Browsing by Author "Howitt, JA"

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    Radionuclide bioaccumulation in trees at an Australian legacy low-level waste site: concentration patterns in branches and foliage
    (American Nuclear Society, 2014-08-24) Wilsher, KL; Johansen, MP; Harrison, JJ; Payne, TE; Howitt, JA; Doran, G; Child, DP; Hotchkis, MAC; Thiruvoth, S; Mokhber-Shahin, L; Twining, JR; Vardanega, CR; Wong, HKY
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    Radionuclide bioaccumulation patterns in vegetation at a legacy low-level waste site
    (Australian Nuclear Science and Technology Organisation, 2012-10-16) Wilsher, KL; Johansen, MP; Howitt, JA; Doran, G; Twining, JR; Child, DP; Dodson, JR; Dore, MJ; Harrison, JJ; Hotchkis, MAC; Mokhber-Shahin, L; Payne, TE; Thiruvoth, S; Wong, HKY
    This study focuses on uptake of radionuclides (RN) into trees at a legacy low level radioactive waste site (the Little Forest Burial Ground (LFBG) near Lucas Heights in southern Sydney). Tree species included: Acacia longifolia longifolia; Syncarpia glomulifera; Eucalyptus paniculate; Leptospermum polygalifolium; and Banksia serrata. Branches – (wood and foliage) were sampled, and soil cores were collected around each tree. Analytical techniques included Inductively Coupled Plasma Atomic Emission Spectrometry and Mass Spectrometry, alpha and gamma spectrometry, Accelerator Mass Spectrometry and Cerenkov counting. Anthropogenic RN measured in trees and soils were 90Sr, 137Cs, 233U, 239+240Pu and 241Am. Median concentrations of RN in trees growing on, or near, the trenches (90Sr - 9.855 Bq/kg, 137Cs - 0.220 Bq/kg, 239+240Pu - 0.004 Bq/kg) were significantly higher than background trees (90Sr – 0.001 Bq/kg, 137Cs – n.d., 239+240Pu - 0.002 Bq/kg). Most trees had higher levels in foliage compared to wood. However; there was large variation among branches within the same tree. Uptake of radionuclides was quantified by the concentration ratio (CR), defined as average concentration in the tree to that of the surrounding soil. CR’s for trees growing around the trenches were an order of magnitude higher than for background trees, which is attributed to the trees taking up radionuclides directly from the subsurface. Our results better quantify the bio-available fraction of radionuclides in the environment at the LFBG, and reveal that site trees are bio-monitors of multiple radionuclides sourced from the sub-surface wastes.
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    Radon tracer flux measurements of CO2, N2O and CH4 at Wagga Wagga: OASIS revisited?
    (Australian Government Bureau of Meteorology, 2017-11-12) Griffith, DWT; Wilson, SR; Griffiths, AD; Chambers, SD; Williams, AG; Werczynski, S; Sisoutham, O; Howitt, JA; Reardon, D; Leuning, R
    Vertical profiles and suitably-conditioned surface time histories of the natural radioactive noble gas radon-222 (radon) have long been demonstrated to be useful as quantitative indicators of diurnal- to synoptic-scale mixing processes within the continental lower troposphere. Radon’s well-characterised and slowly-varying source function over (ice-free)terrestrial surfaces, together with its short half-life of 3.8 days, makes it a particularly suitable passive scalar for the evaluation of boundary layer and convective mixing parameterisation schemes in a range of regional and global climate and pollution transport models. We provide a brief overview of ANSTO measurement programs using radon to characterise vertical mixing in the lower atmosphere, together with examples of their applications in modelling and pollution studies. We then present preliminary results from recent field campaigns collecting high resolution vertical radon profiles in the terrestrial boundary layer over rural New South Wales, using a radon sampler mounted on an instrumented motor-glider. The flights were conducted in the lowest 1000m of the atmosphere and, together with simultaneous ground-based and tower measurements, document the dispersion of radon emissions accumulated below the nocturnal stable inversion into the developing daytime convective boundary layer during the important morning transition period.