PSI - Issue 47

Stavros Tseremoglou et al. / Procedia Structural Integrity 47 (2023) 119–124 Tseremoglou/ Structural Integrity Procedia 00 (2023) 000 – 000

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1. Introduction Crystal scintillators have been widely employed in several technological fields, with a prominent use in medical imaging (Nassalski et al. 2007, Nikl 2006, Valais et al. 2005, Valais et al. 2007, Valais 2008). In harsh environmental applications, where extreme conditions of temperature, pressure or radiaton fluxes occur, the performance of a scintillator is strongly affected by these parameters (Bisong et al. 2019, Patri et al. 2019, Saxena et al. 2019). In this study, the absolute efficiency (AE) dependence of LaCl 3 :Ce single crystal scintillator with temperature change was investigated. LaCl 3 :Ce crystal (density of 3,86 g/cm 3 ) was selected due to its distinct advantages, such as high light yield and fast decay times, providing excellent energy resolution performance (Advantech UK 2022). The reported light yield under 137 Cs 662 KeV γ ray excitation r anges from 40.000 photons /MeV (Guillot-Noel et al. 1999) to 49.000 photons /MeV (Van Loef et al. 2000, Iltis et al. 2006) depending on the size of the crystal (Balcerzyk et al. 2005) and cerium concentration (Van Loef et al. 2000, Guillot-Noel et al. 1999). In addition, its response is clearly linear (Shah et al. 2003), meaning that its light yield is energy independent. The high light yield and the very good linearity of the crystal response, are the reasons for its excellent energy resolution (Shah et al. 2003, Van Eijk 2002). Energy resolution for the 662 keV peak was calculated from 3.1% to 4% (FWHM over peak position) at room temperature for various sizes of crystals, various concentrations of cerium and measurement conditions (Alzimami et al. 2008, Shah et al. 2003, Iltis et al. 2006, Van Eijk 2002). LaCl 3 :Ce single crystal has fast response time with principal decay constant 20-28 ns ( 41- 76% to the total light output) for crystals with 10 - 20% Ce concentration (Shah et al. 2003, Van Loef et al. 2000, Advantech UK 2022). The wavelength range of emission spectrum at ambient temperature is from 300nm to 400nm with maximum peak at 350nm. The crystal has a high melting point at 1135 °C, providing robustness at high temperatures (Advantech UK 2022). Moreover, the AE values of LaCl 3 :Ce crystal at room temperature, were found higher than those of other commonly employed crystals, within a wide tube voltage range (50-150 kVp) (Tseremoglou et al. 2022). 2. Materials and Methods A single cubic-shaped crystal was purchased from Advatech UK Limited, with dimensions of 10 × 10 × 10 mm 3 and having all its surfaces polished (Advantech UK 2022). The Absolute Efficiency (AE) of the crystal was measured as described in literature (Kandarakis et al. 1997, Michail et al. 2019, Ninos et al. 2010), under varying crystal temperatures from 29 to 162 o C, using a Perel 3700-9 2000W heating gun and an infrared digital thermometer (Extech RH101). 3. Results and Discussion Figure 1 shows the variation of AE measured values of the LaCl 3 :Ce crystal, with the temperature ranging from 29 to 162 o C. The examined temperatures are indicative, similar to temperatures that can be found in logging detectors (minus 0 °C to above 200 °C) (Melcher et al. 1991), and kept at this range to avoid excessive heating that could result in possible crystal cracking (Pokluda et al. 2015).