I. Zvara

First attempt to chemically identify element 112

The first attempt to chemically identify one of the recently discovered long-lived isotopes of superheavy elements, namely 283112 (3 min, SF), made at FLNR, Dubna is reported. The nuclide was produced by fusion of accelerated 48Ca with a target of natural U, which contained some Nd to simultaneously produce also short-lived Hg nuclides. According to test experiments with Hg, the expected lighter homologue of element 112, both elements can be isolated from the products of the bombardment in metallic state, and transported from the target in flowing He gas to a detection system, where spontaneous fission and alpha decays 49-s 185Hg) were registered using PIPS detectors. The surface of the detectors was covered with a thin layer of Au or Pd which ensured the detection of Hg with high efficiency due to its chemisorption on these surfaces. While about three SF events could be expected, not a single one was detected at an upper limit for the production cross section of about one picobarn. This may point to a Rn-like rather than Hg-like behavior of element 112. A new experiment is planned, in which both a Rn-like and a Hg-like species could be detected.

Gas Phase Chromatography Experiments with Bromides of Tantalum and Element 105

The retention behavior of volatile bromide molecules of shortlived isotopes of tantalum and element 105 in KCl coated quartz columns was studied using continuous isothermal gas chromatography. HBr and HBr saturated with BBrs vapor were used as reactive gases. The isotopes were produced in the fusion reactions ^°Ne+ Eu and ^^O + ^^^Bk, respectively. The reaction producta were transported from the accelerator to the chromatography set-up with a gas-jet system using an aerosol with He as carrier gas and KCl as transporting particles. The measured retention times are compared to those of N b bromides from a previous study. The retention times of niobium and tantalum bromides are very similar, in agreement with expectations based on the nearly identical Sublimation enthalpies of NbBrj and TaBr;. For the bromides of element 105, higher retention times are found, indicating a lower volatility of lOSBrs than of NbBrs and TaBrs. On the basis of empirical systematics, a Sublimation enthalpy of 138± 15 kJ/mol can be estimated for 105Br5 from the experimental data.

Study of the Solution Chemistry of Element 104 – Kurchatovium

By Z. Szeglowski, H. Bruchertseifen, V. P. Domanov, B. Gleisberg, L. J. Guseva, M. Hussonnois, G. S. Tikhomirova 3 ,1. Zvara and Yu. Ts. Oganessian 1 Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, 141980, Dubna, USSR 2 Zentralinstitut für Isotopenund Strahlenforschung, Leipzig, DDR 3 V. I. Vernadsky Institute of Geochemistry and Analytical Chemistry, 117979 Moscow, USSR 4 Institut de Physique Nucleaire, Orsay, France

Gas phase chromatography of halides of elements 104 and 105

On-line isothermal gas phase chromatography was used to study halides of261104 (T1/2=65 s) and262,263105 (T1/2=34 s and 27 s) produced an atom-at-a time via the reactions248Cm(18O, 5n) and249Bk(18O, 5n, 4n), respectively. Using HBr and HCl gas as halogenating agents, we were able to produce volatile bromides and chlorides of the above mentioned elements and study their behavior compared to their lighter homologs in Groups 4 or 5 of the periodic table. Element 104 formed more volatile bromide than its homolog Hf. In contrast, element 105 bromides were found to be less volatile than the bromides of the group 5 elements Nb and Ta. Both 104 and Hf chlorides were observed to be more volatile than their respective bromides.

ION EXCHANGE EQUILIBRIA AND STOICHIOMETRY OF COMPLEXES OF ELEMENT 104 AND HAFNIUM IN HYDROFLUORIC ACID SOLUTIONS

In bombardments of a Cm + <=2 t^rget with O ions, atoms of 78-s < ̂104 and >=-®Hf (half-lives of a few minutes) wäre simultaneously produced. They were continuously on-line processed in a Wofatit HS 36 anion exchanger column with 0.27 M HF 0.2 or 0.1 M HNO, as the eluent. The elution time and then the distribution coefficients, K^, of fluoride complexes of the elements were evaluated from the numbers of the shortlived nuclei that decayed in the column as well as those which survived. Actually, long-lived descendants rather than the mother activities were detected, which is a distinctive feature of the employed technique. In particular, a total of more than 120 decays of ^^Es descending from ^^104 were registered in the three experiments performed. The obtained K^ values for element 104 and Hf are nearly equal. From measurements of K^ versus the concentration of HNO,, the ionic Charge of the element 104 complex is -1 .9±0 .2 , thus pointing to [104]F; as the chemical State of the element.

RELATIVISTIC EFFECTS IN KURCHATOVIUM CHEMISTRY

Using the relativistic multiconfigurational Dirac-Fock method, the first four ionization potentials of Ku, the promotion energies of the atom, and the atomic and ionic radii were calculated. The enthalpy of sublimation of metallic Ku was estimated. Relativistic SCF-Xα scattering wave Dirac-Slater computations of the tetrachlorides of group IV elements were performed. The lower halides of Ku are predicted to be more stable and less volatile than the respective Hf compounds, due to the ds2 p ground state in the Ku atom.

Chemical identification of element 106 by thermochromatography

For the first time the chemical identification of element 106 was accomplished. The Gas-thermochromatographic experiments with an oxochloride of element 106 are described. Reproducible zones of tracks of fission fragments were observed in the temperature region of 150–250°C. The chemical behavior of element 106 oxochloride is similar to that of the tungsten compound.

Evidence for relativistic effects in the chemistry of element 104

Abstract On the basis of thermodynamic extrapolations, the first transactinide element 104 (Rf=rutherfordium 1 ) is expected to form volatile tetrachlorides of lower volatility than those of the homologous element Hf. In contrast, relativistic calculations predict a higher volatility of RfCl 4 compared to HfCl 4 . The nuclides 261 Rf and 165 Hf, with identical half-lives of 78 s, were simultaneously produced at the U-400 cyclotron of the Flerov Laboratory of Nuclear Reactions (FLNR), Dubna, Russia, by bombarding a mixed 248 Cm/ 152 Gd target with 18 O ions. With the on-line gas chemistry apparatus (OLGA), the retention behavior of volatile Rf- and Hf-chloride in a quartz chromatography column was investigated. The results showed that Rf forms chlorides of higher volatility than those of Hf, in agreement with relativistic calculations. In addition, the behavior of element 104 was investigated in chlorinating, oxygen containing carrier gas, in order to answer the question whether a volatile compound of the form RfOCl 2 exists. The results of our experiments give strong evidence for a transport reaction mechanism where RfOCl 2 exists only in the condensed phase and not in the gas phase.

Fast Continuous Radiochemical Isolation of the Short-Lived Isotopes of Hf, Ta and W Produced by Heavy Ion Induced Reactions

An experimert.tal approach to continuous radiochemical isolation and identification of short-lived isotopes of the elements Hf, Ta and W is described. A multistep procedure is based on transportation of the radioactive nuclides from the cyclotron target to laboratory by an aerosol stream (N, + KCl), separation and dissolution of the aerosol particulates, and isolation of the element under study by ion exchange or extraction techniques. Efficiencies of different steps of the complex procedure were measured and optimal conditions are discussed. The inherent processing time down to 1 0 20 s was achieved. Some new short-lived isotopes of W, Ta and Hf were identified.

Problems in thermochromatographic separation of radioelements

Earlier found correlations between the adsorbability of microamounts of compounds and their volatility in macroamounts plus the recently revealed surprisingly strict and general correlation between boiling points and solely geometric parameters of molecules allow to “measure” fundamental properties of compounds of short-lived man-made transactinoid elements using thermochromatographic principles. Some general topics concerning the separation method are discussed.