PSI - Issue 41

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

83

2

1. Introduction Radiation sensing materials, scintillators, can be applied in diverse fields, including medical, applications in harsh environments, industrial (NDT), etc. (Kandarakis, 2016; Linardatos et al., 2021a, 2021a, 2021b, 2020; Martini et al., 2020, 2019, 2018; Michail et al., 2018a; Mykhaylyk et al., 2019; Yanagida et al., 2013). The radiation flux, as well as the environmental conditions (e.g. temperature) affect the performance of scintillating materials; thus, their influence should be monitored and the materials should be selected depending on their relative performance (Bisong et al., 2019; Karpetas et al., 2017; Lebedev et al., 2019; Patri et al., 2019; Saxena, 2019). A semiconductor scintillator with wide bandgap (2.82 eV) is zinc selenide activated with tellurium – ZnSe:Te (Shi et al., 2015). The properties of ZnSe:Te have attracted a lot of attention for various applications (Ryzhikov et al., 2013). The light output ranges from 2.8∙10 4 photons/MeV to 1.69∙10 5 ph/MeV. The density has a value of 5.42 g/cm 3 and 33 is the effective atomic number (Dafinei et al., 2017; Ryzhikov et al., 2013). The decay time is very short, ranging from 80 μs to 20 ns (Cho et al., 2008), well-suited for use in high frame-rate radiography applications and CT. ZnSe:Te could also be applied in dual-energy systems, as the low-energy photons detector (Linardatos et al., 2020; Ryzhikov et al., 2013), enhancing the capability of the system to discriminate between osseous and muscular tissue, or between low-contrast structures, thus facilitating the diagnosis of osteoporosis, tumors and atherosclerosis (Martini et al., 2021, 2020, 2017; Ryzhikov et al., 2009). Furthermore, ZnSe:Te can be incorporated in high-energy applications, safety (e.g., baggage inspection), space probes, dosimetry, or quantum-dots (Jagtap et al., 2019; Saatsakis et al., 2019). Disadvantages of ZnSe single crystals include their poor transparency and their susceptibility to re-crystallize (Jagtap et al., 2019). The temperature performance of ZnSe:Te is compared with relevant data for CaF 2 :Eu crystals (Rutherford et al., 2016; Saatsakis et al., 2020a). CaF 2 :Eu is a robust crystal resistant to mechanical and thermal shocks that melts at 1360°C; i.e. properties adequate for extreme environments. A summary of ZnSe:Te and CaF 2 :Eu properties is shown in Table 1 (Chen, 2008; Cho et al., 2008; Dafinei et al., 2017; Dujardin et al., 2018; Eritenko and Tsvetyansky, 2020; Fan et al., 2018; Jagtap et al., 2019; Lecoq, 2016; Lecoq et al., 2017; Linardatos et al., 2020; Michail et al., 2019; Saatsakis et al., 2020b; van Eijk, 2002).

Table 1. ZnSe:Te and CaF 2 :Eu properties. Properties

Units g/cm³

ZnSe:Te

CaF 2 :Eu

Density

5.42

3.18 16.5

Atomic Number (Effective) Melting Point Thermal Expansion Coefficient Hardness Emission maximum

33

°K C -1 Mho nm

1779 7.6 x 10 -6 4 640

1360 19.5 x 10 -6 4 435

2. Materials and Methods The crystal samples of this work were cubic, with dimensions of 1x1x1 cm 3 and polished surfaces (Advatech UK, 2022). The samples were exposed to a typical medical diagnostic X-ray spectrum (90 kVp and 89.83 mR) under a CPI series CMP 200 DRMedical X-ray source, in order to measure the light photon intensity dependence with temperature. A supplementary 2 cm aluminum filter was used to harden the X-ray beam (Michail et al., 2018b) and the measurements were performed in the range 20°C to 140°C. The crystal’s temperature was increased using a heating gun (Perel 3700-9), while temperature monitoring was performed with an infrared digital thermometer (Extech RH101) (Saatsakis et al., 2021). The light produced upon X-ray excitation was measured with the crystal placed at the upper-input port of an Oriel 70451 integrating sphere. This sphere was coupled to a photomultiplier tube (EMI 9798B), connected to the output port of the sphere (Saatsakis et al., 2020a). The signal from the extended S-20 photomultiplier's photocathode was