Abstract
Different models are used to analyse the kinetics of the hydrogen released from different polymers (polyethylene (PE), polystyrene, polyphenylvinylene) under a beam of 700 keV He +. The saturated core model provides a simple interpretation of the exponentially decreasing hydrogen yield by the increasing overlapping of the hydrogen depleted cores, allowing a direct comparison of the stability towards irradiation of polymers exhibiting different molecular structures. Improvements of the exponential fits to the gas release versus ion fluence data are obtained when involving the production of molecular hydrogen in the bulk. Significant deviations from the model prediction are however observed at high ion fluences for semi-crystalline polymers like PE. More critical is the failure of such models to explain the strong dependence of the hydrogen yield upon irradiation temperature. The molecular diffusion of the hydrogen produced in the bulk of the film has to be taken into account. The delayed hydrogen component, observed at long irradiation times, can in particular be modeled by the limited diffusion of gas permeating in a dense membrane.
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