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