Effects of temporary fogging and defogging in plastic scintillators

Recent studies have shown that under certain environmental conditions, plastic scintillators which are used in a variety of applications in outdoor environments develop defects called “fogging” resulting in a reduced useful lifetime and increased maintenance cost. Applications of plastic scintillators include scanning recycled steel going into a processing plant, personnel portals to scan employees, and scanning cargo and cars crossing borders of many countries. In this report, fogging was studied in conventional PVT and PS-based plastic scintillators, both field aged and freshly cast. A new fogging-resistant PVT-based formulation developed by scientists at Lawrence Livermore National Laboratory (LLNL) was tested as well. We used accelerated aging experiments via temperature and humidity cycling in controlled laboratory conditions to create observable temporary fogging defects in small samples (≤1 in ³ ). Photoluminescence and optical transmission studies were used to evaluate the effect of the fogging. The time evolution of the induced temporary fogging formation and defogging (i.e. fading of defects in ambient conditions over time) were recorded using optical microscopy, time-lapse photography, and gravimetric analysis.