PSI - Issue 10

N. Martini et al. / Procedia Structural Integrity 10 (2018) 326–332

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N. Martini et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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Fig.2 shows the grain-size deposition per thickness of CaWO 4 , estimated from scanning electron microscope (SEM) images. Qualitatively the mean particle size of CaWO 4 phosphor was 6.02 μ m was estimated from the SEM images using the imageJ analysis software (Huang and Wang (1995), Abramoff et al. (2004)). The calculated screen thickness was 118.9 μ m estimated by ten profile measurements on Fig.2, across the material coating (Michail et al. (2018)). Fig.2 shows indicative measurements.

Fig. 2. Scanning electron microscope (SEM) image of the CaWO 4 scintillating material.

Fig.3 shows an image of the edge phantom obtained using 70 kVp and 50 mAs for the tube current and exposure time product, with the overlaid ROI for the ESF calculation. This energy is also within the energy range of 51-84 keV that can be utilized for testing steel thicknesses between 2.5 and 12.5 mm (IAEA 2011). The edge test device consists of a 1 mm thick W edge plate (1 00×75 mm 2 ) fixed on a 3 mm thick lead plate. Images of the edge, placed at a slight angle in order to avoid aliasing effects, were obtained. The edge spread function, of the small CMOS detector, was calculated by the extraction of a 2×2 cm 2 ROI, which covers approximately 41% of the active area of the small area CMOS sensor (2.7×3.6 cm 2 ), with the edge roughly at the center. In the IEC protocol a 5×10 cm 2 ROI is suggested (IEC 2015). A smaller ROI may not be adequate to observe a possible low-frequency sharpness drop in scintillating screens (Michail (2015b)).

Fig. 3. Slanted edge image of the obtained, under the RQA-5 beam quality.