Mechanism of Formation
The action of the light with the silver halide grains within the emulsion forms sites of metallic silver on the grains. The basic mechanism by which this happens was first proposed by R W Gurney and N F Mott in 1938. The incoming photon liberates an electron from a silver halide molecule, called photoelectron. Photoelectrons migrate to a shallow electron trap site (a sensitivity site), where the electrons reduce silver ions to form a metallic silver speck. A positive hole must also be generated but it is largely ignored. Subsequent work has slightly modified this picture, so that 'hole' trapping is also called into question (Mitchell, 1957). Since then, the mechanism of sensitivity and latent image formation has been greatly improved.
Read more about this topic: Latent Image
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