Radioactive isotopes in carbon dating

The radiocarbon method was developed by a team of scientists led by the late Professor Willard F.Libby of the University of Chicago in immediate post-WW2 years.Herein lies the true advantage of the radiocarbon method, it is able to be uniformly applied throughout the world.Included below is an impressive list of some of the types of carbonaceous samples that have been commonly radiocarbon dated in the years since the inception of the method: The historical perspective on the development of radiocarbon dating is well outlined in Taylor's (1987) book "Radiocarbon Dating: An archaeological perspective".The radiocarbon method is based on the rate of decay of the radioactive or unstable carbon isotope 14 (14C), which is formed in the upper atmosphere through the effect of cosmic ray neutrons upon nitrogen 14.The reaction is: (Where n is a neutron and p is a proton).There is a quantitative relationship between the decay of 14C and the production of a beta particle. That is, the probability of decay for an atom of 14C in a discrete sample is constant, thereby requiring the application of statistical methods for the analysis of counting data.It follows from this that any material which is composed of carbon may be dated.

The rapidity of the dispersal of C14 into the atmosphere has been demonstrated by measurements of radioactive carbon produced from thermonuclear bomb testing.

As 14C decays it emits a weak beta particle (b ), or electron, which possesses an average energy of 160ke V.

The decay can be shown: Thus, the 14C decays back to 14N.

14C also enters the Earth's oceans in an atmospheric exchange and as dissolved carbonate (the entire 14C inventory is termed the carbon exchange reservoir (Aitken, 1990)).

Plants and animals which utilise carbon in biological foodchains take up 14C during their lifetimes.