The surface activity of one-micron particle size γ-octahydro-1,3,5,7-tetranitro-1,3,5,7, tetraazocine (γ-HMX) was studied as a function of cobalt-60 gamma-irradiation in vacuo and in vapors of H 2O, NO and NO 2. Changes in surface activity were measured by a radiometric determination of adsorption of carbon-14 labelled stearyl trimethyl ammonium bromide (STAB) from solution. Observed enhancement of surface activity is attributed to a one-Mrad irradiation-induced adsorbate-substrate interaction which produces polar surface adducts. The mechanism of energy transfer from the bulk of the substrate to the surface-vapor phase interface suggested for various other substrates is postulated to apply to crystalline organic solids such as γ-HMX.