Experimental and numerical analyses on terahertz spectra of oxidized cross-linked polyethylene

Chemically cross-linked polyethylene irradiated by gamma-rays to certain designated doses from 100 to 800 kGy at 100°C in air was analyzed by terahertz spectroscopy. A peak appears at around 1.3 THz when the sample was irradiated by gamma-rays. By referring to the infrared absorption spectra obtained for the same samples, the peak at 1.3 THz was found to be due to an oxidation-related dipole. It was found that this peak can be fitted to both the Debye and the Lorentz functions similarly. In addition, numerical analyses were carried out using the density functional theory. As a result, it was found that the 1.3-THz peak is likely to be ascribable to resonance.