Abstract: The paper presents advances in two sensor technologies: (1) Mercuric Iodide (HgI$-2$/) X-ray Detector Technology and, (2) Large Area Silicon Avalanche Photodiode (APD) Technology, which after years of development have recently produced commercially viable devices. Large Area Silicon Avalanche Photodiodes, which are solid-state light sensitive devices with internal amplification, combine the convenience, ruggedness and low power consumption of traditional semiconductor p-n and p-i-n photodiodes with the high light sensitivity and large photosensitive area approaching the active areas of traditional vacuum photomultiplier tubes. Device approaching 1-inch diameter with internal gain of up to 1000, have been developed by utilizing a beveled edge structure. By combining APD's with scintillation crystals, resolution of 6% (FWHM) was obtained for 662 keV energy line of $+137$/Cs using a CsI(Tl) scintillator, and 7% (FWHM) was obtained using a NaI(Tl) scintillator. Resolution of 14% (FWHM) at room temperature and 11% (FWHM) at 0$DGR@C have been obtained for APD's coupled to BGO scintillators. Rise times of 3 ns were measured by applying an impulse signal input, to a 200 mm$+2$/ device.!16
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