Browsing by Author "Varley, S"
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- ItemANSTO AMS facility sample processing and target preparation: an update(20th International Radiocarbon Conference, 2009-06-01) Jacobsen, GE; Barry, LA; Bertuch, F; Hua, Q; Mifsud, C; Pratap, P; Reilly, N; Varley, S; Williams, AGThe ANSTO AMS Facility has been operating for the past 17 years, and comprises two accelerators complemented with a suite of chemistry laboratories dedicated to the processing of samples for carbon, beryllium, aluminium, iodine, and actinide analyses. The facility performs and supports a wide range of research in the areas of paleoclimate change, water resource sustainability, archaeology, geomorphology, and nuclear safeguards. As a result, the chemistry laboratories are called upon to process a large variety of sample types and increasing numbers of samples. The radiocarbon laboratories process charcoal, wood, sediments, pollen, carbonates, waters, textiles, and bone though the pretreatment stages, combustion or hydrolysis, and graphitization. Over the years, we have continually worked to improve pretreatment methods, reduce sample size, and reduce background. Construction of a dedicated low-background combustion and graphitization system is underway. The cosmogenic laboratories process quartz-bearing rocks and sediments through cleaning, dissolution, separation, and purification of Be and Al and preparation of targets as oxides. In this poster, we will summarize the current methods and developments in the radiocarbon and cosmogenic chemistry laboratories.
- 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.
- ItemCharacterization and ongoing development of the ANSTO AMS radiocarbon small mass H2/Fe graphitization lines(20th International Radiocarbon Conference, 2009-06-01) Williams, A; Varley, SThe ANSTO AMS radiocarbon graphitization laboratory was originally established with a set of 8 graphitization lines, using Zn/Fe and having volumes around 10 to 13 mL. As the demand for smaller sample masses increased, 12 smaller volume (~3.5 mL) H2/Fe graphitization lines were developed. These lines proved to be versatile, as the operating volume could be varied by changing the volume of a removable cold finger, allowing small mass samples of <100 μg C up to ~3 mg C to be graphitized reliably. Following the success of these lines, the original Zn/Fe lines were replaced in 2004 with a second set of 12 H2/Fe lines. In 2006, following the serial failure of the original gauges used for the 3.5-mL lines we had the opportunity to decrease the reaction volume further and thus reduce the graphitization mass limit. This poster will describe the smaller volume (~2.5 mL) versions, of the original H2/Fe graphitization lines; these new lines were developed using stainless steel diaphragm pressure sensors. This development was successful in extending our lower working mass limit down to ~10 μg C at ~50% graphitization efficiency, while still retaining the flexibility to graphitize up to ~3 mg C reliably. We will present the efficiency data and the characterization tests that these lines underwent, following their rebuilding as ~2.5-mL lines. In addition, we will present the development of new graphitization lines, which are in the process of construction. These comprise 3 very small volume (~0.9 mL) H2/Fe graphitization lines (using ceramic diaphragm pressure sensors), with the primary objective of minimizing, and stabilizing, the absolute mass of added extraneous carbon and stabilizing its pMC value. To assist in this objective, we are also developing revised methods for our sample combustion and transfer procedures, and the development of a modified transfer line. Preliminary results from this work will be presented.
- 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
- 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 [3]. 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 [4]. 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 [7]. The fabrication approach developed for the LHF was adapted to a new type of miniaturised furnace we call micro-conventional furnaces (MCF) [8]. 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.
- ItemPhysical hydrogeology and environmental isotopes to constrain the age, origins, and stability of a low-salinity groundwater lens formed by periodic river recharge: Murray Basin, Australia.(Elsevier, 2010-01-15) Cartwright, I; Weaver, TR; Simmons, CT; Fifield, LK; Lawrence, CR; Chisari, R; Varley, SA low-salinity (total dissolved solids, TDS, <5000 mg/L) groundwater lens underlies the Murray River in the Colignan–Nyah region of northern Victoria, Australia. Hydraulic heads, surface water elevations, δ18O values, major ion geochemistry, 14C activities, and 3H concentrations show that the lens is recharged from the Murray River largely through the riverbank with limited recharge through the floodplain. Recharge of the lens occurs mainly at high river levels and the low-salinity groundwater forms baseflow to some river reaches during times of low river levels. Within the lens, flow through the shallow Channel Sands and deeper Parilla Sands aquifers is sub-horizontal. While the Blanchetown Clay locally separates the Channel Sands and the Parilla Sands, the occurrence of recently recharged low-salinity groundwater below the Blanchetown Clay suggests that there is considerable leakage through this unit, implying that it is not an efficient aquitard. The lateral margin of the lens with the regional groundwater (TDS >25,000 mg/L) is marked by a hectometer to kilometer scale transition in TDS concentrations that is not stratigraphically controlled. Rather this boundary represents a mixing zone with the regional groundwater, the position of which is controlled by the rate of recharge from the river. The lens is part of an active and dynamic hydrogeological system that responds over years to decades to changes in river levels. The lens has shrunk during the drought of the late 1990s to the mid 2000s, and it will continue to shrink unless regular high flows in the Murray River are re-established. Over longer timescales, the rise of the regional water table due to land clearing will increase the hydraulic gradient between the regional groundwater and the groundwater in the lens, which will also cause it to degrade. Replacement of low-salinity groundwater in the lens with saline groundwater will ultimately increase the salinity of the Murray River reducing its utility for water supply and impacting riverine ecosystems. © 2010, 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. [1]. 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 [2]. The system will enable the automated processing of 10 samples within 10 hours.