Determination of ²²⁸Ra in environmental water by liquid scintillation spectrometry

[Background] ²²⁸Ra is the first decay daughter of ²³²Th decay chain, it is a low energy β radio-nuclide. [Purpose] To analyse low activity ²²⁸Ra in environmental water. [Methods] The process of concentrating ²²⁸Ra in water is carried out using Ba(Ra)SO₄ co-precipitation method. The stable Ba is measured by atomic absorption spectroscopy (AAS) to determine the yield of ²²⁸Ra under the carrier tape. The ultra-low background liquid scintillation spectrometer (LSC) is used to measure the Ra-concentrated samples, and more accurate and low activity analysis result were obtained. [Results] The yield of ²²⁸Ra obtained via the Ba(Ra)SO₄ co-precipitation method was in the range of 59% ∼ 90%, and the detection limit of ²²⁸Ra was 7.9 mBq · L^-1 (1 L sample, measurement time t = 20 h). As for two types recoveries of ²²⁸Ra, the relative deviation between ¹³³Ba tracer method and atomic absorption spectrometry method is within 7%. The counting efficiency of LSC on ²²⁸Ra/²²⁸Ac is 72.9%. The relative deviation of the spiked water sample measurement is 1.0% ∼ 10%. [Conclusions] This method can achieve more accurate measurement of low activity ²²⁸Ra in water. (authors)