Grain photographic

Harvest mice feasting on wheat grains. Photograph by Stephen Datton/Photo Researchers, Inc. Reproduced by permission. 

Use Chemical intermediate, fine-grain photographic development, vulcanization accelerator. 

Fig. 2. Silica grains photographed using an optical microscope (a) Spherisorb (b) silica gel.

Transmission electron microscopy (tern) is used to analyze the stmcture of crystals, such as distinguishing between amorphous siUcon dioxide and crystalline quartz. The technique is based on the phenomenon that crystalline materials are ordered arrays that scatter waves coherently. A crystalline material diffracts a beam in such a way that discrete spots can be detected on a photographic plate, whereas an amorphous substrate produces diffuse rings. Tern is also used in an imaging mode to produce images of substrate grain stmctures. Tern requires samples that are very thin (10—50 nm) sections, and is a destmctive as well as time-consuming method of analysis. 

Chemical Sensitization. After the photographic microcrystals are precipitated but before they are coated on a support, the crystals are treated to enhance their sensitivity to light. Chemical sensitization is a process which improves that abiUty of the emulsion grains to use the absorbed photons, independent of the wavelength. Various methods of post-precipitation chemical sensitization have been developed to reduce the number of photons required to produce a developable latent-image center. 

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