Top view of the neutron fields in the cyclotron vault for two different positions of the liquid target. The cyclotron is shown with a black circle in the center of the bunker. Thinner concrete walls separate the cyclotron area from the four irradiation areas. 

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... are two possible locations for the 18 F-target in the vault - close to the cyclotron but still externally to it and in a separated irradiation room. Figure 3 shows the distribution of neutrons when using both positions -the highest density shown in black is the exact center of mass of the source from Section 2.2. The source obtained in the step described above is positioned in either location of the target and the particles are transported further depending on their spatial coordinates and momentum vector components in the source ...

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... 2. Fluence (particles per cm 2 per primary particle) of neutrons crossing the target body in the three planes. Proton beam with energy of 24MeV and current of 400 µA impinges into the (x, y) plane. phase space. The vault space is surrounded by 2.5 m thick walls made of high-density concrete as shown in Fig. 3. The target area is not shielded additionally. The neutron distribution homogeneity around the target is disturbed by cyclotron metal parts mostly in Fig. 3(a), inner and outer shield walls (Fig. 3(b)). As it might be assumed that the areas outside the vault will be used for chemical synthesis, target preparation, etc., it is desirable ...

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... beam with energy of 24MeV and current of 400 µA impinges into the (x, y) plane. phase space. The vault space is surrounded by 2.5 m thick walls made of high-density concrete as shown in Fig. 3. The target area is not shielded additionally. The neutron distribution homogeneity around the target is disturbed by cyclotron metal parts mostly in Fig. 3(a), inner and outer shield walls (Fig. 3(b)). As it might be assumed that the areas outside the vault will be used for chemical synthesis, target preparation, etc., it is desirable to minimize any leakages, thus, making the position of the target shown with Fig. 3(b) preferable if no further shielding is used. Additionally, the shielding ...

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... of 400 µA impinges into the (x, y) plane. phase space. The vault space is surrounded by 2.5 m thick walls made of high-density concrete as shown in Fig. 3. The target area is not shielded additionally. The neutron distribution homogeneity around the target is disturbed by cyclotron metal parts mostly in Fig. 3(a), inner and outer shield walls (Fig. 3(b)). As it might be assumed that the areas outside the vault will be used for chemical synthesis, target preparation, etc., it is desirable to minimize any leakages, thus, making the position of the target shown with Fig. 3(b) preferable if no further shielding is used. Additionally, the shielding can be improved as it is shown with Fig. ...

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... homogeneity around the target is disturbed by cyclotron metal parts mostly in Fig. 3(a), inner and outer shield walls (Fig. 3(b)). As it might be assumed that the areas outside the vault will be used for chemical synthesis, target preparation, etc., it is desirable to minimize any leakages, thus, making the position of the target shown with Fig. 3(b) preferable if no further shielding is used. Additionally, the shielding can be improved as it is shown with Fig. 4 where a few centimeters thick marble-enriched concrete is used locally around the target. Further optimization of the thickness of this shielding and its chemical composition still has to be ...

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... 4. Top view of the neutron fields in the vault if the target is positioned as in Fig. 3(b) and shielded locally with marble-enriched ...

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... of long-living ones ( 3 H, 58 Co). This study focuses on the activation of the vault using the distributions from Fig. 2 and Fig. 3. It is assumed that a sacrificial layer takes 20 cm from the wall thickness including also the walls, separating the cyclotron from the irradiation areas. The last ones have thickness of 60 cm. Table 1 shows some of the nuclides generated in the sacrificial layer after a month of operation with daily irradiation conditions as above -6 ...

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... generated in the sacrificial layer after a month of operation with daily irradiation conditions as above -6 hours at 24 MeV and 400 µA, immediately after End of Beam (EOB) and after 3 weeks of cooling time. Table 1. Some of the nuclides generated in the outmost 20 cm of the walls of the cyclotron vault. The irradiating target is positioned as in Fig. 3(b 41 Ar resulting from neutron capture on 40 Ar is also seen in the air of the vault in activities in the range of 1×10 7 Bq -above the limit of 200 Bq/m 3 with respect to the volume of the vault increasing the cooling time before maintenance access. In 18 hours the activity decreases to 3×10 4 Bq with which the specific activity within ...