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In the series of unstable products from the radioactive decay of uranium-238, lead-210 results from the decay of radon-222 and is a precursor of the stable isotope lead-206.
Pb isotopes cannot exchange and secular equilibrium is achieved.
The system consists of a surface barrier detector, preamplifier, amplifier, mixer router, analog to digital converter, multi-channel analyzer, and appropriate computer software.
The samples are counted for periods of 0.25 to 2 days depending upon the activity of Po standard that is added to each sample also serves as an excellent internal standard to monitor the quality of the analysis.
Details are presented in Flynn (1968) and Evans and Rigler (1980) with modifications described in Cornett et al (1984) and Rowan et al (1995).
Service DHI offers dating of sediment cores by means of the 210Pb method and may assist with sampling in both marine and freshwater systems.
At secular equilibrium the activity of the parent isotope is equivalent to that of the daughter isotope.
Sediment systems provide a natural storage system because Pb, Bi and Po are immobile or only mobilized together in these systems.
In all but the top few cm of most sediment cores the sediment is old enough to ensure that the concentration of Pb-210 will be equivalent to that of the shorter-lived daughter isotopes.
Tests of the top few cm and of surficial sediment indicate that the Po and Pb concentrations are quite similar.