Scintillation Process in CsI(Tl). I. Comparison with Activator Saturation Model

The scintillation efficiency of CsI(Tl) crystals, containing varying amounts of Tl, has been measured upon excitation by gamma rays, protons, and alpha particles in the keV and MeV region. The purpose of this program was to provide a critical test of a previously proposed phenomenological model of the scintillation process in activated alkali halides. In order to achieve this goal, special attention has been paid to technical effects which might distort the data, viz., effects dependent on the emission spectrum and the pulse analysis time. It is concluded that the variation of the scintillation efficiency as a function of the stopping power of the incident particle is predicted by the scintillation model when the effect of secondary electrons is taken into account. It is found that the shape of the scintillation efficiency versus dE/dx curve is very nearly independent of Tl concentration. It is concluded from this fact that the decline in scintillation efficiency for highly ionizing particles is not due to saturation of activator centers.