Neutron activation and prompt gamma intensity in Ar/CO${}_2$-filled neutron detectors at the European Spallation Source

Monte Carlo simulations using MCNP6.1 were performed to study the effect of neutron activation in Ar/CO${}_2$ neutron detector counting gas. A general MCNP model was built and validated with simple analytical calculations. Simulations and calculations agree that only the ${}^{40}$Ar activation can have a considerable effect. It was shown that neither the prompt gamma intensity from the ${}^{40}$Ar neutron capture nor the produced ${}^{41}$Ar activity have an impact in terms of gamma dose rate around the detector and background level.