The experiments, performed during the last few years, have lead to the discovery of six new (113-118) superheavy elements (SHE) in the Periodic Table of D.I. Mendeleev and 45 new most neutron-rich (among the presently known) isotopes of elements 104-118.
The new nuclides were synthesized in the fusion reactions between accelerated 48Са ions and nuclear targets 238U, 237Np, 242,244Pu, 243Am, 245,248Cm, 249Cf [1] and 249Bk [2]. Their half-lives vary from 0.5 ms to 30 h depending on the proton and neutron numbers in the synthesized nuclei. The relatively long lifetimes of the new nuclides allowed the conduction of the first experiments devoted to their chemical identification and study of their properties. The identification of the decay chain of element 115, synthesized in the reaction 243Am(48Сa, 3n), was performed by the final decay product, i.e., the element 105 isotope (268Db, Т1/2 = 29 hr), which is a homologue of Ta and Nb [3]. The chemical identification of elements 112 and 114, produced in the reactions 242Pu(48Сa,3n)287114 (α) → 283112 and 244Pu(48Сa,4n)288114 (α) → 284112, was performed in experiments, in which the volatility and adsorption on Au surface were studied [4,5]. It was shown that element 112 is close in its properties to Hg (instead of Rn). Element 114 differs greatly from Pb (volatile, adsorption on the Au surface was observed at temperatures close to –1000 С). On the whole, the data from the chemical experiments are in full agreement with the results of the physical experiments and are an independent evidence of the synthesis of elements 112 and 114 in the reactions 48Са+242,244Pu and the synthesis of elements 113 and 115 in the reaction 48Са+243Am. The first experiments devoted to the properties of element 113 (volatility) were carried out using the reactions 243Am(48Сa,3n) and 249Bk(48Сa,4n).
Taking into account the above results, the search for long-lived isotopes of superheavy elements in nature is reconsidered. Presently the experiment SHIN in the underground low radioactivity laboratory in Modane (LSM), using a neutron multi-detector, is going on with 550g natOs , 100 g natXe and 100 g 136Xe samples [6].
The program of further research for the synthesis and chemistry of SHE includes:
• Chemistry of elements 112-114 in the reactions of 242,244Pu and 243 Am with 48Ca;
Carrying out experiments on the determination of the masses of isotopes of elements 114 and 112, produced in the reaction of 244 Pu and 48Ca, using the newly created at the FLNR Mass Analyzer of Super Heavy Atoms (MASHA).
The work has been performed with the financial support of the Russian Foundation for Fundamental Research (project code 09-03-12029).
References:
1.Yu. Oganessian, J.Phys.G: Nucl.Part.Phys., 2007, 34, R165.
2.Yu. Oganessian et al, PRL (submeted)
3.S. Dmitriev et al, Mendeleev Communications, 2005, 1, 1.
4.R. Eihler et al. Nature, 2007, 447/3, 72.
5.R. Eihler et al. Radiochica Acta, 2010, 9, 133
6.A. Svirikh