Manifestation of relativistic effects in the chemical properties of nihonium and moscovium revealed by gas chromatography studies.

Chemical reactivity of the superheavy elements nihonium (Nh, element 113) and moscovium (Mc, element 115) has been studied by the gas-solid chromatography method using a new combined chromatography and detection setup. The Mc isotope, 288Mc, was produced in the nuclear fusion reaction of 48Ca ions with 243Am targets at the GSI Helmholtzzentrum Darmstadt, Germany. After isolating 288Mc ions in the gas-filled separator TASCA, adsorption of 288Mc and its decay product 284Nh on silicon oxide and gold surfaces was investigated. As a result of this work, the values of the adsorption enthalpy of Nh and Mc on the silicon oxide surface were determined for the first time, - ∆ H ads SiO 2 Mc = 54 - 5 + 11 kJ/mol and - ∆ H ads SiO 2 Nh = 58 - 3 + 8 kJ/mol (68% c.i.). The obtained -ΔH ads values are in good agreement with results of advanced relativistic calculations. Both elements, Nh and Mc, were shown to interact more weakly with the silicon oxide surface than their lighter homologues Tl and Bi, respectively. However, Nh and Mc turned out to be more reactive than the neighbouring closed-shell and quasi-closed-shell elements copernicium (Cn, element 112) and flerovium (Fl, element 114), respectively. The established trend is explained by the influence of strong relativistic effects on the valence atomic orbitals of these elements.

Spectroscopy along Flerovium Decay Chains: Discovery of

A nuclear spectroscopy experiment was conducted to study α-decay chains stemming from isotopes of flerovium (element Z=114). An upgraded TASISpec decay station was placed behind the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. The fusion-evaporation reactions ^{48}Ca+^{242}Pu and ^{48}Ca+^{244}Pu provided a total of 32 flerovium-candidate decay chains, of which two and eleven were firmly assigned to ^{286}Fl and ^{288}Fl, respectively. A prompt coincidence between a 9.60(1)-MeV α particle event and a 0.36(1)-MeV conversion electron marked the first observation of an excited state in an even-even isotope of the heaviest man-made elements, namely ^{282}Cn. Spectroscopy of ^{288}Fl decay chains fixed Q_{α}=10.06(1) MeV. In one case, a Q_{α}=9.46(1)-MeV decay from ^{284}Cn into ^{280}Ds was observed, with ^{280}Ds fissioning after only 518 µs. The impact of these findings, aggregated with existing data on decay chains of ^{286,288}Fl, on the size of an anticipated shell gap at proton number Z=114 is discussed in light of predictions from two beyond-mean-field calculations, which take into account triaxial deformation.

Search for Electron-Capture Delayed Fission in the New Isotope

The electron-capture decay followed by a prompt fission process was searched for in the hitherto unknown most neutron-deficient Md isotope with mass number 244. Alpha decay with α-particle energies of 8.73-8.86 MeV and with a half-life of 0.30_{-0.09}^{+0.19} s was assigned to ^{244}Md. No fission event with a similar half-life potentially originating from spontaneous fissioning of the short-lived electron-capture decay daughter ^{244}Fm was observed, which results in an upper limit of 0.14 for the electron-capture branching of ^{244}Md. Two groups of fission events with half-lives of 0.9_{-0.3}^{+0.6} ms and 5_{-2}^{+3} ms were observed. The 0.9_{-0.3}^{+0.6} ms activity was assigned to originate from the decay of ^{245}Md. The origin of eight fission events resulting in a half-life of 5_{-2}^{+3} ms could not be unambiguously identified within the present data while the possible explanation has to invoke previously unseen physics cases.