Study of the Optical, Infrared, and Luminescent Properties of the UPS-923A Plastic Scintillator after γ-Irradiation

The effect of γ-irradiation from a ⁶⁰Co source in the dose range 5 × 10⁵–10⁷ rad on the optical and luminescent properties of the UPS-923A plastic scintillator based on a polystyrene matrix doped with para-terphenyl (pTP) and a 1,4-bis(5-phenyl-2-oxazolyl)benzene (POPOP) spectral shift additive was investigated. UV–Vis absorption spectroscopy, excitation and photoluminescence spectra, as well as IR spectroscopy methods showed that radiation degradation is selective and primarily affects POPOP molecules containing oxazole rings, while pTP demonstrates higher radiation resistance in the initial stages of irradiation. It has been established that at low doses of irradiation, a relative stabilization of pTP luminescence is observed, while the intensity of POPOP radiation decreases already at doses of about 10⁶ rad. Analysis of the difference spectra and the evolution of the IR bands indicates the destruction of C–N and C–O bonds in the POPOP structure, which leads to a disruption of the energy transfer mechanism between the additives and a decrease in the light output of the scintillator. The results obtained allow us to propose a physicochemical mechanism for the radiation degradation of UPS-923A plastic scintillator and can be used in the development of radiation-resistant organic scintillators for high-energy radiation detectors.