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978-3-8439-0849-8, Reihe Physik

Anne Sauerwein Experimental studies of charged-particle induced reactions and their impact on the nucleosynthesis of p nuclei

118 Seiten, Dissertation Universität Köln (2012), Softcover, A5

This thesis describes the experimental investigation of four charged-particle induced reactions relevant for the astrophysical gamma process, which is part of the p process.

To a large extent, the so-called p nuclei are believed to be produced by sequences of photodisintegration reactions in the gamma process during supernova explosions. Astrophysical network calculations of this process have to account for a huge number of photodisintegration rates including unstable nuclei. Hence, most reaction rates are adopted from theoretical predictions within the scope of the Hauser-Feshbach statistical model. While this model is well established, major uncertainties stem from the various nuclear physics models entering the calculations. In order to improve the predictive power of stellar rate calculations, it is mandatory to provide experimental cross sections which either allow the direct calculation of the stellar rate, or constrain the nuclear physics models entering the rate calculations.

Within the scope of this thesis, both strategies were used. In total, four charged-particle induced reactions were performed, namely 74Ge(p,gamma)75As, 141Pr(alpha,n)144Pm, 168Yb(alpha,gamma)172Hf, and 168Yb(alpha,n)171Hf. For these reactions, the cross sections were obtained within or close to the astrophysically relevant energy range and compared to statistical model calculations. In this way, it was possible to improve the nuclear physics models and to calculate the stellar rates of the investigated reactions as well.

Two different experimental techniques were used to investigate these reactions, namely the activation method and the in-beam technique with high-purity germanium (HPGe) detectors. Both experimental techniques are from now on available at the Institute for Nuclear Physics in Cologne. The in-beam technique with HPGe detectors has been established at the HORUS spectrometer within the scope of this work.