Radiocarbon Dating

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Radiocarbon Dating

• Daniel De Schepper
• NCSS

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Conception

• 1946 suggests that 14C exists in living matter
• Confirmed a year later
• 1949 found that several trees contained roughly
  the same amount of activity due to 14C
• 1960 won Nobel prize

Willard Libby
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• Atmospheric neutron intensity and 14C production
• 14N 1n ? 14C 1H

• CO2 undergoes rapid equilibrium in the
  atmosphere

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Assumptions

• 14C production is constant
• The biosphere and atmosphere have roughly the
  same 14C concentration
• After death there is no 14C exchange and it is
  only affected by radioactive decay

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Some Deviations

• Glacial effects
• Human activity
• Variations in natural production rate

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• Glacial effects
• CO2 solubility is temperature dependant

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• Human activity
• Fossil fuel (Suess) effect and bomb effect

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• Variations in production rate
• Major cause of Suess wiggles

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• The need for calibration
• Dendrochronology

X-axis spans 2000 calendar years Y-axis is in
radiocarbon age (BP) where 0 BP 1950 AD
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Sample Preparation

• Unearth sample
• Physical separation
• Treat with acid
• Convert carbon to CO2 via combustion
• Remove impurities (ie nitrogen oxides, sulfur,
  products of incomplete combustion, and radon)
• Isolate carbon 2 Mg CO2 ? MgO C
• Limit exposure to air

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• Accelerator Mass Spectrometer

• Upper age limit 40,000 years
• Lower age limit 200 years

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Archaeology
1423 to 1445 AD
1260 to 1390 AD
Radiocarbon date
3100 to 4000 BC
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Conclusions

• There are errors in radiocarbon dating due to
  assumptions ? this calls for calibration
• With this radiocarbon dating can be used to
  determine the age of a given sample
• Though variation still persists