Fig. 1. s-process reaction path around Tl and Pb.

a, ²⁰⁵Pb is situated at the end of the s-process path, represented by the sequence of n captures and β decays shown by the blue arrows. Galactic production of ²⁰⁵Pb is exclusive to the s process, which makes it unique among short-lived radionuclides. b, Low-lying nuclear structure of the ²⁰⁵Pb–²⁰⁵Tl system. Decay of neutral ²⁰⁵Pb proceeds by electron capture from the ground state (purple) or from the excited state (magenta) if thermally populated. In fully ionized conditions (shown in red), bound-state β⁻ decay of ²⁰⁵Tl⁸¹⁺ occurs (green) by decay to the 2.3-keV excited state. All half-lives are partial half-lives for that specific transition, but it should be noted that the 2.3-keV excited state is never populated in a neutral atom, and full temperature-dependent and density-dependent rates need to be used.