The chemistry of transactinide elements

The so-called transactinides or superheavy elements (SHEs; Z ≥ 104) represent the least explored area of the Periodic Table. Their electron structures are strongly influenced by relativistic effects, making them particularly suitable study objects for understanding how relativity influences physico-chemical properties of heavy elements. Superheavy elements are produced artificially in heavy-ion fusion-evaporation reactions at large accelerator facilities. Production rates can be as low as a few atoms per week or even month, and many of the accessible isotopes have half-lives of only seconds or even milliseconds. Their chemistry must therefore be investigated one atom at a time using highly efficient and extremely fast experimental techniques.

Our group develops new approaches specifically for these challenging conditions. Gas-adsorption chromatography remains one of our core methods, with experiments prepared and validated using radioactive isotopes of lighter homologs before being transferred to the corresponding superheavy elements. We combine experimental studies with thermochemical models and Monte Carlo simulations to derive fundamental properties such as adsorption and sublimation enthalpies. Current developments in high-temperature 4H-SiC radiation detectors further extend the range of chemical systems accessible by these techniques.

A major focus in recent years has been the development of vacuum adsorption chromatography (VAC), which extends single-atom chemistry to less volatile species and isotopes with half-lives in the millisecond range. Following development and commissioning at PSI, VAC has been successfully demonstrated in online experiments with short-lived Hg and Po isotopes at the Cyclotron Institute at Texas A&M University. This worldwide unique approach opens a path toward chemical investigations of the elements beyond flerovium (Fl, Z = 114).

Our research also extends beyond gas-phase chemistry: We develop liquid-phase and electrochemical methods toward first chemical investigations of elements such as roentgenium (Rg, Z = 111) and explore new chemical observables, including the bond stability of superheavy-element compounds and the direct identification of single-atom chemical species by coupling chromatography with mass spectrometry.

Because superheavy elements can only be produced at a small number of facilities worldwide, this research relies on strong international collaborations. Our experiments and method development involve partners in the United States, Japan, China, and Germany. At PSI, we use the available large-scale research facilities to produce radioactive isotopes of lighter homologs for method development and preparatory experiments. The resulting radiochemical expertise also enables collaborations beyond our core research, e.g., radionuclide production for radiopharmacy, nuclear batteries, quantum-dot doping, and dark-matter research.

The experimental methods developed for SHE research also form the basis of a broader radiochemistry program. Techniques originally developed to handle and characterize very small quantities of short-lived radionuclides are transferred to more applied research questions. Examples include gas-phase studies of Po relevant to Generation-IV nuclear reactor concepts, radionuclide production and separation for radiopharmaceutical applications, advanced radioanalytics, and nuclear forensics. Across these activities, the production of exotic radionuclides, innovative chemical separations, and highly sensitive radioanalytical techniques provide a common methodological basis.

• Chemical investigation of Nh (Z = 113) using advanced gas-adsorption thermochromatography in combination with wide-bandgap semiconductors (diamond or 4H-SiC) as high-temperature radiation detectors.
• Transactinide adsorption chromatography and carbonyl decomposition research, TRACER (project funding, Swiss National Science Foundation) [01/2027-12/2031]
• Electrochemistry with homologs of roentgenium, ELCHOR (Weave proposal, Swiss National Science Foundation) [03/2026-02/2029]
• Radiolanthanide production in core, RAPIC (swissnuclear) [10/2024-09/2028]
• Technological Research Action Necessary for Safe PARtitioning And Nuclear Transmutation, TRANSPARANT (HORIZON-EURATOM-2023-NRT-01-05 via SERI) [01/2025-12/2029]
• Thermal release of Po from liquid lead, TRAPOL (newcleo) [2026-2028]
• PureCOLD 2.0, the new PSI pile-up rejection system for α- and SF-fragment spectroscopy (PSI)