Design of beam shaping assembly for 2.4 MeV electrostatic tandem accelerator-based neutron source for boron neutron capture therapy: A Monte Carlo study.

In this study, the lithium target thickness and a beam-shaping assembly (BSA) system were designed using Monte Carlo N-Particle version 6.2 for a 2.4 MeV, 15 mA proton accelerator-based neutron source. The BSA components consist of lead (Pb), magnesium fluoride (MgF2), boron carbide (B4C), and tungsten (W) used for the reflector, moderator, and collimator, respectively. The specifications (area and thickness) of each BSA part were varied to analyze the characteristics of neutrons passing through the BSA. The system's performance was evaluated based on various indicators, including the epithermal neutron flux, ratio of epithermal to thermal neutrons, fast neutron contamination, gamma contamination, and neutron current to flux ratio. Monte Carlo simulations were conducted to determine BSA specifications that satisfied the neutron beam requirements recommended by the International Atomic Energy Agency. The lithium target thickness was determined to be 90 μm, and BSA's performance was confirmed under various conditions. For the specifications that yielded the highest epithermal neutron flux, the epithermal neutron flux at the BSA exit was 8.89 × 108 cm-2 s-1, the ratio of epithermal neutrons to thermal neutrons was 425.54, the neutron current-to-flux ratio was 0.7, and the dose contaminations due to fast neutrons and gamma rays were 1.20 × 10-13 Gy cm2 and 1.91 × 10-13 Gy cm2, respectively.