Browsing by Author "Hill, D"

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    Characterization of MOSFET sensors for dosimetry in alpha particle therapy
    (Australian Nuclear Science and Technology Organisation, 2021-11-24) Su, FY; Biasi, G; Tran, LT; Pan, VA; Hill, D; Lielkajis, M; Cutajar, D; Petasecca, M; Lerch, MLF; Pastuovic, Z; Poder, J; Joseph, B; Jackson, M; Anatoly, RB
    Alpha particle therapy, such as diffusing alpha-emitters radiation therapy (DaRT) and targeted alpha-particle therapy (TAT), exploits the short-range and high linear energy transfer (LET) of alpha particles to destroy cancer cells locally with minimal damage to surrounding healthy cells. Dosimetry for DaRT and TAT is challenging, as their radiation sources produce mixed radiation fields of α particles, β particles, and γ rays. There is currently no dosimeter for real-time in vivo dosimetry of DaRT or TAT. Metal-oxide-semiconductor field-effect transistors (MOSFETs) have features that are ideal for this scenario. Owing to their compactness, MOSFETs can fit into fine-gauge needle applicators, such as those used to carry the radioactive seeds into the tumour. This study characterized the response of MOSFETs designed at the Centre for Medical and Ra diation Physics, University of Wollongong. MOSFETs with three different gate oxide thicknesses (0.55 µm, 0.68 µm, and 1.0 µm) were irradiated with a 5.5 MeV mono-energetic helium ion beam (He2+) using SIRIUS 6MV accelerator tandem at the Australian Nuclear Science and Technology Organization (ANSTO) and an Americium-241 (241Am) source. The sensitivity and dose-response linearity were assessed by analysing the spatially resolved median energy maps of each device and their corresponding voltage shift values. The re sults showed that the response of the MOSFET detectors was linear with alpha dose up to 25.68 Gy. Also, it was found that a gate bias of between 15 V and 60 V would optimize the sensitivity of the detectors to alpha particles with energy of 5.5 MeV. © The Authors.
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    Charge collection in SOI microdosimeters and their radiation hardness
    (IEEE, 2023-02-03) Pan, VA; Tran, LT; Pastuovic, Z; Hill, D; Williams, JB; Kok, A; Povoli, M; Pogossov, A; Peracchi, S; Boardman, DA; Davis, J; Guatelli, S; Petasecca, M; Lerch, MLF; Rosenfeld, AB
    A new batch of microdosimeters has been extensively studied for their charge collection efficiency (CCE) properties, as well as their radiation hardness for medical, space and accident applications. Silicon-on-insulator (SOI) microdosimeters with an active layer thickness of 10, 20 and 50 μm have been investigated and were characterized with a 24 MeV carbon ion beam as well as a Co-60 gamma source. A negative pulse was observed in addition to the positive pulses generated within the sensitive volumes (SVs) by incident ions which led to undesirable low energy events in the SOI microdosimeters response. To study this phenomenon, the microdosimeters were irradiated with gamma radiation from a Co-60 source with a total dose of 3 and 10 Mrad(Si). It was determined that the negative pulse was originating from the support wafer due to the displacement current phenomenon. Irradiation with the Co-60 source led to a disappearing of the negative pulse due to an increase in recombination within the support wafer while almost no changes in CCE were observed. A radiation hardness study was also performed on the 50 μm SOI microdosimeter with 16 SVs being irradiated with a fluence of ~ 10 8 12 C ions/cm 2 . A CCE deficit of approximately 2% was observed at an operation bias of 10V within the SVs. The findings of this work demonstrate that the SOI microdosimeters can be utilized in space and medical applications as they can handle typical levels of dose encountered in these applications. Additionally, evidence for SOI microdosimeter fabrication standards in terms of support wafer resistivity and buried oxide (BOX) thickness is shown. © 2023 IEEE
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    The effects of temperature and moulting on metal concentrations in decapod crustaceans
    (Australian Nuclear Science and Technology Organisation, 2019-09-03) Hill, D; Cresswell, T; Seery, C; Taylor, J; Mahoney, P
    The predicated rise in sea surface temperature due to climate change may affect the uptake and depuration of contaminants by crustaceans, affecting their survival and reproductive success. Decapod crustaceans are routinely used as bioindicators in environmental research as they are commonly found in aquatic environments, have an omnivorous diet and an important position in food webs. They may also be exposed to a wide range of contaminants present in aquatic ecosystems from urban and industrial processes. Both ambient temperature and moulting of the exoskeleton are known to influence contaminant regulation in these taxa. This study used the radiotracers 109Cd, 54Mn and 65Zn to investigate the internal concentrations of these metals in three ambient temperature treatments, 21 ˚C, 23 ˚C and 25 ˚C, based on predicted increases in sea surface temperatures for Australia. Spotted shore crabs (Paragrapsus laevis) were exposed to two pulses of a mixed radiotracer solution, each followed by a depuration stage of five days. We found no significant effect of ambient temperature on uptake or depuration rates of the three metals. However, across temperatures the rate of uptake was significantly higher than that of depuration for 54Mn and 65Zn. Of 21 crabs, 15 moulted throughout the study and no significant difference was found in the amount of metal taken up pre and post-moult. However, there was a significant difference in whole-body metal burden between non-moulted crabs and moulted crabs immediately after moult. It was determined there was no significant difference in internal metal concentrations of 109Cd, 54Mn and 65Zn over the elevated sea surface temperatures predicted by climate change models and that moulting only significantly affected depuration of the metals.
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    Fate and sublethal effects of metals during amphibian metamorphosis: a systematic review
    (Taylor & Francis, 2021-11-11) Hill, D; Cresswell, T; Bennett, WW; Lanctôt, CM
    Amphibians provide essential ecosystem services and are facing global decline. Exposure to contaminants is a contributing factor to this decline, with permeable skin and early aquatic life likely increasing amphibian susceptibility. Their vulnerability may also be increased through metamorphosis, which involves degeneration of tissues and high energy expenditure. Exposure to metal contaminants may also result in delays to metamorphosis or reduced growth. Understanding how metal burdens change during metamorphosis and the effects metals have on postmetamorphic amphibians is essential to ensure water quality guidelines offer sufficient protection. A systematic review of the literature was conducted to identify the changes in whole-body metal burden and biodistribution pre and postmetamorphosis and the effects of metal exposures on the timing of metamorphosis and size of animals postmetamorphosis. Premetamorphic amphibians were found to have higher metal concentrations than postmetamorphic, suggesting these metals can be largely excreted prior to or during metamorphosis. Only two articles were identified that compared changes in metal biodistribution during metamorphosis, with both reporting decreasing concentrations in the gut from pre to postmetamorphosis. No laboratory studies identified significant effects relating to metamorphosis at concentrations below USEPA chronic water quality criteria. However, delays to timing or growth were observed in field studies where all analyzed metals were below criteria. Many articles did not meet the suggested minimum reporting standards, particularly for the reporting of metal exposure concentrations and physico-chemical conditions of exposure solutions. © 2021 Informa UK Limited