Lindsey Bignell | Australian Nuclear Science and Technology Organization (original) (raw)
Papers by Lindsey Bignell
Applied Physics Letters
We demonstrate modifications to the light yield properties of an organic liquid scintillator due ... more We demonstrate modifications to the light yield properties of an organic liquid scintillator due to the localisation of the tertiary fluorophore component to the surface of Ag-core silica-shell nanoparticles. We attribute this enhancement to the near-field interaction of Ag nanoparticle plasmons with these fluor molecules. The scintillation light yield enhancement is shown to be equal to the fluorescence enhancement within measurement
uncertainties. With a suitable choice of plasmon energy and scintillation fluor, this effect may be used to engineer scintillators with enhanced light yields for radiation detection applications.
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A new method for the absolute radioactivity measurement of radionuclides using a liquid scintilla... more A new method for the absolute radioactivity measurement of radionuclides using a liquid scintillation detector comprising three photomultipliers has been described. The method does not contain any a priori assumption of the photomultiplier detection efficiency and uses a modified Compton Coincidence technique, therefore it has been named the Zero Model By using Coincidence Scintillation (ZoMBieS) method. Validation measurements of the activity of a 63Ni source against the Triple to Double Coincidence Ratio method are presented and the results agree within their k = 1 uncertainties.
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Nuclear Instruments and …, Jan 1, 2008
Three types of lead shielding assemblies were investigated to establish which provides the lowest... more Three types of lead shielding assemblies were investigated to establish which provides the lowest background as preliminary work for determining the efficiency of a High Purity Germanium (HPGe) detector. The background continuum and peaks were examined using gamma spectroscopy with a coaxial and a planar HPGe detector. The 210Pb concentration in each lead sample taken from the assemblies was quantitatively determined. A French lead sample was found to have the lowest background in this relative comparison with a 210Pb concentration of 29.171.3 Bq kg-1.
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Nuclear Science, …, Jan 1, 2008
Monte Carlo simulations have been performed of the decay of a Au-198 solid source within a 4[pi] ... more Monte Carlo simulations have been performed of the decay of a Au-198 solid source within a 4[pi] [beta]-[gamma] coincidence detector. Calculations of the proportional counter efficiency to both beta and gamma emissions are simulated. A comparison of results obtained using the MCNP-5 and Geant4 simulation packages indicates that Geant4 better evaluates K the correction to the coincidence equation than MCNP-5 predictions. This difference can be accounted for in terms of how the codes handle the physical interactions occurring
in the foil and surrounds
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![Research paper thumbnail of The effect of multiple [gamma]-ray interactions on ionisation quenching corrections in liquid scintillants](https://attachments.academia-assets.com/5525782/thumbnails/1.jpg)
](Nuclear Instruments and …, Jan 1, 2010
The effect of multiple γ-ray interactions within a liquid scintillation detector caused by a sing... more The effect of multiple γ-ray interactions within a liquid scintillation detector caused by a single radionuclide decay event on ionisation quenching corrections has been determined. Ionisation quenching corrections to the energy deposition spectrum have been carried out over all electron-generating gamma interactions of the decay event. Comparison has been made with the approximate method typically used to correct for ionisation quench. Both calculations were carried out using the Geant4 simulation package. The two models are compared using the values of detection efficiencies of the logical sum of double coincidence obtained for 131I, 123I and 177Lu measured using the Triple-to-Double Coincidence Ratio method of absolute activity measurement. Finally, predictions are made as to the circumstances under which the two quench correction approaches will be most discrepant.
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Applied Radiation and …, Jan 1, 2010
Radiation transport simulations of the most probable gamma- and X-ray emissions of 123I and 54Mn ... more Radiation transport simulations of the most probable gamma- and X-ray emissions of 123I and 54Mn in a three photomultiplier tube liquid scintillation detector have been carried out. A Geant4 simulation was used to acquire energy deposition spectra and interaction probabilities with the scintillant, as required for absolute activity measurement using the triple to double coincidence ratio (TDCR) method. A sensitivity and uncertainty analysis of the simulation model is presented here. The uncertainty in the Monte Carlo simulation results due to the input parameter uncertainties was found to be more significant than the statistical uncertainty component for a typical number of simulated decay events. The model was most sensitive to changes in the volume of the scintillant. Estimates of the relative
uncertainty associated with the simulation outputs due to the combined stochastic and input uncertainties are provided. A Monte Carlo uncertainty analysis of an 123I TDCR measurement indicated that accounting for the simulation uncertainties increases the uncertainty of efficiency of the logical sum of double coincidence by 5.1%.
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Applied Radiation and Isotopes, Jan 1, 2010
Activity measurements of 3H were performed using the triple to double coincidence ratio method fo... more Activity measurements of 3H were performed using the triple to double coincidence ratio method for the 2009 international comparison organized by the Bureau International des Poids et Mesures (BIPM). The activity obtained by using the FPGA (field programmable gate array) acquisition system and software event analysis was compared to that using MAC3 (Module d’Acquisition de Coincidences triples). Agreement to better than 0.4% was obtained. The stability of sources prepared in Ultima Gold™, Ultima Gold™ LLT, Insta-Gel® Plus and Optiphase “Hisafe”-3 over 140 days is presented.
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Nuclear Instruments and …, Jan 1, 2009
The FASEA (FPGA based Acquisition and Software Event Analysis) system has been developed to repla... more The FASEA (FPGA based Acquisition and Software Event Analysis) system has been developed to replace the MAC3 for coincidence pulse processing. The system uses a National Instruments Virtex 5 FPGA card (PXI-7842R) for data acquisition and a purpose developed data analysis software for data analysis. Initial comparisons to the MAC3 unit are included based on measurements of 89Sr and 3H, confirming that the system is able to accurately emulate the behaviour of the MAC3 unit.
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Chem. Commun., Jan 1, 2010
The photoconversion of photomorphic silver nanoparticles from discs to prisms via citrate mediate... more The photoconversion of photomorphic silver nanoparticles from
discs to prisms via citrate mediated growth on the twin plane
faces of the nanoparticles is demonstrated. This systematic
shape evolution from discs to hexagons and then prisms of
increasing aspect ratios is a result of the growth process being
confined to specific faces of the growing nanoparticles.
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NUCLEAR …, Jan 1, 2008
Several adhesive tapes have been studied in terms of their suitability for securing gold wires in... more Several adhesive tapes have been studied in terms of their suitability for securing gold wires into positions for neutron flux measurements in the reactor core and irradiation facilities surrounding the core of the Open Pool Australian Light water (OPAL) reactor. Gamma ray spectrometry has been performed on each irradiated tape in order to identify and quantify activated components. Numerous metallic impurities have been identified in all tapes. Calculations relating to both the effective neutron shielding properties of the tapes and the error in measurement of the 198Au activity caused by superfluous activity due to residual tape have been made. The most important identified effects were the prolonged cooling times required before safe enough levels of radioactivity to allow handling were reached, and extra activity caused by residual tape when measured with an ionisation chamber. Knowledge of the most suitable tape can allow a minimal contribution due to these effects, and the use of gamma spectrometry in preference to ionisation chamber measurements of the flux wires is shown to make all systematic errors due to the tape completely negligible.
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Sipping measurements were implemented at the Open Pool Australian Light water reactor (OPAL) to t... more Sipping measurements were implemented at the Open Pool Australian Light water reactor (OPAL) to test for failure in reactor fuel elements. Fission product released by the fuel element into the pool water was measured using both High Purity Germanium (HPGe) detection via samples and a NaI(Tl) detection in-situ with the sipping device. Results from two fuel elements are presented.
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Journal of applied …, Jan 1, 2005
Terahertz emission has been observed from (100) Zn-acceptor-doped InAs under illumination by fs p... more Terahertz emission has been observed from (100) Zn-acceptor-doped InAs under illumination by fs pulses of near-infrared radiation. Turning the crystal about the surface normal produces two maxima per rotation, whether the angle of incidence is 45° or 75°, in contrast to (111) p-InAs, where three maxima per rotation have been reported. The emitted terahertz power has a quadratic variation with the pump power and decreases with increasing temperature in the range 20–300 K. This behavior is consistent with a photocurrent surge being the dominant terahertz generating mechanism at low excitation fluences. The p-type InAs generates about two orders of magnitude more power than the standard unbiased terahertz emitter, 1mm thick ZnTe.
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Journal of Materials Science: Materials in …, Jan 1, 2009
Semiconductors are efficient emitters of terahertz (THz, 1012 Hz) radiation. Non-contact means of... more Semiconductors are efficient emitters of terahertz (THz, 1012 Hz) radiation. Non-contact means of accurately measuring the physical parameters of these materials are of great value. The reflectance of polar crystals yields important information. A dramatic change in reflectance occurs in the frequency range between the transverse-optical (TO) and the longitudinal-optical (LO) phonons. For many materials these frequencies are of the order of a few THz. Analysis of the reflectance in and near this region yields (a) the TO phonon frequency ω T , (b) the LO phonon frequency ω L , (c) the low-frequency or DC reflectance R(0), and thence the DC refractive index, n(0), and dielectric constant, ɛ(0); (d) the high-frequency or optical reflectance R(∞), and thence n(∞) and ɛ(∞) and (e) the phonon damping factor Γ. These constants depend on the lattice itself and may be described within the Lorentz model. If, in addition, the crystal possesses free carriers, reflectance measurements further yield (f) the plasma frequency ω P , and thence the carrier concentration n e/h and (g) the plasma damping factor γ which may be understood in terms of the Drude model. Samples in the form of a parallel plate give rise to interference fringes that yield (h) the sample thickness t. We have examined many polar crystals with a view to understanding THz emission from them with the overall goal of improving the emission efficiency. Measurements have been made in the region 1.5–21 THz (50–700 cm−1) of single and multilayer samples. We use the sum rule to check the internal consistency of the experimental measurements. We have re-examined the relationship between the phonon frequencies and the reduced ion mass. We find the effective spring constant is very similar in all I–VII materials studied and likewise within the II–VI and III–V classes. We use shell theory to account for these results.
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Solid-State …, Jan 1, 2009
The low-temperature growth of GaAs1−ySby with y = 0.4 and 0.85 has been reported recently along w... more The low-temperature growth of GaAs1−ySby with y = 0.4 and 0.85 has been reported recently along with characterization by X-ray diffraction, Hall, and current–voltage measurements. Here we extend the characterization by employing reflectance spectroscopy in the range 5–18 THz to confirm the compositions of the grown layers. In the course of this work we established for the first time that GaAs1−ySby may serve as an emitter of THz radiation under optical excitation by ultrashort pulses of near-infrared radiation in two distinct experimental arrangements: THz is generated when an electrical bias is applied through a simple electrode structure, attributed to a photoconductive effect; and THz is generated by the pristine layers themselves, attributed to a surface-field effect. In each case the THz emission is compared directly with that from low-temperature-grown GaAs. The results presented here are for as-grown material. Suitable annealing may improve the THz emission even further.
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Journal of the …, Jan 1, 2008
Our purpose was to determine if GaAsSb might be made to emit THz-frequency electromagnetic radiat... more Our purpose was to determine if GaAsSb might be made to emit THz-frequency electromagnetic radiation. Our result is that, with a suitable electric field imposed and under illumination by ultrashort pulses of near-infrared radiation, GaAsSb indeed emits THz radiation. To the best of our knowledge this is the first report of high-temperature-grown GaAsSb acting as a THz source. THz emission has been observed both by incoherent (pneumatic Golay cell) and by coherent (time-domain spectroscopy using electro-optic detection) experimental configurations. Both simple Ag paint and photolithographically formed Au on Ti antenna structures have been found to produce THz radiation. We compare our results with those from the better-known THz emitter, GaAs. In the case of GaAs, THz radiation is emitted even in the absence of applied bias. This is not the case for GaAsSb. We conclude that the photoconductive mechanism dominates in the emission of THz radiation from epitaxial single-crystal GaAsSb. A further proposal is made that such materials can be used with nanostructured surfaces for special THz-emission characteristics.
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Applied Physics Letters
We demonstrate modifications to the light yield properties of an organic liquid scintillator due ... more We demonstrate modifications to the light yield properties of an organic liquid scintillator due to the localisation of the tertiary fluorophore component to the surface of Ag-core silica-shell nanoparticles. We attribute this enhancement to the near-field interaction of Ag nanoparticle plasmons with these fluor molecules. The scintillation light yield enhancement is shown to be equal to the fluorescence enhancement within measurement
uncertainties. With a suitable choice of plasmon energy and scintillation fluor, this effect may be used to engineer scintillators with enhanced light yields for radiation detection applications.
Bookmarks Related papers MentionsView impact
A new method for the absolute radioactivity measurement of radionuclides using a liquid scintilla... more A new method for the absolute radioactivity measurement of radionuclides using a liquid scintillation detector comprising three photomultipliers has been described. The method does not contain any a priori assumption of the photomultiplier detection efficiency and uses a modified Compton Coincidence technique, therefore it has been named the Zero Model By using Coincidence Scintillation (ZoMBieS) method. Validation measurements of the activity of a 63Ni source against the Triple to Double Coincidence Ratio method are presented and the results agree within their k = 1 uncertainties.
Bookmarks Related papers MentionsView impact
Nuclear Instruments and …, Jan 1, 2008
Three types of lead shielding assemblies were investigated to establish which provides the lowest... more Three types of lead shielding assemblies were investigated to establish which provides the lowest background as preliminary work for determining the efficiency of a High Purity Germanium (HPGe) detector. The background continuum and peaks were examined using gamma spectroscopy with a coaxial and a planar HPGe detector. The 210Pb concentration in each lead sample taken from the assemblies was quantitatively determined. A French lead sample was found to have the lowest background in this relative comparison with a 210Pb concentration of 29.171.3 Bq kg-1.
Bookmarks Related papers MentionsView impact
Nuclear Science, …, Jan 1, 2008
Monte Carlo simulations have been performed of the decay of a Au-198 solid source within a 4[pi] ... more Monte Carlo simulations have been performed of the decay of a Au-198 solid source within a 4[pi] [beta]-[gamma] coincidence detector. Calculations of the proportional counter efficiency to both beta and gamma emissions are simulated. A comparison of results obtained using the MCNP-5 and Geant4 simulation packages indicates that Geant4 better evaluates K the correction to the coincidence equation than MCNP-5 predictions. This difference can be accounted for in terms of how the codes handle the physical interactions occurring
in the foil and surrounds
Bookmarks Related papers MentionsView impact
Nuclear Instruments and …, Jan 1, 2010
The effect of multiple γ-ray interactions within a liquid scintillation detector caused by a sing... more The effect of multiple γ-ray interactions within a liquid scintillation detector caused by a single radionuclide decay event on ionisation quenching corrections has been determined. Ionisation quenching corrections to the energy deposition spectrum have been carried out over all electron-generating gamma interactions of the decay event. Comparison has been made with the approximate method typically used to correct for ionisation quench. Both calculations were carried out using the Geant4 simulation package. The two models are compared using the values of detection efficiencies of the logical sum of double coincidence obtained for 131I, 123I and 177Lu measured using the Triple-to-Double Coincidence Ratio method of absolute activity measurement. Finally, predictions are made as to the circumstances under which the two quench correction approaches will be most discrepant.
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Applied Radiation and …, Jan 1, 2010
Radiation transport simulations of the most probable gamma- and X-ray emissions of 123I and 54Mn ... more Radiation transport simulations of the most probable gamma- and X-ray emissions of 123I and 54Mn in a three photomultiplier tube liquid scintillation detector have been carried out. A Geant4 simulation was used to acquire energy deposition spectra and interaction probabilities with the scintillant, as required for absolute activity measurement using the triple to double coincidence ratio (TDCR) method. A sensitivity and uncertainty analysis of the simulation model is presented here. The uncertainty in the Monte Carlo simulation results due to the input parameter uncertainties was found to be more significant than the statistical uncertainty component for a typical number of simulated decay events. The model was most sensitive to changes in the volume of the scintillant. Estimates of the relative
uncertainty associated with the simulation outputs due to the combined stochastic and input uncertainties are provided. A Monte Carlo uncertainty analysis of an 123I TDCR measurement indicated that accounting for the simulation uncertainties increases the uncertainty of efficiency of the logical sum of double coincidence by 5.1%.
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Applied Radiation and Isotopes, Jan 1, 2010
Activity measurements of 3H were performed using the triple to double coincidence ratio method fo... more Activity measurements of 3H were performed using the triple to double coincidence ratio method for the 2009 international comparison organized by the Bureau International des Poids et Mesures (BIPM). The activity obtained by using the FPGA (field programmable gate array) acquisition system and software event analysis was compared to that using MAC3 (Module d’Acquisition de Coincidences triples). Agreement to better than 0.4% was obtained. The stability of sources prepared in Ultima Gold™, Ultima Gold™ LLT, Insta-Gel® Plus and Optiphase “Hisafe”-3 over 140 days is presented.
Bookmarks Related papers MentionsView impact
Nuclear Instruments and …, Jan 1, 2009
The FASEA (FPGA based Acquisition and Software Event Analysis) system has been developed to repla... more The FASEA (FPGA based Acquisition and Software Event Analysis) system has been developed to replace the MAC3 for coincidence pulse processing. The system uses a National Instruments Virtex 5 FPGA card (PXI-7842R) for data acquisition and a purpose developed data analysis software for data analysis. Initial comparisons to the MAC3 unit are included based on measurements of 89Sr and 3H, confirming that the system is able to accurately emulate the behaviour of the MAC3 unit.
Bookmarks Related papers MentionsView impact
Chem. Commun., Jan 1, 2010
The photoconversion of photomorphic silver nanoparticles from discs to prisms via citrate mediate... more The photoconversion of photomorphic silver nanoparticles from
discs to prisms via citrate mediated growth on the twin plane
faces of the nanoparticles is demonstrated. This systematic
shape evolution from discs to hexagons and then prisms of
increasing aspect ratios is a result of the growth process being
confined to specific faces of the growing nanoparticles.
Bookmarks Related papers MentionsView impact
NUCLEAR …, Jan 1, 2008
Several adhesive tapes have been studied in terms of their suitability for securing gold wires in... more Several adhesive tapes have been studied in terms of their suitability for securing gold wires into positions for neutron flux measurements in the reactor core and irradiation facilities surrounding the core of the Open Pool Australian Light water (OPAL) reactor. Gamma ray spectrometry has been performed on each irradiated tape in order to identify and quantify activated components. Numerous metallic impurities have been identified in all tapes. Calculations relating to both the effective neutron shielding properties of the tapes and the error in measurement of the 198Au activity caused by superfluous activity due to residual tape have been made. The most important identified effects were the prolonged cooling times required before safe enough levels of radioactivity to allow handling were reached, and extra activity caused by residual tape when measured with an ionisation chamber. Knowledge of the most suitable tape can allow a minimal contribution due to these effects, and the use of gamma spectrometry in preference to ionisation chamber measurements of the flux wires is shown to make all systematic errors due to the tape completely negligible.
Bookmarks Related papers MentionsView impact
Sipping measurements were implemented at the Open Pool Australian Light water reactor (OPAL) to t... more Sipping measurements were implemented at the Open Pool Australian Light water reactor (OPAL) to test for failure in reactor fuel elements. Fission product released by the fuel element into the pool water was measured using both High Purity Germanium (HPGe) detection via samples and a NaI(Tl) detection in-situ with the sipping device. Results from two fuel elements are presented.
Bookmarks Related papers MentionsView impact
Journal of applied …, Jan 1, 2005
Terahertz emission has been observed from (100) Zn-acceptor-doped InAs under illumination by fs p... more Terahertz emission has been observed from (100) Zn-acceptor-doped InAs under illumination by fs pulses of near-infrared radiation. Turning the crystal about the surface normal produces two maxima per rotation, whether the angle of incidence is 45° or 75°, in contrast to (111) p-InAs, where three maxima per rotation have been reported. The emitted terahertz power has a quadratic variation with the pump power and decreases with increasing temperature in the range 20–300 K. This behavior is consistent with a photocurrent surge being the dominant terahertz generating mechanism at low excitation fluences. The p-type InAs generates about two orders of magnitude more power than the standard unbiased terahertz emitter, 1mm thick ZnTe.
Bookmarks Related papers MentionsView impact
Journal of Materials Science: Materials in …, Jan 1, 2009
Semiconductors are efficient emitters of terahertz (THz, 1012 Hz) radiation. Non-contact means of... more Semiconductors are efficient emitters of terahertz (THz, 1012 Hz) radiation. Non-contact means of accurately measuring the physical parameters of these materials are of great value. The reflectance of polar crystals yields important information. A dramatic change in reflectance occurs in the frequency range between the transverse-optical (TO) and the longitudinal-optical (LO) phonons. For many materials these frequencies are of the order of a few THz. Analysis of the reflectance in and near this region yields (a) the TO phonon frequency ω T , (b) the LO phonon frequency ω L , (c) the low-frequency or DC reflectance R(0), and thence the DC refractive index, n(0), and dielectric constant, ɛ(0); (d) the high-frequency or optical reflectance R(∞), and thence n(∞) and ɛ(∞) and (e) the phonon damping factor Γ. These constants depend on the lattice itself and may be described within the Lorentz model. If, in addition, the crystal possesses free carriers, reflectance measurements further yield (f) the plasma frequency ω P , and thence the carrier concentration n e/h and (g) the plasma damping factor γ which may be understood in terms of the Drude model. Samples in the form of a parallel plate give rise to interference fringes that yield (h) the sample thickness t. We have examined many polar crystals with a view to understanding THz emission from them with the overall goal of improving the emission efficiency. Measurements have been made in the region 1.5–21 THz (50–700 cm−1) of single and multilayer samples. We use the sum rule to check the internal consistency of the experimental measurements. We have re-examined the relationship between the phonon frequencies and the reduced ion mass. We find the effective spring constant is very similar in all I–VII materials studied and likewise within the II–VI and III–V classes. We use shell theory to account for these results.
Bookmarks Related papers MentionsView impact
Solid-State …, Jan 1, 2009
The low-temperature growth of GaAs1−ySby with y = 0.4 and 0.85 has been reported recently along w... more The low-temperature growth of GaAs1−ySby with y = 0.4 and 0.85 has been reported recently along with characterization by X-ray diffraction, Hall, and current–voltage measurements. Here we extend the characterization by employing reflectance spectroscopy in the range 5–18 THz to confirm the compositions of the grown layers. In the course of this work we established for the first time that GaAs1−ySby may serve as an emitter of THz radiation under optical excitation by ultrashort pulses of near-infrared radiation in two distinct experimental arrangements: THz is generated when an electrical bias is applied through a simple electrode structure, attributed to a photoconductive effect; and THz is generated by the pristine layers themselves, attributed to a surface-field effect. In each case the THz emission is compared directly with that from low-temperature-grown GaAs. The results presented here are for as-grown material. Suitable annealing may improve the THz emission even further.
Bookmarks Related papers MentionsView impact
Journal of the …, Jan 1, 2008
Our purpose was to determine if GaAsSb might be made to emit THz-frequency electromagnetic radiat... more Our purpose was to determine if GaAsSb might be made to emit THz-frequency electromagnetic radiation. Our result is that, with a suitable electric field imposed and under illumination by ultrashort pulses of near-infrared radiation, GaAsSb indeed emits THz radiation. To the best of our knowledge this is the first report of high-temperature-grown GaAsSb acting as a THz source. THz emission has been observed both by incoherent (pneumatic Golay cell) and by coherent (time-domain spectroscopy using electro-optic detection) experimental configurations. Both simple Ag paint and photolithographically formed Au on Ti antenna structures have been found to produce THz radiation. We compare our results with those from the better-known THz emitter, GaAs. In the case of GaAs, THz radiation is emitted even in the absence of applied bias. This is not the case for GaAsSb. We conclude that the photoconductive mechanism dominates in the emission of THz radiation from epitaxial single-crystal GaAsSb. A further proposal is made that such materials can be used with nanostructured surfaces for special THz-emission characteristics.
Bookmarks Related papers MentionsView impact