A Long-Term Stability Study of Counters Consisting of Extruded-Scintillator Strips and Wavelength-Shifting Fibers

The long-term stability of counters consisting of extruded-scintillator strips and wavelength-shifting fibers was studied. The aging study was carried out for scintillators and wavelength-shifting fibers before starting the mass production of counters. Aging at a higher rate and higher temperatures was used in the study, which was then continued as an interesting R&D work. The decrease in the light yield was at a level of 3% per year during an initial 5–6 years. The aging then proceeds slower and nearly ceases after a 26% decrease over 20 years. The study of preliminarily aged samples was repeated after a 2.5-year pause; it showed that the aging rate for these scintillators was less than 0.5% per year at 20°C. The results obtained over 4.5 years by direct measurements and by using a faster-aging technology were in good agreement.