Browsing by Author "Pan, VA"

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    Application of an SOI microdosimeter for monitoring of neutrons in various mixed radiation field environments
    (Institute of Electrical and Electronics Engineers (IEEE), 2022-03-01) Pan, VA; Vohradsky, J; James, B; Pagani, F; Chartier, L; Debrot, E; Pastuovic, Z; Cutajar, D; Poder, J; Nancarrow, M; Pereloma, E; Bolst, D; Lee, SH; Inaniwa, T; Safavi-Naeini, M; Prokopovich, DA; Guatelli, S; Petasecca, M; Lerch, MLF; Povoli, M; Kok, A; Tran, LT; Rosenfeld, AB
    Radiation monitoring in space radiation is complex due to galactic cosmic rays (GCRs), solar particle events (SPEs), and albedo particles. Thermal neutrons are an important component in the Moon radiation albedo field which can cause single event upset (SEU) in electronics when they interact with the 10 B present in electronic components. In this work, we studied an application of silicon on insulator (SOI) microdosimeters for neutron monitoring in various mixed radiation field environments. A 10- μm SOI microdosimeter was utilized in conjunction with a 10 B 4 C thin-film converter to successfully measure the thermal neutron contribution out of field of a therapeutic proton beam as well as an 18-MV X-ray linear accelerator (LINAC). The microdosimeter was placed downstream of the Bragg peak (BP) as well as laterally out of field of the proton beam and at two positions along the treatment couch of the 18-MV LINAC. It was demonstrated that the 10- μm SOI microdosimeter with 10 B 4 C converter is suitable for detection of thermal neutrons with excellent discrimination of gamma, fast and thermal neutron components in the presence of a gamma-neutron pulsed field of an 18-MV LINAC. To reduce the gamma contribution and further improve detection of neutrons in mixed radiation fields, a new 2 μm Mushroom-planar microdosimeter was fabricated and characterized in detail using an ion beam induced charge collection (IBIC) technique with 1.78 MeV He2+ ions. It was demonstrated that this 2 μm SOI microdosimeter can be operated in a passive mode. The SOI microdosimeter with the 10 B 4 C converter can be recommended for the detection of thermal neutrons for SEU prediction in the mixed gamma-neutron fields during space missions, especially for the Moon mission.© Copyright 2025 IEEE
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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