# An Active Irradiation System with Automatic Beam Positioning and Focusing for a Medical Cyclotron
## 3 Results
Figure 7: The two-dimensional profile of the beam measured with the \(\pi^{2}\) detector before (**left**) and after (**right**) the optimisation procedure performed by the AFS. The real dimension of the beam is reported, once the effect of the vertical tilt of the scintillating foil is corrected for. The dark spots in the left figure are due to inhomogeneities in the coating of the scintillating foil. The two examples reported above represent worse cases that will not occur during radioisotope production once the AFS is installed in the cyclotron bunker with the STS. In this case, perturbations will be much smaller and mostly due to drifts of the cyclotron magnetic field caused by temperature increase in the main coil. We are therefore confident that the AFS will be capable to correct the possible perturbations during irradiation with the STS. Figure 10: Beam current on target as a function of time during an optimization procedure when a perturbation is applied by means of the quadrupoles of the BTL. The arrows indicate the phases of the procedure. Figure 9: Beam current on target as a function of time during an optimization procedure when a perturbation is applied by means of the steering magnets of the BTL. The arrows indicate the phases of the procedure. To test the enhancement of the performance elicited by the AFS in the production of radioisotopes using solid targets, we irradiated two natural zinc targets one with a broad and one with a focused beam, as in Figure 7. The targets had a diameter of 6 mm and a mass of 89 \(\pm\) 10 \(\upmu\)g and 87 \(\pm\) 10 \(\upmu\)g, respectively. A target of the same dimensions but made of enriched material is used for the production of \({}^{68}\)Ga at the Bern cyclotron [8]. Since the target station at the end of the BTL is not water-cooled, the irradiation was limited to 2 min with currents of 0.92 and 17.5 nA on target, with the flat and focused beam, respectively. In the first case, the flat beam represents a worse case situation since the beam extracted by the cyclotron has approximately 12 mm FWHM on target in a standard STS. On the other hand, the focused beam is such that all the protons hit the target and, since it is smaller than the target, it represents also an extreme case. For both measurements, we used the same settings for the cyclotron and for the BTL. The produced specific activities of \({}^{66}\)Ga and \({}^{67}\)Ga at End of Bombardment (EoB) were measured by gamma spectroscopy with a High Purity Germanium (HPGe) detector (gamma lines at 1039 keV and 93 keV, respectively). The results are reported in Table 1. The specific activity and the total charge on target are measured using the methodology we developed to assess radioisotope production cross sections [5]. The gain factor in the produced specific activities was found to be about 20. This is in line with the ratio of the current on target measured during irradiation. Once the AFS is installed in front of the STS in the cyclotron bunker, we expect a considerable increase of the production yield of which this extreme case represents an upper limit.