Physical parameters of s-process nucleosynthesis versus [Fe/H]: a) for the mean neutron exposure, τ₀; b) for the overlap factors, r. We adopted the same CEMP-r/s (open circles) and metal-poor barium (filled squares) star samples as collected by Cui et al. (2013a, and references therein). To use as homogeneous a sample as possible, we show only the sample presented in Allen & Barbuy (2006) for the metal-poor barium stars. The open triangles represent the metal-rich barium stars adopted from Pereira et al. (2011).