Energy and Timing Response of Six Prototype Scintillators for TOF-PET

The recent development of fast scintillating crystals with high light output (such as LaBr₃, LYSO, and LSO) has made it possible to incorporate time-of-flight information into whole-body positron emission tomography scanners (TOF-PET). The development of fast scintillators has continued, and scintillators such as CeBr₃ and the six crystals we report on here are candidates for future TOF-PET scanners. We have performed preliminary tests on six prototype scintillating crystals composed of YI₃ (2% Ce), (Lu,Gd)I₃ (2% Ce), Lul₃ (10% Ce), Lul₃ (5% Ce), Lul₃ (2% Ce), and Ce(Br,Cl)₃. The crystals were coupled to a PMT to observe 511 keV photons produced by positron captures in a ²²Na point source. A LaBr₃ coincidence detector was used in order to make timing resolution measurements. The prototype samples had a range of timing resolutions from 160 ps to 250 ps (FWHM). Ce(Br,Cl)₃ was found to have the best timing resolution, with 160 ps, followed by Lul₃ (2% Ce) with 180 ps. These results are competitive with the 160 ps we observed for a pair of LaBr₃ crystals in coincidence with each other. The 2% Ce doped Lul₃ sample was found to have the best overall energy response, with an energy resolution (FWHM) of 6% at 511 keV. Energy resolution and light yield measurements are presented for each of the crystals.