and 204Tl at CERN

Branching points along the s-process path in stellar nucleosynthesis are key isotopes in which there is a competition between two processes: neutron capture (n,γ) and β- decay. This particularity makes the local isotopic abundance pattern around these isotopes very sensitive to their half-life and (n,γ) cross section as well as to the neutron density and the temperature at the stellar scenario being considered. Therefore important information about the latter quantities can be inferred when one knows the corresponding (n,γ) cross sections. This is however difficult because such radioactive isotopes do not exist in nature and thus the material to perform accurate measurements is scarce. Indeed, the (n,γ) cross section of only two, 63Ni and 151Sm, of the 21 most important branching points have been measured by time-of-flight. In order to improve significantly the situation we have launched a program to produce new samples of branching point isotopes and measure their capture cross section at the CERN n_TOF facility. A significant amount of material (~mg) of 147Pm [t1/2=2.6y], 171Tm [t1/2=1.9y] and 204Tl [t1/2=3.8y] (79Se is also foreseen in the near future) has been produced by irradiations of highly enriched precursors in the ILL high-flux reactor and this material serves for preparing high purity samples at PSI. The experiment proposals have been already approved and the capture cros