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The Gurney–Mott theory (also called the Gurney–Mott theory of photographic development) is a classical explanation of the latent image formation in silver halide photographic emulsions—a principle that underlies conventional film-screen radiography and photographic imaging chemistry.

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It explains how invisible latent images are formed in the silver halide crystal grains when they are exposed to X-rays or light, and how these latent images are later amplified during chemical development to produce a visible radiographic image.

![Silver halide is made up of both silver bromide and silver iodide. However, because silver bromide (AgBr) is the primary constituent of the silver halide in the emulsion layer of film, only silver bromide is discussed. The process by which the latent image is formed is precisely the same for silver iodide as it is for silver bromide. Silver (Ag) and bromine (Br) are bound together as a molecule in such a way that they share an electron (1). This electron is shared through ionic bonding because silver is a transitional atom, having only one electron in its outer shell, and it tends to either lose it or share it. The silver in AgBr is in effect an ion because it shares only its outer-shell electron with bromine. Energy in the form of x-rays or light is absorbed by the emulsion layers of radiographic film. This energy absorption raises the conductivity level of the electrons in the AgBr molecules, and these electrons move faster as a result. If enough energy is absorbed by a particular AgBr molecule, it becomes a positive ion of silver, neutral bromine, and a free electron

Image receptors. Radiology Key. Published February 27, 2016. https://radiologykey.com/image-receptors/](attachment:581fcc8b-decb-4571-8077-2ec26aa7c1f0:B9780323069748100128_u12-02-9780323069748.jpg)

Silver halide is made up of both silver bromide and silver iodide. However, because silver bromide (AgBr) is the primary constituent of the silver halide in the emulsion layer of film, only silver bromide is discussed. The process by which the latent image is formed is precisely the same for silver iodide as it is for silver bromide. Silver (Ag) and bromine (Br) are bound together as a molecule in such a way that they share an electron (1). This electron is shared through ionic bonding because silver is a transitional atom, having only one electron in its outer shell, and it tends to either lose it or share it. The silver in AgBr is in effect an ion because it shares only its outer-shell electron with bromine. Energy in the form of x-rays or light is absorbed by the emulsion layers of radiographic film. This energy absorption raises the conductivity level of the electrons in the AgBr molecules, and these electrons move faster as a result. If enough energy is absorbed by a particular AgBr molecule, it becomes a positive ion of silver, neutral bromine, and a free electron

Image receptors. Radiology Key. Published February 27, 2016. https://radiologykey.com/image-receptors/

Historical Context

• Proposed by R. W. Gurney and N. F. Mott in 1938.
• Before this, the mechanism of image formation in photographic emulsions was empirical and not well understood.
• Their theory applied quantum and solid-state physics to explain microscopic changes in silver halide (AgX) crystals when exposed to ionizing radiation or light photons.

The Radiographic Film Emulsion Structure

A typical radiographic film contains:

1. Base – Transparent polyester (polyethylene terephthalate, PET).
2. Adhesive layer – Bonds emulsion to base.
3. Emulsion layer – The active layer containing silver halide (AgBr, AgCl, AgI) microcrystals suspended in gelatin.
4. Protective coating – Thin gelatin layer protecting the emulsion.

The emulsion is the key component in which latent image formation occurs according to the Gurney–Mott mechanism.

Composition of the Silver Halide Crystal

Each silver halide crystal consists of:

• Silver ions (Ag⁺) and halide ions (Br⁻, Cl⁻, or I⁻) arranged in a cubic lattice.