Measurements of gas diffusion in polyethylene irradiated by 5 MeV electron beams

The diffusion coefficient of light gas species in polyethylene is measured through a special apparatus which uses a vacuum chamber and a mass quadrupole spectrometer in order to detect the diffused species. Measurements are performed in thin polyethylene films with different molecular weight, which have been irradiated in air with 5 MeV electron beams. The irradiation modifies the poly-ethylene-inducing cross-linking processes, which reduce the diffusion coefficient. Measurements of the diffusion coefficient as a function of the gas specie and of the absorbed dose are reported. The results indicate that the radiation damage depends on the dose, on the dose rate and on the electronic stopping power. A cross-section of the damage process can be deduced. The polymer diffusion is evaluated as a function of the electron irradiation dose. Special attention is given to black polyethylene, rich in additive carbon for industrial applications which can be improved by treatment with electron beams.