J. Even

Superheavy Element Flerovium (Element 114) Is a Volatile Metal

The electron shell structure of superheavy elements, i.e., elements with atomic number Z ≥ 104, is influenced by strong relativistic effects caused by the high Z. Early atomic calculations on element 112 (copernicium, Cn) and element 114 (flerovium, Fl) having closed and quasi-closed electron shell configurations of 6d(10)7s(2) and 6d(10)7s(2)7p1/2(2), respectively, predicted them to be noble-gas-like due to very strong relativistic effects on the 7s and 7p1/2 valence orbitals. Recent fully relativistic calculations studying Cn and Fl in different environments suggest them to be less reactive compared to their lighter homologues in the groups, but still exhibiting a metallic character. Experimental gas-solid chromatography studies on Cn have, indeed, revealed a metal-metal bond formation with Au. In contrast to this, for Fl, the formation of a weak bond upon physisorption on a Au surface was inferred from first experiments. Here, we report on a gas-solid chromatography study of the adsorption of Fl on a Au surface. Fl was produced in the nuclear fusion reaction (244)Pu((48)Ca, 3-4n)(288,289)Fl and was isolated in-flight from the primary (48)Ca beam in a physical recoil separator. The adsorption behavior of Fl, its nuclear α-decay product Cn, their lighter homologues in groups 14 and 12, i.e., Pb and Hg, and the noble gas Rn were studied simultaneously by isothermal gas chromatography and thermochromatography. Two Fl atoms were detected. They adsorbed on a Au surface at room temperature in the first, isothermal part, but not as readily as Pb and Hg. The observed adsorption behavior of Fl points to a higher inertness compared to its nearest homologue in the group, Pb. However, the measured lower limit for the adsorption enthalpy of Fl on a Au surface points to the formation of a metal-metal bond of Fl with Au. Fl is the least reactive element in the group, but still a metal.

Synthesis and detection of a seaborgium carbonyl complex

A carbonyl compound that tips the scales Life is short for the heaviest elements. They emerge from high-energy nuclear collisions with scant time for detection before they break up into lighter atoms. Even et al. report that even a few seconds is long enough for carbon to bond to the 106th element, seaborgium (see the Perspective by Loveland). The authors used a custom apparatus to direct the freshly made atoms out of the hot collision environment and through a stream of carbon monoxide and helium. They compared the detected products with theoretical modeling results and conclude that hexacarbonyl Sg(CO)6 was the most likely structural formula. Science, this issue p. 1491; see also p. 1451 A special apparatus enables synthesis of a compound with carbon bonds to a short-lived element produced via nuclear reaction. [Also see Perspective by Loveland] Experimental investigations of transactinoide elements provide benchmark results for chemical theory and probe the predictive power of trends in the periodic table. So far, in gas-phase chemical reactions, simple inorganic compounds with the transactinoide in its highest oxidation state have been synthesized. Single-atom production rates, short half-lives, and harsh experimental conditions limited the number of experimentally accessible compounds. We applied a gas-phase carbonylation technique previously tested on short-lived molybdenum (Mo) and tungsten (W) isotopes to the preparation of a carbonyl complex of seaborgium, the 106th element. The volatile seaborgium complex showed the same volatility and reactivity with a silicon dioxide surface as those of the hexacarbonyl complexes of the lighter homologs Mo and W. Comparison of the product’s adsorption enthalpy with theoretical predictions and data for the lighter congeners supported a Sg(CO)6 formulation.

Atom-at-a-time laser resonance ionization spectroscopy of nobelium

Optical spectroscopy of a primordial isotope has traditionally formed the basis for understanding the atomic structure of an element. Such studies have been conducted for most elements and theoretical modelling can be performed to high precision, taking into account relativistic effects that scale approximately as the square of the atomic number. However, for the transfermium elements (those with atomic numbers greater than 100), the atomic structure is experimentally unknown. These radioactive elements are produced in nuclear fusion reactions at rates of only a few atoms per second at most and must be studied immediately following their production, which has so far precluded their optical spectroscopy. Here we report laser resonance ionization spectroscopy of nobelium (No; atomic number 102) in single-atom-at-a-time quantities, in which we identify the ground-state transition 1S0 1P1. By combining this result with data from an observed Rydberg series, we obtain an upper limit for the ionization potential of nobelium. These accurate results from direct laser excitations of outer-shell electrons cannot be achieved using state-of-the-art relativistic many-body calculations that include quantum electrodynamic effects, owing to large uncertainties in the modelled transition energies of the complex systems under consideration. Our work opens the door to high-precision measurements of various atomic and nuclear properties of elements heavier than nobelium, and motivates future theoretical work.

Rapid synthesis of radioactive transition-metal carbonyl complexes at ambient conditions.

Carbonyl complexes of radioactive transition metals can be easily synthesized with high yields by stopping nuclear fission or fusion products in a gas volume containing CO. Here, we focus on Mo, W, and Os complexes. The reaction takes place at pressures of around 1 bar at room temperature, i.e., at conditions that are easy to accommodate. The formed complexes are highly volatile. They can thus be transported within a gas stream without major losses to setups for their further investigation or direct use. The rapid synthesis holds promise for radiochemical purposes and will be useful for studying, e.g., chemical properties of superheavy elements.

New Short-Lived Isotope 221U and the Mass Surface Near N=126

Two short-lived isotopes ^{221}U and ^{222}U were produced as evaporation residues in the fusion reaction ^{50}Ti+^{176}Yb at the gas-filled recoil separator TASCA. An α decay with an energy of E_{α}=9.31(5)  MeV and half-life T_{1/2}=4.7(7)  μs was attributed to ^{222}U. The new isotope ^{221}U was identified in α-decay chains starting with E_{α}=9.71(5)  MeV and T_{1/2}=0.66(14)  μs leading to known daughters. Synthesis and detection of these unstable heavy nuclei and their descendants were achieved thanks to a fast data readout system. The evolution of the N=126 shell closure and its influence on the stability of uranium isotopes are discussed within the framework of α-decay reduced width.

In-situ formation, thermal decomposition, and adsorption studies of transition metal carbonyl complexes with short-lived radioisotopes

Abstract We report on the in-situ synthesis of metal carbonyl complexes with short-lived isotopes of transition metals. Complexes of molybdenum, technetium, ruthenium and rhodium were synthesized by thermalisation of products of neutron-induced fission of 249Cf in a carbon monoxide-nitrogen mixture. Complexes of tungsten, rhenium, osmium, and iridium were synthesized by thermalizing short-lived isotopes produced in 24Mg-induced fusion evaporation reactions in a carbon monoxide containing atmosphere. The chemical reactions took place at ambient temperature and pressure conditions. The complexes were rapidly transported in a gas stream to collection setups or gas phase chromatography devices. The physisorption of the complexes on Au and SiO2 surfaces was studied. We also studied the stability of some of the complexes, showing that these start to decompose at temperatures above 300 ℃ in contact with a quartz surface. Our studies lay a basis for the investigation of such complexes with transactinides.

Decomposition studies of group 6 hexacarbonyl complexes. Part 1: Production and decomposition of Mo(CO)6 and W(CO)6

Abstract Chemical studies of superheavy elements require fast and efficient techniques, due to short half-lives and low production rates of the investigated nuclides. Here, we advocate for using a tubular flow reactor for assessing the thermal stability of the Sg carbonyl complex – Sg(CO)6. The experimental setup was tested with Mo and W carbonyl complexes, as their properties are established and supported by theoretical predictions. The suggested approach proved to be effective in discriminating between the thermal stabilities of Mo(CO)6 and W(CO)6. Therefore, an experimental verification of the predicted Sg–CO bond dissociation energy seems to be feasible by applying this technique. By investigating the effect of 104,105Mo beta-decay on the formation of 104,105Tc carbonyl complex, we estimated the lower reaction time limit for the metal carbonyl synthesis in the gas phase to be more than 100 ms. We examined further the influence of the wall material of the recoil chamber, the carrier gas composition, the gas flow rate, and the pressure on the production yield of 104Mo(CO)6, so that the future stability tests with Sg(CO)6 can be optimized accordingly.

Measurement of the Md3+/Md2+ Reduction Potential Studied with Flow Electrolytic Chromatography

The reduction behavior of mendelevium (Md) was studied using a flow electrolytic chromatography apparatus. By application of the appropriate potentials on the chromatography column, the more stable Md(3+) is reduced to Md(2+). The reduction potential of the Md(3+) + e(-) → Md(2+) couple was determined to be -0.16 ± 0.05 V versus a normal hydrogen electrode.

Precision Measurement of the First Ionization Potential of Nobelium

One of the most important atomic properties governing an elements chemical behavior is the energy required to remove its least-bound electron, referred to as the first ionization potential. For the heaviest elements, this fundamental quantity is strongly influenced by relativistic effects which lead to unique chemical properties. Laser spectroscopy on an atom-at-a-time scale was developed and applied to probe the optical spectrum of neutral nobelium near the ionization threshold. The first ionization potential of nobelium is determined here with a very high precision from the convergence of measured Rydberg series to be 6.626 21±0.000 05  eV. This work provides a stringent benchmark for state-of-the-art many-body atomic modeling that considers relativistic and quantum electrodynamic effects and paves the way for high-precision measurements of atomic properties of elements only available from heavy-ion accelerator facilities.

Improvements to TITAN's mass measurement and decay spectroscopy capabilities

Abstract The study of nuclei farther from the valley of β -stability than ever before goes hand-in-hand with shorter-lived nuclei produced in smaller abundances than their less exotic counterparts. The measurement, to high precision, of nuclear masses therefore requires innovations in technique in order to keep up. TRIUMF’s Ion Trap for Atomic and Nuclear science (TITAN) facility deploys three ion traps, with a fourth in the commissioning phase, to perform and support Penning trap mass spectrometry and in-trap decay spectroscopy on some of the shortest-lived nuclei ever studied. We report on recent advances and updates to the TITAN facility since the 2012 EMIS conference. TITAN’s charge breeding capabilities have been improved and in-trap decay spectroscopy can be performed in TITAN’s Electron Beam Ion Trap (EBIT). Higher charge states can improve the precision of mass measurements, reduce the beam-time requirements for a given measurement, improve beam purity, and open the door to access isotopes not available from the ISOL method via in-trap decay and recapture. This was recently demonstrated during TITAN’s mass measurement of 30 Al. The EBIT’s decay spectroscopy setup was commissioned with a successful branching ratio and half-life measurement of 124 Cs. Charge breeding in the EBIT increases the energy spread of the ion bunch sent to the Penning trap for mass measurement, so a new Cooler PEnning Trap (CPET), which aims to cool highly charged ions with an electron plasma, is undergoing offline commissioning. Already CPET has demonstrated the trapping and self-cooling of a room-temperature electron plasma that was stored for several minutes. A new detector has been installed inside the CPET magnetic field which will allow for in-magnet charged particle detection.