Timing properties of BGO scintillator

Abstract

Light pulse shape, number of photoelectrons per energy unit and obtainable time resolution were studied with a 2 cm diameter and 3 cm high BGO scintillator coupled to an XP 2020 photomultiplier and compared with similar measurements on NaI(Tl) crystal. The observed time resolution of the time spectrum, fwhm equal to 1.3 ns and fwtm equal to 3.5 ns measured with one BGO crystal in coincidence with a CsF scintillator for a 60Co source and the energy threshold set at 100 keV showed that BGO scintillator can easily be used in coincidence experiments. Despite the low light yield, equivalent to 550 photoelectrons per 1 MeV, the time resolution of BGO crystal is only a factor of two worse than NaI(Tl) scintillator. It seems to be associated with the faster initial decay of the light pulse from the BGO crystal, as well as, with the very low afterglow which permits the BGO to work with the true triggering on the first photoelectron which is almost impossible in timing with NaI(Tl) scintillators. The fast component, with a decay time constant equal to 60 ns preceding the known decay with the time constant equal to 300 ns, was found by observing the light shape using the single photon method.