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). - Highlights: • ²²⁸Ra was isolated from ²³²Th salt. • Two methods for Th–Ra separation. • Ra co-precipitation with Pb in the form of Pb(NO₃)₂ from acetic acid solution. • The activity of ²²⁸Ra in the standard solution was related to ²³²Th standard.