ANSTO :: Browsing by Author "Lee, S"

Browsing by Author "Lee, S"

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A 1,500 year south Australian rainfall record based on speleothem hydrological proxies
(AMOS National Conference, 2013-02-11) McDonald, J; Drysdale, RN; Hua, Q; Hodge, E; Treble, PC; Greig, A; Fallon, SJ; Lee, S; Hellstrom, JC
Cave drip water studies at Wombeyan Caves (34°19’S, 149°59’E) demonstrated a marked hydrochemical response to wet/dry phases (McDonald Et al. 2004; 2007). Geochemical Variations in three 20th Century coeval active Speleothems were able to be linked to the instrumental record. Subsequently geochemical relationships were investigated in a long record speleothem(WM7) which grew deeper within the same cave system. Obtaining a robust chronology proved to be challenging, due to the young age of the speleothem and very low uranium concentrations (~10 ppb) the use of U‚Aeseries disequilibrium dating was ineffective to produce a robust chronology. Chronology for WM7 was based on a dense sequence of DCF corrected ages using three different age-‐depth models: Clam (Classical method), and Bacon and OxCal (Bayesian statistical approach) (Hua et al. 2012).The new chronology indicated that WM7 began growth around 4400 cal BP(171 mm). However, since sampling from 0-‐50mm was most intensive, the model is based on this part of the stalagmite and indicates that the top 50 mm of WM7 grew during the past 1360 and 1740 years. An aridity index based on Sr,P, Y, La, and Ba shows that over the last 1,500 years several sustained episodes of wet/arid and otherwise variable phases have occurred. Two sustained wet phases ~ 700-‐880 AD and ~ 900-‐ 1250 AD were followed by ~ 400 years of variable wet/dry conditions, although from ~1300 to 1600 AD a drying trend is indicated, but punctuated by several wetter episodes. The last 200 years indicate sustained drying phases. The OE￥13C record is anomalous from ~ 1880 to present and attributed to the stalagmite’s recording of increasing contribution of fossil fuel to CO2 concentrations. Within the longer-‐time scale oscillations, higher resolution (~ 2-‐5 years) variability is evident, replicating the trend shown by modern annually resolved stalagmites at this site.
Advanced sample environment support for neutron instruments at the Bragg Institute, ANSTO
(Australian Institute of Physics, 2016-02-04) Imperia, P; Booth, N; Lee, S; D'Adam, TM; Manning, AG
Over the last few years a number of advancements have been made in sample environments available to scientists visiting the Neutron Beam Facility run by the Bragg institute at ANSTO (Lucas Heights). Conventional sample environment equipment allows experiments to be carried out from 35mK to 1700K, magnetic fields up to 12T and electric fields up to 10kV. These extremes are not available on all neutron instruments nor with one piece of equipment. However combinations of temperature, magnetic and electric fields are also possible. These conventional sample environments will not be covered here. This presentation will outline advances made in the gas handling, vapour delivery, differential scanning calorimetry (DSC) and spectroscopy at extreme temperatures all carried out simultaneously with neutron data collection. Some examples of the complimentary data collected are also presented. Our automated gas handling system allows gas mixing (up to 4 gases), dosing (volumetric Sievert analysis) up to 200Bar, gas flow and molecular analysis with a dedicated mass spectrometer for kinetics investigations. The Hiden Isochema system is based on their commercial IMI system with the standard reaction chamber removed and replaced by thermalised capillary lines to allow the gas delivery to a sample reactor placed within a cryostat or furnace on the sample stage of our neutron instruments. Two options are available for vapour delivery. For samples that do not outgas a static system can be used where computer controlled valves control the vapour pressure. One valve is used to lower the pressure using a turbo pump and the second one to allow the vapour from the reservoir to increase the vapour pressure. Any non-corrosive liquid can be used in this system. The second vapour system, dynamically controls the vapour and dry gas flow allowing mixing of two vapours and a dry stream of gas or the recirculation of a saturated vapour through a sample reactor The DSC system is based on A Mettler Toledo model DSC1. The furnace has been moved to allow the passage of the neutron beam and Bragg designed crucibles are used to allow scattering experiments to be carried out while DSC data are collected. Quartz and Aluminium crucibles are available and temperature range of 550C to -100C is achievable. Using Ocean Optics spectrometer equipment we have successfully carried out NIR spectroscopy down to 4K while collecting Neutron diffraction data. The use a standard NIR reflection probe and modification of the cryostat sample stick allows the probe to be introduced into the cryostat. A second spectrometer is available for UV-Vis spectroscopy and can be used in a similar method. These spectrometers are also available for use on other scattering instruments over a limited temperature range.
Australian centre for neutron scattering: sample environment report
(Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-19) Manning, AG; Wakeham, D; Davidson, G; Booth, N; Imperia, P; White, R; Lee, S; D'Adam, TM
In the past 2 years since the 2016 AANSS symposium, the sample environment group of the Australian Centre for Neutron Scattering (ACNS) has continued to facilitate neutron experiments and expand sample environment capability. This report will present the current sample environment and laboratory facilities and recent developments. We have made progress in light irradiation and spectroscopy developments; on a new temperature controlled multi-sample changer with tumbling capability; on a rotational PE Cell; and on new sample probes made from composite materials. Other improvements include new high pressure couplings for helium compressors and modifications to a dilution insert to allow larger samples and use in other cryostats extending the capability. Ongoing major projects are a new superconducting split-coil magnet dedicated to SANS and TOFPAS, two new cryostats (1.5 K to 800 K temperature range) with the aim of halving the system and sample cooling time and a new dilution fridge that will allow top-loading of samples and the ability to take much larger samples than the existing dilution insert. There have also been staffing changes with previous Sample Environment Group Leader, Paolo Imperia moving into the Operations Manager position. The new group leader, Rachel White, was recently appointed. Our Laboratory Manager, Deborah Wakeham, joined us in July 2017. © The Authors.
Critical role of Ti4+ in stabilizing high-voltage redox reactions in Li-rich layered material
(Wiley, 2021-07-01) Cho, M; Song, SH; Hong, S; Kim, KS; Avdeev, M; Yoo, JG; Ko, KT; Hong, J; Kim, J; Lee, S; Kim, H
Li-rich layered oxide materials are considered promising candidates for high-capacity cathodes for battery applications and improving the reversibility of the anionic redox reaction is the key to exploiting the full capacity of these materials. However, permanent structural change of the electrode occurring upon electrochemical cycling results in capacity and voltage decay. In view of these factors, Ti4+-substituted Li2IrO3 (Li2Ir0.75Ti0.25O3) is synthesized, which undergoes an oxygen redox reaction with suppressed voltage decay, yielding improved electrochemical performance and good capacity retention. It is shown that the increased bond covalency upon Ti4+ substitution results in structural stability, tuning the phase stability from O3 to O1′ upon de-lithiation during charging compared with O3 to T3 and O1 for pristine Li2IrO3, thereby facilitating the oxidation of oxygen. This work unravels the role of Ti4+ in stabilizing the cathode framework, providing insight for a fundamental design approach for advanced Li-rich layered oxide battery materials.© 2021 Wiley-VCH GmbH
Crystal structure of a non-centrosymmetric system, CuY2Ge2O8
(International Conference on Neutron Scattering, 2017-07-12) Cho, H; Sim, H; Lee, S; Avdeev, M; Noda, Y; Park, JG
A non-centrosymmeric material doesn’t have an inversion symmetry, which could lead to the intrinsic electric polarization. When this system consists of magnetic ions, the electric polarization of the system can be modified by a so-called magnetoelectric coupling under magnetic field. This multiferroic property has been widely studied not only for physical interest but also for industrial application. We synthesized both single crystal and polycrystalline samples of new multiferroic systems, Cu(Y,La) Ge and determined the crystal structure at 300 and 450 K using high-resolution powder and single crystal diffraction studies. According to our studies, both samples having magnetic Cu2+ ions has a monoclinic unit cell (space group I 1 1) without inversion symmetry. We also determined the high temperature structure that has a more symmetric orthorhombic unit cell (I m m 2). Using the structural information, we could calculate the theoretical electric polarization at room temperature phase and found that it reaches the electric polarization of 9.88 μC/cm2 along the a-axis.
High‐voltage‐driven surface structuring and electrochemical stabilization of Ni‐rich layered cathode materials for Li rechargeable batteries
(Wiley, 2020-05-04) Song, SH; Cho, M; Park, I; Yoo, JG; Ko, KT; Hong, J; Kim, J; Jung, SK; Avdeev, M; Ji, S; Lee, S; Bang, J; Kim, H
Layered lithium–nickel–cobalt–manganese oxide (NCM) materials have emerged as promising alternative cathode materials owing to their high energy density and electrochemical stability. Although high reversible capacity has been achieved for Ni‐rich NCM materials when charged beyond 4.2 V versus Li+/Li, full lithium utilization is hindered by the pronounced structural degradation and electrolyte decomposition. Herein, the unexpected realization of sustained working voltage as well as improved electrochemical performance upon electrochemical cycling at a high operating voltage of 4.9 V in the Ni‐rich NCM LiNi0.895Co0.085Mn0.02O2 is presented. The improved electrochemical performance at a high working voltage at 4.9 V is attributed to the removal of the resistive Ni2+O rock‐salt surface layer, which stabilizes the voltage profile and improves retention of the energy density during electrochemical cycling. The manifestation of the layered Ni2+O rock‐salt phase along with the structural evolution related to the metal dissolution are probed using in situ X‐ray diffraction, neutron diffraction, transmission electron microscopy, and X‐ray absorption spectroscopy. The findings help unravel the structural complexities associated with high working voltages and offer insight for the design of advanced battery materials, enabling the realization of fully reversible lithium extraction in Ni‐rich NCM materials. © 2020 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim
Integration of polarised 3He infrastructure with sample environment equipment
(Australian Institute of Physics, 2017-01-31) D'Adam, TM; Booth, N; Davidson, G; Lee, S; Manning, AG; Timperon, N; Imperia, P
Many challenges exist when attempting to integrate polarised 3He infrastructure with neutron beam instruments. This is often due to its sensitivity to the magnetic environment and also due to the compact geometry of many beam lines. One additional consideration is the effect that Sample Environment equipment can have on the functionality of a particular polarised neutron setup. We have been able to provide incident beam polarisation with two separate magnets providing fields at the sample position of up to 2 T. In addition, full polarisation analysis is possible over a temperature range of 30 mK to 800 K. To enable this, some pieces of Sample Environment equipment must be designed specifically for use with polarised 3He and in many cases modifications are necessary to accommodate the sensitive gas. We are also in the process of procuring an 8 T shielded asymmetric magnet suitable for use with polarised 3He infrastructure.
Investigating the origin of salinity and aquifier interaction in a sesonally pumped confined aquifier system in southeast Australia (Western Port Basin)
(Geological Society of Australia, 2014-07-07) Lee, S; Currell, MJ; Cendón, DI
This ongoing study aims to identify the different sources of fresh/saline water, pathways, mechanisms of groundwater salinisation, and factors controlling salt-water intrusion in the Western Port Basin aquifer (Victoria, Australia). The multi-layered aquifer is characterised by variable distributions of fresh and saline groundwater at the coastline, which are speculated to result due to geological heterogeneity, and the influence of past sea levels. The spatial salinity distribution observed indicates that the typical situation of a dense saltwater wedge underlying fresh groundwater does not apply. Further to natural drivers, an understanding of the potential short and long term effects of seasonal pumping for irrigation in the basin is desired, particularly whether it induces migration of water from other areas in the basin or causes leakage from low-permeability horizons. The impact of seasonal pumping on the variation and distribution of salinity was examined at a nested bore site 500 m from the coast. Analyses of chloride concentration and δ18O in groundwater indicate various degrees of mixing between seawater and fresh meteoric groundwater. Multi-depth sampling in the upper aquifer, identified high salinity water with ~19% seawater mixture above slightly less saline water – with ~17% seawater; while samples from the lower aquifer yielded significantly fresher groundwater (~4 to 7% seawater). This is likely to be due to the relatively good connection between the upper aquifer and the ocean, and low-permeability material separating the shallow and deeper aquifers. Seasonal salinity changes were observed as a response to pumping, with salinity in the upper aquifer decreased by ~15.5% at the onset of pumping, and salinisation gradually increased once pumping ceased by ~22%. Recent 14C dating of groundwater in the proximity of the pumping area revealed low radiocarbon activities (<25 pMC) and a lack of tritium, which rules out the possibility of modern recharge reaching the pumping area. A thick Holocene clay cap (ranging from 10 to 30 m) covering significant areas and extending beneath the bay, limits rainfall recharge to the basin margins where the aquifers outcrop. Beneath the shallow bay a paleoriver channel incised deep into the bay floor sediments expose the aquifer to potential vertical and horizontal input from modern seawater. However, the lack of long-term salinisation despite decades of pumping, and the relatively old groundwater ages, imply buffering against saline intrusion by stores of relict fresh water. Incorporation of these results into a conceptual model will contribute to an improved understanding of the groundwater flow system and the long-term implications of pumping on future groundwater sustainability in the Western Port Basin.
Magnetic transitions in the chiral armchair-kagome system Mn2Sb2O7
(American Physical Society, 2017-01-20) Peets, DC; Sim, H; Choi, S; Avdeev, M; Lee, S; Kim, SJ; Kang, H; Ahn, D; Park, JG
The competition between interactions in frustrated magnets allows a wide variety of new ground states, often exhibiting emergent physics and unique excitations. Expanding the suite of lattices available for study enhances our chances of finding exotic physics. Mn2Sb2O7 forms in a chiral, kagome-based structure in which a fourth member is added to the kagome-plane triangles to form an armchair unit and link adjacent kagome planes. This structural motif may be viewed as intermediate between the triangles of the kagome network and the tetrahedra in the pyrochlore lattice. Mn2Sb2O7 exhibits two distinct magnetic phase transitions, at 11.1 and 14.2 K, at least one of which has a weak ferromagnetic component. The magnetic propagation vector does not change through the lower transition, suggesting a metamagnetic transition or a transition involving a multicomponent order parameter. Although previously reported in the P3121 space group, Mn2Sb2O7 actually crystallizes in P2, which allows ferroelectricity, and we show clear evidence of magnetoelectric coupling indicative of multiferroic order. The quasi-two-dimensional “armchair-kagome” lattice presents a promising platform for probing chiral magnetism and the effect of dimensionality in highly frustrated systems. ©2017 American Physical Society
Marine water from mid-holocene sea level highstand trapped in a coastal aquifer: Evidence from groundwater isotopes, and environmental significance
(Elsevier, 2016-02-15) Lee, S; Currell, MJ; Cendón, DI
A multi-layered coastal aquifer in southeast Australia was assessed using environmental isotopes, to identify the origins of salinity and its links to palaeo-environmental setting. Spatial distribution of groundwater salinity (electrical conductivity values ranging from 0.395 to 56.1 mS/cm) was examined along the coastline along with geological, isotopic and chemical data. This allowed assessment of different salinity sources and emplacement mechanisms. Molar chloride/bromide ratios range from 619 to 1070 (621 to 705 in samples with EC > 15 mS/cm), indicating salts are predominantly marine. Two distinct vertical salinity profiles were observed, one with increasing salinity with depth and another with saline shallow water overlying fresh groundwater. The saline shallow groundwater (EC = 45.4 to 55.7 mS/cm) has somewhat marine-like stable isotope ratios (δ18O = − 2.4 to − 1.9 ‰) and radiocarbon activities indicative of middle Holocene emplacement (47.4 to 60.4 pMC). This overlies fresher groundwater with late Pleistocene radiocarbon ages and meteoric stable isotopes (δ18O = − 5.5 to − 4.6‰). The configuration suggests surface inundation of the upper sediments by marine water during the mid-Holocene (c. 2–8 kyr BP), when sea level was 1–2 m above today's level. Profiles of chloride, stable isotopes, and radiocarbon indicate mixing between this pre-modern marine water and fresh meteoric groundwater to varying degrees around the coastline. Mixing calculations using chloride and stable isotopes show that in addition to fresh-marine water mixing, some salinity is derived from transpiration by halophytic vegetation (e.g. mangroves). The δ13C ratios in saline water (− 17.6 to − 18.4‰) also have vegetation/organic matter signatures, consistent with emplacement by surface inundation and extensive interaction between vegetation and recharging groundwater. Saline shallow groundwater is preserved only in areas where low permeability sediments have slowed subsequent downwards propagation. The configuration is unlikely to be stable long-term due to fluid density; this may be exacerbated by pumping the underlying aquifer. © 2015, Elsevier B.V.
New sample environment projects and developments at the Australian Centre for Neutron Scattering
(Australian Institute of Physics, 2019-02-05) White, R; Imperia, P; Booth, N; D'Adam, TM; Davidson, G; Lee, S; Manning, AG; Tobin, S
Since the 2018 meeting the sample environment team at the Australian Centre for Neutron Scattering (ACNS) has progressed the design and construction of the new superconducting split-coil magnet, a fast cooling closed cycle cryostat and a new type of closed cycle dilution refrigerator. The first of the two fast cooling cryostats (compact closed cycle dry cryostats, 1.5 K to 800 K) will arrive in early 2019, with a tested sample cool down of 30 minutes. The new magnet is in the final stages of design, including a sample well for our time-of-flight spectrometer PELICAN. The new magnet will have active magnetic shielding and an asymmetric coil design to allow experiments with polarised neutrons. The expected arrival for the magnet is mid-2019. The closed cycle dilution refrigerator will have high cooling power and a very large sample space allowing a new class of experiments with neutrons at ultra-low temperature, arriving in March 2019. Also presented is the development of carbon fibre sample probes to enable faster cooling and quicker sample changes.
New sample environment projects and developments at the Australian Centre for Neutron Scattering
(International Conference on Neutron Scattering, 2017-07-12) Imperia, P; Booth, N; D'Adam, TM; Davidson, G; Lee, S; Manning, AG
The sample environment team at the Australian Centre for Neutron Scattering (ACNS) has been recently awarded funding for a new superconducting split-coil magnet, a fast closed cycle cryostat and a closed cycle dilution refrigerator of the latest generation. The new magnet design is of particular interest; the brief is complicated by the request to serve two separate classes of instruments: small angle scattering and time of flight. The magnet will have low fringe field, active shield design, and specific requirements for the asymmetric field gradient to allow experiments with polarised neutrons. Low fringe field values are combined with a minimum central field of 7 Tesla, wide “clean” scattering angle and dimensional and weight constraints. The design challenges and possible solutions will be detailed, together with a time frame for delivery and commissioning. The new compact closed cycle cryostat (1.5 K to 800 K) with a small He dump, aims to halve the system and sample cooling time, generating performances comparable to that of wet type “orange” cryostats without the necessity to refill with cryogenic liquids. The closed cycle dilution refrigerator will have high cooling power and large sample space, allowing new class of experiments with neutrons at ultra-low temperature. The most recent equipment built in-house and unique to the ACNS, such as the Peltier sample changer and the thermalised sample tumblers for SANS and USANS, will also be discussed.
New sample environment projects and developments at the Australian Centre for Neutron Scattering.
(Australian Institute of Physics, 2018-01-30) Imperia, P; Booth, N; D'Adam, TM; Davidson, G; Lee, S; Manning, AG; Tobin, S
A peltier controlled sample changer for SANS
(Australian Institute of Nuclear Science and Engineering, 2016-11-29) Lee, S; Booth, N; Imperia, P; Davidson, G
A twelve position sample changer for SANS instruments at ACNS has been developed and will be available for users in the near future. The design philosophy for this project was to make the system as modular and scalable as possible with an emphasis on ease of use for the user and reduced background. The Peltier control system allows each sample to be controlled at different temperatures and allows the possibility of producing very fast temperature changes over a limited range. The system can be controlled via a local Watlow™ touchscreen and remotely via the SICS based neutron instrument control system used at ACNS. The liquid cooled heatsink for the Peltiers provides the support for the spring loaded sample holders, allowing rapid sample changes. The width of the sample changer has been reduced compared to the existing 20 position and with Borated aluminium shielding the background with blocked beam has been improved. The temperature sensors used are K-type thermocouples. Performance and stability tests will be presented. A design for uSANS is being developed.
Preparation of certified reference materials for gross alpha beta measurement
(South Pacific Environmental Radioactivity Association, 2018-11-06) Wilsher, KL; Harrison, JJ; van Wyngaardt, WM; Lee, S; Mokhber-Shahin, L
Gross alpha beta measurement techniques are used for rapid radioanalytical screening of both solid and liquid samples for environmental, scientific and industrial purposes. A number of gross alpha beta measurement techniques are available depending on the sample matrix and each should report the gross or total alpha or beta radioactivity relative to the alpha or beta emitting radionuclide in the calibration source. To establish measurement accuracy and reliability, certified reference materials (CRMs) which are traceable to a national standard should be used to prepare a calibration source in the same geometry as the sample. it was our aim to develop solid CRMs for gross alpha beta techniques using a quartz mineral spiked with standardised and traceable radiotracer solutions. The quartz mineral was pulverised and then sieved to prepare a starting material which had a narrow particle size distribution range to reduce the likelihood of size fractionation. A standard operating procedure for the Malvern Mastersizer 2000 was developed to assess the adequacy of the starting material with the effect of ultrasonics and pump speed being investigated. The starting material vi/as spiked with either 241Am or spiking 99Sr/90Y to prepare the alpha CRM or beta CRM respectively. The solutions were standardised by ANSTO Radionuclide Metrology to provide direct traceability to the Austral an National Standard tor Radioactivity. Spiking was performed using the acetone bath method. The sieved quartz material was mixed with acetone in a large round-bottom flask and accurately known quantities of radionuclide solution added. The flask was rotated on a rotary evaporator tor a few hours to ensure an even distribution of the radionuclide through the quartz. The acetone was evaporated, the dry spiked quartz material transferred to a poly-ethylene bottle and further homogenised by shaking for a few hours using a Turbula mixer. Homogeneity testing using 10 aliquots from each CRM and radionuclide losses on the rotary evaporator glassware and mixing vessel were established using radiochemical separation and alpha spectrometry tor 24‘Am and Liquid Scintillation Counting (LSC) for 90Sr/90Y. Each sample for testing underwent a separation and purification process that included dissolution, precipitation and re-dissolution and column purification using Eichrom® pre-packed cartridge stack of TEVA®, TRU® and Sr-Spec® resins. Canberra Alpha Analyst and Apex Alpha Counting Software was used tor Alpha spectrometry and 90Sr/90Y was measured on a Packard Tri Carb 3lOOTR LSC. This CRM is intended to be used in gross alpha beta counting instrumentation such as gas flow proportional counters and plastic scintillator detector chambers in accordance with lSO18589-6 Measurement of radioactivity in the environment — Soil Part 6: Measurement of gross alpha and gross beta activities and ultimately to be available tor commercial use.
Primary standardisation of technetium-99m by liquid scintillation coincidence counting
(Elsevier B. V., 2020-02) van Wyngaardt, WM; Tobin, SM; Lee, S; Smith, ML; Jackson, TW; Ilter, J; Howe, B; Sarbutt, A
Technetium-99m was standardised by the 4π(LS)ce-γ coincidence extrapolation method. Sensitivity of the 4π(LS) channel to two types of radiation, namely conversion electrons and γ-rays, resulted in incorrect activity values being obtained when this was not adequately accounted for. Measurements were more robust when the LS detection efficiency was optimised, and when a γ-window setting was used that monitored the combined LS efficiency for conversion electrons and γ-rays. The primary standard was internationally compared through participation in the BIPM.RI(II)-K4.Tc99m key comparison. © 2019 Elsevier Ltd
Properties of spin-1/2 triangular-lattice antiferromagnets CuY2Ge2O8 and CuLa2Ge2O8
(American Physical Society, 2017-04-05) Cho, H; Kratochvílová, M; Sim, H; Choi, KY; Kim, CH; Paulsen, C; Avdeev, M; Peets, DC; Jo, Y; Lee, S; Noda, Y; Lawler, MJ; Park, JG
We found new two-dimensional (2D) quantum (S=1/2) antiferromagnetic systems: CuRE2Ge2O8 (RE=Y and La). According to our analysis of high-resolution x-ray and neutron diffraction experiments, the Cu network of CuRE2Ge2O8 (RE=Y and La) exhibits a 2D triangular lattice linked via weak bonds along the perpendicular b axis. Our bulk characterizations from 0.08 to 400 K show that they undergo a long-range order at 0.51(1) and 1.09(4) K for the Y and La systems, respectively. Interestingly, they also exhibit field induced phase transitions. For theoretical understanding, we carried out the density functional theory (DFT) band calculations to find that they are typical charge-transfer-type insulators with a gap of Eg≅2eV. Taken together, our observations make CuRE2Ge2O8 (RE=Y and La) additional examples of low-dimensional quantum spin triangular antiferromagnets with the low-temperature magnetic ordering. ©2017 American Physical Society
Robust chronological reconstruction for young speleothems using radiocarbon
(Elsevier Science Ltd, 2012-12-01) Hua, Q; McDonald, J; Redwood, D; Drysdale, RN; Lee, S; Fallon, SJ; Hellstrom, JC
We have studied two young speleothems, SC4 from Smiths Cave (Christmas Island, eastern Indian Ocean) and WM7 from Wollondilly Cave (Wombeyan caves, SE Australia). Attempts to date these speleothems by the Th/U method have proved unsuccessful with some age reversals for SC4 due to multiple sources of non-authigenic Th. This method has also resulted in imprecise ages for WM7 because of low U concentrations (<10 ppb) and consequently very low levels of authigenic Th-230 relative even to the very low levels of detrital Th-230 present. Here, we present an alternative method for reliable dating of these young speleothems using radiocarbon. Approximately 100 carbonate samples from SC4 and WM7 were analysed for C-14 by accelerator mass spectrometry (AMS). The AMS results indicate that bomb C-14 was evident in the youngest parts of both stalagmites. Two different approaches were used to estimate dead carbon fraction (DCF) values for these stalagmites for the pre-bomb period. For SC4, the DCF values were estimated based on the timing of C-14 dates for that period determined by high-resolution delta O-18 recorded in the speleothem, and the timing of the onset of bomb C-14. For WM7, a "maximum" range of pre-bomb DCF was determined. Chronologies of these speleothems were built based on a dense sequence of DCF-corrected ages using three different age-depth models: Clam (Classical method), and Bacon and OxCal (Bayesian statistical approach). Good agreement between these age-depth models were observed indicating that the top 170 mm of SC4 and the top 50 mm of WM7 grew during the past 550-750 years and 1360-1740 years, respectively. © 2012, Elsevier Ltd.
Robust chronological reconstruction for your speleothems using radiocarbon
(18th INQUA Congress, 2011-07-21) Hua, Q; McDonald, J; Redwood, D; Drysdale, RN; Lee, S; Fallon, SJ; Hellstrom, JC
U/Th dating method is usually employed to build precise and reliable chronologies for speleothems. However, for some speleothems U-series dates may not be useful. We have studied two young speleothems, SC4 from Smiths Cave (Christmas Island, eastern Indian Ocean and WM7 from Wollondilly Cave (Wombeyan caves, SE Australia), with the aim to get a better understanding of past climate and rainfall variability beyond the instrumental records. Attempts to date SC4 by the U/Th method have proved unsuccessful with some age reversals due to multiple sources of non-authigenic Th. In addition, a sample close to the base of speleothem WM7 dated by U-series resulted in an imprecise age of ~4000 ± 500 cal BP (2?), which is due to the fact WM7 has low uranium concentrations (<10 ppb) and consequently contains very low levels of authigenic 230Th for a good U/Th age determination. In this paper, we investigate the possibility of using radiocarbon for the reconstruction of reliable chronologies for these young speleothems. Approximately 100 carbonate samples from the two stalagmites were analysed for 14C using the AMS facilities at ANSTO and ANU. The AMS results indicated that bomb 14C was evident in the youngest parts of both stalagmites. Dead carbon fraction (DCF) values for these stalagmites for the pre-bomb period were estimated based on the timing of 14C dates for that period determined by high-resolution stable isotopes recorded in the speleothems (?18O for SC4 and ?13C for WM7), and the timing of the onset of bomb 14C. Chronologies of these speleothems were built based on a dense sequence of AMS dates using 3 different age-depth models, OxCal and Bacon (Bayesian statistical approach) and Clam (non-Bayesian statistical model). The result of our radiocarbon-based chronologies and their reliability will be discussed for different DCF values including the mean DCF for the pre-bomb period and for different age-depth models. Copyright (c) 2011 INQUA 18
Three impossible things before lunch - the task of a sample environment specialist
(IOS Press, 2017-11-16) Booth, N; Davidson, G; Imperia, P; Lee, S; Stuart, BH; Thomas, PS; Komatsu, K; Yamane, R; Prescott, SW; Maynard-Casely, HE; Nelson, A; Rule, KC
In the course of their day, sample environment professionals can be confronted by numerous technical challenges applicable to a range of scientific questions. This paper presents three successful outcomes from user-posed sample environment challenges for in situ neutron scattering experiments undertaken at the Australian Centre for Neutron Scattering (formerly the Bragg Institute). The sample environments presented here have nothing in common other than their novelty. They may not be the best solution but have been constrained by time, resources and ability. The questions the users posed were: Can we mount a cylinder in cylinder (CIC) rheometer, more regularly used on a small angle scattering instrument, on a diffraction instrument and obtain usable data? Can we supply high-voltage (up to 10 kV) across a sample within the Paris–Edinburgh press while mounted on a powder diffraction instrument? And finally can a Lakeshore 340 and an in-house built liquid conductivity cell do the job of a commercial liquid conductivity meter? This paper presents the engineering and equipment solutions that were used to answer these questions, and in each case the scientific users left with useful, intriguing and, hopefully, publishable data. © 2017 IOS Press

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