1961 can be doubted. But no definite conclusion was reached who and when had discovered element 103. As with element 102, researchers had to work with just a few atoms of element 103. At first, they found the mass numbers and the radioactive properties of the isotopes and only later the methods for evaluating their chemical nature were found. 

In 1999, the Dubna group started a series of experiments with the new concept of using Ca beams for the synthesis of unknown elements beyond Z = 113 (Oganessian 1996). They upgraded their equipment to enhance the sensitivity by a factor 1,000 over the 1985 experiment and started their series with an attempt to produce the new element 114 with the irradiation of... 

The strategy of the Dubna group is to build up a region of nuclides in an internally consistent manner where descendants appearing in decay chains are, in addition, directly synthesized by the complete fusion of heavy ions including using the technique of cross bombardments (O Fig. 19.5). Thus, if one nuclide in this region is safely identified, the whole island is fixed. This process explains the importance of the recent experiment (Hofmann... 

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