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  • Author: Jens Volker Kratz x
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Abstract

The experimental techniques developed to perform rapid chemical separations of the heaviest elements in the aqueous phase are presented. In general, these include transport of the nuclear reaction products to a separation device by the gas-jet technique and dissolution in an aqueous solution containing inorganic ligands for complex formation. The complexes are chemically characterized by a partition method which can be liquid–liquid extraction, ion-exchange- or reversed-phase extraction chromatography. The separated fractions are quickly evaporated to dryness for the preparation of samples for α-particle spectroscopy. Comments are given on the special situation in which chemistry has to be studied with single atoms. Theoretical predictions of chemical properties are compared to the presently known chemical behaviour of rutherfordium, Rf (element 104), dubnium, Db (element 105), seaborgium, Sg (element 106), and hassium, Hs (element 108) and to that of their lighter homologs in the Periodic Table in order to assess the role of relativistic effects in the chemistry of the heaviest elements.

The potential associated with the electrochemical deposition of radionuclides in metallic form from solutions of extremely small concentration is strongly influenced by the choice of the electrode material. In a macroscopic model, the interaction between the microcomponent and the electrode material is described by the partial molar adsorption enthalpy and -entropy. By combination with the thermodynamic description of the electrode process, a potential is calculated that characterizes the process at 50% deposition. Model calculations for Ni-, Cu-, Pd-, Ag-, Pt-, and Au-electrodes and the microcomponents Hg, Tl, Pb, Bi, and Po confirm the decisive influence of the electrode material on the deposition potential. The present study prepares an application of the same model to the superheavy elements 112-116.

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Fully relativistic Density-Functional calculations have been performed for group 7 MO3Cl (M=Tc, Re, and element 107, Bh), for group 8 tetroxides MO4 (M=Ru, Os, and element 108, Hs), and for various aqueous complexes of group 6 elements Mo, W, and element 106, Sg. The electronic structure analysis has shown the transactinide compounds to be very similar to those of the lighter homologs in the respective chemical groups with the covalence increasing with increasing atomic number. Results have shown BhO3Cl to have a trend in volatility in line with that of the lighter homologs in the group. Hydrolysis of element 106 with the formation of anionic oxo-complexes has, however, a reversed trend, so that hydrolysis decreases in the order Mo>Sg>W.

Abstract

This review describes some key accomplishments of Günter Herrmann such as the establishment of the TRIGA Mark II research reactor at Mainz University, the identification of a large number of very neutron-rich fission products by fast, automated chemical separations, the study of their nuclear structure by spectroscopy with modern detection techniques, and the measurement of fission yields. After getting the nuclear chemistry group, the target laboratory, and the mass separator group established at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, a number of large international collaborations were organized exploring the mechanism of deeply inelastic multi-nucleon transfer reactions in collisions of Xe and U ions with U targets, Ca and U ions with Cm targets, and the search for superheavy elements with chemical separations after these bombardments. After the Chernobyl accident, together with members of the Institute of Physics, a powerful laser technique, the resonance ionization mass spectometry (RIMS) was established for the ultra-trace detection of actinides and long-lived fission products in environmental samples. RIMS was also applied to determine with high precision the first ionization potentials of actinides all the way up to einsteinium. In the late 1980ies, high interest arose in results obtained in fusion-evaporation reactions between light projectiles and heavy actinide targets investigating the chemical properties of transactinide elements (Z≥104). Remarkable was the observation, that their chemical properties deviated from those of their lighter homologs in the Periodic Table because their valence electrons are increasingly influenced by relativistic effects. These chemical results could be reproduced with relativistic quantum-chemical calculations. The present review is selecting and describing examples for fast chemical separations that were successful at the TRIGA Mainz and heavy-ion reaction studies at GSI Darmstadt.