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.

The decay properties of 290

The discovery of a new chemical element with atomic number Z=117 is reported. The isotopes (293)117 and (294)117 were produced in fusion reactions between (48)Ca and (249)Bk. Decay chains involving 11 new nuclei were identified by means of the Dubna gas-filled recoil separator. The measured decay properties show a strong rise of stability for heavier isotopes with Z > or = 111, validating the concept of the long sought island of enhanced stability for superheavy nuclei.

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The high nuclear charges of the heaviest elements influence their electronic structure and hence their chemical properties. [1][2][3][4][5] The experimental results so far obtained for the heaviest chemically investigated elements reveal that seaborgium, [6,7] bohrium, [8] and hassium [9] behave as typical representatives of the corresponding Group 6, 7, and 8 of the periodic table. Apparently, relativistic effects do not introduce a perceptible destabilization of the highest oxidation states of these elements in the chemical environments they have been studied in. An even stronger increase of relativistic effects is predicted for the transactinides of Groups 12-18. [1][2][3] Element 112, a representative of Group 12 of the periodic table, has a predicted closed-shell electronic ground-state configuration of [Rn]5f 14 6d 10 7s 2 , rendering this element one of the key elements regarding relativistic effects in the electronic structure. [3,5,10] Recently, our gas chromatography experiments with only two observed atoms of element 112 revealed evidence for a metallic adsorption interaction with the stationary gold surface. [11] Here we present new experimental results with an increased number of observed atoms that confirm these observations and improve their statistical significance. From the complete data set, thermochemical and physical data are deduced for element 112 and compared to the corresponding properties of its homologues in Group 12: Zn, Cd, and Hg. The increased stabilization of the atomic state of element 112 reveals a further enhancement of the relativistic effects with increasing atomic number Z in Group 12.For element 112 a noble-metallic character was predicted from empirical extrapolations. [12,13] Relativistic atomic calculations revealed a contraction of the spherical 7s orbitals, leading to the prediction of an enhanced stability of the elemental atomic state for element 112. Accordingly, a noblegas-like behavior was postulated. [14] Modern calculation methods confirmed a stronger binding of the 7s orbitals. [3] However, the spin-orbit coupling of the 6d orbitals is predicted to lead to an electronic ground state configuration with a 6d 5/2 orbital that is similar energetically and spatially to the 7s orbital, indicating that element 112 could be a noble transition metal [5,15] or even a semiconductor. [16] Based on these strongly differing predictions, it is decisive for experimentalists to be able to distinguish in chemical experiments whether element 112 behaves more as a noble metal or as a noble gas. Therefore, investigation of gas adsorption properties of element 112 on metal surfaces has been suggested. [17] In such studies the energy content of the adsorption bond between element 112 and the metallic stationary phase, the standard adsorption enthalpy at zero surface coverage (DH ads Au ), is determined. This quantity differentiates between metal-bond formation and weak van der Waals physisorption interaction. The semiempirical macroscopic adsorption model based on the Miedema approach ...

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Results from the production and decay properties of element 115 nuclei observed using the reaction 243

The results of two experiments designed to synthesize element 115 isotopes in the 243 Am + 48 Ca reaction are presented. Two new elements with atomic numbers 113 and 115 were observed for the first time. With 248-MeV 48 Ca projectiles, we observed three similar decay chains consisting of five consecutive α decays, all detected in a total time interval of 30 s. Each chain was terminated by a spontaneous fission (SF) with a high-energy release and a lifetime of about a day. With 253-MeV 48 Ca projectiles, we registered a different decay chain of consecutive α decays detected in a time interval of 0.5 s, also terminated by spontaneous fission, but after 1.8 h. The decay properties of the eleven new αand SF-decaying nuclei are consistent with expectations for consecutive α decays originating from the parent isotopes 288 115 and 287 115, produced in the 3n-and 4n-evaporation channels, respectively. Support for the assignment of the atomic numbers of all of the nuclei in the 288 115 decay chain was obtained in an independent experiment in which a long-lived spontaneous fission activity, 268 Db (15 events), was found to be chemically consistent with the fifth group of the periodic table. The odd-odd isotope 288 115 was observed with largest cross section of about 4 pb. In the SF decay of 268 Db, a total kinetic energy of 230 MeV and a neutron multiplicity per fission of 4.2 were measured. The decay properties of the 11 new isotopes with Z = 105-115 and the production cross sections are in agreement with modern concepts of the role of nuclear shells in the stability of superheavy nuclei. The experiments were carried out at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research.