The Fluorescent Decay of CsI(Tl) for Particles of Different Ionization Density

New measurements of the decay of the fluorescence produced in CsI(Tl) have been made for different particles. The detailed shape of the decay is found to depend on the average ionization density ρ. The lifetimes τ of the main components are 0.425 ± 0.025 μsec for 4.8 MeV alpha particles, 0.52 ± 0.01 μsec for 2.2 MeV protons, 0.595 ± 0.02 μsec for 8.6 MeV protons and 0.70 ± 0.025 μsec for 0.66 MeV electrons. The variation of τ and ρ is very similar to that observed by others for the variation of τ with temperature for alpha particles, which suggests that the former may be explained in terms of variations in the effective local temperature. It is shown that the differences in τ are sufficient to allow a single crystal detector to be used in experiments where particle type as well as energy determination are required.