Volatile Evolution from Polymer Materials Induced by Irradiation with Accelerated He⁺⁺ Ions

Abstract

Experimentally investigating ageing caused by irradiation with energetic particles is very difficult. Radioactive sources can be employed but these are difficult to handle and contaminate the material being irradiated precluding subsequent chemical and physical characterisation. The penetration of energetic particles also tends to be small so any change is localised in the near surface region so only a small amount of material is irradiated. Analysing changes in such thin layers causes a number of problems. To simulate ageing induced by particle radiation polymer samples have been exposed to fast He⁺ ions in an accelerated ion beam. The ions pass through a 10μm thick window of Havar foil before impacting upon the sample. Volatile species evolved from the materials upon bombardment are contained within the irradiation chamber by the foil window. Analysis of such species is shown to be a highly sensitive probe for investigating chemical changes in the exposed materials. A number of important chemical changes induced in polymer materials have been identified. Trends in the relative rates of volatile evolution have been identified which correlate with chemical changes identified in other radiation experiments. As these experiments are performed at far slower irradiation rates the large acceleration factors used in ion beam irradiation are discussed along with the implications for using ion beams to simulate alpha particle irradiation.