Simulation of radiation situation inside a cyclotron vault during production of 18F

Abstract The safe operation of medical cyclotrons used for producing PET radiopharmaceuticals like fluorine-18 necessitates a thorough understanding of the surrounding radiation fields. This study presents a comprehensive analysis of the neutron and gamma radiation environment around an IBA Cyclone 18/9. Using the MCNP6.2 code, a detailed model of the cyclotron vault was developed, incorporating radiation sources from both the 18O(p,xn) reaction in the water target and proton beam losses on accelerator components. The simulated dose equivalents were validated against experimental measurements from neutron and gamma probes located outside the vault. Results indicate that while primary gamma rays are effectively shielded, neutrons are the dominant contributor to the dose outside the vault. Furthermore, the gamma dose measured externally is primarily a result of secondary gamma rays produced from neutron interactions with the shielding and structural materials. The agreement between simulation and measurement demonstrates the reliability of the model for evaluating radiation exposure and designing effective shielding around medical cyclotrons.