IEEE Technical Sessions
Co-doped CsI(Tl) for low afterglow
At the 2021 IEEE Nuclear Science and Medical Imaging Conference, Peter Menge, Principal Scientist spoke about introducing metal halide compounds into CsI(Tl) and the effect on afterglow and light output.
Listen to the presentation "Very low afterglow CsI(Tl) scintillator using antimony and other metal cations" from the Industrial Technical sessions.
Abstract: The use of CsI(Tl) scintillator in CT and other fast imaging modalities is hindered by afterglow in which the scintillator continues to emit light after the radiation source has been removed. Blurring, contrast loss and image artifacts result from too much afterglow. The introduction of small amounts of metal halide compounds into CsI(Tl) have been investigated for their effect on afterglow and light output. Thirty-one candidate compounds were tested in grown CsI(Tl) crystals. Eu, Sm, Bi and Yb have been previously identified as afterglow suppressors (and unfortunately light output suppressors as well). In this work, nine new candidates have been discovered to also suppress afterglow albeit with varying effectiveness. The best new candidate is antimony (Sb). Ingots co-doped with Sb have achieved afterglow signals of 0.23% and 0.13% at 100 and 500 ms after x-ray beam shut-off, which is over 60% reduction in afterglow. Typical standard CsI(Tl) values are 0.6% and 0.4%. Most significantly, there is no sacrifice of light output when doped optimally with Sb. The optimal concentration of Sb is 0.02 at% in the melt, which produces a mere 3.2 ppm Sb in the crystal, indicating that only a few ppm of Sb is enough to significantly suppress the afterglow. Further experiments have shown that combining Sb and Bi co-dopants suppresses afterglow to a greater degree than either by themselves. Typical afterglow results are 0.045% and 0.03% at 100 and 500 ms, respectively, with less than 1 ppm of each specie in the crystal and again, no loss in light output. Ingots with Sb and Sb+Bi afterglow suppressants have been scaled up to 8-inch diameter (>1000 cc), which indicates this process is ready for industrialization.