LET effect on cross-linking and scission mechanisms of PMMA during irradiation

Mechanisms of scission and cross-linking are investigated for poly(methyl methacrylate) subjected to various irradiation sources, such as low LET radiation sources (MeV e-beams, Co-60 gamma-rays) and high LET ions (MeV He+, Ar+). PMMA properties were degraded upon irradiation by e-beam and gamma-rays, but were improved upon bombardment with high energy ion beams (HEIB) as a result of cross-linking. The results indicate that high LET produces a high concentration of free radicals over many neighboring molecular chains, facilitating track overlap and enhancing cross-linking over scission, while low LET affects only a single molecular chain, leading to chain scission. (C) 1999 Elsevier Science Ltd. All rights reserved.