After a brief introduction of the role of shell effects in determining the limiting nuclear masses, the experimental investigation of the decay properties of the heaviest nuclei is presented. For the production of superheavy nuclides fusion, reactions of heavy actinide nuclei with 48Ca-projectiles have been used. The properties of the new nuclei, the isotopes of elements 112–118, as well as of their decay products, together with the known data for the light isotopes with Z ⩽ 113, give evidence of the significant increase of the stability with the neutron number of the heavy nucleus. The obtained results are discussed in the context of the theoretical predictions about the ‘island of stability’ of the hypothetical superheavy elements.

The heaviest elements to have been chemically characterized are seaborgium (element 106), bohrium (element 107) and hassium (element 108). All three behave according to their respective positions in groups 6, 7 and 8 of the periodic table, which arranges elements according to their outermost electrons and hence their chemical properties. However, the chemical characterization results are not trivial: relativistic effects on the electronic structure of the heaviest elements can strongly influence chemical properties. The next heavy element targeted for chemical characterization is element 112; its closed-shell electronic structure with a filled outer s orbital suggests that it may be particularly susceptible to strong deviations from the chemical property trends expected within group 12. Indeed, first experiments concluded that element 112 does not behave like its lighter homologue mercury. However, the production and identification methods used cast doubt on the validity of this result. Here we report a more reliable chemical characterization of element 112, involving the production of two atoms of (283)112 through the alpha decay of the short-lived (287)114 (which itself forms in the nuclear fusion reaction of 48Ca with 242Pu) and the adsorption of the two atoms on a gold surface. By directly comparing the adsorption characteristics of (283)112 to that of mercury and the noble gas radon, we find that element 112 is very volatile and, unlike radon, reveals a metallic interaction with the gold surface. These adsorption characteristics establish element 112 as a typical element of group 12, and its successful production unambiguously establishes the approach to the island of stability of superheavy elements through 48Ca-induced nuclear fusion reactions with actinides.

A review of the discovery and investigation of the 'island of stability' of super-heavy nuclei at the separator DGFRS (FLNR, JINR) in the fusion reactions of (48)Ca projectiles with target nuclei (238)U-(249)Cf is presented. The synthesis of the heaviest nuclei, their decay properties, and methods of identification are discussed. The role of shell effects in the stability of super-heavy nuclei is demonstrated by comparison of the experimental data and results of theoretical calculations. The radioactive properties of the new nuclei, the isotopes of elements 112-118 as well as of their decay products, give evidence of the significant increase of the stability of the heavy nuclei with rise of their neutron number and approaching magic number N = 184.

The decay properties of 290

We describe the discoveries of new superheavy nuclei (a) with Z = 107-112 produced in cold fusion reactions between 208 Pb and 209 Bi and beams of A > 50 and (b) with Z = 113-118 in hot fusion reactions between actinide nuclei and 48 Ca. We also discuss the facilities used in these measurements. We compare the behavior of the α-decay energies and half-lives, spontaneous fission half-lives, cross sections, and excitation functions with expectations from theoretical calculations. Finally, we outline future research directions, including studies of the detailed properties of nuclei synthesized at higher yields, searches for new elements with Z = 119 and 120, and developments of new facilities.