Neutron capture studies on unstable 135Cs for nucleosynthesis and transmutation -: art. no. 025803

The neutron capture cross section of the unstable isotope Cs-135 was measured relative to that of gold by means of the activation method. The sample was produced by ion implantation in a high resolution mass separator and irradiated with quasimonoenergetic neutrons at 30 keV and 500 keV, using the Li-7(p,n)Be-7 reaction. An additional irradiation with thermal neutrons has been carried out for defining the sample mass and for measuring the half-life of Cs-136. The neutron capture cross sections were determined as 164+/-10 mb and 34.8+/-3.0 mb at 30 keV and 500 keV, respectively, and were used to normalize the theoretically derived cross section shape. Based on these data, refined statistical model calculations were performed to obtain the (n,gamma) cross sections of the short-lived isotopes Cs-134 and Cs-136 as well. Updated Maxwellian-averaged capture cross sections of all unstable Cs isotopes were calculated for a range of thermal energies characteristic of helium burning scenarios for an improved s-process analysis of the Xe-Cs-Ba region.