A new, simple and precise method for measuring cyclotron proton beam energies using the activity vs. depth profile of zinc-65 in a thick target of stacked copper foils

A H Asad; S Chan; D Cryer; J W Burrage; S A Siddiqui; R I Price

doi:10.1016/j.apradiso.2015.07.017

A new, simple and precise method for measuring cyclotron proton beam energies using the activity vs. depth profile of zinc-65 in a thick target of stacked copper foils

Appl Radiat Isot. 2015 Nov:105:20-25. doi: 10.1016/j.apradiso.2015.07.017. Epub 2015 Jul 15.

Authors

A H Asad¹, S Chan², D Cryer², J W Burrage³, S A Siddiqui⁴, R I Price⁵

Affiliations

¹ Radiopharmaceutical Production & Development (RAPID) Laboratory, Medical Technology and Physics, Sir Charles Gairdner Hospital, Perth 6009, Australia; Department of Imaging & Applied Physics, Curtin University, Perth 6845, Australia. Electronic address: ali.asad@health.wa.gov.au.
² Radiopharmaceutical Production & Development (RAPID) Laboratory, Medical Technology and Physics, Sir Charles Gairdner Hospital, Perth 6009, Australia.
³ Medical Engineering and Physics, Royal Perth Hospital, Perth 6000, Australia.
⁴ Department of Imaging & Applied Physics, Curtin University, Perth 6845, Australia.
⁵ Radiopharmaceutical Production & Development (RAPID) Laboratory, Medical Technology and Physics, Sir Charles Gairdner Hospital, Perth 6009, Australia; School of Physics, University of Western Australia, Perth 6009, Australia.

PMID: 26226219
DOI: 10.1016/j.apradiso.2015.07.017

Abstract

The proton beam energy of an isochronous 18MeV cyclotron was determined using a novel version of the stacked copper-foils technique. This simple method used stacked foils of natural copper forming 'thick' targets to produce Zn radioisotopes by the well-documented (p,x) monitor-reactions. Primary beam energy was calculated using the (65)Zn activity vs. depth profile in the target, with the results obtained using (62)Zn and (63)Zn (as comparators) in close agreement. Results from separate measurements using foil thicknesses of 100, 75, 50 or 25µm to form the stacks also concurred closely. Energy was determined by iterative least-squares comparison of the normalized measured activity profile in a target-stack with the equivalent calculated normalized profile, using 'energy' as the regression variable. The technique exploits the uniqueness of the shape of the activity vs. depth profile of the monitor isotope in the target stack for a specified incident energy. The energy using (65)Zn activity profiles and 50-μm foils alone was 18.03±0.02 [SD] MeV (95%CI=17.98-18.08), and 18.06±0.12MeV (95%CI=18.02-18.10; NS) when combining results from all isotopes and foil thicknesses. When the beam energy was re-measured using (65)Zn and 50-μm foils only, following a major upgrade of the ion sources and nonmagnetic beam controls the results were 18.11±0.05MeV (95%CI=18.00-18.23; NS compared with 'before'). Since measurement of only one Zn monitor isotope is required to determine the normalized activity profile this indirect yet precise technique does not require a direct beam-current measurement or a gamma-spectroscopy efficiency calibrated with standard sources, though a characteristic photopeak must be identified. It has some advantages over published methods using the ratio of cross sections of monitor reactions, including the ability to determine energies across a broader range and without need for customized beam degraders.

Keywords: (62,63,65)Zn monitor reactions; Beam energy measurement; Cu foils; Isochronous cyclotron.

MeSH terms

Copper
Cyclotrons / statistics & numerical data*
Humans
Protons*
Radiometry / statistics & numerical data
Zinc Radioisotopes* / analysis

Substances

Protons
Zinc Radioisotopes
Copper