Precise timing resolution measurements of GSO scintillators with different Ce concentrations combined with silicon photomultipliers

Abstract

Ce doped Gd2SiO5 (GSO) is a scintillator which has relatively fast decay time, high density, high light output, and is used for commercial PET systems. However as time-of-flight (TOF) PET systems become more popular in clinical diagnostic, GSO seems less attractive, because its performance is thought to be insufficient for use in TOF-PET application. Although the timing resolution of the GSO combined with photomultiplier tube (PMT) is known to be inappropriate for TOF-PET system, the performance of GSO coupled to silicon photomultipliers (Si-PM) has not been reported to date. In addition, GSO possesses a variety of decay times depending on its Ce concentration. We measured basic performance of GSOs with different Ce concentrations and then coupled them to Si-PMs to measure the precise timing resolution using a high bandwidth digital oscilloscope. The decay time of GSO with 0.4mol% Ce were longer (63±4ns) compared with those with 1.0mol% (40±2ns) and 1.5mol% (33±1ns). With a Si-PM, the photo-peak channels were almost the same for GSOs with 0.4mol% Ce and those with 1.5mol% Ce, but the GSO with 1.0mol% Ce was ~25% higher. Energy resolutions of these three GSOs were ~13% full-width at half-maximum (FWHM) for 662keVgamma photons without correcting for saturation effects. When coupled to Si-PMs, the timing resolution for GSO with 1.5mol% Ce (decay time 33ns) was 549ps FWHM, almost good enough to use for TOF-PET system. The combination of GSO with 1.5mol% Ce with Si-PM will be an interesting combination to realize low cost TOF-PET systems.