LYCOS RETRIEVER 
Radiocarbon Dating: Samples
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A conference on radiocarbon dating held in October, 1956, resulted in the following conclusions about the reliability of the method: Local variation, especially in shells, can be highly significant. Possible variations in the size of the exchange reservoir under glacial climates are unimportant. The most significant problem is that of biological alteration of materials in the soil. This effect grows more serious with greater age. To produce an error of 50 percent in the age of a 10,000 year old specimen would require the replacement of more than 25 percent of the carbon atoms. For a 40,000-year-old sample, the figure is only 5 percent, while an error of 5000 years can be produced by about 1 percent of modern materials.
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After its introduction five decades ago, radiocarbon dating still remains the primary means for providing archaeological chronology. A review of the plasma-chemical extraction technique that permits direct AMS 14C dating of ancient rock paintings (Russ et al. 1990, Nature 348:710) will be presented. Low-temperature and low-pressure argon and oxygen plasmas, coupled with high vacuum technology, remove carbon containing material in pictograph paints without contamination from inorganic carbon in the rock substrates (CaCO3) or mineral accretions (CaC2O4). The rock painting samples dated so far generally agree with ages expected on the basis of archaeological inference. The technique was used on materials of known 14C activity; results agreed within statistical uncertainty with previously determined ages. To establish that the method and apparatus do not have a significant live carbon background, 14C-free samples were ... measured.
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A dating method based on the measurement on the concentration of radiocarbon (C14) in organic finds. When an organism dies, the absorption of C14 stops, and the radiocarbon begins to decay. As the radioactive half-life of radiocarbon is known, the period of time that has passed since the dying of the organism can be determined. Sample materials are: wood, charcoal, bones, seeds (e.g.).
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In 1988, the Holy See permitted three research centers to independently perform radiocarbon dating on portions of a swatch taken from a corner of the shroud. All three, Oxford University, the University of Arizona, and the Swiss Federal Institute of Technology agreed with a dating in the 13th to 14th centuries (1260-1390), although recently published chemical analysis (see below) indicates that the sample used was invalid. The scientific community had asked the Holy See to authorize more samples, including from the image-bearing part of the shroud, but this request was refused. One possible account for the reluctance is that if the image is genuine, the destruction of parts of it for purposes of dating could be considered sacrilege. Another possible explanation is a reluctance to have the shroud definitively dated.
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As with Assertion 1, Assertion 2 fails to account for the tree-ring calibration which is a routine part of modern radiocarbon dating. Although no convincing argument for a change in the speed of light over time has been made, the question is irrelevant to the validity of tree-ring calibrated radiocarbon dates. As with variation in atmospheric radiocarbon concentration, the decay rate of radiocarbon in tree-ring calibration samples would be affected in exactly the same way as the decay rate of radiocarbon in the specimen to be dated. Calibrated radiocarbon dates are immune to any supposed change in decay rate of radiocarbon. Assertion 2 is false.
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It has long been recognized that if the radiocarbon atoms could be detected directly, rather than by waiting for their decay, smaller samples could be used for dating and older dates could be measured. A simple hypothetical example to illustrate this point is a sample containing only one atom of radiocarbon. To measure the age (that is, the abundance of radiocarbon), the sample can be placed into a mass spectrometer and that atom counted, or the sample can be placed into a Geiger counter and counted, requiring a wait on the average of 8000 years (the mean life of radiocarbon) for the decay. In practice, neither the atoms nor the decays can be counted with 100% efficiency, but the huge advantage for atom counting remains. Samples are ... processed in a lab such as the Beta Analytic Inc.
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