Isotopes of carbon

A solution to the question of the mechanism of these reactions was provided by John D Roberts m 1953 on the basis of an imaginative experiment Roberts prepared a sample of chlorobenzene m which one of the carbons the one bearing the chlorine was the radioactive mass 14 isotope of carbon Reaction with potassium amide m liquid... 

For marble provenance studies, the most successful technique seems to be the measurement, through mass spectrometry, of the abundance ratios of the stable isotopes of carbon and oxygen (116). However, no single technique appears to provide unequivocal results, especially in cases such as the different Mediterranean sources, and a combination is often necessary to arrive at an approximate place of origin (117). 

Atomic Weight. As of this writing (ca 1994) the definition of atomic weights is based on carbon-12 [7440-44-0], the most abundant isotope of carbon, which has an atomic weight defined as exactiy 12 (21). 

To set up a scale of atomic masses, it is necessary to establish a standard value for one particular species. The modem atomic mass scale is based on the most common isotope of carbon, 1 C. This isotope is assigned a mass of exactly 12 atomic mass units (amu) ... 

Carbon-12 is the principal isotope of carbon, but a small proportion of carbon-14 is present in all living organisms. Its nuclei are produced when nitrogen nuclei in the atmosphere are bombarded by neutrons formed in the collisions of cosmic rays with other nuclei ... 

Most CO and CO2 in the atmosphere contain the mass 12 isotope of carbon. However, due to the reaction of cosmic ray neutrons with nitrogen in the upper atmosphere, C is produced. Nuclear bomb explosions also produce C. The C is oxidized, first to CO and then to C02 by OH- radicals. As a result, all CO2 in the atmosphere contains some 0, currently a fraction of ca. 10 of all CO2. Since C is radioactive (j -emitter, 0.156 MeV, half-life of 5770 years), all atmospheric CO2 is slightly radioactive. Again, since atmospheric CO2 is the carbon source for photos5mthesis, aU biomass contains C and its level of radioactivity can be used to date the age of the biological material. 

We proposed to study diet and health by combining bone chemistry and histomorphometry. Diet would be determined by analysis of stable isotopes of carbon and nitrogen in bone protein and some preserved hair. In addition, trace elements would be quantitatively analyzed in preserved bone mineral. Abonyi (1993) participated in the study by reconstructing the diet from historical sources and analyzing various foods. Having analyzed human tissues for stable isotopes and trace elements, and foods for the same variables, we hoped to learn more about 19th century diet in southern Ontario, and at the same time, learn more about paleodiet reconstruction. 

Raw ingredients and cooked recipes were analyzed for stable isotopes of carbon (Abonyi 1993). To our knowledge, no one has determined if there are differences in the stable isotope values of raw and cooked foods, however Hastorf and DeNiro (1985) did compare plant remains that were heated to those that had not been heated. They found no significant difference in isotope values due to heating. Marino and DeNiro (1987) studied the effects ofheating (boiling and roasting) on several types of plants to determine if cellulose... 

Schoeller, D.A., Minagawa, M., Slater, R. and Kaplan, I.R. 1986 Stable isotopes of carbon, nitrogen and hydrogen in the contemporary North American human food web. Ecology ofPood andNutrition 18 159-170. 

Katzenberg, M.A. 1991 Analysis of stable isotopes of carbon and nitrogen. In Pfeiffer, S. and Williamson, R.F., eds.. Snake Hill An Investigation of a Military Cemetery from the War of 1812. Toronto, Dundrun Press 247-255. 

Rau, G.H. (1982). The relationship between trophic level and stable isotopes of carbon and nitrogen. In Coastal water research project biennial report for the years 1981-1982. Edited by W. Bascom. Southern California Water Research Project, Long Beach, Calif, pp. 143-148. 

Recently it has been recognised that the carbon isotope composition of small amounts of plant material may be used to assess differences inpi/pa and W (Farquhar et al., 1982). There are two stable isotopes of carbon, and C, which are in the molar ratio 1 89 in the atmosphere. During assimilation of atmospheric CO2 the plant fixes a smaller ratio... 

The important phenomenon of exponential decay is the prototype first-order reaction and provides an informative introduction to first-order kinetic principles. Consider an important example from nuclear physics the decay of the radioactive isotope of carbon, carbon-14 (or C). This form of carbon is unstable and decays over time to form nitrogen-14 ( N) plus an electron (e ) the reaction can be written as... 

The defining characteristic of an atom of a chemical element is the number of protons in its nucleus. A given element may have different isotopes, which are nuclei with the same numbers of protons but different numbers of neutrons. For example, 12C and 14C are two isotopes of carbon. The nuclei of both isotopes contain six protons. However, 12C has six neutrons, whereas 14C has eight neutrons. In general, it is the number of protons and electrons that determines chemical properties of an element. Thus, the different isotopes of an element are usually chemically indistinguishable. These isotopes, however, have different masses. 

When plants are consumed as food by herbivorous animals, the isotopic signatures in the plants are passed on to the consumers. Therefore, provided the isotopic signatures of C3 and C4 plants are known, determining the isotopie signatures in the tissues of herbivorous animals enables one to determine the relative amounts of C3 and C4 plants that the animals consumed as food, and to reconstruct their diets. Moreover, since carnivorous and omnivorous animals, including humans, feed on herbivorous animals as well as on plants, determining the isotopic signatures of the isotopes of carbon in tissues of ancient animals and humans makes it possible to elucidate the components of their diets. 

The isotopic composition of carbon in the proteins, which are one of the main components of animal tissues, reflects the nature of the food resources in the diet of the animals. Determining the relative abundance of the stable isotopes of carbon in the proteins of bones or hair, for example, can facilitate understanding of the effects that different types of plants or animal food resources had on ancient diets (Katzenberg 2000 Burton 1996). 

The sum of the number of protons plus number of neutrons in the isotope is called the mass number of the isotope. Isotopes are usually distinguished from each other by their mass numbers, given as a superscript before the chemical symbol for the element. Carbon-twelve is an isotope of carbon with a symbol l2C. 

Ans. The first symbol stands for the naturally occurring mixture of isotopes of carbon the second stands for only one isotope—the most common one. 

The two isotopes of carbon that occur naturally are 12C (98.89%) and 13C (1.11%). Cosmic rays produce neutrons that interact with 14N in the upper atmosphere to produce 14C and protons,... 

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