ANSTO :: Browsing by Author "Alexiev, D"

Browsing by Author "Alexiev, D"

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Activity measurements of H-3 using the TDCR method and observation of source stability
(Elsevier, 2010-07) Mo, L; Bignell, LJ; Steele, T; Alexiev, D
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. © 2010, Elsevier Ltd.
Activity measurements of the radionuclide 153Sm for the ANSTO, Australia in the ongoing comparison BIPM.RI(II)-K1.Sm-153
(Institute of Physics, 2005-01-01) Ratel, G; Michotte, C; Reinhard, MI; Alexiev, D; Mo, L
In 2004, the Australian Nuclear Science and Technology Organisation (ANSTO) submitted two samples of known activity of 153Sm to the International Reference System (SIR). The value of the activity submitted was about 920 MBq. This key comparison result has been added to the matrix of degrees of equivalence in the key comparison database that now contains five results, identifier BIPM.RI(II)-K1.Sm-153. © 2005, Institute of Physics
Calibration of the Capintec CRC-712M dose calibrator for 18F
(Elsevier, 2006-04) Mo, L; Reinhard, MI; Davies, JB; Alexiev, D; Baldock, C
Primary standardisation was performed on a solution of 18F using the 4πβ–γ coincidence counting efficiency-tracing extrapolation method with 60Co used as a tracer nuclide. The result was used to calibrate the ANSTO secondary standard ionisation chamber which is used to disseminate Australian activity standards for gamma emitters. Using the secondary activity standard for 18F, the Capintec CRC-712M dose calibrator at the Australian National Medical Cyclotron (NMC) Positron Emission Tomography (PET) Quality Control (QC) Section was calibrated. The dial setting number recommended by the manufacturer for the measurement of the activity of 18F is 439. In this work, the dial setting numbers for the activity measurement of the solution of 18F in Wheaton vials were experimentally determined to be 443±12, 446±12, 459±11, 473±15 for 0.1, 1, 4.5 and 9 ml solution volumes, respectively. The uncertainties given above are expanded uncertainties (k=2) giving an estimated level of confidence of 95%. The activities determined using the manufacturer recommended setting number 439 are 0.8%, 1.4%, 4.0% and 6.5% higher than the standardised activities, respectively. It is recommended that a single dial setting number of 459 determined for 4.5 ml is used for 0.1–9 ml solution in Wheaton vials in order to simplify the operation procedure. With this setting the expended uncertainty (k=2) in the activity readout from the Capintec dose calibrator would be less than 6.2%. © 2006, Elsevier Ltd.
Characterisation of single-crystal mercuric iodide
(Elsevier, 2004-01-21) Alexiev, D; Dytlewski, N; Reinhard, MI; Mo, L
The mobility-lifetime product of electrons and holes in single-crystal mercuric iodide for detector applications was measured to be 4×10−5 and 3×10−5 cm2/V respectively. The charge carriers were optically induced by a near band gap excitation using a GaP (560 nm) light emitting diode. Optical Deep Level Transient Spectrometry measurements of trapping states showed three dominant energy levels at 0.26, 0.8 and 1.4 eV. There is little correlation between trapping levels reported in the literature. © 2004, Elsevier Ltd.
Comparison of LaBr3 : Ce and LaCl3 : Ce with NaI(Tl) and cadmium zinc telluride (CZT) detectors
(Institute of Electrical and Electronics Engineers (IEEE), 2008-06) Alexiev, D; Mo, L; Prokopovich, DA; Smith, ML; Matuchova, M
Energy resolution and detection efficiency were compared between new scintillators, lanthanum bromide (LaBr3:Ce) and lanthanum chloride (LaCl3:Ce) with conventional detectors, sodium iodide NaI(Tl) and cadmium zinc telluride (CdZnTe or CZT). The study has shown that LaBr3:Ce and LaCl3:Ce scintillator detectors provided by Saint-Gobain offer better resolution than NaI(Tl) detector. LaBr3:Ce and LaCl3:Ce detectors could resolve some closely spaced peaks from 133Ba and 152Eu, which Na(I) could not. LaBr3:Ce has slightly better resolution and higher efficiency than LaCl3:Ce. An overall advantage of LaBr3:Ce and LaCl3:Ce detectors over NaI(Tl) and CZT has been discussed. The intrinsic activity of LaBr3:Ce is also demonstrated in this study. © 2008, Institute of Electrical and Electronics Engineers (IEEE)
Construction and implementation of a TDCR system at ANSTO
(Elsevier, 2007-09-03) Qin, MJ; Mo, L; Alexiev, D; Cassette, P
A triple-to-double coincidence ratio (TDCR) liquid scintillation counting system has been recently constructed at Australian Nuclear Science and Technology Organization (ANSTO). A description of the system and measured activities for sources such as 3H, 14C, and 241Am are presented. © 2008, Elsevier Ltd.
Deep level transient conductance spectrometer for high resistivity semiconductors using a marginal oscillator detector.
(Australian Atomic Energy Commission, 1984-09) Alexiev, D; Tavendale, AJ
A deep level transient conductance spectrometer for high resistivity semiconductors, using a radiofrequency (~40 MHz) marginal oscillator as a conductance detector, is described. Spectra are generated by periodically filling deep level trapping centres with carriers stimulated by a pulsed GaAs laser, and processing the trap-emptying conductance signal through an exponential Miller correlator as the sample temperature is slowly ramped. Simple capacitive coupling of samples to the oscillator tank circuit eliminates problems such as unwanted defect annealing and other material changes often associated with the high temperature techniques necessary for ohmic contact formation. Representative deep level spectra are given for semi-insulating Bridgman-grown CdTe.
Deep level transient spectroscopy of n-GaAs surface barrier diodes for nuclear radiation detection
(Australian Atomic Energy Commission, 1981-01) Pearton, SJ; Alexiev, D; Tavendale, AJ; Williams, AA
Deep level transient spectroscopy has been applied for the first time to the study of deep level defects in n-GaAs nuclear radiation detectors. Devices made from commercial bulk and epitaxial material with net donor impurity densities in the range 5 x 10 13 -3 x 10 16 cm -3 have been studied and several common levels observed. The Poole-Frenkel effect has been identified in three levels (Ev + 0.19 eV, Ec - 0.62 eV Ec - 0.73 eV) in the epitaxial GaAs. A value for the Poole-Frenkel constant of β = 4.7 ≥ 1.4 x 10-4 eV V-½ cm½ was obtained compared to the theoretical value for GaAs of 2.3 x 10-4 eV V-½ cm½.
Development of an Australian secondary standard for the reference air kerma rate measurement of 125I seeds
(Springer, 2005-09-01) Davies, JB; Mo, L; Alexiev, D
Calibration of a High-Dose-Rate 1000 Plus ionisation chamber and associated electrometer for the determination of reference air kerma rate for 125I brachytherapy seeds has been developed. Traceability was established from ionisation chamber measurements of an Amersham model 6711125I seed for which a primary standard measurement of reference air kerma rate has been made by the National Institute of Standards and Technology. The status of an Australian secondary standard is to be realised by establishing legal verifying authority from the National Measurement Institute. The calibrated chamber thus provides a measurement from which similar chambers in hospitals may be calibrated. For quality assurance this result was compared with the calibration certificate supplied by the Accredited Dosimetry Calibration Laboratory of the University of Wisconsin, USA. © 2005, Springer.
Digital coincidence counting - initial results
(Elsevier, 2000-08-01) Butcher, KSA; Watt, GC; Alexiev, D; van der Gaast, H; Davies, JB; Mo, L; Wyllie, HA; Keightley, JD; Smith, D; Woods, MJ
Digital Coincidence Counting (DCC) is a new technique in radiation metrology, based on the older method of analogue coincidence counting. It has been developed by the Australian Nuclear Science and Technology Organisation (ANSTO), in collaboration with the National Physical Laboratory (NPL) of the United Kingdom, as a faster more reliable means of determining the activity of ionising radiation samples. The technique employs a dual channel analogue-to-digital converter acquisition system for collecting pulse information from a 4π beta detector and an NaI(Tl) gamma detector. The digitised pulse information is stored on a high-speed hard disk and timing information for both channels is also stored. The data may subsequently be recalled and analysed using software-based algorithms. In this letter we describe some recent results obtained with the new acquistion hardware being tested at ANSTO. The system is fully operational and is now in routine use. Results for 60Co and 22Na radiation activity calibrations are presented, initial results with 153Sm are also briefly mentioned. © 2000, Elsevier Ltd.
Effect of crucible materials on impurities in LPE-GaAs
(Elsevier, 1996-03-01) Mo, L; Butcher, KSA; Alexiev, D
LPE-GaAs grown in carbon, boron nitride and alumina crucibles has been examined using standard characterisation techniques including capacitance-voltage (C-V) measurements and deep level transient spectroscopy (DLTS). The epitaxial layers have net carrier concentration ranging from 5 × 1014 to 8 × 1015 carriers per cm3. DLTS data has shown that all epitaxial layers have deep level traps. © 1996, Elsevier Ltd.
Effect of multiple γ-ray interactions on ionisation quenching corrections in liquid scintillants
(Elsevier, 2010-03-01) Bignell, LJ; Mo, L; Alexiev, D; Hashemi-Nezhad, SR
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. © 2010, Elsevier Ltd.
Electrical, optical and structural properties of lead iodide
(Springer, 2009-03) Matuchova, M; Zdansky, K; Zavadil, J; Danilewsky, A; Maixner, J; Alexiev, D
Lead iodide PbI2 is an excellent and interesting candidate for high efficiency room temperature detectors working in the medium energy range of 1 keV-1 MeV. It can be widely applied in medicine, monitoring ecology, nondestructive defectoscopy and X-ray and gamma spectroscopy. The peculiarities of this material are high resistivity, ability to work in a wide range of temperatures and high chemical stability. The method of preparation was direct synthesis from lead and iodine. The material was further purified by zone melting and grown by Bridgman-Stockbarger method. In this work we have concentrated on the study of the influence of dopants such as lanthanides (Er,Gd, Ho, Tb, Tm, Yb, GdI3, HoI3, GdI3) and elements of other groups, such as Au, Ag, Ge on the physical, electrical and optical properties of the PbI2. These were evaluated by resistivity and low temperature photoluminescence measurements. The Synchrotron X-ray topography was successfully introduced to study defects. The quality of the material was analyzed after synthesis, zone melting and growth. The dependence on the concentration of dopants was investigated too. © 2009, Springer.
Etch rates for (100) gallium arsenide using aqueous h2so4h2o and aqua regia based etchants.
(Australian Nuclear Science and Technology Organisation, 1991-09) Keane, M; Butcher, KSA; Alexiev, D
Etch rate experiments were carried out for (100) GaAs using etching solutions of H2SO4 :H2O2 :H2O (3:1:1 3:1:15) HCl:HNO3 (3:1) HCl:HNO3 :H2O (1: 1:1) and HCl:HNO3 :glycerol (with various dilutions of glycerol). Several differences were seen for the (100) plane compared to previous results for other crystal orientations. The sulphuric acid solutions showed much lower activation energies for etching the (100) plane. The HCl:HNO3 :glycerol solutions showed considerably lower etch rates for the (100) plane probably indicating that they etch GaAs anisotropically. For a 1:1:2 solution of HCl:HNO3 :glycerol a decrease in the etch rate of (100) GaAs was observed in the presence of stirring. This is the opposite result to what is commonly assumed for this polishing etchant. It indicates that the main polishing process attributed to this etchant is not present and in fact the polishing quality of the etchant is probably limited by the etching process which is present.
Evaluation of lead shielding for a gamma-spectroscopy system
(Elsevier, 2008-05-01) Smith, ML; Bignell, LJ; Alexiev, D; Mo, L; Harrison, JJ
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 Pb-210 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 Pb-210 concentration of 29.1 +/- 1.3 Bq kg(-1). © 2008, Elsevier Ltd.
FASEA: a FPGA acquisition system and software event analysis for liquid scintillation counting
(Elsevier, 2009-10-11) Steele, T; Mo, L; Bignell, LJ; Smith, M; Alexiev, D
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. © 2009, Elsevier Ltd.
Growth of high purity liquid phase epitaxial GaAs in a silica growth system
(Elsevier, 1995-12-01) Butcher, KSA; Mo, L; Alexiev, D; Tansley, TL
Liquid phase epitaxial gallium arsenide layers, greater than 200 μm thickness and with a low net carrier concentration (NA,D ≈ 1013 cm−3) have been grown in a silicia growth system with silica crucibles. Analysis of electrical and chemical defects was carried out using capacitance-voltage (C---V) measurements, deep level transient spectroscopy (DLTS) and secondary ion mass spectroscopy (SIMS). Details of the growth procedure are given and it is shown that silicon incorporation in the growth layer is not suppressed by the addition of ppm levels of oxygen to the main hydrogen flow. © 1995, Elsevier Ltd.
High purity liquid phase epitaxial gallium arsenide nuclear radiation detector.
(Australian Nuclear Science and Technology Organisation, 1991-11) Alexiev, D; Butcher, KSA
Surface barrier radiation detector made from high purity liquid phase epitaxial gallium arsenide wafers have been operated as χ- and γ-ray detectors at various operating temperatures. Low energy isotopes are resolved including 241Am at 40°C. and the higher gamma energies of 235U at - 80°C.
Liquid phase epitaxy of gallium arsenide - a review
(Australian Nuclear Science and Technology Organisation, 1992-07) Alexiev, D
Liquid phase epitaxy of gallium arsenide has been investigated intensively from the late 1960's to the present and has now a special place in the manufacture of wide band compound semiconductor radiation detectors. Although this particular process appears to have gained prominence in the last three decades the authors point out that its origins reach back to 1836 when Frankenheim made his first observations. A brief review is presented from a semiconductor applications point of view on how this subject developed.
Lithium compensation of GaAs.
(Australian Nuclear Science and Technology Organisation, 1988-08) Alexiev, D; Tavendale, AJ
Defects generated following Li diffusion into GaAs were studied by optical deep level transient spectroscopy (ODLTS) and deep level transient spectroscopy (DLTS). In an exploratory series of experiments the effect of Li diffusion on existing trap spectra defect generation and as a means for the compensation of GaAs was studied. The variables included diffusion temperature initial trap spectra of GaAs and annealing periods. Detailed measurements of trap energies were made.

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