ANSTO :: Browsing by Author "Boardman, DA"

Browsing by Author "Boardman, DA"

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Application of the CORIS360 Gamma Ray Imager at a light source
(JACoW Publishing, 2021-05-24) Tan, YRE; Boardman, DA; Chartier, L; Guenette, MC; Ilter, M; Watt, GC
The CORIS360 is a gamma-ray imager developed at Australian Nuclear Science and Technology (ANSTO) for identifying and localising sources of radiation typically from gamma emitting radionuclides. The low EMI and low noise power supply features of the imaging technology have enabled it to have a low energy detection threshold and to detect photons as low as 20 keV. This report shall present the initial measurements performed at the Australian Synchrotron, in the storage ring and beamlines, where the imager is able to detect radiation from all sources of synchrotron radiation (dipole, wiggler and undulator). The radiation imaging results from the injection system and scrapers (to dump the stored beam) will be discussed. Future developments for imaging in pulsed radiation environments and time varying environments will also be discussed. © 2021 JACoW
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
Charge transport properties of CdMnTe radiation detectors
(EDP Sciences, 2012-04-11) Rafiei, R; Boardman, DA; Reinhard, MI; Sarbutt, A; Kim, KH; Watt, GC; Uxa, S; Prokopovich, DA; Belas, E; Bolotnikov, AE; James, RB
Growth, fabrication and characterization of indium-doped cadmium manganese telluride (CdMnTe) radiation detectors have been described. Alpha-particle spectroscopy measurements and time resolved current transient measurements have yielded an average charge collection efficiency approaching 100 %. 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 tellurium inclusions within the detector bulk. Further, it has been shown that the role of tellurium inclusions in degrading charge collection is reduced with increasing values of bias voltage. The electron drift velocity was calculated from the rise time distribution of the preamplifier output pulses at each measured bias. From the dependence of drift velocity on applied electric field the electron mobility was found to be μn = (718 ± 55) cm2/Vs at room temperature. © 2012 the Authors, published by EDP Sciences.
A condensed overview of sub-geV hadronic physics in GEANT4
(Australian Nuclear Science and Technology Organisation, 2022-08-11) Brown, JMC; Boardman, DA; Flynn, A
This technical report provides a condensed overview of the underlying physics processes of transport, interaction, and production of sub-GeV hadronic particles in Geant4. The report was developed and funded under Project Arrangement 10256 in collaboration with the Defence Science and Technology Group of the Australian Department of Defence. The material contained in this report provides a complementing resource to the Geant4 Physics Reference Manual (G4PRM) for novice to intermediate user of the Monte Carlo toolkit. The authors acknowledge that this condensed overview draws heavily on the past work of the Geant4 Collaboration (G4Collab) and publications outlined in Section 9 (References).
Evaluation of novel gamma ray imaging technology
(Australasian Radiation Protection Society, 2017-08-09) Guenette, MC; Boardman, DA; Sarbutt, A; Flynn, A; Prokopovich, DA
We present the imaging results from a novel single pixel gamma-ray imaging system, developed at ANSTO, which is capable of providing quantitative, spectroscopic gamma images using a fast and efficient imaging methodology. Gamma ray imaging can assist in surveying active areas by providing information of the radiation environment in areas which are hard to reach (e.g. in enclosed spaces or at height) and by gaining valuable information about the radiation environment whist limiting exposure to personnel in high dose rate environments. The system design provides a large field of view (360° × 70°) and covers a wide energy range of 40 keV to 1.5 MeV. The gamma ray image is overlaid on a 360° panoramic optical image of the scene, which allows for easy location of the gamma emitting radionuclides that are present. By selecting different regions of interest in the recorded gamma spectrum, separate radionuclide specific images, of the area being surveyed, can be visualised. Calibration of the detector allows for quantitative mapping of where each component of the dose rate at the detector originates. This can be converted into activity with a priori knowledge of the scene geometry. Gamma-ray images have been experimentally obtained for both point sources and extended sources in controlled testing environments and these results will be presented. The imaging results from a range of real world operational environments, around the ANSTO site, will be presented and demonstrate the systems capability for locating sources of radiation in nuclear industry applications.
A gamma-ray identification algorithm based on fisher linear discriminant analysis
(Institute of Electrical and Electronics Engineers (IEEE), 2015-12-25) Boardman, DA; Flynn, A
An algorithm for gamma-ray identification applications has been developed and evaluated. The algorithm is based on a Fisher Linear Discriminant Analysis (FLDA) technique that generates loading coefficients that maximize the separation of a particular radionuclide from all the other radionuclides in a training library. Separate experimental data sets were obtained for the algorithms training data and for the performance evaluation. The algorithm was evaluated against a range of radionuclides and acquisitions times. An inverse square root relationship between the cluster standard deviation and its gross mean counts enabled the production of an adaptable threshold. The inverse square relationship between the Mahalanobis distance metric and the Cs-137 standoff distance demonstrated a means to quantify the measured number of counts. The FLDA identification performance, for a number of threat radionuclides (including special nuclear materials), exceeded that of a commercially available peak search algorithm. The high sensitivity and specificity, of the FLDA algorithm, was maintained in low count situations. The poor performance for some radionuclides was attributed to the measured number of counts being below the minimal detectable limit. The FLDA algorithm has the potential to be used in gamma-ray identification applications and, in particular, count starved situations. © 2012, Institute of Electrical and Electronics Engineers (IEEE).
High-purity CdMnTe radiation detectors: a high-resolution spectroscopic evaluation
(Intistute of Electrical Engineers, 2013-02-07) Rafiei, R; Reinhard, MI; Kim, KH; Prokopovich, DA; Boardman, DA; Sarbutt, A; Watt, GC; Bolotnikov, AE; Bignell, LJ; James, RB
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. © 2013, IEEE.
Investigation of Polarisation in CdTe using TCT
(IOP Science, 2016-04-15) Prokopovich, DA; Ruat, M; Boardman, DA; Reinhard, MI
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. © 2014, IOP Publishing Ltd and Sissa Medialab srl.
Performance of a fisher linear discriminant analysis gamma-ray identification algorithm
(Institute of Electrical and Electronics Engineers (IEEE), 2013-04-11) Boardman, DA; Flynn, A
The development of a gamma-ray identification algorithm based on a Fisher Linear Discriminant Analysis (FLDA) approach has previously shown high potential in count starved situations. This work uses 48,000 semi-empirical synthetic spectra to evaluate the algorithm performance over a broad range of dose rates and acquisition times. True positive identifications of 100% were typically seen for dose rates ≥ 0.05 μSv/h and acquisition times ≥10 s. For in air and shielded radionuclide spectra, no false alarms were observed for dose rates ≥ 0.01 μSv/h and acquisition times ≥10 s. The single radionuclide identification performance typically exceeded the ANSI 42.34 standard by a factor of 10 for dose rate and a factor of 10 for acquisition time. The evaluated shielded signatures had no detrimental effects to the identification performance. The correct identification of HEU masked by a 0.5 μSv/h 40K or 60Co source could typically be made for a masking ratio of 10:1 for acquisition times ≥ 1 s. For masking with a 0.5 μSv/h 137Cs source, HEU could be identified at 7:1 ratios for times ≥10 s. The excellent results were obtained for a non-optimal identification threshold. Optimization of the threshold would lead to further performance improvements. © 2013, Institute of Electrical and Electronics Engineers (IEEE).
Positron emission tomography coincidence detection with photon polarization correlation
(SPIE, 2013-02-09) McNamara, AL; Wu, KW; Boardman, DA; Reinhard, MI; Kuncic, Z
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. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE).
Single pixel compressive gamma-ray imaging with randomly encoded masks
(IOP Publishing, 2020-04-15) Boardman, DA; Sarbutt, A; Flynn, A; Guenette, MC
We report on the development and demonstration of a single pixel spectroscopic gamma-ray imaging concept based on the principles of compressed sensing. Compressive gamma-ray images were obtained for both point sources and complex extended sources. The reconstruction of images at different photon energies allowed the spatial mapping of different radionuclides. When compared to traditional aperture based gamma-ray imaging techniques, the point source images were generated with ten times fewer measurements. More complex extended source images were generated with up to three times fewer measurements. Gamma-ray imaging techniques designed around the principles of compressed sensing have the potential to exploit the sparsity typically found in gamma-ray images, leading to a new class of fast and low cost imaging systems. © Copyright 2020 IOP Publishing
The validation of synthetic spectra used in the performance evaluation of radionuclide identifiers
(Elsevier, 2013-07-01) Flynn, A; Boardman, DA; Reinhard, MI
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. © 2013, Elsevier Ltd.

Browsing by Author "Boardman, DA"

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