This paper reports the emission spectra, pulse heights, and decay curves of CsI(Tl) crystals with a Tl + concentration ranging from 10 6 to 10 2 mol under electron and alpha particle excitations. Larger pulse heights from the crystals with Tl + concentration of more than 10 3 mol were observed for a higher ionization density of alpha particle excitation compared with those of electron excitation. This enhancement may be explained in terms of the higher scintillation efficiency for higher Tl + concentration. Decay curves under electron and alpha particle excitations were compared with the decay curve under pulsed UV excitation. The observed decay curves were explained in terms of the sum of the three energy transfer processes to create excited states (Tl + ) : the prompt process, the diffusion process to Tl 0 , and the electron release process from Tl 0 to Tl ++ . Here, Tl 0 and Tl ++ were produced through (Tl + + electron) Tl 0 and [Tl + + hole (or )] Tl ++ .

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