Fast Microcolumnar Scintillator for Radionuclide Imaging

75096S Although CsI(Tl) has become the scintillator of choice for a wide variety of applications, it is not been widely used in radionuclide imaging or computed tomography (CT). The primary reason is the presence of an afterglow component in its scintillation decay, which reduces the energy resolution in emission tomography and results in image blur in CT. In addition, thick, pixelated scintillator structures, needed to overcome the traditional tradeoff between detection efficiency and spatial resolution, do not currently exist. This project addresses the first issue by co-doping the scintillator with ions capable of suppressing the afterglow. The issue of tradeoff between detection efficiency and spatial resolution will be addressed by developing thick, microcolumnar, films of co-doped CsI(Tl). In Phase I: (1) single crystals of co-doped CsI(Tl) material were grown and characterized; (2) a synthesis effort demonstrated the feasibility of depositing the material as a microcolumnar film by vapor deposition techniques; and (3) the resulting films were evaluated to confirm the appropriate scintillation properties. The codoped CsI(Tl) scintillator exhibited a reduction in afterglow of almost two orders of magnitude, compared to current commercial CsI(Tl). Phase II will (1) study the physics of afterglow to gain a better understanding of underlying mechanisms, (2) incorporate selected co-dopants into the CsI(Tl) lattice, (3) characterize the decay time, afterglow, light yield, and time-dependent spectral distribution of the crystals and the microcolumnar films under x-ray excitation, and (4) develop thick, fast films for x-ray and nuclear imaging. Commercial Applications and Other Benefits as described by the awardee: Due to its low cost and excellent properties, the proposed scintillator should find widespread use in small animal/human SPECT/CT imaging systems in particular, and nuclear medicine systems in general. Additional applications include high-speed and ultrahigh-speed x-ray imaging, nondestructive testing, and homeland security.