Research Topics





New Elements: Production and Z-Identification

Search for Elements Beyond Z=118

After the detailed study of the formation and decay of the most neutron-rich currently known isotopes of flerovium (Fl, Z=114), 288,289Fl at TASCA, the focus of our research is now on the synthesis of elements beyond the heaviest currently claimed element, Z=118. Due to the current lack of target isotopes with Z>98, the era of reactions induced by 48Ca (Z=20) appears exhausted and reactions with more symmetric partners, with projectiles beyond 48Ca need to be applied. The body of experimental data on nuclear fusion reactions suggests the asymmetry of a reaction to be of crucial importance for the magnitude of the cross section for producing a desired fusion-evaporation product. Reactions based on a projectile only marginally heavier than 48Ca appear therefore most promising. This simple picture is backed by all recent theoretical calculations, which suggest using reactions induced by 50Ti (Z=22) to synthesize element 119 with a target made from 249Bk (Z=97) and element 120 with a target made from 249Cf (Z=98). A first experiment searching for element 120 was recently performed and proved the UNILAC/TASCA setup to allow the most sensitive searches for new elements beyond Z=118. Currently, a several months long experiment searching for element 119 with the very rare 249Bk provided by our collaborators from Oak Ridge National Laboratory is running.

Z-Identification of Elements beyond Z=112

Cn is the heaviest elements that had its Z experimentally determined in a direct and unambiguous way. The discovery of Cn was achieved at the velocity filter SHIP at GSI through the observation of 277Cn and its α decay descendants all the way to 261Rf and 257No, which were previously known. Establishing the Z of the discovered isotope was thus straightforward. In contrast, decay chains of elements produced in 48Ca-induced fusion reactions with actinide targets end by spontaneous fission of previously unknown isotopes. Accordingly, a direct proof for the Z of the nucleus initiating the decay chain cannot be obtained. A well-known method to directly measure the atomic number is through the observation of characteristic X rays, the energy of which is a fingerprint of Z, according to Moseley's law. An experiment addressing this relies on the α decay of a mother nucleus that populates excited nuclear states in the daughter nucleus. If the decay of the excited state involves the emission of conversion electrons (ce), characteristic X rays will be emitted after ce emission. Experimentally, the required signature is the observation of coincident a particles and X rays. An ideal tool for such studies is the TAsca Small Image mode Spectroscopy setup (TASISpec) at TASCA.

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Chemical Properties of Transactinides

Elements with Z>112: Studies in the Elemental State

The heaviest elements that had their chemical properties studied are copernicium (Cn, Z=112) and flerovium (Fl, Z=114). In several experiments, Cn was established to be a volatile metal, interacting with a Au surface by forming metallic bonds. Only one experiment on Fl is reported to date, which found this interaction to be very weak. This was interpreted to point at the formation of a weak physisorptive bond. However, the uncertainty was so large that a clear discrimination between a metallic and a rather nobel-gas like behavior was not possible. In our experiment, we employed the recoil separator TASCA to produce relatively long-lived Fl isotopes in the 244Pu(48Ca, 3-4n)288,289Fl reaction and to isolate them. Their interaction strength with a Au surface was studied with our gas chromatography and nuclear detection system COMPACT. The results will be published in the near future.

New Compound Classes of Superheavy Elements:
Metal-organic Compounds

Coupling of chemistry setups such as COMPACT to a physical recoil separator like TASCA allows the study of new superheavy element compound classes such as metal-organic ones. The recoil separator deflects the intense heavy-ion beam and guides only atoms of interest, i.e., of the transactinide element to be studied, to the focal plane, where it penetrates a thin vacuum window and is stopped in a gas-filled volume, the "Recoil Transfer Chamber" (RTC). From there, it is available for transport to gas-chromatography devices. Experiments with the lighter homologs of the transactinides were performed at the TRIGA Mainz research reactor, where the 4d homologues (Zr, Nb, Mo, Tc, Ru and Rh) – produced in the neutron-induced fission of 235U or 249Cf – were studied. The 5d homologues (W, Re, Os, Ir) were produced in fusion-evaporation reactions at TASCA. Initial experiments focused on metal-carbonyl complexes. The adsorption properties on different surface materials as well as the chemical stability of the complexes was studied. Experiments on carbonyl-complexes of a superheavy element are currently in preparation.

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Theoretical Chemistry of Heavy and Superheavy Elements

Current and Future Research Interests

Investigations of properties of the heaviest elements belong to the most fundamental areas of chemical science. In this field, theory plays a particularly important role, as only very few properties of the short-lived isotopes of these elements can be measured. In this case the theory not only helps interpret experimental results and facilitate the insight into the studied processes and phenomena, but it does mostly serve as a guiding tool in designing expensive and sophisticated experiments with single atoms. The feature of the present theoretical research is, therefore, a very close link to the experiment. Such a close collaboration during the last 20 years led to remarkable achievements in this field and resulted in much better understanding the chemistry of the heaviest elements, also with respect to their homologs (see, e.g. selected publications).
Since the heaviest elements are those where relativistic effects are of paramount importance, our research is based on most accurate relativistic electronic structure calculations. We use the best relativistic atomic and molecular codes. We also concentrate on development of various physico-chemical models in case the desired properties such, e.g., as adsorption or complex formation, cannot be calculated in a straightforward way.

The topics of our research on the heaviest elements are the following:

  • accurate calculations of atomic properties with the use of ab initio Dirac-Fock-Coulomb (Breit) correlated methods
  • calculations of electronic structure of small molecule properties with the use of ab initio correlated methods
  • large scale calculations of molecular and cluster properties using the 4-component relativistic density functional theory (4c-DFT)
  • predictions of adsorption of atoms and molecules on different (metal and non-metal) surfaces on the basis of the relativistic DFT calculations; development of adsorption models
  • study of aqueous chemistry of the heaviest elements on the basis of the relativistic DFT calculations; predictions of complex formation and extraction behaviour
  • study of redox reactions and predictions of redox potentials of the heaviest elements

The future interests may also cover:

  • solid-state calculations for the heaviest elements
  • calculations of an average charge of heavy-element ions moving in a gas

Our collaborating partners are:

Selected publications:

  • V. Pershina
    Electronic Structure and Properties of the Transactinides and Their Compounds
    Chem. Rev. 96 (1996) 1977-2010
  • V. Pershina and B. Fricke, in:
    Heavy Elements and Related New Phenomena
    W. Greiner, R.K. Gupta, Eds.; World Scientific, Singapore, 1999; Vol. 1, p. 194
  • V. Pershina
    Relativistic electronic structure studies on the heaviest elements
    Radiochim. Acta 99 (2011) 459-476
  • V. Pershina
    Theoretical Chemistry of the Heaviest Elements
    In: The Chemistry of Superheavy Elements (2003)
    Ed. M. Schädel, Kluwer, Dordrecht; pp. 31-94
  • V. Pershina, in:
    Theoretical and Computational Chemistry
    Relativistic Electronic Structure Theory, Part 2: Applications; P. Schwerdtfeger,  Ed.;
    Elsevier, Amsterdam, 2004; Vol. 14, p. 1
  • V. Pershina
    The Chemistry of the Superheavy Elements and Relativistic Effects
    In: Relativistic Electronic Structure Theory, Part II; Ed. P. Schwerdtfeger; Elsevier, Amstrerdam 2002; pp. 1-80
  • V. Pershina
    Electronic Structure and Chemistry of the heaviest Elements
    In: Relativistic Methods for Chemists, Eds. M. Barysz and Y. Ishikawa; Springer, Dordrecht 2010; pp. 451- 520
  • D.C. Hoffman, D.M. Lee, V. Pershina
    Transactinide Elements and Future Elements
    In: The Chemistry of the Actinide and Transactinide Elements, 3rd Edition, Eds. L. R. Morss, N. M. Edelstein, J. Fuger; Springer, Dordrecht, 2006;  pp. 1652-1752
  • A. Türler and V. Pershina
    Advances in the Production and Chemistry of the Heaviest Elements
    Chem. Rev. 113 (2013) 1237–1312
  • more publications

Contact: Dr. Valeria Pershina (V.Pershina@gsi.de)

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Nuclear Chemical Studies

Chemical separation techniques are ideally suited to provide clean samples of long-lived (T1/2 > 1 s) isotopes for nuclear physics studies on their production and decay properties. Through the Z-selective character of chemical separations, valuable information on the identity of the studied nuclei is provided. Recent experiments exploited the outstanding chemical properties of the group 8 tetroxides including HsO4. Single MO4 molecules (M=Os, Hs) can be transported in the gas phase at ambient temperature, in contrast to oxides of almost all other elements. This allows a highly selective and very efficient preparation of samples of single Hs nuclei. The deformed doubly-magic 270Hs (Z=108, N=162) was discovered in the course of these studies, along with its neighbor 271Hs and their daughter isotopes. The production in different nuclear reactions (26Mg+248Cm; 36S+238U) and their decay properties were studied. Current work focuses on the development of a comparably well-suited and highly efficient chemical system for other superheavy elements.

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High-precision Mass Measurements of Exotic Nuclei

Nuclear stability is largely governed by the binding energy of atomic nuclei. Through Einstein's equivalence principle, this is reflected in the mass of a nucleus. Consequently, high-precision mass measurements, usually performed with Penning traps, give access to this basic property of a nucleus. At GSI Darmstadt, we collaborate with the SHE Physics department, which operates the SHIP/SHIPTRAP facility on mass measurements of transfermium nuclei that can only be produced at particle accelerators, with the current focus being on the elements nobelium (No, Z=102), lawrencium (Lr, Z=103), and rutherfordium (Rf, Z=104). At the institute of nuclear chemistry at the University of Mainz, we collaborate with the TRIGA-SPEC collaboration, which operates the TRIGA-Trap double Penning mass spectrometer, a sibling to SHIPTRAP. Here, masses of neutron-rich transuranium isotopes such as 242Pu, 248Cm, or 249Cf can be measured. Through a coupling of the TRIGA-Trap to the TRIGA Mainz research reactor, mass measurements of short-lived fission products from the neutron-induced fission of suitable actinide targets will become possible.

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Radioisotope Production, Purification and Processing for Nuclear Science Experiments

High Power Targets for TASCA Experiments

Every accelerator-based experiment requires a stable target that is irradiated often for extended periods of time with highly intense ion beams. The "Institute for Nuclear Chemistry" in Mainz provides the facilities and expertise to produce high-quality nuclear targets also from the most exotic and often highly radioactive transuranium isotopes including 244Pu, 243Am, 248Cm, 249Bk, and 249Cf. The targets are generally produced by molecular plating, an electrochemical deposition method yielding homogeneous layers that can be produced with high yields.

Actinide Targets for Nuclear Science Experiments

Targets produced by molecular plating are also of interest for nuclear physics experiments in other areas. Targets are produced, e.g., for neutron induced cross section measurements at HZDR Dresden Rossendorf or at CERN ISOLDE (n_TOF collaboration), or for measurements of the low-lying isomeric state in 229Th at LMU Munich (info in english and german).

High Purity Samples of 163Ho for the ECHo-collaboration

Together with researchers from the TRIGA Mainz research reactor, our group is reponsible for the production of radiochemically pure samples of 163Ho within the "Electron Capture in Holmium" (ECHo) collaboration. Sufficient amounts are produced at the high-flux reactor at Institut Laue Langevin in Grenoble, France, and then processed and prepared in joint activities with the group of Prof. Dr. Klaus Wendt at the Institute of Physics at University of Mainz.