Irradiation of PMMA with high energy light ions: The depth distribution for volatile reaction-product emission

Mass spectrometry has been used as an analytical tool in determining the species and quantities of volatile reaction products generated during destruction of polymers by ion implantation. Specifically, one very important objective was to relate the radiation chemistry with the radiation physics of fundamental track formation. Experiments are described in which the depth distribution of the emission of volatile products has been determined for irradiation of PMMA with 35MeV 7Li2+ ions. The mass spectral measurements of the reaction products were carried out on thin PMMA foils as a function of the angle of beam incidence, and hence of penetration depth. Correlation of the differences in mass spectra with the foil number yielded the depth distribution of degassing. Comparison with theory shows that volatile gas degassing, which is itself a consequence of multiple chain scission, can be related to electronic rather than nuclear energy transfer processes. However, the detailed shape of the measured degassing distribution differs from that expected from theory. This clearly points to inherent inadequacies in the simple model for polymer destruction.