The gases produced in gamma and heavy-ion radiolysis of poly(methyl methacrylate)

The production of CO, CO2, H-2 and CH4 gases in the gamma -radiolysis and heavy-ion radiolysis of poly(methyl methacrylate) (PMMA) was investigated. It was found that the dynamic evolution of the radiolytic gases from the polymer surface is controlled by molecular diffusion in the polymer matrix. Diffusion coefficients were extracted by model fits to the observed temporal profiles. The gas yields were determined as a function of the linear energy transfer (LET) in the range of 0.2-830 eV/nm. It was found that for heavy-ion irradiations the total gas yield increases significantly when the LET increases above 80 eV/nm. The results clearly show that the degradation mechanisms of PMMA are affected by LET. It appears that H-2 and CH4 are formed from precursors different than those leading to CO and CO2. The LET dependence suggests that the latter two products are not completely formed from a common precursor, which has been previously proposed. (C) 2001 Elsevier Science Ltd. All rights reserved.