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17 September 2009 Bismuth tri-iodide radiation detector development
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Bismuth tri-iodide (BiI3), a wide band-gap semiconductor, demonstrates many of the material properties necessary for high resolution room temperature gamma-ray spectroscopy. These material properties include high density, large bandgap, and high atomic number. The theoretical intrinsic photopeak efficiency of BiI3 is approximately 2-3 times higher than CdZnTe over the range of 200-3000 keV. BiI3 has a theoretical intrinsic photopeak efficiency of 19% at 662 keV, compared to CdZnTe which has a theoretical intrinsic photopeak efficiency of 13% at 662 keV. A modified vertical Bridgman growth method is being used to grow large, greater than 100 mm3, single BiI3 crystals. Growth parameter optimization has demonstrated that single crystals can be obtained with temperature gradients of 10°/cm or 15o/cm and a growth rate of 0.5 mm/hr, or with a temperature gradient of 10o/cm and a growth rate of 1 mm/hr. Polycrystalline material results from all other growth parameter combinations. X-ray diffraction spectra are used to determine if the crystals are single crystals or polycrystalline. UV-VIS spectra analysis has revealed that the band-gap of BiI3 is 1.72 eV. The resistivity of the crystals has been determined by generating I-V curves to be on the order of 108-109 Ω-cm. Zone refining is being performed to increase the purity of the starting material and the resistivity of the crystals. Detectors have been fabricated with both gold and palladium electrodes.
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Azaree T. Lintereur, Wei Qiu, Juan C. Nino, and James E. Baciak "Bismuth tri-iodide radiation detector development", Proc. SPIE 7449, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XI, 74491M (17 September 2009);

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