M.I. Reinhard

Australian Nuclear Science and Technology Organisation, Kirrawee, New South Wales, Australia

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Publications (70)57.66 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Microdosimetry is an extremely useful technique, used for dosimetry in unknown mixed radiation fields typical of space and aviation, as well as in hadron therapy. A new silicon microdosimeter with 3D sensitive volumes has been proposed to overcome the shortcomings of the conventional Tissue Equivalent Proportional Counter. In this article, the charge collection characteristics of a new 3D mesa microdosimeter were investigated using the ANSTO heavy ion microprobe utilizing 5.5 MeV He2+ and 2 MeV H+ ions. Measurement of the microdosimetric characteristics allowed for the determination of the Relative Biological Effectiveness of the 12C heavy ion therapy beam at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. Well-defined sensitive volumes of the 3D mesa microdosimeter have been observed and the microdosimetric RBE obtained showed good agreement with the TEPC. The new 3D mesa “bridge” microdosimeter is a step forward towards a microdosimeter with fully free-standing 3D sensitive volumes.
    No preview · Article · Apr 2015 · IEEE Transactions on Nuclear Science
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    ABSTRACT: Radiotherapy using heavy ion beam such as Carbon-ion has the advantage for the treatment of deep-seated tumour over conventional radiotherapy with X-rays due to an enhanced dose deposition in the Bragg peak (BP) at the end of the ion range. The highest dose can be deposited in the tumour with much lower doses to the surrounding healthy tissue. The Relative Biological Effectiveness (RBE) of a carbon-ion radiotherapy beam greatly depends on a depth of the target volume in the body and the nuclear fragmentation process that increases close to the BP or spread out BP (SOBP) as well as neutrons. It is important to understand the RBE of the heavy ions in hadron therapy applications in order to deliver correct dose. Microdosimetry is extremely useful technique, used for RBE study in unknown mixed radiation fields typical of hadron therapy. Conventional detectors for microdosimetry consist of tissue equivalent proportional counters (TEPC) which have advantages of a spherical sensitive volume and tissue equivalency through use of a tissue equivalent gas. However, TEPC has several limitations such as high voltage operation, large size of assembly, which reduces spatial resolution and introduces wall effects, and an inability to simulate multiple cells. A new silicon microdosimeter with 3D sensitive volumes (SVs) has been proposed to overcome the shortcomings of the conventional TEPC. The new microdosimeter is called "bridge" microdosimeter as it has thin Si bridges between the SVs to support the Al tracks over the SVs. The charge collection study of the new device and its application for RBE determination in 12C radiation therapy at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan is presented. This work presented the first RBE10 derivation in a 12C ion therapeutic beam using a high spatial resolution silicon microdosimeter and demonstrated a simple and fast method for Quality Assurance in charge particle therapy.
    No preview · Article · Jan 2015 · Journal and Proceedings - Royal Society of New South Wales
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    ABSTRACT: An ultra-thin 3-D detector (U3DTHIN) with a 10- μm-thick active region has been proposed to apply for microdosimetry in heavy ion therapy where the ion beam incidence is normal to the detector. The advantage of the detector is that the detector substrate below the silicon-on-insulator layer has been etched away. Extremely small columnar 3-D electrodes allow the detector to be fully depleted at very low biases with a minimum dead region due to their size. In this paper, a charge collection study of the U3DTHIN detector carried out using an ion beam-induced charge collection (IBICC) technique is presented. The IBICC study utilized a microbeam of 5.5 MeV He2 + and 20 MeV 12C ions focused to approximately 1- μm diameter. Full charge collection was observed from a bias as low as -10 V. A comparison of the detector response when irradiated from the front and rear side is also presented.
    No preview · Article · Nov 2014 · IEEE Transactions on Nuclear Science
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    ABSTRACT: Circular ion-implanted silicon detector of α-particles with a large, 5-cm2, sensitive area has been developed. An advantage of the detector is that the detector surface is easily cleanable with chemicals. The hardened surface of the detector shows no signs of deterioration of the spectroscopic and electrical characteristics upon repeated cleaning. The energy resolution along the diameters of the detector was (1.0±0.1)% for the 5.486-MeV α-particles. Detailed tests of the charge collection efficiency and uniformity of the detector entrance window were also performed with a 5.5-MeV He2+ microbeam.
    No preview · Article · Sep 2014 · Applied Radiation and Isotopes
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    ABSTRACT: Radiation detectors based on diamond are attractive for radiation protection applications in space and aviation due to their radiation hardness, large breakdown voltage, fast signal collection, and low noise, thus representing a valid alternative to silicon-based detector devices. In this paper, we study the tissue equivalence of diamond in proton and alpha particle radiation fields typical of galactic cosmic rays and solar particle events. We determine a method to convert microdosimetric response from diamond to water by means of Geant4 simulations. Results are presented showing that a simple geometrical scaling factor (similar to 0.32) of linear dimensions is adequate to convert experimentally obtained microdosimetric energy deposition spectra in diamond to equivalent microdosimetric energy deposition spectra in water.
    No preview · Article · Aug 2014 · IEEE Transactions on Nuclear Science
  • D A Prokopovich · M Ruat · D Boardman · M I Reinhard
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    ABSTRACT: The polarisation effect in CdTe:Cl has been studied using the Transient Current Technique (TCT) in order to quantitatively evaluate the subsequent changes in the charge transport properties as well as the electric field distribution in the sensor volume. The electric field is calculated from TCT pulses using the Schockley-Ramo theorem. The mobility of the charge carriers as well as their average drift velocity in the CdTe material are determined using the TCT pulse width. Infrared illumination demonstrated a temporary restoration of the electric field. However after a few minutes the polarization effect is resumed, even under constant IR illumination.
    No preview · Article · Apr 2014 · Journal of Instrumentation
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    ABSTRACT: A study of charge collection in SINTEF 3D active edge silicon detectors was carried out at ANSTO using Ion Beam Induced Charge (IBIC) technique. An IBIC study has shown that several different geometries of 3D detectors have full depletion under low applied bias. The effect of fast neutron and gamma radiation on their charge collection efficiency was also investigated. A 3D active edge silicon detector technology has demonstrated extremely promising performance for application of the 3D Sensitive Volumes (SVs) fabrication methods to SOI microdosimetry.
    No preview · Article · Mar 2014 · IEEE Transactions on Nuclear Science
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    ABSTRACT: A 4th generation silicon microdosimeter has been designed by the Centre for Medical Radiation Physics (CMRP) at the University of Wollongong using three dimensional (3D) Sensitive Volumes (SVs). This new microdosimeter design has the advantage of well-defined 3D SVs as well as the elimination of lateral charge diffusion by removal of silicon laterally adjacent to the 3D SVs. The gaps between the sensitive volumes are to be backfilled with PolyMethyl MethAcrylate (PMMA) to produce a surrounding tissue equivalent medium. The advantage of this design avoids the generation of secondary particles from inactive silicon lateral to SVs. The response of the microdosimeter to the neutron field from 252Cf, Pu-Be sources and an avionic radiation environment were simulated using the Geant4 Monte Carlo toolkit for design optimisation. The simulated energy deposition in the SVs from the neutron fields and microdosimetric spectra is presented. The simulation study shows a significant reduction in silicon nuclear recoil contribution to the energy deposition for the novel microdosimeter design. The reduction of silicon recoil events from outside of the SV’s will consequently reduce the uncertainty in the calculated dose equivalent. The simulations have demonstrated that a 3D silicon microdosimeter surrounded by PMMA can produce microdosimetric spectra similar to those of a tissue equivalent microdosimeter.
    No preview · Article · Feb 2014 · IEEE Transactions on Nuclear Science
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    ABSTRACT: An n-SOI microdosimeter which has been proposed as a device for predicting the occurrence of single event effects in semiconductor electronics in the high-energy, mixed heavy ion space radiation environment has been investigated to better understand the charge collection geometry and charge collection mechanisms. Ion beam induced charge collection studies using 20 MeV $^{12}$C ions, 5.5 MeV $^4$He ions, and 2 MeV H ions were carried out, and the effects of different bias conditions, angles of ion incidence, and coincidence analysis were observed to understand the sensitive volume geometry. The energy response of the n-SOI microdosimeter has been observed to exhibit an over-response of 56%, 113%, and 23% for the above ions compared to expected energy depositions calculated using SRIM 2008. No relationship between particle LET AU: Please provide spelling for “LET” and the enhance energy response was apparent. A comparison of experimentally measured and simulated spectra suggest a cylindrical charge collection geometry despite the physical rectangular parallelepiped geometry of the p-i-n diode. This was supported by observing the response of the microdosimeter to ions at oblique ion incidence. A simplified model of diffusion charge collection found that diffusion charge collection contributes to the low-energy tail observed in experimental spectra, but does not account for the observed enhanced energy response. This supports the current theory that the enhanced energy response is a result of a displacement current produced when charge carriers in the substrate induce charge in the SOI layer due to the parasitic capacitance of the buried SiO$_2$ insulating layer.
    No preview · Article · Dec 2013 · IEEE Transactions on Nuclear Science
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    ABSTRACT: Charge transport characteristics of Cd0.95Mn0.05Te: In radiation detectors have been evaluated by combining time resolved current transient measurements with time of flight charge transient measurements. The shapes of the measured current pulses have been interpreted with respect to a concentration of net positive space-charge, which has resulted in an electric field gradient across the detector bulk. From the recorded current pulses the charge collection efficiency of the detector was found to approach 100%. From the evolution of the charge collection efficiency with applied bias, the electron mobility-lifetime product of μnτn = (8.5 ± 0.4) × 10−4 cm2/V has been estimated. The electron transit time was determined using both transient current technique and time of flight measurements in the bias range of 100–1900 V From the dependence of drift velocity on applied electric field the electron mobility was found to be μn = (718 ± 55) cm2/(V.s) at room temperature.
    No preview · Article · Jul 2013 · Journal of Semiconductors
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    ABSTRACT: The charge transport properties of a high-purity CdMnTe (CMT) crystal have been measured at room temperature down to a micron-scale resolution. The CMT crystal, doped with indium, was grown by the vertical Bridgman technique. To reduce the residual impurities in the Mn source material, the growth process incorporated a five-times purification process of MnTe by a zone-refining method with molten Te solvent. The resulting 2.6 mm thick crystal exhibited an electron mobility-lifetime product of μnτn=2.9 × 10-3 cm2V-1. The velocity of electron drift was calculated from the rise time distribution of the preamplifier's output pulses at each measured bias. The electron mobility was extracted from the electric field dependence of the drift velocity and at room temperature it has a value of μn=(950±90) cm2/Vs. High-resolution maps of the charge collection efficiency have been measured using a scanning microbeam of 5.5 MeV 4He2+ ions focused to a beam diameter <; 1 μm and display large-area spatial uniformity. The evolution of charge collection uniformity across the detector has been highlighted by acquiring measurements at applied biases ranging between 50 V and 1100 V. Charge transport inhomogeneity has been associated with the presence of bulk defects. It has been demonstrated that minimizing the content of impurities in the MnTe source material is highly effective in achieving major improvements in the CMT detector's performance as compared to previous data.
    No preview · Article · Apr 2013 · IEEE Transactions on Nuclear Science
  • A Flynn · D Boardman · M.I. Reinhard
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    ABSTRACT: This work has evaluated synthetic gamma-ray spectra created by the RASE sampler using experimental data. The RASE sampler resamples experimental data to create large data libraries which are subsequently available for use in evaluation of radionuclide identification algorithms. A statistical evaluation of the synthetic energy bins has shown the variation to follow a Poisson distribution identical to experimental data. The minimum amount of statistics required in each base spectrum to ensure the subsequent use of the base spectrum in the generation of statistically robust synthetic data was determined. A requirement that the simulated acquisition time of the synthetic spectra was not more than 4% of the acquisition time of the base spectrum was also determined. Further validation of RASE was undertaken using two different radionuclide identification algorithms.
    No preview · Article · Apr 2013 · Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine
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    ABSTRACT: Two-photon annihilation quanta are emitted in a pure quantum state and when detected in coincidence, the photon pairs possess orthogonal polarizations. We propose that this polarization correlation can be exploited in Positron Emission Tomography (PET), which relies crucially on accurate coincidence detection of photon pairs. In this proof of concept study, we investigate how photon polarization information can be exploited in PET imaging by developing a method to discern true coincidences using the polarization correlation of annihilation pairs. We demonstrate that the unique identification of true photon pairs with their polarization correlation can dramatically enhance overall PET image quality, especially for high emission rates, when conventional, energy- based coincidence detection methods become increasingly unreliable. Our results suggest that polarization-based coincidence detection offers new prospects for in vivo molecular imaging with next-generation PET systems.
    No preview · Conference Paper · Mar 2013
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    ABSTRACT: The response of ΔE-E telescope in C12 ion beam at defined positions within the Bragg peak at different depths with 0.5mm step was studied using Geant4 Monte Carlo toolkit. The microdosimetric spectra derived from ΔE stage response using assumption that average chord is 1.8 μm along with simulated scatter plots for the same points. It was demonstrated that microdosimetric spectra is changing dramatically within 0.5 mm depth increments close to and at distal part of the BP that is impossible to observe with TEPC. Fragments (He4, He3, Li7, Be9, B11) and neutrons contributed to microdosimetric spectra and to YD have been analyzed for each position.
    No preview · Article · Jan 2013

  • No preview · Article · Jan 2013
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    ABSTRACT: Silicon microdosimeters for the characterisation of mixed radiation fields relevant to the space radiation environment have been under continual development at the Centre for Medical Radiation Physics for over a decade. These devices are useful for the prediction of single event upsets in microelectronics and for radiation protection of spacecraft crew. The latest development in silicon microdosimetry is a family of large-area n-SOI microdosimeters for real-time dosimetry in space radiation environments. The response of n-SOI microdosimeters to 2 MeV H and 5.5 MeV He ions has been studied to investigate their charge collection characteristics. The studies have confirmed 100% yield of functioning cells, but have also revealed a charge sharing effect due to diffusion of charge from events occurring outside the sensitive volume and an enhanced energy response due to the collection of charge created beneath the insulating layer. The use of a veto electrode aims to reduce collection of diffused charge. The effectiveness of the veto electrode has been studied via a coincidence analysis using IBIC. It has been shown that suppression of the shared events allows results in a better defined sensitive volume corresponding to the region under the core electrode where the electric field is strongest.
    No preview · Article · Dec 2012 · IEEE Transactions on Nuclear Science
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    ABSTRACT: This paper is dedicated to the characterization of a novel diamond microdosimeter prototype with 3D sensitive volumes produced by high energy boron implantation. Diamond has been chosen in order to further improve solid state based microdosimeter in terms of radiation hardness and tissue equivalency. IBIC measurements were undertaken to determine the charge collection efficiency map of the device. It was demonstrated that the proposed ion implantation technology allows for the formation of an array of well defined 3D SVs. A Geant4 application was developed to explain the effect of Al electrode thickness on observed anomaly in deposited energy. Specifics of the results and an update on the current status of the project is presented.
    No preview · Article · Dec 2012 · IEEE Transactions on Nuclear Science
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    ABSTRACT: This paper presents the growth, fabrication and characterization of indium-doped cadmium manganese telluride (CdMnTe) crystals grown by the vertical Bridgman technique. The 10$\,\times\,$ 10$\,\times\,$ 1.9 mm$^{3}$ samples have been fabricated, and the charge collection properties of the CdMnTe detectors have been measured. Alpha-particle spectroscopy measurements have yielded an average charge collection efficiency approaching 100%. Ion beam induced charge (IBIC) measurements have been performed by raster scanning focused 5.5 MeV $^4$ He beams onto the detectors. Spatially resolved charge collection efficiency maps have been produced for a range of detector bias voltages. Inhomogeneities in the charge transport of the CdMnTe crystals have been associated with chains of Te inclusions within the detector bulk, and the reduction in charge collection efficiency in their locality has been quantified. It has been shown that the role of Te inclusions in degrading charge collection is reduced with increasing values of bias voltage. IBIC measurements for a range of low biases have highlighted the evolution of the charge collection uniformity across the detectors.
    No preview · Article · Jun 2012 · IEEE Transactions on Nuclear Science
  • Source
    A.L. McNamara · H Heijnis · D Fierro · M.I. Reinhard
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    ABSTRACT: A Compton suppressed high-purity germanium (HPGe) detector is well suited to the analysis of low levels of radioactivity in environmental samples. The difference in geometry, density and composition of environmental calibration standards (e.g. soil) can contribute to excessive experimental uncertainty to the measured efficiency curve. Furthermore multiple detectors, like those used in a Compton suppressed system, can add complexities to the calibration process. Monte Carlo simulations can be a powerful complement in calibrating these types of detector systems, provided enough physical information on the system is known. A full detector model using the Geant4 simulation toolkit is presented and the system is modelled in both the suppressed and unsuppressed mode of operation. The full energy peak efficiencies of radionuclides from a standard source sample is calculated and compared to experimental measurements. The experimental results agree relatively well with the simulated values (within ∼5 - 20%). The simulations show that coincidence losses in the Compton suppression system can cause radionuclide specific effects on the detector efficiency, especially in the Compton suppressed mode of the detector. Additionally since low energy photons are more sensitive to small inaccuracies in the computational detector model than high energy photons, large discrepancies may occur at energies lower than ∼100 keV.
    Full-text · Article · Apr 2012 · Journal of Environmental Radioactivity
  • David Boardman · Mark Reinhard · Alison Flynn
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    ABSTRACT: The scanning of cargo for radiological and nuclear material is vital in detecting the illicit trafficking of such materials. The deployment of technologies such as Radiation Portal Monitors (RPMs) has enabled screening for the presence of gamma and neutron emitting radionuclides. Although the development of radionuclide detection algorithms is vital to the development of RPMs, only a small amount of the work exists in the published literature. This paper describes the development of an anomalous signature detection algorithm based on Principal Component Analysis (PCA). PCA involves the eigen decomposition of the correlation matrix of a training data set. The distance of an unknown observed spectrum from Naturally Occurring Radioactive Materials (NORM), in a 14 dimensional space, was used to assess the algorithm performance. The PCA algorithm showed an excellent 'anomaly detection' performance for a number of threat sources including Special Nuclear Materials (SNM's). The PCA algorithm has also demonstrated an improved performance over that of a commercially available peak search algorithm. The discrimination of the SNM's sources, from the NORM, consistently improved with increased counts, which is not always true for peak search based algorithms. The algorithm also performed well in count starved spectra, which is of relevance to border security applications of RPMs.
    No preview · Article · Feb 2012 · IEEE Transactions on Nuclear Science

Publication Stats

297 Citations
57.66 Total Impact Points


  • 2002-2014
    • Australian Nuclear Science and Technology Organisation
      • Institute of Materials Engineering
      Kirrawee, New South Wales, Australia
  • 2013
    • University of Western Australia
      • School of Electrical, Electronic and Computer Engineering
      Perth City, Western Australia, Australia
  • 1999-2011
    • University of Wollongong
      • Centre for Medical Radiation Physics
      City of Greater Wollongong, New South Wales, Australia
  • 2007
    • University of Sydney
      • Institute of Medical Physics
      Sydney, New South Wales, Australia