Method to Determine 226Ra in Small Sediment Samples by Ultralow Background Liquid Scintillation

Pb-210 dating of sediment cores is a widely used tool to reconstruct ecosystem evolution and historical pollution during the last century. Although Ra-226 can be determined by gamma spectrometry, this method shows severe limitations which are, among others, sample size requirements and counting times. In this work, we propose a new strategy based on the analysis of Pb-210 through Po-210 in equilibrium by a spectrometry, followed by the determination of Ra-226 (base or supported Pb-210) without any further chemical purification by liquid scintillation and with a higher sample throughput. Although gamma spectrometry might still be required to determine Cs-137 as an independent tracer, the effort can then be focused only on those sections dated around 1963, when maximum activities are expected. In this work, we optimized the counting conditions, calibrated the system for changing quenching, and described the new method to determine Ra-226 in small sediment samples, after Po-210 determination, allowing a more precise determination of excess Pb-210(Pb-210(ex)) The method was validated with reference materials IAEA-384, IAEA-385, and IAEA-313.