[en] Published in summary form only

[en] We identified two α-emitting isotopes of element 107 with masses of 261 and 262 respectively by parent-daughter correlations. For the isotope with mass 262 we found two transitions with (102±26) ms and (7.0±2.1) ms half-life, which we assign to the ground-state and to an isomeric transition, respectively. The half-life of the isotope with mass 261 is (11.8_-2.8^+5.3) ms. Spontaneous fission, which could be assigned to the decay of an isotope of element 107, was not detected in our experiments. This observation is in line with our previous results, indicating a region of nuclei with strong microscopic stabilisation in the trans-actinides. Both new isotopes were produced by complete fusion of ²⁰⁹Bi with ⁵⁴Cr. The production cross sections are (163±34) pb for ²⁶²107 and (36_-14⁺²²) pb for ²⁶¹107. (orig.)

[en] We summarize our experimental results on the investigation of element 107 and discuss the assignment of the observed α transitions in detail. Finally, we summarize what we learned about the spectroscopy of the heaviest elements and on their production. (orig./HSI)

[en] All 17 artificially produced elements heavier than uranium were discovered by nuclear-chemical synthesis. The three heaviest ones - elements 107, 108 and 109 - were snythesized at the heavy-ion accelerator UNILAC in Darmstadt by nuclear fusion from the heaviest stable nuclei, lead-208 and bismuth-209, and the most neutron-rich stable isotopes of chromium and iron: element 107 from bismuth-209 (atomic number Z=83) and chromium-54 (Z=24), element 108 from lead-208 (Z=82) and iron-58 (Z=26), and element 109 from bismuth-209 and iron-58. The first isotopes detected were those with mass numbers 262 (Z=107), 265 (Z=108) and 266 (Z=109); these nuclei are short-lived α-emitters with half-lives of 8.2 ms, 1.8 ms and 3.4 ms, respectively. The yields of these reactions are extremely small; only three atoms of element 109 have ever been observed. Experiments to synthesize element 110 have given ambiguous results. All attempts to detect the 'superheavy' elements with proton numbers near Z=114 and neutron numbers near N=184 have thus far failed. These elements have been predicted theoretically, and many attempts to synthesize them have been made, e.g. at UNILAC by fusion of calcium-48 (Z=20) with curium-248 (Z=96), or by transference of protons in the collision of two very heavy nuclei such as uranium-238 (Z=92). Surprisingly, the heaviest known nuclei are far more stable toward spontaneous fission into two fragments than was expected, but their synthesis is strongly hindered - much more than was initially anticipated. It is this hindrance rather than the decreasing nuclear stability which seems to presently limit the extent of the periodic table: even heavier elements should be able to exist, but no way has yet been found to produce them. (orig.)

[en] Experimental investigations on synthesis and study on transactinide element properties carried out in JINR are reviewed. Features of complex nuclei fusion and the results of their applications for new element synthesis up to atomic number Z=109 are considered. High stability of heavy nuclei with Z=104-109 with respect to spontaneous fission is shown. The possibilities for synthesis of heavier nuclei with Z>109 are discussed, and the results of first experiments on searching for nuclei with Z=110 splitting spontaneously in nuclear reactions with argon and calcium ions are presented

No abstract available

[en] The recent experiments on the synthesis of the heaviest elements led to the discovery of a region of nuclei of an unexpected high ground-state stability. The experimental results on our synthesis of new elements will be discussed as well as our new insights as their ground-state properties. The prospects to proceed to new elements will be outlined. (orig.)

[en] The recent experiments on the synthesis of the heaviest elements led to the discovery of a region of nuclei of an unexpected high ground-state stability. The experimental results on our synthesis of new elements will be discussed as well as our new insights as their ground-state properties. The prospects to proceed to new elements will be outlined. (orig.)

[en] The author reviews the experiments for the production of the elements 104-109, performed at the GSI Darmstadt using the UNILAC and the SHIP spectrometer. Furthermore shell effects in collision dynamics are discussed. (HSI)

[en] The discovery of the elements 107, 108, and 109 in a region of dominating shell stabilization is the most important step on the way to the superheavy nuclei in recent years. These experiments leading to the presently upper end of the periodic table were possible with the velocity filter SHIP to separate the heavy nuclei produced in complete fusion reactions of heavy ions. The identification of the unknown nuclei was established by α-α mother-daughter correlation of the nuclei decaying after the implantation into position sensitive surface-barrier detectors. With this method it is possible to identify even single nuclei of unknown isotopes unambiguously. The limits of sensitivity are production cross-sections of a few picobarns and about 2 μs of nuclear lifetime. With this method the elements 107, 108, and 109 were observed for the first time by their α-decay and identified unambiguously. For element 107 the isotopes with masses 261 and 262, for the element 108 the isotopes with masses 264 and 265, and for element 109 the isotope with mass 266 were found. The halflives range from 0.1 ms to 0.1 s. The highly fissile transactinide nuclei were produced in cold fusion of heavy ions using ^207,208Pb and ²⁰⁹Bi targets, respectively, and ⁵⁰Ti, ⁵⁴Cr, or ⁵⁸Fe beams. The evaluation of the excitation functions for the production of very heavy evaporation residues shows a strong decrease above 25 MeV excitation energy caused by a destruction of the groundstate shell effects at high excitation energies. The strong competition of barrier transmission and survival probability results in rather narrow excitation functions and small production cross sections. The maximum cross section is observed close to the Coulomb barrier and corresponding to projectile energies near 5 MeV/u. (orig.)