  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.
