Reducing Error in Measuring Fallout Pb-210

Science Center, Bent Corridor

Fallout radionuclides are retained in the surface coating of sediment grains, creating an indicator which can be a measurement of erosion in riverine systems. One of the most commonly used isotopes is 210Pb. Most sediment contains both supported 210Pb, which is inside the mineral crystals, and fallout, or “excess”, 210Pb (210Pbex). Traditionally, the fallout radionuclide 210Pb is measured by measuring the total activity of 210Pb and subtracting the estimated activity of supported 210Pb that comes from inside the grain. activity. Because this involves subtracting two large values to get a small one, the errors can be quite high. Our group has developed a new method for preparing samples for analysis that will reduce error. We use 6 M HCl to leach the exterior of the grain from the interior, thus physically separating the supported and excess 210Pb from each other. This summer we improved our abilities to model sample composition and geometry and measure the effect on activities, optimized the ratio of acid required for leaching, and used Python scripting to confirm that total 210Pb activities measured after leaching were the same as those measured before leaching. Our work better quantified parameters to further develop the method of leaching sediment to measure 210Pbex which will reduce errors in the future and therefore improve our ability to accurately track riverine erosion using 210Pbex.