Carbon dating and half life calculations
Carbon dating and half life calculations - accuracy of ancient dating methods
C, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues (1949) to date archaeological, geological and hydrogeological samples.
Its existence had been suggested by Franz Kurie in 1934. The primary natural source of carbon-14 on Earth is cosmic ray action on nitrogen in the atmosphere, and it is therefore a cosmogenic nuclide.
However, open-air nuclear testing between 1955–1980 contributed to this pool.
The different isotopes of carbon do not differ appreciably in their chemical properties.
This is used in chemical and biological research, in a technique called carbon labeling: carbon-14 atoms can be used to replace nonradioactive carbon, in order to trace chemical and biochemical reactions involving carbon atoms from any given organic compound.
By emitting an electron and an electron antineutrino, one of the neutrons in the carbon-14 atom decays to a proton and the carbon-14 (half-life of 5730 years) decays into the stable (non-radioactive) isotope nitrogen-14.
The emitted beta particles have a maximum energy of 156 ke V, while their average energy is 49 ke V.
These are relatively low energies; the maximum distance traveled is estimated to be 22 cm in air and 0.27 mm in body tissue.
The fraction of the radiation transmitted through the dead skin layer is estimated to be 0.11.
Small amounts of carbon-14 are not easily detected by typical Geiger–Müller (G-M) detectors; it is estimated that G-M detectors will not normally detect contamination of less than about 100 000 disintegrations per minute (0.05 µCi).
Liquid scintillation counting is the preferred method.
during his tenure as a professor at the University of Chicago.
Libby estimated that the radioactivity of exchangeable carbon-14 would be about 14 disintegrations per minute (dpm) per gram of pure carbon, and this is still used as the activity of the modern radiocarbon standard.