HalfLife and Rate of Decay; Carbon14 Dating
Carbon14 dating is a radiometric dating method that uses the radioisotope carbon14 (14C) to estimate the age of object.
Learning Objective

Identify the age of materials that can be approximately determined using radiocarbon dating
Key Points
 Carbon14 dating can be used to estimate the age of carbonbearing materials up to about 58,000 to 62,000 years old.
 The carbon14 isotope would vanish from Earth's atmosphere in less than a million years were it not for the constant influx of cosmic rays interacting with atmospheric nitrogen.
 One of the most frequent uses of radiocarbon dating is to estimate the age of organic remains from archaeological sites.
Terms

radioisotope
a radioactive isotope of an element

carbon14
carbon14 is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons.

radiometric dating
Radiometric dating is a technique used to date objects based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products using known decay rates.
Full Text
Radiocarbon dating (usually referred to simply as carbon14 dating) is a radiometric dating method. It uses the naturally occurring radioisotope carbon14 (14C) to estimate the age of carbonbearing materials up to about 58,000 to 62,000 years old.
Carbon has two stable, nonradioactive isotopes: carbon12 (12C) and carbon13 (13C). There are also trace amounts of the unstable radioisotope carbon14 (14C) on Earth. Carbon14 has a relatively short halflife of 5,730 years, meaning that the fraction of carbon14 in a sample is halved over the course of 5,730 years due to radioactive decay to nitrogen14. The carbon14 isotope would vanish from Earth's atmosphere in less than a million years were it not for the constant influx of cosmic rays interacting with molecules of nitrogen (N_{2}) and single nitrogen atoms (N) in the stratosphere. Both processes of formation and decay of carbon14 are shown in .
Formation and Decay of Carbon14
Diagram of the formation of carbon14 (1), the decay of carbon14 (2), and equations describing the carbon12:carbon14 ratio in living and dead organisms
When plants fix atmospheric carbon dioxide (CO_{2}) into organic compounds during photosynthesis, the resulting fraction of the isotope 14C in the plant tissue will match the fraction of the isotope in the atmosphere. After plants die or are consumed by other organisms, the incorporation of all carbon isotopes, including 14C, stops. Thereafter, the concentration (fraction) of 14C declines at a fixed exponential rate due to the radioactive decay of 14C. (An equation describing this process is shown in . ) Comparing the remaining 14C fraction of a sample to that expected from atmospheric 14C allows us to estimate the age of the sample.
Raw (i.e., uncalibrated) radiocarbon ages are usually reported in radiocarbon years "Before Present" (BP), with "present" defined as CE 1950. Such raw ages can be calibrated to give calendar dates. One of the most frequent uses of radiocarbon dating is to estimate the age of organic remains from archaeological sites.
The technique of radiocarbon dating was developed by Willard Libby and his colleagues at the University of Chicago in 1949. Emilio SegrÃ¨ asserted in his autobiography that Enrico Fermi suggested the concept to Libby at a seminar in Chicago that year. Libby estimated that the steadystate radioactivity concentration of exchangeable carbon14 would be about 14 disintegrations per minute (dpm) per gram. In 1960, Libby was awarded the Nobel Prize in chemistry for this work. He demonstrated the accuracy of radiocarbon dating by accurately estimating the age of wood from a series of samples for which the age was known, including an ancient Egyptian royal barge dating from 1850 BCE.
Key Term Reference
 atom
 Appears in these related concepts: Overview of Atomic Structure, Description of the Hydrogen Atom, and Stable Isotopes
 concentration
 Appears in these related concepts: Calculating Equilibrium Concentrations , Diffusion, and Molarity
 decay
 Appears in these related concepts: Radioactive Decay Series: Introduction, Models Using Differential Equations, and Discovery of Radioactivity
 equation
 Appears in these related concepts: Equations and Inequalities, Graphs of Equations as Graphs of Solutions, and What is an Equation?
 halflife
 Appears in these related concepts: Onset, Duration, and HalfLife of Hormone Activity, HalfLife, and HalfLife of Radioactive Decay
 isotope
 Appears in these related concepts: Exponential Decay, Modes of Radioactive Decay, and Isotopes
 radioactive decay
 Appears in these related concepts: Alpha Decay, Nuclear Stability, and Tracers
 series
 Appears in these related concepts: Combination Circuits, Resisitors in Series, and The General Term of a Sequence
 work
 Appears in these related concepts: Heat and Work, Energy Transportation, and The First Law of Thermodynamics
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