Energy Resolution of Scintillators in Connection With Track Structure

The large spread of scintillator performance (light yield and energy resolution) from a theoretical limit shows that we are still far from the deep understanding of the phenomena. Usually, extrinsic aspects of resolution degradation (such as purity, defects, stoichiometry, and so on) are the subject of study. At the same time, intrinsic factors (such as track structure, excitation density, and uniformity) that depend on crystal lattice can play a dominant role in scintillator performance. Some progress in the understanding of these problems is achieved by using the concept of different efficiencies of photon emission from excited regions with different concentrations of electronic excitations. The regions with a high or low concentration of thermalized excitations result in the nonradiative losses of excitations and, therefore, produce additional event-to-event fluctuations. The technique of multidimensional analysis of the time-resolved pulse shape is proposed for the clustering of all the events according to the proximity of the waveform to some centroids of the clusters. This procedure shows that even conventional NaI:Tl and CsI:Tl scintillators allow to achieve an energy resolution of about 3% for 662-keV gamma photons.