Timing and energy characteristics of LaBr3[Ce] and CeBr3 scintillators read by FBK SiPMs

Lanthanum Halide scintillators exhibit high light output and fast decay times. The resulting high radiant flux has enabled the measurement of annihilation photon coincidence timing resolution of <;100ps FWHM as well as with energy resolution<;4% FWHM using conventional PMTs. Taking full advantage of these characteristics in a TOF PET detector is greatly affected by the performance of the photodetector. The ability to fabricate Silicon Photomultipliers (SiPM) pixels of comparable size to the cross section of scintillator pixels used in clinical scanners (4×4mm²) allows the direct coupling of a crystal array to an array of SiPM pixels. SiPMs fabricated at FBK have been designed to offer high Photon Detection Efficiency (PDE), high spatial and temporal transit time uniformity, fast risetime and low noise. The high gain and low noise of the FBK SiPM result in signal amplitude of ~200mV, enabling excellent performance using passive readout circuits. We characterize the response of LaBr₃[Ce] and LYSO scintillators read out by FBK SiPM to annihilation photons. 511KeV photopeak energy resolution of 5.6% and 12.5% is measured with LaBr₃ and LYSO, respectively, despite of the saturation behavior evident at that energy. Coincidence timing resolution of 163ps and 249ps FWHM are measured for 5mm long and 30mm long pixels, respectively. While measured performance with LaBr₃ does not quite yet match performance measured with PMTs, these results are very encouraging considering that QE is not yet well matched to shorter wavelength emission of LaBr₃.