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Department of Anthropology
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Center for Archaeometry and Geochronology
The
term “radiocarbon” in general refers to the naturally occurring radioisotope of
carbon. 14C atoms are continuously formed in the upper atmosphere by the action
of cosmic ray bombardment (neutron) on nitrogen-14 atoms. Once 14C atoms are
formed, they are quickly oxidized to carbon dioxide, which mixes with other
carbon dioxide in the atmosphere.
14C, like all radioactive isotopes, is unstable and constantly changing back to
nitrogen. Over a long period of time, the rate of production and decay of
radiocarbon in the atmosphere tends to reach an equilibrium state. Under this
equilibrium condition, all living organisms should acquire the same 14C
concentration as that of atmospheric carbon dioxide. When a living organism
dies, it is no longer able to exchange carbon freely with atmospheric CO2, and
the initial concentration of 14C begins to decrease by the process of
radioactive decay.
Knowing the initial concentration of 14C and its half-life, it is possible to
calculate how much time has passed since the sample was last in equilibrium with
the atmosphere by measuring the 14C concentration remaining in the sample. Thus,
a radiocarbon date relates to the time elapsed since the 14C concentration was
fixed at the natural level in the sample.
UTCAG currently utilizes the Liquid Scintillation Counting (LSC) method for
Carbon 14 analysis. The LSC method allows dating of samples ranging from 150 to
50,000 years old. Our laboratory is equipped with a benzene synthesis system,
one Packard 2200CA low-level scintillation counter, and one Quantulus 1220 ultra
low-level scintillation counter. We are capable of processing a variety of
samples, including charcoal, wood, bone, paleosol, coral, and shell.
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