Characteristics of undoped and europium-doped SrI<inf>2</inf> scintillator detectors

Abstract

High energy resolution gamma-ray detectors that can be formed into relatively large sizes while operating at room temperature offer many advantages for national security applications. We are working toward that goal through the development of SrI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (Eu) scintillator detectors, which routinely provide <;3.0% energy resolution at 662 keV with volumes >;10 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . In this study, we have tested pure, undoped SrI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> to gain a better understanding of the scintillation properties and spectroscopic performance achievable without activation. An undoped crystal grown from 99.999% pure SrI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> pellets was tested for its spectroscopic performance, its light yield, and uniformity of scintillation light collection as a function of gamma-ray interaction position relative to the crystal growth direction. Undoped SrI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was found to provide energy resolution of 5.3% at 662 keV, and the light collection nonuniformity varied by only 0.72% over the length of the crystal. Measurements of both a 3% Eu-doped and the undoped SrI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> crystal were carried out in the SLYNCI facility and indicate differences in their light yield non-proportionality. The surprisingly good scintillation properties of the pure SrI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> crystal suggests that with high-purity feedstock, further reduction of the Eu concentration can be made to grow larger crystals while not adversely impacting the spectroscopic performance.