Comparative evaluation of ⁶⁷Ga production via the ⁶⁷Zn and ⁶⁸Zn routes on proton cyclotrons: Yield, radionuclidic purity, and cooling-time behavior.

Abstract

Gallium-67 can be produced on proton cyclotrons via the ⁶⁷Zn(p,n)⁶⁷Ga and ⁶⁸Zn(p,2n)⁶⁷Ga routes. In this study, TALYS, SRIM, and FLUKA calculations were combined to compare ⁶⁷Ga production and post-irradiation Ga-isotope purity evolution for the two routes. For the ⁶⁷Zn(p,n)⁶⁷Ga route, ⁶⁷Ga accounted for nearly all radioactive Ga-isotope activity at EOB, with the 99.8% purity threshold met at EOB for the cases considered. For the ⁶⁸Zn(p,2n)⁶⁷Ga route, co-produced ⁶⁸Ga from ⁶⁸Zn(p,n)⁶⁸Ga reduced the EOB radioactive Ga-isotope purity of ⁶⁷Ga, and cooling was required before the threshold was reached. At the purity-threshold time, the ⁶⁷Ga activities of Case I were 38.06 MBq·μAh-1 for the ⁶⁷Zn(p,n)⁶⁷Ga route and 70.38 MBq·μAh-1 for the ⁶⁸Zn(p,2n)⁶⁷Ga route. The corresponding Zn active-layer volumes were 0.0563 and 0.0978 cm³, respectively. For the ⁶⁸Zn(p,2n)⁶⁷Ga route, lowering the exit energy in Case II and Case III extended the proton energy-loss interval for ⁶⁷Ga production, while also increasing the contribution from ⁶⁸Zn(p,n)⁶⁸Ga. The additional ⁶⁷Ga production was partly offset by the longer cooling time associated with co-produced ⁶⁸Ga. The comparison indicates that the relative performance of the two routes depends on the selected energy interval and the associated Ga-isotope purity evolution, rather than on ⁶⁷Ga production alone.