Radiocarbon carbon techniques

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

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). 

All of the above particulate investigations were based on mini-radiocarbon measurement techniques, with sample masses typically in the range of 5-10 mg-carbon. This constituted a major advantage, because it was practicable to select special samples (given region, source impact, sediment depth) and to further subject such samples to physical (size) or chemical separation before 14C measurement. This type of "serial selectivity" provides maximum information content about the samples and in fact it is essential when information is sought for the sources or atmospheric distributions of pure chemical species, such as methane or elemental carbon. 

The relatively rapid acceptance of the general validity of the radiocarbon method by most researchers is indicated by the rapid establishment of other laboratories to perform analyses. Many who attempted to duplicate the procedures required to obtain acceptable values using the solid carbon technique experienced moderate-to-severe difficulties. The result was the substitution of gas or liquid scintillation counting methods. Because of the greater efficiency of such detection systems, these developments permitted the maximum age range to be extended from about... 

Likewise, the continued development of compound-specific radiocarbon dating techniques ushers an exciting dimension to the study of PAHs and other hydrocarbons in modern sediments (e.g., Eglinton et al., 1997 Eglinton and Pearson, 2001 Pearson et al., 2001 Reddy et al., 2002). In particular, compound-specific radiocarbon determination offers a clear distinction to be made between new carbon (e.g., wood burning) and old carbon (petroleum and petroleum combustion). 

Libby, Willard F. (1908-1980). Developed radiocarbon dating technique based on carbon-14. Nobel Prize 1960. 

Radiocarbon dating techniques focus on the point at which the material dated ceases any exchange of carbon with the biosphere the radioactive isotope... 

The following method, using a B a-requiring diatom and measuring the rate of radioactive carbonate uptake of cells exposed to different concentrations of the vitamin, is probably the most sensitive and rapid procedure yet available. It is derived from an initial radiocarbon uptake technique by Gold as modified by Carlucci and Silbemagel (Canadian J. Microbiol., 12 175, 1966). 

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... 

There have recently been significant advances in the technique of carbon 14 measurements, which have permitted the determination of the concentration ratio C14/C12 in samples of small size. Two developments have occurred the first is an entirely new mass-spectrometric separation of Cl4 and Cl2 ions and their subsequent estimation by counting [1-8]1, while the second is simply the extension of conventional proportional counter operation to very small size carbon samples [9]. The first method is very fast, precise, and capable of treating samples of even submilligram size, but requires an expensive installation. The second method is slow (counting times of two months or more are necessary), can probably be made sufficiently precise to handle most problems, works down to sample sizes of 10 mg carbon, and is relatively inexpensive, especially to install in already-existing radiocarbon laboratories. 

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. 

As renewable raw materials began to enter the marketplace, it was inevitable that claims to the level of renewable content in commercial offerings would become an issue of public debate. As previously pointed out in this article, some renewable raw materials have been common to the polyol chemistry for many decades, so claims to at least some renewable content are justified. Because the commercialization of different renewable polyol chemistries has created a highly competitive environment, some scientists in the field have promoted a method for the independent verification of the renewable sourced carbon in the final product [153]. ASTM International has published a concise and informative briefing paper on the method development for the determination of renewable carbon content in carbon-containing substances [154]. The method involves the analysis of content in the finished polyurethane products via radiocarbon dating [155]. The technique is fast and accurate, and has become commonly available by contract analysis through independent analytical laboratories [156]. 

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