September 22nd, 2021
Are you attending IEEE Nuclear Science and Medical Imaging Conference in October? During the Industrial Technical sessions, Cody Hufstetler, Product Engineer will discuss designing a large-format, two-dimensional scintillation array at 9:15 a.m. and then at 9:30 Peter Menge, Principal Scientist, Production Development will discuss introducing metal halide compounds into CsI(Tl) and the effect on afterglow and light output.
Join the session on October 20th at 9:15 and 9:30 a.m., stop by our booth or look for the presentation after the conference.
Abstract: High-resolution x-ray imagers in the medical, security and industrial fields often use linear arrays of scintillation detectors that move relative to the subject to build an image over a period of time. However, in systems or applications that require imaging a large area within one millisecond or less, one of the most exceptional options available is found in large-format, two-dimensional scintillation arrays. These arrays can be built with sub-millimeter pixel sizes and active areas upwards of 40cm square, allowing for high-resolution imaging. These arrays have distinct advantages over other imaging methods, including the ability to take multiple images during one experiment, and the capability to accurately characterize the array for image correction, improving image quality. In this session, we will review the many considerations to make when designing these arrays. The scintillator material is the most obvious concern; however, the method of construction, reflector selection, collimation, focusing, pixel depth, and other factors all contribute to the final image quality, cost, and performance of these arrays.
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.