Single walled carbon nanotubes (SWCNTs) of high purity and multi walled carbon nanotubes (MWCNTs) were radiated by high energies of proton and electron beams. The surface physical properties were examined by XRD and TEM for both irradiated and non-radiated samples to compare the effect of radiation. The possible changes of surface characteristics were investigated by isotherm gas adsorption technique using Ar which can probe the local structure in an order of atomic scale. A series of Ar gas adsorption results measured below 77 K revealed significant changes in surface properties of carbon nanotubes by the bombardment of proton beams, which may induce the local surface defects. It is speculated that reactions on carbon nanotubes radiated by beams were led by kinetic energy transfer of the bombardments. (C) 2007 Elsevier B.V. All rights reserved.