Comparing abundances of parent uranium or thorium to daughter lead from the three above mentioned decay series is fundamental in geochronology.
As a result, all lead in such minerals is radiogenic, with no 204Pb present, and specimens can have anomalously high amount fractions of 206Pb and 208Pb. Certain minerals, such as zircon and monazite, readily incorporate uranium and/or thorium in their structure when forming, but do not incorporate primary lead. 207Pb and 206Pb are also produced, in part, by radiogenic decay of 235U and 238U via the actinium and uranium decay series, respectively, with half-lives of 7.07 × 10 8 years and 4.468 × 10 9 years. 208Pb is produced in part by the decay of radioactive 232Th, which has a total half-life of approximately 1.40 × 10 10 years, via the thorium decay series. 208Pb, the heaviest known stable isotope, comprises about half of the lead in the Solar System and most terrestrial materials and references therein].
Although atomic weight is a dimensionless quantity and, thus, is not a weight, a consensus on the meaning of atomic weight was achieved during the 19 IUPAC General Assemblies as documented on page 1540 of De Bièvre and Peiser. Alternatively, “relative atomic mass (atomic weight), A r” is “The ratio of the average mass of the atom to the unified atomic mass unit”. The “atomic weight,” which is the ratio of the average mass per atom of an element to 1/12 of the mass of an atom of nuclide 12C, is also known as “relative atomic mass”. The three heaviest isotopes are the stable end-products of the radioactive decay of uranium ( 238U to 206Pb 235U to 207Pb) and thorium ( 232Th to 208Pb), resulting in substantially variable atomic-weight values of lead in naturally occurring materials. Overviews of measurements and applications of the isotopes of lead include,. The heavier three stable isotopes, 206Pb, 207Pb, and 208Pb, have radiogenic components, which are used to date rocks and minerals or trace and identify lead sources in the environment. Lead has four stable isotopes ( 204Pb, 206Pb, 207Pb, and 208Pb), each of which is entirely – as with 204Pb – or partially – as with 206Pb, 207Pb, and 208Pb – composed of primordial components from stellar neutron capture. It is proposed that a value of 207.2 be adopted for the single lead atomic-weight value for education, commerce, and industry, corresponding to previously published conventional atomic-weight values. When expressed as an interval, the lead atomic weight is. The highest published lead atomic weight is 207.9351 ± 0.0005 ( k = 2) for monazite from a micro-inclusion in a garnet relic, also from a high-grade metamorphic terrain in north-western Scotland, which contains almost pure radiogenic 208Pb. In a comprehensive review of several hundred publications and analyses of more than 8000 samples, published isotope data indicate that the lowest reported lead atomic weight of a normal terrestrial materials is 206.1462 ± 0.0028 ( k = 2), determined for a growth of the phosphate mineral monazite around a garnet relic from an Archean high-grade metamorphic terrain in north-western Scotland, which contains mostly 206Pb and almost no 204Pb. While elemental lead can serve as an abundant and homogeneous isotopic reference, deviations from the isotope ratios in other lead occurrences limit the accuracy with which a standard atomic weight can be given for lead. These variations in isotope ratios and atomic weights provide useful information in many areas of science, including geochronology, archaeology, environmental studies, and forensic science. The lightest stable isotope, 204Pb, is primordial. The isotopic composition and atomic weight of lead are variable in terrestrial materials because its three heaviest stable isotopes are stable end-products of the radioactive decay of uranium ( 238U to 206Pb 235U to 207Pb) and thorium ( 232Th to 208Pb).
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