Effects of Polymerization Initiators on Plastic Scintillator Light Output

Polymerization initiators are commonly used to lower the processing temperatures and accelerate the synthesis of plastic scintillators. However, these additives can reduce light output. Since plastic scintillator tiles, fibers, and bars are used in countless radiation detection instruments, from PET scanners to LHC calorimeters, any loss in light output immediately degrades the timing and energy resolution of the whole system. Understanding how the initiators alter scintillation performance is therefore important. In this study, five different plastic scintillator samples were produced with varying concentrations of two initiators, 2,2-Azobis(2-methylpropionitrile) (AIBN) and benzoyl peroxide (BPO), along with a reference sample containing no initiators. The relative light yield (RLY) was measured using four different gamma sources. Analyzing the Compton edges revealed that higher initiator concentrations consistently decrease the light output. This study shows that keeping the initiator concentration at 0.2% limits the reduction to 8%, whereas 0.5-1% loadings can lower the yield by 20-35%, providing realistic bounds on initiator levels for future plastic scintillator productions.