Gamma-ray and neutron shielding features for some fast neutron moderators of interest in 252Cf-based boron neutron capture therapy

Monte Carlo simulations (MCNP) were carried out to model suitable Cf-252-based gamma transmission and neutron attenuation geometries to evaluate the gamma-ray shielding features and neutron attenuation capabilities for Al2O3, MgF2, Fluental and AlF3, as fast neutron moderators of potential interest in Cf-252-based Born Neutron Capture Therapy (BNCT) facilities. The mass attenuation coefficient (mu/rho), Half-Value Layer (HVL), Mean Free Path (MFP) and gamma transmission factor (I/I-o) for Al2O3, MgF2, Fluental and AlF3 were simulated at gamma energies, 0.3 MeV, 0.364 MeV, 0.662 MeV, 1.25 MeV and 7.12 MeV. The MCNP simulated mu/rho values were compared to theoretical XCOM values and good agreement was observed. The ratio of total thermal neutron flux to the total fast neutron flux (phi(total) (th)(ermal) /phi (total fast)) and the total flux of gamma rays (phi (total) ((n,gamma) gamma)) resulting from thermal neutron capture (n,gamma) reactions, were simulated and compared as a function of thickness for the four sample moderators. The values of the effective fast neutron removal cross section Sigma(R) (cm(-1)) for the four sample moderators were calculated and compared.