Neutronic Analysis of Non-Self-Shielded Cyclotron: An Integrated Approach Using Experimental Measurements and Monte Carlo Simulations for In-Depth Assessment

Abstract Broad energy spectrum of neutrons is produced in medical cyclotrons during Fluorine-18 production. In this work, a detailed three-dimensional (3D) spatial neutronic analysis was conducted within a cyclotron facility in the vicinity of a non-self-shielded PETtrace cyclotron target, supported by a geant4-based Monte Carlo simulation. Moreover, the presence of a shielding column, made of lead (Pb), which has a relatively high neutron scattering cross section, was evaluated experimentally. Multiple sets of gold (Au) and cadmium (Cd) foils were used in three arrangements to evaluate the thermal and epithermal neutron fluxes utilizing neutron activation analysis (NAA). The evaluated total neutron fluxes were found to be on the order of 1 × 10+6 neutrons/cm2 s in the forward direction at all investigated positions. The findings indicate that the area around the target exhibits a high intensity of both thermal and epithermal neutron flux. Operational factors such as routine cyclotron maintenance and increased target volume also contribute to a rise in thermal neutron flux. In addition, the Pb column causes a significant increase in thermal neutron flux, with enhancements reaching up to 86%. The obtained results will serve as a reference for future safety assessments, including estimates of radioactive waste generation and worker dose exposure over the operational lifetime of the cyclotron facility.