Estimation of induced air activity in 30 MeV proton accelerator: Comparative study of Monte Carlo simulations and analytical calculations

The induced radioactivity concentrations of 41 Ar, 13 N, and 15 O in air in 30 MeV proton accelerator vaults has been estimated using Fluka Monte Carlo simulations and National Council on Radiation Protection (NCRP) 144 based analytical methods. The results obtained by these methods are compared and discussed. It is found that analytical calculations using NCRP 144 guidelines underestimate the 41 Ar concentrations about three times while 15 O concentrations are overestimated about ten times when compared to Monte Carlo estimates. However, the 13 N concentrations estimated by both the methods are found to be in good agreement. It is seen that the analytical calculations ignore the significantly large contribution of 41 Ar formation by the neutrons above thermal energy. The overestimation of 15 O is caused by the large cross-section value assigned in the analytical calculations.