PSI - Issue 41

Dionysios Linardatos et al. / Procedia Structural Integrity 41 (2022) 82–86 Linardatos/ Structural Integrity Procedia 00 (2022) 000–000

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transferred to a Sub-Femtoamp electrometer (Keithley, 6430) (Saatsakis et al., 2019). Then, the luminescence performance was calculated as the absolute efficiency, i.e., the ratio of the light output over the Χ-ray exposure rate (Michail et al., 2019): � � � � � � (1) In this equation, � stands for the X-ray exposure rate and � � for the produced light flux. All units are expressed in �� � � �� ��� � � �� � ⁄ , which stands for efficiency units – EU. 3. Results and Discussion The luminescence efficiency of ZnSe:Te, measured in the temperature range from 20°C to 140°C, from the variation of the recorded photomultiplier tube output, is shown in Figure 1. In this figure ZnSe:Te is shown against a previously published CaF 2 :Eu crystal for comparison. The latter range is indicative and can be found in logging detectors, where temperatures range from 0°C to 200°C (Melcher et al., 1991; Xiang et al., 2016). The temperature was kept in this range in order to avoid any possible damages in the experimental setup from excessive heating (Pokluda et al., 2015). ZnSe:Te follows a similar trend with most crystals, in which as the temperature increases, the light output degrades, compared to the starting point (degradation from 8.8 EU at 20°C to 1.56 EU at 140°C), due to thermal quenching (Melcher et al., 1991). In the work of Mikhailik et al., the luminescence efficiency of ZnSe:Te was examined at cryogenic temperatures and an efficiency drop was found from 8.1 AU (arbitrary units) at 5.5°K to 2.2 AU at 143°K (Mikhailik et al., 2017). The luminescence signal of CaF 2 :Eu follows a similar trend and decreases constantly. Both crystals showed maximum signal at room temperature (8.8 EU at 20°C for ZnSe:Te and 22.01 EU for CaF 2 :Eu at 22°C). In the temperature range 70°C – 140°C, ZnSe:Te shows slight changes from 1.78 EU to 1.56 EU. In every case, the performance of ZnSe:Te is inferior compared to CaF 2 :Eu, due to the inherent properties and possibly due to the specific production method of the particular material sample (Saatsakis et al., 2020b).

Fig. 1. Variation of ZnSe:Te and CaF 2 :Eu luminescence signal with temperature.