Activity standardisation of ²¹⁰Pb by 4πα liquid scintillation counting method

The activity of ²¹⁰Pb in a solution with ²¹⁰Pb-²¹⁰Po in the radioactive equilibrium was determined through its decay product ²¹⁰Po by liquid scintillation counting (LSC), which has, after separation, as a pure α emitting nuclide, detection efficiency practically equal to 1. For the separation of ²¹⁰Po from ²¹⁰Pb solution, two methods based on precipitation of Pb, and Pb with Bi, leaving Po in the solution, were introduced. The first one was precipitation of Pb in the form of Pb(NO₃)₂ from a mixture of acetic acid, toluene, water and HNO₃. The second one was based on co-precipitation of Bi and Pb with KCl from a mixture of organic solvents, where ²¹⁰Bi with ²¹⁰Pb was fixed to the precipitate. The relative standard uncertainty of ²¹⁰Pb activity concentration was estimated to be lower than 0.45%.