Abstract
About 2/3 of the chemical elements in nature were formed in neutron capture reactions. During the life of a star there are certain evolutionary stages where neutrons are available to build up the elements beyond iron which cannot be synthesized by charged particle reactions.The observed abundance pattern allows to distinguish a rapid and a slow neutron capture process (r‐ and s‐process). The r‐process taking place far from the valley of stability is difficult to investigate because of the required extrapolation of nuclear properties to extreme neutron rich nuclei. The s‐process, on the other hand, proceeds along the valley of stability. Therefore, the involved isotopes are accessible to laboratory measurements. This information allows for quantitative calculation of s‐process abundances and other parameters which represent constraints for stellar models.Two examples are outlined: (i) the s‐process branching at A=147, 148 yields a rather accurate value for the neutron density. (ii) Comparison of s‐process abundances with observations of stellar atmospheres are particularly interesting for the unstable isotopes 93Zr, 99Tc and 147Pm. Their deficiency with respect to stable neighbors may yield estimates for the transport time from the stellar interior to the surface.
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