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1. GENERALITY ON EGO PROPERTIES AND APPLICATIONS Bismuth Germanate Ei4Ge3012 (known as EGO) is a synthetic crystal grown as a replacement for the rare natural mineral Bismuth Silicon Oxide (eulytite) Ei4S13012 (ESO). It is a cubic crystal (symmetry 43m, with a tetramolecular cell) with the 6i3+ site coordinated by a distorted octahedron of oxigens. EGO monocrystals were grown by Nitsche in 1965 pulled from a pool of molten material contained in its own powder (other authors synthesized EGO since 1957). Bigger crystals by the Czochralski method were grown in platinum crucibles. Since that time, these monocrystals have been investigated for their electro-optical, electromechanical and luminescence properties, and for use as laser host material for rare earth elements. It presents high density (7.13 g/cm3), hardness of 5 (Mhos scale), melting point of 1050 C and a nearly flat transparent region between 0.3 and 6 um. EGO is an intrisic scintillator and the 480 nm emission band (FWHM = 160 nm) is obtained by excitation at 290 nm or by collision between y-rays and the atoms within the crystals. Around 1980 new interest on EGO arose due to its physical properties which make it suitable to replace for the traditional scintillators as NaI(T1). EGO crystals present many advantages as greater stopping power, much smaller afterglow, smaller radiation damage, nonhygroscopicity, physical ruggedness, so to allow setting-up more compact detectors (volume reduction of a factor 12) and handling much easier. Even if the integrated light output of EGO is one tenth with respect to NaI(T1), this light is still sufficient for readout by photodiodes. Although the energy resolution of EGO at 662 keV is one half of NaI(T1) resolution, its high peak-to-Compton ratio and high full-energy-to-escape-peak ratio is advantageous.
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