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Abstract: The size of alpha-particle tracks on electrochemically etched ultraviolet-irradiated polyallyldiglycol carbonate (PADC) films were studied. PADC films were first irradiated with 3MeV alpha particles and then pre-etched chemically using aqueous 6.25N NaOH solution for 2h. The films were then exposed to incoherent broad-band ultraviolet (UV) radiation provided by a mercury lamp for different durations up to 2h. The films were then electrochemically etched in a 6.25N NaOH solution, with an a.c. voltage of about 1200 and a frequency of 5kHz, for 2h at room temperature. The mean sizes of the tracks (or trees) were measured and were found to increase for short UV exposures and decrease for prolonged UV exposures. The results can be explained by the dominance of chain scission at the beginning of UV exposure and the dominance of cross linking for prolonged UV exposure. This explanation is further supported by results from X-ray photo-electron spectroscopy (XPS). Here, the C–O–C bonds decrease for short UV exposures, which is explained by scission of the polymer chains, and increase again for prolonged UV exposure, which indicates cross linking. From nano-indentation measurements, the hardness and the reduced modulus increase monotonically with the UV irradiation. Apparently, these quantities only characterize the amount of cross linking, and do not give information on the initial scission process. [Copyright &y& Elsevier]