A total of 43 lead (Pb) isotopes are now known, including very unstable synthetic species, but five are used commonly in geochemical research (Figure 1). Lead has four relatively stable isotopes: 204Pb, 206Pb, 207Pb and 208Pb; the final three of which represent ends of decay chains. 206Pb is at the end of the uranium decay chain, 207Pb at the end of the actinium decay chain and 208Pb is at the end of the thorium decay chain. 210Pb is a short-lived naturally occurring isotope with a half-life of 22.6 years; its convenient half-life is widely used for dating glacial age and recent sediments and peat deposits.
The five lead isotope species that are commonly used in geochemical studies.
Lead isotope ratios within the uranium decay chain are a function of the amount of uranium and thorium present. Geological processes affect the amount of U and Th present, thus, lead isotopes serve as a useful tool for understanding the nature and timing of these processes. Since the lead isotopic composition of geologic material is a function of three independent decay chains, there is a great potential for isotopic variability in minerals.
Sample types available for lead analysis: bone, igneous rock, marine sediments, lacustrine sediments, metal artifacts/coins, mineral dust, soil, tooth enamel and water. More information on Sample Types and Selectionfor lead analysis.
Solid Earth Geochemistry / Petrology
Geochemical Fingerprinting: Dust & Archaeology
This geochemical fingerprinting can also be used in archaeological studies. From very early in the study of ancient metals, one important goal was to establish the geological origin of the metal used to make particular metal artefacts, and in this way, directly addressing issues of trade, trade relationships and movement of objects. Since the isotopes of lead do not change their form from its geological origin (or ore form) to the artefact, the artefacts should hold the information on the site location where the lead was mined.
Contaminant Source Tracing
In many cases of homicides there is often a lack of physical evidence to identify the perpetrator. Lead isotopic analysis of small fragments of bullet material can often provide a positive identification to the culprit assuming that the bullet cartridges within a single batch all have the same isotopic composition. For example, different brands of bullets often have distinct lead isotopic signatures. In this way, lead isotopes can be used to match a bullet found on a crime scene with bullets from potential suspects. This works when the full bullet is not available for ballistics testing.
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