Local distribution of alkyl radicals in γ-irradiated polyethylene studied by electron spin echo method

Abstract

In order to study the local distribution of alkyl radicals trapped in γ-irradiated polyethylene, the paramagnetic relaxation of the radicals has been examined by the electron spin echo method. The radicals generated and examined both at 77 K showed the longitudinal relaxation expressed as 1 - exp(- bt 0.62), irrespective of radiation dose and thermal annealing of the irradiated samples. The rate constant b increased linearly starting from a large intersect at zero-concentration with the increasing radical concentration. The analysis of the observed relaxation behavior indicates that the transfer of spin energy between the radicals due to the dipole-dipole interaction is an effective path of the longitudinal relaxation. The large intersect is interpreted so that the alkyl radicals are generated and trapped pairwisely and the energy transfer occurs predominantly between paired radicals. An estimate that the average distance of separation between the paired radicals is 3.5 ± 0.4 nm has been obtained under the assumption that a spur consists of only a single radical pair.