Preparation of 228Ra standard solution

For the preparation of a standard solution of 228Ra, 228Ra was isolated from 232Th salt. Two simple methods were developed for Th-Ra separation. Both are based on a very good solubility of thorium nitrate in organic solvents. The first one used Ra co-precipitation with Pb in the form of Pb(NO3)2 from acetic acid solution. The second method was based on solvent extraction, remaining Th in the organic phase, while Ra was concentrated in the aqueous phase. The activity of 228Ra (up to 20 kBq) in the standard solution was related to the 232Th standard by means of gamma ray spectrometry measurement. The obtained uncertainty was less than 0.7% (k=1). The standard solution was free of 232Th and contained the carrier in the usual concentration (1 g L−1 BaCl2, 10 g L−1 HCl).