Browsing by Author "Silitonga, A"

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    Challenges in the radiochemical separation of marine samples from the Montebello Islands
    (South Pacific Environmental Radioactivity Association, 2018-11-06) Thiruvoth, S; Child, DP; Harrison, JJ; Johansen, MP; Silitonga, A; Vardanega, CR; Wilsher, KL; Wong, HKY
    The Montebello Islands, located off the North Western coast of Western Australia, was used as a nuclear weapons test site by the British government in the 1950s. Three nuclear tests were conducted around the islands. The first in 1952 (W818) detonated in the hull of the HMS Plym anchored in 12 m of water between Alpha and Trimouille Islands, and the second and third tests (MOSAIC G1 and G2) were detonated on 30 m Aluminium towers in May and June 1956, G1 on the Northern Western tip of Trimouille island and G2, the largest test conducted in Australian territory, on Alpha island. The fallout from these tests deposited long-lived anthropogenic radionuclides on nearby islands and ocean surface, host to an array of animals and plants. Marine sand, marine sediment, algae, fish, turtles and turtle eggs, among others, were sampled from the surrounding zones for dose assessment studies, thirty-nine of which were processed for actinide and strontium analysis. Due to the expected presence of discrete radioactive particles in some matrices a three step digestion method was applied to obtain complete dissolution of sample material. To overcome sample heterogeneity, the digest solution was sub-sampled for actinide and Sr-90 analysis by alpha spectrometry and liquid scintillation analysis, for plutonium isotopic analysis by AMS, and for elemental analysis by ICPAES/MS. The radiochemical separation method developed at ANSTO for Am, Pu, Th, U, and Sr for terrestrial soils and sediments (Harrison et al, 2011) was adapted to samples from the marine environment. However, some sample matrices proved to be challenging in achieving acceptable chemical recoveries of strontium due to the high concentrations of native calcium. This current study will discuss the methods used, and challenges overcome, in radiochemical separation for alpha spectrometry and liquid scintillation analysis for a wide range of sample types.
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    Establishing a radioanalytical capability to support cyclotron decomissioning
    (South Pacific Environmental Radioactivity Association, 2022-11-20) Thiruvoth, S; Harrison, JJ; Bedwell-Wilson, J; Cunynghame, T; Martiniello, J; Mokhber-Shahin, L; Silitonga, A
    The 30 MeV cyclotron at the National Medical Cyclotron (NMC) ceased operations in October 2009 after producing medical isotopes for application in nuclear medicine for approximately 20 years. Upon its closure a process of decommissioning commenced. Initially, internal components that make up the cyclotron were removed, leaving behind the vault. The vault is predominantly constructed of concrete and steel reinforcements. Neutron activation of these materials produced radioisotopes that will need to be accurately identified and quantified to support decision making around storage and disposal options of these materials. This is a critical aspect of any cyclotron decommissioning project and has safety, environmental and economic implications. A capability to quantify typical radionuclides found in cyclotron materials is being developed at ANSTO. Cyclotron vault materials that may require assessment are concrete, steel and waters. Radionuclides of interest are typically beta- and gamma-emitting neutron activation products. Non-destructive, high resolution gamma spectrometry will be applied to quantify gamma emitting radionuclides such as 152Eu, 154Eu, 134Cs and 60Co. The complex matrix of some reactor materials will cause attenuation of gamma photons and empirical and/or theoretical corrections will be applied. Beta-emitting radionuclides will require a suite of destructive radioanalytical techniques designed to isolate and quantify beta-emitting radionuclides such as 59Fe and 55Fe. Gross beta counting will assist in identifying which samples will require destructive beta analysis. This presentation will outline the approach taken in identifying a sampling strategy and in the method development for non-destructive and destructive analysis and how this can support future cyclotron decommissioning needs of Australia and our region.
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    Radionuclide distributions and migration pathways at a legacy trench disposal site
    (Elsevier B. V., 2020-01) Payne, TE; Harrison, JJ; Cendón, DI; Comarmond, MJ; Hankin, SI; Hughes, CE; Johansen, MP; Kinsela, AS; Mokhber-Shahin, L; Silitonga, A; Thiruvoth, S; Wilsher, KL
    This paper examines the distributions of several anthropogenic radionuclides (239+240Pu, 241Am, 137Cs, 90Sr, 60Co and 3H) at a legacy trench disposal site in eastern Australia. We compare the results to previously published data for Pu and tritium at the site. Plutonium has previously been shown to reach the surface by a bath-tubbing mechanism, following filling of the former trenches with water during intense rainfall events. This has led to some movement of Pu away from the trenched area, and we also provide evidence of elevated Pu concentrations in shallow subsurface layers above the trenched area. The distribution of 241Am is similar to Pu, and this is attributed to the similar chemistry of these actinides and the likely in-situ generation of 241Am from its parent 241Pu. Concentrations of 137Cs are mostly low in surface soils immediately above the trenches. However, similar to the actinides, there is evidence of elevated 137Cs and 90Sr concentrations in shallow subsurface layers above the trenched area. While the subsurface radionuclide peaks suggest a mechanism of subsurface transport, their interpretation is complicated by the presence of soil layers added following disposals and during the subsequent years. The distribution of 90Sr and 137Cs at the ground surface shows some elevated levels immediately above the trenches which were filled during the final 24 months of disposal operations. This is in agreement with disposal records, which indicate that greater amounts of fission products were disposed in this period. The surface distribution of 239+240Pu is also consistent with the disposal documents. Although there is extensive evidence of a mobile tritium plume in groundwater, migration of the other radionuclides by this pathway is limited. The data highlight the importance of taking into account multiple pathways for the mobilisation of key radioactive contaminants at legacy waste trench sites. Crown Copyright © 2019 Published by Elsevier Ltd.