Spectral Performance of Mercuric Iodide Gamma Ray Detectors at Elevated Temperatures

The development of mercuric iodide (HgI2) as a solid state radiation detector material is motivated by the need for compact spectrometer grade detectors, which operate at ambient temperatures. Among candidates for solid state detectors, mercuric iodide possesses the highest intrinsic resistivity with values ranging from 1012 to 1013 Ohm.cm. It can therefore sustain high bias voltages while still generating low leakage currents. In addition, the large atomic numbers of the constituent elements of mercuric iodide (mercury Z=80 and iodine Z=53) in conjunction with a high density of 6.3 g/cm3 result in a high efficiency for the absorption of higher energy radiation and a potentially high full-energy peak efficiency.

The synthesis and purification processes used in our laboratory result in high purity material from which large (500g) single crystals with high structural quality can be grown using a physical vapor transport method. This makes it possible to fabricate planar detectors with active areas of 6.25 cm2 and thicknesses up to 3mm or more.