Design and Geant4 simulation of an energy degrader system for PIXE and PIGE at the TINT cyclotron facility

This study presents the design and simulation of an energy degrader system for the Thailand Institute of Nuclear Technology (TINT) cyclotron facility, developed to reduce 15–30 MeV proton beams to 2–5 MeV for PIXE and PIGE applications. SRIM and Geant4 simulations were utilized to optimize foil thickness and characterize beam dynamics. Varying the foil thickness (0.1 -1.4 mm) achieved degraded energies between 2 and 15 MeV. However, multiple Coulomb scattering increased the energy spread (1–29%) and RMS transverse emittance 80–395 mm·mrad). Four representative cases yielded energies of 11.8, 9.1, 6.3, and 2.8 MeV, with energy spread peaking at 16.9% for the lowest energy. To mitigate beam quality degradation, a two-stage collimator system was implemented. This reduced the transverse emittance by approximately 5 mm·mrad compared to a single-collimator setup, achieving proton transmission rates of 0.3–2% (0.6–4 µA from a 200 µA initial beam). Radiation safety was evaluated by mapping the neutron ambient dose equivalent, H*(10), using Geant4. Peak neutron dose exceeding 1.5 × 10−12 µSv per primary proton near the degrader assembly, confirming that local shielding with borated polyethylene is essential. These results provide benchmark beam parameters for future PIXE and PIGE applications and support the design of downstream beam transport systems, including a dipole magnet spectrometer for energy selection and analysis.