Measurement Of Radiative Alpha-Capture Cross Sections On Ru-98 And Sm-144 For 7-Process Nucleosynthesis

Since p isotopes cannot be produced in neutron-capture reaction networks, a production mechanism via photodisintegration reactions was proposed - the gamma process. The specific path of this reaction network, however, depends strongly on the statistically averaged ratios for proton-, neutron-, and alpha-decay widths.It was shown in the past, that the uncertainties in the cr-decay widths have an impact on the isotopic abundance of the gamma-process ashes. Besides systematic studies of the alpha+nucleus optical-model potential, direct measurements of (alpha,gamma) reaction are needed to reduce the unpredictability of (gamma, alpha) reaction rates.We present preliminary results from direct measurements of the Ru-98(alpha,gamma) and Sm-144(alpha,gamma) cross sections via in-beam measurements at the University of Cologne and the Ruhr-Universitat Bochum and activation experiments at the Physikalisch-Technische Bundesanstalt in Braunschweig and the Technische Universitat Dresden.The in-beam experiment might help to improve our understanding of the gamma-process contribution to the p nuclei in the A similar to 100 mass region, while the activation experiment is important for the determination of the initial isotopic abundance ratio of the Sm-146/Sm-144 chronometer.