Luminescent Polystyrene Composition Characteristics Stability Forecasting
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Luminescent Polystyrene Composition Characteristics Stability Forecasting Artem Yu. Borisenko and Vitalij G. Senchishin Institute for Single Crystals 4 Novgorodskaja Str, Apt. 108, 61145 Kharkov, Ukraine E-mail: [email protected], [email protected], [email protected] ABSTRACT The stability of properties of luminescent polystyrene compositions depending on their material structure has been studied. The samples obtained by the methods of bulk polymerization and injection molding were used for the experiment. The influence of molecular mass distribution, supramolecular structure, plasticizer concentration and geometrical size of samples on the stability of their properties in severe conditions of natural and radiation aging has been investigated. INTRODUCTION Polystyrene compositions consisting of polystyrene (97.98 %); p-terphenyl (PTP - 2 %); 1.4-di-[-2-(5-phenyloxazolyl)]-benzole (POPOP-0.02 %), are used for manufacturing of scintillators - materials in which radioluminescence appears under the ionizing radiation. Radioluminescence is formed due to sequential transmittance of energy of ionizing radiation from a matrix to the primary and secondary additive [1]. The luminescent spectrum, shown in Figure 1, is formed as a result of two-stage energy transition.
Figure 1. Spectrum of (a) fluorescence and (b) transmittance of: (1) matrix, (2) primary additive PTP, (3) secondary component - POPOP, (4) products of thermo- and radiation oxidation (irradiation dose 50 kGy) [2,3]. BB3.49.1
A photoelectric multiplier (PMT) is used for measuring light output, which is equal to the total intensity of luminescence in the interval of wavelength from 380 to 650 nm (PMT sensitivity area). Scintillators are used for detection of ionizing radiation. They may have the shape of plates, fibers or strips of linear dimensions from 10 to 300 cm. In this connection the main parameter, which is checked for a scintillator is its transparency (absorption coefficient of luminescence light). The intensity of luminescent light collected from the scintillator to the photomultiplier can be described according to the equation [1,2-4]: i = io × exp(-k×x)
(1)
where i is the light output; io is a constant, proportional to scintillation efficiency of the material; k is the absorption coefficient; and x is the distance which the light passes through the material. The absorption coefficient k depends on the structure and properties of the material of the luminescent composition: k = Σ σ(λ)×n(λ)
(2)
where σ(λ) and n(λ) are the absorption constant and concentration of dispersion and absorption centers; and λ is the wavelength [1]. The absorption coefficient value can be changed in the course of time. The luminescent active centers, which absorb light of wavelength up to 410 nm (Figure 1) and emit in the infrared wavelength interval, are generated because of thermo- and radiation destruction and oxidation of the matrix [5-7]. Primarily the energy is transferred to the matrix of composition, which is why the luminescent additives suffer less from destructi
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