[en] Passage of energetic heavy ions produces damage in a polymeric material resulting into the creation of latent tracks due to dissociation of bonds, cross-linking, formation of free radicals, etc. This results in the change of free volume properties which have strong correlation with the macroscopic properties of the materials. Positron annihilation lifetime spectroscopy (PALS) has been developed into a powerful characterization tool for the study of free volume size and free volume fraction in polymeric materials. By measuring the lifetimes of the positron, it may be possible to get fairly accurate estimates of the free volume of Angstrom (0.2-1 nm) range. Makrofol-KG polycarbonate films widely used for ion track registration were irradiated by 145 MeV Ne⁶⁺ ion beam at Variable Energy Cyclotron Centre (VECC), Kolkata, India to the fluences of 10¹⁰, 10¹¹, 10¹² and 10¹³ions/cm². From o-Ps lifetime parameters average free volume were obtained. o-Ps lifetimes were found to decrease with the ion fluence. Microvoid volume decreased by 10.52% at 10¹³ions/cm²