Measurement of the beam energy of a cyclotron using a copper-foils technique

Full text: 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 7-18MeY. 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 (l00, 75, 50 or 25/lm) 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 -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 I IAMeV, 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= IOO/lm) precision (+ 95%CI) of < +0.1 OMeY. 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 1-124, Zr-89 and Cu-64.