Browsing by Author "Kotevski, S"

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    Facility report : ANSTO’s 6 MV NEC SIRIUS accelerator – an update since AMS 14 Ottawa
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Fink, D; Fülöp, RH; Fujioka, T; Kotevski, S; Simon, KJ; Wilcken, KM
    ANSTO’s SIRIUS tandem accelerator is a customised 6 MV tandem accelerator manufactured by NEC and commissioned in 2015. It is a shared AMS and IBA instrument described in detail in Pastuovic et al (2015). Initial AMS performance data for cosmogenic isotopes 10Be, 26Al and 36Cl was presented at the Ottawa AMS14 Conference (Wilcken et al 2019). The AMS spectrometer consists of a 134 sample-wheel MC-SNICS Cs sputter source, a 45-degree spherical ESA (R=300 mm) and a double focusing insulated injection magnet (R=1000 mm, ME=20, vacuum gap = 70 mm). Two stripper gases (typically Ar and He) and thin foils are selectable in the terminal, and the selected charge state is focussed by an in tank electrostatic quadruple triplet positioned in the high energy column section. The high-energy section consists of two identical ME=176 analysing magnets (R=1270 mm) feeding two independent beam line transport systems, one for AMS and the other IBA. The AMS setup includes a post-stripper or energy degrader ladder, a 45-degree spherical ESA (R=3810 mm, gap = 30mm) and two magnetic quadrupoles. A choice of 3 AMS beam lines selectable by a ±30 degree switcher magnet provides options for dedicated radionuclide detection of 10Be (absorber cell), 36Cl and 26Al (multi-anode ionization counter), and an 8 m long TOF setup for future 129I and U-isotope measurements. A suite of sample geochemistry preparation laboratories, including a dedicated laboratory for preparation of in-situ 14C samples ( Fulop et al 2019) and an ice-core storage facility, provide AMS targets of 10Be (meteoric), 10Be, 26Al 14C and 36Cl (in-situ). The cosmogenic chemistry extraction laboratories host many visiting students and researchers to prepare samples and participate in AMS measurements. A wide variety of earth science applications in landscape evolution, sediment transport, tectonics, polar ice sheet stability, Quaternary geochronology supporting paleoclimate research change, solar variability and archaeology are supported. Ancillary facilities at ANSTO provide high precision elemental analyses (eg 9Be and 27Al) using a variety of techniques (ICP-OES, ICP-MS, AA, SEM, and XRF). We present details of recent data on routine AMS accelerator performance, reproducibility and linearity with various AMS standards, transmission, sample throughput, background reduction, and some improvements in sample chemistry methods.
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    Sediment transport dynamics in central Australian low-gradient landscapes quantified with cosmogenic nuclides
    (Science Council of Japan, 2015-07-26) Struck, M; Jansen, JD; Codilean, AT; Fujioka, T; Fink, D; Kotevski, S
    Erosion and sediment routing are key to understanding landscape evolution. In this regard, low-gradient landscapes have remained effectively unstudied in spite of their vast global extent, whereas steep mountain regions have been the focus of most research efforts. Sediment transport and storage is widely thought to occur on much longer timescales in regions of low relief relative to their steep counterparts. Here we apply in situ-produced cosmogenic nuclides to examine the sediment transport and storage history of a low-gradient catchment (Peake River) in arid central Australia. The catchment covers 27,300 km2 with a total relief of 394 m and a mean slope of 32 ± 29 m/km (mean ± 1σ, calculated from 1 arc-sec SRTM). Previous studies in central Australia have focused mainly upon local measurements of landscape lowering and bedrock erosion; however, to better understand the processes shaping these landscapes, we adopt a source-to-sink approach coupling bedrock and hillslope colluvium measurements of cosmogenic nuclides with basin-wide measurements in fluvial sediment. Variation in concentrations and ratios of 10Be and 26Al in sediment provides insights to residence times and burial history as grains are transmitted through the bedrock-hillslope-stream sediment conveyor. Our preliminary results reveal basin-wide erosion rates ranging from 0.2 to 5.8 m/Myr (weighted mean = 0.41 ± 0.03 m/Myr), which are among the lowest rates ever measured. We discuss the sediment dynamics of flat landscapes, emphasizing the contrast with steeper settings. Copyright © 2015, XIX INQUA Congress LOC
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    SIRIUS Performance: 10Be, 26A1 and 36C1 measurements at ANSTO
    (Elsevier, 2019-09-15) Wilcken, KM; Fujioka, T; Fink, D; Fülöp, RH; Codilean, AT; Simon, KJ; Mifsud, C; Kotevski, S
    SIRIUS – a 6 MV pelletron accelerator at ANSTO was delivered and installed in 2014–2015. After initial testing and commissioning phase we have now moved into routine operations. Quality assurance data from the past 2 years demonstrates the excellent performance and SIRIUS is now our preferred instrument for 10Be, 26A1 and 36C1 analyses. © 2019 Elsevier B.V.
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    Soil production and transport on postorogenic desert hillslopes quantified with 10Be and 26Al
    (GeoScienceWorld, 2018-01-02) Struck, M; Jansen, JD; Fujioka, T; Codilean, AT; Fink, D; Egholm, DL; Fülöp, RH; Wilcken, KM; Kotevski, S
    Hillslopes stand at the top of the geomorphic conveyor belt that produces and transports mass throughout landscapes. Quantification of the tempo of hillslope evolution is key to identifying primary sediment production and understanding how surface processes shape topography. We measured cosmogenic 10Be and 26Al on three desert hillslopes in postorogenic central Australia and quantified their soil dynamics and evolution. We found that hillslope morphology is governed by lithological factors, and differing nuclide abundances reflect the main sediment transport processes. Slope wash is widespread, and shrink-swell soil processes drive downslope creep and upward migration of gravels detached from underlying bedrock. We applied Monte Carlo–based inversion modeling to reconstruct soil production and the exhumation histories of stony mantle gravels. Underlying silty soils derive from eolian dust inputs dating to at least 0.2 Ma and possibly more than 1 Ma, in line with intensified aridity. Exposed bedrock erodes at ∼0.2–7 m/m.y., and under soil, it erodes at maximum rates of <0.1 m/m.y. up to 10 m/m.y. Accordingly, particles spend 2–6 m.y. or more in the upper 0.6 m of the bedrock column and an additional ∼0.2–2 m.y. or more within hillslope soils. Such long periods near the surface result in surface particles acquiring inherently low 26Al/10Be ratios. Bedrock erodibility underpins regional variations in erosion rate, and the slow tempo of hillslope evolution is largely independent of base level. This suggests a distinctive top-down evolution among postorogenic hillslopes set by authigenic rates of sediment production, rather than by fluvial incision as in tectonically active settings. © 2021 Geological Society of America
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    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