Bettina Lommel

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 missing mass of the ^{12}C(p,d) reaction has been measured near the η^{'}-meson emission threshold in coincidence with a high-momentum proton to selectively collect η^{'}-^{11}C mesic nucleus formation events at GSI, Germany. A 2.5 GeV proton excites a carbon nucleus in order to form an η^{'}-mesic nucleus emitting a deuteron forward with an energy of ∼1.5 GeV. The deuteron is momentum analyzed by the fragment separator used as a high-resolution spectrometer to deduce the excitation energy of the residual system. The large-acceptance detector WASA surrounding the target identifies high-momentum protons emitted in the decay of the η^{'}-mesic nucleus. The measured semiexclusive spectrum exhibits structures below the threshold though the statistical significance is limited. The spectrum is fitted by theoretically calculated spectra varying optical-potential parameters of the η^{'}-nucleus interaction. The analysis results indicate possible formation of η^{'}-mesic nuclei for the real potential depth of ∼-61 MeV with a local statistical significance of 3.5σ and, taking into account the look-elsewhere effect, a global significance of 2.1σ.

Tungsten is applied as target material for experiments in the field of nuclear spectroscopy. Typically, targets of a thickness range of 100 µg/cm² up to 1000 µg/cm² that can safely stand the irradiation by the intense heavy-ion beam over a substantially long period are requested. Natural tungsten is commercially available as thick foils and as sputtering targets. Enriched tungsten is typically available as metal powder. We report on the production of natural and enriched tungsten targets on carbon backing. We compare the different production processes, taking into account the material yield.

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