Abstract
Recent renewed emphasis placed on gamma-ray detectors for national security purposes has motivated 13 researchers to identify and develop new scintillator materials capable of high energy resolution and 14 growable to large sizes. We have discovered that SrI2(Eu) has many desirable properties for gamma-ray 15 detection and spectroscopy, including high light yield of ~90,000 photons/MeV and excellent light yield 16 proportionality. Furthermore, we have demonstrated growth of crack-free 2” diameter boules. We 17 have measured <2.7% FWHM at 662 keV with small detectors (<1 cm3) in direct contact with a 18 photomultiplier tube, and ~3% resolution at 662 keV is obtained for 1 in3 crystals. Due to the 19 hygroscopic nature of SrI2(Eu), proper packaging is required for field use. This work describes a 20 systematic study performed to determine the key factors in the packaging process to optimize 21 performance. These factors include proper polishing of the surface, the geometry of the crystal, 22 reflector materials and windows. A technique based on use of a collimated Cs-137 source was developed 23 to examine light collection uniformity. Employing this technique, we found that when the crystal is 24 packaged properly, the variance in the pulse height at 662 keV from events near the bottom of the 25 crystal compared to those near the top of the crystal could be reduced to <1%. This paper describes the 26 design and engineering of our detector package in order to improve energy resolution of 1 in3-scale 27 SrI2(Eu) crystals.