Development of transparent ceramic Ce-doped gadolinium garnet gamma spectrometers

Transparent polycrystalline ceramic scintillators based on the garnet structure and incorporating gadolinium for high stopping power are being developed for use in gamma spectrometers. Optimization of energy resolution for gamma spectroscopy involves refining the material composition for high stopping and high light yield, developing ceramics fabrication methodology for material homogeneity, as well as selecting the size and geometry of the scintillator to match the photodetector characteristics and readout electronics. We have demonstrated energy resolution of 4% at 662 keV for 0.05 cm³ GYGAG(Ce) ceramics with photodiode readout, and 4.9% resolution at 662 keV for 18 cm³ GYGAG(Ce) ceramics and PMT readout. Comparative gamma spectra acquired with GYGAG(Ce) and NaI(TI) depict the higher resolution of GYGAG(Ce) for radioisotope identification applications. Light yield nonproportionality of garnets fabricated following different methods reveal that the fundamental shapes of the light yield dependence on energy are not intrinsic to the crystal structure, but may instead depend on trap state distributions. With exposure to 9 MeV Brehmsstrahlung radiation, we also find that GYGAG(Ce) ceramics exhibit excellent radiation hardness.