Browsing by Author "Povoli, 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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    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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    IBIC microscopy – the powerful tool for testing micron – sized sensitive volumes in segmented radiation detectors used in synchrotron microbeam radiation and hadron therapies
    (Elsevier B. V., 2019-11-01) Pastuovic, Z; Davis, J; Tran, LT; Paino, JR; Dipuglia, A; James, B; Povoli, M; Kok, A; Perevertaylo, VL; Siegele, R; Prokopovich, DA; Lerch, MLF; Petasecca, M; Rosenfeld, AB; Cohen, DD
    Ion Beam Induced Charge (IBIC) microscopy performed using highly tuned microbeams of accelerated ions with energies in the MeV range is the powerful tool for analysis of charge carrier transport properties in semiconductor devices based on semiconductor hetero-junction, metal-on-semiconductor and semiconductor-on-insulator configurations. Here we present two cases of recent applications of the IBIC microscopy in the field of medical radiation physics. The reduced-rate ion microbeams with energies in the MeV range and sub-micrometer spot-sizes have been used for the investigations of the charge collection efficiency (CCE) in sensitive volumes of segmented radiation detectors in order to measure the spatial distribution and uniformity of CCE in different polarization conditions. This information allows the determination of the charge carrier transport properties in selected substructures of a particular device and to quantify its ability to accurately determine the energy deposited by incident ionizing radiation - two fundamental requirements of any microdosimeter or detector of ionizing radiation. © 2019 Elsevier B.V.