Showing papers on "Absolute dating published in 1977"

Absolute radiocarbon dating using a low altitude European tree-ring calibration

Abstract: Attempts to produce a calibration curve for the radiocarbon timescale by analysis of known age materials have highlighted the inaccuracies of conventional radiocarbon dating methods The resulting ambiguities have caused a loss of confidence in radiocarbon dating particularly among European pre-historians We describe here an absolute radiometric dating technique involving the investigation of all probable sources of error Accurate measurements were made with an overall precision of less than 25 yr standard deviation, on a floating North of Ireland tree-ring chronology

North American Microtektites, Radiolarian Extinctions and the Age of the Eocene-Oligocene Boundary

Abstract: North American microtektites have been found in one Gulf of Mexico and two Caribbean cores. The microtektite layer occurs in upper Eocene sediment and coincides with the apparent extinction of five radiolarian species. Based on fission-track dating of the microtektites and K-Ar and fission-track dating of North American tektites, the North American microtektites have an absolute age of ∼34 m.y., indicating an age of less than 35 m.y. for the Eocene-Oligocene boundary.

The use and abuse of radiocarbon dating

Abstract: Although most of you know the general theory of radiocarbon dating and many may know more than I about the mechanics of the process, nevertheless, I think it might be interesting for some of you to hear the story of how radiocarbon dating got started. One of the very curious facts in the history of radiocarbon dating is that the radioactive isotope of carbon, 14C, was produced in a laboratory some time before its existence was known in nature. As a matter of fact, it was manufactured at the request of a plant physiologist by a physicist for the expressed purpose of providing a tracer for use in biochemical studies. Behind that story, however, lies the research that ultimately lead to the development of atomic weapons. Not long after Roentgen had discovered x-rays in 1896, the medical profession began to realize that high-energy radiation was a tool of considerable value in diagnosis and treatment of disease. In the early part of the twentieth century, much of high-energy physics research was sponsored by the medical profession. By the middle 1930’s, generation of radioactive substances by particle accelerators, such as the cyclotron, was receiving considerable support from the medical profession. About this time, Martin Kamen, a physicist at the University of California, was assigned to the production of large amounts of the thenknown radioactive isotope of carbon, C . This substance had a half-life of 21 minutes, in other words, 50% of its radioactivity was lost every 21 minutes. While Ruben attempted to complete biochemical experiments based on a detectable period of about 90 minutes, Kamen became involved in a search for a longer lived isotope of carbon. All of the known nuclear reactions that could be employed with the equipment then available were used in this study. It is a curious fact that the most successful reaction was the one considered to be least likely to succeed! Although the details of the research program need not concern us, the actual discovery of 14C is a matter of some interest. In general the two approaches involved the use of fast or high-energy neutrons, or the use of slow or thermal neutrons. Again, for our purposes we may simply view this as a kind of atomic shotgun with different powder charges behind the projectiles or neutrons. Although the fast neutron scheme seemed theoretically the most promising, the slow neutron system was included, largely for the sake of completeness. The set-up was not particularly elaborate, for all they used were two 5-gallon carboys of acidified ammonium nitrate placed near a source of thermal neutrons. (The reason for the use of ammonium nitrate is that the anticipated reaction involved the conversion of 14N to I4C, and ammonium nitrate is a good source of nitrogen). They carefully removed all COz from the carboys, sealed them, and went on about their business. About this time they got their first results with high-energy neutrons and succeeded in proving that they had found a radioactive isotope of carbon and

Yale University Geology and Geophysics Radiocarbon Dates I

Abstract: A radiocarbon dating system has been established at the Department of Geology and Geophysics, Yale University. Liquid-scintillation counting of benzene described by Noakes et al (1965) and Polach and Stipp (1967) is used. The operation is small, geared to solving geochemical problems, through the use of radiocarbon as a dating tool and as a natural tracer in combination with other geochemical parameters. The facility will collaborate on significant archaeologic and geologic problems. However, it will not be a facility to which samples are submitted routinely. The procedure follows those used by the authors cited, with subsequent refinements incorporated. The first ages measured by this method were made on deep-sea cores rich in calcium carbonate. delta/sup 13/C was not measured in these samples but will be measured in samples that require it. The /sup 14/C half-life of 5568 years is used in conformity with the style of the journal. The errors, in years, are 1/sub sigma/ counting errors which include the combined counting uncertainties of sample, background, and standard.