PoS(NIC XI)183 Determination of the Stellar Reaction Rates of 17 O(α ,n) 20 Ne and 17 O(α , γ ) 21 Ne A. Best * University of Notre Dame E-mail: abest1@nd.edu J. Görres University of Notre Dame E-mail: jgoerres@nd.edu M. Wiescher University of Notre Dame E-mail: Michael.C.Wiescher.1@nd.edu S. Falahat Johannes Gutenberg Universität Mainz E-mail: s.falahat@mpic.de K.-L. Kratz Johannes Gutenberg Universität Mainz E-mail: klkratz@uni-mainz.de The reaction 16 O(n, γ ) 17 O acts as a neutron poison in the weak s process by reducing the number of available neutrons in the stellar burning environment. The captured neutrons can be re-emitted into the stellar environment by the reaction 17 O(α ,n) 20 Ne, weakening the poisoning effect of 16 O. This branch competes with the reaction 17 O(α , γ ) 21 Ne. In order to determine the strength of 16 O as a neutron poison one needs to know the ratio of the stellar reaction rates of both channels. Both reactions have been recently measured at the Nuclear Science Laboratory of the University of Notre Dame and preliminary results are presented. 11th Symposium on Nuclei in the Cosmos, NIC XI July 19-23, 2010 Heidelberg, Germany * Speaker. c  Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/