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

The activity of Pb in a solution with Pb-Po in the radioactive equilibrium was determined through its decay product Po 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 Po from Pb 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(NO) from a mixture of acetic acid, toluene, water and HNO. The second one was based on co-precipitation of Bi and Pb with KCl from a mixture of organic solvents, where Bi with Pb was fixed to the precipitate. The relative standard uncertainty of Pb activity concentration was estimated to be lower than 0.45%.