Reduced Afterglow Codoped CsI:Tl for High-Energy Imaging

CsI activated with thallium is one of the most important scintillators in the radiation detection field. With one of the highest conversion efficiencies (60 000 photons/MeV) of all scintillators in current use, along with its high density and effective atomic number, excellent light transport properties, broad commercial availability, and low cost, it has become the detector of choice for a wide variety of applications, especially medical diagnostics. Now, it has become particularly attractive for radiographic scanning and active interrogation of cargo in transit as well. It does have one drawback, however, in its relatively long-lived afterglow, which restricts its use in high-count-rate applications, causing reconstruction artifacts in CT and reduced contrast and image blurring in high-speed radiographic scanning and imaging. In previous work, we have already demonstrated that this afterglow can be substantially suppressed at low energies ( $\mu \text{m}$ thick and up to $45 \times 45$ cm2 in area, and expect yet further development in the future. This provides a combination of high-resolution, high-frame-rate, and large-area capabilities not hitherto available for imaging applications.