Hardness of irradiated poly(methyl methacrylate) at elevated temperatures

The decrease in hardness induced by gamma irradiation in poly(methyl methac rylate) (PMMA) has been investigated. The hardness is assumed to decrease l inearly with the concentration of radiation-induced defects. Annealing at h igh temperatures induces defect annihilation as tracked by an increase in h ardness. The annihilation follows first-order kinetics during isothermal an nealing. The dependence of hardness on the reciprocal of the time constant satisfies the Arrhenius equation, and the corresponding activation energy o f the kinetic process decreases with increasing dose. The hardness of posta nnealed PMMA decreases linearly with increasing dose. (C) 2001 American Ins titute of Physics.