G-values for gas production from ion-irradiated polystyrene

Natural and deuterium-substituted polystyrene targets have been irradiated with energetic ion beams in order to make quantitative measurements of gas emission products. Targets with the deuterium substitution made at the pendant hydrogen group site were compared with targets in which the substitution was made at the hydrogen sites of the pendant phenyl group. The gases were measured with a residual gas analyzer; the primary gas products measured were H2, CH4, C2H2, C3H4, C6H6, and their various deuterium-substituted forms. It was shown that the G-values for the production of gas molecules by ion-irradiation are strongly dependent on the linear energy transfer (LET) of the ion. Evidence was given that the primary origin of the saturated hydrocarbon gas methane could be traced to scission of the polymer main chain while the primary origin of most of the unsaturated hydrocarbon gases could be traced to the pendant phenyl group in the macromolecule. Based upon zero-point energy theory, the effective reaction temperature for C-H bond scission during 1 MeV Ar+ irradiation is ∼1600 C. (orig.)