ANSTO :: Browsing by Author "Fifield, LK"

Browsing by Author "Fifield, LK"

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59Ni production rates in mesosiderites measured with AMS
(Wiley, 1993-07-01) Fink, D; Tuniz, C; Herzog, G; Albrecht, A; Fifield, LK; Allen, GL; Paul, M
The cosmogenic radionuclide 59 Ni(t1/2=76ka) has great potential as a monitor of thermal neutrons in metal-rich extraterrestrial materials. In deep samples from larger meteoroids (which can support a big neutron flux) containing >1% or so of nickel, thermal neturon capture on 58Ni (delta th=4.6b) is the dominate production mechanism. Near the surface of millimeter-sized bodies production occurs via primary proton, fast neutron, and a reaction channels on Fe, Co, and Ni. We have applied AMS to the measurement of 59Ni activities (see [1] for details) in four samples from the metal phase to f the mesosiderites Estherville (fall,1879) and Budulan(find). The activities range from 1.5 to 3.5 dmp/g-Ni. Related work is described in [2,3]. To discuss neutron fluxes in Budulan, we must correct the measured 59Ni activities for terrestrial age. By using measured 41Ca activities (13-19 dpm/kg-Fe [4]) and a maximum production rate PFe(41Ca), in stony irons of 21dpm/kg-Fe [5] we deduce a maximum terrestrial age of 35 ka. After correction for this terrestrial age and normalization of L-chondrite composition [6], the production rates of 59Ni,PFe(59Ni), range from 5-13 dpm/g-Ni; these values are 2-3x greater than those reported in [7] for large irons and ~10x those for chondrites. Albrecht et al. [4] and Fink et al. [8] present 41Ca data in the silicate and metal phases from the same Estherville and Budulan samples. If thermal neutron production were solely responsible for PFe(59Ni) and PS2(41Ca) (the latter corrected for spalliation of oxidized iron in pyroxene), the thermal neutron fluxes, o, inferred from each nuclide in a sample should be the same. We deduce ratios of o(59Ni)/o(41Ca) that range from 0.75 to 1.65. Differences in epithermal yields can account for only a minor fraction of this variation as the ratio of the total resonant neutron absorption intergrals for 40Ca and 58Ni is within 10% of the ratio of the thermal neutron cross sections alone. A twofold change in Budulan's terrestrial age alters the flux ratio by 10% at most. Like 41Ca[9,10], PFe(59Ni) can be used to estimate shielding depths and lower limits on the preatmospheric radius. Calculations by [11] give a maximum value for PFe(59Ni) of 22 atoms/min/g-Ni at the center of an L chondrite with a radius of 300 g/cm2. The 10Be and 26A1 activities in Estherville [5] and respective semi-empirical production rate formulas [12] set a maximum meteoroid radius of 300 g/cm2. Our measured value for 59Ni implies a lower radius limit of 150 g/cm2 and shielding depths of 60-150g/cm2. Similarly, we suggest a radius of 200< R < 400 g/cm2 and shielding depths from 40-200 g/cm2 for Budalan. We infer that the above samples originated at relatively large depths (except for perhaps Budulan 2428) in meteoroids with preatmospheric radii >30cm, assuming a mesosiderite density of 5.5 g/cm3. Interestingly, those samples (Budulan2357 and Estherville 3311) having 41Ca production rates that indicate a higher degree of shielding have flux rations equal to or less than 1; the other two samples have 41Ca contents typical of near-surface exposure and have ratios o(59Ni)/o(41Ca) larger than unity. This correlation indicates that P59 from fast neutron reactions on 60,61Ni enhances 59Ni production at near-surface regions.
Biomedical applications of accelerator mass spectrometry
(Elsevier, 2010-07-30) Fifield, LK; Fink, D
No abstract available.
Constraining groundwater flow, residence ties, interaquifer mixing and aquifer properties using environmental isotopes in the southeast Murray Basin, Australia
(Elsevier B.V., 2012-09-01) Cartwright, I; Weaver, TR; Cendón, DI; Fifield, LK; Tweed, SO; Petrides, B; Swane, IC
Environmental isotopes (particularly δ18O, δ2H, and δ13C values, 87Sr/86Sr ratios, and a14C) constrain geochemical processes, recharge distribution and rates, and inter-aquifer mixing in the Riverine Province of the southern Murray Basin. Due to methanogenesis and the variable δ13C values of matrix calcite, δ13C values are highly variable and it is difficult to correct 14C ages using δ13C values alone. In catchments where δ13C values, 87Sr/86Sr ratios, and major ion geochemistry yield similar a14C corrections, ∼15% of the C is derived from the aquifer matrix in the silicate-dominated aquifers, and this value may be used to correct ages in other catchments. Most groundwater has a14C above background (∼2 pMC) implying that residence times are <30 ka. Catchments containing saline groundwater generally record older 14C ages compared to catchments that contain lower salinity groundwater, which is consistent with evapotranspiration being the major hydrogeochemical process. However, some low salinity groundwater in the west of the Riverine Province has residence times of >30 ka probably resulting from episodic recharge during infrequent high rainfall episodes. Mixing between shallower and deeper groundwater results in 14C ages being poorly correlated with distance from the basin margins in many catchments; however, groundwater flow in palaeovalleys where the deeper Calivil–Renmark Formation is coarser grained and has high hydraulic conductivities is considerably more simple with little inter-aquifer mixing. Despite the range of ages, δ18O and δ2H values of groundwater in the Riverine Province do not preserve a record of changing climate; this is probably due to the absence of extreme climatic variations, such as glaciations, and the fact that the area is not significantly impacted by monsoonal systems. © 2020 Elsevier B.V
Differences in groundwater and chloride residence times in saline groundwater: the Barwon River Catchment of Southeast Australia
(Elsevier B. V., 2017-02-20) Howcroft, W; Cartwright, I; Fifield, LK; Cendón, DI
The residence times of groundwater and chloride and the processes contributing to the development of saline (total dissolved solids (TDS) up to 45,379 mg/L) groundwater within the Barwon River Catchment of southeast Australia were investigated using major ion, stable isotope (δ18O, δ2H, and δ13C) and radioactive isotope (3H, 14C, 36Cl) geochemistry. The elevated groundwater salinity in the region is primarily due to evapotranspiration and recycling of solutes in saline lakes with minor contributions from weathering of halite, silicate and calcite minerals. Groundwater residence times estimated from 14C vary from modern to ~ 20 ka; for groundwater with lower 14C activities, the estimated residence times vary significantly depending on the assumed flow model and the 14C activity of recharge. Chloride residence times downgradient of Lake Murdeduke (a saline through-flow lake in the centre of the catchment) are greater than the corresponding groundwater residence times due to the recycling of Cl within the lake. Precise estimates of chloride residence time could not be determined using 36Cl due to R36Cl in precipitation being lower than that of groundwater. This is most likely due to R36Cl values in rainfall having been higher in the past than they are at present due to climate variability. δ18O, δ2H, and δ13C values also suggest that the region has experienced increasingly more evaporative conditions with time. The results of this study demonstrate that, while Cl is a useful tracer of hydrological processes, it must be applied carefully in arid and semi-arid regions of the world. In particular, recharge rates calculated using chloride mass balance may be underestimated where recycling of Cl has occurred. Crown Copyright © 2017 Published by Elsevier B.V.
Environmental applications of accelerator mass spectrometry
(Elsevier, 2010-09-01) Fifield, LK; Fink, D
Eroding Australia: slowly.
(Elsevier, 2008-07) Heimsath, AM; Chappell, J; Hancock, GR; Fink, D; Fifield, LK
We use in situ produced 10Be and 26Al to quantify erosion rates across a wide variety of field settings in Australia. Here we present the full suite of data from our diverse studies to provide an overview of how Austalia is eroding, as well as showing how robust this methodology is. Field sites range from several soil-mantled landscapes spanning the passive margin escarpment of southeastern Australia, to rocky, bedrock dominated landscapes in the Flinders Ranges and the Central Australia Outback. Also, in the far north, we examine an undisturbed catchment in the rugged topography of Arnhem Land: Tin Camp Creek. We sample detrital sands draining the landscape in a nested fashion at each of our field sites: from small to large catchments. We also sample across the slopes to quantify point-specific rates of soil production and bedrock erosion. Soil production rates and mechanisms across the escarpment have been presented in previous publications and will be used here to compare with a new, ‘humped’ soil prodction function from the Arnhem Land field site. In the rocky landscapes of the Flinders Ranges and MacDonnell Ranges, we sample the blocky slopes as well as catchment sands to constrain a block failure model for slope retreat. Point specific rates are also compared with detrital rates for Kings Canyon and the Todd River drainage to examine the potential for long-term landscape equilibrium. To conclude we show the first, unequivocal example of a regolith mantled landscape eroding in dynamic equilibrium from the western MacDonnell Range. Rates span an order of magnitude, from about 4 to 40 m/Ma across the escarpment in southeastern Australia. The ‘humped’ soil production function peaks at just over 20 m/Ma under about 30 cm of soil and decreases to less than 5 m/Ma under 70 cm of soil. Rates in the Outback are extremely slow, from less than 1 in places to the distance evidence for equilbrium in the Western MacDonnells, at about 7 m/Ma. These results raise many provocative questions and suggest new directions for quantifying how landscapes evolve. Copyright © 2008 Published by Elsevier Ltd.
Evidence for recent interstellar 60Fe on Earth
(Australian National University, 2019-09-09) Koll, D; Faestermann, T; Feige, J; Fifield, LK; Froehlich, MB; Hotchkis, MAC; Korschinek, G; Merchel, S; Panjkov, S; Pavetich, S; Tims, SG; Wallner, A
Over the last 20 years the long-lived radionuclide 60Fe with a half-life of 2.6 Myr was shown to be an expedient astrophysical tracer to detect freshly synthesized stardust on Earth. The unprecedented sensitivity of Accelerator Mass Spectrometry for 60Fe at The Australian National University (ANU) and Technical University of Munich (TUM) allowed us to detect minute amounts of 60Fe in deep-sea crusts, nodules, sediments and on the Moon [1-5]. These signals, around 2-3 Myr and 6.5-9 Myr before present, were interpreted as a signature from nearby Supernovae which synthesized and ejected 60Fe into the local interstellar medium. Triggered by these findings, ANU and TUM independently analyzed recent surface material for 60Fe, deep-sea sediments and for the first time Antarctic snow, respectively [6, 7]. We find in both terrestrial archives corresponding amounts of recent 60Fe. We will present these discoveries, evaluate the origin of this recent influx and bring it into line with previously reported ancient 60Fe findings.
Exposure history of the Torino meteorite
(Wiley, 1996-03) Wieler, R; Graf, T; Signer, P; Vogt, S; Herzog, GF; Tuniz, C; Fink, D; Fifield, LK; Klein, J; Middleton, R; Jull, AJT; Pellas, P; Masarik, J; Dreibus, G
We determined He, Ne, Ar, 10Be, 26Al, 36Cl, and 14C concentrations, as well as cosmic-ray track densities and halogen concentrations in different specimens of the H6 chondrite Torino, in order to constrain its exposure history to cosmic radiation. The Torino meteoroid had a radius of ∼20 cm and travelled in interplanetary space for 2.5–10 Ma. Earlier, Torino was part of a larger body. The smallest possible precursor had a radius of 55 cm and a journey through space longer than ∼65 Ma. If the first-stage exposure took place in a body with a radius of >3 m or in the parent asteroid, then it lasted nearly 300 Ma. The example of Torino shows that it is easy to underestimate first-stage exposure ages when constructing two-stage histories. © 1999-2021 John Wiley & Sons, Inc.
Investigating the lead-210 background in lead materials and chemical reagents
(South Pacific Environmental Radioactivity Association, 2022-11-29) Froehlich, MB; Hotchkis, MAC; Dastgiri, F; Fifield, LK; Koll, D; Merchel, S; Pavetich, S; Slavkovská, Z; Tims, SG; Wallner, A
SABRE (Sodium iodide with Active Background REjection) is a direct detection dark matter experiment based on ultra-pure NaI(Tl) crystals. This experiment is well-shielded against external radiation and thus its background rate is driven by radioactive contaminants in the detector material and in the materials used for the construction of the experimental setup. Such radioactive contamination may come from long-lived, naturally occurring radionuclides or from cosmogenic activation. Therefore, a careful selection and development of ultra-pure materials and equipment is required, as well as a detailed knowledge of the residual radioactivity. Here, we focus on exploring the extraction of the radioisotope lead-210 (210Pb) in analytical grade NaI prior to examining Astro-grade NaI(Tl), which will eventually serve in the SABRE-South experiment as a scintillator detector for dark matter studies based in the Southern Hemisphere. We aim to measure 210Pb in NaI by accelerator mass spectrometry (a single atom counting technique), however this is challenging owing to the anticipated large mass of 1 kg. We will discuss two methods to extract Pb using different resins such as the Anion Exchange Resin (1-X8, 100-200 mesh Chloride form) and Sr® resin (100-150 mm). Furthermore, it is essential that any material and reagents in use should contain as little 210Pb as possible. For the chemical extraction of 210Pb from NaI, a stable Pb carrier is being used, which may contain traces of 210Pb as well. As 210Pb has a half-life of 22.2 years, the “older” the material (i.e., age of manufacturing and processing) the better, as most, if not all, of the 210Pb has decayed. However, 210Pb is a decay product of U, which is omnipresent in the environment. Therefore, if uranium has not been completely removed from the Pb material during processing, 210Pb will be continuously produced. Here, we will present results for a series of Pb materials together with various reagents which were measured using the 1 MV Vega accelerator at ANSTO. Their 210Pb/208Pb isotopic ratios vary between (3-30)´10-14 for the Pb carriers (0.38-173 mBq 210Pb/g) and range from 1´10-14 to 3´10-11 for the reagents (4-194 mBq 210Pb/g), respectively.
Lead-210: a contaminant in particle detectors for dark matter studies
(Australian Nuclear Science and Technology Organisation, 2021-11-17) Froehlich, MB; Merchel, S; Slavkovská, Z; Dastgiri, F; Fifield, LK; Hotchkis, MAC; Koll, D; Pavetich, S; Tims, SG; Wallner, A
The DAMA/LIBRA (DArk Matter/Large sodium Iodide Block for RAre processes) is a very low background NaI(Tl) detector array that has been running for two decades in the Gran Sasso underground laboratory in Italy. It gives a robust annual modulation signal in the 2 to 6 keV region that may be due to dark matter [1]. In order to verify this result with higher sensitivity, the SABRE (Sodium iodide with Active Background REjection) experiment [2] is being developed. Radioimpurities such as ⁴ ⁰ K, ²³⁸ U, ²¹⁰ Pb and ²³²Th, either intrinsic to the detector material or surface contamination, provide a fundamental limit to the sensitivity of SABRE. Therefore, it is crucial to characterise this background for improved identification of any additional signal above it. Here, we focus on ²¹⁰ Pb (half-life of 22.2 years) as its beta decay to ²¹⁰ Bi contributes to the low-energy “dark matter” spectra [3]. Lead-210 measurements are usually performed using alpha -, beta - or gamma counting depending on the sample size and concentration [4]. However, in recent years, the interest and therefore developments to measure ²¹⁰ Pb using accelerator mass spectrometry (AMS) has increased [5], [6]. From a chemical point of view, we need to optimise the Pb extraction of ~1 mg of stable Pb carrier through precipitations and ion exchange chromatography using about a kilogram of NaI. This is not trivial and methods using two different resins, i.e., 1x8 anion exchange resin and Sr® resin, have been tested. It is also essential that the stable Pb carrier and any material and chemical product in use should contain as little ²¹⁰ Pb as possible. Hence, several materials have been investigated including a piece from a 16th century roof and radiation shielding blocks as a source of Pb carrier. Furthermore, we studied PbO and PbF₂ samples to identify the optimal negative-ion beam and the suitability of using either Fe₂ O₃ or NaF as bulk material for the AMS target to reduce the stable Pb content. AMS measurements related to this work have been made using the 14UD pelletron accelerator at the Australian National University and the 1 MV VEGA accelerator at the Australian Nuclear Science and Technology Organisation.
Measurements of 59Ni in meteorites by accelerator mass spectrometry
(Elsevier, 1993-10-01) Paul, M; Fifield, LK; Fink, D; Albrecht, A; Allan, GL; Herzog, GF; Tuniz, C
Isotopic abundances of the radionuclide 59Ni (T12 = 76000 yr) were measured by accelerator mass spectrometry with the 14UD Pelletron tandem accelerator at the Australian National University and a detection system solely based on a multianode ionization chamber. The sensitivity limit in the measurement of 59Ni isotopic abundances is 5 × 10−13, as determined by residual interferences from isobaric 59Co and isotopic 58Ni ions. Cosmogenic 59Ni abundances 59NiNi = (8–20) × 10−12 were measured in four samples prepared from the metal phase of two meteorites (mesosiderites). The ratio of the 59Ni abundances to those measured for 41Ca in the silicate phase of the same samples, is in fair agreement with the ratio of the production rates via thermal-neutron capture on 58Ni and 40Ca. © 1993 Published by Elsevier B.V.
Natural and anthropogenic 236U in environmental samples
(Elsevier, 2008-03-06) Steier, P; Bichler, M; Fifield, LK; Golser, R; Kutschera, W; Priller, A; Quinto, F; Richter, S; Srncik, M; Terrasi, P; Wacker, L; Wallner, A; Wilcken, KM; Wild, EM
The interaction of thermal neutrons with 235U results in fission with a probability of ∼85% and in the formation of 236U (t1/2 = 2.3 × 107 yr) with a probability of ∼15%. While anthropogenic 236U is, therefore, present in spent nuclear fuel at levels of 236U/U up to 10−2, the expected natural ratios in the pre-anthropogenic environment range from 10−14 to 10−10. At VERA, systematic investigations suggest a detection limit below 236U/U = 5 × 10−12 for samples of 0.5 mg U, while chemistry blanks of ∼2 × 107 atoms 236U per sample limit the sensitivity for smaller samples. We have found natural isotopic ratios in uranium reagents separated before the onset of human nuclear activities, in uranium ores from various origins and in water from a subsurface well in Bad Gastein, Austria. Anthropogenic contamination was clearly visible in soil and rivulet samples from Salzburg, Austria, whereas river sediments from Garigliano river (Southern Italy) were close to the detection limit. Finally, our natural in-house standard Vienna-KkU was calibrated against a certified reference material (IRMM REIMEP-18 A). © 2008 Elsevier B.V.
Physical 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, S
A 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.
Preliminary results of CoQtz-N: a quartz reference material for terrestrial in-situ cosmogenic 10Be and 26A1 measurements
(Elsevier, 2019-10-01) Binnie, SA; Dewald, A; Heinze, S; Voronina, E; Hein, AS; Wittmann, H; von Blanckenburg, F; Hetzel, R; Christl, M; Schaller, M; Léanni, L; ASTER Team; Hippe, K; Vockenhuber, C; Ivy-Ochs, S; Maden, C; Fülöp, RH; Fink, D; Wilcken, KM; Fujioka, T; Fabel, D; Freeman, SPHT; Xu, S; Fifield, LK; Akçar, N; Spiegel, C; Dunai, TJ
There is growing interest in geochronological applications of terrestrial in situ-produced cosmogenic nuclides, with the most commonly measured being 10Be and 26A1 in quartz. To extract and then separate these radionuclides from quartz and prepare them in the oxide form suitable for accelerator mass spectrometry (AMS) requires extensive and careful laboratory processing. Here we discuss the suitability of a crushed, sieved and etched, sub-aerially exposed vein quartz specimen (CoQtz-N) to act as a reference material for chemical laboratory preparation and AMS measurements. Splits of CoQtz-N were distributed to eleven target preparation laboratories. The CoQtz-N 10Be targets were then measured at seven different AMS facilities and five of the preparation laboratories had their 26A1 targets measured at four different AMS facilities. We show that CoQtz-N splits are sufficiently homogeneous with regard to nuclide concentrations, that it has been cleaned of any atmospheric derived (i.e. meteoric) 10Be and that it has low concentrations of the major elements that can interfere with Be and A1 extraction chemistry and AMS measurements. We derive preliminary concentrations for 10Be and 26Al in CoQtz-N as 2.53 ± 0.09 × 106 at/g and 15.6 ± 1.6 × 106 at/g, respectively, at the 95% confidence limit. © 2019 Elsevier B.V.
Radio-impurity measurements for a dark matter dodium Iidide detector
(Australian Nuclear Science and Technology Organisation, 2021-11-17) Dastgiri, F; Slavkovska, Z; Froehlich, MB; Hotchkis, MAC; Koll, D; Merchel, S; Pavetich, S; Sims, SG; Fifield, LK; Wallner, A
The first dark matter detector is being built in the Stawell gold mine in south-eastern Australia, as the southern hemisphere arm of an international collaboration SABRE (Sodium Iodide with Active Background Rejection). This experiment employs ultra-low background sodium iodide (NaI) detectors placed in highly shielded vessels across both hemispheres. The aim is to confirm or refute annual modulation claims attributed to dark matter particles by the DAMA/LIBRA collaboration at the Laboratori Nazionali del Gran Sasso in Italy. This requires the lowest possible concentration of radio-contaminants that can be achieved, to minimise the potential for radiation signals that can mimic dark matter particles signals. We report on the techniques employed for the detection of potentially problematic contaminants in the NaI material from which the crystals will be grown. We focus on the establishment of the measurement techniques of ⁴ ⁰ K and ²¹⁰ Pb at the Australian National University and ANSTO. For the measurement of ⁴ ⁰ K, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to measure the concentration of ³⁹ K, and from the well-known natural abundance ratios of ³⁹ K/⁴ ⁰ K, the concentration of ⁴ ⁰ K was inferred. The challenges associated with measuring ultraprecise levels of ³⁹ K, and the techniques of minimising the introduction of potassium in the sample preparation will be discussed. 210-Lead was measured using AMS. The ²¹⁰ Pb concentration in the NaI powder is very low, which necessitates that large amounts (~ 1kg) of the powder need to be processed to result in sufficient atoms for an AMS measurement. This low concentration requires the additions of a Pb-carrier (~ 1mg), which itself needs to contain minimal ²¹⁰ Pb. Several lead materials have been investigated and will be reported. In addition, we will discuss the different lead compounds and cathode materials used to optimise the beam current and minimise the background. Other contaminants of potential interest such as ³H, ²³²Th and ²³⁸ U; especially those identified in DAMA/LIBRA and other NaI detectors will be presented.
Reproducibility and accuracy of actinide AMS – lessons learned from precision studies for nuclear data
(Australian Nuclear Science and Technology Organisation, 2021-11-17) Wallner, A; Christl, M; Hotchkis, MAC; Lippold, J; Froehlich, MB; Fifield, LK; Steier, P; Tims, SG; Winkler, SR
Actinide detection has grown into an important discipline for environmental and geological sciences, for oceanography, e.g. as monitors of anthropogenic activities, but also in nuclear (astro)physics. Consequently, AMS measurements of actinides have become routine at many facilities. In particular, applications in nuclear (astro)physics continue to challenge the present limits in accuracy and abundance sensitivity of actinide detection. Presently, there is a major ongoing effort in experiment and theory to better understand cross sections at thermal and higher neutron energies. These activities are motivated by the urgent need for improved and highly accurate nuclear data for optimised designs of advanced reactor concepts, nuclear fusion reactors, or next generation nuclear power plants (Gen IV) and accelerator driven systems (ADS). One example is the cross-section value for 235U neutron-capture at thermal energies: serving as a so-called thermal constant, this quantity is believed to be known to better than 1%. Despite its importance, direct measurements are rare (only two older data exist for thermal energies) and exhibit large uncertainties, thus its knowledge is based on indirect information. For these applications, accurate actinide data are required, e.g. with uncertainties better than 2-3% for capture reactions. The combination of activation and subsequent AMS detection offers a powerful and complementary tool to measure these cross sections. However, this method had been applied only very recently for measurements on actinides. Importantly, adding an independent technique to established methods helps also to identify unrecognized systematic uncertainties in the existing nuclear database. Several uranium and thorium samples had been irradiated with neutrons of energies between sub-thermal and 22 MeV at seven different neutron-producing facilities. These samples were then analysed at different AMS facilities: at the Vienna Environmental Research Accelerator (VERA), at ANSTO’s ANTARES, at ETH’s TANDY and at HIAF (ANU). These facilities cover terminal voltages for actinide AMS between 0.3 and 4 MV. We present systematic investigations of nuclear data from a series of neutron-irradiated samples that were obtained by AMS. Long-lived reaction products that were measured include Th-229, Pa-231,233, U-233,236 and various Pu isotopes. Some irradiated samples were directly pressed into sample holders. Some samples were dissolved and spiked with well-known amounts of one or more reference isotopes, relative to which the radionuclides were quantified. To achieve the highest accuracy, we compared the results from repeated measurements at the different facilities. We also had to take into account the measurement reproducibility of the individual facilities; an uncertainty component that represents unknown uncertainties beyond counting statistics and other known systematic uncertainties. A comparison of these data provides the present limits in the measurement accuracy of heavy-ion AMS. © The Authors
Sm-146 – feasibility studies to re-date the chronology of the early solar system
(Australian Nuclear Science and Technology Organisation, 2021-11-17) Pavetich, S; Fifield, LK; Froehlich, MB; Koll, D; Slavkovská, Z; Stopic, A; Tims, SG; Wallner, A
AMS measurements of long-lived radionuclides can make significant contributions to the understanding of the temporal evolution of our early solar system. Samarium-146 has a half-life in the order of 100 Myr and decays via emission of α-particles into stable ¹⁴ ²Nd. Due to different geochemical behaviour and the radioactive decay of ¹⁴ ⁶ Sm, the Sm-Nd isotopic system can serve as a chronometer for the early solar system and planetary formation processes. The half-life of ¹⁴ ⁶ Sm, which provides the time scale for this clock, is in dispute. The most recent and notably precise measurements for the half-life are (103±5) Myr (adopted from [1,2]) and (68±7) Myr [3] and differ by more than 5 standard deviations. In addition to potentially resolving this discrepancy, developing AMS for ¹⁴ ⁶ Sm might provide the means to study stellar nucleosynthesis on the proton rich side of the chart of nuclei and serve as radiometric tracer for geosciences. Due to the extremely challenging task of separating ¹⁴ ⁶ Sm from its stable isobar ¹⁴ ⁶ Nd, to date the only AMS measurement of ¹⁴ ⁶ Sm was performed at Argonne National Laboratory with energies in the order of ~880 MeV. At the Heavy Ion Accelerator Facility at ANU, the possibility to measure ¹⁴ ⁶ Sm at energies of 200-250 MeV is being explored. Different sample materials, molecular negative ion beams and detector setups are investigated. So far, the lowest Nd backgrounds, from commercially available sample material without additional Nd separation were achieved using SmO₂ - beams extracted from Sm₂ O₃ samples. In order to explore the limits of the Sm detection capabilities, Sm₂ O₃ samples were irradiated with thermal neutrons in the reactor at ANSTO to produce the shorter lived ¹⁴ ⁵ Sm (t1/2 = (340±3) d [4]) via ¹⁴ ⁴ Sm(n,γ)¹⁴ ⁵ Sm. The production of ¹⁴ ⁵ Sm is easier and faster and the challenges in measuring ¹⁴ ⁵ Sm via AMS are very similar to those measuring ¹⁴ ⁶ Sm. In addition, ¹⁴ ⁵ Sm has the potential to serve as a tracer for future reference materials for AMS measurements of Sm.
Time-resolved interstellar Pu-244 and Fe-60 Ppofiles in a Be- 10 dated ferromanganese crust
(Australian Nuclear Science and Technology Organisation, 2021-11) Koll, D; Wallner, A; Hotchkis, MAC; Child, DP; Fifield, LK; Froehlich, MB; Harnett, M; Lachner, J; Merchel, S; Pavetich, S; Rugel, G; Slavkovska, Z; Tims, SG
More than 20 years have passed since the first attempts to find live supernova Fe-60 (t1/2 = 2.6 Myr) in a deep-sea ferromanganese crust [1]. Within these 20 years, strong evidence was presented for a global influx of supernova dust into several geological samples around 2 Myr ago. Recently, a much younger continuous influx was found in Antarctic snow and in deep-sea sediments [2-4] and an older peak around 7 Myr in deep-sea crusts [5,6]. The long-lived isotope Pu-244 (t1/2 = 80 Myr) is produced in the astrophysical r-process similarly to most of the heaviest elements. Although the production mechanism is believed to be understood, the astrophysical site is heavily disputed. Most likely scenarios involve a combination of rare supernovae and neutron star mergers. The search for Pu-244 signatures in samples with known Fe-60 signatures allows to test for either common influx patterns or independent Pu-244 influxes disentangled from stellar Fe-60. Accordingly, this information provides a unique and direct experimental approach for identifying the production site of the heavy elements. Very recently and first reported in the AMS-14 conference, the first detection of interstellar Pu-244 was published [6]. This was only feasible by achieving the highest detection efficiencies for plutonium in AMS ever reported [7]. The achieved time resolution of 4.5 Myr integrates over the supernova influxes and is therefore not high enough to unequivocally show a correlated influx pattern of Fe-60 and Pu-244. Based on this progress, we are now aiming to measure highly time-resolved profiles of Fe-60 and Pu-244 in the largest ferromanganese crust used so far. Results on the characterization of the crust including cosmogenic Be-10 (t1/2 = 1.4 Myr) dating and a 10 Myr profile of interstellar Fe-60 including the confirmation of the 7 Myr influx will be presented along with first data on interstellar Pu-244.
Tracking the 10Be–26AI source-area signal in sediment-routing systems of arid central Australia
(European Geosciences Union, 2018-05-07) Struck, M; Jansen, JD; Fujioka, T; Codilean, AT; Fink, D; Fülöp, RH; Wilcken, KM; Price, DM; Kotevski, S; Fifield, LK; Chappell, J
Sediment-routing systems continuously transfer information and mass from eroding source areas to depositional sinks. Understanding how these systems alter environmental signals is critical when it comes to inferring source-area properties from the sedimentary record. We measure cosmogenic 10Be and 26Al along three large sediment-routing systems (∼ 100 000 km2) in central Australia with the aim of tracking downstream variations in 10Be–26Al inventories and identifying the factors responsible for these variations. By comparing 56 new cosmogenic 10Be and 26Al measurements in stream sediments with matching data (n= 55) from source areas, we show that 10Be–26Al inventories in hillslope bedrock and soils set the benchmark for relative downstream modifications. Lithology is the primary determinant of erosion-rate variations in source areas and despite sediment mixing over hundreds of kilometres downstream, a distinct lithological signal is retained. Post-orogenic ranges yield catchment erosion rates of ∼ 6–11 m Myr−1 and silcrete-dominant areas erode as slow as ∼ 0.2 m Myr−1. 10Be–26Al inventories in stream sediments indicate that cumulative-burial terms increase downstream to mostly ∼ 400–800 kyr and up to ∼ 1.1 Myr. The magnitude of the burial signal correlates with increasing sediment cover downstream and reflects assimilation from storages with long exposure histories, such as alluvial fans, desert pavements, alluvial plains, and aeolian dunes. We propose that the tendency for large alluvial rivers to mask their 10Be–26Al source-area signal differs according to geomorphic setting. Signal preservation is favoured by (i) high sediment supply rates, (ii) high mean runoff, and (iii) a thick sedimentary basin pile. Conversely, signal masking prevails in landscapes of (i) low sediment supply and (ii) juxtaposition of sediment storages with notably different exposure histories. © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 Licence
Uplift rates defined by U-series and C-14 ages of serpulid-encrusted speleothems from submerged caves near Siracusa, Sicily (Italy)
(Elsevier, 2009-02) Dutton, A; Scicchitano, G; Monaco, C; Desmarchelier, JM; Antonioli, F; Lambeck, K; Esat, TM; Fifield, LK; McCulloch, MT; Mortimer, GE
We have established a plausible rate of uplift near Siracusa in southeastern Sicily (Italy) over the last glacial-interglacial cycle using U-series ages of submerged speleothem calcite and C-14 ages of calcite serpulid layers that encrust the speleothems during cave submergence. The precisely determined ages of these sea level benchmarks were compared with expected relative sea level position based on glaciohydro-isostatic modeling to assess the rate of uplift in this region. When combined with the age of various late Holocene archaeological sites that have been recently described and characterized in terms of their functional position relative to sea level these data collectively define a rate of uplift <= 0.4 mm a(-1) along this portion of the Sicilian coastline. These results are consistent with an age assignment of marine isotope stage (MIS) 5.3 or 5.5 for the Akradina terrace. which in turn places temporal constraints on paleoshorelines above and below this level. © 2008, Elsevier Ltd.

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