Fundamental Study on a High Brightness and High Resolution YAG Screen for Electron Microscopy

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Coupled by a lens optical system with a photo-cathode, a single crystal of YAG (Yttrium Aluminum Garnet) has been used for a scintillator, which exchanges electron images to light images, in a new TV system for an electron microscopy. Lens coupled YAG scintillator system has advantages for damages due to the high energy electron irradiation and for lowering contrast by the x-ray. It was difficult, however, to achieve both high brightness and high resolution with this system, because the high refractive index of YAG reflects most of the light emitted in the crystal at the YAG-vacuum interface. In order to over come this problem of total reflection, we have developed a new scintillator combined a platelet YAG crystal with a glass hemisphere and have designed newly lens optical system.[In the first year] ;1. New type YAG scientillators have been developed, a hemisphere YAG crystal for a 100 kV electron microscope and a combination of platelet YAG and a glass hemisphere for a 1000 kV electron microscope.2. A lens coupling optical system for the 1000 kV electron microscope has been designed.[In the second year] ;1 Combining the new YAG scintillator and the lens optical system with a SIT-type TV-tube, we have produced a new TV system for the high voltage electron microscope, and2. We evaluated its characteristics with a light source and the 1000 kV electron microscope as,(1) Resolution The resolution is 50-60 mum on YAG for 1000 kV electrons.The curvature of a image plane due to the hemisphere can be reduced with a proper focusing condition(2) Brightness The glass hemisphere improves the brightness by a factor of 3.(3) Distortion The distortion due to the hemisphere is -4% at the edge of the TV screen.(4) Diminishing in the surrounding area dose not affect more than 70% in the monitor, and it is improbable.(5) DQE 0.04-0.12Consequently, we demonstrated that the TV-system for HVEM which is resistant to an electron irradiation damage and the effect of x-ray is available.