Effects of Ce concentration on scintillation properties of LaBr/sub 3/:Ce

In this communication we report on our investigation of scintillation properties of LaBr/sub 3/:Ce as a function of Ce concentration. We have studied crystals nominally doped with 0.5, 5, 10, 20, and 30% Ce (by mole). Reports published so far suggested that as the Ce content increases, there is a decrease in light output and little or no change in decay time constants. Our results show that the light output does not change with Ce concentration up to 30% and depends mostly on the crystal and measurement quality. On the other hand we have found timing properties to be a strong function of concentration. As the Ce content increases the principal decay time constant of scintillation decreases from /spl sim/26 ns for 0.5% Ce to /spl sim/17 ns for crystals with >5% Ce. Moreover, there is also a significant change in rise time constants. The rise time measured for a sample doped with 0.5% Ce is up to 9 ns, whereas for samples doped with >10% Ce it reduces to less than 0.5 ns. The change of rise time has a major effect on the timing properties of this scintillator, with timing resolution improving from 390 ps to less than 200 ps (FWHM).