Growth and Characterization of Polycrystalline Lanthanide Halide Scintillators

We are exploring a novel time- and cost-efficient approach to produce robust, large-volume polycrystalline lanthanide halide scintillators using a hot wall evaporation (HWE) technique. To date, we have fabricated LaBr₃:Ce and LaCl₃:Ce films (slabs) measuring up to 7 cm in diameter and 7+ mm in thickness (20 to 25 cm³ in volume) on quartz substrates. These polycrystalline scintillators exhibit very bright emissions approaching those exhibited by their melt-grown crystal counterparts. Scanning electron micrographs (SEMs) and X-ray diffraction analyses confirm polycrystalline growth with columnar structures, both of which help in light piping, thereby contributing to the observed high light yields. The new scintillators also exhibit good energy resolution for γ-rays over the tested range of 60 keV (²⁴¹Am) to 662 keV (¹³⁷Cs), although they have not yet reached that of the corresponding crystals. The measured response linearity over the same energy range is comparable for both our HWE synthesized films and melt-grown commercially-available reference crystals. Similar consistency in response is also observed in terms of their decay time and afterglow behaviors. The data collected so far demonstrate that our HWE technique permits the rapid creation of scintillators with desired structural and compositional characteristics, without the introduction of appreciable defects, and yields material performance equivalent to or approaching that of crystals. Consequently, the deposition parameters may be manipulated to tailor the physical and scintillation performance of the resulting structures, while achieving a cost per unit volume that is substantially lower than that of crystals. In turn, this promises to allow the use of these novel scintillation materials in such applications as SPECT, PET, room-temperature radioisotope identification and homeland security, where large volumes of materials in a wide variety of shapes and sizes are needed. This paper describes our growth and testing of polycrystalline LaBr₃:Ce scintillators and provides comparative characterizations of their performance with crystals.