Bismuth germanate
Bismuth germanium oxide or bismuth germanate is an inorganic chemical compound of bismuth, germanium and oxygen. Most commonly the term refers to the compound with chemical formula Bi4Ge3O12 (BGO), with the cubic evlitine crystal structure, used as a scintillator. (The term may also refer to a different compound with formula Bi12GeO20.)
When subjected to high energy gamma rays, bismuth germanate emits photons of wavelengths between 375-650 nm, with peak at 480 nm. It produces about 8500 photons per megaelectronvolt of the high energy radiation absorbed. It has good radiation hardness (parameters remaining stable up to 5.104 Gy), high scintillation efficiency, good energy resolution between 5-20 MeV, is mechanically strong, and is not hygroscopic. It has very high density, 7.13 g/cm³ and a high Z value. Its melting point is 1050 °C. It is the most common oxide-based scintillator.
Bismuth germanium oxide is used in detectors in particle physics, aerospace physics, nuclear medicine, geology exploration, and other industries. Bismuth germanate arrays are used for gamma pulse spectroscopy. BGO crystals are also used in positron emission tomography detectors.
Commercially available crystals are grown by the Czochralski process and usually supplied in the form of cuboids or cylinders. Large crystals can be obtained.
Bismuth germanate has high electro-optic coefficients (3.3 pm/V for Bi12GeO20),[1] making it useful in nonlinear optics for building Pockels cells, and can also be used for photorefractive devices for ultraviolet range.
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