Trapped radicals induced in poly (tetrafluoroethylene-co-hexafluoropropylene) (FEP) were observed by X-band electron spin resonance (ESR) spectroscopy at room temperature (RT) under atmospheric field after an irradiation with various kinds of high energy ion beams (6MeV/u). The irradiation was carried out to a stacked FEP films under vacuum (<4E-4Pa) at RT with various fluences from 1.0×10 9 to 1.0×10 11ions/cm 2. All ESR spectra indicated an existence of peroxy radicals in each of the FEP films without any relation to a kind of ion and a penetration depth. Obtained depth profiles of radical concentrations induced with each ion beam almost correspond to those of stopping power. The trapped radical concentrations were strongly dependent on stopping power. It was found that G-value of trapped radicals by ion beam irradiation was decreased with increasing a stopping power, and was less than the case of gamma-rays irradiation.
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