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%.