Radiography in Modern Industry - Kodak

Figure 130: Stages in the development of the latent image according to the Gurney-Motttheory.The negatively charged trap can then attract an interstitial silver ion because the silver ion ischarged positively (See Figure 130C). When such an interstitial ion reaches a negatively chargedtrap, its charge is counteracted, an atom of silver is deposited at the trap, and the trap is "reset”(See Figure 130D). This second stage of the Gurney-Mott mechanism is termed the ioniccondition stage, since electrical charge is transferred through the crystal by the movement ofions--that is, charged atoms. The whole cycle can recur several, or many, times at a single trap,each cycle involving absorption of one photon and addition of one silver atom to the aggregate.(See Figure 130, E to H)In other words, this aggregate of silver atoms is the latent image. The presence of these fewatoms at a single latent-image site makes the whole grain susceptible to the reducing action ofthe developer. In the most sensitive emulsions, the number of silver atoms required may be lessthan ten.Radiography in Modern Industry 203