Multiple doping of CsI:Tl crystals and its effect on afterglow

Despite the acknowledged advantages of CsI:Tl in many scintillator applications, a characteristic property that undermines its use in high-speed radiographic and radionuclide imaging is the presence of a strong afterglow component in its scintillation decay. This causes pulse pileup in high count-rate applications, reduced energy resolution in radionuclide imaging, and reconstruction artifacts in computed tomography applications. The research outlined here addresses the specific issue of suppressing the afterglow in CsI:Tl crystals by modifying them with codopants. In previous work we reported that one specific codopant, Eu(2+), was particularly effective in this regard, lowering the normalized intensity of the afterglow in the time range of 10 mus - 100 ms by almost two orders of magnitude compared to conventional material. We also found, however, that the extent of the suppressive effect was significantly influenced by the presence of additional additives, some of which were inadvertently introduced by the very material that provided the primary Eu codopant itself. The effects of these secondary codopants, which include elemental iodine and various oxidic species, are addressed in the present investigation.