Accelerator mass spectrometry (AMS) is used to determine the amount of carcinogen covalently bound to mouse liver DNA (DNA adduct) following very low-level exposure to a "'C-labeled carcinogen. AMS is a highly sensitive method for counting long-lived but rare cosmogenic isotopes. While AMS is a tool of importance in the earth sciences, it has not been applied in biomedical research. The ability of AMS to assay rare isotope concentrations (10Be, 14C, 26Al, 41Ca, and 129I) in microgram amounts suggests that extension to the biomedical sciences is a natural and potentially powerful application of the technology. In this study, the relationship between exposure to low levels of 2-amino-3, 8-dimethyl[2-14C~imidazo[4,5-f]quinoxaline and formation of DNA adducts is examined to establish the dynamic range of the technique and the potential sensitivity for biological measurements, as well as to evaluate the relationship between DNA adducts and low-dose carcinogen exposure. Instrument reproducibility in this study is 2%; sensitivity is 1 adduct per 10"1 nucleotides. Formation of adducts is linearly dependent on dose down to an exposure of 500 ng per kg of body weight. With the present measurements, we demonstrate at least 1 order of magnitude Improvement over the best adduct detection sensitivity reported to date and 3-5 orders of magnitude improvement over other methods used for adduct measurement. An additional improvement of 2 orders of magnitude in sensitivity is suggested by preliminary experiments to develop bacterial hosts depleted in radiocarbon. Expanded applications involving human subjects, including clinical applications, are now expected because of the great detection sensitivity and small sample size requirements of AMS.Carcinogens covalently bound to any of the deoxynucleotide bases present in DNA (DNA adducts) have been proclaimed as markers of carcinogen exposure. The relationship between adduct formation and exposure, however, has been primarily established at high carcinogen doses and not at lower, more environmentally relevant, levels because of limitations in assay sensitivity. As a consequence, the significance of using adducts as a measure of carcinogen exposure in the human population is unknown. Currently, the most sensitive technique for adduct detection is the 32p postlabeling assay. The 32p postlabeling assay has permitted measurement of 1 adduct in 1010 nucleotides and has been used to detect carcinogen-DNA binding in occupationally exposed humans and smokers, but accurate quantitative measurement at levels <1 adduct per 107-101 nucleotides is difficult because of variability in adduct recovery (1-3). The ability of accelerator mass spectrometry (AMS) to measure concentrations of rare isotopes in 20-Asg to 1-mg samples suggested to us that its extension to the biomedical sciences was a natural and potentially powerful application of the technology (4). The great enhancement in 14C detection sensitivity available with AMS offers the distinct advantage of detecting extremely small amount...
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Several geological sources of obsidian in the Pacific Northwest have been characterized by means of their trace element concentrations, as measured by X‐ray fluorescence analysis. The technique is fast and completely non‐destructive, making it well‐suited for identifying the sources of obsidian from which artifacts were fabricated.
The use of energy-dispersive X-ray fluorescence analysis (XES) for the routine identification of three tephras (Mazama, Bridge River, Mount St. Helens Yn) commonly found in archeological sites in British Columbia has been investigated. Researchers have often assumed that chemical analysis of bulk samples of glass separates would be hampered by contamination and weathering effects. Our results indicate that XES of bulk glass separates provides a very reliable method for rapidly identifying the three tephras in question, even with a very simple sample preparation. This should enable persons not skilled in geology or in tephrochronology to collect and to identify samples of these tephras. Finally, as a part of the study, similar measurements were made on the separated glass portions of these three tephras and of three others (Glacier Peak B and G, White River) from northwest North America. The results suggest that this method may provide tephrochronologists with a useful additional tool for studying tephras in other regions.
We present a survey of carbon beam yields from 20 simple carbon compounds using a caesium sputter source and the McMaster University tandem accelerator. The carbon yield was measured as a 35MeV 12C4+ beam. We found that the beam intensities could be related to a grouping of the carbides according to the chemical bonding of the compounds. The usefulness of the compounds for accelerator 14C dating was further related to their preparation chemistries. Strontium carbide was the equal of graphite in negative carbon ion beam production and aluminum carbide was found to be a good candidate for further tests because of its good sputter yield and preparation chemistry. Charcoal was also tested with varying amounts of silver added as a heat conduction aid.
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