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Browsing Conference Publications by Subject "Accuracy"
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- ItemCurious case of 26Al accelerator mass spectrometry(Australian National University, 2019-09-09) Wilcken, KM; Rood, DHAccelerator mass spectrometry measurement of 26Al suffers from low negative ionisation yield that often becomes the limiting factor. To counter the low Al− yield it has been recognised that AlO− produces negative ions much more efficiently and is a potential avenue to improve the measurement precision. When using AlO− for the measurement there is an additional challenge to separate the interfering isobar 26Mg and 26Al, but this can be achieved effectively with gas-filled magnet. However, this seemingly neat solution of using AlO− instead Al− for the measurement does not necessarily yield as clear cut improvements in precision as one would hope. To illustrate this point, data from conventional measurement method at ANSTO is presented and benchmarked against published data using AlO− method
- ItemHigh-precision radiocarbon measurements at the ANTARES AMS Centre(Elsevier, 1996-06-01) Hotchkis, MAC; Fink, D; Hua, Q; Jacobsen, GE; Lawson, EM; Smith, AM; Tuniz, CThe ANTARES AMS Centre at Lucas Heights Research Laboratories is currently used for measurements of the long-lived radioisotopes 14C, 26Al, 36Cl and 129I, with measurement of 10Be and actinides under development. Improved precision for 14C (to 0.5%) has been achieved with the recent commissioning of a 59 sample ion source coupled with automated data acquisition. We have developed rigorous data evaluation methods which are invaluable in assessing reproducibility and aid in the identification of physical problems with the system. Low backgrounds, in the accelerator and in the sample preparation laboratories, have allowed us to measure very old samples (to 50 000 years BP) and are also vital for high-accuracy dating of small samples. © 1996 Elsevier Science B.V.
- ItemImproving the accuracy of aluminium assay in purified quartz for in situ cosmogenic exposure dating(GNS Science, 2011-03-24) Fujioka, T; Fink, D; Mifsud, CPrecise and accurate measurement of the natural aluminium content in purified quartz powder, [Al], extracted from surface bedrock and/or sediment samples for in situ cosmogenic nuclide dating is critical for reliable 26Al exposure ages and 26Al/10Be ratios for burial dating. Numerous articles have cited issues regarding reliability of 26Al ages paired to 10Be ages, not only due to poor statistical error, but also due to uncertainty in [Al]. Loss of Al during aliquot preparation for ICPOES from bulk HF solutions of dissolved quartz or inaccurate assay via ICP (or AA) will result in reduced 26Al concentrations. In turn this will, depending on magnitude of the loss with respect to typical age errors, lead to lower-than-expected 26Al ages when compared to corresponding 10Be ages. If the loss is excessive, this may result in depressed 26Al/10Be ratios and thus a false burial signal. Over the past 4 years we have performed repetitive Al assays from a parent HF solution prepared from ~25 g of a low-iron glass sand (NIST-165a; ~320 ppm [Al]) using identical methods as for all quartz samples. The solution was used as an in-house laboratory standard for [Al] and shows a limiting 1σ of ±5% (n ~50) via ICP-OES at a commercial laboratory. The spread in paired NIST-165a duplicates measured per batch is better than ±1%. To determine the accuracy of our procedures, we prepared sets of solutions (1–10 ppm Al) from 3 different quartz powders using the standard addition method. Initial results indicate a 3-7% offset between [Al] based on the standard addition method and that based on the conventional calibration curve. Copyright (c) 2011 AMS12.
- ItemPlans for AMS dating at Lucas Heights(Australian National University, 1991-01-29) Smith, AM; Bird, JR; Fink, D; Shying, M; Shahgholi, NA refurbished tandem accelerator has been installed at ANSTO for which a major role will be the use of Accelerator Mass Spectrometry (AMS) techniques for measurements of 14C and other radioisotopes such as 10Be, 26Al, and 41Ca. The tandem accelerator is being upgraded with recent advances om accelerator technology aimed at achieving a terminal voltage of 10 MV and other performance features needed for first-rate AMS measurements. Dual ion sources will be used, one being a high intensity source which will be suitable for difficult isotopes such as 10Be, 26Al, and 41Ca, as will as for high throughput in radiocarbon measurements. The second source will be dedicated to high precision radiocarbon measurements with minimum cross-contamination and memory effects. Computer control systems will be used to facilitate high precision measurements on standards and unknowns. In the longer term it is hoped to develop a gas ion source to permit 14C measurements on Co2 obtained directly from field samples. The facility is expected to commence a measurement services in 1992. Sample preparation facilities are being developed concurrently at Lucas Heights and at other places such as radiocarbon laboratories, with special attention to minimising the possibility of contamination of samples at the ultra-low levels which can be measured by AMS (isotope ration of the order of 10-15).
- ItemThe use of internal standards for measurement of temperature in BigDiff(Australian Institute of Physics, 2002-01-29) Ball, CJ; Thorogood, GJA simple furnace has been constructed to enable X-ray diffractograms to be obtained at elevated temperatures in BigDiff, on the Australian beamline at the Photon Factory, Tsukuba, Japan. Measurement of the specimen temperature presents a problem, and this poster describes an attempt to measure the temperature using the thermal expansion of an internal standard. α-alumina was chosen as the internal standard, but because of uncertainty regarding its coefficients of thermal expansion it was decided to compare temperatures based on α-alumina with those based on tungsten, using a composite specimen. Data in BigDiff are recorded on image plates. It has long been known that the direction of reading of an image plate is not strictly parallel to its edge, with the result that the starting angles of strips across the width of a plate are not exactly the same. To overcome this problem exposures at the same temperature were recorded on opposite sides of the plate. Comparison of these diffractograms revealed that the pixel spacing also varied across the width of the plate, and down the length of a strip. As a result it was not possible to calculate cell parameters with sufficient accuracy using Rietveld refinement of the data. Instead, temperatures have been calculated from the shifts of individual lines from their supposed positions at the reference temperature. Comparing temperatures calculated from different lines showed that at each temperature the entire pattern had been shifted parallel to its length by an amount on the order of 50 μm, but not the same for all patterns, presumably because movement of the cassette in BigDiff was not strictly parallel to the guide rails. After making allowance for the above effects temperatures can be measured to a precision of ±2K, but the biggest uncertainty, almost an order of magnitude greater, remains lack of knowledge of the coefficients of thermal expansion.