Energy Resolution of Scintillation Detectors—New Observations

According to the present knowledge, the non-proportionality of the light yield of scintillators appears to be the fundamental limitation of energy resolution. However, several observations collected in the last 10 years on the influence of slow components of the light pulses on energy resolution suggest more complex processes in the scintillators. This was observed with CsI(Tl), ZnSe(Te), undoped NaI at liquid nitrogen temperature and finally for NaI(Tl) at temperatures reduced below 0 $^{\circ}$C. A common conclusion of these observations is the fact that the highest energy resolution, and particularly the intrinsic resolution measured with scintillators, characterized by two components of the light pulse decay, is obtainable when the spectrometry equipment integrates the whole light of both components. In the limiting case, the afterglow could be considered also as a very slow component destroying the energy resolution. The aim of this work is to summarize all above observations looking for their origin.