Method to determine ²²⁶Ra in small sediment samples by ultralow background liquid scintillation

210Pb dating of sediment cores is a widely used tool to reconstruct ecosystem evolution and historical pollution during the last century. Although 226Ra can be determined by γ 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 210Pb through 210Po in equilibrium by α spectrometry, followed by the determination of 226Ra (base or supported 210Pb) without any further chemical purification by liquid scintillation and with a higher sample throughput. Although γ spectrometry might still be required to determine 137Cs 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 226Ra in small sediment samples, after 210Po determination, allowing a more precise determination of excess 210Pb (210Pbex). The method was validated with reference materials IAEA-384, IAEA-385, and IAEA-313. © 2010 American Chemical Society.