Effects of gamma irradiation at different doses up to 135？kGy on polyethylene terephthalate (PET) polymer films have been investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and ultraviolet-visible (UV-VIS) spectroscopy. From XRD analysis, it was found that even at a high dose of gamma irradiation of 135？kGy, crystallinity of the PET samples remain unchanged. However, the FTIR peak at 871？cm？1 (depicting C–H bending mode of out-of-plane vibration) and another at 1303？cm？1 (representing C–H bending mode of in-plane vibration) disappear for gamma-irradiated PET. In this study, it has also been found that γ-irradiation in air enhances the optical absorption in the wavelength region 320–370？nm. This has been attributed to free radicals being produced in the polymer by the γ-radiation. Further, the free radicals react with oxygen of air to form carbonyl group and hydroxyls. With increasing γ-dose, there is a red shift of the UV—near visible cutoff for PET. XRD and FTIR observations on γ-damage have been correlated. 1. Introduction Radiation damage to various polymers [1–12] due to irradiation by either fast ions or energetic neutrons or high energy photons is a topic of practical and theoretical interest. Theoretical effort aims to understand [1–3] topics like the relative contribution of crosslinking and chain scission to the damage and the detailed mechanisms of the damage. The practical interest in such radiation damage pertains to utility factor and various applications. PET or polyethylene terephthalate films have attracted interest as polymers due to their ample application and wide availability. The changes, due to Mo, N, O, and Kr ion irradiations [4, 12] in PET structure, have been reported, and correlation of these changes to other properties were attempted. However, many aspects of damages due to γ-radiation and fast ions are not yet clearly understood so that more experimental data are welcome. A high energy ion affects nuclei of the target solid in addition to its electronic interaction in the solid, and its energy is very often chosen to be much higher than γ-photon energy, here, 1.25？MeV. Electronic excitation can affect polymer bonding with varied results that depend on both the nature of radiation and the nature of the polymer in a complex manner. Our DSC thermogram [9, 10] showed that radiation induced changes of melting point of PEO-salt samples are in opposite directions for 160？MeV Ne6+ ion and 1.25？MeV γ-ray irradiations. This interesting feature hints at different mechanisms of radiation damage in
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