Time decay and photoluminescence measurement of PbWO(sub 4) crystal

摘要

This report presented the experimental characterization of the PbWO(sub 4) crystals that we will be used for the photon detector of the Compton polarimeter at the Jefferson laboratory. We could draw 3 main features from this study. The transmission rate of the crystals is about 60 % in the scintillation wavelength region. From the decay time analysis, we deduced 3 decay components of the PbWO(sub 4), predicted by other measurements: (tau)(sub 1)(approx)5 ns, (tau)(sub 2)(approx)20 ns, (tau)(sub 3)(approx)100 ns, taking respectively 26 %, 30 % and 4 % of the total light amplitude emitted by the crystals. Moreover, we showed the existence of a fourth decay constant ((tau) (sub 4)(approx)1(mu)s) taking 40 % of the total quantity of light which is responsible for the bad precision on the third constant determination. We could not characterize this component accurately because of the limited time range of the recordings. To improve the determination of the super-slow component, we need to perform the measurements again on a longer time scale, on the order of a few microseconds. We eventually measured the light yield of the PbWO(sub 4) crystals. With a first analysis, we found about 3.5 photoelectrons per MeV whereas the constructors note gave about 10. We then reduced the light loss in the experimental set up by wrapping the last open end of the crystal. The results were slightly improved. Eventually, we increased the recording time, to take account the super-low decay, and found that the crystals yield about 6 photoelectrons per MeV which is still less than predicted. (author) 12 refs.