NEW CONCEPTS FOR SCINTILLATOR HGI(2) GAMMA-RAY SPECTROSCOPY/

The construction of a high energy resolution gamma ray detector consis ting of a scintillator/mercuric iodide photodetector combination has b een investigated. Several HgI2 photodetectors have been fabricated and tested with standard NIM electronics. The energy resolution of a scin tillator/HgI2 pair was found to be 4.75%, full width at half maximum, for 662 keV Cs-137 gamma ray photons. Of five detectors fabricated wit h our new technique, all produced resolutions better than 5.6% FWHM. T his technology makes it possible to reliably produce high quality HgI2 photodetectors. New design concepts for the HgI2 photocell, including the transparent entrance electrode, detector geometry, and detector p ackaging, are described in the paper. Advantages of gamma ray spectrom eters based upon crystal scintillators optically coupled to HgI2 photo detectors (in contrast to coupling the scintillators to the more conve ntional light sensors, i.e., photomultiplier tubes (PMTs)) include gre ater ruggedness, improved energy resolution, markedly smaller size and weight, reduced power, and insensitivity to magnetic field perturbati ons.