Radiocarbon production

As solar energy output and radiocarbon production are both tied to sunspot activity, it might be possible to reconstruct past ir-radiance variations from the perturbations in the... 

From both types of isotope analyses, we must conclude that there is no evidence for the large regional water flow that had been assumed until these analyses were performed and discussed. We must now accept that the radiocarbon age of the water in those wells whose analyses have been discussed in this communication can only be explained by the existence of local flow. Other factors possibly affecting the radiocarbon ages are being investigated in this aquifer, such as, e.g., carbon precipitation or dilution (Oeschger, 1974) and subsurface radiocarbon production (Zito et al., 1980). 

At the top of the atmosphere, more properly at altitudes where the density is sufficiently low, high-energy cosmic ray particles cause nuclear chemical reactions with important products. The production of radioactive (or radiocarbon) already has been mentioned. 

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. 

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... 

In this case the units do matter, but the standard ratio, s, enters only in the term that represents the production of radiocarbon. 

The generation process for radiocarbon in the atmosphere makes C02 which enters the biosphere because of the long lifetime the mixing is essentially perfect. We assumed the rate of production to be constant which turns out to be somewhat incorrect. Variations of about 10 percent can be seen back in time to early Egyptian periods and before. The earth s magnetic field was apparently weaker then as the cosmic rays delivered to the surface and the atmosphere were more intense. 

Lingenfelter, R. E., Ramaty, R., Astrophysical and geophysical variations in C14 production, In Radiocarbon Variations and Absolute Chronology, Proc. XII Nobel Symp., New York,... 

Houtermans, J. C., Suess, H. E., Oeschger, H., Reservoir models and production rate variations of natural radiocarbon,... 

In water, the percentage of these degradation products increased with time and amounted to one quarter of the remaining radiocarbon at 24 hr the quantity of 3-methyl-4-nitrophenol and both demethylated products is ca. 7% and 5.5%, respectively. Fenitrooxon was also detected. Because fenitrothion was stable in water under the present experimental conditions, these degradation products are presumably produced by fish metabolism. 

Metabolism studies of methoprene in nonaquatic organisms have provided background data which must be considered prior to discussing the fate of methoprene in aquatic systems. All nonaquatic metabolic studies reported to date have utilized [5-1 C]methoprene. The location of radiocarbon was selected both for ease of synthesis and for anticipated metabolic stability. However, studies in plants and bovines (25, 30, 31) revealed many presumed "metabolites" to be radiolabeled natural products, or "nonmetabolite residues". Primary metabolites of methoprene resulting from ester cleavage and/or (O-demethylation have been... 

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]. 

The chemistry of a fourth coenzyme was at least partially elucidated in the period under discussion. F. Lynen and coworkers treated P-methylcrotonyl coenzyme A (CoA) carboxylase with bicarbonate labelled with 14C, and discovered that one atom of radiocarbon was incorporated per molecule of enzyme. They postulated that an intermediate was formed between the enzyme and C02, in which the biotin of the enzyme had become car-boxylated. The carboxylated enzyme could transfer its radiolabelled carbon dioxide to methylcrotonyl CoA more interestingly, they found that the enzyme-COz compound would also transfer radiolabelled carbon dioxide to free biotin. The resulting compound, carboxybiotin [4], was quite unstable, but could be stabilized by treatment with diazomethane to yield the methyl ester of N-carboxymethylbiotin (7) (Lynen et al., 1959). The identification of this radiolabelled compound demonstrated that the unstable material is N-carboxybiotin itself, which readily decarboxylates esterification prevents this reaction, and allows the isolation and identification of the product. Lynen et al. then postulated that the structure of the enzyme-C02 compound was essentially the same as that of the product they had isolated from the reaction with free biotin, but where the carbon dioxide was inserted into the bound biotin of the enzyme (Lynen et al., 1961). Although these discoveries still leave significant questions to be answered as to the detailed mechanism of the carboxylation reactions in which biotin participates as coenzyme, they provide a start toward elucidating the way in which the coenzyme functions. 

Obviously this wide distribution of the 14C formed in the atmosphere lakes time it is believed to require a period of 500-1000 years. This time is not. however, a deterrent to radiocarbon dating because of two factors die long half-life of I4C and the relatively constant rate of cosmic-ray formation of l4C in the earth s atmosphere over the most recent several thousands of years. These considerations lead to the conclusion that the proportion of 14C in the carbon reservoir of the earth is constant, and that the addition by cosmic ray production is in balance with the loss by radioactive decay. If this conclusion is warranted, then the carbon dioxide on earth many centuries ago had the same content of radioactive carbon as the carbon dioxide on earth today, Thus, radioactive carbon in the wood of a tree growing centuries ago had the same content as that in carbon oil earth today. Therefore, if we wish to determine how long ago a tree was cut down to build an ancient fire, all we need to do is to determine the relative 14C content of the carbon in the charcoal remaining, using the value we have determined for llie half life of 14C. If the carbon from Ihe charcoal in an ancient cave has only as much 14C radioactivity as does carbon on earth today, then we can conclude that the tree which furnished llie firewood grew 5730 30 years ago. 

Radiocarbon dating of archaeological artifacts depends on the slow and constant production of radioactive carbon-14 in the upper atmosphere by neutron bombardment of nitrogen atoms. (The neutrons come from the bombardment of other atoms by cosmic rays.)... 

Vogel, J. S. (1992). Rapid production of graphite without contamination for biomedical AMS. Radiocarbon 34 344-350. 

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