210pb dating

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.Different methods for age estimation were applied including varve counting, C and tephra identification.Microscopic analysis of the varve microfacies revealed that laminations found in Lake Żabińskie were biogenic (calcite) varves.Details are presented in Flynn (1968) and Evans and Rigler (1980) with modifications described in Cornett et al (1984) and Rowan et al (1995).Pb against depth or cumulative weight (to allow for compacting) will be a straight line if the sedimentation rate has been constant.

Pb isotopes cannot exchange and secular equilibrium is achieved.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.For testing Pb dating we used two routinely applied models: Constant Flux Constant Sedimentation (CFCS) and Constant Rate of Supply (CRS).None of the models in their standard forms produced a chronology consistent with varve counts and independent chronostratigraphic markers.

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Therefore for Pb and the uranium series are very mobile or a geo-chemical process (such as different rates of bioaccumulation) fractionates the isotopes and produces different behaviour For analysis by alpha spectroscopy, Po alpha particle is about 5.1 Me V.

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