Production of ⁶¹Cu via the ⁶⁴Zn(p,α)61Cu reaction with high specific activity

Objectives:

Optimized production and separation parameters, use of only ultra-pure reagents with ppt-levels of metal traces are necessary for the production of high specific activities (SA) ⁶¹Cu. From previous studies regarding production of ⁶¹Cu there is little data on SA published. McCarthy et al. [1] measured SA ranging from 47 to 190 GBq/µmol for ⁶¹Cu produced via ⁶¹Ni(p,n)⁶¹Cu and ⁶⁰Ni(d,n)⁶¹Cu reaction. An alternative method for production is the use of the ⁶⁴Zn(p,α)61Cu reaction [2]. The use of 99% enriched ⁶⁴Zn is considerably cheaper than use of enriched ⁶¹Ni.
Methods:
A target setup was developed using approximately 100 mg enriched ⁶⁴Zn electroplated on a massive gold disk for proton irradiation. The radiochemical separation technique included recycling of the target material and was based on ion exchange methods described in the literature [3-8]. It consisted of a system of cation and anion exchange columns. This ion exchanger cascade included a twofold cation exchange step developed for effective removal of gallium by-products (^66/67/68Ga) and one anion exchange step to separate ⁶¹Cu from the target material. This separation procedure took one hour. After the recycling procedure for the target material a new electrodeposition of the ⁶⁴Zn could be carried out. The method used small ion exchange columns, aqueous hydrochloric acid solutions and is described in detail by Thieme et al. [2]. The SA was evaluated by TETA binding assay with radio TLC. Two different cyclotrons were used for the irradiations: a Cyclone 18/9 (IBA, Belgium) at the Insitute of Radiopharmacy in Dresden-Rossendorf with a home-made solid target holder and a CC 18/9 (Efremov Institute, St. Petersburg, Russia) at Turku PET Centre in Turku also with a home-made solid target holder.
Results:
With the Cyclone 18/9 the irradiations were performed with 12 µA of 16 MeV protons on target for 30 min and yielded about 300 MBq ⁶¹Cu at EOB. The CC 18/9 irradiations with 30 µA of 13 MeV protons on target for 30 min yielded 330-400 MBq ⁶¹Cu, and with 3 hours 1150 MBq ⁶¹Cu, respectively. SA of 500 GBq/µmol were achieved with the CC 18/9 which is equipped with a solid target holder completely made of aluminum preventing contamination of the target disk with non-radioactive copper. Compared to the low specific activities, less than 1 GBq/µmol was achieved at the Cyclone 18/9. This low SA is most likely caused by contamination with non-radioactive copper from the currently used solid target holder containing brass/copper parts.
Conclusions:
These results show the possibility to produce high SA ⁶¹Cu (SA up to 500 GBq/µmol) via the ⁶⁴Zn(p,α)⁶¹Cu reaction at low proton energies. Together with the used radiochemical separation method it is possible to produce high quality ⁶¹Cu routinely.