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

Abstract

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 2 (Eu) scintillator detectors, which have already achieved <3.0% energy resolution at 662 keV with volumes >10 cm 3 . In this study, we have tested pure, undoped SrI 2 to gain a better understanding of the scintillation properties and spectroscopic performance achievable without activation. An undoped crystal grown from 99.999% pure SrI 2 pellets was tested for its spectroscopic performance, its light yield, and uniformity of scintillation light collection as a function of gammaray interaction position relative to the crystal growth direction. We measured an energy resolution of 5.3% at 662 keV, and the light collection non-uniformity varied by only 0.72% over the length of the crystal. Measurements of both a 3% Eu-doped and the undoped SrI 2 detector were carried out in the SLYNCI facility to determine their light yield non-proportionality, which will be reported. The surprisingly good scintillation properties of the pure SrI 2 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.

Development of transparent ceramic Ce-doped gadolinium garnet gamma spectrometers

“…This is well-documented for the single crystal scintillator, SrI 2 (Eu) [9][10][11]. In contrast to SrI 2 (Eu), self-absorption by Ce in GYGAG(Ce) results in redshifting of the emission that diminishes the quantum efficiency of conversion with PMT readout, due to the loss in bialkali photocathode sensitivity at longer wavelengths.…”

“…Previous studies have detailed the effect of optical light trapping and methods for mitigation for Eu-doped Strontium Iodide [9][10][11]18], however, that scintillator emits in the blue, where PMT quantum efficiency (QE) is high and nearly invariant. In contrast, between 475 and 650 nm, the PMT QE decreases by a factor of about 4, thus the net result of the light trapping and red-shifting emission as a function of size is decreased effective light yield, as well as position dependent GYGAG(Ce) ceramic fabricated at LLNL, using silicon photodiode readout.…”

Crystal growth and characterization of europium doped KCaI3, a high light yield scintillator

“…The emission maximum is at 466 nm, which can be attributed to the Eu 2+ 5d-4f transition in the KCaI 3 matrix. The exact source of the low intensity emission ''shoulder'' in the 500-550 nm region is unknown but in other scintillators such as SrI 2 :Eu it has been ascribed to either surface hydrate defects or otherwise impurity mediated recombination emission [9]. This same feature has perplexed many researchers as to the exact cause which remains difficult to pinpoint due to the deliquescent nature of the metal halides.…”

Comparative study of nondoped and Eu-doped SrI2 scintillator

“…However, owing to recent progress of crystal growth technology, dramatically improved scintillation properties (eg. scintillation light yield, energy resolution and decay time) have been discovered in Eu-doped SrI 2 crystals [22][23][24][25][26][27][28][29][30][31][32][33]. Eu-doped SrI 2 showed high light yield of 120000 ph/MeV (maximum value was reported in [25]), typically 3% energy resolution at 662 keV (the best value of 2.6% was achieved in [28]), and typically decay time of 1-2 s depending on the Eu concentration.…”

“…Although most studies have been done by doping with Eu, in a view point of condensed matter physics, investigation of nondoped SrI 2 is also an important research in order to gain a knowledge of such excellent scintillation response when doped with Eu ions. In earlier papers [29,31], nondoped SrI 2 was studied and it showed a very complicated scintillation spectrum. The band gap energy was reported as ~5.5 eV, and non-equivalent I sites was suggested [23].…”