Image converters for the high-voltage electron microscope
One of the major concerns of biological electron microscopists has been that of obtaining images of biological specimens with minimal radiation damage. The problem of designing more sensitive imaging devices and materials for the high-voltage electron microscope (HVEM) becomes pressing because: 1) the relative insensitivity of conventional photographic materials to 1-MeV electrons requires inordinately long exposures unless measures are taken to enhance the sensitivity of photographic recording; 2) the relative insensitivity of conventional viewing screens requires excessive beam intensities for scanning the specimen and focusing the image unless means are found to obtain a visible image at lower beam current densities; 3) an increasing part of the practice of high-voltage electron microscopy has involved taking multiple images from the same specimen area, as in taking stereo pairs or more extensive tilt series for three-dimensional reconstruction --- this feature is inherent in high-voltage electron microscopy, and it is occasioned by the wealth of detail offered by semithin sections, which requires three-dimensional methods for decipherment