Browsing by Author "Mo, L"
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- ItemAbsolute activity determination of 198Au solid source using 4πβ -γ coincidence counting corrected by Monte-Carlo calculation(Institute of Electrical and Electronics Engineers (IEEE), 2007-06) Mo, L; Wu, HY; Baldock, CFor the commissioning process of the OPAL nuclear reactor of the Australian Nuclear Science and Technology Organization (ANSTO), the thermal neutron flux is measured through the activity measurement of an activated Au wire, Au-Al (0.112% of Au) alloy wire and Au foil. The absolute activities of 198Au in the form of Au wire, Al-Au wire and Au foil were determined using the conventional 4pibeta-gamma coincidence-counting method. Monte Carlo simulation technique was employed to simulate the complicated absorption and attenuation processes of electrons and gamma photon interactions with the surrounding materials. The Monte Carlo calculated probabilities of escape beta particles, internal conversion electrons and photon-interaction generated photoelectrons and Compton electrons were used to determine the correction term of the coincidence equation. The corrections for the Au wire (length: 8.000 mm, radius: 0.064 mm), Al-Au wire (length: 7.690 mm, radius: 0.255 mm) and Au foil (thickness: 0.025 mm, radius: 3.000 mm) were found to be 5.2%plusmn0.1%, 2.6%plusmn0.1% and 4.2%plusmn0.2% respectively. The study demonstrates that the Monte Carlo calculation for the correction term of the coincidence equation can be applied to the absolute activity determination of radionuclides with well-defined source geometries with an uncertainty of better than 1%. © 2007, Institute of Electrical and Electronics Engineers (IEEE)
- ItemActivity measurements of H-3 using the TDCR method and observation of source stability(Elsevier, 2010-07) Mo, L; Bignell, LJ; Steele, T; Alexiev, DActivity 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.
- ItemActivity 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, LIn 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
- ItemAPMP comparison of the activity measurements of Ba-133 (APMP.RI(II)-K2.Ba-133) and links to the SIR(Institute of Physics, 2009-01-01) Yunoki, A; Mo, L; Shaha, VV; Kartubi, N; van Wyngaardt, WM; Yuan, MC; Nhan, DD; Park, TS; Yuandi, Y; Soodprasert, T; Michotte, CThe international comparison of radioactivity measurements of 133Ba (APMP.RI(II)-K2.Ba-133) was carried out within the framework of the Asia-Pacific Metrology Programme (APMP). In total, ten institutes took part in the comparison, and five institutes undertook absolute measurements. Nine of the results agreed with each other within their specified uncertainties. The source from the same radioactive solution that was used in the comparison was sent to the BIPM/SIR in order to link this regional comparison to the BIPM key comparison reference value (KCRV). The degrees of equivalence between the APMP comparison and the other measurements for 133Ba are presented. © 2009, Institute of Physics
- ItemCalibration of the Capintec CRC-712M dose calibrator for 18F(Elsevier, 2006-04) Mo, L; Reinhard, MI; Davies, JB; Alexiev, D; Baldock, CPrimary 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.
- ItemCharacterisation of single-crystal mercuric iodide(Elsevier, 2004-01-21) Alexiev, D; Dytlewski, N; Reinhard, MI; Mo, LThe 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.
- ItemComparison 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, MEnergy 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)
- ItemComparison of triple-to-double coincidence ratio (TDCR) efficiency calculations and uncertainty assessments for Tc-99(Elsevier, 2010-07) Zimmerman, BE; Altzitzoglou, T; Rodrigues, D; Broda, R; Cassette, P; Mo, L; Ratel, G; Simpson, BRS; van Wyngaardt, WM; Watjen, CA comparison exercise for data analysis was recently conducted by the Liquid Scintillation Counting Working Group (LSCWG) of the International Committee on Radionuclide Metrology (ICRM) to evaluate the uncertainties involved in applying different analysis methodologies (including computer programs) for the triple-to-double coincidence ratio (TDCR) method. The goals of the comparison were to (1) study differences in calculation results from different TDCR analysis programs, (2) investigate differences in analysis techniques and uncertainty assessment philosophies between laboratories, and (3) study the effect of not taking asymmetry of photomultiplier tube (PMT) efficiencies into account on the calculated activity. To achieve this, a single set of TDCR data for the pure beta emitter 99Tc, was distributed to the participants, who analyzed the data according to their normal procedures and report the activity concentration of the 99Tc solution from their results. The results indicate that the presently used programs are generally able to calculate the same activity values, assuming that the correct input parameters are used and that not taking PMT asymmetry into account in the calculations can lead to significant (0.6% for 99Tc) errors in reported results. The comparison also highlighted the need for a more rigorous approach to estimating and reporting uncertainties. © 2010, Elsevier Ltd.
- ItemConstruction and implementation of a TDCR system at ANSTO(Elsevier, 2007-09-03) Qin, MJ; Mo, L; Alexiev, D; Cassette, PA 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.
- ItemDevelopment of activity standard for 90Y microspheres(Elsevier, 2005-08) Mo, L; Avci, B; James, D; Simpson, BRS; van Wyngaardt, WM; Cessna, JT; Baldock, C90Y microspheres are important therapeutic radiopharmaceuticals used in the treatment of liver cancer through a process known as selective internal radiation therapy. SIR-spheres® is a radiopharmaceutical product that is comprised of 90Y microspheres suspended in sterile, pyrogen-free water for injection into patients. It is necessary to establish for the SIR-spheres® production the capability of accurately measuring the activity of this product to a traceable national measurement standard. An activity standard for SIR-spheres® was developed from a standard for 90Y solution, employing a highly quantifiable chemical digestion process. Calibration factors for the manufacturer's ionisation chambers were determined for 1 and 5 ml of the SIR-spheres® product placed in Wheaton vials, for both 34% and 44% of 90Y microsphere concentration. © 2005, Elsevier Ltd.
- ItemDevelopment of an Australian secondary standard for the reference air kerma rate measurement of 125I seeds(Springer, 2005-09-01) Davies, JB; Mo, L; Alexiev, DCalibration 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.
- ItemDigital 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, MJDigital 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.
- ItemEffect of crucible materials on impurities in LPE-GaAs(Elsevier, 1996-03-01) Mo, L; Butcher, KSA; Alexiev, DLPE-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.
- ItemEffect of multiple γ-ray interactions on ionisation quenching corrections in liquid scintillants(Elsevier, 2010-03-01) Bignell, LJ; Mo, L; Alexiev, D; Hashemi-Nezhad, SRThe 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.
- ItemElemental composition of reactively sputtered indium nitride thin films(The Japan Society of Applied Physics, 1996-04-15) Sunil, K; Mo, L; Motlan; Tansley, TLIndium nitride (InN) thin films have been grown on a variety of substrates using low-temperature radio frequency reactive sputtering of indium metal in pure nitrogen plasma. Quantitative compositional analyses of the films, carried out using X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS), suggest that large amounts of oxygen are present in them. The high concentration of oxygen in our films is attributed to the voided microstructure as revealed by cross-sectional scanning electron microscopy. The XPS studies also suggest that the oxygen incorporated into the films is bonded to nitrogen. © 1996, The Japan Society of Applied Physics
- ItemEvaluation of lead shielding for a gamma-spectroscopy system(Elsevier, 2008-05-01) Smith, ML; Bignell, LJ; Alexiev, D; Mo, L; Harrison, JJThree 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.
- ItemFASEA: 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, DThe 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.
- ItemGrowth of high purity liquid phase epitaxial GaAs in a silica growth system(Elsevier, 1995-12-01) Butcher, KSA; Mo, L; Alexiev, D; Tansley, TLLiquid 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.
- ItemInfluence of rejection of a fraction of the single photoelectron peak in liquid scintillation counting(Elsevier, 2006-03-15) Mo, L; Cassette, P; Baldock, CZero discrimination level setting of liquid scintillation systems for counting of all single photoelectron pulses is required by both triple-to-double coincidence ratio (TDCR) and CIEMAT/NIST methods. However, this requirement may not be able to be met in some circumstances. The influence of rejection of a fraction of the single photoelectron peak has been studied both theoretically and experimentally on 3H, 63Ni, 14C and 90Sr/90Y for both the TDCR and CIEMAT/NIST methods. A modified formula for calculation of efficiency is given in consideration of the rejected fraction of the single photoelectron peak. © 2006, Elsevier Ltd.
- ItemMonte Carlo simulation of a Au-198 thin foil: the response of a 4πβ-γ detector(Institute of Electrical and Electronics Engineers (IEEE), 2008-12) Bignell, LJ; Mo, L; Smith, ML; Alexiev, D; Hashemi-Nezhad, SRMonte Carlo simulations have been performed of the decay of a(198) Au solid source within a 4πβ-γ coincidence detector. Calculations of the proportional counter efficiency to both β and γ emissions are simulated. A comparison of results obtained using the MCNP-5 and Geant4 simulation packages indicates that Geant4 better evaluates the K 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. © 2008, Institute of Electrical and Electronics Engineers (IEEE)