Large-area Crystalline Microcolumnar LaBr3:Ce for high-resolution gamma ray imaging

Exploration of a novel and highly time- and cost-efficient approach to produce important lanthanide halide scintillators is being carried out, at RMD. These materials include LaBr₃:Ce, LaBr₃:Pr and LaCl₃:Ce, in large physical sizes and production volumes, in both existing formats and new light-conserving morphologies required for demanding spectroscopic and imaging applications. Synthesis of such structures is accomplished using hot wall evaporation technique, which not only provides us with the control over film stoichiometry required to achieve efficient scintillation, but also permits the control of film morphology to tailor light propagation within the structure. This technique permits fabrication of thick films that can simultaneously provide the high absorption efficiency and high spatial resolution required for small-animal SPECT imaging and other medical and non-medical applications. Here we report on the growth of LaBr₃:Ce scintillator films in our Crystalline Microcolumnar Structure™ (CMS™) form, which preserves response uniformity over the (often large) area of the film, and transparency throughout its thickness. Specifically, we have repeatedly produced LaBr₃:Ce films measuring 6 cm in diameter (limited only by the size of the vapor deposition system used in this development) and approaching 2 cm in thickness, with densely packed microcolumns averaging ~25 μm in diameter. These films show bright light emissions comparable to their crystalline counterparts, and energy resolution of ~9% at 122 keV (⁵⁷Co emission). Imaging data acquired using the University of Arizona Bazooka SPECT detector incorporating our CMS LaBr₃:Ce film demonstrated ~125 μm spatial resolution at 122 keV, which is consistent with the measured intrinsic spatial resolution of 3 line-pair(LP)/mm of the film used, as determined at RMD using X-ray techniques.