V.G.Senchishin
The UPS-97GC polystyrene scintillator developed by author s well as the SCSN-81 one used traditionally in high-energy physicsexperiments have been subjected to long-term stability and heat resistance testing. The light yield and extinction length changes after 500 h heat treatment at 55 and 75 C have been considered. For UPS-97GC, the light yield decrease by 50% has been shown to will occur after 11.5 years and the same extinction length change, approximately after 6.8 years.