T. K. Sato

Measurement of the first ionization potential of lawrencium, element 103

The chemical properties of an element are primarily governed by the configuration of electrons in the valence shell. Relativistic effects influence the electronic structure of heavy elements in the sixth row of the periodic table, and these effects increase dramatically in the seventh row—including the actinides—even affecting ground-state configurations. Atomic s and p1/2 orbitals are stabilized by relativistic effects, whereas p3/2, d and f orbitals are destabilized, so that ground-state configurations of heavy elements may differ from those of lighter elements in the same group. The first ionization potential (IP1) is a measure of the energy required to remove one valence electron from a neutral atom, and is an atomic property that reflects the outermost electronic configuration. Precise and accurate experimental determination of IP1 gives information on the binding energy of valence electrons, and also, therefore, on the degree of relativistic stabilization. However, such measurements are hampered by the difficulty in obtaining the heaviest elements on scales of more than one atom at a time. Here we report that the experimentally obtained IP1 of the heaviest actinide, lawrencium (Lr, atomic number 103), is electronvolts. The IP1 of Lr was measured with 256Lr (half-life 27 seconds) using an efficient surface ion-source and a radioisotope detection system coupled to a mass separator. The measured IP1 is in excellent agreement with the value of 4.963(15) electronvolts predicted here by state-of-the-art relativistic calculations. The present work provides a reliable benchmark for theoretical calculations and also opens the way for IP1 measurements of superheavy elements (that is, transactinides) on an atom-at-a-time scale.

Extraction behavior of rutherfordium into tributylphosphate from hydrochloric acid

The extraction behavior of rutherfordium (Rf) into tributylphosphate (TBP) from hydrochloric acid (HCl) has been studied together with those of the lighter group-4 elements Zr and Hf. The extractability of 261Rf, 169Hf, and 85Zr into TBP was investigated under identical conditions in 7.2–8.0 M HCl by on-line reversed-phase extraction chromatography. The percent extractions of Rf, Hf, and Zr into the TBP resin increase steeply with increasing HCl concentration, and the order of extraction is Zr > Hf ≈ Rf. By considering the order of chloride complexation among these elements, it is suggested that the stability of the TBP complex of Rf tetrachloride is lower than those of Zr and Hf.

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 100u2009ms. 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.

Adsorption behavior of 181W and 93mMo as lighter homologues of seaborgium (Sg) in HF/HNO3 on anion-exchange resin

Adsorption of carrier-free radiotracers 181W and 93mMo produced in the 181Ta(p, n) and natNb(p, n) reactions, respectively, on anion-exchange resin was studied in mixed solution of HF and HNO3 in a concentration range of 10−4–10−1 Mxa0HF/0.1xa0Mxa0HNO3. Distribution coefficients (Kd) of 181W and 93mMo at 70xa0°C showed the V-shaped variation with the minimum at around 10−1 Mxa0HF/0.1xa0Mxa0HNO3, although variation of the Kd values for 93mMo was quite small compared with that for 181W. Formation of oxofluoro complexes for W and Mo is briefly discussed.

Development of a new continuous dissolution apparatus with a hydrophobic membrane for superheavy element chemistry

A new technique for continuous dissolution of nuclear reaction products transported by a gas-jet system was developed for superheavy element (SHE) chemistry. In this technique, a hydrophobic membrane is utilized to separate an aqueous phase from the gas phase. With this technique, the dissolution efficiencies of short-lived radionuclides of 91m,93mMo and 176W were measured. Yields of more than 80xa0% were observed for short-lived radionuclides at aqueous-phase flow rates of 0.1–0.4xa0mL/s. The gas flow-rate had no influence on the dissolution efficiency within the studied flow range of 1.0–2.0 L/min. These results show that this technique is applicable for on-line chemical studies of SHEs in the liquid phase.

Development of a He/CdI2 gas-jet system coupled to a surface-ionization type ion-source in JAEA-ISOL: towards determination of the first ionization potential of Lr (Z = 103)

We report on development of a gas-jet transport system coupled to a surface ionization ion-source in the JAEA-ISOL (Isotope Separator On-Line) system. As a new aerosol material for the gas-jet system, CdI2, which has a low boiling point of 713xa0°C, is exploited to prevent deposition of the aerosol material on the surface of the ion-source. An additional filament is newly installed in the previous ion-source to provide uniform heating of an ionizer. The present system is applied to the measurement of absolute efficiencies of various short-lived lanthanide isotopes produced in nuclear reactions.

Chemical studies of Mo and W in preparation of a seaborgium (Sg) reduction experiment using MDG, FEC, and SISAK

The extraction and reduction behavior of Mo and W, lighter homologs of Sg, was studied in continuous on-line experiments at the JAEA tandem accelerator to develop a new chemistry assembly consisting of a membrane degasser (MDG), a flow electrolytic column (FEC), and the continuous liquid–liquid extraction apparatus (SISAK). Extraction yields of Mo and W from 0.1xa0M HCl/0.9xa0M LiCl into 4-isopropyltropolone (hinokitiol, HT) in toluene were investigated. In the reduction experiment, Mo(VI) was successfully reduced to a lower oxidation state while W(VI) showed no reduction under the given conditions.

Radiochemical studies of the heaviest elements at JAEA

Chemical studies of the heaviest elements in liquid phases at Japan atomic energy agency (JAEA) are reviewed. From the systematic investigation of ion-exchange chromatographic behavior of element 104, rutherfordium (Rf), based on an atom-at-a-time scale, it has been found that the properties of Rf are quite similar to those of the group-4 homologs, Zr and Hf, in the formation of chloride, nitrate, and sulfate complexes, although there are some differences in complexation strength between Rf and the lighter homologues. On the contrary, fluoride complex formation of Rf is significantly different from that of the homologues. Anionic fluoride complexation of element 105, dubnium (Db), has also been studied. The result clearly demonstrates that the fluoride complex formation of Db is considerably different from that of the group-5 homologue Ta, while the behavior of Db is similar to that of the lighter homologue Nb. A new electrochemical approach to the heaviest elements has been successfully conducted by a flow electrolytic column chromatographic method; the oxidation state of element 102, nobelium (No), with single atoms can be controlled with the developed apparatus. Prospects for the future studies on chemical properties of the heaviest elements at JAEA will be briefly considered.

Online chemical adsorption studies of Hg, Tl, and Pb on SiO2 and Au surfaces in preparation for chemical investigations on Cn, Nh, and Fl at TASCA

Abstract Online gas-solid adsorption studies with single-atom quantities of Hg, Tl, and Pb, the lighter homologs of the superheavy elements (SHE) copernicium (Cn, Z=112), nihonium (Nh, Z=113), and flerovium (Fl, Z=114), were carried out using short-lived radioisotopes. The interaction with Au and SiO2 surfaces was studied and the overall chemical yield was determined. Suitable radioisotopes were produced in fusion-evaporation reactions, isolated in the gas-filled recoil separator TASCA, and flushed rapidly to an adjacent setup of two gas chromatography detector arrays covered with SiO2 (first array) and Au (second array). While Tl and Pb adsorbed on the SiO2 surface, Hg interacts only weakly and reached the Au-covered array. Our results contribute to elucidating the influence of relativistic effects on chemical properties of the heaviest elements by providing experimental data on these lighter homologs.

Synthesis and chemical investigation of Sg(CO)

J. Even†1, A. Yakushev 2, Ch.E. D̈ullmann1,2,3, H. Haba4, M. Asai5, T.K. Sato5, H. Brand2, A. Di Nitto3, R. Eichler6,7, F.L. Fan8, W. Hartmann2, M. Huang4, E. J̈ager2, D. Kaji4, J. Kanaya4, Y. Kaneya5, J. Khuyagbaatar 1, B. Kindler2, J.V. Kratz3, J. Krier2, Y. Kudou4, N. Kurz2, B. Lommel 2, S. Miyashita5,9, K. Morimoto4, K. Morita4,10, M. Murakami 4,11, Y. Nagame 5, H. Nitsche12,13, K. Ooe11, Z. Qin8, M. Scḧadel5, J. Steiner 2, T. Sumita4, M. Takeyama 4, K. Tanaka4, A. Toyoshima 5, K. Tsukada5, A. Türler6,7, I. Usoltsev6,7, Y. Wakabayashi 4, Y. Wang8, N. Wiehl 1,3, and S. Yamaki 4,14