Light emission from treated surfaces of poly (ethylene terephthalate)

There has been considerable interest in poly (ethylene terephthalate) (PET) as an undoped scintillation material for charged particle detections. However, light emission from exposed surfaces is limited by the high refractive index. Here, we show the potential applications of surface-treated PET for radioactive contamination inspections. The two large-area surfaces of three 140-mm × 72-mm × 1-mm plates cut from injection-molded PET were treated in three ways: both polished surfaces, one polished and the other roughened (thus, two different entrance faces), and both roughened surfaces. Transmission spectra were acquired to characterize the responses at the PET surfaces by external light. Transmittances were decreased by roughened surfaces; the effect was dominant for short wavelengths, and the transmittance at the emission maximum was less than 1% when both surfaces were roughened. A portable model system, where smeared filter papers or smeared cotton buds were inspected for charged particle detection, was fabricated to characterize the responses at the PET surfaces by internal light. Count rates for a ²⁴¹Am radioactive source and a ⁹⁰Sr radioactive source were increased by the roughened surfaces; count rates when both surfaces were roughened were, respectively, 3.7 and 2.1 times those when both surfaces were polished. Thus, the model system responded well to alpha and beta particles via the PET surface treatments. We revealed that the roughened surfaces diffused light emissions by refraction and bent incident angle at the next boundary surface by reflection. In addition, a strong correlation between increased count rates and decreased transmittances was found via the surface treatments. This knowledge will guide the use of PET in future radiation management.