Katharina Hermainski

The present work aimed at the synthesis of the hitherto unknown Am 231 and known Am 229 isotopes via the 4 n evaporation channels of the fusion reactions of Ca 48 + Re 187 and Ca 48 + Re 185 , respectively. The new isotope Am 231 , with a half-life of 47 − 19 + 85 s , was identified on the basis of five observed α -decay chains. It emits α particles with an energy of 7.11(2) MeV. An upper limit of 0.66 was estimated for the electron-capture decay branch of Am 231 . No α -decay chain from Am 229 was observed, corresponding to a cross-section level of 0.03 nb for the detection of a single event. The α -decay properties of Am 231 are discussed in the framework of the Geiger-Nuttall empirical relation.

The chemistry of the radioelement polonium has attracted increasing attention owing to its formation in accelerator-driven systems and its high radiotoxicity. Being the lighter homologue of the superheavy element livermorium, whose chemistry is still unexplored, studies of polonium provide a benchmark for verifying the structure of the periodic table at the heavy-element frontier. While the reactivity of elemental polonium towards various surfaces in inert or reducing atmospheres has been investigated previously, the reactivity of oxidized polonium towards quartz has not been explored in detail. Here, we report on gas–solid thermochromatography studies of polonium on quartz glass and α-Al₂O₃ surfaces in helium, as well as in oxygen- and water-containing atmospheres in the atom-at-a-time regime. We found that polonium chemically reacts in an oxygen-containing atmosphere, forming two oxidized species, which are less volatile than elemental polonium. The chemical reaction is influenced by the water vapour concentration in the carrier gas and the applied temperature. The adsorption enthalpy of elemental polonium on α-Al₂O₃ in pure helium gas was determined to be −85⁺⁴ ₋₃ kJ mol⁻¹, which is identical to the adsorption enthalpy on quartz as reported earlier. The results of the reported measurements will support future experiments with the superheavy element livermorium.

Beyond the (quasi)stable and abundant elements lead and bismuth, all elements are radioactive, with polonium being the first of a series of radioelements up to primordial uranium. Interest in understanding its chemical behavior is increasing, not least due to its co-production in accelerator-driven systems and high radiotoxicity. Polonium is also the lighter homologue of the superheavy element livermorium, which has not been studied chemically to date. Polonium therefore acts as a benchmark to verify the structure of the periodic table at the heavy-element frontier. Here, we report on gas–solid thermochromatography studies of polonium in the atom-at-a-time regime under helium and hydrogen gas atmospheres. Quartz surfaces with different degrees of hydroxylation were used as a stationary phase. On quartz glass with low OH-concentrations, a volatile species interacting with an adsorption enthalpy of −85⁺³ ₋₂ kJ mol⁻¹ was found and assigned to elemental polonium. On more highly hydroxylated quartz glass, an additional deposition zone due to a species with an adsorption enthalpy of −139⁺⁶ ₋₅ kJ mol⁻¹ was observed and attributed to a polonium species formed by chemical reactions with the surface. Under our experimental conditions, chemical reactions of polonium in the solid phase dominate over reactions in the gas phase. Thus, the nature of the surface should be considered as an important parameter in future gas chromatography studies.

Decay properties of the neutron-deficient Sg isotopes were studied at the gas-filled recoil separator TASCA at GSI, Darmstadt by using the Cr 52 + Pb 206 , 208 reactions. We report on the discovery of the new isotope Sg 257 . Its ground state, tentatively assigned to have 9 / 2 − [734] configuration, was observed to decay by both spontaneous fission and α -particle emission with a half-life of 12.6 − 2.3 + 3.7 ms . The alpha decay from this high-spin state was followed by fission of Rf 253 after 11 μ s . In Sg 259 , we observed strong evidence for the occurrence of a K -isomeric state for the first time in superheavy nuclei with 106 protons. The current experimental findings, discussed within the experimental systematics and theory, indicate that hitherto unseen features of the shell effect on the fission process may be found in the neutron-deficient superheavy nuclei. Published by the American Physical Society 2025

We report the discovery of the new isotope ^{252}Rf. With its extremely short half-life of 60_{-30}^{+90} ns, it expands the range of half-lives of the known superheavy nuclei by about 2 orders of magnitude. This nucleus was synthesized in its high-K isomeric state, for which we measured a half-life of 13_{-3}^{+4} μs. Our results confirm a smooth onset of decreasing ground-state spontaneous fission half-lives in the neutron-deficient Rf isotopes toward the isotopic border of 10^{-14} s, which is the time needed to form an atomic shell. Our findings set a new benchmark for further exploration of phenomena associated with high-K states and inverted fission stability in the heaviest nuclei.

Metal complex – arene dyads typically act as more potent triplet energy donors compared to their parent metal complexes, which is frequently exploited for increasing the efficiencies of energy transfer applications. Using unexplored dicationic phosphonium-bridged ladder stilbenes (P-X²⁺) as quenchers, we exclusively observed photoinduced electron transfer photochemistry with commercial organic photosensitizers and photoactive metal complexes. In contrast, corresponding pyrene dyads of the tested ruthenium complexes with the very same metal complex units efficiently sensitize the P-X²⁺ triplets. The long-lived and comparatively redox-inert pyrene donor triplet in the dyads thus provides an efficient access to acceptor triplet states that are otherwise very tricky to obtain. This dyad-enabled control over the quenching pathway allowed us to explore the P-X²⁺ photochemistry in detail using laser flash photolysis. The P-X²⁺ triplet undergoes annihilation producing the corresponding excited singlet, which is an extremely strong oxidant (+2.3 V vs. NHE) as demonstrated by halide quenching experiments. This behavior was observed for three P²⁺ derivatives allowing us to add a novel basic structure to the very limited number of annihilators for sensitized triplet-triplet annihilation in neat water.