Estimation of Argon-41 concentrations in the vicinity of a high-energy medical accelerator

This study presents the estimation of 41Ar concentrations using the neutron activation method. The distribution of thermal neutron flux in a 15 MV medical accelerator (linac) treatment room was determined and contoured by measuring the radioactivities of indium foils irradiated by thermal neutrons. The 41Ar concentrations were calculated based on the spatial distribution of thermal neutrons. The evolution of 41Ar concentration with time in the treatment room was predicted and the corresponding radiation dose associated with 41Ar was derived and shown to be insignificant for both patients and workers, being below the regulatory level. Indium foil activation method showed high detection sensitivity for estimating the low-level 41Ar in the vicinity of medical accelerators, yielding a minimum detectable concentration of less than 10 Bq m- 3.