Browsing by Author "Sherlock, SL"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    The absolute determination of activity by the efficiency extrapolation method
    (Australian Atomic Energy Commission, 1987-04) Sherlock, SL
    As an agent for the Commonwealth Scientific and Industrial Research Organisation, the Australian Atomic Energy Commission is responsible for the maintenance of the Australian standard of activity. The standard comprises activity measurement procedures involving the operation of 4 pi β-γ coincidence counting equipment. The coincidence method requires the application of correction factors which depend on detection efficiency such as arise for complex decay schemes and internal conversion. These corrections approach unity as the detection efficiency in the β-channel approaches 100 per cent. By performing activity determinations for a range of β detection efficiencies an 'efficiency extrapolation' analysis can be applied which eliminates the need to determine the absolute detection efficiency for each channel.
  • Thumbnail Image
    Item
    Application of the photon-fluence scaling theorem to absorbed dose calorimetry for bremsstrahlung peak energy > 1.02 MeV
    (Australian Nuclear Science and Technology Organisation, 1989-08) Sherlock, SL
    Application of the 'photon fluence scaling theorem' allows the ionization chamber to be placed at points in media where the photon fluence is the same hence eliminating problems with energy response. The theorem is applicable to Compton scattered photons. For photon energies greater than 1.02 MeV pair production alters the photon fluence in such a way as to invalidate the scaling theorem. In this report the effect of pair production is examined so that a correction may be applied to the photon fluence scaling theorem. This correction extends application of the theorem for bremsstrahlung spectra up to at least 25 MeV peak energy.
  • Thumbnail Image
    Item
    The Australian Commonwealth standard of measurement for absorbed radiation dose, Part 1: control, monitoring and performance of the Urquhart graphite microcalorimeter
    (Australian Nuclear Science and Technology Organisation, 1989-08) Sherlock, SL
    As an agent for the Commonwealth Scientific and Industrial Research Organisation, the Australian Nuclear Science and Technology Organisation is responsible for maintenance of the Australian Commonwealth standard of absorbed dose. This standard of measurement has application in radiation therapy dosimetry which is required for the treatment of cancer patients. This report is the first in a series of reports documenting the absorbed dose standard for photon beams in the range from 1 to 25 MeV. The Urquhart graphite micro-calorimeters which is used for the determination of absorbed dose under high energy photon beams has been now placed under computer control. Accordingly a complete upgrade of the calorimeter systems was performed to allow operation in the hospital. In this report control and monitoring techniques have been described with an assessment of the performance achieved being given for 6 and 18 MeV bremsstrahlung beams. Random errors have been reduced to near negligible proportions while systematic errors have been minimized by achieving true quasi-adiabatic operation.
  • Thumbnail Image
    Item
    The Australian Commonwealth standard of measurement for absorbed radiation dose, Part 2 - absorbed dose standard for graphite irradiated by a cobalt-60 teletherapy unit
    (Australian Nuclear Science and Technology Organisation, 1990-06) Sherlock, SL
    This report documents the absorbed dose standard for photon beams in the range from 1 to 25 MeV. Measurements of absorbed dose in graphite irradiated by a beam of cobalt-60 gamma rays from an Atomic Energy of Canada Limited (AECL) E1 Dorado 6 teletherapy unit are reported. The measurements were performed using a graphite calorimeter which is the primary standard for absorbed dose. The measurements are used to calibrate a working standard ion chamber in terms of absorbed dose in graphite.