The production of molecular hydrogen in the radiolysis of isotactic polypropylene (PP), poly(methyl methacrylate) (PMMA), and polystyrene (PS) with protons and carbon ions has been investigated. Previous experimental data on the above polymers with γ-ray and helium ion irradiations have been combined with similar studies on high-density polyethylene (PE) to give a comprehensive survey of the dependence of molecular hydrogen yields on particle linear energy transfer, LET, in the range 0.2-800 eV/nm. The radiation chemical yields of molecular hydrogen are very dependent on LET and generally increase with increasing LET. However, the relative change in hydrogen yield as a function of LET is very different for the various polymers. It appears that with increasing high LET the hydrogen yields for each of the polymers are approaching the same value. This observation suggests that the radiolytic source of molecular hydrogen is similar for all of the polymers and increases with increasing LET of the irradiation. Unexpectedly high yields of molecular hydrogen can have implications in many fields including those that involve heavy charged particles and intense photon sources.

The production of molecular hydrogen in the radiolysis of high-density polyethylene by γ rays and heavy ion beams has been investigated. Only the slightest increase in the radiation chemical yield of 3.1 molecules/100 eV was found from γ rays to protons of 5-15 MeV. A gradual increase in yield was observed on further increasing the linear energy transfer of the incident particles. This increase amounted to almost a doubling in the hydrogen yield from 10 eV/nm protons to about 800 eV/nm carbon ions. The exact reason for the increase in molecular hydrogen yield is uncertain, but it may involve reactions of excited states or enhanced combination reactions of carbon-centered radicals, thereby allowing more hydrogen to escape the particle tracks. Diffusion from the bulk material was found to have a dominant role on the observed dynamic profiles of hydrogen gas. A simple one-dimensional diffusion model was used to estimate the diffusion constant of hydrogen in polyethylene to be 2.2 × 10 -6 cm 2 /s.

The γ-radiolysis of nylons 12, 11, 6/12, 6/9, 6/6, and 6 were investigated. The IR spectra of film samples before and after the γ-irradiation show the formation of amines, aldehydes, and ketones, and suggest that the cleavage of amide group is one of the major processes of radiolysis. The yields of gaseous products and their evolution from the bulk were measured with a quadrupole mass spectrometer. Four gases were determined as the major radiolytic products and their yields were found to be in the order H 2 > CO > CO 2 > CH 4 for all the nylons. The relationship between the gas yields and the chemical composition of the monomer unit shows that the H 2 yield increases with the relative number of H atoms. The results suggest a random distribution of energy leading to H 2 production. It was found that the yields of CO and CO 2 decrease with an increase in the relative number of amide groups on the nylon monomer unit. Since these later products must be derived from the amide group, chain scission and fragmentation at the amide group must decrease with increasing amide contribution to the monomer unit of the polymer chain. The diffusion coefficients of H 2 , CO, and CO 2 gases in the bulk polymer were determined and the results suggest that post-radiation processes exist in the γ-radiolysis of nylons.