M.I. Reinhard

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

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Publications (59)45.69 Total impact

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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.
    Journal of Instrumentation 04/2014; 9(04):P04015. · 1.66 Impact Factor
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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.
    Applied Radiation and Isotopes. 01/2014; 92:96–101.
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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.
    Journal of Semiconductors 07/2013; 34(7):073001.
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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.
    IEEE Transactions on Nuclear Science 04/2013; 60(2):1450-1456. · 1.22 Impact Factor
  • 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.
    Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine 04/2013; 77C:145-152. · 1.09 Impact Factor
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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.
    IEEE Transactions on Nuclear Science 01/2013; 60(6):4289-4296. · 1.22 Impact Factor
  • 01/2013;
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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.
    IEEE Transactions on Nuclear Science 12/2012; 59(06):3110-3116. · 1.22 Impact Factor
  • IEEE Transactions on Nuclear Science 12/2012; 59(6):3110-3116. · 1.22 Impact Factor
  • 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.
    Journal of environmental radioactivity 04/2012; 106:1-7. · 1.47 Impact Factor
  • 01/2012;
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    ABSTRACT: Lethal cell damage by ionising radiation is generally initiated by the formation of complex strand breaks, resulting from ionisation clusters in the DNA molecule. A better understanding of the effect of the distribution of ionisation clusters within the cell and particularly in regard to DNA segments could be beneficial to radiation therapy treatment planning. Low energy X-rays generate an abundance of low energy electrons similar to that associated with MeV protons. The study and comparison of the track structure of photon and proton beams could permit the substitution of photon microbeams for single cell ion irradiations at proton facilities used to predict the relative biological effectiveness (RBE) of charged particle fields. The track structure of X-ray photons is compared with proton pencil beams in voxels of approximate DNA strand size (2 × 2 × 5 nm). The Very Low Energy extension models of the Monte Carlo simulation toolkit GEometry ANd Tracking 4 (Geant4) is used. Simulations were performed in a water phantom for an X-ray and proton beam of energies 100 keV and 20 MeV, respectively. The track structure of the photon and proton beams are evaluated using the ionisation cluster size distribution as well as the radial dose deposition of the beam. A comparative analysis of the ionisation cluster distribution and radial dose deposition obtained is presented, which suggest that low energy X-rays could produce similar ionisation cluster distributions to MeV protons on the DNA scale of size at depths greater than ∼10 μm and at distances greater than ∼1 μm from the beam centre. Here the ionisation cluster size for each beam is less than ∼100. The radial dose deposition is also approximately equal at large depths and at distances greater than 10 μm from the beam centre.
    International Journal of Radiation Biology 01/2012; 88(1-2):164-70. · 1.84 Impact Factor
  • 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.
    IEEE Transactions on Nuclear Science 01/2012; 59(1):154-160. · 1.22 Impact Factor
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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.
    IEEE Transactions on Nuclear Science 01/2012; 59(3):634-641. · 1.22 Impact Factor
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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.
    IEEE Transactions on Nuclear Science 01/2012; 59(6):3126-3132. · 1.22 Impact Factor
  • 01/2012;
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    ABSTRACT: In proton therapy neutrons are introduced to out-of-field regions inside the patient. Clinicians would like to know the absorbed dose being deposited by neutrons separately to that from protons, so as to be able to directly apply their own dose equivalent weighting factors based on their opinion of the biological risk posed by neutrons in this region. The purpose of this study is to investigate a novel approach to experimentally separating the proton and neutron contributions to the absorbed dose in out-of-field regions. The method pairs specially designed silicon PIN diodes with a standard clinical ionization chamber. The sensitivity of the Si diode to non-ionizing energy losses in silicon is exploited, and can be quantified by measuring the shift in forward voltage for a fixed injection current, pre and post irradiation. The mathematical relations that describe the response of the diode and the ionization chamber can be solved simultaneously to give the contributions to the absorbed dose from protons and neutrons separately. Experimental measurements were made at the Loma Linda University Medical Center (LLUMC), Loma Linda, and Massachusetts General Hospital (MGH), Boston, proton therapy facilities. Experimental separation of the partial proton and neutron contributions to the absorbed dose measured at positions lateral to a typical prostate therapy treatment field delivered to a Lucite phantom was successfully performed and compared with results from a GEANT4 simulation. The experimental results matched well with simulation confirming the validity and promise of the novel approach.
    Radiation Measurements 12/2011; 46(12):1368-42. · 0.86 Impact Factor
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    ABSTRACT: The response of a Silicon On Insulator (SOI) Microdosimeter and a silicon PIN diode were tested at the TSL quasimonoenergetic neutron beamline at Uppsala university. The objective was to determine the response of both the SOI Microdosimeter and silicon PIN diode to a high energy quasi-monoenergetic neutron field for potential future application of the devices in aviation dosimetry. PIN diode angular response dependence was also measured to determine the suitability of PIN diodes in a multidirectional high energy neutron field as encountered in aviation environments. Simulations of the response from the SOI Microdosimeter and PIN diode to the field using GEANT4 were obtained to assist in interpreting the experimental measurements.
    IEEE Transactions on Nuclear Science 01/2011; 58(6):3321-3327. · 1.22 Impact Factor
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    ABSTRACT: A novel neutron dosimetry system for avionics and space applications is described. The new dosimetric system is based on Medipix2, a high density silicon based pixilated detector with integrated readout and digital interface circuitry. Real time dose equivalent response to fast neutron fields with flattened energy response is achieved through the coupling of a structured variable thickness polyethylene (PE) over layer with the high density pixilated detector. Experimental results obtained to 14 MeV D-T and Am-Be neutron fields are described along with a comparison to results obtained with GEANT4 simulations.
    IEEE Transactions on Nuclear Science 01/2011; · 1.22 Impact Factor
  • 01/2011;

Publication Stats

127 Citations
45.69 Total Impact Points

Institutions

  • 2005–2014
    • Australian Nuclear Science and Technology Organisation
      • Institute of Materials Engineering
      Kirrawee, New South Wales, Australia
  • 1997–2011
    • University of Wollongong
      • Centre for Medical Radiation Physics
      Wollongong, New South Wales, Australia
  • 2007–2009
    • University of New South Wales
      • School of Electrical Engineering and Telecommunications
      Kensington, New South Wales, Australia
    • Sydney Children's Hospital
      Sydney, New South Wales, Australia