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978-3-8439-2236-4, Reihe Physik

Lars Netterdon
Constraining nuclear-physics input for explosive nucleosynthesis processes via in-beam γ-ray spectroscopy and the activation technique

105 Seiten, Dissertation Universität Köln (2015), Softcover, A5

Zusammenfassung / Abstract

This thesis deals with the measurement of total and partial reaction cross sections for astrophysical applications. Three charged-particle induced reactions have been investigated motivated by improving the experimental database for the astrophysical gamma-process.

The gamma process is believed to be responsible for the main part of the nucleosynthesis of neutron-deficient p nuclei occurring during supernova explosions. As the gamma-process reaction network involves photodisintegration reactions on mainly unstable nuclei, stellar reaction rates are mostly calculated within the scope of the statistical Hauser-Feshbach model. The predictive power of these theoretical predictions can be significantly improved by providing experimental constraints for the underlying nuclear-physics models using absolute cross sections of charged-particle induced reactions.

The three reactions investigated within the scope of this thesis are 89Y(p,gamma)90Zr, 112Sn(alpha,gamma)116Te, and 130Ba(p,gamma)131La. The first one, 89Y(p,gamma)90Zr, served as a commissioning experiment for the recently developed experimental setup in Cologne dedicated to nuclear astrophysics experiments using the in-beam technique with high-purity germanium detectors. Moreover, partial cross sections have been obtained which yield important information on the gamma-ray strength function in 90Zr. The 112Sn(alpha,gamma)116Te reaction effectively embodies the first alpha-particle capture reaction on a heavier nucleus investigated by means of the in-beam technique at astrophysically relevant energies. Total and partial cross sections were measured to address the alpha+nucleus optical model potential (OMP), as well as the gamma-ray strength function in the compound nucleus 116Te. Local modifications of the underlying nuclear-physics input parameters can be used to improve the theoretical predictions of cross sections for other alpha-induced reactions in this mass region, which hints to a more global character of the adopted model.

Finally, the 130Ba(p,gamma)131La reaction has been investigated by means of the activation method. By comparing the total cross section to statistical-model calculations, a locally adopted model for the proton+nucleus OMP was obtained and the stellar reaction rate was put on a firm basis.