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

The activity of Pb-210 in a solution with Pb-210-Po-210 in the radioactive equilibrium was determined through its decay product Po-210 by liquid scintillation counting (LSC), which has, after separation, as a pure a emitting nuclide, detection efficiency practically equal to 1. For the separation of Po-210 from Pb-210 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 Bi-210 with Pb-210 was fixed to the precipitate. The relative standard uncertainty of Pb-210 activity concentration was estimated to be lower than 0.45%.