Browsing by Author "Long, S"

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    Cave radon exposure, dose, dynamics and mitigation
    (National Speleological Society, 2021-03) Waring, CL; Hankin, SI; Solomon, SB; Long, S; Yule, A; Blackley, R; Werczynski, S; Baker, AC
    Many caves around the world have very high concentrations of naturally occurring 222Rn that may vary dramatically with seasonal and diurnal patterns. For most caves with a variable seasonal or diurnal pattern, 222Rn concentration is driven by bi-directional convective ventilation, which responds to external temperature contrast with cave temperature. Cavers and cave workers exposed to high 222Rn have an increased risk of contracting lung cancer. The International Commission on Radiological Protection (ICRP) has re-evaluated its estimates of lung cancer risk from inhalation of radon progeny (ICRP 115) and for cave workers the risk may now (ICRP 137) be 4–6 times higher than previously recognized. Cave Guides working underground in caves with annual average 222Rn activity > 1,000 Bq m⁻3 and default ICRP assumptions (2,000 workplace hours per year, equilibrium factor F ₌ 0.4, dose conversion factor DCF ₌ 14 µSv (kBq h m⁻3)⁻1 could now receive a dose of > 20 mSv y₋1 . Using multiple gas tracers (δ13C-CO2, Rn and N2O), linked weather, source gas flux chambers, and convective air flow measurements a previous study unequivocally identified the external soil above Chifley Cave as the source of cave 222Rn. If the source of 222Rn is external to the cave, a strategy to lower cave 222Rn by passively decreasing summer pattern convective ventilation, which draws 222Rn into caves, is possible without harming the cave environment. A small net annual average temperature difference (warmer cave air) due to geothermal heat flux produces a large net annual volumetric air flow bias (2–5:1) favoring a winter ventilation pattern that flushes Rn from caves with ambient air. Rapid anthropogenic climate change over decades may heat the average annual external temperature relative to the cave temperature that is stabilized by the thermal inertia of the large rock mass. Relative external temperature increases due to climate change (Jenolan Caves, 2008–2018, 0.17°C) reduces the winter pattern air flow bias and increases Rn concentration in caves. © The Authors
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    Localized relaxational dynamics of succinonitrile
    (American Chemical Society, 2009-08-20) van Eijck, L; Best, AS; Long, S; Fernandez-Alonso, F; MacFarlane, D; Forsyth, M; Kearley, GJ
    Succinonitrile (N C-CH2-CH2-C N) is a good ionic conductor, when doped with an ionic compound, at room temperature, where it is in its plastic crystalline phase (Long et al. Solid State Ionics 2003, 161. 105: Alarco et al. Nat. Mater. 2004, 3, 476). We report on the relaxational dynamics of the plastic phase near the two first-order phase transitions and on the effect of dissolving a salt in the plastic matrix by quasi-elastic neutron scattering. At 240 K, the three observed relaxations are localized and we can describe their dynamics (iota approximate to 1.7, 17, and 140 ps) to a certain extent from a model using a single molecule that was proposed by Bee et al. allowing for all conformations in its unit cell (space group IM3M). The extent of the localized motion as observed is however larger than that predicted by the model and suggests that the isomerization of succinonitrile is correlated with a jump to the nearest neighbor site ill the unit cell. The salt containing system is known to be it good ionic conductor, and our results show that the effect of the ions on the succinonitrile matrix is homogeneous. Because the isomerizations and rotations are governed by intermolecular interactions, the dissolved ions have ail effect over ail extended range. Due to the addition of the salt, the dynamics of one of the components (iota approximate to 17 ps) shows more diffusive character at 300 K. The calculated upper limit of the corresponding diffusion constant of succinonitrile in the electrolyte is a factor 30 higher than what is reported for the ions. Our results suggest that the succinonitrile diffusion is caused by nearest neighbor jumps that are localized on the observed length and time scales. © 2009, American Chemical Society
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    The new confocal heavy ion microprobe beamline at ANSTO: the first microprobe resolution tests and applications for elemental imaging and analysis
    (Elsevier B.V., 2017-08-01) Pastuovic, Z; Siegele, R; Cohen, DD; Mann, M; Ionescu, M; Button, D; Long, S
    The Centre for Accelerator Science facility at ANSTO has been expanded with the new NEC 6MV “SIRIUS” accelerator system in 2015. In this paper we present a detailed description of the new nuclear microprobe–Confocal Heavy Ion Micro-Probe (CHIMP) together with results of the microprobe resolution testing and the elemental analysis performed on typical samples of mineral ore deposits and hyper-accumulating plants regularly measured at ANSTO. The CHIMP focusing and scanning systems are based on the OM-150 Oxford quadrupole triplet and the OM-26 separated scan-coil doublet configurations. A maximum ion rigidity of 38.9amu-MeV was determined for the following nuclear microprobe configuration: the distance from object aperture to collimating slits of 5890mm, the working distance of 165mm and the lens bore diameter of 11mm. The overall distance from the object to the image plane is 7138mm. The CHIMP beamline has been tested with the 3MeV H+ and 6MeV He2+ ion beams. The settings of the object and collimating apertures have been optimized using the WinTRAX simulation code for calculation of the optimum acceptance settings in order to obtain the highest possible ion current for beam spot sizes of 1μm and 5μm. For optimized aperture settings of the CHIMP the beam brightness was measured to be ∼0.9pAμm−2mrad−2 for 3MeV H+ ions, while the brightness of ∼0.4pAμm−2mrad−2 was measured for 6MeV He2+ ions. The smallest beam sizes were achieved using a microbeam with reduced particle rate of 1000Hz passing through the object slit apertures several micrometers wide. Under these conditions a spatial resolution of ∼0.6μm×1.5μm for 3MeV H+ and ∼1.8μm×1.8μm for 6MeV He2+ microbeams in horizontal (and vertical) dimension has been achieved. The beam sizes were verified using STIM imaging on 2000 and 1000mesh Cu electron microscope grids. © 2017 Elsevier B.V.
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    Second generation laser-heated microfurnace for the preparation of microgram-sized graphite samples
    (Elsevier, 2015-10-15) Yang, B; Smith, AM; Long, S
    We present construction details and test results for two second-generation laser-heated microfurnaces (LHF-II) used to prepare graphite samples for Accelerator Mass Spectrometry (AMS) at ANSTO. Based on systematic studies aimed at optimising the performance of our prototype laser-heated microfurnace (LHF-I) (Smith et al., 2007 [1]; Smith et al., 2010 [2,3]; Yang et al., 2014 [4]), we have designed the LHF-II to have the following features: (i) it has a small reactor volume of 0.25 mL allowing us to completely graphitise carbon dioxide samples containing as little as 2 μg of C, (ii) it can operate over a large pressure range (0–3 bar) and so has the capacity to graphitise CO2 samples containing up to 100 μg of C; (iii) it is compact, with three valves integrated into the microfurnace body, (iv) it is compatible with our new miniaturised conventional graphitisation furnaces (MCF), also designed for small samples, and shares a common vacuum system. Early tests have shown that the extraneous carbon added during graphitisation in each LHF-II is of the order of 0.05 μg, assuming 100 pMC activity, similar to that of the prototype unit. We use a ‘budget’ fibre packaged array for the diode laser with custom built focusing optics. The use of a new infrared (IR) thermometer with a short focal length has allowed us to decrease the height of the light-proof safety enclosure. These innovations have produced a cheaper and more compact device. As with the LHF-I, feedback control of the catalyst temperature and logging of the reaction parameters is managed by a LabVIEW interface. Crown Copyright © 2015 Published by Elsevier B.V.
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    SIRIUS - a new 6MV accelerator system for IBA and AMS at ANSTO
    (Elsevier, 2016-03-15) Pastuovic, Z; Button, D; Cohen, DD; Fink, D; Garton, D; Hotchkis, MAC; Ionescu, M; Long, S; Levchenko, VA; Mann, M; Siegele, R; Smith, AM; Wilcken, KM
    The Centre for Accelerator Science (CAS) facility at ANSTO has been expanded with a new 6 MV tandem accelerator system supplied by the National Electrostatic Corporation (NEC). The beamlines, end-stations and data acquisition software for the accelerator mass spectrometry (AMS) were custom built by NEC for rare isotope mass spectrometry, while the beamlines with end-stations for the ion beam analysis (IBA) are largely custom designed at ANSTO. An overview of the 6 MV system and its performance during testing and commissioning phase is given with emphasis on the IBA end-stations and their applications for materials modification and characterisation. © Elsevier B.V.