Radiocarbon Dating

Daniel De Schepper

NCSS

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

• Atmospheric neutron intensity and 14C production

• 14N + 1n 14C + 1H

• CO2 undergoes rapid equilibrium in the atmosphere

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

Some Deviations

• Glacial effects

• Human activity

• Variations in natural production rate

Glacial effects CO2 solubility is temperature dependant

Human activity

Fossil fuel (Suess) effect and bomb effect

Variations in production rate

Major cause of Suess wiggles

• The need for calibration– Dendrochronology

X-axis spans 2000 calendar yearsY-axis is in radiocarbon age (BP) where 0 BP = 1950 AD

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

• Accelerator Mass Spectrometer

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

Archaeology

3100 to 4000 BC*

1423 to 1445 AD*

1260 to 1390 AD*

* Radiocarbon date

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