PSI - Issue 66

Martha Dima et al. / Procedia Structural Integrity 66 (2024) 153–160 Author name / Structural Integrity Procedia 00 (2025) 000–000

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sphere (see in Figure 1, GAGG-49 crystal). Temperature was induced with a heating gun (Perel, model 3700-9). An Agilent Technologies model U1253A digital multimeter, combined with a U1185A (J-Type) thermocouple and a temperature sensor adapter was used to monitor temperature.

2.2. Luminescence Efficiency

With the experimental setup described in section 2.1. the light energy flux produced by the Gd ₃ Al ₂ Ga ₃ O ₁₂ samples was recorded and subsequently was divided by the X-ray exposure rate. In this manner the absolute luminescence efficiency was obtained, as described in equation (1): � � � � � � � �� ���� � � � � � �� , (1) In equation (1) � � is the light energy flux (output signal) in units of μ W/m 2 , � is the exposure rate (mR/s). Following, is the current produced by electrometer (i elec ) in pA and S denotes the surface of the crystal, excited by X rays (mm 2 ). The peak sensitivity of the photocathode ( η p ) is expressed in units of pAW -1 . α s is a factor denoting the matching of the emitted spectrum of the light source (in this case Gd ₃ Al ₂ Ga ₃ O ₁₂ crystals) with the optical response of the optical sensor (photocathode). Finally, the percent of the sample’s emitted light escaping the integrating sphere and reacting with the PMT is the geometric light collection efficiency (c g ) having a measured value of 15.6. The units of the luminescence efficiency are EU=( μ W/m 2 )/(mR/s).

Fig. 1. The examined GAGG-45 (left) and GAGG-49 (right) crystals.