Iodine based compound semiconductors for room temperature gamma-ray spectroscopy

Iodine-based compound semiconductors may allow one to build a portable gamma-ray spectrometer with improved efficiency and energy resolution compared to many other portable spectrometer devices. Iodine-based semiconductors have a wide band gap that allows these detectors to operate without any cooling mechanism. Bismuth iodide (BiI3), lead iodide (PbI2) and mercuric iodide (HgI2) have theoretical gamma-ray detection efficiencies approximately 2-3 times higher than CdZnTe, the current compound semiconductor material proposed for use in several homeland/national security applications, over the range of 200-3000 keV. At 662 keV, BiI3, HgI2 and PbI2 have theoretical intrinsic photopeak efficiencies of 16.8%, 19.3% and 19.9%, respectively, while CdZnTe has a photopeak efficiency of 9.03%. In addition, gamma-ray spectrometers made from iodine-based compound semiconductor materials have demonstrated energy resolutions (FWHM) less than 2% at 662 keV. A 2% FWHM represents a significant improvement over many of today's scintillator-based radiation detectors used for homeland/national security purposes. We present some fundamental challenges in working with iodine-based semiconductors, including crystal growth issues and properties of the materials limiting radiation detector size, and the need for advanced electrode designs. Finally, we present elementary measurements illustrating the detection capabilities of iodine-based compound semiconductor materials.