## 3 Results  
### Cyclotron Production Yield and Degraders Used  
Several experiments were performed while using \({}^{89}\)Y-foil and pressed-powder with the different target holders and degraders in aluminum and niobium designed for the \({}^{89}\)Zr production on TR24 and TR19 cyclotrons (Figure 1). Pressing procedures were optimized to provide reproducible and consistent density pellets. Yttrium powder from Alfa Aesar formed successfully compact pressed targets. The preparation and assembly of \({}^{89}\)Y-pressed target are very fast and can be done in few minutes.  
Targets characteristics, measured production yields, and EMA are summarized in Table 2. The proton energies deposited on the targets were maintained between 11-15 MeV for most of our irradiations. The irradiations were first performed on \({}^{89}\)Y-foil target. The production yield using Al-21-1 degrader was 26.4 MBq/\(\upmu\)A\(\cdot\)h using \({}^{89}\)Y-foil (Table 2, entry 1). A similar production yield was obtained by using Nb-13-0.35 degrader and about half the quantity of target material (entry 2). We noticed damage (overheating) to the Nb-13-0.35 degrader when the irradiation time was increased to 4.2 h with a beam current of 10 \(\upmu\)A (Figure 1B).  
The \({}^{89}\)Zr yield was well correlated with proton energy (\(E_{p}\)) and target thickness. By keeping constant the amount of target material and the foil thickness, a slightly higher yield of 27.8 MBq/\(\upmu\)A\(\cdot\)h was obtained by increasing the proton-beam energy deposited to the target material from 11.3 to 13.3 MeV (entries 2-3). When the Y-foil thickness was doubled while using two stacked 0.25-mm thick foils, the production yield was improved to 36.6 MBq/\(\upmu\)A\(\cdot\)h (entries 3 and 6). The amount of \({}^{89}\)Zr produced increased proportionally by increasing the current from 15 to 25 \(\upmu\)A with similar production yields (entries 3-5). Similar production yields were also obtained for irradiations that were made on TR19 and TR24 by selecting the appropriate degrader thickness (entries 3-4).  
To establish the optimal target thickness for the production of \({}^{89}\)Zr, a stacked foil technique was used. The proton-beam energy deposited to the target material was fixed at 11.3 MeV (Figure 3). Similar production yields were found for the first four foils of 6 mm diameter facing the proton beam, indicating that the optimal target thickness was \(\sim\)0.50 mm. Using these conditions, the production yield was 17.1 MBq/\(\upmu\)A\(\cdot\)h.  
Figure 3: Optimization of production yield using foil targets.  
The highest production yield of 56.1 MBq/uA-h was found by increasing the proton-beam energy deposited on the target material up to 15.0 MeV while using an 0.5-mm foil thickness and the Al-13 holder (Table 2, entry 7). Moreover, a current of 40 uA can be applied on the target without any target overheating when using an Al-13 holder for the irradiation (entries 7 and 11).  
The irradiations were initiated on a 0.35-mm thick \({}^{89}\)Y-pressed target. When the 13-mm diameter pressed target was used with Nb-13-0.35 degrader, the production yield was 22.7 \(\pm\) 1.2 MBq/uA-h for a proton-beam energy that was deposited on the target material of 11.3 MeV (entry 8). As seen before for \({}^{89}\)Y-foil targets, the production yield increased by almost two-fold, reaching 37.2 \(\pm\) 1.3 MBq/uA-h, when increasing the target thickness from 0.30 to 0.51 mm and using similar irradiation conditions (entries 9 and 10). A high production yield of 49.5 \(\pm\) 1.2 MBq/uA-h was also obtained for \({}^{89}\)Y-pressed target at the optimum \(\sim\)0.5 mm thickness and E\({}_{\rm p}\) of 15.0 MeV at 40 uA (entry 11). Using these irradiation parameters, similar and optimal production yields were obtained for both \({}^{89}\)Y-foil and pressed targets (entries 7 and 11).