Browsing by Author "Baldock, C"

Now showing 1 - 9 of 9
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    Absolute 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, C
    For 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)
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    An Australian secondary standard dosimetry laboratory participation in IAEA postal dose audits
    (Springer Nature, 2013-02-12) Davies, JB; Izewska, J; Meriaty, H; Baldock, C
    For over 30 years, the International Atomic Energy Agency (IAEA) and the World Health Organization (WHO) have jointly monitored activities of secondary standard dosimetry laboratories (SSDLs) through postal dose audits with the aim of achieving consistency in dosimetry throughout the world. The Australian Nuclear Science and Technology Organisation (ANSTO) maintains an SSDL and is a member of the IAEA/WHO SSDL Network. Postal dose audit results at this Australian SSDL from 2001 to 2011 demonstrate the consistency of absorbed dose to water measurements, underpinned by the primary standard maintained at the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA).© 2020 Springer Nature
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    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.
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    Development of activity standard for 90Y microspheres
    (Elsevier, 2005-08) Mo, L; Avci, B; James, D; Simpson, BRS; van Wyngaardt, WM; Cessna, JT; Baldock, C
    90Y 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.
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    Dosimetry aspects of a non-diffusing genipin-gelatin gel
    (Pergamon-Elsevier Science Ltd, 2013-02-01) Davies, JB; Bosi, SG; Baldock, C
    Genipin-gelatin gel shows promise as a stable, three-dimensional dosimeter for use in quality assurance for radiotherapy treatments. Genipin creates cross-links in gelatin, forming a blue colour that bleaches quantitatively upon irradiation. A formulation suitable for dosimetry was investigated by varying the concentrations of genipin, gelatin and sulphuric acid and determining the dose sensitivity. An important parameter of the gel preparation that affects dose sensitivity is the temperature at which the cross-linking reaction takes place. The most suitable formulation for dose measurements in 1 cm pathlength cuvettes was found to be made from 50 mu M genipin, 4% w/w gelatin and 100 mM sulphuric acid in the final gel. An evaluation of the diffusion coefficient of chromophores in this gel dosimeter demonstrated that this genipin-gelatin gel is a non-diffusing dosimeter. This dosimeter was also evaluated for stability, dose sensitivity, irradiation and measurement temperature dependence and dose rate dependence. No appreciable dependence on dose rate in the range 0.4-40 Gy min(-1) was found. No appreciable dependence on measurement temperature between 15 and 23 degrees C was found. A slight dependence on irradiation temperature was found and this was used to determine the product of the molar linear absorption coefficient and the radiation chemical yield. Finally, the dosimeter measurement uncertainty was evaluated and this was used to determine the dose resolution. Although the focus of this work is on a genipin-gelatin gel dosimeter, the measurement and calibration techniques presented may be applied to any gel dosimetry system measured spectrophotometrically. © 2013, Elsevier Ltd.
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    A genipin-gelatin gel dosimeter for radiation processing
    (Pergamon Elsevier Science Ltd, 2012-08-01) Davies, JB; Bosi, SG; Baldock, C
    Genipin, a fruit extract from Gardenia jasminoides Ellis, forms cross-links in solutions of gelatin, to form a blue hydrogel that bleaches quantitatively upon irradiation and the colour change can be measured with a spectrophotometer. With the addition of sulphuric acid this dosimeter is sufficiently sensitive for quality assurance of radiotherapy level dosimetry. Without sulphuric acid the gel has a reduced sensitivity and responds linearly with dose between 100 and 1000 Gy, making it potentially useful as a dosimeter for radiation processing applications such as the phytosanitary irradiation treatment of food. We investigated the dose response characteristics of this new formulation and found that the darker gels are more sensitive to dose and have a reduced uncertainty. © 2012, Elsevier Ltd.
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    Influence of rejection of a fraction of the single photoelectron peak in liquid scintillation counting
    (Elsevier, 2006-03-15) Mo, L; Cassette, P; Baldock, C
    Zero 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.
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    Radiological characterization and water equivalency of genipin gel for x-ray and electron beam dosimetry
    (IOP Publishing, 2011-08-07) Gorjiara, T; Hill, R; Kuncic, Z; Bosi, SG; Davies, JB; Baldock, C
    The genipin radiochromic gel offers enormous potential as a three-dimensional dosimeter in advanced radiotherapy techniques. We have used several methods (including Monte Carlo simulation), to investigate the water equivalency of genipin gel by characterizing its radiological properties, including mass and electron densities, photon interaction cross sections, mass energy absorption coefficient, effective atomic number, collisional, radiative and total mass stopping powers and electron mass scattering power. Depth doses were also calculated for clinical kilovoltage and megavoltage x-ray beams as well as megavoltage electron beams. The mass density, electron density and effective atomic number of genipin were found to differ from water by less than 2%. For energies below 150 keV, photoelectric absorption cross sections are more than 3% higher than water due to the strong dependence on atomic number. Compton scattering and pair production interaction cross sections for genipin gel differ fromwater by less than 1%. The mass energy absorption coefficient is approximately 3%higher thanwater for energies<60 keVdue to the dominance of photoelectric absorption in this energy range. The electron mass stopping power and mass scattering power differ from water by approximately 0.3%. X-ray depth dose curves for genipin gel agree to within 1% with those for water. Our results demonstrate that genipin gel can be considered water equivalent for kilovoltage and megavoltage x-ray beam dosimetry. For megavoltage electron beam dosimetry, however, our results suggest that a correction factor may be needed to convert measured dose in genipin gel to that ofwater, since differences in some radiological properties of up to 3% compared to water are observed. Our results indicate that genipin gel exhibits greater water equivalency than polymer gels and PRESAGE formulations. © 2011 IOP Publishing LTD.
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    Temperature dependence on the dose response of the Fricke-gelatin-xylenol orange gel dosimeter
    (Elsevier, 2010-05) Davies, JB; Baldock, C
    The effect of temperature during optical absorbance measurements and irradiation on the values of the molar absorption coefficient, (εm)t, and radiation chemical yield, Gt′, respectively, for the Fricke–gelatin–xylenol orange (FGX) gel dosimeter were investigated. At 20°C, the product (εm)tGt′ was found to be 6.76×10−3 m2 J−1. While an irradiation temperature coefficient, k2, was evident (−0.53% °C−1), no temperature effect was found during measurement in the range 16–25°C. © 2010, Elsevier Ltd.