Statistical studies on the light output and energy resolution of small LSO single crystals with different surface treatments combined with various reflector materials

The optimization of light output and energy resolution of scintillators is of special interest for the development of high resolution and high sensitivity PET. The aim of this work is to obtain statistically reliable results concerning optimal surface treatment of scintillation crystals and the selection of reflector material. For this purpose, raw, mechanically polished and etched LSO crystals (size 2 x 2 x 10mm(3)) were combined with various reflector materials (Teflon tape, Teflon matrix, BaSO4) and exposed to a Na-22 source. In order to ensure the statistical reliability of the results, groups of 10 LSO crystals each were measured for all combinations of surface treatment and reflector material. Using no reflector material the light output increased up to 551 +/- 35% by mechanical polishing the surface compared to 100 +/- 5% for raw crystals. Etching the surface increased the light output to 441 +/- 29%. The untreated crystals had an energy resolution of 24.6 +/- 4.0%. By mechanical polishing the surface it was possible to achieve an energy resolution of 13.2 +/- 0.8%, by etching of 14.8 +/- 0.7%. In combination with BaSO4 as reflector material the maximum increase of light output has been established to 932 +/- 57% for mechanically polished and 895 +/- 61% for etched crystals. The combination with BaSO4 also caused the best improvement of the energy resolution up to 11.6 +/- 0.2% for mechanically polished and 12.2 +/- 0.3% for etched crystals. Relating to the light output there was no significant statistical difference between the two surface treatments in combination with BaSO4. In contrast to this, the statistical results of the energy resolution have shown the combination of mechanical polishing and BaSO4 as the optimum. (C) 2002 Elsevier Science B.V. All rights reserved.