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We have developed Lu 0 4 Gd 1 6 SiO 5 :Ce (LGSO) crystals as a new scintillator for medical applications. Scintillation properties of LGSO crystal of various Ce concentrations and their dependence on annealing effect were studied. Its absorption coefficient at 511 KeV gamma rays is 0.70 cm 1 . We observed that the light output and decay time are dependent on the Ce concentration in the crystal. Decay constant decreases with increasing Ce. Annealing of the colored crystal having 2.0 mol% Ce makes it colorless with better scintillation properties: large light output (40% of NaI:Tl), good energy resolution (8.3% for 4 6 20 mm 3 crystal) and fast decay constant (65 ns of primary component and 180 ns of secondary component).

Several LGSO samples with different Ce doping were studied in comparison to GSO crystal. The light output, non-proportionality of the light response, energy resolution and intrinsic resolution were measured and compared to the intensity of the afterglow recorded in the second range of time. A high light output of 17000 1700 ph/MeV and a good energy resolution of 6 5 0 2% for 662 keV gamma rays from a 137 Cs source were obtained for the best sample, doped with 1 mol% of Ce. The energy resolution and, in particularly the intrinsic resolution varied with the concentration of Ce in the tested crystals and were not correlated with their common non-proportionality characteristics. In contrast, the observed correlation of the intrinsic energy resolution of the LGSO crystals and the intensity of their afterglow indicates that the energy resolution of scintillation detectors may be affected by a strong afterglow of the crystals. Thus, it suggests to the manufacturers to make more efforts to reduce afterglow in the crystals.Index Terms-Afterglow, Ce doped scintillators, energy resolution, non-proportionality of the light yield.

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