Stanford Scintillator Materials Group

Development of a High Speed Growth Technology for Single Crystal Halide Scintillators

This program focuses on the development of a technology for producing halide scintillator crystals at lower cost than conventional crystal growth methods. The materials of interest are the new high light output and high energy resolution single crystal detector materials, SrI₂, LaBr₃ and the elpasolite compounds. The method involves growth speeds up to 10 times greater than that current methods used for growing these crystals and in a continuous rather than a batch process. In addition, an array of cross sectional shapes such as thick sheets, cylinders or rectangular bars can be made to help reduce machining costs and well as expensive material loss due to the fabrication process. The method, the Edge-defined Film Fed Growth (EFG) technique, has been shown to be a viable commercial manufacturing method (Si, Al₂O₃, and CdTe) and theories involved in the growth process are well established. The experimental work is aided by computer modeling and design of furnace components leading to optimized processing parameters, and the scintillating properties of the crystals produced will be compared to state-of-the-art materials prepared by conventional methods.

The EFG process involves the use of a thermally conducting die/shaper inserted into the melt. The melt is drawn up to the die surface creating a thin film across the die surface. A seed crystal of a predetermined orientation is inserted into the film and withdrawn so as to propagate a single crystal of cross-sectional shape the same as the outer dimensions of the die. Many different shapes can be continuously grown such as cylinders, tubes, rectangular bars and sheets. Growth can be made continuous by automatically recharging the crucible during growth and changing the height of the growth chamber can extend the length of the crystal.