Radiocarbon carbon

O Brien, B.J. (1986) The use of natural and anthropogenic 14C to investigate the dynamics of soil organic carbon. Radiocarbon 28, 358-362. 

Craig H (1969) Abyssal carbon radiocarbon in the Pacific. Journal of Geophysical Research 74(23) 5491-5506. 

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. 

The content of the material in a carbon reservoir is a measure of that reservoir s direct or indirect exchange rate with the atmosphere, although variations in solar also create variations in atmospheric content activity (Stuiver and Quay, 1980, 1981). Geologically important reservoirs (i.e., carbonate rocks and fossil carbon) contain no radiocarbon because the turnover times of these reservoirs are much longer than the isotope s half-life. The distribution of is used in studies of ocean circulation, soil sciences, and studies of the terrestrial biosphere. 

Throughout this chapter many of the arguments are based on an assumption of steady state. Before the agricultural and industrial revolutions, the carbon cycle presumably was in a quasi-balanced state. Natural variations still occur in this unperturbed environment the Little Ice Age, 300-400 years ago, may have influenced the carbon cycle. The production rate of varies on time scales of decades and centuries (Stuiver and Quay, 1980,1981), implying that the pre-industrial radiocarbon distribution may not have been in steady state. 

Fossil fuel emissions alter the isotopic composition of atmospheric carbon, since they contain no C and are depleted in C. Releasing radiocarbon-free CO2 to the atmosphere dilutes the atmospheric C content, 3delding lower C/C ratios ("the Suess effect"). From 1850 to 1954 the C/C ratio in the atmosphere decreased by 2.0 to 2.5% (Fig. 11-23) (Suess, 1965 Stuiver and Quay, 1981). Then, this downward trend in C was disrupted by a series of atmospheric nuclear tests. Many large fission explosions set off by the United States with high emission of neutrons took place in 1958 in the atmosphere and the Soviet Union held extensive tests during... 

Craig, H. (1957b). The natural distribution of radiocarbon and the exchange time of carbon dioxide between atmosphere and sea. Tellus 9,1-17. 

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. 

Bischoff JL, Fitzpatrick JA (1991) U-series dating of impure carbonates An isochron technique using total-sample dissolution. Geochim Cosmochim Acta 55 543-554 Broecker WS, Olson EA, Orr PC (1960) Radiocarbon measurements and annual rings in cave formations. Nature 185 93-94... 

Some radioisotopes are continuously being produced by the bombardment of atoms on the surface of the earth or in its atmosphere with extraterrestrial particles or radiation. One of these is carbon-14, also known as radiocarbon, which is widely used for dating archaeological materials (see Textbox 55). Many radioisotopes that are not primordial or are not created by natural processes are now produced artificially using specialized equipment many of the "artificial" isotopes are of use for probing and analyzing materials. 

The half-life (t1 ) of a radioisotope is the amount of time it takes for that isotope to undergo radioactive decay and be converted into another. It is also a measure of the stability of the isotope the shorter its half-life, the less stable the isotope. The half-life of radioisotopes ranges from fractions of a second for the most unstable to billions of years for isotopes that are only weakly radioactive. In the case of radiocarbon (carbon-14), for example, the half-life is 5730 years (see Fig. 61). 

Radiocarbon Counting of beta radiation or amount of carbon-14 Organic matter Textbox 52... 

Two of these isotopes, carbon-12, the most abundant, and carbon-13 are stable. Carbon-14, on the other hand, is an unstable radioactive isotope, also known as radiocarbon, which decays by the beta decay process a beta particle is emitted from the decaying atomic nucleus and the carbon-14 atom is transformed into an isotope of another element, nitrogen-14, N-14 for short (chemical symbol 14N), the most common isotope of nitrogen ... 

The decay of radiocarbon (see Fig. 61) into nitrogen-14 proceeds at a constant rate, and its half-life is 5730 + 40 years (see Textbox 14). This means that in any material containing carbon, some radiocarbon atoms disintegrate before 5730 years have elapsed and others later after 5730 + 40 years have elapsed, however, only half of the original atoms of the carbon-14... 

FIGURE 61 The decay of radiocarbon. Radiocarbon is a radioactive isotope whose half-life is 5730 + 40 years. This means that half of the original amount of radiocarbon in any carbon-containing sample will have disintegrated after 5730 years. Half of the remaining radiocarbon will have disintegrated after 11,400 years, and so forth. After about 50,000 years the amount of radiocarbon remaining in any sample is so small that older remains cannot be dated reliably. 

Soon after their creation, the newly formed radiocarbon atoms react with atmospheric oxygen to form radioactive carbon dioxide, molecules of carbon dioxide in which the carbon atom is radiocarbon ... 

The carbon dioxide molecules including a radiocarbon atom are chemically undistinguishable from those of ordinary carbon dioxide, with which it mixes, and eventually, carbon dioxide, including a radiocarbon atom, is homogeneously distributed throughout the earth s atmosphere and hydrosphere. Thus there is a state of constant production, distribution, and decay of radiocarbon, which results in the relative amount of radiocarbon in the atmosphere and hydrosphere remaining constant. In this homogeneously distributed condition, radiocarbon enters the carbon cycle - as the... 

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