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By combining two unique facilities at the Gesellschaft fuer Schwerionenforschung (GSI), the Fragment Separator (FRS) and the Experimental Storage Ring (ESR), the first direct measurement of a proton capture reaction of stored radioactive isotopes was accomplished. The combination of well-defined ion energy, an ultra-thin internal gas target, and the ability to adjust the beam energy in the storage ring enables precise, energy-differentiated measurements of the (p,gamma) cross sections. The new setup provides a sensitive method for measuring (p,gamma) reactions relevant for nucleosynthesis processes in supernovae, which are among the most violent explosions in the universe and are not yet well understood. The cross sections of the 118Te(p,gamma) and 124Xe(p,gamma) reactions were measured at energies of astrophysical interest. The heavy ions were stored with energies of 6 MeV/nucleon and 7 MeV/nucleon and interacted with a hydrogen gas-jet target. The produced proton-capture products were detected with a double-sided silicon strip detector. The radiative recombination process of the fully stripped ions and electrons from the hydrogen target was used as a luminosity monitor. Additionally, post-processing nucleosynthesis simulations within the NuGrid [1] research platform have been performed. The impact of the new experimental results on the p-process nucleosynthesis around 124Xe and 118Te in a core-collapse supernova was investigated. The successful measurement of the proton capture cross sections of radioactive isotopes rises the motivation to proceed with experiments in lower energy regions. [1] M. Pignatari and F. Herwig, “The nugrid research platform: A comprehensive simulation approach for nuclear astrophysics,” Nuclear Physics News, vol. 22, no. 4, pp. 18–23, 2012., Durch die Kombination zweier außergewöhnlicher Anlagen der Gesellschaft für Schwerionenforschung (GSI), dem Fragmentseparator (FRS) und dem Experimentier-Speicherring (ESR), wurden die ersten direkten Messungen von Protoneneinfangsreaktionen an gespeicherten radioaktiven Isotopen durchgeführt. Die Kombination aus genau bekannter Ionenenergie, einem sehr dünnen Gastarget und der Möglichkeit, die Energie des Strahls im Ring zu regulieren, ermöglicht präzise, energiedifferenzierte Messungen der (p,) Wirkungsquerschnitte. Mit dem neuen Aufbau steht eine sensitive Methode zur Messung von (p,) Reaktionen zur Verfügung, die für Nukleosyntheseprozesse in Supernovae relevant sind, welche zu den gewaltigsten Explosionen im Universum gehören und noch nicht vollständig verstanden sind. Im Rahmen dieser Arbeit wurden die Wirkungsquerschnitte der Reaktionen 118Te(p,) und 124Xe(p,) bei Energien von astrophysikalischem Interesse gemessen. Die schweren Ionen wurden mit Energien von 6 MeV/Nukleon und 7 MeV/Nukleon gespeichert und wechselwirkten mit einem Wasserstoff-Gasjet-Target. Die beim Protoneneinfang entstandenen Ionen wurden mit einem doppelseitigen Siliziumstreifendetektor nachgewiesen. Die nach der Rekombination der ionisierten Atome mit den Elektronen aus dem Wasserstofftarget ausgesendete Strahlung, wurde als Luminositätsmonitor verwendet [1]. Diese Messungen folgen einem im Jahr 2016 durchgeführten Proof-of-Principle-Experiment zur Validierung der Methode an dem stabilen Isotop 124Xe [2]. Zusätzlich wurden post-processing Nukleosynthese Studien, innerhalb der Nu-Grid [3] Plattform durchgeführt. Der Einfluss der neuen experimentellen Daten auf die Nukleosynthese von 118Te und 124Xe in Kernkollaps Supernovae wurde untersucht. Die erfolgreiche Messung von Protoneneinfangswirkungsquerschnitten an radioaktiven Isotopen motiviert weitere Experimente in niedrigeren Energiebereichen durchzuführen.

The determination of astrophysically relevant neutron-induced cross sections is particularly difficult when the involved isotopes are radioactive or the cross sections are very small. Activation experiments at reactors offer the possibility to overcome these limitations with high neutron fluxes. The flux determination is typically based on the activation of two monitors with known cross sections to separate the different flux components. The usually applied cadmium difference method allows a distinction between the thermal and the epithermal part. By a combination of two linear functions representing both monitors the neutron flux components can be determined. However, if more than two monitors are used, the linear system of equations is overdetermined, which allows the identification of a probability distribution. In this proceeding, the feasibility and relevance of this method is demonstrated.

About 50% of the elements heavier than iron are produced during the slow neutron capture process. This process occurs in different stellar sites at various energies. To understand the ongoing nucleosynthesis, the probability of a neutron capture for different temperatures and therefore for different stellar sites is essential. Activation experiments using the 7Li(p,n) reaction as neutron source were performed. At a temperature of kBT = 25 keV the cross sections were determined for 27Al, 37Cl and 41K. A new method was developed to perform activation experiments at even lower temperatures. For a proof of principle, the cross section for 64Ni was measured at kBT = 25 keV as well as for kBT = 6 keV. To study the impact of isomeric states at higher energies, activations of 181Ta were performed using two different proton energies.