To determine the safety of using argon as a deuteron beam stopping material, the  ⁴⁰Ar(d,p)⁴¹Ar cross section was measured at average deuteron energies of 3.6 MeV, 5.5 MeV, and 7.0 MeV using an activation method. A 16-MeV deuteron beam produced by Lawrence Berkeley National Laboratory's 88-Inch Cyclotron was degraded to each energy by nickel foils and the front wall of an aluminum gas chamber. The reduced-energy deuterons were used to activate a sample of ^natAr gas. After each irradiation, the gas chamber's  ⁴¹Ar activation was measured with a high-purity germanium detector. The cross sections measured were larger than a previous measurement by ∼40%.