Density effect of rare earth chloride solution in estimation of Ra²²⁸ from Ac²²⁸

The finely ground monazite is processed with hot NaOH to separate the phosphate component as Tri-Sodium Phosphate. Then mixed hydroxide is treated with HCl at controlled pH to separate rare earth as rare earth chloride solution. The rare earth chloride solution also contains ²²⁸Ra along with other radioactive daughter. The concentration of ²²⁸Ra is determined by estimating the 911 keV gamma emitted by ²²⁸Ac. A 2 x 2 NaI(Tl) gamma spectrometer having MDA of 34 Bq/l is used for this purpose. Since the RE elements are having high Z value the change in the concentration of the RE greatly affects the estimation of the ²²⁸Ra. So the present study was carried out to understand the behaviour of 911 keV gamma energy at different concentration of RE. The density of the RE solution at the plant generally vary between 200 gpl to 250 gpl solution. A known quantity of ²²⁸Ra was added to the solution and the solution was kept for more than 36 hours, so that the ²²⁸Ra and ²²⁸Ac reach secular equilibrium. Then these solutions were analysed in the NaI(Tl) spectrometer. The empirical equation can be used in the evaluation of ²²⁸Ra content in plant samples