Carbon radiocarbon dating

The constant half-life of a nuclide is used to determine the ages of archaeological artifacts. In isotopic dating, we measure the activity of the radioactive isotopes that they contain. Isotopes used for dating objects include uranium-238, potassium-40, and tritium. However, the most important example is radiocarbon dating, which uses the decay of carbon-14, for which the half-life is 5730 a. 

Nuclear testing has increased the amount of carbon-14 in the air, and sensitive radiocarbon dating techniques take this increase into account. 

Hedges, R.E.M., Lee-Thorp, J.A. and Tuross, N. 1995 Is tooth enamel carbonate a suitable material for radiocarbon dating Radiocarbon 37 285-290. 

A more recently developed technique, known as the accelerator mass spectrometry (AMS) radiocarbon dating technique, based on counting, in a mass spectrometer, the relative amount of radiocarbon to stable carbon isotopes in a sample (see Textbox 10). 

A mass of evidence seems to confirm that the mixing rate of radiocarbon in the atmosphere is rapid, and that with respect to its radiocarbon content the atmosphere can be considered as a homogeneous entirety. The contamination of samples with matter from an extraneous source can nevertheless invalidate this assumption. Two types of contamination can be differentiated physicochemical contamination and mechanical intrusion. There are two forms of physicochemical contamination. One is due to the dilution of the concentration of radiocarbon in the atmosphere by very old carbon, practically depleted of radiocarbon, released by the combustion of fossil fuel, such as coal and oil. The other is by the contamination with radiocarbon produced by nuclear bomb tests during the 1950s and later in the twentieth century. The uncertainties introduced by these forms of contamination complicate the interpretation of data obtained by the radiocarbon dating method and restrict its accuracy and the effective time range of dating. 

Most bone is, at present, dated by radiocarbon dating the carbon-containing components of the bone (see Textbox 52). Relatively large samples are... 

Carbon Dioxide. Carbon dioxide, also a colorless and odorless gas, makes up about 0.03% of dry air. Carbon dioxide is introduced into the atmosphere by several natural processes it is released from volcanoes, from burning organic matter, and from living animals as a byproduct of the respiration process. It is for this latter reason that carbon dioxide plays a vital role in the carbon cycle (see Fig. 62), which makes possible one of the more important scientific tools in archaeology, radiocarbon dating (see Textbox 52). 

The radiocarbon age from Equation (16.2) is expressed in years BP, i.e. Before Present, where Present, by convention, is 1950 AD. Actually, 1950 is considered the reference year in radiocarbon dating, especially due to historical reasons. Following the same convention, in Equation (16.2), when measuring 14/f(t), its value is usually normalized to the concentration of a standard material in 1950 the normalized value is expressed in units of pMC (per cent of Modem Carbon), the standard material being 100 pMC. 

A.J.T. Jull, DJ. Donahue and P.E. Damon, Factors affecting the apparent radiocarbon age of textiles a comment on Effects of fires and biofractionation of carbon isotopes on results of radiocarbon dating of old textiles the Shroud of Turin , by D.A. Kouznetsov et al., J. Archaeol. Sci. 23, 157 160 (1996) D.A. Kouznetsov, A.A. Ivanov and P.R. Veletsky, Effects of fires and biofractionation of carbon isotopes on results of radiocarbon dating of old textiles the Shroud of Turin, J. Archaeol Sci. 23, 109 121 (1996). 

One of the limitations of radiocarbon dating artifacts is due to the half-life of the carbon-14, 5730 years. In radiochemistry, a good rule of thumb is the following when an element decays for more than about 10 times its half-life, there is very little left to measure accurately. In the case of C-14, that time is 10 x 5730 yr or 57300 years. 

The first entry in Table 4 refers to the accelerator (AMS) experiments noted earlier in which we investigated (a) the feasibility of direct atom counting given only a few micrograms of carbon (using the new international radiocarbon dating... 

The basic assumption of constant atmospheric X4C activity in radiocarbon dating is not strictly valid. We now have a record of the fluctuation of atmospheric 14C variations for the last 8,400 years B.P. obtained by measurement of the isotopes of carbon in dendrochron-ologically dated wood. Prior to contamination of atmospheric 14C activity by fossil fuel combustion and nuclear technology in the 20th century, the first-order secular variation can be closely approximated by a sine curve with a period of 10,600 years and an amplitude of ... 

Purser, K. H., Hanley, P. R., A carbon-14 dating system, In Proc. 1st Conference on Radiocarbon Dating with Accelerators, University Rochester, 165-186, 1978. 

Libby, L. M., Globally Stored Organic Carbon and Radiocarbon Dates, J. Geophys. Res., 1973, 78, 7667-7670. 

The physicochemical basis behind the technique of radiocarbon dating is the isotopic abundances of carbon s three isotopes 12C is the normal form and constitutes 98.9 per cent of all naturally occurring carbon. 13 C is the other naturally occurring isotope, with an abundance of about 1 per cent. 14C does not occur naturally, but tiny amounts of it are formed when high-energy particles from space collide with gases in the upper atmosphere, thus causing radiochemical modification. 

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