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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Results from the tandem mirror experiment are described. The configuration of axial density and potential profiles are created and sustained by neutral-beam injection and gas fueling. Plasma confinement in the center cell is shown to be improved by the end plugs by as much as a factor of 9. The electron temperature is higher than that achieved in our earlier 2XIIB single-cell mirror experiment.PACS numbers: 52.55. Mg, 52.55.Ke This Letter reports the first results obtained from the tandem mirror experiment (TMX) at the Lawrence Livermore Laboratory. Steady-state tandem-mirror plasmas have been produced and an electrostatic barrier that improves plasma confinement has been observed. The tandem-mirror configuration 1 ' 2 can enhance the performance of a magnetic-mirror thermonuclear reactor. Such a reactor would produce power in a cylindrical, high-/3, magnetic solenoid. End losses from this center cell are reduced by electrostatic endplug barriers of positive potential, which turn back those low-energy ions which escape through the magnetic mirror. These potential barriers are established on both ends of the center cell by high-density, high-temperature, mirror-confined plasmas, which have a larger ambipolar potential than does the center-cell plasma.Earlier tandem-mirror experiments, 3 in which plasma guns were used to establish end-plug densities larger than those in the center cell, have produced potential wells. Langmuir-probe measurements indicated that the magnitude and scaling of the potential-well depth is consistent with theoretical predictions. Our results demonstrate that we can produce and sustain a tandem-mirror plasma configuration by use of neutral beams to fuel the end plugs and gas to fuel the center cell. This method can be extrapolated to continuously operated systems. Our experiments further demonCee coil Baseball coilSolenoid coils Octupole coil -Plasma flux tube 1132 Neutral beam injectors Startup plasma guns FIG. 1. Schematic diagram of TMX magnet and neutral-beam system.

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