Browsing by Author "Williams, AA"
Now showing 1 - 17 of 17
Results Per Page
- Item15th International Conference on Accelerator Mass Spectrometry(Australian Nuclear Science and Technology Organisation, 2021-11-15) Bertuch, F; Child, DP; Fink, D; Fülöp, RH; Hotchkis, MAC; Hua, Q; Jacobsen, GE; Jenkinson, A; Levchenko, VA; Simon, KJ; Smith, AM; Wilcken, KM; Williams, AA; Williams, ML; Yang, B; Fallon, SJ; Wallner, TOn behalf of the AMS-15 Organising committee, we would like to thank you for attending the 15th International Conference on Accelerator Mass Spectrometry. Held as an online event for the first time, the 2021 conference attracted over 300 attendees with presentations delivered by colleagues and professionals from around the globe.Applications of AMS to the world’s most pressing problems/questions: A-1 : Earth’s dynamic climate palaeoclimate studies, human impacts on climate, data for climate modelling. A-2 : Water resource sustainability groundwater dating, hydrology, water quality and management A-3 : Living landscapes soil production, carbon storage, erosion, sediment transport, geomorphology. A-4 : Catastrophic natural events volcanoes, cyclones, earthquakes, tsunamis, space weather, mass extinctions. A-5 : Advancing human health metabolic and bio-kinetic studies, bomb-pulse dating, diagnostics and bio-tracing. A-6 : Challenges of the nuclear age nuclear safeguards, nuclear forensics, nuclear waste management, nuclear site monitoring, impacts of nuclear accidents. A-7 :Understanding the human story archaeology, human evolution and migration, history, art and cultural heritage A-8 : Understanding the cosmos fundamental physics, nuclear astrophysics, nuclear physics AMS Research and Development: T-1 : Novel AMS systems, components and techniques T-2 : Suppression of isobars and other interferences T-3 : Ion sourcery T-4 : New AMS isotopes T-5 : Advances in sample preparation T-6 : Data quality and management T-7 : Facility Reports (Poster Presentation only)
- ItemAMS radiocarbon dating of micro samples from the rock paintings of Malakula (Vanuatu)(Oxford University School of Archaeology, 2002-04-09) Zoppi, U; David, B; Wilson, M; Hua, Q; Williams, AA; Watchman, ANot available
- ItemANSTO Radiocarbon Laboratory: developments to meet the needs of our community(Australian Nuclear Science and Technology Organisation, 2021-11-17) Bertuch, F; Williams, AA; Yang, B; Nguyen, TH; Varley, S; Jacobsen, GE; Hua, QThe radiocarbon chemistry laboratories in the Centre for Accelerator Science at the Australian Nuclear Science and Technology Organisation (ANSTO) have a role providing support to AMS measurements for government organisations, industry, and academia in Australia and overseas. Over recent years the radiocarbon laboratories at ANSTO have expanded to support projects that address unique challenges which include environmental issues, the sustainable management of water resources, climate variability, ecological studies, and research into Indigenous heritage. The increase of work in these areas has seen a growing demand for processing samples of groundwater, rock art, ice cores, tree rings and Antarctic mosses. Here we will present an update of our procedures for processing a diverse range of sample types. We will also describe developments such as an automated dissolved organic carbon (DIC) extraction system for water samples, and our automated AAA pretreatment system. We will also outline our range of graphitisation systems which include a set of 24 Fe/H2 graphitisation units, 6 microconventional furnace (MCF) Fe/H2 graphitisation lines, a laser heated furnace (LHF) graphitisation system, and an Ionplus AGE-3 graphitisation system (owned by UNSW). Our MCF and conventional graphitisation lines have been designed to handle and reliably produce graphite targets containing as little as 5 μg and 10ugC of carbon respectively), making the graphitisation of minute carbon samples from rock art and ice cores possible.
- ItemApplication of environmental isotopes to study aquifer interactions and their impact on groundwater salinisation in western Victoria(Australian Institute of Nuclear Science and Engineering (AINSE), 2007-11) Raiber, M; Webb, JA; Jacobsen, GE; Chisari, R; Williams, AA; Neklapilova, B
- ItemBeryllium-10 in forams and marine sediments; a new chemo-stratigraphic tracer for the late quaternary(Eleventh International Conference on Accelerator Mass Spectrometry, 2008-09) Levchenko, VA; Opdyke, BN; Fink, D; Mifsud, C; Williams, AAThe production rate of cosmogenic isotopes 10Be and 14C is influenced by varitions in the primary cosmic ray flux and by charges of the Earth's magnetic field, which has experienced a number of significant perturbations during the late Quaternary (e.g. Lashamp Mono Lake excursion, circa 41 ka BP). Understanding these changes and synchronising variations in palaeomagnetic intensity derived from various marine sediment cores can often help constrain the quality of 14C dating, particularly in the interval between 20 and 50 ka ago, and establish reliable chronologies for ocean sedimentation rate changes. A common proxy for these palaeomagnetic changes is atmospheric fallout of 10Be in bulk sediments. However terrigenous and recycled sediments also deliver high 10Be concentrations thus strongly complicating the process required to isolate direct atmospheric from continental derived 10Be. As an alternative to geochemical speciation, grain size or leaching procedures in sediments we suggest that changes in 10Be concentrations in planktonic foraminifera can be used as a global stratigraphic marker. We are investigating planktonic foraminifera collected from Core MD - 982167, which was recovered from the Scott Plateau in the Eastern Indian Ocean at latitude of 13° S. The MD- 982167 already has an established stable isotope stratigraphy and a high sedimentation rate of 10 to 20 cm per ka. Initial results of paired 14C and 10Be determinations in foraminifera and fine fraction of the core sediments as a function of core depth have been obtained and subsequently will be compared to palaeomagnetic measurements currently in progress. An improved chronology for this high resolution core that has recorded brief, less than one thousand year duration, climatic events during the studied time interval will allow much better correlation between marine sedimentary records and the detailed chronologies established from the ice cores.
- ItemDeep level transient spectroscopy of n-GaAs surface barrier diodes for nuclear radiation detection(Australian Atomic Energy Commission, 1981-01) Pearton, SJ; Alexiev, D; Tavendale, AJ; Williams, AADeep level transient spectroscopy has been applied for the first time to the study of deep level defects in n-GaAs nuclear radiation detectors. Devices made from commercial bulk and epitaxial material with net donor impurity densities in the range 5 x 10 13 -3 x 10 16 cm -3 have been studied and several common levels observed. The Poole-Frenkel effect has been identified in three levels (Ev + 0.19 eV, Ec - 0.62 eV Ec - 0.73 eV) in the epitaxial GaAs. A value for the Poole-Frenkel constant of β = 4.7 ≥ 1.4 x 10-4 eV V-½ cm½ was obtained compared to the theoretical value for GaAs of 2.3 x 10-4 eV V-½ cm½.
- ItemDeep level transient spectroscopy of y-ray induced defects in germanium(Australian Atomic Energy Commission, 1980-12) Pearton, SJ; Williams, AA; Tavendale, AJDeep level transient capacitance spectroscopy has been used to examine γ-ray induced defect centres in germanium crystals grown under widely varying conditions. A deep acceptor level at Eν + 0.38 eν has been observed for the first time in all p-type samples; this was removed by annealing at 675 deg C for three hours. A new deep donor level at Eс - 0.42 eν observed in n-type material was not removed by this procedure.
- ItemDevelopment and characterisation of a small mass H2/Fe graphitisation line(12th International Conference on Accelerator Mass Spectrometry, 2011-03-24) Varley, S; Williams, AA; Nguyen, THWe will present the commissioning data for our prototype, small volume, conventional graphitisation line and a comparison will made with our 2.5 mL general purpose graphitisation lines. This new graphitisation line has an internal volume of ~1.1 mL and uses the H2/Fe graphitisation method. An Impress ME506 ceramic diaphragm pressure sensor is used in a custom stainless steel housing, which also incorporates the gas inlet valve and Ultratorr® style ports for connection of a replaceable graphitisation tube and cold finger. A custom designed, water cooled,resistance heated tube furnace is used to heat the Fe catalyst / reaction volume. To use with the new graphitisation line we have developed a small volume CO2 transfer line, which allows transfers from the sample combustion tube directly into the graphitisation line unit. This new transfer line has been developed using CF UHV fittings to minimise the possibility of sample contamination and leaks. Information will also be presented on a water-cooled, Peltier based chiller unit which is used to freeze out, at -52ºC, the water produced in the H2/Fe reaction. Protocols have been developed to minimise (and standardise) the quantity of the background carbon incorporated in the overall processing of the sample into graphite. Copyright (c) 2011 AMS12
- ItemDevelopments in micro-sample 14C AMS at the ANTARES AMS facility(Elsevier, 2010-04-01) Hua, Q; Williams, AA; Levchenko, VA; Ying, B; Smith, AMWe continue development of micro-sample radiocarbon sample preparation and AMS measurement at the ANTARES AMS facility. We routinely prepare samples containing 10–200 μg of carbon using an iron catalyst with an excess of hydrogen in 2.5 mL graphitisation reactors. These use a tube furnace to heat the catalyst to 600°C and a Peltier-cooled water trap. Samples containing just a few micrograms of carbon can be prepared. We describe progress with a 0.5 mL laser-heated ‘microfurnace’ we are developing for the rapid and efficient graphitisation of 5 μg samples. Following operating experience with a prototype unit, work has commenced on the development of a second-generation device with the goal of fully automated operation with minimal introduction of extraneous carbon. Key to development of micro-sample 14C AMS is the ability to reliably handle the graphite/iron sample and to mount it in the ion source target holder. We have developed a target holder that permits the sample to be loaded in a 1 mm diameter recess and rear pressed, ensuring a high quality surface finish, at a reproducible depth. Additionally we have developed a method for systematically aligning the sample stage with the cesium beam following ion source servicing. Crown copyright © 2009 Published by Elsevier B.V.
- ItemForensic applications of 14C bomb-pulse dating(Elsevier, 2004-08-01) Zoppi, U; Skopec, Z; Skopec, J; Jones, G; Fink, D; Jacobsen, GE; Tuniz, C; Williams, AAAfter a brief review of the basics of 14C bomb-pulse dating, this paper presents two unique forensic applications. Particular attention is dedicated to the use of the 14C bomb-pulse to establish the time of harvest of illicit drugs such as heroin and opium. Preliminary measurements of 14C concentrations in milligram samples taken from seized drugs are presented. 14C bomb-pulse dating can determine whether drug distribution originates from stockpiles or recent manufacture, and support the action of law enforcement authorities against criminal organisations involved in drug trafficking. In addition, we describe the dating of wine vintages for a number of authenticated single label vintage red wines from the Barossa Valley – South Australia. Our results show that radiocarbon dating can be used to accurately determine wine vintages and therefore reveal the addition of unrelated materials of natural and synthetic origin. © 2004 Elsevier B.V.
- ItemGraphitisation & measurement of microgram radiocarbon samples at ANSTO(Australian Nuclear Science and Technology Organisation, 2021-11-17) Smith, AM; Hua, Q; Varley, S; Williams, AA; Yang, BThe Centre for Accelerator Science (CAS) at ANSTO has been providing radiocarbon analyses for the user community and internal projects for two and a half decades. Early on, there was a need to develop the measurement capability for samples containing just tens of micrograms of carbon [1, 2]. We have continued to develop this capability since. At first effort was directed at optimising our ‘conventional’ graphitisation furnaces . These have a minimum reaction volume of ~ 2.5 mL and reduce CO₂ to graphite over an Fe catalyst at 600 °C in an excess of hydrogen. CAS operates a bank of 24 conventional furnaces which provide for the bulk of our sample graphitisation for samples containing > 5 μg of carbon. In 2003 we began developing a novel, miniaturised graphitisation furnace which used a focused infrared laser to heat the Fe catalyst in a quartz crucible, with the temperature measured indirectly by infrared thermometry . The prototype unit had an internal reaction volume of ~0.5 mL including pressure transducer and the two subsequent furnaces ~ 0.3 mL. These small volumes allow a higher initial pressure for small amounts of CO₂ , improving the efficiency of conversion to graphite. Efficient trapping of the water vapour produced during the reaction and careful selection of the catalyst are also key to optimising graphitisation of small samples [5, 6]. By localising the heated region within the reaction volume, the addition of extraneous carbon is minimised in these furnaces and samples containing just 1-2 μg of carbon are routinely prepared. The laser heated furnaces (LHF) are preferred for processing the very small samples derived from our ¹⁴ C in situ program . The fabrication approach developed for the LHF was adapted to a new type of miniaturised furnace we call micro-conventional furnaces (MCF) . These furnaces have a minimum reaction volume of ~ 0.9 mL with a small tube furnace to heat the catalyst. Variable temperature cold traps have been developed to optimise sample processing with samples as small as 5 μg of carbon routinely prepared. The MCF are used extensively in conjunction with ¹⁴ C measurements of CO, CO₂ and CH₄ derived from ice core and firn air samples. We present an overview of micro-sample graphitisation and measurement at CAS.
- ItemLoss and gain of carbon during char degradation(Elsevier, 2017-03-01) Bird, MI; McBeath, AV; Ascough, PL; Levchenko, VA; Wurster, CM; Munksgaard, NC; Smernik, RJ; Williams, AAWe report results of a study examining controls on the degradation of chars produced at 300, 400 and 500 °C from radiocarbon-free wood, deployed for three years in a humid tropical rainforest soil in north Queensland, Australia. The chars were subjected to four treatments (i) no litter (ii) covered by leaf litter, (iii) covered by limestone chips to alter local pH, and (iv) covered by limestone chips mixed with leaf litter. Radiocarbon, stable isotope and proximate analyses indicate significant ingress of exogenous (environmental) carbon and mineral material, strongly correlated with loss of indigenous (char) carbon from the samples. While indigenous carbon losses over three years were generally <8% for the char produced at 500 °C char under any treatment, chars formed at lower temperatures lost 5–22% of indigenous carbon accompanied by ingress of up to 7.5% modern exogenous carbon. The data provide clear evidence of a direct link between the ingress of exogenous carbon, likely at least partly due to microbial colonization, and the extent of char decomposition. Failure to account for the ingress of exogenous carbon will lead to a significant under-estimate of the rate of char degradation. © 2016, Elsevier Ltd.
- ItemRadiocarbon age constraints for a pleistocene–holocene transition rock art style: the northern running figures of the East Alligator River region, western Arnhem Land, Australia(Elsevier, 2017-02-01) Jones, T; Levchenko, VA; King, PL; Troitzsch, U; Wesley, D; Williams, AA; Nayingull, AIn this article we present nine radiocarbon age determinations producing a minimum age and a minimum age range for a regionally distinct rock art style known as the Northern Running Figures from Red Lily Lagoon, western Arnhem Land Australia. These radiocarbon determinations provide age constraints for both Pleistocene and early Holocene rock art in western Arnhem Land. The radiocarbon age determinations are produced from extracting calcium oxalate contained within mineral crusts associated with the rock art. Significantly this study employs a novel separation technique, designed to effectively isolate the oxalate compounds from the mineral crust sample using chemical pre-treatment, and demonstrates significant time offsets between radiocarbon age determinations for the calcium oxalates and other carbon inclusions contained within mineral crusts.© 2016, Elsevier Ltd.
- ItemTesting line for processing of dissolved inorganic carbon from water for radiocarbon dating determining the efficacy of trapping carbon dioxide for an automated system(Australian Nuclear Science and Technology Organisation, 2021-11-17) Yang, B; Williams, AA; Nguyen, TH; Varley, S; Freeman, PANSTO’s radiocarbon capability experiences a high demand for processing groundwater samples for studies in water resource sustainability. Currently water samples are processed manually using extraction of DIC by acidification of the water and sparging with high purity helium gas (He), then cryogenic trapping of the CO₂ with recirculation of the He carrier gas to effect complete trapping of the CO₂ . This method is based on that of McNichol et al. . In order to increase our capacity to extract the dissolved inorganic carbon (DIC), we are developing an automated DIC extraction system. To develop this system and test that efficacy of redesigned traps to completely capture the CO₂ without recirculation of the carrier gas, a manual test DIC line was set up to sparge acidified water with He. This line operates at ambient pressure (1 bar) and is filled with He. CO₂ gas is recovered from 50ml of the water sample by adding 5ml of 85% of phosphoric acid inside a 250ml reaction vessel. The He carrier gas is sparged at a flow rate of 30ml/min and then passed through two water traps to remove water; and two CO₂ traps to collect CO2 gas. Complete recovery of CO₂ is determined by passing the He flow through a CO₂ analyser to verify there is no presence of residual CO₂ gas. By using a temperature controller which was designed in-house the temperature of both the water trap and the CO₂ trap can be adjusted from -170°C to -60°Cwhich optimises the trapping temperature. We found that the best trapping temperatures for H₂ O and CO₂ are -110°C and -160°C, respectively. The CO₂ trapping efficiency of our system is over 99%, this was tested by trapping a CO₂ /He gas mixture containing 1mg C of CO₂ gas. The CO₂ gas is then transferred into a storage vessel until all samples on the system are processed. The CO₂ is then manually transferred to break seals for purification of the CO₂ by heating to 600°C over CuO and Ag wire. The test line has also been tested with groundwater samples. Based on the test, we are going to construct an automated DIC line in which all manual valves in the testing line will be replaced by automated valves to be controlled by computer. In addition, the water samples selector and circulation loop were designed by refer the report . The system will enable the automated processing of 10 samples within 10 hours.
- ItemTime history of a human kidney stone determined by bomb-pulse dating(Cambridge University Press, 2015-01-06) Levchenko, VA; Williams, AAAn in vivo grown human kidney stone was dated using the atmospheric bomb pulse. The growth period was found to be 17.6 yr for a sample size of 6 mm across. The step dissolution method was used, as one of several possibilities, to produce depositional subsamples. A noticeable dead carbon presence is detected in the modern industrialized diet, and as a consequence in human metabolites. The importance for correction when applying bomb-pulse dating is noted. © 2016 by the Arizona Board of Regents on behalf of the University of Arizona
- ItemTransient capacitance measurements of deep level defects introduced in y-ray compensated germanium by long-term annealing at room temperature(Australian Atomic Energy Commission, 1980-09) Pearton, SJ; Williams, AA; Tavendale, AJ; Lawson, EMDeep level transient spectroscopy (DLTS) has been applied to defect centres in γ-ray compensated germanium that has been subjected to long-term annealing at room temperature. Deep donor levels (Ec - 0.36 eV Ec - 0.20 eV) have been observed for the first time; annealing at 675ºC for 3 hours increased their concentration in proportion to the free carrier density indicating stable defect-impurity complexes. Recently irradiated samples from the original material have not shown these levels. The results support Russian work on the compensation mechanism - the formation of electically inactive vacancy-donor complexes.
- ItemTransient conductance spectroscopy measurements of defect states in y-irradiated n-channel silicon field effect transistors with possible y-dosemeter applications(Australian Atomic Energy Commission, 1980-12) Pearton, SJ; Tavendale, AJ; Williams, AAA deep level transient capacitance spectroscopy (DLTS) system modified for the measurement of transient conductance has been used to observe gamma-ray induced defect centres in the gate junction of 2N4416 Si field effect transistors. The defect concentrations increased linearly wth gamma-dose in the range 50 kGy to 10 x 10 3 kGy (5-1000 Mrad) for the common E(c) - 0.17 eV level and in the range 500 kGy to 10 x 10 3 kGy (50- 1000 Mrad) for the levels E(c) - 0.22 eV and E(c) - 0.44 eV. Another common level a hole trap at E(v) + 0.42 eV was the only minority trap observed. The technique may be useful for measuring gamma-fluxes in situations inaccessible to standard dosemeters (e.g. flux-mapping).