130 likes | 150 Views
Learn about the use of radiocarbon (14C) dating by Dr. Eric Grimm from Illinois State Museum. Understand carbon isotopes, decay processes, calibration methods, and how radiocarbon measurements are made. Explore the significance of the IntCal09 Calibration Curve and its application in dating archaeological findings. Discover the fascinating world of radiocarbon dating in this comprehensive guide.
E N D
Telling Time: The use of radiocarbon (14C) in dating Dr. Eric Grimm, Illinois State Museum
Carbon Isotopes 13C 12C 6 protons 6 neutrons 14C 6 protons 7 neutrons 6 protons 8 neutrons
β−decay 14C 14N – – 14 7 14 6 C N + e + ve electron (beta particle) electron antineutrino
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 one 14C atom per trillion atoms of 12C.) Short time to count (<30 min) and requires small amount of carbon (1 mg).
14 7 14 6 n+ N C + p neutron proton
IntCal09 Calibration Curve Tree Rings Marine Data
0.168 0.832 5450-5586 5329-5377