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Telling Time: The use of radiocarbon ( 14 C) in dating Dr. Eric Grimm, Illinois State Museum

Telling Time: The use of radiocarbon ( 14 C) in dating Dr. Eric Grimm, Illinois State Museum

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Text of Telling Time: The use of radiocarbon ( 14 C) in dating Dr. Eric Grimm, Illinois State Museum

  • Telling Time: The use of radiocarbon (14C) in dating

    Dr. Eric Grimm, Illinois State Museum

  • Carbon Isotopes6 protons6 neutrons6 protons7 neutrons6 protons8 neutrons

  • 14Cdecay

  • The half-life of 14C is 5730 40 years, although this value may not be very accurate. Most radiocarbon dates are reported with the Libby half-life 5568 30 years. Calibration corrects for errors in the exact value.

    After about 10 half lives, too little 14C remains to be measured.

  • Two methods for making radiocarbon measurements:

    Decay count or conventional methods. Beta particles emitted from a sample are counted. Two techniques:Gas proportional counting. Carbon converted to a gas (e.g. carbon dioxide).Liquid scintillation. Carbon is converted to a liquid (e.g. benzene).Requires a relatively long time to count (24+ hours) and large amount carbon (1 g).

    Accelerator Mass Spectrometry (AMS). The number of carbon atoms and proportions of isotopes are directly counted. (The natural abundance of 14C is about one14C atom per trillion atoms of12C.) Short time to count (

  • n + N 147C + p 146neutronproton

  • IntCal09 Calibration CurveTree RingsMarine Data

  • IntCal09 Calibration Curve

  • IntCal09 Calibration Curve

  • 0.1680.8325329-53775450-5586

  • http://calib.qub.ac.uk/calib/

  • Radiocarbon dates from Kettle Lake, North Dakota

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