Terahertz spectroscopic observation of oxidation of ethylene-propylene-diene-copolymer

Flame-retardant ethylene-propylene-diene copolymer, which is the polymer insulating material most abundantly used for safety-related electric cables in nuclear power plants, was irradiated with gamma-rays to certain designated doses from 500 to 1500 kGy at room temperature or 100 °C in air, and absorption spectra were measured at terahertz frequencies. A broad absorption is induced by the irradiation in a range from 0.5 to 3.1 THz. It is confirmed that this absorption is induced by oxidation, by comparing its frequency spectrum with spectra of polyethylene obtained numerically by doing quantum chemical calculations and experimentally by measuring its absorption at THz frequencies. Therefore, the degree of oxidation of this copolymer can be estimated by the intensity of the broad absorption at these THz frequencies.