Development of Eu:SrI₂ Scintillator Array for Gamma-Ray Imaging Applications

Eu:SrI₂ bulk single crystals with 1.5-in diameter were grown using the Bridgman-Stockbarger technique and special-shaped crucibles. We will report on the growth of the 1.5-in size Eu:SrI₂ single crystal and the preliminary test of the same sample cut in size of 10 × 10 × 10 mm³ with polishing. An energy resolution of 3.2% full width at half maximum (FWHM) was obtained for ¹³⁷Cs. After cutting and polishing the grown crystal to the size of 3 × 3 × 3 mm³, 8 × 8 matrix Eu:SrI₂ arrays were fabricated. We made a test module consisting of Eu:SrI₂ arrays, which was optically coupled with position sensitive photomultiplier tube (PSPMT) and multi-pixel photon counter (MPPC) array. The position and energy performance of the test module were evaluated using ¹³⁷Cs and ⁵⁷Co radioactive sources. As a result, we were able to resolve all pixels clearly. A good energy resolution of 6.7% ± 0.7% (FWHM) and 8.2% ± 2.5% (FWHM) for 662 keV was obtained using PSPMT and MPPC arrays, respectively. In the same way, energy resolution of 12.7% ± 1.3% and 14.7% ± 3.4% (FWHM) for 122 keV was obtained using PSPMT and MPPC-array, respectively. These energy resolutions considerably degraded compared with an energy resolution of the single piece of Eu:SrI₂ sample owing to the thinness of the Teflon reflector. This conclusion can be considered as a strong motivation for future research on the choice of reflector materials and structure of the Eu:SrI₂ array.