Radioactivity of Lead-205

${\mathrm{Pb}}^{205}$ has been produced by the ${\mathrm{Pb}}^{204}(n, \gamma ){\mathrm{Pb}}^{205}$ reaction in the Materials Testing Reactor. The ${\mathrm{Pb}}^{205}$/${\mathrm{Pb}}^{204}$ atom ratios of 0.001175±0.000060 and 0.005064±0.000063, respectively, were measured in a mass spectrometer for lead samples irradiated in the MTR for approximately 3 months and 1 year. The neutron capture cross section of ${\mathrm{Pb}}^{204}$ for MTR neutrons is 0.7±0.2 barn. The partial half-life of ${\mathrm{Pb}}^{205}$ for $L$-electron capture is (3.0±0.5)×${10}^7$ years. The $\frac{K}{L}$ electron capture ratio of ${\mathrm{Pb}}^{205}$ is ≤6×${10}^{-4\mathrm{}}$, and the disintegration energy is probably less than 86 kev. No gamma rays were observed in the decay of ${\mathrm{Pb}}^{205}$.