Insight Into The Role Of Free Volume In Irradiation Resistance To Discoloration Of Lead-Containing Plexiglass

Lead-containing plexiglass is prepared successfully via copolymerization of lead-methacrylate (Pb(MAA)(2) and the acrylic monomer such as methyl methacrylate, methyl acrylate, ethyl acrylate, and butyl acrylate. The results show that as-prepared plexiglass has good photons shielding performance and resistance to the discoloration induced by radiation (10 kGy gamma-ray), and the alteration of shielding performance can be well described by the Monte Carlo Code simulations (MCNP5). Using two plasticized systems, the external-plasticized one with various n-octanoic acid concentrations and the internal-plasticized one with different acrylic monomer, as the target samples, it is found that free volume plays dominant role in the irradiation resistance via the positron annihilation lifetime spectroscopy and electron paramagnetic resonance characterizations. The larger the free volume, the greater the quenching probability of free radicals during irradiation. Because the primary type of radiation-induced color centers are annealable color centers, the effect of annealing of irradiation-induced discoloration of lead-containing plexiglass is remarkable. Differing from common treatments of improving irradiation resistance, the increased free volume via plasticization gives plexiglass good resistance to discoloration. This study discloses valuable information around improving irradiation shielding performance and resistance to the radiation-induced discoloration for the plexiglass-based materials.