Browsing by Author "Jackson, M"

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    3D sensitive volume microdosimeter with improved tissue equivalency: charge collection study and its application in 12C ion therapy
    (IOP Publishing, 2018-02-06) James, B; Tran, LT; Bolst, D; Prokopovich, DA; Reinhard, MI; Lerch, MLF; Petasecca, M; Guatelli, S; Povoli, M; Kok, A; Matsufuji, N; Jackson, M; Rosenfeld, AB
    This research focuses on the characterisation of a new 3D sensitive volume (SV) microdosimeter covered with polyimide – a material which closely mimics human tissue. The electrical and charge collection properties of the device were investigated and its application in 12C ion therapy were studied. Charge collection studies revealed uniform charge collection and no cross talk between adjacent SVs. To study the microdosimetric response in 12C ion therapy, the new polyimide mushroom microdosimeter were placed at various positions along the central axis of a 290 MeV/u 12C ion spread out Bragg peak (SOBP) at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. From these microdosimetric spectra, dose mean lineal energy $(\overline{{y}_{D})}$ and RBE10 results were obtained, with RBE10 increasing from 1.3 at the entrance to 2.7 at the end of the SOBP. The results obtained in this work show that the new generation of mushroom microdosimeters, covered with tissue equivalent polyimide material, are a useful tool for quality assurance in heavy ion therapy applications. © Open Access - CC BY - IOP Publishing Ltd.
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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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    Ion beam irradiation effects in strontium zirconium phosphate with NZP-structure type
    (Elsevier Science BV, 2014-03-01) Gregg, DJ; Karatchevtseva, I; Thorogood, GJ; Davis, J; Bell, BDC; Jackson, M; Dayal, P; Ionescu, M; Triani, G; Short, KT; Lumpkin, GR; Vance, ER
    Ceramics with the sodium zirconium phosphate or NZP type structure have potential as nuclear waste form and inert matrix materials. For both applications the material will be subjected to self-radiation damage from alpha-decay of the incorporated actinides. In this study, ion-beam irradiation using Au- and He-ions has been used to simulate the consequences of a-decay and the effects of irradiation on the structural and macroscopic properties (density and hardness) have been investigated. Irradiation by Au-ions resulted in a significant volume contraction of similar to 7%, a reduction in hardness of similar to 30% and a loss in long-range order at fluences above 10(14) Au-ions/cm(2). In contrast, little effect on the material properties was noted for samples irradiated with He-ions up to a fluence of 10(17) ions/cm(2). Thermal annealing was investigated for the highest fluence Au-ion irradiated sample and significant decomposition was observed. © 2014, Elsevier Ltd.
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    Solid-state microdosimeter for personal radon dosimetry in mines and caves
    (ICRP, 2019-11-17) Tran, LT; James, B; Prokopovich, DA; Boardman, DA; Werczynski, S; Chambers, SD; Waring, CL; Williams, AG; Povoli, M; Lok, A; Jackson, M; Rosefeld, AB
    Radon gas can be found naturally from the materials in which it is formed that contain traces of uranium, actinium, thorium, or neptunium. Uranium and radium are commonly found in soil, rocks and water, especially in enclosed spaces such as mines, caves, cellars or poorly ventilated houses. Radon levels found in uranium, coal and metal mines, especially underground mines, can be up to orders of magnitude above ambient outdoor levels. Radon progeny attach easily to dust particles that can deposit in the lungs when inhaled. Once deposited in the lungs, the radon progeny emits alpha particles, mostly from short lived isotopes 218Po (T1/2 = 3.1 min, E = 6 MeV) and 214Po (T1/2=164.3 µs, E = 7.7 MeV), irradiating and damaging the DNA of lungs or proximal organ tissue, which may increase the risk of developing lung cancer - the second most common cause after smoking. Therefore monitoring radon levels in mines and caves is strictly required in order to protect workers from the health effects of radon exposure. Current radon detectors are bulky, expensive and only measure radon concentration, requiring conversion from concentration to dose which can result in large uncertainties [1]. This work presents a newly developed portable silicon on insulator (SOI) microdosimeter system for use in radon rich environments to measure the dose equivalent caused by 222Rn and its decay progeny. The microdosimeter used in this work is the Mushroom microdosimeters invented and developed by the CMRP, University of Wollongong and fabricated in collaboration with SINTEF MiNaLab, Oslo, Norway. The detector system directly measures in real time dose equivalent H(µSv/h) in a 222Rn gas environment rather than its calculation based on radon activity and dose conversion factor (DCF) as currently. The experiment was carried out at ANSTO environment lab where 245 kBq 226Ra source provides a radon concentration of approximately 150kBq/m3. A dose rate equivalent of 15.4 mSv/h and average quality factor ( ) of 19.96 was measured by the microdosimeter system for the given radon concentration. This result demonstrated that the microdosimeter system can be used in caves, mines for radon dose equivalent monitoring. Miniaturization of electronic personal microdosimeter is in progress and the preliminary results will be presented at the conference.