Spatially resolved UV-VIS characterization of radiation-induced color centers in poly(styrene) and poly(vinyltoluene)

Abstract

Polystyrene (PS) and polyvinyltoluene (PVT) are in common use as base materials for plastic scintillators. Uv-vis spectroscopy was performed on irradiated disks of PS and PVT and the damage and recovery of these disks were monitored over time. By mounting the disks between quartz glass slides air diffusion was limited to two dimensions, and when the slides were mounted on a micrometer stage assembly, a one dimensional diffusion profile was measured. It was discovered that the absorbances of PS and PVT at certain wavelengths increases for several hours after the irradiation has ended when high dose rates of 6 Mrad/hour are used. It was also found that the visibly sharp annealing boundary that penetrates into the irradiated polymers consistently measured 0.03 inches wide for PS for all wavelengths between 375 and 470 nm and that therefore the oxygen induced bleaching of color centers proceeds at the same rate for all color centers in this wavelength range. A simple self-diffusion model was fit to the boundary velocity data. The self-diffusion coefficients (D 0) were calculated for PS and PVT: D 0( PS) = 1.3 × 10 −8 cm 2/ sec and D 0( PVT) = 1.7 × 10 −7 cm 2/ sec.