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Thermal Ionization/Mass Spectrometry (TIMS):
Inductively Coupled Plasma-Mass Spectrometry
(ICP-MS): price not available.
for example West
Coast Analytical Service)
of Rochester ICP-MS Laboratory)
There are 32 lead isotopes in all; a complete
listing is available at Resource-World.net.
Five isotopes are significant for environmental
(which are stable, the latter three are produced
as the stable end product of uranium and thorium
decay), and 210Pb
(a radioactive intermediate of 238U
The stable isotopes
occurs naturally and is not produced through radioactive
decay; the other stable Pb isotopes are radiogenic
and produced by the decay of other elements:
decays to 206Pb
decays to 207Pb
decays to 208Pb
Lead isotope ratios 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. Because
the lead isotopic composition of geologic material
is a function of three independent decay chains,
there is a great potential for isotopic variability
As an example, uranium and thorium concentrate
in the liquid phase during melting and crystallization
of magma, and are subsequently incorporated into
acidic, silica-rich components. Thus, granites
have high uranium and thorium content compared
to basaltic rocks. Thorium is enriched compared
to uranium in low-calcium granites. Sedimentary
and igneous rocks have similar thorium/uranium
ratios, but carbonate-rich rocks are strongly
enriched in uranium.
In contrast to the stable isotopes of lead, 210Pb
is a radioactive intermediate in the complex decay
series of 238U.
There are numerous intermittent daughter isotopes,
among them is the radioactive gas, 222Rn
= 3.8 days). As a gas, radon makes its way out
of the ground or water and into the atmosphere.
The flux of radion averages 42 atoms/min. cm2
of land surface. This radon then decays in the
atmosphere to the relatively stable isotope 210Pb
= 22.3 years). 210Pb
is quickly removed from the atmosphere through
precipitation and is deposited in lakes, glaciers,
ice and snow, where it eventually decays to 206Pb.
Periodic Table - Lead for more information
on lead isotopes.
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Lead isotopes are most commonly measured using
thermal ionization mass spectrometry (TIMS).
Since there is only one nonradiogenic isotope,
instrument fractionation cannot be corrected (see
Sr-Rb), thus, care
must be taken when running a sample.
Pb must be separated for most environmental work.
Because it is very easily contaminated; clean
lab techniques are required.
Pb isotopes are reported as a ratio with respect
to the non-radiogenic isotope, 204Pb.
Ranges for most natural materials are as follows:
U-Pb, Th-Pb, and Pb-Pb isotopic ratios may be
used in age dating and petrogenetic tracing of
igneous, metamorphic, and hydrothermal rocks.
Since there is a divergence in chemical behavior
between uranium, thorium, and their daughter elements,
many geological processes can lead to extensive
fractionation of the various isotopes. This results
in distinctive patterns that allow determination
of rock histories.
Because Pb is produced through unique decay reactions,
several methods can be used to determine the ages
of rocks and the geologic processed that have
affected them. Chief among these are:
1) common Pb methods, or single stage models
(e.g., Holmes-Houtermans model; see Holmes 1946,
Houtermans 1946) for lead minerals that have single-stage
histories, i.e., that experienced no lead gain
or loss. Such models plot trajectories of Pb growth
after a primeval Pb state from the time of deposition
in the earth's crust. The Holmes-Houtermans model
provides an equation to date samples of common
Pb. The model assumes 1) that at the time the
Earth was forming, U, Th, and Pb were uniformly
distributed; 2) that when the Earth became hardened
small differences appeared in the U/Pb ratio,
which changed as the result of U decay; and 3)
that from the time common Pb minerals (such as
galena) are formed, their isotopic composition
2) two-stage models provide a refinement to the
above models. These assume a primordial composition
for Pb, which is then followed by a value for
the date of the lead incorporation into a rock
or an ore deposit; this may then be followed by
the age of a subsequent metamorphic event or geochemical
differentiation which results in lead gain or
loss. Such models frequently use U-Pb Concordia
Diagrams to plot 207Pb/235U
and compare the ratios with a concordia line that
indicates the path that would be followed if the
minerals had not suffered chemical disturbance.
The amount of lead loss is shown as a chord connecting
age of the material and the time lead was lost.
For more information on geologic dating methods,
see Faure 1986 (pp. 309-340).
The most common applications of Pb isotopes in
hydrological sciences are:
1) using the distinct isotopic composition of
lead ratios in surface waters to identify pollution
for example, Viers
et al. 1999)
2) using 210Pb
to date recent deposition of snow, lake sediments,
has a half-life of 22.3 years, allowing dating
within the past 100 years. It is also useful in
determining changes in ambient environmental conditions.
3) determining the relative importance in stream
water of atmospheric Pb (which concentrates in
the upper soil layers) versus the Pb in groundwater
that is derived from chemical weathering processes.
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Aside from the geological applications identified
in the "Measurement Techniques" section
above, lead ratios can help to trace pollution
in the atmosphere.
and Graney for more information)
Similarly, lead isotopes can be used in archaeology
to date ores used in artifacts.
Center for Materials Research and Education
for more information on use of lead isotope analysis
for the dating of artifacts)
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- Attendorn, H.-G., and R.N.C. Bowen, Radioactive
and Stable Isotope Geology, Chapman and
Hall, New York, 1997.
- Bowen, R., Isotopes in the Earth Sciences,
Elsevier, New York, 1988.
- Faure, G., Principles of Isotope Geology,
2nd ed., John Wiley & Sons, New York, 1986.
- Flegal, A.R., H. Maring, and S. Niemeyer,
Anthropogenic lead in Antarctic sea water, Nature
365, Sept. 1993.
- Holmes, A., An estimate of the age of the
earth, Nature, 157, 680-684, 1946.
- Houtermans, F.G., Die Isotopenhäufigkeiten
im natürlichen Blei und das Alter des Urans.
Naturwissenschaften, 33, 185-186, 219,
- Stacey, J.S., and J.D. Kramers, Approximation
of terrestrial lead isotope evolution by a two-stage
model, Earth Planet. Sci. Let., 26, 207-221,
- Sturges, W.T., and L.A. Barrie, Lead 206/207
isotope ratios in the atmosphere of North America
as tracers of U.S. and Canadian emissions, Nature,
239, Sept. 1987.
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Lead Isotope Analysis
Bentor, Y., Lead, ChemicalElements.com
Boston College, Dept. of Chemistry, Web
Elements - Lead
- Properties and Isotopes
Georgia State University, Nuclear Physics Laboratory,
in the Rocks
Keeler, G.J., and J.R. Graney, Final Report:
Applications of Novel Instrumentation for Measurement
of Lead Isotopes in Atmospheric Pollution Source
Apportionment Studies, EPA Grant Number:
Kysar Mattietti, G., J. Lewis, and R. Wysoczanski,
Isotope Study of the Paleogene Igneous Rocks
of the Sierra Maestra, Southeastern Cuba,
Geological Society of America Annual Meeting,
Berkeley Laboratory, Isotopes Project Home Page,
Ridge National Laboratory, Isotope
Production and Distribution - Lead
College, Chemlab Server, Periodic
Table of Isotopes
Smithsonian Institution, Smithsonian Center
for Materials Research and Education, Annual
Report FY 1995, Lead Isotope Program
Table - Lead (http://wwwrcamnl.wr.usgs.gov/isoig/period/pb_iig.html)
J.H., M. McCoy, J.F. Quinn, and M.L. Johnson,
source pollution modeling in the north coast
of California within a GIS: a predictive
screening tool for watershed management, paper
presented at the 1999 ESRI User's Conference
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