Assignment Gurney-MOTT Theory PDF

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VIA ALYSSA L. PLACENCIA

BSRT-II

GURNEY-MOTT THEORY SUMMARY What is a Latent image? A Latent image is an invisible image formed when a silver halide grain is exposed to X-ray or light form intensifying screen. Even this image is invisible this exposure to x-rays or renders the film susceptible to the chemical action of the developer. This means that the silver halide grain that has been exposed to radiation and it can be developed into a visible image. There are several theories that surrounds how does Latent Image Formation, example of this is the GURNEY-MOTT THEORY,in this topic will be focusing on the GurneyMott Theory it is looking for all layers of the Radiographic Film. But in order to understand the principles of Latent Image Formation, we need to look at the Emulsion layer. The Emulsion Layer made of millions of silver halide grain suspended in the gelatin, all surrounding a region containing a sensitivity specs. A main role of silver sulphide is to provide traps for positive holes; after doing 80 the sulphide molecule dissociates into AgS and an interstitial cation. In terms of this model a discussion is given of reciprocity failure, development, the role of iodide and of other phenomena. Earlier hypotheses due to Eggert and to Gurney and Mott are used, according to which the primary action of the light is to free photoelectrons and positive holes and the formation of silver specks involves the movement of silver ions. The stable latent image is seen as a positively charged silver speck on the surface of a halide grain, or in the case of internal image at a dislocation. The minimum stable image is a positively charged group of four silver atoms, the formation of which requires three electrons. The sub-image is a neutral pair of silver atoms and requires two electrons for its formation. A main role of silver sulphide is to provide traps for positive holes; after doing 80 the sulphide molecule dissociates into AgS and an interstitial cation. In terms of this model a discussion is given of reciprocity failure, development, and the role of iodide and of other phenomena. The size of a silver cluster in the latent image can be as small as a few silver atoms. However, in order to act as an effective latent image center, at least

four silver atoms are necessary. On the other hand, a developed silver grain can have billions of silver atoms. Therefore, photographic developer acting on the latent image is a chemical amplifier with a gain factor up to several billion. The development system was the most important technology that increased the photographic sensitivity in the history of photography....