The results of the treatment of activated carbons prepared from Turkish Elbistan lignite with gamma-irradiation from a Co-60 source are presented and associated volatilization of surface material of the activated carbon as a means to obtain a physical modification of the material is discussed in terms of changes in surface area, free radical concentrations and structural changes determined with FTIR and solid-state C-13 NMR spectroscopical methods. BET areas of irradiated samples are measured to be greater than those of non-irradiated samples; this might be considered as an indication to some loss of material from the surface by gamma-irradiation. gamma-Irradiation caused remarkable erosion on the surface with the loss of some carbonaceous matter by probable bond cleavage reactions. As the activation temperature was raised, both of the carbon content and the intensities of the carbon functionalitics decreased in the C-13 NMR spectra. The observation of symmetric shapes in the ESR spectra might be considered as an indication to the delocalization of the electrons over the graphite-like microcrystallites present in the active carbons. The broadening of the ESR signals in the present work might be both due to the effect of oxygen during the measurements in lower activation temperatures and the enhanced effect of the presence of Fe3+ ion in the form of pyrites in the mineral matter the lignite used. Increase of the relative intensities of free radicals with activation temperature may be indicative of some molecular cracking leading to organic radicals. Irradiation of the activated carbon samples seemed to increase the peak widths and g-values. g-value of 2.003 was due to semiquinone-type free radical which was probably created in oxidation reaction during activation processes. (c) 2004 Elsevier Ltd. All rights reserved.