Performance evaluation of newly developed SrI₂(Eu) scintillator

The development of europium-doped strontium iodide (SrI₂(Eu)) has attracted considerable attention, because of its excellent material properties as regards gamma-ray scintillator applications. These include its excellent energy resolution, high light output (>80,000ph/MeV), and high effective atomic number (Z=49). Here we report on the performance of ϕ 1 in×1 in SrI₂(Eu) cylindrical crystals newly fabricated by Union Materials Inc. In this study, we measured the energy resolution and light output at 10 °C temperature intervals between −40 and 40 °C, using an optically coupled 2-in photomultiplier tube (PMT) (Super Bialkali, Hamamatsu). The SrI₂(Eu) light output increased by 0.12%/°C as the temperature decreased. At −40 °C, we obtained the optimal energy resolution recording 2.91±0.02% full width at half maximum (FWHM) for 662 keV gamma rays measured with ¹³⁷Cs. For comparison, we also measured the same crystal using both a large-area (19×19 mm²) avalanche photodiode detector (APD) and 8×8 multi-pixel photon counter (MPPC) arrays of 3×3 mm² pixels. The energy resolutions of 2.94±0.02%, 3.14±0.06% and 3.99±0.01% were obtained using PMT, APD, and MPPC, respectively, as measured at −20 °C. We also measured the inherent background of SrI₂(Eu) in a cave composed of Cu–Pb blocks with their thickness of 5–10 cm confirming that SrI₂(Eu) has an extremely low inherent background radiation. In this study, we have shown that SrI₂(Eu) is a promising scintillator that can be utilized for radiation measurements incorporating low-energy X-rays to high-energy gamma rays, and can thus be applied in various medical, industrial, and environmental treatment fields in the near future.