The scintillation decay time constant for NaI(Tl) detectors is 230 ns. That is a factor of 20 to 100 times longer than is typical of the fast scintillators that are best for timing. As a result, the last portion of each anode pulse from a NaI(Tl) detector consists of individual, single-photon pulses. If the dead time of the timing discriminator is as short as 10 ns, the discriminator will trigger once on the leading edge of the anode pulse and then multiple times at the end of the anode pulse. This multiple triggering on a single pulse can be prevented by choosing a timing discriminator that allows selecting a non-extending dead time of approximately 1 µs. The blocking outputs of the Models 583B, 584, and 935 offer that capability. Several other slow scintillators (e.g., CsI(Na), CsI(Tl), and BaF₂) require a similar solution.

Faster scintillators, exhibiting decay times of the order of 5 ns, do not require a special dead time setting.