Scintillators photon emission rate

Is measured for Lumlnol In the liquid scintillation counter, any strongly quenched scintillation cocktail will produce an equivalent Lumlnol photon emission rate given by... 

The rate of emission of photons from a scintillator is XNoeh, where N0 is the total number of photons emitted and X is the decay constant of the phosphor. For Nal(Tl) the decay time x (=A I) 220ns, whereas for fast plastic x 2ns (i.e., in the first ns 40% of the light from a plastic scintillator is typically emitted, whereas only 0.5% is emitted from Nal(Tl)). 

Chemiluminescence and photoluminescence are other forms of interference that can reduce the accuracy of LS techniques. Chemiluminescence describes the emission within the scintillation cocktail of photons that result from a chemical reaction common initiators are samples with an alkaline pFl or the presence of peroxides. Photoluminescence can occur when the scintillation cocktail is exposed to ultraviolet light. Some substances in the cocktail, notably the scintillator, are excited and then emit light when the species return to ground state. The effect of photoluminescence is reduced in LS systems by decay when the sample train is held in a dark environment for a few minutes prior to counting. On the other hand, chemiluminescence may have a slow decay rate that requires a change in sample preparation to eliminate the chemical that causes it. Some LS systems identify luminescence by pulse shape and indicate its relative extent. 

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