Hydrogen production in gamma-ray and helium-ion radiolysis of polyethylene, polypropylene, poly(methyl-methacrylate), and polystyrene

The production of molecular hydrogen in the radiolysis of high-density poly ethylene, isotactic polypropylene (PP), poly(methyl-methacrylate) (PMMA), a nd polystyrene (PS) by gamma rays and 5-20-MeV helium ions was investigated . Molecular hydrogen is the dominant gaseous product from these polymers, a nd the yields with gamma rays are 3.3, 2.6, 0.24, and 0.033 molecules per 1 00 eV of energy absorbed for polyethylene, PP, PMMA, and PS, respectively. The decrease in observed hydrogen is due to increased branching and the che mical nature of the groups on the side chains. There is an increase in hydr ogen production with increasing linear energy transfer (LET) from gamma ray s to helium ions, but the relative increase depends on the polymer type. Wi th incident 5-MeV helium ions, the respective yields of molecular hydrogen are 4.6, 3.2, 0.62, and 0.15 molecules per 100 eV. The increase in molecula r hydrogen with increasing LET may be due to changes in the kinetics of hyd rogen precursors in the particle tracks. The differences in the relative in creases in molecular hydrogen with increasing LET for each of the polymers suggests that self-scavenging reactions may be important for low LET partic les. (C) 2000 John Wiley & Sons, Inc.