•Saed Dababneh¹, Panayotis A. Assimakopoulos², Sotirios Harissopoulos³, Michael Heil¹, Franz Käppeler¹, Dimitrios Karamanis², Nikolas Patronis² und Ralf Plag^1
3NCSR "Demokritos", Institute of Nuclear Physics, 15310 Athens, Greece
¹Forschungszentrum Karlsruhe, Institut für Kernphysik, Postfach 3640, D-76021 Karlsruhe, Germany
²The University of Ioannina, Department of Physics, Nuclear Physics Laboratory, 45110 Ioannina, Greece

First results of the measurement of the neutron capture cross section of the unstable isotope ¹³⁵Cs at 30, 200, and 500 keV are reported. The sample consists of only @  2×10¹⁵ atoms and was produced by ion implementation in a high resolution mass separator. The activation technique is used to obtain the cross section by irradiation in a quasi monoenergetic neutron beam. This will allow to determine the stellar cross section at the thermal energies characteristic for He burning scenarios, in particular at kT  @  8 keV and @  26 keV. The induced activities are measured with a high efficiency detection system consisting of two Ge Clover arrays in close geometry. It is planned to determine the number of ¹³⁵Cs nuclei in the sample by a final activation with thermal neutrons.