Experiments at the limits of stability: exploring physical and chemical properties of superheavy elements

Understanding the strong force and its consequences for nuclear structure is one of the major goals of contemporary nuclear physical research.

This is being best performed at the limits of existence, i.e. in the regions of extreme neutron-to-proton ratios and with superheavy elements (SHE). The experimental investigation of SHE, i.e., nuclei with atomic numbers Z≥ 104, addresses fundamental physical and chemical questions. SHE owe their existence solely to nuclear shell stabilization effects. Beyond the closed spherical shells at Z=82 and N=126, theoretical calculations suggest the next shell closures at Z=114, 120, or 126, and N=172 or, more frequently, N=184. On the way to this long-sought "island of stability of superheavy elements", deformed shell closures have been identified at N=152, Z=108 and N=162. Over the past decades, intense research at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, six new elements with Z=107-112 were discovered, and more recently, element 114 was observed.The location in N and Z of the next spherical shell closure, however, is still open. Therefore, experiments on the synthesis of new elements with Z>118 are currently being prepared, supported by studies of nuclear reaction mechanisms.

Obtaining a fundamental understanding of the nuclear structure through decay spectroscopic studies of excited, especially of isomeric states will assist in pin-pointing the location of proton- and neutron shell-closures. Highly accurate mass measurements with Penning traps complement the broad research program, which will yet be expanded to laser spectroscopic measurements in the near future.

Chemical studies of superheavy elements – which are often called the "transactinides" as they follow the actinide series – trace the influence of relativistic effects on the electronic shell structure. These effects may give rise to changes in chemical behavior of these elements compared to the properties of their lighter homologs in the periodic table. Current research addresses the question whether element 114 behaves chemically similarly to its lighter homolog lead or rather like a noble gas. To obtain a better understanding as well as a correct interpretation of the experimental data, fully-relativistic quantum chemical calculations are being performed. In the last few years, novel methods gave access to new chemical compound classes of superheavy elements. Furthermore, nuclear chemical studies are the most sensitive ones available for the separation and study of long-lived nuclides, as they occur, e.g., around the deformed doubly-magic nucleus, or as they can be produced in multi-nucleon transfer reactions with heavy actinide target nuclei. This class of reactions is investigated by the Helmholtz Young Investigator Group IRiS, which is currently being established.

The research section "Physics and Chemistry of Superheavy Elements", SHE, at the Helmholtz Institute Mainz is the condensation nucleus of a research network that combines the strengths of nuclear physics, nuclear chemistry, and atomic physics, to further SHE research in the framework of international collaborations at the GSI and, thus, to answer the pressing questions in physics and chemistry of the superheavy elements. The respective partners at the GSI are the departments "Superheavy elements" and "Nuclear chemistry". The University Mainz with its proven expertise in these areas is an ideal partner and features unique infrastructure at the Institute for nucelar chemistry  for methodical developments at the research reactor TRIGA as well as for radiochemical work with exotic radioisotopes for the production of transuranium targets.


The research sections SHE Chemistry (Head: Prof. Dr. Christoph E. Düllmann, c.e.duellmann(at)gsi.de) and SHE Physics (Acting Head: Dr. Fritz P. Heßberger, f.p.hessberger(at)gsi.de) exploit a world-unique combination of experimental facilities:

  • the velocity filter SHIP (GSI)
  • the Penning trap system SHIPTRAP (GSI)
  • the gas-filled separator TASCA (GSI) 
  • the multicoincidence spectroscopy setup TASISpec (GSI)
  • the research reactor TRIGA Mainz (Institute for Nuclear Chemistry, University Mainz)
  • the Penning trap- und laserspectroscopy setup TRIGA-SPEC (Institute fpr Nuclear Chemistry, University Mainz)
  • radiochemical laboratories (GSI and Institute for Nuclear Chemistry, University Mainz)
  • irradiation cave for chemical and nuclear chemical experiments (GSI)
  • fast automated chemical separation system (GSI and Institute for Nuclear Chemistry, University Mainz)
  • target laboratories for the production of radioactive (Institute for Nuclear Chemistry, University Mainz) and stable isotopes (GSI)

The research section SHE has strong links to the other research sections ACID, (construction of a prototype cavity for a future dedicated linear accelerator for superheavy element research at GSI), MAM (operates Penning trap- and laser-based experiments, similar to SHIPTRAP and TRIGA-SPEC), SPECF (research to understand the strong force), and THFL (links to the relevant theory groups, e.g., through the HIM guest scientist program).

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