Measurement of the Beam Energy of a Cyclotron using a Copper-Foils Technique

  • Mr Ali Asad, Australia
  • Roger Price, Department of Medical Technology abd Physics- Sir Charles Gairdner Hospital, Australia
  • Mr Adam Fleming, School of Physics, University of Western Australia, Australia
  • John Burrage, Deparmtent of Medical Engineering and Physics- Royal Perth Hospital, Australia
  • Mr David Cryer, Department of Medical Technology abd Physics- Sir Charles Gairdner Hospital, Australia
  • Mr Sun Chan, Department of Medical Technology abd Physics- Sir Charles Gairdner Hospital, Australia
  • Tom Deans
  • Salim Saddiqui

    • The 18MeV cyclotron at SCGH (Perth) daily produces PET radioisotopes. An external beam line, incorporating an in-house designed target-holder, has been utilised to explore (p,x) solid targetry in the proton energy-range 7-18MeV. Some solid-targetry techniques require a degrader for reducing beam energy. We investigated a technique to measure the proton-beam energy, with or without a degrader.
    Stacks of natural-copper (Cu) foils (31% Cu-65, 69% Cu-63), purity >99.98% and thicknesses (100, 75, 50 or 25μm) were proton-bombarded in separate runs. In separate determinations for each run, activities of Zn-63, Zn-65 and (depending on beam energy) Zn-62 in each foil were then measured by HPGe γ-spectroscopy, and together with stopping-power and reaction-specific cross section data were used to calculate incident beam energy. Materials for a degrader were aluminium and graphite with calculated thicknesses of 0.920 and 1.128mm, respectively, designed to reduce the energy from 18MeV to 11.4MeV, specifically to optimise the reaction Ni-64(p,n)Cu-64, currently under study in our laboratory. Beam energies thus derived from Zn-63 or Zn-65 had (eg; for thickness=100μm) precision (+ 95%CI) of < +0.10MeV.
    Conclusion; the method can precisely determine the energy of the proton beam, using either Zn-63 or Zn-65. It is sufficiently precise to determine the energy decrease arising from deliberate insertion of a beam degrader, in the event of the need to optimize the beam energy, for particular (p,x) solid-targetry reaction, over the proton energy range 7-18MeV, embracing production of a range of biomedically relevant isotopes such as I-124, Zr-89 and Cu-64.