Fluorescence and absorption of a polystyrene-based scintillator exposed to UV laser radiation

Abstract

We have established that exposure of polystyrene-based scintillator samples to UV laser radiation (248 nm) leads to a significant decrease in the fluorescence intensity. We have carried out a spectral analysis of the luminescent and absorption properties of the scintillator, which allowed us to determine the major factor in the decrease in luminescence intensity of the samples exposed to UV radiation. We propose a new hypothesis for the mechanism of the processes leading to the decrease in light output of the scintillator during operation. Introduction.A plastic scintillator is a composite consisting of an optically transparent plastic and added luminophores. A plastic scintillator displays bright luminescence when exposed to ionizing radiation and is rather stable relative to such exposure. Scintillators are made from such composites in the form of optical fibers, films, and plates with large surface area, and also bulk blocks of any size or shape, which significantly expands the possibilities for their application. The advantage of plastic scintillators is their fast response (the radioluminescence lifetime ranges from fractions of a nanosecond to several nanoseconds). They are used for radiation detection and dosimetry.The most widely used plastic scintillators are based on polystyrene with added luminophores: p-terphenyl (p-TP) and 1,4-bis(2-(5-phenyloxazolyl))benzene (POPOP). Polystyrene plastic is the most radiation resistant among the known synthetic polymers [1]; it has high transparency over a broad spectral range (λ > 290 nm). However, we should point out that the indicated characteristic is seen only in the very pure polymer. Commercial polystyrene contains impurities and structural defects absorbing in the 290-400 nm region [2][3][4].A general disadvantage of plastic scintillators is gradual loss of scintillation efficiency during operation. As the absorbed dose of ionizing radiation increases, the light output of the scintillator decreases. As the characteristic for radiation resistance, we take the value of the absorbed dose D 1/2 at which the light output is half of the initial value. For polystyrene scintillators, D 1/2 ≈ 600 kGy [3].The radiation-induced physicochemical changes leading to a decrease in the light output of a plastic scintillator have been the subject of many studies [3,[5][6][7][8][9][10]. Special attention has been focused on the loss of transparency in the plastic. It has been established that this is due to the appearance of "induced" absorption bands that are relatively intense in the 300-400 nm region and low-intensity in the visible region. The bands that appeared were assigned to macroradicals formed on exposure to radiation, some of which proved to be short-lived while others were rather stable. These data provided the basis for established ideas about the reasons for radiation-induced wear in plastic scintillators. We should point out that in some papers (see, for example, [9]), bands were seen which could not be attributed to radicals, and they were assigned to unident...

Organic and Inorganic Metal Halide Tandem Scintillator for Dual-Energy Flat-Panel X-ray Imaging

“…Ir(ppy) 3 has significant advantages in both aspects. 38 We observed that Ir(ppy) 3 has a lifetime of 1.3 μs, consistent with the findings of earlier studies, 39 as shown in Figure 2d. Figure 2d shows that the lifetime of Ir(ppy) 3 is much shorter than that of commercial inorganic scintillators such as CsI:Tl and previously reported phosphorescent organic scintillators, which have decay lifetimes in the millisecond range.…”

“…We investigated the light decay and afterglow properties of Ir­(ppy) 3 , which are two crucial factors limiting the use of inorganic scintillators, such as CsI:Tl. Ir­(ppy) 3 has significant advantages in both aspects . We observed that Ir­(ppy) 3 has a lifetime of 1.3 μs, consistent with the findings of earlier studies, as shown in Figure d.…”

Syntheses and luminescent properties of a copolymer of terbium‐p‐aminobenzoic acid–methacrylic acid and styrene

“…However, after polymerization, new UV absorbance peaks of the copolymer occurred. Nurmukhametov et al conjectured that different optical centers formed during polymerization. It has been shown by NMR that during polymerization styrene molecules can be chemically bonded with each other not only ‘head to tail’ but also ‘head to head’ and ‘tail to tail’, leading to formation of defective units in the polystyrene chain .…”

A multichannel neutron flux monitoring system for a boron neutron capture therapy facility

“…The main reason is the fact that the excitation energy of the primary fluorophore is transferred to molecules of the spectrum shifter by the radiation transfer. For small scintillator samples of ∼ 150 µm, the probability of these UV photons escaping from the sensitive detector volume can no longer be considered negligible [7]. Unfortunately, the detection efficiency of plastic scintillators is significantly smaller in comparison with inorganic single crystals and thus it is rather hard to get reliable data under X-rays for small samples.…”